Joint Collaborative Team on Video Coding (jct-vc) Contribution

3.5Profile, level, and constraint definitions

JCTVC-M0094 Proposal of the profile/level for Range extensions [T. Suzuki, N. Saunders, S. Karl (Sony)] [late]

Presented in joint discussion with MPEG REq VCEG etc. For further study.

JCTVC-M0173 Removing a Level Restriction on Coding Tree Block Size [E. Pinhasov, S. Riabtsev, A. Menachem]

Would require corrigendum or additional profiles. No action. [some notes may be in other draft report]

CTB size 32 that is always split may be one way to deal with this for an encoder.

3.6HEVC and RExt use cases (requirements related)

See also M0094. [possible additional notes in other draft report.]

JCTVC-M0172 Use cases and requirements for lossless and screen content coding [T. Vermeir (Barco)]
JCTVC-M0175 On the support for alpha channel in HEVC [M. Naccari, M. Mrak (BBC)]
JCTVC-M0190 Requirements for medical imaging applications [P. Amon, A. Hutter, U.-E. Martin, N. Wirsz (Siemens)]
JCTVC-M0255 Decoding a 10-bit HEVC sequence using an 8-bit decoder [D. Flynn, G. Martin-Cocher, D. He (RIM)]

HEVC, like other well-known codecs, contains profiles that accommodate the decoding of non-8-bit video sequences. In particular, HEVC contains a 10-bit profile that permits the carriage of 10-bit video sequences. However, for some implementations, the extra resources required for conformance to a higher bit-depth operating point can be prohibitive, yet there exist circumstances where a decoder may wish to offer best-effort decoding of a bitstream. Two techniques are presented that facilitate the decoding of 10-bit video bitstreams using an 8-bit decoder (but a 10-bit parser). The first uses the normal 8-bit reconstruction process, while the second involves addition of a rounding process during the reconstruction process. PSNR losses using low-delay main-10 bitstreams reportedly average at a 6 dB and 2.5 dB respectively. Further results are presented and specification text is provided for a possible annex.

Presentation not uploaded.

Two example reduced-precision decoding processes were described.

Potential normative and informative approaches were discussed.

The normative approach could potentially specify a decoding profile that has no corresponding bitstream conformance profile, but rather uses decoding of a bitstream of a higher capability bitstream conformance profile.

The functionality seems useful, but a requirement would need to be established (at the parent body level) for a normative approach.

It was commented that there are other reduced-quality decoding schemes that get applied in practice (e.g. for trick mode playback), and these are generally not documented in the standard (at least not normatively). The presenter suggested that this process might differ more substantially from the ordinary decoding process than what might apply in other such cases.

The scheme was presented specifically for 8 bits decoding of 10 bit video, although it could apply to other combinations.

It seems desirable to study this type of scheme, consider what is the best way to perform such a reduced-precision decoding process, analyze the conditions under which it might work well and under which it would not work so well.

It was suggested that having some degree of encoder optimization to mitigate the effect might provide a benefit.

For further study.

JCTVC-M0443 Cross-check of JCTVC-M0255 [?? (??)] [late]
JCTVC-M0315 AhG8: Requirements for wireless display applications [J. Sole, R. Joshi, M. Karczewicz (Qualcomm)]
JCTVC-M0348 AHG8: Quantitative measurement for subjectively lossless screen content coding [Tao Lin, Shuhui Wang, Kailun Zhou, Qiang Shen (Tongji Univ.)]

One of the key issues in subjectively lossless screen content coding is asserted to be to develop a quantitative measurement for assessing subjective losslessness. It is suggested that the assessment should guarantee absolutely subjective losslessness. Considering the well-known human visual masking effect, this contribution proposes considering a local area (such as 4x4 block) based and number of distinct colours related PSNR measurement for subjective losslessness. Moreover, this contribution discusses theoretical and experimental supports for the proposed quantitative measurement. Experimental results were also reported that were suggested to show that the measurement gives a more reasonable and correlated assessment of subjective losslessness than single PSNR measurement, resulting in a much lower bit rate than what would be needed for mathematically lossless coding. The measurement is also intended to help improving subjectively lossless coding technology.

The contribution suggested, as a starting point, a measure that considers the number of distinct (8b-ti tri-stimulus) colours and PSNR in 4×4 regions to determine whether the coding in each region is considered visually lossless or not.

In experiments, the contributor indicated that QP around 30 (all-intra) was approximately where distortions seemed to start to become visible on screen content. Another contributor said that contribution M0320 reported that QP around 27 was observed to be such a value.

A participant commented on the well-known concept of "just-noticeable differences".

Further study was encouraged, as it would be desirable to have improved objective quality measurement techniques to assist in our work.

Consulting with others such as V. Baroncini and VQEG might provide useful guidance on finding practical objective quality metrics for use in our work.

M0320 was noted to be related.

JCTVC-M0320 AHG8: More investigation on screen content coding [H. Yu (Huawei), X. Wang, J. Ye] [late]
JCTVC-M0429 Update on Cross-segment Decoding [Jiangtao Wen, Spencer Cheng (??)] [late]