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let pngImageData = imageObj.pngData()
let jpegData = imageObj.jpegData(compressionQuality: 1)
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// Swift 5+ Answer
let manager = PHImageManager.defaultManager()
let option = PHImageRequestOptions()
var thumbnail = UIImage()
option.synchronous = true
manager.requestImageForAsset(asset, targetSize: CGSize(width: 100.0, height: 100.0), contentMode: .AspectFit, options: option, resultHandler: {(result, info)->Void in
thumbnail = result!
})