Most of medical images, especially tomographic images, are in digital. It is worth getting these digital data onto the personal computer and doing extra post-processing without much difficulties. The extra processing of obtained medical images may not give the great benefits for clinical purpose, however it is recommended to analyze obtained images more quantitatively for publication or presentation of one's results. Simple post-processing of MR and SPECT images was achieved using a public domain image processing software (NIH Image 1.56) on a Macintosh computer. The general concepts of the file transfer, the reading of the images into the software, and some examples of the processing are to be discussed.