I have to make some histogram corrections to nighttime photographs where it is essential to keep the average brightness (luminance) constant. (The photos illustrate the human perception in nighttime traffic, as far as this is possible by means of photography.)

However, there seems to be no way to display the histogramm in terms of brightness in Gimp (?). The "value" seems to be just max(R,G,B). But luminance is generally caculated by
Y = 0.2126 R + 0.7152 G + 0.0722 B
see http://en.wikipedia.org/wiki/Luminance_%28relative%29.

Wouldn't it make sense to offer this option?

BTW: The histogram window always switches back to "value" when I start to modify the graduation curve. At the moment, I want to keep it at RGB, as this comes as close as (momentarily) possible to the above equation.

Wolfgang Hugemann
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