image paralax effect

page.xaml

<ScrollView x:Name="scrollView" StyleId="scrollView">
    <StackLayout VerticalOptions="Fill" BackgroundColor="Fuchsia">
        	<Image x:Name="photoImage" />
        	....

page.xaml.cs

protected ovveride void OnAppearing()
{
	scrollView.Scrolled += (sender, e) => Parallax();
	Parallax();
	...
}

void Parallax()
		{
			if(_imageHeight <= 0)
				_imageHeight = photoImage.Height;

			var y = scrollView.ScrollY * .4;
			if(y >= 0)
			{
				//Move the Image's Y coordinate a fraction of the ScrollView's Y position
				photoImage.Scale = 1;
				photoImage.TranslationY = y;
			}
			else
			{
				//Calculate a scale that equalizes the height vs scroll
				double newHeight = _imageHeight + (scrollView.ScrollY * -1);
				photoImage.Scale = newHeight / _imageHeight;
				photoImage.TranslationY = scrollView.ScrollY / 2;
			}
		}