Skip to Content

image processing

Selective Color Boosting (Photoshop Tutorial)

|Tutorials|5 Comments

In this astrophotography image processing tutorial, I will explain an easy way to selectively boost the colors in your image. I like to call the technique “selective color boosting“.

Increasing the saturation of your deep-sky object can bring out the true beauty of your subject, and better showcase the contrasting elements of the nebula or galaxy.

The amount of “boosting” is up to you of course. Some prefer bright, vibrant colors, while others prefer a toned-down “natural” look. I’d like to consider my images to be somewhere in the middle. 

The definition of a “true-color” image varies, but the techniques described in this tutorial are generally accepted in the astrophotography realm. 

Selective Color Boosting for Astrophotography

The Triangulum Galaxy in RGB (Dedicated Astronomy Camera).

Long exposure astrophotography can reveal the colors of all deep-sky objects and galaxies. By exaggerating these colors through post-processing, we can increase the impact of the image.

In this tutorial, I’ll use Adobe Photoshop to accomplish our tasks. This software includes countless tools to perform the finishing touches on your images. (See the rest of the astronomy and astrophotography software I use).

I have also found it to be a fantastic start-to-finish image editor, with the help of a few third-party plugins of course. But we’ll get to that in a minute.

The example images in this article were captured using a variety of cameras, from an astro-modified DSLR camera to a monochrome CCD camera. The color boosting methods I describe will work for all color images, whether they are broadband RGB, LRGB, narrowband, bi-color, etc. 

The data used in this tutorial was registered, stacked, and calibrated in DeepSkyStacker first. If you need help with the pre-processing stages of deep-sky astrophotography, be sure to check out my premium image processing guide

For an overview of this process, please watch my video tutorial on YouTube:

How to Boost the Colors in Your Astrophotography Images

Astrophotography is a broad term and covers a wide variety of disciplines from wide-angle Milky Way nightscapes, to high-magnification planetary imaging. 

The methods of boosting color discussed below are most applicable to deep-sky imaging of nebulae and galaxies, but can also be applied to all forms of digital photography.

In a nutshell, you need to carefully isolate the areas of color that you wish to enhance, and leave the rest of the image alone. 

If you globally increase the saturation of your astrophoto, you run the risk of intensifying noise, color-mottling, and other nasty surprises hiding in your data. 

For example, in my image of the Whirlpool Galaxy shown below. I wanted to focus on boosting the colors of the areas of pink hydrogen inside of the spiral arms, without oversaturating the blue areas of the galaxy. 

whirlpool galaxy

The Whirlpool Galaxy in LRGB (Mono CCD and telescope).

The same selective color boosting method can be used on a wide-angle nightscape image too. The most challenging part of the process is the selection itself.

In the example image below, I again carefully isolated the areas of pink hydrogen emission nebulae. I was able to increase the saturation of these areas and brighten them with a careful mask selection. 

Truth be told, I could have done a better job at masking the darker areas of the night sky, but I think you get the idea. 

The Milky Way

The Core of the Milky Way. Canon DLSR and a wide-angle lens. 

As you can see, this technique gives you full control over the amount of saturation in your image in each area. The key concept is that you’re being very specific about which areas of color are boosted.

A basic saturation slider adjustment to the image as a whole will degrade the quality of your image significantly. 

With some inspiration to get your creative juices flowing, let’s get into the nuts and bolts of the process.

When to Start Boosting Colors

The timing of these actions on your image is up to you, but I highly recommend leaving it until the end. 

After the pre-processing stages (DeepSkyStacker, Astro Pixel Processor, etc.)

The first few steps you take towards processing your image should focus on balancing the RGB levels in the histogram and applying basic curve adjustments that bring up the signal.

Here is a basic image processing workflow timeline that I generally follow:

  1. Levels Adjustment
  2. Curves Adjustment
  3. Balance Levels
  4. Neutralize Background
  5. Curves Adjustment
  6. Star Color Adjustment
  7. Star Minimize
  8. Selective Color Boosting
  9. Noise Reduction
  10. Sharpening

You may want to make some less dramatic stretches to your colors along the way, but leave the selective color boosting method until the end of your workflow. 

The reason for this is that your image won’t be in a state that portrays what the final colors will look like until the end of your workflow. 

Soul Nebula

The Soul Nebula captured using a DSLR camera and a small refractor.

How to Select Specific Colors

There are two selection tools in Adobe Photoshop that allow you to isolate specific areas of your image. One (Color Range) makes an early, rough selection based on your input. The second (Select and Mask), is much more powerful and allows you to refine a detailed mask over your image.

With a careful selection and masking process, you can then create a new adjustment layer to increase saturation and vibrance. The same powerful masking technique also allows you to carefully adjust the highlights on your image, noise, sharpening, and much more.

In the image of the Pleiades shown below, I selected the outer nebulous regions of the object to increase saturation and bring up the midtones. 

new adjustment layer

At the heart of this image processing technique is the Color Range tool. This magnificent tool was introduced way back in Adobe Photoshop 3.0, and photographers have been enjoying it ever since. 

Select Color Range

The Color Range tool in Photoshop is an effective way to start the selection process. I like to use this tool to create a rough mask that can later be refined.

You can find this tool in the main menu under Select > Color Range…

select color range

The Color Range Tool is under the “Select” heading in the main menu.

This opens up a new dialogue box with a number of options to choose from. The drop-down menu at the top labeled “select” is where you will need to decide which method you would like to use to quickly grab the details you’re interested in.

I find “sampled colors” to be the most effective because you can use the eyedropper tool to manually point to the colors in your image you would like to enhance. 

The “highlights’ selection method is also very useful, as this is often the best way to separate your deep-sky subject (and stars) as a whole from a background sky.

sampled colors

“Sampled Colors” lets you manually pick the color range in your image.

No matter which selection method you use, you’ll want to do a basic refinement of your selection using the preview window. Make sure the “Selection” option is ticked during this stage.

In my image, I want to select the blue areas of the Trifid Nebula, so I can apply a targeted adjustment to this element only.

You simply need to click the eyedropper on the color range you would like to isolate, and the preview window will display a rough mask over these regions in the preview window. 

You can also change the selection preview dropdown menu to “Grayscale” for a live preview of your upcoming mask on your full-size image.

color range selection

The preview window provides a rough idea of your initial selection (change the selection preview to grayscale to see a full-size image).

You can adjust the “fuzziness” and “range” sliders to increase the selection of the mask. Make sure that you have the “localized color clusters” checkbox ticked off for full control. 

The eyedropper with the “+” and “-” icons next to them allows you to add or subtract from your selection, but they are a little too unrefined to be effective for our purposes.

The point of this step is to isolate the areas of color in your image that you wish to boost the colors in. Don’t worry about getting too specific at this point, as we will refine the mask substantially in the next step. 

When you are happy with your rough color range selection, you can click the OK button. Now you should see the “marching ants” selection on your original image, which is not a very helpful indication of our selection.


Our initial color range selection is applied. 

The Select and Mask Tool

When it comes to processing astrophotography images, the Select and Mask tool is probably the most important tool in all of Photoshop. To really get the most out of your images, isolating one element from another is essential.

The Select and Mask tool allows you to refine your selections with an extremely robust set of adjustment options. Learning how to harness the power of this feature will most certainly improve your astrophotography image processing skills.

I will use the terms “selection” and “mask” interchangeably, as they are essentially the same thing. When we create a “layer mask” it just means that we are isolating a portion of the image to either be left-alone or targeted for adjustments.

With your original Color Range selection still active, navigate to the main menu, and click Select > Select and Mask

The Select and Mask tool. 

An important step to remember here is that you will want to make sure your original, rough, color range selection is active (as indicated by the marching ants on your image) before invoking the Select and Mask feature. 

There is a lot going on in the Select and Mask dialogue box. Below, I have provided an overview of the key adjustment sliders you’ll want to pay attention to when processing a deep-sky image. Click the image for a larger version. 

select and mask astrophotography

The purpose of this tool is to allow you to make precise refinements to your selection, and provide a clear indication of where this mask will be applied. 

There are several options to choose from when it comes to the way the mask is displayed on your image. The view modes are as follows:

  • Onion Skin
  • Marching Ants
  • Overlay
  • On Black 
  • On White
  • Black and White
  • On Layers

In my eyes, the Black and White view mode is by far the most useful. You may see the Onion Skin view mode appear by default, which I have found to be the second-best option from this list. 

Adjusting the Sliders to Refine Your Mask

The three most important sliders to adjust in the Select and Mask dialogue box are Contrast, Feather, and Shift Edges. A balanced approach between all three will yield the best results.

The Contrast slider is used to further separate your masked area from the rest of the image. With the Black and White view mode active, increasing the Contrast Slider will result in a more defined “shape” of the color range, with less of a transition area between the highlights and shadows.

Photoshop settings

The important adjustment sliders in the Select and Mask tool.

The Feather slider is the most important of them all because this creates a smooth transition between the edges of your mask and the background. Aim for super-soft edges around your targeted area to avoid harsh edges between your manipulated elements. 

The Shift-Edges slider is useful for expanding the area of your selection mask overall, retaining any feathering settings you have put in place. Between these three adjustment sliders, you should be able to create the ultimate layer mask for your image.

Note: You can use the brush tool (set to your desired width and softness) to remove specific areas of your selection. On a PC, just hold down the Alt key to subtract from the image when painting with the brush tool.

Accept the Mask and Create and a New Adjustment Layer

The default action that takes place after hitting OK on the dialogue box is to output to a selection. This will display the marching ants view overlay on your image. 

From here, you will want to create a new adjustment layer to apply your desired saturation boost and any other effects. For increasing color, you’ll want to choose the Vibrance… adjustment layer.

vibrance adjustment layer

The advantage of this procedure is being able to see a full-size preview of your image with your targeted adjustments to the selection happening in real-time. 

You may want to choose “output to: new layer“, as this will essentially accomplish the same result.

In this scenario, you would simply edit the new layer with your desired effects rather than as a new adjustment layer. 

Selective Color Boosting

By now you should have a solid understanding of how the color range selection tool works, and why it’s important to isolate the specific areas of your image that you want to manipulate.

With a well-defined selection mask placed over your image (remember, the white areas will be affected, the dark will not) you can begin to increase the vibrance and saturation of the important colors of your nebula or galaxy.

In case you’re getting a little lost in the order of things, here is a step-by-step path to get you up to speed:

  1. Select > Color Range
  2. Use Sampled Colors from Dropdown Menu
  3. Place the eyedropper on the color range you would like to boost
  4. Adjust the fuzziness and range sliders to roughly isolate these colors in the image
  5. Click OK to confirm your rough selection
  6. Open Select > Select and Mask to further refine your selection
  7. Use the Feather, Contrast, and Shift Edges sliders to create a smooth mask on your subject
  8. When you are happy with the selection (remember, no hard-edges!), click OK
  9. With the selection active, click Layer > New Adjustment Layer > Vibrance

The following illustration shows what your screen should look like at this stage. The new adjustment layer is the top-most layer, which ensures that your edits will be seen as you make adjustments. 

boost saturation

Adjust the vibrance and saturation sliders to your selected area.

Now, you can adjust the vibrance and saturation sliders to increase the color of your selected area. Pay close attention to your image at a glance at this stage.

Remember, drastic changes made to isolated areas of the image run the risk of looking unnatural. This is another reason why creating a mask with a soft, feathered edge is very important.

Any areas where the mask stops abruptly may appear odd in your final result. The more you “push” the data, the more pronounced this effect becomes. 

In the example below, I chose to increase the saturation of the warmer colors in the image. The Pinwheel Galaxy appears as a very cool blue color when stretched, and I wanted to contrast these cool areas with the warmer core of the galaxy. 

Pinwheel Galaxy

In this image of M101, Selective Color Boosting was used to keep the core warm, and the spiral arms cool.

There are no rules when it comes to the exact saturation settings you should use to enhance the color of your image.

I tend to bump the sliders up to about 15-20, depending on the deep-sky object, and the desired look I am going for. Once you are happy with the amount of boosting to the saturation and vibrance you have applied, you can simply close the properties window.

The new adjustment layer will sit on top of the other layers in your image. From here, you can save the file with the layers intact (.PSD file), or simply flatten the image and save it as a JPEG or TIFF. 

saturation settings

Typical vibrance and saturation settings for a deep-sky image.

Adjusting Color Balance, and Photo Filters

Since you have gone to the trouble of creating a highly selective layer mask, why not use it to make other color enhancements as well? 

In certain situations, creating a color balance adjustment layer is helpful. You can gently pull the colors towards a cooler or warmer result as desired. 

If bumping up the saturation and vibrance sliders don’t achieve the look you are going for, you can also try a specific photo filter

warming filter

The color balance and photo filter adjustment layers can be useful for certain looks.

I have found the warming filter to be useful for enhancing star colors, and the cooling filter to be useful for a natural background sky. In all scenarios, you’ll want to mask the area that you are applying the color filter to. 

Adjust the Opacity of the Adjustment Layer

Remember, you can always adjust the opacity of your new adjustment layer, and tone down the amount of saturation in your image.

If you feel like you have overdone it, just bring the opacity slider down to about 25%. Turn the layer visibility on and off to observe the subtle enhancement this technique makes to your astrophoto. 

I usually make my vibrance/saturation layer rather aggressive, and then bring the opacity slider down to about 50% to “normalize” things a little bit. 

You will have to practice the selective color boosting technique on a few images to really get a feel for it. The more types of images you perform this task on, the more comfortable you’ll feel.

Remember, this method can be useful for all types of astrophotography, not just deep space nebulae and galaxies. 

nightscape photography

Final Thoughts and Advice

If you were able to follow along with this tutorial, you should have a good feel for the Select and Mask tool, and its power. You can use the same selection process to perform other tasks on your image, from noise reduction to sharpening.

Although the examples in the tutorial focused on selective color boosting nebulae and galaxies, the technique works exceptionally well when processing star colors, too.

In this case, you would want to mask out the stars in the image on their own, so you have full control over their saturation without disrupting the rest of the image. 

For the wide-field view of the Eagle Nebula shown below, I isolated the stars using the “highlights” color range mode and increased their saturation independently from the rest of the image. 

star colors

The colorful stars surrounding the Eagle Nebula.

If you are unsure about how far to take your image, in terms of boosting saturation, I find it useful to use a reference image. I often search for APOD images of my target and see the direction that other amateur and professional astrophotographers have chosen to steer the image in.

If I could offer one more piece of advice, I would like to remind you why you began your journey in astrophotography: enjoyment. Adjust your personal images in whichever way you think looks best.

If you have found this image processing tutorial useful consider purchasing my premium astrophotography image processing guide

More Image Processing Tutorials:

Related Tags

Topaz Labs DeNoise AI Review

|Image Processing|12 Comments

The goal of Topaz Labs DeNoise AI is to reduce digital image noise while preserving detail and increasing image sharpness. If you’re no stranger to astrophotography image processing, that almost sounds too good to be true.

I was skeptical of the application myself but now find myself using it in some capacity for every astrophoto I process. I believe that Topaz Labs DeNoise AI is a powerful tool that amateur astrophotography enthusiasts should consider adding to their bag of processing tricks.

In fact, I even added a new section about Topaz DeNoise AI in my premium astrophotography image processing guide. I have no interest in spending time learning and writing about tools with a short shelf-life, and I don’t see myself shying away from DeNoise AI anytime soon. 

Until discovering this photo noise reduction software, I typically used the built-in noise reduction features of Adobe Camera Raw. This works well enough but is not nearly as reliably effective as the one-click, automatic noise reduction function of DeNoise Ai.

Whether you use Topaz Labs DeNoise AI to batch process a handful of night sky images in Lightroom or use it to subtly control the noise in your deep-sky images in Photoshop, this advanced learning software feels like it was built for astrophotography.

If you have experience using other noise reduction tools such as Skylum Luminar, Noise Ninja, DXO Prime, or any other of the many options available, please let me know how my results with DeNoise AI compare in the comments. 

Photo noise reduction software

Download: Topaz DeNoise AI 30-Day Trial

Topaz Labs DeNoise AI Review

As you may already know, noise can be a big problem for amateur astrophotography, especially when using a DSLR or mirrorless camera with a high ISO setting. I have personally been battling noise in my astrophotography images for nearly a decade. 

Even with great image acquisition best practices, lots of data, and a cool astronomy camera, you will likely still need to minimize the noise in your image at some point in the image processing stages of astrophotography.

In general, the tricky part of applying a noise reduction filter to your image is the possibility of detail loss, which can create a blurry looking image.

Noise Reduction

I originally shrugged off anything to do with this software due to the fact that I am a diehard Adobe Photoshop fan. I realize that many people are not willing to fork out the dough for a Creative Cloud subscription, but I certainly am. I’ve been using Adobe Software for nearly 20 years, and get full value out of my subscriptions to Photoshop and Premiere. 

I’ve used many third-party plugins with Photoshop in the past (see the resources page for a few that stand out), but the Topaz Labs DeNoise AI plugin is different. I don’t believe any of the software I have installed in the past actually tapped into the benefits of artificial intelligence that continues to get better over time. 

Topaz Labs DeNoise AI allows you to download a full-featured 30-day trial, so you’ve got nothing to lose. I took advantage of this opportunity, fell in love with the tool, and gladly forked out the cash for a lifetime license of the software. 

In this post, I’ll explain how to incorporate Topaz DeNoise into your astrophotography image processing workflow, and why I think it’s a no brainer for anyone that spends as much time photographing space as I do.  

Is it a Photoshop Plugin?

First things first, you’ll need to install the software on your computer. Topaz DeNoise is available for both Mac and PC operating systems. For better or for worse, I am a diehard PC user, and I installed the lightweight software on my Windows 10 desktop.

I am using Topaz Labs DeNoise AI as a Photoshop 2020 plugin exclusively. Users have the option of using the DeNoise AI as a standalone program, or a plugin in Adobe Lightroom or, of course, Topaz studio.

I don’t typically utilize the batch processing feature of Topaz DeNoise AI and prefer to invoke the tool on a per-image basis when noise reduction is needed.


A before/after example of Topaz DeNoise AI on the Orion Nebula

As far as astrophotography goes, I am sure that most users will use the tool as a Photoshop plugin as I do, during the post-processing stages of their workflow. However, daytime photographers may find the tool handy when editing photos in Lightroom.

This is one of the biggest reasons why I was able to introduce the Topaz Labs DeNoise AI into my existing workflow so effortlessly. I simply run the tool on a new layer in Photoshop just as I would with any other Photoshop filter or external plugin.

Topaz Labs DeNoise is available as a plugin for the following applications:

  • Adobe Photoshop
  • Adobe Lightroom
  • Corel PaintShop Pro
  • Serif PhotoPlus

I absolutely love the simplicity of the user interface (UI). At its core, the software has to be good at one thing, and that’s effective noise reduction. The minimalist interface, large buttons, and massive preview window make it very easy to see what’s taking place. 

DeNoise AI Photoshop Plugin

The Problem with Noise in Astrophotography

Many factors come into play when assessing the reasons why your astrophoto is so noisy. Sensor design, size, and the camera settings used when the photo was taken are the most obvious. 

Noise is the unwanted, randomly placed “grain” caused by your digital camera’s sensor. Noise often increases when using higher ISO settings, and appears as uneven color and grainy pixels distributed throughout your image.

It is most noticeable in solid areas of color, especially darker areas such as a black night sky. This can be a major problem for astrophotography, as our images usually have plenty of dark sky areas in them, surrounding the subject. 

When you attempt to brighten your astrophoto to reveal faint structures of nebulae, stars, and galaxies, you also risk increasing the presence of noise. 

When you zoom in on your image at 100% magnification, don’t be surprised to find grainy, random color specks, and overall inconsistency in the darker areas

The two ugly sides of the noise equation are Luminance Noise and Chrominance Noise. This article will help you understand what causes noise in digital photography.

The Signal-to-Noise Ratio

The best way to reduce noise in your astrophotography images is to improve the signal-to-noise ratio (SNR). Meaning, capture as many sub-exposures as possible and integrate the data using software such as DeepSkyStacker, Astro Pixel Processor, or PixInsight.

By nature, long-exposure photography in dark situations is just asking for noise. But amateur astrophotographers have found ways to overcome this issue to a large extent through image stacking, and calibration frames such as dark frames

Yes, this practice is essential for creating a quality astrophoto, but sometimes it just isn’t enough. I’ve found myself in situations where over 5 hours of data were collected with my DSLR camera, and the healthy SNR still wasn’t enough to achieve an image with a smooth, sharp background. 

A neutral, smooth background sky is one of the toughest challenges in the world of astrophotography image processing. Finding ways to isolate this element of the image, and tame the noise and unsightly artifacts found within it is essential. And this is exactly where Topaz Labs DeNoise AI shines. 

The chroma noise reduction feature is especially handy in these situations, but monitoring your image as a whole during this step is a must. I can’t stress enough the fact that masking (see my Select and Mask tutorial), isolating, and defining each element of your astrophotography image is paramount for success.

How to Use Topaz Labs DeNoise AI

The software is simple to download and install, and automatically integrates itself into Adobe Photoshop. There is no need to drag-and-drop specific files into the program folders as you do with other third-party plugins. 

At its core, DeNoise AI is a photo noise reduction software. More specifically, the tool was designed to enhance sharpness, remove chroma noise, and eliminate noise without losing details. The official Topaz DeNoise user guide includes a complete list of primary functions.

It’s safe to say that astrophotography was not the primary intended use for Topaz DeNoise AI, but it happens to benefit from it a great deal. The horizontal and vertical banding lines, black level correction, and high ISO image recover features are the most utilized aspects.

To run the plugin in Photoshop, you simply need to navigate to the Filter drop-down menu. At the bottom of the list, you should see Topaz Labs > Topaz DeNoise AI. If this option is greyed out, make sure your image is in 16-bit or 8-bit mode (it will not work in 32-bit mode). 

Upon activating the plugin, you’ll be delivered with a large preview window of the image with the noise reduction effects applied, next to your original (split view). 

preview image

You’ll notice that the software interface presents you with two processing models: DeNoise AI and AI Clear. You’ll want to use the DeNoise AI option, as it is the newer feature and tends to work a lot better than the previous AI Clear mode (which was a feature of the original Topaz Studio).

With the DeNoise AI model selected, you can now select your noise reduction mode. I recommend trying out the “auto” mode on your image, as applying this filter to your picture often does a fantastic job (you can thank millions of AI training images for this).

DeNoise AI user interface

The Manual Mode gives you much more control over the noise reduction filter. You can independently adjust the following sliders to your taste:

  • Remove Noise
  • Sharpen
  • Recover Original Details

Best Practices for Astrophotography Images

Deep-Sky Astrophotography

I primarily shoot deep-sky astrophotography images through a telescope, of distant nebulae and galaxies. For these types of photos, Topaz DeNoise AI is an incredible tool to help remove an uneven background sky. 

The chroma noise reduction slider is especially handy when dealing with an astrophoto with a noisy, unevenly colored background sky.

I’d still mask the nebula or galaxy (and in most cases, the brighter stars) in the image before running Topaz DeNoise, but you can count on the DeNoise filter to improve the ugly luminance and chroma noise in the darker regions.

The power of DeNoise Ai in these situations should not be understated. Astrophotographers (particularly ones shooting with a DSLR camera) have been dealing with this problem for many years, and this software handles it better than any other tool I’ve ever used. 

nebula example

Nightscape Photography

I’ve stated how impressive the tool works for images of nebulae and galaxies, but what about a wide-angle shot of the Milky Way? Well, I tested that scenario on an image of the Milky Way I captured under dark skies with a Rokinon 14mm F/2.8 lens. 

As you can see, Topaz Labs DeNoise AI did a fantastic job of preserving important details of this demanding image, while making a noticeable improvement to the overall aesthetics by smoothing out grainy areas of the picture.

DeNoise AI example on the Milky Way

I don’t think that this post-processing tool can totally make up for an image shot using an ISO setting that was too high, but it may be able to save some of the images you originally thought were just too noisy to share.

Usage Tips

The best part about Topaz Labs DeNoise AI is how simple it is to use. Most often, I utilize the “auto” feature of the plugin and apply the default AI noise reduction amount to my image. It’s best to apply this action to a new layer on top of the image, so you can adjust the opacity and overall impact of the effect.

The “Auto” Noise Reduction setting works surprisingly well most of the time. 

Usually, I will apply the DeNoise AI layer at approximately 65% over the entire image. Then, it is wise to monitor any negative changes to the look of the stars in your image. I have found that sometimes the DeNoise AI plugin will change the shape of small-to-medium-sized stars, and even create “holes” in them.

To avoid this scenario, you have a few options. You can create a layer mask in Photoshop to protect all of the stars in the image before running Topaz Labs DeNoise AI.

You could also (this is my favorite method), apply the DeNoise action to the entire image globally, and then use the eraser brush (set to the opacity, softness, and size of your choice) and carefully reveal each element in the image from beneath the DeNoise layer.

This may seem like a painstaking process, but I have found this way to offer the most control.

california nebula

DeNoise AI has helped me revive some of my noisier images from the archives.

AI-Powered Noise Reduction

I know that most of you are no stranger to the concept of machine learning. Essentially, the team at Topaz Labs trained an AI model using specific filters to produce remarkable results.

This process is well-beyond my capabilities and understanding as an amateur astrophotographer, but that doesn’t mean I can’t leverage this AI power to create better images.

This article explains how Topaz Labs used millions of clean and noisy images to train the software to understand what to remove (chroma and luminance noise), and what not too (important details, colors, and sharpness). 

To witness this AI technology in action, all you need to do is appreciate the automatic results of the DeNoise AI plugin on one of your noisy astrophotos. 

landscape images

System Requirements

A number of people have reminded me that you should consider the system requirements of this software before purchasing the plugin.

I am currently using Topaz DeNoise (version 2) on my Windows 10 Desktop with an Intel Core i7-9700K processor @ 3.60 GHz, and 16 GB of RAM. The Graphics Card is an NVIDIA GeForce RTX 2060.  

On my machine, the DeNoise AI preview window updates really fast and applying the filter takes about 1-2 seconds. However, slower machines will inevitably bring this process to a crawl, so I looked into the system requirements Topaz recommends.

CPU Minimum

  • Intel i5 or equivalent (3.0GHz and above)
  • AMD Ryzen 5 or equivalent (3.0GHz and above)

CPU Recommended

  • Intel i7 or greater (4GHz and above)
  • AMD Ryzen 7 or greater (4GHz and above)

Graphics Card Minimum

  • NVIDIA 2GB of dedicated VRAM (GT 740 or greater)
  • AMD 2GB of dedicated VRAM (Radeon 5870 or greater)

Graphics Card Recommended

  • NVIDIA 4GB of dedicated VRAM (GTX 970 or greater)
  • AMD 4GB of dedicated VRAM (Radeon RX 460 or greater)


  • Minimum: 8GB
  • Recommended: 16GB
  • Optimal: 32GB

If your computer meets the recommended requirements for the software, Topaz Labs states that ‘Users should experience no performance issues, though slowness may occur with large files”. I have found this to be true in my experience using the software on a fast Windows 10 PC. 

Final Thoughts

Processing astrophotography images can be challenging, especially when you haven’t collected the amount of data you hoped to. It would be nice to acquire 10+ hours of exposure time on each target, but that isn’t realistic for a lot of people.

Topaz Labs DeNoise AI allows you to make the most of your data integration. If you’re sitting on a handful of images that aren’t quite “post-worthy”, run them through DeNoise AI and give them a second look. 

One of the most exciting parts of this experience, for me, was going through some old astrophotos and seeing which ones I could potentially recover. Tools like DeNoise AI have the ability to breathe new life into old projects.

To justify the cost of a new software tool, you need to receive a lot of value from it. I truly think that you will enjoy using Topaz Labs DeNoise AI on your astrophotos now, and in the future. 

M82 Galaxy

Helpful Resources:

Related Posts:

Related Tags

Andromeda Galaxy Astrophotography Tutorial

|Galaxies|16 Comments

In this post, I’ll walk you through the image processing steps I used to create the image of the Andromeda Galaxy shown below. This astrophotography tutorial uses Adobe Photoshop to bring out the intense colors and detail of a galaxy that was photographed using a DSLR camera and a small telescope. 

You can follow along and process the exact same data I did (download here), or you can try these techniques on your version of the Andromeda Galaxy taken using your own equipment. If you choose to download my data and process it, you can skip straight to the Photoshop portion of this tutorial. 

This tutorial uses DeepSkyStacker and Adobe Photoshop. If you are new to this process, you may find the following DeepSkyStacker tutorial useful. The images used in this tutorial were captured using a Canon EOS 60Da DSLR camera with the RAW image type selected.

Messier 31 – The Andromeda Galaxy.

The equipment used for this shot:

telescope equipment

The camera and telescope equipment used for the photo on this page.

About the Image

This image was captured on a clear night under Bortle Scale Class 4 skies. A William Optics Zenithstar 73 telescope was used like a telephoto lens on my Canon DSLR camera. The telescope tracked the apparent movement of the night sky thanks to Sky-Watcher HEQ5 equatorial telescope mount. 

You can watch the complete journey leading up to this image in the following video: Photographing the Andromeda Galaxy. The images were collected while we camped under the stars on a beautiful August night. 

The final stacked image includes 67 x 2-minute exposures (2 Hours, 14 Minutes Total) at ISO 800. Calibration frames were used (15 x darks, flats, and bias) to help calibrate the final integration.

Wide-Field Version 

Roughly a month after capturing the original version of the Andromeda Galaxy shared on this page, I photographed this amazing object again from even darker skies. This time around, I used an ultra-wide-field refractor telescope, the William Optics RedCat 51.

The 250mm field of view at F/4.9 created the widest, deep image of the Andromeda Galaxy I’ve ever taken. Using the same image processing techniques shared on this page, I created the following image using 100 x 2-minute exposures with my Canon DSLR.

Andromeda Galaxy RedCat 51

The Andromeda Galaxy captured using the William Optics RedCat 51. 

I blended in my previous version of M31 using the Zenithstar 73, but only at about 25% opacity. I believe this helped to showcase a bit more of the outer structure details. 

Andromeda Galaxy Image Processing Tutorial

The goal of this image processing tutorial is not for you to follow my process step-by-step to achieve the same result, but to get a better understanding of the tools and techniques I use to edit my astrophotography images. No matter what level of experience you have, I am confident that you will find a number of helpful tricks you can use while processing your own image of the Andromeda Galaxy. 

before and after photo

Assessing your Data

After collecting your images of the Andromeda galaxy with your camera, you need to organize all of the files on your computer so that you can easily find them. I like to sort all of the picture files and calibration frames into separate folders.

Create a folder for your light frames, dark frames, bias frames, and everyone’s favorite, flat frames. The root folder should include the date the images were taken so you have all of the information you need to reference later including the moon phase and location.

You may also want to include the telescope, camera, and filter that were used in the folder name, as these details may be hard to remember years later. Here is a look at the folder structure for my data on the Andromeda Galaxy.

folder structure

Make your life easier by taking the time to organize your images and calibration frames into folders.

You may find it useful to go through your light frames in a RAW image preview software such as Adobe Lightroom or Adobe Bridge. Delete any frames that have airplanes, or satellites passing through them, or that are not the full exposure length. If your tracking accuracy and autoguiding were successful, you should not have to delete any frames due to poor tracking. 

With the files organized and easy to find, we can now import the image data into DeepSkyStacker for calibration and integration. This will create an intermediate file that can then be processed extensively in Adobe Photoshop. 

Stacking and Calibration

DeepSkyStacker will allow us to calibrate our data using support frames, and improve the signal-to-noise ratio of the final image through integration. The software will automatically align and register the images on top of one another, to reduce noise and increase the signal (light) in the image.

To start, select all of your light frames (the actual pictures) by clicking the Open picture files button on the top left of the screen. This is where you will choose all of the images on the Andromeda Galaxy you would like to stack. If you have organized your images and folders neatly, and have filtered out any images that should not be in there, this process will be very easy. 


Load all of your light frames (picture files) into DeepSkyStacker.

You will then need to repeat the process, for your calibration frames. Click on the buttons for dark frames, flat frames, and bias frames in the top left-hand menu of DeepSkyStacker. I recommend using at least 15 support frames to properly calibrate the image for further processing. 

You can review the details of your image files in the lower portion of the screen.

This is a great time to check to make sure the following:

  • Your light frames are all the same exposure length and ISO
  • Your dark frames match the exposure length and ISO of your lights
  • Your Bias frames are the fastest exposure length possible
  • You have loaded at least 15 flat frames into DeepSkyStacker

image stacking

Review the details of your image files in the lower half of the DeepSkyStacker dashboard.

If everything looks in order, you can go ahead and click check all, followed by Register checked pictures. From here, we will need to make sure that a few key settings are used so that DeepSkyStacker can properly integrate and calibrate the image data. 

Register and Stacking Settings

Use the Register Settings shown in the image below as a reference. Because we have used all of the recommended calibration frames, and have pre-screened the images, these settings should work well. Feel free to try using the exact settings I have used to stack the image, including the sigma-clipping combination method to stack the light frames. 

deepskystacker settings

Recommended Settings in DeepSkyStacker.

You can change the Star detection threshold in the advanced tab of the Register Settings. The setting you use will depend on the type of data you are stacking. For this image, I suggest using a threshold of 25%, as it will speed up the stacking process significantly, and 456 stars are more than enough to successfully register the image. I have always kept the “Reduce the noise by using a Median Filter” option checked. 

star detection threshold

As for the Stacking Parameters (which can be accessed by clicking the button in the Register Settings box), I suggest leaving the default settings in place under the light, dark, flat, and bias tabs. You can select the Enable 2x Drizzle option if you want, but be warned that your computer will kick into overdrive, and the output file will be massive. (learn more about the benefits of using drizzle). 

stacking parameters

Now, click the OK button and review the final Stacking Steps of your image, and the estimated total exposure time. The total integrated exposure time for my image of the Andromeda Galaxy is 2 hours, and 14 minutes. 

Your stacked image of the Andromeda Galaxy may look very different than mine. Everything from the amount of exposure time invested in the image, to the filter used will affect this. 

The resulting image of the Andromeda Galaxy shown below has a typical look to broadband, color images shot using my DSLR camera. This is our intermediate file, that is now calibrated to reduce much of the noise and artifacts present in a single exposure. 

astrophotography image

The stacked 32-Bit TIF file created by DeepSkyStacker.

The integrated data now has a much better signal-to-noise ratio, which will make the processing and manipulation techniques in Adobe Photoshop much more effective. The final processed image will look much different than the version you see at this stage.

Image Processing in Adobe Photoshop

Adobe Photoshop is a powerful tool for processing astrophotography images. It is a robust graphics software designed primarily for photography and design, but many amateur (and professional) astrophotographers use Photoshop for astrophotography image processing. 

Adobe offers a subscription service for their complete Creative Cloud Suite, or for stand-alone products such as Adobe Lightroom or Photoshop.

Adobe Photoshop CC

Download Photoshop CC (Single App Plan)

Open the Stacked TIF Image

The first thing we need to do is open the file that DeepSkyStacker created using all of our pictures and calibration data. By default, DeepSkyStacker will output the intermediate file as a 32-bit .TIF, in the destination you have selected in the settings.

The default name of this file will be Autosave.TIF. You can change this file location in the output tab of the stacking settings option.

Alternatively, you can save the stacked .TIF file by clicking Save picture to file, at which point it will convert the image to 16-bit mode. We need to convert the 32-bit image to 16-bit to fully process the file in Adobe Photoshop anyway.

Now it’s time to open the TIF file you created in Adobe Photoshop. If you are opening the Autosave.TIF file that DeepSkyStacker created on it’s own, you first need to convert the image to 16-bit, by clicking Image > Mode > 16-Bits/Channel.

You will now have complete access to all of Photoshop’s tools to manipulate the data.

Crop and Initial Curve Stretch

I like to start by cropping the image slightly, just enough to remove any stacking artifacts around the edges of the image. This can create an inaccurate histogram reading, and you wouldn’t want to include these edges in your final image. You can use the Crop tool, or simply select the area you would like to keep (98% of the image), and click Image > Crop from the main menu. 

The first change we will make to the data is a simple curves stretch. Using the Curves tool (Image > Adjustments > Curves), perform a basic curve stretch using the image below as a reference. Now, the data is non-linear, and has been manipulated to help us better see the dynamic range of this object. All of the amazing deep-sky astrophotography images you have ever seen were “stretched” like this. 

curves stretch

My initial curves adjustment.

For this object, it is important that we do not over-stretch the core of the Andromeda Galaxy. It is the brightest area of the object, and details surrounding it could easily be lost. To avoid this, you can either blend in shorter exposure images of the core using a layer mask, or isolate this area (again, using a mask) so that you do not stretch this data as far as the surrounding details.

In the next step, I’ll show you an easy way to selectively stretch all of the areas of the image except the bright core. 

Selective Curve Stretch

To start, we’ll select the brightest area of the image using a mask. Click on Select > Color Range > Sampled Colors. Now, use the eyedropper tool within the Color Range dialog box to select the nucleus of the Andromeda Galaxy. 

Feel free to use settings similar to the ones below on your image. This will create a rough mask that we now need to refine.

color range

Now, navigate over to the Select and Mask tool (Select > Select and Mask) to soften the edges around the selection. This is an important step because we need to create a smooth transition between the areas at the edges of the mask. 

Once you are happy with the amount of feathering around the mask (using the Feather slider in the Select and Mask dialog box), you can click OK, and the selection mask will activate. Now that we have defined the area we want to leave untouched, we need to click Select > Inverse to apply our curves adjustment to. 

Perform a modest curves stretch as you did in the last step, and notice that the areas we have masked off (the nucleus of the Andromeda Galaxy) remain unchanged. You may want to make several iterations of this process, making small curves stretches each time. 


Before and after making a selective curves adjustment. 

If you were too aggressive in your selective curve stretch, you will create an unnatural looking transition between the core of the galaxy and the mid-tone areas. To avoid this, find a balance between the amount of feathering at the edges of your mask and the amount of curve adjustments you make. 

The same process of masking the bright core of the galaxy can be used on the surrounding stars in the image. This technique is a great way to pull your data forward without bloating the stars. 

Color Balance the Image 

At this stage, we will balance the color of the image by setting the black point, and the white balance. Start by creating a Threshold Adjustment Layer (Layer > New Adjustment Layer > Threshold). This creates an exaggerated view of the image showcasing the brightest and darkest areas of the image.

Threshold Adjustment Layer

A threshold adjustment layer used for setting the black and white points. 

We’ll use this layer to plot our black and white prints of the image. The black point is used to balance the background night sky to a neutral grey, while the white point is used to set a natural white color as we know it on Earth from the Sun. 

Using the slider in the properties tab of the threshold adjustment layer, choose an area of the sky that contains no stars, and is not touching the galaxy. Use the Color Sample Tool (found in the main toolbar) to plot 2 points on the image where there is nothing but dark sky.

Make sure that the Sample Size (found at the top left of the screen) is set to 5 by 5 average for the best results. 

Setting the Black and White Points

Now, plot a point on the image that is the brightest “white” area of the picture. In most cases, this is a star, but this time I have chosen to use the center of the galaxy core to set the white balance. For the most accurate rendition of colors, you will want to use a star that is the same type (G2V class) as our Sun.

These plotted points will now give us a reading of the pixel information and the current balance of colors in the image. To see this information, turn off (or delete) the threshold adjustment layer, and open the Info window (Window > Info).  

At this stage, we just need to balance the colors out a bit. If your image is like mine, it is very brown and ugly at the moment. We can balance the colors by adjusting each color channel independently and matching the values of our plotted points.

With the Info window open, click on Image > Adjustments > Levels. From the levels window, select each color channel from the drop-down menu and adjust the sliders. For my first levels adjustment, I have set the black point to read 20, 20, 20 across the RGB channels. These values will increase shortly, as we will pull the data forward even more. 

color balance

This is a good time to save the image. For all further edits, it is wise to create new layers on top of the original. This way, you can save the file with each adjustment made on its own layer. Label each layer with the adjustment you have made, and then you can save the complete .PSD file with the ability to go back and edit at any stage later. 

Targeted Curves Adjustment 

A powerful way to make a targeted curves adjustment in Adobe Photoshop is to hold down CTRL on your keyboard and plot a temporary reference point. With the Curves window open, hold down CTRL and click an area of the background sky. Now, holding down CTRL once more, click an area of the Andromeda Galaxy that you would like to brighten (the mid-tones at the edges of the galaxy),

If you noticed, the histogram on the Curves window now has two points plotted on the graph. You can now “pull” at the data with a targeted approach, as you now know where specific pixel data lies in the graph. The goal is to bring out the mid-tones, without bringing up the dark sky, or disturbing the bright core of the galaxy.

Curves Photoshop

Making a curves adjustment with plotted points on the histogram. 

At this stage, we can now see a lot more of the galaxy structure. The image is far from done, but it’s nice to see all of the interesting details of our deep sky object. This is another great time to save the image. I also like to use the History state feature of Adobe Photoshop (Window > History) if I ever need to go back and make small changes during my process.

Saturation Boost

You may want to increase the saturation of the colors in your image (watch my video tutorial on boosting colors). I find the best way to accomplish this is to create a Hue/Saturation Adjustment Layer. We need to define specific areas of the image to apply this effect to, and the Color Range Tool is a convenient option. 

Go to Select > Color Range > Highlights, and adjust the slider to define the areas of light we would like to increase the color of. In my case, I have chosen the bulk of the highlights, as I would like to increase the saturation of the galaxy as a whole, and the brightest stars in the field.

To refine the selection, you can use the Select and Mask Tool, or simply Select > Modify > Feather using a value of 1 or 2. 

With the selection active, go to Layer > New Adjustment Layer > Hue Saturation. Now you can adjust the Saturation slider to taste, boosting the intensity of the colors in your image. This is where your personal taste dictates the direction of the image. I would suggest not going overboard with your saturation boost adjustment. 

At this point, I recommend creating a visual merge (Shift + Ctrl + Alt + N + Eon the keyboard), and naming this layer “SATURATION”. If you have followed a similar path to me, your image and layers will look a little something like this:

Andromeda Galaxy Photoshop Tutorial

The Andromeda Galaxy with a selective boost in saturation. 

If you want to dive deeper into this process, you can read my full tutorial on selective color boosting for a complete breakdown of the technique.

Minimize Stars

Minimizing the size of the stars in your image is a great way to draw more attention to your deep-sky object. I find it to be one of the most dramatic differences between a good astrophotography image, and a great one. 

Reducing the size of the stars in your image is easy, but you will need to monitor a few things along the way. First, create a new layer, and name it STAR MINIMIZE. That way, we can turn the layer on and off to see the difference it made. 

Start by using the Color Range Tool again, selecting Highlights from the drop-down menu. Adjust the slider so that most of the stars are selected, but not the entire disc of the galaxy.

The goal is to select only the stars, so we can apply a minimizing effect on them. We will need to refine this selection and remove the bright areas of the galaxy, as we want these areas to remain unchanged. 

Using the Lasso Tool (found in the main toolbar), hold down the ALT key, and draw around the areas of the Andromeda Galaxy that you do not want to apply a star minimizing effect to. Holding ALT will ensure that this action de-selects area of the selection. 

star minimize

Settings for minimizing stars with the minimum filter in Adobe Photoshop. 

Now, go to Select > Modify > Expand, and expand the selection by 1 pixel. You should notice that the “marching ant” selection has changed and that there is now more room around the star selected. You may want to expand the selection by 1 more pixel, depending on the aggressiveness of the original selection made.

Next, go to Select > Modify > Feather, and use a Feather Radius of 1 pixel. This has softened up the selection around the edges, which is important for blending purposes. 

With our selection carefully refined, we can apply the star minimizing effect to the stars. Go to Filter > Other > Minimum, and use a radius of 1.0 pixels. Make sure that the Preserve option is set to Roundness and click OK. Click anywhere on the selection using the Lasso Tool to deselect it. 

Here is what my image of the Andromeda Galaxy now looks like with smaller stars.

Smaller Stars

Noise Reduction and Artifact Removal

If your stacked image includes 3+ hours worth of exposure time, chances are the noise is minimal. For my data, there is still quite a but of camera noise in the images, even using 67 light frames and calibration data. There is also an unnatural glow coming from the bottom of the image.

Let’s start with the noise. I prefer to use the noise reduction tool found within Adobe Camera Raw. To access this feature, click Filter > Camera Raw Filter. The noise reduction tool is found under the Detail Tab and can be controlled using the Luminance slider under the Noise Reduction heading. 

Zoom into the image to about 200%, and experiment using different levels of noise reduction on the slider. You can also mask and sharpen the image using this tool, but I don’t recommend doing that yet (even though I did in the example). Here are the noise reduction settings I chose to use for my image of Andromeda. 

noise reduction settings

Use the sharpening tool found under the detail tab of Adobe Camera Raw. 

Now that the noise is under control, we can tackle the subtle glow at the bottom of the image. In this situation, I think the easiest way to correct this is by copying the top most layer, and reducing the brightness. Then, I can remove the areas of the image that I do not want to darken using a simple mask and the Eraser Tool

Odd gradients like this are some of the most challenging processing scenarios, and can usually be avoided with proper flat frame calibration. I’m not quite sure what went wrong this time (the horizontal banding indicates it could be something to do with the dark or bias frame signal), but luckily fixing a subtle horizontal gradient like this is not too difficult. 

Gradient Xterminator is a handy third-party plugin for removing gradients and vignetting in your images. This is the method I used on the Andromeda Galaxy image, although I have shared ways to remove gradients without Gradient Xterminator in the past. 

Using Photoshop Actions

I have installed a useful astrophotography image process Action Set to my version of Adobe Photoshop, and I find it exceptionally useful. The Astronomy Tools Action Set contains many time-saving, powerful actions you can apply to your image with the click of a button. You do not need these actions to create amazing images in Photoshop, but I find them to be very handy.

If you are using this action set, I like to run the “Enhance DSO and Reduce Stars” action at this point. It can make a dramatic difference to the image in a single click. It basically pulls the faint details of the galaxy forward and applies another star minimizing effect the image. I prefer to set this layer to 50% opacity once complete.

You can also try running the “Make Stars Smaller” action, which should be used carefully as it can eat away at the stars in your image. 

Here is a look at each layer of the process, to give you a clear idea of when each processing technique took place.

processing steps

Each layer of the image is labeled with the processing step that took place. 

Selective Sharpening

It is wise to only sharpen the areas of your images that you intend to sharpen and to not simply run a sharpen filter over the entire image. For example, you would not want to sharpen empty areas of the background sky or the larger stars with a pleasingly soft glow. 

Again, we’ll use a mask selection to isolate the areas we would like to sharpen. The Select > Color Range > Highlights method works well, and be sure to refine the mask with careful feathering.

The sharpening filter I enjoy most is the one found inside of Adobe Camera Raw. This tool features a number of useful options to apply just the right amount of crispiness to your image. You’ll find it under the Detail Tab of Adobe Camera Raw (Filter > Camera Raw Filter).

Andromeda Galaxy

Finishing Touches

From this point forward, you need to decide the overall story you want to tell with the image. You can apply subtle tweaks to enhance the details of the image you enjoy most, whether that is having tiny stars across the field, cool blues in the galaxy, or a well-defined core. It may take several astrophotography image processing sessions to understand what makes a great image in your eyes. 

You may want to adjust the orientation of the image, too. For the Andromeda Galaxy, I like to see it in portrait orientation so the galaxy is on an angle. To me, this gives the Andromeda Galaxy more depth and better showcases its spiral structure.

One tip I’d like to share is to process two entirely different versions of the image. This means starting from scratch, making subtly different decisions about each action along the way. Then, compare both processes of the image, and decide which one you like best. Often times, I will combine the two processed image together with the top layer at 50%. 

With the selective masking techniques I shared in this tutorial, you’ll have countless ways to process your image of the Andromeda Galaxy in the fashion that you prefer. 


I hope you have enjoyed this image processing tutorial on the Andromeda Galaxy. To keep up with my latest videos, tutorials, and equipment reviews, please subscribe to the AstroBackyard Newsletter

Download My Image Processing Guide

If you would like to learn about every astrophotography image processing technique I use in DeepSkyStacker and Photoshop, you can download my premium guide. The PDF download contains over 100 pages of the specific steps I take to process all of my images. The guide is available here.

image processing guide

Related Posts:

Related Tags

Use the Select and Mask Tool in Photoshop

|Tutorials|4 Comments

The Select and Mask Tool in Photoshop CC is a powerful way to edit selective areas of your astrophotography images. Whether you want to separate the stars from your deep-sky target, or apply subtle noise reduction to the background sky of your image, the select and mask feature will get you there.

Adobe Photoshop CC is an effective way to process astrophotography images, in a very creative and enjoyable way. If you use Photoshop to process your astrophotos as I do, this tutorial should be very useful to you.

Adobe Photoshop CC

Download Photoshop CC (Single App Plan)

About a year ago, I experienced the true power of the Select and Mask tool in Photoshop first hand. It has quickly become one of my favorite and most-used features of this application for processing my deep sky astrophotography images.

The Select and Mask tool allows you to get very specific about each and every edit you make to your images. Creating layer masks is one of Photoshop’s core features, and it is especially useful when editing astrophotography images. 

Photoshop Tutorial

The Select and Mask Tool

The Select and Mask tool is Adobe Photoshop’s powerful selection tool with advanced mask refinement options. It gives you complete control over your layer mask and allows you to precisely define the edges of your selection.

When processing a deep sky astrophotography image, it is often beneficial to select different aspects of your images and process them independently from one another. For example, there are times when you will want to increase the brightness of a nebula, without bloating the stars in your image.

When selecting these areas to process, you want to avoid creating a hard, unnatural edge between your selective area and the original. For this reason, being able to accurately feather your selection allows you to control the amount of softness between these areas and naturally blend them together.

In the example below, you’ll see how I have increased the saturation of the Lagoon Nebula, without adding color noise to the background sky or stars.

By using the Select and Mask tool to define the colors found in your deep-sky target,  you have complete control over the amount of saturation applied. By using the selection mask as a reference, you can confirm that you are only applying these effects to the nebula, and not the image as a whole.

Where to Find the Select and Mask Tool

Those that are using the latest version of Adobe Photoshop can navigate to the Select and Mask tool from the Main Menu Bar in a few ways. The most direct route to this feature is:

Select > Select and Mask

This is the path most people will take that are using the Select and Mask for general photography purposes, but not necessarily astrophotography. Here, you’ll find tools such as the Quick Selection Tool and the Refine Edge Brush.

These features are useful for accurately masking a subject and removing them/including them on a new background. The Onion Skin view mode is particularly useful here, as it adjusts the opacity to provide you with a useful view of both layers at a time. 

Although this is a “one-stop’ shop” for refining your mask selection, I don’t consider it to be the best way to utilize this tool for astrophotography image processing purposes. Instead, I prefer to start with the following path:

1. Select > Color Range

To start, use the traditional method of making your selection based on my original image processing workflow. This will give us a rough selection to start with, that we can refine further using the Select and Mask tool. 

In the example below, I used the Sampled Colors option in the “Select” drop-down menu. When making a selective increase to color saturation, it’s often best to sample the dominant colors of your deep-sky object.

You can also use the Highlights selection mode, and adjust the Fuzziness slider to include the areas of light (signal) in your image. Keep in mind, this method will usually include your stars, as well as your deep-sky target. In many cases, you will want to separate the selections between the two. 

Select color range tool in Photoshop

With the “Marching Ants” now showing (the dotted lines that Photoshop uses to indicate a selection), we can now refine our selection mask by navigating the Select and Mask button in the Select drop-down menu.

I cover this topic in-depth in my detailed selective color boosting tutorial.

2. Select > Select and Mask

Here is where things get interesting. I suggest using the Black and White view mode, as it is the most helpful masking overlay for our purposes. The black areas of the image are un-selected, while the white areas are where we will isolate our adjustments to.

By far, the most powerful refinement tool here is the Feather slider. This is where we can adjust the amount of blending refinement between our subject and the rest of the image.

The Select and Mask Tool

Feel free to adjust the Radius slider in the Edge Detection area if desired, although I usually leave this slider alone personally. You may find the Smooth slider found underneath the Global Refinements heading to be useful as well.

The great thing about the Select and Mask feature is the ability to preview changes made to your layer mask in real-time. You can adjust the sliders on the right, and monitor how these changes affect your selection before activating the selection.  

I recommend only adjusting the Feather and Shift Edges sliders under the Global Refinements heading to start. In my opinion, these two adjustments have the biggest overall impact on the usefulness of your selection when it comes to astrophotography.

Shift Edges will expand your selection to include even more of your original selection (your subject). In turn, you are also selecting more of the image overall, and becoming less selective about where you will apply edits to. 

Feather will increase the softness of your selection at the edges, creating a smoother, more natural blend between the areas you enhance and the rest of your image. I believe that the true value of the Select and Mask tool lies in this feature alone. 

Refine your selection using feather

As you can see, you’ve got some decisions to make here. I suggest using a middle ground between the examples above. Here are the exact settings I used to select the Omega Nebula in my example.

selection settings

Applying Effects to Your Selection

The whole point of spending so much time and effort refining our selection is to make powerful adjustments to the selection from increasing saturation to sharpness. Having the ability to make accurate selections that will blend seamlessly into the original image is an incredibly powerful tool.

Any adjustments made to the selection can then be isolated and organized in its own layer, and the level of opacity can be adjusted to taste. Slowly applying subtle enhancements to your image in a very intentional and responsible way can lead to some incredibly powerful images. 

Some of the primary adjustments I apply to selected areas of my astrophotography images include:

  • Saturation Increase
  • Noise Reduction
  • Sharpening
  • Star Minimizing

All of these enhancements can be made to specific aspects of the image in an organized way. This technique ensures that you do not apply enhancements in one area, that degrade the image in another. For example, you can apply a stronger level of noise reduction to the areas of your background sky, while leaving the delicate sharpness of details within your deep-sky object intact. 

An example of this technique in practice when using a third-party plugin like Topaz DeNoise AI to reduce the noise in your image. Although this took benefits from machine learning and largely understands which areas of the image to “leave alone”, you’ll still want to protect the critical regions of detail in the image using a layer mask before running the tool. 

Use it to Create New Adjustment Layers

The Select and Mask tool is best utilized when in combination with an adjustment layer. Adjustment layers are a key element of a non-destructive image processing workflow, as they allow you to go back and make changes to the layer.

One example of an effective adjustment layer is one that sharpens the fine details of your subject, yet does not sharpen the background noise, stars, or any other aspect you do not wish to sharpen.

You can use the Select and Mask tool to isolate the areas of your image you want to sharpen, and feather the edges of your mask to blend the affected area into the background sky.

Use the advanced mask refinement tools to target your area of interest, and apply your sharpening adjustments using the Adobe Camera Raw filter.

New Adjustment Layer

By applying the sharpening enhancements to an isolated area, you can sleep comfortably knowing that you have not degraded the quality of your starry background sky.

The same process can be applied to image enhancements such as increasing star color, correcting gradients, and many more useful image processing tasks.

I hope that this tutorial has inspired you to try the valuable Select and Mask tool found within Adobe Photoshop CC. For my latest updates, tutorials, and reviews, please subscribe to the AstroBackyard Newsletter

Photoshop image processing tutorial

Interesting Note:

The photo of the Lagoon Nebula above (and in the video) was captured using amateur, affordable astrophotography gear back in 2013. It is possible to photograph incredible deep sky objects in space using an ordinary DSLR camera and small telescope with the right approach.  Here is a breakdown of the equipment used for this photo:

astrophotography telescope

The Explore Scientific ED80 Triplet APO Refractor.

Download My Image Processing Guide

If you would like to learn about every astrophotography image processing technique I use in DeepSkyStacker and Photoshop, you can download my premium guide. The PDF download contains over 100 pages of the specific steps I take to process all of my images:

image processing guide

Related Posts:

Related Tags

Remove Gradients in Your Astrophotos with Photoshop

Adobe Photoshop is the preferred weapon of choice for many astrophotographers of varying levels of experience.  The intuitive user interface and limitless image processing capabilities make it a real contender in the astrophotography world.

The seamless integration with the .RAW image files produced by a Digital Camera makes Photoshop an attractive choice for photographers using popular Canon and Nikon DSLR’s.

I have included a section on gradient removal in my premium astrophotography image processing guide for those interested. 

It continues to be my personal favorite tool for processing astrophotography images.

The M78 nebula in OrionWhether you are brand new to astrophotography image processing, or a seasoned veteran, an uneven field in your image is something that every astrophotographer will deal with at some point.

The steps I will discuss below can be done in Photoshop without using any additional plugins. However, I strongly recommend investing in the Astronomy Tools Action Set, and Gradient Xterminator.  They are well worth the expense and can make a monumental difference to your images.

This Photoshop tutorial involves the following:

  •   Assessing your uneven field
  •   Removing the DSO from your image
  •   Creating a synthetic flat frame
  •   Subtracting the flat frame from your image


An Effective Photoshop Technique for Removing Gradients

One of the most time consuming and frustrating stages of your image processing workflow can be dealing with gradients.  Your background sky goes from a dark blue to pink as the encroaching glow of city light pollution stains your image.  Luckily, there is an extremely useful and effective method for removing gradients using Photoshop.

This method involves creating a synthetic flat frame and subtracting it from your original image.

Quickly correct your uneven field

The method you’ll see me use in the video below is a very popular way to remove gradients using Photoshop.  Variations of this technique have been used by amateur astrophotographers for years.  I do not take credit for this method.  Like almost everything else I have learned about this hobby, I picked this up by watching and reading countless image processing tutorials shared by others.

Video: How to Remove Gradients in Photoshop:

This technique works better on some deep-sky images better than others.  Large targets such as nebulae that fill the entire frame will be difficult to tackle using this process.  In my example, the Leo Triplet of galaxies worked very well, as they are surrounded by a large area of surrounding space.

Assessing the Data

  1. Start by opening up your final stacked image.  I use DeepSkyStacker to register and stack all of my image frames.
  2. Crop your image to remove the stacking artifacts and overlapping frames.
  3. Convert the image from 32bit to 16 bit, to open up further editing options in Photoshop.
  4. Perform a quick levels adjustment, bringing the left-hand slider up against the data on the histogram.
  5. Make a curves adjustment, pulling the details contained in your deep-sky object forward.
  6. By now, you should have a good idea of how bad the vignetting and color gradients are in your image.


Gradient issues in a astrophotography image

A curves adjustment will show the uneven field

Removing the DSO from the image

Now comes the fun part.  This is where you either have the option of running a third-party plugin such as Gradient XTerminator or tackling the issue yourself.  It’s beneficial to learn this method of removing gradients in photoshop for all types of astrophotography including wide field Milky Way shots.

  1. First, copy your original image layer and paste it on top.  Name it “Gradients”
  2. Copy this layer to a new image. Select All > Copy > File > New > Paste.
  3. On the new image that was just pasted, remove the deep-sky objects from the field of view.

This can be done in various ways, but I prefer to use the healing brush.  The important part to remember is that we are only interested in the color information of the background sky.  We don’t want to change the data found in the deep-sky objects themselves.  See this in action in the video above.


Using the healing brush in Photoshop

Remove the DSO using the healing brush

Creating a Synthetic Flat Frame

Now that we have a version of our image without our deep-sky object(s), we can correct the uneven field in the background sky.  At this point, you may also want to remove any bright stars that may negatively affect the resulting synthetic flat frame.

Richard Hum had this to say on YouTube:

What I usually find helpful is to use Select > Color Range > Highlights to select the stars, and then do a content-aware fill. I find it works better than not removing the stars and just doing dust and scratches. You can use the Select and Mask tool to refine your selection mask.

  1. Now, we need to blur the details of our copied DSOless image. Choose Filter > Noise > Dust and Scratches.
  2. For my camera’s resolution in the example, a Radius value of 80 pixels was used, and a Threshold of O.
  3. You should now see a blurred version of the background sky, with an evident uneven field.


creating a synthetic flat frame

Our synthetic flat frame

Applying the Flat frame to your Image

  1. Now, go back to your original image, and make sure you have the “Gradients” layer we created selected
  2. Next, choose Image > Apply Image.
  3. From the Source drop-down menu, select the copied, blurred image we just created. (Untitled-1)
  4. From the Blending Mode dropdown, select Subtract.
  5. Leave the Opacity at 100%, and set the Offset to 30 and hit, OK.


Deep sky astrophotography

Your new and improved image

Your new image with the gradients layer on top should look much better.  The “Gradients” layer we created can be scaled back by using the Opacity slider on the layer.  You may not need to use this layer at 100% to completely correct your gradient issues, but expect to have it set to between 80%-100% in most cases.

This layer can be toggled on and off to review and inspect the improvements to your image.  If necessary, you can go back and test some of the variables including changing the Radius value, and/or removing the stars before blurring the frame.

From this point, you can go about your image processing as you normally would, with a much improved, even background sky.

Widefield images captured with my camera lens suffer from horrible vignetting in my backyard.  The gradient removal technique above was used on this image of the Orion constellation to correct the background sky:

Orion constellation

The Orion constellation from my backyard

Try this method on some of your existing widefield images that suffer from a gradient in the background sky.  An uneven field is a common problem in almost all astrophotos, so mastering this technique will come in handy in your future endeavors.

Did you know you can sell your astrophotos as stock photography?  I have sold several of my images on Shutterstock over the past 3 years.  View my portfolio.

You can stay up to date with the latest images and information on the AstroBackyard Facebook page, or by following me on Twitter and Instagram.

Until next time, clear skies!

Related Posts

Astrophotography Tutorials – AstroBackyard

Astrophotography Tutorial – Deep Sky Image Processing in Photoshop

Galaxy Season Target – The Leo Triplet of Galaxies

My Complete Deep Sky Astrophotography Equipment Setup

Beginner Astrophotography Telescopes – My Top Picks


Astrophotography Tutorials –

Gradient Xterminator – Photoshop Plugin

Astronomy Tools Action Set – Pro Digital Software

Related Tags

Deep Sky Image Processing in Photoshop

Well, this is it.  In this deep sky image processing tutorial, I’ll be combining all of the data I was able to collect on the Orion Nebula this winter.  As we transition into Spring, a new array of deep-sky imaging targets will present themselves.  The winter astrophotography targets in the Orion constellation will have to wait another year to get photographed.

The camera used for this image was a Canon EOS Rebel T3i (600D), an excellent choice for beginners looking to dive into deep sky astrophotography.

Deep Sky Image Processing

Processing Walkthrough – Orion Nebula with a DSLR

Canon DSLR for astrophotography

The total amount of detail I was able to capture on M42 this winter was 3 Hours and 8 minutes of color RGB data.  I will be incorporating 2 hours and 40 minutes of Ha data into the final image using the HaRGB processing technique.  In this post, I’ll show you exactly how I process my image of the Orion Nebula using Adobe Photoshop.  I’ll start with the Autosave.tif file produced by DSS.

Some of the images used in my final photo were shot during the AstroBackyard YouTube video: Let’s Photograph the Orion Nebula.


The screenshot below shows the results of registering and stacking 4 nights worth of imaging from my backyard.  This winter has been plagued with numerous cloudy nights, so I had to capture photons here and there, under varying sky conditions.

Yes, it is very white!  That’s light pollution for you.


Orion Nebula stacked .TIF file in DeepSkyStacker

The photo sets from each imaging session were loaded into the group tabs of DeepSkyStacker.  My modified Canon T3i camera was set to ISO 800 for each imaging session, but I bumped the exposure time up to 3.5 minutes for the fourth and final set.

Using the group tabs in DSS

  • Dec 22, 2016 – 23 frames – 180″ @ ISO 800
  • Feb 2, 2017 – 24 frames – 180″ @ ISO 800
  • Feb 3, 2017 – 10 frames – 180″ @ ISO 800
  • Feb 27, 2017 – 11 frames – 210″ @ ISO 800

Image sets 1-3 were stacked using darks, bias and flat calibration/support frames. The final and fourth set did not use flat frames as I was not able to shoot them the morning after the imaging session.

I do not make any adjustments to the stacked image in DeepSkyStacker.  I bring the 32-bit Autosave.tif file into Adobe Photoshop for all post-processing.

Processing in Adobe Photoshop

I use two Photoshop Plugins in this tutorial, Astronomy Tools Action Set, and Gradient Xterminator.  See all of the astrophotography software I use here.

Cropping/Rotating the file in Photoshop

The first thing I like to do is to rotate and crop the image.  A temporary levels adjustment was made to get a better look at the edges of the frame.  As you can see, my frames rotated and shifted slightly between the imaging sessions.  This creates an unusable sky at the edges of the image, so I will crop the image to about 85%.  In the future, I plan to incorporate a plate-solving software such as AstroTortilla to help line up my images over multiple nights.

deep sky image processing

Rotating and cropping the image in Photoshop

To save some of the outer regions around the nebula, I will have to repair some of the outer background sky using the healing brush, and the content-aware fill tool in Photoshop.  Ideally, you would want to keep as much of your original frame as possible.  Once I have cropped the image, I will adjust the black point of the image.

Levels Adjustment / Setting Blackpoint

As you can see in the image below, the histogram shows that the majority of the image data is contained in the mid-level tones.  I will move the slider to the left of the histogram over until it touches the information contained within the image.  This will darken the background sky and increase the contrast of the original image.

Levels adjustment

the first levels adjustment creates much more contrast in the image

The slider to the right of the data was moved inwards as well.  It’s important that you do not clip the data and lose any pixel information.  You may notice that the core of the Orion Nebula is completely white and “blown out”, I will correct this issue later on.

Before setting the initial black-point, I will give the image a semi-aggressive curve stretch to reveal more of the outer nebulosity.  This will also discern where the nebula ends and the background sky begins. Before Photoshop will let us make this adjustment, we will need to convert the image from a 32-bit file to a 16-bit file.

Image > Mode > 16 Bits/Channel

An HDR Toning window will open up.  Avoid choosing the tempting default preset of Local Adaptation, and instead, select Exposure and Gamma from the Method selection area. Leave the default exposure and gamma settings.  As this tutorial moves on, we will be creating our own HDR (High Dynamic Range) version of the Orion Nebula using very specific actions and settings.

At this point, you can adjust the levels once more, as there is likely empty space to the left of the data in the histogram again.  You may also choose to create a copy of your original layer, or create a new adjustment layer to work from.  Having snapshots of your image at each stage of the processing workflow will help you go back and fine-tune your edits.  Personally, I like to use a mixture of new layer copies using the History feature of Adobe Photoshop.

Here is what my initial curve stretch looks like:

curves adjustment in Photoshop


The curves stretch I applied brought forward the fainter details of the outer nebulosity.

Here is a little trick I like to use: With the curves window open, hold down CTRL, and click an area of the nebula you want to bring forward.  This will plot a point on the histogram you can pull from to stretch that particular tonal range.  You can also plot an additional point of a neutral area of background sky, and know that you are pulling data forward from only the nebula itself, and not the space around it.

Levels Once the curve stretch has been applied there are two ways to set the black point of the image.  The Set Gray Point eyedropper in the levels window is great for a quick overall adjustment.  Although some astrophotographers will argue that this method results in a loss of overall range of data.   You can also manually set the color of your background sky by plotting a Color Sampler eye dropper in a neutral area of space.

Using the Info window, adjust the left-hand slider on each RGB level until the values are balanced.  A background sky with Red/Green/Blue values of about 30/30/30 is a good starting point.

Creating a star mask

If you don’t want to risk the chance of brightening the stars in your image and blowing them out, try using a layer mask to protect them from growing in size and intensity.  The art of stretching the deep-sky object, but not the stars is a constant challenge when processing astrophotography images.

You can create this mask by using the Color Range tool.  Select > Color Range.

Select Color RangeThen, use the eyedropper to select a medium-sized star within the frame.  Adjusting the Fuzziness slider will affect how much of the color range (and stars) will be selected.

You will have to experiment with the fuzziness slider to select your intended amount of stars.  In my example, I used a value of 140.  After the stars have been selected, I suggest softening the selection for a more natural blend in the mask.  To do this:

Select > Modify > Expand (2 Pixels)

Select > Modify > Feather (3 Pixels)

Again, these values will vary based on your image scale. If you are shooting wide field through a Canon T3i or similar model, these settings should work well.

Like many tasks in Photoshop, there are numerous ways to accomplish a layer mask adjustment.  For this step, I prefer to invert the selection of stars (Select > Inverse) and make my curve adjustment to all areas of the image except the star mask I created.

Here is what my image of the Orion Nebula looks like at this stage:

Image Processing - Orion Nebula

I cropped the image in a little more and used Gradient Xterminator around the edges of the DSO to balance the background sky.  Again, the core is still blown out at this stage.  I will add 2 additional stacks of 15 and 30-second images of the bright core to reveal the full range of detail in the Orion Nebula.

Astronomy Tools Action Set

At this stage of my image processing workflow, I will use my first action from Noel Carboni’s action set.   The action is called Local Contrast Enhancement.

This action does a great job at sharpening details and increasing the contrast of the deep-sky object.  It is wise to create a new layer with this action applied, so you can toggle the effect on and off.  For my image, I am going to apply a layer with this action at 75% opacity.  I have also created a mask on this layer so that it does not affect the areas of space where I do not want to increase the contrast.

Directly after this action, I prefer to run Enhance DSO and Reduce Stars.  This action can takes up to a minute or more to complete, depending on your image and the computer you are using.  Again, a new layer using this action is recommended, as this action can dramatically change the look of your image.

Here is a before/after look at my image after running Local Contrast Enhancement and Enhance DSO and Reduce Stars:

Photoshop actions before - after

Before and After applying actions in Photoshop

To make a new adjustment layer with all previous actions and adjustments made, use the keyboard shortcut: CTRL + ALT + SHIFT + N + E.  This is a very helpful technique to use as your continue to add adjustment layers to your image.

Applying the “Tamed Core” Layer

At this stage, I will apply a pre-processed stack of shorter exposures to the image.  To capture these images I shot a series of 15-second and 30-second exposures with the goal of collecting detail in the brightest areas of the Orion Nebula.  A good indicator of this dynamic range in values is the ability to discern the individual stars in the Trapezium.

The short exposures were stacked in DeepSkyStacker using dark, bias and flat frames just as the primary image was.

Orion Nebula Core ExposureThese layers were processed in the exact same fashion as the primary image.  This means that similar adjustments were made to the levels, curves, and actions – but in an isolated area.

Blending the two images will be a lot easier if they have been pre-processed in the same manner.  Some may argue that combining the core should have taken place much earlier in the process.  However, this timing of this workflow works best for my personal taste.  With so many opinions about how to properly process a deep sky image, I prefer to lean towards the workflow that I enjoy most.  This way, I can enjoy the hobby for years to come.

Here’s where it gets fun

Select the image of the detailed core, and paste it onto your original image as a new layer.  Rather than using a traditional mask method, I like to use a feathered eraser brush at an opacity of 15%.  This allows me to subtly remove the unwanted data on the top layer (the core), one brush stroke at a time.

When I need to see the faint details of the edges of the core layer, I simply create a 100% white layer and place it as the layer below.  The amount of brightness of the core is a matter of taste.  This aspect of the image has varying points of view as to how an HDR Orion Nebula is “supposed to look”.

I personally think that the Orion Nebula should have a bright core!  With the right amount of blending it is possible to show the full range of detail and keep the core as the brightest area of the image.  Flattening core to a lower brightness than the outer nebulosity can give the nebula a plastic look.

Blending the core

Layering in the core can take a long time if you are particular about the overall look of your image.  I used several copies of both stacks of shorter exposures to gradually work the new core into my existing image.

Final Processing Steps

With the full dynamic range captured in the image (depending on who you ask), I can now go ahead and make my final image processing steps to further increase the color and detail of the image.

Color sampler toolAt this point, I like to double check the levels of color in the background sky.  Using the Color Sampler Tool in 2 areas of the background sky indicates that the image is rather well balanced at the moment.

Increase Vibrance and Saturation

To increase the saturation of the Nebula without bringing noise and unwanted color from the background sky, I’ll use the Select Color Range tool again.  This time, use the eyedropper to select the color from the nebula you wish to intensify.  I choose the mid-level pink areas of Orion.

You may also want to run some actions on your image such as Increase Star Color, and Make Stars Smaller.  As always, apply these actions to a new layer so that you can control the amount of the adjustment using the opacity slider.  I will often use both of these actions, in small amounts.

Adding a layer of H-Alpha

This is where the image really starts to “pop”.  I shot over 2 hours worth of data through a 12nm Astronomik clip filter with my Canon T3i.  I will combine this data with the RGB image we just processed using the HaRGB processing technique outlined in this tutorial:

Deep Sky Image Processing in HaRGB – Tutorial

Orion nebula in Ha

The Orion Nebula in Ha

The image above is 32 X 5-minute subs @ ISO 1600

If you are interested learning how to shoot H-Alpha with your DSLR camera, read my post on how a DSLR Ha Filter can improve your astrophotography.

Without explaining every detail in the HaRGB tutorial I linked above, the premise is basically to add the Ha as a luminosity layer at about 75% over your original color image.

Because the data in the core of the H-Alpha version of Orion was blown out, it is important to note that I removed this area of the Ha luminosity layer, so that I did not lose any detail in the final composite image.  By turning the Ha layer off and on, you can determine which areas of the nebula are being improved, and which areas are losing detail and/or color.  I prefer to create another layer mask using the Ha layer, leaving only the key improvement areas at the full 75% opacity.

Below is my final image of the Orion Nebula using the processing methods outlined above:

Orion Nebula - AstroBackyard

Final Image Details:


Mount: Sky-Watcher HEQ5 Pro Synscan
Telescope: Explore Scientific ED102 CF
Imaging Camera: Canon T3i (600D) Modified
Filters: Hutech IDAS LPS, Astronomik 12nm Ha
Flattener/Reducer: William Optics FF III
Guide Scope: Orion Mini 50mm, Starwave 50mm
Guide Camera: Meade DSI, Altair Astro GPCAM2 AR0130


Image Aquisition: BackyardEOS
Autoguiding: PHD2 Guiding
Registering/Stacking: DeepSkyStacker
Image Processing: Adobe Photoshop CC

Exposure Details:

RGB: 3 Hours, 8 Minutes (55 frames)
Ha: 2 Hours, 40 Minutes (32 frames)
Total Integrated Exposure: 5 Hours, 48 Minutes

Photoshop TutorialI am always looking to improve my deep sky image processing techniques.  For a video presentation of these techniques in action, please visit the AstroBackyard YouTube Channel.  If you like to see more of my deep sky astrophotography images, please have a look at the Photo Gallery.

This winter was a memorable one for me.  By sharing my experiences in the backyard on this blog and on YouTube, I was able to connect with fellow backyard astronomers on a deeper level.  There may not have been many clear nights, but the ones that were felt extra special.  Until next time, clear skies!

Deep Sky Image Processing Help:

Settings for DeepSkyStacker

Video Tutorial: Deep Sky Image Processing in Photoshop

Astrophotography Image Processing Video (YouTube)



Related Tags

Screen Calibration

|Image Processing|5 Comments

When I purchased a new laptop computer back in 2016 for image processing and video editing and was quickly reminded of the importance of having a well-calibrated computer monitor.

The brightness of my new laptop screen was intense. It appears to be about 25% brighter than my well-calibrated 23 Inch external IPS monitor.  

When it comes to editing and viewing astrophotography images, the screen you’re using can really change the appearance of your results. If it’s too dim, you may not see all of the hidden imperfections in your data.

This results in astrophotography images that are less than pleasing to the eye. I’ve had to re-process many of my own photos in the photo gallery after discovered that they did not look the way I intended them to on different screens.

Screen Calibration for Astrophotography

If you have been processing your astrophotography images on a dim monitor, you may be in for an unpleasant surprise when you see them on a bright screen for the first time.

This can be a bit of an unsettling moment, especially if you’ve never been through this exercise before.

When you upload your image to the web, you have to accept the fact that people from all over the world may view your work on monitors and screens that display images MUCH different than yours.

Having a monitor that is too bright will show all of the impurities in your background sky.

One of the most extreme examples of the “bright screen effect” is to view your image on a mobile phone with the brightness tuned all the way up. Most people do not leave their mobile screens at this intense level at all times, but its interesting to see a potential worst-case scenario.

astrophotography tutorial

A common tactic beginners use (myself included), is to decrease the brightness or contrast of the image to “hide” the imperfections present in the background sky.

Noise, color blotches, and a generally poor signal-to-noise ratio turn to black. Unfortunately, this method degrades image quality and you lose an incredible amount of detail in your image. Don’t hide your sky!

It is wise to make sure your computer screen is giving you an accurate rendition of the image you worked so hard to capture. There are many ways to calibrate your computer monitor settings, including online tools and dedicated devices that can match specific color profiles.

The device below (Spyder5 Colorimeter), helps you share and print your images with the look you intended.


The Dataclor Spyder5Pro color accuracy device

A colorimeter will usually have a room light sensor that measures the lighting conditions of your room. If there has been a change in lighting in the room, it alerts you to modify your calibration settings for optimal color accuracy.

This creates a unique color profile for each of your monitors, and it can help you get a better match between your photos on screen and in print.

Why should you calibrate your monitor?

By spending a little time adjusting the calibration settings of your monitor, you can help ensure that the colors and brightness of your astrophotos are represented accurately.

I’ve never used a Colorimeter myself, but I have spent a lot of time adjusting settings manually to find the right balance. When I decide to start printing my photos, I think the Colorimeter is a good idea.

In terms of photography, screen calibration can have a dramatic effect on your online experience whether you are processing astrophotography images or not. You can ensure that you are seeing the images displayed on screen as they were intended to be viewed.  

This is especially important for creative professionals such as Graphic Designers, Photographers and Video Production teams.  

The idea is to have your monitor conforming to a preset color benchmark such as the sRGB or Adobe RGB color space.

screen brightness for astrophotography


How do your astrophotography images appear on other screens?

How to Manually Calibrate your Screen for Astrophotography

The first step towards adjusting your computer monitor display settings is by using the interface on the unit itself. Some models have more in-built control options than others. 

If you use an external monitor like me, it will have a set of controls, usually at the front and under the screen.

My ViewSonic LED monitor has the typical bare-bones contrast, brightness, and color mode. You’ll want to make sure that you do not have any ambient lighting in the room affecting your views, so close the blinds and turn off the light.

Do not calibrate your monitor in a bright, sunlit room, or with reflections appearing on-screen.

For accurate results, face your screen head-on, with your eye lined up with the top of the screen.

Calibration Tools and Adjustments

It is necessary to have some reference material on-screen that will let you know if you’ve pushed your settings too far one way or the other.  See the grayscale chart from APCmag below:

screen calibration tool

You should be able to distinguish between each shade of white/black

Using the Color Calibration Feature in Windows 10

If you are using Windows 10, they have a nifty color calibration walk-through that is great for making adjustments called Display Color Calibration.  

It will take you through a number of tests to see just how far off your display is.  They call it “color” calibration, but it’s really an overall screen calibration test.  

You can get to it by following this command path:  Start Menu > Settings > System > Display > Advanced Display Settings > Color Calibration.  The following calibration images are used in the Windows color calibration test.

Have you Checked Your Gamma Today?

“Gamma defines the mathematical relationship between the red, green, and blue color values that are sent to the display and the amount of light that’s ultimately emitted from it.”

Adjusting the gamma on your screen

In the image above, you should not see any overly obvious “dots” within the circles.

The Brightness Effect

As I stated earlier, having a display that is too bright can absolutely wreak havoc on an astrophoto that has been stretched too far. I know about this phenomenon all too well, as I like to stretch my data to its full potential (and sometimes go too far).

The tell-tale signs of an astronomical image that has been stretched too far, or with serious gradient and vignetting issues – is a muddy, green/brown background sky.  

The sky may appear to have a nice neutral dark grey or black on your dim monitor, but on your nephews brand new ultra-backlit iPhone, it’s a multicolored mess. 

Even images on APOD can appear to diminish in quality under the scrutiny of an overly bright display.

Here’s an image you can use as a guide.  You should be able to distinguish between the mans shirt and the background.  The black “X” in the background should be barely visible.

monitor calibration test


Contrast – Don’t Overdo it

Using the image below, adjust the contrast settings of your monitor so that the background appears black and not grey. If you have lost details in the white shirt the man is wearing, such as the buttons and creases, you have pushed the contrast too far.

adjusting contrast

My Best Advice

My advice is to process the image on image on a screen that has been calibrated as best as possible.  If you have access to an overly bright, unforgiving display – maybe have a look at your image on that as well.  

It can be useful to see an exaggerated version of your subject and fix any issues that really jump out at you.

It may be helpful to view your processed image on several different screens (including your phone) to get a feel for the middle ground. I usually preview my images on at least 3 monitors before posting online.

Take a look a few example astronomy photos taken by professionals on Astronomy Picture of the Day. Use the color, levels and background sky you see in their photos as a guideline. Chances are, the photos you see here will look great, no matter which display screen you view them on.  

Horsehead Nebula

This is because they have taken the precautions needed to ensure that their images are an accurate representation of scientific data, including screen calibration.  Many of these astrophotographers have dedicated calibration tools to help them keep their displays accurate.

I have had many issues with uneven sky backgrounds in the past, primarily due to the lack of using flat frames.

The dim monitors hide this messy background making the sky to appear a nice dark grey or black. There is value in viewing your images on a variety on screens to learn how to better process your images.  

I hope that this write-up has opened your eyes to the importance of screen calibration when processing astrophotography images.  

As for getting your night sky photos printed? I’ll save that for another post.

Watch my Astrophotography Image Processing Tutorial (Photoshop)


Related Tags

Selective Processing for More Detail

Staying Inside – Image Processing

The unseasonably cold weather and precipitation we have experienced here in Southern Ontario have given me the perfect opportunity to go through my old astrophotography images and reprocess the data.  I have been advancing my image-processing skills by studying current astronomy images taken by the pros.

Being a creative professional myself, I have always understood and appreciated the power of inspiration. I am always interested in new image-processing techniques, Photoshop tutorials and new software that can enhance my work.  Through selective processing, I have been able to squeeze out the most amount of detail from my astro images.

Western Veil Nebula

The Western Veil Nebula – I reduced the stars to show more contrast in the nebula

My latest take on The Swan Nebula is my favorite version yet. Through selective processing, I was able to tame the background stars, while intensifying the gorgeous pinks and reds in the nebula itself.  

I also recently reprocessed my wide-field image of the Western Veil Nebula, with a focus on reducing star size, and overall image contrast and color. The “witch’s broom nebula” is a tough process, especially if you have to deal with a severe gradient behind all of those stars. After assessing the gradient in Photoshop, (mostly due to heavy light-pollution) I can easily even out the sky background using the Gradient Xterminator plugin.

I am quite pleased at my latest results of the Eagle Nebula as well. I went through my astrophotography folders from the past 4 years (like I said, it’s been cloudy!)  and found a set of almost 2 hours of frames on M16 that I had not previously used!  

I combined all of the data together from May 2012, and May 2013 in DeepSkyStacker to create an image with over 3 hours of exposure time.  I decided to keep the extremely wide-field view captured by my 80mm telescope, rather than cropping the photo around the nebula.

This image really benefited from the selective processing technique. By reducing the stars on a separate layer, I was able to keep all of the detail found in the nebula.

Eagle Nebula - 80mm Telescope

Wide field image of the Eagle Nebula with my 80mm telescope

Image Processing Techniques

One of the processing techniques I have been implementing into my photos is to process different elements of the image separately. By this, I mean to process the background, the stars and the nebulosity on their own.  

I am able to do this by selecting each element of the image and stretching the data without affecting the other areas. For example, I can boost the vibrance and saturation of the nebula or galaxy without adding additional noise to the background of space and stars.

As I have stated many times, I prefer to tame the stars in the image to be as small as possible. Normally, I would run the “make stars smaller” action to the entire image in Photoshop.

This actually starts to diminish the precious detail in your deep-sky object that you worked so hard to capture! Many other actions that are intended to correct issues with the background space and stars can take away from your subject as well.

You can also manually Remove the Stars Completely from your image using photoshop.

Swan Nebula - 8 Inch telescope

My latest version of the Swan Nebula

Selective Processing

There are several ways to accomplish the selective processing technique to your astronomy photos.  You can create multiple adjustment layers of your image in Photoshop, and apply the various actions to each element of the image on a separate layer.

I use the Select and Mask tool to refine my selections before applying effects. This ensures that each new adjustment layer is blended naturally into the final image.

 Once you have applied your desired settings applied to each layer, you can use layer masks to combine all aspects of the photograph into one.  This means you will likely have layers for:

  • The Background Space – With a balanced black-point set

  • The Background Stars – Small, sharp and with lots of accurate colour

  • The Brighter Stars – Soft, or with Diffraction Spikes and Color

  • The Deep-Sky Object – Full of luminance, color and detail

  • The Core or Brightest Area of the DSO – reduced to show detail, not blown out

Selective Processing - Astrophotography

Processing the nebulosity separately from the background stars in Photoshop

You can also process the selected elements of your images as separate documents.  Sometime I prefer to do this to really focus on achieving the best possible result for my focus area, without the temptation to poke around at another feature.  

Once you have processed each version of the image with your focus area maximized, you can then combine the images using layer masks.  The blending and layer masking is definitely the most delicate stage of the process.  You can really make a mess of an image by failing to inspect all areas of your image before flattening.

I find it helpful to use a reference image of your deep-sky target. This is the best way to make sure you have not overstretched your image data, and that your colors and details are an accurate portrayal of that particular deep sky wonder. I often look for inspiration on APOD!  

To stay connected with me and my latest astrophotography images, please follow my Facebook Page.  I hope you are all excited about the wonderful deep-sky targets that will be gracing our night sky the coming months, I sure am!


Astrophotography for Beginners – The Basics

How to choose an Astrophotography Camera – My Advice

Top 5 Telescopes for Beginners – My Advice

Related Tags