Film-Tech Forum ARCHIVE: 3D Ghosting

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Posted by Larry Zuverink (Member # 1483) on 10-19-2007, 02:46 PM:

Anyone have any idea what causes 3D ghosting. We were told that Hurley screens cause this. However we have 4 screens not doing it and one that is. Of course Christie and Real D both blame the screen. All 5 of these screens are brand new.

Posted by David Zylstra (Member # 4230) on 10-19-2007, 04:15 PM:

I know that certain 3D technologies require what they call "ghost busting" where they do something to each eye's picture to cancel out bleed through of the polarizers (this was why DCI came up with a spec for 3D to work towards single inventory and put "ghost busting" responsibility onto the hardware).

One thing to check would be to make sure the copy of NBC in question is one that is meant for RealD and not Dolby or another 3D system - I wonder if somehow that screen has a non-"ghost busted" DCP . . . . . sheer speculation on my part.

Posted by Ken Lackner (Member # 1002) on 10-19-2007, 05:51 PM:

I assume you have made sure that the Z-Screen is fully in place and completely level.

How can you tell if the copy of NBC is intended for Real D? I had an issue with mine. It was somewhat noticeable with the pumpkin policy. The screen is a Harkness 240, same as we have used in the past for Meet The Robinsons, and I did not have this problem before.

I wonder if it could have anything to do with the fact that in this auditorium the projector is slightly angled because it is off-center. I could not shift the lense far enough to get the image centered without vignetting, so I had to angle the projector. Could the ghosting at all be the result of the fact that the projector is not exactly perpendicular to the screen? (Wondering if that affects the polarization at all.)

Posted by David Zylstra (Member # 4230) on 10-19-2007, 08:15 PM:

If it worked for MTR then it should work for NBC . . . . . . the only thing I found that would show which system the DCP is for is "GB" on the hard drive label (I assume "GB" = "Ghost Busted"), but the wrong label could have been put on the wrong hard drive. Our original RealD for Monster House was set up with the digital projector off center due to the 35mm still being in place and we did not have any trouble like this so I don't think the angle is it.

I think the only way to prove if it is content related is to play test content that is known to be truly for RealD (if you had any trailers left over from MTR that would work - but I'm sure it has all been deleted by now).

Posted by Larry Zuverink (Member # 1483) on 10-20-2007, 09:17 AM:

Hey Dave,
Good to hear from you. So If I understand you corectly I should be able to bring content from a theatre that is not ghosting, that should tell me if it a ghost busting problem.

Posted by Chris Slycord (Member # 4239) on 10-20-2007, 09:36 AM:

If the problem is the content itself and not the projector/screen, then yeah it would stand to reason that putting in known good content would display fine.

And if it still doesn't work, you know it wasn't the contents that were messed up.

Posted by Scott McGuire (Member # 4508) on 10-20-2007, 11:26 AM:

Or you could take what could be that possible bad content and run it in a projector that is not ghosting. same thing either way.

Posted by Darryl Spicer (Member # 711) on 10-20-2007, 12:49 PM:

When it comes to the content I would think it is from the same hard drive for all screens. In the digital world you would not need more than one hard drive. Just load the content to each server or a central server with the one drive.

Try restarting the Real-D unit and run the test pattern provided for the Nightmare Before Christmas program. Check to make sure you see the left eye word with your right eye closed and vice verse. If you do not see this correctly flip the phasing switch on the back of the Real-D unit. I don't know if that will fix the ghosting problem but it's worth a shot.

Posted by David Zylstra (Member # 4230) on 10-20-2007, 02:47 PM:

Darryl - each 3D system/server combination requires special encoding - i.e. for MTR I heard there were 7 different DCP masters created due to quirks of each server manufacturer and 3D system (i.e. a copy that worked on a DoReMi/RealD would not work properly on a DoReMi/Dolby3D or Dolby/Dolby3D, etc).

Larry - Yes I would verify that the content between locations work - in the interest of time (and if the trailers show the same ghosting) you can just try the trailers from the HD instead of the entire feature.

Posted by Mark Gulbrandsen (Member # 72) on 10-20-2007, 03:31 PM:

Is the ghosting problem an artifact generated by the single projector systems... real-D or Dolby 3-D?

BTW David: Dolby has not licensed any other server manuafacturers as of yet to include their 3-D system but they anticipate doing so right after the first of the year.

I have a two projector 3-D install comming up soon so it'll be very interesting to see if any ghosting problems exist. I've seen other two projector 3-D systems and there was no obvious ghosting issue.

Mark

Posted by Larry Zuverink (Member # 1483) on 10-20-2007, 04:24 PM:

Sorry,
It's a Christie CP2000 Projector, Doremi Server, and a Real d Z Screen system. The Christie tech says everything is set up correctly and they are blaming the Hurley screen. RealD does not recommend Hurley. Hurley however has not heard of any 3D problems with their screens. The ghosting as I called it is most noticeable on the Nightmare 3D preview when the pumpkin head comes out of the screen. It looks like a larger soft image of the pumpkin on both sides. It is eye specific. If you close your left eye only the right image and the right larger soft image (off the right side) is visible. I also removed the porthole window to make sure that it wasn't a weird reflection between the Z Screen and the port hole.

Posted by David Zylstra (Member # 4230) on 10-20-2007, 05:12 PM:

quote: Mark Gulbrandsen
BTW David: Dolby has not licensed any other server manuafacturers as of yet to include their 3-D system but they anticipate doing so right after the first of the year.

At ShowEast DoReMi told me that their server worked with Dolby, but I didn't pursue any further specifics on "right now" or "coming soon". . . . .

The way I understand the ghosting is that it is bleed through of the polarizers - i.e. the right eye lens cannot completely block the left eye information and vice-versa so they do something to each eye's image that cancels out the "ghost" . . . . . I'm not sure which systems are subject to this effect, but if a 2 projector install uses the same type of polarizer it might be.

Just a thought - I wonder if the cause could be bad glasses? taking a pair from a good location would easily prove that.

Posted by Tristan Lane (Member # 1169) on 10-20-2007, 08:11 PM:

quote: David Zylstra
DoReMi told me that their server worked with Dolby

Doubtful, since the color correction required by the Dolby 3D system is done within the player, not in the projector. In fact, If I understand the system correctly, you could utilize the factory color settings and still achieve proper color by correcting it with the Dolby player. Doremi may be working on adding the color correction functionality to their software but that is just speculation. The question I have is: Will the current Doremi hardware support the additional resource demands of color correcting? The reason for doing it within the player is because each eye requires a separate MCGD.

In regards to ghosting:
There's a number of reasons the ghosting could be happening.

- Think of it like a shutter timing issue, where if the active polarizer isn't timed correctly with the frames being displayed, causing a partial bleed to the other eye.
- Faulty polarizer or glasses, that aren't "filtering" each eye fully.
- The screen surface may not be maintaining the polarization properly.
- The controller for the z-screen isn't set up correctly
- Or, you may be noticing what another forum member has described as a latency issue caused by alternating left/right frames from the single projector.

Question
Does the ghosting appear similar to travel ghost? (i.e.: it is only appearing on one side of a specific object or area?") Or is it appearing on either side of the image?

Posted by Mark Gulbrandsen (Member # 72) on 10-20-2007, 11:21 PM:

Paul Pearson told me at Shoeast that Dolby will begin licensing their 3-D stuff to other server manufacturers. Dolby has evidently realized that they alone with just a pittance of servers out there can't make a return on installing it on just their own processors.

Mark

Posted by Ken Lackner (Member # 1002) on 10-21-2007, 08:19 AM:

Hi Tristan. Good to hear from you. Hope things are well.

In my case, the ghosting was on both sides. It was particularly noticeable with the pumpkin. Also noticeable during the Disney 3D test frame. When I would close my right eye, I could clearly see the word LEFT, which tells me the phasing was okay, but I could also see a very faint image of the word RIGHT. And vice versa. I am going to go back and check my MTR locations, but I don't recall this happening there.

Good idea to check with different pairs of glasses. If that doesn't turn out to be the problem, how can you determine if the problem is with the Z-Screen or Real D controller box?

Posted by Mark J. Marshall (Member # 1409) on 10-22-2007, 11:57 AM:

Interesting thread. This doesn't sound like he's describing the alternating eyes / latency problem that I've noticed on every single projector digital 3D setup I've seen since he's only seeing it in one theater out of five. That problem is most noticeable during scenes with a lot of motion, and very difficult to see during scenes with little to no motion.

Larry, you said you have a CP2000, Doremi, and Real D system. Are the other four identical to this one in every way? Also have you noticed any problems with any other 3D movies in that house before?

Posted by Larry Zuverink (Member # 1483) on 10-22-2007, 02:55 PM:

Yes, They are all the same. These are all new installs. However we have been going back and checking the other screens and they all show the problem but to a much less degree. We are going to check out a Harkness screen with the same system that has been installed for a while.
Ken, This theatre we are noticing the problem with is also off center. I noticed you said you have a Karkness screen. Does Harkness make a specific screen for real D or are all their screens real D approved.

Posted by Josh Kirkhart (Member # 1046) on 10-22-2007, 04:55 PM:

Swap the Z-screen and real d box from another install seperatly.
Obviously disconnect power to anything when servicing equipment and never do anything you are uncomfortable or unsure about.

Have seen this issue on other occasions, it either has to do with the settings in the reald box or the z-screen. The setting used in your setup are basic default settings in the unit. Your Christie tech can access those settings and verify.

If the swap works, make note of the affected equipment with serial of bad unit and get tech to request replacement. Real d will have one out real quick.

Dont hesitate to cycle power on the reald box.

Posted by David Zylstra (Member # 4230) on 10-22-2007, 07:17 PM:

quote: Larry Zuverink
I noticed you said you have a Karkness screen. Does Harkness make a specific screen for real D or are all their screens real D approved.

When we put our 2 RealD screens in the only "recommended" silver screens were from MDI or Harkness - we had to make sure we specified it was for RealD on the order . . . . . . we used Harkness for 2 reasons - some MDI screens for Chicken Little were visibly mottled and our other existing screens are Harkness (we could have gotten an MDI screen quicker) . . . . . Thinking back I seem to recall a conversation I had with RealD about the MDI screen being slightly better (it's been pretty long), but I can't remember what the differences were.

Posted by Ken Lackner (Member # 1002) on 10-22-2007, 07:42 PM:

Larry, Harkness only has one Silver Screen...the Spectral 240. Real D, as I'm sure you know, does require a silver screen, and they do recommend this one. (I spoke with them today.)

The rep that I spoke with said that the ghosting is most likely specific to the content. I went back to one of my MTR locations today. I did notice the ghosting during the Disney 3D Test Frame, the Pumkin, and certain scenes of NBC. But I played the 2-minute MTR test clip that was still on the server, and there were no problems with that. Nor were there any issues with the Journey 3D rating tag or trailer. She said that the ghosting is most noticealbe with light content on a dark backround, and my tests would seem to agree.

Posted by Larry Zuverink (Member # 1483) on 10-24-2007, 12:04 PM:

Confirmed ghosting to some degree on the Harkenss screen as well. The one that was really bad was improved by moving the projector to the center window but is still not what I would call acceptable. I'm still trying to figure out if ghosting is inherent to Doremi players.

Posted by David Zylstra (Member # 4230) on 10-24-2007, 03:04 PM:

From Ken's comments, your observations and what I know about the different 3D systems I'd say it is a combination of content, projection angle and the inherent bleed through of the polarizers . . . . . . I don't think it's the DoReMi, but you never know . . . . .

Larry - you are welcome to come my way and look Novi's copy of NBC to see how it compares to yours (I can't see any ghosting on it, but I've only watched the first few minutes trying to see if it shows the ghosting)

Does the ghosting change depending on viewing angle? (just a thought)

Posted by Ken Lackner (Member # 1002) on 10-24-2007, 07:47 PM:

I've noticed the same amount of ghosting on a Dolby and a Doremi, so it's not the player.

Both sites have the projector off-center by about six feet. One has the projector angled (because lens shift alone was not enough to center the image), one does not. They both have roughly the same ghosting.

I've settled on the content as the cause and although it is noticeable to me, it is not too objectionable.

Posted by Larry Zuverink (Member # 1483) on 10-29-2007, 12:43 PM:

quote: David Zylstra
I'd say it is a combination of content, projection angle and the inherent bleed through of the polarizers

So what is a acceptable level of bleed through of the polarizers? Is there a SMPTE standard and how is it measured?

Posted by David Zylstra (Member # 4230) on 10-29-2007, 01:14 PM:

Therein lies the issue . . . . . . no standards yet . . . . . DCI added 3D to the spec earlier this year to work towards a single inventory file (which puts the "ghost busting" responsibility on the hardware instead of source file) . . . . . nothing in the addendum addressed bleed through so I don't know if there will ever be a standard . . . .

Hopefully the filmmakers will figure out how to minimize the bleedthrough during production (i.e. if the issue is with light content on a dark background then try to reduce scenes with objects significantly brighter than the background).

I wonder if the Dolby 3D system shows any ghosting(not a Dolby server with RealD, but a Dolby server with a Dolby 3D system)

Posted by Kacie MacLagan (Member # 3637) on 11-09-2007, 06:04 AM:

I can say I know that there are new settings that have come out for the real D setups in the past week or so. When the settings were added to a screen that was ghosting it reduced it quite a bit. The disney test screen where the right and left were visible (slightly) when you close the opposite eye was now no longer visible.

I think that the pumpkin trailer is a huge problem. I saw a movie on a site that they said never has a problem with ghosting with it, and that trailer was the same on sites that reported ghosting.

Posted by Mark Gulbrandsen (Member # 72) on 11-09-2007, 08:08 AM:

In learning how to read whats in a Code Key yesterday I saw that there are non-ghosting versions of some of the 3-D titles. So the ghosting issue looks to be controled more through the software the content resides on. Any one else noticed this in their code keys?

The keys are pretty interesting and contain alot of information. Knowing how to read whats in the keys can speed up(cutting it down to minutes literally) getting a correct key when you get one that doesn't work. Server hash, play dates, title, language, sound format, etc. are all in there and easy to see via any web browser.

Mark

Posted by Ken Lackner (Member # 1002) on 11-10-2007, 08:14 AM:

Mark, are you referring to the KDM? Care to share what you learned?

Posted by Mark Gulbrandsen (Member # 72) on 11-10-2007, 09:44 AM:

Briefly,

You can open any KDM's contents with a standard web browser and look at whats inside. SOme of it will be obvious such as title, sound format, language, 3-D or 2-D, etc. On the server hash line you need the certificate generated by it's manufacturer when it's built to be able to double check against that. So keeping the Server hash on a computer so those reading keys can have easy access to it is a good idea. KNowing all this can easily prevent you from loosing any shows if you check the week's KDM(s) before hand.

FOr instance, a local theater got a digital print and a good KDM for it for the forst week. The second week's kdm was incirrect and the film wouldn't play (Audio does btw!). SO comparing this weeks KDM info with lasts weeks can tell you where the problem lies. IN this case say the server hash was wrong. You can call the KDM guy(or gal) at that distributer and tell them whats wrong with the new KDM. Some people at distribution will be surprised and some won't and you'll get a good KDM alot faster than if you hadn't looked into the problem.

Eventually everyone running digital booths should know how to look at whats in theor KDM's. KDM's can also be issued for multiple screens or even all screens in a given complex with each server's hash on a different key. all e-mailed at the samne time. We move film prints today... we will need an entire set of keys to move digital prints.

Mark

Posted by Ken Lackner (Member # 1002) on 11-11-2007, 07:15 AM:

I really need to learn more about XML. I have a program at home that uses XML files to map the keys to the RF remote on my PC. Here's another good excuse to learn more about it. But I digress. I opnened up a KDM and didn't see anything recognizable. What is the server hash? The KDM I opened was for NBC on a Dolby server. How can I tell that the content is 3D? There are many references to X509. What is that?

Sooo many more questions, but we'll start with those.

Posted by Mark Gulbrandsen (Member # 72) on 11-11-2007, 09:19 AM:

You don't need to understand XML to be able to open it up as you obviously have, its all in there in plain english.

There is a line that has START DATES/TIME and the END DATE/TIME in it, it should be VERY obvious. The time in the KDM by the way is Grenwich Mean Time so
HERE to convert that over to standard/daylight savings time.

The server's serial number is presented in HEX format... so you will need to be able to convert that over to Decimal. That can be done HERE, be sure to select the hex to decimal in the drop down box first! After converting you can then check if the server serial number on the KDM matches your server's serial number or not.

There is another line in there somewhere just a bit down from the Time/Date line that contains the film title. It may be abbreviated so look closely... The title is the first thing in the line and beyond that you'll find language version, sound format(4.1, or 5.1, etc), 3D or not, and other pertinant data that all relates to the version of the film on the hard drive you receive.

The server hash is not really identified... you need to know your server's hash to be able to recognize it.... its a string of letters/numbers not long and not short.

When I get back to work tommrrow I'll save one to WORD and post at least the pertinent lines of info or you can IM me through here for my e-mail address and e-mail me yours and I can highlight the stuff and then e-mail it back to you or I can post it here if you give me the ok.

Mark

Posted by Ken Lackner (Member # 1002) on 11-11-2007, 11:12 PM:

Mark, I didn't mean where is the server hash in the KDM file. I mean what is the server hash? I've never heard that term before.

Posted by Mark Gulbrandsen (Member # 72) on 11-12-2007, 08:15 AM:

Oh... The server hash is something thats generated at the time the certificcate for the server is generated by its manufacturer. You have to get the certificate for a particuluar server from them.... the hash is contained within the certificate.

Mark