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Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc. |
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1st Apr 2010, 3:39 pm | #21 |
Retired Dormant Member
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Re: "SECAM has 819 lines"
That rings a bell. I believe the problem is that if a VCR or a set-top box uses a character generator to insert text on top of SECAM-encoded video, it causes horizontal lines to the right of the inserted text. I remember seeing an example of this. This must have given the French a strong incentive to develop the RGB-based Peritel connection, aka SCART.
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1st Apr 2010, 4:14 pm | #22 |
Rest in Peace
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Re: "SECAM has 819 lines"
So we can thank the French for giving us, albeit in a roundabout way, decent pictures without the coding footprint by forcing manufacturers to produce component video from AV accessories. Good on yer.
Cheers Brian |
1st Apr 2010, 4:36 pm | #23 |
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Re: "SECAM has 819 lines"
I think the French also led the way with component working in studios too. For much the same reasons. You can't fade or mix SECAM without doing horrible things to the picture quality and the only other alternative was to do all the studio stuff in PAL, then transcode to SECAM for transmission.
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2nd Apr 2010, 3:53 am | #24 | |
Nonode
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Location: Papamoa Beach, Bay of Plenty, New Zealand
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Re: "SECAM has 819 lines"
Quote:
The SECAM system itself has also been described as a product of national pride. Perhaps that is a little unfair, as its origin seems to have had a reasonable technical basis at the time. On the other hand, the persistence with the SECAM system once PAL was developed, but before any regular French colour broadcasting commenced, might have had something to do with national pride. None of the literature to which I have easy access makes any mention of an 819-line version of SECAM. In fact Jackson and Townsend state: “The SECAM system, invented by Henri de France, was developed in Europe for 625/50 scanning, like PAL, as a means of overcoming the susceptibility of the NTSC system to differential phase distortion.” And then: “Early versions of SECAM used amplitude modulation in common with PAL and NTSC, but this proved unsatisfactory.” Evidently the original SECAM reference, which I have not seen, is “Le système de télévision en couleurs sequential simultané”, by H. de France, in “L’Onde Electricité”, Volume 38, 1958. This would probably answer a lot of questions, including what colour work was done with 819 lines. In looking for SECAM 819 line references, I also came across some other comments by Carnt and Townsend (Volume 2, 1969) in respect of French dual-standard colour receiver practice. On IF bandwidth, it is stated: “Cheaper receivers use the same narrow-band I.F. for both standards, but the better models use a 9 MHz I.F. with a narrow-band filter after the U.H.F. tuner.” I seem to recall reading elsewhere that 9 MHz was about as good as it got for monochrome 819-line receivers. In the same section, C&T also comment: “Most colour tubes use dot structures which were originally designed for minimum moiré patterns on 525-line transmissions, but operation on [monochrome] 819 lines is normally acceptable unless there is a considerable amount of high-video frequency detail in the picture. Moiré patterns are more noticeable on 625-line transmissions”. One is left to infer that shadow-mask tubes optimized for 819 lines might not have existed. As a sidebar question, were later colour tubes, such as the Mullard 20AX series, optimized for 625-lines? Cheers, |
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3rd Apr 2010, 3:45 am | #25 |
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Re: "SECAM has 819 lines"
On this page, about halfway down, is a picture of what SECAM looks like with inlaid text:
http://www.pembers.freeserve.co.uk/W...Standards.html |