Support for TWAIN-compatible applications

In order to support TWAIN applications with private capabilities, WIA drivers can use a technique known as pass-through functionality. The pass-through mechanism refers to the way a TWAIN-compatible application communicates with a WIA driver, using the data source manager and the TWAIN compatibility layer as intermediaries. It's important to note that TWAIN capability pass-through is supported only in Windows XP and later operating system versions.

All communication between a TWAIN-compatible application and the WIA driver goes first to the data source manager (twain_32.dll), which in turn calls into the TWAIN compatibility layer (wiadss.dll). The TWAIN compatibility layer then calls the IWiaItemExtras::Escape method, which calls the IStiUSD::Escape method. The TWAIN compatibility layer calls only the IWiaItemExtras::Escape method. The driver developer should be concerned only with the device receiving an IStiUSD::Escape call. For more information about IWiaItemExtras::Escape, see the Microsoft Windows SDK documentation.

The purpose of TWAIN pass-through functionality is to provide support to driver writers who are making the transition from TWAIN drivers to WIA drivers. It isn't intended for adding TWAIN features to a WIA driver. If your WIA driver doesn't require support for TWAIN, you shouldn't add this functionality to your driver.

The following articles are discussed in this section:

Enabling TWAIN Capability Pass-Through in a WIA Driver

Using the IStiUSD Escape Method