CIELAB Chroma Research Articles

Preparation and thermochromic behavior of low-temperature thermochromic microcapsule temperature indicators

Studies have rarely investigated thermochromic materials at refrigeration temperatures (about 8 °C). In this study, such a temperature indicator that can change color at refrigerated temperature was synthesized. Crystal violet lactone (CVL) and lauryl gallate (LG) were dissolved in methyl laurate (ML) at a phase change temperature of 7 °C. A series of low-temperature reversible thermochromic leuco dyes were obtained and used to prepare low-temperature reversible thermochromic microcapsule (TCM) temperature indicators. The FTIR results show that the thermochromic behavior of TCM temperature indicator was determined by LG controlling CVL to open and close the ring for reversible conversion between the lactone structure (colorless) and conjugated structure (colored). The effects of the mass ratio of the three components (wCVL:wLG:wML) on the thermochromic behavior were analyzed according to the CIE Lab chromaticity indexes. The total thermochromic color difference between leuco dye and TCM temperature indicator reached the maximum when the wCVL:wLG:wML was 1:3:125. The TCM temperature indicator gradually changed from dark blue to white from 1 °C to 8 °C. The DSC results show that the decolorization temperature of TCM temperature indicator was very close to the melting point of ML. In addition, microencapsulation prevented the phase separation of leuco dyes and improved the stability of thermochromic materials. The results indicate the enormous potential of TCM temperature indicator for studying thermochromic materials at low temperatures and in temperature monitoring of refrigerated food packages.

Microwave-assisted and conventional phenolic and colour extraction from grape skins of commercial white and red cultivars at veraison and harvest

Phenolics and colourants in grape skin vary among cultivars. Their extraction under efficient and environmentally friendly methods is of high industry importance. Grape berry skins from six white and six red commercial Australian cultivars were collected at veraison and harvest over a single vintage. Phenolics and colourants were extracted from the skins of individual cultivars under microwave-assisted (MAE) and conventional thermal extraction (CTE) methods. The settings for each method, previously identified, were fixed at levels maximising total phenolic (TP) extraction from the mixture of those same white skins at veraison and harvest and, unconnectedly, from the mixture of the red skins at veraison and harvest. For white and red grapes, the current study quantifies the variation in TP and colour (CIELAB chroma C∗), which can be attributed to the joint effects of method of extraction, cultivar and time of berry development. The efficiencies of the extraction methods are compared for each cultivar. For each method, the average TP content achieved across corresponding individual skin collections and the TP extractions from their mixtures are well aligned for red cultivars and with a few exceptions for white cultivars. The results are of interest to researchers in phenolic and colour extraction, oenology and industrial post-winemaking waste management.

ATR-MIR Spectroscopy Predicts Total Phenolics and Colour for Extracts Produced by Microwave-Assisted or Conventional Thermal Extraction Methods Applied Separately to Mixtures of Grape Skins from White or Red Commercial Cultivars

Attenuated total reflectance mid-infrared (ATR-MIR) spectra were collected from 480 grape skin extracts produced in a wide range of conditions. The conditions were created at different phases in parallel response surface RS-optimisation experiments aiming to maximise the total phenolics in red and white grape skin extractions by microwave-assisted (MAE) or conventional thermal (CTE) methods. Skins mixtures for six white and six red Australian commercial cultivars were prepared from grapes collected at veraison and harvest. The total phenolics were measured for individual extracts with the Folin-Ciocalteu method. Partial least squares (PLS1) regression was employed on the spectra to predict the total phenolics (TP) and colour (CIELAB chroma C*) of individual extracts. Models based on the raw spectra and their second derivative (Savitzky-Golay, 20 points) were examined using the full range of spectra 4000–400 cm−1, and sub-ranges: 4000–1100 cm−1, 1500–400 cm−1, 1500–1100 cm−1 and 1457–1168 cm−1. The PLS1 models based on the second derivative of the range of 4000–1100 cm−1 provided the best results for both TP and C*, for each skin colour. Overall, the residual predictive deviation (RPD) exceeded 3.0, indicating the PLS1 models’ ability for fair classification, suitable for screening. A comparative analysis was performed for the range of 4000–1100 cm−1 between the spectra of white and red skin mixture extracts: the peaks at 3840 cm−1, 2940 cm−1, 2358 cm−1, 2197 cm−1, 2136 cm−1, 1725 cm−1, 1100 cm−1 and 1148 cm−1 are flagged to be investigated in further research. ATR-MIR spectroscopy can reduce the time and costs of TP and C* analyses in grape skin extracts.

Comparative analysis of methods and model prediction performance evaluation for continuous online non-invasive quality assessment during drying of apples from two cultivars

Quality attributes such as moisture content, colour parameters and shrinkage of apples change undesirably during the drying process. Drying is a highly dynamic process, thus, an effective optimisation in terms of product quality and process performance requires continuous non-invasive measurement of the parameters in question. In this study, visual to near infra-red hyperspectral imaging was used in combination with the respective gold standard methods to estimate moisture ratio, CIELab chromaticity, browning index, shrinkage, and rehydration ratio of apple slices during the hot air-drying process. Two varieties (cv. Elstar and Golden delicious) of apples at three slice thicknesses (2, 3, and 4 mm) were dried at 60 °C and 70 °C. Prediction models for the space-averaged spectral reflectance curves were built using the partial least square regression method and including both varieties. The performance of moisture ratio prediction was excellent (adj R2 = 0.94, RMSEP = 0.076) and the Variable Importance in the Projection value cut off above 0.8 at 970 nm and L* at 685 nm. Similarly, partial least square regression modelling showed a good prediction for a*, b* value, BI, shrinkage and acceptable prediction for L* and RR. The model performance was robust to the system settings irrespective of slice thickness, drying temperature and apple variety. Additionally, method comparisons using Bland-Altman, Bablok, and Deming regression were performed. The results confirm that the compared destructive (laboratory gold standard) and non-destructive hyperspectral methods can be interchangeably used within the limit of agreement (±1.96 standard deviations) and precision for determination of the MR, CIELAB chromaticity and BI, shrinkage, and rehydration ratio. Therefore, these results confirm that hyperspectral imaging system can be used in online monitoring of the apples during the drying process, and thus, in the optimisation of product and process performance quality attributes.

Comparison of visual (MUNSELL) and instrumental measures (CIELAB) of coloured textile standard samples

Purpose This paper aims to compare visual (Munsell) and instrumental (CIELAB) attributes of SCOTDIC colour standards. Design/methodology/approach SCOTDIC cotton and polyester standards of defined hue, value and chroma were subjected to spectrophotometric assessment for finding the corresponding instrumental parameters. The visual and instrumental parameters were compared. Findings The correlation between SCOTDIC value and CIELAB lightness is quite high. Correlation coefficient between SCOTDIC hue and CIELAB hue angle and the correlation between SCOTDIC chroma and CIELAB chroma were only moderate because the CIELAB chroma varied widely at higher chroma. When the standards of SCOTDIC hues having erratic hue angles at two extremes are excluded, the Correlation coefficients between SCOTDIC hue and CIELAB hue angle become high. Research limitations/implications The psychophysical data (visual) are difficult to match with physical data (instrumental). Originality/value The object of the present research is to study and compare visual (Munsell) and instrumental (CIELAB) colorimetric parameters. Munsell scale is physically exemplified by SCOTDIC fabric samples available in two sets, namely, cotton and polyester sets.

Perceived speed of changing color in chroma and hue directions in CIELAB.

In dynamic LED lighting, the perceived speed of changing color is an important concept; however, there exists no suitable temporal color space. In a psychophysical experiment, we compared the perceived speed of periodic temporal transitions in CIELAB chroma and hue directions around five base colors [the five Munsell hues: 5R (red), 5Y (yellow), 5G (green), 5B (blue), and 5P (purple)]. The experiment was conducted in a light laboratory, with the main illumination stimulus subtending a visual angle of 101×77 deg. In sequential paired presentations, observers were asked to identify which transition appeared faster, and points of subjective equality between transitions were computed. The speed of transitions was defined in CIELAB ΔEab*/s, which was shown to be temporally non-uniform; uniformity was improved using a modified color space based on speeds in the DKL space of Derrington etal. [J. Physiol.357(1), 241 (1984)].

Influence of ethylene and ethephon treatments on the peel color and carotenoids of Gannan Newhall navel orange during postharvest storage

Gannan Newhall navel orange was treated by ethylene and ethephon separately. The color of Gannan Newhall navel orange peel was influenced significantly by ethylene and ethephon treatments. During postharvest storage, the ratio of chlorophylls and carotenoids in the peel reduced which led the peel color changing from green to yellow when treated by ethephon and to orange-red when treated by ethylene. Results of the CIELAB chroma system evaluation were consistent with sensory evaluation. Ethylene and ethephon treatments decreased β-carotene and lutein contents and increased β-cryptoxanthin content largely (converted β-carotene to β-cryptoxanthin) in citrus peel. Besides, ethylene and ethephon treatments could convert yellow violaxanthin to neoxanthin or zeaxanthin. In ethylene treatment, its peel color changing to orange-red due to β-cryptoxanthin converted to β-citraurin, which made Gannan Newhall navel orange exhibited the welcomed color (orange-red). It was desirable for citrus postharvest process. Practical applications The color of citrus fruit has become an important factor affecting fresh fruit price and market competitiveness. Studies have shown that citrus peel color is mainly affected by the content and proportion of chlorophylls and carotenoids. This study is aimed to illustrate the transformation of carotenoids and the mechanism of regulation of ethylene on the navel orange peel changing from green to orange-red. The results of this research could provide scientific supports for citrus's atmosphere controlled storage, which could produce added value.

Understanding AuNP interaction with low-generation PAMAM dendrimers: a CIELab and deconvolution study

Low-generation polyamidoamine (PAMAM) dendrimers are known to adsorb on the surface of gold nanoparticles (AuNPs) causing aggregation and color changes. In this paper, a thorough study of this affinity using absorption spectroscopy, colorimetric, and emission methods has been carried out. Results show that, for citrate-capped gold nanoparticles, interaction with the dendrimer is not only of an electrostatic character but instead occurs, at least in part, through the dendrimer’s uncharged internal amino groups. The possibilities of the CIELab chromaticity system parameters’ evolution have also been explored in order to quantify dendrimer interaction with the red-colored nanoparticles. By measuring and quantifying 17 nm citrate-capped AuNP color changes, which are strongly dependant on their aggregation state, binding free energies are obtained for the first time for these systems. Results are confirmed via an alternate fitting method which makes use of deconvolution parameters from absorbance spectra. Binding free energies obtained through the use of both means are in good agreement with each other.

A Cross‐cultural comparison of saturation, vividness, blackness and whiteness scales

AbstractIn a typical Euclidean three‐dimensional colour space such as CIELAB, the ‘third‐dimension’, such as CIELAB chroma, has long been criticized as being confusing and difficult to understand for naïve observers and it had relatively poor consistency in visual assessments. As an attempt to find a promising replacement to existing ‘third‐dimension’, two psychophysical experiments were conducted in this study using naïve observers. In the first experiment, 24 Korean observers assessed 48 NCS colour chips in terms of bright, light‐heavy, active‐passive, fresh‐stale, clean‐dirty, clear, boring, natural‐not natural, warm‐cool, intense‐weak, saturated, vivid‐dull, distinct‐indistinct, full‐thin and striking. According to experimental results, ‘saturated’ and ‘vivid‐dull’ were found to highly correlate with CIELAB chroma and were thus regarded as good candidates to become alternatives to existing ‘third‐dimension’. In the second experiment, 40 Korean and 68 British observers assessed more than 100 samples in terms of saturation, vividness, blackness and whiteness. Thus, observers assessed 120 samples for saturation, vividness and whiteness. For blackness, 110 samples were assessed. In both experiments, the colour samples were presented in a viewing cabinet and assessed individually. Principal component analysis identified two components that were associated with CIELAB lightness and chroma. In general, there was a similarity between the visual results of the British and Korean observers. High correlation coefficients were found for the following comparisons: predicted values of Berns' depth model versus the present ‘saturation’ response; Berns' clarity versus ‘vividness’ response; Berns' vividness versus ‘blackness’ response; and CIELAB lightness versus ‘whiteness’ response. © 2016 Wiley Periodicals, Inc. Col Res Appl, 42, 203–215, 2017

Colour preference, naturalness, vividness and colour quality metrics, Part 2: Experiments in a viewing booth and analysis of the combined dataset

In Part 2 of this work, observers scaled colour preference, naturalness and vividness visually on interval scales (0–100) labelled by semantic categories (e.g. ‘moderate’, ‘good’ and ‘very good’) in the context of food lighting using the same questionnaire as in Part 1. Seven multi-LED light sources with more or less object saturation effect illuminated a viewing booth with coloured food objects. The two datasets (Part 1: room + Part 2: viewing booth) were merged and the observers’ assessments were predicted by recent colour quality indices and CIELAB chroma differences. Linear combinations of selected pairs or triads of descriptors were used to predict the merged dataset. Criterion values to achieve ‘good’ preference, naturalness and vividness level were determined.

CIELab chromaticity evolution to measure the binding free energy of non-colored biomolecules to gold nanoparticles

We explore the possibilities of the CIELab chromaticity system parameters' evolution in order to study the interaction between four non-colored biological reactants and the red-colored, non-functionalized citrate gold nanoparticles.

Effects of chromatic image statistics on illumination induced color differences

We measure the color fidelity of visual scenes that are rendered under different (simulated) illuminants and shown on a calibrated LCD display. Observers make triad illuminant comparisons involving the renderings from two chromatic test illuminants and one achromatic reference illuminant shown simultaneously. Four chromatic test illuminants are used: two along the daylight locus (yellow and blue), and two perpendicular to it (red and green). The observers select the rendering having the best color fidelity, thereby indirectly judging which of the two test illuminants induces the smallest color differences compared to the reference. Both multicolor test scenes and natural scenes are studied. The multicolor scenes are synthesized and represent ellipsoidal distributions in CIELAB chromaticity space having the same mean chromaticity but different chromatic orientations. We show that, for those distributions, color fidelity is best when the vector of the illuminant change (pointing from neutral to chromatic) is parallel to the major axis of the scene's chromatic distribution. For our selection of natural scenes, which generally have much broader chromatic distributions, we measure a higher color fidelity for the yellow and blue illuminants than for red and green. Scrambled versions of the natural images are also studied to exclude possible semantic effects. We quantitatively predict the average observer response (i.e., the illuminant probability) with four types of models, differing in the extent to which they incorporate information processing by the visual system. Results show different levels of performance for the models, and different levels for the multicolor scenes and the natural scenes. Overall, models based on the scene averaged color difference have the best performance. We discuss how color constancy algorithms may be improved by exploiting knowledge of the chromatic distribution of the visual scene.

Methodology for constructing a colour‐difference acceptability scale

Observers were invited to report their degree of satisfaction on a 6-point semantic scale with respect to the conformity of a test colour with a white reference colour, simultaneously presented on a PDP display. Eight test patches were chosen along each of the +a*, -a*, +b*, -b* axes of the CIELAB chromaticity plane, at Y = 80 ± 2 cd.m(-2) . Experimental conditions reliably represented the automotive environment (patch size, angular distance between patches) and observers could move their head and eyes freely. We have compared several methods of category scaling, the Torgerson-DMT method (Torgerson, W. S. (1958). Theory and methods of scaling. Wiley, New York, USA); two versions of the regression method i.e. Bonnet's (Bonnet, C. (1986). Manuel pratique de psychophysique. Armand Colin, Paris, France) and logistic regression; and the medians method. We describe in detail a case where all methods yield substantial but slightly different results. The solution proposed by the regression method which works with incomplete matrices and yields results directly on a colorimetric scale is probably the most useful in this industrial context. Finally we summarize the implementation of the logistic regression method over four hues and for one experimental condition.

The Effects of Perceptual Based Image Gloss and Color on the Evaluation of Image Preference

This study explores the correlation between perceptual based image gloss and color attribute and proposes a model of predicting the preference of business graphic images. The gloss perception is affected by various factors such as luminance, color, substrate, and micro gloss. For quantifying gloss, physical gloss measurement and visual gloss model has been developed with an acceptable correlation between objective measurement and subjective assessment. However, how the gloss perception correlates with color on customer-like image under a typical office viewing condition has been a remaining question. To answer this question, this study focuses on the effect of both image gloss perception and highly chromatic colors on the overall image preference. Vividness is a term representing chromaticness of colors. The color attribute of business graphic images is explained as vividness attribute by preferred-vividness and vividness metrics. Three psychophysical experiments are conducted in total: gloss perception on print samples on plain paper, preferred image gloss from various test images, overall image preference based on vividness and gloss level of the whole print. Consequently, business graphic image preference is modeled by CIELAB Chroma and lightness, and mean gloss.

J. Cosmet. Sci., 59, 431–440 (September/October 2008) Red pigment from Lithospermum erythrorhizon by supercritical CO2 extraction

SynopsisIn this study, a stable red pigment was prepared from Lithospermum erythrorhizon via supercritical carbon dioxide extraction. The optimal extraction conditions were 400 bar and 60°C. The patch tests indicated that up to 10% of the red pigment was acceptable from a skin irritation standpoint. According to the results of the CIE LAB chromaticity test, the color difference was acceptable when compared to commercial synthetic red pigments. The light‐illuminated color stability test indicated that the pigment was more stable than the red pigment extracted with ethanol. The higher stability was also demonstrated in the DPPH anti‐oxidant activity test. The supercritical red pigment harbored elevated amounts of shikonin and derivatives, and appears to be usable as a stable red pigment for cosmetic color products.

Colorimetric study of SCOTDIC colour specifier

In this study, SCOTDIC cotton standard colours (a physical exemplification of the Munsell system) were studied extensively. L*, a*, b* values were measured and plotted to check the uniformity of the Munsell (SCOTDIC) hue, value and chroma values in a CIELAB diagram. Although for some borderline hues the hue angles were quite different than expected (around 0° or 360°), the correlation between SCOTDIC hue and CIELAB hue angle was fairly good and the correlation between SCOTDIC value and CIELAB lightness was also quite high. However, the correlation between SCOTDIC chroma and CIELAB chroma was only moderate. In the CIELAB diagram, the constant SCOTDIC hue and constant chroma loci took the shape of approximately linear radial lines starting from the origin and approximately concentric circles with the origin as their centres, respectively. However, some deviations were observed for high chroma colours and yellow hues in the respective cases. The instrumentally predicted Munsell notations were compared with the actual SCOTDIC notations. Some deviations of the SCOTDIC system from the Munsell system were observed.

Physical evidence in drug intelligence, Part 2: discrimination of packaging tapes by colour

The authors have considered routine exploitation of physical evidence from seized shipments of illicit drugs for intelligence purposes. Part 1 of this series addressed the identification of polymer type within the adhesive of packaging tapes and raised important issues with regard to how data should be collated in a database as a basis for reliable drug intelligence. This article expands on this topic by addressing the use of colour for achieving the same aim. By using a relatively simple instrumental technique to analyse opaque ‘brown’ packaging tapes, it was found that colour was an effective way to discriminate between different adhesive tape samples. However, initial results showed that the analysis of colour in packaging tapes was more complex than assigning semi-subjective names to particular hues (e.g. light brown, green brown, etc.). Instead, samples in the population often differed only slightly from one another and hence proved difficult to categorise. Thus, a database or analyst must avoid using such ‘discrete’ labels and instead make use of ‘continuous’ numerical data. Here, CIELab chromaticity coordinates were used to define representative colour spaces for each tape sample and these were then compared to determine whether two such volumes intersected. This process would decide whether or not the samples could be discriminated. While several sets of data were compared, further work needs to be carried out into the consistency of colour within single rolls of tape or batches of tape.

Quality improvement of non-sulphited mango slices by drying at high temperatures

An optimum drying routine for producing non-sulphited mango slices has been developed. The interaction of essential drying parameters (air temperature, air velocity, dew point, slice thickness and drying time) on water activity ( a W) and browning was determined. Microbiological stability of the dried product was achieved at a moisture content of 17% wet base (w.b.) corresponding to a W = 0.6. Browning was monitored by the red colour shade of the product (CIE-Lab chromaticity coordinate a*). Drying air temperature and drying time were shown to be the primary factors influencing product colour and a W. In contrast to common practice, drying for about 6 h at elevated air temperature (80 °C), instead of 50 or 60 °C for a longer time, was optimal, since significant colour changes of the mango slices were not observed even without the use of any chemical or thermal pre-treatment. Moreover, at increased temperature, drying time was considerably shortened from about 9 h to 6 h, resulting in significant extension of the drying capacity. Industrial Relevance The suggested process concept for dried mango slices based on high-temperature drying is of utmost significance for the international marketing of dried fruit products. Chemical pre-treatments such as sulphitation often used to minimise quality deficiencies could be avoided. Sulphitation has been recently under critical consideration with respect to allergen labelling of foodstuffs implemented by EU-Member States in November 2004 (Directive 2003/89/EC) [Directive 2003/89/EC. Official Journal of the European Union, 25.11.2003, pp. L308/15–18 ( http://europa.eu.int/eur-lex/pri/en/oj/dat/2003/l_308/l_30820031125en00150018.pdf)]. Export quality was improved and the drying process simplified, improving the utilisation of drying capacities. Particularly referring to an application of the technology in small- and medium-sized enterprises with limited investment possibilities, the suggested novel drying procedure in mango processing aimed at the optimisation of well-established simple drying methods instead of choosing technically more sophisticated technologies.

Color and Texture Image Retrieval Using Chromaticity Histograms and Wavelet Frames

In this paper, we explore image retrieval mechanisms based on a combination of texture and color features. Texture features are extracted using Discrete Wavelet Frames (DWF) analysis, an over-complete decomposition in scale and orientation. Two-dimensional (2-D) or one-dimensional (1-D) histograms of the CIE Lab chromaticity coordinates are used as color features. The 1-D histograms of the a, b coordinates were modeled according to the generalized Gaussian distribution. The similarity measure defined on the feature distribution is based on the Bhattacharya distance. Retrieval benchmarking is performed over the Brodatz album and on images from natural scenes, obtained from the VisTex database of MIT Media Laboratory and from the Corel Photo Gallery. As a performance indicator recall (relative number of correct images retrieved) is measured on both texture and color separately and in combination. Experiments show this approach to be as effective as other methods while computationally more tractable.

Design and performance of a color chart based in digitally processed images for sensory evaluation of piquillo peppers (Capsicum annuum)

AbstractA chart of color standards for visual color evaluation of the piquillo pepper (Capsicum annuum) has been designed. The chart comprises six rectangular regions of digitally processed images of piquillo peppers covering the observed visual range of variability in this product. Colorimetric characterization of piquillo peppers and the color chart has been made using instrumental color measurements. Both trained and untrained sensory panels tested the reliability of the designed color chart. The Pearson correlation coefficient between color chart scores and subjective color quality scores is 0.831 (P < 0.01). Correlation between all instrumental color coordinates, with the exception of CIELAB a*, and visual color chart scores are significant at P< 0.001 and Pearson correlation coefficients range from −0.747 with CIELAB chroma C* to −0.926 with CIELAB hue angle h. Repeatability of visual color chart scores is completely satisfactory, having found no statistically significant differences between color chart scores in samples evaluated twice by panelists. © 2004 Wiley Periodicals, Inc. Col Res Appl, 29, 305–311, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20026