Accumulating charge from multiple imaging exposure periods

A method for operating a photosensor comprising an array of photodetectors, the method comprising:

• providing a plurality of pulses of a pulsed light output;
• and
• for one or more pulses of the pulsed light output,
• at each photodetector of a plurality of photodetectors of the array of photodetectors,
• accumulating a first charge for light received from a current pulse of the pulsed light output based on an amount of light incident upon the photodetector during a first exposure period for the current pulse and adding the first charge to charge accumulated for light received at the photodetector from a pulse during each first exposure period of one or more previous pulses of the pulsed light output to form an updated first charge,
• accumulating a second charge for light received from the current pulse of the pulsed light output based on an amount of light incident upon the photodetector during a second exposure period of the current pulse and adding the second charge to charge accumulated for light received at the photodetector from a pulse during each second exposure period of the one or more previous pulses of the pulsed light output to form an updated second charge, and
• converting the updated first charge and the updated second charge to digital values.

A pulsed time-of-flight depth camera system, comprising:

• a light source;
• an image sensor comprising an array of photodetectors, and a charge storage mechanism associated with each photodetector, each of the charge storage mechanism and associated photodetector being configured to allow charge to be transferred between the charge storage mechanism and the associated photodetector;
• a logic device;
• and
• a storage device comprising instructions stored thereon that are executable by the logic device to, for each photodetector of the array of photodetectors:
• provide a pulsed light output via the light source;
• accumulate a first charge for light received from a first pulse of the pulsed light output on the photodetector during a first exposure period for detecting reflected light from the first pulse of the pulsed light output;
• transfer the first charge to a charge storage mechanism;
• accumulate a second charge for light received from the first pulse of the pulsed light output on the photodetector element during a second exposure period for detecting reflected light from the first pulse of the pulsed light output;
• transfer the second charge accumulated on the photodetector to the charge storage mechanism;
• transfer the first charge back to the photodetector to receive an additional first charge at the photodetector;
• accumulate the additional first charge for light received from a second pulse of the pulsed light output on the photodetector during a first exposure period for detecting reflected light from the second pulse of the pulsed light output to form an updated first charge;
• transfer the updated first charge on the photodetector to the charge storage mechanism;
• transfer the second charge back to the photodetector to receive an additional second charge at the photodetector;
• accumulate the additional second charge for light received from the second pulse of the pulsed light output on the photodetector during a second exposure period for detecting reflected light from the second pulse of the pulsed light output to form an updated second charge, and
• convert the updated first charge and the updated second charge to digital values.