Why you can't color calibrate (deep) space photos:
Jul 21, 2025
Color is the most disputed part of astrophotography. It seems like no two images have the same colors, and the internet is full of disputes over what colors are correct or natural.
Human vision and perception are very complex. This description is hugely simplified as to fit in a blog post. If you want details, consult a textbook.
Roughly speaking, our eyes have four types of photoreceptors. The most abundant, rods, provide a black-and-white view of the world: very detailed but with no color. The others are cone cells, each type responds to a particular part of the visible spectrum:
Left: All that you will ever see.
Right: Infinite abyss of the IR.
The peaks of these wavelength ranges roughly correspond to the colors red, green, and blue. Because there’s a lot of overlap between the red and green cones, our brain subtracts some green from red, yielding this spectral response:
Yes, this results in red having negative sensitivity @500 nm.
The perceived color depends on the ratio between the signals from each type of cone, which corresponds to the ratio of red, green and blue light entering your eye.
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