Game Development Reference
In-Depth Information
a majority of graphic cards can display images only in the rectangular format (most
of the time in 4/3 or 16/9 format), the image projected on the screen also needs to be
in the same format. This excludes the possibility of full screen projection on square
screens, as often seen in visiocube type of systems. In general, the CRT projectors have
sufficiently smooth adjustments of the geometry of the projected images. On the other
hand, the LCD and DLP projectors offer very little flexibility and need to be connected
to additional hardware devices (Cyviz).
The geometry of the projected images can be controlled by displaying a test pattern
consisting of circles and horizontal, vertical and diagonal lines. The diagonal lines are
very useful to identify the problems of isotropy of the projection. While projecting
images on large screens, it is often necessary to distort a projected image (which is
originally even) so that it is adjusted as per the shape of the projection surface. The
most common distortions are due to either an off-centred projection on a plane surface
or an uneven projection surface. Both the problems can of course arise at the same
time. To offset the distortions of the resultant images, the systems make it possible
to adjust to any projection surface, plane or skew. For example, WARP system from
Barco is embedded in the projector for a fine calibration of the image geometry. It is
also possible to pre-distort the images in a software package just before sending them
to the projector, but at the cost of a significant power loss. In order to guarantee a
perfect continuity or superposition of images, it is also essential to ensure uniformity
in colours and brightness of images displayed on all the screens. Otherwise, setting all
the projectors manually turns out to be a long and tedious task. Companies such as
Barco with Dynacolor and CLO, or ICATIS with CaliWall (ICATIS), offer Automatic
Calibration Solutions. The advantage of this tool is that it makes it possible to calibrate
any set of projectors, even the standard ones, in terms of colour, brightness, geometry
and blending. Finally, it is also important that the characteristics, and particularly the
colour, of the screens are uniform from one screen to the other. This is particularly
important while using floor screens (more sturdy), which would not necessarily have
the same properties as vertical screens. Finally, using certain screens in direct projec-
tion and others in retro-projection can still be an element to be controlled in order to
guarantee uniformity of colours on each screen.
11.2.3.4 Stereoscopy
All techniques of stereoscopy based on a separation of images by eyeglasses are possible.
In active stereoscopy, the most common solution to generate the two images cor-
responding to the right and left eye is using an OpenGL Quad-Buffer graphic card.
Unlike the standard card, this application designs alternately in four buffers instead
of the traditionally used two (two per eye). If multiple graphic cards are used to
display images on contiguous screens or on the same screen (to increase the reso-
lution), a Genlock mechanism is indispensable to synchronise the vertical scanning
of graphic cards. It is in fact necessary to ensure that the two juxtaposed images are
displayed at exactly the same time so as to guarantee the synchronisation of the eye-
glasses with all the screens simultaneously. This synchronisation can be either through
a software package (Soft-Genlock) or an item of hardware, which in some graphic
cards is an integrated function (3DLabs or Nvidia), or in the form of external devices.
To increase the performances of the system, the image calculation of each eye can
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