US Patent 10936841 Darkfield tracking

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.