Psychophysical Determination of the Relevant Colours That Describe the Colour Palette of Paintings

In an early study, the so-called “relevant colour” in a painting was heuristically introduced as a term to describe the number of colours that would stand out for an observer when just glancing at a painting. The purpose of this study is to analyse how observers determine the relevant colours by describing observers’ subjective impressions of the most representative colours in paintings and to provide a psychophysical backing for a related computational model we proposed in a previous work. This subjective impression is elicited by an efficient and optimal processing of the most representative colour instances in painting images. Our results suggest an average number of 21 subjective colours. This number is in close agreement with the computational number of relevant colours previously obtained and allows a reliable segmentation of colour images using a small number of colours without introducing any colour categorization. In addition, our results are in good agreement with the directions of colour preferences derived from an independent component analysis. We show that independent component analysis of the painting images yields directions of colour preference aligned with the relevant colours of these images. Following on from this analysis, the results suggest that hue colour components are efficiently distributed throughout a discrete number of directions and could be relevant instances to a priori describe the most representative colours that make up the colour palette of paintings.FEDER Funds by the Spanish Ministry of Science Innovation and Universities (MICINN, grant number RTI2018-094738-B-I00

How good are RGB cameras retrieving colors of natural scenes and paintings?—A study based on hyperspectral imaging

RGB digital cameras (RGB) compress the spectral information into a trichromatic system capable of approximately representing the actual colors of objects. Although RGB digital cameras follow the same compression philosophy as the human eye (OBS), the spectral sensitivity is different. To what extent they provide the same chromatic experiences is still an open question, especially with complex images. We addressed this question by comparing the actual colors derived from spectral imaging with those obtained with RGB cameras. The data from hyperspectral imaging of 50 natural scenes and 89 paintings was used to estimate the chromatic differences between OBS and RGB. The corresponding color errors were estimated and analyzed in the color spaces CIELAB (using the color difference formulas ΔE*ab and CIEDE2000), Jzazbz, and iCAM06. In CIELAB the most frequent error (using ΔE*ab) found was 5 for both paintings and natural scenes, a similarity that held for the other spaces tested. In addition, the distribution of errors across the color space shows that the errors are small in the achromatic region and increase with saturation. Overall, the results indicate that the chromatic errors estimated are close to the acceptance error and therefore RGB digital cameras are able to produce quite realistic colors of complex scenarios.This work was supported by the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Funding UIDB/04650/2020

What Neuroimaging of the Psychedelic State Tells Us about the Mind-Body Problem

Recent neuroimaging studies of the psychedelic state, which have commanded great media attention, are reviewed. They show that psychedelic trances are consistently accompanied by broad reductions in brain activity, despite their experiential richness. This result is at least counterintuitive from the perspective of mainstream physicalism, according to which subjective experience is entirely constituted by brain activity. In this brief analysis, the generic implications of physicalism regarding the relationship between the richness of experience and brain activity levels are rigorously examined from an informational perspective, and then made explicit and unambiguous. These implications are then found to be non-trivial to reconcile with the results of said neuroimaging studies, which highlights the significance of such studies for the mind-body problem and philosophy of mind in general

A psychophysical analysis of the discernible palette for colour names

A laboratory-based experiment with a colour-calibrated display was used to collect examples of colours that participants associate with each of 9 colour names. The gamut volumes for each of the clusters of colours in CIELAB space were calculated and a computational method was used to estimate how any distinct colours could be placed within each of these volumes. In the case of one of the colour names (pink), an unconstrained web-based experiment was carried out and the gamut volume for pink was similar to the gamut volume derived from the laboratory experiment. It was assumed that colours separated by more than 1 CIELAB unit would be visually distinguishable. The study gave estimates for the number of discernible colours for each of the 9 colour names. The work suggests that although focal colours may exist for each of the colour names used in the study, these colour names are generally not precise communicators of colour and different people might have quite different ideas, for example, about what is being communicated when people use specific colour names

Gamut extension algorithm development and evaluation for the mapping of standard image content to wide-gamut displays

Wide-gamut display technology has provided an excellent opportunity to produce visually pleasing images, more so than in the past. However, through several studies, including Laird and Heynderick, 2008, it was shown that linearly mapping the standard sRGB content to the gamut boundary of a given wide-gamut display may not result in optimal results. Therefore, several algorithms were developed and evaluated for observer preference, including both linear and sigmoidal expansion algorithms, in an effort to define a single, versatile gamut expansion algorithm (GEA) that can be applied to current display technology and produce the most preferable images for observers. The outcome provided preference results from two displays, both of which resulted in large scene dependencies. However, the sigmoidal GEAs (SGEA) were competitive with the linear GEAs (LGEA), and in many cases, resulted in more pleasing reproductions. The SGEAs provide an excellent baseline, in which, with minor improvements, could be key to producing more impressive images on a wide-gamut display

Signal detection using pseudocolor scales

Historically, gray scale has been the standard method of displaying univariate medical images. A few color scales have been proposed and evaluated, but have had little acceptance by radiologists. It is possible that carefully desired scales might give lesion detection performance that equals gray scale and improves performance of other tasks. We investigated 13 display scales including the physically linear gray scale, the popular rainbow scale and the other 1 1 perceptually linearized scales. One was the hot body (heated object) scale and the other 10 were spiral trajectories in the CIELAB uniform color space. The experiments were performed using signals added to white noise and a statistically defined (lumpy) background. In general, the best performance was obtained using the gray scale and the hot body scale. Performance for the rainbow scale was very poor ( about 30% of gray scale performance)

The development of methodologies for color printing in digital inkjet textile printing and the application of color knowledge in the Ways of Making Project

Digital textile printing (DTP) offers creative potential and entrepreneurial business models in textile design. Designers are no longer restricted to a number of colors or pattern repeat. It has become possible to print fabric without large set-up costs. This relatively sustainable technology reduces water-usage and dye-wastage. DTP meets Just in Time, Concept to Consumer demand, reducing stock wastage. However, there is a marked difference between screen-color to print-color and software allows a user to select colors unprintable using CMYK (cyan, magenta, yellow, black) colorants. Color results are further affected by factors such as structure and composition of the fabric, dye type, printer communications, fabric pre-treatments and secondary processes. A textile designer will be required to understand and experiment with a number of variables in order to feel color-confident. This paper presents investigations which focused on developing methods to aid a designer’s color expectation knowledge, using a Practice-as-Research methodology. Outcomes include a color reference book, digital lap dip tests presented as color maps, and a set of indicator ICC profiles, generated from data accumulated through measuring printed color differences on a variety of substrates. These visual prompts are intended to support designers to build their own internal color look-up table enabling them to predict and resolve color issues during the design process.Finally, the paper concludes by presenting a Case Study detailing an application of these color methods by the researcher for the Ways of Making project, a collaboration between Sir Peter Blake, Worton Hall Studios and Centre for Fine Print Research (CFPR) at University of West of England (UWE). Here, the indicator profiles were applied to Blake’s images, altering the color data to create experimental color modifications and printed onto silk. An initial selection of works from the project were exhibited at London Original Print Fair, Royal Academy, April 2019