W3C CSS2 Cascading Style Sheets, level 2 - instructional media + ...

14.3 Gamma correction
For information about gamma issues, please consult the the Gamma Tutorial in
the PNG specification ([PNG10]).
In the computation of gamma correction, UAs displaying on a CRT may
assume an ideal CRT and ignore any effects on apparent gamma caused by
dithering. That means the minimal handling they need to do on current platforms
is:
PC using MS-Windows
none
Unix using X11
none
Mac using QuickDraw
apply gamma 1.45 [ICC32] (ColorSync-savvy applications may simply pass
the sRGB ICC profile to ColorSync to perform correct color correction)
SGI using X
apply the gamma value from /etc/config/system.glGammaVal (the
default value being 1.70; applications running on Irix 6.2 or above may
simply pass the sRGB ICC profile to the color management system)
NeXT using NeXTStep
apply gamma 2.22
"Applying gamma" means that each of the three R, G and B must be converted
to R’=R gamma , G’=G gamma , B’=B gamma , before being handed to the OS.
This may rapidly be done by building a 256-element lookup table once per
browser invocation thus:
for i := 0 to 255 do
raw := i / 255.0;
corr := pow (raw, gamma);
table[i] := trunc (0.5 + corr * 255.0)
end
which then avoids any need to do transcendental math per color attribute, far
less per pixel.
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