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2011, Applied Optics
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2013, Journal of the Optical Society of America A
2013, Color Research & Application
repository.lib.ncsu.edu
2014, Journal of the Optical Society of America A
2012, Reflection, Scattering, and Diffraction from Surfaces III
2014, Handbook of Digital Imaging
Andreia Ruivo, Teresa Almeida, Fernando Quintas, Robert Wiley, Magda Troeira, Nuno Paulino, César A.T. Laia, Carlos A. Queiroz, António Pires de Matos, Book of Abstracts, AIC Colour 2013 - 12th Congress of the AIC: "Bringing Colour to Life", 8th-12th July 2013, Newcastle upon Tyne, p. 44.
Lanthanide ions display intense photoluminescence under UV light. When incorporated in glass they are used not only in technological applications, but in artworks as well. Luminescent soda-lime silicate glasses with compositions similar to those used in utilitarian and decorative applications, doped with small amounts of different lanthanide oxides, namely europium, terbium, cerium, dysprosium, samarium and thulium, have been prepared in our laboratories. A few examples of their application in artworks will be presented.
1997, IEEE Transactions on Image Processing
This paper surveys current technology and research in the area of digital color imaging. In order to establish the background and lay down terminology, fundamental concepts of color perception and measurement are first presented using vector-space notation and terminology. Present-day color recording and reproduction systems are reviewed along with the common mathematical models used for representing these devices. Algorithms for processing color images for display and communication are surveyed, and a forecast of research trends is attempted. An extensive bibliography is provided
2004
AIC 2004, Color and Paints, Proceedings of the Interim Meeting of the International Color Association, 356 págs.
2005, Progress in Organic Coatings
2006, Color Research & Application
2012, Journal of the Optical Society of America A
2006, Journal of the Optical Society of America A
A quarter of a century ago, the first systematic behavioral experiments were performed to clarify the nature of color constancy—the effect whereby the perceived color of a surface remains constant despite changes in the spectrum of the illumination. At about the same time, new models of color constancy appeared, along with physiological data on cortical mechanisms and photographic colorimetric measurements of natural scenes. Since then, as this review shows, there have been many advances. The theoretical requirements for constancy have been better delineated and the range of experimental techniques has been greatly expanded; novel invariant properties of images and a variety of neural mechanisms have been identified; and increasing recognition has been given to the relevance of natural surfaces and scenes as laboratory stimuli. Even so, there remain many theoretical and experimental challenges, not least to develop an account of color constancy that goes beyond deterministic and relatively simple laboratory stimuli and instead deals with the intrinsically variable nature of surfaces and illuminations present in the natural world.
Light is used to illuminate objects in the built environment. Humans can only observe light reflected from an object. Light absorbed by an object turns into heat and does not contribute to visibility. Since the spectral output of the new lighting technologies can be tuned, it is possible to imagine a lighting system that detects the colours of objects and emits customised light to minimise the absorbed energy. Previous optimisation studies investigated the use of narrowband LEDs to maximise the efficiency and colour quality of a light source. While these studies aimed to tune a white light source for general use, the lighting system proposed here minimises the energy consumed by lighting by detecting colours of objects and emitting customised light onto each coloured part of the object. This thesis investigates the feasibility of absorption-minimising light source spectra and their impact on the colour appearance of objects and energy consumption. Two computational studies were undertaken to form the theoretical basis of the absorption-minimising light source spectra. Computational simulations show that the theoretical single-peak spectra can lower the energy consumption up to around 38 % to 62 %, and double-peak test spectra can result in energy savings up to 71 %, without causing colour shifts. In these studies, standard reference illuminants, theoretical test spectra and coloured test samples were used. These studies are followed by the empirical evidence collected from two psychophysical experiments. Data from the experiments show that observers find the colour appearance of objects equally natural and attractive under spectrally optimised spectra and reference white light sources. An increased colour difference, to a certain extent, is found acceptable, which allows even higher energy savings. However, the translucent nature of some objects may negatively affect the results.
This anthology starts from the many misunderstandings that often arise when colour and light are discussed. It aims to present different scientific approaches in a broad epistemological perspective, to clarify conflicting use of concepts and to suggest possible ways of improving inter-disciplinary understanding. It is one of the outcomes of the research project SYN-TES: Human colour and light synthesis - towards a coheren field of knowledge. It also includes an introduction written by Professor C.L. Hardin. Available as an e-publication and as printed book at: books.aalto.fi.
2007, Colorimetry
2006, Visual neuroscience
To what extent do observers' judgments of surface color with natural scenes depend on global image statistics? To address this question, a psychophysical experiment was performed in which images of natural scenes under two successive daylights were presented on a computer-controlled high-resolution color monitor. Observers reported whether there was a change in reflectance of a test surface in the scene. The scenes were obtained with a hyperspectral imaging system and included variously trees, shrubs, grasses, ferns, flowers, rocks, and buildings. Discrimination performance, quantified on a scale of 0 to I with a color-constancy index, varied from 0.69 to 0.97 over 21 scenes and two illuminant changes, from a correlated color temperature of 25,000 K to 6700 K and from 4000 K to 6700 K. The best account of these effects was provided by receptor-based rather than colorimetric properties of the images. Thus, in a linear regression, 43% of the variance in constancy index was explained by the log of the mean relative deviation in spatial cone-excitation ratios evaluated globally across the two images of a scene. A further 20% was explained by including the mean chroma of the first image and its difference from that of the second image and a further 7% by the mean difference in hue. Together, all four global color properties accounted for 70% of the variance and provided a good fit to the effects of scene and of illuminant change on color constancy, and, additionally, of changing test-surface position. By contrast, a spatial-frequency analysis of the images showed that the gradient of the luminance amplitude spectrum accounted for only 5% of the variance.
2010, Journal of vision
2012
All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, except as permitted by the UK Copyright, Designs and Patents Act 1988, without the prior permission of the publisher.
2009, Color Research and Application
In this work, we have studied the relationship among the colorimetric properties of different types of paper, having different finishing and grammage. Their color reproduction capability has also been analyzed by using the same printing technology (inkjet printing). On the one hand, we have plotted CIELAB data under the illuminant D50 into constant lightness and hue-angle planes to be compared with MacAdam limits and with Pointer's real-world surface color. On the other hand, we have calculated the volume gamut of the color solid associated to each color paper gamut. Analyzing the results, we have checked that there is not any clear relationship among the colorimetric properties of paper (for instance, CIE whiteness index, etc.) and the color gamut volume associated. However, the colorimetric parameters associated to the printed sample showed a quite good linear correlation between the minimum lightness (or the maximum blackness value) of the printed color chart and the color gamut volume. In particular, the greatest color gamut volume corresponds to the glossy papers taking into account this correlation for inkjet printing. © 2009 Wiley Periodicals, Inc. Col Res Appl, 34, 330–336, 2009
2019, Proceedings of the 29th CIE SESSION
Calculated hue shifts could vary widely for spectrally similar light sources, which suggests a limitation of the current hue shift formulae for non-white light sources. Calculated differences in the hue appearance of 24 colour samples under 279,936 iteratively-generated test SPDs versus two reference illuminants were compared using four hue shift formulae that are based on two widely used colour spaces, CIE 1976 L* a* b* (CIELAB) and colour appearance model 2002 (CAM02). Hue shift equations did not correlate well, even when only nominally "white" light sources were considered. Results suggest that the underlying difference between the hue shift formulae might be the non-uniform scaling of redness-greenness (a) and yellowness-blueness (b) coordinates in CIELAB and CAM02-UCS. A chromatic adaptation transform correction improved the correlation between lightness in CIELAB and CAM02-UCS when the test light sources were nominally "white," but caused irregularities for non-white light sources. Further research is needed for visual assessment of the hue shifts and to evaluate the hue shift formulae.
2016, CIE Lighting Quality and Energy Efficiency Conference 2016, Melbourne: Commission Internationale de L'Eclairage
1997, Applied Optics
A hyperspectral camera based on a novel physical concept has been realized and patented at the National Metrological Research Institute (INRIM). The camera has high light collection capability leading to low exposure times with respect to other hyperspectral techniques. Preliminary results, in the range 400-720 nm, have been presented in 2010. The instrument can generate, for each acquisition, a 3D matrix called “hyperspectral cube” where the first two coordinates are the pixel positions of the scene and the third one is the total spectral information of each pixel. Here we present the upgraded version of the device together with the latest results in color analysis in different scientific fields ranging from biology to cultural heritages. These results show the high spatial and spectral resolution achievable with this hyperspectral camera.
The article explains the basic concepts of colorimetry and deals with issues of assessment reflectance quality of special plaster coatings in accordance with current methods of measuring spectral reflectance of the International Commission on Illumination (CIE). The results demonstrate that in the case of coatings with high gloss values (more than 70 GLS in the geometry 60) leads to a linear increase of specific purity depending on the specific increase luminance in the case of measuring devices fitted diffusion geometry. Conversely, if the angle-measuring instrument fitted geometry values of specific purity correlated with values of specific brightness. Analysis BRDF, respectively BSRDF function showed that the previously used dichromatic spectral reflectance model must be extended by an additional parameter explaining the correlation between chroma and lightness at the diffusion measurement geometry.
2003, Journal of Esthetic and Restorative Dentistry
1991, Color Research & Application
2012, Optics Express
2015, Proceedings of the 21st International Conference LIGHT SVĚTLO 2015
1994, Proceedings: Biological Sciences
Quantitative measurements of perceptual colour constancy show that human observers have a limited and variable ability to match coloured surfaces in scenes illuminated by different light sources. Observers can, however, make fast and reliable discriminations between changes in illuminant and changes in the reflecting properties of scenes, a discriminative ability that might be based on a visual coding of spatial colour relations. This coding could be provided by the ratios of cone-photoreceptor excitations produced by light from different surfaces: for a large class of pigmented surfaces and for surfaces with random spectral reflectances, these ratios are statistically almost invariant under changes in illumination by light from the sun and sky or from a planckian radiator. Cone-excitation ratios offer a possible, although not necessarily unique, basis for perceptual colour constancy in so far as it concerns colour relations.