Problem with pixelIndex in QImage

[danilodsp]

I do not understand this problem.
I normally use a QImage, but now this happening a problem that I can not see.

In my .h:

QImage *mascara; // Máscara para filtro

QImage *mascara; // Máscara para filtro

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In my .cpp:

mascara = new QImage(2,2,QImage::Format_Indexed8);
 
    mascara->setPixel(0,0,5);
    mascara->setPixel(0,1,5);
    mascara->setPixel(1,0,5);
    mascara->setPixel(1,1,5);
    QString test;
    test.setNum(mascara->pixelIndex(0,0));
    ui->console->appendPlainText(test);

mascara = new QImage(2,2,QImage::Format_Indexed8);

    mascara->setPixel(0,0,5);
    mascara->setPixel(0,1,5);
    mascara->setPixel(1,0,5);
    mascara->setPixel(1,1,5);
    QString test;
    test.setNum(mascara->pixelIndex(0,0));
    ui->console->appendPlainText(test);

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I do not see the pixel that I placed. In test no have the value 5.

[stampede]

I guess its because you forgot to set a color table. In the used image format, pixel value is an index in color table, which you have to set before specifying pixel values.
Something like this will work:

QImage img(2,2,QImage::Format_Indexed8);
    img.setColor(0,5);
    img.setColor(1,3);
    img.setPixel(0,0,0);
    img.setPixel(0,1,1);
    qDebug() << img.pixel(0,0); // prints 5
    qDebug() << img.pixel(0,1); // prints 3

QImage img(2,2,QImage::Format_Indexed8);
    img.setColor(0,5);
    img.setColor(1,3);
    img.setPixel(0,0,0);
    img.setPixel(0,1,1);
    qDebug() << img.pixel(0,0); // prints 5
    qDebug() << img.pixel(0,1); // prints 3

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Its explained in docs with more details : link

[danilodsp]

Thank you very much!