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.