Television lines (TVL) is a specification of an analog camera or monitor's horizontal
image resolution
Image resolution is the level of detail of an image. The term applies to digital images, film images, and other types of images. "Higher resolution" means more image detail.
Image resolution can be measured in various ways. Resolution quantifies ...
. 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
The Electronic Industries Alliance, EIA 1956 Resolution Chart (until 1975 called RETMA Resolution Chart 1956) is a test card originally designed in 1956 to be used with black and white analogue TV systems, based on the previous (and very similar ...
.
Definition
TVL is defined as the maximum number of alternating light and dark vertical lines that can be resolved per picture height.
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 monitor with 400 TVL, 200 vertical dark lines can be counted over width on monitor (Note that the of monitor height is used rather than the of whole monitor width).
TVL is an inherent quality of a camera or monitor, influenced by the visual bandwidth of the
transmission system
In telecommunications, a transmission system is a communication system that transmits a signal from one place to another. The signal can be an signal (electrical engineering), electrical, fiber-optic communication, optical or radio wave, radio s ...
used. It should not be confused with the number of horizontal scanning lines of such systems, which e.g.
625 lines
625-line (or CCIR 625/50) is a late 1940s European analog standard-definition television resolution standard. It consists of a 625-line raster, with 576 lines carrying the visible image at 25 interlaced frames per second. It was eventually ...
for the
PAL
Phase Alternating Line (PAL) is a color encoding system for analog television. It was one of three major analogue colour television standards, the others being NTSC and SECAM. In most countries it was broadcast at 625 lines, 50 fields (25 ...
system,
525 lines
525-line (or EIA 525/60) is an American standard-definition television resolution used since July 1, 1941, mainly in the context of analog TV broadcast systems. It consists of a 525-line raster, with 486 lines carrying the visible image at 30 ...
for the
NTSC
NTSC (from National Television System Committee) is the first American standard for analog television, published and adopted in 1941. In 1961, it was assigned the designation System M. It is also known as EIA standard 170.
In 1953, a second ...
system.
Limitations
Since analog transmission of video is
scan line
A scan line (also scanline) is one line, or row, in a raster scanning pattern, such as a line of video on a cathode-ray tube (CRT) display of a television set or computer monitor.
On CRT screens the horizontal scan lines are visually discernib ...
-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
Radio is the technology of communicating using radio waves. Radio waves are electromagnetic waves of frequency between 3 hertz (Hz) and 300 gigahertz (GHz). They are generated by an electronic device called a transmitter connec ...
or by
cable
Cable may refer to:
Mechanical
* Nautical cable, an assembly of three or more ropes woven against the weave of the ropes, rendering it virtually waterproof
* Wire rope, a type of rope that consists of several strands of metal wire laid into a hel ...
.
# The reception and reproduction of the picture on a TV set.
See also
*
Kell factor
The Kell factor, named after RCA engineer Raymond D. Kell, is a parameter used to limit the bandwidth of a sampled image signal to avoid the appearance of beat frequency patterns when displaying the image in a distinct display device, usuall ...
, 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
{{Analogue TV transmitter topics
Television technology