[bug #68049] imread() is slow

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URL:
  <https://savannah.gnu.org/bugs/?68049>

                 Summary: imread() is slow
                   Group: GNU Octave
               Submitter: dasergatskov
               Submitted: Sat 14 Feb 2026 09:37:14 PM UTC
                Category: Octave Function
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Performance
                  Status: None
             Assigned to: None
         Originator Name:
        Originator Email:
             Open/Closed: Open
         Discussion Lock: Unlocked
                 Release: dev
        Operating System: Any
           Fixed Release: None
         Planned Release: None


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Follow-up Comments:


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Date: Sat 14 Feb 2026 09:37:14 PM UTC By: Dmitri A. Sergatskov <dasergatskov>
While working on some other image-reletad bugs i noticed that `imread()` (but
in fact `__magic_read__.cc`) is way too slow.
E.g. using attachde (file 3.jpg)

octave:1> tic; [im, map, alpha] = imread ("3.jpg"); toc
Elapsed time is 0.544399 seconds.
## Reading the same file off the disk is fast
octave:2> tic; s=fileread("3.jpg"); toc
Elapsed time is 0.0105002 seconds.

Also processing this file by GM is also fast:

$ gm identify -verbose 3.jpg 
Image: 3.jpg
  Format: JPEG (Joint Photographic Experts Group JFIF format)
  Geometry: 4096x3072
...
    Tainted: False
  User Time: 0.040u
  Elapsed Time: 0m:0.046155s
  Pixels Per Second: 260.0Mi

So I think "imread" should be at least 5x faster.

Looking at __magick_read__.cc sourse I see that it mixes up C-style vs
Fortran-style (Octave) arrays, but that cannot account for all the
slowness...

Dmitri.
-- 







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