General aviation pilot reported a near miss during final approach with an aircraft that took off underneath the reporter's aircraft and then caused an NMAC.

Narrative

As I approached Lincoln airport; I entered the pattern at the 45 degree to downwind to land at runway 15. I made the appropriate callouts at the 10 mile; 5 mile and at the 45. Call was made at the downwind; downwind leg; base leg for 15; and final. On short and final I looked down and recognized Aircraft Y holding short for 15 takeoff. As I continued to descend; this plane started to roll from hold short onto the runway. I announced 'IM ON FINAL' again however the plane continued to roll and liftoff directly underneath me. I stopped descending and deviated to the east of the runway to avoid collision. I had to divert to the east; crossing over Alpha taxi way and FBOs and re-entered the pattern for landing. I realize this is not proper pattern procedure but was done as the only recourse of avoiding collision. I re-entered the pattern for landing. Aircraft Y left the area after take off; called out over the radio to 'let it go' (even as we were still within 150 feet horizontally from each other) It appears this was a female student pilot and male instructor. Conditions were VFR; CTAF was in use and no warning was given. Potential student pilot AND instructor misjudgment and situational unawareness.