Critique of Forrest Gump

Forrest Gump (1994)

Background

The movie chronicles the adventures of Forrest Gump (played by Tom Hanks), a somewhat dim witted man who lived through the 50s to the 80s.

Feather in the Opening Scene

The movie begins with a feather falling from the sky and eventually landing against Gump's right shoe. The scene is one fluid shot, with no camera changes, so there is little doubt that the "feather" in the first two images is computer generated, and that the "feather" in the last frame is real. But what puzzled us is the seamless transition from a computer modeled feather over to a real world. Within a span of eight frames, one can see the fading from one feather to another, but the question is how they removed the real feather while the fake one was falling.

We chose this scene because our original thought was that they probably had to track the real feather falling in order to overlay the CG feather at the correct time. It seems likely, however, that they did not track the feather but instead did any changes by hand.

Tang's Analysis

After examining the clip several times, I believe that the visual editors computer generated a portion of Gump's right shoe. Specifically, they overlayed the footage with a "shoe" lacking the feather. Several clues lead me to this conclusion:

1. First, the first view of the shoe (not shown above) is from a distance. The camera does not focus upon it; the viewer cannot determine if there is a feather there or not.
2. By the time one can see the shoe, the camera has slowed down. True, the computer would need to synchronize with the camera movement, but this is not a Herculean task.
3. Third, only part of the shoe needs to be modeled. Specifically, the computer would only need to draw the front left quarter of Gump's right shoe.
4. Furthermore, during the time that it needs to be modeled, the shoe is not moving -- only the camera is floating about.
5. This may or may not be an artifact of the television, but it appeared to me that the shoe suddenly changes color. This seemed to coincide with the feather darkening, as the computer model blends into the real one.
6. Finally, the geometry of the shoe appears to alter during the scene. It looks like the shoe is fatter in the beginning, but suddenly slenders during the same time as the transition. Again, this may be caused by sub-optimal viewing conditions or by sleep deprivation.

Eric's Analysis

My explanation was slightly different. I think the visual editors made a difference map and extracted the feather from the shoe till the appropriate time. We both agree that the feather had to be CG.

1. First, They made one shot with the feather on the shoe.
2. Second they made a second shot (or just the affected portion of a shot) with no feather on the shoe.
3. They then made a difference map and extracted the feather from the shoe till the point where it lands on the shoe.
4. They then computer generated the feather and synchronize it to land on the shoe right as they take the mask off.
5. This seems to be the case for several reasons.  First, it seems to be the easiest way by far.
6. Second the feather can be seen on the shoe from a distance (they forgot to take it out in one of the "far-off" shots).
7. Third you can see a slight color change right as the feather lands on the shoe. This would mark the change from CG graphics to the real shot.

How it was really done

According to a post on the alt.movies.visual-effects newsgroup, the "Making of Forrest Gump" segment on the laser disc describes how the shot was generated:

1. First, the feather was suspended in front of a blue or green screen and filmed twisting and turning in the air.
2. The scene was choreographed and shot without a feather floating through the air, but with a real feather on Hanks' foot. The real feather can be glimpsed in the final shot during one brief pan where Hanks is visible in the background.
   
3. The bluescreened feather was digitized and manipulated. A virtual shot was constructed which matched the original (real camera) shot, and digitized footage of the feather twisting and turning in the air was inserted. In addition, the feather was manipulated to move closer to and further from the camera, since the original bluescreened footage was at a static distance from the camera.
4. Specific frames from the feather footage were pasted together to form the final twirling path of the feather as it fell. Computer generated reflections and shadows were inserted when necessary (for instance, when the feather passes over the car and lands on the man's shoulder).
5. Finally, the feather came down toward Hanks' foot, morphing into the real feather at the last minute. The real feather was airbrushed out of the earlier frames by hand, allowing frame-by-frame touchups and providing a very smooth transition.

There is some argument, especially on alt.movies.visual-effects, as to whether this constitutes CG or not. Many people maintain that since the path of the feather was completely manipulated and not natural, this is CG. Other say that since the original frames of the feather were digitized from real life, this can't be Computer Generated. In any case, a large portion of the effect was done by hand, lessening the digital influence on the scene.

In conclusion, we tended to overanalyze and over-digitize the scene, when in fact most of the work was not done with finesse, but with sheer brute force. Only recently have movies started doing complete 3D models of objects that interact seamlessly with real-life objects.

Critique by Group 1 [the to-be-renamed group], Spring 2000, Mark Haines, Eric Stevens, and Jason Tang

Last modified 1 May 2000.
Jason Tang / tang@jtang.org