Ghosting (television)

For related terms, see Ghost image (disambiguation).
Not to be confused with screen burn-in.

In television, a ghost is a replica of the transmitted image, offset in position, that is super-imposed on top of the main image.

A simulated example of severe ghosting in an analog TV broadcast.

Analog ghosting

Ideal situation for TV signal propagation: The signal leaves the transmitter (TX) and travels through one path to the receiver (the TV set, which is labeled RX)
An object (an aircraft) complicates the system by adding a second path. The signal arrives at RX by two paths which have different lengths. The main path is the direct path, while the second is a reflection from the plane.
A "ghost eliminator" sold to consumers in the 1960s and 70s to make ghosting less visible. This unit was a simple resistive attenuator.

Common causes of ghosts (in the more specific sense) are:

Note that ghosts are a problem specific to the video portion of television, largely because it uses AM for transmission. SECAM TV uses FM for the chrominance signal, hence ghosting only affects the luma (video) portion of its signal. TV is broadcast on VHF and UHF, which have line-of-sight propagation, and easily reflect off of buildings, mountains, and other objects.

The audio portion uses FM, which has the desirable property that a stronger signal tends to overpower interference from weaker signals due to the capture effect. Even when ghosts are particularly bad in the picture, there may be little audio interference.


If the ghost is seen on the left of the main picture, then it is likely that the problem is pre-echo, which is seen in buildings with very long TV downleads where an RF leakage has allowed the TV signal to enter the tuner by a second route. For instance, plugging in an additional aerial to a TV which already has a communal TV aerial connection (or cable TV) can cause this condition.

Digital ghosting

Ghosting is not specific to analog transmission. It may appear in digital television when interlaced video is incorrectly deinterlaced for display on progressive-scan output devices.

See also


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