[AG-TECH] screens/projectors set up

Jim Wellings jim.wellings at usu.edu
Mon Sep 27 11:18:03 CDT 2004

Setting up the projectors so they all match is difficult. 
The brightness and color of each projector will change as the lamps and LCD
chips age. If you are using (as we did) projectors with different amounts of
lamp time the color will not match. If they are all new projectors they should
be close, or you should be able to adjust color temperature, brightness and
contrast to match.
The accurate alignment is affected by zoom setting, keystoning and even focus -
a few tiny errors add up quickly - 
we set up the center projector first, adjusting size and position, then we
measured the width of the image on the screen. This measurement then became the
measurement from lens center to lens center from the center projector to each
side projector. This seemed to lessen the side to side keystoning - if you have
to twist the projector on the mount to get the image edges to align, the
keystoning will make it really hard to get a seamless image.
I used a background image to align the projectors, then changed it to black
once I had them aligned. The alignment is pretty good, but the color difference
is distracting. We will swap out the offending projector to hopefully correct
Jim Wellings
Video Network Engineer/Operations Supervisor
Utah State University
Logan UT 84322-8500
jim.wellings at usu.edu

>>> "Osland, CD (Chris) " <C.D.Osland at rl.ac.uk> 9/27/2004 3:34:27 AM >>>

The main 'trick' is to set the background to black.  Then, when
two images don't quite abut, or overlap, there is no double
intensity or gap in the background.  Then it's just a matter of
normally arranging the windows so they don't span projectors.
Once you get into edge-blending (the term that describes the handling
of overlapping areas) you are into SERIOUS amounts of money for
hardware: I haven't seen a software solution.  You can do a bit
with the intensity control on each projector, but there will usually
be a bit of a mismatch with commodity level projectors.

Another thing I do is run our 1024x768 (native) projectors with
1280x960 signals.  This gives a dramatic increase in the number of
pixels (2 such projectors have more pixels than 3 1024x768 projectors)
and makes it much easier to fit 3x3 medium size windows on each
projector, without using the shift-m trick which crops edges off
the windows (maybe losing vital bits of some carefully judged
framing).  For AG images the results are fine; for PowerPoint
etc. they are acceptable.



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

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

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> -----Original Message-----
> From: owner-ag-tech at mcs.anl.gov [mailto:owner-ag-tech at mcs.anl.gov]On
> Behalf Of Natalia Costas Lago
> Sent: 25 September 2004 17:18
> To: ag-tech at mcs.anl.gov
> Subject: [AG-TECH] screens/projectors set up
> Hi everybody,
> We are in the latest stage in building our node. The problem 
> we have right
> now is how the projectors can't be tunned so the transition from one
> screen to the next is smooth (it seems to be very difficult from the
> technicians to tune the position and the color). I wonder is 
> there is some
> trick AG users have to fix this.
> Maybe the screens overlap and there is some software that handles the
> overlapping area?
> We have another problem as the central projector seems to 
> have a slightly
> different brightness (even though the settings are the same for the 3
> projectors). But we havent tried to fix this so far.
> Any help about this issue is greatly appreciated.
> Kind regards,
> Natalia.
> -----------------------------------
> Natalia Costas Lago
> mailto: natalia at cesga.es
> Centro de Supercomputacion de Galicia (CESGA)
> Center for High Performance Computing
> Avenida de Vigo, s/n Campus Sur
> 15705 Santiago de Compostela - SPAIN
> Tel: +34  981 56 98 10
> Fax: +34  981 59 46 16
> http://www.cesga.es/

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