[Octave-bug-tracker] [bug #65347] imread and imshow/imagesc combination does not support image file controlled by transparency.

[Liang Tang]

URL:
  <https://savannah.gnu.org/bugs/?65347>

                 Summary: imread and imshow/imagesc combination does not
support image file controlled by transparency. 
                   Group: GNU Octave
               Submitter: lt1234
               Submitted: Thu 22 Feb 2024 02:04:47 PM UTC
                Category: Octave Function
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Incorrect Result
                  Status: None
             Assigned to: None
         Originator Name: lt1234
        Originator Email: 
             Open/Closed: Open
                 Release: 8.2.0
         Discussion Lock: Any
        Operating System: Microsoft Windows
           Fixed Release: None
         Planned Release: None


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Follow-up Comments:


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Date: Thu 22 Feb 2024 02:04:47 PM UTC By: Liang Tang <lt1234>
Hi, 

I understand transparency/alpha is not implemented in Octave.  This report is
to point to a condition that the result is completely incorrect due to the
current implementation.  Thanks.  

imread does not alter the values of the [n,n,3] based on the
transparency/alpha.  imshow does not take transparency as an input.  
Therefore transparency of an image is completely lost once it is read in.  For
a sample file in qt folder, the display is incorrect.  

im from doc_search is a [50,50,3], with a constant value for each of rgb.
Transparency determines the display.  

[im, cmap,
trans]=imread('C:\Octave\Octave-8.2.0\mingw64\qt5\doc\global\template\style\doc_search.png');
%
figure; subplot(1,2,1); imshow(im);  subplot(1,2,2); imshow(trans);
saveas(gcf, 'doc_search.ofig');







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