Davide Gadia

... ment. The resolution of the final result here presented is not the most adequate to eliminate the stripes effect and to fully display the desidered effect, but however still is remarkable the green-blue shade of the object on the lower right. Original image courtesy of Wendy Carlos. ...

... 39–45 (2007) 2. Levoy, M., Pulli, K., Curless, B., Rusinkiewicz, S., Koller, D., Pereira, L., Gintzon, M., Anderson, S., David, J., Ginsberg, J ... 145–154 (2004) 7. Ruiz, R., Weghorst, S., Savage, J., Oppenheimer, P., Furness, TA, Dozal, Y.: Virtual Reality for Archeological Maya Cities. ...

ABSTRACT Brain-Computer Interfaces (BCIs) provide users communication and control capabilities by analyzing their brain activity. A technique to implement BCIs, used recently also in Virtual Reality (VR) environments, is based on the Steady State Visual Evoked Potentials (SSVEPs) detection. Exploiting the SSVEP response, BCIs could be implemented showing targets flickering at different frequencies and detecting which is gazed by the observer analyzing her/his electroencephalographic (EEG) signals. In this work, we evaluate the use of stereoscopic displays for the presentation of SSVEP eliciting stimuli, comparing their effectiveness between monoscopic and stereoscopic stimuli. Moreover we propose a novel method to elicit SSVEP responses exploiting the stereoscopic displays capability of presenting dichoptic stimuli. We have created an experimental scene to present flickering stimuli on an active stereoscopic display, obtaining reliable control of the targets’ frequency independently for the two stereo views. Using an EEG acquisition device, we analyzed the SSVEP responses from a group of subjects. From the preliminary results, we got evidence that stereoscopic displays represent valid devices for the presentation of SSVEP stimuli. Moreover, the use of different flickering frequencies for the two views of a single stimulus proved to elicit non-linear interactions between the stimulation frequencies, clearly visible in the EEG signal. This suggests interesting applications for SSVEP-based BCIs in VR environments able to overcome some limitations imposed by the refresh frequency of standard displays, but also the use of commodity stereoscopic displays to implement binocular rivalry experiments.

Tuning Retinex for HDR Images Visualization / Davide Gadia, Daniele Marini, Alessandro Rizzi - In: Final programme and proceedings of CGIV 2004, Second European Conference on Color in Graphics, Imaging, and Vision and Sixth International Symposium on Multispectral ...

In real world no color exists. Only spectral light distributions interact to form the final color sensation. This paper presents preliminary experiments whose purpose is to test the robustness of a spatial color computation in relation to changes in the acquisition of spectral information. The basic idea is that human vision system has evolved into a robust system to acquire visual information, in this case the color, adapting to varying illumination conditions to guarantee color constancy. The presented experiments test changes in the output of a Retinex-derived tone mapping operator, varying illuminants and color matching function curves. Synthetic high dynamic range multispectral images have been computed by a photometric ray tracer using different illuminants. Then, using standard and modified color matching functions, a set of high dynamic range RGB images has been created. This set has been converted to standard RGB images using a linear tone mapping algorithm with no spatial color computation and one based on Retinex, performing a spatial color normalization. A discussion of the results is presented.

A relevant problem in the evaluation of illumination conditions on ancient paintings and frescos is the needing of some kind of measure of the perceived light not only from a metrological point of view, but also considering the visual perception of the observers. In this paper, we propose a comparison between different lightness definitions applied to lighting measurements acquired by Imaging Luminance Measurement Device (ILMD) on paintings illuminated by daylight, in order to setup a more comprehensive system to evaluate the effective quality of the illumination of museums and art galleries. We actually considered some well-known lightness definitions working on the global image, but we want to investigate local adaptation algorithms.

ABSTRACT A colorimeter is a common tool used for the profiling of visualization devices. Different kinds of colorimeters can be found on the market, with different characteristics and performances. They are based on different working principles, from tristimulus colorimeters to actual spectrophotometers and their prices range from few hundreds to thousands of Euros. In this work we describe and analyze a recently introduced colorimeter which may be of particular interest for the research community, since it is an open hardware project and that, consequently, grants the public availability of data about its hardware and its firmware together with device drivers as free software.

In real world no color exists. Only spectral light distributions interact to form the final color sensation. This paper presents preliminary experiments whose purpose is to test the robustness of a spatial color computation in relation to changes in the acquisition of spectral information. The basic idea is that human vision system has evolved into a robust system to acquire visual information, in this case the color, adapting to varying illumination conditions to guarantee color constancy. The presented experiments test changes in the output of a Retinex-derived tone mapping operator, varying illuminants and color matching function curves. Synthetic high dynamic range multispectral images have been computed by a photometric ray tracer using different illuminants. Then, using standard and modified color matching functions, a set of high dynamic range RGB images has been created. This set has been converted to standard RGB images using a linear tone mapping algorithm with no spatial color computation and one based on Retinex, performing a spatial color normalization. A discussion of the results is presented.

Tuning Retinex for HDR Images Visualization / Davide Gadia, Daniele Marini, Alessandro Rizzi - In: Final programme and proceedings of CGIV 2004, Second European Conference on Color in Graphics, Imaging, and Vision and Sixth International Symposium on Multispectral ...