Modèle de perception couleur. Application à l'évaluation de qualité d'images
Color perception model. Application to image quality assessment
OPEN ACCESS
The design of image visual quality objective criteria is very useful in order to optimize the performances of image processing systems for storage and transmission of visual data. An objective quality criterion should provide quality measures in good correspondence with human judgment. So, it is necessary to introduce the main properties of the human visual system (HSV) in the design of such a criterion.
This paper presents a very elaborated model of color images perception by the HVS. It takes into account and models in a coherent way the key functions of human perception: visual space for color representation, contrast sensitivity functions for achromatic and chromatic components respectively, perceptual channels decomposition, intra and inter pathways masking functions. All these models have been deduced from the interpretation of results of psychophysics experiments. Next, we present an application of the perception model to the design of an objective quality criterion with full reference for color images. This application is based on a critical analysis of different ways to construct the pooling function of perceived errors including inter-pathway pooling, inter-channel pooling and spatial pooling. The entire objective quality criterion have been tested on a database of natural color images which have been stressed with distortions of different nature and strength. Performances in terms of correlation with mean human judgment is more than 0.94 and 97 % of images are correctly assessed according to the accuracy on the subjective rate given by observers.
Résumé
La conception de critères objectifs d'évaluation de qualité visuelle des images est d'une grande utilité afin d'optimiser les performances des systèmes de traitement d'images pour le stockage et la transmission de l'information visuelle. Un critère objectif de qualité doit fournir des mesures de qualité en forte correspondance avec le jugement humain. Il est donc nécessaire d'intégrer des modèles des principales propriétés du système visuel humain dans la conception d'un tel critère. Ce papier présente un modèle très élaboré de perception des images couleur par le système visuel humain (SVH). Il prend en compte et modélise de façon cohérente les fonctions clé de la perception : espace de représentation visuelle des couleurs, fonctions de sensibilité aux contrastes des composantes achromatique et chromatiques, décomposition en canaux perceptifs, fonctions de masquage intra et inter composante. Tous ces modèles ont été déduits à partir de résultats de tests psychophysiques et de leur interprétation. L'application du modèle de perception à la conception d'un critère objectif de qualité d'images couleur avec image de référence est ensuite effectuée. Elle se base sur une analyse critique des différentes façons de construire une fonction de cumul des dégradations perçues: cumul inter-composante, cumul inter-canal, cumul spatial. L'ensemble du critère objectif de qualité a été testé sur une base d'images naturelles couleur ayant subies des dégradations de nature et de force différentes. Les performances en terme de corrélation avec le jugement humain moyen est supérieure à 0,94 et 97 % des images sont correctement évaluées au regard de la précision sur les notes subjectives données par l'humain.
Quality assessment, human color perception, masking effect, psychovisual color space
Mots clés
Évaluation de qualité, perception couleur humaine, effet de masquage, espace couleur psychovisuel
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