Layer Masks
In preference to deleting pixels from an
image it is better to
create a
Layer Mask which can then be painted black (or grey) to conceal (or
partially conceal) areas of the original image (will not work
on
Background Layer) These areas can be restored at any time simply by
painting with white.
The mask is shown as a thumbnail to the right of the image thumbnail on the Layers Palette and also as a channel on the Channels Palette. Note that the image and the mask are linked together, and that the link can be removed by clicking it, allowing the mask to be moved independently of the image.
When the layer is active, either the image OR the mask can be the active item. This is denoted by the double line around the icon and by the symbol in the Layer Status Box, a brush for the image or a dark square with small white circle for the mask.
Mask manipulation.
Add a Layer Mask by clicking the appropriate icon (2nd left) at the bottom of the Layers Palette. This produces a blank white mask and no change to the image. If you hold down the [Alt] key while clicking the Add Mask icon, the resulting mask will be completely filled with black and the layer will be completely transparent.
If there is an active selection on the layer at the time you add a mask, then the selected area will remain un-masked. If you hold down the [Alt] key, then only the selected area will be masked.
The black area on the mask thumbnail is the masked portion. Increase it by making sure the mask is active (double line border and mask symbol in layer status box) and painting with black. Painting with white erases the masking and restores image pixels.
Temporarily turn the mask OFF by holding down [Shift] and clicking the MASK icon. A red cross-out will appear on the MASK icon. Repeat the action to turn back ON.
Load the mask icon full size on the screen by holding down [Alt] and clicking the MASK icon. Repeat to restore.
Load the mask on to the image as a red semi-transparent overlay (like Quickmask) by holding down [Shift][Alt] and clicking the MASK icon. Repeat to remove. Adjust the transparency by double-clicking the mask icon (no keys this time) and changing settings on the panel.
You can load a mask as a selection on to the main image by holding down the [Ctrl] key and clicking the mask icon.
Reverse the selection if you need to by clicking Select on the main menu and choosing Inverse. Or use [Shift] [Ctrl] [I] on the keyboard.
Unlink Image and Mask by clicking the small chain between the icons on the Layers Palette. Repeat to re-link.