I cannot control the scanner to save single-sided documents

[lurenfan]

I am using the twain module recently, when calling the method XferImageByFile, if there is only one file with scanning, it can be called twice to save the front and back files separately, but when I scan continuously and only the front side of the document, there will be problems. I Tried to set CAP_DUPLEX and CAP_DUPLEXENABLED to disable double-sided scanning, it does not work