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Updated: 12/13/2011 Part II
DigitalBroadcasting
The World Moves to DTV
Changes in analog signal reception result from factors such as a poor or misdirected antenna and changing weather conditions. But even under these conditions an analog signal may still be viewable and you may still hear the sound. With digital television, the audio and video must be synchronized digitally, so reception of the digital signal must be very nearly complete. The nature of digital TV results in a perfect picture initially, until the receiving equipment starts picking up interference or the signal is too weak to decode. With poor reception some digital receivers will show a "blocky" video or a garbled picture with significant damage, other receivers may go directly from a perfect picture to no picture at all. This phenomenon is known as the digital cliff effect.
In June 2009, all major broadcast stations in the United States switched to DTV. We say "major" because some lower power TV stations were allowed to stay with the NTSC analog standard for a period of time. Some countries don't plan a complete analog-to-digital transition until around 2020. There are two basic international standards for digital broadcasting, the ATSC (Advanced Television Systems Committee) standard adopted by United States and Canada, and DVB-T (Digital Video Broadcast – Terrestrial) system used in most of the rest of the world. Although the ATSC approach has weaknesses, most notably the ability to hold up under mobile conditions, it includes important features such as 5.1-channel surround sound using the Dolby Digital AC-3 format. The reduced bandwidth requirements of lower-resolution images allow up to six standard-definition subchannels or datacasting channels within the 6 MHz TV channel. How these will be developed and used remains to be seen.
The table below summarizes the difference between the analog and digital
broadcast systems.
As you can see, the ATSC standard is capable of 16:9 images up to 1920 by 1080 pixels in size and resolution, which is more than six times the display resolution of the earlier analog standard. In addition, many different image sizes can be supported. These include:
We'll illustrate the difference in clarity between SDTV and HDTV in Part Two of this module, and we'll explain surround sound and 5.1 audio in Module 42.
This did not happen for four reasons. First, TV stations had launched a major educational campaign about the switch that had lasted for months, second, most viewers were receiving the stations by cable or by satellite, which were not affected, third, for some time new TV sets had been equipped to handle ATSC signals, and, finally, the government went so far as to issue vouchers to help pay for set-top boxes to enable existing over-the-air NTSC receivers to convert to over-the-air ATSC signals.
When projected on a 16 x 9-foot screen and
observed from normal viewing distance, the picture detail in good (1,080p) HDTV systems appears to equal
or better that attained by projected 35mm motion
picture film. The enlarged illustrations on the left show the relative pixel detail of SDTV and HDTV. (The illustrations assume a 40-inch TV screen.) SDTV produces an image with about 200,000 pixel (picture) points. HDTV increases that by a factor of about 10 to two million pixels.
All other things being equal, the difference in perceived picture sharpness centers on the number of (visible) scanning lines, which here ranges from SDTV's 480 lines to HDTV's 1,080 lines. The although the 1080p system delivers the sharpest images, the approach is so technically demanding it can only be distributed by non-broadcast systems. However, it can be converted to film and projected in a theater without most patrons ▲realizing they're seeing video.
We discuss the relative
advantages of film and video and the differences between their quality
and costs in more detail Converting Wide-Screen Formats
Three approaches are used:
If we shoot the original HDTV/DTV (or wide-screen film) with the narrower 4:3 cutoff area in mind, losing the information at the sides of the picture should not be an issue. (This is the area on each side of the red box in the photo below, which, as noted, is referred to as a center-cut of the full 16:9 raster.) We refer to the procedure of
keeping essential subject matter out of the cutoff areas as shoot-and-protect.
In the above picture, cutting off the sides would not be an issue; but what if you had the two parrots talking (??) to each other from the far sides of the screen?
In this case, a letterbox approach can be used, as shown here. But you can see the problem. The result is blank areas at the top and bottom of the frame. Often, we reserve the letterbox approach for the opening titles and closing credits of a production, and pan-and-scan is used for the remainder. Since some directors feel that pan-and-scan introduces pans that are artificial and not motivated by the action (nor the composition they originally intended). They may try to insist their work be displayed using letterbox conversion. Originally, producers feared that audiences would object to the black areas at the top and bottom of the letterbox frame. (More than one person who rented a film (video) in the letterbox format brought it back to the video store complaining that something was wrong with the tape.) Today, however, viewers accept this format.
The effect is especially noticeable when people are part of the scene -- people who, as a result, suddenly become rather thin. (Not that all actors would complain!) Compare the two images above. Note how the bird in the squeezed 4:3 ratio on the right seems to be thinner than the bird on the left. Another way of visualizing the major SDTV-to-HDTV
and HDTV-to-SDTV conversion approaches is illustrated SDTV to HDTV In-Set Conversion Approaches
Clearly, all these approaches leave something to be desired, so today savvy producers originate productions in the 16:9 wide-screen format using the "shoot-and-protect" approach we've discussed.
Digital Cinema
Satellite facilities distributed the video version to digitally equipped theaters, which used high-definition video projectors. The difference between the film and video versions was difficult for audiences to discern. Since 2000, there have been major improvements in the video projection process. By 2007, the images from the best video projectors were sharper than those of 35mm film projectors. Film crews shot Star Wars: Attack of the Clones -- which more than 90 theatres around the world projected in its digital form -- entirely on 24p video (which we covered earlier). Whereas film and processing would have cost several million dollars, the cost of videotape for this production was only about $15,000.
A major step toward video projection in theaters was taken with the release of the 3-D motion picture, Beowulf. The "film" was also seen as representing a major step forward in ▲digital animation. Beowulf is based on a famous Old English epic poem about a warrior who fights terrorizing monsters -- designed to be all the more scary in 3-D. Despite the limited number of theaters equipped with 3-D video projectors and the fact that patrons had to wear special glasses, this film toped the box office when it was released in late 2007. But the all-time box office record was set in late 2009 and early 2010, when the 3-D "film" Avatar quickly became the largest grossing film in history. Many theaters used video projectors for this production.
Plus, pirating
(creating and selling illegal copies) is a constant problem,
costing the motion picture industry billions of dollars in lost
revenue.
Pirating feature films is far more difficult when they're encrypted
and either sent directly to theaters via satellite, or, more commonly, delivered to theaters on a high-capacity disk drive or a recording medium such as videotape. We discuss the issue of
pirating in more detail
We can immediately play back and evaluate a scene we shoot in video -- even while the actors and production personnel are still in position. With film the hours of delay involved in processing and preparing film "rushes" (rough prints for quick screening) make this impossible. Today, however, most film directors use video assist, or shooting on film and simultaneously viewing and recording scenes on video. This means they can play back and evaluate their work as they go along. Finally, not only are postproduction costs far less with video, but visual effects are much more easily and inexpensively produced.
Digital theaters can operate with fewer
employees, representing a considerable
cost savings over time. Offsetting this savings, however, is the
initial
investment for digital projectors and the associated computer -- an
estimated $60,000 to $120,000 per theater screen Is 3-D Production FinallyGoing to Catch On?
In anticipation to a move to 3-D production the 2010 and 2011 National Association of Broadcasters conventions where new technology is typically introduced featured a wide array of 3-D production equipment.
Even so, the move to 3-D TV is having a difficult time --
primarily because of a shortage of programming and the need to wear special
glasses.
The latter was eliminated as an issue when a prototype of a large-screen, 3-D TV set was demonstrated for audiences in 2011. Unlike previous 3-D sets, no special glasses were required and the 3-D image held up at different viewing angles.
For a more detailed look at the
various DTV and high-definition standards in the United States,
including those for digital cinema
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