Color Characterization and Modeling of a Scanner

The quality of digital color image capture systems like scanners and digital cameras is determined by the range of colors they can accurately sense and record. This range of colors is known as the color gamut of the system. Each image capture system has its own color space defined by its set of illuminants and color sensors. Such a device-dependent color space is specific and unique to the system. In order that these capture systems be evaluated and compared, the colors sensed by them need to be plotted in a common color space which is independent of any particular system. Such color spaces, called device-independent color spaces, have been defined by Commission internationale de l'éclairage(CIE).The goal of this research is to characterize and model a color scanner and determine its color gamut. Such a color gamut is defined by a transformation matrix that converts the colors in the device dependent color space to those in a standard device-independent color space like CIE XYZ, L*a*b*. In this work, two methods have been used to determine the transformation matrix, namely, a model-based method and a regression based method. The model based method describes the scanner system in terms of its lamp spectrum and the spectral responses of its sensors to the reflectance of the target to be scanned. The regression-based method finds a transformation matrix by mapping the color values of a particular target as recorded by the scanner to its actual values in XYZ space, by regression.The accuracy with which each method describes the system has been determined and compared. In addition, the system under test is compared with other scanner systems by plotting the color gamuts of each.