Geometric selection outlines

Tools for creating simple geometric selection outlines occupy the very first slot in the Photoshop toolbox. By default, the rectangular marquee tool has the stage. You select the elliptical, single-row, and single-column marquee tools from the flyout menu that appears when you drag from the marquee tool icon.

Tip Press M to select the tool that's currently visible in the toolbox. Press M again to toggle between the rectangular and elliptical marquee tools. Alternatively Alt click jF the tool icon to toggle between the rectangular and elliptical marquee tools.

The marquee tools are more versatile than they may appear at first glance. You can adjust the performance of each tool as follows:

* Constraining to a square or circle: Press and hold Shift after beginning your drag to draw a perfect square with the rectangular marquee tool or a perfect circle with the elliptical marquee tool. (Pressing Shift before dragging also works if no other selection is active; otherwise, this adds to a selection, as I explain later in the "Ways to Change Selection Outlines" section.)

* Drawing a circular marquee: When I was perusing an online forum a while back, someone asked how to create a perfect circular marquee. Despite more than a month of helpful suggestions — some highly imaginative — no one offered the easiest suggestion of all (well, I ultimately did, but I'm a know-it-all). So remember to press Shift after you begin to drag and you'll be one step ahead of the game.

♦ Drawing out from the center: Press and hold Alt after you begin dragging to draw the marquee from the center outward instead of from corner to corner. (Again, pressing Alt before dragging works if no selection outline is active; otherwise, this subtracts from the selection.) This technique is especially useful when you draw an elliptical marquee. Locating the center of the area you want to select is frequently easier than locating one of its corners — particularly because ellipses don't have corners.

Tip Moving the marquee on the fly: While drawing a marquee, press and hold the spacebar to move the marquee rather than resize it. When you get the mar quee in place, release the spacebar and keep dragging to modify the size. The spacebar is most helpful when drawing elliptical selections or when drawing a marquee out from the center — this eliminates the guesswork, so you can position your marquees exactly on target.

♦ Selecting a single-pixel line: Use the single-row or single-column tools to select a single row or column (respectively) of pixels. I use these tools to fix screw-ups such as a missing line of pixels in a screen shot, to delete random pixels around the perimeter of an image, or to create perpendicular lines in a fixed space.

♦ Constraining the aspect ratio: If you want to create an image that conforms to a certain aspect ratio, you can constrain either a rectangular or an elliptical marquee so that the ratio between height and width remains fixed, no matter how large or small a marquee you create. To accomplish this, select Constrained Aspect Ratio from the Style pop-up menu on the Options bar, as shown in Figure 8-3. Enter the desired ratio values into the Width and Height option boxes. (Press Enter to display the Options bar.)

Figure 8-3: Select Constrained Aspect Ratio from the Style pop-up menu on the Options bar to constrain the width and height of a rectangular selection outline.

Tip If you work with a digital camera, you may find this feature especially helpful.

Digital cameras typically produce images that fit the 4x3 aspect ratio used by computer screens and televisions. If you want to crop an image to a standard photo size — say, 4 x 6 inches — enter 4 and 6, respectively, in the Width and Height option boxes and press Enter to confirm your changes. Then drag the marquee around to select the portion of the picture you want to retain, as shown in the figure, and choose Image ^ Crop.

Remember that you're just establishing the image aspect ratio here, not setting the output width and height. So you could just as easily enter 2 and 3 in the Width and Height option boxes. The size of the final, cropped image depends on how large you draw the marquee and the Resolution value you set in the Image Size dialog box.

* Sizing the marquee numerically: If you're editing a screen shot or some other form of regular or schematic image, you may find it helpful to specify the size of the marquee numerically. To do so, select Fixed Size from the Style pop-up menu and enter size values in the Width and Height option boxes. To match the selection to a 640 x 480-pixel screen, for example, change the Width and Height values to 640 and 480, respectively. Then click in the image to create the marquee.

You can now set the marquee size in any unit of measurement you like. Just type the number followed by one of these units: px (pixels), in, mm, cm, pt (points), pica, or %.

* Drawing feathered selections: A Feather option box is available when you use either marquee tool. To feather a selection is to blur its edges beyond the automatic antialiasing afforded by most tools. For more information on feathering, refer to the "Softening selection outlines" section later in this chapter.

* Creating jagged ellipses: By default, elliptical selection outlines are antialiased. If you don't want antialiasing — you might prefer harsh edges when editing screen shots or designing screen interfaces — deselect the Anti-aliased check box. (This option is dimmed when you use the rectangular marquee because antialiasing is always on for this tool.)

Photoshop novices often misunderstand the rectangular and elliptical marquee tools and expect them to create filled and stroked shapes. In the past, the program offered no tools for creating such shapes — you had to draw a geometric marquee and then fill or stroke the selection. Now Photoshop provides the shape tools, which can create filled vector and raster shapes. You can apply strokes and other effects to these shapes if you like. Chapter 14 takes you on a guided tour of the shape tools.

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