Adding and subtracting by command

Photoshop provides several commands under the Select menu that automatically increase or decrease the number of selected pixels in an image according to numerical specifications. The commands in the Select ^ Modify submenu work as follows:

* Border: This command selects an area of a specified thickness around the perimeter of the current selection outline and deselects the rest of the selection. For example, to select a 6-point-thick border around the current selection, choose Select ^ Modify ^ Border, enter 6 in the Width option box, and press Enter. But what's the point? After all, if you want to create an outline around a selection, you can accomplish this in fewer steps by choosing Edit ^ Stroke. The Border command, however, broadens your range of options. You can apply a special effect to the border, move the border to a new location, or even create a double-outline effect by first applying Select ^ Modify ^ Border and then applying Edit ^ Stroke.

* Smooth: This command rounds off the sharp corners and weird anomalies in the outline of a selection. When you choose Select ^ Modify ^ Smooth, the program asks you to enter a Sample Radius value. Photoshop smoothes out corners by drawing little circles around them; the Sample Radius value determines the radius of these circles. Larger values result in smoother corners.

Tip The Smooth command is especially useful in combination with the magic wand. After you draw one of those weird, scraggly selection outlines with the wand tool, use Selects Modify^ Smooth to smooth out the rough edges.

* Expand and Contract: Both of these commands do exactly what they say, either expanding or contracting the selected area by a specified amount. For example, if you want an elliptical selection to grow by 8 pixels, choose Select ^ Modify ^ Expand, enter 8, and call it a day. These are extremely useful commands; I refer to them several times throughout the book.

Photoshop 6 enables you to expand and contract selections by as many as 100 pixels, up from the previous limit of 16. The upper limits of the Border and Smooth commands were raised also (to 200 and 100 pixels, respectively), but my guess is that you'll have less reason to take advantage of those changes than you will the new ranges for Expand and Contract.

Both Expand and Contract have a flattening effect on a selection. To round things off, apply the Smooth command with a Sample Radius value equal to the number you just entered into the Expand Selection or Contract Selection dialog box. You end up with a pretty vague selection outline, but what do you expect from automated commands?

In addition to the Expand command, Photoshop provides two other commands — Grow and Similar — that increase the area covered by a selection outline. Both commands resemble the magic wand tool because they measure the range of eligible pixels by way of a Tolerance value. In fact, the commands rely on the same Tolerance value (on the Options bar) that you set for the magic wand. So if you want to adjust the impact of either command, you must first select the magic wand and then apply the commands:

* Grow: Choose Select ^ Grow to select all pixels that both neighbor an existing selection and resemble the colors included in the selection, in accordance with the Tolerance value. In other words, Select ^ Grow is the command equivalent of the magic wand tool. If you feel constrained because you can only click one pixel at a time with the magic wand tool, you may prefer to select a small group of representative pixels with a marquee tool and then choose Select ^ Grow to initiate the wand's magic.

* Similar: Another member of the Select menu, Similar works like Grow, except the pixels needn't be adjacent. When you choose Select ^ Similar, Photoshop selects any pixel that falls within the tolerance range, regardless of the location of the pixel in the foreground image.

Note Although both Grow and Similar respect the magic wand's Tolerance value, they pay no attention to the other wand options — Contiguous, Use All Layers, and Anti aliased. Grow always selects contiguous regions only; Similar selects noncontigu ous areas. Neither can see beyond the active layer or produce antialiased selection outlines.

One of the best applications for the Similar command is to isolate a complicated image set against a consistent background whose colors are significantly lighter or darker than the image. Consider Figure 8-9, which features a dark and ridiculously complex foreground image set against a continuous background of medium-to-light brightness values. The following steps explain how to separate this image using the Similar command in combination with a few other techniques I've described thus far.

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