you can enable anti-aliasing by turning it on QDeclarativeView,
QDeclarativeView view;
view.setRenderHints(QPainter::Antialiasing | QPainter::SmoothPixmapTransform);
view.setResizeMode( QDeclarativeView::SizeRootObjectToView );
view.setSource(QUrl("qrc:/main.qml"));
view.show();
Be that as it may, the image looks good when stretched, I suggest you use an svg image instead of a png image.
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