Simple methods for the design of 2D recursive digital filters with noncircular cutoff boundary

The authors present several methods for the design of 2D filters with noncircular cutoff boundaries. One-dimensional filters are used as the main building block and other building blocks are formed by various transformations. It is shown that cascading an appropriate number of these building blocks will yield a 2D filter approximating to the desired cutoff boundary. The proposed methods are very simple and require no optimisation. However, optimisation techniques are also utilised if higher accuracies are needed. Examples are given to illustrate the uses of the proposed techniques