Editing Transform coding (section)

==Colour television==
{{Further|YIQ}}

=== NTSC ===
One of the most successful transform encoding system is typically not referred to as such—the example being [[NTSC]] color [[television]]. After an extensive series of studies in the 1950s, [[Alda Bedford]] showed that the human eye has high resolution only for black and white, somewhat less for "mid-range" colors like yellows and greens, and much less for colors on the end of the spectrum, reds and blues.

Using this knowledge allowed [[RCA]] to develop a system in which they discarded most of the blue signal after it comes from the camera, keeping most of the green and only some of the red; this is [[chroma subsampling]] in the [[YIQ]] [[color space]].

The result is a signal with considerably less content, one that would fit within existing 6&nbsp;MHz black-and-white signals as a phase modulated differential signal. The average TV displays the equivalent of 350 pixels on a line, but the TV signal contains enough information for only about 50 pixels of blue and perhaps 150 of red. This is not apparent to the viewer in most cases, as the eye makes little use of the "missing" information anyway.

=== PAL and SECAM ===
The PAL and SECAM systems use nearly identical or very similar methods to transmit colour. In any case both systems are subsampled.