Patent ID: 6133955
Filing Date: 2000-10-17
Classification: G06T,H04N

Abstract:
A method for encoding a binary alpha block (BAB) of M.times.N binary pixels within a current frame based on the current frame and a previous frame including a multiplicity of BAB's, M and N being positive even integers, respectively, wherein each binary pixel has a binary value representing either an object pixel or a background pixel, comprising the steps of:(a) sampling every other horizontal lines of the BAB to generate a first block of (M/2).times.N binary pixels starting from either a first or a second horizontal line of the BAB, wherein the first horizontal line is a topmost horizontal line of the BAB;(b) sampling every other vertical lines of the first block to generate a first sample block of (M/2).times.(N/2) binary pixels as a base layer starting from either a first or a second vertical line of the first block, wherein the first vertical line is a leftmost vertical line of the first block;(c) generating a reconstructed first block of (M/2).times.N binary pixels by inserting (N/2) number of reconstructed vertical lines sequentially at locations of vertical lines not sampled in the step (b) under the condition that (N/2) number of vertical lines of the first sample block are placed at locations of the vertical lines sampled in the step (b), the reconstructed vertical lines being produced based on the vertical lines of the first sample block and each binary pixel of the reconstructed vertical lines referred to as a first target pixel being made by using a corresponding first context value based on a predetermined probability table, wherein the corresponding first context value for the first target pixel is calculated by using the context values of 8 binary pixels including a binary pixel located at an identical position to that of the first target pixel within the previous frame and 7 binary pixels located at a upper left, left, lower left, above, upper right, right and lower right positions, respectively, of the first target pixel within the reconstructed first block; and(d) producing a reconstructed BAB, being referred to as a first reconstructed BAB, of M.times.N binary pixels by inserting (M/2) number of reconstructed horizontal lines sequentially at locations of horizontal lines not sampled in the step (a) under the condition that (M/2) number of horizontal lines of the reconstructed first block are placed at locations of the horizontal lines sampled in the step (a), the reconstructed horizontal lines being produced based on the horizontal lines of the reconstructed first block and each binary pixel referred to as a second target pixel being made by using a corresponding second context value based on a predetermined probability table, wherein the corresponding second context value for the second target pixel is calculated by using the context values of 8 binary pixels including a binary pixel located at an identical position to that of the second target pixel within the previous frame and 7 binary pixels located at an upper left, above, upper right, left, lower left, below, lower right positions, respectively, of the second target pixel within the reconstructed BAB.