When you select part of an image, the area that is not selected is “masked” or protected from editing. So, when you create a mask, you isolate and protect areas of an image as you apply color changes, filters, or other effects to the rest of the image. You can also use masks for complex image editing such as gradually applying color or filter effects to an image.

Examples of masks

A.

Opaque mask used to protect the background and edit the butterfly

B.

Opaque mask used to protect the butterfly and color the background

C.

Semitransparent mask used to color the background and part of the butterfly

Masks are stored in alpha channels. Masks and channels are grayscale images, so you can edit them like any other image with painting tools, editing tools and filters. Areas painted black on a mask are protected, and areas painted white are editable.

Use Quick Mask mode to convert a selection to a temporary mask for easier editing. The Quick Mask appears as a colored overlay with adjustable opacity. You can edit the Quick Mask using any painting tool or modify it with a filter. Once you exit Quick Mask mode the mask is converted back to a selection on the image.

To save a selection more permanently, you can store it as an alpha channel. The alpha channel stores the selection as an editable grayscale mask in the Channels palette. Once stored as an alpha channel, you can reload the selection at any time or even load it into another image.

Selection saved as an alpha channel in Channels palette