Archived Tech-Notes
Published by: Larry Bloomfield & Jim Mendrala The following are our current e-mail addresses:
E-mail = hdtvguy@garlic.com or 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 Some of the information may be out of date.
**********************************************Tech Notes
Published by: Larry Bloomfield & Jim Mendrala
(408) 778-3412 or (661) 294-1049
E-mail = larrybend@aol.com or J_Mendrala@compuserve.com
July 30, 1999
Tech Note - 035
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Talent does what it can -- Genius does what it must!
Our Mission: Sharing experiences, knowledge, observations, concerns, opinions or anything else relating to Electronic Cinema, DTV, etc., with fellow engineers and readers. We publish when there is something to share. The Tech Notes are only sent (BCC) directly to those who have asked to be on the mailing list, however feel free to forward them, intact, to anyone who you think might be interested. There is no charge for this Newsletter, no one gets paid (sigh), there is no advertising and we do not indorse any product or service(s). The ideas and opinions are those of the individual authors. We still administer everything manually. We don't use any "majordomo" automatic servers. We do hope that everyone will participate with comments, experiences, questions and/or answers. We now have over 435 subscribers and growing. This is YOUR forum!
Past issues are available at: WWW.SCRI.COM
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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" effect.
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.
Shutter Opening 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.
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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 links.
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 come.
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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."
Many broadcaster 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.
No completion 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
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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 Ideal Husband."
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.
For additional information visit: http://www.dfits.org
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Subj: PSIP
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.
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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.
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Subj: Video Servers/Disk-Based Formats To Replace Beta SP / Tape as Primary On-Air Formats
From: SCRI
(Ed Note: The following is our way of saying thanks to SCRI posting this on their web site.)
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
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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 cooperation.
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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 either e-mail or land lines (408) 778-3412, (661) 294-1049 or fax at (661) 294-0705. News items, comments, observations, opinions, etc., are encouraged and always welcome from our readers; material may be edited for brevity, but usually not. Tech Note articles may be reproduced in any form provided they are unaltered and credit is given to both Tech Notes and the originating authors, when named. If they are to be used by a publication that normally compensates their writers, please contact us first.
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