VIT signals
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In television broadcasting, VIT signals (vertical interval test signals) are a group of test signals inserted in the composite video signal. These signals are used to weight
Blanking in CVS
In a
Vertical blanking
In each field vertical blanking is about 1612 μs in System B (also G and H; analogue system in most of Europe) and 1333 μs in System M (analogue TV system in USA). This duration is equal to 25 lines in system B and 21 lines in system M.[2] Although 7.5 lines are used for synchronization of the image, the remaining lines can be used for other purposes.[3] Two of these lines in each field are reserved for test signals. Since there are two fields in each frame (image), the number of lines reserved for test signals is four per frame.
Test signals
In both systems, line numbers 17 and 18 are assigned for VIT signals in each field. (These line numbers are used just for the first field. For second field, they correspond to line 280 and 281 in system M, and line 330 and 331 in system B.)
Usually the following test signals are used:
- Luminance bar (low frequency tilt)
- 2T signal (Overshoot)
- 20T signal (differential gain and phase)
- Staircase (luminance linearity)
- Group of sine waves with different frequencies (video characteristics)
- Color carrier superimposed on staircase (differential gain and phase)
- Group of color carriers with different amplitudes (intermodulation of luminance and color)
See also
- Signal generator
- TV transmitter
References and notes