In our previous studies we found that excessive spatial resolution can be partially recovered by error-free compression. However, the excessive gray dynamic resolution is not reducible as far as information content is concerned. Both information evaluation and preliminary clinical tests indicated that no information existed beyond 9-bit when digitized by a sample size of 180 (mu) with laser film digitization or computed radiography. In this study, we found that a high compression method can only achieve a small fraction of true compression efficacy over an error-free compression for a well-defined digital radiographic imaging system. This implies that the following two procedures contain similar digital information: (a) digitization of a 12- bit image and processing by a moderate irreversible compression (e.g., DCT type compression) and (b) digitization of the same image 8-bit followed by an error-free compression method (e.g., DPCM/arithmetic coding). Images processed by the above methods require about the same digital storage. The image quality of 12-bit with 5:1 irreversible compression is very close to that of 8-bit with 3:1 error-free compression. Higher compression efficiency (e.g., 0.5 bit/pixel) using procedure (a) would degrade the image quality particularly in edges and small structures. This is because the quantization procedure acts as a filter in the DCT compression. Without the interference of noise, the compression efficiency of using irreversible and reversible compression techniques are comparable as far as information is concerned.

Date Published: 30 June 1993
PDF: 6 pages
Proc. SPIE 1897, Medical Imaging 1993: Image Capture, Formatting, and Display, (30 June 1993); doi: 10.1117/12.146978

Published in SPIE Proceedings Vol. 1897:
Medical Imaging 1993: Image Capture, Formatting, and Display
Yongmin Kim, Editor(s)