Introducing a new color balance mode in darktable

LGG formulas can’t work with scene referred linear data.

Also note that the Sat formula uses REC.709 constants, and should instead be customizable, or auto-filled software depending. The clamp featured in the ASC is also a problem for some implementations, including ACES, which has it removed.

Fulcrum based Power is also easily achieved via a simple divide by fulcrum → Power → multiply by fulcrum chain.

Manipulations should all be applied on linear, ideally scene linear data, hence why most contemporary pipelines have an assumed fixed reference space with a scene referred linear model, and tack on the nonlinear camera rendering transforms as a non-destructive view. Calculations / manipulations are all done against the scene referred linear values, and transformed under the camera rendering transform, keeping the reference space always linearized.

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