A digital image processing method for image registration, that acquires a reference intensity image and a floating intensity image that is to be registered; and preprocesses the reference and the floating images, before converting the preprocessed reference image to a vectorized reference image. Subsequently, the vectorized reference image is converted to a reference index image. Additional image processing includes spatially transforming the preprocessed floating image using a transformation matrix; converting the transformed floating image to a vectorized floating image; converting the vectorized floating image to a floating index image; and obtaining joint statistics of the index images. Other steps include, computing a cost function due to misalignment of the two images using the joint statistics; and updating the transformation matrix and repeating several aforementioned steps, if the cost function does not satisfy a predefined criterion, otherwise, applying the transformation matrix to an acquired floating intensity image.