Film-Tech Forum ARCHIVE: Christie, WCLs, and RealD

This is topic Christie, WCLs, and RealD in forum Digital Cinema Forum at Film-Tech Forum ARCHIVE.

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Posted by Jeffrey Allen Rydell (Member # 5378) on 03-02-2010, 11:39 PM:

Hi, guys.

First post after some searching didn't turn up an answer to this week's puzzlement. I'm a fairly new projectionist at a Carmike. After being out of a self-taught 35mm gig over a decade ago, I'm now struggling to catch up with the transition to Digital.

We're using both the CP2000 S and H models, on common height screens, with WCL lenses. First up, the WCLs are used in both 3D formats mostly, it seems, to provide a swingable mount for the Z Screen polarizer. The problem is that the Flat 3D content needs to be pretty radically scaled down on the imager to fit on the screen, introducing anomalies (of the 'jaggie' persuasion) in the process. There are several screen presets of varying degrees of rescale to choose from via the touch pad controller. These have apparently been made available by RealD rather than Christie- which isn't encouraging for the possibility of getting around the image degradation.

I can take out the WCL and just project through the prime lens, using the swing arm as an 'empty' mount for the Z Screen, and size the image back up to full resolution by selecting the initializing 'No Crop' screen file, but that's where things get especially screwy - in all 3D channels, there's top/bottom image crop - an unacceptable amount in 3D Flat. Yet I can run a 3D framing chart in a 2D channel, and no such cropping is evident (only the expected outta-whack color).

Anybody know what gives, and if there's a better workaround than simply scaling the image down digitally, and throwing away resolution in the process?

Thanks for indulging an introductory post that's probably both obtusely phrased and demonstrably 'green' on the subject at hand.

-Jeff

Posted by David Zylstra (Member # 4230) on 03-03-2010, 08:36 AM:

The need for 3D scaling is due to a limitation in the processing power of the driver boards (or so I have been told). Something to do with the original TI boards being designed for 120hz max and 3D with a single projector runs at 144hz - to get around this limitation the image is scaled down to a size smaller than the scope image height that can be processed without causing more anomolies (I'm told that while it may run full frame 3D for a little while the processing eventually melts down). The 144hz for 3D is because of the "triple flash" used on single projector 3D - each eye is 24 frames per second, 3D has 1 image for each eye so the file is 48 frames per second (or 48hz) where the left and right images are alternated, the projector then takes the 48 frames per second and flashes each eye's image 3 times alternating between eyes so 48hz X 3 = 144hz.

Your CSE should have set up your lens with 2 marked settings - 1 for 2D and 1 for 3D. On our screens that are set up the same as yours we have to manually zoom the lens to make the picture bigger for 3D to fit the screen.

There is a very expensive upgrade that can be done to the older Christie projectors that allows them to run 3D in its native resolution, but it requires sending the projector back to the factory.

Posted by Jeffrey Allen Rydell (Member # 5378) on 03-03-2010, 08:55 AM:

quote: David Zylstra
...to get around this limitation the image is scaled down to a size smaller than the scope image height that can be processed without causing more anomolies (I'm told that while it may run full frame 3D for a little while the processing eventually melts down)

Thanks for the reply, David.

Funny thing is, I've been running AVATAR in scope in full resolution since day one, on each of our four 3D-capable screens. Now, there is mild cropping at top and bottom, but so minor I elected it the lesser of two evils when faced with the other option of both digitally 'de-scaling' and then optically zooming back up the smaller resultant image. 3D flat, on the other hand, is way past any sort of acceptable presentation were I to do the same there.

Sounds like this is some version of what I'd feared - a 'cludge' worked out between Christie and RealD to get an image on screen with an agreed-upon amount of compromise affecting the end result.

-Jeff

Posted by David Zylstra (Member # 4230) on 03-03-2010, 11:12 AM:

The compromise is on all first generation TI light engines so the limitation is universal to all early DLP projectors regardless of manufacturer.

Posted by Demetris Thoupis (Member # 833) on 03-03-2010, 01:26 PM:

You could double flash. Even if you tripple flash in 1st generation the scaling will NOT project the full image but still crop a bit. You can see this very clearly if you use the Dolby masking test for 1:85 and 2:39 in their DSP and DSS units.
Demetris

Posted by Jeffrey Allen Rydell (Member # 5378) on 03-03-2010, 06:17 PM:

Thanks, guys. I'll just minimize the re-scaling on my end, and live with it.

Stoopid bleeding edge! [Wink]