Acceptable compression ratios for CR images for PACS archives

We make a preliminary study with a ROC experiment to determine the acceptable levels of image compression that may be utilized for PACS archives. CR images of 1760 X 2140 pixel size and 10 bit depth are studied. The experiment uses wavelet algorithm for image compression and printed films for image viewing. The 'internal standard' experiment results in an acceptable value of compression ratio of 6 for imperceptible difference (da' equals 1) between the compressed and the uncompressed image. Such ratio would lead a storage reduction factor of 9.6 for these images. The information capacity of the CR images may be extrapolated to be 40 bits per millimeter of viewing area.