Version: 0.9.2 (using KDE KDE 3.5.7) Installed from: Gentoo Packages OS: Linux The Adjust Curves plugin would be immensely more powerful when you can apply the curve on individual channels in the HSV and HSL color spaces. So, apart from R, G and B, there should be four additional channels: H, S, V and L. Having both L and V is a key feature here, because HSL reduces saturation as you darken the image, while HSV increases saturation as you darken the image. In case you have a bright washed-out sky that needs adjusting, you adjust the V channel in HSV space. In case you have a dark lifeless foreground, you adjust the L channel in HSL space. Having both a color space dropdown menu and a channel dropdown menu would be even better. http://www.normankoren.com/light_color.html
Image Editor G'MiC-Qt tool with Colors/Curves filter also to adjust HSV or HSL color spaces. https://i.imgur.com/eqB61BV.png Gilles Caulier