On resizing images in the DCT domain

This paper presents a general method for producing a mapping from the DCT domain to another DCT domain that results in an image that has been resized in the spatial dimension. Although the mapping is implemented entirely in the DCT domain, it can be thought of as a transformation into the spatial domain using a combined inverse DCT and resizing operator followed by a combined forward DCT and another resizing operator. Final image quality can be traded off for lower implementation complexity and a wide range of complexity versus final quality operation points can be chosen for each scale factor. Current existing methods often suffer from a lack of flexibility (i.e. work for only one or at most a few resizing factors, have only one or two levels of complexity) or require more operations to achieve similar levels of final image quality. When constructing the mapping, a multiplierless DCT approximation can be used for fast implementation with excellent results. The use of the DCT approximation confers several benefits upon the proposed mapping including multiplierless implementation or at most integer rather than floating point operations.