I am going to jump into this discussion with an idea, not based upon any
direct knowledge I have as to why Photoshop is designed as it is, but
with a mind toward human vision.
Human vision is not linear at all. We see by two structures, rods, which
perceive luminosity without color, and cones, three forms of which each
see a different light frequency range, the "red" cones actually peak at
yellow, green cones peak at green and blue cones peak in the violet part
of the spectrum. These structures are not evenly distributed in terms
of numbers or locations. Rods are more concentrated at the edges of our
retina and are used in our peripheral vision, which has poor color
vision. Cones are more concentrated in the middle of the retina.
While the percentages of the three cone cells vary considerably between
adults, thus creating the various levels and forms of color blindness,
overall adults have very poor blue-violet color perception. We are born
with less blue cones than either the red or green. Early in life,some
are destroyed by UV light entering the eye. The UV also damages the
transparent and neutral lens of the eye, slowly yellowing it until it is
almost orange juice color as we pass middle age. While this yellowing
actually filters the UV light reaching the retina, and therefore
protects the blue cones left, it also filters out a huge amount of the
blue light that reaches the retina, so a mixture of low blue cones to
begin with, damage by UV early in life, and then a fairly heavy yellow
orange filtration, means our blue perception stinks.
While we are very attentive to reds, due to the evolutionary
significance of red to yellow, it is the second smallest number of
cones. So, while we are more aware of reds, we actually have less red
cones to see it with. Our largest number of cones are greens, in most
people by a substantial amount. This allows us to see green
differentials quite well, and is probably significant because vegetation
coloration can be important to survival.
Now, I'm not sure what Photoshop is up to with their Granger Calibration
Chart differences (yet at least - I've asked a friend who is a color
engineer if he had any comments) but as someone who has a background
with the human side of color perception, it may be that Adobe has made
some accommodation for the species who use their programs, with our
non-linear color perception.
Art
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