I don't see a way to specify the matrix used to perform a desired
perspective transformation manually.  Of course, I can adjust it by
dragging handles, but it would be much easier for me to calculate what I
need and then enter the elements of the matrix by hand.

Needless to say, a typical gimp user would not be able to do this, but I
am a mathematician who has taught geometry many times during my
professional life, so I know what to do.  I don't need an explanation of
how the matrix is formed and what it does since I can work that out by

The gimp manual is not helpful.  It refers the reader to the section on
convolution filters, but that appears to have to do with modifying
pixels in place rather than moving the pixels---a rather misleading
reference.  Perhaps something entirely different happens if you use the
full matrix, but the documentation is silent on that matter.

Of course, I can try to produce what I want by moving the handles, but
for slight adjustments of large images, that is difficult if not
impossible.  It helps if I increase the magnification enormously, but it
is still awkward.  It would be a lot simpler to be able to enter the
matrix elements directly. 

Leonard Evens <[EMAIL PROTECTED]>
Mathematics Department, Northwestern University

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