Ivan Reitman is finally satisfied with Ghostbusters. For the June 29 DVD release of his 1984 hit starring Bill Murray, the director saw to it that everything looks just right, which wasn't the case with the first, supposedly definitive laserdisc edition. ''I don't know what happened,'' he says, ''but it pumped up the light level so much you saw all the matte lines. I was embarrassed about it all these years.'' Not only are the blacks back for DVD, all the effects shots are complete. ''When we went out into release, about half a dozen shots were unfinished,'' recalls Reitman, who had to rush his $30 million production. ''It mostly had to do with the marshmallow man. The amazing thing is, people didn't care.''