Updated:  12/13/2011

Part II

Digital

Broadcasting

The World Moves to DTV

By 2010 about half of the world's major countries had converted to digital broadcasting.  Digital TV uses a more efficient transmission technology allowing for improved picture and sound quality. In addition, digital signals provide more programming options through the use of multiple digital subchannels (channels of information within the basic broadcast signal).

Compared to analog signals, digital broadcast signals react differently to interference. Common problems with over-the-air analog television include ghosting of images (seeing multiple faint images at the same time; note photo), noise or "snow" because of a weak signal, etc.

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. 

The first country to make a complete switch to digital over-the-air (terrestrial) broadcasting was Luxembourg, in 2006.  Shortly thereafter, the Netherlands made the switch.  Finland, Andorra, Sweden and Switzerland followed in 2007.

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.

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:

•  Standard definition—480i (interlaced), to maintain compatibility with existing NTSC sets

•  Enhanced definition—480p, (progressive), about the same quality as current DVDs

•  High definition—720p

•  High definition—1080i (the highest definition currently being broadcast)

•  High definition—1080p (Blu-ray equipment and a few cable operators )

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.

It was thought that the move to digital and the "sudden" loss of all major NTSC television stations in the U.S. would be met with widespread viewer consternation. In fact, TV stations braced themselves for an avalanche of unhappy viewers demanding to know what happened to their TV stations.

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. 

Compare the screen enlargements shown here that represent HDTV and the standard NTSC systems.

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.

In the graph on the right, the taller the red bar, the sharper the picture. Note that the interlaced (i) and progressive (p) approaches to scanning result in a significant difference in apparent picture sharpness (measured in terms of discerned pixel points of detail).

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 often make comparisons between video and film quality. But video and film are inherently different media, and the question of their relative "quality" (a word that can mean many things to many people) has been the subject of lively debate.  Both sides claim their medium is superior.   

When we compare film and video media in a broadcast application, the differences between video and film are based more on differences in their traditional production approaches than on inherent differences between the media.

We discuss the relative advantages of film and video and the differences between their quality and costs in more detail here.
 

Converting Wide-Screen Formats

Production facilities make the conversion of 16:9 HDTV/DTV images to the standard 4:3 aspect ratio in the same way they convert wide-screen films to SDTV. (We'll cover in-set conversion approaches later.)

Three approaches are used:

First, is when the conversion involves cutting off the sides of 16:9 image to a narrower 4:3 size. We refer to this as an edge crop or 4:3 center cut.

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.

Second, the entire production can go through a process called pan-and-scan. In this case a technician reviews every scene and programs a computer-controlled imaging device to electronically pan the 4:3 window back and forth over the larger, wide-screen format. The red arrows in this illustration suggest this panning movement.

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?

Finally, if the full HDTV/DTV frame contains important visual information (as in the case of written material extending to the edges of the screen), panning-and-scanning will not work.

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.

There is another way of handling the 16:9 to 4:3 aspect ratio difference -- especially for titles and credits. You've probably seen the opening or closing of a film on television horizontally "squeezed" in. We refer to this optical technique as anamorphic conversion.

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 here.
 

SDTV to HDTV In-Set Conversion Approaches  

HDTV receivers can also (roughly speaking) convert SDTV (4:3) and HDTV (16:9) aspect ratios. Manufacturers build three options into many HDTV receivers:

• Zoom - Proportionally expands SDTV horizontally and vertically to fill the 16:9 screen. This eliminates the unused blank areas we would normally see at the edges of the picture, but it also crops off some of the SDTV picture in the process.
  
  
• Stretch - Expands SDTV horizontally to fill the 16:9 screen. This makes objects a bit wider than they would normally be.
  
  
• Combined zoom/stretch - A hybrid of the zoom and stretch modes that minimizes the cropping effect of the zoom mode and the image distortion of the stretch mode.

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

In November 2000, moviegoers saw the film Bounce in both film and high-definition video.

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.

More and more "films" intended for theaters are being shot with high-definition video. After elements such as special effects, editing, and color correction are completed, a technician can convert the final product to 35mm motion picture film, or more commonly now record it on a hard disk for distribution to theaters.

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.  

Each year, the motion picture industry spends almost a billion dollars duplicating films and distributing them to theaters around the U.S. and the world. Films have limited life; they collect dirt and scratches and soon must be replaced. Video can cut the billion-dollar figure to a fraction of this amount. This file on digital cinema has more information on this.

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 here.

In addition to cost savings, digital cinema offers production advantages.

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.

The chart below indicates the excepted growth of theaters moving to some form of digital "film" projection.

Percentage of U.S. Digital Theaters 2005   (3%) 2006 2007 2008 2009 2010 2011   (70%) Today, most audiences can't tell the difference between professional film and video projection systems.

Traditional "Hollywood thinking" has long opposed production with video equipment for "serious, professional work."  However, today, the cost savings for video production alone, not to mention video's many production, post-production and distribution advantages, make the move to video for both production and theater presentation inevitable. The key differences between film and video are discussed here.

In addition to showing feature films, theaters with digital projectors can provide patrons with other entertainment, such as live concerts, Broadway shows, sporting events and productions aimed at special audiences.

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 Finally

Going to Catch On?

Over the years, three-dimensional (3-D) movies and TV programs often tried, but failed, to catch on with the general public. However, new technology such as HDTV, digital video projectors, Blu-ray discs, 3-D cable networks and the award-winning films such as the Avatar, which most people saw in 3-D, have are given 3-D a boost.

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. 

This link will take you to more information on 3-D film and video production.

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You can find information on film revenues, top grossing films and the future of motion pictures here.

For a more detailed look at the various DTV and high-definition standards in the United States, including those for digital cinema   click here.

In the next module, we'll begin discussing audio and video equipment, starting with a key part of a video camera: the lens.