you again brought up a good point!
The PolygonItem does not suppot content-scaling like the MultiResolutionImage does. So you would need to implent this “content-scaling” on your own.This is a suggestion how to do that:
Set the texture property to your hd2 image, and then set the scale property of your PolygonItem to 0.25. If you use the hd image, set the scale to 0.5.
Ideally you can then find out based on the xScaleForScene which image and scale factor you should take. Have a look at the implementation of the and MultiResolutionImage component and ContentScaleFileChooser (this one is not in the doc but in the engine sources).
That way your images should look sharp on any resolution.