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Create a temporary quick mask

To use Quick Mask mode, start with a selection and then add to or subtract from it to make the mask. You can also create the mask entirely in Quick Mask mode. Color differentiates the protected and unprotected areas. When you leave Quick Mask mode, the unprotected areas become a selection.

Note: A temporary Quick Mask channel appears in the Channels panel while you work in Quick Mask mode. However, you do all mask editing in the image window.
  1. Using any selection tool, select the part of the image you want to change.
  2. Click the Quick Mask mode button  in the toolbox.

    A color overlay (similar to a rubylith) covers and protects the area outside the selection. Selected areas are left unprotected by this mask. By default, Quick Mask mode colors the protected area using a red, 50% opaque overlay.

    Selecting in Standard mode and Quick Mask mode

    A.
    Standard mode

    B.
    Quick Mask mode

    C.
    Selected pixels appear as white in channel thumbnail

    D.
    Rubylith overlay protects area outside selection, and unselected pixels appear as black in channel thumbnail

  3. To edit the mask, select a painting tool from the toolbox. The swatches in the toolbox automatically become black and white.
  4. Paint with white to select more of an image (the color overlay is removed from areas painted with white). To deselect areas, paint over them with black (the color overlay covers areas painted with black). Painting with gray or another color creates a semitransparent area, useful for feathering or anti-aliased effects. (Semitransparent areas may not appear to be selected when you exit Quick Mask Mode, but they are.)
    Painting in Quick Mask mode

    A.
    Original selection and Quick Mask mode with green chosen as mask color

    B.
    Painting with white in Quick Mask mode adds to the selection

    C.
    Painting with black in Quick Mask mode subtracts from the selection

  5. Click the Standard Mode button  in the toolbox to turn off the quick mask and return to your original image. A selection border now surrounds the unprotected area of the quick mask.

    If a feathered mask is converted to a selection, the boundary line runs halfway between the black pixels and the white pixels of the mask gradient. The selection boundary indicates the transition between pixels that are less than 50% selected and those that are more than 50% selected.

  6. Apply the desired changes to the image. Changes affect only the selected area.
  7. Choose Select > Deselect to deselect the selection, or save the selection by choosing Select > Save Selection.
    You can convert this temporary mask to a permanent alpha channel by switching to standard mode and choosing Select > Save Selection.