Image Stacking Software
Choosing astrophotography image stacking software that complements your editing workflow and produces reliable results is one of the first hurdles every amateur astrophotographer faces. There are many great options available, but the right choice depends on whether you are stacking deep-sky images, Milky Way nightscapes, or planetary video.
Image stacking combines multiple photos of the same object to improve the overall signal-to-noise ratio and reduce noise in the final image. This is something I do for each and every one of my astro-images, whether it is a wide-field nightscape or a high-resolution deep-sky object.
Which Image Stacking Software Should You Use?
For free astrophotography stacking software, DeepSkyStacker is my favorite straightforward deep-sky option, while Siril is the strongest cross-platform choice.
Sequator is ideal for Windows-based Milky Way and nightscape stacking, and AutoStakkert! is purpose-built for planetary, lunar, and solar video. PixInsight offers the highest level of control, but it also has the steepest learning curve.
The process of image stacking is usually accomplished by aligning and averaging the image frames, which enhances the overall image quality and helps to bring out subtle, essential details. By combining several shorter-exposure images, the technique can also be used to make images with an ultra-long total integrated exposure time.
Example: 60 x 3-minute exposures = 3 hours of total overall exposure time.
Image stacking is one of the most important aspects of astrophotography image processing, and mastering this process will allow your images to reach their full potential. The process may seem confusing at first, so I have created a premium image-processing guide (with detailed stacking instructions) for beginners.
If you are interested in learning more about specific astrophotography image processing techniques, be sure to check out the astrophotography tutorials section of this website. You can also view my extensive list of astrophotography resources, which includes tools for acquisition, planning, and even weather forecasting.
Related Article: Choosing an Image Processing Software
Astrophotography Image Stacking Software
There are several tools and methods available for astrophotography image stacking, from manually aligning and stacking image frames in Photoshop to sophisticated software tools like DeepSkyStacker and Siril.
The bottom line is that stacking more usable images usually produces a cleaner result. The improvement follows diminishing returns, however, so strong frames are more valuable than simply increasing the count with poor data. For me, a typical deep-sky image project includes anywhere from 4-10 hours of total exposure time.
In this article, I will focus on the best software for astrophotography image stacking, based on your unique goals and desired user experience.
This image includes nearly 10 hours of total integrated exposure time through image stacking.
How do you Stack Images in Astrophotography?
A typical deep-sky astrophotography stacking workflow calibrates the light frames, aligns them using the stars, and then integrates them into a master image. Software may use averaging, median stacking, quality weighting, and pixel-rejection methods depending on the data and settings. The process begins by collecting a sequence of exposures of the same target using consistent camera settings.
If you have ever taken a single 30-second exposure at night with your DSLR camera at ISO 800-1600. You will notice a noticeable amount of noise in the image. Image stacking software can help remove noise and increase the overall amount of light (or signal) collected.
Whether I am using a simple DSLR camera and lens on a star tracker, or a dedicated astronomy camera and a large telescope, I always capture multiple image exposures of each target. These sequences can range from 20 to 200 frames. In the image below, you can see how much more detail I was able to bring out on a wide-angle photo of the night sky.
A stack of 15 images will have a much better signal-to-noise ratio than a single image exposure.
Because the signal (the light emitted by stars and deep-sky objects) is constant, it will compound as you collect more and more overall exposure time. The noise, however, is random. The stacking software will essentially cancel out these unwanted artifacts.
Stacking rule of thumb: Under similar conditions, four good exposures provide roughly twice the signal-to-noise ratio of one exposure. Reaching another twofold improvement requires about 16 exposures, which is why total integration time matters so much.
The basic process is as follows:
- Align the images using software such as DeepSkyStacker. This step ensures that the individual image frames are properly aligned before stacking.
- After alignment, integrate the images using an appropriate stacking method. Average integration with pixel rejection is common for deep-sky data, while median stacking can be useful for rejecting outliers in some smaller image sets.
- Once the stacking process is complete, the final image will be a composite of all the images used in the stack, with much of the noise and other unwanted artifacts reduced.
- To calibrate the images and remove unwanted artifacts such as dust motes and vignetting, flat frames must be incorporated into the stacking process.
- Finally, you can post-process the stacked image with editing software like Adobe Photoshop or PixInsight to boost saturation and perform other adjustments to get the final desired result.
Please note that this is a very basic example of image stacking, and does not include the advanced calibration side of things. By subtracting dark frames and bias frames, you can further improve the overall quality of the master image.
There are several great software tools available for image stacking, and the good news is, many of them are free. Let’s take a look at a few of them.
Best Image Stacking Software for Astrophotography
The following list of software tools has been vetted by myself or others I know who have successfully processed many deep-sky images. I have intentionally not numbered the stacking tools on this list to highlight that the best image-stacking software is the one you feel most comfortable using —and, more importantly, understand.
Remember that image stacking is part of the pre-processing stages. This will create an intermediate file that you can then bring into a tool like Photoshop or PixInsight to edit to your heart’s delight.
Astrophotography Stacking Software Comparison
The best software for processing astrophotography data depends on the subject, operating system, budget, and amount of control you want. This comparison provides a quick starting point before the detailed reviews below.
| Software | Best For | Operating Systems | Cost |
|---|---|---|---|
| DeepSkyStacker | Beginner-friendly deep-sky calibration and stacking | Windows, macOS, Linux | Free, open source |
| Siril | Complete cross-platform deep-sky workflow | Windows, macOS, Linux | Free, open source |
| Sequator | Milky Way photos and nightscapes | Windows | Free |
| PixInsight | Advanced deep-sky stacking and processing | Windows, macOS, Linux | Paid |
| Astro Pixel Processor | Deep-sky mosaics and guided integration | Windows, macOS, Linux | Paid |
| AutoStakkert! | Planetary, lunar, and solar lucky imaging | Windows | Free |
| Adobe Photoshop | Small nightscape stacks and final editing | Windows, macOS | Subscription |
Looking for star stacking software? If you mean a star stacker for noise reduction, use Sequator for Windows nightscapes. Choose StarStaX when the goal is to blend exposures into star trails. Photoshop and GIMP can handle small manual layer stacks, but dedicated software is better suited to deep-sky calibration and integration.
For camera RAW files, FITS data, and calibration frames, use a dedicated astro stacking software such as DeepSkyStacker, Siril, PixInsight, or Astro Pixel Processor. Large projects benefit from plenty of RAM, fast multi-core processing, and enough SSD space for temporary calibration and registration files.
Adobe Photoshop
Website: https://www.adobe.com/ca/products/photoshop.html
One of the simplest ways to begin image stacking is to do it manually in Adobe Photoshop. Utilizing layers, place and align each one of your image frames on top of one another and gradually reduce the opacity.
This is a great way to see the power of signal-to-noise ratio at work, as you can watch your master image file gradually improve as you add each new layer. Even though Photoshop technically can auto-align layers for you, it often results in an error because the tool wasn’t meant for astrophotography.
Adobe Photoshop is best used for simpler astrophotography projects, such as a series of 6-12 images of the Milky Way or a starry nightscape image. The graphic below shows a typical method of image stacking in Photoshop by manually placing and aligning layers of the same image on top of one another.
Manual Image Stacking in Adobe Photoshop.
Photoshop was not designed as dedicated astro stacking software and does not provide a streamlined calibration workflow for dark, bias, and flat frames. For tools designed for this task, read on.
DeepSkyStacker
Website: https://github.com/deepskystacker/DSS/releases
DeepSkyStacker is my overall favorite image-stacking tool for astrophotography.
DeepSkyStacker is popular software for calibrating, registering, and stacking deep-sky astrophotography images. It has a user-friendly workflow, which makes it relatively easy for beginners to learn and use. The software can automatically align and stack multiple images, helping reduce noise and preserve faint details for later processing.
The software offers various noise-reduction options, including automatic hot-pixel removal, dark-frame subtraction, and flat-field correction. DeepSkyStacker is compatible with a wide range of image formats, including RAW, TIFF, and FITS, which makes it easy to work with different types of images.
DeepSkyStacker is freeware, which means it’s free to download and use. There is a large community of users who share their experiences and tips for using the software, which can be helpful for beginners. The software does a great job of stacking deep-sky images of galaxies and nebulae, and even comets.
Current DeepSkyStacker releases are available for Windows, macOS, and Linux. Because platform requirements can change between releases, check the notes on the official download page before installing it.
Siril
Website: https://siril.org/
Siril is a free image stacking and processing software with advanced features.
Siril is an open-source software for stacking and processing astronomical images. It offers advanced image calibration tools, such as dark frame subtraction, flat field correction, and bias correction to improve the quality of your final integration.
It offers a wide range of image processing tools, such as color balance, contrast, and brightness adjustments. It can also run scripts to automate the image processing and stacking workflow, saving a lot of time.
Siril is available for Windows, Mac, and Linux, which makes it accessible to most users. It’s open-source software, which means it’s free to download and use. Many amateur astrophotographers use Siril and share their experiences and tips on YouTube, which is very helpful for beginners.
Siril supports various image formats like FITS, SER, AVI, PNG, TIFF, and more. Siril is especially useful for advanced users who want to automate their workflow.
Sequator
Website: https://sites.google.com/view/sequator/
Sequator is easy to use and my go-to option for Milky Way Photography and Nightscapes.
Sequator is free Windows software designed primarily for stacking wide-field nightscapes. I usually recommend it to those shooting with a DSLR or mirrorless camera and a tripod, taking wide-angle photos of the night sky.
Like all the astrophotography image-stacking tools on this list, it can stack multiple image frames to reduce noise and create a master image for further processing. I like to use Sequator on wide-angle nightscape-style shots like constellations and Milky Way photography.
Sequator offers some advanced image calibration tools, without the confusion and daunting task of learning new software. It is likely the most beginner-friendly tool on this list. I have found that it stacks images faster than DeepSkyStacker, even when using calibration frames (darks) for deep-sky images.
Below, you can watch my video tutorial using Sequator on my astrophotography images:
It has a clever tool for separating (masking) the foreground of your image, so it stacks only the stars in the night sky. This is handy when capturing nightscapes, where the ground is moving independently of the sky. It supports RAW image format files from your DSLR or mirrorless camera, but it is not meant for dedicated astronomy camera files (FIT).
PixInsight
Website: https://pixinsight.com/
The WBPP script automatically finds and stacks each file from a large ‘batch’ of images for a particular project.
PixInsight is a professional-grade image-processing software widely used in astrophotography for stacking, processing, and analyzing images. It offers advanced alignment and stacking features for astrophotographers ready to tackle the complexities of this advanced tool.
Like other image-stacking tools, PixInsight offers noise-reduction options such as automatic hot-pixel removal, dark-frame subtraction, and flat-field correction, with more parameters to adjust than you could ever imagine. I stick to the Weighted Batch Pre-Processing (WBPP) stacking script, as this automates much of the experience and does a great job.
If you plan to use PixInsight for image stacking, you will benefit from the many online tutorials, such as those by Shawn Neilson (Visible Dark Astro). The following video discusses his PixInsight stacking methods for the best results.
Overall, PixInsight is a powerful and versatile software with advanced tools for amateur astrophotographers who want to do it all. The software is not cheap, but it is a one-time purchase.
Astro Pixel Processor
I found Astro Pixel Processor to be powerful and effective, but the user interface can be confusing at times.
Website: https://www.astropixelprocessor.com/
Astro Pixel Processor, often called ‘APP’ was developed by Mabula Haverkamp. He has developed innovative features and algorithms for the software, including its unique debayer algorithm, Adaptive Airy Disc, Local Normalization Correction, and fully automatic N-View mosaics.
The author of the software has stated that the goal of APP is to ‘make a complete Deep-Sky Image Processing application that maintains ease of use while automatically using the most advanced algorithms to provide excellent results without the need to tweak dozens of parameters.’
I know of several fellow astrophotographers who enjoy and use the mosaic tool in Astro Pixel Processor, a complex task for any image stacking tool. To date, I have only used APP a handful of times, and it has provided great results using the default parameters.
AutoStakkert!
I use Autostakkert! to process my planetary images by extracting image frames from a video file.
Website: https://www.autostakkert.com/
Autostakkert! is free planetary astrophotography image-stacking software. I use this when photographing planets through my telescope at high magnification. It is relatively simple to use and is suitable for images of the moon, planets, and the sun.
The process of stacking individual image frames from a video file format is quite different from long-exposure deep-sky astrophotography. The key to this process is selecting the best image frames (with the least amount of atmospheric disturbance) to stack and produce the final output.
Planetary versus deep-sky stacking: Planetary software analyzes hundreds or thousands of short video frames and keeps the sharpest moments of steady seeing. Deep-sky software instead calibrates and aligns longer exposures before integrating them to improve the signal-to-noise ratio.
My go-to source for everything related to planetary imaging is ‘InsertAstroNameHere’ (Matt Smith) on YouTube. The following video really helped me understand this software when I got started with planetary imaging and Autostakkert!.
It’s worth noting that a typical planetary image processing workflow involves another tool called Registax. This allows you to use wavelet processing to reveal more details on the planet’s surface.
Smart Telescopes
If you want to let a smart telescope handle the image stacking for you, there are several great options available to amateur astrophotographers today. They can automatically take a series of image exposures, align them, and stack them for a better image.
For example, the live stacking feature on the Seestar S50 does a great job of registering and combining images, given they were taken on an Alt-Az tracking mount. I also found that DWARF 3 (shown below) did a great job of image stacking internally.
Smart telescopes like the Dwarf 3 can internally stack images for you (live stacking) to produce a cleaner image.
All of these devices offer the option to stack your own image frames separately for more control. For those just looking to explore space without learning to use image-stacking software, smart telescopes are a fantastic option.
Common Image Stacking Problems
- Images will not align: Remove frames with clouds, severe trailing, or too few detectable stars, then try a lower star-detection threshold.
- The stack looks soft: Inspect frame quality and exclude exposures affected by poor focus, wind, tracking errors, or bad seeing.
- Hot pixels or dust spots remain: Confirm that your dark, flat, and bias or flat-dark frames match the lights and are assigned correctly.
- The foreground is blurred: For tracked nightscapes, stack the sky and foreground separately or use a masking tool such as Sequator.
Summary
Select an image-stacking software that suits your personal comfort level in terms of user experience. For example, for Milky Way Photography, a tool like Sequator is likely all you will need to create a clean image to edit in Adobe Photoshop.
If you are an advanced deep-sky astrophotographer seeking to calculate the ideal image scale for your telescope system to achieve maximum resolution, PixInsight has the power and functionality you need. I tend to stick with DeepSkyStacker and the WBPP script in PixInsight for most of my personal astrophotography projects.
No matter which stacking software you choose, you will benefit significantly from the many astrophotography tutorials found on YouTube.