Archived Tech-Notes
Published by: Larry Bloomfield & Jim Mendrala The following are our current e-mail addresses:
E-mail = hdtvguy@garlic.comor J.Mendrala@ieee.org
We have copied the original Tech-Notes below as it was sent out. Some of the information may be out of date.
**********************************************North West Tech Notes % Larry Bloomfield & Jim Mendrala
521 Forest Grove Dr.
Bend, Oregon 97702
(541) 385-9115Email = larrybend@aol.com
J_Mendrala@compuserve.com---------------------------------------------------------------------------
--------------------------------------------------------------------------June 3, 1997
NWTN - 003---------------------------------------------------------------------------
---------------------------------------------------------------------------For the first several issues I have been advised to print our mission statement so no one will have any question why we are doing this.
We feel that there is a need to have an electronic listening post, clearing house or informal source for what's happening in this rapidly developing world of DTV, ATV, ATSC and HDTV, etc., etc., etc. We have never claimed to be experts. Our only claim to fame in this arena is that Jim goes to as many meetings on the subject matter in Southern California and I scan as many trade publications as possible and the two of us talk to a lot of folks everyday, get together and discuss what's happening. We both want and need to know what's going on in this area of our industry and we both do a fairly good job of getting our thoughts down on paper. With respect to writing this newsletter, as the saying goes: "It's a job and somebody has to do it."
Please keep in mind that this effort will be successful ONLY with the assistance of those who help by contributing information to us and have the professional desire to keep us all on the cutting edge of this technology. We will share what we get from you.
This is a work of love. We see a need and we're doing this solely with the idea of keeping ourselves and our associates informed. We ask no compensation for our efforts, just the
latest information you may have on what's going on. We will not pass on anything that cannot be verified or the source cannot be identified. If we inadvertently pass on erroneous information, we will make every effort to get it corrected as soon as possible. All this is for obvious reasons.
We've received permission from several publications to quote them during this past so we can not start comment on what others are saying. In addition to this, we need you to share your experiences, knowledge or anything else relating to this area of our industry. Feel free to e-mail us and we will make every effort to share it with our fellow broadcasters and anyone else interested.
Our statement in our first two issues about there being a lot of confusion out there seems to be somewhat prophetic. In addition to the technical aspects of what is and will be happening, we must also look at what needs to be addressed with respect to program sources and how we will interface with film or most any other programming source that may come down the "pike."
Who will we send these issues to? As I've just stated: "Anyone interested." Just e-mail us your request to be added to the mailing list and it's done! Feel free to forward this on to your associates, but let them know that you've done so and it's not directly from us. If we send it to you and you're not interested, just let us know and we will take you off the mailing list.
Our first offering in this issue is from Jim Mendrala. It is a paper he submitted to SMPTE. It is presented here for your information and education in hopes that we all can have a better understanding of what the total industry is facing in an effort to bring better quality everything to the viewing audience. Film to Data (storage) transfer is a critical part of this process. So here we go with number three.
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Contribution to SMPTE
19.18 WG on Telecine Practice
by Jim Mendrala (9/6/94)
IMAGE CUT-OFF
The compositional area that a cinematographer frames in the camera viewfinder is not always the same area that is projected on the motion picture screen or is scanned on the television system. It is generally less, but in the case of HDTV more, and the proportions will differ, depending upon several factors.
Motion picture films are not always projected or televised in their original width or format. They may be blown-up or reduced to a larger or smaller film width for various reasons or uses, or they might be scanned on a telecine for television with a different aspect ratio. Also, motion pictures are photographed for projection in various aspect ratios (height of the projected picture divided into its width). The aspect ratio (A/R) used to film the picture is not always the same as that employed to project or televise the film. To further complicate matters motion pictures for theatrical projection are filmed with both flat and squeezed images.
Conventional spherical lenses record flat, or unsqueezed images. Anamorphic lenses, such as employed in the Panavision system, produce squeezed images. An anamorphic lens compresses the image horizontally but does not alter its height. Lenses used to photograph 35mm Panavision, and similar 'scope type pictures, employ a 2X squeeze ratio which provides the camera aperture with an apparent width that is double its actual width. In effect, the 35mm camera aperture photographs a squeezed image area that would require a 70mm aperture if a similar picture were filmed with a conventional spherical lens recording a flat image. The projector uses a similar lens or prism system that unsqueezes the image and spreads it out to its original width.
In motion pictures, image cut-off begins in projection: all projector apertures, regardless of film width, are slightly smaller all around than camera apertures, to avoid projecting unexposed areas of the original camera film, and to mask any bits of dust, dirt or hairs that may cling to the edges of the camera aperture. The percentage of the image cropped by the projector is greater for smaller film formats.
In television, image cut-off begins when a transfer is made from film to the electronic medium with its fixed aspect ratios, namely 4:3 and the new HDTV 16:9 A/R. This is done so that, again, any bits of dust, dirt or hairs that may cling to the edges of the camera aperture are not scanned.
There is only slight cropping when full frame 35mm, 16mm or Super-8 is blown up or reduced from one format to another because all of these formats are basically filmed in the original silent screen's 4 to 3 proportions, or with an aspect ratio of 1.33/1. When films being blown-up or reduced have different aspect ratios, however, portions of the original pictures will be cut off. This occurs when 16mm is blown-up to 35mm wide screen for projection with aspect ratios from 1.66/1 to 1.85/1, or when a 'scope film is optically scanned to produce a 16mm or 35mm flat film for television transmission. The 2.35/1 A/R 'scope format must be reproportioned by cropping to 1.33/1 or 1.78/1 A/R. This requires optically printing or scanning the picture so that various areas, generally the middle or either side, are presented.
Image cut-off first reared its ugly head on February 15, 1932 when Academy Aperture was introduced to provided an industry standard for filming sound pictures. The full frame silent aperture had to be trimmed on one side to make room for the sound track, and the height of the picture was reduced somewhat to preserve the 4 to 3 proportions, of the 1.33/1 A/R of the original silent films. This resulted in a projection aspect ratio of 1.37/1.
Various flat image wide-screen formats were developed in the 50's to compete with the newly-introduced anamorphically-squeezed CinemaScope (now obsolete). CinemaScope had an aspect ratio of 2.55/1 when first introduced with its magnetic stereophonic sound tracks. This was later reduced to 2.35/1 A/R when the picture was trimmed to make room for an optical track. This was done because many theaters refused to equip their projectors with magnetic sound heads.
The problem of elongating the aspect ratio of flat films so that their screen proportion would approximate that of CinemaScope was solved by reducing the height of the projected image, using a shorter focal length projection lens and blowing up the picture onto a larger screen. The fact that the projected picture was much grainier and that 25% of the photographed image was wasted was completely ignored! Aspect ratios of 1.66/1, 1.75/1, and 1.85/1 were employed by different producers at various times. The Academy Aperture was retained for both shooting and projection. Marks were simply drawn on the ground glass as a guide to composing the picture for the particular projection aspect ratio required. It is important to note that all wide-screen films employ aspect ratios based on the projection aperture not the camera aperture. At present, most films shot for the United States are generally composed for a 1.85/1 A/R, while European films are generally composed for the 1.66/1 A/R.
Surveys of theaters throughout the world have shown that actual projection screenings fall somewhere between 1.66/1 and 1.85/1, with the average about 1.75/1.
The projection problem complicates composing for flat wide-screen films in the camera because the top and bottom of the frame are imaginary lines. The camera person is at the mercy of the projectionist for both up-and-down framing and choice of mask. Screen proportions may further mutilate the composition. There is no guarantee that flat wide-screen films in any aspect ratio will appear on the screen as composed in the camera.
American producers, generally, do not shoot with a hard matte in the camera which would result in the desired aspect ratio on the original negative. However the cinematographer does compose with some aspect ratio, other than the 4:3 or 1.33/1 full aperture A/R, based on lines drawn on the graticule or focusing screen. All American releases are generally slated for showing on television later and an elongated A/R hard matte in the camera would result in masking at the top and bottom (letterbox) of the television display. Therefore, the entire aperture must be "protected", i.e., kept clear of lights, mike booms, scaffolding, etc. Although these things will not be seen on the theatrical screen, they will appear on standard 4:3 A/R television sets.
Some American producers may make an optical dupe negative with a hard matte (music video producers seem to do it a lot). Release prints will then be projected with the assurance that no more than the area composed will appear on the screen, but less may appear if the theater's projection system and screen cutoff part of the picture, or if the film is Pan-Scan'ed in the telecine. The producer can go back to the original negative if it has not been cropped for later use on television. A few European producers, notably the Italians, shoot with a hard matte in the camera, but since they generally film with a 1.66/1 A/R this is less of a problem than with 1.85/1 A/R.
Flat wide-screen systems are wasteful of film because an area only three perforations high (instead of four) is actually projected. Although a smaller area than the Academy Aperture is now projected onto larger screens than before, the projected image is better because of the advances made in color film Manufacturing. Flat wide-screen pictures could be projected with a three perforation high frame and thus save 25% in film length and considerable transportation charges, particularly with air shipments. This would require recording the sound track for that speed and would require projector changes from three to four perforation pulldown when both 'scope and flat films are projected on the same program. Semi-scope two perforation high pictures (similar to Techniscope as filmed in the camera) could also be projected in an elongated 2.35/1 A/R with flat images. A special sound track would be required, however, because of the 45 feet per minute projection speed.
There is really no reason for using Academy Aperture (or full aperture with an Academy mask) in the camera. Most films are shot with a full aperture. The compositional area for either television (safe action) or the particular wide-screen aspect ratio in use is marked on the focusing ground glass or the monitoring viewfinder, if the camera is so equipped. A full aperture is used so that all of the picture area available is photographed. The markings will insure that the picture is properly composed and the printer will mask the sound track area. The fullest possible aperture provides the optical camera person or the telecine operator with extra area, if required to flop the film (turned to reverse screen direction), or if the film has to be larged to hide a mike boom which inadvertently appears at the top of the frame, or if the product in a commercial has to be moved slightly to one side or the other for titling purposes or other reasons.
Removing the Academy Aperture prevents back-lights from flaring, kicking or bending off the the edge of the the Academy Aperture mask. It also places the camera aperture on three sides farther away from the projector or scanned area and prevents any bits of dust, film chips or hairs that may pick up on the edges of the camera aperture from showing on the screen or from being transferred into an electronic image.
Many theaters today are equipped with screens whose proportions and masking are compromises. 'Scope films are cut off. A survey made by the Aspect Ratio sub committee for the Working Group on HDTV found that of 200 theaters surveyed in the Southern California area, the screen A/R averaged about 2.0/1. It seemed like the theaters wanted wide screens but the auditorium height was the limiting factor in one dimension and the auditorium width limited the screen width in the other dimension. Signs, titles, names, inserts or extreme close-ups are composed within a "safe action" area so that they will not be rendered meaningless if cropped in wide screen projection.
Camera and projector aperture dimensions, and ground glass markings, for all film formats are given in Table 1. The full 35mm aperture is used for process backgrounds, instrumentation cameras and other purposes where the full negative area is not wasted. It may also be used for various wide-screen aspect ratios and later reduced or recentered for projection or scanned area.The Academy Aperture and other aspect ratios are only used for ground glass marks so that the picture is centered and composed for the intended A/R but the full 35mm aperture is exposed. A contact print results in a properly composed picture, with the aspect ratiodesired, when projected, provided that projection is with the proper mask, and with the proper focal length lens and the screen does not crop the image.The reduced image displayed on standard home TV receivers present serious cropping problems for theatrical films and other motion pictures shot for other purposes. Action at the outer edges of such films will be cut off, as will titles composed for the full frame. Various methods are used for picking up different sections of the picture (usually the middle or either side, but systems are in use that offer more choices, including panning during the scene, i.e., Pan-Scan). HDTV set manufacturers have tightened up the amount of overscan and it is now being considered to reduce the Safe Action area for HDTV to 5% below the projected aperture dimensions.Most American television networks at this time do not permit masking of any kind which would produce a border at the top and bottom of the picture.
Local television stations, however, often transmit a masked 'scope print, in more or less its original format as an elongated image with black borders on the top and bottom (letterbox).
Theatrical film titles suffer the most when televised unless they were originally filmed with the television safe title area in mind, or are placed at the side of a 'scope picture in a manner that fits the standard TV format. This is particularly noticeable in old movies shot with an
Academy Aperture. Titles filmed in 'scope are often transmitted squeezed which works out okay unless players appear behind them (this produces an stretched appearance that is particularly distressing when cowboys are shown riding horses). Many producers use titles against nondescript back-grounds and choose type that looks well condensed or unsqueezed.
Another method is to optically print in a decorative border on the top and bottom of the frame to fill the entire scanned area.
The modern cinematographer shooting either a theatrical film or a film for television simply composes for the particular medium. But there is no way of knowing where or how a picture will be used later. Most theatrical films wind up on television. Many television pictures are released to theaters.
Any format may be reduced or blown-up to any other format, transferred to another medium, such as film to tape or tape to film, and both can be later transferred to CDs (compact disks) which are already able to accommodate the standard 3:4 A/R as well as the new 16:9 A/R. The optical cinematographer and the telecine operator should be given the greatest image area available to work with.
To reduce the aspect ratio dilemma, an aspect ratio that is closer to the
raming of any composed film would be desirable. Taking into consideration all of the known aspect ratios, the Aspect Ratio subcommittee conceived and submitted to the Working Group on HDTV (N15.04) aspect ratios that fit this prerequisite. It was unanimously agreed upon by the WGHDTV, SMPTE and accepted by the United States, Canada, and the World. It is the now famous 16:9 or 1.78/1 aspect ratio.
HDTV Systems around the world immediately adopted the new aspect ratio, even though some had started with a 5:3 or 1.66/1 A/R. Now lets see how this A/R works on a HDTV telecine. Suppose a film is shot with a hard matte 1.66/1 A/R and scanned to HDTV to fill the 1.78/1 or 16:9 A/R. Only a small part of the picture at the top and bottom is lost. If the producer wants to preserve the aspect ratio, then only a small portion is letterboxed on the left and right sides of the picture. If the film is shot in a hard matte 1.85/1 A/R, then only a small part of the picture on the left and right is lost. Again, if the producer wants to preserve the aspect ratio, then only a small portion would be letterboxed on the top and bottom and the aspect ratio is reserved.
If a film is shot in 'scope (2.35/1) and unsqueezed to the original aspect ratio, then a slightly larger letterbox cropping on the top and bottom will be seen. On the other hand, if the image is blown-up on the telecine to fill the height, then only a slightly larger portion of the picture on the left and right is lost.
In the United States, most films are shot full aperture so if the cinematographer composes to the 1.78 composition will look good on HDTV as well as theaters in various other countries. Films shot in 1.66/1 and projected in 1.85/1 will only lose slightly more of the top and bottom of the image.
It might have occurred to some of you reading this by now that if theaters would standardize their motion picture screens to the new 16:9 format, all aspect ratios could easily be accommodated. Only a small adjustment of the proscenium surrounding the motion picture screen would be required to preserve the composed-for aspect ratio.
Television today with its fixed aspect ratio of 1.33/1 (4:3) has a SMPTE Recommended Practice (RP 27.3-1989) - Specifications for Safe Action and Safe Title Areas. HDTV does not.
HDTV Television telecine operators today are using the SMPTE Recommended Practice (RP 110-1992) - Specifications for an Alignment Test Film for Anamorphic Attachments to 35mm Motion Picture Projectors - to align their telecines even though the 1.78/1 A/R is not on the film. SMPTE at this time has yet to come up with a recommended practice for scanning the HDTV aspect ratio.
Motion picture theaters should be encouraged and SMPTE should recommend 16:9 A/R screens with an adjustable proscenium for the various reasons mentioned above.
I hope the above clarifies the Image Cut-Off problem and how the 16:9 A/R can bring the creativeness of the cinematographer or HDTV director/cameraperson to the motion picture screen or the HDTV screen, be it a CRT or an HDTV projection system (with its inherent ability to handle a greater gamut of color).
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Subj: Preparing for Wide screen World
There is a book by Clay Gordon of Rebo Studios titled "The Guide to High Definition Video Production: Preparing for a Wide screen World". It is a paperback and is $44.95. For more information on this and other HDTV books visit <http://www.display.org/sid/hdtvbook.html>.
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Sorry this is late getting out, but we just got it. Perhaps we'll have a report on it.
Subj: SG Audio Prod/Post Ent. Prgm. Meeting
Here are the details:
SG Audio Prod/Post Entertainment Programs - A12.68
7:00am - 9:00am, Wednesday, June 4, 1997
Sony Music Entertainment
2100 Colorado Ave.Santa Monica, CAA Continental Breakfast will be provided by Sony.SMPTE Hollywood Section
7:45pm at the LA Zoo
Gene Autry Western Heritage Museum
4700 Western Heritage WayLos Angeles, CA 90027The program is: "DTV Deployment-Computer Industry Planning". The speakerwill be Craig Mundie, Senior VP, Consumer Division, Microsoft Corp. The "DTV Team" consists of Microsoft, Intel, Compaq with a specific view of a service model and a family of display formats that are already influencing platform architectures.The meeting will provide an in depth look at what is termed "Digital Convergence for the Consumer".---------------------------------------------------------------------------
Subj: Quotations.
From: Charles A. Pantuso
Regarding your recent synopsis of my comments at the USC seminar:
Charles Pantuso, HD Vision, quoted Shakespeare with "Having is not as pleasurable as wanting." He said this applies to HDTV equipment.
HDTV is viewing angle plus resolution. Channel numbers will become meaningless with the new DTV system. Plant wise, HDTV will follow SMPTE 292M with a bit serial interface of 1.5 Gbps. There are some good web sites for info at :
www.smpte.org
www.fcc.govwww.atsc.org.Although Spock may have been quoting Shakespeare I was quoting Spock in the AMOK TIME episode from the original series.The quote was not referring to HDTV equipment. It was referring to the regulatory framework for advanced television that we now find ourselves in.
Channel numbers will not become meaningless. They will be even more important. They will just not be tied to RF frequencies anymore, and might not translate from broadcast to satellite to cable. (This is more or less the situation now with regular NTSC television.)
The key point of using SMPTE-274M/SMPTE-292M for production is that it provides a single format that is capable of embedding all of the progressive formats at low frame rates (24, 30), while still allowing a single format for production and distribution. The quality is sufficient for the derivation of all of the other formats, including 1280x720x60 progressive.
Regards,
Charlie
Ed. Note: Sorry for the misquote. Hope this corrects the situation.
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Subj: Information available in print
Tektronix has two new additions to their series of information booklets:
TOMORROW'S NEWSROOM TODAY -- A Video and Networking Division Tutorial dated April, 1997 (although this isn't exactly digital TV or HDTV, we'll probably be using these techniques on it.
A GUIDE TO PICTURE QUALITY MEASUREMENTS FOR MODERN TELEVISION SYSTEMS dated April, 1997. Contact your Tektronix sales person or office for a copy.
We have been informed by our good friend Dave Hill of LDL Communications (LARCAN) that interested parties can contact him at "dhill@larcan.com" -- (less the quotation marks) for information on the new EEV Digital UHF IOT Tubes. He will send you a brochure.
TV TECHNOLOGY, in their May 22nd issue express an interesting concern for the potential lack of crews needed for DTV Towers in their series entitled Making The Transition -- Digital TV. If you do not subscribe, you can get more information about this issue by calling (703) 820-3245.
TELEVISION BROADCAST, in their May, 1997 issue present an interesting view on the future of LPTV stating in their caption: ".....Not all LPTV and Translator Stations will survive.." If you do not subscribe, you can get information about this issue by calling (212) 378-0462.
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Subj: NAB and your coverage
And finally, this last item for our third issue: NAB has sent out letters to their NAB/MSTV members with materials that they say: "....are important for understanding the potential impact of digital television (DTV) on your station's operation. They include some interesting color maps. Ours showed our NTSC 62.34 dBu 50% contour and our DTV 38.88 dBu 90% contour for comparison sake. As they said: "A picture is worth a thousand words." If you are a member, be on the look out for this. It is dated May 30, 1997. If you are a member and don't get this letter and its' enclosures, call them at (202) 861-0344 (Victor Tawil - MSTV or Art Allison - Science and Technology (202) 429-5418.
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The NWTN is published for broadcast professionals who are interested in DTV, HDTV etc. by Larry Bloomfield, Chief Engineer, KTVZ, Bend, Oregon and Jim Mendrala, Consulting Engineer, Val Verde, California. We can be reached by either e-mail or land line (541) 385-9115, (805) 294-1049 or fax at (805) 294-0705. Thanks to the folks at Communications General Corporation for inspiring us to do this. News items are always welcome from our readers letters may be edited for brevity.
larrybend@aol.com --------- J_Mendrala@compuserve.com
NWTN articles may be reproduced in any form provided they are unaltered and credit is given to the North West Technical Notes and the originating authors, when named.
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