Gaussian Blur Filter Reversal: iOS - ios

Question

I've got a gaussian blur which I'm doing for an app.
//Get a UIImage from the UIView
UIGraphicsBeginImageContext(self.view.bounds.size);
[self.view.layer renderInContext:UIGraphicsGetCurrentContext()];
UIImage *viewImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
//Blur the UIImage
CIImage *imageToBlur = [CIImage imageWithCGImage:viewImage.CGImage];
CIFilter *gaussianBlurFilter = [CIFilter filterWithName:#"CIGaussianBlur"];
[gaussianBlurFilter setValue:imageToBlur forKey:#"inputImage"];
[gaussianBlurFilter setValue:[NSNumber numberWithFloat:2] forKey:#"inputRadius"];
CIImage *resultImage = [gaussianBlurFilter valueForKey:#"outputImage"];
UIImage *endImage = [[UIImage alloc] initWithCIImage:resultImage];
//Place the UIImage in a UIImageView
newView = [[UIImageView alloc] initWithFrame:self.view.bounds];
newView.image = endImage;
[self.view addSubview:newView];
It works great, but I want to be able to reverse it and return the view back to normal.
How can I do this as trying to simply remove the blur's view from it's superview didn't work. I've also tried setting various properties to nil with no luck.

Answer 1

Keep a pointer to viewImage in a property
#property (nonatomic, strong) UIImage* originalImage;
then after
UIImage *viewImage = UIGraphicsGetImageFromCurrentImageContext();
add
self.originalImage = viewImage;
To revert your image:
newView.image = self.originalImage;
when you apply the blur it does not alter viewImage.. you have created a separate CIImage which gets blurred, and you make a new UIImage from the blurred CIImage.

Answer 2

First thing i saw in your code is that you don't apply the filter in a async task. blur the image take time, so if you don't want to freeze the main thread you should use:
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
//blur the image in a second thread
dispatch_async(dispatch_get_main_queue(), ^{
//set the blurred image to your imageView in the main thread
});
});
To can reverse the original image, you just put the blurred copy in other imageView that appear over the original. In my case the original image isn't a imageView, but the view itself. So i only add a imageView in my view to set the blurred image, and set to nil when i want to reverse.
Finally, if you want to avoid the blink when you set the blurred image, you can play with alpha in animations to make a soft transition:
[self.blurredImageView setAlpha: 0.0]; //make the imageView invisible
[self.blurredImageView setImage:blurredImage];
//and after set the image, make it visible slowly.
[UIView animateWithDuration:0.5 delay:0.1
options:UIViewAnimationOptionCurveEaseInOut
animations:^{
[self.blurredImageView setAlpha: 1.0];
}
completion:nil];
Here is my complete methods:
- (void)makeBlurredScreenShot{
UIGraphicsBeginImageContextWithOptions(self.view.bounds.size, self.view.opaque, 0.0);
[self.view.layer renderInContext:UIGraphicsGetCurrentContext()];
UIImage *imageView = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
CIContext *context = [CIContext contextWithOptions:nil];
CIImage *sourceImage = [CIImage imageWithCGImage:imageView.CGImage];
// Apply clamp filter:
// this is needed because the CIGaussianBlur when applied makes
// a trasparent border around the image
NSString *clampFilterName = #"CIAffineClamp";
CIFilter *clamp = [CIFilter filterWithName:clampFilterName];
if (!clamp)
return;
[clamp setValue:sourceImage forKey:kCIInputImageKey];
CIImage *clampResult = [clamp valueForKey:kCIOutputImageKey];
// Apply Gaussian Blur filter
NSString *gaussianBlurFilterName = #"CIGaussianBlur";
CIFilter *gaussianBlur = [CIFilter filterWithName:gaussianBlurFilterName];
if (!gaussianBlur)
return;
[gaussianBlur setValue:clampResult forKey:kCIInputImageKey];
[gaussianBlur setValue:[NSNumber numberWithFloat:8.0] forKey:#"inputRadius"];
CIImage *gaussianBlurResult = [gaussianBlur valueForKey:kCIOutputImageKey];
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
CGImageRef cgImage = [context createCGImage:gaussianBlurResult fromRect:[sourceImage extent]];
UIImage *blurredImage = [UIImage imageWithCGImage:cgImage];
CGImageRelease(cgImage);
dispatch_async(dispatch_get_main_queue(), ^{
[self.blurredImageView setAlpha: 0.0];
[self.blurredImageView setImage:blurredImage];
[UIView animateWithDuration:0.5 delay:0.1
options:UIViewAnimationOptionCurveEaseInOut
animations:^{
[self.blurredImageView setAlpha: 1.0];
}
completion:nil];
});
});
}
- (void)removeBlurredScreenShot{
[UIView animateWithDuration:0.5 delay:0.1
options:UIViewAnimationOptionCurveEaseInOut
animations:^{
[self.blurredImageView setAlpha: 0.0];
}
completion:^(BOOL finished) {
[self.blurredImageView setImage:nil];
}];
}

Answer 3

Like I said in my previous comment, you could create a property/iVar that holds the image before the effect is applied and revert in case you want to undo.
if(!_originalImage)
_originalImage = [[UIImage alloc] init];
_originalImage = viewImage; //(Creates a copy, not a C-Type pass-by-reference)
// Do your Blur Stuff
// Now somewhere down the line in your program, if you don't like the blur and the user would like to undo:
viewImage = _originalImage;
As per your comment on #HeWas's answer, you shouldn't blur the view completely. If the view is getting blurred, there's something else you are doing wrong elsewhere in your program.