[BC] CBS Color...lived on

[Brian Urban]

And color wheels are still with us.  Some DLP TV's and DLP projectors use
color wheels with amazing results.  Unless your DLP equipment specifically
says that it contains 3 micromirror devices, then it almost certainly has a
color wheel.


On 5/31/06 6:39 PM, "James Snyder" <broadcastlist at dtvexpress.net> wrote:

>>> Kevin Tekel:
>>> The only difference between IBOC and the CBS spinning-disc
>>>  color TV system is that the CBS system actually worked.
>> ____________
>> 
>> Well, it took no more r-f bandwidth than monochrome TV, so it was better
>> than IBOC in that respect.  But it still had serious problems, such as:
>> 
>> 1) Incompatibility with existing B&W TV sets
> 
> Yes and no.  Most TV sets from that time could be modified to receive
> the broadcasts.  The adaptors could be built for about $50 (which was
> not a small amount of money for that era), but they could be built
> and they generally worked.
> 
> The one saw from that era was that one could put a color wheel in
> front of a B+W tube modified for 441 line reproduction and get decent
> color.  The mod would work, but not very well.  That doesn't mean B+W
> sets couldn't have been modified to get the color system in B+W
> perfectly fine.
> 
> 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.
> 
>> 2) Severe flicker on highly saturated primary colors in the scene
> 
> This was a function of the display device.  If the display device was
> designed & implemented correctly, there was no flicker in highly
> color saturated portions of the picture.
> 
>> 3) Poor color registration for moving images (eg, a pitched baseball could
>> morph through the RGB color sequence repeatedly as it traveled across the
>> screen)
> 
> Only if the equipment was not properly set up.  That 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.  If the equipment was properly set up, color wheel
> color could be perfectly registered.
> 
> It is important to note that the 'color wheel' portion of this
> standard was simply an early design of what later would be an
> electronic process called 'line sequential color'.  That very process
> survived nearly to the end of the NTSC era as the primary
> transmission standard for all video for all space activities at NASA
> until around 2001 when it was finally replaced by HD.  NASA didn't
> use color wheels or any other physical adaptation, they simply
> displayed electronically what the color wheel did physically.  NASA
> used line sequential color because it was much more robust in the
> hostile transmission environments of space than the subcarrier &
> phase sensitive NTSC.
> 
>> 
>> NTSC eliminated all three of the above problems, and also stayed within the
>> r-f channel bandwidth.
>> 
>> Yes, NTSC is affected by the differential gain and phase of its video and
>> r-f  distribution paths.  So is monochrome -- it's just harder to see the
>> effects.  NTSC became very stable once the distribution paths had decent
>> transmission characteristics (starting about 35 years ago).
>> 
>> RF
> 
> If you consider "distribution paths had decent transmission
> characteristics" to be cable TV, then you are correct.  NTSC
> over-the-air has NEVER had decent transmission characteristics
> because of multipath.  If you use a current consumer NTSC set today
> with rabbit ears in an urban area with heavy multipath you will get
> the same type of picture our parents saw in the 1950s and you will
> know why NTSC was dubbed "Never Twice the Same Color".
> 
> The CBS system did indeed work.  It survived past the turn of the
> millenium.  NTSC compatible color was a decision based on both
> technical and political decisions.  Whether that decision was correct
> is for each of us to decide on our own.  Each system had its own
> positives and negatives.
> 
> James
> 
> 
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-- 
Brian Urban
KUT Radio
University of Texas at Austin
Office 512-471-1085
Cell 512-940-4757