The image gradient histogram and associated orientation signatures

The conventional image intensity histogram has played a major role in some image processing operations, such as image enhancement. In this paper, we introduce two related concepts. First, we define the gradient histogram of an image as an entity which describes the (statistical) orientation properties of the image. Using gradient histograms, we then introduce a class of image orientation signatures, periodic functions of one variable which characterize the image and possess useful translation and scaling invariance properties. Orientation signatures have been successfully applied to the problem of 3D object attitude determination from a single camera image