Appendix 1

Appendix 1: Understanding the NTSC Video Format and Digital Video
compressed more than the Y, then the color information is uniformly effected but the Y, the blackand-white
part of the information, is uncompressed and sharp.
This compression is now achieved by skipping R−Y and B−Y pixels. The grouping is done in groups
of four pixels. A numbering system is used to express which pixels are being recorded and which
are skipped. The Y is expressed fi rst, followed by the compression cadence. So assuming that all of
the Y pixels are recorded to keep the image sharp, the fi rst number in the compression is four, all
four pixels of Y recorded. Now let’s say that only half of the color pixels are going to be recorded.
So, we only record the odd-numbered R−Y pixels and the even-numbered B−Y pixels on each video
line. Because the compression is line by line, the vertical resolution is unaffected, the horizontal
luminance is equally unaffected, but the horizontal chrominance is down by half and the recorded
data is down by 33 percent.
This is referred to as 4 : 2 : 2 color compression and it is used in many digital formats. Uncompressed
color is referred to as 4 : 4 : 4. In 4 : 2 : 0 the compression is not line by line, but in pairs of lines.
Again, all of the luminance is recorded, but the R−Y is recorded in odd-numbered pixels in the fi rst
two video lines and the B−Y is recorded into the even-numbered pixels on the next two lines. There
is also 4 : 1 : 1, where the compression is line by line but the color information is only recorded for
one pixel in the group of four.
True, this requires lots of math at the input and output of the video, but math is what computers do
best. If this reduces bandwidth, it’s well worth the math. After all, that’s what compression is. The
amazing thing is that this process is going on in real time while the digital video is being played or
recorded; millions of calculations being performed every second.
Video has come a long way from Philo’s potato fi eld, and while digital imaging seems to have separated
itself into a different category entirely, its video roots run deep. It’s unlikely Philo ever imagined
metadata being interleaved into the video data stream, yet alone recording video with a data stream
in the fi rst place. And there will be equally unimaginable developments in the future. Philo said that
the proudest moment in his life was when live television was transmitted from the moon to the earth
during the Apollo moon landings. Today almost all broadcast television is transmitted from satellites
in space. And because of improved compression, soon that same transmitted digital video will be
theatrical quality.
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