| JCTVC-B040 [C. Lai, Y. Lin (HiSilicon)] New intra prediction using the correlation between pixels and lines
A new spatial prediction scheme is presented for intra encoding by taking full use of the correlation between lines and pixels instead of blocks. Unlike the traditional block-based intra prediction, the spatial correlation is explored by using the line-based and resample-based intra prediction to improve compression performance of intra encoding. Compared with H.264/AVC High Profile under CfP ALPHA testing condition except that GOP structure is all intra pictures, the new experimental results shows an average 5.07% bit rate saving for all sequences, and about 5.71% average for HD (720P, 1080P and 1600P).
Refers to JCTVC-A025 and JCTVC-A111 Goal to perform prediction from close-by samples; line-based intra prediction 1x16, 16x1 (for 16x16 blocks), 2x8, 8x2 (for 8x8 blocks); nine directional modes implemented for each which are realized by shifting the block rows/columns circularly before the prediction and transform; DCT of corresponding size is applied. Another approach is made by interleaving horizontally plus vertically.
Only for 8x8 and 16x16 blocks currently
This increases (due to lots of additional modes that need to be checked) the encoder complexity significantly, but at the decoder the additional complexity is less (except for need to implement additional versions of DCT, pixel shifts etc.)
Implementation into KTA6.2r1. Average bitrate saving is roughly 5%, by tendency slightly higher for low rates, and also for higher resolutions.
Recommend for TE, supported also by MSRA
JCTVC-B042 [A. Tanizawa, J. Yamaguchi, T. Shiodera T. Chujoh, T. Yamakage (Toshiba)] Improvement of intra coding by bidirectional Intra Prediction and One-dimensional directional unified transform
This contribution introduces an intra prediction method combining two AVC based intra prediction (BIP: Bi-directional Intra Prediction) and combinations of pre-defined 1-D transforms depending on the intra prediction direction (1DDUT: 1 Dimensional Directional Unified Transform). BIP and DUT were included in the CfP submission of JCTVC-A117 [1]. 1DDUT is an improvement of DUT to increase the BD-rate gain.
A test was conducted under the test condition of the Transform AHG. For I slice only coding structure, the average BD-rate gain is 3.72% for BIP, 5.64% for 1DDUT and 8.76% for the combination of BIP and 1DDUT. For CS1 coding structure, the average BD-rate gain is 2.06% for BIP, 2.35% for 1DDUT and 4.16% for the combination of BIP and 1DDUT.
Refers to VCEG-AE14 and JCTVC-A117. BIP and weighted sub-block coding order. Directional unified transform (type A and B) based on scanning the field of prediction samples in various sequences depending on prediction direction.
Transform basis is said to have been trained on a set of data outside the sequences under test. In a first step, matrices were trained for each directional mode, in a second step the unification is done by clustering the residuals of the directional prediction based on correlation statistics and selecting the two bases with best performance.
Bi-directional prediction increases encoder complexity by factor 1.5, decoder complexity only marginally.
Results based on KTA: 3.7% for BIP only, 5.6% for 1D-DUT, 8.7% for combinations with transform (for I only coding). In terms of coding gain, almost same performance as MDDT, but simplification claimed. Currently works for block sizes up to 16x16.
It was suggested to study this in a TE (BIP only) provided that supporting partner is found.
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