1. A method for deriving a descriptor of an interest point in an image having a plurality of pixels, the interest point having a location in the image and an orientation, the method comprising: identifying a neighbourhood around the interest point aligned with the orientation of the interest point, the neighbourhood being divided into sub-regions, each sub-region comprising a set of pixels; inspecting contrasts at pixels of the set of pixels in the sub-regions in at least two directions having a fixed relation to the orientation using at least one first digital filter to thereby generate first scalar contrast measures for each direction independently, each first scalar contrast measure being a component of an intensity gradient represented by the change of contrast or image intensity along each direction at each pixel of the set of pixels; and generating a multidimensional descriptor comprising first elements, each first element being a second scalar contrast measure that is a combination of the first scalar contrast measures from only one direction.