in this update,
* either the starting pixel(corner) or the center of window location may be specified (see README)
* by specifying the starting/ending pixel locations, the reference/search window may go beyond the range of the original images. Zeros are filled in instead. In this case, the offset fields at the edge may be incorrect.
* The range check is no longer needed. It only runs in DEBUG mode and issues warning messages when pixels are outside the image range.