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Re: Matching the distortion of a wall when outputting to a projector...

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Joshua Steadman
Re: Matching the distortion of a wall when outputting to a projector...
on Sep 2, 2010 at 1:24:22 pm

I'm working on an AfterEffects sequence that will be played from a multimedia player connected to a projector capable of outputting an HD signal (my sequence is at 720p). The projector will be mounted 12'10" high and will project the content onto a slightly curved wall. The wall is 15' wide by 8' high, and the center of the wall is 9' from the projector.

The producer and I want to take the distortion created by this into account and apply an inverse-distortion to our content so that to a viewer standing in front of the wall, the image appears to have no distortion.

I tried outputting a test jpeg with an AE-generated grid and projecting that image onto a curved surface here in the studio, to test workflow. With my still camera I then took a picture of the distorted projection, brought that into AE, and am attempting to use the bezier warp tool to match the distort (or really, to do an inverse of the distort), but am having trouble getting it to look just right.

Is there a better way to do this? A different effect I'm overlooking? Or, even better, something that doesn't just rely on eyeballing the entire procedure; the grid helps, but it still feels like I'm guessing. Also wondering if I need to make my comp larger than 1280x720 so that I'm able to warp beyond the canvas and still have control over those points. Of course then when I output I'm guessing I'll use an alpha channel on the QT to make sure the projector doesn't just project black onto the screen where there's no image...

We aren't able to use a program like Watchout; am needing to do all this within AfterEffects.

Am running this on a mac, 2.93 GHz Quad-Core Intel, 8 GB RAM, Mac OS 10.6.4, AE CS4.



Thanks for the help;
Joshua Steadman
steadyfilm@mac.com
Raleigh, NC USA





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Walter Soyka
Re: Matching the distortion of a wall when outputting to a projector...
on Sep 2, 2010 at 4:24:40 pm

[Joshua Steadman] "We aren't able to use a program like Watchout; am needing to do all this within AfterEffects."

Ok, so Watchout is out, but what about renting a separate hardware warp engine? That's really the best way to do this...

[Joshua Steadman] "I tried outputting a test jpeg with an AE-generated grid and projecting that image onto a curved surface here in the studio, to test workflow. With my still camera I then took a picture of the distorted projection, brought that into AE, and am attempting to use the bezier warp tool to match the distort (or really, to do an inverse of the distort), but am having trouble getting it to look just right."

Barring a real warp engine, I'd suggest a couple changes to your workflow.

First, I'd work in your regular 1280x720 comp for production. As the last step, I'd precomp that into a separate 1280x720 comp for warping and output.

Working with a digital camera as you are may be introducing additional optical distortion from the camera's lens. Get in the space with an AE machine, drop a grid in your production comp, then switch to the warped output comp. Apply your Bezier warp, send that full-screen on a second output to the projector, and tweak live.

An alpha channel won't be necessary (or useful). Just keep a black background in your warped output comp.

Finally, cross your fingers that nothing moves from when you test to when you render final output!

Walter Soyka
Principal & Designer at Keen Live
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
RenderBreak Blog - What I'm thinking when my workstation's thinking
Creative Cow Forum Host: Live & Stage Events


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Joshua Steadman
Re: Matching the distortion of a wall when outputting to a projector...
on Sep 2, 2010 at 5:47:58 pm

First, I'd work in your regular 1280x720 comp for production. As the last step, I'd precomp that into a separate 1280x720 comp for warping and output.


Check, will do on that. Should make the process easier.



Working with a digital camera as you are may be introducing additional optical distortion from the camera's lens. Get in the space with an AE machine, drop a grid in your production comp, then switch to the warped output comp. Apply your Bezier warp, send that full-screen on a second output to the projector, and tweak live.

Yes, forgot to mention I ended up doing this as well. I tweaked live, but wasn't happy with what I was supposed to be tweaking to. Even with the grid in place, I felt like I was guessing. Is there a way to have corrected points I'm mapping the grid to in place?




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Walter Soyka
Re: Matching the distortion of a wall when outputting to a projector...
on Sep 2, 2010 at 6:09:46 pm

I've reconsidered the 1280x720 production comp. Work in 1920x1080 instead so you'll have more pixels available for smoother distortion later. Your warped output comp should match projection.

Check out the Watchout manual for some examples of what your Bezier warp will look like. You could also use a combination of Bezier warp and Bulge or Optics Compensation. I'd get the top straight, then get the bottom straight, then deal with any irregularity in the middle. Use as few handles as possible.

If you are simultaneously warping for curvature and keystone correction, this will be considerably harder. You might consider double-precomping and roughing in perspective with Corner Pin before handling the curvature. Better still -- move the projector!

Walter Soyka
Principal & Designer at Keen Live
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
RenderBreak Blog - What I'm thinking when my workstation's thinking
Creative Cow Forum Host: Live & Stage Events


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Joshua Steadman
Re: Matching the distortion of a wall when outputting to a projector...
on Sep 2, 2010 at 6:59:10 pm

Walter--
So a possible workflow for our curved screen (which is 15x8' but only 8.5 inches deep at it's most concave point):

1. Adjust keystone correction in hardware and get projected image to fill entire screen.

2. Put up a 1280x720 grid and make note of bowing (outward at bottom, inward at top)

3. Adjust/Warp the production to account for bowing

This keeps all keystone correction in hardware, and we just account for the bowing in the production.

Thanks for all input;
Joshua Steadman
steadyfilm@mac.com
Raleigh, NC USA




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Dave LaRonde
Re: Matching the distortion of a wall when outputting to a projector...
on Sep 2, 2010 at 5:26:02 pm

This issue has cropped up a couple of time when people want to project video onto walls.

My reaction is this: there is only ONE SPOT in this space where your painstakingly-warped image is going to look right: at the projector.

People are going to be walking around, right. Their perspective on the image will be constantly changing, right? Thus, it will look warped -- but in a different manner -- no matter where they are.

Unless someone has compelling arguments to the contrary -- and I'm all ears on this topic -- I say you're beating your head against a wall, so to speak, to achieve something that's unattainable.

Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA


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Joshua Steadman
Re: Matching the distortion of a wall when outputting to a projector...
on Sep 2, 2010 at 5:43:42 pm

David-
Thanks for the input. Both the producer and myself realize we're only correcting for a person standing directly in front of the wall/projection, but we're still going down this road. Goal here is to make it look right from dead on, and let the other perspectives be slightly warped.

As far as a workflow, I've done a live preview in AfterEffects to a projector with a grid superimposed over a test image, but I'm unable to warp satisfactorily. When I am warping, am I supposed to be warping the image to please the eye, or putting the grid points to other specific points? In the case of the latter, what are my other points? It almost seems like I need to somehow have a second grid which is completely true (not warped) that is superimposed over the projected (warped) grid. That seems impossible.

If the answer here is WatchOut, we both accept that. But I'd like to know if we're almost there, but missing a small step that would enable our current workflow.

Thanks,
Joshua Steadman
steadyfilm@mac.com
Raleigh, NC USA




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Dan Quintero
Re: Matching the distortion of a wall when outputting to a projector...
on Sep 3, 2010 at 9:13:49 pm

Dave, that sounds like something you'd hear at a news station.

I'd say don't ignore it. If you can hook up a laptop to a projector and tweak it live onto the wall or a similar wall, it shouldn't take too long to get it right. Can't tell you off the top of my head which effect would be best, but it should definitely be fixable/manageable.

Go fly fishing.


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