Abstract: A sensor device (10) for photon-based imaging comprising one or more photon detectors configured to produce a plurality of photon detection signals in response to a plurality of photon detection events, wherein each photon detection event has a corresponding detection time and wherein the detection times of the plurality of photon detection events are distributed in accordance with a distribution over time; and processing circuitry configured to perform a sketching process using timing information of the plurality of photon detection events to obtain a compressed representation of the distribution over time, wherein the sketching process comprises: generating a plurality of feature values based on the timing information of the plurality of photon detection events using one or more feature functions; combining the generated plurality of feature values to obtain the compressed representation of the distribution over time, wherein the feature functions have one or more properties such that combining the pluralit