Method and system for describing an image

It is an object of the present invention to provide a method and system capable of efficiently describing an image from local features. 

According to an aspect of the present invention, there is provided a method for describing an image by means of its local characteristics, comprising: preprocessing an image for reducing at least one of the following effects: radiometric noise, geometric quantization or image lattice; extracting a plurality of key points from said image; for each key point, extracting a circular patch, applying a trace transform, thus transforming each of said corresponding circular patches into respective bidimensional functions, thus obtaining a plurality of rows of values of length of normal, the length of normal being the normal contained in the circular patch; applying a frequency transform to each of said rows of values of lenth of normal, thus obtaining, for each row of values of length of noraml, a row of module values; eliminating the DC value of each of said module values, thus creating a local descriptor of each key point of the image, the descriptor being formed by said rows of module values from which the respective DC values have been eliminated.

The trace transform is preferably normalized in order to reduce the influence of signal intensity and make the algorithm robust against light intensity variations.