The color measurement system for spot color printing basing multispectral camera

Color measurement and control of printing has been an important issue in computer vision technology. In the past, people have used density meter and spectrophotometer to measure the color of printing product. For the color management of 4 color press, by these kind meters, people can measure the color data from color bar printed at the side of sheet, then do ink key presetting. This way have wide application in printing field. However, it can not be used in the case that is to measure the color of spot color printing and printing pattern directly. With the development of multispectral image acquisition, it makes possible to measure the color of printing pattern in any area of the pattern by CCD camera than can acquire the whole image of sheet in high resolution. This essay give a way to measure the color of printing by multispectral camera in the process of printing. A 12 channel spectral camera with high intensity white LED illumination that have driven by a motor, scans the printing sheet. Then we can get the image, this image can include color and printing quality information of each pixel, LAB value and CMYK value of each pixel can be got by reconstructing the reflectance spectra of printing image. By this data processing, we can measure the color of spot color printing and control it. Through the spot test in the printing plant, the results show this way can get not only the color bar density value but also ROI color value. By the value, we can do ink key presetting, that makes it true to control the spot color automatically in high precision.