Who Said It's Not The Projector?
by Michael Karagosian
© 2000 MKPE Consulting All rights reserved worldwide
Published in the December 2000 issue of Digital Cinema Magazine
and the March 2001 issue of In Focus Magazine
It's no surprise that the eyes on digital cinema tend to focus on the projector. The early ShoWest 1999 demonstrations of Texas Instruments (TI) DLP Cinema and the then Hughes/JVC ILA projector (now simply JVC) made it clear that there were significant visual differences in digital projection technologies. The following year, at ShoWest 2000, the demonstration of side-by-side projections of DLP Cinema and 35mm film were revealing, clearly showing the strengths of both digital and film technologies.
The ILA projector disappeared from the race, and most of us are aware that today's prototype digital cinema installations are based on a single projection technology, the TI DLP Cinema. In fact, at the time of this writing, all digital cinema installations are based on prototype projectors supplied directly by TI. In mid-2000, TI licensed three companies to commercially build and sell their technology. However, these manufacturers have only just come forth with their production models, so we have yet to see production units in the field.
We are only in the very infancy of digital cinema, and just how young this business is can be seen in the decision to utilize a single brand of projector in today's prototype digital cinema. Back in 1999, while audiences at ShoWest were watching the same or similar material shown on different digital projectors, there wasn't an emphasis on the fact that the digital source material was not interchangeable. While the demonstration material was sourced from similar playback devices at each projector, those being the JVC D5 recorders using outboard D5 compression, the colorimetry of the source material was not the same. In short, each recording was "color timed", scene-by-scene, in the transfer lab to match the color characteristics of the different projectors. For the same reason, the decision to use the two makes of projector in the public Phantom Menace demonstrations also required the creation of two differently mastered digital movie files.
There are several reasons as to why digital cinema isn't ready for full-scale rollout. The practical need for multiple means of movie file delivery to the exhibitor, the current limitation of a single vendor for image compression, the lack of a conditional access system to govern authorized users, and the absence of data security in today's prototype systems come to mind. But tucked away on that same list is the need for single inventory, back at the distributor, for digitally mastered files. Or in other words, without a method for mapping the intended visual presentation to the inherent colorimetry of the projector, we're stuck with a single projector type for viewing digital movies. Obviously, at a time in history when we're practically addicted to the rate of change of digital technology, nobody wants digital cinema to be married to a single projector.
Recognizing the opportunity, there are many interesting projection technologies in development. How these technologies solve the colorimetry problem is not clear. But the starkly different approaches to digital cinema projection is fascinating, and we'll explore that in this article.
We've already mentioned the TI DLP Cinema projector (http://www.dlp.com/cinema/), used in 50% of the digital Phantom Menace screenings, and the only choice on the market today for digital cinema. Projectors based on the DLP Cinema chip, also known as the "black chip", are now sold exclusively by the three licensees Barco, Christie Digital Systems, and Digital Projection. The chip holds an array of 1280 x 1024 moving mirrors. These mirrors are individually flipped at a high rate to create a gray scale for each of three primary colors. As a result, an entire frame is created and projected at a time, versus more traditional CRT-like methods that rely upon scanning. The name "black chip" was coined due to the black that is deposited between the mirrors, reducing the reflected light between mirrors to improve the contrast ratio, a unique feature of this chip over other DLP chips. While the ability to project an entire frame at a time makes it efficient in terms of light transfer, it's also its main handicap. Scaling this technology from the 1.3 million mirrors required of today's "black chip" to the 2 million mirrors required of digital HDTV (1920 x 1080) poses severe fabrication yield problems - problems which TI is diligently working on. Even though the current chip cannot produce HDTV resolution, it has provided a great start for digital cinema, and will probably be with us for awhile.
The JVC (http://pro.jvc.com/pro/hjt/products/ila12k.html) ILA-12K projector was used in the other 50% of the Phantom Menace digital screenings. ILA stands for Image Light Amplifier. The technology is based on writing a low-intensity image onto a liquid crystal by means of an electron gun. The refractive characteristics of the crystal are modulated by the electron beam. The liquid crystal rests on top of a stationery mirror, onto which a high-intensity polarized light source is focused. As the electron beam image alters the refractive characteristics of the crystal, the high intensity light source is modulated accordingly. Unfortunately, the complex design of the ILA projector made it tedious to align and a redesign was never introduced. Instead, JVC introduced a pixilated integrated circuit version of this technology called D-ILA. These chips have an array of liquid crystals, built on a reflective surface, where the crystals are modulated to control the reflection of high intensity, polarized reflected light. At Infocomm 2000, JVC announced a 2048 x 1536 pixel D-ILA chip, capable of supporting digital HDTV. Kodak has announced that they are conducting tests of this chip, and other potential projector manufacturers are also said to be sampling it. Of all the non-DLP technologies presented here, D-ILA is the most mature. Expect a D-ILA digital cinema projector to be demonstrated sometime in 2001.
Silicon Light Machines (http://www.siliconlight.com) received a lot of press this year when they granted an exclusive license to Sony for display applications of their Grating Light Valve (GLV) technology. Following the granting of this license, the company was purchased by Cypress Semiconductor. The GLV is also an integrated circuit technology, but based on chip-scale ribbons of reflective aluminum which can be bent using electrostatic forces generated on the chip. In practice, light from a laser is reflected off many segments of the ribbon, collected, and projected. A linear array of these creates a vertical column of image. This vertical column is then scanned across the screen, creating a full picture. The GLV modulates the reflected beam by moving the ribbons just enough to create wave-level interference, modulating the intensity of the reflection. Since a binary method isn't used for modulation, the GLV is theoretically capable of generating an infinite gray scale, and a large contrast ratio. The modulation can take place at very high speeds, allowing frame rates as high as 120 Hz. Those who have seen small screen demonstrations of this projection technology rave about the quality. One of the major strengths of the GLV is that, at it's core, it relies only upon a vertical column of pixel elements, and not a raster of elements. This significantly reduces the cost, and improves the scalability of the product. However, the biggest barrier that the GLV has in regards to digital cinema applications is the powerful lasers required. Unfortunately, these aren't available off-the-shelf, and the development cost of appropriate lasers prior to the Sony deal was prohibitive. Over the next few years, Sony is expected to put this technology to work in their consumer displays, probably as a replacement for the aging Trinitron. It will probably be awhile before large screen GLV projectors will appear on the market.
Principia LightWorks, Inc. is also developing a new method for digital cinema projection, which is similar to but a major improvement over today's CRT projectors. CRT projectors are still considered to have the highest quality images among commercially available projectors today, largely because the number of lines of resolution are not limited by a pixelated display method. Principia's technology is based on their Laser Cathode Ray Tube, or L-CRT. As in a traditional CRT, electron beam scanning is used but, rather than striking a faceplate coated with red, green and blue phosphors, the electron beam strikes a semiconductor crystal faceplate. When excited by the beam, the semiconductor crystal produces light by laser action, resulting in a CRT-style projector with ultra-high brightness. It's expected that the low manufacturing cost and high quality of the L-CRT will make this attractive for large screen digital projection. Principia LightWorks has recently begun projecting digital HDTV images. Expect to see a public demonstration of L-CRT technology in 2001.
A simple, yet potentially powerful improvement over the older ILA projector is in development by Chromalux, Inc. The projector uses an offset electron gun to write to a LCD crystal, causing the crystal to gate light following the beam action. A second, mated electron gun forces the crystal to return to it's quiescent state at the same speed that the crystal was written, dramatically reducing smear. Unlike the reflective method used by similar projectors, Chromalux simply passes light directly through the liquid crystal and then to the lens, for minimum absorption by the crystal. As with other CRT-driven projectors, the Chromalux system is not matrix based and therefore does not have the limitations of a pixilated system. The Chromalux image can be geometrically shaped without loss of light or resolution, and is said to conservatively produce 3300 lines of resolution per frame, also with a large contrast ratio. While private demonstrations have been taking place, public demonstrations are not expected for at least 2 more years.
Keep your eyes open. Without doubt, the best is yet to come.