Image construction method, fingerprint image construction apparatus, and program

1. An image construction method, in which an apparatus equipped with a sensor mechanism to read a series of partial images representing a fingerprint from a finger which conducts a slide operation

successively stores partial images read by the sensor mechanism,

sets an inspection region, which is used to find a difference quantity between a latest partial image and an already acquired partial image in the successively stored partial images, in the already acquired partial image along a displacement direction of a plurality of consecutive already acquired partial images,

sets a retrieval range for a position of superposition of the latest partial image on the already acquired partial image on the basis of a position of the inspection region,

causes displacement of the latest partial image with respect to the already acquired partial image in the retrieval range and finds a difference quantity between the already acquired partial image and the latest partial image concerning the inspection region every displacement,

determines displacement of the latest partial image corresponding to a minimum difference quantity among the found difference quantities as the position of superposition, and

disposes the latest partial image in the position of superposition with respect to the already acquired partial image and stores the latest partial image.

2. The image construction method according to claim 1 , wherein when setting the inspection region, the apparatus finds the displacement direction on the basis of a sign of sum total of displacement quantities of the plurality of already acquired partial images, and sets the inspection region in a position at a predetermined distance from a central part of the already acquired partial image along the displacement direction.

3. The image construction method according to claim 1 , wherein when setting the inspection region, the apparatus finds the displacement direction on the basis of a sign of sum total of displacement quantities of the plurality of already acquired partial images, determines a movement quantity from the position of the inspection region set last time on the basis of a variation level among the displace quantities, and sets the inspection region in a position at a distance equivalent to the movement quantity from the position set last time along the displacement direction.

4. A fingerprint image construction apparatus including a sensor mechanism which reads a series of partial images representing a fingerprint from a finger which conducts a slide operation, a memory mechanism which successively stores the series of partial images read by the sensor mechanism, and a control mechanism which conducts on the series of partial images stored by the memory mechanism, wherein

the control mechanism comprises:

a retrieval condition determination unit which sets an inspection region, which is used to find a difference quantity between a latest partial image and an already acquired partial image in the partial images successively stored by the memory mechanism, in the already acquired partial image along a displacement direction of a plurality of consecutive already acquired partial images, and sets a retrieval range for a position of superposition of the latest partial image on the already acquired partial image on the basis of a position of the inspection region;

a difference quantity computation unit which causes displacement of the latest partial image with respect to the already acquired partial image in the retrieval range, and finds a difference quantity between the already acquired partial image and the latest partial image concerning the inspection region every displacement;

a position relation computation unit which determines displacement of the latest partial image corresponding to a minimum difference quantity among the found difference quantities as the position of superposition; and

an image disposition unit which disposes the latest partial image in the position of superposition with respect to the already acquired partial image in the memory mechanism.

5. The image construction apparatus according to claim 4 , wherein when setting the inspection region, the retrieval condition determination unit finds the displacement direction on the basis of a sign of sum total of displacement quantities of the plurality of already acquired partial images, and sets the inspection region in a position at a predetermined distance from a central part of the already acquired partial image along the displacement direction.

6. The image construction apparatus according to claim 4 , wherein when setting the inspection region, the retrieval condition determination unit finds the displacement direction on the basis of a sign of sum total of displacement quantities of the plurality of already acquired partial images, determines a movement quantity from the position of the inspection region set last time on the basis of a variation level among the displace quantities, and sets the inspection region in a position at a distance equivalent to the movement quantity from the position set last time along the displacement direction.

7. A computer program stored on a computer readable storage medium that when executed causes a computer connected to a sensor mechanism to read a series of partial images representing a fingerprint from a finger which conducts a slide operation, the computer program causing the computer to execute the steps of:

successively storing partial images read by the sensor mechanism,

setting an inspection region, which is used to find a difference quantity between a latest partial image and an already acquired partial image in the successively stored partial images, in the already acquired partial image along a displacement direction of a plurality of consecutive already acquired partial images,

setting a retrieval range for a position of superposition of the latest partial image on the already acquired partial image on the basis of a position of the inspection region,

causing displacement of the latest partial image with respect to the already acquired partial image in the retrieval range and finding a difference quantity between the already acquired partial image and the latest partial image concerning the inspection region every displacement,

determining displacement of the latest partial image corresponding to a minimum difference quantity among the found difference quantities as the position of superposition, and

disposing the latest partial image in the position of superposition with respect to the already acquired partial image and storing the latest partial image.

8. The computer program according to claim 7 , wherein when setting the inspection region, the program causes the computer to execute finding the displacement direction on the basis of a sign of sum total of displacement quantities of the plurality of already acquired partial images, and setting the inspection region in a position at a predetermined distance from a central part of the already acquired partial image along the displacement direction.

9. The computer program according to claim 7 , wherein when setting the inspection region, the program causes the computer to execute finding the displacement direction on the basis of a sign of sum total of displacement quantities of the plurality of already acquired partial images, determining a movement quantity from the position of the inspection region set last time on the basis of a variation level among the displace quantities, and setting the inspection region in a position at a distance equivalent to the movement quantity from the position set last time along the displacement direction.