Comments on "Fast Radix-9 Algorithm for the DCT-IV Computation"

—Recently, a fast radix-algorithm for an efficient computation of the type-IV discrete cosine transform (DCT-IV) has been proposed in [1], where is an odd positive integer. In particular, based on the proposed fast algorithm, optimized efficient 3-, 5-, and 9-point scaled DCT-IV (SDCT-IV) modules have been derived in [1]. As a response, an improved efficient optimized 9-point scaled DCT-IV (SDCT-IV) module in terms of the arithmetic complexity is presented. The improved optimized efficient 9-point SDCT-IV module requires 17 multiplications, 53 additions, and three shifts. Consequently, the arithmetic complexity of extended fast mixed-radix DCT-IV algorithm for composite lengths is also significantly improved.