If I create a file with blue zero everywhwere and red and green non-zero, all points are 100% saturated in Photoshop because one channel is zero. The PSCS3 saturation slider does nothing on the + side.
But opening the same file in ACR and moving its saturation slider to plus values DOES change the red and green values. ACR has to be using a different algorithm for saturation. What is it?