GIMP Bible

Chapter 6. Working with Layers and Masks

IN THIS CHAPTER

• Creating and modifying layers

• Organizing your layers into groups

• Applying masks to layers

One of the primary features that defines an advanced image editing application is a robust layer system. As a tangible comparison, think of a layer as a single sheet of acetate. By drawing on multiple sheets and stacking them on top of one another, you have a lot of flexibility in the process you use to create your images. With the additional power of the digital medium, you have even more control and flexibility because you can have one layer influence the look of the layers beneath it, rather than simply being stacked above. It's through layers that digital artists do complex compositing and image enhancement. Digital painters use layers to logically separate their work so, for example, they can freely adjust colors without messing up their line work.

Going hand-in-hand with layers is the concept of a mask. In traditional art, a mask is an object used to block part of the work so it isn't affected when new paint is applied. As an example, airbrush artists often mask off large sections of their painting surface, leaving only the section that they're interested in working on. Traditional photographers use masks in the darkroom to limit what parts of the photographic paper get exposed to the image in their film negative. In GIMP, each layer can have a mask that dictates which parts of the layer are visible, and at what opacity. The really cool ...