Video - A Practical Guide to Video and Audio Compression - page 105

Table 5-6 Sampling Pixel Maps

Physical Usable Description

X Y WH

640 480 640 480 Square sampled image for VGA computer displays

but not used in studio situations

780 525 648 480 Square pixel sample rates for NTSC 525i30 imaging

systems used in the United States

944 625 768 576 Square pixel sample rates for PAL 625i25 imaging

systems used in Europe

858 525 720 480 Rec 601 component 4:2:2 sample rates for NTSC

525i30 imaging systems used in the United States

858 525 704 480 Reduced visible area variant of Rec 601 component

4:2:2 sample rates for NTSC 525i30 imaging
systems used in the United States

864 625 720 576 Rec 601 component 4:2:2 sample rates for PAL 625i25

imaging systems used in Europe

910 525 768 483 Composite sample rates for NTSC 525i30 imaging

systems used in the United States

1135 625 948 576 Composite sample rates for PAL 625i25 imaging

systems used in Europe

948 576 in order to operate on square pixels, but the images must be scaled correctly

when converted back to video.
This has implications for artwork that is used for DVD menus, for example.

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5.11 Color Information

Three separate red, green, and blue (RGB) signals are combined in analog TV broadcast-
ing using some very complicated modulation and matrix-mixing techniques. The RGB
values are combined to generate a monochrome image. This is viewable on a black and
white monitor and is referred to as the luma component. That same matrix calculation also
generates two additional difference images that describe the color. Because the modula-
tion frequencies are different, the luma and chroma signals are separated in the receiver.
Even in the analog world, there is some video compression being applied. The chroma
information is filtered to remove high-frequency color changes so that the analog signal
occupies less bandwidth. This works quite well because the eye is less sensitive to color
changes than it is to light-intensity changes. The detail is preserved in the luma channel.
Extreme loss of detail in the chroma is sometimes apparent when you see a soccer
player wearing a red shirt running across a green soccer field. The chroma signal is