The invention is applied to image processing schemes by providing at least one auxiliary block processing mode in addition to the standard default block processing mode of the scheme. An image to be decoded is divided into a number of image blocks (800) having multiple image elements (810). These blocks (800) are individually compressed by means of a default compressing mode or an auxiliary compressing mode, depending on which mode that results in a smallest error metric. A portion (980) of the resulting compressed block (900) is used to discriminate between the two modes. In the auxiliary mode, the remaining payload portion (990) of the compressed block (900) can be used for encoding purposes, whereas the default mode can in addition utilize the discriminating portion (980).