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