[BC] CBS Color...lived on

[RRSounds@aol.com]

James, at the risk of furthering the list's reputation for 
nit-picking, I would like to add a couple of comments to yours:

In a message dated Wed, 31 May 2006 19:39:14 -0400, James Snyder 
<broadcastlist at dtvexpress.net> writes:
<<
>The CBS system produced 441 lines with full resolution in both luma
>and chroma.  The NTSC compatible color system produces about 330
>lines out of the 525 line scanning standard because of the decimation
>of luma frequencies to fit the 3.58 subcarrier, which produces about
>80 lines of chroma resolution.  For the sake of compatibility we gave
>up a third of the potential luma resolution.
 >>

First, I believe you are confusing horizontal and vertical resolution.

The vertical resolution of NTSC is 525 lines, but some of those lines 
are consumed by sync, leaving about 500 lines of actual, active 
vertical picture information. NTSC's vertical resolution is not 
modified by bandwidth limitations, and is identical for the B/W and 
color standards, i.e., about 500 lines vertical resolution.

According to Donald Fink's "The Forces at Work Behind the NTSC 
Standards" at <www.ntsc-tv.com>, the CBS system was an incompatible 
405 (not 441) vertical line system. I'm not sure how many of those 
405 lines were used for sync, but I think we can safely assume that, 
in addition to being incompatible with existing B/W sets, the CBS 
system had about 20% *less* overall vertical resolution than NTSC.

The "330" you quote is for *horizontal* luminance resolution, which 
is where the first NTSC compromise occurred. Horizontal resolution IS 
bandwidth-dependent. While they aren't really 'lines' but rather the 
maximum number of black-to-white (or vice-versa) transitions per 
horizontal line, 330 'lines' is indeed the typical maximum in the 
luminance channel for an NTSC broadcast transmission.

And therein lies another possible source of confusion: Because 
fully-compliant NTSC resolution can be better (and is, in the studio 
before transmission), the real limitation is indeed the transmission 
medium (over the air and cable), a bandwidth restriction imposed by 
the 6 MHz analog broadcast channel. Before it hits the transmitter, 
NTSC video can actually look pretty damn good.

The horizontal chrominance bandwidth for NTSC is where we really lose 
out (typically **40** lines, 80 at best), and where the CBS system 
was far superior. NTSC color transmission, (kind of like MP3 for 
audio) took advantage of human eye's lesser sensitivity to 
chrominance than luminance. Since the vertical resolution for color 
is not compromised in any way, it was acceptable to most consumers. 
And in the 1950s, what could they compare it to?

Even in SP mode, standard VHS VCRs rarely had a horizontal luminance 
resolution of better than 230 lines; *much* less for chrominance. At 
the other end of the scale, S-VHS and Laserdisks (both analog) can do 
better than 400 lines horizontal luminance and DVDs (pure digital) 
can exhibit resolution in excess of 500 lines, all the while still 
following the NTSC standard. (S-video's claimed capability for 
horizontal chrominance resolution is 120 lines.)

Aside from the occasional green face and horizontal color smearing, 
the thing that really annoys me about NTSC color is 'dot crawl,' 
which Faroujda and others sought to fix, with mixed results.


<<
>...early equipment was primitive compared to the later 
>all-electronic line sequential equipment used by NASA which didn't 
>require any mechanical devices to work properly. ... <snip>...NASA 
>didn't use color wheels or any other physical adaptation, they 
>simply displayed electronically what the color wheel did physically.
 >>


I believe you are wrong here, and that the NASA "Moon" color camera 
was indeed mechanical, with a 'color wheel.'
In an article at <www.hq.nasa.gov/alsj/Shooting-Moonwalks.pdf> Sam 
Russell, then employed by NASA writes:

    "Color wheel? Yes! Within the camera, a wheel with red,
    green and blue filter segments was rotating in front of
    the sensor tube at exactly one-third the field rate, to
    expose the sensor to red, then green, and then blue light
    in successive fields. Here on Earth, a scan converter would
    store these fields on analog disk drives, and then generate
    NTSC video."

Clarifications from those in the know are, of course, appreciated. 
I'm not an expert, I just read a lot!


Kind Regards,
David