Medical Image Processing: From Lossless to Lossy Compression

Compressed image will always reduce the image fidelity. This is especially so if the image is compressed at lower bit rates, which most of the time cannot be tolerated. Compression is necessary in medical field due to the limited transmission bandwidth and storage capacity. In this paper, performance of the controversial lossy compression on medical modalities using the new JPEG2000 and the more conventional JPEG is being studied. The common objective measure, peak signal-to-noise ratio (PSNR) is definitely not adequate as a perceptual quality measurement. Therefore, subjective measures such as picture quality scale (PQS) and mean opinion score (MOS) are used as the benchmark instead, along with the statistical and frequency measures for the image characteristics evaluation. Three types of medical modalities are used - X-ray, ultrasound and computed tomography (CT). From these various measurements, the general acceptable compression bit rate for each of the medical modality is determined.