JVET-Y0114 Non-EE2: Dependent quantization with 4 states for chroma components [Y. Chen, E. François, F. Galpin, P. de Lagrange (InterDigital)]
This contribution proposes to apply dependent quantization with 4 states for chroma components in stead of using the current dependent quantization with 8 states in ECM-3.1, keeping luma component using dependent quantization with 8 states. It aims to reduce the implementation complexity for the encoder.
The following average results are reported for dependent quantization with 4 states for chroma components relative to ECM-3.1 (dependent quantization with 8 states for chroma components) under common test conditions:
AI: 0.03%, -0.12%, -0.11% (Y, Cb, Cr) at 98% encoding time and 100% decoding time;
RA: 0.02%, -0.09%, -0.09% (Y, Cb, Cr) at 99% encoding time and 100% decoding time;
LB: 0.00%, -0.23%, -0.23% (Y, Cb, Cr) at 96% encoding time and 100% decoding time.
The effect in encoder run time is negligible, and the effect is mainly some very small shift of quality from luma to chroma. Main intent of the contribution is to show that 8 states are not really necessary for chroma.
ECM supports both 4 and 8 states, can be selected by encoder but always identical for luma and chroma.
In the current stage of exploration, this is not important.