Painting Program Layers

When you create a new bitmap image file, the image consists of only a background. Think of this background as the canvas under a painting where the canvas can be white, or the current program background colour. With a 'Layers' option, you can then add one or more new layers to the image.

Think of layers as transparent sheets of acetate that are layed on top of the background. Where no image data has been placed onto a layer, you can see through to any other visible layers plus the background at the bottom of the layers. Layers enable you to edit specific areas of your image without affecting data on other layers, or just affecting data on a linked combination of layers.

All layers in an image file share the same number of pixels, the same number of channels, and the same image mode - i.e. RGB, CMYK, Greyscale. Image files created in versions of Adobe Photoshop earlier than 3.0 consist only of a single background layer so if you open and add layers to the earlier version image files using Adobe Photoshop 3.0+, you have to save them in the Adobe Photoshop 3.0+ format to retain the extra layer information.

Unlike Saved Selections, increases in the file size depend upon the amount of image data contained in each layer created, which in turn is dependant on the number of channels - or Mode. (Every saved Selection increases the image file size by exactly one channel - i.e. +1/3 of an RGB image)

Using the Layers palette
You use the Layers palette to create, copy, merge, and delete layers, and to create layer masks plus the layers palette also lets you hide and show individual layers. To display the layers palette: Choose 'Show Layers' from the Window menu.

The Layers palette lists the layers, starting with the topmost layer in the image file and the background is always at the bottom of the list. Only one layer can be active at a time but you may also perform some tasks on other layers at the same time by 'linking' them together and once you have created one or more layers the original background can be deleted. The hierarchal position of a layer can be changed by simply dragging it up or down the list, while each layers opacity can also be changed so allowing underlying lower layers to show through.

Note: Image files created using the 'Transparent' option in the New dialog box are created without a background but will always have a default background when saved as a bitmap.