I spend some time solving this one. So here i leave it for future reference:
It seems that Qt adds 4 bytes per line if image width is not multiple of four.
// copy from oF to Qt
qImage = QImage(w, h, QImage::Format_RGB888);
for (int y = 0; y < qImage.height(); y++)
{
memcpy(
&qImage.bits() [y*qImage.bytesPerLine()],
&ofImage.getPixels().getData() [y*ofImage.getPixels().getBytesStride()],
qImage.bytesPerLine()
);
}
If anyone has a better fix please let me know.