Selective Color adjustment is an interesting thing. It can change the Cyan, Magenta, Yellow and Black values...
within a set of values found in a drop down menu:
The best way to learn this tool is by experimenting on hue gradient (the Gradient Tool has one in a can). In the top hue gradient I de-saturated and lightened the yellow by sliding the reducing its amount of black and I made the green more blue decreasing its yellow.
To a painter and a compositor is is probably not wildly useful, but to a photographer it is wildly more useful than the awful Color Balance adjustment.
The saturation map
This Adjustment tool does have one fascinating application: to make a saturation map:
- To every value in the drop-down menu except the White, Neutral and Black, reduce the Black value to -100%.
- To the White, Neutral and Black increase the Black value to +100%.
This will give you a saturation map of the image. In the saturation map of the painting below on the left by Thomas Moran the lightness value of the cliff and the sky are about the same, but the saturation values (left) show it to have a higher saturation value.
It can also be used as a mask in a saturation adjustment. To do so:
- Make a saturation map of your image.
- Lay down a Hue Saturation adjustment on top of your image and set its saturation value to zero.
- Copy the saturation map.
- Alt click on the mask of the Hue Saturation adjustment (to reveal its mask) and paste the saturation map into the mask.
- Voila! You may need to invert the mask.
- You may also wish to edit the value of the mask to taste, e.g. use the black and white target eyedroppers on the dark and light value to force the contrast of the mask.