Film-Tech Forum ARCHIVE: Is digital IMAX 2K

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Posted by Antti Nayha (Member # 4980) on 01-30-2012, 08:41 AM:

(Edit: sorry, wrong forum. Admins, please feel free to move this to Digital Cinema.)

There’s some conflicting information going around about the resolution of dual-projector digital IMAX, aka. LieMAX. Let’s clear this up once and for all, shall we?

As we all know, the fact is that they’re currently using two 2K projectors with overlapping images. But already back in 2009 or 2010, I read somewhere that the two projectors are actually not aligned at exactly the same position, but the pixel grids have a difference of exactly half a pixel (can’t find the source now, of course).

So with a setup like that and a 4K source, you could theoretically extract two slightly different 2K images for each projector and achieve a resolution higher than 2K. Think of it as a modern version of interlaced video. Although I still can’t imagine how the alignment could ever be made perfect enough for this to actually work.

Now, I noticed that at least M:I4 was distributed to digital IMAX venues as a 4K DCP, which would only make sense if the above is true.

Then again, some people are claiming that the two projectors are aligned at exactly the same point, pixel by pixel, both projecting the exact same 2K image. I think someone who works at an IMAX theatre even said this on this forum a while ago…?

Posted by Bobby Henderson (Member # 840) on 01-30-2012, 06:11 PM:

The two IMAX projectors in standard 2D mode show the same image slightly overlapped on each other to increase brightness for large screen use and do more to hide the visible pixel grid. The movie file being fed to the projectors has 2K native resolution.

4K has quadruple the pixel count of a 2K image. So the idea of giving a pair of 2K projectors slightly different image data each would in the end only yield have the native resolution of a 4K image.

Posted by Antti Nayha (Member # 4980) on 01-31-2012, 05:13 PM:

Yeah, I didn’t mean to imply that 2 x 2K would somehow equal 4K. But conceivably they could take a 4K DCP and extract the two half-pixel-offset 2K images from it in real time, thus achieving a slightly higher resolution than 2K. That is, if the physical alignment of the projectors could ever be made that perfect.

If they’re not doing that, why are the specially prepared, IMAX-branded DCP’s 4K instead of 2K? (Or at least M:I4 is.)

Posted by Jonathan Goeldner (Member # 4854) on 02-01-2012, 10:58 AM:

isn't the plan though for the 15/70 IMAX theater conversions the new dual projector setup would be 4K

Posted by Carsten Kurz (Member # 5396) on 02-01-2012, 05:55 PM:

quote: Antti Nayha
If they’re not doing that, why are the specially prepared, IMAX-branded DCP’s 4K instead of 2K? (Or at least M:I4 is.)

What tells you that they get special IMAX 4k DCPs? Also I don't think that this kind of in-line processing is allowed - the content is encrypted.

Yes, I guess that the future generation of digital IMAX will have 4k, maybe dual 4k projectors. However, for the largest screens it seems that even the brightest xenon projectors currently available wouldn't give sufficient light for 3D. That's why IMAX invested so much into laser projection technology. Because this seems better suited to scaling brightness for the largest screens.

Anyway - MI4 is available in IMAX DMR on film, so why bother about 2*2k...

- Carsten

Posted by Antti Nayha (Member # 4980) on 02-01-2012, 06:47 PM:

quote: Carsten Kurz
What tells you that they get special IMAX 4k DCPs?

Well, I saw one. [Smile]

Of course, they could simply be future-proofing their stuff for an upcoming 4K system.

quote: Carsten Kurz
Anyway - MI4 is available in IMAX DMR on film, so why bother about 2*2k...

No real reason at all, just curious. As I said, there are all kinds of rumors floating around.

It’s been announced that IMAX and Kodak are going to roll out their laser system already in 2013 (no word yet about the resolution, but 4K would seem most likely indeed). Barco, on the other hand, estimates that it will take another 3–5 years before their offering is ready to market. Naturally, they claim that it’s technically superior.

Posted by Jonathan Althaus (Member # 5042) on 02-02-2012, 09:09 AM:

Kodak-40,000 Lumens
Current Barco 4k-43,000 Lumens
Barco Laser-55,000 Lumens

Posted by Jonathan Goeldner (Member # 4854) on 02-02-2012, 10:47 AM:

^ interesting

I saw 'Underworld Awakening' on the XD screen and the brightness of the Barco projector was excellent, given that it is a darkly lit movie anyways. Comparing it to the ETX Christie dual projector system over at AMC Tysons, the XD trounces it by a mile. every.. single.. time.

Posted by Elise Brandt (Member # 5552) on 02-02-2012, 11:48 AM:

Nothing to add but: Antti!! Hey! Why the heck have I not seen you around here? *krhm* although number of posts would explain that yeah, but still. Yay!

Posted by Carsten Kurz (Member # 5396) on 02-04-2012, 06:08 AM:

quote: Antti Nayha
Well, I saw one. Of course, they could simply be future-proofing their stuff for an upcoming 4K system.

Well I do not doubt you saw a 4k DCP. But what tells you it was a special IMAX 4k DCP?
I don't think they need to future-proof their systems for 4k. 4k DCPs are common for a couple of years now.

As for the 2*2k, digital IMAX has special projector mounts that can be electronically shifted. Add to that fully automated x/y/z lensshift and zoom on their lenses, so pixel-accurate adjustment is probably possible.

Yet wondering wether they still use 2k projectors for new installs.

- Carsten

Posted by Antti Nayha (Member # 4980) on 02-04-2012, 01:34 PM:

The DCP I saw had ”IMAX” written all over it, also in the filename if I remember correctly. Might be able to check that tomorrow.

And aren’t all digi-IMAX DCP’s specially prepared anyway? Last time I checked, they were doing special image processing (maybe audio as well?) to their DCP’s, using the same ”DMR” brand as their blowups to true 15/70mm IMAX. Even though I don’t suppose they’re using the same master for both.

If IMAX already has a 4K system out, they’re certainly being tight-lipped about it.

PS. Hi Elise! I’ve been a long-time lurker here, but for whatever reason only started posting actively a month ago or so…

Posted by Marcel Birgelen (Member # 6801) on 02-28-2012, 12:10 PM:

Sorry for bumping this topic, but I landed here because I had exactly the same question as the topic starter, after Googling a bit around, I got some conflicting information.

I recently watched the first two movies in a local digital IMAX (aka LieMAX): MI4 (2D) and Journey 2 (Stereo-3D). REAL 15/70 IMAX has almost become extinct around here, the only real IMAX theatres left witin about a 4 hours drive only show the standard documentaries they've been showing for ages.

I've noticed that all the preshow content was projected trough a single projector, the second projector only kicks in right before the first "look-how-fabulous-we-are" IMAX trailer.

First I thought they might be slicing up the image vertically or horizontally, but after looking back to the projector booth, I could clearly see two full images being reflected on the glass in front. Also, getting that right without a visible seam might be even harder than projecting two images on top of each other.

During the MI4 presentation, the auditorium was almost empty, so I took the opportunity to walk to the screen. The Screen-door effect is clearly visible close upfront and you can clearly see pixels in a grid that looks rectangular to me.

So it looks like they manage to project two images exactly over each other. I cannot say if they project EXACTLY the same image from both projectors, but at least it alligns perfectly on the screen as a single pixel grid.

I still don't know how they achieve this, or more specifically, how they maintain this level of calibration.

There is a camera mounted near the booth pointed at the screen, that looks like an ordinary security camera, it is not even pointed straight at the screen, but with an angle. I guess you could use that to match both pictures using some predetermined test patterns, but I highly doubt you could detect alignment mismatches during a running show, let alone correct them on the fly, without a decent test pattern on-screen.

Posted by John Thomas (Member # 6509) on 02-29-2012, 03:00 AM:

I know there are different series of D-IMAX setups, so I can only describe the one I work with:

It's aligned (ideally) every morning. The projectors take about a half hour to warm up the lamps (which stay on all day), and then with the auditorium pitch-black it fires test patterns back and forth to get the pictures aligned as well as the luminance as close as possible between the two projectors. This is what the camera is for.

What's being calibrated is what IMAX calls the "Image Enhancer," or IE. From what I can tell, it warps the two images ever so slightly so that they do in fact overlap perfectly once they're fired at the screen. Ours has two nVidia Quadro FX 4800's achieving this. Not sure what other hardware is involved with the IE.

This calibration is particularly important because changing lamps requires you to physically wheel one of the projectors out of the way in order to get your hands into the other one.

Posted by Marco Giustini (Member # 4544) on 12-09-2012, 01:58 PM:

That explains the experience I had today.
I saw my first Digital Imax, Skyfall.
From the middle of the auditorium I could clearly see the pixels and jagged borders. I thought the projectors were two 4K machines overlapping 100%, I did not realise they are actually 2x2K machines.
This is ridiculous; I now see why you call it LieMax. Outrageous, I am not going to pay £17 again to watch a grid of pixels on a big screen. I really wonder how come IMAX has decided that this is acceptable.

Edit: now I'm thinking about, the setup you're suggesting should result in a 4K picture - ish. I am confused. Am I supposed to see pixels and jaggies from the middle of the auditorium???

Posted by Jonathan Goeldner (Member # 4854) on 12-09-2012, 02:09 PM:

quote: Marco Giustini
That explains the experience I had today.
I saw my first Digital Imax, Skyfall.
From the middle of the auditorium I could clearly see the pixels and jagged borders. I thought the projectors were two 4K machines overlapping 100%, I did not realise they are actually 2x2K machines.
This is ridiculous; I now see why you call it LieMax. Outrageous, I am not going to pay £17 again to watch a grid of pixels on a big screen. I really wonder how come IMAX has decided that this is acceptable.

Edit: now I'm thinking about, the setup you're suggesting should result in a 4K picture - ish. I am confused. Am I supposed to see pixels and jaggies from the middle of the auditorium???

I remember asking the IMAX rep at the opening of the AMC Hoffman IMAX-D screen about the resolution and when he told me it was only two 2K projectors' - that really surprised me. Guess this will change for the better if and when the laser technology comes out at the end of next year.

Posted by Carsten Kurz (Member # 5396) on 12-09-2012, 02:18 PM:

Two 2k images overlapping will not give 4k resolution. The pixelshape and size will still be 2k, even with more or less overlapping. So, yes, on a large screen, I consider it perfectly normal to see jaggies from a center position.

When IMAX laid this out, 4k DLP was not available. I heard IMAX was recently throwing out the original Christie CP2000 machines to be subsequently replaced by BARCOs. However, I have not seen any indication wether they now use 4k Barcos. Of course, 4k for digital IMAX should be a no brainer, but who knows...

- Carsten

Posted by Marco Giustini (Member # 4544) on 12-09-2012, 02:20 PM:

I am so disappointed, the picture was "digital", NO detail was visible, only bunches of pixels. I really don't get how someone at IMAX looked at the first setup and said "Yes, this is amazing, it looks as good as the 15/70, let's go for it".
Mine was a proper IMAX screen, with the 70mm projector still sitting there.

Posted by Jonathan Goeldner (Member # 4854) on 12-09-2012, 09:11 PM:

@ Carsten: I though the Barco changeover WAS for the reason of the laser projection upgrade.

Posted by Andrew Thomas (Member # 7000) on 12-09-2012, 10:54 PM:

Other than the screen size being so large, I've never been impressed by 15/70 IMAX. I would rather have that resolution on a much smaller screen. Digital IMAX screens I've seen are about the right size, but the 2K resolution is far too low.

Posted by Marco Giustini (Member # 4544) on 12-10-2012, 04:09 AM:

Then they simply cannot charge customers to see a pixellated image, that's it.

The only 15/70 Imax I've seen was waaay better.

I give up with Imax. The sound was ok and loud, but it's absolutely not worth £17, which are $27!

Posted by Carsten Kurz (Member # 5396) on 12-10-2012, 05:56 AM:

quote:
@ Carsten: I though the Barco changeover WAS for the reason of the laser projection upgrade.

I don't know if they have signed anything regarding laser retrofit systems. To my knowledge, the laser retrofit systems are only intended to equip the remaining 15/70 sites with very large screens.

Barco has only demonstrated that retrofit system, as all other manufacturers incl. Sony have.

Why they decided to go with Barco instead of Christie, I don't know. Maybe it's just because Barco has the brightest xenon DLP projector confirmed. And maybe Barco could promise the earliest availability for their laser retrofit engine.

- Carsten

Posted by Mark Strube (Member # 4190) on 12-10-2012, 08:23 PM:

quote: Carsten Kurz
Why they decided to go with Barco instead of Christie, I don't know.

Price.