Antti S. Lankila wrote:
I do want to point out one advantage of using, say gamma=2.2 in lieu of
the actual sRGB formulas in some situations: exponentiation permits
separate treatment of alpha and color components. For instance
(component * alpha)^2.2
is just
component^2.2 * alpha^2.2
and this comes into play when library users read in, say, PNG, and see
some alpha values and prepare that texture for pixman. In the past, they
would have multiplied the components by alpha (I imagine), but now they
must only raise the alpha to 2.2 first before the texture is ready for
consumption by pixman. However, full sRGB formula requires:
lin2srgb(srgb2lin(c) * a)
which will be far more work to implement, and the results aren't going
to be any different in practice.
Even if you use lookup tables and implement the linear portion of sRGB,
I think it is close enough to a gamma curve that you can pretend the
function is communative/additive. I would simplify composite
calculations by assuming
srgb2lin(a*b) == srgb2lin(a)*srgb2lin(b)
even though this is not true.
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