Maurizio Rossi

Color management and color perception issues in a virtual reality theater

In the last years, relevant efforts have been dedicated to the development of advanced technological solutions for immersive visualization of Virtual Reality (VR) scenarios, with particular attention to stereoscopic images formation. Among the various solution proposed, INFITECTM technology is particularly interesting, because it allows the reproduction of a more accurate chromatic range than anaglyphs or polarization-based approaches. Recently, this technology was adopted in the Virtual Theater of the University of Milan, an immersive VR installment, used for research purposes in the fields of Human-machine interaction and photorealistic, perceptual-based, visualization of virtual scenarios. In this paper, we want to present a first set of measures related to the determination of an accurate chromatic, colorimetric and photometric characterization of this visualization system. The acquired data are analyzed in order to evaluate the efective inter-calibration between the four devices and for the determination of an accurate description of the actual effect of the INFITECTM technology. This analysis will be the basis for the future integration of visual perception and color appereance principles in the visualization pipeline, and for the development of robust computational models and instruments for a correct color management in the visualization of immersive virtual environments.

Postfiltering for color appearance in synthetic image visualization

In the photorealistic image synthesis process, an accurate approximation of the spectral light radiance field of a synthetic scene is carefully reproduced, with the goal of generating a synthetic image that is indistinguishable from the actual one. The paradigm of photorealism requires a comparison of the real scene and its synthetic reproduction, and the two visual representations should be studied under the same conditions to make a correct comparison and evaluate the degree of accuracy. To reproduce the same observing conditions, we need to define a sort of synthetic observer (given the impossibility to enter into a synthetic world) to compensate the deep differences in the viewing conditions, between the real and synthetic images. Various solutions have been proposed to this end; most of them are based more on perceptive measures of the human visual system (HVS) under controlled conditions, rather than on the HVS behavior under real conditions, e.g., observing a natural image and not a controlled black and white or colored pattern. Besides the comparison problem, difficulties can arise from the visualization phase, whose purpose is to display the final results of the simulation model on a monitor screen or printed paper. This is known as the tone reproduction problem, and in most cases, one has to find the best solution to compress an extended dynamic range of the computed light field into the limited range of displayable colors. Several solutions have been proposed to solve this problem. On the contrary, no mapping is usually made in case of low luminance and extremely limited dynamic range images, and consequently photorealism and visual appearance are lost. We propose a working hypothesis to solve the appearance and the tone reproduction problems in the synthetic image generation, integrating the Retinex model into the photorealistic image synthesis context, including in this way a model of the HVS in the image synthesis process.

Photorealistic rendering over the Internet for restoration support of ancient buildings

In the field of cultural heritage restoration, experts are extremely interested in the analysis of the large amounts of data describing the condition and history of ancient monuments. In this paper we describe a method and its implementation for providing high quality photorealistic image synthesis of ancient buildings over the Internet through VRML and Java technology. A network-based Java application manages geometric 3D VRML models of an ancient building to provide an interface to add information and to compute high quality photorealistic snapshots of the entire model or any of its parts. The poor quality VRML real time rendering is upheld by a slower but more accurate rendering computed on a radiometric basis. The input data for this advanced rendering is taken form the geometric VRML model. We have also implemented some extensions to provide spectral dat including the measurement of light and materials obtained experimentally. The interface to access the ancient building database is descriptive VRML model itself. The Java application enhances the interaction with the model to provide and manage high quality images that allow visual qualitative evaluation of restoration hypotheses by providing a tool to improve the appearance of the resulting image under assigned lighting conditions.

Post-filtering for color appearance in synthetic-image tone reproduction

In the Photorealistic Image Synthesis process the spectral content of the synthetic scene is carefully reproduced, and the final output contains the exact spectral intensity light field of the perceived scene. This is the first important step toward the goal of producing a synthetic image that is indistinguishable from the actual one, but the real scene and its synthetic reproduction should be studied under the same conditions, in order to make a correct comparison and evaluate the degree of photorealism. To simplify this goal, a synthetic observer could be employed to compensate differences in the viewing conditions, since a real observer cannot enter into a synthetic world. Various solutions have been proposed to this end. Most of them are based more on perceptive measures of the Human Visual System (HVS) under controlled conditions rather than on the HVS behaviour under real conditions, e.g., observing a common image and not a controlled black and white striped pattern. Another problem in synthetic image generation is the visualization phase, or tone reproduction, whose purpose is to display the final result of the simulation model on a monitor screen or on a printed paper. The tone reproduction problem consists of finding the best solution to compress the extended dynamic range of the computed light field into the limited range of the displayable colors. We would like to propose a working hypothesis to solve the appearance and the tone reproduction problems in the synthetic image generation, integrating the Retinex model into the photorealistic image synthesis context, including in this way a model of the human visual system in the synthesis process.

Representation of chromatic distribution for lighting system

For the luminaire manufacturer, the measurement of the lighting intensity distribution (LID) emitted by lighting fixture is based on photometry. So light is measured as an achromatic value of intensity and there is no the possibility to discriminate the measurement of white vs. colored light. At the Laboratorio Luce of Politecnico di Milano a new instrument for the measurement of spectral radiant intensities distribution for lighting system has been built: the goniospectra- radiometer. This new measuring tool is based on a traditional mirror gonio-photometer with a CCD spectraradiometer controlled by a PC. Beside the traditional representation of photometric distribution we have introduced a new representation where, in addition to the information about the distribution of luminous intensity in space, new details about the chromaticity characteristic of the light sources have been implemented. Some of the results of this research have been applied in developing and testing a new line of lighting system “My White Light” (the research project “Light, Environment and Humans” funded in the Italian Lombardy region Metadistretti Design Research Program involving Politecnico di Milano, Artemide, Danese, and some other SME of the Lighting Design district), giving scientific notions and applicative in order to support the assumption that colored light sources can be used for the realization of interior luminaries that, other than just have low power consumption and long life, may positively affect the mood of people.

AdvanceDesign in Lighting

This paper intends to lay the investigative basis on the elements that contribute to design, in terms of conditions and practices useful in encouraging continuous innovation, in the field of Lighting Design. Advance Lighting Design (ALD) and its vision are presented as a multidisciplinary approach, which should not be understood within the limitations of a pluridisciplinary approach, that simply combines different skills, mainly for the purpose of comparison, but rather employs interdisciplinary methodologies that, through mixing different types of knowledge, try to extract a new epistemology. The paper provides also case histories that exemplify ALD experiences.