Creates a DcsDocument object from UIImage.
UIImage The image data to create object from.
When image is not nil, it will detect the boundary of the document and process it asynchorously. init will return immediately, in other words, it doesn't wait for the process to finish. At this time, isReady returns NO. When the process is done, isReady returns YES.
|Image is nil||DcsValueNotValidException|
|Some operations to DcsDocument are done before isReady turns true.||DcsDocumentNotReadyException|