Monochrome QImage transformation - void area looks black

[KBA]

Hi there,

I want to rotate a monochrome image of Type QImage using QImage::transformed method.
After applying rotation, the background color of the void area is always black.

The Image before Rotation lookes like this:
12674

After rotation, of 45° clockwise, it lookes like this:
12675

But it should look like this:
12676

My question is how can I make sure that the void area color is white?
Thanks in advance!

Here is my sample code:


#include <QImage>
#include <QPainter>

int main()
{
// size of square Image
const int nSize = 100;

// create monochrome Image
QImage img = QImage(nSize, nSize, QImage::QImage::Format_Mono);

QPainter pnt;
pnt.begin(&img);

// fill background with white
pnt.fillRect(0, 0, nSize, nSize, Qt::color0);
pnt.setPen(QPen(Qt::color1));
// draw a rectangle
pnt.drawRect(0, 0, nSize-1, nSize-1);
pnt.end();

img.save("original.bmp");

// rotate image
QMatrix m;
m.rotate(45);
img = img.transformed(m);
img.save("rotated.bmp");

return 0;
}

[high_flyer]

Please stop posting duplicate posts/threads.

To your question:
This is just a guess:
Since this is a monochrome image, when you transform it, the areas out side the rect are not being painted on - which means they stay 0, which means black.
Try using QImage::transformed().