[AG-TECH] AG Projector options?

[Osland, CD (Chris)]

shudo at ni.aist.go.jp raises the question about videowall area
versus number of pixels, and this was part of other people's
reply as well, with the comment being made about minimum angular
size needing to be investigated in the AG context.

The fact that current VIC will only subsample 2:1 (Small) or
pixel replicate 1:2 (Large) is certainly a factor that affects
the decision, at present.

We also find that the angle the whole wall subtends to the audience
(i.e. the angle a person's head has to swing to move from looking at
the left hand edge of the videowall to looking at the right hand
edge) has to be thought about.  At present for a person in the
middle of the front row in our new room this is about 90 degrees,
and about 80 degrees for someone at the end of the front row.
Much more than this (our about-to-be-old room had 110 and 90
respectively) is a problem if many site are active, or there is
a big DPPT or VNC frame in the middle, forcing video feeds to
the edges of the videowall.

Similarly I prefer the bottom of the image to be no higher than
18 inches / 450 mm for a 20 foot wide videowall; this allows the
vertical centre of the wall to be at eye height.

[BTW, I found that getting the geometry right for the projected
images abutting exactly was impossible on a vertical wall without
resorting to digital keystone correction, so I'm tilting the wall -
which is a screen on a wooden frame.  The screen is perforated, so
I can range the four loudspeakers on stands, at eye height, along
the back behind the screen, so they are invisible.]

Getting back to pixels versus area, my estimate is that Medium
images on a 20 foot wide (5 foot high) videowall run off 3 1280x1024
projectors, while they will be physically 25% smaller in each
dimension, would still be usefully large.  For a videowall with
larger area, I would expect that it would have to be further from
the audience (or the left to right angle will be a problem as noted
above), and so there would be no net gain.

Economically, I like (and had not thought of) the idea of having
8 £3000 projectors rather than 3 £15,000 projectors:

8 x 1024x768  = 6.3 Mpixels for £24K =  £3.8K / Mpixel
3 x 1280x1024 = 3.9 Mpixels for £45K = £11.4K / Mpixel

Unless people are rear-projecting with a 4x2 array of projectors,
I'm interested to know how you get the geometry right without
people bumping heads on the projectors!

Enough - I've rambled on far too long!

Cheers

Chris
____________________________________________________________________
Chris Osland                         Office tel: +44 (0) 1235 446565
Digital Media and Access Grid      Medialab tel: +44 (0) 1235 446459
BIT Department             Access Grid room tel: +44 (0) 1235 445666
e-mail:   C.D.Osland at rl.ac.uk               Fax: +44 (0) 1235 445597

CLRC Rutherford Appleton Laboratory (Bldg. R18)
Chilton, DIDCOT, Oxon OX11 0QX, UK

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