Quantization techniques for the compression of chest images by JPEG-type algorithms

The Joint Photographic Expert Group (JPEG) compression standard specifies a quantization procedure but does not specify a particular quantization table. In addition, there are quantization procedures which are effectively compatible with the standard but do not adhere to the simple quantization scheme described therein. These are important considerations, since it is the quantization procedure that primarily determines the compression ratio as well as the kind of information lost or artifacts introduced. A study has been conducted of issues related to the design of quantization techniques tailored for the compression of 12-bit chest images in radiology. Psycho-physical based quantization alone may not be optimal for images that are to be compressed and then used for primary diagnosis. Two specific examples of auxiliary techniques which can be used in conjunction with JPEG compression are presented here. In particular, preprocessing of the source image is shown to be advantageous under certain circumstances. In contrast, a proposed quantization technique in which isolated nonzero coefficients are removed has been shown to be generally detrimental. Image quality here is primarily measured by mean square error (MSE), although this study is in anticipation of more relevant reader performance studies of compression.