Cropping image with CIImage.ImageByCroppingToRect or CICrop in MonoTouch

Question

I have a very large image that I would like to show a 200x200px thumbnail of (showing a portion of the image, not a strethed version of the entire image). To achieve this I am looking into using CIImage.ImageByCroppingToRect or CICrop - but I am not able to get anything useful. Either the result is just black (I assume what I see is the black portion of the cropped image) or I get a SIGABRT ("Cannot handle a (6000 x 3000) sized texture with the given GLES context!")

There is a ObjC sample in this thread: Cropping CIImage with CICrop isn't working properly

But I haven't managed to translate it in to C# and get it working properly.

Answer 1

Here's a MonoTouch port of the answer from the post you mentioned:

var croppedImaged = CIImage.FromCGImage (inputCGImage).ImageByCroppingToRect (new RectangleF (150, 150, 300, 300));              
var transformFilter = new CIAffineTransform();
var affineTransform = CGAffineTransform.MakeTranslation (-150, 150);
transformFilter.Transform = affineTransform;
transformFilter.Image = croppedImaged;           
CIImage transformedImage = transformFilter.OutputImage;