[Octave-bug-tracker] [bug #47746] imwrite writes incorrect TIFF pixel values from uint8 array on i686-linux-gnu

[Mike Miller]

URL:
  <http://savannah.gnu.org/bugs/?47746>

                 Summary: imwrite writes incorrect TIFF pixel values from
uint8 array on i686-linux-gnu
                 Project: GNU Octave
            Submitted by: mtmiller
            Submitted on: Wed 20 Apr 2016 07:30:42 PM PDT
                Category: Octave Function
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Incorrect Result
                  Status: None
             Assigned to: None
         Originator Name: 
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any
                 Release: dev
        Operating System: GNU/Linux

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Details:

On Debian i686, the imwrite function writes an incorrect TIFF file from an
array of uint8 pixel values.

I think this is the same as previously reported bugs, for example bug #33317,
but it has not yet been investigated.

I have two builds on up to date Debian systems, the only difference being i686
vs x86_64, and the results of imwrite show an off-by-one error in the TIFF
file produced by imwrite. This shows up as unit test failures in imread.m and
imwrite.m. See for example
https://buildd.debian.org/status/fetch.php?pkg=octave&arch=i386&ver=4.0.1-1&stamp=1458697721

This minimal example shows the error on Debian i686:


x = uint8 (0:255);
imwrite (x, "test.tif");
y = imread ("test.tif");
assert (x, y);                     ## FAILURE
assert (y, [x(1), x(2:end) - 1]);  ## SUCCESS


Using hexdump on the file shows that the error is in the written TIFF file,
not in the reading back of the file. Also reading the file with imread in a
64-bit Octave shows the incorrect vector.




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