// Create the CIImage from a file
CIImage heron = CIImage.FromCGImage (UIImage.FromFile ("heron.jpg").CGImage);

// Create a CIConvolution9Horizontal filter with the input image
var convolution_9_horizontal = new CIConvolution9Horizontal () {
	Image = heron,
	Weights = new CIVector (new float [] {1, -1, 1, 0, 1, 0, -1, 1, -1}),
};

// Get the altered image from the filter
var output = convolution_9_horizontal.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);