Ghosting
Also called: television ghosts, multipath ghosting, double image, ghost images
Ghosting is the faint offset duplicate image seen on analog TV. Learn how signal reflections cause it and how to build it with ECHO PARASITE in After Effects.
WHAT CAUSES IT
Ghosting is a faint second image displaced to the right of the main picture, produced when a broadcast signal reaches the antenna by more than one path. The direct signal arrives first. A copy bounced off a building, hill, or aircraft takes a longer route and arrives later, and radio waves cover about 300 meters per microsecond, so every 300 meters of extra path adds one microsecond of delay. The active line of an NTSC picture lasts about 52.6 microseconds, so a delay of one microsecond places the ghost around two percent of the picture width to the right of the main image. The reflected copy is usually weaker and may have inverted polarity depending on the reflection, which makes the ghost a negative image. The receiver adds the delayed copy to the real signal, and the line draws both. A ghost that arrives after the main signal is a post-ghost, while one that arrives before it, because the direct path is the weaker one, is a pre-ghost.
WHAT IT LOOKS LIKE
A faint duplicate of bright edges offset a few percent of the picture width to the right, softer and dimmer than the main image. It follows the picture exactly, so a white shirt has a second pale shirt beside it, and text shows a doubled outline. In weak reception, several ghosts at different offsets stack, producing a streaky smear. Some ghosts are inverted, appearing dark where the main image is bright. Ghosting does not decay in time like a video trail; it is a spatial offset within a single frame, so it moves in sync with the main image.
WHERE YOU SEE IT
Over-the-air analog television, especially in cities with tall buildings or mountains, rabbit-ear antennas, and old cable installations with impedance mismatches. It shows up in documentary footage of 1970s and 1980s broadcasts, vintage news clips, and retro-styled television graphics. In modern work it is used to give video a weak analog reception look, and it is a standard part of the dead channel and broadcast signal-loss aesthetic.
RECREATE IT
ECHO PARASITE
CONTROLS ECHO GHOSTS, ECHO DECAY, ECHO SCALE
ECHO GHOSTS creates the delayed duplicates, ECHO DECAY sets how quickly they fade, and ECHO SCALE can scale them. For classic multipath ghosts, keep the duplicate close to the original and weak. This recreates the look rather than a physical single-frame offset, so judge the placement visually and avoid heavy settings that turn it into video trails.
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HOW TO MAKE IT IN AFTER EFFECTS
1. Put your footage in a composition and pre-compose it. 2. Apply ECHO PARASITE. 3. Raise ECHO GHOSTS until a faint second copy of bright edges appears. 4. Use ECHO DECAY so the copy is weaker than the main image; a real ghost is usually a fraction of the main signal strength. 5. Keep ECHO SCALE low for a normal ghost, or nudge it slightly for a soft reflection that does not line up perfectly. 6. Zoom to 100 percent on a bright edge such as a window or a title, and judge the offset; it should be small, a few percent of the width. 7. If the ghost should come and go, as it does when an aircraft passes, keyframe ECHO GHOSTS up and down over several seconds. 8. Add noise or chroma bleed for a fuller weak-reception look. 9. Avoid stacking more than two ghosts unless the shot is meant to show terrible reception.
QUESTIONS
- What causes ghosting on analog TV?
- The signal arrives at the antenna by both a direct path and a longer reflected path. The delayed copy is added to the main signal and drawn slightly to the right on the screen, giving a faint duplicate image. Moving reflectors such as aircraft make the ghost flutter, and fixed buildings give a steady ghost. Both are copies of the same program riding on the carrier.
- Why is the ghost on the right?
- Because the reflected signal arrives later in each line, and the electron beam is scanning from left to right. A later arrival means the copy is drawn further along the line. Longer delays move the ghost further to the right, so you can estimate the extra path length of a reflection from how far across the picture the second image sits.
- How do I remove ghosting?
- Use a directional antenna, change its position, or use an amplifier with better selectivity. Some analog televisions had ghost cancellation, and digital broadcasts handle multipath with error correction instead. Digital television replaced analog partly because it handles reflections far better. Multipath that ruined an analog picture is often fully corrected in a digital broadcast.
- Is ghosting the same as motion trails?
- No. Ghosting is a spatial duplicate within a single frame, caused by signal reflections. Trails come from persistence or feedback across frames, where earlier images remain visible. An editor sees the difference quickly. A ghost holds a fixed offset on every frame, while trails smear along the path of moving objects and fade across time.