"GIMP" Color picker should have a Lch plane mode
Operating System: All (I am using Windows 10)
Description of the feature
GIMP 2.10 introduced a LCh color picker option, but the rectangular "GIMP" color picker pane to the left still uses HSV. Instead of showing a slice of HSV with a fixed H, the picker should show a slice of the Lch colorspace at the fixed h instead when Lch is chosen. (This feature is still absent in 2.99.4.)
The "wheel" chooser can also use a fixed-L slice for Lch.
Use cases
The new pane will generally help users navigate the Lch color space, showing its boundaries (within the current colorspace) and whatnot. In particular, it is quite useful to pick a set of colors at a fixed L value.
Implementation notes
- The current HS at fixed V rectangle fills the entire window area it is provided. However, with a Lab slice, it is probably meaningful to preserve the aspect ratio.
- Getting the boundary of the slice is non-trivial as it depends on the working color profile; you can't really expect it to be analytic. The
colour
andcolorio
Python packages show the volume by making a grid/mesh of the source (working) space surface and converting it to the target (Lab) space. I think the precision would be fine since it's only for picking colors. A volume can be computed each time a profile is loaded.