How to scan two sides and multiple documents available in the feeder

[seevali]

With the below settings, the NAPS2 (desktop) application automatically scans all the documents in Duplex mode (see Paper Source).

But in this library I can't set Duplex (refer bellow code snipet)

// Select between Flatbed/Feeder
using var item = device.FindSubItem("Feeder");

I can scan all the documents by calling transfer.Download() until all the documents are scanned.

Please help to implement this.

---

PS: OR Is it possible to use the NAPS2.Core.dll (found in the installation directory of NAPS2.exe) and achieve my requirment?

[cyanfish]

The readme has a code sample for duplex. Have you tried that?

[seevali]

Yes. It throws an error when setting below;

item.SetProperty(WiaPropertyId.IPS_DOCUMENT_HANDLING_SELECT, WiaPropertyValue.DUPLEX | WiaPropertyValue.FRONT_FIRST);

Error: Could not set property 3088 (Document Handling Select) value to "12

But I found this SOF answer https://stackoverflow.com/a/30938732/1550721.

And calling the item.StartTransfer() twice I was able to get images of both sides.

Sample code:

device.SetProperty(WiaPropertyId.IPS_DOCUMENT_HANDLING_SELECT, WiaPropertyValue.FEEDER | WiaPropertyValue.DUPLEX);
device.SetProperty(WiaPropertyId.IPS_PAGES, 1);

item.SetProperty(WiaPropertyId.IPS_DOCUMENT_HANDLING_SELECT, WiaPropertyValue.DUPLEX);

try
{
    while (true)
    {
        using var transfer1 = item.StartTransfer();
        transfer1.PageScanned += (sender, args) =>
        {
            using (args.Stream)
            {
                var bitmap = new Bitmap(args.Stream);
                // Do something with the image
            }
        };

        // Do the actual scan
        transfer1.Download();

        using var transfer2 = item.StartTransfer();
        transfer2.PageScanned += (sender, args) =>
        {
            using (args.Stream)
            {
                var bitmap = new Bitmap(args.Stream);
                // Do something with the image
            }
        };

        // Do the actual scan
        transfer2.Download();
    }
}
catch (WiaException ex) when (ex.ErrorCode == WiaErrorCodes.PAPER_EMPTY)
{
}

[cyanfish]

I've removed FRONT_FIRST from the readme as it may not be well supported. Also I've added a line to set IPS_PAGES to ALL_PAGES (0) which is at least supposed to mean that you don't need to call StartTransfer/Download multiple times (though I haven't tested this with a duplex scanner).