The Calibration Accuracy of Display White Point by Visual Calibrator under Various Illuminations

摘要

We have developed a method to calibrate a display to a predetermined state and to make an ICC display profile by visual calibration for soft proofing. Our method adjusts a color of display white point to a color of a white object under a viewing illuminant, so our method can calibrate the display white point for any viewing illuminant. In order to calibrate the tone reproduction curve of a display, the brightness and hue of a continuous tone image is adjusted to the brightness and hue of a binary image. In addition, three pairs of images having different values of brightness are used. These methods can calibrate the display which has complex tone reproduction curve like LCD displays. In Electronic Imaging 2005, we reported that these methods can calibrate tone reproduction curves of LCD displays accurately. In this paper, we evaluated the matching accuracy between display white point and paper white under various illuminances and color temperatures to bear out the effect of our method under practical illumination. We found from this experiment that the matching accuracy was almost the same in all illumination conditions. Furthermore, all subjects calibrated the chromaticity of display white point more bluish than the chromaticity of paper white in all illumination conditions, and the dispersion of yellow-blue direction was larger than that of red-green direction. This yellow-blue direction was almost the same as the long axis of MacAdam ellipse. We also evaluated the capability of color discrimination between display and paper in various illumination conditions. At 500lx or less, many subjects made judgments that the color of display white point was similar as the color of paper white when color difference between display and paper was small, but the correlation of color difference with judgement was small at 1000lx or more. The cause of these results is the maximum luminance of the display was darker than that of paper at 1000lx or more. These results suggest that ISO 3664:2000 P2 condition is appropriate to compare the image on computer display with that on paper at the same time.