Min-Su Cheon

Improved Video Compression Efficiency Through Flexible Unit Representation and Corresponding Extension of Coding Tools

This paper proposes a novel video compression scheme based on a highly flexible hierarchy of unit representation which includes three block concepts: coding unit (CU), prediction unit (PU), and transform unit (TU). This separation of the block structure into three different concepts allows each to be optimized according to its role; the CU is a macroblock-like unit which supports region splitting in a manner similar to a conventional quadtree, the PU supports nonsquare motion partition shapes for motion compensation, while the TU allows the transform size to be defined independently from the PU. Several other coding tools are extended to arbitrary unit size to maintain consistency with the proposed design, e.g., transform size is extended up to 64 × 64 and intraprediction is designed to support an arbitrary number of angles for variable block sizes. Other novel techniques such as a new noncascading interpolation Alter design allowing arbitrary motion accuracy and a leaky prediction technique using both open-loop and closed-loop predictors are also introduced. The video codec described in this paper was a candidate in the competitive phase of the high-efficiency video coding (HEVC) standardization work. Compared to H.264/AVC, it demonstrated bit rate reductions of around 40% based on objective measures and around 60% based on subjective testing with 1080 p sequences. It has been partially adopted into the first standardization model of the collaborative phase of the HEVC effort.

Quadtree Based Nonsquare Block Structure for Inter Frame Coding in High Efficiency Video Coding

A concept of a quadtree based nonsquare block coding structure is presented in this paper for the emerging High Efficiency Video Coding standard, which includes a quadtree based asymmetric motion partitioning scheme and a nonsquare quadtree transform (NSQT) algorithm. Nonsquare motion partitioning in inter frame coding provides the possibility of getting more accurate prediction results by splitting one coding block into two nonsquare prediction blocks. Contrary to the traditional symmetric motion partitions (SMP), asymmetric motion partitions (AMP) are proposed to improve the coding efficiency, especially for the coding blocks with irregular object boundaries. NSQT is designed for nonsquare prediction blocks (SMP and AMP), which combines square and nonsquare transform blocks in a unified transform structure. It exploits the directional characteristic of an image block to improve the transform efficiency. The combination of nonsquare partitions and NSQT provides high coding flexibility and low implementation cost for both encoder and decoder design. Simulation results show that about 0.9%-2.8% bit-rate saving can be achieved in terms of different configurations, and subjective quality can also be improved.

Coding efficiency improvement of HEVC using asymmetric motion partitioning

In this paper, coding efficiency improvement of HEVC using asymmetric motion partitioning (AMP) is provided based on HM-6.0. AMP allows asymmetric shape partition mode of prediction unit (PU) for inter prediction. AMP improves the coding efficiency, since irregular image patterns, which otherwise would be constrained to being represented by a smaller symmetric partition, can now be more efficiently represented without requiring further splitting. For encoder speed up, additional conditions are checked before doing motion estimation for each motion partitions. If the certain conditions are met, additional motion estimation, which is main source of encoder complexity for AMP, can be skipped. Experimental results demonstrate that AMP with encoding speed-up shows 0.8% coding efficiency improvement with 14% encoding time increase. Especially for videoconference sequences, coding efficiency improvement reaches to 1.4%.

New fast DCT algorithms based on Loeffler's factorization

This paper proposes a new 32-point fast discrete cosine transform (DCT) algorithm based on the Loefflers 16-point transform. Fast integer realizations of 16-point and 32-point transforms are also provided based on the proposed transform. For the recent development of High Efficiency Video Coding (HEVC), simplified quanti-zation and de-quantization process are proposed. Three different forms of implementation with the essentially same performance, namely matrix multiplication, partial butterfly, and full factorization can be chosen accord-ing to the given platform. In terms of the number of multiplications required for the realization, our proposed full-factorization is 3~4 times faster than a partial butterfly, and about 10 times faster than direct matrix multiplication.