Compression of medical images is of great importance in the implementation of systems such as PACS (Picture Archival and Communication System) and teleradiology. Significant compression is only achievable by lossy methods, though distortion must be kept low to preserve all the diagnostic information. The JPEG lossy compression standard has some shortcomings, in particular block distortion. We investigated two block-based DCT transform techniques which tend to suppress the block effect, the DCT/DST coder and the LOT coder, and compared them with JPEG and an ordinary DCT coder for different types of medical images. The results show that the LOT coder performs best at all compression ratios for all kinds of investigated medical images. At very high image quality, JPEG is preferable for it requires almost the same bit rate as the LOT and is computationally less demanding.
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