Apparatus for optical sensing includes first matrix of optical sensing elements, arranged on a semiconductor substrate in rows and columns. A second matrix of storage nodes is arranged on the substrate such that respective first and second storage nodes in the second matrix are disposed in proximity to each of the sensing elements within the first matrix. Switching circuitry couples each of the sensing elements to transfer photocharge to the respective first and second storage nodes. Control circuitry controls the switching circuitry in a depth sensing mode such that over a series of detection cycles, each of the sensing elements and a first neighboring sensing element are connected together to the respective first storage node during the first detection interval, and each of the sensing elements and the second neighboring sensing element are connected together to the respective second storage node during the second detection interval.