Mask part of an image
- In the Layers palette, select the layer or layer set you want to mask. If the layer is a background layer, double click its name to convert it to a standard, unlocked layer. Name it and click OK.
- Using a selection tool, select the area in the image that you want to show. The mask you create will hide the nonselected areas. If it is easier, you can instead select the area you want to hide.
- If you selected the area that you want to show, choose Layer > Add Layer Mask > Reveal Selection. If you selected the area you want to hide, choose Layer > Add Layer Mask > Hide Selection. A layer mask thumbnail appears in the Layers palette on the same layer as the image.
How To Tip:
Mask part of an image by converting a selection into a mask.
You can hide a portion of an image using a mask. Photoshop provides several ways to mask an image. The simplest is the layer mask, a bitmap image that hides the pixels beneath it. The original image remains intact. You can create a layer mask from a selection and later edit it with the painting tools.
To preview the mask or refine the selection with a brush, click the Quick Mask Mode button 
in the toolbox. Photoshop covers the nonselected areas of the image in a translucent color. While not a true mask, this mode lets you preview a mask and makes it easy to see and edit the selection boundary. To refine the selection boundary, select a brush tool. Paint with black to add to the mask; paint with white to reveal more of the image. When you're satisfied with the mask, click the Standard Mode button 
to see the selection boundary again.
To later edit the mask, select the mask thumbnail that appears next to the thumbnail of the layer in the Layers palette. Using a brush from the toolbox, paint with black to add to the mask, or paint with white to reveal more of the underlying image.
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