Yes the proper method to get resolution is with DG_IMAGE / DAT_IMAGEINFO / MSG_GET operation triplet.
This triplet should always be used to determine what kind image image data is returned prior to every transfer.
Requesting the scanner for a pixel type, bit depth, or a resolution, is only a request. It is not guaranteed that is what you will get. Some scanners offer an automatic color detection. They might return jpeg compressed data for color images and G4 compressed data for b&W pages. (But no TWAIN driver should return compressed data unless requested by the application)
Yes it would be a bug with this TWAIN driver if the DIB does not contain the correct resolution.
Regards,
Jim Watters
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