It should be pretty straight forward. Attached is an example of what you're talking about. It should do all of the conversions for you automatically. Once you've calibrated your image to mm, that should be the standard for the following steps.
Regards,
Matt S.
LabVIEW Integration Engineer with experience in LabVIEW Real-Time, LabVIEW FPGA, DAQ, Machine Vision, as well as C/C++. CLAD, working on CLD and CLA.