Patent ID: 6049567
Filing Date: 2000-04-11
Classification: G06T,H04N

Abstract:
A mode coding method in 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 integers, respectively, wherein each binary pixel has a binary value representing either an object pixel or a background pixel, comprising the steps of:(a) performing sub-sampling on the BAB within the current frame according to a predetermined sub-sampling rule to thereby generate a sample block of (M/K).times.(N/K) binary pixels within the current frame, wherein M and N are multiples of K which is a predetermined positive integer, respectively;(b) generating a reconstructed BAB of M.times.N binary pixels according to a predetermined reconstruction rule based on the sample block within the current frame;(c) evaluating the difference between the reconstructed BAB and the BAB within the current frame, then if there is no difference therebetween, generating a first mode signal informing that there is no difference therebetween and hence the difference is not coded, and if there is the difference therebetween, generating a second mode signal informing that there is the difference therebetween and at the same time generating a second error data block of M.times.N binary pixels representing the difference to be encoded as an encoded second error data block;(d) in an inter mode, performing sub-sampling on the BAB's within the previous frame according to the predetermined sub-sampling rule to thereby generate a multiplicity of corresponding sample blocks of (M/K).times.(N/K) binary pixels within the previous frame;(e) in the inter mode, comparing the sample block within the current frame with the corresponding sample blocks within the previous frame and then detecting a corresponding second sample block most similar to the sample block within the current frame among the corresponding sample blocks within the previous frame as a predicted sample block to thereby produce a motion vector having vertical and horizontal components representing the displacement between the sample block within the current frame and the predicted sample block;(f) in the inter mode, based on the motion vector, detecting a BAB most similar to the BAB within the current frame among the BAB's within the previous frame as a predicted BAB, evaluating the difference between the BAB within the current frame and the predicted BAB, then if there is no difference therebetween, generating a third mode signal informing that there is no difference therebetween and hence the difference is not coded, and if there is the difference therebetween, generating a fourth mode signal informing that there is the difference therebetween and at the same time generating a fourth error data block of M.times.N binary pixels representing the difference to be encoded as an encoded fourth error data block; and(g) in case that the BAB within the current frame is encoded in an intra mode, since one of the first and the second mode signals is generated in the step (c), providing the generated mode signal in the step (c) as a selected mode signal and in case that the BAB within the current frame is encoded in the inter mode, if one mode signal among the first to the fourth mode signals is produced in the steps (c) and (f), providing the produced mode signal in the steps (c) and (f) as a selected mode signal and if two mode signals among the first to the fourth mode signals are generated at the same time in the steps (c) and (f), selecting and providing one of the two generated mode signals in the steps (c) and (f) as a selected mode signal according to a first predetermined selection rule.