@twain spec – pg 435 wrote:
Note for File transfers:
Since only certain file formats support compression, this capability must be negotiated after
setting the desired file format with ICAP_IMAGEFILEFORMAT.
Try setting ICAP_IMAGEFILEFORMAT Then the compression not the other way around.
And the bit with trying to set the cap when twstate=6, capabilities can only be negotiated in State 4 (unless special arrangements are made
using the CAP_EXTENDEDCAPS capability). Search the spec for CAP_EXTENDEDCAPS.
.