Analog video signals 79
The following illustrates interlaced and non-interlaced video signals:
frame 0
frame 1
Y non-interlaced video signal
INAR005 Composite video
PRE19LIMMAY 2 signal
even field 0
odd field 0
even field 1
odd field 1
frame 0
frame 1
interlaced video signal
A composite video signal is an analog signal that contains both timing (that is,
synchronization) and video data in a single signal. Composite video signals are
usually in a standard format such as NTSC, PAL, or SECAM. The RS-170
monochrome video signal is an example of this type of video signal.
Synchronization
Synchronization indicates the end of a line or frame and the start of a new one. In
composite signals, two types of pulses are needed to determine where every pixel
should be "placed" in the final digital image. These pulses are the horizontal
synchronization (hsync) and vertical synchronization (vsync).
A hsync pulse separates each video line and indicates where the beginning of the
next scan line is to occur. A vsync pulse separates two frames (or fields) and
indicates where the top of the next frame (or field) is.
During a horizontal or vertical synchronization, the video signal drops below the
blanking level (explained later) to the sync tip level. For a RS-170 signal, the
synchronization tip level is -0.286V.
Amplitude and reference levels
A video signal has a definite voltage range that defines the amplitude of that signal.
For example, since the RS-170 video signal ranges from -0.286V to +0.714V, it
has an amplitude of 1V.
