stereoscopic 3d projection

[thatmattrogers]

I have absolutely no experience with 3d projectors, so forgive me if this is a dumb question.

I have run diy 3d content through Isadora before using 2 separate projectors with polarising filters covering the lenses.
this worked OK but setup was sometimes prohibitively long. So I'm looking into getting a 3d capable projector to streamline the process.

So, is it possible to run 3d content from isadora to a 3d projector? if so what do I need to consider?

As they all seem to receive a 3d signal via a single HDMI how will I need to prepare the 2 streams of footage to create a single file that works?

thanks in advance.

(and apologies if the answer is going to be painfully obvious when I get my hands on a projector.)   

[thatmattrogers]

ok, I've done a bit of of reading and some thinking.

PLEASE PLEASE let me know if I'm making any foolish assumptions.

it seems as though 3d capable projectors just need a video file with both sets of video in it. 

eg. If the target display is 1920x1080 it just needs to be a 3840x1080 video feed containing the two videos (left and right) side by side.

so... Theoretically...

I could set up a 3840x1080 stage (stage 1) to send to the projector, then have 2 projector actors in my scene. One mapped to the left of the stage and the other mapped to the right.

then I would be providing a video stream that the 3d projector could interpret

I'm going to have to get my hands on a projector to test this, but it feels like it would work.

[thatmattrogers]

of course this work around is only going to work if the stage is built from a single display. if I attempted to use multiple projectors to create a larger screen then it would fall apart.

so I'm still open to suggestions re: 3D projection setups.

[Maximortal]

what kind of 3d technique are you using? active glasses, silver screen and passive glasses?

[fubbi]

I second @maximortal, the important factor is what you want to hand out to your audience. No 3d without glasses. 

Theoretically it should be possible to make frame sequential transmission (which is what your "3d ready" projector wants) by alternating 2 images, one for each eye. Then anaglyph glasses, either polarised or blue/red (my fav).

Something like a 30hz pulse generator driving a selector or router. I guess you would want 60fps with every second frame being the image for the other eye and just stream it out over HDMI. Theoretically.

It would certainly be interesting to see that work, has anyone tried it?

[thatmattrogers]

@maximortal I'm using passive polarised glasses. 

[thatmattrogers]

@fubbi ok that's an interesting thought. You're right in theory. As long as I'm rapidly switching between 2 video sources at 3hz then it should be indistinguishable from an interpolated stereoscopic video.

I shouldn't be able to borrow a projector later in the week, then I'll do some tests and let you know how it goes.

[Maximortal]

i used Isadora for 3d projection using silver screen and passeve polarizated glasses. I got footage with side side frame. I had 1 movie player then with izzymap I cropped the frame then it go to the differen projector. Each projector had a polarizatig filter in front. Having just 1 movie player is very important for having a perfect sync between frames.

[thatmattrogers]

@maximortal that's exactly how I used to do it, I'm now looking at ways to use a projector that has an inbuilt 3d feature. Meaning that I have less hassle with polarising filters and the time it takes to perfectly alignin 2 images.

From what I can tell there's 3 ways that 3d projectors take an image to use for 3D

1: one above the other (literally a 1920x2160 image with both 1080p videos stacked on top of one another)

2: side by side (a bit more complicated, this is 2 1080p videos horizontally squashed to half width so they can both fit on a single 1080p stream)

3: interpolated (switching between the 2 videos rapidly at 60hz)

I'm getting hold of a projector that has a 3d feature later this week, and the experiments I'll be doing are: 

1: create some custom video content that conforms to the"over/under" and "side by side" formats

2: set up some kind of rapid switching

Either of these methods are theoretically fine, but I'm concerned that they won't play nicely if I want to create a larger surface with multiple projectors. For that I'd probably need something in the stage setup area that supports it. But it'll be interesting trying.

If you have any suggestions of how I could improve on my methodology, I'm open to any advice that you can offer.

[Maximortal]

on my experience most important thing is frame time alignment. If I had to do something like you I'll try to create a unique footage and the crop it. I'm pretty sure that your 3d projector automatically recognise type of signal and convert it into 3d projection

[DillTheKraut]

@thatmattrogers

If you go with passive polarized glasses, there is no single projector only solution, as you need two different physicaly optical systems (lenses/filters).

There is a single projector solution though.

An actively alternating polarization filter takes the position of the active glases and 'convertes' the picture for passive polarized ones.

But keep in mind, that this solution has a reduction of the projectors brightness in half of the original. 50% for each eye.

As far as I know, '3D ready' projectors usualy have an option to choose between the 3D modes, 'side by side', 'top - bottom' or interleaved (alternating frames). But every Projector works a little bit different and you should study the specs.

Especialy the side by side may differe by the projectors. While some only take FullHD content (resulting in two times 980 x 1080 scaled to 1920), others may take 4k (but usually you then would need 4k content with two times 1920 x 2140)

In both cases the content is squeezed horizontly to fit next to each other in the full frame. The projector then unsqueezes them and scales it to its native output resolution with alternating the left and right picture.

Best

Dill