I have an image that I like, however, the blacks are a bit to dark. I tried using the Gimp tool "Colors->Curves" where I can set the maximum value that gets brightened, however, this not only increases the brightness of colors where all channels are dark but also the dark channels of colors that have one channel that isn't dark.
What I want is a tool that increases brightness for all colors for which the sum of all channels is below a specific value. How can I do that (preferably Gimp, but I would also be happy for any tool that works on Windows or Linux that doesn't cost money)?
For example I have this image:
What I want is something link this:
But when I use curves in Gimp to try to increase the brightness of dark colors I get this:
(The actual image is more complex so manually editing the colors is not feasible)