Image sensor with in-pixel background subtraction and motion detection

A method, comprising:

• capturing, during a first image capture period in which an infrared illumination source is deactivated, a first image of an external scene, wherein capturing the first image includes exposing photosensors of a global shutter image sensor to first ambient light from the external scene without exposing the photosensors to illumination from the infrared illumination source, wherein the global shutter image sensor includes (i) a plurality of pixel cells corresponding to the photosensors and (ii) a corresponding plurality of sample and hold circuits;
• saving first image pixel values corresponding to the first image in a voltage domain on first capacitors by, for each pixel cell of the plurality of pixel cells, outputting the first image pixel values to a respective sample and hold circuit of the plurality of sample and hold circuits;
• capturing, during a second image capture period in which the infrared illumination source is activated to direct infrared light into the external scene, a second image of the external scene, wherein capturing the second image includes exposing the photosensors of the global shutter image sensor to a combination of second ambient light from the external scene and illumination from the infrared illumination source;
• saving second image pixel values corresponding to the second image in the voltage domain on second capacitors by, for each pixel cell of the plurality of pixel cells, outputting the second image pixel values to the respective sample and hold circuit of the plurality of sample and hold circuits;
• and
• detecting an object in a foreground of the external scene based at least in part on a difference between the first image pixel values and the second image pixel values in the voltage domain.