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2. Basics of Image Processing

## 2.9 Adjustment Layers

Adjustment layers modify - similar to clipping layers - the appearance of the layers drawn before the adjustment layer. In order to do this one or more adjustments are assigned to the adjustment layer (see chapter 7.5.11 and following), and the layer content is used as mask, the so-called adjustment mask. This adjustments can be a histogram correction (levels), a color adjustment or even a filter.

The following example shows a text layer containing the text "Working Layer" placed on an image. The assigned adjustment inverts the image everywhere the text is drawn:

If a gray image is used as adjustment layer, only parts of an image can be color adjusted without modifying the original. By using a color filter (see chapter 7.5.27) you can restrict the effect of an adjustment layer to areas with a given brightness and/or color.

Every layer type including groups can be made an adjustment layer. Best suited are vector layers, text layers and gray images without transparency. Color images or gray images with transparency should only be used if really necessary, because they are displayed noticeably slower.

If you want to edit an adjustment layer, this may be a bit troublesome, because the real layer is not visible, just the effect of the adjustment assigned to it. Therefore you can turn off the adjustment temporarily by using the Layer Attributes dialog (see chapter 4.11). Another possibility is to click on the layer’s thumbnail in the Layer List (see chapter 4.7) while holding Alt. If you do so, the mask of the adjustment layer will be shown like a simply gray image.

As said before adjustment layers are similarly compared to clipping layers, but there is a significant difference: clipping layers are only affecting the layers inside their group, and adjustment layers are affecting the whole document. So if you want to restrict an adjustment layer to a group, you have to turn on the attribute "draw isolated". An isolated group is draw as a unity (see also chapter 4.11). If you want to restrict the effect of an adjustment layer to a single image, you can group it with that image layer. The easiest way to do that is either on creation or by dragging the adjustment layer onto the image layer in the Layer List (see chapter 4.7).

The mask of an adjustment layer can be blurred and inverted using the Layer Attributes (chapter 4.11).