alt Hacker News> A fun tangent on the "green cast" mentioned in the post: the reason the Bayer pattern is RGGB (50% green) isn't just about color balance, but spatial resolution. The human eye is most sensitive to green light, so that channel effectively carries the majority of the luminance (brightness/detail) data.
From the classic file format "ppm" (portable pixel map) the ppm to pgm (portable grayscale map) man page:
https://linux.die.net/man/1/ppmtopgm
The quantization formula ppmtopgm uses is g = .299 r + .587 g + .114 b.
I also love the quote in there...
Quote
Cold-hearted orb that rules the night
Removes the colors from our sight
Red is gray, and yellow white
But we decide which is right
And which is a quantization error.
Replies
If someone's curious about those particular constants, they're the PAL Y' matrix coefficients: https://en.wikipedia.org/wiki/Y%E2%80%B2UV#SDTV_with_BT.470
> The quantization formula ppmtopgm uses is g = .299 r + .587 g + .114 b.
Seriously. We can trust linux man pages to use the same 1-letter variable name for 2 different things in a tiny formula, can't we?
Funnily enough that's not the only mistake he made in that article. His final image is noticeably different from the camera's output image because he rescaled the values in the first step. That's why the dark areas look so crushed, eg around the firewood carrier on the lower left or around the cat, and similarly with highlights, e.g. the specular highlights on the ornaments.
After that, the next most important problem is the fact he operates in the wrong color space, where he's boosting raw RGB channels rather than luminance. That means that some objects appear much too saturated.
So his photo isn't "unprocessed", it's just incorrectly processed.