A human visual system based image coder

Over the years, society has changed considerably due to technological changes, and digital images have become part and parcel of our everyday lives. Irrespective of applications (i.e., digital camera) and services (information sharing, e.g., Youtube, archive / storage), there is the need for high image quality with high compression ratios. Hence, considerable efforts have been invested in the area of image compression. The traditional image compression systems take into account of statistical redundancies inherent in the image data. However, the development and adaptation of vision models, which take into account the properties of the human visual system (HVS), into picture coders have since shown promising results. The objective of the thesis is to propose the implementation of a vision model in two different manners in the JPEG2000 coding system: (a) a Perceptual Colour Distortion Measure (PCDM) for colour images in the encoding stage, and (b) a Perceptual Post Filtering (PPF) algorithm for colour images in the decoding stage. Both implementations are embedded into the JPEG2000 coder. The vision model here exploits the contrast sensitivity, the inter-orientation masking and intra-band masking visual properties of the HVS. Extensive calibration work has been undertaken to fine-tune the 42 model parameters of the PCDM and Just-Noticeable-Difference thresholds of the PPF for colour images. Evaluation with subjective assessments of PCDM based coder has shown perceived quality improvement over the JPEG2000 benchmark with the MSE (mean square error) and CVIS criteria. For the PPF adapted JPEG2000 decoder, performance evaluation has also shown promising results against the JPEG2000 benchmarks. Based on subjective evaluation, when both PCDM and PPF are used in the JPEG2000 coding system, the overall perceived image quality is superior to the stand-alone JPEG2000 with the PCDM

Spread spectrum-based video watermarking algorithms for copyright protection

Merged with duplicate record 10026.1/2263 on 14.03.2017 by CS (TIS)Digital technologies know an unprecedented expansion in the last years. The consumer can now benefit from hardware and software which was considered state-of-the-art several years ago. The advantages offered by the digital technologies are major but the same digital technology opens the door for unlimited piracy. Copying an analogue VCR tape was certainly possible and relatively easy, in spite of various forms of protection, but due to the analogue environment, the subsequent copies had an inherent loss in quality. This was a natural way of limiting the multiple copying of a video material. With digital technology, this barrier disappears, being possible to make as many copies as desired, without any loss in quality whatsoever. Digital watermarking is one of the best available tools for fighting this threat. The aim of the present work was to develop a digital watermarking system compliant with the recommendations drawn by the EBU, for video broadcast monitoring. Since the watermark can be inserted in either spatial domain or transform domain, this aspect was investigated and led to the conclusion that wavelet transform is one of the best solutions available. Since watermarking is not an easy task, especially considering the robustness under various attacks several techniques were employed in order to increase the capacity/robustness of the system: spread-spectrum and modulation techniques to cast the watermark, powerful error correction to protect the mark, human visual models to insert a robust mark and to ensure its invisibility. The combination of these methods led to a major improvement, but yet the system wasn't robust to several important geometrical attacks. In order to achieve this last milestone, the system uses two distinct watermarks: a spatial domain reference watermark and the main watermark embedded in the wavelet domain. By using this reference watermark and techniques specific to image registration, the system is able to determine the parameters of the attack and revert it. Once the attack was reverted, the main watermark is recovered. The final result is a high capacity, blind DWr-based video watermarking system, robust to a wide range of attacks.BBC Research & Developmen

The aceToolbox: low-level audiovisual feature extraction for retrieval and classification

In this paper we present an overview of a software platform that has been developed within the aceMedia project, termed the aceToolbox, that provides global and local lowlevel feature extraction from audio-visual content. The toolbox is based on the MPEG-7 eXperimental Model (XM), with extensions to provide descriptor extraction from arbitrarily shaped image segments, thereby supporting local descriptors reflecting real image content. We describe the architecture of the toolbox as well as providing an overview of the descriptors supported to date. We also briefly describe the segmentation algorithm provided. We then demonstrate the usefulness of the toolbox in the context of two different content processing scenarios: similarity-based retrieval in large collections and scene-level classification of still images