Quick Mask Mode

Quick Mask Mode lets you edit a selection as a mask while viewing your image.  The advantage of this is that you can use almost any Photoshop tool or filter to modify the mask.  For example, if you create a rectangular selection with the marquee tool, you can enter Quick Mask Mode and use the paintbrush to extend or contract the selection, or use a filter to distort the edges of the selection.  You can also use selection tools, because the quick mask itself is not a selection.


Quick Mask Mode
This invokes the Quick Mask mode.  A Color overlay (50% opaque red, similar to a piece of rubylith) covers the area outside the selection.  Use any of the painting or editing tools, or select a filter or adjustment command to modify the mask.  By default painting with black adds to the mask, shrinking the selection.  Painting with white has the opposite effect.  Painting with gray creates a semitransparent area, useful for feathering or anti-aliased effects.

Standard Mode
This turns off the Quick Mask and returns to your original image.