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This format has the same color structure as RGB, but it includes an alpha channel that is used to display various levels of transparency. The transparency value is set from 0 to 1, where 1 corresponds to opacity. It is described using the CSS3 programming language.

This format was created by Nokia for use in its proprietary phones. A bitmap image was used to transfer image files between devices over a wireless connection. It was mainly used when exchanging multimedia text messages that support inserting pictures.