Signal analysis and compression performance evaluation of pathological microscopic images

Digitizing high-quality microscopic images and developing input/output technology for displaying those results is critical to telepathology in which pathological microscopic images are transferred to remote locations where they are diagnosed by specialists. Here, the authors discuss the results achieved by directly digitizing (nonfilm process) pathological microscopic images at a 2 k×2 k resolution, and then using a super-high-definition imaging system to analyze the signals and evaluate compression performance. The authors start off by digitizing samples that a pathologist actually uses in making a diagnosis. They then analyze the images´ color distribution and spatial frequency characteristics by comparing them to general images. This makes it apparent that such pathological images characteristically contain high spatial frequencies in their chrominance components. The authors also discuss the evaluation results of color differences for L ^*a ^*b ^* space and compression ratios achieved when using JPEG to encode pathological images. Finally, the authors present a subjective evaluation of the influence that subsampling of chrominance components has on image quality.