[Octave-bug-tracker] [bug #37681] imread function when used with indexed images returns a matrix with 0 values, that are not accepted by other image funcs

[anonymous]

URL:
  <http://savannah.gnu.org/bugs/?37681>

                 Summary: imread function when used with indexed images
returns a matrix with 0 values, that are not accepted by other image funcs
                 Project: GNU Octave
            Submitted by: None
            Submitted on: Tue 06 Nov 2012 05:12:15 PM UTC
                Category: None
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: None
                  Status: None
             Assigned to: None
         Originator Name: Lucas Sa
        Originator Email: address@hidden
             Open/Closed: Open
         Discussion Lock: Any
                 Release: 3.6.2
        Operating System: GNU/Linux

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Details:

Using <b>[X, map] = imread</b> will give me a matrix X with values from 0 to
n-1, while all other image functions expect index mapping from 1 to n, such as
imshow, ind2rgb, ind2gray. 

This fact makes the execution of a simple <b>imshow('some_file.gif')</b> to
show something different from the original image. imshow(<b>X+1</b>, map)
would show it fine as well.

The function ind2rgb, for example, even has a validation for indices less than
1 in line 43 of ind2rgb.m:

  ## Check if X is an indexed image.
  if (ndims (x) != 2 || any (x(:) != fix (x(:))) || <b>min (x(:)) < 1</b>)
    error ("ind2rgb: X must be an indexed image");


To replicate the error, you can imread any indexed image (such as GIF) and try
to use the referred functions with the results.

Is it normal to receive 0 values in X matrix? I am using octave 3.6.2 and
graphicsmagick 1.3.16.




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