  The forthcoming Versatile Video Coding (VVC) standard adopts the
trellis-coded quantization, which leverages the delicate trellis graph to map
the quantization candidates within one block into the optimal path. Despite the
high compression efficiency, the complex trellis search with soft decision
quantization may hinder the applications due to high complexity and low
throughput capacity. To reduce the complexity, in this paper, we propose a low
complexity trellis-coded quantization scheme in a scientifically sound way with
theoretical modeling of the rate and distortion. As such, the trellis departure
point can be adaptively adjusted, and unnecessarily visited branches are
accordingly pruned, leading to the shrink of total trellis stages and
simplification of transition branches. Extensive experimental results on the
VVC test model show that the proposed scheme is effective in reducing the
encoding complexity by 11% and 5% with all intra and random access
configurations, respectively, at the cost of only 0.11% and 0.05% BD-Rate
increase. Meanwhile, on average 24% and 27% quantization time savings can be
achieved under all intra and random access configurations. Due to the excellent
performance, the VVC test model has adopted one implementation of the proposed
scheme.
