Stacking your astrophotography pictures is crucial to get rid of noise and reveal hidden details. One of the most popular software for stacking, the Deep Sky Stacker, is unfortunately unavailable for macOS. Should we, the Mac users, be sad because of this? Well, maybe, but we are certainly not lost. There are other programs that can do the job just like the Deep Sky Stacker, or even better. In this post, I will show you one of the best astrophotography stacking software options for macOS – the Starry Sky Stacker (download on the Mac App Store).
What is stacking in astrophotography
In astrophotography, stacking is a process of combining multiple exposures (all with the same settings – ISO, exposure time, aperture, etc.) into a one, so-called, stack. In the stacking process, every pixel in the final stack image is created by averaging pixels from the proper places from so-called subs (those single exposures, often called as light frames). The stack has the same pixel resolution and, before further post-processing, it looks almost the same as every single exposure it has been produced of.
Why should you stack your astrophotography pictures
You should stack your multiple astrophotography pictures to improve signal-to-noise ratio, which leads to removing unwanted camera sensor noise and revealing faint details on
Single exposure vs. stacked image
What is Starry Sky Stacker
Starry Sky Stacker is astrophotography stacking app for macOS written by Ralph Hill. It has multiple functions for creating good quality stacks for further processing:
- Combining single exposures using different algorithms (you can choose which one you want to use) – median, mean, max, or min
- Aligning your subs if they were not tracked accurately
- Estimating the quality of your subs and letting you decide which ones to use for the final stack integration
- Optionally using also dark and flat frames
How to use Starry Sky Stacker
Prepare your TIFF subs
Always use RAW as your camera format, not JPG. JPG is a lossy file format and don’t preserve all that data that came from the night sky, and your goal is to reveal as many details as possible. To do that, always shoot and process your pictures in RAW and other lossless formats (like TIFF).
Starry Sky Stacker uses TIFF file format for internal processing. It’s best to export your RAWs to TIFF with default values using some RAW processing software (like Capture One).
Load your subs into the Starry Sky Stacker
Select your subs and load them into the program. If you want to use darks or/and flats, check “show image classification” tick. If you have only light frames, then leave unchecked. After a few seconds (depending on the number of your subs and the power of your machine, it may be longer) you will see a screen like this one below. There you can exclude some worse subframes (with passing clouds on them e.g.), and after that, click “Composite”.
Tweak composition details
Images are aligned, you just have to select the composition algorithm, and optionally you can play with brightness and contrast settings. I usually use the median algorithm, and leave brightness and contrast settings default (I do that kind of further post-processing in PixInsight and Affinity Photo later). Click “Save” and choose the final stacked picture location on your drive. Your stack is ready for post-processing!