provide contrast change by color not by pixel

[macias]

I found this thread:
viewtopic.php?f=3&t=12272

which is about documentation, but later deal with changes in the contrast-stretch feature.

I would like to post an explicit report about it, however my wish may go in different direction than this expressed in the mentioned report.

The thing is current contrast-stretch is based on pixel count, so even applying the same parameters the effect will be different for different images (I mean, number of blacks/whites). My wish is to provide another CS feature which would be completely independent of pixels, but would only rely on colors.
Example -- user has grayscale image. User would like to shift all pixels which are 30% white as white, and the rest as black (extreme example but I would like to stretch the difference). Now -- it may happen that there are only such pixels which are 30% white, so in effect user would get completely white image. So be it -- but as you see this CS-color feature does not depend on pixel count, but on pixels property -- color only.

Just if anybody is curious, I work with images which are pretty similar in color profile, but vary a lot in whites/blacks count. So each time with current CS I have to change the parameters (actually I gave up, because it is faster to do it in Gimp, than trial&error to get the same results, the same final color profile).

But if I am not mistaken I am not the only one who would like to see this supplementary CS.

[fmw42]

It is not clear to me what you are requesting!

Have you tried -level or -level-colors?

[macias]

I tried now and it is what I wished for, sorry then.

However from this experience -- subwish for documentation, it would be helpful to add in contrast sections

see also: -level

Thank you!

[anthony]

Look at IM Examples, Color Modifications.

It documents and examples these operators.