Evaluation of performance of various color‐difference formulae using an experimental black dataset

The objective of this study was to develop a specific visual dataset comprising black‐appearing samples with low lightness (L* ranging from approximately 10.4 to 19.5), varying in hue and chroma, evaluating their visual differences against a reference sample, and testing the performance of major color difference formulas currently in use as well as OSA‐UCS‐based models and more recent CAM02 color difference formulas including CAM02‐SCD and CAM02‐UCS models. The dataset comprised 50 dyed black fabric samples of similar structure, and a standard (L*= 15.33, a* = 0.14, b* = ?0.82), with a distribution of small color differences, in ΔE^*_ab, from 0 to approximately 5. The visual color difference between each sample and the standard was assessed by 19 observers in three separate sittings with an interval of at least 24 hours between trials using an AATCC standard gray scale for color change, and a total of 2850 assessments were obtained. A third‐degree polynomial equation was used to convert gray scale ratings to visual differences. The Standard Residual Sum of Squares index (STRESS) and Pearson's correlation coefficient (r), were used to evaluate the performance of various color difference formulae based on visual results. According to the analysis of STRESS index and correlation coefficient results CAM02 color difference equations exhibited the best agreement against visual data with statistically significant improvement over other models tested. The CIEDE2000 (1:1:1) equation also showed good performance in this region of the color space. © 2013 Wiley Periodicals, Inc. Col Res Appl, 39, 589–598, 2014     

Does hue affect the perception of grayness?

Although gray is defined as an achromatic color sensation varying only in lightness, in practice, grayness can be tinged by any hue within a limited range of chroma. Given the fact that preferred perceived white and black are slightly chromatic, the hypothesis tested in this study is that the preferred perceived object gray is also slightly chromatic. Two psychophysical experiments were carried out to test this hypothesis. A total of 56 color normal subjects assessed 27 different gray patches that varied mainly in hue, in three separate trials. Subjects selected a subset of samples (10 in the first experiment and five in the second experiment) that were considered “most gray” resulting in 168 selected sets of samples. Subjects then ranked their selected subset of samples from most to least gray. A total of 1225 assessments were thus obtained (750 assessments in the first experiment and 465 in the second experiment). Results from both experiments were in good agreement and indicate that greenish blue grays in the range of 190° to 235° of CIELAB hue angle were selected as most gray, thus indicating that the perception of grayness is influenced by hue. © 2014 Wiley Periodicals, Inc. Col Res Appl, 40, 374–382, 2015     

A diagnostic expert system for the dyeing of protein fibres

Coloration of protein fibres is characterised by many variables, each with a different effect on the final product. Because the process can be rather complicated, it is often difficult to achieve the right colour in the first dyeing attempt. Determining the root causes of a given problem tends to be even more challenging. While quality requirements in the textile industry have become increasingly rigorous, seasoned coloration experts have become rather scarce. This situation has exacerbated the need for the development and implementation of expert systems to augment available expertise in this domain. In addition, benefits associated with computer‐based diagnostic systems have become increasingly evident over the past few decades, and the field remains an active area of research. Here we report the design and development of a diagnostic expert system for the dyeing of protein fibres. The system is designed to aid in the identification of root causes of problems with a view to enabling users to arrive quickly at remedial solutions. The performance of the system has been tested and evaluated by human experts and deemed to be highly satisfactory. This diagnostic system can be used to teach students, may be utilised by novice colourists as a problem‐solving tool, and may be employed as a supplementary knowledge resource by seasoned dyers.     

Cognitive comparison of unique and intermediate hues

Eight panels were prepared using the most highly chromatic Natural Colour System (NCS) samples for each hue. Each panel consisted of a test hue and two reference hues, the samples representing either mean unique hues (uH) R, Y, B, or G as determined in earlier experiments or intermediate hues half way between them, (iHs) Or, Pp, YG, and BG. Subjects were asked to determine whether they considered it possible to match the test hue with the reference hues. A total of 45 color‐normal subjects participated in the study in three separate trials with at least 24 h gap between consecutive trials. The results, with very few exceptions, showed that a match was considered possible for the four iHs based on a mixture of adjacent pairs of uHs, while the majority did not believe uHs could be matched based on amounts of adjacent iHs. Statistical analysis of the test results indicates that responses for the two sets of panels were significantly different (P ～ 0, df = 539). The results provide support for Hering's uHs concept. However, a number of subjects believed that a mixture of adjacent iHs can result in a match of the reference uHs. Potential causes may include the use of experimental mean unique and intermediate hues and learned facts of colorant mixture. © 2014 Wiley Periodicals, Inc. Col Res Appl, 40, 264–269, 2015     

Innovative critical solutions in the dyeing of protein textile materials

Even though animal fibres contribute a comparatively low proportion of world fibre production, they are highly sought after and play a significant role in the luxury, high value-added end of the market. Natural protein fibres have two major classes, which may be categorized as keratin fibres (hair or fur), such as wool, cashmere, and other animal hairs, and secreted (insect) fibres with silk as the main fibre in this category. Colouration of protein fibres is characterized by many variables, each with a different effect on the final product. Indeed it is quite complicated to achieve the intended colour in the first dyeing attempt. Dyeing defects are not always due to the actual dyeing process, but may be introduced in earlier production and processing stages. This work attempts to provide a detailed review of the major issues in the dyeing of various protein textile materials in different forms such as loose fibre, yarn, fabric, and garment. An overview of different types of protein fibres is given and a summary of current industrial practices for the dyeing of protein fibres is provided followed by key variables that affect the control of colour in the dyeing of protein fibres. Key steps and critical factors involved in the production of dyed protein textile materials are described in detail and solutions to the problems that may arise at each stage are provided.