The Experts below are selected from a list of 90 Experts worldwide ranked by ideXlab platform
Peter Hanselaer - One of the best experts on this subject based on the ideXlab platform.
-
a Memory Colour quality metric for white light sources
Energy and Buildings, 2012Co-Authors: W. R. Ryckaert, Kevin Smet, Geert Deconinck, Peter Hanselaer, Michael R PointerAbstract:Abstract Over the past years, the tremendous progress in solid-state lighting technology, especially in terms of energy-efficiency, has increased the interest in solid-state lighting (SSL) as an alternative to conventional sources in general lighting applications. Colour quality is one of the key challenges for SSL, as lighting with a poor Colour quality is often unacceptable in general lighting. For many lighting designers and architects, the CIE Colour rendering index is the current standard to assess Colour quality of a light source. Unfortunately, it correlates poorly with the visual appreciation of many SSL sources. In this paper a Colour quality metric is presented that references to the Memory Colours of familiar objects. The basic idea is simple: the closer a light source renders Colours to what is expected, the better will be the Colour quality. A correlation analysis, based on data from several psychophysical studies described in literature, has shown that the metric correlates highly with the visual appreciation of white light sources. Some of the key differences between the Memory Colour quality metric and the CIE Colour rendering index are shortly illustrated, as well as its potential for the design of more energy-efficient light source spectra showing good Colour quality.
-
Optimization of Colour quality of LED lighting with reference to Memory Colours
Lighting Research & Technology, 2012Co-Authors: Kag Smet, W. R. Ryckaert, Geert Deconinck, Peter HanselaerAbstract:Simulated and real tri- and tetrachromatic light-emitting-diode (LED) clusters were optimized for luminous efficacy of radiation (LER) and the Memory Colour quality metric developed by the authors. The simulated clusters showed no significant differences in achievable Colour quality and LER between the different cluster types investigated. The real clusters (composed of commercially available LEDs) showed substantial differences in achievable Colour quality and LER between the different cluster types investigated. The real clusters also exhibited a large drop in LER and Memory Colour quality compared to the simulated clusters due to the limited range of available peak wavelengths and spectral halfwidths. A real tetrachromatic LED lamp, constructed with commercial red, green, blue and warm white LEDs, was optimized for LER and Colour quality. In a psychophysical experiment, several aspects of the Colour quality of the LED lamp (optimized for 2700 K) and an incandescent lamp were assessed by 18 observers. T...
-
Colour appearance rating of familiar real objects
Color Research & Application, 2011Co-Authors: Kevin Smet, W. R. Ryckaert, Geert Deconinck, Michael R Pointer, Peter HanselaerAbstract:The determination of the long-term Memory Colours of objects has been the subject of investigation for many years. Colour acceptance boundaries have been determined from the visual assessments of objects under variable illumination or by presenting manipulated images of objects on a calibrated computer display. However, a systematic and quantitative rating of the Colour of real objects with respect to Memory Colour is not available at this moment. In this article, nine familiar real objects with Colours distributed around the hue circle were positioned in a specially designed LED illumination box. For each object, approximately hundred real illumination spectra were synthesized in a random order keeping the luminance of the object approximately constant. Observers were asked to rate, on a five-point scale, the similarity of the perceived object Colour to their idea of what the object looked like in reality. By avoiding specular reflections, the observer was unable to identify any clues as to the Colour of the illumination. For each object, similarity ratings showed a good intraobserver and interobserver agreement. The ratings of all the observers were pooled and successfully modeled in IPT Colour space by a bivariate Gaussian distribution. It was found that the chromaticity corresponding to the highest rating tended to be shifted toward higher chroma in comparison with the chromaticity calculated under D65 illumination. The bivariate distributions could be very useful in applications where the quantitative evaluation of the Colour appearance of an object stimulus is required, such as in the evaluation of the Colour rendering capabilities of a light source. © 2010 Wiley Periodicals, Inc. Col Res Appl, 36, 192–200, 2011;
-
Optimal Colour quality of LED clusters based on Memory Colours.
Optics express, 2011Co-Authors: Kevin Smet, W. R. Ryckaert, Geert Deconinck, Michael R Pointer, Peter HanselaerAbstract:The spectral power distributions of tri- and tetrachromatic clusters of Light-Emitting-Diodes, composed of simulated and commercially available LEDs, were optimized with a genetic algorithm to maximize the luminous efficacy of radiation and the Colour quality as assessed by the Memory Colour quality metric developed by the authors. The trade-off of the Colour quality as assessed by the Memory Colour metric and the luminous efficacy of radiation was investigated by calculating the Pareto optimal front using the NSGA-II genetic algorithm. Optimal peak wavelengths and spectral widths of the LEDs were derived, and over half of them were found to be close to Thornton's prime Colours. The Pareto optimal fronts of real LED clusters were always found to be smaller than those of the simulated clusters. The effect of binning on designing a real LED cluster was investigated and was found to be quite large. Finally, a real LED cluster of commercially available AlGaInP, InGaN and phosphor white LEDs was optimized to obtain a higher score on Memory Colour quality scale than its corresponding CIE reference illuminant.
Kevin Smet - One of the best experts on this subject based on the ideXlab platform.
-
a Memory Colour quality metric for white light sources
Energy and Buildings, 2012Co-Authors: W. R. Ryckaert, Kevin Smet, Geert Deconinck, Peter Hanselaer, Michael R PointerAbstract:Abstract Over the past years, the tremendous progress in solid-state lighting technology, especially in terms of energy-efficiency, has increased the interest in solid-state lighting (SSL) as an alternative to conventional sources in general lighting applications. Colour quality is one of the key challenges for SSL, as lighting with a poor Colour quality is often unacceptable in general lighting. For many lighting designers and architects, the CIE Colour rendering index is the current standard to assess Colour quality of a light source. Unfortunately, it correlates poorly with the visual appreciation of many SSL sources. In this paper a Colour quality metric is presented that references to the Memory Colours of familiar objects. The basic idea is simple: the closer a light source renders Colours to what is expected, the better will be the Colour quality. A correlation analysis, based on data from several psychophysical studies described in literature, has shown that the metric correlates highly with the visual appreciation of white light sources. Some of the key differences between the Memory Colour quality metric and the CIE Colour rendering index are shortly illustrated, as well as its potential for the design of more energy-efficient light source spectra showing good Colour quality.
-
Colour appearance rating of familiar real objects
Color Research & Application, 2011Co-Authors: Kevin Smet, W. R. Ryckaert, Geert Deconinck, Michael R Pointer, Peter HanselaerAbstract:The determination of the long-term Memory Colours of objects has been the subject of investigation for many years. Colour acceptance boundaries have been determined from the visual assessments of objects under variable illumination or by presenting manipulated images of objects on a calibrated computer display. However, a systematic and quantitative rating of the Colour of real objects with respect to Memory Colour is not available at this moment. In this article, nine familiar real objects with Colours distributed around the hue circle were positioned in a specially designed LED illumination box. For each object, approximately hundred real illumination spectra were synthesized in a random order keeping the luminance of the object approximately constant. Observers were asked to rate, on a five-point scale, the similarity of the perceived object Colour to their idea of what the object looked like in reality. By avoiding specular reflections, the observer was unable to identify any clues as to the Colour of the illumination. For each object, similarity ratings showed a good intraobserver and interobserver agreement. The ratings of all the observers were pooled and successfully modeled in IPT Colour space by a bivariate Gaussian distribution. It was found that the chromaticity corresponding to the highest rating tended to be shifted toward higher chroma in comparison with the chromaticity calculated under D65 illumination. The bivariate distributions could be very useful in applications where the quantitative evaluation of the Colour appearance of an object stimulus is required, such as in the evaluation of the Colour rendering capabilities of a light source. © 2010 Wiley Periodicals, Inc. Col Res Appl, 36, 192–200, 2011;
-
Optimal Colour quality of LED clusters based on Memory Colours.
Optics express, 2011Co-Authors: Kevin Smet, W. R. Ryckaert, Geert Deconinck, Michael R Pointer, Peter HanselaerAbstract:The spectral power distributions of tri- and tetrachromatic clusters of Light-Emitting-Diodes, composed of simulated and commercially available LEDs, were optimized with a genetic algorithm to maximize the luminous efficacy of radiation and the Colour quality as assessed by the Memory Colour quality metric developed by the authors. The trade-off of the Colour quality as assessed by the Memory Colour metric and the luminous efficacy of radiation was investigated by calculating the Pareto optimal front using the NSGA-II genetic algorithm. Optimal peak wavelengths and spectral widths of the LEDs were derived, and over half of them were found to be close to Thornton's prime Colours. The Pareto optimal fronts of real LED clusters were always found to be smaller than those of the simulated clusters. The effect of binning on designing a real LED cluster was investigated and was found to be quite large. Finally, a real LED cluster of commercially available AlGaInP, InGaN and phosphor white LEDs was optimized to obtain a higher score on Memory Colour quality scale than its corresponding CIE reference illuminant.
W. R. Ryckaert - One of the best experts on this subject based on the ideXlab platform.
-
a Memory Colour quality metric for white light sources
Energy and Buildings, 2012Co-Authors: W. R. Ryckaert, Kevin Smet, Geert Deconinck, Peter Hanselaer, Michael R PointerAbstract:Abstract Over the past years, the tremendous progress in solid-state lighting technology, especially in terms of energy-efficiency, has increased the interest in solid-state lighting (SSL) as an alternative to conventional sources in general lighting applications. Colour quality is one of the key challenges for SSL, as lighting with a poor Colour quality is often unacceptable in general lighting. For many lighting designers and architects, the CIE Colour rendering index is the current standard to assess Colour quality of a light source. Unfortunately, it correlates poorly with the visual appreciation of many SSL sources. In this paper a Colour quality metric is presented that references to the Memory Colours of familiar objects. The basic idea is simple: the closer a light source renders Colours to what is expected, the better will be the Colour quality. A correlation analysis, based on data from several psychophysical studies described in literature, has shown that the metric correlates highly with the visual appreciation of white light sources. Some of the key differences between the Memory Colour quality metric and the CIE Colour rendering index are shortly illustrated, as well as its potential for the design of more energy-efficient light source spectra showing good Colour quality.
-
Optimization of Colour quality of LED lighting with reference to Memory Colours
Lighting Research & Technology, 2012Co-Authors: Kag Smet, W. R. Ryckaert, Geert Deconinck, Peter HanselaerAbstract:Simulated and real tri- and tetrachromatic light-emitting-diode (LED) clusters were optimized for luminous efficacy of radiation (LER) and the Memory Colour quality metric developed by the authors. The simulated clusters showed no significant differences in achievable Colour quality and LER between the different cluster types investigated. The real clusters (composed of commercially available LEDs) showed substantial differences in achievable Colour quality and LER between the different cluster types investigated. The real clusters also exhibited a large drop in LER and Memory Colour quality compared to the simulated clusters due to the limited range of available peak wavelengths and spectral halfwidths. A real tetrachromatic LED lamp, constructed with commercial red, green, blue and warm white LEDs, was optimized for LER and Colour quality. In a psychophysical experiment, several aspects of the Colour quality of the LED lamp (optimized for 2700 K) and an incandescent lamp were assessed by 18 observers. T...
-
Colour appearance rating of familiar real objects
Color Research & Application, 2011Co-Authors: Kevin Smet, W. R. Ryckaert, Geert Deconinck, Michael R Pointer, Peter HanselaerAbstract:The determination of the long-term Memory Colours of objects has been the subject of investigation for many years. Colour acceptance boundaries have been determined from the visual assessments of objects under variable illumination or by presenting manipulated images of objects on a calibrated computer display. However, a systematic and quantitative rating of the Colour of real objects with respect to Memory Colour is not available at this moment. In this article, nine familiar real objects with Colours distributed around the hue circle were positioned in a specially designed LED illumination box. For each object, approximately hundred real illumination spectra were synthesized in a random order keeping the luminance of the object approximately constant. Observers were asked to rate, on a five-point scale, the similarity of the perceived object Colour to their idea of what the object looked like in reality. By avoiding specular reflections, the observer was unable to identify any clues as to the Colour of the illumination. For each object, similarity ratings showed a good intraobserver and interobserver agreement. The ratings of all the observers were pooled and successfully modeled in IPT Colour space by a bivariate Gaussian distribution. It was found that the chromaticity corresponding to the highest rating tended to be shifted toward higher chroma in comparison with the chromaticity calculated under D65 illumination. The bivariate distributions could be very useful in applications where the quantitative evaluation of the Colour appearance of an object stimulus is required, such as in the evaluation of the Colour rendering capabilities of a light source. © 2010 Wiley Periodicals, Inc. Col Res Appl, 36, 192–200, 2011;
-
Optimal Colour quality of LED clusters based on Memory Colours.
Optics express, 2011Co-Authors: Kevin Smet, W. R. Ryckaert, Geert Deconinck, Michael R Pointer, Peter HanselaerAbstract:The spectral power distributions of tri- and tetrachromatic clusters of Light-Emitting-Diodes, composed of simulated and commercially available LEDs, were optimized with a genetic algorithm to maximize the luminous efficacy of radiation and the Colour quality as assessed by the Memory Colour quality metric developed by the authors. The trade-off of the Colour quality as assessed by the Memory Colour metric and the luminous efficacy of radiation was investigated by calculating the Pareto optimal front using the NSGA-II genetic algorithm. Optimal peak wavelengths and spectral widths of the LEDs were derived, and over half of them were found to be close to Thornton's prime Colours. The Pareto optimal fronts of real LED clusters were always found to be smaller than those of the simulated clusters. The effect of binning on designing a real LED cluster was investigated and was found to be quite large. Finally, a real LED cluster of commercially available AlGaInP, InGaN and phosphor white LEDs was optimized to obtain a higher score on Memory Colour quality scale than its corresponding CIE reference illuminant.
Karl R. Gegenfurtner - One of the best experts on this subject based on the ideXlab platform.
-
A Bayesian Model of the Memory Colour Effect
i-Perception, 2018Co-Authors: Christoph Witzel, Maria Olkkonen, Karl R. GegenfurtnerAbstract:According to the Memory Colour effect, the Colour of a Colour-diagnostic object is not perceived independently of the object itself. Instead, it has been shown through an achromatic adjustment method that Colour-diagnostic objects still appear slightly in their typical Colour, even when they are Colourimetrically grey. Bayesian models provide a promising approach to capture the effect of prior knowledge on Colour perception and to link these effects to more general effects of cue integration. Here, we model Memory Colour effects using prior knowledge about typical Colours as priors for the grey adjustments in a Bayesian model. This simple model does not involve any fitting of free parameters. The Bayesian model roughly captured the magnitude of the measured Memory Colour effect for photographs of objects. To some extent, the model predicted observed differences in Memory Colour effects across objects. The model could not account for the differences in Memory Colour effects across different levels of realism in the object images. The Bayesian model provides a particularly simple account of Memory Colour effects, capturing some of the multiple sources of variation of these effects.
-
Memory Colours affect Colour appearance
The Behavioral and brain sciences, 2016Co-Authors: Christoph Witzel, Maria Olkkonen, Karl R. GegenfurtnerAbstract:Memory Colour effects show that Colour perception is affected by Memory and prior knowledge and hence by cognition. None of Firestone & Scholl's (F&S's) potential pitfalls apply to our work on Memory Colours. We present a Bayesian model of Colour appearance to illustrate that an interaction between perception and Memory is plausible from the perspective of vision science.
-
Effects of Memory Colour on Colour constancy for unknown Coloured objects.
i-Perception, 2012Co-Authors: Jeroen J. M. Granzier, Karl R. GegenfurtnerAbstract:The perception of an object's Colour remains constant despite large variations in the chromaticity of the illumination—Colour constancy. Hering suggested that Memory Colours, the typical Colours of objects, could help in estimating the illuminant's Colour and therefore be an important factor in establishing Colour constancy. Here we test whether the presence of objects with diagnostical Colours (fruits, vegetables, etc) within a scene influence Colour constancy for unknown Coloured objects in the scene. Subjects matched one of four Munsell papers placed in a scene illuminated under either a reddish or a greenish lamp with the Munsell book of Colour illuminated by a neutral lamp. The Munsell papers were embedded in four different scenes—one scene containing diagnostically Coloured objects, one scene containing incongruent Coloured objects, a third scene with geometrical objects of the same Colour as the diagnostically Coloured objects, and one scene containing non-diagnostically Coloured objects (eg, a yellow coffee mug). All objects were placed against a black background. Colour constancy was on average significantly higher for the scene containing the diagnostically Coloured objects compared with the other scenes tested. We conclude that the Colours of familiar objects help in obtaining Colour constancy for unknown objects.
-
Object Knowledge Modulates Colour Appearance
i-Perception, 2011Co-Authors: Christoph Witzel, Hanna Valkova, Thorsten Hansen, Karl R. GegenfurtnerAbstract:We investigated the Memory Colour effect for Colour diagnostic artificial objects. Since knowledge about these objects and their Colours has been learned in everyday life, these stimuli allow the investigation of the influence of acquired object knowledge on Colour appearance. These investigations are relevant for questions about how object and Colour information in high-level vision interact as well as for research about the influence of learning and experience on perception in general. In order to identify suitable artificial objects, we developed a reaction time paradigm that measures (subjective) Colour diagnosticity. In the main experiment, participants adjusted sixteen such objects to their typical Colour as well as to grey. If the achromatic object appears in its typical Colour, then participants should adjust it to the opponent Colour in order to subjectively perceive it as grey. We found that knowledge about the typical Colour influences the Colour appearance of artificial objects. This effect was particularly strong along the daylight axis.
Dimitria Electra Gatzia - One of the best experts on this subject based on the ideXlab platform.
-
Cognitive Penetration and Memory Colour Effects
Erkenntnis, 2019Co-Authors: Dimitria Electra GatziaAbstract:Cognition can influence action. Your belief that it is raining outside, for example, may cause you to reach for the umbrella. Perception can also influence cognition. Seeing that no raindrops are falling, for example, may cause you to think that you don’t need to reach for an umbrella. The question that has fascinated philosophers and cognitive scientists for the past few decades, however, is whether cognition can influence perception. Can, for example, your desire for a rainy day cause you to see, hear, or feel raindrops when you walk outside? More generally, can our cognitive states (such as beliefs, desires or intentions) influence the way we see the external world? In this paper, I discuss three experiments on Memory Colour effects. In these experiments, subjects systematically made different Colour matches or adjustments for object-patches representing objects that have prototypical Colours and neutral object-patches. I argue that these differences are not merely differences in judgments but are best explained in terms of phenomenology. However, I show that these differences in phenomenology can be explained without reference to cognitive states such as Colour concepts or beliefs.