Game Development Reference
In-Depth Information
The DLP (Digital Light Processing) video projectors are based on a technology
developed by Texas Instruments. This is based on a matrix of thousands of micromir-
rors lit up by a lamp, where each mirror corresponds to one pixel to be displayed. These
mirrors can be oriented individually, without affecting the others, and can rotate each
by about ten degrees at the frequency of about 5000Hz. This way, these mirrors reflect
more or less light by temporal modulation, individually determining the intensity of
each pixel. These are optical semi-conductors of sorts. This technology is referred to
as “reflective'' technology. For example, to display an image of 1024
×
768 pixels,
only the 1024
768 pixels at the centre of the matrix are used, while the others per-
manently remain in a position that does not reflect the light on the screen. There are
mono-chip DLPs, where only a single matrix of mirrors is used and tri-chip DLPs using
three different matrices for the three primary colours. In the case of a single chip, the
colour is produced sequentially by passing through a colour wheel. In the case of three
chips, a prism divides the light beam of the lamp into three primary colour beams.
These beams each light up one of the chips and are then re-combined before being
projected. Projectors based on DLP chips have the capacity of providing images with
high luminous power, ranging from 1500 to 12000 lumens, and also at a sufficiently
high frequency to enable active stereoscopic systems to be used. Images with high con-
trasts (ratio of about 1300:1 to 5000:1) can also be obtained using this technology.
The colour quality is lower than the CRT projectors, especially in case of black, but is
certainly better than an LCD projector. The possible resolutions are also intermediate,
the maximum being about 2048
×
1080. The DLP technology makes it possible to
create projectors that are small in size and light in weight, but its implementation still
remains costlier than an LCD system.
The LCOS (Liquid Crystal On Silicon) video projectors use a combination of the
two technologies mentioned above. Like the DLP, even this is a reflective technology
that uses liquid crystals applied directly on the mirrors. The luminous intensity of each
pixel is thus modulated not by changing the mirror angle, as the mirrors remain fixed,
but by controlling the opacity of the liquid crystals. The LCOS projectors generally
use three chips, one for each primary colour. These projectors are generally top-of-the-
range, and are expensive, but offer very good performances. Their resolution can reach
2048
×
1560 pixels. Unlike in LCD projectors, no pixelization of the projected image
is visible thanks to their high resolution. Moreover, the pixel borders are less clear than
the DLP mirrors, thus giving smoother images. On the other hand, the main limitation
of the LCOS technology is that the contrast ratios that it can reach are limited to a range
of 500:1 to 1000:1. The luminosity of these projectors ranges between 1000 and 2500
lumens. Weighing at least 6 kg, these projectors are certainly not suitable for mobile
applications. With their price and their top-end characteristics making them a rare and
exclusive product, they are not suitable for the mainstream market. It is for this reason
that manufacturers still hesitate to invest in this technology. Companies like Philips or
Intel have chosen to step out of the market of these chips or the projectors using them,
whereas other manufacturers like JVC or Sony continue their development.
×
11.2.3.7 Passive screens for video projection
Projection screens being the inseparable partners of projectors, their selection requires
considering a number of criteria. Their quality largely influences the quality of the
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