Fulvio Moschetti

New dictionary and fast atom searching method for matching pursuit representation of displaced frame difference

Matching pursuit decomposes a signal into a linear expansion of functions selected from a redundant dictionary, isolating the signal structures that are coherent with respect to a given dictionary. In this paper we focus on the Matching Pursuit representation of the displaced frame difference (dfd). In particular, we introduce a new dictionary for matching pursuit that efficiently exploits the signal structures of the dfd. We also propose a fast strategy to find the atoms exploiting the maximum of the absolute value of the error in the motion predicted image and the convergence of the MSE with the rotation of the atoms. Results show that the fast strategy is quite robust when compared to exhaustive search techniques and it improves the results of a suboptimal search strategy based on a genetic algorithm.

A statistical adaptive block-matching motion estimation

We address the problem of motion estimation (ME) in digital video sequences and propose a new fast, adaptive, and efficient block-matching algorithm. Higher quality and efficiency are achieved using a statistical model for the motion vectors. This model introduces adaptation in the search window, drastically reducing the number of positions where correlation-type computation is performed. The efficiency is further improved by progressively undersampling the macroblock. Patterns for undersampling are proposed to obtain the maximum benefit from single instruction multiple data (SIMD) instructions. In contrast with existing motion-estimation techniques, search strategy and subsampled patterns are closely linked. This shows that a good search strategy is much more important than blindly reducing the number of pixels considered for the matching pattern. We describe an implementation of the proposed matching strategy that exploits the very long instruction word (VLIW) and SIMD technology available in the new Itanium processor family. Results show that the proposed algorithm adapts easily to the evolution of the scene avoiding annoying quality drops that can be observed with other deterministic algorithms. The total number of operations required by the proposed method is inferior to those required by traditional approaches.

Ridgelet transform applied to motion compensated images

Wavelet transform is a powerful instrument in catching zero-dimensional singularities. Ridgelets are powerful instrument in catching and representing mono-dimensional singularities in bidimensional space. In this paper we propose a hybrid video coder scheme using ridgelet transform for the first approximation of line-edge singularities in displaced frame difference images. We demonstrate the potential of ridgelets and results show substantial improvements when compared to wavelet only based coder.

Low bit rate quality assessment based on perceptual characteristics

Peak signal-to-noise ratio (PSNR) is not a good measure of perceived picture quality, especially at low bit rates of coding. This paper proposes a new approach for computing perceptual distortion for visual signal in order to provide an objective measure for perceptual quality at low bit rate coding in typically mobile communications. The regions with three major perceptually disturbing artifacts, namely, damaged edge, blockiness and ringing, are detected as the basis of assessment. The correlation of the metric with human perception has been demonstrated with low bit rate CIF test data.

Automatic object extraction and dynamic bitrate allocation for second generation video coding

We describe a system for automatic objects extraction and dynamic bitrate allocation in a second generation object based video coder, targeting surveillance sequences. We combine model-based statistical change detection with a multiresolution-based approach for object extraction. Masks are redefined at a block level resolution and refined to improve the coding quality exploiting spatio-temporal considerations. We propose a dynamic adaptation of the quantization step of the MPEG-4 coder, based on motion information of the extracted objects. The results outperform traditional frame based coders at very low bit-rates. The masks proposed dramatically improve the coding performance, even when compared to ideally extracted masks.

Hierarchical mode search with classification of bisectional prediction modes based on the position of motion boundary [video coding]

Video coding schemes, equipped with various kinds of prediction modes, improve coding efficiency by offering efficient prediction modes that adapt to the motion in a macroblock (MB). Operation time for motion estimation and mode selection, on the other hand, increases with the number of prediction modes. We have proposed a motion compensated prediction method (arbitrary-shape partitioning motion compensation: APMC) equipped with various inter prediction modes which adapts to the motion boundary of objects on an MB basis. This paper confirms the coding efficiency of APMC in comparison to the final specification of H.264/AVC and introduces a method to improve the computational performance of APMC by using a hierarchical mode search method based on motion boundary position within MBs. Simulation results show that APMC improves coding efficiency by about 5% in comparison with the final specification of H.264/AVC, and the proposed hierarchical mode search method decreases the operation time to about 60%, while maintaining the coding efficiency.

Bidimensional dictionary and coding scheme for a very low bitrate matching pursuit video coder

In this paper we present a video coder based on a redundant dictionary that employs nonseparable bidimensional functions. The algorithm used for the representation of the residual of motion estimation is matching pursuit (MP). The proposed dictionary has new features capable of catching curved and oriented contours typical of the residual of motion estimation in natural video sequences. An adaptive grid approach is adopted for the coding of atoms and this is combined with an innovative coding method employing an arithmetic encoder. The proposed coder shows improvements over H.264 in terms of compression efficiency, with up to 20% gains for very low bitrates.

A nested-multilevel redundancy exploitation for fast block matching

In this paper we propose a block matching algorithm (BM) that reduces the computational burden of the motion estimation in an hybrid video encoder. To decrease the global complexity it acts at three different levels represented by the frame itself, the searching window and the macroblock (MB). To achieve an optimal performance also onto current general purpose processors provided with SIMD register files, a particular sub-sampling pattern of the MB is used. The algorithm shows a lower complexity than the three step search (TSS). In sequences where the motion field is formed by large motion vectors, the quality performance can be better than the full search algorithm (FSA) with an a priori fixed maximum motion vector. The algorithm is in fact able to adapt itself to the sequence.

A video coder for low bitrate mobile video streaming

Achieving very low bitrates for video applications in a mobile environment is essential. Video codecs standards evolution had a tremendous impact in the development of digital video, making possible today widespread usage of video data. At the same time it had an impact on the direction of research, biasing most of the efforts towards block based video. Alternative approaches may though lead towards different architectures able to provide higher compression efficiency. In this paper we propose a Matching Pursuit (MP) based video coder that adopts a generalized sub-pixel motion compensation and arithmetic coding. We introduce a new dictionary, and an adaptive grid for atom coding combined with an arithmetic coder. Comparison with H.264 show an improvement of up to 20% in compression efficiency for the same PSNR

Generalized motion compensation and arithmetic coding for matching pursuit coder

Matching pursuit (MP) based video coder represents an active alternative to conventional block based DCT based architectures R Neff et al. (1997). In this paper we propose a generalized motion compensation method and an entropy coding method for MP based coder. Motion vectors are combined with the cut-off frequency level of loop filters applied to the reference frame. Exploiting the characteristics of MP atoms, the latter are efficiently coded by employing an adaptive grid size combined with context based adaptive arithmetic coder. Reordering of atoms in each grid is also applied. Simulation results show that our proposed method outperforms traditional fixed grid based approach.