Transform Domain-Based Perceptual Detection and Reduction of Blocking Artifacts

In this paper, provide a simple and effective method for measuring blocking artefacts with an ideal 2-D step function in this study. First, a basic edge detection technique for measuring blocking artefacts is proposed. The ideal 2-D step function is chosen based on the presence of blocking artefacts in the edge image. The blocking artefact reduction algorithm in frequency domain is designed to extract all of the parameters required to detect the presence of blocking artefacts and replace the optimal step function with a ramp function by replacing the coefficient of the first row of horizontal blocks with the coefficient of the shifted block. The proposed strategy was tested on various standard benchmark photos and found to increase the perceptual quality of JPEG compressed images after blocking artefact removal with the proposed method

A hybrid system for video compression based on H.264 and JPEG2000

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2009.Includes bibliographical references (leaves 55-56).A video compression system is created that combines the JPEG2000 and H.264 standards. JPEG2000 is used to encode the I-frames, while H.264 is used to encode the P-frames. The goal of this thesis is to evaluate the performance of this hybrid system. The system is evaluated using a set of eight test video sequences, which cover a range of resolutions (CIF to 1920 x 1080) and picture content. Rate-distortion performance analysis shows the two systems to be comparable. Subjective analysis reveals that the artifacts of JPEG2000 are propagated to the P-frames. This can be useful in reducing blocking artifacts at low bit-rates. However, blurriness and fuzzy edges, which are the artifacts of JPEG2000, replace the blocking artifacts.by Zhenya Gu.M.Eng

Efficient compression of motion compensated residuals

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

A SVD based scheme for post processing of DCT coded images

In block discrete cosine transform (DCT) based image compression the blocking artifacts are the main cause of degradation, especially at higher compression ratio. In proposed scheme, monotone or edge blocks are identified by examining the DCT coefficients of the block itself. In the first algorithm of the proposed scheme, a signal adaptive filter is applied to sub-image constructed by the DC components of DCT coded image to exploit the residual inter-block correlation between adjacent blocks. To further reduce artificial discontinuities due to blocking artifacts, the blocky image is re-divided into blocks in such a way that the corner of the original blocks comes at the center of new blocks. These discontinuities cause the high frequency components in the new blocks. In this paper, these high frequency components due to blocking artifacts in monotone area are eliminated using singular value decomposition (SVD) based filtering algorithm. It is well known that random noise is hard to compress whereas it is easy to compress the ordered information. Thus, lossy compression of noisy signal provides the required filtering of the signal

Compressão de dados sensoriais em sistemas robóticos

One of the main problems in the development and debugging of robotic systems is the amount of data stored in files containing sensor data (ex. ROS proprietary log files - BAGS). If we consider a robot with several cameras and other sensors that collect information from the environment several times per second, we quickly obtain very large files. Besides the concerns regarding storage and, in some cases, transmission, it becomes extremely hard to find important information in these files. In this thesis, we tried to solve both problems studying and implementing data compression solutions to reduce the referred files. The main focus was image and video compression, by far the most storage consuming data. Moreover, we conducted a detailed study about the effect of lossy compression methods in the performance of some state of the art image analysis algorithms. Another contribution was the development of an intelligent video player to help roboticists in their work while they evaluate the recorded data after experiments. Parts of the video that do not contain relevant information are skipped during the play. Based on the results, we concluded that ROS native compression is not sufficient. Furthermore, solutions based on ROS, or virtually any robotic system that has to deal with image/video data, would benefit with the use of a H.265 codec, as it provides the smallest number of bits per pixel without a significant penalty on the performance of image analysis algorithms.Um dos principais problemas no desenvolvimento e depuração de sistemas robóticos é a quantidade de dados armazenados em ficheiros contendo dados sensoriais (ex. ficheiros de log proprietários de ROS - Bags). Se considerarmos um robô com várias câmaras e outros sensores, que recolhem informação do ambiente diversas vezes por segundo, obtemos rapidamente ficheiros muito grandes. Além das preocupações com o armazenamento e, em alguns casos, a transmissão, torna-se extremamente difícil encontrar informações importantes nesses ficheiros. Nesta dissertação, procuramos a melhor solução para os dois problemas estudando e implementando soluções de compressão de dados para reduzir os ficheiros referidos. O foco principal foi compressão de imagem/video, de longe, os dados que consomem mais armazenamento. Além disso, realizamos um estudo detalhado sobre o efeito de compressão com perdas no desempenho de alguns algoritmos de análise de imagem estado da arte. Outra contribuição foi o desenvolvimento de um leitor de vídeo inteligente para ajudar os roboticistas no seu trabalho enquanto avaliam os dados gravados. Partes do vídeo que não contêm informações relevantes são aceleradas durante a leitura. Com base nos resultados, concluímos que a compressão nativa de ROS não é suficiente. Além disso, soluções baseadas em ROS, ou de um modo geral qualquer sistema robótico que precise de lidar com dados de imagem/vídeo, beneficiaria com o uso de um codec H.265, uma vez que fornece o menor número de bits por pixel sem penalização significativa da eficiência dos algoritmos de análise de imagem.Mestrado em Engenharia de Computadores e Telemátic