Shape coding
Shape coding is a method of design of a control that allows the control's function to be signified by the shape of the control. It was used successfully by Alphonse Chapanis on airplane controls to improve aviation safety.
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MPEG-4 Video Object Plane Decoder and the functionality
The shape information is referred to as alpha planes. The techniques to be adopted by the standard will provide lossless coding of alpha planes and lossy coding of shapes and transparency information since the shape size scalable, thus allowing a tradeoffs between bit rate and accuracy of shape representation. Furthermore, intra and inter shape prediction is envisioned so as to allow both efficient random access operations as well as efficient compression of shape and transparency information.
Alpha planes Binary (each pixel is either 0 or 255). Grey scale (each pixel is 8 bit).