Evaluation of methods for verifying the performance of color‐measuring instruments. Part I: Repeatability

Wyble, David R.; Rich, Danny C.

doi:10.1002/col.20320

Cited by 22 publications

(22 citation statements)

References 7 publications

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“…The short‐term repeatability is typically dE ab < 0.05 or even dE ab < 0.01 for d/8 measurements. But long‐term reproducibility and inter‐instrument agreement are generally larger: typically, dE ab < 0.3 or dE ab = 0.2–0.5, with dE ab < 0.15 for d /8 measurements . More specifically, in Table , we have summarized the reported repeatability and reproducibility for a number of widely used commercial spectrophotometers.…”

Section: Improving the Process Of Setting Qc Color Tolerancesmentioning

confidence: 99%

Setting tolerances on color and texture for automotive coatings

Kirchner

Ravi²

2012

Color Research & Application

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In the automotive industry, color quality control is increasingly done by reflection measurements. We discuss how color tolerances are set in specifications to suppliers of add‐on parts and to paint suppliers. We mention several factors that often lead to unrealistically tight settings, and therefore to incorrect rejections and unnecessary high productions costs. We show that this is likely to occur when the dEab color difference equation is used, or when a strict criterion separating pass from fail is used instead of specifying a “grey area” where instrumental monitoring needs to be followed by visual assessments. Unrealistically, tight tolerances also result from halving tolerances in the supply‐customer chain in an attempt to compensate color variations due to uncontrolled application conditions. Tolerances should be widened further when a gap separates an add‐on part from the car body, making visual discrimination of color differences less critical. Other common situations where tolerances should be widened are the presence of visual texture in effect coatings, the lightness of metallic coatings becoming very high (L*> 100) and measurement geometries close to the gloss angle. Finally, we address the issue that instrumental color tolerances should not be tighter than what is allowed by instrumental reproducibility, repeatability, and inter‐instrument agreement. Accounting for these factors, we provide a set of reasonable values for tolerances on color and on visual texture parameters, based on our own practical experience. But realistic tolerance values depend very much on actual conditions, and should be agreed in tripartite discussions among automotive industry, suppliers of add‐on parts, and paint supplier. © 2012 Wiley Periodicals, Inc. Col Res Appl, 39, 88–98, 2014

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Section: Improving the Process Of Setting Qc Color Tolerancesmentioning

confidence: 99%

Setting tolerances on color and texture for automotive coatings

Kirchner

Ravi²

2012

Color Research & Application

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“…Assessment of the performance of the spectrophotometer used – Repeatability (short‐term), reproducibility, inter‐instrument reproducibility, and accuracy – were tested (21). Measurements were performed on the middle third of the facial surface of an extracted human central right incisor and on a ‘2M2’ shade tab.…”

Section: Methodsmentioning

confidence: 99%

Metameric effect between natural teeth and the shade tabs of a shade guide

Corcodel

Helling

Rammelsberg

et al. 2010

European J Oral Sciences

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Corcodel N, Helling S, Rammelsberg P, Hassel AJ. Metameric effect between natural teeth and the shade tabs of a shade guide. Eur J Oral Sci 2010; 118: 311–316. © 2010 The Authors. Journal compilation©2010 Eur J Oral Sci The objective of this study was to evaluate metameric effects, that is, the dependence of the colours of teeth and shade tabs on the illuminant used. The colours of 49 teeth of 37 participants and of the corresponding shade tabs of the 3D‐Master (VITA Zahnfabrik; colour match ΔEab< 2) were measured using an intra‐oral spectrophotometer (VITA Easyshade). Spectral reflectance data (from 400 to 700 nm) were recorded. Commission Internationale de l’Éclairage (CIE) L*a*b* values were calculated for D65 (reference daylight), A (incandescent light), and TL84 (store/office light) as reference illuminants. A modified metamerism index (Mod‐M) and hue‐angle ratios were calculated to express differences between tooth and tab colour relative to the difference observed under D65 illumination. The Mod‐M for teeth and tabs was greater than unity (indicating a greater colour difference relative to D65) by 57.1% for A and by 49.3% for TL84. Hue‐angle ratios of teeth and tabs using the test illuminants were different from those obtained using the standard illuminant D65. If teeth and shade tab matching is conducted using daylight illumination, the colour difference may not be the same under other lighting conditions, leading to perceptible, or even unacceptable, colour differences under these conditions.

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“…4,5,7 For verifying the performance of Easyshade and the validity of the tooth color measurements for the exemplary color space, tests were done on repeatability, reproducibility, inter-instrument reproducibility, and accuracy. 12 Repeatability (short). Thirty measurements on identical spots of an extracted tooth and a shade tab of the 3D-Master shade guide (middle third of facial surface).…”

Section: Verifying the Performance Of Easyshadementioning

confidence: 99%

Using discrete optimization for designing dental shade guides

Cocking

Helling

Oswald

et al. 2009

Color Research & Application

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A key criterion in the design of dental shade guides used for matching tooth color is that the shade tabs cover the natural tooth color space as completely as possible with a manageable number of tabs. Earlier studies have designed hypothetical shade guides from a given population of tooth colors described in the CIELAB system using the goal of minimizing the mean coverage error. In this study, we investigate this topic using the goal of maximizing coverage, meaning that as many measured colors as possible were within a given color difference from the nearest shade tab of the guide. We use techniques of linear discrete optimization to determine the positions of the shade tabs and consider both color difference formulas, CIELAB and CIEDE2000, in an exemplary tooth color population. We obtain coverage error and coverage figures for hypothetical shade guides of various numbers of tabs designed with the goal of either minimizing coverage error or maximizing coverage. Results show that discrete optimization and the goal of maximizing coverage could be used to improve shade guide development. The described technique could be used not only for dental shade guides development, but also for any purpose requiring coverage of as many colors as possible while keeping the number of reference colors manageable.

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Evaluation of methods for verifying the performance of color‐measuring instruments. Part I: Repeatability

Cited by 22 publications

References 7 publications

Setting tolerances on color and texture for automotive coatings

Setting tolerances on color and texture for automotive coatings

Metameric effect between natural teeth and the shade tabs of a shade guide

Using discrete optimization for designing dental shade guides

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