iXBT Labs - Computer Hardware in Detail






Choosing a Home Theater Projector

TV sets vs. projectors, DLP vs. LCD, key parameters, etc.

November 28, 2008

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Projector types

So, if the above-mentioned advantages of projectors weigh down their drawbacks, and you have decided to buy one to watch movies, you should choose what type you want. In fact, you can watch movies with any projector. Except for the stationary models, there are two classes of projectors -- office models for presentations and home theater models. Let's start with office projectors. They are generally of little use for video playback because of their noisy cooling systems (especially in compact, but bright models), mediocre color rendition (especially DLP projectors), pronounced rainbow effect (DLP projectors), low contrast (LCD projectors), low resolution (most of them support 1024x768), 4:3 format (while movies and even TV series are often wide), no digital inputs with HDCP support. However, there are some exceptions. For example, Acer P1265 is equipped with DVI input with HDCP support, and Toshiba TDP-EW25 has a wide panel, offers good color rendition, and works rather quietly. InFocus X8 is another interesting product, good for both home and office. It's equipped with a wide panel. But unfortunately, a transparent segment in its light filter reduces color brightness significantly.

Epson's model range includes EH-TW420 (wide panel, HDMI input). This product is positioned as an affordable and easy-to-use family projector for games and movies. But in fact it's practically a full counterpart of Epson EB-W6 for presentations.

Thus, if you buy a projector for presentations, but also intend to watch movies from time to time, choose a model at least without some of these drawbacks, which limit video playback usage of a projector.

There are three groups of theater projectors:

  1. All-in-one entertainment centers.
  2. Entry-level theater projectors.
  3. High-End theater projectors.

This division into categories is quite subjective, but it helps to know your way around variety of products.

All-in-one entertainment centers consist of a projector, a player, and an acoustic system in a single enclosure. Typical representatives of this group are Optoma DV10,

Epson EMP-TWD10 and Epson EH-DM2.

As a rule, such devices are not very expensive, but they may still be more expensive than a kit of cheap entry-level components: projector, DVD player, and two speakers. The key advantage of combined devices is easy installation (you just power it up and point it at the screen) and usage. The main drawback is mediocre characteristics of built-in speakers. However, such devices usually allow to plug an external receiver and obtain sterling 5.1 audio. Video inputs are also welcome. They allow to plug external video sources -- for example, you may always resort to video inputs, if the built-in player breaks down or does not support stop the latest video formats. So, all-in-one entertainment centers are a good choice for children's rooms, for mobile usage -- when you often have to move the device (even if within the room), and also of you want to get a large screen with minimum installation efforts (fussing with cables and mounting components).

The group of entry-level theater projectors includes most models, which support resolutions up to 1280x720. Some projectors from this category are designed as products for games, for example, Panasonic PT-AX200E or Epson EH-TW420. They differ from theater projectors in slightly lower requirements to their noise level and image quality, and probably, in lighter design. For example, light instead of black enclosures. Entry-level theater projectors offer a good image quality/price ratio. So they are a good choice, until HD content becomes more accessible, and prices for Full HD projectors become lower.

High-End theater projectors are Full HD models in the first place. Besides, we can also mention projectors with the resolution of 1280x720 and high image quality. This way or another, they are pushed out of the market by projectors with 1920x1080 video output. An expensive projector with 1280x720 video output is not expedient these days.


Leaving uber-expensive three-chip DLP projectors beyond the scope of this article, the only choice for home theater projectors is either single-chip DLP projectors or LCD projectors (Epson was the first to call them 3LCD to indicate three LCD panels), or projectors that use LCOS technology (SXRD by Sony). Despite the number of differences, LCOS technology is closer to 3LCD, so practically everything in this article written about LCD may also apply to LCOS. Also note that theater DLP projectors usually use a six-segment color filter, where red, green, and blue colors appear twice. But there are some exceptions.

Let's list advantages (drawbacks appear as the lack of advantages) of theater DLP and LCD projectors.

DLP pros:

  • High contrast
  • Excellent color uniformity across the screen

LCD pros:

  • 'Natural' image formation, no 'rainbow' effect
  • Higher efficiency, lower power intake at the same light flux level

It's a short list, because the best representatives of modern theater projectors, both DLP and LCD, are identically good in other respects. Let's analyze each point.

High contrast of DLP projectors is provided by high efficiency of micromirrors in a DMD chip -- light falls either on the screen or on the light dump. Typical ANSI contrast of theater DLP projectors is 650:1, while it rarely raises above 300:1 in LCD models. However, Epson designed a special polarization filter (the DeepBlack technology) that increases contrast by 70% -- from 223:1 (ANSI contrast) in EMP-TW1000 to 380:1 in EMP-TW2000 with the same optics. The new EH-TW5000 projector will offer even higher contrast -- we'll find out how much higher in our tests. We can assume that after Epson "skims the cream off" DeepBlack, its counterparts will be also used by other companies that manufacture LCD projectors. As a result, the contrast gap between DLP and LCD will narrow down considerably.

DLP projectors provide excellent color uniformity across the screen because the light goes through one and the same route, while LCD models split the light into three rays, which pass through three chips and then recombine into one ray again. Any differences in passing/reflecting components on the way of split rays result in local decrease/increase in brightness of one of the colors. As a result, there appear color blotches on the white and/or black field. To solve this problem, LCD projectors resolve to various tricks, up to software color correction in local areas. The best representatives of theater LCD projectors practically don't suffer from this problem -- barely noticeable color bleeding does not interfere with watching movies at all.

Single-chip DLP projectors suffer from the "rainbow effect". Announcements that the problem is solved are nothing more than make-believe attempts of PR departments. Rainbow appears when your eyes move fast, and bright image elements on the screen resolve on the retina to color components. The rainbow effect shows as red/green/blue shadows at the edges of contrast light objects (especially white) perpendicular to eye movements. Theater DLP projectors provide high color frequency (usually 240 Hz at 60 Hz frame rate, or even 360 Hz) that weakens the rainbow effect.

Tests show that watching movies with DLP projectors for a long time may result in eye strain. However, the rainbow effect differs for different people. Many users don't notice it at all, others suffer from it (especially people with nystagmus disease -- spontaneous flailing movements of eye balls -- fortunately, only one person out of 1500 people suffer from this disease). Perhaps, the rainbow effect may be especially irritating, when DLP projectors are used for games. So, you should find out how you feel about this effect prior to buying such projector.

LCD projectors has higher efficiency, that is they consume less power to produce the same light flux. The rotating color filter of single-chip DLP projectors absorb lights -- over-simplifying a bit, we can say that only one third of the light from the lamp reaches the screen. That's why single-chip DLP projectors dissipate more heat with the same brightness level, which may lead to higher noise or bigger dimensions of the enclosure. They also consume a bit more power, but that's not a principal difference.

Both technologies (DLP and LCD) continue to evolve. New generations of LCD and DMD chips increase their pass/reflex capacity together with contrast and brightness. Another consequence is thinner dark borders between pixels in LCD chips -- we can even say that modern CLD projectors have solved this problem completely (growing resolutions also contributed to the solution). We've already mentioned the polarization filter that increases contrast of LCD projectors significantly. We'd like to mention the recent initiative put forward by Texas Instruments, which decided to promote BrilliantColor technology for DLP projectors. There is nothing principally new in this technology -- it's intended to increase color gamma and brightness by adding new colors to the color filter or using color boundaries. BrilliantColor implementations may vary from different manufacturers. The progress of DLP projectors may also have to do with adopting the three-chip design in mass-production models (as for now, three-chip projectors are more expensive than three single-chip models). Besides, using LEDs as light sources may weaken the rainbow effect and raise efficiency of DLP projectors. It will also help reduce the noise from cooling systems in both types of projectors (DLP and 3LCD) or even design passive cooling systems.

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