Chyba znalazłem coś sensownego!
http://www.cs.wfu.edu/%7Eburg/nsf-du...ased/Ch3CS.pdf
Strona 31 :
"Among the three color channels, the human eye is most sensitive to green and least sensitive to blue. This fact is reflected in the way that RGB color is transformed to grayscale. Say that you have a pixel with color channels equal to the values R, G, and B. The grayscale equivalent of this, which we'll call L, is

L= 0.30 * R + 0.59 * G + 0.11 * B

Some scanners or photographic processing programs give you access to a luminance histogram (also called a luminosity histogram) corresponding to a color image. A luminance histogram converts the RGB values into luminance, as shown above, and then creates the histogram from these values."