Systems and methods for touch and press detection using a sensor

1. A device, comprising:

a fingerprint sensor; and

a processor configured to:

detect presence of a finger on the fingerprint sensor;

cause the fingerprint sensor to take a plurality of measurements using multiple successive frames of the fingerprint sensor;

for each measurement in the plurality of measurements, compute a metric associated with the measurement at a given frame corresponding to the measurement;

at a first particular frame, determine that the finger has settled on the fingerprint sensor based on the metric at the first particular frame;

based on determining that the finger has settled, determine that a finger touch has occurred;

at a second particular frame, determine that the metric at the second particular frame has exceeded a press threshold; and

based on determining that the finger has exceeded the press threshold, determine that a finger press has occurred.

2. The device of claim 1 , wherein determining that the finger has settled comprises determining that the metric at the first particular frame exceeds a settled value threshold.

3. The device of claim 2 , wherein the settled value threshold is predetermined.

4. The device of claim 2 , wherein the settled value threshold is adaptively determined.

5. The device of claim 4 , wherein adaptively determining the settled value threshold comprises:

computing a difference value between the metric at two frames;

determining that a ratio of a value of the metric at one frame of the two frames and the difference value is less than a first threshold; and

setting a value of the metric at one of the two frames as the settled value threshold.

6. The device of claim 4 , wherein adaptively determining the settled value threshold comprises:

computing a histogram of pixel values associated with a given measurement;

computing a first metric associated with a center of the histogram and a second metric associated with a range of pixel values of the histogram;

determining that a ratio of the first metric and the second metric is less than a threshold value; and

based on determining that the ratio exceeds the threshold value, setting the settled value threshold based on the first metric.

7. The device of claim 4 , wherein adaptively determining the settled value threshold comprises:

determining that, at the first particular frame, a number of pixels of the fingerprint sensor covered by the finger exceeds a coverage threshold; and

computing a difference value of two values of the metric corresponding to two different frames, and determining that the difference value is less than a difference threshold.

8. The device of claim 1 , wherein the fingerprint sensor comprises a capacitive fingerprint sensor, and the metric comprises an average capacitance value, a median capacitance value, or a mode capacitance value.

9. The device of claim 1 , wherein the fingerprint sensor comprises an optical fingerprint sensor, and the metric comprises an average grayscale value, a median grayscale value, or a mode grayscale value.

10. The device of claim 1 , wherein the press threshold is set based on a value of the metric when the finger has settled on the fingerprint sensor.

11. The device of claim 1 , wherein an interrupt is generated based on determining that the finger press has occurred.

12. The device of claim 1 , wherein a graphical user interface of the device is changed based on determining that the finger press has occurred.

13. The device of claim 1 , wherein the metric at the second particular frame is computed using the same set of pixels of the fingerprint sensor as used to compute the metric at the first particular frame.

14. The device of claim 1 , wherein the processor is configured to:

identify a second set of pixels covered by the finger when the finger has settled on the fingerprint sensor, wherein the metric at the second particular frame is computed using the second set of pixels without using other pixels of the fingerprint sensor not included in the second set of pixels.

15. The device of claim 1 , wherein the processor is configured to:

sub-sample the pixels of the fingerprint sensor, wherein taking the plurality of measurements comprises taking measurements of sub-sampled pixels of the fingerprint sensor.

16. A method for performing press detection, comprising:

detecting, by a processor, presence of a finger on a fingerprint sensor;

causing the fingerprint sensor to take a plurality of measurements using multiple successive frames of the fingerprint sensor;

for each measurement in the plurality of measurements, computing, by the processor, a metric associated with the measurement at a given frame corresponding to the measurement;

at a first particular frame, determining, by the processor, that the finger has settled on the fingerprint sensor, wherein determining that the finger has settled comprises determining that the metric at the first particular frame exceeds a settled value threshold;

based on determining that the finger has settled, determining, by the processor, that a finger touch has occurred;

at a second particular frame, determine that the metric at the second particular frame has exceeded a press threshold; and

based on determining that the finger has exceeded the press threshold, determine that a finger press has occurred.

17. The method of claim 16 , wherein determining the settled value threshold comprises:

computing a difference value between the metric at two frames;

determining that a ratio of a value of the metric at one frame of the two frames and the difference value is less than a first threshold; and

setting a value of the metric at one of the two frames as the settled value threshold.

18. The method of claim 16 , wherein determining the settled value threshold comprises:

computing a histogram of pixel values associated with a given measurement;

computing a first metric associated with a center of the histogram and a second metric associated with a range of pixel values of the histogram;

determining that a ratio of the first metric and the second metric is less than a threshold value; and

based on determining that the ratio exceeds the threshold value, setting the settled value threshold based on the first metric.

19. The method of claim 16 , wherein the press threshold is set based on a value of the metric when the finger has settled on the fingerprint sensor.

20. The method of claim 16 , wherein the metric at the second particular frame is computed using the same set of pixels of the fingerprint sensor as used to compute the metric at the first particular frame.

21. The method of claim 16 , further comprising:

identifying a second set of pixels covered by the finger when the finger has settled on the fingerprint sensor, wherein the metric at the second particular frame is computed using the second set of pixels without using other pixels of the fingerprint sensor not included in the second set of pixels.

22. A non-transitory computer-readable storage medium storing instructions that, when executed by a processor, causes a computing device to perform press detection, by performing steps comprising:

detecting presence of a finger on a fingerprint sensor;

causing the fingerprint sensor to take a plurality of measurements using multiple successive frames of the fingerprint sensor;

for each measurement in the plurality of measurements, computing a metric associated with the measurement at a given frame corresponding to the measurement;

at a first particular frame, determining that the finger has settled on the fingerprint sensor, wherein determining that the finger has settled comprises determining that the metric at the first particular frame exceeds a settled value threshold;

based on determining that the finger has settled, determining that a finger touch has occurred;

at a second particular frame, determine that the metric at the second particular frame has exceeded a press threshold; and

based on determining that the finger has exceeded the press threshold, determine that a finger press has occurred.

23. The computer-readable storage medium of claim 22 , wherein the press threshold is set based on a value of the metric when the finger has settled on the fingerprint sensor.

24. The computer-readable storage medium of claim 22 , wherein the instructions are further configured to cause the computing device to:

identify a second set of pixels covered by the finger when the finger has settled on the fingerprint sensor, wherein the metric at the second particular frame is computed using the second set of pixels without using other pixels of the fingerprint sensor not included in the second set of pixels.