Channel Mixer For Preview
Sometimes it’s very difficult to find all the spots on skin. Try creating a Channel Mixer adjustment layer to turn the image into a high-contrast black-and-white image. Turn on the Monochrome checkbox, and move the Red slider to -100, the Green slider to +50, and the Blue slider to +150. This adjustment layer is just for a preview, so don’t try to retouch on it. Create a blank layer, and retouch on it.
by Calvin Hollywood