SECAM and Congruence (geometry): Difference between pages

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Two sets in '''R'''<sup>''n''</sup> (and especially two shapes in '''R'''<sup>''2''</sup>) are called ''congruent''

SECAM (Sequential Couleur avec Mémoire) is an [[analog television]] system, using [[frequency modulation]] to encode [[chrominance]] information. It is so named because it uses memory to store lines of color information, in order to eliminate the color artifacts found on NTSC systems.

if one can be [[mapping|mapped]] onto the other by a combination of a [[translation]], [[rotation]] and [[reflection]].

Two sets that are not congruent are called ''non-congruent''.

It was developed for the same purpose as [[PAL]], but uses a different (and many would argue inferior) mechanism to do so. R-Y and B-Y information is transmitted in alternate lines, and a video line store is used to combine the signals together. This means that the vertical colour resolution is halved relative to PAL and NTSC.

For instance:

It was introduced in France in 1967, where it is still used; it has also been adopted in many former French colonies, as well as parts of Eastern Europe (Bulgaria, Yugoslavia) and the former Soviet Union. Many have argued that the

primary motivation for the development of SECAM in France was to protect French

television equipment manufacturers and make it more difficult to view non-French programming. Political factors from the [[Cold War]]

have also been attributed to the adoption of

SECAM in Eastern Europe, as its use made it impossible for most Eastern Europeans

to view television which was broadcasted from outside the [[Iron curtain]] which

were mostly using [[PAL]].

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There are three varieties of SECAM. French SECAM is used in France and its

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former colonies; MESECAM is used in the Middle East and ; D-SECAM is used in the [[Commonwealth of Independent States]] and Eastern Europe.

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The first two figures are congruent to each other. The third is a different size, and so is [[similar]] but not congruent to the others; the fourth is different altogether. Note that congruences alter some properties, such as location and orientation, but leave others unchanged, like [[distance|distances]] and [[angle|angles]]. The latter sort of properties are called [[invariants]] and studying them is the essence of geometry.

American engineers have been known to claim that SECAM stood for "System Essentially Contrary to the American Method".

Unlike PAL or NTSC, analog SECAM television could not easily be edited in its native form: instead, post-production was done in PAL, and the result then trans-coded into SECAM at the point of transmission.