Publications by Touradj Ebrahimi

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In the last years, light field imaging has experienced a surge of popularity among the scientific community for its capability of rendering the 3D world in a more immersive way. In particular, several compression algorithms have been proposed to efficientl ...

Crowdsourcing is becoming a popular cost effective alternative to lab-based evaluations for subjective quality assessment. However, crowd-based evaluations are constrained by the limited availability of display devices used by typical online workers, which ...

The Joint Photographic Experts Group (JPEG) is currently in the process of standardizing JPEG XL, the next generation image coding standard that o↵ers substantially better compression efficiency than existing image formats. In this paper, the quality assessment framework of proposals submitted to the JPEG XL Call for Proposals is presented in details. The proponents were evaluated using objective metrics and subjective quality experiments in three di↵erent laboratories, on a dataset constructed for JPEG XL

While the emerging MPEG-4 standard has raised the need for efficient object-based compression, the future MPEG-7 standard motivates further research in the field of progressive, quality-scalable, and semantic representations for indexing and retrieval applications in particular. In this paper a mesh-based video compression scheme is proposed that integrates shape, motion and texture representations in a consistent way and provides a content-based, quality-scalable, separate bitstream syntax. A complete vide

High bit depth data acquisition and manipulation have been largely studied at the academic level over the last 15 years and are rapidly attracting interest at the industrial level. An example of the increasing interest for high-dynamic range (HDR) imaging ...

Replica detection is a prerequisite for the discovery of copyright infringement and detection of illicit content. For this purpose, contentbased systems can be an efficient alternative to watermarking. Rather than imperceptibly embedding a signal, content-based systems rely on image similarity. Certain content-based systems use adaptive classifiers to detect replicas. In such systems, a suspect image is tested against every original, which can become computationally prohibitive as the number of original ima

The ability of High Dynamic Range imaging (HDRi) to capture details in high-contrast environments, making both dark and bright regions clearly visible, has a strong implication on privacy. However, the extent to which HDRi affects privacy when it is used instead of typical Standard Dynamic Range imaging (SDRi) is not yet clear. In this paper, we investigate the effect of HDRi on privacy via crowdsourcing evaluation using the Microworkers platform. Due to the lack of HDRi standard privacy evaluation dataset,

The compression of visual information in the framework of multimedia applications is discussed. To this end, major approaches to compress still as well as moving pictures are reviewed. The most important objective in any compression algorithm is that of compression efficiency. High-compression coding of still pictures can be split into three categories: waveform, second-generation, and fractal coding techniques. Each coding approach introduces a different artifact at the target bit rates. The primary object

The ability of high dynamic range (HDR) to capture details in environments with high contrast has a significant impact on privacy in video surveillance. However, the extent to which HDR imaging affects privacy, when compared to a typical low dynamic range (LDR) imaging, is neither well studied nor well understood. To achieve such an objective, a suitable dataset of images and video sequences is needed. Therefore, we have created a publicly available dataset of HDR video for privacy evaluation PEViD-HDR, whi

We present an automatic content-based video transcoding algorithm which is based on how humans perceive visual information. The transcoder support multiple video objects and their description. First the video is decomposed into meaningful objects through semantic segmentation. Then the transcoder adapts its behaviour to code relevant (foreground) and non relevant objects differently. Both objectbased and frame-based encoders are combined with semantic segmentation. Experimental results show that the use of

Universal Multimedia Access (UMA) refers to the ability to access by any user to the desired multimedia content(s) over any type of network with any device from anywhere and anytime. UMA is a key framework for multimedia content delivery service using metadata. This report consists of three parts. The first part of this report analyzes the state-of-the-art technologies in UMA, identifies the key issues and gives what are the new challenges that still remain to be resolved in UMA. The key issues in UMA inclu

Current image coding standards provide limited support for privacy and security features. An exception is the JPSEC standard, which defines security extensions in JPEG 2000 specifications (part 8). Notwithstanding this shortcoming, the JPEG committee is cu ...

In this paper we describe a database containing subjective assessment scores relative to 78 video streams encoded with H.264/AVC and corrupted by simulating the transmission over error-prone network. The data has been collected from 40 subjects at the prem ...

In this paper, we present full-reference as well as no-reference metrics for typical JPEG 2000 compression artifacts, namely blur and ringing. These metrics are based on an analysis of the edges and adjacent regions in an image. Their perceptual significance is corroborated through subjective experiments. The proposed measurement algorithms are shown to perform well over a wide range of image content and compression ratios. They have low computational complexity and are near real-time. Potential application

Gradient boosting is a machine learning method, that builds one strong classifier from many weak classifiers. In this work, an algorithm based on gradient boosting is presented, that detects event-related potentials in single electroencephalogram (EEG) trials. The algorithm is used to detect the P300 in the human EEG and to build a brain-computer interface (BCI), specifically a spelling device. Important features of the method described here are its high classification accuracy and its conceptual simplicity

Assessing and comparing the performance of watermarking algorithms is di cult.The visibility of the watermark is an important aspect in this process.In this paper,we propose two metrics for evaluating the visual impact of video watermarks.Based on several different watermarking algorithms and video sequences,we identify the most prominent impairments as spatial noise and temporal icker.We design the corresponding measurement algorithms and corroborate their performance through subjective experiments.

With the growing ubiquity and mobility of multimedia-enabled devices, universal multimedia access (UMA) is emerging as one of the important components for the next generation of multimedia applications. The basic concept underlying UMA is universal or seamless access to multimedia content, by automatic selection and adaptation of content based on the user's environment. UMA promises an integration of these different perspectives into a new class of content adaptive applications that could allow users to acc

The procedures commonly used to evaluate the performance of objective quality metrics rely on ground truth mean opinion scores and associated confidence intervals, which are usually obtained via direct scaling methods. However, indirect scaling methods, su ...

Olfactory perception is a complex phenomenon associated with other processes such as cognition and emotion. Due to this complexity, there are still open issues and challenges regarding olfactory psychophysiology. One challenge concerns the investigation of ...

High Dynamic Range (HDR) imaging is expected to become one of the technologies that could shape next generation of consumer digital photography. Manufacturers are rolling out cameras and displays capable of capturing and rendering HDR images. The popularit ...

Touradj Ebrahimi

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VALID: Visual quality Assessment for Light field Images Dataset

Crowd-based quality assessment of multiview video plus depth coding

Assessment of quality of JPEG XL proposals based on subjective methodologies and objective metrics

Progressive mesh-based coding of arbitrary-shaped video objects

JPEG XT: A Compression Standard for HDR and WCG Images [Standards in a Nutshell]

A Novel Replica Detection System using Binary Classifiers, R-trees, and PCA

Crowdsourcing-based Evaluation of Privacy in HDR Images

Visual Data Compression for Multimedia Applications

Evaluation of privacy in high dynamic range video sequences

Semantic Segmentation and Description for Video Transcoding

New Frontiers in Universal Multimedia Access

JPEG Privacy and Security framework for social networking and GLAM services

Subjective assessment of H.264/AVC video sequences transmitted over a noisy channel

Perceptual Blur and Ringing Metrics: Application to JPEG2000

A Boosting Approach to P300 Detection with Application to Brain-Computer Interfaces

Toward perceptual metrics for video watermark evaluation.

Metadata-driven multimedia access

How to Benchmark Objective Quality Metrics from Paired Comparison Data?

Multivariate Spectral Analysis for Identifying the Brain Activations During Olfactory Perception

A JPEG backward-compatible HDR image compression