I am running Photoshop CS5 on a windows 8.1 machine. Is there anyway to get the software to recognize my HP Scanjet 4850? 8.1 is 64 bit. I assume Photoshop can only then run as 64 bit. right? And the Twain will only work with 32bit?
Correct. The TWAIN Plug-in only supports 32-bits on Windows.
Personally, I do all my scanning in the background with the stand-alone scanner software. All TWAIN really does is call that software, so there’s no quality difference, plus you’re not locking Photoshop up just to doing scanning. You can retouch and edit images in Photoshop while you scan in the background – which I find is far more efficient.