If you are working with ODB++ than I would recommend you use our tool built specifically for PCB/ODB++ files, called FAB 3000. https://www.numericalinnovations.com/collections/fab-3000-gerber-cam
FAB 3000 is 64-bit (while ACE is only 32-bit) and can easily import and ODB++ and then export to a Bitmap (any resolution or size). Here's a quick video showing me import an ODB++ and export a bitmap with 5000 DPI (you can choose any resolution),
Note: We also offer a command-line tool and library (*.dll, *.so) that can perform the ODB to Bitmap conversion silently, https://www.numericalinnovations.com/collections/cam-library
Thanks again, and I look forward to hearing from you.