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Synergies between in-loop and out-of-loop mapping for HDR-PQ content

Citation Author(s):
Miloš Radosavljević, Alan Stein
Submitted by:
Edouard Francois
Last updated:
14 March 2022 - 11:48am
Document Type:
Presentation Slides
Document Year:
Edouard Francois
Paper Code:
eCF Paper Id: 1642515633154 / DCC ID 187

This paper presents experimental results related to adaptive video content mapping used as a compression tool for HDR-PQ content. The purpose of adaptive video content mapping is to adapt the video signal dynamically depending on its statistical properties in order to better exploit the signal codewords range. Adaptive video content mapping has been investigated during the Versatile Video Coding (VVC) standard development with two main implementation designs: in-loop mapping, and out-of-loop mapping. In VVC, the in-loop implementation was finally adopted with a tool named “Luma Mapping with Chroma Scaling” (LMCS). Thanks to its in-loop implementation, LMCS offers high flexibility (high temporal adaptivity, content type adaptivity) and implementation benefits (no need to manage multiple conformance points, one after the decoder, and one after a post-decoder inverse mapping). Nevertheless, it was also observed that for HDR-PQ content, out-of-loop mapping can bring additional coding gains. The paper investigates potential synergies between the in-loop LMCS and out-of-loop mapping. Out-of-loop mapping is implemented as a pre-encoding process, with inverse mapping applied as post-decoding inverse process. A Supplemental Enhancement Information (SEI) message is used to convey the out-of-loop mapping data aside from the video bitstream. Performance results are reported for HDR-PQ content, with out-of-loop mapping only, and with out-of-loop mapping combined with LMCS.

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