Thursday, June 28, 2007
Masking Essentials I
Mastering the art of the mask will empower you to control your images with precision
Selections: Save, Load And Combine
Selections, alpha channels and layer masks are intertwined; they're essentially different aspects of one another, and any one can become another.
Saving a selection creates an alpha channel, while loading an alpha channel creates an active selection. A layer mask can be loaded as a selection by clicking on the mask and loading it as a selection (Select > Load Selection). (Alternately, you can hold the Command key and click on the mask; a targeted layer mask will appear in the Channels palette.
You can drag and drop a selection from one document to another. You can load an alpha channel from one document into another if both documents are open.
While simply loading a new selection will replace an active selection, you can load a selection from more than one alpha channel at a time. In the Load Selection dialog box, you can choose from Add to Selection, Subtract from Selection and Intersect with Selection. (Some advanced users like to use the Image > Calculations feature to perform these kinds of tasks.)
Selection To Layer Mask
If you create a layer mask without an active selection, you can choose from Reveal All (white mask) or Hide All (black mask). If a selection is active when you create a layer mask, you can choose from Reveal Selection (the selected area becomes white, the unselected area becomes black) or Hide Selection (the selected area becomes black, the unselected area becomes white). Work from the broad to the specific. If you want to isolate a specific area, first select it broadly and then refine it further.
You can move a mask from one layer to another by dragging and dropping it. Hold the Option/Alt key when you do this and the mask will be copied to the destination layer; you can even replace one mask with another this way. One mask can affect many layers if you put the layers in a layer set and mask the layer set.
While a layer or layer set can only have one mask, there's a way to have more than one mask affect a layer or layer set; mask the layer or layer set and put it in a layer set with another mask. This is particularly useful if you want to combine different types of masks, such as a contour mask and a gradient mask, and want to retain the ability to control the components independently of one another.
When you're moving from selection to alpha channel to layer mask or from layer to layer mask, make sure that you target the component you want to affect. A highlight color and a bold outline in your Layers and Channels palettes will indicate where you are at any given point in time.
Seeing The Mask
It helps to see what you're doing. If you can see a mask better, you can make it better. You can see a mask in a number of ways. Option-click the mask to display it in black-and-white. Shift-click the mask to disable it. Option/Shift-click the mask to display the mask and the image at the same time in the same window. The default color and opacity are red and 50%, but you can change these defaults by double-clicking on the mask.
You can see the image and the mask at the same time in separate windows (Window > Arrange > New Window), which may or may not be matched in zoom ratio and location (Window > Arrange > Match Zoom and Location).
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