Fairly often we get questions from developers new to TWAIN asking why their
application works great when compiled as a 32-bit application but none of their
scanners show up in x64 bit mode. (With the possible exception of a few software
based testing scanners.)
The reason your scanner is missing when you compile as a x64 bit application
is that your scanner doesn't have a 64-bit TWAIN driver. Yes, it supports your
64-bit operating system, but it is still only a 32-bit driver and 32-bit
implementation of TWAIN. In order to show up to TWAIN in a 64-bit application it
needs to implement the full 64-bit TWAIN interface. This limitation is not
unique to us, all products that use TWAIN have this same exact limitation.
We provide 64-bit builds of our DotTwain DLLs (EZTwain too) so that you can
be ready when the device manufacturers do release 64-bit drivers. The TWAIN
64-bit specification has been out a few years now, so realistically
manufacturers could release devices that support 64-bit TWAIN communication any
time now. It is just easier for both you and us to have them available now
rather than playing catch up once these devices are available.
However, for now, until you actually have a scanner in your possession that
has genuine 64-bit drivers you will need to target 32-bit TWAIN.
Also, note: if you have never installed any 64 bit TWAIN drivers/data
sources, you may run into an exception when attempting to invoke commands that
communicate with the system Twain manager (Acquisition.ShowSelectSource(),
Device.TryOpen(), Device.Acquire(), etc...) you'll want to gracefully handle
that exception to inform your user that the required TWAIN manager is not
present and that they will need to install a valid 64 bit twain driver in order
to use scanning within that application.
The TWAIN working group has created a TWAIN Sample DataSource. You can
download it here:
https://github.com/twain/twain-samples
Please note: for actual 64 bity version, make sure you download the installer
for win64
For more information, please see:
INFO: Bitness Roundup Whitepaper: x86, x64, AnyCPU
Original Article:
Q10346 - FAQ: Common Problems with x64 TWAIN Scanning