 
 // MARK: - CoreImage
     
-    let sharedCIContext = CIContext(options: [kCIContextPriorityRequestLow: true])
+    private let sharedContext = CIContext(options: [kCIContextPriorityRequestLow: true])
     
     /** Core Image helper methods.
      */

         - parameter context: Core Image context, uses shared context by default.
         - parameter filter: Image filter. Function automatically sets input image on the filter.
         */
        public func nk_filter(filter: CIFilter?, context: CIContext = sharedCIContext) -> UIImage? {
            guard let filter = filter else {
                return nil
            }

         - parameter context: Core Image context, uses shared context by default.
         - parameter filter: Closure for applying image filter.
         */
        public func nk_filter(context context: CIContext = sharedContext, closure: CoreImage.CIImage -> CoreImage.CIImage?) -> UIImage? {
            func inputImageForImage(image: Image) -> CoreImage.CIImage? {
                if let image = image.CGImage {
                    return CoreImage.CIImage(CGImage: image)
