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Horizontal resolution specification
Television lines
(
TVL
) is a specification of an analog camera or monitor's horizontal
image resolution
.
[1]
The TVL is one of the most important resolution measures in a video system. The TVL can be measured with the standard
EIA 1956 resolution chart
.
[2]
Definition
[
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]
TVL is defined as the maximum number of alternating light and dark vertical lines that can be resolved per picture height.
[3]
A resolution of 400 TVL means that 200 distinct dark vertical lines and 200 distinct white vertical lines can be counted over a horizontal span equal to the height of the picture. For example, on 4 by 3 inches (10.2 cm × 7.6 cm) monitor with 400 TVL, 200 vertical dark lines can be counted over 3 inches (7.6 cm) width on monitor (Note that the 3 inches (7.6 cm) of monitor height is used rather than the 4 inches (10 cm) of whole monitor width).
TVL is an inherent quality of a camera or monitor, influenced by the visual bandwidth of the
transmission system
used. It should not be confused with the number of horizontal scanning lines of such systems, which e.g.
625 lines
for the
PAL
system,
525 lines
for the
NTSC
system.
[3]
Limitations
[
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]
Since analog transmission of video is
scan line
-based, the same number of
horizontal
lines is always transmitted. However, several factors impede the ability to display fine detail within a line:
- The camera or other source of material.
- The storage and processing of the picture.
- The transmission of the TV signal e.g. broadcast by
radio
or by
cable
.
- The reception and reproduction of the picture on a TV set.
See also
[
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]
- Kell factor
, which limits the vertical resolution in analog television, and both horizontal and vertical resolution in digital television, to a fraction of the number of scan lines or pixels
References
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]