fxguide has an interview with Disney's stereographer regarding the 3D conversion of The Lion King, recently re-released in cinemasa. Below is an extract regarding the method used for conversion.
"After that I would watch the film and basically chart out what I felt the emotional content was. I tried to quantify what the peak point of action was and make that a ’10′, and what were the quieter moments with expositional dialogue or that just were a breather in between action or big emotional beats, and these would be a ’1′.
Then I created these depth mark-ups, which was really the most intense part. For the shots that are 10s, like Scar having his final encounter in the showdown in Simba, or the big emotional moments when Simba sees his father in the sky – for those moments what you want to do is give them the most stereoscopic depth as you can, while keeping it comfortable for the audience. In the quieter moments, I give it the least amount that will still make the shot look good. I want all the shots to have an aesthetically pleasing quality and feel like nothing’s cardboard in them."