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Andromeda Galaxy Astrophotography Tutorial

|Galaxies|6 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. 

Andromeda Galaxy Image Processing Tutorial

The goal of the 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 the 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. 

deepskystacker

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 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/After

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 points 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 currunt 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 of your image. 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. 

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 to 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 labelled with the processing step that took place. 

Selective Sharpening

It is wise to only sharpen the ares 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 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 a 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. 

astrophotography

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

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Use the Select and Mask Tool in Photoshop

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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 like 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.

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 selection 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 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. 

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

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Remove Gradients in Your Astrophotos with Photoshop

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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.

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 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.

Wide field 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

Resources:

Astrophotography Tutorials – PhotographingSpace.com

Gradient Xterminator – Photoshop Plugin

Astronomy Tools Action Set – Pro Digital Software

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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.

DeepSkyStacker

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.

DeepSkyStacker

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:

Hardware:

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

Software:

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)

 

 

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Screen Calibration

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.

colorimeter

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)

 

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