[Octave-bug-tracker] [bug #61845] [octave forge] (image) speed of imrotate with bicubic interpolation increased

[Hartmut]

URL:
  <https://savannah.gnu.org/bugs/?61845>

                 Summary: [octave forge] (image) speed of imrotate with
bicubic interpolation increased
                 Project: GNU Octave
            Submitted by: hardy
            Submitted on: Mon 17 Jan 2022 10:17:55 PM UTC
                Category: Octave Forge Package
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Performance
                  Status: None
             Assigned to: None
         Originator Name: 
        Originator Email: 
             Open/Closed: Open
                 Release: other
         Discussion Lock: Any
        Operating System: Any

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Details:

I have observed the following: When you run this little script, that rotates
an image several times with imrotate:


pkg load image
I = checkerboard(120);
tic;
for n=1:10
  J = imrotate(I,36,'bicubic','crop',1);
end
t=toc


Then the execution speed is significantly increased in current dev image (what
should become image-2.14.0), compared to the current image release 2.12.0. I
have observed this on windows and linux, and I have observed this under
serveral versions of core Octave (6.3.0 and 7.0.90).

Example: 
* Octave 6.3.0 (linux) and image-2.14.0 -> 6s
* Octave 6.3.0 (linux) and image-2.12.0 -> 3s

The other interpolation methods (nearest or bilinear) are not affected by this
speed increase.

Is this a "speed regression" introduced by the recent code changes regarding
bicubic interpolation? Can we improve this, back to (more or less) the old
speed?




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