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Grokking The Gimp
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3.1.1.1 The Rectangle Select and Ellipse Select Tools

The Rectangle Select and Ellipse Select tools are used for selecting rectangular and elliptical regions in an image. A selection is initiated by clicking and dragging in the image window, and the selection is completed by releasing the mouse button. The selection process is interactively facilitated by an outline of the selection that can be seen while the mouse is being dragged.

Figure  3.2 shows examples of both the Rectangle Select and Ellipse Select tools.

  
Figure 3.2: The Rectangle Select and Ellipse Select Tools
Figure 3.2

When completed, selections are displayed as moving dashed lines, traditionally referred to as the Marching Ants.   In the figure, the arrows are just for illustrating where the selections begin and end. They don't actually appear when you use these tools. The arrows' tails show where the selections were initiated, and the heads show where they were terminated. Note that for the Ellipse Select tool the selection is inscribed in a rectangle defined by the arrow's head and tail.

A perfectly square selection  can be made with the Rectangle Select tool, and a perfectly circular  selection can be made with the Ellipse Select tool. The trick is to use the Shift key, but read on carefully. Two other selection tricks are also performed with the Shift key (see Section  3.2 for the other). To avoid confusion, it is important to pay close attention to how this works.

To obtain a perfectly square or circular selection, begin the selection by clicking and dragging in the image window. While the mouse button is down, press the Shift key. In the image window, the resulting selection shape becomes a perfectly square or circular, depending on the tool you are using. The Shift key must remain pressed until the selection is finished and the mouse button has been released. Only then may the Shift key be released. If the Shift key is released before the left mouse button, the selection will revert to a normal rectangle or ellipse selection. The results of using the Shift key with the Rectangle Select and Ellipse Select tools are illustrated in Figure  3.3.

  
Figure 3.3: Making Perfectly Square and Circular Selections with the Rectangle Select and Ellipse Select Tools
Figure 3.3

Instead of initiating a rectangular or elliptical selection at one corner and terminating at the opposite one, it is also possible to initiate from the selection's center, terminating at a corner. The trick for this is similar to the technique just described for creating a perfectly square or circular selection. It is done by pressing the Control key after initiating the selection with the left mouse button. The Control key must remain pressed until after the mouse button is released. To combine perfectly square or circular selections in conjunction with center initiated ones, the Shift and Control keys must both be pressed after the left mouse button is clicked and remain so until after the mouse button is released.

Grokking The Gimp
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  Published under the terms of the Open Publication License Design by Interspire