Sometimes one would like to be able to create a HaldCLUT of processing done by some hardware or software which does not permit you to pass through it a HaldCLUT identity image. One solution would be to photograph the identity image (or some color target with patches), process that raw photo in said hardware/software and save as a separate file, and then use the before/after non-raw images to create the HaldCLUT.
For example, to create a HaldCLUT of a camera’s “Portrait creative style”, you could shoot some target, process the raw photo in-camera to apply the style, and then end up with two JPEGs - a reference image and the styled image. Now the difference must be mapped so that a HaldCLUT can be created.
Could G’MIC help with that?