Using Masks to Increase Luminance
We learned the following technique for increasing image brilliance (luminance) from Katrin Eismann. As we have already seen, a mask is nothing more than a grayscale image, and a luminosity mask is actually a monochrome image created from an existing color image using grayscale values that represent the colors present in the original. A luminosity mask is easy to create.
We open the Channels panel, select RGB, and load the selection by clicking on the icon. (To change the luminance of a single channel, select the Channels panel and use it for your selection or mask.)
We then save the selection (Select ▸ Save Selection ...