An auto white balance method includes converting a color space of an input image from an RGB color space into the Commission International de I'Eclairage (CIE) L*a*b* color space, determining at least a portion of pixels of the input image, assumed that a reference white color is changed, in a range of a predetermined L*a*b* value as pixels to be used for estimating the reference white color, determining averages of an L* value, an a* value, a b* value of the determined pixels to be used for estimating the reference white color as a reference white color estimation value, and calculating a color gain to move the reference white color estimation value to a target value for a predetermined white balance.