Investigating the effect of texture on the performance of color difference formulae

To predict the perceived color differences, the effect of the surface texture on the performance of the color difference formulae was investigated. To this end, knitted polyester fabrics with eight different textures were prepared. The fabrics were dyed by seven dyestuffs in five different depths. The selected pairs from the five samples with different depths in each hue covered small to large color differences. The assessed pair of samples had the same texture and hue, but different depths. A panel of 23 observers assessed the color differences of the pairs by gray scale method. The results showed that for the textile samples with different texture structures, the CIEDE2000 (2:1:1) performed the best followed by CMC (2:1:1), CIE94 (2:1:1), and CIELAB with approximately same performance. In addition, the magnitude of color difference influenced the ability of the formulae to predict the visual assessments and the best performance obtained for medium color differences. The comparison between eight different texture groups indicated that the texture structures of the pairs significantly affected the performance of the color difference formulae. For instance, the PF/3 measures obtained for the eight texture groups by CIEDE2000 (2:1:1) color formula could be varied between 21.98 and 33.37 PF/3 units. © 2009 Wiley Periodicals, Inc., Col Res Appl, 2010.     

Spectral interpolation errors

Several CIE Technical Committees discussed the advantages and disadvantages of different spectral interpolation methods during the past years. Linear, Lagrange, cubic spline, and Sprague methods were under discussion. We have investigated the colorimetric differences caused by using the different interpolation methods, and showed that Lagrange, cubic spline, and Sprague methods provide very similar results for most well‐behaved spectra. As a further result, we found that the 5‐nm sampling and using the 5 nm tables of the CIE Technical Report “Colorimetry” is almost as good as an interpolation to 1‐nm sampling and colorimetric calculation using the 1‐nm tables of the CIE colorimetric standards. © 2005 Wiley Periodicals, Inc. Col Res Appl, 30, 348–353, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.     

Reproducibility of the bromthymol blue standards used for color specification of virgin olive oil

Three replicates were prepared for each of 60 BTB (bromthymol blue) standards, which are usually employed to determine the color of virgin olive and seed oils, and their colors were measured by spectrophotometric and spectroradiometric techniques on a monthly basis over a year. Although in principle both techniques are valid, their results are weakly correlated. The major color change of the BTB standards occurred soon after sample preparation; after 5 mon, the color stabilized at approximately 3.0 Commission Internationale de l’éclairage 1976-(L^*a^*b^*) (CIELAB) units, with respect to the initial values. Therefore, after preparation, a certain waiting period would be advisable before using the BTB standards. The color of the BTB standards changes over time in the sense of becoming lighter, more saturated, and less greenish. In the monthly periods after the fifth month, the average color change of the BTB standards was negligible, being slightly lower than the average variability of the three replicates (which is around 1.5 CIELAB units).     

CIELAB与CIECAM02明度均匀性的研究

选用孟塞尔新标数据,对CIELAB和CIECAM02的明度均匀性进行研究。通过MATLAB编程实现数据的转换和处理,并对孟塞尔明度值V和CIELAB颜色空间的L值、及V值和CIECAM02色貌模型J值采用最小二乘法拟合绘图,并结合均方差和相关系数对拟合结果进行评价。结果证明CIELAB的明度均匀性优于CIECAM02。为颜色空间的修正、优化和应用提供理论和实验参考。     

Color image fidelity metrics evaluated using image distortion maps

Several color image fidelity metrics are evaluated by comparing the metric predictions to empirical measurements. Subjects examined image pairs consisting of an original and a reproduction. They marked locations on the reproduction that differed detectably from the original. We refer to the distribution of error marks by the subjects as image distortion maps. The empirically obtained image distortion maps are compared to the predicited visible difference calculated using (1) the widely used root mean square error (point-by-point RMS) computed in uncalibrated RGB values, (2) the point-by-point CIELAB ΔE₉₄ values (CIE, 1994), and (3) S-CIELAB ΔE₉₄, a spatial extension of CIELAB ΔE metric. The uncalibrated RMS metric did not predict the perceptual image distortion data well. The point-by-point CIELAB ΔE₉₄ metric provided better predictions, and the S-CIELAB metric, which incorporated the spatial color sensitivity of the eye, gave the most accurate predictions. None of the metrics provided an excellent fit to the data. Image areas with poor predictions were concentrated in regions containing large negative local contrast. When these areas were excluded from our data analysis, both S-CIELAB and CIELAB predictions had much better agreement with the perceptual data. This suggests that the next step in improving color image fidelity metrics is to redefine color difference formula such as CIELAB ΔE₉₄ in terms of local contrast.     

Photocolorimetric determination of yolk colour in relation to selected quality parameters of eggs

BACKGROUND: Determination of egg yolk colourity and colour was carried out by means of a new photocolorimetric methodology based on the CIELAB system. Measurements (after gloss elimination) were performed using a Color Guide Sphere Spex photocolorimeter. For comparison, a standard method according to the Yolk Colour Fan^® (Roche) was used. RESULTS: Yolk colourity was measured in 252 eggs from layers of Isa Brown breed (aged 51–80 weeks). The colourity parameter L* ranged from 43.42 to 68.51. The parameter a* ranged from 0.05 to 13.49 and the parameter b* ranged from 22.38 to 48.18. The normal (Gaussian) distribution curve for the individual parameters was validated. The resulting number of 8700 combinations of yolk colour parameters was given by multiplication of possible results in the experiment while taking into account the instrumental accuracy. All results according to the Yolk Colour Fan^® (Roche) scale represented a range of three colour stripes. CONCLUSION: The photocolorimetric determination is more precise than the Yolk Colour Fan^® (Roche) method. No correlation between yolk colourity parameters and yolk cholesterol concentration was found. The highest correlation (r = ?0.919) was observed between yolk colourity parameter b* (yellow colour) and total egg weight. Copyright © 2009 Society of Chemical Industry     

Time course of the colour of young red wines from Vitis vinifera L. during ageing in bottle

The colour characteristics of red wines from Vitis vinifera L. cv Tempranillo, Graciano and Cabernet Sauvignon (vintage 2000) from Navarra (Spain), was studied during 26 months of ageing in bottle through the evaluation of the wine visible spectrum and of several colorimetric indices (colour intensity, %red, %yellow, %blue, %dA and tint) and CIELAB variables (L*, C*, h, a* and b*). During ageing in bottle, the spectrum of Tempranillo wine (pH 4.3) mainly changed in the absorbance range between 420 and 500 nm, whereas Graciano (pH 3.5) and Cabernet Sauvignon (pH 3.6) wines registered a decrease in absorbance in the interval between 500 and 560 nm. The time course of the different wine colour parameters was found to fit either a second‐order polynomium or a linear model, depending on the grape variety employed. CIELAB variables could be described in terms of their colorimetric index counterparts, showing b* and h relative greater errors. Although the wine total chromatic changes in CIELAB units registered after 26 months of ageing in bottle indicated changes perceivable by the human eye (ΔE* ≥ 2.7) for the three varieties studied, Graciano and Cabernet Sauvignon wines showed a more balanced colour evolution than Tempranillo wine.     

Assessing the affective feelings of two‐ and three‐dimensional objects

The aim of this study is to investigate the impact of physical appearance attributes (in terms of color and shape) on our affective feelings of 2D and 3D objects. Twelve colors were studied, each consisting of 12 two‐dimensional and 12 three‐dimensional shapes. This resulted in 144 2D and 144 3D color‐shape combinations. Each color‐shape combination was assessed using 20 emotion scales in a viewing cabinet by a panel of observers with normal color vision. The results show that there are five underlying factors of these 20 scales, i.e., “activity,” “weight,” “heat,” “softness,” and “complexity”. The first three factors were mainly related to color and the other two were linked with shape. © 2008 Wiley Periodicals, Inc. Col Res Appl, 34, 75–83, 2009.     

A hypothesis regarding the poor blue constancy of CIELAB

The poor blue constancy of the CIELAB equations has been noted by a number of researchers, and various proposals have been made to address this shortcoming. The specific issue is the tendency for highly chromatic blues to appear more purple as the chroma is reduced for a constant hue angle. The root cause for the poor CIELAB blue constancy has been an open question, although one possibility is a basic deficiency in the CIELAB equations. An alternative hypothesis is that the equations, in combination with color matching functions with a distinct secondary lobe on the x‐bar or long‐wavelength sensitive channel, such as those found on the International Commission on Illumination (CIE) 1931 and 1964 Standard Observers, are problematic. The spectral curves of a constant hue IPT (Intensity, Protan, and Tritan) blue step ramp displayed on a CRT are used to explore this hypothesis. Additional discussion examines the use of sharpened sensors and achieving parallel tritanopic confusion lines in the CIELAB color space. The results suggest that use of the CIE Standard Observers with the CIELAB equations results in poor blue constancy and distorted tritanopic confusion lines. © 2003 Wiley Periodicals, Inc. Col Res Appl, 28, 371–378, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.10180     

The feasibility of establishing new color image scales using the magnitude estimation method

Color image is one of the most important factors in art and design. In general, artists and designers apply their own personal image meanings into their work. However, the image meaning for a specific work is frequently in conflict with those of the general observer. Thus it is necessary and important to derive one set of merit color image scales which can be utilized to predict the color image meanings of works in parallel with the average person's perception and which can also serve as a guide for artists and designers. In this study, the psychophysical method (magnitude estimation method), usually used in visual measurement of color appearance, was employed to attempt to establish new color image scales to evaluate the color image meanings of works matching those of the average person. The results show that new color image scales WIP are developed, and the relativity between the latest color image scales WIP and the color attributes (say Lightness L*, Hue h, and Chroma C*) of the CIELAB color space is also discussed. The total mean value of coefficient of variation for the results of visual assessment in the experiment of evaluating the color image meanings of the 207 color specimens used, in general, is about 36, similar to that for those experiments conducted using the psychological method. Also, a good relationship between the new color image scales and the color attributes of the CIELAB color space can be found. © 2007 Wiley Periodicals, Inc. Col Res Appl, 32, 463–468, 2007