[ptx] luminance processing

[Chris]

On Sep 24 23:11, Philippe Gac wrote:
> 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.

Have you tried all the Filters/Colors/Decompose possibilities? Maybe
the LAB decomposition could be helpful (Luminance, A/B component).

> 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).

I think fog causes information loss, thus cannot be perfectly hide. The
fog makes the hisogram narrower, everything goes to grey. The deeper the
fog is, the more greyish (or greyish blue under the sky) the image part is.