METHOD AND SYSTEM FOR FUZZY CLUSTERING OF IMAGES

• US 20090074305A1
• Filed: 11/11/2008
• Published: 03/19/2009
• Est. Priority Date: 03/28/2001
• Status: Active Grant

• Current Assignee: Hamid Jafarkhani, Vahid Tarokh
• Original Assignee: Hamid Jafarkhani, Vahid Tarokh
• Inventors: Jafarkhani, Hamid, Tarokh, Vahid
• Granted Patent: US 7,796,821 B2
• Time in Patent Office: Days
• US Class Current: 382/225
• CPC Class Codes: G06F 18/2323 based on graph theory, e.g. minimum spanning trees [MST] or graph cuts

Abstract

An approach to clustering a set of images based on similarity measures employs a fuzzy clustering paradigm in which each image is represented by a node in a graph. The graph is ultimately partitioned into subgraphs, each of which represent true clusters among which the various images are distributed. The partitioning is performed in a series of stages by identifying one true cluster at each stage, and removing the nodes belonging to each identified true cluster from further consideration so that the remaining, unclustered nodes may then be grouped. At the beginning of each such stage, the nodes that remain to be clustered are treated as all belonging to a single candidate cluster. Nodes are removed from this single candidate cluster in accordance with similarity and connectivity criteria, to arrive at a true cluster. The member nodes of this true cluster are then removed from further consideration, prior to the next stage in the process.

Claims

1. A method for clustering a set of N images into P final clusters, where N and P are integers, comprising:

(a) calculating at least one similarity measure S_i,j between members of each pair of images, where said S_i,j represents the similarity measure between an ith image and an jth image with i and j being image indices;

(b) calculating a total connectivity value for each of the images remaining to be clustered, where said total connectivity value for each image being defined as a sum of a function f of the similarity measures associated with that image;

(c) identifying, from among said images remaining to be clustered, a maximum total connectivity value T_max corresponding to an image I_max, where said image I_max belonging to a current cluster C which initially includes all images remaining to be clustered;

(d) removing, from the current cluster C, at least one image based on at least one of its similarity measure with image I_max and its total connectivity value within the current cluster C;

(e) adding, to the current cluster C, images having a similarity measure that is greater than a threshold T3;

(f) calculating, for each image within the current cluster C, a total connectivity value based on those images within the current cluster C;

(g) removing, from the current cluster C, those images having a total connectivity value less than a threshold T4; and

(h) repeating said steps (f) and (g) until no further images are removed to thereby establish the current cluster C as one of the final clusters.

2. The method of claim 1, further comprising:

(i) removing all images in the current cluster C from further consideration; and

(j) repeating steps (b)-(i) until all N images are assigned to a final cluster.

3. The method of claim 2, further comprising:

applying a non-linear function to each similarity measure, prior to calculating the total connectivity value.

4. The method of claim 3, wherein the non-linear function is a transcendental function.

5. The method of claim 4, wherein the transcendental function is a hyperbolic tangent.

6. The method of claim 5, wherein each similarity measure S_i,j is transformed according to a formula tanh(5×

S_i,j), prior to calculating a total connectivity value.

7. The method of claim 2, wherein the function f is an identity function.

8. The method of claim 2, wherein the function f is a nonlinear function.

9. The method of claim 2, wherein in step (e), at least one image is removed from the current cluster based on its similarity measure with image I_max, and then at least one other image is removed from the current cluster based on its total connectivity value within the current cluster.

10. The method of claim 2, wherein in step (e), at least one image is removed from the current cluster based on its total connectivity value within the current cluster, and then at least one other image is removed from the current cluster based on its similarity measure with image I_max.

11. The method of claim 2, wherein in step (e), images having a similarity measure with I_max that is less than a threshold T1 are removed from the current cluster.

12. The method of claim 2, wherein in step (e), a number N1 images having the N1 lowest similarity measures with I_max are removed from the current cluster.

13. The method of claim 2, wherein in step (e), images having a total connectivity value which differs from t_max by more than a threshold T2 are removed from the current cluster.

14. The method of claim 13, wherein images having a similarity measure with I_max that is less than a threshold T1 are removed from the current cluster.

15. The method of claim 14, wherein at least one image is removed from the current cluster based on its similarity measure with image I_max, and then at least one other image is removed from the current cluster based on its total connectivity value within the current cluster.

16. The method of claim 13, wherein a number N1 images having the N1 lowest similarity measures with I_max are removed from the current cluster.

17. The method of claim 16, wherein at least one image is removed from the current cluster based on its similarity measure with image I_max, and then at least one other image is removed from the current cluster based on its total connectivity value within the current cluster.

18. An apparatus for clustering a set of N images into P final clusters, where N and P are integers, comprising:

means for calculating at least one similarity measure S_i,j between members of each pair of images, where said S_i,j represents the similarity measure between an ith image and an jth image with i and j being image indices;

means for calculating a total connectivity value for each of the images remaining to be clustered, where said total connectivity value for each image being defined as a sum of a function f of the similarity measures associated with that image;

means for identifying, from among said images remaining to be clustered, a maximum total connectivity value t_max corresponding to an image I_max, where said image I_max belonging to a current cluster C which initially includes all images remaining to be clustered;

means for removing, from the current cluster C, at least one image based on at least one of its similarity measure with image I_max and its total connectivity value within the current cluster C;

means for adding, to the current cluster C, images having a similarity measure that is greater than a threshold T3;

means for calculating, for each image within the current cluster C, a total connectivity value based on those images within the current cluster C; and

means for removing, from the current cluster C, those images having a total connectivity value less than a threshold T4, wherein said total connectivity value calculating and said image removing are repeated until no further images are removed to thereby establish the current cluster C as one of the final clusters.

19. The apparatus of claim 18, further comprising:

means for removing all images in the current cluster C from further consideration, wherein one or more of said calculating, said identifying, said removing, and said adding are repeating until all N images are assigned to a final cluster.

20. A computer-readable medium having stored thereon a plurality of instructions, the plurality of instructions including instructions which, when executed by a processor, cause the processor to perform steps of a method for clustering a set of N images into P final clusters, where N and P are integers comprising:

(a) calculating at least one similarity measure S_i,j between members of each pair of images, where said S_i,j represents the similarity measure between an ith image and an jth image with i and j being image indices;

(b) calculating a total connectivity value for each of the images remaining to be clustered, where said total connectivity value for each image being defined as a sum of a function f of the similarity measures associated with that image;

(c) identifying, from among said images remaining to be clustered, a maximum total connectivity value T_max corresponding to an image I_max, where said image I_max belonging to a current cluster C which initially includes all images remaining to be clustered;

(d) removing, from the current cluster C, at least one image based on at least one of its similarity measure with image I_max and its total connectivity value within current cluster C;

(e) adding, to the current cluster C, images having a similarity measure that is greater than a threshold T3;

(f) calculating, for each image within the current cluster C, a total connectivity value based on those images within current cluster C;

(g) removing, from the current cluster C, those images having a total connectivity value less than a threshold T4; and

(h) repeating said steps (f) and (g) until no further images are removed to thereby establish the current cluster C as one of the final clusters.