# US 2019/0171858 A1 · Darkfield tracking > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2019/0171858 A1 - Document ID: US20190171858A1 - Status: Published application - Kind: A1 - Application number: 16/206,527 - Filed: 2018-11-30 - Published: 2019-06-06 - Earliest claimed: 2017-12-01 - Assignees: InvenSense, Inc. - Applicants: InvenSense, Inc. - Inventors: Abbas ATAYA; Bruno FLAMENT - Web page: https://patentgrep.com/patent/US20190171858A1 ## CPC - G06V 40/1306: {non-optical, e.g. ultrasonic or capacitive sensing} - G06V 40/12: Fingerprints or palmprints - G06V 40/1371: {Matching features related to minutiae or pores} - G06V: IMAGE OR VIDEO RECOGNITION OR UNDERSTANDING ## Abstract In a method for darkfield tracking at a sensor, it is determined whether an object is interacting with the sensor. Provided an object is not interacting with the sensor, a determination that a darkfield candidate image can be captured at the sensor is made. It is determined whether to capture a darkfield candidate image at the sensor based at least in part on the determination that a darkfield candidate image can be captured at the sensor. Responsive to making a determination to capture the darkfield candidate image, the darkfield candidate image is captured at the sensor, wherein the darkfield candidate image is an image absent an object interacting with the sensor. A darkfield estimate is updated with the darkfield candidate image. ## Claims ### Claim 1 A method for darkfield tracking at a sensor, the method comprising: determining whether an object is interacting with the sensor; provided an object is not interacting with the sensor, making a determination that a darkfield candidate image can be captured at the sensor; determining whether to capture a darkfield candidate image at the sensor based at least in part on the determination that a darkfield candidate image can be captured at the sensor; responsive to making a determination to capture the darkfield candidate image, capturing the darkfield candidate image at the sensor, wherein the darkfield candidate image is an image absent an object interacting with the sensor; and updating a darkfield estimate with the darkfield candidate image. ### Claim 2 (depends on 1) The method of claim 1, wherein the determination to capture the darkfield candidate image is also based at least in part on making a determination that a minimum amount of time has passed since a most recent darkfield candidate image capture. ### Claim 3 (depends on 1) The method of claim 1, wherein the determination to capture the darkfield candidate image is also based at least in part on making a determination that a temperature change since a most recent darkfield candidate image capture has exceeded a temperature threshold. ### Claim 4 (depends on 1) The method of claim 1, further comprising: provided an object is interacting with the sensor, generating an object lifting signal when it is determined the object is no longer interacting with the sensor. ### Claim 5 (depends on 1) The method of claim 1, wherein the updating the darkfield estimate with the darkfield candidate image comprises: merging the darkfield candidate image with the darkfield estimate. ### Claim 6 (depends on 1) The method of claim 1, wherein the updating the darkfield estimate with the darkfield candidate image comprises: provided the darkfield estimate is not stored, storing the darkfield candidate image as the darkfield estimate. ### Claim 7 (depends on 1) The method of claim 1, wherein the sensor is an ultrasonic sensor, wherein the determining whether an object is interacting with the sensor comprises: transmitting signals at ultrasonic transducers of the ultrasonic sensor; receiving reflected signals at ultrasonic transducers of the ultrasonic sensor; and provided the signals are not indicative of an object interacting with the ultrasonic sensor, determining that an object is not interacting with the ultrasonic sensor. ### Claim 8 (depends on 7) The method of claim 7, further comprising: comparing the reflected signals to a void flags threshold around a moving average; and provided the reflected signals are within the void flags threshold, determining that the signals are not indicative of an object interacting with the ultrasonic sensor. ### Claim 9 (depends on 8) The method of claim 8, further comprising: updating the moving average provided the signals are within a moving average threshold, wherein the moving average threshold is larger than the void flags threshold. ### Claim 10 (depends on 8) The method of claim 8, further comprising: provided the reflected signals are within the void flags threshold, making the determination that a darkfield candidate image can be captured at the sensor. ### Claim 11 (depends on 1) The method of claim 1, further comprising: responsive to detecting an object interacting with the sensor, capturing an image comprising the object; and correcting the image using the darkfield estimate. ### Claim 12 (depends on 1) The method of claim 1, further comprising: provided an object is interacting with the sensor, making the determination that a darkfield candidate image cannot be captured at the sensor. ### Claim 13 (depends on 12) The method of claim 12, further comprising: responsive to making the determination that a darkfield candidate image cannot be captured at the sensor, activating a timer; and responsive to a predetermined period of the timer lapsing, repeating the determining whether an object is interacting with the sensor. ### Claim 14 (depends on 12) The method of claim 12, further comprising: responsive to making the determination that a darkfield candidate image cannot be captured at the sensor, comparing a signal received at the sensor to a sensor temperature correlation scheme; and modifying signal thresholds according to the sensor temperature correlation scheme during the determining whether an object is interacting with the sensor. ### Claim 15 (depends on 1) The method of claim 1, further comprising: provided an object is not interacting with the sensor: determining a temperature of the sensor; associating the temperature with a corresponding pixel value; and storing the temperature and pixel value pair. ### Claim 16 (depends on 1) The method of claim 1, wherein determining whether an object is interacting with the sensor comprises: measuring a temperature of the sensor; receiving a pixel value for a pixel of the sensor; comparing the pixel value to an expected pixel value based on the temperature of the sensor; and determining whether an object is interacting with the sensor based on the comparing the pixel value to an expected pixel value based on the temperature of the sensor. ### Claim 17 (depends on 16) The method of claim 16, wherein the pixel value is received for a plurality of pixels. ### Claim 18 An electronic device comprising: a fingerprint sensor; a memory; and a processor configured to: determine whether an object is interacting with the fingerprint sensor; provided an object is not interacting with the sensor, make a determination that a darkfield candidate image can be captured at the sensor; determine whether to capture a darkfield candidate image at the sensor based at least in part on the determination that a darkfield candidate image can be captured at the sensor; responsive to making a determination to capture the darkfield candidate image, capture the darkfield candidate image at the sensor, wherein the darkfield candidate image is an image absent an object interacting with the sensor; and update a darkfield estimate with the darkfield candidate image. ### Claim 19 (depends on 18) The electronic device of claim 18, wherein the processor is further configured to: merge the darkfield candidate image with the darkfield estimate. ### Claim 20 (depends on 18) The electronic device of claim 18, wherein the fingerprint sensor is an ultrasonic fingerprint sensor, wherein the processor is further configured to: transmit signals at ultrasonic transducers of the ultrasonic sensor; receive reflected signals at ultrasonic transducers of the ultrasonic sensor; and provided the signals are not indicative of an object interacting with the ultrasonic sensor, determine that an object is not interacting with the ultrasonic sensor ### Claim 21 (depends on 18) The electronic device of claim 18, wherein the processor is further configured to: responsive to detecting an object interacting with the fingerprint sensor, capture an image comprising the object; and correct the image using the darkfield estimate. ### Claim 22 (depends on 21) The electronic device of claim 21, wherein the processor is further configured to: forward the image to a matcher for authentication. ### Claim 23 A non-transitory computer readable storage medium having computer readable program code stored thereon for causing a computer system to perform a method for darkfield tracking at a sensor, the method comprising: determining whether an object is interacting with the sensor; provided an object is not interacting with the sensor, making a determination that a darkfield candidate image can be captured at the sensor; determining whether to capture a darkfield candidate image at the sensor based at least in part on the determination that a darkfield candidate image can be captured at the sensor; responsive to making a determination to capture the darkfield candidate image, capturing the darkfield candidate image at the sensor, wherein the darkfield candidate image is an image absent an object interacting with the sensor; updating a darkfield estimate with the darkfield candidate image; responsive to detecting an object interacting with the sensor, capturing an image comprising the object; and correcting the image using the darkfield estimate. ### Claim 24 (depends on 23) The non-transitory computer readable storage medium of claim 23, wherein the updating the darkfield estimate with the darkfield candidate image comprises: merging the darkfield candidate image with the darkfield estimate. ### Claim 25 (depends on 23) The non-transitory computer readable storage medium of claim 23, wherein the sensor is an ultrasonic sensor, wherein the determining whether an object is interacting with the sensor comprises: transmitting signals at ultrasonic transducers of the ultrasonic sensor; receiving reflected signals at ultrasonic transducers of the ultrasonic sensor; and provided the signals are not indicative of an object interacting with the ultrasonic sensor, determining that an object is not interacting with the ultrasonic sensor.