CIFilter Blur

blur-and-darken.m

// Fix for https://github.com/bryanjclark/ios-darken-image-with-cifilter

-(instancetype)darkened:(CGFloat)alpha andBlurredImage:(CGFloat)radius blendModeFilterName:(NSString *)blendModeFilterName {

  CIImage *inputImage = [[CIImage alloc] initWithImage:self];

  CIContext *context = [CIContext contextWithOptions:nil];

  //First, create some darkness
  CIFilter* blackGenerator = [CIFilter filterWithName:@"CIConstantColorGenerator"];
  CIColor* black = [CIColor colorWithRed:0.0f green:0.0f blue:0.0f alpha:alpha];
  [blackGenerator setValue:black forKey:@"inputColor"];
  CIImage* blackImage = [blackGenerator valueForKey:@"outputImage"];

  //Second, apply that black
  CIFilter *compositeFilter = [CIFilter filterWithName:blendModeFilterName];
  [compositeFilter setValue:blackImage forKey:@"inputImage"];
  [compositeFilter setValue:inputImage forKey:@"inputBackgroundImage"];
  CIImage *darkenedImage = [compositeFilter outputImage];

  // JAL: Extend the image to infinity
  CGAffineTransform transform = CGAffineTransformIdentity;
  CIFilter *clampFilter = [CIFilter filterWithName:@"CIAffineClamp"];
  [clampFilter setValue:inputImage forKey:kCIInputImageKey];
  [clampFilter setValue:[NSValue valueWithBytes:&transform objCType:@encode(CGAffineTransform)] forKey:@"inputTransform"];
  CIImage *infiniteImage = [clampFilter outputImage];

  //Third, blur the image
  CIFilter *blurFilter = [CIFilter filterWithName:@"CIGaussianBlur"];
  [blurFilter setDefaults];
  [blurFilter setValue:@(radius) forKey:@"inputRadius"];
  [blurFilter setValue:infiniteImage forKey:kCIInputImageKey];
  CIImage *blurredImage = [blurFilter outputImage];

  // JAL: Make sure you're using the extents of the non-infinite input image as your rect
  CGImageRef cgimg = [context createCGImage:blurredImage fromRect:inputImage.extent];
  UIImage *blurredAndDarkenedImage = [UIImage imageWithCGImage:cgimg];
  CGImageRelease(cgimg);

  return blurredAndDarkenedImage;
}