80 Appendix B: Camera interface reference
The voltage of a black pixel is referred to as the black level or black reference level,
and the voltage of a white pixel is referred to as the saturation level or white reference
level. In the RS-170 video signal, the black level is +0.054V and the saturation
level is +0.714V.
Active video
The portion of the video signal above the black level contains the active video (that
Y is, the part of the video waveform that is actually visible on the display screen),
while the portion of the video signal below the black level contains all the
synchronization information.
R Blanking periods
A 5 A video signal has both vertical and horizontal blanking periods. The blanking
period is the portion of a video signal after the end of a frame (vertical blanking)
IN 0 or line (horizontal blanking), and before the beginning of a new frame or line.
During the blanking period, the video signal is "blanked" so that the path of the
0 scan beam in CRT displays cannot be seen while it returns to the beginning of the
next frame or line. To blank the video signal, the voltage is brought down to a
blanking voltage, that is, equal to or below the black level.
IM 2 ❖ The video information during a blanking period does not contain any valid image
data.
L Y Back and front porch
A vertical or horizontal blanking period is made up of a front porch period, a back
E A porch period, and a synchronization pulse. The back porch period precedes the
active video period, whereas the front porch period follows the active video period
PR19 M and precedes the next synchronization pulse.
