Defining Color Tolerance

What is Color Tolerance?

Color Tolerance is a measure of the acceptable difference between different colors, which determines whether the color deviation range is within the expected range. Color tolerance uses standardized values to quantify the similarity or difference between colors, which is particularly critical in color-sensitive industries such as printing, textile and electronic manufacturing.

Color tolerance is critical in industry because different batches of products may have slight color differences due to materials, lighting, temperature, etc. By defining and controlling the tolerance range, the industry can maintain a high degree of consistency in product color under changing materials, lighting, and environmental conditions. Standardized tolerance values ensure color quality and consistency, avoid customer dissatisfaction caused by color differences, and ensure color consistency during the production process.

Relationship between color difference tolerance and Delta E

Delta E (ΔE) is a standard method for quantifying color difference. The lower the Delta E value, the smaller the difference between the two colors. The color difference tolerance is generally set based on different standards of Delta E (such as ΔEab, ΔE94 and ΔE*00) to control color changes within an acceptable range.

Evaluation method of color difference tolerance

The evaluation of color tolerance requires comprehensive consideration of multiple factors. First, we need to determine the color standard for evaluation, which is usually established by the industry or national standards agency. Second, we need to select appropriate lighting conditions and observation angles to ensure the objectivity and accuracy of the evaluation results. In addition, for the visual evaluation method, we need to provide professional training for the evaluators and select representative people to conduct the observation.

Color difference tolerance and calculation methods in different color spaces

The tolerance between the standard value and the measured value can be calculated by measuring the coordinate distance between the standard color and the sample color in the L*a*b three-color space. The color difference space area described by the color tolerance is divided into three types: box tolerance (CIELab), fan tolerance (CIE LCH) and spherical tolerance (CMC2:1). The smaller the volume of the color difference space area described by the tolerance, the higher the accuracy of the color.

1. CIELAB Tolerance Method

The CIELAB tolerance formula is centered on the standard and then gives individual L*a*b* values a positive or negative (+/-) error range, plotted as a square tolerance range.

△L*=L*sample-L*standard (brightness difference)

△a*=a*sample-a*standard (red/green difference)

△b*=b*sample-b*standard (yellow/blue difference)

This tolerance formula can simply and directly show the cause of color error, as shown in the following table:

2. CIELCH Tolerance Method

CIE LCH is centered on the standard and then gives individual LCH values, plus or minus error (+/-) ranges, plotted as fan-shaped tolerance ranges.

△L*=L*sample-L*standard (brightness difference)

△C*=△C*sample-△C*standard (saturation difference)

△ Ｈ * = [ (△ Eab) 2 - (△ L *) 2 - (△ C) 2] 1/2 (hue difference)

From the LCH tolerance formula, we can clearly analyze the causes of color saturation and hue errors as shown in the following table:

3. CIE △Eab tolerance method

The calculation of CIE*Eab tolerance is based on the definition of "tolerance sphere" to measure color difference by taking standard color samples or original technical parameters as reference points in L*a*b* color space. In practical applications, the color sample to be tested and the standard color sample to be compared (such as output color) are placed on the color difference sphere to measure the color difference between the two. If the color difference value is within the tolerance sphere, the color difference is considered acceptable; if it exceeds the tolerance sphere, it is unacceptable.

CMC color difference model

The size of the tolerance sphere is usually set according to the customer's requirements for acceptable color difference. The color difference value is expressed as ΔE. Usually:

· In the printing industry, color differences between ΔE values of 2 and 5 or 6 are acceptable.

· When ΔE<2, the color difference is difficult to detect by visual observation.

· Higher tolerance values (ΔE < 4) allow for color differences that can be discerned by the naked eye but will not significantly affect the visual effect.

The CIE*Eab tolerance formula is as follows:

In the formula, ΔE*ab represents the total color difference, and ΔL*, Δa*, and Δb* represent the differences in color brightness and chromaticity, respectively.

Generally, the larger the ΔE*ab value, the greater the color difference. The acceptable range of color difference will vary in different situations. For example:

· The human eye's tolerance for color evaluation is about 75% accurate.

· The accuracy rate when calibrating the film is about 85%.

· The accuracy rate of the sphere calibration is as high as 95%.

Therefore, when selecting color difference tolerance, the appropriate tolerance standard should be selected according to the actual application scenario to meet the needs of color quality control.

Applications of Color Tolerance

Color tolerance is widely used in quality control to ensure the color consistency of products and avoid color deviation between batches. Through tolerance management, the color consistency between batches can be effectively maintained, which is especially important for color-sensitive products such as textiles and automobiles. Color tolerance also ensures that consumers get a uniform appearance experience, thereby enhancing the brand image. Different industries set appropriate tolerance standards according to their characteristics to ensure the stability of color under different production conditions.

Color Tolerance categories and settings

Objective Tolerance and Subjective Tolerance

Objective tolerance is based on the data results of measuring instruments, while subjective tolerance relies on the visual judgment of the human eye and is usually used in scenarios where human visual experience needs to be considered.

Static Tolerance and Dynamic Tolerance

Static tolerance is the color difference tolerance set under the same environmental conditions, while dynamic tolerance takes into account changes in environmental conditions, such as differences in lighting or viewing angles.

Factors affecting tolerance setting

Light source and environmental factors

Different lighting and environmental conditions will affect color performance, so lighting consistency must be considered when setting tolerances.

Material and surface properties

Different materials reflect color differently, and surface texture and glossiness can also affect the visibility of color differences.

Observation angle and measurement geometry

Changes in viewing angle and measurement conditions will cause color differences to appear differently, so standardized measurement methods and consistent viewing angles need to be considered when setting tolerances.

How to set appropriate Color Tolerance?

The setting of color tolerance needs to be based on the final use of the product and customer needs to ensure that specific requirements are met. Customer expectations have an important impact on the formulation of color tolerance standards, especially in high-end product manufacturing. In the process of tolerance setting, you may encounter challenges in light, environment, materials, etc., which need to be solved by optimizing the test environment. By regularly calibrating and adjusting the color tolerance, the stability and consistency of product color can be ensured.

Color difference tolerance standards in different industries

Printing industry: Usually the tolerance value is set between 2-5ΔE to ensure the color consistency of printed products.

Automobile manufacturing: The color consistency of the car body is extremely high, and the tolerance value is usually set within 1-2ΔE.

Textile industry: Due to the possibility of slight differences between dye batches, the tolerance range is generally looser, but it is still necessary to ensure consistent color tone.

Cosmetics industry: Strict requirements for consistency in appearance and texture, and color difference tolerances are usually set very small to ensure color consistency of products under different light sources.