  When an X-ray photon lands into a pixel (event pixel), the primary charge is
mainly collected into the event pixel. If the X-ray landing position is
sufficiently close to the pixel boundary, the primary charge spills over to the
adjacent pixel forming split events. We can easily understand that there are
three parameters coupled together; the X-ray landing position inside the pixel,
the X-ray event pattern and the primary charge cloud shape. We can determine
any one of them from the other two parameters. Since we know the charge cloud
shape using the multi-pitch mesh experiment, we can calculate the X-ray landing
position with subpixel resolution using the event pattern. We applied our
method to Ti-K X-rays for the charge-coupled device with $12 \mu$m square
pixel. Once the primary charge splits into the adjacent pixel, we can determine
the X-ray landing position with subpixel resolution. Using three- or four-pixel
split events, we can determine the X-ray landing position with an accuracy of
less than $1 \mu$m. For a two-pixel split event, we obtained a similar position
accuracy in the split direction with no improvement in the direction
perpendicular to it. We will discuss the type of CCD which can achieve the
subpixel resolution for the entire area of the CCD.
