The invention relates to a method as well as a system, a device, an encoder and a decoder, and a computer software product for image processing by the method. In the invention, the number of bits is limited in the bit string of a pixel to be processed, wherein the pixel is encoded with the limited number of bits. A prediction value corresponding to said pixel is searched for. If it is found, the difference between the pixel and the prediction value is determined, to select the method for encoding the bit string of said pixel. Also, a code word is encoded in the bit string, to indicate the selected encoding method. If the prediction value is missing, the number of bits in said pixel is limited by quantizing. By means of the invention, a fixed number of bits is obtained for all encoded pixels in an image.