This paper addresses the problem of quality estimation of digitally coded video sequences. The topic is of great interest since many products in digital video are about to be released and it is thus important to have robust methodologies for testing and performance evaluation of such devices. The inherent problem is that human vision has to be taken into account in order to assess the quality of a sequence with a good correlation with human judgment. It is well known that the commonly used metric, the signal-to-noise ratio is not correlated with human vision. A metric for the assessment of video coding quality is presented. It is based on a multi-channel model of human spatio-temporal vision that has been parameterized for video coding applications by psychophysical experiments. The visual mechanisms of vision are simulated by a spatio-temporal filter bank. The decomposition is then used to account for phenomena as contrast sensitivity and masking. Once the amount of distortions actual...

This paper describes a spatio-temporal model of the human visual system (HVS) for video imaging applications, predicting the response of the neurons of the primary visual cortex. The model simulates the behavior of the HVS with a three-dimensional filter bank which decomposes the data into perceptual channels, each one being tuned to a specific spatial frequency, orientation and temporal frequency. It further accounts for contrast sensitivity, inter-stimuli masking and spatio-temporal interaction. The free parameters of the model have been estimated by psychophysics. The model can then be used as the basis for many applications. As an example, a quality metric for coded video sequences is presented. 1. INTRODUCTION Impressive progresses have been made during the last decade in the field of still image and video processing. The importance that visual information and communication took in today's society gave birth to an increasing demand for fast and efficient ways of transmitting visu...

In this paper, a computational metric that incorporates many aspects of human vision and color perception to predict the quality of color coded images is presented. The proposed distortion measure is built on opponentcolors theory and on a multi-channel model of spatial vision. The metric has been validated by psychophysical data on 400 images and two human observers. 1 INTRODUCTION Image quality assessment is an important and yet unsolved problem in image processing. For years, engineers have been designing and testing devices using the peak signal-to-noise ratio (PSNR) despite the fact that it is rarely correlated with human judgment. The inherent problem with the PSNR is that it does not take into account viewing conditions and spatial pattern sensitivity. The most recently published computational metrics for image quality assessment have incorporated vision models for spatial pattern sensitivity and visual masking [1--3, 10]. This paper extends one of these metrics [1] to include...

Digital images have become an important source of information in the modern world of communication systems. In their raw form, digital images require a tremendous amount of memory. Many research efforts have been devoted to the problem of image compression in the last two decades. Two different compression categories must be distinguished: lossless and lossy. Lossless compression is achieved if no distortion is introduced in the coded image. Applications requiring this type of compression include medical imaging and satellite photography. For applications such as video--telephony or multimedia applications some loss of information is usually tolerated in exchange for a high compression ratio.

This paper presents a process able to mark digital pictures with an invisible and undetectable secrete information, called the watermark. This process can be the basis of a complete copyright protection system. The process first step consists in producing a secrete image . The first part of the secret resides in a basic information that forms a binary image. That picture is then frequency modulated. The second part of the secret is precisely the frequencies of the carriers. Both secrets depends on the identity of the copyrightowner and on the original picture contents. The obtained picture is called the stamp. The second step consists in modulating the ampitude of the stamp according to a masking criterion stemming from a model of human perception. That too theoretical criterion is corrected by means of morphological tools helping to locate in the picture the places where the criterion is supposed not to match. This is followed by the adaptation of the level of the stamp at that places. The so formed watermark is then added to the original to ensure its protection. That watermarking method allows the detection of watermarked pictures in a stream of digital images, only with the knowledge of the picture owner's secrets. Keywords: copyright protection, watermark, secrete key, masking, human vision model, perceptivecomponents, morphology, robustness, detection, correlation. 1 GENERAL

This paper presents an additivewatermarking technique for grey scale pictures, which can be extended to video sequences. It consists of embedding secretly a copyright information (a binary code) in the picture without degrading its quality. Those bits are encoded through the phase of Maximal Length Sequences (MLS). MLS are sequences having good correlation properties, which means that the result of the autocorrelation is far greater than crosscorrelations, i.e. correlations made with shifted version of this sequence. This embedding is performed line by line going from the top to the bottom of the picture as the objectivewas to implementalow cost and real time embedding method able to work for common video equipments. The very embedding process is underlain by a masking criterion that guarantees the invisibility of the watermark. This perceptive criterion, deduced from physiological and psychophysic studies, has already proved its efficiency in a previously presented paper (Conference SPIE '96). It is combined with an edge and texture discrimination to determine the embedding level of the MLS, whose bits are actually spread over 32 by 8 pixel squares. Eventually, some preliminary results are presented, which analyze the efficacy of the decoding as well as the resistance of the watermark towards compression and robustness against malevolent treatments.

In this paper, we wish to present a process enabling to mark digital pictures with invisible and undetectable secret information. This so-called watermarking process is intended to be the basis of a complete copyright protection system. It consists in constructing a band-limited image from binary sequences with good correlation properties and in modulating some randomly selected carriers. The security relies on the secrecy of these carrier frequencies, which are deduced from a unique secret key. Then the amplitude of the modulated images is modified according to a masking criterion based on a model of the Human Visual System. The adding of the modulated images to the original is supposed to be invisible. The resulting image fully identifies the Copyright Owner since he is the only one able to detect and prove the presence of the embedded watermark thanks to his secret key. This paper also contains an analysis of the robustness of the watermark against compression and image processing. work supported by a grant F.N.R.S. - Alcatel Bell 1 General introduction The emerging new digital image services and the rapid developmentofmultimedia services rely not only on the increasing availability of digital networks and servers but also on efficient security tools. Among them, there is, nowadays, a strong need for suitable techniques to protect the work authors' and providers' interests 1 . Indeed, the nature of digital media itself threatens its own viability: ffl First, the digital replication of digital works is not only easy but also perfect. ffl The ease of transmission and multiple uses is worrying too. Once a single illegal copy has been made, it is instantaneously widely accessible, without anycontrol of the owner of the original picture. ffl Finally, the plast...

This paper attempts to present a survey of quantitative quality/impairment metrics based on human visual sensitivity, and to describe a couple of quantitative metrics recently developed and reported for digital image and video coding.

Digital watermarking consists of hiding subliminal information into digital media content, also called host data. It can be the basis of many applications, including security and media asset management. In this paper, we focus on the imperceptibility requirement for image watermarking. We present the main features of the Human Visual System (HVS) to be translated into watermarking technology. This paper highlights the need for dedicated inputs from the human vision community.

This work addresses the optimization of TVresolution MPEG-2 video streams to be transmitted over packet networks facing a given packet loss probability. Several studies have already been carried out on this speci c problem [1, 2, 3]. The main contribution of this work resides in the design of a new exible scene-complexity adaptive mechanism, namely the Perceptual Syntactic Information Coding (PSIC) mechanism. The PSIC adaptively modulates the number of macroblocks per slice in order to optimize the global video qualitywhichdepends on both the video encoding quality and the video degradations due to data loss during the transmission. We compare its performance against a xed-length slice scheme to be transmitted over ATM networks using AAL-5. All the quality assessments are based on a perceptual quality metric, MPQM 1, whichproved to behave consistently with human judgements [4]. Results show that the proposed mechanism behaves much better in terms of global perceptual video quality. 1.