Mode filters and their effectiveness for enhancing colour images

Mode filters are less well known than median filters: this is because they are more difficult to implement, and their detailed specification turns out to be less straightforward. However, early success using the 'truncated median filter' implementation suggested that further investigation of their performance would be worthwhile. In particular, performance with colour images was a vital concern which needed to be addressed. In addition, there were questions about the shape and size distortions that this type of filter might be subject to. All these aspects are covered in the present paper. On the one hand, it is shown that performance with colour images is impressive, not merely with regard to the earlier image enhancement application but also for the purpose of noise elimination. On the other hand, the edge shifting properties of this type of filter are similar to those of the median filter, and the mode filter offers no particular advantage in this respect.