The GIMPs Selection Tools

Notice that the GIMP has a floating Toolbox window, not unlike the one found in Photoshop. This Toolbox is divided into upper and lower halves; the top half contains tool icons, whereas the bottom half displays options for the currently selected tool (see Figure 3-13). Starting with the top row of tools, five different selection methods are available. Selections are crucial for detailed image manipulation, because you need to be able to move and apply effects to individual elements of the image. That's why the GIMP offers five different methods for the same task.













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Figure 3-13. The lower half of the GIMP's Toolbox displays options for the current tool.

First is the Rectangle Select tool, at upper left, which is straightforward. With this tool selected, click anywhere in the image window; while holding down the button, drag the mouse pointer diagonally. This action results in a rectangle of tiny black and white dashes being drawn around your selection, sometimes called marching ants because of the motion of the dashes. Any operation you choose from the GIMP's Colors or Filters menu is now applied only to the area inside the rectangle, not the entire image.

If you select the wrong part of the image, you have three options for adjustment. First, you can mouse over a corner of the rectangular selection, and a small square appears just inside that corner; click and drag inside this square, and you can change the position of that corner of the selection (see Figure 314). Second, mouse over the middle of any of the sides, and then click and drag to adjust the rectangle in only that dimension. Or third, click the center of the selection, and, while holding down the mouse button, drag the entire selection to another part of the image without changing the selection's shape. If you're not happy with the selection, you can either click None on the GIMP's Select menu or click outside the existing selection to begin anew.

Figure 3-14. Click inside the corner of the rectangular selection to drag it inwards or outwards.

Next along in the top row of tools is the Ellipse Select tool; apart from its shape, it works the same way as the rectangle select tool. To make an elliptical selection that is a regular circle, select the Fixed check box and select "Aspect ratio" in the lower half of the GIMP's Toolbox.

After that comes the Free Select tool, represented by a lasso icon. With a mouse or laptop trackpad, free selections are most useful for roughly defining an area. If you have a touch-sensitive graphics tablet with a stylus, and a steady hand, you may also find the free select tool capable of more detailed work.

The next tool is the Fuzzy Select tool, which has a magic wand icon. This selects regions on the basis of similar color. Because a real photograph may have thousands of different colors or very few tones, this tool must have adjustable sensitivity in order to be useful. You make this adjustment using the Threshold control in the lower half of the GIMP's Toolbox. The default maximum color difference setting is 15, but you may have to increase this value to get the result you want. Hold down the Shift key to grow the selection with successive clicks. If you go too far and grow the selection to cover part of the image that you don't want, click Edit > Undo Fuzzy Select, or press the keyboard shortcut for Undo (Ctrl+Z). It's well worth practicing with the Fuzzy Select tool, because you can use it to select complex shapes with great accuracy (see Figure 3-15).

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Figure 3-15. The Fuzzy Select tool is very useful for selecting complex shapes.

The Select by Color tool works similarly to Fuzzy Select, except that it operates across the entire image instead of just the adjacent area. In the flower photo example, you can select all the areas that are the same shade of pink with just one click.

On the second row of tools are three more ways to create selections. First is the Scissor Select tool, which uses edge detection to help you trace the outline of shapes. With this tool active, click all around the object you want to select. The GIMP does its best to trace the outline of that object. How well it performs this task depends in part on how accurate your mouse clicks are, of course. When you return to the point at which you started the selection and complete the loop, click inside the selection to finalize it; the marching ants now appear (see Figure 3-16).

Figure 3-16. Scissor Select uses edge detection to trace shapes.

Next up is the Foreground Select Tool, which requires you to draw a lasso by clicking and dragging the cursor around the area you're interested in. As you release the mouse button, the lasso cursor changes to a paintbrush cursor. The rest of the image is now masked in a transparent blue to show that it's outside this area. (You can use the Toolbox options to mask in red or green, if you prefer.) After that, click a foreground part of the image, and the rest of the foreground is selected automatically (see Figure 3-17).

Figure 3-17. The Foreground Select tool can isolate parts of an image, with some help from your eye.

You can grow the foreground selection using the paintbrush cursor and successive clicks, or clicks and drags; unlike the Fuzzy Select tool, you don't have to hold down the Shift key to do this. If this tool automatically selects an area that isn't part of the foreground, hold down the Ctrl key, and the tool's icon changes from a paintbrush to an eraser; you can now remove the incorrect area from the selection. Press the Enter key when you're happy with the selection you've made, and the masked image changes to the marching ants again.

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