Thank's Fabio
I don't get it I'm afraid.
Sure I don't want to change color in the Mask.
But the Mask is for edit a color pic.
The command color curve works fine with a Mask on it.
"the Histogram Stretch is needed anyway because the "mask image" must have exactly a 16 bit dynamic"
Don't understand why I have to stretch it.
Some times I have done it inside gimp if I want the Mask going from pitch Black to bright white.
But often a gray scale is fine.
Even a total gray Mask all pix. Same Val. Can be used to ajust the effect. And that's not a 16bit dynamic mask.
I might be missing something...
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HEQ5 Pro 150PDS 60mm guide. Asiair.
Asi294mc. AA8.