In a discussion of creating a saturation mask, @dmstraker and @smadell referred to an equation involving channels:
Saturation=(max(SR,SG,SB)-min(SR,SG,SB))/max(SR,SG,SB)
The only way I can see to access these Source Channels is in Apply Image. However Apply Image deals with two images, a Source and a Destination. This calculation deals with just one. The information on Field Equations in Filter > Distort > Equations makes no mention of channels.
How would I create a greyscale saturation layer from an RGB layer, which I can then convert to a mask?
John