Going Hybrid: Does LCOS Outshine Its Competition?

Strike up a conversation about projector technologies, and you’ll probably end up discussing the merits of LCD versus DLP. Those two imaging systems have the lion’s share of the projector market, though they’re not the only game in town. LCOS (Liquid Crystal on Silicon) is another imaging technology that’s well worth considering. It combines some of the best qualities of LCD and DLP, and is a particularly good choice for displaying video.

Much of the mystery surrounding LCOS grows out of a confusion over which projectors are based on the technology. You may be surprised to learn that JVC’s D-ILA, Sony’s SXRD, and Canon’s REALiS projectors are all LCOS based.

Why have different names for the same display engine? JVC invented the technology and named it D-ILA, which stands for Direct Image Light Amplifier. As the inventor, JVC holds multiple patents that protect its methods for manufacturing the D-ILA components. To get around those patents, other companies have developed different processes for manufacturing the same components. They can’t use the D-ILA designation, so they’ve adopted the generic LCOS name or created a new name to emphasize their improvements to the original technology.

As a reflective LCD technology, LCOS is a kind of hybrid projector system. “We use three LCD panels, so we share some of the properties of LCD, such as better color reproduction,” says Ricardo Chen, a technical marketing and sales training manager with Canon USA. While they’re similar in their color output, LCOS’s LCD panels can reach higher resolutions than regular LCD panels, because of the way the panels are engineered. “On a regular LCD panel, every pixel has circuitry around it,” Chen explains. “With LCOS, all the circuitry is in the back of the panel. That allows you to fit more pixels onto a panel, which is why you can get a higher resolution.”

Smaller, tightly packed pixels improve the overall displayed image. “Our pixel structure isn’t visible,” says Edgar Shane, a senior engineering manager for JVC Professional Products. “We call it a virtually invisible pixel structure. You don’t see the pixels, even if you come very close to the screen.”

Because there’s no partition between the pixels, LCOS projectors don’t suffer from the screen door effect, where the pixel structure becomes a distraction for the viewer. “Our pixels are defined only by the electrodes on the mirrored back panel,” says Shane. “You have a very mild blending between pixels within the LCD structure, and you don’t have any physical separation between LCD pixels in the LCD plane. That renders very nice, smooth, film-like images.”

The seamless pixel structure also benefits from the fact that LCOS is a reflective technology. “LCOS behaves almost like the micromirrors would on a DLP device,” says Chen. “While DLP reflects its light off of moving mirrors, LCOS reflects its light off the mirrored back of the LCD panel.” LCD projectors, on the other hand, are a transmissive technology. They shine the light directly through the LCD panel.

Just as LCD projectors can suffer from the screen-door effect, one-chip DLP projectors can suffer from the rainbow effect, where you may see a flash of colors when the projected image contains a quick cut or fast movement. LCOS doesn’t have that problem. “There’s absolutely no rainbow effect,” says Shane. “There’s no scanning effect because of ‘wobulation’ [a cost-saving display technology invented by HP that works by overlapping pixels]. It’s very much like a slide projector or film projector, where the colors are mixed simultaneously.”

LCOS’s reflective design also extends the life of the panels. “Some people complain that with LCD, after a long period of time, the panel itself starts getting burned,” explains Chen. “The image begins to have a bluish or greenish color. That’s the panel being damaged by the light.” That doesn’t occur with a reflective technology. “If you were to place a photograph outside in the sun, the direct light from the sun would eventually burn all the colors out of the photograph,” he says. “If you put a mirror outside, however, and have the sun bounce light off it, the mirror could bounce the light all day without any damage. You wouldn’t see any color difference.”

DLP has a clear advantage over LCD when it comes to contrast levels, so you might assume LCOS would have the same limitation because of its LCD panels. In fact, LCOS has a wider contrast range than LCD, because once again-like DLP-it’s a reflective technology. “DLP’s reflective micromirrors move the light to one direction or another direction to create an on-off type of situation,” says Chen. “On a LCOS reflective panel, you have the same situation, because you have a reflective LCD panel. As the light hits the panel, the light is either polarized or non-polarized. It’s the polarization that creates the same kind of on-off you get with DLP. Therefore you have a higher contrast.”

How high can the contrast go on a LCOS projector? JVC recently introduced the DLA-RS1 ($6,295), a D-ILA projector with a native 15,000:1 contrast ratio, which JVC claims is a first for a home cinema projector. Weighing a hefty 26.5 pounds and sporting a brightness rating of only 800 ANSI lumens, this one is clearly targeted at home theater applications. It also features an assortment of video inputs (component, composite, S-Video and two HDMI) and a low noise level (27dB).

Shane points out that all of JVC’s projectors are now native 1080p with a true 1920 by 1080 resolution. “DLP-based projectors-especially rear projection screens-are sometimes labeled as 1080, but they use wobulation, so they don’t have that native resolution. They use just half of the image on one side, and on the other side, they’re trying to use less pixels to produce a full size image.”

Canon is taking a different approach to boosting the contrast ratio of its LCOS projectors. The company’s REALiS SX60 ($5,999) offers a Home Cinema Mode that doubles the native contrast ratio from 1,000:1 to 2,000:1. The SX60 achieves this by reducing the brightness of the projector’s native 2,500 ANSI lumens. This split personality is an acknowledgement that projectors often do double duty as both business and home projectors. The same projector that presents data or video at a company’s marketing meeting on Friday may display the big sports game at an executive’s home the next day.

Sometimes innovations in one product are actually borrowed technologies from another product. Sony is taking some of the technologies from its LCOS-based digital cinema projectors and applying them to the company’s LCD-based business projectors. The result is a merging of LCOS and LCD technologies, to which Sony has given the name BrightEra.

“We took some of the learning that we developed for our SXRD panels, and then reapplied it back to high-temperature polysilicon devices,” says Kevin Handerson, a Sony projectors marketing manager. “We don’t think high-temperature polysilicon is at the end of its technological road.”

BrightEra’s LCD panels are still transmissive rather than reflective, but the LCD molecules are now vertically aligned. “The vertically aligned structure allowed us to implement a normally black aperture,” explains Handerson. “Unlike most LCD crystals, which are normally white, and to which you apply the voltage to turn it black, this one is the other way around.” Because the crystals are natively black rather than natively white, a BrightEra projector can handle blacker blacks than a traditional LCD-based projector. “In darker rooms, this higher contrast ratio really pays off, especially with video,” he says.

And where LCOS holds an advantage over LCD because of its tightly packed pixels, BrightEra helps to close that gap by reducing the size of each pixel without reducing the brightness. “We’ve made some advances in shrinking the switching transistors, so we have a higher aperture ratio on the panel itself,” says Handerson. “This kicks down the shadow lines between the pixels, which occur at the junction points where the switching transistors are located. Those have shrunken, and the signal paths themselves have also shrunken.” This lets Sony use a smaller panel for the same level of brightness, or to draw more brightness out of the same size panel. “We could build less costly projectors that have better performance specs,” he says.

So far, Sony has released two projectors with BrightEra improvements-the VPL-FE40 ($7,950) and VPL-FX40 ($6,150). Both are rated at 4,000 ANSI lumens, with the VPL-FE40 having a native SXGA+ resolution, and the VPL-FX40 having a native XGA resolution. Sony prefers not to publish contrast ratios for its projectors because there’s currently no industry standard for measuring contrast levels. “We definitely don’t emphasize it, but if someone requests bids or information, then we’ll tell them as best we can, as long as we’re clear about how it was measured,” says Handerson. “Sometimes in those situations, the best thing is to bring the projectors to the location where they would be using it, and show the material they would actually be showing. We then ask them whether it meets their needs.” Ultimately, that’s the only way anyone can be sure a projector’s specifications will match up with the job at hand.