[opendtv] Re: Digital vs. Analog Quality

  • From: "Dale Kelly" <dalekelly@xxxxxxxxxxx>
  • To: <opendtv@xxxxxxxxxxxxx>
  • Date: Wed, 09 Jul 2008 16:26:47 -0700

Craig wrote:
> provide 120 lines of color resolution, which is the spec
> cited for NTSC (but not for all colors because of the 0.5 MHz
> bandpass for Q). It may have had a bit more resolution internally,
> but the outputs are base band are limited by the NTSC specification.

As a practical matter: consumer grade NTSC TV sets limit both color carriers
to 0.5 MHz bandwidth. This feature, while degrading color performance, saved
the cost of adding a second post demodulator delay line to compensate for
unequal filter delays. This design was possibly changed in recent analog
tuners but I don't know if that is the case.....

My point is: any composite color signal applied to an analog NTSC set
through the tuner or composite video connector will be degraded to 0.5 MHz
bandwidth.

> -----Original Message-----
> From: opendtv-bounce@xxxxxxxxxxxxx
> [mailto:opendtv-bounce@xxxxxxxxxxxxx]On Behalf Of Craig Birkmaier
> Sent: Wednesday, July 09, 2008 5:41 AM
> To: opendtv@xxxxxxxxxxxxx
> Subject: [opendtv] Re: Digital vs. Analog Quality
>
>
> At 1:56 PM -0400 7/8/08, Cliff Benham wrote:
> >Craig Birkmaier wrote:
> >...baseband NTSC could be
> >>far better than transmitted NTSC. True for the luminance, but not
> >>true for the color difference signals.
> >
> >I think there are several examples of wideband color difference
> >signals being used in NTSC. As far back as the late 1970s, baseband
> >NTSC has been capable of 120 lines of chroma resolution. This
> >includes Laserdisk and later in the early 1980s, analog component
> >recording formats, notably Betacam.
>
> Neither of these are valid examples.
>
> Laserdisc is an analog format with extended frequency response for
> the luminance component - in the range of 4.9 to 5.4 MHz. Laserdis
> uses the same subcarrier based system for the carriage of the color
> components. I found one reference that suggests that the internal
> recorded bandwidth for the subcarrier signal is 1.5 MHz, qwhich could
> allow for improved color recording in the Q channel. The system is
> said to provide 120 lines of color resolution, which is the spec
> cited for NTSC (but not for all colors because of the 0.5 MHz
> bandpass for Q). It may have had a bit more resolution internally,
> but the outputs are baseband are limited by the NTSC specification.
>
> see: http://home.online.no/~espen-b/ld/
>
>
> Betacam is an analog component format with R-Y and B-Y sampled at
> half the bandwidth for the luminance channel - i.e. 4:2:2. It
> provided a HUGE improvement over composite video recording formats
> for several reasons:
>
> 1. NO mixing of the color and luma components as with
> subcarrier-based systems. The color components are completely
> recoverable without the problems of separating luma and subcarrier
> via comb filtering techniques.
>
> 2. The R-Y and B-Y color difference signals are sampled at 1/2 the
> bandwidth of the luminance signal This is more than double the  color
> information  in NTSC (about 8x the bandwidth of the NTSC Q component.
>
> Alas, when a Betacam machine encodes the analog component signals
> into a baseband NTSC output, the color signals are bandpass limited
> to NTSC specs. The good news is that the color difference signals are
> "oversampled" relative to NTSC and can be recovered accurately - thus
> the composite output is MUCH cleaner than for any heterodyne color
> recording system.
>
> The BREAKTHRU with Betacam was the availability of analog component
> outputs, which could be used to feed an analog component video mixer
> that did not suffer from the limitations of composite video
> processing. I am reasonably knowledgeable about this, having built a
> prototype analog component mixer for Sony for the 1983 NAB. This was
> followed by an RGB 1600 series mixer, which both Sony and Grass
> Valley used at NAB in 1984 - This was the year we had two Eiodophor
> projectors displaying analog component video on huge screens above
> the NAB booth. It was also the year that we introduce the Model 100.
> After building the 1600 series mixer using RGB processing we realized
> that these were the wrong components to process - it was difficult to
> get three mixers to track in a perfectly  linear fashion - any
> non-linearities showed up as shifts in the luminance level. So when
> we built the first commercial analog component switcher - the Model
> 100 CV - we change the components to Y, R-Y, B-Y. This allowed for
> excellent linearity in the luminance component - any tracking errors
> were shifted to the color difference components and were far less
> noticeable.
>
> I might add that there were a number of improved NTSC encoders and
> NTSC enhancements developed in the same time frame as Betacam.
> Central Dynamics developed an excellent NTSC encoder that carefully
> limited the energy from the subcarrier in three dimensional space so
> that it did not overlap with the energy from the luminance signal.
> This allowed decoders to produce improved color components largely
> free from the luma/cross color issues in most NTSC decoders.
>
> And Yve Farudja came up with several excellent NTSC enhancements with
> significantly improved performance, but the world was more interested
> in moving to HD.
>
> >[Betacam]"provides a crisp, true broadcast quality product with 300
> >lines of horizontal luma resolution, and 120 lines chroma resolution
> >(versus ~30 for Betamax/VHS)."
> >http://en.wikipedia.org/wiki/Betacam
>
> Luma - 300 lines, which is better than the 240 line (typical) from NTSC
>
> Chroma- 120 lines - this is the same as NTSC, but is misleading, as
> only certain colors actually have this resolution. Any color based on
> the ! component has far less resolution
>
> Betamax/VHS - really poor color performance due to heterodyne color
> recording - FAR LESS color information and far more color distortion
> than a clean NTSC baseband signal.
>
> Regards
> Craig
>
> >
> >
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