Equipment for detecting impurities in transparent material comprising a light source to illuminate the material, a camera to detect light transmitted through the material and signal-processing apparatus for processing and analysing signals from the camera representing the light transmission through the material. Dark custom-tinted paints or stains are tinted lighter from a dark-colored base, not darker from a white or light colored base as is done in conventional point-of-sale systems. The method further includes deriving at least one motion vector of the bi-predictive block by applying a bit operation to the selected list 0 motion vector. and the dimensional change in the whole board can be reduced.