// Create the CIImages from a file
CIImage flower = CIImage.FromCGImage (UIImage.FromFile ("flower.png").CGImage);
CIImage clouds = CIImage.FromCGImage (UIImage.FromFile ("clouds.jpg").CGImage);
CIImage xamarinAlpha = CIImage.FromCGImage (UIImage.FromFile ("XamarinAlpha.png").CGImage);

// Create a CIBlendWithAlphaMask filter with our three input images 
var blend_with_alpha_mask = new CIBlendWithAlphaMask () {
	BackgroundImage = clouds,
	Image = flower,
	Mask = xamarinAlpha
};

// Get the blended image from the filter
var output = blend_with_alpha_mask.OutputImage;

// To render the results, we need to create a context, and then
// use one of the context rendering APIs, in this case, we render the
// result into a CoreGraphics image, which is merely a useful representation
//
var context = CIContext.FromOptions (null);

var cgimage = context.CreateCGImage (output, output.Extent);

// The above cgimage can be added to a screen view, for example, this
// would add it to a UIImageView on the screen:
myImageView.Image = UIImage.FromImage (cgimage);