Colour Quality Evaluation of Bluish-Green Serpentinite Based on the CIECAM16 Model

The CIECAM16 colour appearance model is currently a model with high prediction accuracy. It can solve the problem of predicting the influence of different observation conditions on the colour of gemstones. In this study, a computer vision system (CVS) was used to measure the colour of 59 bluish-green serpentinite samples, and the tristimulus values were input into the CIECAM16 forward model to calculate the colour appearance parameters of serpentinite under different surrounds, illuminances, and light sources. It was found that the darkening of the surround causes the lightness and brightness to increase. Pearson’s r of brightness and colourfulness with illuminance is 0.885 and 0.332, respectively, which predicts the Stevens and Hunt effects. When the light source changes from D65 to A, the calculated hue angle shifts to the complementary area of the A light source, which is contrary to the CVS measurement result. The D65 light source is more suitable for the colour presentation and classification of bluish-green serpentinite.

COLOUR FIDELITY AND ILLUMINANCE TRADE-OFF: TESTING LIGHTING VALUES

The higher the colour fidelity of a light source, the lower its luminous efficacy of radiation because the light source spectrum must deviate from V(λ) to deliver the higher fidelity. Two experiments probed the trade-off between energy efficiency and colour quality. Experiment 1 required participants to simultaneously view pairs of light sources differing in colour fidelity, at either a higher (346 lx) or lower (277 lx) illuminance. Participants performed a timed reading task and judged the colour appearance of the pair. There were no effects of illuminance, but larger colour fidelity differences between the light sources in the pair correlated with lower appearance judgements. Experiment 2 simulated the effect of light sources on defined reflectance spectra. The results showed that improvements of colour fidelity above what is often considered satisfactory can yield more satisfying illumination while using the same amount of power.

TESTING THE PERFORMANCE FOR UNRELATED COLOUR APPEARANCE MODELS

Most colour appearance models (CAMs) have been developed to predict the colour appearance only for related colours in different viewing conditions. More recently, CAMs to predict for unrelated colours have been proposed due to the availability of the experimental data. This paper investigates the performance of the three promising colour appearance models for unrelated colours, i.e. CAM15u, CAMFu and CAM20u using an experimental dataset carefully accumulated by Fu et al. in term of CV values. The results showed that the latest CAM20u outperformed the other models. CAMFu, as the oldest model, whose performance was much worse than other two models in predicting brightness and colourfulness, and performed well in predicting hue composition, while CAM15u gave a moderate performance in predicting brightness and colourfulness, but performed slightest worse than the others for hue composition.

TWO-DIMENSIONAL COLOUR APPEARANCE SCALES FOR COLOUR STIMULI HAVING HIGH DYNAMIC RANGE

New colour appearance scales close to daily experience and image quality enhancement are highly desired including whiteness, blackness, vividness and depth. This article describes a new experiment to accumulate the data under HDR (high dynamic range) conditions. The data were then used to test the performance of different colour appearance scales such as CIELAB and CAM16-UCS plus the recent extension by Berns’ Vab*, Dab*. The results showed those Berns’ scales gave reasonable performance. However, there was no scale capable of predicting colour appearance data covering a wide dynamic range. New scales were developed based on the absolute scales of brightness and colourfulness of CAM16-UCS and gave accurate prediction to the data.

REFERENCE WHITE IN A COMPLEX VIRTUAL REALITY ENVIRONMENT

This study aims to investigate what a reference white really means in a complex scene setting in a virtual environment, specifically whether a reference white is determined by the brightest white object in the entire environment, or is it determined by the brightest white object in the field of view. To achieve the aim, three psychophysical experiments were conducted, one situated in a real room and the other two in virtual reality. Experimental results show that colour appearance in VR is comparable to colour appearance in a real space. Regarding reference white, the brightest white object is not necessarily regarded as the reference white especially when it is located far away from the test colour. The brightest white object needs to be located within the viewing field for the test colour in order to be regarded as the reference white.

Testing Colour Appearance Model Based UCS Using HDR, WCG and COMBVD Datasets

Two colour appearance models based UCSs, CAM16-UCS and ZCAM-QMh, were tested using HDR, WCG and COMBVD datasets. As a comparison, two widely used UCSs, CIELAB and ICTCP, were tested. Metrics of the STRESS and correlation coefficient between predicted colour differences and visual differences, together with local and global uniformity based on their chromatic discrimination ellipses, were applied to test models' performance. The two UCSs give similar performance. The luminance parametric factor kL, and power factor γ, were introduced to optimize colour-difference models. Factors kL and γ of 0.75 and 0.5, gave marked improvement to predict the HDR dataset. Factor kL of 0.3 gave significant improvement in the test of WCG dataset. In the test of COMBVD dataset, optimization provide very limited improvement.

Characterization of the physical properties and sensory acceptability of Caulerpa racemosa grain beverage

Caulerpa racemosa grain was a healthy product and high nutrition. This study applied study was applied Caulerpa racemosa grain in the beverage with the addition of alginate powder. Thus, the present work was aimed to determine the properties of beverage C. racemosa grain formulated with the alginate concentration was varied (0; 0.025; 0.05; 0.075; 0.10 and 0.125 %). The testing of quality beverage C. racemosa viscosity was analyzed using viscometer methods. The colorimeter investigated the colour. The sensory acceptability hedonic and score method (colour, appearance, aroma, taste, texture, and overall acceptance) used a 5-point. Results showed that alginate used alginate 0.025%, the highest preference, aroma, and appearance scores. The addition of alginate increased alginate was increased the viscosity of beverage C. racemosa grain. The colour of C. racemosa grain progressively became light as the level of alginate grew. However, the increased alginate is not significant enough to change the redness and greenness value of C. racemosa grain beverage. The panelists have preferred to drink the selected Caulerpa grain beverage (concentration sodium alginate 0.025%), with slightly viscous.

Individual Differences in Colour Perception: The Role of Low-Saturated and Complementary Colours in Ambiguous Images

Individual differences in colour perception, as evidenced by the popular debate of “The Dress” picture, have garnered additional interest with the popularisation of additional, similar photographs. We investigated which colorimetric characteristics were responsible for individual differences in colour perception. All objects of the controversial photographs are composed of two representative colours, which are low in saturation and are either complementary to each other or reminiscent of complementary colours. Due to these colorimetric characteristics, we suggest that one of the two complementary pixel clusters should be estimated as the illuminant hue depending on assumed brightness. Thus, people perceive the object's colours as being biased toward complementarily different colour directions and perceive different pixel clusters as chromatic and achromatic. Even though the distance between colours that people perceive differently is small in colour space, people perceive the object's colour as differently categorized colours in these ambiguous photographs, thereby causing debate. We suggest that people perceive the object's colours using different “modes of colour appearance” between surface-colour and self-luminous modes.

New colour appearance scales under high dynamic range conditions

New colour appearance scales close to daily experience and image quality enhancement are highly desired including whiteness, blackness, vividness and depth. This article describes a new experiment to accumulate the data under HDR (high dynamic range) conditions. The data were then used to test the performance of different colour appearance scales such as CIELAB and CAM16-UCS plus the recent extension by Berns' Vab*, Dab*. The results showed those Berns' scales gave a reasonable performance. However, it was found no scale is capable of predicting colour appearance data covering a wide dynamic range. New scales were developed based on the absolute scales of brightness and colourfulness of CAM16-UCS and gave accurate predictions to the data.

Colour Calibration of a Head Mounted Display for Colour Vision Research Using Virtual Reality

Virtual reality (VR) technology offers vision researchers the opportunity to conduct immersive studies in simulated real-world scenes. However, an accurate colour calibration of the VR head mounted display (HMD), both in terms of luminance and chromaticity, is required to precisely control the presented stimuli. Such a calibration presents significant new challenges, for example, due to the large field of view of the HMD, or the software implementation used for scene rendering, which might alter the colour appearance of objects. Here, we propose a framework for calibrating an HMD using an imaging colorimeter, the I29 (Radiant Vision Systems, Redmond, WA, USA). We examine two scenarios, both with and without using a rendering software for visualisation. In addition, we present a colour constancy experiment design for VR through a gaming engine software, Unreal Engine 4. The colours of the objects of study are chosen according to the previously defined calibration. Results show a high-colour constancy performance among participants, in agreement with recent studies performed on real-world scenarios. Our studies show that our methodology allows us to control and measure the colours presented in the HMD, effectively enabling the use of VR technology for colour vision research.