[bug #67989] (Image) Octave image ordfilt2 is slower than matlab

"Dmitri A. Sergatskov" <[email protected]> Wed, 11 Feb 2026 22:31:40 -0500 (EST)
Newsgroups	gmane.comp.gnu.octave.bugs
Message-ID	<[email protected]>
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Follow-up Comment #6, bug #67989 (group octave):

Matlab is probably using Intel IPP library for that. Hard to compete with
those but we can try. With attached
(file __spatial_filtering__das_100.cc) replacement for
"__spatial_filtering__.cc" in the package I see:


octave:1> Img = imread("3.jpg");
octave:2> whos Img
Variables visible from the current scope:

variables in scope: top scope

  Attr   Name        Size                     Bytes  Class
  ====   ====        ====                     =====  ===== 
         Img      3072x4096x3              37748736  uint8

Total is 37748736 elements using 37748736 bytes

octave:3> pkg load image
octave:4> tic; d=ordfilt2((Img(:,:,1)),1,true(7,7)); toc 
Elapsed time is 0.027658 seconds.
octave:5> tic; d=ordfilt2((Img(:,:,1)),1,true(7,7)); toc 
Elapsed time is 0.021487 seconds.
octave:6> tic; d=ordfilt2((Img(:,:,1)),25,true(7,7)); toc 
Elapsed time is 0.122359 seconds.
octave:7> tic; d=ordfilt2(double(Img(:,:,1)),25,true(7,7)); toc 
Elapsed time is 0.150791 seconds.


Attached also is a recent hg snapshot of "image" package with replaced
__spatial_filtering__.cc 
(file image_das_20260211.tgz)
You should be able to install it as usual. 
It may be helpful if your CXXFLAGS are set to "-O3 -mtune=native" and also OMP
is enaled.

I tested with recent Octave-12 snapshot on Fedora 43 (x86-64; Ultra 9 285) and
on MacOS (M4). 

I think further improvements are possible with different filter algorithm
(e.g. "Huang sliding window"), but that is for somebody else.

Dmitri.
-- 


(file #58236, file #58237)

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Additional Item Attachment:

Name: __spatial_filtering__das_100.cc Size: 32KiB

<https://file.savannah.gnu.org/file/__spatial_filtering__das_100.cc?file_id=58236>

Name: image_das_20260211.tgz         Size: 462KiB
    <https://file.savannah.gnu.org/file/image_das_20260211.tgz?file_id=58237>


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