Explain in detail what a slice is, how it is used, and how it is created.

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A slice is a defined rectangular area in a document that performs a specific function, such as opening a different Web page, when the page is viewed in a Web browser. Another common application of slices is the creation of image maps. An image map is a graphic containing one or more invisible regions, called hot spots, which are hyperlinked. For example, you could slice a map of the United States into an image map by assigning hot spots to each state. Clicking an individual state then would cause the browser to perform a designated task such as displaying a different Web page or moving to another location on the current page.

Slices give you better control over the function and file size of your image because you can optimize slices to load individually. An image may have many slices — all of which are reassembled when the Web page is displayed. When you save a sliced image for the Web, each slice is saved as an independent file with its own settings and color table; the slice preserves hyperlinks and special effects.

You create a slice by using the Slice Tool or by creating layer-based slices, which are slices that are created automatically from the contents of a layer. The Slice Tool is located with the Crop Tool on the Tools panel. Once you create a slice, you can select, move, resize, or align it. You can assign each slice an individual hyperlink.

When you create a slice, Photoshop displays a number and a badge. A slice badge is an icon that appears next to the slice number, indicating certain information about the slice. A slice badge indicates whether the slice is image based, layer based, or has no content. Photoshop displays a blue slice number and blue slice badge on user-defined slices; automatically created slices display gray slice numbers and gray slice badges.

Numbering of slices is from left to right and top to bottom, beginning in the upper-left corner of the image. If you change the arrangement or total number of slices, Photoshop updates the slice numbers to reflect the new order.

The Slice Tool options bar allows you to designate an exact size for the slice or use guides to create a slice.