Example
// resize the image to be contained within a maximum width and height, keeping aspect ratio
public static UIImage MaxResizeImage(this UIImage sourceImage, float maxWidth, float maxHeight)
{
var sourceSize = sourceImage.Size;
var maxResizeFactor = Math.Min(maxWidth / sourceSize.Width, maxHeight / sourceSize.Height);
if (maxResizeFactor > 1) return sourceImage;
var width = maxResizeFactor * sourceSize.Width;
var height = maxResizeFactor * sourceSize.Height;
UIGraphics.BeginImageContext(new CGSize(width, height));
sourceImage.Draw(new CGRect(0, 0, width, height));
var resultImage = UIGraphics.GetImageFromCurrentImageContext();
UIGraphics.EndImageContext();
return resultImage;
}