On comparison of intra line copy and intra string copy for HEVC screen content coding

Recently, Intra Line Copy (ILC) and Intra String Copy (ISC) have been introduced as effective means for screen content coding during the development of HEVC Screen Content Coding Extensions. Although conceptually sharing the same theoretical basis, which is essentially string matching, they differ from each other in a number of significant ways. This paper presents detailed comparisons between them with respect to their compression performance, runtime complexity and memory access bandwidth, in order to better understand their merits and faults. Experimental results indicate that they perform comparably to each other, with ILC generally performing better in coding mixed content and ISC better in coding pure screen content. When considering the impact on the memory access bandwidth and coding performance trade-offs, local search for ILC/ISC becomes more favorable than full-frame search in low-delay real-time applications.