Introduction to Working with Layers

Imagine you want to compose an image from several images that you've stored on your computer. Well, you can do just that! The process is similar to the production of animated cartoons. You begin with a background image. Then you place one or more transparent foils (which are layers comprising image elements on top of transparent backgrounds) on the bottom, or opaque, background layer. A stack, a collage of single images, is created, one on top of the other. Certain file formats let you save those images with foils and layers, to a single file. The layers remain as single images in this one file, so they can be edited and altered afterward. During the editing process, you can move these layers to the front or the back of the image to determine which layer should overlay the other. In GIMP, file formats for saving images with layers are XCF and PSD.

Figure 3.6

The layers of a collaged image: (1) aircraft, (2) shadow (of the aircraft), (3) hangar, (4) window pane (layer with glass effect showing through, almost transparent), and (5) background with landscape

Figure 3.6

The layers of a collaged image: (1) aircraft, (2) shadow (of the aircraft), (3) hangar, (4) window pane (layer with glass effect showing through, almost transparent), and (5) background with landscape

To edit images with layers in GIMP, access the Layers dialog in the Layers, Channels, and Paths dock. If it isn't present, you can call it up by choosing Windows > Dockable Dialogs or Windows > Layers, Channels, Paths, Undo from the image window.

3.3 I N TRODU C TI ON TO WORKI N G WI TH LAYERS

Figure 3.7

Finished image (see layers.xcf in the FinishedImages folder on the DVD) and Layers dialog

There are several advantages to working with layers:

• Images with layers can be composed (collaged) from a stack of image elements on transparent foils.

• Layers can be easily duplicated.

• Layers are independent of one another so they can be freely positioned and changed.

• Layers can be linked and edited jointly in order to scale them simultaneously at the same ratio. Afterward, remove the link to edit the layers individually.

• The order in which the layers are stacked can be changed; this enables you to create depth by placing one image on top of another.

• Layers can have transparent areas so that objects can be placed on top of your image without covering the background. Image objects on layers beneath are visible through the transparent image area. Transparent areas with no subjacent image object visible depict a gray-and-white checkered pattern.

• The opacity of layers can be changed (opaque, semi-opaque, or translucent). Translucency allows you to see through an image element.

Figure 3.7

Finished image (see layers.xcf in the FinishedImages folder on the DVD) and Layers dialog

This is of great importance when working with selections and layers.

An image object is bound to a layer. A selection isn't. You can create a selection on one layer and apply it to any other layer. It works only on the active layer. The active layer is the layer that is selected. Therefore, it is marked in the Layers dialog by a different color. However, only when you carry out a work step (i.e., filling, color corrections, or copying) does something happen on the chosen layer. When copying, this isn't even an alteration of the image content of the selected layer. Only through a subsequent insertion will something visible happen.

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