Performance analysis of compression techniques for pathological microscopic images

Telepathology is aiming at pathological diagnoses based on microscopic images of cell samples through broadband networks. The number of pixels in pathological microscopic (PM) images is said to be approximately 4 to 6 million. In this paper, digital PM images are made without films using a super high definition (SHD) image prototype system, which has more than double the number of pixels and frame frequency than those of HDTV images. First, color distribution and a spatial spectrum are analyzed in order to estimate compression characteristics of the images. In addition, the lossless and lossy JPEG coding characteristics are investigated. In the lossless compression, the PM images have compression ratios which are very close to 1, while the general images have compression ratios around 2. The PM image compression ratios in the lossy JPEG coding, where the L*a*b* color difference is less than 2 to 3, are found to almost equal those of the lossless JPEG (Joint Photographic Coding Experts Group) using arithmetic coding. The PM image coding performance in the lossy JPEG coding is also found to be inferior to that of general images including still life images, portraits, and landscapes.