There are provided an image processing method and an imaging device module capable of properly calculating a black level when brightness on the positive maximum value side in a brightness histogram of an optical black region are clipped to an upper limit brightness, that is, when brightness on the positive maximum value side in a brightness histogram of an optical black region exceed an upper limit brightness. An image processing method includes forming a brightness histogram of pixels in an optical black region of an imaging face of an imaging device; shifting the brightness histogram toward where a brightness pixel value is zero until a peak value of the brightness histogram becomes smaller than an upper limit of a pixel value, when the peak value is equal to or larger than the upper limit brightness of the pixel value; and calculating a black level based on a peak value which became smaller than the upper limit.