Yunyang Dai

Direct Techniques for Optimal Sub-Pixel Motion Accuracy Estimation and Position Prediction

Direct techniques for the optimal resolution estimation and position prediction of subpel motion vectors (MVs) based on integer-pel MVs are investigated in this paper. Although it is common to determine the optimal MV position by fitting a local error surface using integer-pel MVs, the characteristics of the error surface have not been thoroughly studied in the past. Here, we use an approximate condition number of the Hessian matrix of the error surface to characterize its shape in a local region. By exploiting this shape information, we propose a block-based subpel MV resolution estimation method that allows each block to choose its optimal subpel MV resolution for the optimal rate-distortion (R-D) performance adaptively. Furthermore, we propose two MV position prediction schemes for ill and well-conditioned error surfaces, respectively. All proposed techniques are direct methods, where no iteration is required. Experimental results are given to show the R-D performance of the proposed subpel MV resolution estimation and position prediction schemes.

Lossless video compression with residual image prediction and coding (RIPC)

A lossless video compression scheme is proposed based on residual image prediction and coding (RIPC) in this work. We first study different prediction schemes used in lossless coding, and observe that prediction residuals are not white but in form of granular noise. This study reveals a need to treat residual images with granular noise carefully. Then, we propose a new scheme, called RIPC, to encode the residual image effectively. Experimental results show that the proposed RIPC scheme outperforms the H.264 lossless intra prediction (H.264-LS) and JPEG-LS with a bit rate saving of 20% and 12%, respectively.

Efficient block-based intra prediction for image coding with 2D geometrical manipulations

A novel block-based intra-prediction scheme is proposed for efficient image (or intra-frame) coding, where we apply various 2D geometrical manipulations to reference image blocks to enrich the pool of prediction blocks for a given target block. As compared with the traditional line-based intra prediction in H.264/AVC, the new scheme offers a significant coding gain (about 0.24-1.23dB in the PSNR value with the same bit rate) at the cost of higher complexity. Several techniques to reduce the search complexity are also discussed.

Enlarged Block Sizes and Motion Search Ranges for High Definition Video Coding

A rate-distortion (R-D) model is derived to investigate the potential coding gain from the use of a larger macroblock size for high definition (HD) video coding in this work. Coding rates of using different block sizes for HD video coding are compared with the R-D model, and limitations of the current coding techniques that might impede the additional R-D gain of using enlarged MB for HD coding are explained. Experiments show that an average bit rate gain of 27 % across QP range can be achieved by using enlarged MB and extended motion search range.

Multi-order-residual (MOR) video coding: framework, analysis, and performance

A novel multi-order-residual (MOR) coding approach is proposed for high-bit-rate video compression in this work. We show that a significant amount of short and medium-range correlations due to the use of a fine quantization parameter cannot be easily removed by the well known motion compensated prediction process in the high-bit- rate coding scenario. Consequently, the video coding performance degrades rapidly as quality increases. To address this issue, we propose a Multi-Order-Residual (MOR) coding scheme that encodes prediction residuals in multiple stages according to their correlation characteristics. Then, we adopt different compensation and coding schemes in different stages. Experimental results are given to show the proposed MOR scheme outperforms H.264/AVC by a significant margin.

A second-order-residual (SOR) coding approach to high-bit-rate video compression

A novel video compression scheme that exploits the idea of second-order-residual (SOR) coding is proposed for high-bit-rate video applications in this work. We first study the limitation of todays high performance video coding standard, H.264/AVC, and show that it is not effective in the coding of small image features and variations for high-bit-rate video contents. For low to medium quality video streams, these small image features can be removed by the quantization process. However, when the quantization stepsize becomes small in high-bit-rate video, their existence degrades the rate-distortion coding performance significantly. To address this problem, we propose a coding scheme that decomposes the residual signals into two layers: the first-order-residual (FOR) and the second-order-residual (SOR). The FOR contains low frequency residuals while the SOR contains the high frequency residuals. We adopt the H.264/AVC for the FOR coding and propose two schemes, called SOR-freq and SOR-bp, for the SOR coding. It is shown by experimental results that the proposed FOR/SOR scheme outperforms H.264/AVC by a significant margin (with about 20% bit rate saving) in high-bit-rate video.

Rate-Distortion (RD) Analysis of Subpel Motion Vector Resolution Selection for Video Coding

A rate-distortion (RD) model for subpel motion vector (MV) selection is proposed for power-efficient video coding in this work. To reduce the encoder complexity, the block texture feature is used in the proposed RD model to predict the potential subpel MV gain for a given block. If the gain is not sufficiently large, we may choose integer or half-pel MV to save the search and interpolation cost at the encoder. Quantization noise and external noise are included in the model to improve the prediction accuracy furthermore. The resultant model is shown to be reliable in predicting the RD gain for different subpel resolutions. It is shown by experimental results that the proposed subpel MV selection scheme can maintain the RD performance similar to full subpel MV while reducing encoder complexity significantly.

Fast 2D intra prediction (2DIP) mode decision for image and video coding

A 2D intra prediction with geometrical manipulations (2DIP) was proposed in [1] to enhance the intra coding performance of H.264/AVC. However, the complexity of 2DIP is high if the full search scheme is used. In this work, we investigate ways to speed up the intra prediction mode decision for 2DIP. To achieve this, we first conduct a block correlation analysis that reveals the unique characteristics of 2DIP. Based on the analysis, a fast 2DIP search scheme is proposed to reduce the encoder complexity, where a block classification method is used to identify blocks using LIP only, a good initial search position is predicted and a block pruning technique is introduced. It is shown by experimental results that the fast 2DIP search can reduce the complexity of the full search significantly with little loss in the RD performance.

Decoder-Friendly Subpel MV Selection for H.264/AVC Video Encoding

A decoder-friendly subpel motion vector (MV) selection scheme for H.264/AVC video encoding is proposed in this work. First, the rate-distortion (RD) relationship with respect to subpel MVs is examined to shed light on the tradeoff of R-D performance degradation and complexity reduction in different block types. It is observed that the R-D gain of some macroblocks (MB) is greatly enhanced by employing subpel MVs while others are not. An SAD-based approach is adopted to decide whether the subpel MV scheme is needed for a certain MB. To enhance the prediction accuracy, the correlation of MVs in the spatial domain is also exploited. Our scheme further introduces decoder complexity budget to aid the designer in making design tradeoffs. Experimental results indicate that our scheme is flexible enough that the actual achieved complexity is very close to the target complexity budget under different QP settings.

SIMD - efficient loop unrolling design for embedded multimedia applications

Due to the rising complexity of modern embedded media applications (EMAs), compilers must have the capability to exploit superword level parallelism (SLP). This work analyzes the memory access patterns found in EMAs and presents a scheme to calculate the loop unrolling factor to utilize these patterns fully to generate efficient single instruction multiple data (SIMD) instructions. The loop nest is also considered for actual memory access patterns, which can be used to improve the efficiency of the compiler. We observe a performance improvement by an average factor of 12 times for manual experiments conducted on the TriMedia TM-1300 processor for the H.264 encoding application.