Television lines (TVL) is a specification of an analog camera or monitor's horizontalimage resolution.^[1] The TVL is one of the most important resolution measures in a video system. The TVL can be measured with the standardEIA 1956 resolution chart.^[2]

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 thetransmission system used. It should not be confused with the number of horizontal scanning lines of such systems, which e.g.625 lines for thePAL system,525 lines for theNTSC system.^[3]

The following table shows the horizontal resolutions of some analog video systems:^{[4][5][6][7][8][9]}

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Since analog transmission of video isscan line-based, the same number ofhorizontal lines is always transmitted. However, several factors impede the ability to display fine detail within a line:

1. The camera or other source of material.
2. The storage and processing of the picture.
3. The transmission of the TV signal e.g. broadcast byradio or bycable.
4. The reception and reproduction of the picture on a TV set.

• 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

• Television technology

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