In this letter, we present an authentication and recovery scheme to protect images. The image blocks are DCT transformed and then encoded with different patterns. An optimal selection is adopted to find the best pattern for each block which results in better image quality. Both the recovery and check data are embedded for data protection. The experimental results demonstrate that our method is able to identify and localize regions having been tampered with. Furthermore, good image quality for both watermarked and recovered images are effectively preserved.

A direct inter-mode selection algorithm for P-frames in fast homogeneous H.264/AVC bit-rate reduction transcoding is proposed in this paper. To achieve the direct inter-mode selection, we firstly develop a low-complexity distortion estimation method for fast transcoding, in which the distortion is directly calculated from the decoded residual together with the reference frames. We also present a linear estimation method to approximate the coding rate. With the estimated distortion and rate, the rate-distortion cost can be easily computed in the transcoder. In our algorithm, a method based on the normalized rate difference of P-frames (RP) is used to detect the high motion scene. To achieve fast transcoding, only for the P-frames with RP larger than a threshold, the rate-distortion optimized (RDO) mode decision is performed; meanwhile, the average cost of each inter-mode (ACM) is calculated. Then for the subsequent frames transcoding, the optimal coding mode can be directly selected using the estimated cost and the ACM threshold. Experiments show that the proposed method can significantly simplify the complex RDO mode decision, and achieve transcoding time reductions of up to 62% with small loss of rate-distortion performance.

H.264/AVC encoder employs rate control to adaptively adjust quantization parameter (QP) to enable coded video to be transmitted over a constant bit-rate (CBR) channel. In this topic, bit allocation is crucial since it is directly related with actual bit generation and the coding quality. Meanwhile, the rate-distortion-optimization (RDO) based mode-decision technique also affects performance a lot for the strong relation among mode, bits, and quality. This paper presents a multi-stage rate control scheme for R-D optimized H.264/AVC encoders under CBR video transmission. To enhance the precision of the complexity estimation and bit allocation, a frequency-domain parameter named mean-absolute-transform-difference (MATD) is adopted to represent frame and macroblock (MB) residual complexity. Second, the MATD ratio is utilized to enhance the accuracy of frame layer bit prediction. Then, by considering the bit usage status of whole sequence, a measurement combining forward and backward bit analysis is proposed to adjust the Lagrange multiplier λMODE on frame layer to optimize the mode decision for all MBs within the current frame. On the next stage, bits are allocated on MB layer by proposed remaining complexity analysis. Computed QP is further adjusted according to predicted MB texture bits. Simulation results show the PSNR improvement is up to 1.13 dB by using our algorithm, and the stress of output buffer control is also largely released compared with the recommended rate control in H.264/AVC reference software JM13.2.

3D video, which consists of a sequence of mesh models, can reproduce dynamic scenes containing 3D information. To summarize 3D video, a key frame extraction method is developed using rate-distortion (R-D) trade-off. For this purpose, an effective feature vector is extracted for each frame. Shot detection is performed using the feature vectors as a preprocessing followed by key frame extraction. Simple but reasonable definitions of rate and distortion are presented. Based on an assumption of linearity, an R-D curve is generated in each shot, where the locations of the key frames are optimized. Finally, R-D trade-off can be achieved by optimizing a cost function using a Lagrange multiplier, where the number of key frames is optimized in each shot. Therefore, our system will automatically determine the best locations and the number of key frames in the sense of R-D trade-off. Our experimental results show the extracted key frames are compact and faithful to the original 3D video.

The selection of motion vectors plays an important role in the error propagation process between inter-frames. In this letter, an end-to-end prediction error calculation method is proposed and is used for the rate-distortion optimized selection of motion vectors. Simulation results show that the robustness of encoded video streams under error-prone environment is improved.

The rate-distortion optimization (RDO) method is an informative technology that improves the coding efficiency, but increases the computational complexity, of the H.264 encoder. In this letter, a fast Macroblock mode determination algorithm is proposed to reduce the computational complexity of the H.264 encoder. The proposed method reduces the encoder complexity by 55%, while maintaining the same level of coding efficiency.

A flexible and robust rate-distortion optimization algorithm is presented to select macroblock coding mode for H.264/AVC transmission over wireless channels subject to burst errors. A two-state Markov model is used to describe the burst errors on the packet level. With the feedback information from the receiver and the estimation of the channel errors, the algorithm analyzes the distortion of the reconstructed macroblock at the decoder due to the channel errors and spatial and temporal error propagation. The optimal coding mode is chosen for each macroblock in rate-distortion (R-D)-based framework. Experimental results using the H.264/AVC test model show a significant performance of resilience to the burst errors.