gistfile1.m

  CIFilter *resizeFilter = [CIFilter filterWithName:@"CILanczosScaleTransform"];
  [resizeFilter setValue:ciImage forKey:@"inputImage"];
  [resizeFilter setValue:[NSNumber numberWithFloat:1.0f] forKey:@"inputAspectRatio"];
  [resizeFilter setValue:[NSNumber numberWithFloat:xRatio] forKey:@"inputScale"];
 
  CIFilter *cropFilter = [CIFilter filterWithName:@"CICrop"];
  CIVector *cropRect = [CIVector vectorWithX:rect.origin.x Y:rect.origin.y Z:rect.size.width W:rect.size.height];
  [cropFilter setValue:resizeFilter.outputImage forKey:@"inputImage"];
  [cropFilter setValue:cropRect forKey:@"inputRectangle"];
  CIImage *croppedImage = cropFilter.outputImage;

  CGImageRef cgImg = [context createCGImage:croppedImage fromRect:[croppedImage extent]];

  UIImage *returnedImage = [UIImage imageWithCGImage:cgImg scale:1.0f orientation:UIImageOrientationUp];
  
  CGImageRelease(cgImg);
  [resizeFilter setValue:nil forKey:@"inputImage"];
  [cropFilter setValue:nil forKey:@"inputImage"];