A phase shift like you describe in the image could be caused if the byte
offset in the file to the start of the image bytes is calculated
incorrectly. The image always starts at the beginning of a 2880-byte
FITS block, e.g., at byte 2880, 5760, 8640, ..., etc. and is the first
FITS block following the header block that contains the END keyword.

Bill Pence

gberz3 wrote:
Hi All,

I have written an application to read FITS files. I now have an
anomaly where some images have a "split" in them. Basically it
appears that the image is shifted to the right or left by so many
pixels and "wraps" around. This doesn't happen, however if I open it
in GIMP using the FITS plugin, or with various other FITS Viewers.
I'm curious as to what could be happening. Is there some type of
"key" in the data that would tell me about a particular offset? I've
checked headers between "good" files and the "split" ones and there
seems to be no relevant differences. In fact, most of the split
images only have SIMPLE, BITPIX, NAXIS, NAXIS1, NAXIS2, and no other
data.

Any input would be most appreciated.