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:
original.gif

After rotation, of 45° clockwise, it lookes like this:
rotated.gif

But it should look like this:
rotated_correct.png

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;
}

#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;
}

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