Computer Color Matching Alogrithm

Computer Color Matching (CCM) has become one of the standard methods in the paint, plastics and ink industry for fast and accurate recipe prediction. The advantages when compared to manual matching include better first shot accuracy, reduced number of corrections, exact prediction of metamerism and price and thus higher efficiency and productivity.

A color matching system consists of a spectrophotometer, a PC and the matching software itself. The major differences between systems are the spectrophotometer, the mathematical algorithm of the software, the software features and user-friendliness of the software and, last but not least, the ongoing service and support offered by the supplier.

The accuracy of a match is dependent not only on the software and its mathematics but also on the accuracy of the calibration samples, the reproducibility in production and between the laboratory and the production. The quality of production can only be influenced by the user of the matching system. However the reliability of the measurements directly depends on the instrument used.

In this context, the short- and long-term repeatability of a spectrophotometer is very important as is the inter-instrument and inter-model agreement.

A critical case in color matching, which cannot be solved by standard matching software is mat­ching of products which are neither opaque nor transparent, but translucent. In theses cases, not only the color but also the opacity has to be matched. This cannot be achieved with the commonly used Kubelka-Munk-Model or Lambert-Beer Law. Other physical models have to be found to de­scribe the complex effect of absorption and scattering of such layers.

A layer is translucent, if there is a difference between the measurements of the layer over white background compared to the one over black background. Therefore paints and inks are applied on contrast cards and plastic samples are measures over such cards or with help of the opacity holder of the instrument.

The bigger the color difference between the layer over white and over black, the more translucent it is. For translucent layers, there are 2 more variables to take into account: the thickness of the layer and the background. Both will change the color appearance if they are changed.

Latest CCM technology uses multi-flux algorithm and is able to handle translucent coatings.