swift擷取圖檔像素顔色值

extension UIImage{

    /**
    擷取圖檔中的像素顔色值

    - parameter pos: 圖檔中的位置

    - returns: 顔色值
    */
    func getPixelColor(pos:CGPoint)->(alpha: CGFloat, red: CGFloat, green: CGFloat,blue:CGFloat){
        let pixelData=CGDataProviderCopyData(CGImageGetDataProvider(self.CGImage))
        let data:UnsafePointer<UInt8> = CFDataGetBytePtr(pixelData)
        let pixelInfo: Int = ((Int(self.size.width) * Int(pos.y)) + Int(pos.x)) * 4

        let r = CGFloat(data[pixelInfo]) / CGFloat(255.0)
        let g = CGFloat(data[pixelInfo+1]) / CGFloat(255.0)
        let b = CGFloat(data[pixelInfo+2]) / CGFloat(255.0)
        let a = CGFloat(data[pixelInfo+3]) / CGFloat(255.0)

        return (a,r,g,b)
    }

}