An apparatus for modifying predicted values in a predicted image for input to a decoder starts by taking the most significant information bit plane from the predicted image and submitting it to the decoder to be decoded. Subsequent information bit planes are then taken in descending order and submitted to the decoder, but first each of these information bit planes is modified at the locations of prediction errors identified in the preceding information bit plane by comparing that information bit plane with the corresponding decoded bit plane. The modifications improve the general accuracy of the decoded image, enabling the decoder to decode the bit planes with less additional coded information than would otherwise be required. The apparatus is useful in distributed video coding systems.