Electronic Cinema 
by Jim Mendrala
for TV Technology, © 1995 All rights reserved.

Electronic Cinema is being discussed and worked on by several American and foreign companies. Theatergoers, in the not to distant future, will see bright, high resolution images of at least 35mm quality, projected onto the big wide screen. This idea of converting movies into a high-resolution, digital bit stream (or packets of data) and delivering that bit stream to theaters with quality as good as the film itself has the major motion picture studios turning an eye towards the economic realities of electronic distribution - "Electronic Cinema".

 Electronic Cinema can bring a number of important advantages to the evolution of the motion picture film industry. First is the amount of time and money saved, an especially important consideration to the producer and/or distributor. Second, Electronic Cinema can equal or better the very best cinema of today with its 35mm or 70mm quality images. Technically, with today's technology, there isn't any reason why film images (limited only by the film itself) cannot be projected electronically onto the big screen.

 Some believe that HDTV is the cinema of the future. But HDTV has some inherent problems as we shall see. Its resolution, though high, is only capable of super-16mm quality. The incompatible frame rate, inadequate bandwidth, inadequate number of scan lines, interlaced fields, and bandwidth limited color, all combine to stymie efforts at real qualitative improvements in image quality for the wide-screen cinema. The broadcast-imposed standards of the television industry have tended to thwart the application of a time- and money-saving video technology to a major field of application - namely Electronic Cinema.

 Today, movies are printed and the prints are sent via land, sea, and air to the various theater chains. Even though security is tight, piracy of the print to be shown does happen. Prints for a typical movie are expensive. They can average as much as $2700 per print copy. Prints also show wear and tear. Prints get scratched and cinched. Prints break and have to be spliced back together while the audience sits and waits. Sometimes print reels inadvertently get shown out of sequence. Also, when switching from one reel to another, the film might be projected out of focus, sometimes for only a short time, sometimes for the length of the whole reel.

 In the near future, a whole new way of delivering movies will evolve. Films today, with existing HDTV technology, can be transformed into a digital signal using either the NHK 1125/60 HDTV system or the European 1250/50 HDTV system. With the 1125/60 HDTV system, the frame rate is 30 frames per second (fps). This is not desirable, since film in the U.S. is shot and projected at 24 fps.

 The 1125/60 HDTV telecine must convert the 24 fps to 30 fps using the 3:2 pulldown technique. Not a very good idea. Various digital compression schemes, such as MPEG, have ways to look only at the actual 24 fps, thus freeing up some of the time that would be wasted on compressing a video frame made up of one field of the previous film frame and one field of the next film frame. Sometimes the 3:2 pulldown detectors get fooled. This is another reason why Electronic Cinema cannot be led by conventional HDTV television technology that is being advocated in this country.

 The American Society of Cinematographers (ASC) have insisted upon a 24 fps rate. With the European 1250/50 HDTV system, the frame rate is 25 fps. This is closer to the 24 frame rate used in the U.S. and the one the (ASC) is insisting on. Film in European and other 50 Hz countries is projected at 25 frames per second. The difference between 24 and 25 is 4%. With Electronic Cinema films can be shown at their original frame rates, be it 24 fps or 25 fps.

 Both of the above HDTV systems use a 2:1 interlace, yet the film is scanned progressively and converted to interlaced scan. The main reason for using the 2:1 interlace was primarily to reduce flicker. Electronic Cinema progressively scans the film. One major service bureau presently scans the film progressively and generates a digital file for every frame, with a resolution equal to or better than the film itself. We have seen the results on the wide-screen in such films as Forest Gump, Apollo 13 and others. Those digital bit streams were put back on film with no apparent loss of resolution even though they were manipulated through various types of computers.

 As you can see, capturing a film digitally with quality as high as the film itself is being done today.

 Let's look at a typical film projector. The projector has either a two or three blade shutter that allows each frame to be displayed two or three times per frame. Thus, what is seen on the screen is either a 48 or 72 picture-per-second picture but at a 24 fps rate. Because of the light loss with a 3 blade shutter most theaters use a two blade shutter. This gives a picture a perceptible flicker that gets worse as the amount of light is increased. Flicker tends to disappear when the display rate approaches 60 fps. With today's digital technology, to display a picture 2 or 3 times between frames is not a problem. 24 fps can be displayed at 72 (3x24) picture-per-second and 25 fps can be displayed at 75 pictures-per-second, well above where flicker tends to be perceptible. MPEG compression, in a way, does this now when the 24 frame image is decompressed and it's output displayed at 30 fps.

 Most compression schemes are upward scalable. This means that if MPEG, as an example, was used, it could be scaled to do wide- screen, Electronic Cinema including scope-type films with their 2.35:1 aspect ratio and beyond.

 Today, when a producer or film studio transfers a film to video, the process is very lengthy. A colorist does a scene-by-scene color correction on the film. The film from the film lab, as good as it is, is not as color correct as is required in a HDTV viewing situation. After the scenes are color corrected, the film is transferred into a digital signal and recorded. Electronic Cinema would be no exception. A colorist would be required here also. As a matter of fact, the only difference is that the film would be observed on a large screen not some small CRT type of monitor. Because of the CRT's phosphores, CRT's cannot display as much color as the film image contains. New projectors can display as much color as the film has. HDTV has reduced resolution in the color. Equal resolution color is a must for big wide-screens, something HDTV cannot deliver.

 Lately, a new person has been added to the list. A compressionist. Sometimes the colorist does both functions and is known as a Compression/Colorist. That person not only optimized the color but also the compression. The main reason for the need of the compressionist is that today films are destined for bandwidth-limited systems. A CD-ROM, for example, cannot support the high data rates necessary for wide-screen, high- resolution pictures. Even the new Digital Video Disk (DVD) is only up to standard broadcast quality. The so called "Sweet Spot" in MPEG encoding for professional broadcast quality is around 6 MHz. For HDTV and wide-screen Electronic Cinema, the data rates are much higher. Today, it is not only possible to record that high amount of data with existing technology, but it is possible to distribute that data by fiber optics or, more economically, via satellite.

 Today's satellites are designed for the traditional data, communication, and television type of signals. Even with today's satellites though, the much better Electronic Cinema type of pictures are possible. In the near future, satellites dedicated to Electronic Cinema movie distribution will be in place to replace the current system of distribution.

 Since the signal is digital, no loss of quality would be visible to the moviegoer. And because it is digital, various encryption schemes could be employed to protect the feature from unauthorized exhibition or piracy.

 Once the digital bit stream reaches the theater, either via fiber optics or satellite, it finally needs to be displayed.

 Projection systems today fall into three main categories, emissive, transmissive light valve, and reflected light valve. Emissive displays are based upon cathode ray tubes (CRT) or laser technology. CRT projectors today are relatively dim and limited to approximately 1 Kw power input. The best CRT projectors give a maximum light output of approximately 1,000 lumens at peak white. CRT projectors can suffer poor resolution in the corners, spot growth at high beam currents, or visible line structure at low beam currents. Laser CRT projectors offer potentially higher power and more efficient operation but depend on very low operating temperatures and the efficiency of the blue lazing material is low. Laser projectors in general require mechanical scanning and high power demands and potentially high costs. Image speckle has been an obstacle in laser projectors even though techniques can minimize this problem.

 Until the Liquid Crystal Display (LCD) projector, large screen projectors were based on electron beam addressed oil films to produce high brightness projected images. These projectors require continuous adjustment during their operating life.

 LCD Projectors based upon transmissive active matrix light valves, however, have efficiency losses due to polarization and partial blocking of the light path by the active matrix. They also deliver pixelized images, with low resolution, which is inherent in their design. Image lag is also a problem on some displays.

 Reflective LCD light valves deliver, a very bright, pixel-free image with more than 400% more contrast and much higher resolution. The reflective LCD is addressed with a low level infrared, high resolution CRT imaged onto a layer of liquid crystal (one for each of the tri-stimulus colors, RGB).

 Digital Micromirror Device (DMD) projectors are reflective also but unlike CRT's or reflective LCD's, use tiny micro-size mirrors to reflect the light through a lens to the screen. Pulse width modulation also known as Digital Light Processing (DLP) modulates the intensity of the light as seen on the screen by the eye. This produces a linear modulation or unity gamma (i.e., gamma = 1.0). A DMD device for each of the primary colors (RGB)) is used and being solid state, like a CCD color camera, requires only a simple one-time registration. Interlaced pictures are not suited to DMD devices, however, as only half the maximum possible picture brightness would result. By using progressive scan, the vertical spatial bandwidth is increased by about 60%. DMDs are inherently flicker free devices with no lag. The DMD type of projector produces a picture which is similar to projected film. The technology is scaleable and can provide aspect ratios of the projected image to include all known aspect ratios, such as 2.35:1 (scope), 2.2:1, 1.85:1 (wide screen), 1.78:1 (HDTV - 16x9), 1.66:1 (15x9), and 1.33:1 (4x3).

 Electronic Cinema being developed today will evolve into a more efficient way of delivering to the moviegoer a bright, sharp, excellent color, high resolution, in focus, movie feature presentation with digital clarity and digital CD quality multi- track surround sound audio.

 The loss of prints enroute to the theater will be eliminated. Film breaks will be eliminated. Scratched or cinch marked prints will be a thing of the past. Encrypting of the digital data will make piracy extremely difficult. Satellite delivery will make distribution costs plummet. All solid state DMD type of projectors will make digital display of the movie possible and relatively maintenance free, a real advantage to the cineplex theaters of tomorrow.
 
 

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© 1998-2001 by James A. Mendrala








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