Change a black pixel to a blue pixel in an image

Hi guys,

I've wrote this piece of code that should make the black part of an image into a blue part. But the code doesn't change the black into the blue it never comes in the if test I think.

Could someone help me?

Code:

---

QImage background;
    QImage world(1500, 768, QImage::Format_RGB32);
    QSize sizeImage;
    int height, width;
    background.load("Background.png");
    world.fill(1);
 
    QPainter painter(&world);
    sizeImage = background.size();
    width = sizeImage.width();
    height = sizeImage.height();
 
    const QRgb black = 0;
    const QRgb blue = 255;
    for(int y = 0; y < height; y++) {
        for(int x = 0; x < width; x++) {
            if (background.pixel(x,y) == black) {
                background.setPixel(x,y,blue);
            }
        }
    }
 
    painter.drawImage(0,0,background);
 
    //adding new image to the graphicsScene
    QGraphicsPixmapItem item( QPixmap::fromImage(background));
    QGraphicsScene* scene = new QGraphicsScene;
    scene->addItem(&item);
 
    QGraphicsView view(scene);
    view.show();

---

Kind regards,

have you define black and blue correctly? seems to be the problem if you are saying that it never enters the IF....try using Qt::black

While the use of integers to initialise a QRgb looks odd it is correct language-wise. QRgb is a typedef equivalent to unsigned int.

It is not working as expected because setting the value this way has set the alpha channel to 0: the colour exists but is 100% transparent and will not match an opaque black/blue pixel. Try setting the colours using the qRgb() macro or, as KillGabio suggests, using symbolic names.