[ptx] luminance processing

[Philippe Gac]

hi all,

I upgraded my php script and uploaded some quite high res mountain pics
see http://pho.ediphi.org/04/Alp/rando/index.htm

I got much trouble with luminance management:
- underexposition or overexposition leading to poor contrast
- vignetting
- camera settings (variable when not in pano mode)
- moving clouds

and with saturation management:
- fog
- overexposition

GIMP, allows to map RGB values according to a curve and color is often changed as the respective proportions of R, G and
B are not preserved when the function is not linear. Often, for example, the sky gets greenish. You could decompose the
channels into Hue, Saturation and value, operate on the value layer, adjust the saturation, and then recombine this into
RGB...

A free program, ImageAnalyser, does this in one step, mapping "luminance", other parameters being kept equal. To reduce
fog, I wished such a generalized mapping for saturation but there is no such feature, only the common linear mapping. I
wonder I this could even be useful: one try with GIMP was not that successful.

Mapping value (RGB synchronously) as when lowering gamma tends to exagerate the saturation in R, G, and B and dodge the
other colors. The fog is less visible but coulours are not natural (as can be seen on my pics).

Does anyone know of adequate tools for all that?

regards

philippe