1. An automated computer-implemented method of processing a digitally coded image in which picture elements are each represented by a color value, said method comprising, for each of a plurality of said picture elements, using a programmed computer having a CPU, memory and I/O ports configured to: (a) perform a plurality of comparisons, each comparison comprising comparing a first picture element group of plural pixels, which first group comprises the picture element under consideration and at least one further picture element in the vicinity thereof with a second picture element group of plural pixels, which second group comprises a base picture element and at least one further picture element, the number of picture elements in the second group being the same as the number of picture elements in the first group and the position of each further element of the second group relative to the base picture element of the second group being the same as the position of the respective further element of the first group relative to the picture element under consideration, wherein each comparison determines whether the two groups match in the sense that they meet a criterion of similarity; and (b) when at least one comparison results in a match, computing a replacement color value for the picture element under consideration, the replacement color value being a function of the color value for the base picture element of each second group for which a match was obtained.