Picture elements of a digitally coded image are each represented by a color value. The value of an element x is adjusted by firstly making a number of comparisons between elements elsewhere in the image. This comparison involves comparing a first picture element group (which may comprise the picture element x under consideration and at least one further picture element in the vicinity thereof) with a second picture element group. The second picture element group comprises a base picture element y 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. The comparison determines whether the two groups match in the sense that they meet a criterion of similarity. When at least one comparison results in a match, a replacement color value for the picture element under consideration is generated, as a function of the color value for the base picture element of the second group for which a match was obtained.