Extension of a human visual system model for display simulation C´ edric Marchessoux 1 , Alexis Rombaut 2 , Tom Kimpe 1 , Brecht Vermeulen 2 and Piet Demeester 2 1 : BARCO N.V., Medical Imaging Division, President Kennedypark 35, 8500 Kortrijk, Belgium 2 : Ghent University, INTEC, Gaston Crommenlaan 8 bus 201, Ghent, Belgium ABSTRACT In the context of medical display validation, a simulation chain has been developed to facilitate display design and image quality validation. One important part is the human visual observer model to quantify the quality perception of the simulated images. Since several years, multiple research groups are modeling the various aspects of human perception to integrate them in a complete Human Visual System (HVS) and developing visible image difference metrics. In our framework, the JNDmetrix is used. It reflects the human subjective assessment of images or video fidelity. Nevertheless, the system is limited and not suitable for our accurate simulations. There is a limitation to RGB 8 bits integer images and the model takes into account display parameters like gamma, black offset, ambient light... It needs to be extended. The solutions proposed to extend the HVS model are: precision enhancement to overcome the 8 bit limit, color space conversion between XYZ and RGB and adaptation to the display parameters. The preprocessing does not introduce any kind of perceived distortion caused for example by precision enhancement. With this extension the model is used in a daily basis in the display simulation chain. Keywords: Human Visual System Modeling, Image Quality, Display simulation 1. INTRODUCTION In the context of a new methodology to compare and validate medical displays, a virtual medical imaging chain, starting from simulation of the image acquisition, over a hardware and software image processing pipeline, ending in the visualization by the medical specialist on the image display was developed. 1 The virtual image chain has been developed for quantifying perceived and clinical quality of medical displays (Medical Virtual Image Chain: MEVIC). This image chain is inspired from the Image Quality Circle developed by Engeldrum. 2–4 Thanks to the Image Quality Circle, the correlation between perceived judgments and physical parameters can be found. The virtual image chain is modeled as a cascade of three main modules: ”virtual image capture”, ”virtual display” and a ”virtual specialist”. The figure 1 represents the framework of the medical virtual image chain with the cascade or pipeline of three modules. One of the most important modules is the virtual specialist or in other words: the Human Visual Observer Model (HVOM). The output of the display simulation is a map of colored intensities corresponding to each individual pixel colored intensity distribution in cd/m 2 . The color space representation is XYZ developed by the CIE (Commission Internationale de l’´ eclairage) in 1931. Simply speaking, outcome from the display are pixels in floating point values and are the input of the HVOM. Therefore, a suitable HVOM has to be found in the literature, adapted or developed. Considerable research by various groups went into the study and the integration of various aspects of human perception in Human Visual System (HVS) modeling and developing visible image difference metrics to quantify perceived differences between two images. Some complete HVS models proposed in the literature such as the Visible Differences Predictor 5 or the Just Noticeable Metrix-IQ from Sarnoff institute, 6 result in visible differences maps, combining subjective and objective factors. In our framework, the JNDmetrix is used thanks to the program JNDMetrix-IQ, a discontinued commercial product of Sarnoff Corporation for the computation of the JND. This module, called ”JNDModule” in the MEVIC platform, is the first Human Visual Observer Model. Further author information: (Send correspondence to Alexis Rombaut or C´ edric Marchessoux) Alexis Rombaut: E-mail: Alexis.Rombaut@intec.ugent.be, Telephone: +32 9 331 49 79 C´ edric Marchessoux: E-mail: cedric.marchessoux@barco.com, Telephone: +32 56 233 533 1