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2. Basics of Image Processing

## 2.4 Basics for Image Layers

### 2.4.1 Lasso/Mask

The mask is a gray image with the same size as the corresponding image layer. Each image pixel corresponds with one mask pixel. Like the transparency controls, how transparent a pixel is, the mask controls, how strong a pixel will be affected by an image operation. A value of 0 in the mask protects a pixel from being changed, a value of 255 offers no protection. As the mask is a gray image, it can be edited with nearly all image tools.

The lasso is a vector object, that - similar to the mask - controls which parts of an image layer can be edited. There are special lasso tools for the creation of a lasso: the rectangular lasso tool, the circle lasso tool and the free lasso tool (see chapter 6.3.4 and chapter 6.3.5).

You may ask now, why there are two ways to protect parts of an image from editing. The answer is quite simple: there are not two ways. Every time a lasso is created or changed, the mask is changed automatically, too. And every time the mask is changed, the lasso is changed accordingly. Therefore the terms "mask" and "lasso" only describe different points of view of the same thing.