Colour Appearance Modelling for Self-luminous Colours

An experimental setup and procedure for the evaluation of self- luminous colours viewed against both dark and luminous backgrounds is presented. Physical and visual data of self-luminous colours is gathered in order to develop a Colour Appearance Model for self-luminous colours under different viewing conditions. This model is needed for the evaluation of light sources. This record was migrated from the OpenDepot repository service in June, 2017 before shutting down

Configurational assignment and 1H NMR spectral parameters of isomeric 1,2-diacetoxy-4-alkyl-3-methylcyclopentanes

The 1H NMR spectral parameters of all eight 1,2-diacetoxy-3,4-dimethylcyclopentanes and 1,2-diacetoxy-4-t-butuyl-3-methylcyclopentanes are discussed

Cyclopentanones : stereochemistry of the lithium-liquid ammonia reduction of 2, 3-dialkyl-5-hydroxy-2-cyclopentenones

The stereochemistry of the lithium-liquid ammonia reduction of 2, 3-dimethyl-5-hydroxy-2-cyclopentenone (1) and 3-t.butyl-2-methyl-5-hydroxy-2-cyclopentenone (2) is studied in function of a set of proton donors. A high degree of stereoselectivity is observed as practically only two (predominantly one isomer) out of the eight diastereoisomeric 3, 4-dialkyl-1, 2-cyclopentane diols 3 or 4 are formed

Hydroxylation and epoxidation studies of some 3,4-dialkylcyclopentenes

The hydroxylation and the epoxidation of the cis and trans isomers of 3,4-dimethylcyclopentene and 4-t-butyl-3-methylcyclopentene have been studied. The stereoselectivity was studied as a function of the basic conformation of the individual cyclopentenes; the conformations were determined by 1H NMR spectroscopy

Overall gloss evaluation in the presence of multiple cues to surface glossiness

Human observers use the information offered by various visual cues when evaluating the glossiness of a surface. Several studies have demonstrated the effect of each single cue to glossiness, but little has been reported on how multiple cues are integrated for the perception of surface gloss. This paper reports on a psychophysical study with real stimuli that are different regarding multiple visual gloss criteria. Four samples were presented to 15 observers under different conditions of illumination in a light booth, resulting in a series of 16 stimuli. Through pairwise comparisons an overall gloss scale was derived, from which it could be concluded that both differences in the distinctness of the reflected image, and differences in luminance affect gloss perception. However, an investigation of the observers’ strategy to evaluate gloss indicated a dichotomy among observers. One group of observers used the distinctness-of-image as a principal cue to glossiness, while the second group evaluated gloss primarily from differences in luminance of both the specular highlight and the diffuse background. It could therefore be questioned if surface gloss can be characterized with one single quantity, or that a set of quantities is necessary to describe the gloss differences between objects.status: publishe

Integration of multiple cues for the evaluation of surface gloss

This study reports on a psychophysical experiment with real stimuli that differ in multiple visual gloss criteria. Four samples were presented to 15 observers under different conditions of illumination, resulting in a series of 16 stimuli. Through pairwise comparisons, a gloss scale was derived and the observers’ strategy to evaluate gloss was investigated. The preference probability matrix P indicated a dichotomy among observers. A first group of observers used the distinctness-of-image as a principal cue to glossiness, while a second group evaluated gloss primarily from differences in brightness. It could therefore be questioned if surface gloss can be characterized by one single quantity, or that a set of quantities is necessary to describe differences in gloss.status: publishe

Geometry of illumination, luminance contrast, and gloss perception

The influence of both the geometry of illumination and luminance contrast on gloss perception has been examined using the method of paired comparison. Six achromatic glass samples having different lightness were illuminated by two light sources. Only one of these light sources was visible in reflection by the observer. By separate adjustment of the intensity of both light sources, the luminance of both the reflected image and the adjacent off-specular surroundings could be individually varied. It was found that visual gloss appraisal did not correlate with instrumentally measured specular gloss; however, psychometric contrast seemed to be a much better correlate. It has become clear that not only the sample surface characteristics determine gloss perception: the illumination geometry could be an even more important factor.status: publishe

Characterization of stripe figure on finished wood

Wood is a very popular and preferred material for many applications because of its remarkable decorative peculiarities. A very interesting feature related to the appearance of wood is called ribbon stripe or stripe figure. Stripe figure is perceived as a series of longitudinal parallel stripes which alternate in colour shade. When the sample is slightly rotated, the bright stripes become dark and vice versa. This gonio-apparent effect provides the wood with a very dynamic appearance, distinguishing the material from alternatives such as laminate. In this paper, stripe figure is quantified by measuring and analyzing the absolute spectral bidirectional reflectance distribution function (BRDF) for different incident and viewing angle combinations. In a first step, perpendicular illumination is used and the viewing angle is varied in four half planes. Asymmetric BRDF values are found if the observation plane is parallel with the ribbon direction, in contrast to the behaviour in the plane perpendicular to it. In a second experiment, both incident and viewing angle are changed simultaneously, simulating the general observer behaviour when assessing the appearance of the sample. Important differences in lightness between two adjacent positions on the sample are recorded when slightly rotating the sample around an axis perpendicular to the ribbon pattern, revealing the characteristic contrast flop. Again, if the other rotation direction is chosen, almost no variation is observed. These observations can be attributed to the particular orientation of the fibres in combination with the external reflectance at the finishing top layer. Analogous effects are present in the hue, especially on the yellow-blue axis, but are almost absent on the red-green axis. The quantitative results reported in this paper can be used for camera-based selection of wood samples and to improve the quality of computer renderings of these natural materials.status: publishe

Investigation of the interaction between and the integration of multiple visual gloss cues in the overall gloss evaluation process

The understanding of how human observers evaluate and interpret surface gloss has received increased attention during the last decades. Several studies were conducted that confirm the multi-dimensional nature of gloss perception [1-6]. From a study with digital image representations, Pellacini et al. [2] reported that two dimensions were sufficient to characterize apparent gloss differences; contrast gloss and distinctness of image gloss (DOI). In accordance with Pellacini et al., we recently showed that for high-gloss samples with invariant DOI, the contrast between the reflected image of the source and the sample background affects gloss perception. Consequently, the sample glossiness could be drastically influenced by introducing a light source that is positioned out of the specular field of view [7]. This notion agrees with other recent studies that emphasize the influence of the light field on gloss perception [8-10], and was further exploited in a magnitude estimation experiment from which a psychophysical scaling function was derived. The function relates visual gloss estimations to the measured luminance of both the reflected image and the off-specular sample background [11,12]. In the present study samples with a different DOI are introduced, in order to investigate both the interaction between and the integration of multiple visual cues for the perception of surface gloss. Spectral and spatial reflectance characteristics of the samples are determined by measurement of the BRDF with a home-built spectroradiometer [13]. A test booth with two tunable light sources [7] is utilized to change the apparent gloss of the samples by adjusting the luminance of both the specular highlight and the sample background. This makes it possible to generate samples with conflicting cues, e.g. a strong highlight yet low DOI vs. a weak highlight yet high DOI. Through paired comparisons, the importance of each cue in the overall gloss evaluation process is investigated.status: publishe

Luminance-based specular gloss characterization

Gloss is a feature of visual appearance that arises from the directionally selective reflection of light incident on a surface. Especially when a distinct reflected image is perceptible, the luminance distribution of the illumination scene above the sample can strongly influence the gloss perception. For this reason, industrial glossmeters do not provide a satisfactory gloss estimation of high-gloss surfaces. In this study, the influence of the conditions of illumination on specular gloss perception was examined through a magnitude estimation experiment in which 10 observers took part. A light booth with two light sources was utilized: the mirror image of only one source being visible in reflection by the observer. The luminance of both the reflected image and the adjacent sample surface could be independently varied by separate adjustment of the intensity of the two light sources. A psychophysical scaling function was derived, relating the visual gloss estimations to the measured luminance of both the reflected image and the off-specular sample background. The generalization error of the model was estimated through a validation experiment performed by 10 other observers. In result, a metric including both surface and illumination properties is provided. Based on this metric, improved gloss evaluation methods and instruments could be developed.status: publishe