Re: [Gimp-user] Histogramm -- values

[Wolfgang Hugemann <Auto Hugemann de>]

> > Elle Stone and Nicolas Robidoux, can you please also have a
> > look on this topic? Thank you in advance.

Wow, this was a very elaborate answer ...

Fred Weinhaus also answered me and he is pointing to some transfer 
functions that ImageMagick uses, see 
http://www.imagemagick.org/script/command-line-options.php#intensity.

He also gives some helpful illustrations what effects different transfer 
functions have on the image:
http://www.fmwconcepts.com/imagemagick/color2gray/index.php

I understand what Elle says in regard to histogram clipping, i.e. max(R, 
G, B) being very helpful for finding the white point -- while min (R, G, 
B) in regard to the black point is missing.

Perhaps one should give the user just a few more options what to display 
in the histogram and how to transfer R, G, B into a single 'value'. I 
would be very lucky with 'Rec709Luma' as defined by ImageMagick. I 
understand that GIMP internally uses the sRGB colour space at the moment 
(?).

A standalone feature for GIMP would be the possibility to display a 
cumulated histogram, which would for instance demonstrate the effect of 
equalisation better than an ordinary histogram. This should be easy to 
implement, I guess, and would be a simple check box for the user.

BTW: Besides equalisation, one could also try to meet other cumulative 
histogram distribution, like a Gaussian bell curve, see 
http://www.fmwconcepts.com/imagemagick/redist.

Wolfgang Hugemann