Colour measurement correction model for improving inter-instrumental agreement

Pao Yue-kong Library Electronic Theses Database

Colour measurement correction model for improving inter-instrumental agreement

 

Author: Chung, Yiu-sing
Title: Colour measurement correction model for improving inter-instrumental agreement
Degree: Ph.D.
Year: 2003
Subject: Hong Kong Polytechnic University -- Dissertations
Colorimetry
Department: Institute of Textiles and Clothing
Pages: xix, 164, lxxv leaves : ill. ; 30 cm
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b1692731
URI: http://theses.lib.polyu.edu.hk/handle/200/4239
Abstract: Accurate colour measurement is a very important factor to determine the quality of finished products in the colour-related industries, such as paint, printing or textiles. In the past, visual colour assessment was used to match colours and physical samples played an important role. The drawback of the visual colour assessment is that, even in the case of well trained colourists. performance is influenced by a number of parameters including psychological, medical and environmental factors. In addition, during the transportation and assessment of the physical samples, there is the risk of soiling. These factors may account for mistakes in colour identification, even in the case of well trained and experienced colourists. The objective colour communication method is an alternative method to enhance both colour matching and colour assessment. Because of advances in spectrophotometry and information technology, colour quality may be expressed in a digital format and communicated to other parties by electronic means. This format of colour communication represents the trend in view of the regionalisation and globalisation of the textile and apparel industries. The spectrophotometer is one of the important instruments for colour matching and colour measurement. It performs at a finite level of accuracy but, as an electro-mechanical-optical device, it exhibits measurement errors relative to a theoretically error-free instrument that users must accept. Most of the modem spectrophotometers have satisfactory repeatability and the suppliers of these instruments claim that the repeatability of the measurement on the same instrument is lower than 0.01 CIELAB ΔE units. In this research project, it was found that the repeatability of the advanced spectrophotometers ranged from 0.044 to 0.112 CIELAB ΔE units for the dual beam spectrophotometers while, for the single beam spectrophotometer, the repeatability ranged from 0.115 to 0.377 CIELAB ΔE units. When considering the inter-instrumental agreement of different makes of spectrophotometers, the manufacturers also claim that the inter-instrumental agreement of those of similar design is lower than 0.15 CIELAB ΔE units. However, in this research, it was found that the inter-instrumental agreement between the spectrophotometers manufactured by the same manufacturer ranged from 0.526 to 0.611 CIELAB ΔE units. The inter-instrumental agreement between the spectrophotometers manufactured by different manufacturers ranged from 0.575 to 0.854 CIELAB ΔE units. Since the inter-instrumental agreement of the spectrophotometers is very low. various mathematical models have been developed in order to improve the inter-instrumental agreement between spectrophotometers. In past research, those mathematical models were developed using calibration data from the GLOSSY Ceramic Tiles which may not be suitable for application to textile and paper samples. For the above-stated reasons, in this project a new mathematical model, named the R-Model, was developed using both GLOSSY and MATT Ceramic Tiles. Spectral data from 400 - 700 nm was analysed using the concept of bandpass correction as well as the multilinear regression method. The performance of R-Model was found to be better than that of the previous models. The improvement of the inter-instrumental agreement was up to 90% for the ceramic tiles. Moreover, the inter-instrumental agreement for the other coloured samples such as textile and paper samples also improved accordingly, from 26.1% to 57.6% and 13.7% to 61.1% respectively. Using this model, the global colour communication between designers, coloration companies and buyers can be further enhanced, and also the non-physical sample communication method through the use of digital reflectance data can become feasible.

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