Improvement in the locally optimum run-length compression of CT images

In the locally optimum run-length compression of X-ray CT images, differential entropy is selected as the criterion for compression. The reported compressed results for 12 bit CT images are 8-9 bits per pixel, which are far from the differential entropies of the boundaries of the compression, from 5.5 to 6 bits per pixel. Our analysis shows that the compression strategy is defective and this is one reason why the compression cannot reach the boundary. Significant improvement has been achieved and the results challenge the selection of differential entropy as a 'theoretical bench mark' for compression.