L/M-fold image resizing in block-DCT domain using symmetric convolution.

Image resizing is to change an image size by upsampling or downsampling of a digital image. Most still images and video frames on digital media are given in a compressed domain. Image resizing of a compressed image can be performed in the spatial domain via decompression and recompression. In general, resizing of a compressed image in a compressed domain is much faster than that in the spatial domain. We propose a novel approach to resize images with L/M resizing ratio in the discrete cosine transform (DCT) domain, which exploits the multiplication-convolution property of DCT (multiplication in the spatial domain corresponds to symmetric convolution in the DCT domain). When an image is given in terms of its 8 x 8 block-DCT coefficients, its resized image is also obtained in 8 x 8 block-DCT coefficients. The proposed approach is computationally fast and produces visually fine images with high PSNR.