Alexis Michael Tourapis

Enhanced predictive zonal search for single and multiple frame motion estimation

Motion Estimation (ME) for video coding has taken an entirely different direction with the emergence of zonal algorithms. These algorithms made it possible to significantly reduce, if not almost eliminate, the tremendous computational overhead of motion estimation that was incurred in a video encoding system, while having little if any loss in quality. In this paper we further improve on these algorithms with the introduction of the Enhanced Predictive Zonal Search Algorithm (EPZS). By considering an additional set of predictors, improving the thresholding process, and simplifying the search pattern employed by these algorithms, we not only manage in achieving better output quality, but also reduce complexity of the motion estimation process even further. Our algorithm was compared with the algorithms accepted in the Optimization Model 1.0 of MPEG-4, and our simulations prove its outright superiority versus the existing algorithms. Furthermore we present a 3-Dimensional implementation of EPZS, which can be easily applied in the case of multiple frame motion estimation (ITU H.263++ and H.26L).

Predictive motion vector field adaptive search technique (PMVFAST): enhancing block-based motion estimation

Motion Estimation (ME) is an important part of most video encoding systems, since it could significantly affect the output quality of an encoded sequence. Unfortunately this feature requires a significant part of the encoding time especially when using the straightforward Full Search (FS) algorithm. In this paper a new algorithm is presented named as the Predictive Motion Vector Field Adaptive Search Technique (PMVFAST), which significantly outperforms most if not all other previously proposed algorithms in terms of Speed Up performance. In addition, the output quality of the encoded sequence in terms of PSNR is similar to that of the Full Search algorithm. The proposed algorithm relies mainly upon very robust and reliable predictive techniques and early termination criteria, which make use of parameters adapted to the local characteristics of a frame. Our experiments verify the superiority of the proposed algorithm, not only versus several other well-known fast algorithms, but also in many cases versus even the Full Search algorithm.

Fast mode decision and motion estimation for H.264 with a focus on MPEG-2/H.264 transcoding

The H.264 standard achieves much higher coding efficiency than previous video coding standards, due to its improved inter and intra prediction modes which come with a cost of higher computational complexity. When transcoding to H.264 from MPEG-2, motion information from MPEG-2 can be used to speed up the motion search. Fast mode decision algorithms are proposed for B and P frames, and a fast intra prediction algorithm is developed for intra coding. In addition, fast motion estimation is developed by reusing the motion information from MPEG-2. Simulation results demonstrate that we can achieve significant complexity reduction while maintaining the coding efficiency.

New results on zonal based motion estimation algorithms-advanced predictive diamond zonal search

Zonal based motion estimation algorithms have been gaining in popularity in video coding. This is due to their superior performance and reduced complexity versus other conventional algorithms. In this paper we propose a further improvement on these algorithms named the Advanced Predictive Diamond Zonal Search (APDZS). The proposed algorithm introduces the concepts of multiple initial predictor candidates and adaptive thresholding, and manages to significantly improve the reliability and performance of the estimation. Extensive simulation results demonstrate that the performance of this algorithm is equivalent in terms of PSNR, to that of the brute force full search algorithm even for the most complicated sequences, with almost negligible complexity.

Adaptive spatio-temporal filtering for video denoising

Video denoising is an important feature of many modem video encoding architectures since it can considerably enhance coding efficiency while at the same time improving objective and subjective quality. In this paper, a new scheme for video denoising based on spatio-temporal filtering is presented, which can be used as a preprocessing stage within a video encoder. Spatial filtering is performing through the adaptive selection and combination of a wavelet based and a 2D Wiener filter, while for temporal filtering we employ bidirectional block based motion compensation using the Enhanced Predictive Zonal Search (EPZS) algorithm. Experimental results are presented which show a significant improvement in video quality when the denoised video sequence is encoded with an H.264 encoder.

Optimizing the MPEG-4 encoder-advanced diamond zonal search

Motion estimation (ME) is an important part of the MPEG-4 encoder, due to its significant impact on the bitrate and the output quality of the encoded sequence. Unfortunately this feature occupies a significant part of the encoding time especially when using the straightforward full search (FS) algorithm. The diamond search (DS) was recently accepted as a fast motion estimation algorithm for the MPEG-4 VM. In this paper we propose a new algorithm named advanced diamond zonal search (ADZS), which is significantly faster than DS (in terms of number of checking points and total encoding time) and gives similar, if not better, quality (in terms of PSNR) of the output sequence. This is more obvious in the high bit rate cases. Our experiments verify the superiority of the proposed algorithm.

Temporal interpolation of video sequences using zonal based algorithms

Temporal interpolation has been proposed as a solution for increasing temporal resolution or even for predicting missing or corrupted frames within a video sequence. In this paper new techniques on temporal interpolation are presented, by mainly exploiting properties of the very popular and highly efficient zonal based motion estimation algorithms, and by introducing several other techniques such as multihypothesis motion compensation, motion classification and temporal/spatial filtering. In addition we further give an analysis on when temporal interpolation should be employed, thus possibly avoiding unwanted artifacts created from this process, while at the same time significantly improving the overall performance of the interpolation.

New predictive diamond search algorithm for block-based motion estimation

In this paper a new fast motion estimation algorithm is presented. The algorithm, named as Predictive Diamond Search, is actually based on the Diamond Search (DS) algorithm, which was recently adopted inside the MPEG-4 standard. The DS algorithm, even though faster than most known algorithms, was found not to be very robust in terms of quality for several sequences. By introducing a new predictive criterion and some additional steps in DS, our simulation results show that the proposed algorithm manages to have similar complexity with the DS algorithm, while having superior and more robust quality, similar to that of the Full Search algorithm.

An advanced zonal block based algorithm for motion estimation

Efficient motion estimation is very important for compressing video in standards like MPEG1/2/4 and ITU-T H.261/263. In this paper a new algorithm is presented which can outperform most of the traditional fast motion estimation algorithms in both speed and quality. In addition, in some cases this algorithm can achieve even better visual quality, than the “optimal” but computational intensive “full search” algorithm.

Direct macroblock coding for predictive (P) pictures in the H.264 standard

In this paper we introduce a new Inter Macroblock type within the H.264 (or MPEG-4 AVC) video coding standard that can further improve coding efficiency by exploiting the temporal correlation of motion within a sequence. This leads to a reduction in the bits required for encoding motion information, while retaining or even improving quality under a Rate Distortion Optimization Framework. An extension of this concept within the skip macroblock type of the same standard is also presented. Simulation results show that the proposed semantic changes can lead to up to 7.6% average bitrate reduction or equivalently 0.39dB quality improvement over the current H.264 standard.