Method for capturing fingerprint image, apparatus for capturing fingerprint image, and electronic device
Embodiments of the present disclosure provide a method for capturing a fingerprint image, an apparatus for capturing a fingerprint image, and an electronic device, where the method includes: controlling a fingerprint sensor to capture at least one frame of image based on each candidate exposure time among N candidate exposure times respectively; determining N values of a feature parameter corresponding to the N candidate exposure times according to the at least one frame of image captured in each exposure time, where the feature parameter is used to indicate a degree of influence of a refresh period of a display screen on the fingerprint image captured by the fingerprint sensor; determining a candidate exposure time corresponding to a first value indicating a smallest degree of influence among the N values as a target exposure time; and controlling the fingerprint sensor to capture the fingerprint image based on the target exposure time.
1. A method for capturing a fingerprint image, comprising:
controlling a fingerprint sensor to capture at least one frame of image based on each candidate exposure time among N candidate exposure times respectively, the N candidate exposure times comprising a first exposure time greater than a preset exposure time, a second exposure time shorter than the preset exposure time, and the preset exposure time, wherein a difference between the first exposure time and the preset exposure time and a difference between the preset exposure time and the second exposure time are each a positive integer multiple of a preset step size and less than the preset exposure time, and N is a positive integer greater than or equal to 3;
determining N values of a feature parameter corresponding to the N candidate exposure times according to the at least one frame of image captured in the each exposure time, wherein the feature parameter is used to indicate a degree of influence of a refresh period of a display screen on the fingerprint image captured by the fingerprint sensor;
determining a candidate exposure time corresponding to a first value indicating a smallest degree of influence among the N values as a target exposure time; and
controlling the fingerprint sensor to capture the fingerprint image based on the target exposure time.
2. The method according to claim 1 , wherein the feature parameter comprises at least one of: a temporal noise, a spatial noise, a signal to noise ratio, and a horizontal stripe intensity.
3. The method according to claim 1 , wherein the feature parameter comprises a temporal noise, and the controlling the fingerprint sensor to capture the at least one frame of image based on each candidate exposure time among the N candidate exposure times respectively comprises:
controlling the fingerprint sensor to capture M frames of images based on an i-th candidate exposure time among the N candidate exposure times, wherein M is a positive integer greater than 1, and i is a positive integer less than or equal to N; and
the determining the N values of the feature parameter corresponding to the N candidate exposure times according to the at least one frame of image captured in the each exposure time comprises:
acquiring a standard deviation of pixel values corresponding to a same fingerprint sensor pixel in the M frames of images; and
determining a temporal noise value corresponding to the i-th candidate exposure time according to an average value of standard deviations corresponding to P fingerprint sensor pixels, wherein P is a positive integer greater than 1.
4. The method according to claim 1 , wherein the feature parameter comprises a spatial noise, and the controlling the fingerprint sensor to capture the at least one frame of image based on each candidate exposure time among the N candidate exposure times respectively comprises:
controlling the fingerprint sensor to capture M frames of images based on an i-th candidate exposure time among the N candidate exposure times, wherein M is a positive integer greater than 1, and i is a positive integer less than or equal to N; and
the determining the N values of the feature parameter corresponding to the N candidate exposure times according to the at least one frame of image captured in the each exposure time comprises:
acquiring an average value of pixel values corresponding to a same fingerprint sensor pixel in the M frames of images; and
determining a spatial noise value corresponding to the i-th candidate exposure time according to a standard deviation of average values corresponding to P fingerprint sensor pixels, wherein P is a positive integer greater than 1.
5. The method according to claim 1 , wherein the feature parameter comprises a horizontal stripe intensity, and the controlling the fingerprint sensor to capture the at least one frame of image based on each candidate exposure time among the N candidate exposure times respectively comprises:
controlling the fingerprint sensor to capture Q frames of images based on an i-th candidate exposure time among the N candidate exposure times, wherein Q is a positive integer, and i is a positive integer less than or equal to N; and
the determining the N values of the feature parameter corresponding to the N candidate exposure times according to the at least one frame of image captured in the each exposure time comprises:
determining a horizontal stripe intensity value corresponding to the i-th candidate exposure time according to peak-to-peak values of a plurality of fingerprint sensor pixels in each frame of image among the Q frames of images.
6. The method according to claim 1 , wherein the feature parameter comprises at least one of a temporal noise, a spatial noise and a horizontal stripe intensity, and the first value is a smallest value among the N values.
7. The method according to claim 1 , wherein the feature parameter comprises a signal to noise ratio, and the first value is a largest value among the N values.
8. The method according to claim 1 , wherein the preset step size comprises a time difference between times of completing exposure of two adjacent rows of fingerprint sensor pixels of the fingerprint sensor or a time difference between times of starting exposure two adjacent rows of fingerprint sensor pixels of the fingerprint sensor.
9. The method according to claim 1 , wherein the at least one frame of image is 5 frames of images.
10. An apparatus for capturing a fingerprint image, comprising: a processor configured to:
control a fingerprint sensor to capture at least one frame of image based on each candidate exposure time among N candidate exposure times respectively, the N candidate exposure times comprising a first exposure time greater than a preset exposure time, a second exposure time shorter than the preset exposure time, and the preset exposure time, wherein a difference between the first exposure time and the preset exposure time and a difference between the preset exposure time and the second exposure time are each a positive integer multiple of a preset step size and less than the preset exposure time, and N is a positive integer greater than or equal to 3;
determine N values of a feature parameter corresponding to the N candidate exposure times according to the at least one frame of image captured in the each exposure time, wherein the feature parameter is used to indicate a degree of influence of a refresh period of a display screen on the fingerprint image captured by the fingerprint sensor;
determine a candidate exposure time corresponding to a first value indicating a smallest degree of influence among the N values as a target exposure time; and
control the fingerprint sensor to capture the fingerprint image based on the target exposure time.
11. The apparatus according to claim 10 , wherein the feature parameter comprises at least one of: a temporal noise, a spatial noise, a signal to noise ratio, and a horizontal stripe intensity.
12. The apparatus according to claim 10 , wherein the feature parameter comprises a temporal noise, and the processor is specifically configured to:
control the fingerprint sensor to capture M frames of images based on an i-th candidate exposure time among the N candidate exposure times, wherein M is a positive integer greater than 1, and i is a positive integer less than or equal to N;
acquire a standard deviation of pixel values corresponding to a same fingerprint sensor pixel in the M frames of images; and
determine a temporal noise value corresponding to the i-th candidate exposure time according to an average value of standard deviations corresponding to P fingerprint sensor pixels, wherein P is a positive integer greater than 1.
13. The apparatus according to claim 10 , wherein the feature parameter comprises a spatial noise, and the processor is specifically configured to:
control the fingerprint sensor to capture M frames of images based on an i-th candidate exposure time among the N candidate exposure times, wherein M is a positive integer greater than 1, and i is a positive integer less than or equal to N;
acquire an average value of pixel values corresponding to a same fingerprint sensor pixel in the M frames of images; and
determine a spatial noise value corresponding to the i-th candidate exposure time according to a standard deviation of average values corresponding to P fingerprint sensor pixels, wherein P is a positive integer greater than 1.
14. The apparatus according to claim 10 , wherein the feature parameter comprises a spatial noise, and the processor is specifically configured to:
control the fingerprint sensor to capture Q frames of images based on an i-th candidate exposure time among the N candidate exposure times, wherein Q is a positive integer, and i is a positive integer less than or equal to N; and
determine a horizontal stripe intensity value corresponding to the i-th candidate exposure time according to peak-to-peak values of a plurality of fingerprint sensor pixels in each frame of image among the Q frames of images.
15. The apparatus according to claim 10 , wherein the feature parameter comprises at least one of a temporal noise, a spatial noise and a horizontal stripe intensity, and the first value is a smallest value among the N values.
16. The apparatus according to claim 10 , wherein the feature parameter comprises a signal to noise ratio, and the first value is a largest value among the N values.
17. The apparatus according to claim 10 , wherein the preset step size comprises a time difference between times of completing exposure of two adjacent rows of fingerprint sensor pixels of the fingerprint sensor or a time difference between times of starting exposure of two adjacent rows of fingerprint sensor pixels of the fingerprint sensor.
18. The apparatus according to claim 10 , wherein the at least one frame of image is 5 frames of images.
19. The apparatus according to claim 10 , wherein the apparatus and the fingerprint sensor are encapsulated together.
20. An electronic device, comprising a display screen, a fingerprint sensor, and an apparatus for capturing a fingerprint image, wherein the fingerprint sensor is arranged under the display screen, and wherein the apparatus comprises a processor, the processor is configured to:
control the fingerprint sensor to capture at least one frame of image based on each candidate exposure time among N candidate exposure times respectively, the N candidate exposure times comprising a first exposure time greater than a preset exposure time, a second exposure time shorter than the preset exposure time, and the preset exposure time, wherein a difference between the first exposure time and the preset exposure time and a difference between the preset exposure time and the second exposure time are each a positive integer multiple of a preset step size and less than the preset exposure time, and N is a positive integer greater than or equal to 3;
determine N values of a feature parameter corresponding to the N candidate exposure times according to the at least one frame of image captured in the each exposure time, wherein the feature parameter is used to indicate a degree of influence of a refresh period of a display screen on the fingerprint image captured by the fingerprint sensor;
determine a candidate exposure time corresponding to a first value indicating a smallest degree of influence among the N values as a target exposure time; and
control the fingerprint sensor to capture the fingerprint image based on the target exposure time.