Simplify the following text for a Grade 9 native English-speaking person.
Original: GIMP 's original creators , Spencer Kimball and Peter Mattis , began developing GIMP in 1995 as a semester-long project at the University of California , Berkeley .
Simplified: The GIMP was started in 1995 by Spencer Kimball and Peter Mattis and is now taken care of by a group of volunteers as part of the GNU Project .