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Grokking The Gimp
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3.1.2.2 Feathering

Feathering is a selection edge treatment similar to antialiasing. It works by changing the alpha value of pixels as a function of their radial distance from the selection edge. Figure  3.13

  
Figure 3.13: The Effect of Feathering
Figure 3.13

illustrates an example of a feathered selection. Figure  3.13(a) shows how two guides have been placed to aid in framing a selection using the Ellipse Select tool.

As shown in Figure  3.13(b), a value of 40 has been chosen for the Feather Radius in the Tool Options dialog for this selection tool. Furthermore, Antialiasing has been turned off. The result of inverting the selection and cutting away the background is shown in Figure  3.13(c). This result is actually displayed on a yellow background so that the transparency of the flower pixels can be better seen. Also, superimposed on Figure  3.13(c) is the original elliptical selection.

The transparency of the flower image shown in Figure  3.13(c) is 50% at the selection edge. The transparency increases moving outward from the edge and decreases moving inward from it. The rate at which the transparency changes while moving away from the selection edge is determined by the Feather Radius. For this example, the value chosen is 40, meaning that there is a feathering effect up to 40 pixels away in both directions from the selection edge. Note that for all the selection tools, feathering is off by default.

Partially selected pixels are discussed again in Section  4.1.7.

Grokking The Gimp
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