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

[H. G.]

URL:
  <http://savannah.gnu.org/bugs/?44830>

                 Summary: image package: imtransform gives different numbers
on simple rotation
                 Project: GNU Octave
            Submitted by: hardy
            Submitted on: Di 14 Apr 2015 10:21:45 GMT
                Category: Octave Forge Package
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Matlab Compatibility
                  Status: None
             Assigned to: None
         Originator Name: 
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any
                 Release: 3.8.2
        Operating System: Any

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Details:

Here is a simple script to show the behavior:


clear;
pkg load image;

M = [0 1 0; 0 1 0; 0 1 0];
a=45;
t = maketform('affine',[cosd(a) sind(a) 0; -sind(a) cosd(a) 0; 0 0 1]);
imtrans = imtransform(M,t,'fillvalues',0)


The result of current Octave (3.8.2) and the imtransform script from the image
package (2.4.0) gives the following result:


      0         0         0          0
      0   0.33333         1          0
      0         1   0.33333          0
      0         0         0          0


Matlab gives this result with different numbers:


      0         0    0.2426          0
      0    0.4142    0.8787     0.1005
 0.2426    0.8787    0.1716          0
      0    0.1005         0          0


Since the applied geometrical transformation is a simple rotation by 45
degrees, I was expecting the same results from both Matlab and Octave. Both do
use the same (default) type of interpolation method (bilinear). And both
resulting matrices have the same dimensions.

Nevertheless the resulting numbers differ :( What is working different here?




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