convert C# Xamarin.forms.image to CGImage

I am trying to convert a Xamarin.forms.image to a CoreGraphics.CGImage.

void saveImg(Xamarin.Forms.Image image)
    {

        CoreGraphics.CGImage CGImage = (CoreGraphics.CGImage)image;
    }

although this does not work...

ERROR Message : "Cannot convert type 'Xamarin.Forms.Image' to 'CoreGraphics.CGImage' "

What is the propper way to convert this image?