[Gimp-developer] Gamma slider adjustments don't work in unbounded mode sRGB

[Elle Stone <ellestone ninedegreesbelow com>]

Gamma slider adjustments don't work in unbounded mode sRGB:
http://ninedegreesbelow.com/gimpgit/unbounded-srgb-levels-gamma-slider.html

If gamma slider adjustments don't work, then Curves will also fail, even 
if it's possible to make Curves work on unbounded data without clipping.

The suggestion was made that compressing the data to fit within the 
bounded range 0.0 to 1.0, performing an editing operation, then 
uncompressing back to the original range, might solve the problem of 
operations failing in the unbounded mode sRGB color space.

Unfortunately compressing before doing a gamma slider adjustment, 
followed by uncompressing, produces entirely different results than 
doing the gamma slider adjustment on the uncompressed data in the first 
place: x^a is not equal to ((x+y)^a - y).

A solution to the problem of gamma slider adjustments not working in 
unbounded mode sRGB is to use the chromaticities of the source color 
space to make a linear gamma color space in which to do Gamma slider 
adjustments.

Elle