Honeywell HDVR, Reference Manual

Page: 219 / 238

Rev 1.00 201 Document 900.0261
04/05
G
Video Formats and Digital Video
This appendix explains video formats and compression rates.
Frames and Fields
A single video image is called a frame. A frame is made up of a series of horizontally
scanned lines. Each frame is made up of two fields:
• All the odd numbered lines
• All the even numbered lines
The two fields that make up a single frame are drawn on the screen one after the other,
interlacing them to create the full picture. The interweaving of these two fields allows the
apparent refresh rate of a video frame to appear to the human eye to be twice that of the
actual refresh rate. Thus the perception of screen flicker is reduced and the eye is fooled
into seeing smooth motion when the picture changes.
NTSC and PAL
There are many possible ways to combine the luminance and chrominance information
of a video signal into a single composite signal. Broadcast standards have been
developed so that composite broadcast signals can be received and decoded by
televisions that use the same standard.
NTSC
NTSC (National Television Standards Committee) is a standard that was developed in the
1950s in the USA. It was the first black and white compatible, simultaneous color
transmission system used for public broadcasting. It is used in the USA, Canada, Japan,
and many other countries using an alternating current of 60 Hz. Occasionally NTSC has
been called ‘Never Twice the Same Color’ because of the hue errors that are sometimes
a problem with NTSC signals.