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QImageWriter and EXIF

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  • S Offline
    S Offline
    samdol
    wrote on last edited by
    #1

    Hi,

    I used QImageReader to read image from file and QImageWriter to save imge to file. The issue is that when I save image to file using QImageWriter, it looses EXI
    F information of image. Is there any way in Qt I don't loose EXIF information when I save image to file?

    1 Reply Last reply
    1
    • SGaistS Offline
      SGaistS Offline
      SGaist
      Lifetime Qt Champion
      wrote on last edited by
      #2

      Hi,

      There was at some point the QExifImageHeader class that might be of interest.

      Interested in AI ? www.idiap.ch
      Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

      S 1 Reply Last reply
      1
      • SGaistS SGaist

        Hi,

        There was at some point the QExifImageHeader class that might be of interest.

        S Offline
        S Offline
        samdol
        wrote on last edited by
        #3

        @SGaist
        Thanks, I have checked it, but there seems some bug for Gps info. For example, when I run following code, I think exif values should not change.

            QExifImageHeader header;
            header.loadFromJpeg("C:/myfile.jpg");
            QExifValue value_GpsLatitude = header.value(QExifImageHeader::GpsLatitude);
            QExifValue value_ImageWidth = header.value(QExifImageHeader::ImageWidth);
            QExifValue value_Make = header.value(QExifImageHeader::Make);
            QExifValue value_Model = header.value(QExifImageHeader::Model);
            header.setValue(QExifImageHeader::GpsLatitude, value_GpsLatitude);
            header.setValue(QExifImageHeader::ImageWidth, value_ImageWidth);
            header.setValue(QExifImageHeader::Make, value_Make);
            header.setValue(QExifImageHeader::Model, value_Model);
            header.saveToJpeg("C:/myfile.jpg");
        

        But when I run it, GpsLatitude value has changed. Do you think it is a bug?
        And how can I read GpsLatitude?
        When I run the following,

           qDebug()<<"laa: "<< QString::number(value_GpsLatitude.toRational().first)+"/"+QString::number(value_GpsLatitude.toRational().second);
        

        I always get "0/0" which is not correct.

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        • Pablo J. RoginaP Offline
          Pablo J. RoginaP Offline
          Pablo J. Rogina
          wrote on last edited by
          #4

          @samdol what about this EXIF helper code?

          Upvote the answer(s) that helped you solve the issue
          Use "Topic Tools" button to mark your post as Solved
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          Don't ask support requests via chat/PM. Please use the forum so others can benefit from the solution in the future

          S 1 Reply Last reply
          0
          • SGaistS Offline
            SGaistS Offline
            SGaist
            Lifetime Qt Champion
            wrote on last edited by
            #5

            Might be, I can't confirm, I don't have images containing such data to test.

            Interested in AI ? www.idiap.ch
            Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

            S 1 Reply Last reply
            0
            • Pablo J. RoginaP Pablo J. Rogina

              @samdol what about this EXIF helper code?

              S Offline
              S Offline
              samdol
              wrote on last edited by samdol
              #6

              @Pablo-J.-Rogina
              Thank you, I used it before. but it only reads exif information. Because I want to preserve EXIF after save image, I need a method to read/write exif.

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              • SGaistS SGaist

                Might be, I can't confirm, I don't have images containing such data to test.

                S Offline
                S Offline
                samdol
                wrote on last edited by samdol
                #7

                @SGaist
                I found that Reading Gps information should be like this,

                  qDebug()<<"laa: "<< QString::number(value_GpsLatitude.toRationalVector().at(0).first)+"/"+QString::number(value_GpsLatitude.toRationalVector().at(0).second);
                  qDebug()<<"laa: "<< QString::number(value_GpsLatitude.toRationalVector().at(1).first)+"/"+QString::number(value_GpsLatitude.toRationalVector().at(1).second);
                  qDebug()<<"laa: "<< QString::number(value_GpsLatitude.toRationalVector().at(2).first)+"/"+QString::number(value_GpsLatitude.toRationalVector().at(2).second);
                

                But I still don't understand why it changes Gps value after

                header.saveToJpeg("C:/myfile.jpg");  
                

                It changes even without

                header.setValue(QExifImageHeader::GpsLatitude, value_GpsLatitude);
                

                It seems a bug.
                You may get test jpg file with gps_tag from here

                L 1 Reply Last reply
                0
                • S samdol

                  @SGaist
                  I found that Reading Gps information should be like this,

                    qDebug()<<"laa: "<< QString::number(value_GpsLatitude.toRationalVector().at(0).first)+"/"+QString::number(value_GpsLatitude.toRationalVector().at(0).second);
                    qDebug()<<"laa: "<< QString::number(value_GpsLatitude.toRationalVector().at(1).first)+"/"+QString::number(value_GpsLatitude.toRationalVector().at(1).second);
                    qDebug()<<"laa: "<< QString::number(value_GpsLatitude.toRationalVector().at(2).first)+"/"+QString::number(value_GpsLatitude.toRationalVector().at(2).second);
                  

                  But I still don't understand why it changes Gps value after

                  header.saveToJpeg("C:/myfile.jpg");  
                  

                  It changes even without

                  header.setValue(QExifImageHeader::GpsLatitude, value_GpsLatitude);
                  

                  It seems a bug.
                  You may get test jpg file with gps_tag from here

                  L Offline
                  L Offline
                  Luisa
                  wrote on last edited by
                  #8

                  @samdol I have the same problem.

                  If I load metadata and then I save without changing anything I read incorrect value.
                  Have you find a solution?

                  QExifImageHeader * source = new QExifImageHeader();
                  QExifValue *vale;
                  source->loadFromJpeg(filedest);
                  source->saveToJpeg(filedest);
                  QExifImageHeader * dest = new QExifImageHeader();
                  dest->loadFromJpeg(filedest);
                  

                  Thanke you for your help

                  Luisa

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                  0
                  • SGaistS Offline
                    SGaistS Offline
                    SGaist
                    Lifetime Qt Champion
                    wrote on last edited by
                    #9

                    IIRC, when I took a look at it, there was an issue with handling some of the tags. I can't remember exactly what it was.

                    Interested in AI ? www.idiap.ch
                    Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

                    L 1 Reply Last reply
                    0
                    • SGaistS SGaist

                      IIRC, when I took a look at it, there was an issue with handling some of the tags. I can't remember exactly what it was.

                      L Offline
                      L Offline
                      Luisa
                      wrote on last edited by
                      #10

                      @SGaist Do you know a library that I could use to read / write exif files? I need to cross compile it for a system embedded. I tried exiv2 with poor results

                      jsulmJ 1 Reply Last reply
                      0
                      • L Luisa

                        @SGaist Do you know a library that I could use to read / write exif files? I need to cross compile it for a system embedded. I tried exiv2 with poor results

                        jsulmJ Offline
                        jsulmJ Offline
                        jsulm
                        Lifetime Qt Champion
                        wrote on last edited by
                        #11

                        @Luisa https://github.com/libexif/libexif

                        https://forum.qt.io/topic/113070/qt-code-of-conduct

                        L 1 Reply Last reply
                        2
                        • jsulmJ jsulm

                          @Luisa https://github.com/libexif/libexif

                          L Offline
                          L Offline
                          Luisa
                          wrote on last edited by
                          #12

                          @jsulm I try to use this library but I have some problem with GPSAltitude and so on...

                          Have you some example to write GPS param into file jpg?
                          and Usercomment field?

                          Thank you so much

                          jsulmJ Pablo J. RoginaP 2 Replies Last reply
                          0
                          • L Luisa

                            @jsulm I try to use this library but I have some problem with GPSAltitude and so on...

                            Have you some example to write GPS param into file jpg?
                            and Usercomment field?

                            Thank you so much

                            jsulmJ Offline
                            jsulmJ Offline
                            jsulm
                            Lifetime Qt Champion
                            wrote on last edited by
                            #13

                            @Luisa Sorry, I don't have any examples

                            https://forum.qt.io/topic/113070/qt-code-of-conduct

                            L 1 Reply Last reply
                            0
                            • jsulmJ jsulm

                              @Luisa Sorry, I don't have any examples

                              L Offline
                              L Offline
                              Luisa
                              wrote on last edited by
                              #14

                              @jsulm :-(

                              mrjjM 1 Reply Last reply
                              0
                              • L Luisa

                                @jsulm :-(

                                mrjjM Offline
                                mrjjM Offline
                                mrjj
                                Lifetime Qt Champion
                                wrote on last edited by
                                #15

                                @Luisa
                                Hi
                                I was wondering if the sample
                                https://github.com/libexif/libexif/blob/master/contrib/examples/write-exif.c
                                combined with the info from
                                https://libexif.github.io/internals/exif-entry_8c-source.html

                                EXIF_TAG_USER_COMMENT
                                EXIF_TAG_GPS_VERSION_ID
                                EXIF_TAG_GPS_ALTITUDE_REF:

                                might work ?

                                1 Reply Last reply
                                2
                                • L Luisa

                                  @jsulm I try to use this library but I have some problem with GPSAltitude and so on...

                                  Have you some example to write GPS param into file jpg?
                                  and Usercomment field?

                                  Thank you so much

                                  Pablo J. RoginaP Offline
                                  Pablo J. RoginaP Offline
                                  Pablo J. Rogina
                                  wrote on last edited by
                                  #16

                                  @Luisa said in QImageWriter and EXIF:

                                  I try to use this library but I have some problem with GPSAltitude and so on...

                                  Could you please show the issue?

                                  Upvote the answer(s) that helped you solve the issue
                                  Use "Topic Tools" button to mark your post as Solved
                                  Add screenshots via postimage.org
                                  Don't ask support requests via chat/PM. Please use the forum so others can benefit from the solution in the future

                                  1 Reply Last reply
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