Forums > MaxMSP


Nov 15 2008 | 4:03 pm

this is a general question that doesn’t directly relate to the max program but I figured this would be a good place to start asking…

I’m working on a project in which I need to project on a sheet of something from both sides so that both projections can be seen from both sides.

I’m considering a frosted plexiglass sheet. Has anyone ever done anything similar to this? any suggestions?

Also, does anyone know a simple way to reflect the pwindow horizontally.

Nov 15 2008 | 5:48 pm

Nov 15 2008 | 6:00 pm

the only thing is that I’m going to be running 2 projectors (one one each side of the scrim)so that both projections will meld together on both sides. is that feasible?


Nov 15 2008 | 7:17 pm

James Leonard IV skrev:
> the only thing is that I’m going to be running 2 projectors (one one each side of the scrim)so that both projections will meld together on both sides. is that feasible
Why? There is absolutely NO need to project on both sides, unless what
you’re projecting onto is, indeed, opaque, which it won’t be.

If you want some of what you’re projecting to be mirrored, then I’d do
that in the box before sending it to the projector.

Hope this helps… at least a bit :)


Nov 15 2008 | 8:42 pm


two separate live video feeds. I know that it will show on both sides.

I just need to know if it’s possible or if the light will cancel each other out in some weird way

Nov 15 2008 | 9:42 pm
Nov 20 2008 | 9:50 pm

Nov 21 2008 | 12:09 am

–> Also, does anyone know a simple way to reflect the pwindow horizontally.

Simple enough, several ways to do it: usesrcdim / dstdim, then reverse the corner points; even more straightforward, jit.rota, boundmode 2, x_zoom = -1. instead of normal (1.) I don’t know which is more expensive computationally, probably not an issue in this case.

I like the dual-projection idea, with them melding into each other, if you get something interesting maybe post a video. I’ve done some dual-projections onto the same side of a screen and it was pretty cool in itself. Also, using a camera to capture the video and then project it onto itself, with some jit.brcosa and other effects, and you’ve got some interesting delay patterns to play with.

Even a hardware plastic sheet that’s frosted (like paint tarps) could work, but you’ll probably have wrinkles from being folded. Can’t beat the price though :)

Nov 21 2008 | 12:31 am

Just make sure the cloth or fabric you use is very thick. Any thin fabric will allow the light from one projector to bleed through to the other side, and you’ll end up seeing double images. A better idea might be to hang to pieces of fabric back to back, separated by a half inch or so. That way, there’s very little chance of bleed through.

If you have a bright enough projector, then any kind of fabric will work. If you have a not-so-bright projector, then you’ll probably want to experiment with different fabric to find the most reflective type.

Also, if your image is not bright enough, you can just make the image smaller (by moving the projector closer to the screen, or by zooming if you have a zoom lens). One of the traditional units of luminance which is typically used for projection situations is the "foot lambert". The formula for figuring out how many foot lamberts you are getting is:

Luminance (in ft.-Lamberts) = Lumens / Area

where Lumens is the brightness of your projector in lumens, and where Area is the surface area of the projected image (in square feet). For a dark room, you want about 10-20 foot lamberts. For a typically lit room, 30-50. For a brightly lit room, 75-150. This calculation holds only for projection surfaces that have a "gain" of 1. In other words, projection surfaces that reflect as much energy as they receive. So, if your frosted fiberglass has a gain of 0.5, then you just halved your foot lamberts. For uncommon materials, you obviously won’t be able to find a gain spec. However, all manufactured projection surfaces have a measured gain, and usually the surfaces that have a gain higher than 1 have bad off-axis response, since they are focussing the light more towards the viewers that are on-axis with the screen.

Probably a little more than you wanted to know. Just make sure your impromptu projection surface is opaque and white.

Nov 21 2008 | 12:34 am

Also, keep in mind that real, manufactured projection screens from companies like Da-Lite or Draper are relatively inexpensive. Depends on your budget. You can get a small one for one or two hundred bucks. Might be worth it depending on the situation.

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Forums > MaxMSP