Gate weave
Also called: film weave, frame wobble, film jitter, projector weave
Gate weave is the small shifting of a film frame in the gate, vertically and horizontally. See why it happens and how to build it with Super8 Film Lab.
WHAT CAUSES IT
Gate weave is the slight random movement of each film frame within the camera, printer, or projector gate, so the image position changes a little from frame to frame. Film moves through the mechanism in steps. A claw engages a perforation, pulls the film down one frame, retracts, and the film is held still while the shutter is open. At 18 frames per second, the claw acts 18 times a second. Professional cameras and printers use registration pins that lock the film in exactly the same position for each exposure. A Super 8 cartridge relies on the claw and a pressure plate, and the clearance between the plate and the film allows the frame to sit a tiny bit differently each time. Perforation tolerances, worn claws, film shrinkage, and wandering across the gate width add horizontal movement. The result is a slow drift of the frame, with a small jitter on top of it. The error is usually a fraction of a percent of the frame width, but on a large screen it is easily visible.
WHAT IT LOOKS LIKE
The whole picture moves a little, both up and down and left and right, at the frame rate. Static objects and the frame border wobble gently, as though the camera were on a very slightly unsteady tripod. Locked-off shots and titles show it most clearly, because the eye has a still reference. The motion is smooth and random, not a regular oscillation, and its amplitude is small, usually less than a percent of the frame. Vertical jitter is most noticeable on horizontal lines such as horizons and window frames. Sometimes the movement is accompanied by a faint flicker.
WHERE YOU SEE IT
Super 8, 8mm, and 16mm home movies, old projected prints, silent film transfers, and any scan of film that was not stabilized. It is a defining trait of the projected film experience, since the picture is never perfectly still. High budget productions that used registration pins show far less. In digital productions, gate weave is added subtly to make graphics and visual effects sit in a film frame instead of a perfectly steady digital one.
RECREATE IT
SUPER8 FILM LAB
CONTROLS GATE WEAVE, EXPOSURE FLICKER, GRAIN
GATE WEAVE moves the frame in small random steps, so keep it low enough that it is felt more than seen. Pair it with a small amount of EXPOSURE FLICKER for the instability of a real mechanism. GRAIN completes the picture, because weave without any texture reads as a digital shake. Too much weave looks like handheld camera motion and not like a film gate.
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HOW TO MAKE IT IN AFTER EFFECTS
1. Open the footage in SUPER8 FILM LAB, a standalone Windows application, not an After Effects plugin. 2. Raise GATE WEAVE from its minimum and view a locked-off section of the shot, where the movement is easiest to judge. 3. Set the amount so the frame edge moves slightly and the picture feels unsteady, not shaky. 4. Add a little EXPOSURE FLICKER and GRAIN so the result feels like film and not a digital stabilizer. 5. Export the render and bring it into After Effects. 6. If you also exported grain, bloom, or halation passes, stack them above the main clip using the blend instructions that accompany the export. 7. Be careful with titles and graphics: if you want them to weave with the picture, render them before applying the effect, and if you want them steady, place them above. 8. Watch a few seconds at full speed, because weave is a motion effect and cannot be judged on a still. 9. If the framing looks tight, scale the final layer a little so the weave does not expose the edges of the picture.
QUESTIONS
- What is the difference between gate weave and camera shake?
- Camera shake moves the view of the scene, so foreground and background shift against each other. Gate weave moves the entire frame uniformly, with the border, titles, and grain moving together, and the amount is small and mostly random. Look at the frame edge or a title: if everything moves in lockstep, it is gate weave and not camera movement.
- Why does Super 8 weave more than 35mm?
- Super 8 cartridges lack the registration pins that professional cameras and printers use to lock each frame in position. The film sits in the gate by the claw and pressure plate alone, and the frame is small, so the same error shows more.
- Can gate weave be removed?
- Yes. Film scanners and stabilization software track the perforations or the picture and re-register each frame. Many archives scan with perforation tracking to remove it, and some restorers leave a little back for authenticity. A perfectly stable frame can feel sterile on film footage, so many finishers keep a trace of motion on purpose.
- How much gate weave is enough?
- Just enough that a locked-off shot feels alive. If a viewer notices it as motion, it is too much. A good test is to compare a static title with and without it, then choose the lowest amount you can still sense.