Background Image

If your document doesn't have a background (because you accidentally deleted or renamed the background), you can convert one of the existing layers into a background by choosing Layer > New > Background from Layer. Just changing the layer's name back to “Background” will not do the job. To quickly turn off all the eyeballs in the Layers palette and view only the layer you're interested in, simply Option-click (Mac) or Alt-click (Windows) one of the eyeball icons. Option or Alt-clicking a second time will bring those same layers back into view. If you'd rather make all the layers visible, Control-click (Mac) or right-click (Windows) on the eyeball icon and choose Show/Hide All Other Layers. You can change the checkerboard's appearance by choosing Edit > Preferences > Transparency & Gamut. You can even change it to solid white by changing the Grid Size setting to None.

The Background image in Photoshop (which some people refer to as the Background layer) is a bit different than the other layers that make up your image. If you liken the layers to the individual pages in a pad of tracing paper, you could think of the pad's cardboard backing as the Background image. It might be the same size and it relates to the other pages in the pad, but it has some qualities that make it quite different.

The Background image has the same limitations as most of the common file formats in use today (such as JPEG and EPS): it's always 100% opaque, no part of the background can extend beyond the document's bounds, and it's not actually considered a layer since most file formats don't support layers (with a few exceptions such as .PSD and .TIFF formats). In fact, that's the whole reason why the Background image exists. If all your document contains is the Background, then you should be able to save the image in just about any file format without losing information. That's also why most images start life as a Background image—because they originated in a file format that didn't support layers or came from a program that doesn't support layers. When you save a layered document into a file format that doesn't support layers (like JPEG), Photoshop will automatically combine all the layers that make up your image and turn the result into a Background image (known as flattening).

The Background image always displays a lock symbol to indicate that it cannot be repositioned with the Move tool, moved up or down in the layers stack, or be made transparent. For that reason, many tools will work differently when the Background image is active. For instance, the Eraser tool will paint with your Background color when the Background image is active since it is not able to make areas of the Background image transparent.

With all that said, you don't actually have to have a Background in your document. If you want to convert the Background into a normal layer, just change its name (the Background image must be named “Background,” otherwise it becomes a normal, unlocked layer). To change the name of a layer, double-click the layer's name in the Layers palette and type a new name.