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Is there a "rotate colors" to alpha

I've read a dozen of forum answers about how to suppress "a color" but I can't find how to change a color range. Yet, the "rotate colors" tool enables me to beautifully target the desired range, but I can only change it to another color (not including white unfortunately). I can't change it to transparent.

I have many methods (including by moving sensitivity or selection type (composite, saturation, Hue, etc) oh each tool) to no avail, mainly because the zone has different shades of green and has hair accross it:
o select by color
o select with magic wand
o Color to alpha
o and several other methods I don't even remember now, probably all tools that can be found in "Colors".

What is frustrating is that I know from "rotate colors" that GIMP can identify this range.

Any ideas welcome!

Thanks a lot,

Once you have mapped the range to a (narrow) color, you can use C2A on that color?

Consider also that:
  • the  Color and Fuzzy select can do selection on criteria other than plain color: hue, saturation, specific color channel
  • you can make a copy of your layer an optimize it for a selection (contrast, etc...) and then use that selection to operate on the initial layer.
Oh my mistake I had written « Alpha to transparency » in the methods I tried instead of “Color to alpha” (edited now).

Yep I've tried that but it doesn't do the trick unfortunately, even by playing with the settings. I directly use the color picker to click on the color I want to delete but it deleted the hair too (target color is green, hair medium brown)

I see you edited your message too to complete it :
regarding you first point : yep I played with all those options
regarding your second point, this means using masks, right?
Thank you,

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