Editing And Modifying Selection Masks Tutorials

Very rarely is a new selection perfect. Invariably, you have to do some work on it before you can use it. Fortunately, after you have stored the selection in an alpha channel, you can modify it in a number of ways. You can use painting tools, transform commands, or filters to modify the alpha channel and then load it as a selection mask.

Using Painting Tools and Filters
Because selection masks are composed of grayscale images, you can use only black and white paint, or shades of the two, to modify a mask. When you activate an alpha channel containing a selection that you wish to modify, the foreground and background colors are automatically set to white and black, respectively. However, when you enter Quick Mask mode (Q), the foreground and background colors are set to black and white, respectively.

Painting with black in the alpha channel expands the masked areas and contracts the selected areas; painting with white has the opposite effect: masked areas contract and selected areas expand. If you paint with a shade of gray, areas become partially masked or partially selected, depending on the intensity of the gray. You can paint with a shade of gray by varying the opacity for the Brush tool from the options bar, or by using the numeric keyboard: Tap 1 to 10 to alter in 10% increments, for example; tap 2 to change the opacity to 20%; or tap a figure between 1 and 100.

There is one other way to paint with shades of gray without having to change the foreground color. If you have a pen and tablet, you can open the Brushes palette and enable Pen Pressure in the options for Other Dynamics. Now when you paint, you can control the shades by simply applying more or less pressure.

When it comes to modifying active selections, the Quick Mask mode is particularly good for running filters on the selection. When the mode has been invoked, you can use filters to contract, expand, soften, harden, or transform selection edges. For example, you can use the blur filters to soften edges (as noted previously), the Maximum and Minimum (Filter > Other) to expand and contract selected areas, respectively, and the distort or artistic filters to create fanciful selections. Try the various filters to see which ones work and which don’t (Figure 9-9). Not all filters can be applied in Quick Mask mode.

Figure 9-9: A frame created by (1) applying a border to a selection, (2) entering Quick Mask mode, (3) applying the Fresco filter, (4) creating a new layer and filling with a color, and (5) applying a layer style.

Here’s another use for Quick Mask mode and filter combo. It’s almost impossible to create smooth selections with the Lasso tool. If you need to smooth the jagged edges before you can use a selection, you have two options. One, choose Select > Modify > Smooth and enter a numeric value in the Smooth dialog box or, two, enter Quick Mask mode and apply Filter > Noise > Median. Both will produce similar results, but with the latter method, you will have visual feedback.

Warp Command
The new Warp command warps not only filled objects, type, and shapes but also selections. Using a combination of preset and custom warps, you can create almost any shape you can imagine. To warp a selection, take the following steps:

With a selection active, choose Select > Transform Selection or right-click (Windows), Ctrl-click (Mac OS) the selection and then choose Transform Selection from the contextual menu.
Next, click the warp icon in the options bar to invoke the Warp command (Figure 9-10).




Figure 9-10: The options bar showing options for the transform command: A. Warp Style pop-up menu; B. Change The Warp Orientation (available after a warp style is selected); C. Switch Between Free Transform and Warp Modes.




To effect a distortion, drag one of the four corner handles, one of the eight individual control points, or click in the mesh and then drag (Figure 9-11).




Figure 9-11: A selection being warped by using the Edit > Transform Selection > Warp command; A. Corner handle; B. Original selection bounding box; C. Control point.




When you are happy with the distortion, click the commit icon in the options bar or press Enter (Windows), Return (Mac OS).
To move the selection bounding box, hold down Ctrl (Windows), cmd (Mac OS), click in the bounding box, and drag.

As does the Type tool, the Warp command has preset warps that can be accessed from the Warp Style pop-up menu in the options bar after the command is invoked (Figure 9-10). Furthermore, after you select a style, two other options become available to you. One, you can enter precise numeric values in the bend and distort text boxes; two, you can change the orientation by clicking the Change Warp Orientation button next to the Warp Style pop-up menu (refer to Figure 9-10).

Note: You cannot enter numeric values if you have chosen None or Custom from the Warp Style pop-up menu.

Preventing Rounded Corners when Expanding
When you expand a rectangular selection and stroke it by more than a pixel, you might have noticed that the stroke acquires rounded corners (Figure 9-12). This is not caused by a setting that you might have overlooked; it’s just the way the feature works. To prevent this unwanted side effect, you can employ one of the following three workarounds:

Stroke inside the selection but be prepared to lose some of your image content.
Expand the selection in one-pixel increments and then stroke inside. To do so, choose Select > Modify > Expand. If you need to modify by a large amount, create an action and run it on the selection as many times as necessary (see Chapter 15).
With the selection active, enter Quick Mask mode. Choose Filter > Other > Maximum and enter the number of pixels by which you want to expand the selection. Exit Quick Mask mode and then stroke inside without fear of rounded corners.

Figure 9-12: Rectangular selection produces rounded corners when stroked on the outside.