Color Difference Calculation of Prints for Machine Vision System

Machine vision inspection system plays an increasingly important role in the printing process control, which is one of the development trends of the printing process control technology. This paper discusses the methods to inspect color of printed images online by a digital camera, by which the CIELAB color difference can be calculated directly from sampled RGB value. The algorithm is discussed in detail, and an experiment is conducted to test the method. The calculation results show that there is either linear or polynomial transformation relationship between CIEXYZ tristimulus and RGB values sampled by the camera, so the CIEXYZ tristimulus and CIELAB color difference can be expressed by the sampled RGB values. The calculation method proposed in this paper is proved by the experiment to be simple and practical, and the accuracy can meet the industry requirements.