According to "Analysis of Coding Tools in HEVC Test Model (HM 1.0) – Overview", two configurations of typical coding tools of H.265 or HEVC are suggested: High Efficiency and Low Complexity, as listed in the following table.
Table 1 Structure of tools forming the high efficiency and low complexity configurations of the HM
|High Efficiency||Low Complexity|
|Coding unit tree structure (8×8 up to 64×64 luma samples)|
|Transform unit tree structure (maximum of 3 levels)||Transform unit tree structure (maximum of 2 levels)|
|Transform block size of 4×4 to 32×32 samples (always square)|
|Angular intra prediction (maximum of 34 directions)|
|DCT-based interpolation filter for luma samples (1/4-sample, 12-tap)||Directional interpolation filter for luma samples (1/4-sample, 6-tap)|
|Bi-linear interpolation filter for chroma samples (1/8-sample)|
|Advanced motion vector prediction|
|Context adaptive binary arithmetic entropy coding||Low complexity entropy coding phase 2|
|Internal bit-depth increase (4 bits)||N/A|
|N/A||Transform precision extension (4 bits)|
|Adaptive loop filter||N/A|
The following figure shows the framework of HEVC test model (HM) decoder. The yellow, blue and white boxes indicates the building blocks for only high efficiency configuration, only low complexity configuration, and both configurations, respectively.