A white balance adjustment method includes capturing a raw image where an arrangement format of the raw image is BGb/GrR, extracting color scale values of each color channels, and obtaining cumulative proportion of color scale values in each channel. Cumulative proportion of each channels are compared with default minimum and maximum values, to get a cumulative proportion which is above a maximum value treated as a reference white, and a cumulative proportion below the minimum value treated as a reference black. The color scale values are re-quantized according to the obtained reference white and black, by using a color histogram equalization method.