A method for multipath error compensation for an indirect time of flight range calculation apparatus, the method comprising: a structured light source illuminating a scene and employing an illumination pattern comprising regions of no illumination; and an array of photodetectors generating (204, 206) a plurality of sets of signals in response to irradiation with light reflected from the scene, the plurality of sets of signals comprising a set of signals generated substantially contemporaneously by each photodetector element of the array of photodetectors in accordance with an indirect time of flight measurement technique; the method characterised by: an unstructured light source illuminating the scene during a plurality of consecutive time frames; the structured light source illuminating the scene concurrently with the illumination of the scene by the unstructured light source, the illumination by the structured light source occurring during predetermined frames of the plurality of consecutive time frames; deriving an error estimate from the plurality of sets of signals generated during a selected time frame of the plurality of consecutive time frames and another time frame temporally about the selected time frame, illumination by the unstructured light source occurring during the selected time frame and illumination by both the structured and unstructured light sources (142, 144) occurring during the another time frame; and applying the error estimate in a range calculation with respect to the scene; wherein the error estimate is derived in respect of the regions of no illumination using a priori knowledge of the illumination pattern. a structured light source illuminating a scene and employing an illumination pattern comprising regions of no illumination; and an array of photodetectors generating (204, 206) a plurality of sets of signals in response to irradiation with light reflected from the scene, the plurality of sets of signals comprising a set of signals generated substantially contemporaneously by each photodetector element of the array of photodetectors in accordance with an indirect time of flight measurement technique; the method characterised by: an unstructured light source illuminating the scene during a plurality of consecutive time frames; the structured light source illuminating the scene concurrently with the illumination of the scene by the unstructured light source, the illumination by the structured light source occurring during predetermined frames of the plurality of consecutive time frames; deriving an error estimate from the plurality of sets of signals generated during a selected time frame of the plurality of consecutive time frames and another time frame temporally about the selected time frame, illumination by the unstructured light source occurring during the selected time frame and illumination by both the structured and unstructured light sources (142, 144) occurring during the another time frame; and applying the error estimate in a range calculation with respect to the scene; wherein the error estimate is derived in respect of the regions of no illumination using a priori knowledge of the illumination pattern. an unstructured light source illuminating the scene during a plurality of consecutive time frames; the structured light source illuminating the scene concurrently with the illumination of the scene by the unstructured light source, the illumination by the structured light source occurring during predetermined frames of the plurality of consecutive time frames; deriving an error estimate from the plurality of sets of signals generated during a selected time frame of the plurality of consecutive time frames and another time frame temporally about the selected time frame, illumination by the unstructured light source occurring during the selected time frame and illumination by both the structured and unstructured light sources (142, 144) occurring during the another time frame; and applying the error estimate in a range calculation with respect to the scene; wherein the error estimate is derived in respect of the regions of no illumination using a priori knowledge of the illumination pattern.