bugGNU Octave - Bugs: bug #65347, imread and imshow/imagesc...


bug #65347: imread and imshow/imagesc combination does not support image file controlled by transparency.

Submitter:  Liang Tang <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 Open/Closed:  * Open
Release:  * 8.2.0 Operating System:  * Microsoft Windows
Fixed Release:  None Planned Release:  None
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Thu 22 Feb 2024 02:04:47 PM UTC, original submission:  


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');

Liang Tang <lt1234>


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Attach Files:

Attached Files
file #55735:  qt_png_files.zip added by lt1234 (9KiB - application/x-zip-compressed)


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    Date Changed by Updated Field Previous Value => Replaced by
    2024-02-22 lt1234 Attached File- Added qt_png_files.zip, #55735

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