抄録
RGB values from CCD cameras are device-dependent, and are not able to be simply converted into international color standard CIE XYZ (and Lab) values. We have developed a calibration method from these RGB values to CIE Lab values by using a standard color sample set. We achieved the accuracy of ΔEab 2.23 (standard deviation of error×2.5) by applying a couple of calculation techniques to the calibration. First, accuracies of X, Y and Z estimations in the lower range are enhanced, while those in the higher are diminished. In the converting equations from XYZ to Lab, XYZ values are powered by third. Hence, estimation error in low XYZ region reduces Lab estimation accuracy more effectively. The second method is interactive modifications of X and Z values. Values of a and b is derived by Y and X, and Y and Z, respectively. For example, a combination of larger estimation error in Y and smaller estimation error of Z yields very high deviation of b. To avoid this, we modified Z and X values based on Y estimation error, i.e. reduced X is applied to regression equations when Y is underestimated.
