Selections
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Chapter 6. Selections

This chapter gives a short introduction on selections.

You can select a part of an image masking off the rest. This is handy when you want to cut, copy or just modify a part of the image without affecting the rest. For processing selected objects chalk applies a mask. Each pixel of the selection is processed based on a value of its mask, or the “level of the selection”, that can range from 0 (unselected) to 255 (selected). Yes, that is right, you can have fractionally selected pixels. And by working on individual pixels you can “paint” your selection.

The selection mask is visualized with unselected pixels having a blueish tint, and selected pixels looking like normal. Fractionally selected pixels are shown as something in between. Additionally a red border is drawn around the selected areas. Fractionally selected pixels are inside the border, so even inside the red border you can possibly see the blueish tint on some pixels.

Making a selection

A whole range of tools exist to make selections. From rectangles, ellipses and freehand to the more exotic like color range select. When you make several selections they add up. So a rectangle select followed by an ellipse select select both areas. Later on, you can subtract areas from the selection by using, for example, the Erase Selection tool.

To get back to normal (no active selection), choose Select->Deselect. To select all pixels, choose Select->Select All.

You may think that those two actions give the same result, but it is much more efficient to have no active selection than to have selected everything.

After having deselected you can bring your selection back by choosing Select->Reselect.

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