Method and apparatus for binary shape encoding

An apparatus for encoding a binary alpha block(BAB) consisting of M.times.N binary pixels included in a video signal, M and N each being a positive even integer, comprising:

• horizontal sub-sampling means for sampling every other horizontal lines of the BAB to generate a first block starting from either a first or second horizontal line of the BAB, wherein the first horizontal line is the topmost horizontal line of the BAB;
• vertical sub-sampling means for sampling every other vertical lines of the first block to generate a first sample block as a base layer starting from either a first or second vertical line of the first block, wherein the first vertical line is the leftmost vertical line in the first block;
• base layer encoding means for encoding the first sample block to thereby produce coded base layer data;
• and
• enhancement layer encoding means for enhancement layer encoding based on the BAB, the first block and the first sample block to thereby provide coded horizontal and vertical enhancement layer data.