DLP vs. LCD - Home Theater Projectors

DLP vs. LCD Projector Advice: Home Theater Projectors
03/04/2006-Art Feierman

Overview and Technology
DLP vs LCD Home Theater Projectors
DLP vs LCD Featherweight Projectors (under 5lbs.)
DLP vs LCD Portable Projectors
DLP vs LCD Fixed Installation projectors
A look at other technologies: LCOS, LED, CRT, Laser (coming soon)

Overview of DLP vs. LCD projectors for home theater

There are different criteria for choosing between these two technologies, when purchasing a home theater projector.

Ergonomics is a key area. In the lower price ranges (currently under $3000), LCD's usually have a big advantage in this catagory, notably their wider range zoom lenses and lens shift.

Other key issues including achieving great black levels so you can see details in dark scenes and not have large pretty dark areas come up as a large flat area devoid of detail.

Items like DLP's Rainbow Effect which bothers a very small percentage of people, and LCD's Screen Door Effect, which limits how close you can sit to the screen with an LCD projector, are other key determining factors.

We'll also look at advanced techologies - normally referred to as "AI" for artificial intelligence (no, not the real thing), that are becoming more common. There are some great benefits to using "AI" but also some drawbacks. This section will attempt to explain some of them.

Color accuracy, is of course important, but not a defining difference between LCD and DLP. Brightnes also varies from projector model to model, but neither technology is inherently brighter.

Ergonomics

The LCD models most often are better ergonomically, providing zoom lenses with more range on the zoom, making placement easier in your room. They also tend to offer lens shift which allows flexibility in how high or low you mount the projector relative to your screen.

Typically LCD home theater projectors offer from 1.5:1 up to 2:1 ranges on their zooms. Translated: 2:1 means that you can adjust the size of the image, so that the closest you can place the projector to fill a given size screen, is half the distance of the furthest away.

This allows enough placement flexibility, to typically put the projector anywhere in the room from half way back to mounting it on the back wall (depending on the screen size and room dimensions, but that's why I said "typically".

With DLP, the zoom range is typically from 1.2:1 to 1.4:1, allowing far less placement options. As a result there are some people who ultimately buy LCD projectors, simply because, the competing DLP projectors just won't work, in their room.

The other key difference I mentioned is lens shift. Virtually no DLP projectors selling for under $3000 at this time offer it, whereas almost every LCD projector selling for $1500 or more does offer it.

Lens shift (actually variable lens shift) let's you place the projector over a wide range vertically. Almost always it guarantees that you can get a rectangular image anywhere from placing it even with the bottom of your screen to even with the top. With some models you can start well below bottom and go to well above the top.

The DLP design is less conducive to using lens shift and as a result, only more expensive DLP models offer it at this time, and none in the $2000 and under selling price range. The end result, without lens shift the projector needs to be in a certain height, relative to the screen. Typically about even (or just above the top of the screen, when ceiling mounting), or just below the bottom (on a table). That can vary though, one new home theater projector, the Optoma HD72, typically sits a foot to a foot and a half below the bottom of the screen, or an equal amount, when mounted above.

If you don't place the projector at the correct height, you get a trapazoidal image, which can be corrected with digital keystone correction. Unfortunately keystone correctionadds visible distortion to the image and is best avoided.

Brightness

For home theater projectors, brightness takes on a secondary role. True, some people will need a brighter projector than others, due to room conditions and screen size, but today's projector technology for business projectors starts at about 1500 lumens, and most are 2000 lumens or more. By comparison, most home theater projectors claim 800 to 1400 lumens (in their brightest modes), and typically produce only 250 - 500 lumens in their best modes. After all, technically most home theater projectors are designed to function in a very dark to fully darkened room.

Basically, home theater projector manufacturers are damping down brightness in favor of improving other characteristics of projectors deemed more important for a high quality home theater image.

There are a few very bright home theater projectors, such as Sanyo's PLV-70 (being phased out at this time, and their replacement PLV80 (2200 and 3000 lumens respectively). Sanyo also offers their WF10, an extremely powerful 16:9 projector used for both home theater and commercial applications. The Sanyo WF10 offers 5000 lumens. These however, are the exceptions in the under $10,000 range.

More bright home theater (and dual mode business and home theater projectors) appear as you start looking at 3 chip DLP projectors, but with their typically $15,000 plus prices, relatively few home theater projector buyers end up with these. The three chip DLP's will often offer up 2500 to 7000 lumens, and are capable of handling either extremely large home theaters (screens of 130" diagonal and larger), (or screening rooms), or for dealing with much higher levels of ambient light. Even these projectors will produce lower lumens in their best modes.

Even though most home theater projectors are not very bright in best modes, they all have "bright" or "dynamic" or "vivid" (you get the idea) named modes, that are much brighter. The manufacturers realize that people often don't want to watch in the dark, or can't fully darken the room. (If you have 10 people over to watch a football game, do you really want to be in the dark?) There is definitely some sacrafice of quality in the brighter modes, but, you aren't going to be quite as critical watching that football game, or a sitcom, as watching a movie.

Contrast Ratios - no longer a great indicator

This section is pretty long, if you aren't into the details of how these numbers can be misleading, you can skip the "My thoughts on how AI works" section.

Until recently, high contrast ratios were considered one of the holy grails sought by home theater projector buyers. High contrast, in its own right, helps with the relative richness of colors between darker and brighter ones, and adds apparent depth to the image, but far more importantly, it has related to black levels.

Since neither DLP nor LCD projectors can produce a true black - instead only relatively dark shades of gray, this causes the loss of shadow detail. Contrast ratios have been widely used as a measure of achieving better black levels. A contrast of 2000:1 produces "blacker blacks" than 500:1. And until the last year or so, contrast ratio has been a good guide for determining how close to black a projector could produce.

Today, however, more and more home theater projectors - most notably LCD types, are using "AI" (artificial intelligence) to come up with much greater contrast ratios. Unfortunately, the techniques used may give higher contrast ratios, but often with little or no consistant improvement in achieving blacker blacks.

Before I continue in this critical area, consider that with the current technology level, DLP projectors are inherently much higher than LCD models, in terms of contrast. For example on the business projector side, the typical LCD projector claims 400 - 500:1 contrast ratios. On the DLP side, 2000:1 - 2500:1. And that's a couple of steps up in terms of performance. Let me clarify to say that once you look at final products however, in the $2500 and under price range LCD has closed the gap, when compared to the DLP projectors. (I'm referring to DLP projectors that mostly use Darkchip2 DLP chips.) Once you move up in price, DLP projectors start sporting Darkchip3 with much higher contrast ratios and much better black levels.

My thoughts on how AI typically works

A typical "AI" function to enhance contrast ratio, is to vary the brightness of the projector, scene by scene. Imagine an outer space scene on a DLP projector, with a lot of stars. You look at space, and its very dark gray, the stars stand out, but you aren't seeing real black. Switch to an LCD projector and space just got lighter gray, and the stars (maybe not as many), still show up, but there is less contrast between space and the stars

Let's also assume that none of the stars are really very bright - they are not full white but rather various intensities of gray, with the brightest stars being only 50% the brightness of full white.

With AI, you could, either by dimming the lamp for the frame in question, or by stopping down a mechanical iris in the lens, or both, darken the entire scene. Now, less light exits the projector, by half. So space just got that much darker - which is what you want. Electronically, though, to keep the stars the same brightness as before, the AI also adjusts their brightness - if the value of a stars brightness was 40% of white, it changes those pixels to 80%. Bottom line, space got darker, stars stay the same actual brightness, and you have a better image.

Great, but what happens in the next frame, if we add a moon, or more stars, or a planet, that has components that are already at 100% brightness (and this doesn't have to be white, it could be full red, or any other color or group of colors). Now, if you dim the projectors output, you are stuck. Those "bright" stars, Planets, and moons, also have to dim. The result is that the brightest parts of the image aren't anywhere near as bright as it should be.

End result, the AI normally wouldn't attempt to dim the lamp or close the iris.

So in one case, we were able to reduce overall black levels, so that blacks are much closer to black, and in the next frame, no adjustment.

Contrast is normally the ratio between the darkest a projector can produce, and the brightest.

Projector manufacturers tend to rate their contrast with AI on, by measuring the lowest output (black) with everything stopped down, possibly reducing brightness as much as 80% or more. Then they measure the brightest they can produce (on a different frame, or test pattern). This get's you an impressive contrast ratio, but doesnt really work all the time, does it?

Now imagine our star scene again. For 7 or 8 seconds we have been watching the beginning of perhaps, one of the Star Wars movie openings, basically just a field of stars. With AI, the projector is stopped all the way down, and blacks are looking pretty black. But, waiit, a large planet comes into view, and it is bright - the lamp brightens, the iris opens, and the planet becomes as bright as it should. Look out, in the second or so as the image transitions, the "black" space just got 2 or 3 or more times brighter, and you are watching this happen.

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This can be annoying. And you don't need just outer space scenes. In reviewing one projector I described a scene in a movie, where the backdrop is dark paneled walls, and there were nor really bright objects in the scen, a man with a bright white shirt enters the foreground, and all of a sudden the walls get brighter. In that particular scene, as he moves around, it looks like someone out of sight is playing with a light dimmer on the wall of the room. In other words, there are limits (so far) in using AI, so that it can be detectable, and sometimes annoying. I went as far as to recommend, since it was veru noticeable, that many owners might want to turn off the Auto Lamp function on that projector.

So, a good contrast ratio, is still highly desireable, but when you start seeing over 3000:1 on a lot of projectors, it's no longer a good indicator of those highly desired blacks, and accompanying shadow details.

In summary, DLP home theater projectors have the advantage of naturally, much better contrast, and, while neither technology can produce a true black, generally, DLP projectors get closer, producing very, very dark grays, vs. LCD's very dark grays. This means "blacker blacks" and more detail in dark areas. DLP projectors also have a pixel structure which is less noticeable, and are virtually immune to the "screen door effect". DLP projectors are also known for having a more film-like quality, although LCD projectors are catching up quickly in this area.

Contrast and Movies

We probably all agree, that we do want the blackest blacks, and the shadow detail that they can reveal. But how much is enough.

I had the opportunity to speak with a Hollywood colorist some months back.(He is responsible for getting the balance right for transferring film to DVDs. DVDs of course have different properties than the original movie film. I can't confirm his numbers, but he indicated that as almost all non-animated movies are still shot with film ( a couple of Star Wars, and others excepted). Further he indicated that the contrast ratio of the color films today is somewhere in the 6000:1 range. That raises the question - if the film only has 6000:1, what benefit would you get if your projector really had 15,000:1 contrast. The answer - I would conjecture, none or very little, unless you are dealing with a movie or other material, that bypasses the film process. Even then, the digital movie cameras would have their own maximum contrast. Basically you want to reproduce faithfully with your projector, not monkey around with settings that change the way the material was meant to be viewed.

Back to DLP vs LCD

With the LCD panels inherently having lower contrast, LCD home theater projector manufacturers added AI. Bingo, those high new contrast ratios. Now DLP, in the never ending war of specs are also adding AI to their projectors, Now, we are seeing $2000 home theater projectors today with claims as high as 7000:1 for LCD and 4500:1 for DLP. Move up a bit in price, and, for example, you'll now find a 10:000:1 contrast claim on the $6000 BenQ PE8720 DLP projector. (That's the one I use in my home theater.)

Take it all with a grain of salt (or a pound?). The bottom line is which projector looks best. Which can get you that black space scene, which can pull out the details in an extremely dark scene, like in the movie The Fugitive, where the train is coming to hit the bus. On most older home theater projectors you see nothing but the train's light. On newer better projectors, details appear...

Rainbows and Screen Doors

Rainbows - A small percentage of DLP projector owners will see the Rainbow effect, a sort of strobing caused by the color wheel. Most of us never see it or only if we move our heads suddenly we might catch a tiny flash of rainbows (red/green/blue). Most of todays $2000 and over home theater projectors use color wheels that now spin at 5X (or 5 times the speed of the original DLP projectors of almost 10 years ago). Some, spin at 4X. Unfortunately, there are no published numbers to indicate what percentage of people will detect the effect. Mind you, even if you can spot it occasionally, it might not bother you. A rare few find it fatiguing, including one of the reviewers of a major HT (home theater) magazine. If you are shopping for under $1500 DLP home theater projectors, most are now 4X, but there are still some 2X out there. Definitely more people will notice it on the 2X projectors. As one reviewer noted, why even worry about 2X. There are enough 4X low cost projectors around to bypass the 2X projector group completely. Not a bad idea. Who needs the aggravation.

Bottom line - on Rainbow Effect - if it doesn't bother you, don't worry about it. If you get a DLP home theater projector, as soon as you get it, fire it up and watch a movie. (If your room is under construction, fire it up anyway, on a wall some where. Most dealers offer a limited amount of time to return the product if you don't like it, So test the projector and get this issue out of the way.

Screen Door Effect

Time to pick on LCD projectors now. The Screen Door Effect (SDE) is caused due to the physical structure of the pixels, creating a pattern when viewing fine details with patterns in them. One example is the grass on a football field. If you are sitting close enough to your screen, that the pixels are just becoming visible, it may create a pattern with the grass that causes the image to no longer look sharp, but instead, distorted. This can be very annoying.

The simple solution is to sit far enough back so that this problem does not manifest itself.

Unfortunately that may be further back than you like to sit, to get properly immersed. I would venture to say, that with most LCD based home theater projectors the safe seating would put you about the equivilent of the very back of a movie theater or close to it.

I like to sit close (at movie theaters, about 1/3 back) that gives me tremendous immersion into the movie. With most LCD home theater projectors that is too close, and some SDE will be apparent.

That makes DLP better for sitting closer.

See, no easy best choice between LCD and DLP projectors.

Mind you, even DLP projectors also create SDE, for they too use fixed pixel structures. The DLP chip, creates pixels, however that are noticeably less visible than LCD. I would venture, that normally you would have to sit about as close as the first row in a movie theater to detect SDE with a DLP.

Accoustic projection screens

Note, for those considering placing your center speaker behind your screen, there are accoustic screens offered by most screen manufacturers. They typically use small pinholes to pass the sound through. This pattern of holes, can greatly excerbate SDE. It is reported that these screen manufacturers have been making significant strides with newer generations of accoustic screens, but I haven't worked with them. As a result, I won't venture an opinion, as to how much or little they worsen the SDE problem.

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