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Alpha Channels and Masks

When you use the command Select, Save Selection, you're creating an alpha channel, a representation of the selection saved in a channel. Alpha channels are stored with the image, whereas selections are lost when deselected. Like other channels, an alpha channel is a grayscale representation. As an 8-bit image, there is a maximum of 256 shades of gray in the channel. In a 16-bit image, there are thousands of levels of gray. Each level of gray represents the level of selection for each pixel. For example, a pixel colored 50% gray in an alpha channel is 50% selected when the channel is loaded again as a selection.

Alpha channels can be created from scratch as well as from an existing selection. As a channel, they can also be edited as though they were grayscale images, with tools, filters, adjustments, and more.


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