You have four marquee selection tools although you'll generally use only two of them. Figure 8-6 shows the marquee selection tools, along with each tool's Options bar configuration.
You drag the very-useful Rectangular Marquee and Elliptical Marquee tools to make selections. Click and drag in any direction to make your selection. After you start dragging, hold down the Shift key (while still dragging) to constrain proportions. When you constrain the proportions of a selection, you create a square or circle rather than a rectangle or an ellipse. If you start dragging a selection and press the Option (Mac)/Alt (Windows) key, the selection centers itself on the point where you click. The Shift and Option/Alt keys can be used together. Holding down the Shift key before you click and drag adds the selection to any existing selection. Holding down the Option/Alt key before dragging subtracts the new selection from any existing selection.
The Single Row Marquee and Single Column Marquee tools are simply clicked at the point where you want a 1-pixel selection, running from side-to-side or from top-to-bottom. These tools create selections that extend the full width or full height of your image. You might use these tools to create a grid-like selection that you can fill with color. Or you might never use them at all.
Take another glance at the Options bars in Figure 8-6. The four buttons to the left in the Options bar, which you can use with any of the tools, determine how the tool interacts with an existing selection.
^ New Selection: When you select the first button, any selection that you make replaces an active selection (deselecting any previous selection). If, with a selection tool, you click inside an active selection when the first option is active, you can drag that selection in your image without moving any pixels. (When you haven't already made a selection, these tools always make a new selection, regardless of which button is active.)
^ Add To: When you have an active selection and need to add to that selection, use the second button (or simply press and hold down the Shift key while dragging).
^ Subtract From: When you have a selection and need to deselect part of it, use the third button. Say, for example, that you make a round selection and want to chop out the middle to make a donut shape. Click the third button, and then drag within the original selection to deselect the donut hole.
^ Intersect With: You have a selection, but you want to keep only part of the selection. You could set your selection tool to subtract from the existing selection, or you could intersect with that original selection and deselect a number of areas at once.
Figure 8-7 presents a visual explanation of how all four buttons work. On the left, you see the selected option for the active marquee selection tool. Next is an original selection. In the third column, you see another selection being made (with the selection tool dragged from the lower-right to the upper-left). Finally, on the right, you see the result of combining the two selections.
In the bottom-most example, you could do a whole series of subtractions from the existing selection to chop off the "points," but using the intersect option takes care of the job with a single drag.
While you're dragging a selection with the Rectangular Marquee or the Elliptical Marquee tool, you can hold the mouse button down and press and hold the spacebar to reposition the marquee. When you've got it where you want it, release the spacebar and continue to drag.
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