  A charge-coupled device (CCD) is a standard imager in optical region in which
the image quality is limited by its pixel size. CCDs also function in X-ray
region but with substantial differences in performance. An optical photon
generates only one electron while an X-ray photon generates many electrons at a
time. We developed a method to precisely determine the X-ray point of
interaction with subpixel resolution. In particular, we found that a
back-illuminated CCD efficiently functions as a fine imager. We present here
the validity of our method through an actual imaging experiment.
