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Subj: 24 Frame
Progressive Television Cameras
By Jim Mendrala
Since Hollywood is moving rapidly to 24p production
in HDTV, the need for 24 fr/sec progressive cameras will become
a necessity. Now we all know that you can capture images at
24 times a second, as this is what the film industry has been doing
for the past 75 years or so. Prior to that, Edison, who invented
the motion picture, felt that the best compromise was around 16
to 18 fr/sec. The requirement for sound upped the frame rate
to a fixed 24 fr/sec. Television here in the US doesn't run
film at 24 fr/sec but at 23.98 fr/sec so that it is compatible with
NTSC television. Europe runs the film at 25 fr/sec so that
it is compatible with PAL and SECAM.
However, what about the picture? If you
capture an image with a 30 fr/sec interlaced TV camera, the camera
is in reality shooting at 60 fields per second. Since the
image is discharged completely per field, this results in an exposure
time of 16.7 msec or about 1/60th of a second. The images
played back are very acceptable, but when you slow the frame rate
down and increase the exposure time, motion starts to become blurry.
In order to make
a compromise between blurry motion and avoid "skipping"
or "chatter," a compromise must be reached.
The film world has known for years that a shutter
speed that is too short will give the movie a "skipping"
or "chatter" look to it. We in television sometimes
refer to this as "judder" or "strobing."
The majority of motion picture cameras are equipped
with a revolving disk shutter with an open segment. The open
portion of the disk exposes the film while it is at rest in the
film aperture. The closed portion obscures the light while
the intermittently moving film is being pulled down into position
for the next exposure. 90 percent of all professional motion picture
scenes are captured or photographed with cameras equipped with 170
to 180 degree shutters operating at 24 fr/sec. Exposure time,
expressed in fractions-of-a-second, is determined by the angular
opening of the shutter and the number of frames exposed per second.
The smaller the angular opening and/or the faster the frame rate
the shorter the exposure. Since the film must be moved into
position and registered before the shutter opens by necessity, the
shutter is less than the frame rate.
Reducing the shutter angle results in shorter
exposure and sharper images of moving subjects. However, it
also increases the time interval between exposures and records a
smaller sample of the overall action. Reducing the shutter
angle records a series of sharper images that are more widely spaced
in time. The image displacement between frames on rapidly
moving subject matter is often greater than the eye can accommodate
and results in a so-called "skipping" or "chatter"
The skipping effect can be explained, however,
as follows: a certain displacement of objects takes place on the
film from frame to frame. This displacement when viewed as
it appears on the screen also constitutes a displacement on the
retina of the viewer's eye. The viewing cells on the retina,
however, are not directly adjacent to each other. They are
spaced at approximately 7.14 minutes of arc. Therefore, if
an object viewed on the screen is displaced more than can be sensed
within the above angle on the retina, it causes "skipping"
of viewing cells, which in turn disrupts or "chops" the
continuity of the motion. This effect is dependent on several
factors: screen brightness, focal length of the camera lens, frame
rate, shutter exposure time and viewing angle. Those of us
that can remember the old westerns movies are familiar with the
wagon wheels going in the wrong direction.
The recommended panning speed for a 35 mm camera
running at 24 fr/sec with a 180-degree shutter and a 50 mm lens
is 90 degrees in 23 seconds. If the camera is running at 60
fr/sec with the same lens and same shutter angle, then the panning
speed for a 90-degree pan is reduced to 8 seconds. You can
see how this will impact sports coverage and why many are in favor
of a higher frame rate.
It has been found that to shoot images at a faster
frame rate is better than to cut the shutter angle. This was
done during the 1984 Summer Olympics. ABC-TV modified an HDTV
camera that captured a standard 480 x 360 image at 90 fr/sec, interlaced.
The video was played back at 30 fr/sec, interlaced, for beautiful
sharp slo-mos of the gymnastic teams.
In a video camera, the sensor captures the image.
It is either a CCD device or a tube such as a Saticon, Plumbicon
or a vidicon. That image is discharged completely for the
next exposure. If it isn't, then you will see lag. In
the CCD camera, the image must be shifted into a frame store and
read out line by line and column by column. When the image
is shifted into the frame store, the light is blocked coming from
the lens to not contaminate the pixels as they are shifted into
the frame storage device. This occurs during vertical blanking.
In a film camera running at 24 fr/sec the camera
captures one frame every 1/24th of a second but it takes half of
that time, or about 1/46th of a second, to move the film and position
it before the shutter opens. Therefore, the film gets an exposure
of about 1/50th of a second. In a video camera that acquires
the image in a full 1/24 of a second minus the short vertical blanking
time, the exposure is too long and captures too much motion blur
rendering the image soft.
in degrees = Exposure Time x 360 x fr/sec
Shutter opening in degrees is called the "shutter
angle." For example, If the camera could expose the film
in 1/24th of a second, the shutter angle would be 360 degrees.
However, since the shutter is open only about half the time, the
shutter angle is only 180 degrees.
So what has to be done in a video camera when
the exposure time is more than 20 msec? You guessed it the
camera has to have a shutter to reduce the motion blur that is acquired
by the sensor. But that shutter time cannot be too short or
the image will start to exhibit a judder (chatter) or strobe (skipping).
We can see this a lot in sports broadcasts or
in home camcorders, where the camera shutter time is excessively
short. There is a fine line as to what the tradeoff is in
shutter angle, but a TV camera running at 24p fr/sec or 30p fr/sec
will have to have an electronic shutter to reduce the amount of
motion blur to make the images appear more acceptable on the new,
large, big screens.
In case you are wondering, to photograph a TV
screen running NTSC video, the shutter at 24 fps has to be open
exactly 16.68 msec to record one complete field. This results
in a shutter angle of 144.14 degrees. The movie "City
on Fire" used that shutter angle to photograph the monitors
in the TV station control room. "Meteor" also used
this same shutter angle of 144.14 degrees for the shots of the approaching
meteor on the TV monitor in the mission control room. Since
this was a scope film, the monitor had more than 800 lines of horizontal
resolution and the video came directly off the film chain to take
advantage of the higher bandwidth and resolution of the system.
The "Buffalo Bill Show", which ran on NBC used a shutter
of 180 degrees as the video displayed on the monitors photographed
in that show were running at 23.98 fr/sec as were the movie cameras.
Subj: Some Missing Links
By: Larry Bloomfield
What has been known to many as A-SKY-B (American
Sky Broadcasting) in the Phoenix suburb of Gilbert, Arizona, is
probably the largest multichannel capacity, single point of control
broadcast operation in the world and it will belong to EchoStar
by the time this gets to print? Housed in a very modern structure,
this ultramodern broadcast plant is impressive from both the outside
as well as its capabilities inside. Standing in the midst
of the main operations area, one cannot help but be ah-struck, indeed!
Originally commissioned by the satellite branch
of the Murdock Broadcast Empire, A-SKY-B has been plagued with its
problems. Without having a program so one could distinguish
who was doing what with whom, and when, it's hopefully all in the
past now. The net result is that EchoStar now has a plant
they can be proud of, but can't use! All the links to the
chain aren't in place.
Peter J. Lude, Senior Vice President, Systems
Engineering & Marketing, Broadcast & Professional Group,
at Sony Electronics said that everything Sony was responsible for
is in and working, but because of missing parts, it was not possible
to completely do a proper shakedown. The most significant
of these parts are the compression system, the subscription management
system (SMS) and the conditional access (CA) equipment.
In other "Sky" projects, around the
world, these three areas have been supplied, with no great surprise,
by the Murdock owned NDS company. In checking with NDS's Newport
Beach, California offices, I was told that the equipment was ready
for shipment, but when the musical ownership games began, the orders
were canceled. There's little doubt that EchoStar will have
their own ideas on what kind of equipment will replace the missing
Getting a plant capable of ultimately 500 channels
ready for operation was no easy task for Sony and their clan.
Sony was committed to demonstrate 320 operational channels, 120
of which will be dedicated to near video on demand (NVOD) pay-per-view
(PPV) type programming. In addition to this the plant would
also have the ability to air two dozen live events at the same time
on other channels. No easy task, considering the behind the
scenes program management, with all the "automatic" caching
and recording, plant configuration and other housekeeping chores
required of the software program driving the whole operation.
The hero of the hour was South African born Peter
Emanuel, a very gifted and bright software engineer in the employ
of one of Sony's subcontractors. Emanuel spend many hours
hassling with the traffic and control software both in his San Jose,
CA office and at Gilbert, AZ, trying to make it all come together
and work properly, in a timely fashion. The software is an
adaptation of software designed for smaller operations with lessor
demands. In an eleventh hour end run, Emanuel came through
and saved everyone's skin.
Now it's all
up to EchoStar to access what they've got and gotten themselves
into, put the SMS, CA, etc. in place and turn on the switch at a
plant which will remain the biggest and best for a long time to
Subj: Meeting the Demand
By: Larry Bloomfield
With more than 1,575 full power television stations
making the transition to digital, not to mention all the low power
stations and translators, they will all have to have, at minimum,
three very important additions to their broadcast plants: (1) a
new "digital" transmitter, (2) a very flat transmission
line and (3) a very broadband, flat response antenna system.
The demand this digital television transition makes on the manufacturing
community is being met with various degrees of agility. Most
have had to expand their capabilities and such is the case of a
well know player in the broadcast arena, Andrew Corporation.
Tinley Park, Illinois, will soon see a new 36,000
square foot facility that will house Andrew Corporation's Global
Broadcast Headquarters along with the company's production and research/development
endeavors in the area of transmission line and antenna products.
"We've increased our
manufacturing capability in order to meet the growing demand for
our complete line of broadcast products," said Kinsley Jones,
business unit manager, Andrew broadcast products. "In
the US, the large number of stations transitioning to digital television
means manufacturers must add capacity to meet the demand.
The recent acquisition of Passive Power Products Inc. gives us the
full range of DTV-ready products to provide complete RF systems
to our customers."
engineers are familiar with the list of products made in Tinley
Park by Andrew, such as: the ALP Series antennas for low or medium
power broadcast applications, their HMD Series broadcast antennas
for wireless cable applications, the GUIDELine circular waveguide,
the WIDELine and MACXLine rigid coaxial transmission line for high
power VHF and UHF transmission requirements, along with the connectors
and accessories for HELIAX air dielectric cable.
As part of this expansion project, Andrew Corporation
will be constructing an anechoic chamber to support their R &
D work and for the production tuning of various products.
Despite the present building project in Tinley
Park, IL, Andrew Corporation has no plans to move any of their other
manufacturing efforts to the new facilities. Andrew Corporation's
Orland Park, Illinois will continue to make the Air dielectric HELIAX
cable, TRASAR and PANAR high power VHF and UHF antennas, and the
combines and filters will continue to be made at Andrew Passive
Power in Gray, Maine.
date for the Tinley Park, Illinois facility has been indicated.
For further information
about Andrew Corporation or their products and services, visit their
Web site at http://www.andrew.com
Subj: DFITS Meeting
in Hollywood California
By Jim Mendrala
At the DFITS
(Digital Film Image Transfer Society) meeting held Wednesday, July
28, 1999 the topic of discussion was the recent electronic cinema
presentations of "Star Wars: Episode I" and "The
Tours of Cinesite's
Phillips "Spirit" Datacine Scanner Suite were being conducted
while the E-Cinema discussion was going on.
All that attended the meeting had seen at least
one digital presentation and some had seen all three presentations,
Texas Instruments DLP Cinema, CineComm's Hughes-JVC presentation
and Kodak's film presentation. Generally, the group thought
that the E-Cinema presentations were great. Some said the
images needed more pixels. 1280 was not enough for the ones who
sat up front. Quite a few were able to identify the video
camera sequences. There were not many negative comments, most
comments were positive. Bill Hogan, Sprocket Digital, described
in detail what had been done to get the pictures from that IP to
the screen using the two totally different projection technologies.
A new electronic movie that will start running
July 30th will be Disney's "Tarzan." It will be
a total digital presentation as the CGI files have been converted
to video and placed into a 1920 x 1080 raster using the center 1280
x 1024 pixels. The Texas Instrument's DLP Cinema projector
will use a 1.5x anamorphic lens to unsqueeze the image back to it's
original 1.85:1 aspect ratio. This presentation from beginning
to end will be totally digital. There isn't any analog processing
anywhere in the system.
The digital presentation of the "Tarzan"
movie will shown at three venues. AMC's Media Center north
6 in Burbank, CA. Edwards Irvine Spectrum Complex in Irvine CA.
In addition, at AMC's Pleasure Island multiplex at Disney World
in Orlando, FL.
information visit: http://www.dfits.org
By Larry Bloomfield
PSIP is the part of the data stream in a digital
signal that tells the receiver-decoder what channel to display,
among other things. This is especially true for multicasting.
For example, if you wanted to identify your DTV programming with
your NTSC channel, for whatever reason, the PSIP information can
be edited to say whatever channel or number you tell it.
The reason for bring this up is that there are
some brave stations who have started multicasting. Should
programming or other recorded data be shared from one of them in
the form of rebroadcasts, exchanged tapes, etc., it is possible
it may carry PSIP information. It might be wise to check to
ensure that you are not passing on someone else's PSIP information.
In other words, any station that is re-broadcasting a transport
stream (TS) recording may be sending incorrect PSIP information
if the original source station had PSIP present to begin with.
That is beginning to be the case.
When PSIP is present, the receiver can be smart
enough to ignore the frequency information field since it 'knows'
what frequency the TS actually was received on. This enables
lessor expensive translators in that they will not have to process
the TS. Unfortunately however, if a TS is just retransmitted
without any editing of the PSIP, the source's major-minor channel
number is all the receiver has to display, leading to possible confusion.
It is expected that once all broadcasters get PSIP capability, these
glitches should go away.
Subj: DirecTV's New Relationships
By: Larry Bloomfield
For DirecTV, "June," 1999 was certainly
"Busting Out All Over," as the Rogers and Hammerstine
song title proclaimed. If you have $1.5 billion to invest
in Hughes Electronics, you too could share the spotlight equally
with American Online (AOL), because that's what they anted up.
With all the strategic alliances being formed between cable and
the networks, it only stands to reason that the DTH arena would
also be interested in something similar an effort to remain competitive.
The alliance makes as much sense as any other
broadcaster, terrestrial, cable or satellite, striking a deal with
any of the ISP, be they local or national. Perhaps the local
broadcaster can learn from the big boys. It has and will happen!
But the deal goes much farther than one might notice at first look.
For openers, the market response to DirecTV's
venture into the wonderful world of the Internet, DirecPC, has not
exactly been something that Hughes has to boast about, so far.
With the largest of the Internet Service Providers (ISP) in bed
with them, however, Hughes's position should grow to be much stronger.
It only stands to reason that the alliance should accelerate DirecTV
subscriber growth in this area. It would also appear that
the deal with AOL will help to enhance DirecPC's plans for Spaceway,
Hughes proposed broadband/satellite project. Hughes expects
to transition DirecPC customers to Spaceway, once the service is
available in 2002.
As for AOL, it appears to be a win-win situation.
Don't forget the recent acquisition by AOL of CompuServe.
They too will be part and parcel to all of this. It will expand
AOL's, market place into an area, giving them an avenue for their
new AOL-TV interactive television, and the AOL-Plus, a high-speed
upgrade for users that also will be possible via DSL lines from
regional bells SBC Communications and Bell Atlantic AOL has been
talking about. There is little doubt; the CompuServe subscribers
won't be left out in the cold.
Calls to both Hughes (DirecTV) and America Online
about the joint venture got little more than what the press releases
had to say on the matter. One Hughes spokesperson did say
that they plan to work with AOL in developing new content and interactive
services. Nothing was mentioned about AOL continuing to look
into cable for high-speed data transfers that is nearly 3 times
faster than what current satellite television technology can offer,
which is nearly 40 time faster than a 28.8 kilobit-per-second analog
modem via the conventional telephone system. Although DirecPC
currently provides broadband download speeds up to 14 times faster
than the standard 28.8 kilobits-per-second analog modem via the
conventional phone, it doesn't appear that the current state-of-the-art
technology or bandwidth can compete with what cable has to offer.
The numbers and a bit of good old common "Yankee
horse sense" will tell the most casual observer that they two
giants compliment each other. Jointly, both AOL and DirecTV
have about 24 million subscriptions to premium interactive and entertainment
services worldwide, generating some $6 billion in customer fees.
That's nothing to balk at.
Despite these pro's, one must consider the possible
down side to this. Unlimited AOL service prices out in the
mid $20 range. There is no doubt that this new ISP in the
sky will be considerably more pricey, both initially and recurrently.
Satellite bandwidth is expensive. Another, somewhat obvious
point to consider is this is simplex, or one way through the satellite.
Nothing is mentioned about a back channel that will most likely
be via standard modem connection through the Phone Company.
And finally, in speaking to a couple of DirecPC users, I'm told
that transfer rates slow to no faster than a poor V.90 connection.
So, go figure!
This DirecTV/AOL deal will help implement the
two company's earlier agreement to develop a "combination"
set-top receiver to make DirecTV/AOL TV available to consumers next
year. There will no doubt be a goodly amount of cross marketing
between the two companies to package and extend the reach of both
AOL TV and DirecTV. With this joint venture into the set top
box market, any current subscriber cannot help but wonder if this
means that all the plethora of advertising one has to cope with
every time they sign on to AOL will now manifest itself as one more
bunch of garbage to be deleted for their TV screen.
One can't help but wonder if the DirecTV/AOL
venture will take the same tact of other service providers, like
cell phone where you get equipment in exchange for long term commitments.
Once you mix DTV and the 'Net together in the same box, all kinds
of interesting marketing possibilities come to mind.
As a subscriber to both DirecTV and AOL, I can't
help but wonder, and I'm probably not alone, how this will affect
our standings and if we will realize any financial incentive, when
the ink is dry on this deal to stay, switch or go elsewhere.
Both of these companies are notorious for their promotions to incite
new subscribers, but have offered little to those of us who've been
with them for the duration.
Subj: Video Servers/Disk-Based
Formats To Replace Beta SP / Tape as Primary On-Air Formats
(Ed Note: The
following is our way of saying thanks to SCRI posting this on their
According to SCRI's recent Broadcast / Pro Video
Industry Trends Report ('99-2000), in 1999, Beta SP (33.5%) is the
leading format used for on-air play in '99. Video servers
(15.1%) are beginning to show their significance, moving into 2nd
position, followed by Digital Beta (12.4%).
Video servers are expected to take over as the
leading on-air medium by 2000, with 36% of broadcasters expecting
to be relying on video servers as their primary delivery format
at this time. Another 6.1% expect to use hard disks/ disk
arrays and/or disk recorders, bringing the server/disk-based formats
share up to 42.1%. Betacam SP (13%) is on the decline.
Digital formats have made some inroads here -- Digital Betacam (13%),
DVCPRO (8.3%), Betacam SX (5%), Digital-S (4.4%) and D-5 (2.8%).
This report provides manufacturers with a roadmap
of the shifting Broadcast and Professional Video Marketplace as
we move into the new millennium. The report tracks all the
key technology issues, like DTV, video networking and transport,
video formats, equipment budgets and production activity trends,
incidence of traditional and new video applications like webvideo
and CD-ROM and DVD Production. To view the table of contents
go to: http://www.scri.com/sc_sur.html
ED Note: In the past, Larry Bloomfield has not
had FAX receive capabilities. This has become a problem in
his efforts to keep on the cutting edge of information. Many
we deal with here at the Tech Notes still have not realized the
benefits and speed of e-mail. It has, therefore, become necessary
to retain the services of an on line company who will accept fax
material and deliver it to Larry's e-mail address in a timely fashion.
It is requested that only as a last resort, if you do not have e-mail
capabilities or the document material cannot be sent via e-mail
and you must sent the material via FAX, please use the following
number: (419) 710-1913. Thanks for your understanding and
The Tech Notes are published for broadcast professionals,
and others, who are interested in Electronic Cinema, DTV, etc.,
by Larry Bloomfield and Jim Mendrala. We can be reached by
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