The Layers palette in GIMP is a feature that all GIMP users should take time to understand. It offers great power and flexibility allowing users to produce creative results by combining layers within an image in different ways.
When you open an image or new document in GIMP, there will always be a background layer displayed in the Layers palette. New layers that are added to the document will be inserted above the background. You can hide a layer by clicking on the eye icon that appears next to it and clicking again will show the layer again. To the right of the eye icon is an unmarked button that allows you to link layers together.
If you're not familiar with using layers, one way to visualize the concept is to think of each layer as a sheet of acetate, stacked with other sheets. Painting on part of a layer will hide some of the layers below, but allow other parts to show through. However, the Mode and Opacity features offer a flexibility that you cannot achieve when combining sheets of acetate.
Mode
This drop down allows you to select from a variety of different blend modes that will change how layers combine within a document. By default, the Normal mode makes the pixels in a layer opaque, but the other modes will combine layers in different ways to offer a variety of different effects. You can read about some of the more common blending modes offered by image editors in this glossary entry on blending modes. I've also written about using blending modes to fake some adjustment layer effects in GIMP and that may be of interest if you use GIMP to edit your digital photos.
Opacity
This slider allows you to easily adjust the opacity of a layer from full opacity through to completely transparent. You can use this in combination with blending modes to produce some very subtle effects.
Lock
This checkbox allows you to lock the pixels in the selected layer so that transparent pixels cannot be painted on. This may be useful if you want to change the color pixels in a layer without affecting transparent pixels.
Layer Visibility
To the left of each layer in the Layers palette is a eye icon. Clicking this will hide the layer and the icon will disappear. You can click the blank space to make the layer visible again.
Link Layers
To the right of the layer visibility buttons is an unmarked button that you can click to link layers. When clicked, a chain icon appears in the space and all layers that have the chain icon visible are linked so that if one is moved or transformed, the other layers move or transform in unison.
• How to Link Layers in GIMP
The bar at the bottom of the Layers palette contains a range of controls that allow you to work with layers within a document and these are, from left to right, as follows.
Create a New Layer
Clicking this will add a new blank layer to your document. The new layer will be inserted into the document immediately above the currently selected layer. If you have a floating layer active in your document, for instance if you've pasted an image into your document, clicking this will apply the floating layer to a new separate layer.
Raise Layer
Clicking this button will move the currently selected layer upwards within the stack of layers. You can also change the order of layers by clicking on a layer and dragging it within the layer stack.
Lower Layer
This has the effect of moving the currently active layer downwards, one layer at a time for each click.
Duplicate Layer
Clicking this will place a duplicate of the currently selected layer immediately above it within the layer stack.
Anchor Floating Layer
If you have pasted an image into your document, clicking this button will merge it with the layer immediately below it.
Delete Layer
You can click this to delete the currently selected layer from your document.