This work proposes a novel algorithm to extract three-dimensional angular velocity of a sphere from a sequence of high-speed digital images of this sphere and its marker stickers. This technique can capture the angular velocity omega of a sphere made to move at a specific angle from the camera by an offset DC motor and its speed vertical bar omega vertical bar with an error lower than 5%. The method is then applied to measure individual grain rotation dynamics at the boundary during a bulk avalanche to extract the instantaneous contour of each angular velocity component which is in qualitative agreement to that reported from a complementing discrete element simulation. The angular velocity of individual grains vertical bar omega(p)vertical bar is further analyzed with its local packing density and configuration to confirm that the sudden rise of vertical bar omega(p)vertical bar is always accompanied by local dilatation upon particle rearrangement. (C) 2018 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.