This kind of curves look overall like the standard rgb curves but they could help with very saturated colors or with strong primaries.
They work in a similar way of the rawtherapee’s luminance curves, the difference is that we process the rgb input too with curves , find the (rgb+curves) luminance and “merge” with the (input luminance + curve)
Example from a Playraw, look at the car’s rear lights
RGB=RGB Y_input = R * 0.2126729 + G * 0.7151521 + B * 0.0721750 Y_output=Y_input + curve RGB2=RGB + curve Y2=R2 * 0.2126729 + G2 * 0.7151521 + B2 * 0.0721750 (luminance of RGB2) RGB_output= (RGB2 / Y2) * Y_output
It could be possible to test these curves in rawtherapee ?