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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 -> Colour 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.

  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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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 favourite 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 Deep Sky Stacker 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 benefitted 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.  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!

Resources:

Astrophotography for Beginners – The Basics

How to choose an Astrophotography Camera – My Advice

Top 5 Telescopes for Beginners – My Advice

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Making the Most of it!

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Setting up my Astrophotography gear in the dark
Setting up my astrophotography gear at the CCCA Observatory using only red lights to preserve my night vision.
I had a long, eventful night at the CCCA Observatory this past Saturday. I wasn’t even planning on going, as a heart-breaking defeat of my Toronto Raptors at the hands of the Brooklyn Nets was fresh on my mind. I started packing up my astro-gear at 7:45pm. With the sun setting at 8:05pm, and a 45 minute drive ahead of me, I knew I would be breaking one of my own astronomy rules: Setting up in the dark.

By the time I arrived, it was pitch black, with only the stars and my red headlamp to light my way. I witnessed some amazing views of Mars and Saturn through my ED80 before setting my DSLR up for a night of astrophotography. I forgot a key element of any astrophotography imaging session, my guide scope. Forgetting something at home that is essential for imaging is always a frustrating experience. I knew my plans of taking 5 minute exposures of the Seagull Nebula were ruined.

Messier 3

Messier 3 – Globular Cluster

Messier 3 – Globular Cluster

I decided to take some 30 second unguided exposures of the globular star cluster known as M3. I have seen this cluster through a 20″ dobsonian telescope, and to this day, it is still my favourite sight through a large telescope.

The Sunflower Galaxy

Messier 64 – The Sunflower Galaxy

Next, I chose to image a galaxy in the constellation Canes Venatici known as M63, or, the Sunflower Galaxy. In hindsight, it was not such a great choice, considering it’s size and my limited exposure time.

The good news is that this was really a “bonus night” anyway, as the moon rose early at about 1:00am. By then, some friends had come to join me and were dazzled by views of Saturn.  The next 2 weekends are when I really plan to get some good imaging done!

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