Input and output index mappings for a prime-factor-decomposed computation of discrete cosine transform

A formal direct derivation of the prime-factor-decomposed computation algorithm is presented. The derivation is direct in the sense that it is based on the real cosine function without resort to the discrete Fourier transform expressions or the complex functions. Based on the equations obtained from the derivation, input and output index mappings are introduced in the form of tables. This tabulation enables any prime-factor-decomposable discrete cosine transform (DCT) to be implemented in a straight-forward manner. The use of the index mapping tables is demonstrated for the 12-point DCT