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9.2I2R proposed simplification of MDDT

9.2.1.1.1.1.1.1.1JCTVC-C037 TE7: Results for mode-dependent fast separable KLT for block-based intra coding [C. Yeo, Y. H. Tan, Z. Li, S. Rahardja (I2R)]

To simplify the operation of Mode Dependent Directional Transform (MDDT), a Mode-Dependent Fast Separable KLT for Block-based Intra Coding was previously introduced that requires only two transform matrices: a "DCT" and a "derived KLT". The derived 4x4 KLT also reportedly has a structure that can be exploited to reduce the operation count of the transform operation. This contribution provides test results as stipulated in TE7. Experimental results reportedly show that the proposed technique matches the performance of MDDT even though the approach requires no training, and has lower operation count and storage costs.

It was remarked that the "derived KLT" is essentially the same as a form of DST.

The proposal uses two transforms per block size instead of 18. The scheme was applied to two block sizes: 4x4 and 8x8.

A coding loss of 0.1% was reported overall for HE intra-only conditions relative to the anchor (which used MDDT).

It was remarked that an adaptive scan order is part of the scheme.

It was asked how much the coding loss would be if using just one transform. We don't know the answer to that. Roughly 1-2% was suggested as a reasonable guess.

9.2.1.1.1.1.1.1.2JCTVC-C070 TE7: Cross-check for I2R proposal on mode-dependent fast separable KLT for block-based intra coding [X. Zhu, L. Yu (Zhejiang Univ.)]

This contribution presented cross check results of I2R proposal on mode-dependent fast separable KLT for block-based intra coding. Due to lack of time, not all data was checked – only some randomly selected points had been checked. The sequences checked reportedly had the same PSNR and bit rate with the corresponding data given by proponent. The source code was studied and determined to match the proposed algorithm.

9.2.1.1.1.1.1.1.3JCTVC-C090 TE7: Cross-verification results of mode-dependent fast separable KLT for block-based intra coding from I2R [X. Zhao, L. Zhang, S. Ma, W. Gao (Peking Univ.)]

This contribution reported Peking Univ. cross-verification results of the I2R proposal on mode-dependent fast separable KLT for block-based intra coding in response to the Tool Experiment TE7.

Some minor differences were observed between Peking Univ. and I2R results, which could be induced by the different platforms used (Peking Univ.: WindowXP, I2R: Linux). However, the average rate-distortion performance results of I2R and Peking Univ. were reported to be equal.

9.2.1.1.1.1.1.1.4JCTVC-C158 TE7: Cross verification of MDDT simplification JCTVC-B024 [K. Andersson (Ericsson)]

This contribution was a cross-verification of the TE7 MDDT Simplification that was proposed in JCTVC-B024. The PSNRs, bit rates and BD-rate measurements provided by IR2 were matched. The result reportedly shows that the BD bit rate loss is 0.1% and 0.0% for high efficiency configurations all intra and random access respectively compared to the anchor TMuC 0.7 reference configuration. The encoding and decoding time were approximately unaffected.

9.2.1.1.1.1.1.1.5JCTVC-C039 Choice of transforms in MDDT for unified intra prediction [C. Yeo, Y. H. Tan, Z. Li, S. Rahardja (I2R)]

A simplification of Mode-Dependent Directional Transform (MDDT) was previously proposed in JCTVC-B024 that requires only two transform matrices: a "DCT" and a "derived KLT". However, the choice of transforms in JCTVC-B024 was only specified for the 9 intra prediction modes present in AVC. In this proposal, a choice of transforms is presented for the 34 intra prediction modes possible in the unified intra prediction in TMuC. As in the earlier proposal, only two transform matrices are necessary, and no training is required.

This document provided information on how the proposed scheme was harmonized with Unified Intra Prediction (adding more prediction direction types to the transform selection table) for use in TE7. The testing performed in TE7 used this scheme.

9.3Huawei proposed simplification of MDDT

9.3.1.1.1.1.1.1.1JCTVC-C102 TE7: Symmetry-based simplification of MDDT [H. Yang, J. Zhou, H. Yu (Huawei)]

In the last meeting, symmetry-based simplification of MDDT (SMDDT) was proposed to reduce the number of transform matrices in the current MDDT implementation. And the SMDDT technique was included in TE 7 for further investigation. According to the TE7 specification, SMDDT has been implemented in the TMuC software and evaluated under the common test conditions since the last meeting. This document reported the performance of the proposed SMDDT technique and discussed the complexity.

Five transforms, with flipping and transposing, were used. Fewer scan orders were used in this proposal than in the I2R proposals. It was claimed that this proposal requires less data storage.

Overall, a 0.1% bit rate increase was reported.

9.3.1.1.1.1.1.1.2JCTVC-C038 TE7: Cross-check results of MDDT simplification proposal from Huawei [C. Yeo, Y. H. Tan, Z. Li, S. Rahardja (I2R)]

This contribution provided a summary of the cross-checks performed by the Institute for Infocomm Research on the Huawei MDDT simplification proposal. The simulation results reportedly closely match the results provided by Huawei. The software source code was studied algorithmically as well as executed.

9.3.1.1.1.1.1.1.3JCTVC-C192 TE7: Cross-verification results of Huawei proposal on simplified MDDT for intra prediction residual [Y. Choe, J. Kim (Yonsei Univ.), Y-G. Kim (KGIT)]

This document reported cross-verification results of simplified MDDT (SMDDT) for intra prediction residual proposed by Huawei, according to the description of TE7. The verification task had been done successfully and the results reportedly match almost exactly those provided by Huawei. The algorithm was studied as well as executing the software.

9.3.1.1.1.1.1.1.4JCTVC-C106 Symmetry-based scan order sharing scheme for MDDT [H. Yang, J. Zhou, H. Yu (Huawei)]

This proposal was used in the TE for the scheme proposed in JCTVC-C102. However, it can reportedly also apply in the context of other schemes and was therefore proposed separately in this contribution.

In this proposal, a symmetry-based scan order (SSO) sharing scheme was proposed to further simplify the mode-dependent directional transform (MDDT). Based on the symmetry among all intra prediction directions, the number of scan maps can reportedly be reduced by the proposed SSO while the coding performance is kept unchanged. The proposal suggested that the proposed SSO scheme be adopted as an improvement of the current MDDT implementation in TMuC.

When implemented in the current MDDT implementation in TMuC, it was reported that this scan order method results in a memory savings with no performance loss.

Disabling scan order adaptivity reportedly resulted in very little compression performance loss (0.0% to 0.1%). It was remarked that if the gain from scan order adaptivity is that small, perhaps we shouldn't use it (in the HHI coefficient coding scheme as well).

The contributor suggested that a harmonization of simplified MDDT schemes may also be feasible.

Further study was encouraged.