Method, apparatus and system for generating a feature vector

1. A method of generating a feature vector for an image, the method comprising:

determining values from a plurality of points in a region of the image, each of the values being determined using at least two of the plurality of points;

determining a periodic sequence of the determined values based on an order of the plurality of points, the periodic sequence being phase variant to a starting point of the ordered plurality of points, the order of the plurality of points being determined according to a predetermined rule; and

generating the feature vector for one of the points from a frequency domain representation of the periodic sequence, the feature vector being invariant to rotation with respect to the plurality of points.

2. The method according to claim 1 , wherein the feature vector comprises magnitude components of a Fourier transform.

3. The method according to claim 1 , wherein the feature vector represents a second order difference of phase.

4. The method according to claim 3 , further comprising concatenating the second order difference of phase with magnitude values.

5. The method according to claim 1 , wherein the determined values represent areas of normalized triangles.

6. The method according to claim 1 , wherein the points are locations of words.

7. The method according to claim 1 , wherein the points are locations of letter extenders.

8. The method according to claim 1 , wherein the points are locations of letter descenders.

9. The method according to claim 1 , further comprising determining further periodic sequences.

10. The method according to claim 9 , further comprising generating further feature vectors and concatenating the further feature vectors to produce a large feature vector.

11. The method according to claim 1 , further comprising: matching the generated feature vector with one or more other feature vectors; accumulating scores based on matching feature vectors; and identifying a document based on the accumulated scores.

12. An apparatus for generating a feature vector for an image, the apparatus comprising:

module for determining values from a plurality of points in a region of the image, each of the values being determined using at least two of the plurality of points;

module for determining a periodic sequence of the determined values based on an order of the plurality of points, the periodic sequence being phase variant to a starting point of the ordered plurality of points, the order of the plurality of points being determined according to a predetermined rule; and

module for generating the feature vector for one of the points from a frequency domain representation of the periodic sequence, the feature vector being invariant to rotation with respect to the plurality of points.

13. A system for generating a feature vector for an image, the system comprising:

a memory for storing data and a computer program;

a processor coupled to the memory for executing said computer program, said computer program comprising instructions for:

code for determining values from a plurality of points in a region of the image, each of the values being determined using at least two of the plurality of points;

code for determining a periodic sequence of the determined values based on an order of the plurality of points, the periodic sequence being phase variant to a starting point of the ordered plurality of points, the order of the plurality of points being determined according to a predetermined rule; and

code for generating the feature vector for one of the points from a frequency domain representation of the periodic sequence, the feature vector being invariant to rotation with respect to the plurality of points.

14. A non-transitory computer readable medium having a computer program stored thereon for generating a feature vector for an image, the program comprising:

code for determining values from a plurality of points in a region of the image, each of the values being determined using at least two of the plurality of points;

code for determining a periodic sequence of the determined values based on an order of the plurality of points, the periodic sequence being phase variant to a starting point of the ordered plurality of points, the order of the plurality of points being determined according to a predetermined rule; and

code for generating the feature vector for one of the points from a frequency domain representation of the periodic sequence, the feature vector being invariant to rotation with respect to the plurality of points.