system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How the new Titanic 3-D film is going to take the old film and manipulate it into 3-D.

Basically what do they do to a film when it's finished to make it 3-D?
gpt
Think of it this way: you take a picture from a magazine. It's 2d obviously, but it was taken of a 3D landscape. Maybe it's Leonardo DiCaprio standing in front of a tree, which is in front of a building. So you cut out Leo, then you cut out the tree, leaving the building as the backdrop. Then, you glue Leo's picture to a stick and attach it to the top of a table. You do the same with the tree, but you position it a few inches behind Leo, so that when you look at it head on, Leo covers the hole in the tree pic, and he appears closer to you (which he now actually is). Then you take the background image and put it behind everything else. Viola, you just made a 2d thing "3D". Obviously, this isn't going to look perfect, but the illusion is there. This is what they do to movies that weren't shot in 3D, using computers, of course. The effect is not really that good, and some viewers complain a lot when it's done.