Mukherjee, Jayanta and Mitra, S.K.,
Arbitrary resizing of images in the DCT space (2005),
IEE Proc. Vision, Image and Signal Processing,
vol. 152, No. 2, pp.155-164.  Abstract. 
Using spatial relationship of the block DCT coefficients and sub-band approximations, algorithms for image halving and doubling operations are presented in this paper. The computational steps identified in the process provide a general framework for image resizing operations. Some of the previously reported image halving and doubling algorithms are shown as their special cases. The proposed approach is general enough to accommodate resizing operations with arbitrary factors, namely with integral and rational factors. An interesting application of these methods shown here is the conversion in the compressed domain of images (video frames) from one format to another.