GB/T 39648-2020Textiles - Tests for colour fastness - Determination of colour fastness grades by digital imaging techniques (English PDF)

1 Scope

This Standard specifies the methods for evaluating the discoloration grade of the specimen (according to Annex A) and the evaluation of the staining grade of the standard backing fabric (according to Annex B) by digital imaging techniques in the color fastness test. It also specifies the requirements of digital imaging system.

This Standard does not apply to the grading of light fastness tests of textiles.

NOTE: In the color fastness test of textiles described in the ISO 105B series of standards, the gray sample card is not used for the discoloration assessment of the specimen.

This Standard describes the apparatus, equipment settings and calibration methods for assessing discoloration and staining.

2 Normative references

The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.

GB/T 6151, Textiles - Tests for colour fastness - General principles of testing (GB/T 6151-2016, ISO 105-A01:2010, MOD)

CIE S 012/E, Standard method of assessing the spectral quality of daylight simulators for appraisal and measurement of colour CIE 13.3,1995, Method of measuring and specifying the colour rendering properties of light sources, 2nd edition

3 Terms and definitions

For the purposes of this document, the following terms and definitions apply.

4 Instruments and equipment

Annex A (normative) Grading of the degree of discoloration of the specimen

A.1 Principle Measure the original specimen and the tested specimen. The test area is manually selected by the operator or automatically selected by the software. Use CIEDE2000 to calculate color difference. It is converted into a color-changing gray card level through the formula.

A.2 Terms and definitions A.2.1 original specimen The reference sample for evaluating discoloration specified in GB/T 6151.

A.2.2 tested specimen The specimen undergone the color fastness test.

A.2.3 uniform coloured area The test area of the tested specimen is uniform in color.

NOTE: In this definition, the texture, gloss or other characteristics of the specimen that may affect the visual effect of color can be ignored.

A.2.4 non-uniform coloured area The test area of the tested specimen is not uniform in color.

NOTE: In this definition, the texture, gloss or other characteristics of the specimen that may affect the visual effect of color can be ignored.

A.2.5 multi-coloured test specimen Contain multiple colors within the test area of the specimen.

A.3 Instruments Digital imaging devices shall be validated, calibrated or calibrated as described in Chapter 4 and Annex C.

A.4 Specimen preparation

Annex B (normative) Evaluation of the degree of staining of the specimen

B.1 Principle Measure original and post-tested linings. Calculate color difference according to CIEDE2000. Convert it to a stained gray card grade through a calculation formula.

B.2 Instruments Digital imaging devices shall be validated and calibrated as described in Chapter 4 and

Annex C. B.3 Specimens

The original lining and the post-tested lining shall be fixed on white paper or card that is visually uniform and free of fluorescence and opacity. Measure and store the data of the original lining first. It is then compared to the test data of the post-tested lining. The lining specimens within a calibration cycle shall be the same batch of standard lining fabrics.

B.4 Procedures B.4.1 Monochrome specimen B.4.1.1 Measure the color of the original lining. For multifiber lining, the color of each composition shall be measured separately. It is also possible to use the stored raw data of standard lining. But it shall belong to the same batch of standard lining fabrics. Then measure the color of the post-tested lining of the same composition.

B.4.1.2 For uniform coloured area, calculate the arithmetic mean. If the staining on the lining is non-uniform, by mutual agreement, measure the areas with the most severe color change. In this case, the areas with the most severe color changes are selected by the "operator-selected area" (3.5) method, rather than all test areas. The use of this method is noted in the report.

B.4.2 Multi-coloured test specimens For each colour of the multi-coloured test specimen, repeat the test procedures for the monochromatic specimen according to B.4.1. Test results for each color need to be reported separately.

If the different colors of the specimen are stained with each other, then in accordance

Annex C (normative) Verification chart

C.1 Purpose The verification chart is to convert the RGB value of the image captured by the digital camera into the CIEXYZ value, so as to facilitate the measurement of the color of the image.

C.2 Number of colors in verification chart The verification chart shall be composed of at least 150 color blocks of different colors, so as to ensure the measurement accuracy within the CIE color space.

C.3 Color reference measurement of verification chart Use a spectrophotometer (diffuse: 8°, including specular component) to measure the color of each color patch in the verification chart. The measuring instrument shall be maintained at least once a year in accordance with the instructions of the instrument. Its performance shall be checked by a series of reference materials. These reference materials shall be certified and calibrated. The reflectance values are traceable to national standards.

C.4 Measurement data of verification chart The reflectance data of each color block is recorded and stored in the system software as reference data for each camera calibration.

After each periodic maintenance of the instrument, or after using a new calibration color card, new spectral data shall be replaced.

C.5 Requirements for verification chart Before cutting each color block in the chart, its color shall be measured to ensure the accuracy of chart verification.

The size of each color block shall meet the requirements of the measurement software to measure each color. Generally, about 10mmx10mm is more suitable.

When installing the color block on the chart template, care shall be taken to avoid contamination or damage to the surface color.

Each color block shall be separated by a black border. Adhere a layer of stencil to the

Annex D (informative) Summary of the international joint test report on the grading of color fastness to digital imaging techniques

D.1 Introduction The full detailed report has been submitted to ISO TC 38/SC 1 N2476. This appendix is a brief summary of the report and conclusions.

D.2 Test range The contents of the inter-laboratory test analysis are as follows:

a) Visual assessment:

- Differences between assessors;

- Differences between laboratories.

b) The effect of different calculation formulas for staining and discoloration.

c) Consistency between instruments.

D.3 Methods D.3.1 Laboratories and assessors This international inter-laboratory test consists of 7 laboratories, 17 assessors (technicians): 3 each in laboratories in China, Korea, Sweden and France, 1 in a laboratory in the US, 2 in each of the UK and German laboratories. However, it shall be noted that after 3 Korean technicians perform visual assessment separately, the average value is used only for analysis. Therefore, the data assessed by the other 14 individuals are all valid. In these tests, all assessors are trained and experienced in the eye grading of colour fastness.

D.3.2 Samples There are a total of 72 samples used for staining evaluation, 48 pairs of samples used for discoloration evaluation. There are differences in lightness, chroma, hue or comprehensiveness between dyed cloth samples. It can produce 72 color changing samples. 8 sets of multifiber samples are stained. Different staining grades can be produced for different fiber components. All samples are bound on visually uniform white cards. They are identified with a unique number. Each laboratory grades the