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Grokking The Gimp
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3. Selections

Selections are extremely important tools for working with digital images. They are a means for partitioning an image into two groups of pixels: those we want to work on and those we do not. Selections allow the selective application of enhancements, functions, filters, and plug-ins to specific target regions of an image. Furthermore, selections are essential tools for compositing image material from several sources into a single image. This is core to collage and photo montage, two subjects developed in detail in Chapter  7.

This chapter covers the selection tools in the GIMP. However, the material presented here is really only half the story on the subject of selections. The other half is presented in Chapter  4, which covers masks. As described there, selections and masks are really just two implementations of the same principle. They both result in a separation of subject from background. They arrive at this result, however, using different and very complementary methods. You really need both to get the best selection results.

Selections are the scalpel of the image manipulator's toolbox, and you will use them a lot. Because selections can easily be the most time-consuming and frustrating part of a project, it is important to know how to use the selection tools artfully and effectively. This chapter explains how each selection tool works, and it presents the array of GIMP functions that are directly related to selections. Furthermore, the conditions for which each selection tool is most effective are described, and each tool is rated against the others for its usefulness.

Before launching into the descriptions of the various selection tools, it is worthwhile to mention where selections fit into the structure of images. The relationship of pixels, channels, layers, and images was described in Section  2.2. Where, then, do selections fit in? A selection can be seen in the image window--does that mean it is part of the image? The answer to these questions won't be fully given until Chapter  4, which covers masks. However, for now it suffices to know that selections are special channels, independent of the image layers, and whose selective effects apply only to the active layer. 


Grokking The Gimp
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