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Photoshop CS5: The Missing Manual by Lesa Snider

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Selecting Irregular Areas

As you might imagine, areas that aren't uniform in shape or color can be a real bear to select. Luckily, Photoshop has a few tools in its arsenal to help you get the job done as easily as possible. In this section, you'll learn about the three lassos and the Pen tool, as well as a few ways to use these tools together to select hard-to-grab areas.

Using the Lasso Tools

The Lasso toolset contains three freeform tools that let you draw an outline around the area you want to select. If you've got an amazingly steady mouse hand or if you use a graphics tablet (see the box on The Joy of Painter), you may fall in love with the plain ol' Lasso tool. If you're trying to select an object with a lot of straight edges, the Polygonal Lasso tool will do you proud. And the Magnetic Lasso tries to create the selection for you by examining the color of the pixels your cursor is hovering above. The following sections explain all three lassos, which share a toolset at the top of the Tools panel (see Figure 4-14).

So many lassos, so little time! The regular Lasso tool is great for drawing a selection freehand, the Polygonal Lasso is good for drawing selections around shapes that have a lot of straight lines, and the Magnetic Lasso is like an automatic version of the regular Lasso—it tries to make the selection for you.

Figure 4-14. So many lassos, so little time! The regular Lasso tool is great for drawing a selection freehand, the Polygonal Lasso is good for drawing selections around shapes that have a lot of straight lines, and the Magnetic Lasso is like an automatic version of the regular Lasso—it tries to make the selection for you.

Lasso tool

The regular Lasso tool lets you draw a selection completely freeform as if you were drawing with a pencil. To activate this tool, simply click it in the Tools panel (its icon looks like a tiny lasso—no surprise there) or press the L key. Then just click your document where you want the selection to start and drag to create a selection. Once you stop drawing and release your mouse button, Photoshop automatically completes the selection with a straight line (that is, if you don't complete it yourself by mousing over your starting point) and you see marching ants.

Tip

It's nearly impossible to draw a straight line with the Lasso tool, unless you've got the steady hand of a surgeon. But if you press and hold the Option key (Alt on a PC) and then release your mouse button, you'll temporarily switch to the Polygonal Lasso tool so you can draw a straight line (see the next section). When you release the Option (Alt) key, Photoshop completes your selection with a straight line.

The Options bar (shown in Figure 4-14) sports the same settings whether you have the Lasso tool or the Polygonal Lasso tool active. Here's what it offers:

  • Mode. These four buttons (whose icons look like pieces of paper) let you choose among the same modes you get for most of the selection tools: New, "Add to selection", "Subtract from selection", and "Intersect with selection". They're discussed in detail back on pages 139–140.

  • Feather. If you want Photoshop to blur the edges of your selection, enter a pixel value in this field. Otherwise, Photoshop won't do any feathering. (See the box on The Softer Side of Selections for more on feathering.)

  • Anti-alias. If you leave this setting turned on, Photoshop slightly softens the edges of your selection, making them less jagged—The Rectangular and Elliptical Marquee Tools has the details.

Polygonal Lasso tool

If your image has a lot of straight lines in it (like the star in Figure 4-15), the Polygonal Lasso tool is your ticket. Instead of letting you draw a selection that's any shape at all, the Polygonal Lasso draws only straight lines. To use it, click once to set the starting point and move your cursor along the shape of the item you want to select; click again where the angle changes. Simply repeat this process until you've outlined the whole shape. It's super simple to use, as Figure 4-15 illustrates. To close your selection, hover above the first point you created. When a tiny circle appears below your cursor (it looks like a degree symbol), click once to close the selection and summon the marching ants.

The Polygonal Lasso tool is perfect for selecting geometric shapes and areas that have a lot of angles. However, if you want to temporarily switch to the regular Lasso tool, press and hold Option (Alt on a PC) to draw freehand.

Figure 4-15. The Polygonal Lasso tool is perfect for selecting geometric shapes and areas that have a lot of angles. However, if you want to temporarily switch to the regular Lasso tool, press and hold Option (Alt on a PC) to draw freehand.

Tip

To bail out of a selection you've started to draw with the Polygonal or Magnetic Lasso tools, just press the Esc key.

Magnetic Lasso tool

This tool has all the power of the other Lasso tools, except that it's smart—or at least it tries to be! Click once to set a starting point, and from there the Magnetic Lasso tries to guess what you want to select by examining the colors of the pixels your cursor is hovering above (you don't even need to hold your mouse button down). As you move your cursor over the edges you want to select, it sets additional anchor points for you (think of anchor points as fastening points that latch onto the path you're tracing; they look like tiny, see-through squares). To close the selection, hover above your starting point. When a tiny circle appears below your cursor, click once to close the selection and summon the marching ants (or you can close the selection with a straight line by triple-clicking).

As you might imagine, the Magnetic Lasso tool works best when there's good contrast between the item you want to select and the area around it (see Figure 4-16). However, if you reach an area that doesn't have much contrast—or if you reach a sharp corner—you can give the tool a little nudge by clicking to set a few anchor points of your own. If it goes astray and sets an erroneous anchor point, just hover over the bad point with your mouse and press the Delete key (Backspace on a PC). Then move back to the troubled area of your selection and click to set more anchor points until you reach an area of greater contrast where the tool can be trusted to set its own points.

If you're trying to select an object on a plain, high-contrast background, the Magnetic Lasso works great because it can easily find the edge of the object. For best results, glide your cursor slowly around the edge of the item you want to select (you don't need to hold your mouse button down). To draw a straight line, you can temporarily switch to the Polygonal Lasso tool by Option-clicking (Alt-clicking on a PC) where you want the line to start and then clicking where you want it to end. Photoshop then switches back to the Magnetic Lasso and you're free to continue gliding around the rest of the object's jagged edges.

Figure 4-16. If you're trying to select an object on a plain, high-contrast background, the Magnetic Lasso works great because it can easily find the edge of the object. For best results, glide your cursor slowly around the edge of the item you want to select (you don't need to hold your mouse button down). To draw a straight line, you can temporarily switch to the Polygonal Lasso tool by Option-clicking (Alt-clicking on a PC) where you want the line to start and then clicking where you want it to end. Photoshop then switches back to the Magnetic Lasso and you're free to continue gliding around the rest of the object's jagged edges.

Tip

If you're not crazy about the Magnetic Lasso's cursor (which looks like a triangle and a horseshoe magnet), press the Caps Lock key and it changes to a brush cursor with a crosshair at its center. Press Caps Lock again to switch back to the standard cursor. Alternatively, you can use Photoshop's preferences to change it to a precise cursor; Cursors shows you how.

You can get better results with this tool by adjusting the Options bar's settings (see Figure 4-16). Besides the usual suspects like selection modes, feather, and anti-alias settings (all discussed on pages 139–140), the Magnetic Lasso also lets you adjust the following:

  • Width determines how close your cursor needs to be to an edge for the Magnetic Lasso to select it. Out of the box, this field is set to 10 px, but you can enter a value between 1 and 256. Use a lower number when you're trying to select an area whose edge has a lot of twists and turns and a higher number for an area with fairly smooth edges. (To select the yellow rose in Figure 4-16, you'd use a higher setting around the petals and a lower setting around the leaves because they're so jagged.)

    Tip

    You can change the Width setting in 1-pixel increments as you're drawing with the Magnetic Lasso by pressing the open and close bracket keys. You can also press Shift-[ to set the width to 1 and Shift-] to set it to 256.

  • Contrast controls how much color difference there needs to be between neighboring pixels before the Magnetic Lasso recognizes it as an edge. You can try increasing this percentage when you want to select an edge that isn't well defined, but you might have better luck with a different selection tool. If you're a fan of keyboard shortcuts, you can press > or < to increase or decrease this setting in 1% increments. Press >-Shift or <-Shift to set it to 1% or 100%, respectively.

  • Frequency determines how many anchor points the tool lays down. If you're selecting an area with lots of details, you'll need more anchor points than for a smooth areas. Setting this field to 0 makes Photoshop add very few points, and 100 makes it have a point party. The factory setting—57—usually works just fine. Press the ; or ' key to increase or decrease this setting by 1, respectively; add the Shift key to these keyboard shortcuts to jump between 1 and 100.

  • Use tablet pressure to change pen width. If you have a pressure-sensitive graphics tablet, turning on this setting—whose button looks like a pen tip with circles around it—lets you override the Width setting by pressing harder or softer on your tablet with the stylus. (The box on The Joy of Painter has more about graphics tablets.)

Selecting with the Pen Tool

Another great way to select an irregular object or area is to trace its outline with the Pen tool. Technically, you don't draw a selection with this method; you draw a path (Installing New Brushes), which you can then load as a selection (Making Selections and Masks with Paths) or use to create a vector mask (Using Vector Masks). This technique requires quite a bit of skill because the Pen tool isn't your average, everyday, well…pen, but it'll produce the smoothest-edged selections this side of the Rio Grande. Head on over to Chapter 13 to read all about it.

Creating Selections with Channels

As you'll learn in Chapter 5, the images you see onscreen are made up of various colors. In Photoshop, each color is stored in its own channel (which is kind of like a layer) that you can view and manipulate. If the object or area you're trying to select is one that you can isolate in a channel, you can load that channel as a selection with a click of your mouse. Chapter 5 discusses this incredibly useful technique in detail, starting on Deleting Alpha Channels.

Note

You can also paint selections by using Quick Mask Mode, which is discussed in this chapter starting on Using Quick Mask Mode.

Using the Tools Together

As wonderful as the aforementioned selection tools are individually, they're much more powerful if you use them together.

Remember how every tool discussed so far has an "Add to selection" and "Subtract from selection" mode? This means that, no matter which tool you start with, you can add to—or take away from—the active selection with a completely different tool. Check out Figure 4-17, which gives you a couple of ideas for using the selection tools together. And thanks to the spring-loaded tools feature (see the tip on Tip), switching between tools is a snap.

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