Scanning Films and Transparencies

If a scanner is equipped to acquire images from films or transparencies, the scanner must be placed in transmissive mode.  For normal (paper) scanning, the device is set in reflective mode.  Reflective and transmissive modes are described by TWAIN as the light path.  Usually, setting the light path turns on or off the back light of the scanner.

If there is TWAIN support for reflective and transmissive scanning, DTWAIN allows switching between reflective and transmissive acquisition by usage of the following functions

Enabling Refllective / Transmissive acquisitions

DTWAIN_SetLightPath

Testing for support

DTWAIN_IsLightPathSupported

Retrieving Current Light Path

DTWAIN_GetLightPath

Please note that only TWAIN devices that support these options can be controlled by your application.  A few devices that have transparency units do not have a TWAIN interface to control the unit.  For some devices, the DTWAIN_IsLightPathSupported will return FALSE even if the device may have a transparency unit, all due to the fact that the device's TWAIN driver has no interface to the transparency unit.