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Convert QImage into binary Matrix

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qimagematrixconvert
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  • VRoninV Offline
    VRoninV Offline
    VRonin
    wrote on last edited by VRonin
    #2
    char **matrix = new char* [image.width()];
    for(int i=0;i<image.width();++i)
    matrix[i] = new char [image.height()];
    for(int i=0;i<image.width();++i){
    for(int j=0;j<image.height();++j)
    matrix[i][j] = QColor(image.pixel(i,j)).black() > 127 ? 0:1;
    }
    

    Remember to delete the matrix to avoid memory leak or use something like QScopedArrayPointer

    "La mort n'est rien, mais vivre vaincu et sans gloire, c'est mourir tous les jours"
    ~Napoleon Bonaparte

    On a crusade to banish setIndexWidget() from the holy land of Qt

    AlvaroSA 1 Reply Last reply
    2
    • VRoninV VRonin
      char **matrix = new char* [image.width()];
      for(int i=0;i<image.width();++i)
      matrix[i] = new char [image.height()];
      for(int i=0;i<image.width();++i){
      for(int j=0;j<image.height();++j)
      matrix[i][j] = QColor(image.pixel(i,j)).black() > 127 ? 0:1;
      }
      

      Remember to delete the matrix to avoid memory leak or use something like QScopedArrayPointer

      AlvaroSA Offline
      AlvaroSA Offline
      AlvaroS
      wrote on last edited by
      #3

      @VRonin Thanks a lot for answering me my friend.

      Now I would like to write the image in a txt.
      i do this:

          QString outputFilename = QFileDialog::getSaveFileName(this, "Guardar TXT", "/home", "files TXT (*.txt)");
          QFile outputFile(outputFilename);
          outputFile.open(QIODevice::WriteOnly);
      
              if(!outputFile.isOpen()) //If the user have choosen a file then:
              {
                 //
              }
      
          /* Point a QTextStream object at the file */
          QTextStream outStream(&outputFile);
          outStream << &matrix;
      

      but it writes just the memory direction, not the matrix... coudl you help me?

      VRoninV 1 Reply Last reply
      0
      • AlvaroSA AlvaroS

        @VRonin Thanks a lot for answering me my friend.

        Now I would like to write the image in a txt.
        i do this:

            QString outputFilename = QFileDialog::getSaveFileName(this, "Guardar TXT", "/home", "files TXT (*.txt)");
            QFile outputFile(outputFilename);
            outputFile.open(QIODevice::WriteOnly);
        
                if(!outputFile.isOpen()) //If the user have choosen a file then:
                {
                   //
                }
        
            /* Point a QTextStream object at the file */
            QTextStream outStream(&outputFile);
            outStream << &matrix;
        

        but it writes just the memory direction, not the matrix... coudl you help me?

        VRoninV Offline
        VRoninV Offline
        VRonin
        wrote on last edited by VRonin
        #4

        @AlvaroS The answer requires you to specify the format of the file, I'll use a MS Excel compatible one:

        QTextStream outStream(&outputFile);
        for(int i=0;i<image.width();++i){
        for(int j=0;j<image.height();++j){
        if(j>0)
        outStream << '\t';
        outStream << matrix[i][j];
        }
        outStream << '\n';
        }
        
        

        Remember to delete the matrix!!!

        "La mort n'est rien, mais vivre vaincu et sans gloire, c'est mourir tous les jours"
        ~Napoleon Bonaparte

        On a crusade to banish setIndexWidget() from the holy land of Qt

        AlvaroSA 1 Reply Last reply
        0
        • VRoninV VRonin

          @AlvaroS The answer requires you to specify the format of the file, I'll use a MS Excel compatible one:

          QTextStream outStream(&outputFile);
          for(int i=0;i<image.width();++i){
          for(int j=0;j<image.height();++j){
          if(j>0)
          outStream << '\t';
          outStream << matrix[i][j];
          }
          outStream << '\n';
          }
          
          

          Remember to delete the matrix!!!

          AlvaroSA Offline
          AlvaroSA Offline
          AlvaroS
          wrote on last edited by
          #5

          @VRonin Thanks a lot again!!

          The formar that I need is binary format

          VRoninV jsulmJ 2 Replies Last reply
          0
          • AlvaroSA AlvaroS

            @VRonin Thanks a lot again!!

            The formar that I need is binary format

            VRoninV Offline
            VRoninV Offline
            VRonin
            wrote on last edited by
            #6

            @AlvaroS That is a bit generic... let's use an example:

            if the image is (b=black, w=white):
            bwb
            wwb

            what would you want to see in the file?

            "La mort n'est rien, mais vivre vaincu et sans gloire, c'est mourir tous les jours"
            ~Napoleon Bonaparte

            On a crusade to banish setIndexWidget() from the holy land of Qt

            1 Reply Last reply
            0
            • AlvaroSA AlvaroS

              @VRonin Thanks a lot again!!

              The formar that I need is binary format

              jsulmJ Offline
              jsulmJ Offline
              jsulm
              Lifetime Qt Champion
              wrote on last edited by
              #7

              @AlvaroS To add to @VRonin : you could use 1 bit for each pixel and store 8 pixels in one byte. And you need to store the dimensions of the image (for example how many pixel in each row), else you will not know how to read the image later (except all images have the same dimentions).

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

              AlvaroSA 1 Reply Last reply
              0
              • jsulmJ jsulm

                @AlvaroS To add to @VRonin : you could use 1 bit for each pixel and store 8 pixels in one byte. And you need to store the dimensions of the image (for example how many pixel in each row), else you will not know how to read the image later (except all images have the same dimentions).

                AlvaroSA Offline
                AlvaroSA Offline
                AlvaroS
                wrote on last edited by
                #8

                @jsulm yes, that is what I want.

                use 1 bit for each pixel and store 8 pixels in one byte...
                Can I do that just with a for?

                Thanks!

                1 Reply Last reply
                0
                • jsulmJ Offline
                  jsulmJ Offline
                  jsulm
                  Lifetime Qt Champion
                  wrote on last edited by
                  #9

                  Well, you can: you can treat matrix as an one-dimentional array.

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

                  1 Reply Last reply
                  0
                  • jsulmJ Offline
                    jsulmJ Offline
                    jsulm
                    Lifetime Qt Champion
                    wrote on last edited by jsulm
                    #10

                    Something like (didn't test):

                    for(int i=0;i<(image.width() * image.height()) / 8; ++i)
                        quint8 byte = 0;
                        for (j=0; j < 8; ++j) {
                            byte |= (matrix[i*8 + j] ? 1 : 0)<<(7-j);
                        }
                        // Write byte to file
                    // Don't forget to write (image.width() * image.height()) % 8 last pixels
                    

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

                    1 Reply Last reply
                    1
                    • VRoninV Offline
                      VRoninV Offline
                      VRonin
                      wrote on last edited by VRonin
                      #11

                      slightly more refined solution using the fact that QImage uses "a matrix" internally

                      QDataStream outStream(&outputFile);
                      outStream << image.height()<< image.width(); /* You need this to recover the image size, if not needed remove*/ 
                      QImage testImage= image.convertToFormat(QImage::Format_Mono,Qt::MonoOnly); /* 1 bit= 1 pixel*/
                      testImage.invertPixels(); /* black is 1 and white is 0 normally, you need the opposite so invert*/
                      const int bytesInWidth  =
                          testImage.width()/8
                          + (testImage.width()%8>0 ? 1:0);
                      /*This is image.width()/8  rounded up */
                      for(int i=0;i<testImage.height();++i)
                                  outStream.writeRawData((const char*)(testImage.constScanLine(i)),bytesInWidth);
                      
                      

                      "La mort n'est rien, mais vivre vaincu et sans gloire, c'est mourir tous les jours"
                      ~Napoleon Bonaparte

                      On a crusade to banish setIndexWidget() from the holy land of Qt

                      1 Reply Last reply
                      1

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