Working with Masks

A mask hides some parts of an image and lets other parts show through. This is extremely useful when you want to hide parts of an image but you don't want to lose any data in your file by having to delete parts of it.

Earlier, we discussed one kind of mask: creating a clipping path for placing images into page-layout applications. But there are also needs for masking inside Photoshop itselfsuch as when you want to have one photo blend into another, or when you want to make a quick selection.

Layer Masks

When it comes to creating a mask for a layer, Photoshop makes the task pretty easy. Using your selection method of choice, choose the layer in the Layers palette, select the area of the image that you want to remain visible, and click on the Add Layer Mask button at the bottom of the Layers palette. This does two things right off the bat: First, it masks the image in your document; second, it creates a second thumbnail in your layer (see Figure 5.53). In fact, let's take a closer look at what's going on in the Layers palette.

Figure 5.53. A layer mask applied to a layer.

You'll notice that a masked layer has two thumbnails with a link icon in between them. The thumbnail on the left is the image itself, and the thumbnail on the right is the mask. To edit and work with your image, click on the left icon to highlight it. Any edits you make to that layer will occur to the image itself. If you click and highlight the thumbnail on the right, you can edit the mask itself (see Figure 5.54).

Figure 5.54. In this illustration, the mask thumbnail is highlighted.

By the Way

If you're unsure of whether you're in the image-editing mode or the mask-editing mode, take a quick look at your document's title bar.

As you move the image with the Move tool, the mask moves along with it because the link icon between the two thumbnails indicates that they are locked to each other. If you click on the link, it disappears, enabling you to move the image and mask independently of each other (see Figure 5.55).

Figure 5.55. The image and the layer mask, unlinked.

To remove a mask, drag the mask thumbnail to the Layer's palette Trash icon (in the lower right of the palette). You'll get a dialog box asking whether you want to apply the mask (which will delete the parts of the image that are masked) or discard it (and the image will return to its full view).

Vector Masks

Although Photoshop has vector tools, it's not a vector-based drawing program. Photoshop uses vector outlines to create masks filled with color. For example, when you draw a rectangle using Photoshop's Rectangle tool with the Shape Layers option chosen in the Tool Options bar, a mask (which is the vector path) is created, filled with the color of your choice (which is fill pixels). You can also create vector masks by choosing Layer, Vector Mask, Reveal All or Layer, Vector Mask, Hide All.

Quick Mask Mode

Masks and selections are nearly one and the same. Sometimes you want to create a simple quick selection, and you can best do that by using one of Photoshop's many painting tools. That's where Quick Mask comes into play. Press the Q key on your keyboard to enter Quick Mask mode. You can tell you're in Quick Mask mode because it's indicated in the document's title bar.

When you're in Quick Mask mode, anything you paint or draw shows up in a transparent red color (see Figure 5.56). Press Q again, and whatever was not red becomes your selection (see Figure 5.57). This is extremely useful for creating selections that you will use in a layer mask. For example, imagine that you want a photo to fade into the layer under it. So you select the layer that the photo is on, press Q, select the Gradient tool, drag a gradient, and press Q againyour selection is now the gradient. Then you click on the New Layer Mask button, and you're done.