Mike McNamee tries to navigate around the world of the projected image
The question over which projector to buy continues to arise on a weekly
basis. To try to clear the fog a little we decided to compile some basic
statistics to assist in the quest! As soon as we started to assemble a
database of available projectors, the size of the problem became apparent.
Give or take a few dozen, there seems to be a choice of 380 projectors in
any of eight resolutions, three distinct technologies and 20 manufacturers.
The prices range from a few hundred to more than £23,000 – there is plenty
to go at!
The Technologies
These are as follows:
DLP Digital Light Processing
LCD Liquid Crystal Diode
LCoS Liquid Crystal on Silicon
DLP has traditionally been sold on its high brightness specification. It has
the disadvantage of a greatly reduced colour gamut, poor performance in the
yellows and, for some, an annoying flickering as the wheel rotates in front
of the light source. At its worst this flickering can cause migraine and
certainly does so for your Editor. There is a new ISO measure of quality for
projectors which firmly puts DLP in its place. In the two graphs (extracted
from the 3LCD paper) data out towards the upper right of the graph are
superior and the LCD technology is outstandingly better than DLP. We were
unable to duplicate their findings for want of the laboratory equipment, but
our measurements of gamut volumes track the published findings closely. The
LCoS system is used by the Canon XEED range of projectors and is something
of a hybrid which takes the best of both the other technologies. They are
popular with camera clubs partly due to Canon's willingness to demonstrate
their units at clubs.
"LCD technology is outstandingly better than DLP"
The Contrast Ratio Myth
If you read the advertising blurb you could be forgiven for thinking that
contrast ratio was an important part of a projector specification. This is a
myth, put about by DLP manufacturers as it is one of the sole measurement
parameters which is higher than LCD systems! The majority of projection is
carried out in less than ideal surroundings. The ideal is total darkness but
this is frequently compromised by light leakage around blinds or, in a
public place, by the illuminated safety-exit signs. Such apparently trivial
sources of light devastate the contrast ratio which you may have just paid a
premium for, and are usually outside your control. In the graphs created by
Lumita (who are, it should be stressed, an LCD specialist!) the contrast
ratio is reported against room illumination, including the source of
contaminating light. This shows that the InFocus IN26 suffers a drop from
2300:1 down to 100:1 by the light leaking through blinds (to create a 30 lux
ambient light level in the room). For those unfamiliar with what 30 lux is
like, think coal-cellar! By this stage the differences between the lower
starting LCD technology and DLP are insignificant – it is not worth paying a
premium for high contrast ratio unless you can achieve total black-out and
are comfortable in doing so. You certainly cannot lecture or present in such
a low illumination level as you cannot see either your audience or your
notes.
Brightness
There is a relationship between brightness and cost – more brightness
equates to more money as our graph shows. However, there is brightness and
brightness out there! Typically brightness is measured and advertised in
ANSI lumens and ranges from about 1,200 to 3,500 in 'domestic' systems but
can go up to 10,000 for large venue projectors (costing many tens of
thousands of pounds). However, the white brightness is false if it is made
up of say strong blue and green values, allied with a weak red value. In
other words the RGB individual brightnesses distort the colours because of
their individual strengths and weaknesses, typically seen as a distortion in
the colour gamut, with some parts of the gamut volume heavily clipped. In
practice what is seen is a projector with a high claimed brightness
producing a significantly duller image than a projector with a more evenly
balanced, but lower, headline brightness. As a generalisation, the larger
room that you project in, the greater the brightness you need to employ.
As photographers you have to understand one thing – we count for very little
in the market place. In the same manner as monitors are targeted at business
and gaming users, projectors are targeted at business users and home cinema
use. The majority of end-users, and the target market, do not care overmuch
about colour reproduction accuracy – that seems to be an exclusive province
of photographers!
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