Adjust saturation. Changes the saturation of each visible pixel of the layer or composite image.
Saturation adjustment (-100…+100 int).
op_saturation=-100 fully desaturates the image.
Layer command. Applies to the current layer or to the composite image if
layer=comp. Ignored by effect layers.
op_saturation=0, for no change in saturation. CMYK images or layers are converted to RGB before the operation is applied.
Manipulate a color photograph to achieve a “high-key” appearance: