HighDPI support for QImage

QImage should have a convenience method which returns the device independent size, which is calculated by using the setDevicePixelRatio

QImage image(…, QSize(256, 256));
image.setDevicePixelRatio(2);
image.height(); //                  => 256
image.deviceIndependentHeight();// => 128 (new API)

QImage also should have a constructor in which it is possible to set the device pixel ratio:

QImage(int widthDip, int heightDip, qreal dpr, Format format)