Optimized scan sequence for biometric sensor

1. An imaging device included in an electronic device for imaging an input object, the imaging device comprising:

a light source that emanates light to a sensing region in which the input object to be imaged is placed;

a collimator filter layer;

an image sensor array disposed below the collimator filter layer, wherein the collimator filter layer blocks some light reflected from the input object while other light reflected from the input object passes through apertures in the collimator filter layer and arrives at the image sensor array; and

a controller configured to cause a first image of the input object to be captured with the light source turned on, and to transmit the first image to a processor associated with the electronic device to perform image matching against one or more template images before causing a second image of the input object to be captured with the light source turned off.

2. The imaging device of claim 1 , further comprising:

a coarse sensor array, wherein the controller is further configured to determine that the input object has settled in the sensing region before causing the first image of the input object to be captured with the light source turned on.

3. The imaging device of claim 2 , wherein determining that the input object has settled comprises determining that a number of regions of the coarse sensor array that is covered by the input object in a first frame is within a threshold of a number of regions of the coarse sensor array that is covered by the input object in a second frame that is after the first frame.

4. The imaging device of claim 2 , wherein the image sensor array is an optical sensor array and the coarse sensor array is a capacitive sensor array, wherein the coarse sensor array has a coarser image resolution than the image resolution of the image sensor array.

5. The imaging device of claim 2 , wherein the controller is configured to send an interrupt to the processor is response to determining that the input object has settled in the sensing region, wherein the interrupt is configured to wake the processor.

6. The imaging device of claim 1 , wherein the controller is further configured to:

determine presence of the input object in the sensing region before determining that the input object has settled in the sensing region; and

send an interrupt to the processor is response to determining the presence of the input object in the sensing region, wherein the interrupt is configured to wake the processor.

7. The imaging device of claim 1 , wherein performing image matching comprises subtracting, for each pixel location in the first image, a default intensity value from an intensity value of the pixel in the first image, and performing image matching using a resultant image of the subtracting, for each pixel location in the first image, the default intensity value from the intensity value of the pixel in the first image.

8. The imaging device of claim 1 , wherein the controller is configured to:

cause a second image of the input object to be captured with the light source turned off and

transmit the second image to the processor associated with the electronic device to perform image matching based on the first image and the second image.

9. The imaging device of claim 8 , wherein performing image matching based on the first image and the second image comprises subtracting, for each pixel location in the first and second images, an intensity value of the pixel in the second image from a corresponding intensity value of the pixel in the first image to generate a delta image, and performing image matching using the delta image.

10. The imaging device of claim 1 , wherein the light source comprises light emitting diodes included as part of a display of the electronic device.

11. A method for imaging an input object, the method comprising:

determining that the input object has settled in a sensing region associated with an electronic device;

causing a first image of the input object to be captured with a light source turned on, wherein light emanating from the light source is reflected from the input object, and wherein some light reflected from the input object is blocked by a collimator filter layer while other light reflected from the input object passes through apertures in the collimator filter layer and arrives at an image sensor array that captures the first image of the input object; and

transmitting the first image to a processor associated with the electronic device to perform image matching against one or more template images before causing a second image of the input object to be captured with the light source turned off.

12. The method of claim 11 , wherein causing the first image of the input object to be captured with the light source turned on is performed in response to determining that the input object has settled in the sensing region.

13. The method of claim 12 , wherein the electronic device includes a coarse sensor array, and wherein determining that the input object has settled in the sensing region comprises determining that a number of regions of the coarse sensor array that is covered by the input object in a first frame is within a threshold of a number of regions of the coarse sensor array that is covered by the input object in a second frame that is after the first frame.

14. The method of claim 13 , wherein the image sensor array is an optical sensor array and the coarse sensor array is a capacitive sensor array, and wherein the coarse sensor array has a coarser image resolution than the image resolution of the image sensor array.

15. The method of claim 11 , further comprising:

sending an interrupt to the processor is response to determining that the input object has settled in the sensing region, wherein the interrupt is configured to wake the processor.

16. The method of claim 11 , wherein performing image matching comprises subtracting, for each pixel location in the first image, a default intensity value from an intensity value of the pixel in the first image, and performing image matching using a resultant image of the subtracting, for each pixel location in the first image, the default intensity value from the intensity value of the pixel in the first image.

17. The method of claim 11 , further comprising:

causing a second image of the input object to be captured with the light source turned off; and

transmitting the second image to the processor associated with the electronic device to perform image matching based on the first image and the second image.

18. The method of claim 17 , wherein performing image matching based on the first image and the second image comprises subtracting, for each pixel location in the first and second images, an intensity value of the pixel in the second image from a corresponding intensity value of the pixel in the first image to generate a delta image, and performing image matching using the delta image.

19. A non-transitory computer-readable storage medium storing instructions that, when executed by a processor, cause an electronic device to image an input object, by performing the steps of:

determining that the input object has settled in a sensing region associated with the electronic device;

causing a first image of the input object to be captured with a light source turned on, wherein light emanating from the light source is reflected from the input object, and wherein some light reflected from the input object is blocked by a collimator filter layer while other light reflected from the input object passes through apertures in the collimator filter layer and arrives at an image sensor array that captures the first image of the input object; and

transmitting the first image to a processor associated with the electronic device to perform image matching against one or more template images before causing a second image of the input object to be captured with the light source turned off.

20. The computer-readable storage medium of claim 19 , wherein the electronic device includes a coarse sensor array, and wherein determining that the input object has settled in the sensing region comprises determining that a number of regions of the coarse sensor array that is covered by the input object in a first frame is within a threshold of a number of regions of the coarse sensor array that is covered by the input object in a second frame that is after the first frame.