By CNET Asia staff
20/08/2008
URL: http://asia.cnet.com/buyingguides/home_av/0,39066264,62044996,00.htm

Introduction

The backbone of early movie theaters, modern digital projectors have evolved tremendously and are now common sights in auditoriums, offices and even private home theaters. They're also a lot more affordable these days and offer a big-screen experience that's second to none. In a nutshell, these light cannons are most cost-effective for screen sizes in excess of 60 inches, considering the exorbitant pricing of similarly sized flat-panel TVs such as Panasonic's S$99,000 103-inch plasma.

Type of projectors

Although there's a dazzling array of makes and models available in the market, projectors can be segmented into two broad categories: Home theater and multimedia.

Home theater

These home theater projectors can be easily identified by their widescreen (16:9) format and high-contrast performance. Optimized for movie playback in light-controlled environments, most have only modest brightness levels and are shipped in mainly three film-based native resolutions, from standard-definition 480p to high-def 720p and 1080p.

Common resolution	Pixel size (H x V)	Applications
480p	854 x 480	DVD
720p	1,280 x 720	Entry HD
1080p	1,920 x 1,080	A.k.a. full-HD for Blu-ray

Other auxiliary functions targeted at enhancing picture quality include powerful video processors, Imaging Science Foundation Certified Calibration Configuration (ISF 3C) for professional color tuning, dynamic iris control to boast dynamic contrast, etc.

The dynamic iris, in particular, works by restricting light output on-the-fly to yield deeper blacks in dark scenes, while allowing maximum emission during bright clips. Using an InFocus Play Big IN83 as an example, this enables a three-fold leap from a native 5,000:1 contrast to 15,000:1.

Multimedia

The business-centric counterparts of their home theater siblings, multimedia or data projectors emphasize brightness for presentations and produce mainly standard 4:3 aspect ratio projection in computer-based resolutions. The latter encompasses entry-level SVGA and popular XGA sets to Excel spreadsheet-friendly SXGA and rare WXGA wide entries, among others.

Common resolution	Pixel size (H x V)	Aspect ratio	Applications
SVGA	800 x 600	4:3	Small meeting room
XGA	1,024 x 768	4:3	Conference room
SXGA	1,280 x 1024	4:3	CAD/CAM, Excel spreadsheet, etc.
WXGA	1,280 x 800	16:10	Widescreen laptops

Besides resolutions, multimedia projectors can be subcategorized into portable, conference room and auditorium models in terms of form factor and brightness. As a quick reference, a true mobile portable will have a weight of less than 2kg. On the other hand, the light output of the conference and auditorium equivalents is rated at over 2,000 and 4,000 lumens, respectively.

As for the extra bits, expect productivity enhancements ranging from wireless connectivity option and integrated network administration to a secondary lamp for redundancy and instant powering-up plus shutdown capabilities. Some higher-end kits also have onboard multimedia playback for PC-less presentation via a memory card slot and PowerPoint conversation software.

LCD vs. DLP vs. LCoS

You may have come across the mammoth three-gun CRT projectors of yesteryear, but the latest crop of digitized beamers are now powered by three display technologies: LCD, DLP and LCoS. Each of these has been implemented in home theater and multimedia applications, differentiated by their unique strengths and weaknesses as follows:

Liquid Crystal Display (LCD)

The most mature technology among the trio, LCD projectors have an underlying optical engine that comprises three independent liquid crystal display panels for the primary red, green and blue colors. Each of these transmissive panels contains thousands of pixels used to modulate light from a lamp, which is then combined by a prism to form a full-color image onscreen. Currently, almost all offerings under this genre are using Epson's 3LCD engine.

Pros	Cons
Short to mid throw	Screen door effect
Vertical and horizontal lens shift	Dead pixel and dust blob
High brightness	Panel convergence problem
Sharper image	Grayish black
Excellent color saturation	Somewhat bulky
Most affordable

Due to the LCD panels' wider pixel structure, there's a tendency that the projections can be a bit more pixelated or even exhibit a "chicken wire" grille-like effect. They're also prone to dead/fixed pixels plus dust blobs that are trapped on the panel overtime. Nonetheless, these issues have been greatly minimized with the new-gen engines, though color haloing can still be a potential problem due to the panels' misalignment.

Digital Light Processing (DLP)

An innovation from Texas Instruments, DLP uses a chip embedded with millions of microscopic mirrors which represent each individual pixel. This is used to reflect light in conjunction with a spinning color wheel comprising filters in different shades, including primary colors to render an image. Premium models, on the other hand, have three of such DLP chips similar to the LCD, capable of delivering even richer hues without the bottleneck of a color wheel.

Pros	Cons
Deeper blacks	Mid to long throw
Smoother images	Rainbow anomaly
High brightness	Most models lack lens shift
Higher contrast than most LCDs	Three-chipper extremely pricey
Compact one-chipper
Relatively inexpensive

One major concern for single-chip DLPs is the infamous rainbow anomaly or streaks of random colors. This is most apparent in slower 2x to 3x speed color wheels, as well as during fast-moving scenes, etc. Furthermore, most entry to midrange DLPs lack both lens shift and powerful optical zooms, making them less flexible to set up and requiring longer throw distances to cast similarly sized projections.

Liquid Crystal on Silicone (LCoS)

A hybrid implementation of LCD and DLP technologies, LCoS has liquid crystals in place of the DLP's mirrors. But like LCDs, a LCoS projector's optical engine typically employs three chips for the primary colors. Despite its late entry and modest market share, there're already two major derivatives available now, namely JVC's Direct Drive Image Light Amplifier (D-ILA) and Sony's Silicon X-tal Reflective Display (SXRD).

Pros	Cons
Short to mid throw	Low brightness for home theater models
Vertical and horizontal lens shift	Somewhat bulky
Higher resolution	Limited selection
Smoother images	Pricey
Excellent color saturation
High native contrast for home theater models

There're definitely more pros than cons, though the LCoS beamers' high starting price make them less attractive than the inexpensive LCDs and DLPs. Added to that, choices are limited with entry sets surfacing only in the recent years. A proper darkroom is also highly recommended for most LCoS home theater models to offset their low brightness performance and capitalize on their superb native contrast.

Key features

Every specific application will have its unique projector requirements. That said, here's our list of key features which you should take a closer look at, particularly brightness and throw distance for determining possible screen sizes and contrast for vivid pictures. This does not count the beamer's native resolution to resolve fine details (refer to "Types of projectors"), plus other extras to facilitate ease of installation and more.

Contrast

Contrary to popular belief, contrast tops resolution and is crucial for home theater beamers, especially for smaller sub-100-inch screens. It's frequently used as a yardstick to gauge picture saturation and depth, as well as shadow details and black levels. You'll find it rated in native and dynamic (or full on/off) contrast, with the latter is usually presented in inflated theoretical numbers.

This "dynamic" performance is measured on individual black (off) and white (on) screens, often with the assistance of up to two dynamic irises as discussed earlier. This works out fine on paper, except that in reality most movie scenes have dark and bright components concurrently that are more accurately represented by native contrast. Refer to the following table for a brief overview.

Dynamic Contrast	General classification	Remarks
<= 1,000:1	Multimedia projectors	Can be higher for selected models
> 1,000:1 to 2,000:1	480p	Good enough for causal movie playback
> 2,000:1 to 10,000:1	720p, entry 1080p	Entry point for movie buffs and enthusiasts for respectable blacks
> 10,000:1 to 20,000:1	Midrange 1080p	Improved blacks, saturation and depth
>20,000:1	High-end 1080p	Inky blacks and revealing shadow details

Brightness

This is another important consideration, but is more relevant for multimedia projectors commonly deployed in lit environments. Measured in ANSI lumens, brightness is usually governed by the onboard lamp power. Some of the higher-end installation models have more than one bulb, too, used for redundancy as well as boosting higher combined luminance.

There's no hard and fast formula to calculate the required brightness, though a basic rule of thumb is to peg it against room lighting conditions and intended screen size. The brighter it gets or the larger the projection, the more lumens a multimedia projector has to offer to prevent washed-out images and to maintain a sufficiently bright picture. Refer to the following table for a rough guide.

Brightness (ANSI lumens)	General classification	Remarks
<= 1,000	LCoS-based and budget home theater projectors	Strictly for dark and light-controlled environments
> 1,000 to 2,000	LCD/DLP home theater and budget multimedia projectors	Suitable for mildly lit entertainment and meeting rooms
> 2,000 to 3,000	Entry multimedia	Suitable for conference and classrooms
> 3,000 to 4,000	Midrange multimedia	Suitable for board and training rooms
> 4,000	High-end multimedia	Suitable for large venues such as auditoriums and churches

Key features

Throw distance

Just like your digital camera, a projector also comes with an attached optical lens for focusing and zooming. Putting aside the nitty-gritty such as lens aperture, you'll have to consider two major parameters to determine a beamer's throw capability: Throw ratio and zoom factor. A short throw model, for example, will require less projector-to-screen spacing to produce a sizeable image.

To factor for both standard and wide aspect beamers, the throw ratio is calculated by dividing lens-to-screen distance with the length of the projected image. This works out to a large projection in a shallower space given a low value, and vice versa. A zoom-capable lens will have a similar effect, except that this is a case of the higher, the better; while you tend to lose some screen luminance, the more powerful it gets.

Lens shift/Digital keystone

These affect ease of installation by manipulating the alignment of the projection. With lens shift, you don't have to line up the beamer perfectly with the screen. Best of all, this has minimal picture quality penalty since it physically repositions the lens within a range. Vertical and horizontal lens shift are almost standard in LCD/LCoS home theater projectors and considered a luxury for others.

Digital keystone adjustment is used to correct geometry distortions such as a skewed trapezoidal image due to a hasty setup, uneven support, etc. Unlike lens shift, vertical keystone is a given in most current offerings and have been further automated in some cases. The only caveat is a detrimental impact on the visuals in sharpness. Horizontal keystone is also available, but hardly mainstream.

Video processor

This is another norm to cover common video post-processing, such as scaling an incoming feed to match the projector's native resolution or applying noise reduction. Going one step further, home theater beamers have dedicated engines that perform other nifty stuff. These include interlace-to-progressive scan, video-to-film frame-rate conversion, advanced edge enhancement, and more.

Among the popular chips are the PixelWorks DNX, Faroudja DCDi Edge and an improved DCDi Cinema, followed by the enthusiast-grade HQV Reon-VX and flagship HQV Realta exclusive for premium models renowned for their jaggie-free HD upscaling performance. While most chips are integrated right into the projectors, the Optoma HD81-LV's version is installed in an external box.

Price parameters

Projectors can be a heavy investment for work and play. Though they're available in different brands and makes with diverse capabilities, they can nevertheless be categorized into various distinct price categories based on resolution, brightness, contrast, etc.

Price bracket	Multimedia	Home theater
<= S$1,200	SVGA	480p
> S$1,200 to S$2,500	XGA (2,000++ ANSI lumens)	720p
> S$2,500 to S$4,000	XGA (3,000++ ANSI lumens), SXGA, WXGA, portable	1080p (< 10,000:1 dynamic contrast)
> S$4,000 to S$7,000	XGA (4,000++ ANSI lumens)	1080p (< 20,000:1 dynamic contrast)
> S$7,000	UXGA (1,600 x 1,200)/industrial	1080p (>= 20,000:1 dynamic contrast)

Disclaimer: The above is strictly for reference and does not cover some of the exceptional models.

Connectivity options

A quick peek at a projector's input and output panel is enough to intimidate any layman since it's laden with a myriad array of audio, video and control ports. Ironically, you'll probably be using a subset except for the most complicated commercial installation. Some models also offer multiple jacks from the same genre for redundancy, though cabling cost is another consideration, especially for ceiling-mounted sets.