Layers are daunting at first; they are so powerful and offer such a wide range of features it is hard to know where to start.
Never Edit Original Files
Before you start experimenting with images, make sure you copy your practice images to a separate directory and do not play with the originals. This is the basic principle of digital imaging manipulation, and if you make a mess of the images, as you most certainly will, delete the messy copies and make new copies to continue experimenting.
To help dispel some of the mystery we are looking at the basic operation of the layer dialog boxes for two popular software programs for digital image manipulation, Adobe Photoshop and the Gimp.
The Gimp can save in, and read, Photoshop PSD format preserving layer information so there is a degree of file interchangeability between the two applications. This technique is adapted from the traditional film darkroom where negatives were stacked in layers in the printing process to form a combined image. In the digital darkroom, separate digital images are similarly stacked as virtual layers to produce the same result.
One benefit of using layers is the flexibility it allows for editing and changing your mind. The example pictures are screen shots of the dialog boxes from Adobe Photoshop CS2 and the free open source equivalent, the Gimp.
The explanatory text and arrows are on a separate layer allowing them to be moved and changed, while the other layers remain untouched. One way of creating a new layer in an image is via the layer menu system at the top of the main image. Both applications also have a new layer icon along the bottom row of the layer dialog box. It looks like a sheet of paper. The dialog box indicates the active layer by highlighting the background of the layer name. Mouse clicking on the name of a layer makes it the active layer for editing.
This brings us to the eye on the left hand side of the layer details. If you can see the eye then the associated layer is visible, and is available for editing and shows in any printing or final file save versions. Mouse click on the eye and it, along with its layer become invisible. However, they are still there ready for use whenever they are required. Like physical layers, the order they are stacked in is important, as a solid object in the top layer will hide anything below it. Apart from the basic background layer, the order of layers in the stack is easily changed.
In Photoshop, move the mouse pointer over the layer name in the dialog box so that you see a pointy finger, then drag the layer above or below other layers.
In the Gimp, there are arrows along the bottom of the layer dialog box, they will move the active layer up or down the layer stack.
Saving the composite file as a .psd in Photoshop or .xcf in the Gimp retains all the layers as separate entities. Saving as a jpeg requires combining all the visible layers or flattening, Photoshop, or merged, the Gimp. These commands are in the layer menu of the main image menu system.
Layers can develop into complex structures and a bit of practical experimenting helps associate the commands with their function.
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