The purpose of this video is to guide viewers through the process of defining targets, calculating tolerances, and applying modern color difference models in quality control. By combining visual acceptance with statistical analysis and accounting for inter-instrument agreement, manufacturers can establish practical, perception-based tolerances that maintain product quality and customer satisfaction. The module also highlights how advanced tolerancing methods such as CMC, CIE94, and CIE2000 improve alignment between measurement data and human visual perception.

Introduction

Color standards and tolerances are essential tools in ensuring consistent product quality across manufacturing processes, suppliers, and geographic locations. This module explains how to establish color targets, calculate tolerances, and apply advanced tolerancing models that better reflect human perception.

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Establishing Targets

Targets begin with visual acceptance—a mutual agreement between customer and supplier about what constitutes acceptable color. A set of acceptable samples is measured instrumentally, and the averaged results from the starting point for target values. This ensures that instrumental data is tied directly to what people agree “looks right.”

Instrument Dependence and Agreement

Color measurement is instrument dependent. Even identical models from the same manufacturer may report slightly different values. To ensure consistency across multiple sites, Inter-Instrument Agreement (IIA) must be factored into tolerances. This can be achieved by circulating reference samples for measurement across all instruments and combining results.

Statistical Basis of Tolerances

Once acceptable samples are measured, tolerances are derived from statistical variation. Standard deviation is calculated, and a general rule of three times the standard deviation equals a 99% confidence level. This approach defines the tolerance window around the target values, providing an objective, repeatable framework for quality control.

Combining Uncertainty and IIA (Inter-Instrument Agreement)

When targets are distributed across multiple locations, tolerances must account for both measurement variation and inter-instrument agreement (IIA). These uncertainties can be combined mathematically by taking the square root of the sum of the squares. The resulting tolerance range is slightly broader but ensures consistency across different instruments and sites.

Evolution of Tolerancing Models

Traditional tolerances based only on L*, a*, and b* values may not fully reflect visual sensitivity. To address this, advanced models were developed:

• CMC (Color Measurement Committee)
• CIE94
• CIE2000

These models incorporate chroma, hue, and lightness weighting to better align with how humans perceive differences. The L:c ratio, often set at 2:1, reflects the fact that people notice hue and chroma shifts more readily than lightness changes.

Practical Application of CMC

When statistical tolerances and IIA values are applied to CMC, the model often shows that tolerances are still within a commercially acceptable match, typically defined as ΔE less than 1. In many cases, tolerances for L* can be expanded while still remaining visually acceptable, demonstrating how perception-based models provide greater flexibility without sacrificing quality.

Conclusion

Standards and tolerances are built on a combination of visual agreement, statistical rigor, and perceptual models. By starting with visual acceptance, calculating targets and tolerances statistically, accounting for inter-instrument variation, and applying advanced tolerancing equations, manufacturers can ensure consistent, high-quality color that meets both technical and customer expectations.

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To learn more about Color and Color Science in industrial QC applications, click here: Fundamentals of Color and Appearance

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