A fast approximate algorithm for scaling down digital images in the DCT domain

We present a fast approximate algorithm for scaling down an image by a factor of two, when the input and output streams are both in the form of 8/spl times/8 discrete cosine transform (DCT) transform blocks, as with JPEG coded images. Roughly speaking, the algorithm requires 80% fewer operations than the naive algorithm of inverting the transform, scaling in the spatial domain, and transforming the resulting image.