Read this introduction to layer masks first.

Let's say we have two layers in Photoshop, each with a different filtering, and you want parts of both in the final image. Luminance masks will help you do that without a lot of manual painting.



The bottom layer here (#1) is more lightly filtered than the layer above it (#2). While the top layer is selected, click the rectangular button indicated in #2 to make a layer mask. Go to "Apply image..." (#3).



As you can see in the image mask in #4, the darker areas of the image show more of the lower layer while the lighter areas show more of the more heavily filtered top layer. If you use the invert option in #5, the opposite is true. Whether you invert or not depends on whether you want lights or darks to be more filtered, and which layer is on top. This part isn't perfect, so you can adjust the mask "luminance" with levels (#6).



The levels settings used (#7) depend entirely on the image. Moving the black slider right makes the dark parts on the mask darker. Adjusting the white slider on the right changes the light parts of the image. Moving the gamma (gray) left makes the midtones brighter and vice versa if the gamma is lowered (move right).

The final image is in #8.

Updated by Aurelia about 14 years ago