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Pixmap from QImage is broken

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littlecmspixmapimageimage display
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  • C Christian Ehrlicher
    10 Feb 2022, 17:59

    Put your qDebug() before the return in MainWindow::colorManage() will show you the warnings. Putting them after the return statement is somewhat useless.

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    ademmler
    wrote on 10 Feb 2022, 20:07 last edited by ademmler 2 Oct 2022, 20:13
    #4

    @Christian-Ehrlicher thx for your hint - I have overseen this :-)

    I have done this and here is the output:
    21:12:06: Starting /Users/ademmler/QtTryouts/GraphicsViewer/build/debug/GraphicsViewer.app/Contents/MacOS/GraphicsViewer ...

    Hence no error at all. As i wrote to SGaist the final image (saved to hardest for debugging) is fine. It really seems to be an issue with
    QPixmap pixmap = QPixmap::fromImage(toDisplay);

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    • S SGaist
      10 Feb 2022, 19:54

      Hi,

      Just in case, there are several return statement in the LittleCMS sample code, you should check all of them.

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      ademmler
      wrote on 10 Feb 2022, 20:10 last edited by
      #5

      @SGaist the result from littlecms is perfectly fine. As you can see from the image saved next to the executable.
      Especially when I load this into my graphics scene the result is ok:
      QPixmap pixmap;
      pixmap.load("toDisplay.jpg");

      but if I do this:
      QPixmap pixmap = QPixmap::fromImage(toDisplay);

      the image is "distorted/broken) somehow ...

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        mchinand
        wrote on 10 Feb 2022, 21:42 last edited by mchinand 2 Oct 2022, 22:15
        #6

        What is the format of the QImage (toDisplay->format())? Can you show exactly what you mean by 'the image is distorted/broken'.

        A 1 Reply Last reply 11 Feb 2022, 09:05
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          Christian Ehrlicher
          Lifetime Qt Champion
          wrote on 11 Feb 2022, 05:56 last edited by Christian Ehrlicher 2 Nov 2022, 06:09
          #7

          When I run your program, cmsCreateMultiprofileTransform() returns a nullptr and (since I corrected the qDebug - output) get the warning 'Couldn't create color transform !' and then a QMessageBox that the image conversion failed.

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          A 2 Replies Last reply 11 Feb 2022, 09:04
          1
          • C Christian Ehrlicher
            11 Feb 2022, 05:56

            When I run your program, cmsCreateMultiprofileTransform() returns a nullptr and (since I corrected the qDebug - output) get the warning 'Couldn't create color transform !' and then a QMessageBox that the image conversion failed.

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            ademmler
            wrote on 11 Feb 2022, 09:04 last edited by ademmler 2 Nov 2022, 09:10
            #8

            @Christian-Ehrlicher thx for your response.

            I have corrected my code - as you mentioned - but I do not get this warning.
            I get an broken image displayed. Here is a screenshot:
            http://code.ademmler.com/gvimg01.png

            And here is what qt saved to hard disk:
            http://code.ademmler.com/toDisplay.jpg

            Note:
            I have also contacted the author of little CMS - he wrote this sample code.
            I got stuck between opinions and thoughts

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            • M mchinand
              10 Feb 2022, 21:42

              What is the format of the QImage (toDisplay->format())? Can you show exactly what you mean by 'the image is distorted/broken'.

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              ademmler
              wrote on 11 Feb 2022, 09:05 last edited by ademmler 2 Nov 2022, 09:10
              #9

              @mchinand https://littlecms.com/blog/2020/12/09/using-lcms2-on-qt/

              little cmd uses a different format than qt - that is what the author wrote about it.
              I just try to create a working minimal sample ...

              Here is what the resulting image looks like:
              http://code.ademmler.com/gvimg01.png

              And here is what qt saved to hard disk:
              http://code.ademmler.com/toDisplay.jpg

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                ademmler
                wrote on 11 Feb 2022, 09:26 last edited by
                #10

                And here is the pixmap saved to hard disk:
                http://code.ademmler.com/qtPixmap.jpg

                Which is also ok - hence I do not understand what's going wrong with displaying this ...

                J 1 Reply Last reply 11 Feb 2022, 09:36
                0
                • A ademmler
                  11 Feb 2022, 09:26

                  And here is the pixmap saved to hard disk:
                  http://code.ademmler.com/qtPixmap.jpg

                  Which is also ok - hence I do not understand what's going wrong with displaying this ...

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                  J.Hilk
                  Moderators
                  wrote on 11 Feb 2022, 09:36 last edited by
                  #11

                  @ademmler have you checked the format of toDisplay ? Image::save does take guesses if the format is missing or wrong.
                  Also you should check the return type of save, in case saving fails and you actually see the file of a previous attempt


                  Be aware of the Qt Code of Conduct, when posting : https://forum.qt.io/topic/113070/qt-code-of-conduct


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                  Q: What does it do?
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                  A 2 Replies Last reply 11 Feb 2022, 09:39
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                  • C Christian Ehrlicher
                    11 Feb 2022, 05:56

                    When I run your program, cmsCreateMultiprofileTransform() returns a nullptr and (since I corrected the qDebug - output) get the warning 'Couldn't create color transform !' and then a QMessageBox that the image conversion failed.

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                    ademmler
                    wrote on 11 Feb 2022, 09:38 last edited by
                    #12

                    @Christian-Ehrlicher said in Pixmap from QImage is broken:

                    When I run your program, cmsCreateMultiprofileTransform() returns a nullptr and (since I corrected the qDebug - output) get the warning 'Couldn't create color transform !' and then a QMessageBox that the image conversion failed.

                    Are you working on MacOS or Windows?
                    Have you littlecms installed ? Or checked if you can use the libs I provided?

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                    • J J.Hilk
                      11 Feb 2022, 09:36

                      @ademmler have you checked the format of toDisplay ? Image::save does take guesses if the format is missing or wrong.
                      Also you should check the return type of save, in case saving fails and you actually see the file of a previous attempt

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                      ademmler
                      wrote on 11 Feb 2022, 09:39 last edited by
                      #13

                      @J-Hilk Gold idea - I will check.

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                      • J J.Hilk
                        11 Feb 2022, 09:36

                        @ademmler have you checked the format of toDisplay ? Image::save does take guesses if the format is missing or wrong.
                        Also you should check the return type of save, in case saving fails and you actually see the file of a previous attempt

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                        ademmler
                        wrote on 11 Feb 2022, 09:49 last edited by
                        #14

                        @J-Hilk

                        Here is what I see in the debugger. Looks like all "images" have content.
                        http://code.ademmler.com/debugger.png

                        Pls - where can I see the "return value type" in this window?

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                          ademmler
                          wrote on 11 Feb 2022, 11:30 last edited by ademmler 2 Nov 2022, 11:31
                          #15

                          Here is the reason and solution. Thanks to Marti Maria - the author of littlecms -
                          to sort this out ...

                          This program does not work because you missed the part on
                          https://littlecms.com/blog/2020/12/09/using-lcms2-on-qt/ that says:

                          Alpha channels are supported as long as the image is not using premultiplied alpha. To get alpha channel make sure to include cmsFLAGS_COPY_ALPHA in the flags field. This is explained in LittleCMS documentation.

                          So, try: toDisplay = colorManage(sourceImage, profiles, INTENT_PERCEPTUAL, cmsFLAGS_COPY_ALPHA);*

                          This fixed the issue for me.

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                          11 Feb 2022, 09:39

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