Over the past several years, digital projectors
have been subject to the same influences that have effected virtually everything
else in digital products – constant improvement in technologies and features
coupled with an almost parallel decrease in the price. When this occurred
with personal computers, the rate of adoption skyrocketed; and it is now
precisely what we are starting to see with projectors. When you think back only a few years ago, even though everyone was looking to buy a PC, there were many
with little understanding of what they were actually buying. For those who had even a fair knowledge of computers, barely a week went by without someone asking them what was the difference between a hard drive and a floppy drive, what were these kilobyte and megabyte things, or what was meant by a modem’s baud rate. We are now
witnessing a similar trend with projectors.
But why? The first thing we should appreciate is that as projectors have improved in technology
and features, their versatility and application have increased dramatically.
We have projectors that apart from
being extremely easy to use, can move from a business machine to an entertainment device in
seconds; and it’s the latter of these that is really pushing the projector adoption
rate ever upward. Take a look for a minute at that which is set to become the norm for home video entertainment – video cassette
recorder/ player, DVD player, cable/satellite and free-to-air television broadcasting, digital photograph slide shows,
sophisticated gaming consoles and, of course, the personal computer. Yes, we have
omitted the television, but for good reason.
As more and more of the abovementioned home video entertainment device or services
are purchased by people, the quality of the television itself has become one of the major
sticking features. We have all these great sources of entertainment, but to go out and
purchase a "big screen" to really give it impact can cost up to and beyond ten thousand dollars.
On the other hand, a high quality projector can be purchased for a fraction of the price. This is
precisely one of the main reasons for the uptake. They’re bigger in screen size, smaller in
physical size and cost less. But…before you buy that projector, it helps to understand
what the new wave in specifications is all about. In particular, contrast ratio,
keystone correction and luminance rating.
Brightness At A Glance – ANSI
Luminance is what the human eye sees and is defined as the amount of light reflected off a
surface. In ancient times, in order to measure brightness, the candle was a standard of
measurement (the amount of light a candle projects in any one direction) and a lumen was
defined as one candle per square metre. Since candlelight can vary, a more scientific
standard of measurement needed to be defined. The American National
Standards Institute (ANSI) developed a stringent set of light measuring rules that more
precisely defined the amount of luminance given off by a projector. The ANSI rating also dictates
that the projected image must be measured at nine points on the screen and the final ANSI
rating of any given projector is the average of these nine measured points. To provide you
with a "quick glance" guide to a projector’s ANSI lumens and its best use, refer to the table at
the bottom of this page.
When it comes to brightness, especially in projectors that will
be used in a home theatre environment, there is a very important point to consider –
bright is not necessarily better. An important point to consider when talking about projectors is
that there are two primary types on the market – Digital Light Processing (DLP) and
Liquid Crystal Display (LCD). Naturally there are advocates for both types, but when it comes to
colour control and fidelity, LCD really does have a major advantage. By using three
separate LCD panels – one each for red, green and blue – each can be controlled
independently for brightness and contrast, leading to vastly superior colour fidelity.
Clearly Better From Any Angle
– Keystone Correction
Keystone correction essentially corrects trapezoidal distortion. When the projector is not
positioned at the centre of the screen, the image is projected at an angle and may appear
distorted. Depending on the projector you purchase, you will have anywhere up to
a 30 degree vertical keystone correction capability. In some of the higher end
models the projector can automatically detect and adjust keystoning, although in most
projectors for the home and small business environments, a few button presses on the remote
control is all that’s required.
Black or White – Contrast Ratio
Contrast Ratio is the ratio between white and black. The larger the contrast ratio the
greater the ability of a projector to show subtle colour details and tolerate extraneous room
light. Contrast measures the ratio of the light output of an all white image and the light output
of an all-black image. LCD projector contrast ratios range from 300 to 1200. When
comparing the contrast ratio of projectors, make sure you are comparing the same type of
contrast. Users quite often focus on the projector’s ANSI lumens ratings rather than consider how
everything actually works together to provide the best possible colour reproduction.
Contrast ratio is equally as important as ANSI lumens and with LCD projectors, because of
the ability to control all three LCD panels independently (see ANSI Lumens), do not require an
enormously bright lamp to generate superior contrast ratio and colour reproduction.