Quick Mask Mode - Photoshop

This is pulled straight from HERE, adobe's help section of their website. Some personal additions were made, and are in a differing, bold font.

To use Quick Mask mode to create and edit selections quickly, 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.

Using any selection tool, select the part of the image you want to change.


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 


To edit the mask, select a painting tool from the toolbox. The swatches in the toolbox automatically become black and white.

The Selection tools, such as the magnetic lasso, can also be used in quick mask mode. A good trick using the magnetic lasso tool is to select areas that would be difficult to use paint tools on, and hit Backspace [windows] or option + delete [Mac] to fill with black, and control + backspace [windows] or command + delete [Mac] to fill the selection with white.


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 


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.


Apply the desired changes to the image. Changes affect only the selected area.


Choose Select > Deselect to deselect the selection.


Note: 


You can convert this temporary mask to a permanent alpha channel by switching to standard mode and choosing Select > Save Selection.

Change Quick Mask options 

Double-click the Quick Mask Mode button  in the toolbox.


Choose from the following display options:


Masked Areas




Sets masked areas to black (opaque) and selected areas to white (transparent). Painting with black increases the masked area; painting with white increases the selected area. When this option is selected, the Quick Mask button in the toolbox becomes a white circle on a gray background .




Selected Areas




Sets masked areas to white (transparent) and selected areas to black (opaque). Painting with white increases the masked area; painting with black increases the selected area. When this option is selected, the Quick Mask button in the toolbox becomes a gray circle on a white background .




Note: 


To toggle between the Masked Areas and Selected Areas options for quick masks, Alt-click (Windows) or Option-click (Mac OS) the Quick Mask Mode button.




To choose a new mask color, click the color box, and choose a new color.


To change the opacity, enter a value between 0% and 100%.


Both the color and opacity settings affect only the appearance of the mask and have no effect on how underlying areas are protected. Changing these settings may make the mask more easily visible against the colors in the image.




Inverting Selection in Quick Mask Mode
Go to image > adjustments > Invert.


When you're working in a mask control or command + I inverts the selection, when you're working with the selection outline it's control + shift + I, or command + shift + I on a Mac for the Inverse Command.
















Final Tip: exit quick mask mode and switch to the layers panel, Add Layer Mask by clicking on the layer mask icon at the bottom of the panel to mask away whatever is unselected.