Sadly, layers aren't all fun and games. First, if an image contains layers, saving it to any other format other than Photoshop or TIFF formats merges all the layers into one. The Photoshop, TIFF, and PDF formats are the only formats that preserve layers. (The ability to preserve layers in TIFF and PDF formats is a new feature in Photoshop 6.) Second, every layer you add also makes your file size grow. And third, layers can really slow down Photoshop. To keep running at peak efficiency, it's best to juggle as few layers at a time as possible.

You're going to want to merge layers every so often to keep your image manageable. So here are your merging options:

• To merge several layers into one, hide all layers except the ones you want to merge. In other words, eyeball icons should appear in front of the layers you want to merge. Hide the eyeball if you don't want to merge the layer. Then choose Merge Visible from the Layers palette menu or from the regular Layer menu at the top of the Photoshop window. Or, even simpler, press Shift + Ctrl + E (Shift + Command + E on a Mac).

You can merge one layer with other layers to which it has been linked. Choose Merge Linked from the Layers palette menu or from the top Layer menu. Easier yet, press Ctrl + E (Command + E on a Mac). Note that the Merge Linked command changes to the Merge Down command if you have no linked layers selected. Merge Down will merge your selected layer with all layers residing below it.

• If you want to flatten the entire image and get rid of all the layers, choose the Flatten Image command from the palette menu or from the Layer menu. You can undo the command right after you choose it by pressing Ctrl + Z (Command + Z on a Mac). If you performed other operations after flattening, you can undo by using the History palette.