Articles and whitepapers

Choosing a DLP Projector (1/3/2004)

By Len Carlton

Plasma display, LCD TV, rear projection TV, front projection - each has its place. Many plasma and LCD screens are now producing good picture quality, take little space and can be attractive pieces of furniture. Their main limitation is size. Plasma screens are now available with over 60-inch screens, but when over 50 inches, are very expensive. LCD manufacturers claim to own the future, but cost- effective LCD is currently limited to around 30-inch screens. For the true cinema experience at home, front projection is still the best option, producing images up to 250 inches. Moreover, during the last two years, picture quality has improved beyond recognition, and prices are now well within most people's reach.

Home Cinema Projectors

If you are long out of nappies a 'projector' may bring to mind a whirring, clanking behemoth situated in the centre of the room with two film reels forever jamming, and a scratchy, flickering grey image. The world moves on apace, and today projectors can be tiny, almost silent, producing amazing pictures - far more impressive than you might see at the cinema - and providing a serious large-screen alternative to TV or plasma TV.

In recent years, the great majority of projectors have been manufactured for business presentations, with home cinema products being somewhat specialist. More recently, home use has been estimated to be approaching 20% of total projector sales. Whilst many so-called 'home cinema' projectors are still no more than business projectors thinly disguised in pretty boxes, there is now an excellent choice of stunning products available. There are even a few projectors being designed specifically for Europe, rather than an afterthought from the US market.

LCD and DLP projectors

You will soon discover that you have a choice of LCD (Liquid Crystal Display) and DLP (Digital Light Processing) projectors. LCD projectors usually contain three separate LCD glass panels, one each for red, green, and blue components of the image signal being fed into the projector.

DLP is a proprietary technology developed by Texas Instruments. Instead of having glass panels through which light is passed, the DLP chip is a reflective surface made up of hundreds of thousands of tiny mirrors, each representing a single pixel. Light from the projector's lamp is directed onto the surface of the DLP chip. The mirrors wobble back and forth up to 5000 times per second, directing light either into the lens path to turn the pixel on, or away from the lens path to turn it off. In order to define colour, there is a colour wheel that consists of red, green, blue, and sometimes white (clear) filters. This wheel spins between the lamp and the DLP chip and alternates the colour of the light hitting the chip from red to green to blue. This activity modulates the light and produces the image that is projected onto the screen.

The Optoma RD65 - the world's first 65-inch HD2 DLP HDTV

There has been much debate over the differences between DLP and LCD technologies, most of which you can find on the web. As cost has become lower, the most obvious benefits derived from DLP technology is small package size, reduced pixelation, and better colour saturation with the introduction of the six-segment 4 x speed colour wheel. The accepted conclusion within the industry is that DLP is the best solution all round for home cinema, although the LCD option can be cheaper.

Choosing the best projector

Contrast and grey levels

In many films, such as the opening scenes of Gladiator, the atmosphere can be dark and grey, with action taking place at night or in the shadows. If your grey-levels are not distinct, all you will see are outline movements in a sea of dark grey. The best home cinema projectors offer very high levels of contrast with 2000:1 becoming de rigueur for enthusiasts. This level of contrast is actually much higher than you see at your local cinema. It is difficult to believe some manufacturers claims for contrast, and it is always good to view the picture before you buy.

Colour (and Rainbow)

Colour preference tends to be subjective and again it is always useful if you can see a demonstration. Many projectors offer the capability to adjust the contrast, brightness, gamma, gain and bias, by each colour to your own preference. It is particularly helpful if your projector has an adjustment memory for each hardware input, since a DVD, VHS or digital box will each output different colour. A light-hearted word of advice - once you know how to adjust the colour you will forever be fiddling, as every DVD film or TV programme has different characteristics.

DLP projectors are without doubt the first choice for home cinema (HC), but a word of warning: be sure that you buy a recent model with a x4 speed wheel, as this faster speed wheel virtually eliminates the rainbow effect evident on older models. It is also important that your HC projector has at least a six-colour wheel with no white segment, as this will give you much truer colour representation. The reason that most business projectors have a white segment is to increase the brightness capability for lighter rooms. Many HC projectors are adapted business models and some adaptations are better than others. An indication of whether your DLP is a dedicated HC design is if it has no white segment, but instead offers at least RGBRGB.

Brightness

A major function in business projector pricing is brightness. Brighter models carry a premium and display well in light conditions and in auditoriums. Higher brightness is not necessarily a benefit in HC and can even be a problem. At home, most people will watch movies with the lights switched off and the curtains drawn in near-dark conditions, with no bright-green neon exit signs in the corners, thankfully. Under these conditions, 750 - 1000 ANSI lumen is more than enough brightness. If you go much over 1200 lumen, the light reflection from your screen or wall will dazzle you and reflect onto your surroundings, lighting up the room.

Video signal formats

Try reading a technical book on this subject. I did, once. Simplified, a picture is made up of lots of lines of dots which can be transmitted using a number of different compression formats. Once received by the TV or projector, the signal is decompressed to generate the picture. Some formats are more highly-compressed than others to make them cheaper or quicker to send. The problem with highly-compressed formats is that some of the detailed information is lost, leading to a potential loss of quality in the final picture output. You will get far superior pictures from a component or RGB signal as they use less compression. S-Video is something of a compromise, the resulting picture is OK, but not suitable for real HC. Do not use composite video for HC - it is horrible.

Connectivity

As mentioned before, most projectors are designed for the US market, with European video capability added afterwards. This creates a potential problem for European users, particularly if you do not want to invest in specialist high-cost AV equipment. The main difference between the US and Europe is SCART. Invented by the French as PERITEL, and adopted by the rest of Europe, it is completely unknown in the US and in the Far East. SCART is that connector in the back of your TV, your digital set-top box, your DVD player, your VCR and on your games console. Your DVD player may have component output (all Toshibas do) and you should use it in preference to S-Video. Your VCR may only have SCART. Your digital set top box will probably only have SCART.

As you have gathered by now, I am suggesting that your HC projector should have SCART input capability. You do not actually need a SCART connector on your projector, but you do need to connect from a SCART. But it goes further. Many projectors will accept a signal from a SCART connector and provide an adaptor for that purpose, but it will be SCART composite only. What you need is SCART RGB - remember RGB gives much superior picture to composite. While many suppliers will specify SCART, if they do not specify SCART RGB, it will almost certainly not be.

Size and Noise

Of course size matters, but in this case smaller is better. Many HC enthusiasts have their projectors installed with a custom screen and full audio facilities - a true 'Home Cinema.' There are also a growing number of users who prefer a mobile solution, using the projector in the lounge for movies, in the games room for their computers or even taking it to a friend's place to watch the big match. Whether for mobility or as a less intrusive piece of mounted home equipment, smaller is certainly better.

Imagine a touching love scene with an emotional poignant silence and all you can think about is an annoying buzzing noise just behind you. The projector has a fan to keep it cool and this can be quite loud in some machines. Whether a noise is intrusive or not can be somewhat subjective, but I would suggest a guideline of below 32dBA, and preferably below 30dBA. Try to listen to a model in a quiet environment before you buy.

Different types of DLP projector

There are several manufacturers making excellent HC DLP projectors, many of the best are almost unheard of. It is not necessarily the bigger brand name that makes the best projectors. DLP projectors are based on four or five DLP chips of differing size and resolution. Higher resolution should in theory allow better picture quality with greater detail, but this is only one factor, albeit an important one. The lower-cost DLP projectors will normally have a native (not compressed) resolution of 800x600, 800x480 or 800x450, and are perfectly capable of producing great pictures on screens up to about 12 feet wide. With a bigger picture, the individual pixels may become apparent in some scenes. Pay a little more and you can get native 1024x768 and 1024x576 with more individual pixels allowing sharper images.

The ThemeScene H30 DLP projector offers high video quality for less than GB1500

At the top-end of the market there is 1280x720, giving even greater resolution, particularly useful for HDTV. There is some debate as to whether this is better than 1024x576 in Europe, since European PAL TV has 576 lines, so why have more horizontal pixels than this?

Conclusion

The world is your oyster when it comes to choosing a model to suit you. There are models for almost every pocket. To find a pearl, try to see a choice of models in a dark, quiet environment, then take it home and enjoy.

Len Carlton is Head of Projector Business for Optoma Europe Ltd - a subsidiary of the world's largest manufacturer of DLP projectors and supplier of the ThemeScene range of Home Cinema projectors.

www.themescene.tv