Finger movement detection method and apparatus

• US 20030185425A1
• Filed: 01/29/2003
• Published: 10/02/2003
• Est. Priority Date: 03/27/2002
• Status: Active Grant

• Current Assignee: Cypress Semiconductor Corporation (Infineon Technologies AG)
• Original Assignee: Fujitsu Limited
• Inventors: Nishikawa, Shou
• Granted Patent: US 7,064,743 B2
• Time in Patent Office: Days
• US Class Current: 382/124
• CPC Class Codes: G06F 3/03547 Touch pads, in which fingers can move on a surface
• CPC Class Codes: G06V 40/1335 Combining adjacent partial images (e.g. slices) to create a composite input or reference pattern; Tracking a sweeping finger movement

Abstract

A fingerprint area and a barycentric position of the area are obtained for a current sensor image, and an area near the barycentric position is divided into a plurality of small blocks. An image area that agrees with a fingerprint image is searched for, for each of the small blocks with respect to the fingerprint area in a previous sensor image. A candidate vector is obtained from a deviation between the position of the small block in the current sensor image and the position of the image area in the previous sensor image corresponding to the small block. A candidate vector with the highest matching degree between the fingerprint images in the current and previous sensor images is selected from the candidate vectors to obtain a detected vector, and the detected vector is corrected to exclude an influence of erroneous detection and to control a movement of a pointer.

Claims

1. A finger movement detection method comprising:

a fingerprint detection step of detecting a fingerprint in an area smaller than a fingertip to obtain a first sensor image and a second sensor image; and

a pattern matching step of extracting a partial image area of the obtained second sensor image as a small block, searching for an image area having a fingerprint pattern that agrees with a fingerprint pattern in the small block of the second sensor image from the first sensor image, and obtaining a vector indicating a movement of a finger, based on a displacement of the small block in the second sensor image from the image area in the first sensor image corresponding to the small block.

2. The finger movement detection method according to claim 1, wherein the pattern matching step includes extracting a plurality of the small blocks from the second sensor image, searching for the image area in the first sensor image corresponding to each of the small blocks, and obtaining a plurality of vectors indicating the finger movement, based on a displacement of the respective small blocks in the second sensor image from the respective image areas in the first sensor image corresponding to the respective small blocks, and

the method further comprises a vector evaluation step of selecting a vector having a highest matching degree from the plurality of vectors as a vector indicating the finger movement, when the fingerprint image in the first sensor image and the fingerprint image in the second sensor image are superimposed on each other based on the respective vectors.

3. The finger movement detection method according to claim 2, further comprising a vector correction step of correcting a combined vector to a vector indicating the finger movement, the combined vector being obtained by combining a mean vector between a vector that is obtained by multiplying a vector newly selected at the vector evaluation step by a first coefficient and a vector that is previously obtained by being multiplied by the first coefficient, with a vector obtained by multiplying a previously combined vector by a second coefficient.

4. The finger movement detection method according to claim 3, wherein the first coefficient is determined based on a direction of a vector newly selected at the vector evaluation step with respect to the mean vector.

5. The finger movement detection method according to claim 1, further comprising a fingerprint area judgment step of judging a fingerprint area where a fingerprint image exists, from the first sensor image, after processing at the fingerprint detection step, wherein

the pattern matching step includes searching for the image area corresponding to the small block extracted from the second sensor image, from the fingerprint area judged at the fingerprint area judgment step.

6. The finger movement detection method according to claim 5, wherein the fingerprint area judgment step includes judging a fingerprint area where the fingerprint image exists from the second sensor image, and obtaining a barycentric position of the fingerprint area in the second sensor image, and

the pattern matching step includes extracting the small block near the barycentric position obtained at the fingerprint area judgment step.

7. A finger movement detection apparatus comprising:

a fingerprint sensor that detects a fingerprint in an area smaller than a fingertip to obtain a first sensor image and a second sensor image; and

a pattern matching unit that extracts a partial image area of the second sensor image as a small block, searches for an image area having a fingerprint pattern that agrees with a fingerprint pattern of the small block in the second sensor image from the first sensor image, and obtains a vector indicating a movement of a finger, based on a displacement of the small block in the second sensor image from the image area in the first sensor image corresponding to the small block.

8. The finger movement detection apparatus according to claim 7, further comprising a frame memory that stores the first sensor image and the second sensor image obtained by the fingerprint sensor.

9. The finger movement detection apparatus according to claim 7, wherein the pattern matching unit extracts a plurality of the small blocks from the second sensor image, searches for the image area in the first sensor image corresponding to each of the small blocks, and obtains a plurality of vectors indicating the movement of the finger, based on a displacement of the respective small blocks in the second sensor image from the respective image areas in the first sensor image corresponding to the respective small blocks, and

the apparatus further comprises a vector evaluation unit that selects a vector having a highest matching degree from the vectors as a vector indicating the finger movement, when the fingerprint image in the first sensor image and the fingerprint image in the second sensor image are superimposed on each other based on the respective vectors.

10. The finger movement detection apparatus according to claim 9, further comprising a vector correction unit that corrects a combined vector to a vector indicating the finger movement, the combined vector being obtained by combining a mean vector between a vector that is obtained by multiplying a vector newly selected by the vector evaluation unit by a first coefficient and a vector that is previously obtained by being multiplied by the first coefficient, with a vector obtained by multiplying a previously combined vector by a second coefficient.

11. The finger movement detection apparatus according to claim 10, wherein the first coefficient is determined based on a direction of a vector newly selected by the vector evaluation unit with respect to the mean vector.

12. The finger movement detection apparatus according to claim 7, further comprising a fingerprint area judgment unit that judges a fingerprint area where a fingerprint image exists, from the first sensor image, wherein

the pattern matching unit searches for the image area corresponding to the small block extracted from the second sensor image, from the fingerprint area judged by the fingerprint area judgment unit.

13. The finger movement detection apparatus according to claim 12, wherein the fingerprint area judgment unit judges a fingerprint area where the fingerprint image exists from the second sensor image, and obtains a barycentric position of the fingerprint area in the second sensor image, and

the pattern matching unit extracts the small block near the barycentric position obtained by the fingerprint area judgment unit.

14. A pointing method comprising steps of:

obtaining a vector indicating a movement of a finger, by using a finger movement detection method including

detecting a fingerprint in an area smaller than a fingertip to obtain a first sensor image and a second sensor image, and

extracting a partial image area of the obtained second sensor image as a small block, searching for an image area having a fingerprint pattern that agrees with a fingerprint pattern in the small block of the second sensor image from the first sensor image, and obtaining a vector indicating the movement of the finger, based on a displacement of the small block in the second sensor image from the image area in the first sensor image corresponding to the small block; and

controlling a movement of a pointer displayed on a screen, based on the vector.

15. A pointing apparatus comprising:

a finger movement detection apparatus including

a fingerprint sensor that detects a fingerprint in an area smaller than a fingertip to obtain a first sensor image and a second sensor image, and

a pattern matching unit that extracts a partial image area of the second sensor image as a small block, searches for an image area having a fingerprint pattern that agrees with a fingerprint pattern of the small block in the second sensor image from the first sensor image, and obtains a vector indicating a movement of a finger, based on a displacement of the small block in the second sensor image from the image area in the first sensor image corresponding to the small block; and

a control unit that controls a movement of a pointer displayed on a screen, based on the vector indicating the movement of the finger obtained by the detection apparatus.