I would think Paramount Pictures would have the tools and the technology to take such a picture. They have also been editing pictures before "Photoshop" was even invented. They probably invented many of the techniques used for editing.
But really we are impressed by the technical aspects of the picture?
If all of this talent was really on one stage at one time together, that is the true miracle of this picture.
Personally I doubt they were all there at one time. After all ... It’s Hollywood ...