gistfile1.cs

	public class ImageEx : Image
	{
		public static readonly BindableProperty AspectExProperty =
			BindableProperty.Create<ImageEx, AspectEx>(p => p.AspectEx, AspectEx.AspectFit, BindingMode.OneWay, null, OnAspectExPropertyChanged);

		static void OnAspectExPropertyChanged(BindableObject bindable, AspectEx oldValue, AspectEx newValue)
		{
			var aspectEx = (AspectEx)newValue;
			Aspect aspect;
			if (Enum.TryParse (aspectEx.ToString (), out aspect)) {
				(bindable as ImageEx).Aspect = aspect;
			}
		}

		public AspectEx AspectEx
		{
			get { return (AspectEx)base.GetValue(AspectExProperty); }
			set { base.SetValue(AspectExProperty, value); }
		}

		protected override SizeRequest OnSizeRequest(Double widthConstraint, Double heightConstraint)
		{
			// the returned sizeRequest contains the dimensions of the image
			SizeRequest sizeRequest = base.OnSizeRequest(double.PositiveInfinity, double.PositiveInfinity);

			switch (AspectEx) {
				case AspectEx.Uniform:
					var innerAspectRatio = sizeRequest.Request.Width / sizeRequest.Request.Height;

					if (Double.IsInfinity (heightConstraint)) {
						if (Double.IsInfinity (widthConstraint)) {
							// both destination constraints are infinity
							// use the view's size request dimensions
							widthConstraint = sizeRequest.Request.Width;
							heightConstraint = sizeRequest.Request.Height;
						} else {
							// destination height constraint is infinity
							heightConstraint = widthConstraint * sizeRequest.Request.Height / sizeRequest.Request.Width;
						}
					} else if (Double.IsInfinity (widthConstraint)) {
						// destination width constraint is infity
						widthConstraint = heightConstraint * sizeRequest.Request.Width / sizeRequest.Request.Height;
					} else {
						// both of the destination width and height constraints are non-infinity
						var outerAspectRatio = widthConstraint / heightConstraint;

						var resizeFactor = (innerAspectRatio >= outerAspectRatio) ?
							(widthConstraint / sizeRequest.Request.Width) :
							(heightConstraint / sizeRequest.Request.Height);

						widthConstraint = sizeRequest.Request.Width * resizeFactor;
						heightConstraint = sizeRequest.Request.Height * resizeFactor;
					}
					sizeRequest = new SizeRequest (new Size (widthConstraint, heightConstraint));
					break;
			case AspectEx.None:
				sizeRequest = new SizeRequest (new Size (sizeRequest.Request.Width / 2, sizeRequest.Request.Height / 2));
				break;
			}

			return sizeRequest;
		}
	}

	public enum AspectEx
	{
		/// <summary>Scale the image to fit the view. Some parts may be left empty (letter boxing).</summary>
		AspectFit,
		/// <summary>Scale the image to fill the view. Some parts may be clipped in order to fill the view.</summary>
		/// <remarks />
		AspectFill,
		/// <summary>Scale the image so it exactly fill the view. Scaling may not be uniform in X and Y.</summary>
		Fill,
		/// <summary>Scale the image to fill the view while it preserves its native aspect ratio.</summary>
		Uniform,
		/// <summary>The image preserves its original size.</summary>
		None
	}

Thank you for this, it's working great after a lot of obsolete tags are included. Can you update the code so these obsolete tags can be removed ?