An explanation of video projection technologies and the acronyms that define them
“ACRONYMAPHOBIA”: A vague, previously indefinable, underlying fear among technophiles of not being capable of understanding the ever-increasing variety of video projection display technologies and their inevitable acronyms.
LCD, DLP, LCOS, 3LCD, CRT, LED, OLED, SED, WWJD! “STOP! I can’t take it anymore!”.
Step away from the screen and put down the remote…slowly. Breathe. Let’s talk this out.
ALL THAT AND A BOX OF CHIPS: COMPREHENSION
Although all of us are familiar with the idea of not needing to totally comprehend something in order to benefit from it (i.e. I don’t really know how my microwave oven works but pass me another warm sweet roll please).
I believe it’s important for those of us committed to being leaders in the use of today’s technology in ministry to gain at least a basic (and preferably an in-depth) understanding of the current and emerging technologies behind (or more accurately, inside) the video projection technologies, along with the strengths and weaknesses of each, which, by the way, is precisely the primary goal of this article. Such knowledge will not only greatly assist us in selecting the best display technology for our unique application and budget but also help us to be wise stewards of our God-entrusted financial resources.
If better, smaller, cheaper, faster is the mantra of technological progress in general then better, smaller, cheaper, brighter could easily be the mantra for video projection technologies in particular. This is demonstrated most clearly in the significant advances made in the manufacturing of the primary component within your “box” projector: the imaging chip (which actually consists of several components). Today’s current crop of video projectors is almost entirely built around four primary display technologies: LCD, 3LCD, DLP and LCOS. Each technology has unique strengths, limitations and technologies.
Before venturing into comparing the strengths and limitations of these image display technologies, here is a short and very basic primer on how each of them work. These explanations were sourced directly from product manufacturers, namely, Hitachi (LCD & 3LCD), Canon (LCOS), and Texas Instruments (DLP).
LCD (LIQUID CRYSTAL DISPLAY)
LCD is the projection technology you are probably most familiar with as it has been around the longest. One of the first applications of LCD panels was with an overhead projector as a light source.
“LCD imaging technology features three liquid crystal panels to create the image on the screen,” says John Glad, Product Manager at Hitachi America, Ltd. “These panels allow light to pass through them to create the image.”
The image is then projected through a lens and on to the screen. Unlike DLP which is a reflective technology, LCD relies on light actually passing through its translucent glass panels which means it is a transmissive system (as opposed to a reflective system like DLP).
“As the new kid on the block, 3LCD is a new display technology that builds on LCD technology and is continuing to build in momentum.” explains Glad. “Although LCDs are a critical component of 3LCD systems and from which 3LCD derives its name, the two technologies are not the same.”
Glad continues, “3LCD technology employs a series of dichroic mirrors to focus separate light from a high pressure mercury lamp into red/green/blue signals where they are, in turn, focused through three separate LCD or high temperature polysilicon (HTPS) panels to provide high levels of light transmission and high color reproducibility. The three HTPS panels then refocus their separate colors through a prism that combines them and feeds them through a projection lens. By borrowing from both DLP (reflective technology) and LCD (pass through ‘transmissive’ technology) 3LCD hopes to bring together the best of both worlds.”
DLP (DIGITAL LIGHT PROCESSING)
In 1987, Texas Instruments invented DLP technology which uses an optical semiconductor, known as a Digital Micromirror, or DMD to create its projected images. Michael P. Guillory, Worldwide Marketing Communication Manager for DLP® Products at Texas Instruments breaks it down, “DLP technology includes an optical semiconductor which contains over a million tiny, microscopic mirrors which reflect light to create an all digital image.”
How tiny are these mirrors? About 1/5 the width of a human hair. The mirrors are mounted on hinges with a very small space between each mirror (less than 1 micron). Electrodes are used to control each mirror. These tiny mirrors have the ability to tilt from + 10 degrees to -10 degrees based on the digital signal it is receiving. Just imagine being able to flip a light switch “on” and “off” several thousand times per second. Now THAT would be annoying!
The light source reflecting off of the DLP chip is projected as the video image via a lens. “Each frame of a video clip needs to be processed; digitally separated into its red, green and blue components and digitized into hundreds of thousands of samples (sample count is based on chip resolution) for each color. The individual samples control individual mirrors.” Guillroy explains.
LCOS (LIQUID CRYSTAL ON SILICON)
“LCOS is a reflective technology (like DLP) that uses liquid crystals (like LCD). Unlike LCD, LCOS does not have circuitry for each pixel.” says Ricardo A. Chen, the Manager of Technical Marketing & Sales Training for Canon’s Consumer Imaging Group’s Video Marketing Division.
“One of the initial challenges with LCOS projectors was their size. Because of this sophisticated technology, LCOS projectors tended to be heavier and bulkier than their LCD and DLP counterparts. Additionally, efforts to manufacture an LCOS projector that provided both high contrast and high brightness were fruitless—models would either have one or the other.
“Canon, however, has developed a solution to the LCOS size issue with its patented, proprietary AISYS (Aspectual Illumination System) optical engine.”
Chen illustrates even further. “AISYS incorporates a unique Optical Illumination System that maximizes the light path from the projector’s lamp to its lens. In conventional LCOS projectors, if the distance between the lamp and panel is shortened to improve brightness, the illumination strikes the LCOS panels at a wide angle, resulting in light seepage and reduced contrast. AISYS uses a compressor lens and a condenser lens to remedy this problem. The condenser lens increases the brightness, while the compressor lens adjusts the light direction so that it hits the PBS (polarized beam splitter) and LCOS panels at an angle that preserves high contrast.
“The optical path of a Canon AISYS-enhanced, LCOS-based projector is complex but effective. It basically involves three LCOS panels (red, green, and blue) precisely aligned with a special prism known as a PBS. The polarization allows light to pass in two directions at once.
“The PBS also handles the process of color separation and combination. The PBS separates the light so that each panel only receives red, green, or blue light. The light is polarized in one direction before it hits the LCOS panel, and in the other direction as it leaves the panel. If the polarization is shifted from the original polarization, then the PBS reflects that light towards the projection lens path.
“The color phase plate and every other component employed in the separation and combination of light have been optimized to match the polarization properties of the PBS. The final path for the light to travel is through a high-performance 1.7x genuine Canon optical zoom lens. The lens coating prevents ghosting and flare, maintaining optimum image quality.”
PROJECTION TECHNOLOGY COMPARISON
As part of my research for this article I asked manufacturers to “make their case” for why theirs is the superior projection technology. I then combined their feedback with additional non-manufacturer research in my quest for good old-fashioned “no spin” reporting.
Even with my last name only one letter away from one of these technologies (I bought a vowel) I have no vested interest in your choosing one technology over another. (i.e. I’m not a dealer for a particular manufacturer).
Since LCD and DLP have been around a lot longer than LCOS and 3LCD most of the current comparison data revolves around comparing these two technologies.
Traditionally LCD has held an advantage in pricing although cost is quickly becoming less and less of an advantage for LCD projectors especially compared with DLP which has seen substantial price reductions. As indicated at www.projectorpoint.co.uk LCD has also demonstrated a bit better contrast ratios over DLP and is a bit more ‘light efficient’ than DLP, which means if you put the same wattage lamp in both an LCD projector and a DLP projector the LCD will usually produce a brighter image. LCD images can display better color saturation than DLP which can fool people into thinking a particular LCD projector is brighter than a DLP projector although the whites on the DLP projector could actually be brighter.
Older LCD projectors often suffer from a bad case of the “screen door” effect which simply means a displeasing matrix or grid is visible in the image. Imagine looking at the image through a screen door and you’ll know what I’m talking about. (a.k.a. the “chicken wire” effect). Another disadvantage of LCD is the possibility of “dead” pixels. This is barely noticeable with only a few dead pixels but once the number of these “permanently off” pixels are found in a display it becomes highly distracting. Since LCD’s have a fixed number of pixels (resolution) if you are inputting an image which has a higher resolution (HD, etc.) than the projector’s fixed native resolution, the image has to be scaled down to match the projector’s resolution thereby degrading the image quality.
3LCD claims significant advantages over DLP because it uses three chips to form a full-color picture. DLP projectors, however use only a single chip, sequentially displaying RGB images in rapid succession, which can create a strobing image. This phenomenon is known as the “rainbow effect,” and it forces the viewer’s eyes to work harder to focus on the picture. 3LCD technology enables each of its three panels to reproduce up to 8 bits – 256 levels of brightness per color, resulting in 24 bit color – 16.7 million true colors on screen. The way in which the 3LCD projection system projects the component red, green and blue colors simultaneously provides colors that are clean and accurate, with no color break-up which is also, some claim, less stressful on the user’s eyes. Your mileage may vary.
3LCD projectors generate less heat than the competition and are very light efficient. 3LCD projection systems also claim dazzling brightness, true-to-life color saturation, and razor-sharp contrast for displaying digital content.
Manufacturers of 3LCD video projectors claim their method of employing a series of dichroic mirrors to focus separate light from a high pressure mercury lamp into red/green/blue signals ensures that all three primary colors are transmitted constantly, always providing the brightest and sharpest image. They also claim that this allows for more accurate color reproduction thanks to better control and recombination of the RGB signals.
DLP (DIGITAL LIGHT PROCESSING)
DLP technology has been used in projectors for over 10 years now, but just recently has become particularly popular and has now exceeded 50 percent market share in front projectors worldwide.
What has made the DLP chip so popular is its ability to create a sharp, bright, and clear image that doesn’t suffer from a potential LCD phenomenon often referred to as Color Decay. If you’ve ever seen a projector image that has a yellow or green tint to it, that’s probably an LCD projector that has experienced Color Decay. Color Decay may manifest itself over time in the form of inaccurate colors (usually resulting in a yellow or green hue on the screen). When this occurs, the projector’s LCD panels cannot be repaired. Instead, they must be replaced, which could be expensive.
DLP technology, on the other hand, simply reflects the light onto the screen and does not bear the brunt of the light source, making it practically impervious to any picture degradation or Color Decay over time.
DLP picture technology offers other advantages beyond just picture reliability. Contrast ratios (how black is the black and how white is the white) tend to be higher on a DLP projector. This improves the picture quality and increases performance in higher brightness environments. You might also notice better video performance on a DLP projector with a smooth, film-like performance.
Some downsides to DLP technology is the potential “rainbow effect” in lighter parts of the image and color saturation could be a bit lower with DLP than LCD although these issues were much more apparent in older DLP projectors using four segmented color wheels as opposed to newer units which use color wheels with six segments and spin faster, which help overcome these limitations. DLP, although prices have dropped dramatically, could still be a bit higher priced than LCD units.
LCOS (LIQUID CRYSTAL ON SILICON)
For years, LCOS has been overlooked due to higher pricing, but recent advantages in technology have brought the price down.
LCOS displays are either three-panel or single-panel. In three-panel systems each of the three primary colors (red, blue and green) has their own chip with the images combined optically. Single-panel systems use one chip to display the red, blue and green elements in rapid succession allowing the human eye to perceive a smooth color/image flow.
LCOS does not have circuitry for each pixel. The lack of circuitry for each pixel makes for larger pixel aperture which, in turn, virtually eliminates the screen door effect. The heat sinks on the back of the LCOS panels cool better than with LCD panels, giving LCOS panels a longer lifespan due to a better ability to withstand heat.
It is especially well-suited for displaying small print in spreadsheets and other PC-generated graphics. LCOS also provides grid-free images, high resolution, and faster response times—which makes it an ideal projector for video playback. The contrast ratios are not as high as with DLP, but the pixels are smoother, which gives LCOS-generated images a more natural look.
PIXEL THIS: CONCLUSION
Your eyes are the ultimate judge.
Clearly, projecting images on large screens in large spaces can present many challenges. Ambient light, viewing angles, screen size and location, audio, budget and other factors all must be considered when determining the appropriate projector for each specific projection application. The good news is that each technology provides excellent image projection value and quality.
Regardless which projector and projection technology you invest in the following is a brief summary of the primary considerations you’ll want to keep in mind:
1) Contrast Ratio – How well a projector can produce black blacks and white whites is a significant factor in overall picture quality. The higher the better.
2) Brightness – It’s almost impossible to beat the buy-the-brightest-projector-you-can-afford philosophy but be careful to avoid only comparing brightness.
3) Color Saturation/Accuracy – Do the colors of computer graphics and video footage appear washed out or even over saturated? Are they true to life?
4) Pixel Density – This is especially important if you want to project high definition video and/or images. As with contrast ratio get the highest pixel count you can. 1024 x 768 will suffice for standard definition DVD but 720p HDTV signals need a 1280 x 720 pixel count and a 1080i signal requires a 1920 x 1080 pixel count for optimum image quality.
5) Texture – What I call the “feel” of the overall image? Does it appear realistic (flesh tones), pleasing (not harsh), smooth, consistent and devoid of distracting artifacts, rainbow or screen door effects.
Of course, the above distinctions need to be made with a properly-adjusted video projection unit so don’t assume the factory settings are optimum right out of the box.
Thanks to the steady advancement in image display technology on all fronts it’s a great time to purchase a video projection unit which can not only meet, but exceed your needs and expectations. By doing a bit of homework (thanks for reading this article!), evaluating projected images first hand and arming yourself with key questions when shopping you’ll position your ministry to gain the greatest benefit and value possible from today’s line up of excellent video projection technologies. And you’ll overcome Acronymaphobia to boot!