[Octave-bug-tracker] [bug #35846] Imwrite inaccurate

[anonymous]

URL:
  <http://savannah.gnu.org/bugs/?35846>

                 Summary: Imwrite inaccurate
                 Project: GNU Octave
            Submitted by: None
            Submitted on: Чтв 15 Мар 2012 08:12:22
                Category: Interpreter
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Inaccurate Result
                  Status: None
             Assigned to: None
         Originator Name: Vladimir Vasiliev
        Originator Email: address@hidden
             Open/Closed: Open
         Discussion Lock: Any
                 Release: 3.6.1
        Operating System: GNU/Linux

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Details:

Seems to be the same as bugs #29359 and #33317, but they point to MS Windows
as os and old octave. Grayscale images are not saved well in such formats, as
pgm, png or tiff.

I think the test in bug #33317 isn't very good because of one-dimension of img
(it works well for me).

This code does not work in octave 3.6.1, GNU/Linux (graphicsmagick 1.3.14).
Also tested in old octave 3.2.4 under windows - same result.


img = uint8(50*eye(10));
imwrite(img,'test.pgm');
img2 = imread('test.pgm');
sum(sum(img-img2))
ans = 10


After saving I viewed image 'test.pgm' in xnview, using "Display color
information" option and noticed, that pixels on diagonal have intencity 49,
not 50.

I have also tried testing graphicsmagick with various grayscale images and did
not notice any inaccuracy (i used 'gm convert input.pgm input.png' and 'gm
compare -metric mse input.pgm input.png').




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