IMAGE TRANSFORMATIONS IN THE COMPRESSED DOMAIN

Image processing techniques which involve direct manipulation of the compressed domain representation of an image to achieve the desired spatial domain processing without having to go through a complete decompression and compression process. The techniques include processing approaches for performing the eight operations in D.sub.4 (the dihedral group of symmetries of a square) on JPEG images using the discrete cosine transform (DCT) domain representation of the images directly. For a task such as image rotation by 90.degree. (an operation in D.sub.4), DCT-domain based methods can yield nearly a five-fold increase in speed over a spatial-domain based technique. These simple compressed-domain based processing techniques are well suited to the imaging tasks that are needed in a JPEG-based digital still-camera system.