A preliminary comparison of CIE color differences to textile color acceptability using average observers

Ninety‐six nylon pairs were prepared, including red, yellow, green, and blue standards, each at two lightness levels with CIE94 ΔE units ranging from 0.15 to 4.01. Visual assessments of acceptability were carried out by 21 females. Logistic regression compared visual results to four color‐difference equations, CIELAB, CMC, CIE94, and CIEDE2000. It was found that CMC most closely represented judgments of average observers. © 2005 Wiley Periodicals, Inc. Col Res Appl, 30, 288–294, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20124     

Image quality evaluation for high dynamic range and wide color gamut applications using visual spatial processing of color differences

High dynamic range (HDR) and wide color gamut imagery has an established video ecosystem, spanning image capture to encoding and display. This drives the need for evaluating how image quality is affected by the multitudes of ecosystem parameters. The simplest quality metrics evaluate color differences on a pixel‐by‐pixel basis. In this article, we evaluate a series of these color difference metrics on four HDR and three standard dynamic range publicly available distortion databases consisting of natural images and subjective scores. We compare the performance of the well‐established CIE L*a*b* metrics (ΔE₀₀ , ΔE₉₄ ) alongside two HDR‐specific metrics (ΔE_Z [J_za_zb_z], ΔE_ITP [IC_TC_P]) and a spatial CIE L*a*b* extension (). We also present a novel spatial extension to ΔE_ITP derived by optimizing the opponent color contrast sensitivity functions. We observe that this advanced metric, , outperforms the other color difference metrics, and we quantify the improved performance with the steps of metric advancement.     

Influence of repeated firings on the color parameters of two different all‐ceramic materials

All‐ceramics materials have been widely used in dental practice due to advantages of esthetic outcome. Color parameters, one of the major factors for the esthetic outcome, are affected from different factors such as repeated firings, chemical composition and thickness. In clinical practice, ceramics were frequently subjected to the repeated firings, but the effects of the repeated firings on the color parameters have been underestimated or unknown, so the aim of the study was to evaluate the effects of the repeated firings on the color parameters of all‐ceramic materials. Two commercially available A2 shaded all‐ceramic systems were used in this study (lithium disilicate pressable ceramics and computer aided design/computer aided manufacturing [CAD/CAM] fabricated zirconia). Ten samples for each group (zirconia and lithium disilicate) were prepared and subjected to repeated firings, respectively (1st, 3rd, 5th). Color measurements were performed after each repeated firings using a colorimeter (Minolta CR 321, Konica Minolta, Tokyo, Japan). The perceptibility threshold and acceptability threshold for color changes (ΔE₀₀) was defined as 0.8 and 1.8, respectively. Statistical analysis of the results was performed by using repeated measures ANOVA for color parameters and using non‐parametric Kruskal‐Wallis and Mann‐Whitney‐U test for ΔE₀₀ values (P < .05). L*, a* values showed statistically significant differences for lithium disilicate pressable ceramics and were not significant the zirconia specimens. ΔE₀₀ values were above the perceptibility level for both lithium disilicate and zirconia specimens. Repeated firings affect the color parameters of the lithium disilicate specimens. As a result of repeated firings, lithium disilicate ceramics become lighter and greener.     

精对苯二甲酸颜色的定量表示和测量

对现有的3种颜色测量方法:目视法、光电积分法及分光光度法进行了比较。探讨了PTA颜色的定量表示和测量方法。     

Multivariate Gaussian subspatial regression applied to predict the effect of phosphate crystallization aging on the color in silicious conglomerates

A new methodology has been applied to the experimental data obtained about a white siliceous conglomerate from Zamora (Spain), which was subjected to 25 cycles of 2 types of aging [freezing/thawing with cooling/heating (T1) and freezing/thawing with cooling/heating + phosphate crystallization (T2)]. Our model (multivariate Gaussian subspatial regression) allows the behavior and prediction of the chromatic coordinates (L*,a*,b*), including more than 25 cycles, to be analyzed. This model is much more flexible than classical models as it allows multiple variable combinations to be predicted in a dynamic way. The final result showed that the conglomerate experiences darkening, yellowing, and reddening, as the number of cycles increase and that the darkening is much less pronounced in T2 due to phosphate crystallization.     

Comparison of the metrics between the CIELAB and the DIN99 uniform color spaces using dental resin composite material values

The sizes for the perceptible or acceptable color difference measured with instruments vary by factors such as instrument, material, and color‐difference formula. To compensate for disagreement of the CIELAB color difference (ΔE^*_ab) with the human observer, the CIEDE2000 formula was developed. However, since this formula has no uniform color space (UCS), DIN99 UCS may be an alternative UCS at present. The purpose of this study was to determine the correlation between the CIELAB UCS and DIN99 UCS using dental resin composites. Changes and correlations in color coordinates (CIE L*,a*, and b* versus L₉₉, a₉₉, and b₉₉ from DIN99) and color differences (ΔE^*_ab and ΔE₉₉) of dental resin composites after polymerization and thermocycling were determined. After transformation into DIN99 formula, the a value (red–green parameter) shifted to higher values, and the span of distribution was maintained after transformation. However, the span of distribution of b values (yellow–blue parameter) was reduced. Although color differences with the two formulas were correlated after polymerization and thermocycling (r = 0.77 and 0.68, respectively), the color coordinates and color differences with DIN99 were significantly different from those with CIELAB. New UCS (DIN99) was different from the present CIELAB UCS with respect to color coordinates (a and b) and color difference. Adaptation of a more observer‐response relevant uniform color space should be considered after visual confirmation with dental esthetic materials. © 2006 Wiley Periodicals, Inc. Col Res Appl, 31, 168–173, 2006     

Correlation and modeling between color variation and quality of the surface between accelerated and natural tropical weathering in Acacia mangium,Cedrela odorata and Tectona grandis wood with two coating

To prevent the photodegradation process, a wide range of coatings have been developed. This study evaluated wood color change (ΔE*) and the surface quality index (SQI) generated by ASTM D‐660 standards in wood protected with polyurethane and varnish finishes of three tropical species (Acacia mangium, Cedrela odorata and Tectona grandis) in two weathering conditions (natural and accelerated condition). In addition, a model was developed to predict ΔE* and SQI in natural weathering based on ΔE* and SQI from accelerated weathering. The results showed that the application of these finishes generated variations in the color parameters of wood before being exposed to the elements. Additionally, it was found that finishes generated increases in ΔE*, especially the varnish type finish, and decreasing of SQI. Finally, models were found to predict color changes or surface quality in natural weathering based on color changes or surface quality in accelerated weathering. The model algorithm was expressed by ΔE* or SQI measured (X) and time exposure (t) in accelerated weathering by equation . With these models, it is possible to predict the equivalence of exposure times in natural weathering in tropical conditions for different kinds of finishes in three tropical species. © 2013 Wiley Periodicals, Inc. Col Res Appl, 39, 519–529, 2014     

On the relations between color,gloss, and surface texture in injection‐molded plastics

The relation between color and gloss of injection‐molded plastic specimens was evaluated by means of a 45°/0° geometry spectrophotometer and a glossmeter. The specimens were plaques having one smooth, glossy field and one rougher, textured region made of two different polymeric materials (acrylonitrile‐butadiene‐styrene and polypropylene) in a range of colors. A significant influence of the lightness L* of the specimens on the measured gloss of the textured field, with a low gloss appearance, was found. This can probably be attributed to a contribution from bulk scattering, which is linked to the reflectance from within the specimen. The influence of texture on the measured color of the plaques was assessed by evaluating the color difference between the smooth field and the more textured area on the specimens. When the surface was textured, the color changed; in general it became lighter and less saturated. The magnitude of the change depended on the color of the material. The darker the material was, the larger was the increase in lightness L* as the surface became rougher. The shift in chroma C* was determined not only by the saturation but also by the lightness of the specimens. Darker specimens exhibited a larger decrease in chroma when the surface was textured. The change in the measured color caused by increasing the surface roughness could be predicted in a satisfactory manner using a model developed for xerographic printing paper. © 2009 Wiley Periodicals, Inc. Col Res Appl, 34, 291–298, 2009     

Clarification of differences between variable achromatic color and variable chromatic color methods in the Helmholtz–Kohlrausch effect

The Helmholtz–Kohlrausch effect consists of two different approaches: the variable achromatic color (VAC) and variable chromatic color (VCC) methods. In this article the difficult conceptual difference between the methods is clarified using new explanations with their schematic figures. The concept of loci with various parameters on B / L or L / Y ratios is completely different between the two methods. The VCC method can determine perceived lightness values for achromatic and chromatic colors in the whole color space. The VAC method gives perceived lightness deviation between reference achromatic color and each of the various test chromatic colors both kept at the same Munsell Value. The VAC method can never give any information on equiperceived lightness to test chromatic colors. Despite the difference between the two methods, misuse of the VAC method is sometimes found for perceived lightness studies of various chromatic colors, because of its ease in observations. An example is shown for the L scale of OSA‐UCS. © 2006 Wiley Periodicals, Inc. Col Res Appl, 31, 146–155, 2006     

Evaluation of intermodel agreement using ISO 13655 M0, M1, and M2 measurement modes in commercial spectrophotometers

Spectrophotometers are routinely used for color measurement and color management in many commercial printing and proofing workflows. In the case of media containing optical brightening agents, ultraviolet (UV)‐induced fluorescence has led to poor levels of agreement between models from different manufacturers, and different models from the same manufacturer. A relevant standard, ISO 13655, has been revised and now clearly defines measurement modes and conditions for the UV component in spectrophotometers. ISO 13655:2009—Graphic Technology—Spectral Measurement and Colorimetric Computation for Graphic Arts Images now defines four measurement modes: M0, M1, M2, and M3. The intermodel difference between 10 commercially available spectrophotometers is evaluated for different substrate types in measurement modes (M0, M1, and M2) as allowed by each instrument. In particular, the authors compare devices using M0 legacy mode versus newer instruments that are compliant with the new M1 and M2 (UV‐included and UV‐excluded) measurement modes. A finding with significant practical applications is that there is greatly improved intermodel agreement between the new generation of ISO 13655‐compliant instruments in M1 (D50) mode when compared with the previous generation of hand‐held spectrophotometers. © 2016 Wiley Periodicals, Inc. Col Res Appl, 42, 27–37, 2017     

Similarities and differences between the concepts of operability and flexibility: The steady‐state case

This article presents a comparative review on the operability and flexibility concepts and their application to process design and control. First, the operability and flexibility methodologies are summarized. Then the application of the operability framework to steady‐state and dynamic systems is illustrated through the examination of several example categories such as linear and nonlinear, square and non‐square systems. The flexibility approach based on the active set strategy is used to study the same examples from the flexibility point of view. The discussed results show that the operability and flexibility approaches examine a process from different perspectives and provide valuable complementary information. © 2009 American Institute of Chemical Engineers AIChE J, 2010     

Investigating the trade-off between operating revenue and CO2 emissions from crude oil distillation using a blend of two crudes

Blending of different crude types is frequently used in petroleum refineries to improve their profitability and products yields. However, energy consumption and consequential CO₂ emissions strongly depend on the types of crude being processed. The trade-off between CO₂ emissions and economic objectives, such as net revenue, is investigated for cases of different crude blends using the multi-objective optimization approach. The first objective is the minimization of CO₂ emissions whilst the second objective is maximizing the net revenue from the crude distillation unit (CDU). A rigorous model is used to estimate CO₂ emissions from different sources within the CDU. This emissions model incorporates pinch analysis for heat integration, to optimize the distribution of utilities related to emissions. Blends of two crudes, 36 API and 27.7 API, are used as feedstock to a rigorous CDU model of the atmospheric crude tower, vacuum tower and heat exchanger network. Lighter crude blends recorded higher CO₂ emissions and net revenue compared with the heavier blend due to the greater distilled fraction. However, CO₂ emissions did not vary linearly with the fraction of each crude, as the heat exchanger network also influenced the degree of heat recovery and consequently the level of CO₂ emissions. The multi-objective solutions show the influence of all 13 of the process variables on the objectives.