@pgpetrov Indeed, I can see the difference. I think to some extent this is unavoidable, because we're scaling the image whereas the non-zooming image is being displayed 1:1. Whenever you scale an image, you're going to lose a little quality.
If you wanted to make sure it was exact, I imagine you probably could do the math to make sure it's positioned at exactly the same scale.
You might want to try fiddling with the minPixelRatio option; I'm not sure it will have any effect in this case though.
...and of course for HDPI screens, you might want to get the latest from master.