International organisation for standardisation organisation internationale de normalisation

5.14.3Dequantization

5.14.3.1.1.1.1.1.1JCTVC-H0312 Non-CE4: Clipping of Transformed Coefficients before De-Quantization [X. Li, X. Guo, S. Lei (MediaTek)]

This was presented together with H0541.

5.14.3.1.1.1.1.1.2JCTVC-H0366 Non-CE4: Cross-check of clipping of transformed coefficients before de-quantization (JCTVC-H0312) [B. Li (USTC), J. Xu (Microsoft)]
5.14.3.1.1.1.1.1.3JCTVC-H0541 Non CE4: Limiting dynamic range when using a quantization weighting matrix [Louie Kerofsky, A. Segall (Sharp)]

This contribution examined dynamic range issues related to quantization weighting matrices as identified in JVTVC-G1044. This contribution reported that under extremely low weight and QP values, levels exceeding 16-bits may occur and that with extremely high weights and QP values, intermediate values exceeding 32-bits may occur. This contribution proposed limiting level values prior to dequantization to 15-bits for the 4x4 block size and limiting levels to 16-bits for all other block sizes. The proposed method reportedly allows a dequantization implementation with a weighting matrix to need at most 16-bit multiplies with intermediate values within 32-bits.

This contribution was provided together with H0312, in which proposed text was provided.

In terms of the required computations, the level limit used for clipping depends on QP, TU size and bit depth.

The reported problem only appears in the context of the use of quantization matrices .

In discussion, it was remarked that this could be achieved by encoder restriction (and that a similar discussion was noted to have occurred in previous meetings), and that there is no doubt that there is a problem to be solved.

Decision: Adopt (text in H0312) as a "placeholder: to solve the problem, and further study in a quantization AHG whether this is the ultimate solution.
5.14.3.1.1.1.1.1.4JCTVC-H0532 Quantization reconstruction offset [J. Wang, X. Yu, D. He, G. Martin-Cocher (RIM)]

The document proposed to include a quantization reconstruction offset on the picture level as an extra functionality for supporting grain noise coding and texture preservation.

It was asked in discussions whether this could be achieved by encoder optimization, and the answer did not seem fully clear. No action was taken on this.

5.14.3.1.1.1.1.1.5JCTVC-H0736 Clarification on Tickets 313 and 315 [K. Chono (NEC), K. Sugimoto (Mitsubishi)]

This contribution identified a mismatch between text and software in regard to QP range.

Decision (SW): Fix software to match text (using an "AVC-style" QP range adjustment for bit depth).