iOS images in Xamarin Forms

So I have an image with 3 different resolutions:

camera.png
camera@2x.png
camera@3x.png

All with a build action of "Bundle Resource".

If I do ImageSource.FromFile("camera.png"); it always retrieves the low quality camera. I thought that depending on what device you are using a different resolution image would be used?

Do these first need to be part of an ImageAsset?

Images.xcassets doesn't show up under my resources directory as per - http://developer.xamarin.com/guides/ios/application_fundamentals/working_with_images/displaying-an-image/#asset-catalogs