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2.3.  Ellipse Selection Tool

Revision History
Revision $Revision: 1.53 $ 2006-02-09 j.h

Figure 8.5.  Ellipse Select icon in the Toolbox

Ellipse Select icon in the Toolbox

The Ellipse Selection tool is designed to select circular and elliptical regions from an image, with high-quality anti-aliasing if you want it. For information on selections and how they are used in GIMP see Selections; for information on features common to all selection tools see Selection Tools.

This tool is also used for rendering a circle or ellipse on an image. To render a filled ellipse, create an elliptical selection, and then fill it using the Bucket Fill tool. To create an elliptical outline, the simplest and most flexible approach is to create an elliptical selection and then stroke it. However, the quality of anti-aliasing with this approach is rather crude. A higher quality outline can be obtained by creating two elliptical selections with different sizes, subtracting the inner one from the outer one; however this is not always easy to get right.

2.3.1.  How to Activate

The Ellipse Selection Tool can be activated from an image menu as Tools->Selection Tools->Ellipse Select; from the Toolbox by clicking on the tool icon ; or from the keyboard using the shortcut e.

2.3.2.  Key modifiers

[Note] Note

See Selection Tools for help with modifier keys that affect all these tools in the same way. Only effects that are specific to the Ellipse Select tool are explained here.

  • Ctrl: Pressing the Ctrl key after starting your selection, and holding it down until you are finished, causes your starting point to be used as the center of the selected ellipse, instead of a corner of the rectangle that may contain it. Note that if you press the Ctrl key before starting to make the selection, the resulting selection will be subtracted from the existing selection.

  • Shift: Pressing the Shift key after starting your selection, and holding it down until you are finished, constrains the selection to be a circle. Note that if you press the Shift key before starting to make the selection, the resulting selection will be added to the existing selection.

  • Ctrl-Shift: Pressing both keys combines the two effects, giving you a circular selection centered on your starting point.

2.3.3.  Options

Figure 8.6.  Tool Options for the Ellipse Select tool

Tool Options for the Ellipse Select tool
[Note] Note

See Selection Tools for help with options that are common to all these tools. Only options that are specific to the Ellipse Select tool are described here.

You can access to the Ellipse Selection options by double-clicking on the icon.

Antialiasing

Checking this option will make the edge of the selection appear smoother, by partially selecting pixels that the edge passes through. The idea of antialiasing is discussed in more detail under the glossary entry Antialiasing. You will probably find that you get more satisfactory results by using it, in most cases. The main situation where you might want not to use it is in cutting and pasting, where partial selection can sometimes create strange color fringes.

Auto Shrink Selection

The Auto Shrink Selection checkbox will make your next selection automatically shrink to the nearest elliptical shape available on the image layer. The algorithm for finding the best ellipse to shrink to is "intelligent", which in this case means that it sometimes does surprisingly sophisticated things, and sometimes does surprisingly strange things. In any case, if the region that you want to select has a solid-colored surround, auto-shrinking will always pick it out correctly. Note that the resulting elliptical selection does not need to have the same shape as the one you sweep out.

If Sample Merged is also enabled, then the Auto Shrink will use the pixel information from all the layers of the image. For further information regarding Sample Merge, see the glossary entry Sample Merged.

Size Constraints

Figure 8.7.  Size Constraint Option Menu for the Ellipse Select tool

Size Constraint Option Menu for the Ellipse Select tool

This menu allows you the option of constraining the shape of the ellipse in three different ways.

  • Free Select.  This option places no constraint on the ellipse.

  • Fixed Size.  This will allow you to manually specify a size for the selection using the Width, Height, and Unit controls.

  • Fixed Aspect Ratio.  This option allows you to resize the selection while keeping the aspect ratio fixed according to the two numbers entered in the Width and Height controls.


 
 
  Published under the terms of the GNU General Public License Design by Interspire