Grayscale image Color Conversion

[alainstgt]

I am not sure wether I understood your request the right way. I am assuming that you want to convert all black pixels to full transparency and all other pixels to red.
The first point is your loop which is not correctly initialized. Even if you initialized x and y outside the loop, latest when scanning the second column your variable y will be out of range, so the inner loop will be performed only once.

Your loop should look like

for ( x = 0; x < secondaryImage.width(); ++x )
{
    for ( y = 0; y < secondaryImage.height(); ++y )
    {
         if ( secondaryImage.pixel( x, y ) == Qt::black )
             secondaryImage.setPixel( x, y,  QColor( 0, 0, 0, 0 ));   // fully transparency, color doesn´t matter
         else
             secondaryImage.setPixel( x, y, Qt::red );
    }
}

for ( x = 0; x < secondaryImage.width(); ++x )
{
    for ( y = 0; y < secondaryImage.height(); ++y )
    {
         if ( secondaryImage.pixel( x, y ) == Qt::black )
             secondaryImage.setPixel( x, y,  QColor( 0, 0, 0, 0 ));   // fully transparency, color doesn´t matter
         else
             secondaryImage.setPixel( x, y, Qt::red );
    }
}

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I did not test the code!

[2lights]

Loop: Thanks that sorted the "out of scope problem"

Though the image editing.... Nothing happens
Any Ideas is there another way of changing colour

For the time being i'm inverting pixels of whole image until I get a more graphic appealing solution

[alainstgt]

can you show the whole code you are using?

[2lights]

The Inversion Color of image
Loading Image function

QFileDialog dialog2(this, "Upload secondary");
    dialog2.setNameFilter(tr("Images (*.png *.xpm *.jpg *.bmp)"));
    dialog2.setViewMode(QFileDialog::Detail);
 
    if(dialog2.exec())
    {
        imageFileName2 = dialog2.selectedFiles().first();
    }
 
    primaryImage.load(imageFileName1);
    primaryImage.invertPixels();

QFileDialog dialog2(this, "Upload secondary");
    dialog2.setNameFilter(tr("Images (*.png *.xpm *.jpg *.bmp)"));
    dialog2.setViewMode(QFileDialog::Detail);

    if(dialog2.exec())
    {
        imageFileName2 = dialog2.selectedFiles().first();
    }

    primaryImage.load(imageFileName1);
    primaryImage.invertPixels();

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In paint Function:

painter.drawImage(QPoint(0, 0), secondaryImage);

painter.drawImage(QPoint(0, 0), secondaryImage);

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The Changing color version of program ie(commented out until solution found)

for (int x = 0; x < secondaryImage.width(); ++x)
    {
        for (int y = 0; y < secondaryImage.height(); ++y)
        {
             if ( secondaryImage.pixel(x, y) == Qt::black)
                 secondaryImage.setPixel(x, y, QColor( 0, 0, 0, 0 )); //This line gives compiler error :confused:
             else
                  secondaryImage.setPixel( x, y, Qt::red ); //Nothing happens here :(
    }
    }

for (int x = 0; x < secondaryImage.width(); ++x)
    {
        for (int y = 0; y < secondaryImage.height(); ++y)
        {
             if ( secondaryImage.pixel(x, y) == Qt::black)
                 secondaryImage.setPixel(x, y, QColor( 0, 0, 0, 0 )); //This line gives compiler error :confused:
             else
                  secondaryImage.setPixel( x, y, Qt::red ); //Nothing happens here :(
    }
    }

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Ideas most welcome