sigmoid: color processing bug or doc error?

[kofa (István Kovács)]

A colour wheel from Wikipedia with sigmoid in rgb ratio mode:

In per channel mode with preserve hue = 100%:

Accroding to darktable 4.4 user manual - sigmoid, the two should be equivalent:

preserve hue (per channel mode only)
Choose how much to preserve hue – 100% preserves the spectral hue of the image (identical to using the “rgb ratio” color processing mode)

Comparing snapshots:

Is the documentation wrong, or is that the intended behaviour, and a bug has crept in? @jandren, perhaps?

[jandren (Jakob Andrén)]

Thanks for asking!

Identical definition of hue. So the chroma and brightness will be different. Maybe I should contribute a clarification to the manual?

[paperdigits (Mica)]

Yes please

[kofa (István Kovács)]

Thanks for the clarification (both here and in the docs)!