Whiteness,chromaticness, and blackness symmetries for CIELAB,with a numerical example

Whiteness, chromaticness, and blackness are defined for CIELAB. These NCS‐like color attributes offer an alternative to lightness and chroma for describing color. Their hue‐preserving symmetries are derived for tristimulus color space. A numerical example provides what theory predicts are visually uniform sequences of colors with constant lightness, whiteness, chromaticness, or blackness. Numerical approximation is unnecessary. Such sets of symmetric colors in one hue are visually interesting, and useful for computer aided design. The appropriateness of such attributes for CIELAB is briefly discussed. © 2010 Wiley Periodicals, Inc. Col Res Appl, 2010     

Influence of cosurfactant in microemulsion systems for color removal from textile wastewater

Microemulsion systems have proved very efficient in color removal from textile wastewater using n‐butyl alcohol as cosurfactant. The cosurfactant has a very important role in microemulsified systems, as it is responsible for their stability, mainly in systems formed by ionic surfactants. Although very efficient, n‐butyl alcohol is partially soluble in water, which would permit its passage to the effluent. In this work, isoamyl and octyl alcohols, due to their lower solubility in water, were used as cosurfactants to evaluate their influence in color removal. The colorimetry system used was the CIE L*a*b* (CIELAB) color space and CIE L*a*b* color difference (ΔE*_ab). The wastewater used in this study was the reactive exhausted dye liquor from a dye house (first discharge) containing Procion Yellow H‐E4R (CI Reactive Yellow 84), Procion Blue H‐ERD (CI Reactive Blue 160) and Procion Red H‐E3B (CI Reactive Red 120). The obtained results were modeled using an experimental planning (the Scheffé net) and evaluated through isoresponse diagrams by correlation graphs between experimental values and those obtained by the models with an error lower than 4%. All the optimized systems were very efficient and more than 94% of the dyes contained in the effluent were removed. The microemulsion load capacity was determined using a synthetic solution containing, the same dyes present in the reactive exhausted dyebath, but 200 times concentrated, and the dyes extraction was more than 99.6%. By comparing n‐butyl, isoamyl and octyl alcohols, it was observed that the system using isoamyl alcohol presented slightly better color removal and much higher load capacity than the n‐butyl and octyl alcohols. Copyright © 2004 Society of Chemical Industry     

A proposal for the modification of s‐CIELAB

The s‐CIELAB is a powerful tool in evaluating color reproduction errors in images. However, the formula is not yet completed, and a few refinements to the formula will enhance the accuracy of this tool. From a simple simulation, a black‐and‐white pattern causes unexpected false color components when using the s‐CIELAB formula. We show how these false color components are obtained with this formula. The main reason is a combination of components from different lowpass filters (LPFs). We show a method that improves this situation by introducing new psychological values and propose a modification to the formula employed by s‐CIELAB. The new formula is compatible with the psychological values L*u*v*, and a simulation with general images shows that the new method does not cause any false color components.     

An optical model relating (L*a*b*) values for a scattering surface covered with a scattering layer to (L*a*b*) values for the uncovered surface and its application to tooth colour

The appearance of human dentition is important both psychologically and commercially. Many people perceive the lightness and chromaticity of their teeth as key factors in their overall appearance leading to large businesses in materials for colour‐matched fillings and crowns and in tooth whitening products. The human eye is very sensitive to small colour differences, recognizing a row of highly colour‐matched crowns as unnatural yet seeing excessive colour variation or darkness as unattractive. One cause of tooth discolouration is a darkening of the dentine, visible through the enamel. This has lead the authors to develop a model capable of relating ( ) measurements on a scattering surface, in our case dentine, to ( ) measurements when overlaid by a translucent scattering layer, in our case tooth enamel. The model can be used when any scattering layer is superimposed on a coloured surface. In contrast to existing models, no spectral measurements are necessary allowing the use of colourimeters rather than spectrophotometers. However, there are limitations on the degree of colour saturation for both the coloured surface and the scattering layer as the model uses an approximation valid only for weakly saturated colours. As neither the enamel nor the dentine have strongly saturated colouration, the limitation is entirely acceptable for our work. The use of ( ) measurements directly rather than having to measure the spectrum of reflected light is of practical importance as such measurements in a dental surgery are impossible in all but exceptional cases whilst ( ) measurements in the surgery are routine. © 2014 Wiley Periodicals, Inc. Col Res Appl, 40, 504–517, 2015     

Using symmetry to understand the attributes of color

The common attributes of color are distinguishable by their symmetries. Hue, saturation, chroma, chromaticness, whiteness, and blackness symmetries are discussed. Symmetries are generally not sufficient to specify unique formulas for color attributes, nor are they an endorsement of color model accuracy. However, symmetries do provide constraints for valid formulae, which are useful even when symmetries are only approximate. They also provide an alternate conceptual understanding of color attributes that differs from standard color science definitions. Symmetries provide a simplified framework for calculating groups of colors that share color attributes. Color models examined include the Hunt Model, a simple color model (SCM), various CIE color spaces, and IPT. A general functional form describes symmetries and scaling laws for many color models, and exceptions are discussed. © 2007 Wiley Periodicals, Inc. Col Res Appl, 33, 27–44, 2008     

Relationship between the colour and the chemical structure of carotenoid pigments

Several carotenoids were isolated and their colours were ascertained objectively to establish relationships between the chemical structures of those pigments and their actual colours, considering the coordinates of the uniform space CIELAB. The results of this study revealed that the different carotenoids surveyed could be grouped in the a^∗b^∗ plane according to the number of conjugated double bonds. For yellowish carotenoids, it was observed that a^∗ values clearly decreased from those with 11 conjugated double bonds (c.d.b.) to those with 9 c.d.b., although this trend reversed in the case of carotenoids with 7 c.d.b.. In terms of hue (h_ab), it was seen that the decrease in conjugation of the molecules involved a slight rise in h_ab. On the other hand, the aperture of the end rings or the increase in conjugation involved clear increases in hue.     

Measuring the colour of virgin olive oils in a new colour scale using a low-cost portable electronic device

The Modified Uniform Oil Colour Scale (MUOCS) is proposed for the colour specification of virgin olive oils. MUOCS has 60 standard colours, the same number as the two previous scales available for the same purpose: Uniform Oil Colour Scale (UOCS) and Bromthymol Blue (BTB). A remarkable improvement in accuracy can be achieved from MUOCS standards: For a broad dataset of 1700 virgin olive oils produced in Spain during four different harvests, the average colour differences to the closest standards were 2.86, 3.99, and 8.17 CIELAB units using MUOCS, UOCS and BTB, respectively. A low-cost (<60 Euros) portable electronic device is proposed for the colour specification of virgin olive oils based on MUOCS and BTB standards. This device can operate with USB connection to a computer or AAA batteries, and is based on fast (<0.25 s) transmittance measurements of the virgin-olive-oil sample placed in a 5-mm pathlength quartz cell. The device may avoid the use of expensive laboratory instrumentation for colour measurement and can be easily employed by non-technician users. For a reduced set of commercial virgin olive oils with random colours, the MUOCS classifications provided by our device agreed with those given by conventional spectrophotometric measurements in 92% of the cases.     

LEtter to the Editor – On Depth and Brightness

This communication contains Rich's Letter to the Editor commenting on a recent article by Roy S. Berns, and Bern's Reply to the Letter. The letter introduces more information on the concepts of Depth and Brightness as well as references. © 2014 Wiley Periodicals, Inc. Col Res Appl, 2014     

Practical demonstration of the CIEDE2000 corrections to CIELAB using a small set of sample pairs

A set of 10 color pairs was proposed and produced in 2002 to show the advantages of the CIEDE2000 color‐difference formula with respect to CIELAB. These 10 color pairs illustrated each of the five corrections to CIELAB proposed by CIEDE2000. The 10 color pairs were visually assessed, under reference conditions close to those proposed by CIEDE2000, by two groups of 31 and 21 inexperienced observers, using two different gray scales. Average visual results in these experiments fitted CIEDE2000 predictions much better than CIELAB, as shown by a decrease of Standardized Residual Sum of Squares values of about 20 units. Current visual results showed only the improvement of CIEDE2000 upon CIELAB in predictions of perceived color differences, but they are not recommended for testing new advanced color‐difference formulas. © 2012 Wiley Periodicals, Inc. Col Res Appl, 38, 429–436, 2013.     

Glucosinolates, l-ascorbic acid,total phenols,anthocyanins, antioxidant capacities and colour in cauliflower (Brassica oleracea L. ssp. botrytis); effects of long-term freezer storage

Blanching and one year freezer storage were performed on one purple, two white and two green varieties of cauliflower (Brassica oleracea L. ssp. botrytis) to assess the effects on several health-related phytochemicals. Blanching, prior to freezing, reduced total aliphatic and indole glucosinolates (GLS) by 31% and 37%, respectively. l-ascorbic acid (L-AA), total phenols (TP), anthocyanins, FRAP and ORAC were on average reduced by 19, 15, 38, 16 and 28%, respectively. The colour measured as CIELAB parameters was partly affected by blanching: lightness was significantly reduced in the white cultivars and in a romanesco type cultivar. Chromaticity was reduced in the coloured cultivars with a twice-as-large reduction in the purple cultivars. Hue increased for all samples, except for the purple cultivar where a decrease was found. Long-term freezer storage did not affect total aliphatic and indole GLS in cauliflower in a major way. Freezer storage did result in an average L-AA decrease of 24% for all but the purple cultivar. Some reductions in the TP levels were also found but not to the extent found for L-AA. When an effect was found in the FRAP and ORAC values, the reductions occurred towards the end of the storage period and were 15% and 37%, on average, respectively. Long-term freezer storage did not affect the anthocyanin content and only minor effects were found for the colour parameters.