A time-integrating pixel sensor (100) having a photo-detector (102), a capacitor (104), a comparator (110) and a pixel data buffer (114). In operation, the photo-current from the photo-detector charges the capacitor and produces a photo-voltage. The photo-voltage sensed by the capacitor and a reference voltage (108) is compared with the comparator. If the photo-voltage exceeds the reference voltage, a global code value is latched into the pixel data buffer. The optical power falling on the photo-detector is determined from the latched code value. An array of sensors is incorporated into a semiconductor device together with circuitry (116) to read and decode the pixel data buffers. The reference voltage may be varied in time to increase the dynamic range of the sensor.