Base64 en/decode in Swift

Base64.swift

//create image instance
//with image name from bundle
var image : UIImage = UIImage(named:"imageNameHere")!
var imageData = UIImagePNGRepresentation(image)

//OR with path
var url:NSURL = NSURL(string : "urlHere")!
var imageData:NSData = NSData.dataWithContentsOfURL(url, options: nil, error: nil)

//Encoding
let base64String = imageData.base64EncodedStringWithOptions(.allZeros)
println(base64String)

//Decoding
let decodedData = NSData(base64EncodedString: base64String, options: NSDataBase64DecodingOptions.fromRaw(0)!)
var decodedimage = UIImage(data: decodedData)
println(decodedimage)
yourImageView.image = decodedimage as UIImage

how do you use this with base64 string?

whats the meaning of (.allZeros)???? can u explain me plz....