The easiest way to understand what a visual effects team can do is to look at an example. The first example that we will use involves a surprising number of techniques to completely change the landscape from a wooded field to a seaside town! This is a shot from the movie "The Patriot."
To get a feeling for the total transformation, take a look at these two short videos. The first shows the original shot as filmed. The second shows the scene as it appears in the movie:
The shot arrives as a piece of film, and the first step is to scan this film into digital form so it can be manipulated. Scanning is done frame by frame (movie film is shot at 24 frames per second), and then each frame is stored as an individual full-color image with a resolution of 2,048 by 1,556 pixels. The section of video shown in the two previous videos is 20 seconds long, or about 480 frames.
First, a variety of things might be done to the original shot to clean it up, correct the color and so on. Since the camera pans across the scene in this shot, the next step is to build a 3-D model of the camera so that all of the visual effects the team will create will mesh with the original scene exactly.
One of the first steps taken to add visual effects to the scene is the rotoscoping. An artist sits at a computer and, frame by frame, outlines the portion of the original shot that will be used in the final version. The breastworks, a portion of the field and several of the running soldiers will all be used, but the explosion seen on the left and everything else will be removed. The artist will outline these elements and essentially "lift" them out of the frame.
Another camera crew has created an ocean shot -- in this case the ocean is not far from the CFX studio in Hollywood! Once the ocean shot is cleaned up and color-corrected, it and the rotoscoped scene can be integrated:
Another artist in the paint department has been working on a matte painting of the town. This is a high-resolution digital image created using a painting/illustration package.
Once the town is added in, the scene looks like this:
In this shot there are a number of boats encircling the town and firing on it. The boats are all computer generated. Each one is modeled and then added to the shot:
The cannon fire for the boats is its own stand-alone effect that is created separately and then added to the shot.
A variety of other effects are added to the shot, including things like smoke over the town, people in the town, a large explosion on the right, etc.
The final step in the process is compositing all of the different components of the shot (the rotoscoped foreground, the water, the town, people in the town, the boats, the cannon fire, the smoke, the explosion, birds flying overhead and so on) layer by layer to create the final shot as it will appear in the movie. Once digitally composited, the shot is written back to film so that it can be spliced into the movie.
The small images used here don't really do justice to the shot -- when you see "The Patriot" on a huge screen in a theater, you can see the incredible detail that has been added to make this shot look totally realistic.
As you might imagine, creating a scene like this is time-consuming. Even though the shot only appears on screen for 20 seconds, hundreds of hours go into the visual effects to create a rich, convincing visual image. In this video, several of the artists who worked on the shot describe how long the shot took. It is an amazing process that involves an entire team of people, and this process may be repeated several hundred times in a single film! In "The Patriot," 150 shots in the film involve visual effects like these.