Someone asked on Reddit if there was a way to make a selection based on saturation values inside Photoshop. I didn’t know of one, but the idea sounded interesting so I had a bit of a play.
Several trial and error events later and I’ve found a method that seems to work pretty well. You can use the ‘Difference’ blending mode on a desaturated copy of the layer to find the least saturated pixels, which can be used as a alpha channel. To save me explaining all the steps right now here’s a handy action to play with;
The action should run through its steps and leave you with a new selection of the highest saturated pixels in the image. It’ll also save this selection as a new channel called “Saturation”. You can select the lowest saturated pixels by inverting the selection (or channel) and sorta tweak the ‘range’ by using levels on the saturation channel before selecting.
I’ll admit I haven’t yet found all that many uses for this selection; although if you open a photograph, select the most (or least) saturated colours then bring up the Hue/Sat control, you can make a more evenly saturated picture which can look pretty cool. Boosting the saturation of only the lowest saturated pixels means you can raise them a lot higher before it starts to produce artifacts.
Have fun, and if you find any more uses please leave a note in the comments.