I’ve seen the term used for night photography.
What exactly is happening?
In: Technology
Image stacking is the process of taking multiple photos of the same object at the exact same settings and taking a pixel by pixel average.
It is not a process of taking multiple pictures with different settings and combining them artistically as another poster said. That is called High Dynamic Range (HDR) processing.
Image stacking is done because objects in space are really really dim. To get something to show up you have to leave the shutter open a really long time (hours, not seconds). But since the sky moves, tracking the sky accurately is essential. Tracking errors will make stars look like ovals (or worse, streaks).
So instead of trying to take 1 four hour (240 minute) photo and hope tracking errors don’t destroy it, you take 150 two minute pictures and figure on throwing 30 of them in the trash. This would leave you with the same 4 hours worth of “data”.
Once you align (register) the images, software calculates an average value for each pixel. The noise (random error) averages away leaving more of the true image being noticeable. But because it’s a two minute exposure instead of a 4 hour exposure, it’s still pretty dark. Further processing is needed to increase brightness, contrast, sharpness etc, same as any other photo. If you did this without stacking, you would be brightening all the noise too.
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