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7th Meeting: Torino, July 2017 2017-07-16 11:02
Chroma Adjustment for SDR Video
Authors: J. Ström Ericsson P. Wennersten Ericsson K. Andersson Ericsson Rickard Sjöberg Ericsson
Abstract
This contribution discusses an alternative way of subsampling 4:4:4 sequences to 4:2:0 called chroma adjustment. This method was originally created for HDR content as reported in JCTVC-Z0022, but this document asserts that it may be beneficial also for certain SDR sequences with saturated colors such as CampfireParty. Compared to the version of CampfireParty currently used in JVET, the contribution claims that the chroma adjustment version can avoid amplification of noise in some areas, avoid suppression of noise in other areas and avoid a blurring of some edges. The contribution measures the increase in luminance quality from the chroma adjustment method by measuring PSNR on a gamma corrected version of luminance. It is reported that this results in a BD rate change of -21% for CampfireParty for random access over the current 4:2:0 sequence. The contribution however claims that the perceptual effect seems smaller than this figure suggests, perhaps due to the sequence being noisy. The contribution asserts that non-saturated sequences do not benefit as much from the processing, and results for a non-saturated sequence (TrafficFlow) are also reported, -1%. Furthermore, the contribution notes that the chroma positions in the current 4:2:0 sequence are incorrect. The contribution proposes to that the CampfireParty sequence should be replaced by the one obtained using the proposed technique, and that 4:4:4 representations of all current test sequences should be made available.
Meeting Notes
JVET-G0067 Chroma Adjustment for SDR Video [J. Ström, P. Wennersten, K. Andersson, R. Sjöberg (Ericsson)]

This contribution discusses an alternative way of subsampling 4:4:4 sequences to 4:2:0 called chroma adjustment. This method was originally created for HDR content as reported in JCTVC-Z0022, but this document asserts that it may be beneficial also for certain SDR sequences with saturated colours such as CampfireParty. Compared to the version of CampfireParty currently used in JVET, the contribution claims that the chroma adjustment version can avoid amplification of noise in some areas, avoid suppression of noise in other areas and avoid a blurring of some edges. The contribution measures the increase in luminance quality from the chroma adjustment method by measuring PSNR on a gamma corrected version of luminance. It is reported that this results in a BD rate change of −21% for CampfireParty for random access over the current 4:2:0 sequence. The contribution however claims that the perceptual effect seems smaller than this figure suggests, perhaps due to the sequence being noisy. The contribution asserts that non-saturated sequences do not benefit as much from the processing, and results for a non-saturated sequence (TrafficFlow) are also reported, −1%. Furthermore, the contribution notes that the chroma positions in the current 4:2:0 sequence are incorrect. The contribution proposes to that the CampfireParty sequence should be replaced by the one obtained using the proposed technique, and that 4:4:4 representations of all current test sequences should be made available.

Definitely the chroma positions in CampfireParty are wrong. Should be type 0 in ffmpeg conversion that was used.

Campfire is the most extreme case.

Question: Does it have impact on the compression benefit of JEM vs HM? Not known.

It was mentioned that the picture examples shown also seem to remove some sharpness from luma.

Generally, Campfire is a good sequence to spot coding artefacts.

Actions:

  • Correction of chroma positions in CampfireParty using HDRtools.
  • Building Hall, Daylight Road and Park running also need to be checked for correct chroma position (Type 0). Side activity (J. S., Teruhiko S. & original proponents will check and report back). It was later confirmed that the three sequences need to be modified.

Decision(CTC): Replace the four sequences mentioned above by new version (different names). Original providers will regenerate the sequences.

Further study on other aspects.

References:
JCTVC-W0052 JCTVC-W0056 JCTVC-W0107 JCTVC-X0036 JCTVC-X0054 JCTVC-X0072 JCTVC-Y0030 JCTVC-Y0033 JCTVC-Y0034 JCTVC-Z0022
ARCHIVE v2 :
JVET-G0067.docx JVET-G0067_Chroma_Adjustment_for_SDR_Video.pdf
Decisions
Further study on other aspects.
Citation