TWAIN and WIA are standards for communicating between imaging devices (e.g. scanners) and software applications.
If you have a scanner and it is "TWAIN compliant", you can use it to scan directly into any software application that supports TWAIN, for example a raster to vector conversion program. This means that after you scan, the scanned image will appear in the application already open.
When you scan using an application that supports TWAIN, the scanning dialog and the options it contains are specified by your scanner's manufacturer (Canon, Epson, HP, Contex, Graphtec etc.) and will therefore vary depending on the type of scanner you have.
WIA (Windows Image Acquisition) is a Microsoft utility that is supplied as part of Windows. Like TWAIN, WIA allows you to scan directly with a "WIA compliant" scanner into any application that supports WIA or TWAIN - all TWAIN compliant applications support WIA as well.
Unlike TWAIN, however, the scanning dialog that appears when you scan and the controls on it are variations on a basic Microsoft design. This means that the level of functionality and scanning control that are available in a WIA interface are less comprehensive than in a well-written TWAIN interface.
To the best of our knowledge all desktop scanners support TWAIN and WIA, as do most modern large format scanners.
However, if you have an older large format scanner, it is unlikely to support TWAIN or WIA. In this case you will not be able to scan directly into TWAIN/WIA compliant applications such as most raster to vector conversion software.
If your scanner doesn't support TWAIN/WIA and you want to get scanned images into a TWAIN/WIA compliant application you need to use the software supplied with your scanner to scan your drawings, save them as TIFF, BMP or similar, then load the saved scan into your application.
Alternatively, there is a German software program from SCP called EasyTWAIN that makes non-TWAIN compliant scanners TWAIN compliant so you can use them to scan images directly into your TWAIN compliant software applications. EasyTWAIN supports a wide range of older large format scanners.