It would be useful to able to apply SigmoidalContrast() to a particular channel. For example, the ImageMagick commandline equivalent of:

magick -channel R sigmoidal-contrast 5,100%

Describe the solution you'd like

Ideally, pass in Channels as a parameter to SigmoidalContrast(), as is possible with the Evaluate() function, so an override like:

image.SigmoidalContrast(Channels, Percentage, Percentage)

Describe alternatives you've considered

I've thought about extracting the channel, applying the function, and then rewriting it but it seems like overkill.