How to convert color EMF spool file to grayscale or Black /white spool file?

[semaphore]

Hello

I make R&D virtual printer driver and I am using HP Color LaserJet 8500 PCL driver for
EMF spool file generation. It is not grayscale supported printer driver .SO when I print color
Document to black/ white use with color selection. But the EMF spool files in color.
If I convert EMF to BMP, the BMP size is as per as printer size 5000*4000 …so large. So it takes more time for image processing.
SO
Any one suggests how to convert direct color EMF file to black/ white or gray scale EMF file.
or
Suggest any grayscale, Color and Black/White also default EMF spool file generator Printer name.
Or
Any otherWay?
Thanks
Mahendra