Deep Sky Stacker: How to Get Great Results!

Deep Sky Stacker is absolutely free. How can it help you with your astrophotography? Let’s find out.

If you want to photograph deep-sky objects, you have a big challenge ahead. Take one long exposure photo, and you’ll see a lot of noise and not much signal. In other words, a pretty poor image. How do you fix this?

The answer is to take many photographs and then stack the images together. This is where Deep Sky Stacker comes in. DSS will stack images for you and allow you to do some quick processing and editing before you move into your image editing software.

In this post, we’ll explore how you can utilise the DSS program to produce stunning astrophotos with remarkable detail, using your DSLR camera and Adobe Photoshop. Take a look at the image below for an example of what you can achieve.

The above image is of the Black Eye Galaxy. This was created from more than 300 images stacked together.

What is Deep Sky Stacker?

DeepSkyStacker is one of the most popular stacking tools that astrophotographers use for astrophotography¹. It doesn’t cost anything and can sort your images taken with a DSLR camera and rank them in order of quality. After stacking, it allows you to make some adjustments using Adobe Photoshop and stretch the image if you wish. There are many other features related to imaging that we will come to shortly. Best of all, DSS is easy to use and quite quick to run.

The software was developed in 2006 by Luc Coiffier.

In addition to what we have said above, this stacking software enables you to do the following: support windows, panel processing.

• Align your images
• Stack images together so that noise is reduced
• Use your calibration frames as you stack (darks, flats and bias frames).
• Make it possible to create a clear image by stacking shorter exposures.

Deep Sky Stacker (DSS) is not the only program that does astrophotography stacking. For example, I also like Siril, a free program similar to DSS that offers features like tags, DSLR support, and a stacking panel.

If you were to manually process imaging using a DSLR on Windows, it would be both difficult and time-consuming. However, with DSS, these steps become easier and more accurate.

How does DSS work?

Now that you know how useful a program like DSS is for Windows, let’s look at how it works for image display. DSS is a panel that works well with DSLR cameras.

First, astrophotography software aligns your images by matching the stars in your picture. It works out how each light frame has moved from a reference frame. Once it has done this, it places each frame captured by DSLR cameras perfectly on top of the others and averages out the image. This process of averaging increases the signal-to-noise ratio. Both the noise and the signal become clearer². This increase in signal-to-noise ratio enables the details of your object to be revealed in your final astrophotography image.

The improvement in signal-to-noise ratio increases with the number of pictures you take, as follows:

The signal-to-noise ratio of DSLR cameras for astrophotography increases proportionally to the square root of the number of images, making processing more effective.

In other words, taking 100 photos with DSLR cameras would increase the signal-to-noise ratio for astrophotography images by 10 times.

Taking 50 astrophotography photos with a DSLR camera increases the signal-to-noise ratio by 7 times. Just 10 images will improve it by three times. In other words, the more images you take, the better your final astrophoto with enhanced light will be.

It’s also a good idea to dither³ while you are imaging. Dithering moves each frame slightly enabling DSS to average out any noise which is present over the signal. This is especially helpful with walking noise which affected my images badly.

Taking calibration frames also helps. Bias and dark frames can be subtracted from the image to remove noise created by your camera and the temperature of the sensor. Flat frames can remove dust and stray light from your optics by subtracting this after you capture images.

Steps to Use DSS

I’m going to run through the steps you can follow to get the most out of the program on Windows. These steps will help you optimize processing and time settings.

1. Install the software from this site – (make sure to get the latest version and check for updates regularly).
2. Open up your images in by clicking on Open Picture Files
3. Add your calibration frames
4. Register the images by checking them all and clicking register images.
5. In the register settings tab, choose the star detection level, to detect enough stars in your images. Aim to detect approximately 150 stars. While the exact number may fluctuate based on the specific image you’re working with, targeting around 150 stars generally yields good results. This ensures the software can accurately align your images, enhancing the final composition without overloading the processing.
6. Prepare to stack images – check settings.

How to Identify and Remove Low-Scoring Images Before Stacking

When preparing your images for stacking, it’s crucial to identify and eliminate low-quality frames. These steps will guide you through the process:

• Browse Your Images: Start by going through all the registered frames in your collection. Look for any signs of imperfections, such as star trails, which can occur if your equipment moved slightly during the capture.
• Evaluate Image Quality: Click on an image once to examine it more closely. Ensure the image is displayed clearly by checking if a visual indicator, like a top bar turning blue, signals that it’s currently being viewed.
• Detect Issues: Pay attention to the score of each frame. A significantly lower score can point to problems like camera shake or slight misalignments that result in blurred or elongated star appearances.
• Remove Subpar Frames: If an image’s quality isn’t up to par, locate the checkbox or similar option next to it. Deselect this option to ensure the image won’t be part of the stacking process. By doing this, you eliminate the risk of ending up with a compromised final image.
• Complete the Registration: After filtering out the underperforming frames, your remaining images are primed for stacking, promising a clearer and higher-quality final product.

Taking these steps ensures that only the best shots contribute to your stacked image, enhancing overall quality.

7. Stack the images

8. Use the software to do some processing if you want or go to your processing software. I use Photoshop for this, but you can use an alternative such as Gimp (free) or Pixinsight (paid).

That’s all there is to using DSS for astrophotography to stack your camera images.

Adjustments for Stacking Parameters

When preparing to stack your images, it’s crucial to set the stacking parameters for the best results. Here’s a step-by-step guide on what to modify:

1. Light Tab Adjustments
   First, access the Light tab in the stacking settings. This section allows you to alter the way your software analyzes light levels within your images.
2. Kappa-Sigma Clipping Settings
   Utilize the Kappa-Sigma Clipping options to eliminate inconsistent elements across frames, such as airplane or satellite trails. This adjustment is particularly beneficial when capturing celestial objects like comets, as it prevents stars from blurring due to movement.
3. Entropy Weighted Average
   Consider activating the Entropy Weighted Average, also known as High Dynamic Range, to incorporate all data points from each frame into the final image. Be cautious if you’re using a full-frame camera, as this setting can be demanding on processing resources. It’s wise to test various stacking modes to determine which yields the best outcome.
4. Background Calibration Settings
   Set both RGB Channels Background Calibration and Per Channels Background Calibration to “No” to ensure the software does not perform background calibration. You should see “No Background Calibration” in the settings.

After making these adjustments, confirm by clicking OK. The software will then stack your images, using these personalized settings.

How Kappa-Sigma Clipping Enhances Stacking

In step two above, Kappa-Sigma Clipping is set. This is used in the image stacking process to improve the quality of the final image. This setting enhances the image fixing common issues such as unwanted artifacts.

Main Functions:

• Artifact Removal: During image stacking, unwanted elements like airplane or satellite trails often appear in individual frames. Kappa-Sigma Clipping effectively identifies and excludes these inconsistencies, ensuring they do not affect the final image.
• Consistency Check: By comparing each pixel across multiple frames, this technique isolates data that consistently appears, eliminating irregular artifacts like satellite trails or airplanes in the field of view. This consistency filtering improves the stacked image.

Step-by-step Process:

1. Frame Analysis: Each image frame is analyzed to detect pixel variations. Those that deviate significantly from the mean are earmarked for exclusion.
2. Deviation Threshold: Kappa-Sigma Clipping sets a threshold based on statistical parameters (the ‘Kappa’ factor), defining which variations are discarded.
3. Image Synthesis: Only the stable, consistent data from the frames remain, allowing for a clear and uninterrupted final image.

Overall, Kappa-Sigma Clipping optimizes the stacking process by ensuring only reliable data contributes to the final output, resulting in cleaner and more precise imagery. This technique is highly valuable in fields where visual accuracy and detail are paramount.

Post-Processing Steps After Stacking to Enhance Your Image

After stacking your images into a TIFF file, the final task is fine-tuning it for brilliance. This step is crucial to unveil the hidden details within your data. Here’s how you can optimize your final image through post-processing:

1. Color Correction and Balancing
   • Adjust the white balance to ensure accurate color representation.
   • Enhance color saturation and contrast, bringing out vivid hues.
2. Noise Reduction
   • Employ noise reduction techniques to clean up any graininess or artifacts. This ensures a smoother and more polished finish.
3. Sharpening Details
   • Apply sharpening filters to emphasize details, without overdoing it—striking a balance between clarity and natural look.
4. Highlight and Shadow Adjustment
   • Adjust the highlights and shadows by using curves stretching and levels adjustment. You want to stretch the image enough to reveal the details of your nebula or other deep sky objects but don’t overstretch it, so it gets washed out. Also, adjust the levels so you don’t clip your data, and the background and shadows look good.
5. Cropping and Composition
   • Crop the image to improve its composition, focusing on the most interesting aspects of your subject.
6. Final Touches
   • Consider a final review of the adjustments, making any necessary tweaks for coherence and impact. this step is a question of your own taste and what you consider looks best.

By thoughtfully executing these steps, you’ll transform your stacked data into a stunning, professional-quality final image.

I compared several sky stacking programs for digital SLR and DSLR cameras and found that deepskystacker (DSS) was one of the best in terms of the quality of the final image. It was also easy to use. I also had a positive experience with Siril, without any complaints. However, I did encounter some difficulties with the star detection threshold, which I now realize was likely due to my inexperience and the image quality, rather than the program itself.

This video is a good DSS tutorial in ten simple steps. Enjoy!

Tips for getting the best results with DSS

These are a few essential tips to make sure you use the settings of the software to get the most out of it. Make sure to use images in your content to enhance its visual appeal. With a bit of attention to these details, you can optimize your experience with the software.

• Check that a sufficient number of stars are detected in your images. These are used to align them properly. If fewer than 150 stars are detected, consider selecting a different frame to improve the alignment process. Click on another image to try again. This step is crucial because if too few stars are identified, the software might struggle to stack the images effectively. On the other hand, if too many stars are detected, the stacking process will take too long. The software will work extremely hard during the final stacking, potentially leading to longer processing times. Therefore, balance is key – ensure that the number of stars detected is just right.
• Make sure you shoot your pictures of deep-sky targets in RAW or FITS format, depending on your camera’s output. RAW files retain more image data and dynamic range. This allows you to adjust exposure, contrast, and color balance without losing detail. RAW files give you all the information captured by your camera’s sensor. The benefits of taking RAW photos include enhanced detail in your astrophotography images. Dynamic Range is maximized, and colours are more accurate.
• Your final stacked image should be saved as a.tif or.fits file. These file types contain more information and are best for further processing.
• Use the automated calibration feature, which produces the best image with the least amount of noise.

Challenges with Saving Images in Deep Sky Stacker

Users can encounter specific challenges in saving the final image. Understanding these issues can help make the process easier.

File Format Compatibility

A common problem is that sometimes the software saves the image in a format incompatible with standard image processing tools. This can be frustrating when you’re eager to start post-processing your astrophotography.

Solution:
To ensure compatibility, use the “Save Picture to File” option in the processing menu. This allows you to choose the file type that best fits your needs.

File Destination Confusion

Another challenge is that the image might be saved in a different directory than expected. The default setting often leads to saving the image in the last directory where a similar file was stored, rather than your current working folder.

Solution:
Before finalizing the save, double-check the directory to ensure your image goes to the intended location. This small step can save a lot of time in searching for misplaced files later.

By being aware of these challenges and their solutions, you’ll be better prepared for a smoother experience with Deep Sky Stacker.

I hope you now appreciate why Deep Sky Stacker is a popular choice for astrophotographers, and how it can help you stack your astrophotos. Stacking is a process that all astrophotographers need to use, so why not try using this reliable software? I have had some issues with the software, but it is easy to find bug fixes and solutions online because of its large user base.

Good luck with your images! I’d love to get your comments below, especially if you have any advice or suggestions on how best to use this deep sky stacker program or any questions you may have

References

1. Andrea Minoia. Astrophotography Stacking Software – Which One to Use? https://nightskypix.com/astrophotography-stacking-software/
2. Rupesh Sreeraman. This is how image stacking reduces noise and recovers signal. https://petapixel.com/2020/10/28/eli5-this-is-how-image-stacking-reduces-noise-and-recovers-signal/
3. Jim De Lillo. Improve image quality by dithering. https://telescope.live/blog/improve-image-quality-dithering