[Octave-bug-tracker] [bug #44830] image package: imtransform gives different numbers on simple rotation

[H. G.]

Follow-up Comment #4, bug #44830 (project octave):

One key to this difference between the Matlab and the Octave function
"imtransform.m", might be the thinking (and calculating) behind the function
"findbounds.m".

Only if I do the following change to line 45 and 46 of findbounds.m
(image-2.4.0)

    [xcp, ycp] = meshgrid (linspace (inbnd(1,1)-0.5, inbnd(2,1)+0.5, 3),
                           linspace (inbnd(1,2)-0.5, inbnd(2,2)+0.5, 3));

with the control points in the input space expanded by 0.5 in each direction,
then I can reproduce the Matlab results of findbound.m as stated in the Matlab
help ( http://de.mathworks.com/help/images/ref/findbounds.html ).

But this seems not the only necessary change. With this adjusted findbounds
function, the demo script of the original post only changes to

imtrans =

   0.00000   0.00000   0.00000   0.00000   0.00000   0.00000
   0.00000   0.00000   0.00000   0.00000   0.00000   0.00000
   0.00000   0.00000   0.40000   1.00000   0.00000   0.00000
   0.00000   0.00000   1.00000   0.40000   0.00000   0.00000
   0.00000   0.00000   0.00000   0.00000   0.00000   0.00000
   0.00000   0.00000   0.00000   0.00000   0.00000   0.00000

which is not yet the same as the Matlab result.

I suspect, there must be other resulting changes in imtransform.m to adjust to
this different thinking of "input space dimension".

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