A fast efficient computation of cubic-spline interpolation in image codec

It is shown that cubic-spline interpolation (CSI) can be performed by a fast and efficient computation for the encoding and decoding processes of image coding. It requires substantially fewer additions and multiplications than the original CSI algorithm. Furthermore, a new type of overlap-save scheme is utilized to solve the boundary-condition problems that occur between two neighboring subimages in the actual image. It is also shown that a very efficient nine-point Winograd discrete Fourier transform (WDFT) can be used to replace the fast Fourier transform (FFT) needed to implement the CSI scheme in the modified JPEG encoder. Finally, the proposed fast new CSI algorithm with a compression ratio of 9:1 is used along with the JPEG standard to speed up the modified JPEG encoder-decoder and still obtain a better quality of reconstructed image for higher compression ratios.