[bananas] serious programming feature

[Eric Greisen]

We have discovered that images with their Clean components may be used
as models only in the original 2^N form or in carefully selected
subimages (maintaining the original central pixel as the central
pixel).  Casually selected subimages, such as the model sources
shipped with AIPS to this point, do not work correctly.  We will be
looking to see if we can correct this error.  Unfortunately, at the
first examination of the problem, it appears that we need to add
things to the header to avoid the problem in future.  This does little
for images already computed however.  It will take us some time to
implement any solution to this difficulty since it touches on many
areas at once.  Unfortunately, the center of an image has real meaning
when doing FFTs even if the reference pixel is elsewhere.  Thus the
central pixel is build into quite a bit of the imaging and model
subtraction code.

I suspect that users normally use their original images for the model
images and thus have not encountered this problem.  We should have
heard from someone over all these years if that were not the case.

Eric Greisen