// Create a CIImage from a File.
CIImage flower = CIImage.FromCGImage (UIImage.FromFile ("flower.png").CGImage);

// Create the Color Invert Filter
var invert = new CIColorInvert ()
{
	Image = flower
};

// Get the Filtered Image
var output = invert.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);