问如何在swift中暂时灰显我的uiImage？

EN

func imagePickerController(picker: UIImagePickerController, didFinishPickingImage image: UIImage, editingInfo: [String : AnyObject]?) {

    let path = NSTemporaryDirectory().stringByAppendingString("image.jpeg")

    if let data = UIImageJPEGRepresentation(image, 0.8) {
        data.writeToFile(path, atomically: true)

    }

    self.dismissViewControllerAnimated(true, completion: {})

    let credentialsProvider = AWSCognitoCredentialsProvider(regionType:CognitoRegionType,
        identityPoolId:CognitoIdentityPoolId)
    let configuration = AWSServiceConfiguration(region:CognitoRegionType, credentialsProvider:credentialsProvider)
    AWSServiceManager.defaultServiceManager().defaultServiceConfiguration = configuration

    let ext = "jpeg"

    let uploadRequest = AWSS3TransferManagerUploadRequest()
    uploadRequest.body = NSURL(string: "file://"+path)
    uploadRequest.key = NSProcessInfo.processInfo().globallyUniqueString + "." + ext
    uploadRequest.bucket = S3BucketName
    uploadRequest.contentType = "image/" + ext


//here I would like to present a greyed out photo until it's fully uploaded:
    imageView.image = image


    progressBar.hidden = false
    uploadRequest.uploadProgress = { (bytesSent, totalBytesSent, totalBytesExpectedToSend) -> Void in
        dispatch_async(dispatch_get_main_queue(), { () -> Void in
            if totalBytesExpectedToSend > 0 {
                self.progressBar.progress = Float(Double(totalBytesSent) / Double(totalBytesExpectedToSend))

            }
        })
    }
    let transferManager = AWSS3TransferManager.defaultS3TransferManager()
    transferManager.upload(uploadRequest).continueWithBlock { (task) -> AnyObject! in
        if let error = task.error {
            print("Upload failed ❌ (\(error))")
        }
        if let exception = task.exception {
            print("Upload failed ❌ (\(exception))")
        }
        if task.result != nil {



            let s3URL = NSURL(string: "http://s3-eu-west-1.amazonaws.com/\(S3BucketName)/\(uploadRequest.key!)")!
            //print("Uploaded to:\n\(s3URL)")
            self.photoURL = s3URL.absoluteString
            print(self.photoURL)

        }
        else {
            print("Unexpected empty result.")
        }
        return nil
    }


}