Biometric information processing device, biometric-information processing method, and computer-readable storage medium

1. A biometric-information processing device comprising:

a processor; and

a memory which stores a plurality of instructions, which when executed by the processor, cause the processor to execute,

generating a biometric image representing biometric information on a surface of a specific portion of a user;

dividing the biometric image into multiple blocks;

estimating, for each of the multiple blocks, a prior complexity degree indicating complexity of a pattern of part included in the biometric information and represented in the block, on a basis of a difference between a direction of the pattern of the part included in the biometric information and represented in the block and a direction of a pattern of other part included in the biometric information and represented in the block adjacent to that block;

determining, for each of the multiple blocks, a posterior complexity degree indicating complexity of an image of the part included in the biometric information and represented in the block, on a basis of features indicating a complexity degree of an image represented in the block; and

detecting the block having a difference between the posterior complexity degree and the prior complexity degree as a distorted block in which the part included in the biometric information and represented in the block has distortion, by comparing the posterior complexity degree with the prior complexity degree for each of the multiple blocks.

2. The device according to claim 1 ,

wherein, with respect to the distorted blocks, the distortion detector determines a first barycenter of the blocks in which the posterior complexity degrees are smaller than the prior complexity degrees and a second barycenter of the blocks in which the posterior complexity degrees are larger than the prior complexity degrees, and estimates a direction in which the user presses the portion against the processing device, on a basis of a direction from the first barycenter to the second barycenter.

3. The device according to claim 1 ,

further comprising, with respect to the distorted blocks, when at least one of the number of blocks in which the posterior complexity degrees are smaller than the prior complexity degrees and the number of blocks in which the posterity complexity degrees are larger than the prior complexity degrees is larger than a first threshold, generating the biometric image by re-capturing the biometric information of the user.

4. The device according to claim 1 ,

further comprising, when the number of distorted blocks in the biometric image is larger than a second threshold, re-generating the biometric image by re-capturing the biometric information of the user.

5. The device according to claim 1 , further comprising:

storing a position of at least one first feature point in biometric information of the specific portion of a registered user, the at least one first feature point being extracted from a registered biometric image representing the biometric information of the specific portion of the registered user;

extracting, from the biometric image, a position of at least one second feature point in the biometric information of the specific portion of the user; and

determining a degree of similarity between the biometric information of the specific portion of the registered user and the biometric information of the specific portion of the user in accordance with a degree of matching between the at least one first feature point and the at least one second feature point,

wherein the degree of similarity is determined by reducing a first weight for the degree of matching of the second feature point included in the distorted blocks with the first feature point to have a value smaller than a second weight for the degree of matching of the second feature point not included in the distorted blocks with the first feature point.

6. The device according to claim 2 , further comprising:

determining a reference point in the biometric information represented in the biometric image; and

moving a position of the reference point along the direction from the first barycenter to the second barycenter to make a position included in the biometric information and indicated by the reference point when the biometric information represented in the biometric image has no distortion and a position included in the biometric information and indicated by the moved reference point match each other.

7. A biometric-information processing method comprising:

generating a biometric image representing biometric information on a surface of a specific portion of a user;

dividing the biometric image into multiple blocks;

estimating, for each of the multiple blocks, a prior complexity degree indicating complexity of a pattern of part included in the biometric information and represented in the block, on a basis of a difference between a direction of the pattern of the part included in the biometric information and represented in the block and a direction of a pattern of other part included in the biometric information and represented in the block adjacent to that block;

determining, for each of the multiple blocks, a posterior complexity degree indicating complexity of an image of the part included in the biometric information and represented in the block, on a basis of features indicating a complexity degree of an image represented in the block; and

detecting the block having a difference between the posterior complexity degree and the prior complexity degree as a distorted block in which the part included in the biometric information and represented in the block has distortion, by comparing the posterior complexity degree with the prior complexity degree for each of the multiple blocks.

8. The method according to claim 7 ,

wherein, with respect to the distorted blocks, the detecting determines a first barycenter of the blocks in which the posterior complexity degrees are smaller than the prior complexity degrees and a second barycenter of the blocks in which the posterior complexity degrees are larger than the prior complexity degrees, and estimates a direction in which the user presses the portion, on a basis of a direction from the first barycenter to the second barycenter.

9. The method according to claim 7 ,

wherein, with respect to the distorted blocks, when at least one of the number of blocks in which the posterior complexity degrees are smaller than the prior complexity degrees and the number of blocks in which the posterity complexity degrees are larger than the prior complexity degrees is larger than a first threshold, the generating re-generates the biometric image by re-capturing the biometric information of the user.

10. The method according to claim 7 ,

wherein, when the number of distorted blocks in the biometric image is larger than a second threshold, the generating re-generates the biometric image by re-capturing the biometric information of the user.

11. The method according to claim 7 , further comprising:

storing a position of at least one first feature point in biometric information of the specific portion of a registered user, the at least one first feature point being extracted from a registered biometric image representing the biometric information of the specific portion of the registered user;

extracting, from the biometric image, a position of at least one second feature point in the biometric information of the specific portion of the user; and

determining a degree of similarity between the biometric information of the specific portion of the registered user and the biometric information of the specific portion of the user in accordance with a degree of matching between the at least one first feature point and the at least one second feature point,

wherein the determining the degree of similarity determines the degree of similarity by reducing a first weight for the degree of matching of the second feature point included in the distorted blocks with the first feature point to have a value smaller than a second weight for the degree of matching of the second feature point not included in the distorted blocks with the first feature point.

12. The method according to claim 8 , further comprising:

determining a reference point in the biometric information represented in the biometric image; and

moving a position of the reference point along the direction from the first barycenter to the second barycenter to make a position included in the biometric information and indicated by the reference point when the biometric information represented in the biometric image has no distortion and a position included in the biometric information and indicated by the moved reference point match each other.

13. A non-transitory computer-readable storage medium storing a biometric-information processing program that causes a computer to execute a process comprising:

dividing a biometric image representing biometric information on a surface of a specific portion of a user into multiple blocks;

estimating, for each of the multiple blocks, a prior complexity degree indicating complexity of a pattern of part included in the biometric information and represented in the block, on a basis of a difference between a direction of the pattern of the part included in the biometric information and represented in the block and a direction of a pattern of other part included in the biometric information and represented in the block adjacent to that block;

determining, for each of the multiple blocks, a posterior complexity degree indicating complexity of an image of the part included in the biometric information and represented in the block, on a basis of features indicating a complexity degree of an image represented in the block; and

detecting the block having a difference between the posterior complexity degree and the prior complexity degree as a distorted block in which the part included in the biometric information and represented in the block has distortion, by comparing the posterior complexity degree with the prior complexity degree for each of the multiple blocks.

14. The computer-readable storage medium according to claim 13 , further comprising:

storing a position of at least one first feature point in biometric information of the specific portion of a registered user, the at least one first feature point being extracted from a registered biometric image representing the biometric information of the specific portion of the registered user;

extracting, from the biometric image, a position of at least one second feature point in the biometric information of the specific portion of the user; and

determining a degree of similarity between the biometric information of the specific portion of the registered user and the biometric information of the specific portion of the user in accordance with a degree of matching between the at least one first feature point and the at least one second feature point,

wherein the determining the degree of similarity determines the degree of similarity by reducing a first weight for the degree of matching of the second feature point included in the distorted blocks with the first feature point to have a value smaller than a second weight for the degree of matching of the second feature point not included in the distorted blocks with the first feature point.

15. The computer-readable storage medium according to claim 13 , further comprising:

determining a reference point in the biometric information represented in the biometric image; and

moving a position of the reference point along the direction from the first barycenter to the second barycenter to make a position included in the biometric information and indicated by the reference point when the biometric information represented in the biometric image has no distortion and a position included in the biometric information and indicated by the moved reference point match each other.