Vignetting seems to be another serious problem. In a normal enlarger we have somewhat abundant source of light. The limited rectangle of light from my digital mask will get darker towards its corners. There are two solutions for the problem:
1. Digital. I can print a clear negative, scan the print and use it as a mask in PS.
2. Analog. I can expose a piece of T-MAX, develop and use it on top of my negative carrier just like a center filter.