Comparison of adaptive prediction and quantization schemes in intraframe video signal coding by subband decomposition

This paper deals with Pseudo-QMF sub-band coding of color TV signals based on DPCM schemes with scalar quantization . The coding scheme includes two operating modes. The first one, named intraframe and presented here, is used to code the beginning of a sequence and to process the scene cuts . The second one is an interframe coding mode, which allows to take into account the temporal correlations. The proposed methods are based upon predictive coding system and scalar quantization and the objective is to get an excellent visual quality of the decoded images . First, we proposed three sets of adaptive prediction functions and compared them . Then we developed three adaptive quantization schemes with differents complexity of adaptation. All these methods have been tested and compared in terms of entropic gain over PCM coding scheme and also in terms of locally and globally visual quality . Finaly we present our results in terms of bit-rate, peak SNR and visual quality of reconstructed images.Ce papier concerne le codage en sous-bandes par filtrage Pseudo-QMF des signaux d'images de télévision couleur. Le schéma général d'un tel système de codage comprend un mode intra-image dont nous allons ici présenter plusieurs variantes que nous avons étudié, qui permet de coder la première image dans une séquence d'images et de traiter les changements de plan, et un mode inter-images qui prend en compte les corrélations temporelles présentes dans la séquence à coder. Les méthodes proposées sont basées sur des codages prédictifs et des quantifications scalaires, la qualité visée des images reconstruites devant être excellente. D'abord nous proposons et comparons un ensemble de trois fonctions de prédiction adaptatives. Ensuite nous développons trois stratégies de quantification présentant des niveaux d'adaptativité différents. Toutes ces méthodes sont comparées entre elles d'abord en terme de gain entropique par rapport à un codage MIC (Modulation d'Impulsion Codée) pour la prédiction puis par mesure et appréciation de la qualité visuelle globale et locale en termes de débit, rapport signal à bruit et qualité d'image obtenue

Object-based video representations: shape compression and object segmentation

Object-based video representations are considered to be useful for easing the process of multimedia content production and enhancing user interactivity in multimedia productions. Object-based video presents several new technical challenges, however. Firstly, as with conventional video representations, compression of the video data is a requirement. For object-based representations, it is necessary to compress the shape of each video object as it moves in time. This amounts to the compression of moving binary images. This is achieved by the use of a technique called context-based arithmetic encoding. The technique is utilised by applying it to rectangular pixel blocks and as such it is consistent with the standard tools of video compression. The blockbased application also facilitates well the exploitation of temporal redundancy in the sequence of binary shapes. For the first time, context-based arithmetic encoding is used in conjunction with motion compensation to provide inter-frame compression. The method, described in this thesis, has been thoroughly tested throughout the MPEG-4 core experiment process and due to favourable results, it has been adopted as part of the MPEG-4 video standard. The second challenge lies in the acquisition of the video objects. Under normal conditions, a video sequence is captured as a sequence of frames and there is no inherent information about what objects are in the sequence, not to mention information relating to the shape of each object. Some means for segmenting semantic objects from general video sequences is required. For this purpose, several image analysis tools may be of help and in particular, it is believed that video object tracking algorithms will be important. A new tracking algorithm is developed based on piecewise polynomial motion representations and statistical estimation tools, e.g. the expectationmaximisation method and the minimum description length principle

Rate control algorithm based on quality factor optimization for Dirac video codec

Rate control plays an essential role in video coding and transmission to provide the best video quality at the receiver end given the constraint of certain network conditions. This paper proposes a rate control algorithm for the wavelet-based open-source Dirac video codec. The existing Dirac architecture has a constant-quality control mechanism based on rate–distortion optimization (RDO), giving variable bitrate. The proposed algorithm exploits the existing constant-quality control, which is governed by a parameter called quality factor (QF) to give a constant bitrate. A mathematical model called the rate–quality factor (R–QF) is derived to generate optimum QF for the current coding frame using the bitrate resulting from the encoding of the previous frame in order to meet the target bitrate. The proposed algorithm is a complete one-pass process and does not require complex mathematical computation. The process of calculating the QF is simple and, further, calculation is not required for each coded frame. It also provides the rate control solution for both intra-frame-only and inter-frame coding modes. The experimental results show that the proposed algorithm can control the bitrate precisely (i.e. within 1% of target bitrate in average for inter-frame coding mode and near-perfect flat response in generated bits vs. frame number curve in intra-frame-only coding mode). Moreover, the variation of bitrate over each group of pictures (GOP) in interframe coding mode is lower than that of H.264 using JM11. This is an advantage in preventing the buffer overflow and underflow for real-time multimedia data streaming. More importantly, there is no PSNR performance loss because of application of the proposed rate control algorithm. It gives superior quality over relatively static motion sequences and fast motion sequences with average quality as shown in the analysis and evaluations presented in this paper

Rate control algorithm based on quality factor optimization for Dirac video codec

Rate control plays an essential role in video coding and transmission to provide the best video quality at the receiver end given the constraint of certain network conditions. This paper proposes a rate control algorithm for the wavelet-based open-source Dirac video codec. The existing Dirac architecture has a constant-quality control mechanism based on rate–distortion optimization (RDO), giving variable bitrate. The proposed algorithm exploits the existing constant-quality control, which is governed by a parameter called quality factor (QF) to give a constant bitrate. A mathematical model called the rate–quality factor (R–QF) is derived to generate optimum QF for the current coding frame using the bitrate resulting from the encoding of the previous frame in order to meet the target bitrate. The proposed algorithm is a complete one-pass process and does not require complex mathematical computation. The process of calculating the QF is simple and, further, calculation is not required for each coded frame. It also provides the rate control solution for both intra-frame-only and inter-frame coding modes. The experimental results show that the proposed algorithm can control the bitrate precisely (i.e. within 1% of target bitrate in average for inter-frame coding mode and near-perfect flat response in generated bits vs. frame number curve in intra-frame-only coding mode). Moreover, the variation of bitrate over each group of pictures (GOP) in interframe coding mode is lower than that of H.264 using JM11. This is an advantage in preventing the buffer overflow and underflow for real-time multimedia data streaming. More importantly, there is no PSNR performance loss because of application of the proposed rate control algorithm. It gives superior quality over relatively static motion sequences and fast motion sequences with average quality as shown in the analysis and evaluations presented in this paper