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Grokking The Gimp
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3.3.11 The By Color Function

The By Color selection tool, found in the Image:Select menu, is similar to the Magic Wand in that it automatically selects pixels in the active layer that are close in color to a seed pixel value. The difference, however, is that the selected pixels are not obtained by growing a contiguous region around the seed. The By Color selection tool selects all the pixels in the layer that are within a specified threshold of the seed pixel's color. This is a subtle but important difference. It means that if two regions of similar pixel colors are separated by one of very different values, the By Color selection tool will get both regions, and the Magic Wand will not.

Choosing By Color brings up the dialog pictured in Figure  3.18(a).

Figure 3.18: The By Color Selection Tool
Figure 3.18

This dialog box allows a Fuzziness Threshold to be chosen. The default is normally 15, but here it has been set to 30. This number determines how far a pixel can vary in color from the seed pixel's and still be selected. The seed is chosen by clicking in the image window.

Clicking in the image window produces a black and white mask in the thumbnail area of Figure  3.18(a). This mask corresponds to a selection in the image window, as can be seen in Figure  3.18(b). The selection can be removed by clicking on the Reset button in the By Color Selection dialog.

When the dialog's Replace radio button is selected, clicking a second time in the image window replaces the selection that was there with one based on the new seed pixel's color. The three other radio buttons in the dialog can be used to add, subtract, or intersect the selection created with the By Color function with an existing selection in the image window. Adding, subtracting, and intersecting selections was explained in Section  3.2.

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