Fast algorithms for type-III DCT of composite sequence lengths

This correspondence presents an odd-factor algorithm for the type-III discrete cosine transform (DCT) for uniform or mixed radix decomposition. By jointly using the old-factor and the existing radix-2 algorithms, a general decomposition method for arbitrarily composite sequence length is developed. A reduction of computational complexity can be achieved compared with that needed by other reported algorithms for M=2^m. The decomposition approach has a simple computational structure and supports a wider range of choices for different sequence lengths