Patent ID: 9077960
Filing Date: 2015-07-07
Classification: H04N

Abstract:
1. A method of encoding digital media data, the method comprising: using a computing device that implements an encoder, applying a transform to a current cluster of blocks of the digital media data to produce a set of transform coefficients for the respective blocks; determining a block pattern for the current cluster of blocks, wherein the block pattern comprises a pattern of symbols indicating whether encoding of coefficients in corresponding ones of the blocks in the current cluster of blocks is skipped; conditionally, based on a prediction mode determined from causal statistics of previously encoded block patterns, applying an operation to the pattern of symbols of the block pattern for the current cluster of blocks, thereby altering the pattern of symbols such that a probability of the symbols in the block pattern having a given value tends toward a probability suited to efficient variable length entropy coding, wherein the causal statistics are maintained in two state variables that are updated based on a number of set bits in the block pattern for the current cluster of blocks and that, once updated, are used to make a determination of a prediction mode for a block pattern for a next cluster of blocks, the determination being based in part on a comparison of a first of the state variables to a second of the state variables; and encoding the block pattern in a compressed bitstream using a variable length entropy coding, wherein the compression efficiency of the variable length entropy coding relates to the probability of occurrence of the given value.