an error is identified in a video image by calculating frequency - related coefficients for blocks of the image and considering the statistical distribution of said coefficients . the variance of the coefficients is calculated and a block of original image data is concealed if the variance calculated is significantly higher than a stored threshold and / or if said variance calculated is significantly different from variance values derived for similarly positioned blocks within a previous frame . concealment is effected by selecting image data from a previous frame , displaced in response to transmitted motion vectors .