Apply CIGaussianBlur only to a small part of an image

Question

I need to apply a CIGaussianBlur filter only on a small part of an image like this:

Is there any way to do this? For example when I apply the filter perhaps I think that I have to specify the dimension of the filter (someone like CGRectMake).

var imageToBlur = CIImage(image: coro.logo)
var blurfilter = CIFilter(name: "CIGaussianBlur")
blurfilter.setValue(imageToBlur, forKey: "inputImage")
blurfilter.setValue(2, forKey: "inputRadius")
var resultImage = blurfilter.valueForKey("outputImage") as! CIImage
var blurredImage = UIImage(CIImage: resultImage)
self.immagineCoro.image = blurredImage

Answer 1

The idea is to make a new image from a rect in the source image, blur this new image then composite it back into the source.

I'm making this an extension to UIImage for an easier usage.

extension UIImage {

    func getImageFromRect(rect: CGRect) -> UIImage? {
        if let cg = self.CGImage,
            let mySubimage = CGImageCreateWithImageInRect(cg, rect) {
                return UIImage(CGImage: mySubimage)
        }
        return nil
    }

    func blurImage(withRadius radius: Double) -> UIImage? {
        let inputImage = UIKit.CIImage(CGImage: self.CGImage!)
        if let filter = CIFilter(name: "CIGaussianBlur") {
            filter.setValue(inputImage, forKey: kCIInputImageKey)
            filter.setValue((radius), forKey: kCIInputRadiusKey)
            if let blurred = filter.outputImage {
                return UIImage(CIImage: blurred)
            }
        }
        return nil
    }

    func drawImageInRect(inputImage: UIImage, inRect imageRect: CGRect) -> UIImage {
        UIGraphicsBeginImageContext(self.size)
        self.drawInRect(CGRectMake(0.0, 0.0, self.size.width, self.size.height))
        inputImage.drawInRect(imageRect)
        let newImage = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        return newImage
    }

    func applyBlurInRect(rect: CGRect, withRadius radius: Double) -> UIImage? {
        if let subImage = self.getImageFromRect(rect),
            let blurredZone = subImage.blurImage(withRadius: radius) {
                return self.drawImageInRect(blurredZone, inRect: rect)
        }
        return nil
    }

}

Usage:

// your image
let sourceImage = UIImage(...)

// the rect to blur
let targetZone = CGRectMake(-50, sourceImage.size.height - 220, sourceImage.size.width + 100, 220)

// apply our functions to the source image
if let resultImage = sourceImage.applyBlurInRect(targetZone, withRadius: 6.0) {
    // use resultImage
}

Before:

After:

Answer 2

Try to use this

func blurImage(image:UIImage, forRect rect: CGRect) -> UIImage?
    {
        let context = CIContext(options: nil)
        let inputImage = CIImage(CGImage: image.CGImage!)


        let filter = CIFilter(name: "CIGaussianBlur")
        filter?.setValue(inputImage, forKey: kCIInputImageKey)
        filter?.setValue((70.0), forKey: kCIInputRadiusKey)
        let outputImage = filter?.outputImage

        var cgImage:CGImageRef?

        if let asd = outputImage
        {
            cgImage = context.createCGImage(asd, fromRect: rect)
        }

        if let cgImageA = cgImage
        {
            return UIImage(CGImage: cgImageA)
        }

        return nil
    }