JVET-AO0194 [AHG11]: Luma Chroma Balancing for DCVC End-to-End Learned Intra Frames [M. Aderdor, T. Solovyev, E. Alshina (Huawei)]

This contribution presents the effect of using chroma QP offset to shift coding gains from chroma to luma in the case of external I-frames. Learning based end-to-end codecs such as DCVC-FM and DCVC-RT are trained on RGB / YUV444 based loss functions that treat all channels equally. When applied to YUV 4:2:0, these codecs tend to show disbalanced results with much higher gain in the chroma components. Previous contributions with DCVC codecs all used a pre- and post-processing method to shift coding gain from chroma to luma. This contribution aimed to shift gains from chroma to luma more efficiently by using chroma QP offset. CTC results using DCVC-RT I-frames on top of NNVC 15 configured as VTM 23.13 are the following:

With DCVC-RT as an external I-frame coder, no chroma scaling:

RA: -1.0% (Y) -21.8% (U) -18.8% (V)

With DCVC-RT as an external I-frame coder with ChromaQPOffset=2:

RA: -3.5% (Y) -6.00% (U) -3.50% (V)

It was commented that be beneficial also to study for other algorithms if they might be improved in performance by such a modification.

It was agreed to use this configuration change along with DCVC-RT.