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astrophotography tutorial

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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Manual Stacking in Photoshop for Reduced Noise

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Even without a tracking mount, your astrophotography images can benefit from manual stacking in Photoshop. This method involves aligning exposures and combining them into a master composite.  It can make a big impact on your astrophotos by reducing noise and improving the signal-to-noise ratio.

The images used in the example were captured using a camera lens in place of a telescope. A wide-angle lens can be a tremendous way to photograph a large area of the night sky at once, rather than zooming in on a deep sky object.

manual stacking in Photoshop

This night sky photo contains 11 exposures stacked manually in Photoshop

This technique requires no darks frames, no stacking software, and no tracking mount.

The 2 software applications used in this tutorial are Adobe Bridge and Adobe Photoshop. (Lightroom will also work) The main idea is to reduce noise by layering single exposures gradually, effectively canceling out much of the noise from a single frame.  The key is to gradually reduce the opacity of each layer until you reach the top of the image set.

Basic Astrophotography Camera Settings and Tips

Manual stacking is easy with Adobe Photoshop

Let’s say you have taken a 30-second exposure of the starry night sky with your camera on a tripod.  By taking 10-12 shots of the same scene, your final composite version will have much less noise, a smoother background, and more detail.

Watch the video tutorial below:


In my example, the camera happened to be sitting on top of a telescope on a German equatorial mount.  Don’t confuse this fact into thinking this method does not work without a tracking mount.  30-second exposures at wide focal lengths do not contain much star-trailing and are perfect candidates for this treatment.

The reason this technique is referred to as “manual stacking” is that the user layers each exposure manually, rather than loading the frames into Deep Sky Stacker.  The simplicity and effectiveness of this technique is something all astrophotography enthusiasts can benefit from.

Manual Stacking Example

If you are interested in the full explanation of this process, follow the link below.

Astrophotography Tutorial – Align and stack exposures in Photoshop

Capture longer exposures

A small tracking camera mount such as the iOptron SkyTracker Pro allows you to shoot longer exposures than you can on a stationary tripod. The SkyTracker compensates for the rotation of the Earth, meaning that objects in space stay put as your camera collects light.
 
This is a useful piece of astrophotography gear if you plan on photographing the Milky Way. The following images uses 60 x 2-minute exposures at ISO 1600. The individual images were stacked using DeepSkyStacker, but similar results could be produced using the manual stacking process.
 
The Milky Way

What’s New?

My deep-sky imaging has been put on hold as it has been cloudy for nearly 3 weeks straight. This weather is sure to get any backyard astrophotographer down. However, my passion for imaging couldn’t be stronger as I have recently added some new astrophotography equipment to my arsenal.  This time, it was my primary imaging camera that needed replacement.

New Camera: Canon Rebel T3i (600D)

After much consideration, I have decided to finally upgrade my primary imaging camera to a Canon Rebel T3i.  If you follow AstroBackyard on Facebook, you may have heard that this DSLR was professionally modified for astrophotography by removing the IR cut filter.  The Canon 600D features an 18MP CMOS sensor capable of producing images 5184 x 3456 pixels in size.  This is a huge leap from the 12MP 450D sensor I was using.

Modified Canon T3i for astrophotographyPowering the camera for a full night of imaging requires more than a single battery charge.  I purchased an AC adapter to plug the camera into an electrical outlet for unlimited power.  I never had this function with my previous imaging camera, and fumbled around with batteries for far too long.  I also sprung for a remote shutter release cable with a built-in intervalometer.  The great news is that this model is compatible with my Canon Xsi as well.

The AC Adapter for the Canon T3i is available on Amazon

Canon t3i AC adapter

 

I am really excited to start using this camera for deep-sky imaging.  Although tests show that the thermal noise level is comparable with the 450D, the Canon T3i’s increased resolution means larger astrophotos with enhanced detail. Also, the flip-out LCD screen will come in handy when focusing using live view.  This camera was modified by Astro Mod Canada.

Drone Footage?

Did you notice the aerial footage in the latest AstroBackyard video on YouTube?  That video was shot at a friend’s house using a DJI Phantom 4 in his backyard. I absolutely love drone footage and hope to get one of my own in the near future.  There are infrequent situations where that type of footage makes sense for an astrophotography video, but I’ll find a way to work them in!

I’ve also been working away trying to improve the resources on this website.  The photo gallery, equipment, and tutorial sections have seen a number of changes this month.  Thank you to everyone who has taken the time to comment on my blog posts, I really appreciate the kind words.  For the latest information and photos, please follow AstroBackyard on Facebook.

Latest Image Re-Process: The Eagle Nebula

DSLR astrophotography

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Astrophotography Video Tutorial

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Astrophotography Video Tutorial

Astrophotography Video Tutorial

In my first ever astrophotography video tutorial, I take a crack at the Rosette Nebula using data collected in February 2014. I have plans of shooting a video about light frame acquisition in the future, but this one is about what happens after you have already captured your data.  This astrophotography video tutorial may be useful to anyone who has questions about the stacking process, and processing the created .TIF file in Adobe Photoshop.

I must admit, I learned a lot about how I could improve upon these videos in the future during the process.  Putting together an online tutorial video using a particular piece of software is harder than it looks!  Nevertheless, I believe new astro-imagers will find some useful information in my video.

My astrophotography processing techniques

In the video, I discuss the importance of organizing and inspecting your raw image files before you dive-in to Deep Sky Stacker.  The application I find most useful for this stage is Adobe Bridge.  I subscribe to the Adobe Creative Suite that includes all of the Adobe applications, so using Bridge as my default image viewer was a no-brainer.  I know that Adobe Lightroom is another popular choice for this purpose as well. Alternative methods for viewing RAW image files on your PC are Faststone Image Viewer, Canon EOS Utilities and installing the proper codec on your particular version of Windows to preview the files.  I have used Faststone Image Viewer and Canon EOS Utilities, but I have not tried the Windows Codec option.


Video Summary

Using DeepSkyStacker, I register and stack over 2 hours worth of 3.5 minute light frames I captured of the Rosette Nebula with my Canon Xsi and ED80 Telescope. As always, dark frames are subtracted from the final image to produce a final image with a higher signal-to-noise ratio.  I then locate and open the 32 bit Autosave.tif file into Adobe Photoshop CC for further processing using helpful astrophotography plugins including Gradient Xterminator and the Astronomy Tools Action Set.  The order of the actions I make when processing an astrophoto from the RAW image files to the final result are as follows:

  1.  Stack and register light and dark frames in DSS
  2.  Open Autosave.tif file in Adobe Photoshop
  3.  Slight Image Crop to remove stacking artifacts
  4.  Removal of gradient and vignetting via Gradient Xterminator
  5.  Levels Adjustment
  6.  Convert to 16-bit/channel image
  7.  Curves Adjustment
  8.  Astronomy Tools Action > Local Contrast Enhancement
  9.  Astronomy Tools Action > Enhance DSO and Reduce Stars
  10.  Astronomy Tools Action > Increase Star Colour
  11.  Astronomy Tools Action > Make Stars Smaller
  12.  Balance neutral background sky colour
  13.  Increase Saturation
  14.  Final Curves Tweaks

The Learning Curve

Up until this point, I’ve been the student, not the teacher.  I want to show beginners how I process my astrophotography images, but my presentation skills leave much to be desired. I have always been an artist at heart, so my methods may seem unorganized and random to the general public.  I am more likely to “trust my eyes” rather than a set of numbers and graphs, although I recognize their value.  I feel that through the process of teaching others how to capture and edit photographs of the night sky, I will gain a deeper appreciation and knowledge of the hobby for myself.  Thank you to everyone who has subscribed to my YouTube channel so far.  I am just getting started.

 

AstroBackyard on YouTube

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