Cristian Bonanomi

Assessing stereo blindness and stereo acuity on digital displays

Previous studies on stereoscopic acuity have shown that the percentage of stereo blind subjects is relevant. Moreover, stereoscopic visualization is becoming widely diffused in different fields, like, e.g., entertainment, surgery or VR training, where it is necessary an accurate assessment of stereoscopic abilities of the involved subjects. Therefore, there might be the need of performing a stereo blindness and stereo acuity test before each visualization session involving stereoscopic images. In this paper, we propose a method to assess stereo acuity and stereo blindness directly on the chosen device, under the same visualization condition and setup adopted for the tasks to perform, in order to have the same perceptual response. We present software-based tests suitable for a generic stereoscopic displays, and we compare their effectiveness performing a comparison with a standard physical, card-based, test commonly used in assessment of stereo acuity and stereo blindness. We provide to the reader all the details to perform autonomously the tests, of which images will be downloadable from web.

YACCD2: yet another color constancy database updated

In this paper we present an upgraded version of an image database (IDB) presented here in 2003 to test color constancy and other kinds of visual and image processing algorithms. Big technology improvements have been done in the last ten years, however the motivations to present this upgrade are not only technological. We decided to address other visual features related to vision, like dynamic range and stereo vision. Moreover, to address computer vision related problems (e.g. illuminant or reflectance estimation) we have made available a set of data regarding objects, backgrounds and illuminants used. Here we present the characteristics of the images in the IDB, the choice made and the setup of acquisition.

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.

Unsupervised digital movie restoration with spatial models of color

In this paper, we present an efficient approach to digital color restoration, based on the idea of recovering the appearance of color rather than the original color signal, since, in most of the cases, for old films the original reference is missing, and new films or digital coding can be subject to severe gamut transformations. This approach is based on the application of algorithms inspired by the capabilities of the Human Vision System of automatically adjust to the variation of color and lightness in the scene. The proposed method allows more unsupervised restoration. We present an overview of the approach, characteristics of this family of algorithms, and restoration examples.

From printed color to image appearance: tool for advertising assessment

Abstract. We present a methodology to calculate the color appearance of advertising billboards set in indoor and outdoor environments, printed on different types of paper support and viewed under different illuminations. The aim is to simulate the visual appearance of an image printed on a specific support, observed in a certain context and illuminated with a specific source of light. Knowing in advance the visual rendering of an image in different conditions can avoid problems related to its visualization. The proposed method applies a sequence of transformations to convert a four channels image (CMYK) into a spectral one, considering the paper support, then it simulates the chosen illumination, and finally computes an estimation of the appearance.

Milano Retinex family

Abstract. Several different implementations of the Retinex model have been derived from the original Land and McCann’s paper. This paper aims at presenting the Milano-Retinex family, a collection of slightly different Retinex implementations, developed by the Department of Computer Science of Universitá degli Studi di Milano. One important difference is in their goals: while the original Retinex aims at modeling vision, the Milano-Retinex family is mainly applied as an image enhancer, mimicking some mechanisms of the human vision system.

Experimental assessment of color-rendering indices and color appearance under varying setups

The Color-Rendering Index (CRI) for light source is a quantitative measure of the capability to preserve color appearance of illuminated objects. Recently, CRI has had a renewed interest because of the new LED-based lighting systems. These sources usually have a Color-Rendering Index rather low, but a good preservation of color appearance and a pleasant visual appeal. Various attempts to develop a more reliable new color-rendering index have been done so far, but researchers are still working on the topic. This article presents the open issues related to CRI and discusses some of the approaches available in literature. In order to have a baseline to verify the above points, we present an experiment performed with human observers to assess the appearance preservation of a color under a set of light sources. The test protocol uses 3D reference objects and can be used as an alternative way to assess CRI. The results are then compared with a range of available color rendering indices. The goal is not to make a rank among CRIs, rather to assess their variability relative to human judgment through different setups and light sources.

An experiment on the color rendering of different light sources

The color rendering index (CRI) of a light source attempts to measure how much the color appearance of objects is preserved when they are illuminated by the given light source. This problem is of great importance for various industrial and scientific fields, such as lighting architecture, design, ergonomics, etc. Usually a light source is specified through the Correlated Color Temperature or CCT. However two (or more) light sources with the same CCT but different spectral power distribution can exist. Therefore color samples viewed under two light sources with equal CCTs can appear different. Hence, the need for a method to assess the quality of a given illuminant in relation to color. Recently CRI has had a renewed interest because of the new LED-based lighting systems. They usually have a color rendering index rather low, but good preservation of color appearance and a pleasant visual appearance (visual appeal). Various attempts to develop a new color rendering index have been done so far, but still research is working for a better one. This article describes an experiment performed by human observers concerning the appearance preservation of color under some light sources, comparing it with a range of available color rendering indices.

A novel approach to visual rendering of astro-photographs

When we perform a visual analysis of a cosmic object photograph the contrast plays a fundamental role. A linear distribution of the observable values is not necessarily the best possible for the Human Visual System (HVS). In fact HVS has a non-linear response, and exploits contrast locally with different stretching for different lightness areas. As a consequence, according to the observation task, local contrast can be adjusted to make easier the detection of relevant information. The proposed approach is based on Spatial Color Algorithms (SCA) that mimic the HVS behavior. These algorithms compute each pixel value by a spatial comparison with all (or a subset of) the other pixels of the image. The comparison can be implemented as a weighted difference or as a ratio product over given sampling in the neighbor region. A final mapping allows exploiting all the available dynamic range. In the case of color images SCA process separately the three chromatic channels producing an effect of color normalization, without introducing channel cross correlation. We will present very promising results on amateur photographs of deep sky objects. The results are presented for a qualitative and subjective visual evaluation and for a quantitative evaluation through image quality measures, in particular to quantify the effect of algorithms on the noise. Moreover our results help to better characterize contrast measures.

Tuning a computer based stereo blindness assessment

Previous studies on stereoscopic acuity have shown that the percentage of stereo blind subjects is relevant. Therefore, there is the need of performing a stereo blindness and stereo acuity test before each visualization session involving stereoscopic images. In this paper we propose a computer based test suitable for a generic stereo displays, with the aim of testing different visual parameters to design the most efficient test possible.