We are crossing a dividing line in the technical business
of television and post production. The line is a sharp separation
between what we've known as television and what will become
of it. Producers ask about the future value of production
material as they realize the images they create are mortal
in the face of technological change. The question of how to
prepare production material for future generations is an excellent
one which strikes at the very heart of what the Digital Television
future is all about.
Phrases like "future-proofing" come into being,
indicating an uncertain outcome of today's efforts and the
desire to use the produced material in a future application.
Produced material is correctly considered a valuable asset
that must be protected. Super16mm and 35mm film formats as
well as High Definition Television images come to mind as
being future-proof. The produced material needs to be used
in today's broadcast and distribution channels as well as
the Digital Television standard in the near future and any
future application that may come along. The producer must
decide on the potential future value of the material before
proceeding on a production path.
The answer to future-proofing material is not a simple one.
We will discuss the different broadcast video standards and
explain some of the issues involved with each. We will address
some current assumptions about film and video quality and
will cover how they relate to the coming Digital Television
standards. We will also discuss how the production standards
chosen affect the immediate delivery and long term shelf life
of the product.
The DTV (Digital Television) and ATV (Advanced Television)
terms are commonly used interchangeably, but they are distinctly
separate items. We'll decipher how video and film formats
relate to future-proofing but first lets talk about the DTV
Digital Television (DTV) is scheduled to replace all existing
terrestrial analog NTSC television transmissions in the U.S.
by the year 2006. This doesn't necessarily affect home video
formats, direct satellite transmission or cable television
but the range of services and potential improvement in image
quality will probably drive those industries as well. Several
simultaneous Standard Definition Television (SDTV) image streams
or a single High Definition Television (HDTV) image will make
up the television programming broadcasts. SDTV is considered
roughly the same quality level as today's television broadcasts
and HDTV relates to a number of higher definition video standards.
In any case, a television image in SDTV or HDTV will be transmitted
in 16:9 aspect ratio. Both of these broad television formats
are considered to be "ATV".
Advanced Television Standards:
In fact, there are 18 different television standards that
may be broadcast under the name "Advanced Television".
This may seem like a lot of different standards but the ability
to tailor a digital signal to a task specific function could
lead to many more "standards". The ATSC has constrained
the list of possibilities to only 18.
"Table 3" describing ATV television standards.
Part of the ATSC "A/53"
You may be able to count more or less of them depending on
how deep you get on permutations (and we will resist describing
all of them) but it seems there will be only a few standards
in general use. The standards are named with the number of
scan lines and one of two scanning types; interlaced or progressive.
A "480i" standard means the television screen contains
480 usable scan lines with interlaced scanning, roughly the
equivalent of our current NTSC broadcast standard. Horizontally,
there are 704 active picture elements (pixels) on each line
for 16:9 images. The "1080i" standard has 1080 displayable
lines and 1920 pixels across the screen. The "i"
with these numbers stands for "interlace" which
describes a television frame that is broken into two "fields",
transmitted sequentially and reassembled as a complete frame
at the home receiver. This is the principle of current NTSC
television and will be continued into the DTV world.
The antonym of interlace is "progressive" where
the entire frame is transmitted as one element. Using progressive
scanning dramatically increases the apparent resolution of
an image but has other penalties in bandwidth requirements
and receiver manufacturing costs. There are heated arguments
over which scanning format to choose for broadcast. Each network
and service provider faced with this decision believe they
have the right answer. As conventional wisdom changes like
the wind, other scanning formats will rise and fall in popularity
as technology progresses. Fortunately, the receiver manufacturers
belonging to the Consumer Electronics Manufacturer's Association
(CEMA) will build DTV receivers that will decode and display
all 18 broadcast standards.
Digital Television Services:
The DTV transmission is a digital broadcast service that is
not necessarily an exclusive television programming channel
as we know it. A single DTV channel may include a variety
of data services sharing the channel space. The broadcaster's
selection of a pixel count and scan type affects the picture
quality reaching the home and the amount of broadcast real
estate needed to get it there. They have the ability to sell
data services over the same channel shared by television images.
The issue of picture quality boils down to the digital data
rates reserved for the television image.
This thinking is certainly on the minds of many broadcasters
as they work out the financial models in their DTV future.
It is possible to "bit starve" the television image
in favor of data payload on the DTV channel thus trading image
quality to make room for other paying services. It is also
possible to increase the quality of the television image beyond
the intended "Table 3" constraints. By using some
proposed data tricks, one network has spoken of broadcasting
sporting events at 90 frames per second at HDTV resolution.
Time and funding will tell if that noble effort will succeed.
The earliest over the air DTV broadcasts will simply be standard
definition television connected to a DTV encoder carrying
existing programming. These broadcasts will be the "480i"
variety. Broadcasters will gradually begin integrating a library
of programming intended for future DTV transmission. First,
16:9 aspect programming with standard resolution is the easiest
thing to accomplish. In the future, higher resolution images
will become more commonplace as the older programs and production
equipment are retired.
The production standard used is not necessarily the same
as the broadcast standard. Of primary concern to producers
is the quality of the original material and it's future value.
Broadcasters will be converting images from their native production
format to fit into their broadcast chain. Regardless of the
original image quality (pixel count), the common denominator
in all produced material will be the image aspect ratio.
The current NTSC broadcasts are in 4:3 aspect ratio. This
means that no matter what the screen size is, the image will
measure 4 units wide and 3 units tall. The primary feature
of the ATV formats is a 16:9 picture aspect ratio, which comes
out to be about 20% wider than a 4:3 image of equal height.
Think of a 4:3 aspect ratio as 12:9 when comparing it to 16:9.
Independent of the aspect ratio is the number of scan lines
available on the screen and the number of pixels available
across the width of the screen. The higher the line and pixel
count, the better the potential resolution of the image.
One of the available realities in the ATV world is the need
to incorporate images from current tape libraries. The largest
change for ATV and biggest hurdle to using existing material
is the issue of image aspect ratio. Current video libraries
are all 4:3 aspect ratio and must be converted to fit in a
16:9 world, whether it is HDTV or SDTV. Essentially, all available
4:3 aspect program material has become obsolete. The producer
must decide to either blow up the picture so the original
image sides fill the screen, or allow black side panels on
the 16:9 screen thus keeping the original aspect ratio of
the source image.
The penalty for blowing up the picture is that the top and/or
bottom of the screen will be removed creating a framing problem.
Things normally in the frame may get cut off, or a medium
shot of a person's face becomes a close-up, each changing
the meaning of the image. In addition to the framing problems,
a blowup from a video original degrades the image quality
with visible artifacts. The producer must make compromises
when reframing each scene during the blowup process.
A producer with film elements available, especially widescreen
film, will have the advantage of re-transferring the image
elements and reassembling an ATV compatible product, possibly
reusing the entire audio track. Film shot in 4:3 ratio will
present the same difficulty while deciding where to reframe
the image, but degradations caused by refaming are quite minimal
when done at the telecine transfer step compared to a similar
action using video as the source. Standard definition video
material finished in 16:9 format may be applied directly as
an SDTV product.
Major manufacturers of professional video camera equipment
such as Sony, Panasonic, Ikegami, Philips and others offer
standard resolution NTSC cameras capable of switching between
the current 4:3 aspect and the 16:9 widescreen ATV aspect.
These cameras will allow producers to create video images
in the correct aspect ratio for ATV product, making it easier
to reversion video originated material for future broadcast.
The DTV standard does not define the image resolution required
for broadcast of an ATV image allowing both standard and high
resolution images. The producer should consider the alternatives
presented with the various film and video formats when thinking
of immediate, short term program delivery and future-proofing
The number of scanning lines available on the video picture
become the limiting factor for vertical resolution. More scan
lines in the television system generally translate to higher
vertical resolution. The issue of interlaced scan versus progressive
scan also comes into play when judging picture quality. A
progressive scan picture with only 720 scan lines ("720p")
has nearly the same apparent vertical resolution as 1080 lines
with interlaced scanning ("1080i"). The interlaced
scan method is a form of compression that degrades the picture
The current NTSC analog television scanning system is nearly
identical to the 480i ATV standard. With the same number of
scan lines delivered to the home as 480p (progressive), the
home viewer will perceive a much higher resolution image.
If television programming is created in a progressive scan
standard and delivered to the home in that manner, many of
the artifacts attributed to interlace will disappear.
The expense of manufacturing a large tube-type progressive
scan display system is high compared to interlaced displays.
It is more likely that the home receiver will have an interlaced
display and the progressive scan material will be converted
to interlace at the home receiver. Film is well suited to
a progressive scan delivery system. Hopefully, the technical
and economic hurdles will be overcome so we may actually see
it in the home.
Large screen flat panel displays are coming to market that
will allow a progressive scan image to be displayed correctly.
An image that was created as an interlaced product will carry
the artifacts of interlacing to any progressive scan display.
You can successfully make an interlaced image from a progressive
image but the reverse is not true.
Image Quality Considerations:
Video cameras have gotten very good in the areas of resolution,
dynamic range, sensitivity and noise. Film stocks have steadily
improved over time as well. We must consider these areas when
talking about picture quality in any format.
The subject of image resolution, or sharpness, will be the
real key to future-proofing. Please forgive me as I tech-out
for a moment here. The measurement of horizontal resolution
in an image is the maximum number of black and white vertical
bars that can be visually resolved within the horizontal dimension
equal to the picture height. In other words, no matter what
the picture size or aspect ratio is, you carve out a square
on the screen (where width equals height) and count how many
black and white vertical bars you can cram into that area
and still see them. This is true for film or video and is
expressed as "TVL/PH", or "TV Lines per Picture
Height". The vertical bars are considered vertical "lines"
which are not to be confused with the fixed number of active
scan lines available on the television screen.
The resolution measurement for a camera involves shooting
a test chart with a series of patches containing measured
vertical black and white bars of different packing densities.
To measure resolution of a video camera, a video waveform
monitor will directly display the ability to resolve each
vertical line in the patches. For film, a microdensitometer,
essentially a microscope with a light meter, is used to examine
the image of the black and white bar patches and determine
how well the film can separate them. With each test patch
that has bars closer together, the cameras have a harder time
resolving the individual bars and tend to progressively blur
them together until they turn a flat gray at the extreme upper
limit of resolving power.
Example of resolution test chart
Measuring how much the black and white bars blend together
is expressed as a percentage of what they were originally,
namely 100% black and 100% white. A 100% response indicates
that nothing was lost in the camera. It's possible to have
a measurement of over 100% after gamma and aperture correction,
but we'll discard that discussion for now. An 80% response
on a higher resolution patch is considered very good, showing
only mild degradation. Once you get a high enough packing
density of black and white bars and the residual falls into
the 20% range, you can start to write off the existence of
any significant resolution elements.
A test like this will show that Super16mm film can resolve
fewer vertical lines than some current standard resolution
video cameras. A present day NTSC video camera can resolve
upwards of 750 vertical lines whereas Super16mm film has lost
half of its resolution powers at around 500 lines. These numbers
represent what is available in the camera and does not take
into account what happens to the signal when processed further
in a video system.
Once either of these images are converted to a digital video
recording at 4:3 (standard television) aspect ratio, the resolution
is limited to 567 TVL/PH on a D2 machine and 535 TVL/PH on
a D1 or Digital Betacam machine. The limits occur due to the
available pixel count per line of the digital television system
If a 4:3 video image is stretched horizontally about 20%
to a 16:9 aspect ratio, whether film or video originated,
the horizontal resolution of a D1 or Digital Betacam image
is reduced to 402 TVL/PH. There will be fewer pixels available
inside your square resolution test area because they've been
pulled horizontally to make the screen wider. Even so, the
video camera, which started with more resolution, has a measurable
sharpness advantage over Super16mm film. Based on this, a
high quality standard definition video camera will have a
measurable resolution advantage over Super16mm film in the
Kodak has converted the measurement of film granularity to
the equivalent of video noise. They calculated that Kodak
EXR5254 film in a Super35mm format, a size used for 16:9 production,
has a 50db signal to noise ratio. Signal to noise in television
is a measurement of how much the picture content overpowers
background noise. A number of 50db means that the noise or
grain pattern is .01% of the picture content. Every increment
of 10db is a multiplication factor of 10, so a 60db ratio
is one-tenth the noise of 50db and 40db is ten times the noise
of 50db. A higher number is better. The Sony HDC-500 HDTV
video camera measures at a 54db signal to noise ratio, slightly
better than the Super35mm film stock. Comparing that to Super16mm
with only 42db and 16mm at 40db, the Super16mm and 16mm film
doesn't compare favorably. By these tests, Super16mm film
has more than ten times the noise of a present day HDTV camera.
Film is acknowledged to have a minimum dynamic range of about
8 or 9 stops. That is the lighting difference between the
brightest and darkest object in a scene without overexposing
the image and without losing detail to noise or film grain.
Jeff Cree, Sony's guru on video cameras, demonstrated how
a Sony DVW-700 video camera can make a remarkable picture
on a table-top scene with 11 stops difference between lightest
and darkest objects. A properly exposed video camera, without
any clipped elements in the picture, can reasonably be expected
to approach the exposure quality of a film originated image.
Film is no doubt the most flexible format for working in varying
lighting conditions. The exposure index of a video camera
cannot be adjusted like a film camera and extremely sensitive
film stocks can make excellent exposures with candle light.
There is no such thing as "fast" video tape. However,
some video cameras have signal to noise ratios in the 60 to
65db area which allow for additional video "gain"
to be added without dragging up the noise in the blacks. With
these cameras, reasonably good pictures can be made in extremely
low light situations that will rival most standard film stocks.
Standard Definition Television:
The current component digital standard, considered the top
of the heap today, is ironically the lowest acceptable image
quality in the realm of ATV. An official CBS Engineering document
written by Henry Mahler concluded that the lowest quality
image available in our current television standard is a component
digital recording at 16:9 aspect ratio. It was rated lower
than even composite digital (D2) images in his report. The
16:9 SDTV images we can make today will match the quality
of SDTV transmissions on a DTV channel and can be included
in a product intended for HDTV distribution if necessary.
High Definition Television:
The term "High Definition Television" is considered
anything that is better than what we get today. Any scan line
count greater than 480 is generally considered "High
Definition". Even 480 lines transmitted as progressive
scan is considered a "High Definition" image. The
top of the heap would be the 1080 line HDTV standard which
several broadcasters have elected to support.
The 1080 HDTV standard will point out some of the inherent
shortcomings of Super16mm film. Joe Flaherty, Senior Vice
President of CBS, gave a speech in 1997 where he spoke of
his "concern about the long term asset value of Super16mm
material as HDTV product because of Super16mm's low performance".
He also showed several objective tests that compared the various
film and video formats with compelling results. For example,
resolving an image that demands 600 TVL/PH showed that an
HDTV video camera can attain an 80% response, 35mm film has
a 73% response, Super16mm has a 36% response and regular 16mm
film only has a 23% response. Looking at the visual comparison
of an HDTV camera and 35mm film transfer to HDTV shows little
difference between them. Looking at Super16mm is a stark contrast
to the 35mm film and HDTV video camera. Mr. Flaherty concluded
that Super16mm film is not acceptable if the final destination
is intended to be an HDTV standard, and therefore could not
be considered a future-proof imaging format.
To be fair, the tests performed by CBS were met by the film
community with howls of disapproval. Accusations were made
about creating results born of vested interest against Super16mm
film. It has essentially brought on a minor war between several
interested parties. We've seen some very good looking Super16mm
film and can hardly complain about the quality or apologize
for the lack of resolution. However, the material shown by
Mr. Flaherty was presented in a scientific, factual manner
without an overt bias to any format. In fact, care was taken
not to treat any format more favorably than another. For instance,
a telecine colorist would normally crank in almost twice the
noise reduction and image enhancement into a Super16mm film
transfer than a 35mm film. This correction was apparently
not done in these tests. Handling the Super16mm in the same
way as the 35mm simply pointed out some differences between
It has been suggested that an even more objective test would
have been to show projected film against the telecine transfer
to prove or disprove the telecine's ability to handle Super16mm
film. In any case, it is generally acknowledged in the film
production community that 35mm film has a distinct advantage
over Super16mm in all aspects except cost.
The following drawing is an indication of the difference
between the area of a 35mm film frame and a Super16mm film
The flexibilities of working in a 35mm film format will also
allow adjustments to the images in the form of blowups and
framing corrections in future product without suffering degradations
as severe as those in Super16mm.
HDTV video cameras that exist now boast 1,000 TVL/PH of horizontal
resolution, exceeding the available resolution of 35mm film.
The potential exists for an HDTV video production to exceed
the quality of an original film negative. The disadvantage
of using a video format to acquire original images is a degraded
flexibility for future reversioning. Once an image is limited
by a video standard, the image resolution and aspect ratio
is a permanent part of the image wherever it goes.
There are valid fears of future technical advances making
the new HDTV standards obsolete. For instance, using an interlaced
HDTV video standard for production will not allow smooth integration
of the images into a possible future progressive scan product.
A 35mm film original, on the other hand, can be converted
to any television standard in the present or future without
fear of making the images obsolete.
Creating an HDTV video product using the highest pixel count
possible would be the best choice for future reversioning
of video originated material. The highest quality HDTV video
standard approaches the upper limits of what the human eye
can detect and future compromises during reversioning will
minimize the impact on image resolution. However, the pixels
of a digital video image are in fixed rows and columns which
translates directly from scan lines and horizontal pixel count.
Technically, there is a danger of introducing artifacts into
a video image called "aliasing" when altering the
original placement of pixels during any conversion process.
Since film has no regular pixel structure, there can be no
aliasing artifacts when adjusting the position of a film image.
There are several alternative paths to making good ATV pictures,
each with their rewards and troubles.
Upconversion to HDTV:
Technically, standard resolution television images can be
converted to HDTV images with the use of an upconvertor. This
device is a television standards converter that will interpolate,
or "line double" standard resolution images to effectively
be HDTV. If elements of current video tape libraries are to
be included in HDTV product, upconversion is the only answer.
Decisions about aspect ratio and framing will be encountered
during upconversion of 4:3 programs. Programming finished
as 16:9 SDTV video may be upconverted without regard to aspect
There will be a strong budgetary temptation to use upconversion
as a means to create HDTV masters using standard component
digital editing equipment. A Digital Betacam master can be
upconverted for delivery as an HDTV program. Even though high
quality upconversions subjectively look appealing on an HDTV
monitor, the upconvertor cannot manufacture resolution that
does not exist in the original material. The television picture
may be HDTV in an electrical sense, but not in image quality.
There will also be a strong temptation for some service bureaus
to offer SDTV upconversion as a means to create HDTV programming
without educating the client that it isn't true "high
definition". It allows the service bureau to extend the
useful life of their installed equipment base and possibly
delay purchasing significant HDTV equipment. They can charge
the client less than what full resolution HDTV would cost
and demonstrate the quality of the upconverted images on monitors
not likely to show the differences. The client who is not
prepared to understand the issues is subject to getting hoodwinked
into accepting it as true HDTV. This will not help the client
in efforts to future-proof the product.
The issues of upconversion relate to image quality. A standard
definition image will turn into a standard definition image
with more scan lines. Increasing the scan line count will
reduce some of the problems associated with our current television
system. The image, however, is still short on the high frequency
detail that makes a higher resolution image. Also, a standard
image with 350,000 pixels upconverted to a two million pixel
image will challenge the DTV encoder unnecessarily and degrade
the image further at the home DTV receiver. Since the DTV
standards allow for broadcast of what is essentially our current
television resolution, the image will look better if it is
transmitted as SDTV and not upconverted to an artificially
high pixel count.
Broadcasters who are making the move to HDTV realize that
upconversion will be necessary for all existing material,
but they stress that upconversion is unacceptable when the
opportunity for native HDTV production is available. They
also stress that upconverted material must not be intercut
with native HDTV material because of the dramatic resolution
differences. All new production for several networks will
mostly come from 35mm film transferred to HDTV formats.
Broadcast television will see HDTV originated commercials,
a likely early contributor to HDTV material, intercut with
upconverted SDTV program material. The visible differences
between these image types may accelerate the desire to replace
standard resolution material as quickly as possible.
Downconversion from HDTV:
High quality original images will allow for conversion to
any lesser standard. The opposite is not true for upconverted
images since the highest image quality available will be limited
by the originating image standard. In order to future-proof
new production, television producers should consider the shift
to 35mm film. Film can be transferred to the coming HDTV standards
Broadcasters will be simulcasting material in both HDTV and
current NTSC channels for a number of years. CBS and NBC will
be deriving the NTSC simulcasts from downconverted HDTV source
material when possible and will avoid upconversion.
The use of 35mm film has historically outlasted video originated
material and will also allow future television standards to
be accommodated. The only reason shows like "I Love Lucy"
are still around is because they were originated on film.
The first few years of "Johnny Carson", originated
on video, don't exist anymore. Some film producers I've talked
to in Hollywood are advocating originating on 35mm and cutting
the film negative for program finishing. That way the finished
product exists as a complete entity that can be pulled out
of the can years from now and run exactly like it was cut.
Image Compression on Transmission:
Compression is going to be upon us in the DTV world. The compression
scheme for broadcast is called MPEG2 which can take the data
required to create a video image and pack it more efficiently
before it is broadcast. Our current NTSC television is an
analog compression scheme where color is added to a monochrome
picture by using otherwise wasted parts of the television
transmitter power curve. Every compression scheme has its
artifacts. MPEG2 and NTSC are no exception. The DTV broadcasts
reaching the home will contain artifacts not present in the
original material. We are exchanging one set of artifacts
(NTSC) for another (MPEG).
The MPEG2 compression scheme has the ability to adapt to
picture content. A video image is broadcast as a series of
still frames, one after the other. MPEG2 takes advantage of
the fact that much of a video frame is usually identical to
the previous frame as well as the following frame. Instead
of transmitting an entire video frame every time, the MPEG2
transmission scheme only needs to transmit a complete image
every 8 to 15 frames. The rest of the frames are created by
transmitting only what is different between the frames. With
a relatively still scene, where the only thing moving may
be someone's mouth, very little data needs to be transmitted
to keep that scene in motion. As the image becomes more complex,
the MPEG2 data rate will rise to accommodate the additional
data needed to complete the frames.
The MPEG2 ATV encoder will be able to detect the presence
of film originated material. Film, which runs at 24 frames
per second in the U.S., must be transferred to video using
a method that divides the 24 frames into the 30 available
television frames. Every other film frame is held for 1.5
television frames, or three fields. Since the extra fields
are redundant data, the MPEG2 encoder removes them and saves
the transmission bandwidth. The home television receiver is
told of the omission and will repeat the redundant fields
during the display process.
The home television receiver is going to be a bag of tricks
by itself. The set manufacturers will be trying to figure
out how to make the sets cheaper so people will buy them.
Along with that comes all kinds of schemes on how give the
public a range of seemingly identical television receiver
offerings with different price points that in reality perform
wildly different. Be on the lookout for DTV receivers that
can receive all DTV transmissions, either SDTV or HDTV, but
convert everything to display on a less expensive standard
resolution screen. Even though the transmitter is sending
HDTV, the receiver is showing something less than HDTV.
Stress on MPEG2:
As a picture gets more complex with large amounts of fast
motion and changes to the image, the MPEG2 compressor may
be overrun with data that it cannot transmit fast enough.
The MPEG2 encoder may decide to discard the high resolution
elements of the image allowing the frames to be completed
at some lower resolution. Fortunately, the human eye cannot
resolve detail in fast motion anyway, so there is less need
to transmit it. If done properly, the MPEG2 encoder will be
able to significantly mask the absence of detail without calling
too much attention to the failure mode it is in.
One of the things that can stress an MPEG2 encoded television
image is noise. Active noise, or film grain, can be construed
as motion to the MPEG2 compressor. Noise or film grain is
also a high resolution image element that adds to the complexity
of the image. If the noise becomes excessive, the picture
quality may be compromised if the required data rate overruns
the DTV channel's ability to transmit it. The presence of
noise decreases the headroom the MPEG2 encoder has before
entering a failure mode. This is yet another reason to avoid
using Super16mm film in favor of HDTV video or 35mm film.
Another pitfall of film is gate weave. Using the steadiest
possible film transport in a telecine will reduce the amount
of interframe motion that can tax an MPEG2 compression scheme.
Using 35mm film instead of Super16mm makes it easier to create
steady film transfers. Of course, HDTV video originated material
has no gate weave.
Compression in Post Production:
There has been a lot written about compression in post production.
Compression has always been with us. The question becomes
"how much compression can we stand?" The NTSC television
standard is an analog compression scheme that compresses the
color about 6:1 before adding it to the transmitted picture.
The component digital 4:2:2 standard is also a compressed
image where half of the color samples are missing. That's
2:1 compression in the color samples. Digital Betacam compresses
a little more than 2:1 to make digital component recordings
on Betacam tape. All of these compression schemes exist for
one reason; to economically perform a recording or transport
function that otherwise wouldn't be possible.
The HDTV video signal contains almost six times the data
of a standard resolution image. To record that kind of data
economically on technology available today requires the use
of compression. For example, a full bandwidth HDTV digital
tape recorder (Toshiba/Philips D6 format) costs $400,000 today.
A video recorder that can record an almost identical picture
with 4:1 compression (Panasonic D5 format) costs $95,000.
Most people will accept the compression as long as they can't
see the picture degradation and the D5 format does a very
good job. The Sony HDCam format uses 6:1 compression. The
HDCam shoulderable camera and studio recorders will be priced
even lower than the D5 format.
Out of the 1920 pixels available in HDTV, the HDCam format
will only record 1440 of them. Fortunately, there is very
little detail information available in any standard scene
beyond 1440 horizontal pixels. The resolution differences
between the HDCam format and a full 1920 pixel recording are
nearly invisible. The pictures are nothing to apologize for
and the format will find its way into HDTV post production
despite the theoretical quality reduction. For future-proofing,
care must be taken to select a video recording format that
provides the best cost/performance ratio.
Compression damages the ability to do multiple generation
work, but it can have its place in areas where you only expect
to go two or three generations. Transferring film original
to a compressed video format is not a bad choice as long as
the compression has no first generation losses. Cascading
more than one compression scheme during post production may
generate additional image artifacts and should be monitored
to minimize them. As a point of comparison, the home delivery
of HDTV images will incorporate 50:1 compression ratios and
is not likely to be damaged by minor artifacts accumulated
in post production. However, once compression artifacts enter
a finished product they cannot be removed.
Film, especially 35mm formats and above, is currently considered
to be the ultimate uncompressed, unadulterated image carrier
available. Actually, film itself has compression characteristics.
Film does an excellent job of compressing lighting ratios
found in reality to the grains of the chemical storage media.
Shooting an image of the sun, for instance, does not yield
a film image as bright as the sun. Film will scale the relative
exposure of the scene to what it can reproduce.
The 24 frame exposure rate of film conserves film stock while
making an acceptable compromise in motion artifacts, sometimes
known as "judder". The frame rate compresses the
real time "reality" of life into brief time slices.
Increasing the frame rate to 30 frames per second will improve
the judder, noise and the apparent resolution of the film
by putting more photosensitive grains in the path of the image.
The ultimate film speed that will perfectly match the projected
DTV standards would be 60 frames per second. That isn't likely
to occur in normal production because of cost.
Film To Data:
For future-proofing, the best way to preserve film images
(other than keep the film in perfect condition) is to record
the images as data, not as video. Transferring film to video
immediately limits the quality of the images to whatever the
television standard allows. If the same film was scanned at
high resolution and each frame stored as an image file, the
image may be retrieved at a later date and converted to any
television standard. A high resolution scan will easily scale
to any likely video line count or frame rate. This includes
exporting stored images as PAL since the film image is digitally
stored frame for frame and not at the mercy of any television
One likely preference of ATV broadcasts is to create material
with an interlaced scanning technique. This allows material
from current video systems, all of which use interlace scanning,
to be easily incorporated into an ATV product. Interlaced
scanning also can have significant motion artifacts, especially
when dealing with film originals transferred via a telecine
process. Film is more akin to a progressive scan video system.
From a progressive scan original, a conversion can be done
to an interlaced product. The opposite is not true. Once the
images are scanned with an interlaced scanner, the artifacts
are built in to the images. This is another consideration
for future-proofing of production images.
Philips is showing the Spirit DataCine that has the ability
to scan motion picture film and record the raw digital data
onto one of many data archive formats. The scanning is done
without regard to current or future television standards and
is done in a progressive scan process. The data can be recovered
and perfectly adapted to any future television standard since
the images have not been touched by any television standard
at all. The data from the scanner is good enough to output
the images back to film. Degradation of the original digital
data recording medium can be monitored and, if necessary,
transferred to any future data medium without degrading the
images. This theoretically will allow storage of the original
data indefinitely, possibly long after the original film has
Several other film to data recorders are in operation designed
for creating digital effects on feature films. The Kodak Cineon
and Quantel Domino can scan a film negative at enormous resolutions
(up to 4,000 pixels by 4,000 lines) into a computer workstation
and output the result, including 3D embellishments, back to
35mm film without degradations. These types of data recorders
may come into more common use, but they are currently in the
"wretched excess" column of standard video post
The future-proof image library will be able to incorporate
all of the available video, data and film standards. The future
value of the image asset will be determined by two things;
the quality of the image and the ability to find and retrieve
it. Several types of computer based image storage and retrieval
systems are in use world-wide. The successful systems will
allow standard database architectures and a variety of storage
medium options to suit the needs of the library. Accurate
data entry, flexible search and retrieval and the highest
quality image available will insure the future life of the
For an immediate delivery mechanism, HDTV video originated
product may be considered better than 35mm film. When the
subject of asset futures comes into play, the producer may
need to think again about an originating format. Film is the
one medium capable of crossing most of the boundaries that
exist in program delivery. It can be transferred to all present
and future image transport formats including the current NTSC
and PAL video frame rates. Particularly, the use of 35mm film
closely matches the High Definition television formats coming
into being. The quality of Super16mm film is suited for program
material with modest performance expectations compared to
35mm film. Transferring 35mm film original to digital data
will ensure the longevity and recoverability of the original
HDTV video production may rival or exceed the image quality
of 35mm film and allows for downconversion to any lesser video
standard. However, any video image standard will become a
limiting factor for future use of the product. The resolution,
bit depth and aspect ratio become frozen in the video product
and cannot be changed without some compromise. In particular,
the subject of interlace versus progressive scan image formats
may become a factor in judging the future value of an image
asset. Products are being designed and tested that will capture
live images at 1080 lines with progressive scanning. The equipment,
particularly the recorders, will have to bear enormous data
rates to store these images. They will be the direct rival
of 35mm film capture when available.
The safest format for the foreseeable future is 35mm film.
The next best format is HDTV video origination for all its
resolution abilities. Super16mm film allows the same image
flexibility as 35mm film without the quality. For a future-proofing
function, film has been proven to outlast video tape for durability
and certainly outlast video tape formats for popularity. The
least desirable format for future-proof images is standard
definition video at 16:9 aspect even though it will outperform
Super16mm film in an immediate delivery mode. The need for
upconversion from lesser formats will certainly reduce the
future value of image assets and should be avoided.
Sr.VP, Director of Technology
Henninger Media Services
Also of interest: 24 frame
HDTV production and distribution.