Real World Adobe® Photoshop® CS2 [Electronic resources] : Industrial-Strength Production Techniques نسخه متنی

Selection Tools

Although there are a mess o' ways to make a selection in Photoshop (we'll look at just about all of them in this chapter), there are three basic selection tools in the Tool palette: the Marquee tool, the Lasso tool, and the Magic Wand (see Figure 8-1). While some people eschew these tools for the more highfalutin' selection techniques, we find them invaluable for much of our day-to-day work.

The important thing to remember about these selection tools (and, in fact, every selection technique in Photoshop) is that they can all work in tandem. Don't get too hung up on getting one tool to work just the way you want it to; you can always modify the selection using a different technique (this idea of modifying selections is very important, and we'll touch on it throughout the chapter).

Tip: You Can Always Move Your Selection

One of the most frequent changes you'll make to a selection is moving it without moving its contents. For instance, you might make a rectangular selection, then realize it's not positioned correctly. Don't redraw it! Just click and drag the selection using one of the selection tools. The selection moves, but the pixels underneath it don't. Or, press the arrow keys to move the selection by one pixel. Add the Shift key to move the selection ten pixels for each press of an arrow key.

Tip: Moving a Selection While Dragging

One of the coolest (and least known) selection features is the ability to move a marquee selection (either rectangular or oval) while you're still dragging out the selection. The trick: hold down the Spacebar key while the mouse button is still held down. This also works when dragging frames and lines in Adobe InDesign and Adobe Illustrator.

Tip: Adding to and Subtracting from Selections

No matter which selection tool you're using, you can always add to the current selection by holding down the Shift key while selecting. Conversely, you can subtract from the current selection by holding down the Option key. Or, if you want the intersection of two selections, hold down the Option and the Shift keys while selecting (see Figure 8-2). If you don't feel like remembering these keyboard modifiers, you can click on the Add, Subtract, and Intersect buttons on the far-left side of the Options bar instead.

Tip: Select It Again

While Bruce is the steady-and-sure type, David tends to rush through Photoshop like a madman. One result is that David often deselects a selection without having thought through the implications (like "will I need this again?"). Fortunately, when he finds he does need that old selection again, he can recall it by pressing Command-Shift-D (or choosing Reselect from the Select menu).

Tip: Transforming Selections

When you choose Transform Selection from the Select menu, Photoshop places the Free Transform handles around your selection and lets you rotate, resize, skew, move, or distort the selection however you please. When you're done, press Enter or click the Checkmark button in the Options bar.

Even less obvious is that after you choose Transform Selection, you can pick options from the Transform submenu (under the Edit menu) or type transform values into the fields in the Options bar. For example, if you want to mirror your selection, turn on Transform Selection, drag the center point of the transformation rectangle to the place around which you want the selection to flip, then choose Flip Vertical or Flip Horizontal from the Transform submenu (see Figure 8-3).

Marquee

The Marquee tool is the most basic of all the selection tools. It lets you draw a rectangle or oval selection by clicking and dragging. If you hold down the Shift key, the marquee is constrained to a square or a circle, depending on whether you have chosen Rectangle or Ellipse in the Marquee Options bar. (Note that if you've already made a selection, the Shift key adds to the selection instead.) If you hold down the Option key, the selection is centered on where you clicked.

Tip: Pull Out a Single Line

If you've ever tried to select a single row of pixels in an image by dragging the marquee, you know that it can drive you batty faster than Mrs. Gulch's chalk scraping. The Single Row and Single Column selection tools (click and hold the mouse button down on the Marquee tool to get them) are designed for just this purpose. We use them to clean up screen captures, or to delete thin borders around an image. They're also useful with video captures, because each pixel row often equals a video scan line.

You can cycle through the rectangular, elliptical, single row, and single column selection tools by choosing from the Tool palette, but it's faster to press M once to select the tool, then press Shift-M to cycle through the tools (Option-clicking on the Marquee tool in the Tool palette also cycles through them).

Tip: Selecting Thicker Columns and Rows

If you want a column or row that's more than one pixel wide/tall, set the selection style to Fixed Size on the Options bar, and type the thickness of the selection into the Height or Width field (note that you have to type a measurement value, like "px" for pixels, or "cm" for centimeters). In the other field, type some number that's obviously larger than the image, like 10,000px. When you click on the image, the row or column is selected at the thickness you want.

Tip: Selecting that Two-by-Three

You've laid out a page with a hole for a photo that's 2 by 3 inches. Now you want to make a 2-by-3 selection in Photoshop. No problem: Choose Constrained Aspect Ratio from the Style popup menu in the Options bar (when you have the Marquee tool selected). Photoshop lets you type in that 2-by-3 ratio.

If you're looking to select a particular-sized area, you can select Fixed Size from the Style popup menu, and type any measurement you want ("in" for inches, "px" for pixels, and so on).

Lasso

The Lasso tool lets you create a freeform outline of a selection. Wherever you drag the mouse, the selection follows until you finally let go of the mouse button and the selection is automatically closed for you (there's no such thing as an open-ended selection in Photoshop; see Figure 8-4).

Tip: Let Go of the Lasso

Two of the most annoying attributes of selecting with the Lasso are that you can't lift the mouse button while drawing, and you can't draw straight lines easily (unless you've got hands as steady as a brain surgeon's). The Option/Alt key overcomes both these problems.

When you hold down the Option key, you can release the mouse button, and the Lasso tool won't automatically close the selection. Instead, as long as the Option key is held down, Photoshop lets you draw a straight line to wherever you want to go. This solves both problems in a single stroke (as it were).

The folks at Adobe saw that people were using this trick all the time and decided to make it easier on them. Photoshop includes a Straight-line Lasso tool that works just the opposite from the normal Lasso toolwhen you hold down the Option key, you can draw nonstraight lines. If you press the L key once, Photoshop gives you the Lasso tool; then press Shift-L, and you get the Straight-line Lasso tool. (Of course, the Shift key trick won't work if you've turned off the Use Shift Key for Tool Switch option in the Preferences dialog box.)

In order to close a selection when you're using the Straight-line Lasso tool, you have to either click at the beginning of the selection or double-click anywhere.

Tip: Select Outside the Canvas

You may or may not remember at this point in the book that Photoshop saves image data on a layer even when it extends past the edge of the canvas (out into that gray area that surrounds your picture). Just because it's hidden doesn't mean you can't select it. If you zoom back far enough, and enlarge your window enough (or switch to full-screen mode) that you can see the gray area around the image canvas, you can hold down the Option key while using the Lasso tool to select into the gray area. (Ordinarily, without the modifier key, the selections stop at the edge of the image.)

Magnetic Lasso

The Magnetic Lasso tool (it, too, is hiding in the Tool palette behind the Lasso tool) lets you draw out selections faster than the regular Lasso tool. This tool can seem like magic or it can seem like a complete waste of timeit all depends on three things: the image, your technique, and your attitude.

To use the Magnetic Lasso tool, click once along the edge of the object you're trying to select, then drag the mouse along the edge of the selection (you don't have toand shouldn'thold down the mouse button while moving the mouse). As you move the mouse, Photoshop "snaps" the selection to the object's edge. When you're done, click on the first point in the selection again (or triple-click to close the path with a final straight line).

So the first rule is: Only use this tool when you're selecting something in your image that has a distinct edge. In fact, the more distinct the better, because the program is really following the contrast between pixels. The lower the contrast, the more the tool gets confused and loses the path.

Here are a few more rules that will help your technique.

Be picky with your paths. If you don't like how the selection path looks, you can always move the mouse backward over the path to erase part of it. If Photoshop has already dropped an anchor point along the path (it does this every now and again), you can remove the last point by pressing the Delete key. Then just start moving the mouse again to start the new selection path.

Click to drop your own anchor points. For instance, the Magnetic Lasso tool has trouble following sharp corners; they usually get rounded off. If you click at the vertex of the corner, the path is forced to pass through that point.

Vary the Lasso Width as you go. The Lasso Width (in the Options bar) determines how close to an edge the Magnetic Lasso tool must be to select it. In some respects it determines how sloppy you can be while dragging the tool, but it becomes very important when selecting within tight spots, like the middle of a "V". In general, you should use a large width for smooth areas, and a small width for more detailed areas.

Fortunately, you can increase or decrease this setting while you move the mouse by pressing the square bracket keys on your keyboard. (For extra credit, set Other Cursors to Precise in the General Preferences dialog box; that way you can see the size of the Lasso Width.) Also, Shift-[ and Shift-] set the Lasso Width to the lowest or highest value (one or 40). If you use a pressure-sensitive tablet, turn on the Stylus Pressure checkbox on the Options bar; the pressure then relates directly to Lasso Width.

Sometimes you want a straight line. You can get a straight line with the Magnetic Lasso tool by Option-clicking once (at the beginning of the segment) and then clicking again (at the end of the segment).

Occasionally, customize your Frequency and Edge Contrast settings. These settings (on the Options bar) control how often Photoshop drops an anchor point and how much contrast between pixels it's looking for along the edge. In theory, a more detailed edge requires more anchor points (a higher frequency setting), and selecting an object in a low-contrast image requires a lower contrast threshold. To be honest, we're much more likely to switch to a different selection tool or technique before messing with these settings.

The last rule is patience. Nobody ever gets a perfect selection with the Magnetic Lasso tool. It's not designed to make perfect selections; it's designed to make a reasonably good approximation that you can edit. We cover editing selections in "Quick Masks," later in this chapter.

Tip: Scrolling While Selecting

It's natural to zoom in close when you're dragging the Magnetic Lasso tool around. Nothing wrong with that. But unless you have an obscenely large monitor, you won't be able to see the whole of the object you're selecting. No problem; the Grabber Hand works just fine while you're selectingjust hold down the Spacebar and drag the image around. You can also press the + and - (plus and minus) keys to zoom in and out while you make the selection.

Magic Wand

The last selection tool in the Tool palette is the Magic Wand, so-called more for its icon than for its prestidigitation. When you click on an image with the Magic Wand (dragging has no effect), Photoshop selects every neighboring pixel with the same or similar gray level or color. "Neighboring" means that the pixels must be touching on at least one side (see Figure 8-5). If you want to select all the similar-toned pixels in the image, whether they're touching or not, turn off the Contiguous checkbox in the Options bar before clicking.

How similar can the pixels be before Photoshop pulls them into the selection? It's entirely up to you. You can set the Tolerance setting on the Options bar from 0 to 255. In a grayscale image, this tolerance value refers to the number of gray levels from the sample point's gray level. If you click on a pixel with a gray level of 120 and your Tolerance is set to 10, you get any and all neighboring pixels that have values between 110 and 130.

In RGB and CMYK images, however, the Magic Wand's tolerance value is slightly more complex. The tolerance refers to each and every channel value, instead of just the gray level.

For instance, let's say your Tolerance is set to 10 and you click on a pixel with a value of 60R 100G 200B. Photoshop selects all neighbors that have red values from 50 to 70, and green values from 90 to 110, and blue values from 190 to 210. All three conditions must be met, or the pixel isn't included in the selection (see "Grow," later in the chapter for more info).

Bruce almost never uses the Magic Wand; he finds it too limiting, so he uses Color Range instead (which we talk about later in this chapter). David finds himself using the Magic Wand frequently. However, he almost Chapter 6, Image Adjustment Fundamentals); when he's just trying to pick up a color, he uses 3 by 3 Average.

Tip: Reverse Selecting

One simple but nonobvious method that we often use to select an area is to select a larger area with the Lasso or Marquee tool and then Option-click with the Magic Wand tool on the area we don't want selected (see Figure 8-6).

Floating Selections

We need to take a quick diversion off the road of making selections and into the world of what happens when you move a selection. Photoshop has traditionally had a feature called floating selections. A floating selection is a temporary layer just above the currently selected layer; as soon as you deselect the floating selection, it "drops down" into the layer, replacing whatever pixels were below it. When you move a selection of pixels within an image, Photoshop acts as though those pixels were on a layer. Unfortunately, while these floating selections act like layers, they don't show up in the Layers palette.

The Photoshop engineering team has been trying to get rid of floating selections for years, but there are still a few instances where they appear. In general, however, we prefer to avoid floating selections and instead move pixels to a real layer for accurate positioning.

Tip: Forcing a Float

If you want to cut out the pixels and float them (so that a blank spot remains where the pixels were), you can drag the selection with the Move tool. (You can get the Move tool temporarily by holding down the Command key.) If you'd rather copy the pixels into a floating selection, you can hold down the Option/Alt key while dragging. Note: The floating selections doesn't appear on the Layers palette.

Tip: Floating Selections Are Layers, Too

You can change the mode of a floating selection to Multiply, Screen, Overlay, or any of the others. You can even change its opacity. But if the floating selection doesn't appear in the Layers palette, how are you to make these changes? After floating the pixels, select Fade from the Edit menu. (Nonintuitive, but true.) However, as soon as you try to paint on it, or run a filter, or do almost anything else interesting to the floating selection, Photoshop deselects it and drops it back down to the layer below it. That's one reason we would rather just place pixels onto a real layer before messing with them.