Yoshiro Udagawa

Color image processing in CANON's digital camera

A new TTL white balance method is studied to get a good white balance for a wide variety of illumination in digital camera system. Parameters of white balance are decided only by analyzing a single shot of images in this method. A locus of a white point under various illumination is plotted in a certain 2D color space, and the point in the space that is assumed to correspond to a white point in the scene is compared to the locus. Four complementary color filters (cyan, yellow, magenta and green) attached on a CCD imager generate four color signals, which are transformed by a 3 X 4 matrix into three of red, green and blue. The adaptive matrix method corresponding to the color temperature of illumination is compared to the fixed matrix method. Calculating the adaptive matrix is based on the Von Kries Law.