Colour Science

Is the Yakut fox green?, or remarks on some colour names in Turkic, Uralic, and Yeniseic

by Marek Stachowski

Imitation, Artificiality and Creation: the colour and perception of the earliest glass in New Kingdom Egypt

by Chloe N. Duckworth

Cambridge Archaeological Journal (in press)

INTRODUCTION:

The creation of glass demanded from the start an empirical understanding of a range of... more INTRODUCTION:

The creation of glass demanded from the start an empirical understanding of a range of complex technological processes and the addition of numerous ingredients from potentially diverse sources. As such, the scientific approach which has dominated recent research into the earliest man-made glass has provided essential insight into its production processes, and has also been used to address larger scale considerations, most notably provenance (Sayre and Smith 1961; Henderson 1988; Rehren 2000; Shortland 2000; Shortland and Tite 2000; Mass et al. 2002; Henderson et al. 2005; Rehren and Pusch 2005; Shortland and Eremin 2006; Shortland et al. 2007; Rehren 2008; Henderson et al. 2010). But there is another side to understanding ancient glass: the reasons behind its consumption and use, the ‘why’ of its production as well as the ‘how’.

It is this ‘why’ which stands as the primary focus of the present article. It is suggested that by placing the material properties of glass at the centre of its investigation a novel picture of the perception of glass can be developed, crucially one which is supported by newer readings of the linguistic and textual evidence.  Much of the following discussion draws on an existing – and eminent – body of literature on the earliest glass and other vitreous materials. Previous research (see for example Shortland 2001; Shortland 2007) has shown that glass was a highly valued material in Late Bronze Age Egypt (and perhaps somewhat less so in Mesopotamia), yet there remain questions as to how and why it was valued. It has not been uncommon in earlier publications to refer to glass as an ‘imitation’ of precious  stones (see for example Oppenheim 1970, 10-15; Moorey 1994, 211; Stern 1998, 191; Sciama 1998, 6; Robson 2001, 52; Rehren and Pusch 2005, 1756). On the other hand, the term ‘imitation’ and the related term ‘substitution’ have fallen out of use of late, perhaps because of their somewhat derogatory connotations in light of the value of glass: as noted by Nicholson and Shaw (2000, 195), glass may be seen as an artificial stone but should by no means be considered a cheap substitute.

It is here argued that, if seen as a form of created stone, glass acted as a material expression of the power of the ruling elite. Central to this is colour: as the visual signal through which the value of precious stones was recognized and – to some extent – realized, colour was a vital factor in control over the material, and the act of imparting colour to glass was probably surrounded by a certain degree of deliberate mystification. Furthermore, the ability to produce glass from locally available raw ingredients would not have acted against its high value:  if we accept that the ruling elite had control over its production, we must ask by what mechanisms they were able to restrict access to glass. The material nature of glass suggests that this is most likely to have been practised through difficulty of production rather than exoticism, which was not necessarily a desirable feature per se.

The present article is about Egyptian glass, specifically focusing on that from the 18th and 19th Dynasties. Because much of the earliest glass found in Egypt was probably imported from Mesopotamia, however, and given that Akkadian was the key language of international correspondence at the time, the evidence of Mesopotamian language and glassware are also considered where these are thought to be relevant to the Egyptian case. Theories on materiality and colour in archaeology are also discussed and are intended to extend beyond the material boundaries of glass studies.

POSTER at ECVP 2011: Accommodation to chromatic gratings.

by Sarah M Haigh

Haigh, S. M., Allen, P. M., & Wilkins, A. J. (2011). Accommodation to chromatic gratings. Perception, 40 (ECVP Abstract Supplement), 80.

Wilkins, Tang, Irabor and Coutts (2008) measured discomfort from isoluminant square-wave gratings and showed that the... more Wilkins, Tang, Irabor and Coutts (2008) measured discomfort from isoluminant square-wave gratings and showed that the discomfort increased with the separation within the CIE UCS diagram of the chromaticities of the component bars, regardless of the hue. The gratings with larger separation elicited a cortical haemodynamic response of greater magnitude. The discomfort and larger haemodynamic response may arise because accommodative mechanisms relax when the chromaticity difference is large – Allen at al. (2010) found a greater lag of accommodation to achromatic gratings for those who found them uncomfortable. We therefore used an open field autorefractor to measure the accommodative response to the gratings. No correlation was found between the separation of chromaticities and the accommodative response, suggesting that the discomfort is not due to a failure to accommodate to the stimuli. However, participants who experienced pattern-related visual stress, showed a greater accommodative lag to the gratings overall than those who were symptom-free. This suggests that although accommodative mechanisms are unlikely to cause the discomfort, those who find gratings uncomfortable generally relax their accommodation when looking at an uncomfortable target.

References
Allen, P., Hussain, A., Usherwood, C., Wilkins, A. (2010). Pattern-related visual stress, chromaticity and accommodation. Investigative Ophthalmology and Visual Science, 2010(51), 6843-6849.
Wilkins, A. J., Tang, P., Irabor, J., Baningham, L., Coutts, L. . (2008). Cortical haemodynamic response to coloured gratings. Perception, 37(ECVP Abstract Supplement), 144.

POSTER at AVA 2011: Colour separation and aversion

by Sarah M Haigh

Haigh S M, Tang P, Barningham L, Coutts L, Allen P M, Wilkins A J, 2012, "Colour separation and aversion" i-Perception 3(4) 232

Aversion to achromatic patterns is well documented but relatively little is known about discomfort from chromatic... more Aversion to achromatic patterns is well documented but relatively little is known about discomfort from chromatic patterns. Large colour differences are uncommon in the natural environment and deviation from natural statistics makes images uncomfortable (Fernandez & Wilkins, 2008, Perception, 37(7), 1098-113; Juricevic, Land, Wilkins & Webster, 2010, Perception, 39(7), 884-899). We report twelve studies documenting a linear increase in aversion to chromatic square-wave gratings as a function of the separation in UCS chromaticity between the component bars, independent of their luminance contrast. Two possible explanations for the aversion were investigated: (1) accommodative response, or (2) cortical metabolic demand. We found no correlation between chromaticity separation and accommodative lag or variance in lag, measured using an open-field autorefractor. However, near infrared spectroscopy of the occipital cortex revealed a larger oxyhaemoglobin response to patterns with large chromaticity separation. The aversion may be cortical in origin and does not appear to be due to accommodation.

Colour, Shape, and Music: The Presence of Thought Forms in Abstract Art

by Zoe Alderton

Magick in Theory and Practice: Ritual Use of Colour in Kenneth Anger’s Invocation of My Demon Brother

by Deborah Allison

Published in Senses of Cinema, issue 34, January-March 2005.

A Novel Image Re-Indexing by Self Organizing Motor Maps

by Sebastiano Battiato

Monitoring winery waste composting by means of colour measures

by Remigio Paradelo

Óptica Pura y Aplicada (2010). Co-authored with B. Prieto, A.B. Moldes & M.T. Barral. In Spanish.

In this work, the suitability of colour monitoring during composting is reported. Two composting experiments were... more In this work, the suitability of colour monitoring during composting is reported. Two composting experiments were conducted with winery wastes for five months in the laboratory. In the first experiment the composting of spent grape marc was studied, whereas in the second a mixture of hydrolyzed grape marc (residue of the treatment for biotechnological production of additives), wine lees and CaCO3 was composted. In addition to monitoring common chemical parameters, the colour of the materials was determined, both in the Munsell system and in the CIELAB space. During the five months of composting, the winery wastes showed a very low degree of evolution in their chemical properties, restricted to the first three months. The colour parameters were modified with composting time, particularly in the first months, indicating their relationship with the evolution of the materials in composting.

Isolation of opponent-colour mechanisms at increment threshold

by David Foster

An experimental examination was made of some paradigms designed to isolate the opponent-colour system at increment... more An experimental examination was made of some paradigms designed to isolate the opponent-colour system at increment threshold. The effectiveness of a uniform white conditioning field spatially coincident with a 1.05-deg uniform test field was assessed by measuring intensity thresholds for simple detection and for colour discrimination. Values were obtained both by a method of adjustment and by a two-interval forced-choice procedure. For sufficiently high luminances of the conditioning field (3000 td or greater) little or no difference was found between simple-detection and colour-discrimination thresholds over the critical test-flash spectral range 520-620 nm, implying that the paradigm produced almost complete isolation of the opponent-colour system at increment threshold. A control experiment in which thresholds were obtained for a conditioning field larger than the test field gave less satisfactory isolation; near 580 nm the luminance system was found to be at least 0.31 log unit more sensitive than the opponent-colour system. A comparison was also made of the spatially coincident field paradigm with a paradigm in which a modified test stimulus of low temporal and spatial frequency content was presented on a large conditioning field. Test spectral sensitivity curves for simple detection obtained by a method of adjustment showed little difference in effectiveness in opponent-colour isolation.

Four issues concerning colour constancy and relational colour constancy

by David Foster

Four issues concerning colour constancy and relational colour constancy are briefly considered: (1) the equivalence of... more Four issues concerning colour constancy and relational colour constancy are briefly considered: (1) the equivalence of colour constancy and relational colour constancy; (2) the dependence of relational colour constancy on ratios of cone excitations due to light from different reflecting surfaces, and the association of such ratios with von Kries’ coefficient rule; (3) the contribution of chromatic edges to colour constancy and relational colour constancy; and (4) the effects of instruction and observer training. It is suggested that cognitive factors affect colour constancy more than relational colour constancy, which may be an inherently more robust phenomenon.

Psychophysical estimates of the number of spectral-reflectance basis functions needed to reproduce natural scenes

by David Foster

Theoretical analyses of spectral reflectances of natural surfaces suggest that their perceived colors can be well... more Theoretical analyses of spectral reflectances of natural surfaces suggest that their perceived colors can be well reproduced by approximations comprising combinations of three or four spectral basis functions. The aim of the present work was to assess psychophysically the number of basis functions necessary to reproduce entire natural outdoor scenes. Hyperspectral images of 20 such scenes were each subjected to a principal component analysis and then reproduced with a variable number of basis functions. The quality of the color approximation under daylight illumination was quantified theoretically in CIELAB space and psychophysically by spatial and temporal two-alternative forced-choice measurements in which the original and the approximated images were compared on a calibrated color monitor. Although five basis functions produced on average unit error in CIELAB space, original images were visually indistinguishable from their approximations only if there were at least eight basis functions. The combination of the spectral diversity of the natural world and the observed levels of color discrimination suggest that estimates of the minimum number of basis functions necessary to reproduce natural scenes may need to be revised upward.

Chromatic induction and the layout of colours within a complex scene

by Jeroen Smeets

Luminance—color correlation is not used to estimate the color of the illumination

by Jeroen Smeets

Combining local and global contributions to perceived colour: An analysis of the variability in symmetric and asymmetric colour matching

by Jeroen Smeets

Colour constancy from temporal cues: better matches with less variability under fast illuminant changes

by David Foster

To test whether temporal transient cues could improve colour- constancy estimates, surface-colour matches were made... more To test whether temporal transient cues could improve colour- constancy estimates, surface-colour matches were made across two Mondrian patterns illuminated by different daylights: the patterns were presented either in the same position in an alternating sequence or, as a control, simultaneously side-by- side. The degree of colour constancy was significantly higher with sequential stimulus presentation than with simultaneous presentation, in the best condition reaching 0.87 on a scale of 0 to 1 for matches averaged over 20 observers. The variance between observers was also markedly reduced with sequential stimulus presentation. The visual system appears to have mechanisms not requiring adaptation that can provide almost unbiased information about surface colour under changing illuminants.

Number of perceptually distinct surface colors in natural scenes

by David Foster

The ability to perceptually identify distinct surfaces in natural scenes by virtue of their color depends not only on... more The ability to perceptually identify distinct surfaces in natural scenes by virtue of their color depends not only on the relative frequency of surface colors but also on the probabilistic nature of observer judgments. Previous methods of estimating the number of discriminable surface colors, whether based on theoretical color gamuts or recorded from real scenes, have taken a deterministic approach. Thus, a three-dimensional representation of the gamut of colors is divided into elementary cells or points which are spaced at one discrimination-threshold unit intervals and which are then counted. In this study, information-theoretic methods were used to take into account both differing surface-color frequencies and observer response uncertainty. Spectral radiances were calculated from 50 hyperspectral images of natural scenes and were represented in a perceptually almost uniform color space. The average number of perceptually distinct surface colors was estimated as 7.3 x 10^3, much smaller than that based on counting methods. This number is also much smaller than the number of distinct points in a scene that are, in principle, available for reliable identification under illuminant changes, suggesting that color constancy, or the lack of it, does not generally determine the limit on the use of color for surface identification.

Approaching ideal observer efficiency in using color to retrieve information from natural scenes

by David Foster

Variations in illumination on a scene and trichromatic sampling by the eye limit inferences about scene content. The... more Variations in illumination on a scene and trichromatic sampling by the eye limit inferences about scene content. The aim of this work was to elucidate these limits in relation to an ideal observer using color signals alone. Simulations were based on 50 hyperspectral images of natural scenes and daylight illuminants with correlated color temperatures 4000 K, 6500 K, and 25,000 K. Estimates were made of the (Shannon) information available from each scene, the redundancies in receptoral and postreceptoral coding, and the information retrieved by an observer identifying corresponding points across image pairs. For the largest illuminant difference, between 25,000 K and 4000 K, a postreceptoral transformation providing minimum redundancy yielded an efficiency of about 80% in the information retrieved. This increased to about 89% when the transformation was optimized directly for information retrieved, corresponding to an equivalent Gaussian noise amplitude of 3.0% or to a mean of 3.6 x 10^4 distinct identifiable points per scene. Using color signals to retrieve information from natural scenes can approach ideal observer efficiency levels.

Färg i norr och södervettande rum. Kulörtonförskjutning genom varierande ljusförhållanden

by Maud Hårleman

Colour changes in prints during long-term dark storage of prints

by Carinna Parraman

The 4th International Conference on: Preservation and Conservation Issues in Digital Printing and Digital Photography, 27–28 May 2010, The Institute of Physics, London

The most significant impact on colour fading in prints is exposure to light and air.However what happens to coloured... more The most significant impact on colour fading in prints is exposure to light and air.However what happens to coloured prints during long-term storage in boxes, drawers and on shelves? Measurements of samples, printed in July 2005, stored in a range of light and
darkened storage conditions have shown some interesting initial results. As more emphasis is placed on the effects of light, the dark stability of inkjet prints is relatively overlooked when considering how to preserve or store coloured prints. This study and presentation builds on previous research [1] and has concentrated on the changes to colour during storage. With reference to ASTM F2035 - 00(2006) Standard Practice for Measuring the Dark Stability of Ink Jet Prints, the Standards outline points out that whilst natural aging is the most reliable method of assessing image stability, materials and inks any data that is produced quickly becomes redundant; therefore accelerated aging is more preferred. However, the fine art materials in this study are still very much in circulation. The leading fine art papers, and pigmented ink-sets used in these trials are still being used by artists. We can therefore demonstrate the characteristics of colour changes and the impact of ink on paper that utilises natural aging methods.

A report on the CREATE Italian event: Colour in cultural heritage

by Carinna Parraman

Co-authored with Nicola Ludwig, Department of Physics, State University of Milan, Italy via Celoria 16 20133 Milano, Italy. Email: nicola.ludwig@unimi.it; Marcello Picollo, Istituto di Fisica Applicata “Nello Carrara” of the National Research Council of Italy (IFAC-CNR), Via Madonna del Piano 10, 50019 Sesto Fiorentino, Italy. Email: m.picollo@ifac.cnr.it;  Alessandro Rizzi,  Dipartimento di tecnologie dell’informazione, Università degli Studi di Milano, via Bramante 65 26013 Crema, Italy. Email: alessandro.rizzi@unimi.it

The group CREATE - Colour Research for European Advanced Technology Employment - came together in 2006 to promote and... more The group CREATE - Colour Research for European Advanced Technology Employment - came together in 2006 to promote and exchange research and knowledge about colour through a series of conferences and training courses. The courses and conferences began in September 2007 and will end in June 2010. The long-term objective is to develop between artists, designers, technologists and scientists a cross disciplinary approach to improving the professional use of colour. This paper reports on the developments and activities of the Create group and its most recent event on cultural heritage: “Colour Heritage and Conservation”, which was held in Italy in October 2009.