Gaussian Blur Over Image - iOS 8

问题

I have a moving background image and I want to blur the bottom part of it out. I would do it with just photoshop but since the image moves, it wouldn't work very well.

Here is what I mean (look at the bottom of the image) :

So basically like the effect the dock has on the iPhone. I'm using iOS 8 but not Swift.

回答1:

I have done a small example based on the photo you have there. My algorithm is as follows:

Extract a portion of image from bottom.
Apply gaussian filter to it and blur it.
Then, create a new image context, draw original image on it.
Then, draw the blurred portion of the image to place it exactly over the original image.
Extract the new image from the context.

Here is a source code for doing so,

 @implementation ViewController


- (void)viewDidLoad{

  [super viewDidLoad];
  UIImageView *imageView = [[UIImageView alloc] init];
  imageView.frame = self.view.bounds;
  [self.view  addSubview:imageView];
  imageView.contentMode = UIViewContentModeScaleAspectFit;
  UIImage *image = [UIImage imageNamed:@"monogram.jpg"];
  imageView.image = [self imageWithBlurredImageWithImage: image andBlurInsetFromBottom: 200 withBlurRadius:3];
}

- (UIImage*)imageWithBlurredImageWithImage:(UIImage*)image andBlurInsetFromBottom:(CGFloat)bottom withBlurRadius:(CGFloat)blurRadius{
  UIGraphicsBeginImageContext(image.size);
  CGContextRef context =  UIGraphicsGetCurrentContext();
  CGContextScaleCTM(context, 1, -1);
  CGContextTranslateCTM(context, 0, -image.size.height);
  CGContextDrawImage(context, CGRectMake(0, 0, image.size.width, image.size.height), image.CGImage);
  CGContextDrawImage(context, CGRectMake(0, 0, image.size.width, bottom), [self blurImage: image withBottomInset: bottom blurRadius: blurRadius].CGImage);
  image = UIGraphicsGetImageFromCurrentImageContext();
  UIGraphicsEndImageContext();
  return image;
}

- (UIImage*)blurImage:(UIImage*)image withBottomInset:(CGFloat)inset blurRadius:(CGFloat)radius{

  image =  [UIImage imageWithCGImage: CGImageCreateWithImageInRect(image.CGImage, CGRectMake(0, image.size.height - inset, image.size.width,inset))];

  CIImage *ciImage = [CIImage imageWithCGImage:image.CGImage];
  CIFilter *filter = [CIFilter filterWithName:@"CIGaussianBlur"];
  [filter setValue:ciImage forKey:kCIInputImageKey];
  [filter setValue:@(radius) forKey:kCIInputRadiusKey];

  CIImage *outputCIImage = filter.outputImage;
  CIContext *context = [CIContext contextWithOptions:nil];

  return [UIImage imageWithCGImage: [context createCGImage:outputCIImage fromRect:ciImage.extent]];

}
@end

And here is the screenshot of the result.

来源：https://stackoverflow.com/questions/25897867/gaussian-blur-over-image-ios-8

标签

ios

objective-c

gaussian