Two-dimensional transform domain decimation techniques

Decimation is normally carried out in two passes; lowpass filtering and subsampling where the latter is normally performed in the time domain. This paper describes a technique whereby both the operations can be combined in the transform domain. The two-dimensional decimation scheme is first implemented in the discrete Fourier transform domain and then extended to the discrete cosine transform domain. It is further applied to a non-sinusoidal i.e. Hadamard transform domain. The effect of using ideal filter transfer function in transform domain decimation on the quality of the decimated images is investigated. This approach results in greater computational efficiency as the constraint of filter length to meet certain specifications is removed permitting the use of smaller transform block sizes.