Example of how to implement zoom in images in Xamarin.Forms applications. - http://julianocustodio.com/zoom-image

DoubleExtensions.cs

using System;

namespace DemoZoomImage
{
    public static class DoubleExtensions
    {

        public static double Clamp(this double self, double min, double max)
        {
            return Math.Min(max, Math.Max(self, min));
        }

    }
}