LMCS updating issue

[Michel0914]

The current LMCS encoder design in VTM only analyzes intra pictures (or every 1sec for low delay case) to determine LMCS parameter values that apply until the next intra picture. LMCS is applied only for videos with standard range (i.e., LMCS is disabled for full range pictures.)

However, there is a case where video range changes from standard range to full range (e.g., fades, transitions, etc.) between intra pictures. In this situation, LMCS won’t be updated and is applied to full range frames which will cause performance drop.

A possible solution to solve this issue is to analyze signal range for every frame before applying LMCS. If the current frame is, or changes to, full range, disable LMCS and update the LMCS encoder parameters.

The proposed solution can fix this issue and won’t change CTC results. (Merge request will be submitted soon)

[Michel0914]

A MR is submitted to fix this issue:
​https://vcgit.hhi.fraunhofer.de/jvet/VVCSoftware_VTM/-/merge_requests/2051