Layers are a very important aspect of The GIMP. By drawing parts of your image on separate layers, change, move, or delete those parts without damaging the rest of the image. To understand how layers work, imagine an image created from a stack of transparent sheets. Different parts of the image are drawn on different sheets. The stack can be rearranged, changing which parts are on top. Individual layers or groups of layers can shift position, moving sections of the image to other locations. New sheets can be added and others set aside.

Use the ‘Layers’ dialog to view the available layers of an image. The text tool automatically creates special text layers when used. The active layer is highlighted. The buttons at the bottom of the dialog offer a number of functions. More are available in the menu opened when a layer is right-clicked in the dialog. The two icon spaces before the image name are used for toggling image visibility (eye icon when visible) and for linking layers. Linked layers are marked with the chain icon and moved as a group.

Only layers with transparency (an alpha channel) can be placed above other layers in a stack. To add this to a layer, right-click and select it from the menu.

GIMP has three image modes — RGB, Grayscale, and Indexed. RGB is a normal color mode and is the best mode for editing most images. Grayscale is used for black-and-white images. Indexed limits the colors in the image to a set number. It is mainly used for GIF images. If you need an indexed image, it is normally best to edit the image in RGB then convert to indexed right before saving. If you save to a format that requires an indexed image, GIMP offers to index the image when saving.

The GIMP includes a wide range of filters and scripts for adding special effects to an image or making artistic manipulations. They are available in ‘Filters’ and ‘Script-fu’. Experimenting is the best way to find out what is available. ‘Xtns’ in the toolbox includes a number of items for creating buttons, logos, and other things.