Archived from groups: alt.video.digital-tv (
More info?)
Sal M. Onella wrote:
> "Antwarp" <virihater@large.net> wrote in message
> news:c7o8g601ud3@enews2.newsguy.com...
>
>
> < snip >
>
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>> Spinning disk? As in Nipkow disk? It's last gasp was thought to be
>> during color tv development - almost 60 years ago.
>
> Not quite. The spinning disk is a color wheel for field-sequential
> color. It was CBS Labs' system of choice around 1950. NASA used this
> method for at least some of the color video cameras that went to the
> moon. The image scanning is electronic, so the disk is not modeling
> the Nipkow method.
Yep - the use of colour sequential scanning on the colour Apollo material is
apparent on fast movement - such as when the top of LEM took off to return
to the orbiting Command Module - the bits of material flying off in all
directions split up into R,G and B bits!
In the UK Wireless World ran an article when PAL UHF colour transmissions
started, detailing how to convert a B&W TV to Colour using a colour
sequential disc. It worked by having a PAL decoder that output just Red,
Green then Blue signals on sequential fields to feed the B&W tube (I think -
not frames) which was synced to a motorised disc. The result was a 16.7fps
colour system (albeit with some motion information up to 50fps but with
colour break up!) Pretty much the same system as CBS promoted for display -
though the transmission system was regular PAL (and 2/3 of the colour
information was thrown away)
I'm not an expert on DLP - but AIUI the colour scan rate is at least 3x the
input signal field rate (the motors in higher end single chip units run at
multiple speeds and have 6 segments to allow a higher field rate without the
motor having to spin as fast as a 3 segment - reducing noise) so that no
colour temporal resolution is chucked away. However colour sequential
presentation does introduce artefacts - with some people finding the
"rainbow" artefacts, which become more obvious if you move, quite
objectionable. Of course this is not a function of DLP technology in
itself - you can use 3 DLP chips (just as you can use 3 CRTs or 3 LCDs)
Steve
Steve