Three-dimensional tranform compression of images sets

Transform-based compression methods achieve their effect by taking advantage of the correlations between adjacent pixels in an image. Algorithms based on the full-frame discrete cosine transform have achieved compression ratios as high as 15:1 with almost imperceptible image degradation, when applied to 2K x 2K x 8-bit radiographs. For time-sequenced studies such as digital subtraction angiography, pixels are correlated between images, as well as within an image. By using three- dimensional transforms, correlations in time as well as in space can be exploited for compression. In this study, sequences consisting of either four 1K x 1K x 8-bit or 16 512 x 512 x 8-bit images are compressed by using a single full-volume, three-dimensional, cosine transform, followed by quantization and bit-allocation. The resultant image fidelity versus compression ratio is superior to that achieved by compressing each image individually