Luminosity Blend Mode

The Luminosity blend mode creates the same result as the “color” mode if the layers are reversed, i.e. the color layer is underneath. The luminosity values within an RGB image have a number of useful applications. The luminosity values can be extracted from an RGB image (from the channels palette) and saved as an alpha channel, used as a layer mask or pasted as an independent layer above the layer.

Increase contrast using Luminosity

To increase an image's contrast using the Luminosity Blend Mode, with the image open

1. Load the luminosity of the image by, in the Channels palette Ctrl+click the RGB channel.
2. Control+J to copy the luminosity as a layer and name lighten.
3. Change the lighten layer's blend mode to Screen. This lightens the highlights.
4. To increase contrast we now want to darken the shadows.
5. Click the Background layer and load the luminosity by Ctrl+Click on the RGB channel as in step 1.
6. Inverse the selection by Shift+Ctrl+I
7. Ctrl+J to load the selection to a layer and name darken.
8. Change blend mode to Multiply.
9. The image's contrast has been increased.