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Chapter 15. MASKS

Chapter 15. MASKS

THIS CHAPTER COVERS two special methods for saving and reshaping a selection: alpha channels and Quick Mask mode.

If you save a selection to a specially created grayscale channel, called an alpha channel, you can load the selection onto the image at any time. A selection that has an irregular shape that would be difficult to reselect would be a logical candidate for this operation. A file can contain up to 24 channels, though from a practical standpoint, since each channel increases a picture's storage size (depending on the size of the selec- tion area), you should be judicious when adding alpha channels. Alpha channels are accessed via the Channels palette , and are saved or loaded onto an image via Select menu commands or the Channels palette. (To create a layer clipping path in place of an alpha channel to conserve file storage space, see page 274.)

Using Photoshop's Quick Mask mode, the selected or unselected areas of an image can be covered with a semi-transparent colored mask, which can then be reshaped using any editing or painting tool. Masked areas are protected from editing. Unlike an alpha channel, a Quick Mask cannot be saved, but when you return to Standard (non-Quick Mask) mode, the mask will turn into a selection, which can be saved.

Note: If you're unfamiliar with Photoshop's basic selection tools, read Chapter 5 before reading this chapter.

Layer masks are covered in Chapter 14.

A selection that is saved in an alpha chan-nel can be loaded onto any image whenever it's needed.

Note: To convert an alpha channel into a spot color channel, see page 196.



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