I am only barely familiar with both MicroStudio and Processing so probably not the most reliable source, but to my knowledge Processing is for graphics programming whereas Microstudio is for games programming.

Of course theres a lot of overlap between the two, but I'd guess Processing is more powerful (or at least, more easily powerful) for pure graphics rendering than MicroStudio, but MicroStudio can do a lot more (or again, at least a lot more easily), like handling inputs and playing sounds and so on