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Re: [Phys-l] experiments with dyes (was: happy equinox)



On 03/28/2008 08:47 AM, Clarence Bennett wrote:

Is this the reason that yellow, light green and light blue, that look
so good on laptops where power points are prepared, vanish into the
background when projected?

There is no very good reason for such colors to vanish. The
physics of laptop screens and the physics of VGA projectors
is too similar.

1) One "junk effect" that may intrude is lousy black level
on the projection screen. This an easily happen if the room
lights are left on. Remember that the screen doesn't
know where the projector is; it send to your eye light
coming from anywhere, including stray light from any
source.

And what can be done about it?

Well, one thing that helps tremendously, if you have the
resources, is to use a rear projection screen. That
requires having some huge piece of real-estate behind
the screen, painted black.

The low-budget version of that, if you're stuck using a
front-surface projection screen, is to make the room
as dark as you can. This is what movie houses do. Of
course this has some disadvantages in a classroom setting.


2) Another problem is that (for no very good reason) the color
profile of the projector may be different from the color profile
of the laptop screen.

And what can be done about it?

In Linux, it is possible to set the GLUT (graphics lookup table)
for each device separately, so as to make the overall path
(GLUT + hardware) behave according to some standard. This
should help a lot.

I'm pretty confident a MAC can do the same, but I don't know
the details. I've got nothing to say about MS Windows.

For background information about gamuts and device profiles,
see
http://www.av8n.com/imaging/color-management.htm