Kang Wook Chun

An HDTV-to-SDTV spatial transcoder

Both high-definition television (HDTV) and, standard-definition television (SDTV) use the MPEG-2 video coding standard, but they have different spatial resolutions. In order to support the interlaced video coding, MPEG-2 incorporates various macroblock prediction modes. Thus, the HDTV-to-SDTV transcoding needs to handle spatial resolution downscaling and various MEPG-2 macroblock prediction modes. We investigate schemes to exploit the correlations between the input and output video in the design of an HDTV-to-SDTV transcoder so that the computation can be greatly saved while the quality of video is preserved as much as possible. First, by utilizing the motion vectors and macroblock coding modes of the input video, efficient motion reestimation and macroblock mode decision algorithms are proposed. Then a novel picture target bit allocation algorithm taking advantage of the coding statistics of the input video is presented. Simulation results showing the effectiveness of the proposed approaches are also presented.

Multi-resolution block matching algorithm and its VLSI architecture for fast motion estimation in an MPEG-2 video encoder

This paper proposes a high-performance multi-resolution motion estimation algorithm (HMRME) for MPEG-2 video encoding, which satisfies high estimation performance and efficient very large scale integration (VLSI) implementation. HMRME is based on a characteristic that field motion vectors (MVs) are very similar to their corresponding frame MV. Firstly, HMRME performs frame-based motion estimation (ME) as follows: at the coarsest level, two MV candidates are found on the basis of minimum matching error. The two MV candidates from the coarsest level search and the other one based on spatial MV correlation are used as center points for three local searches at the middle level. At the finest level, a frame MV is obtained from a local search around a single candidate from the middle level search. Field MVs are estimated with the single MV candidate from the middle level search of frame ME as initial estimates at the finest level, without any coarser level searches. This paper also describes a VLSI architecture based on HMRME. This architecture is designed to provide a good tradeoff between on-chip memory size and I/O bandwidth with high throughput. We implemented this architecture with about 140 K gates and 2.5 K bytes static random access memory for a large search range of [-192.0, +191.5] by using a synthesizable Verilog HDL.

Noise power estimation for effective de-noising in a video encoder

This paper presents a noise estimation algorithm using multiresolution motion estimation in a video encoder. Firstly, the motion estimator finds minimum block-matching errors at the finest resolution and the middle resolution for each macroblock. Secondly, if the minimum block-matching error at the finest resolution of a certain macroblock is less than a particular threshold, the variance of the inter-macroblock is computed. And then, we employ the square of the minimum block-matching error at the middle resolution as a predictor of the variance of the desired inter-macroblock without noise. The noise variance in the macroblock can be estimated by subtracting the predictor from the variance of the inter-macroblock. Finally, the noise variances estimated only for the well-motion-compensated macroblocks are averaged in each frame. Experimental results show that the proposed noise estimation is very accurate with negligible computational cost.

Transform-domain Wiener filtering for H.264/AVC video encoding and its implementation

For coding efficiency as well as noise reduction, efficient de-noising needs to be performed prior to video encoding. This paper proposes a transform-domain Wiener filtering scheme in an H.264/AVC video encoder. We show that the generalized Wiener filtering for each integer-transformed block is equivalent to multiplication of multiplication factor (MF) in a block with a proper filter coefficient matrix in a quantization process. Also, we implement efficiently the proposed scheme by employing several predetermined modified MFs for quantization. Experimental results show that the proposed de-noising scheme provides outstanding coding efficiency as well as noise reduction in an H.264/AVC video encoder.

Motion re-estimation for HDTV to SDTV transcoding

Both High-Definition Television (HDTV) and Standard-Definition Television (SDTV) use the MPEG-2 video coding standard, but they have different spatial resolutions. In order to support interlaced video coding, MPEG-2 incorporates various macroblock coding modes. Thus the HDTV to SDTV transcoding needs to handle non-integer factor spatial resolution down-scaling and various MPEG-2 macroblock coding modes. Taking into consideration the details of MPEG-2 macroblock coding modes, we propose motion re-estimation algorithms specially tailored for HDTV to SDTV transcoding.

A rate-constrained fast full-search algorithm based on block sum pyramid

This paper presents a fast full-search algorithm (FSA) for rate-constrained motion estimation. The proposed algorithm, which is based on the block sum pyramid frame structure, successively eliminates unnecessary search positions according to rate-constrained criterion. This algorithm provides the identical estimation performance to a conventional FSA having rate constraint, while achieving considerable reduction in computation.

Fast multi-resolution motion estimation algorithm and its VLSI architecture

This work presents a fast multi-resolution block-matching algorithm (FMRME) for MPEG-2 video encoding, which provides an outstanding PSNR performance close to the full search algorithm. We also propose the hardware architecture of the FMRME for real-time MPEG-2 video encoding with a large search range of [-192.0, +191.5]. Due to efficient data reuse and parallel processing, the utilization percentage of PE is also very high. We implemented this architecture with about 100 K gates and 5 K bytes SPSRAM.

Bit-allocation for transcoding pre-encoded video streams

In video transcoding, useful coding statistics become available when the input video stream is decoded. It is possible to utilize these statistics to improve the transcoding performance. In this paper we investigate how to use these statistics to perform the picture bit-allocation for transcoding a pre-encoded video bit-stream. We propose a scheme to estimate the complexities of the pictures of the output video using the coding statistics computed from the input video stream. Based on the estimated picture complexity, we present a picture bit-allocation algorithm for the rate-control of the transcoding process. The algorithm is simple to compute, and effectively improves the video quality and reduces the picture quality variations.

Interpolative mode prediction for efficient MPEG-2 video encoding

This paper presents an algorithm to predict interpolative motion compensation (MC) mode without computing interpolative SADs (Sum of Absolute Difference) for B-picture coding in an MPEG-2 video encoder. Firstly, an initial MC mode is selected among forward frame/field MC and backward frame/field MC for each macroblock (MB) in a Bpicture. This is accomplished by comparing four minimum SADs corresponding to the above-mentioned MC modes, and choosing a minimum SAD among them. Secondly, if the SAD corresponding to the selected mode is less than a specific threshold, we set the selected MC mode to the final MC mode. Otherwise, an MC mode of the current MB is determined between interpolative frame MC and interpolative field MC. If the sum of SADs of forward frame MC mode and backward frame MC mode is less than that of SADs of forward field MC mode and backward field MC mode, the final MC mode is set to an interpolative frame MC. Otherwise, the final MC mode is set to an interpolative field MC mode. Experimental results show that the proposed algorithm is comparable with as brute-force MC mode selection method as in conventional MPEG-2 video encoding. In addition, the proposed algorithm may noticeably reduce the memory bandwidth in implementation of MPEG-2 video encoder.

A rate-constrained full search algorithm for fast motion estimation in a video encoder

This puper prescnrs a fast f i r11 search algorithni for r~ite-consrraiiicrl nrorion estimation (ME). The proposed algoritltn~. xfiiclr is based on the block S U ~ I pyrarnid frame stnicfiire. ,sncce.ssivelv eliminates unnecessar). search positions according to rate-constrained criterion. This nlgorithnr provides rhe identical rstiniation perfomionce to a coiirmtianul full seurch algoritlmi (FSA) having rate-constraint. while achieving considerable reduction in computation. Index Terms Motion estimation. ralemnstraint. full search.