Mapping of intra string copy parameters for HEVC screen content coding

In intra string copy (ISC) technique for screen content coding, since the two string matching parameters, string position offset (pos) and string length (len), exhibit some unusual characteristic, directly applying the existing HEVC binarization to the one-dimentional (1-D) string matching parameters results in poor entropy coding performance. To solve this problem, in this paper, we propose a bijective mapping scheme for the 1-D string matching parameters in ISC. Firstly, a string matching parameter mapping enhanced ISC coding system architecture including encoder and decoder is given. Secondly, some findings of the unusual characteristic of the offset and length from the histogram statistical analysis are presented. Based on the findings, finally, bijective mappings for 1-D string matching parameters and HEVC-compliant binarizations for the post-mapping string matching parameters are proposed. When compared to ISC based on SCM1.0 encoder, experiments show that for screen content of text and graphics with motion, the mapping can improve coding performance by 3-6% with almost negligible coding complexity increase.