[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

HDTV: CBS and 16mm

The following is an editorial from Christopher Bacon of DuArt
Film & Video, NYC, NY USA.  He can be reached at ka2iqb at aol.com.

Just got around to reading last month's SMPTE Journal, and saw
something that made me wonder if it isn't time the digital TV industry
stopped in for a reality check.  The article that got me to wondering
is on the CBS High Definition Film Tests, and it describes the
research and testing CBS did before they came out with their
pronouncement earlier this year that neither regular nor super 16mm
film are suitable for broadcasting under the Advanced Television

First off, one has to be concerned about the inherent fallacy of the
"more is better" school of thought.  By itself, more lines of
resolution does not make one picture or transmission system better
than another.  More horsepower doesn't automatically make one car
handle better than another one, nor did television sets with more
tubes (remember those?) necessarily work better than those with fewer.
Beyond a certain minimum resolution, which has more to do with the
size of your viewing screen and the distance you sit from it than
anything else, factors such as proper contrast, accurate color
rendition, and freedom from motion artifacts are probably just as
important as resolution, if not more so.  If resolution really was the
only thing that mattered, we'd do a lot better if we went back to
monochrome TV, since the need to sense and display three simultaneous
color images instead of one reduces the maximum resolution possible in
any practical video system that operates in real time.

The article is full of impressive math and graphs to prove what many
of us suspected all along: namely that regular and super 16mm film do
not have as much resolution as 35mm film.  This shouldn't come as any
surprise, since a 16mm film frame has only 25% of the silver grains of
a 35mm frame, and fewer of them are used in a regular 16mm frame than
super.  What did come as a surprise is that the super 16mm resolution
was not proportionally less than that of 35mm; the difference was only
about 30%.

One part of the CBS methadology was particularly unfortunate, and that
was the choice of a Sony HD telecine for the tests.  The reason given
for this was because it was felt that no other telecines of
sufficiently high resolution were available at the time.  It is
unfortunate because there were only two Sony telecines in existence
then, both under lock and key at Sony Pictures in Culver City.
Probably a few other TIG participants have encountered telecines that
seem to produce identical results on 35mm, but found one particular
machine that doesn't do so well on 16mm as the others.  The smaller
the frame size, the more your mileage may vary, and since its specs
have not been published so far as I know, we have no way of knowing
how a Sony telecine would stack up against a better-known benchmark
such as the Philips Spirit.

Maybe there is a good reason for that.  The test results indicate that
35mm film, as scanned on the Sony HD telecine, does not have quite as
much resolution as HDTV.  But the Sony HD telecine uses the same type
of CCD sensor block as a Sony HD video camera!  Since the film image
has to pass through at least two sets of lenses (one on the film
camera and then whatever they use in the telecine), while the video
image only has to pass through one lens on the video camera, the deck
is stacked!  Measured this way, no film on earth will ever appear to
have as much resolution as HD video.  Those of us who have some
familiarity with film scanners know that it is common to scan 35mm
film frames to resolutions several times that of HDTV; 16mm film
scanning is not so common but it can actually yeild results comparable
to HDTV resolutions.  What they have really proved is that the Sony HD
telecine is not so HD after all.  Yes Virgina, there really is a
reason why telecines like the Philips Spirit and the Cintel C-Reality
scan at higher resolutions and then interpolate down to HDTV.

But my biggest beef is with the conclusion of the article in which the
author states, based on the previously mentioned testing, that CBS has
determined that 16mm film is unacceptable for ATV.  In the fifth
version of their "Final Order and Report," the FCC mandated that
digital TV broadcasting will become the law of the land in the year
2006, unless more than 5% of us are still glued to our old analog TV
sets.  What does the FCC say about the definition of the ATV signal?
Only that it has to be at least comparable in resolution to NTSC!  In
other words, you could take any old analog NTSC tape machine, plug it
into a MPEG encoder and transmit the resulting digital bit stream, and
you have just complied with everything the FCC has to say about the
matter.  If 16mm film is good enough for today's programming, it will
be good enough for a significant part of tomorrow's as well, at least
until there is a sufficient number of truly high definition TV sets
and broadcasters in operation to make the jump to 35mm worthwhile.

That day may be further off than one might expect, Grand Alliance and
CBS hoopla notwithstanding.  In order to fit their high definition
1125-line picture into the ATV bitstream, CBS is going to have to
compress it on the order of 60:1.  So far, nobody except John
Watkinson has pointed out that when people tell you how good highly
compressed video looks, they usually started out with plain old
composite analog or 601 component digital.  Both are comparatively
wasteful in their use of bandwidth and have lots of room for
compression.  But that becomes less and less true as resolution is
increased and more information is packed in.  Compressing an HDTV
signal into 1/60th of its original "space" without losing the ability
to restore it to a reasonable facsimile of its former appearance is an
entirely different challenge than squashing NTSC.  CBS' HDTV may end
up looking so much like everybody elses' regular definition on our
"competitively priced" digital television receivers that we won't be
able to tell the difference.  But we won't know that until somebody
gets busy and invents a competitively priced digital TV receiver!

Christopher Bacon

mailinglist digest available
TIG subscriber count is 842 on Tue Aug 12 13:36:06 PDT 1997
the Telecine Internet Group  <http://www.alegria.com/telecinehome.html>