The Ultimate 3D projection system: A Practical Discussion Thread - Page 24

Thank you CINERAMAX. Very interesting to hear pro advices and comments. We little DIY people are often in our own small world and have to experiment with no help from outside. I am very impressed by you setups. Debate level has been raised one step up, here.

You may be right about RealD but I still want to explore more about not having a silver screen, if you dont mind.

If I get it right, Dolby/Infitec and Panavision are two technologies that do not require the use of a silver screen.

Panavision seems very promising as it does not ask for color correction.

I am a little doubtful for (reasonable) home theater applications though.
- Most of us use UHP lamps with inadequate spectrums: low on red and high spike on green. I think color correction would still be necessary, unless we use xenon lamps.
- 10 bands instead of 6 means 9 gaps instead of 5, meaning more light loss (gaps width must be maintained to prevent crosstalk).

As we are short of light most of the time in 3D, I wouldn't recommend Panavision but stay with Dolby instead. I may be wrong here.

Loose color correction in the projectors can be easily implemented. For those who are not convinced that slightly different colors is not an issue:
http://celluloidjunkie.com/2010/06/1...ers-3d-market/
"Dichroic passive glasses allow the viewer to view distinct images in each eye. Though the image reaching each eye is actually different, the viewer's brain puts the images together providing the sensation of seeing a full color spectrum"

I would be much more interested in Dolby's cat 832 plastic glasses if it is a huge improvement on reflections. I just don't know where to get them (or a least a couple of them to experiment).

Jack

That is right with the Panavision, did not even think of uhp, you may be right.

I am very interested too in your research, keep up the good work.

I can pick Dolby glasses up next week in LA. PM me the second week of June, I'll have 2 of each.

Cheers, and thanks!

Great ! Have a good trip.
Jack

Very interesting to hear about some of the more pro setups and what may be around the corner for consumer setups. Thanks for sharing info Cinermax

I presume the real3d setups you have been working with are still circ polarised based? The biggest draw back with these in the consumer space has been that the screens have proved to be the weakest link; prone to hotspotting and graininess (as well as being the biggest source of ghosting). Have the setups you work with managed to solve some of these issues?

I note you mentioned spherical screens which would help remove the hotspotting. Is this the method you use to reduce it or are their more advanced materials out there? Although I'm in the process of setting up this type of screen, more for the greater sense of immersion (120 or 180'degree) than for reducing hotspotting, generally this type of screen is just too hard to setup for most home use. So for polarised to work better in the home for most people, it probably needs to solve these issues while using a flat screen.

Thats one of the benefits of the infitec/Dolby method which can use any screen type which makes it easier for consumers where generally ease of setup and cost are the two key factors.

The Severtson drop down screen has grain, but it is highly even so with the glasses on, at a little distance, it is quite enjoyable; the hot spot is there, but it is preferable to seeing the reflection of ones own eyes all the time that just drives me nuts.

The TORUS screen is purchased through Stewart and it would be skinned with their 3 gain silver. I have been doing these for years, not too many but when I do It always amazes me what a great screen it is. This screen and a Polarizer friendly rear projection screen like Nippuras is the high-end video route for me.







11.5 by 22 3D passive rear screen

270" diagonal 3D passive screen, tested with Sony Ciinealta 4K and RealD dual lens system for the NHK. Polarizer friendly!



I aspire to having this one day.

The Stewart torus screen you mentioned looks very nice. Not enough wrap around for me but it looks superb for films. (I still have to look into if I get a screen commissioned or if it's possible to order one- just early days for me researching this).

The 270 incher is incredible and definitely something to aspire to. Don't think I'll have the space for such a beast though!

Interesting what you mentioned on panavision. I wasn't familiar with it but that looks like a great solution as it doesn't need the colour correction. (although I don't know enough to judge if jack-baeur's comments on UHP lamps do make that redundant but can see how this could cause an issue). Interesting how this could be more light efficient on xenon's though than the Dolby approach. The Sony vpl vw100 are xenon based and not too overpriced they could be worth testing out with this approach. (not sure I'm brave enough to take a punt to test it out though in case it doesnt work well)

How about these torusses for wrap around, they call them partial domes. That is where the 3-D silver technology got developed for at Stewart.

For the right coin they will ray trace you a custum radius based on your eye points for zero hotspot in one or more locations.

For the above one I did there were six pair of eye points. For your one sitter sim, just one pair.







there are other solid screen companies that do this, one australian. One perforated metal.

Thanks that's more the sort of shape I'm going to build. I'm sure getting a pro based solution will cost an arm and a leg and probably a bit overkill in terms of quality for what I need. So will initially attempt the design of it myself and see how I get on.

Hello again,

sorry I haven't got any pictures of the SPAR filters yet, i'm moving to a new home, I'm busy unmounting and carefully rolling the silverscreen for transport. These screens are very fragile you can't roll them too tight of wrinkles will cause permanent damage.
I expect the screen to be up and running in about a week (maybe a little more).
I'll do the pictures once everything is installed at the new home.

For those who want to try Dolby but are not sure whether their projectors have enough setting range to do the correction.

I have build biased test patterns with primaries and secondaries. No need for glasses and/or filters. This is simulation (for UHP lamps).

Once corrected by your projectors, they should both look the same left and right. They look exactly the same when I use my AVS script (in which I am most confident).

Jack

Awesome contribution, thanks! I'm not sure if I'm even ever going to try passive/dual projector Dolby, but you making this available makes me want to experiment with it at some point. Excellent work!
-PS: Jack, did Chloe O'Brian help you out with these patterns and upload them to your mobile from CTU? ;-)

Are you awesome or what? my glasses are already on the way. but before they arrive I can do adjustments and this is perfect for me as my projector hasn't got cms or other fancy settings!

I finally found a second used projector to match my existing panny LCD to do passive. I just wonder if would be handier to just buy two cheap 1080p dlp projectors and dedicate them to 3D.
How do you dual projetor guys handle 2D?

Chloe has always been the thinking head


http://www.avsforum.com/avs-vb/showt...9#post20500659
See last section.

About my patterns:
Filters are supposed to have 40% average transmission (*). But they can go up to 90% for some colors.
The correction takes the 60% loss into account.
Here is how it looks after my AVS script:


Of course, correction by the projectors is not so good but more than decent.

(*) 40% transmission is about the same as polarizers.

Jack

Thanks j-b very useful and will be an ideal test when I have filters. I ordered a some Dolby glasses earlier today but not sure where I can get hold of the ones with glass lenses. Any ideas?

Out of interest could you post a picture using just your projector correction to see how that compares to the script?

Thanks

Edit: just saw that you mentioned I can test these out on projectors first, without filters. Will give that a go on a couple of different models I have to hand to see if any of those will work.

Yunti pm sent for the glasses. I dont know if I can give the link here?

Wasn't sure if you had a low spec CPU and that was why you couldn't do both but it looks like it takes more processing than I realised.

Trying to use the graphics cards for the colour processing would probably mean doing this via DXVA. Presumably most graphics cards would be quick enough to do it via this method but this isn't an area I know that much about so can't really suggest how you would get started.

That's exactly what I was doing.... Here you are:





I took a photo in both cases, just to make things comparable.

EDIT: I added the black and white check to make sure colors are the same brigthness. (Just noticed that I can improve matching by decreasing all right values about 10%, or increase left if I have enough margins... To be confirmed with real filters on. Remember this is simulation here.).

With the projectors, green is the color which is most impaired. Please note that theses patterns show pure primaries and secondaries. In normal viewing, a very few scenes are detected by my eyes (very picky ones) as not matching. And only when I close one eye then the other. (Nobody in my typical audience never complained about it). At least they are of the same brigthness. This is the best tradeoff I found.(If I use the same color space for both eyes, Green becomes OK but Red and Blue do not match. And.... they are not of the same brightness at all). Green is responsible for 60% luminance, red for 30% and blue for 10%. So keeping greens the same brightness is easier. But help yourself with the settings....

Also remember that this is simulation. My feeling is that real correction with filters is a little better, but not much.


Great! Let's share experiments here.


That's the reason why I chose to do the projector correction instead of the AVS script. Not perfect, but fair enough. At least I can do FI with no visual color flaws.

EDIT 2: Using CMS, I am now able to desaturate right green, which is much better:


Jack

I know what ghosting is but what causes it? Basically is it the silverscreen being poor quality or more a projector issue?

I am trying to decide between eventually trying the Dolby 3D vs the RealD set up. Do I have this right: if I do Dolby 3D then inorder to get the correct/same color in both the left and right eyes I need to use the settings in each projector to adjust the setting to match the visual picture but the settings will be different within each projector?

Ghosting is the visible result of crosstalk. Crosstalk is generated by the hardware you are using. All along the decoding chain, from bluray player to your eyes, crosstalk will pop up at the precise moment when you want to put two images on the same screen.

As long as both images are processed separately, there is no crosstalk. (I have heard people say there is ghosting in some blurays. This is nonsense)

On sequential projectors, crosstalk starts in the projector. Not enough blank delay between R and L images generates crosstalk. Slow panels also gererate crosstalk. That's why mono DLPs are good at 3D. You also add crosstalk with the active glasses. They do not block light completely when they are off and also have a duty cycle that needs blank time delay. All these constraints lead to poor light transmission.

When you are running dual projectors, images are separate until they reach the screen. There is no crosstalk within the projectors. The weakest part is the silver screen. Polarizing filters (either the ones from the projectors or the ones from the glasses) have a very good extinction ratio (300-1000). The silver screen is only 80-150.

The worst ever filtering is with circular filters rather than linears. Thats the reason why IMAX keeps using linears. But linears have a drawback: you cannot tilt your head without getting ghosting.

Circular filters are still used by RealD with succes, but they use ghostbusting pre-process. It eliminates ghosting by sending a negative image to the other eye. So there is still crosstalk, but no ghosting any more. But this has two disadvantages:
1. Ghosting cannot be killed in black areas, where it is most needed (you cannot send blacker than black)
2. As each eye has to see both images at the same time to do the subtraction, projectors have to be be lined up at the pixel. Or you use a single projector and Z-filter.

It is also likely that circular polarization requires color correction. These polarizers are built using a linear filter on top of a wave retarder. Wave retarders properties depend on the wavelength of light. Different colors means different wavelengths. All colors are not processed the same.

That's why the Dolby solution is so wanted: You eliminate the need for a silver screen and you can have loose projector alignment. Also, extinction ratio is much better.


You're right. You need different settings (or you use the coming pterodactyl's box...)

Jack

I just ordered a snakebyte HDMI 3d cable with the darbeevission 3d chip. 29.99 for 2m cable. can't wait to see the 3d!

From what I've read in this thread (and the specs on the 3D XL), it sounds like the 3D XL doesn't support frame sequential encoding. Is this correct?

Is it possible for a configuration with 2 3D XL units to deliver full frame 1080p resolution to each eye? If so, what encodings would support that?

Frame Packing 3D format, as used for Blu-ray 3D, provides full 1080p resolution for each the right and left video streams. See the Basic 3D Video FAQs thread for more info on the mandatory 3D formats required by the HDMI 1.4a specification. Frame sequential encoding is a computer-based 3D format and not a mandatory video format for 3DTVs based on the HDMI 1.4a specification.

Thank you, that's a relief.

Several people have lamented the lack of frame sequential encoding support. What are people missing out on without it? I would imagine that PC's in particular could be updated and configured to output in one of the mandatory formats.

Only nVidia supports 3D Frame packed. ATI cards do not, so that is the problem. Of course, if you have dual projectors and a PC you would be silly (imo) not to run 1080P 60 to each projector (bypassing the 3D-XL's). The point of the 3D-XL's is to take frame packed from blu-ray players/ps3.

Remote Control question:
It seems best to use two of the same PJ so that colour/brightness is as close as possible... but then how do you use a remote (universal or otherwise?) to control one PJ and not the other? Are there PJ models that have remote "channels" to avoid miscontrolling the other PJ?

For my projectors, in order to control only one of them, I press the menu button physically on the one projector I want to use, then control with the remote. As long as you don't press the menu button, the arrow, ok and escape keys have no effect on the other projector.

Do you use both or a third PJ for 2D viewing? It seems just getting one of them turned on for 2D would be the hardest part.

Same as BlackShark. Once a menu pops up, all subsequent commands only affect this menu.

But I dont activate the menu with the buttons on the projector. Instead, I put a piece of scotch tape protuding out on the side of the IR receivers. One on the right and one on the left. So I aim the remote either at the right wall or the left wall.

When I want both, I aim the remote at the screen.

Jack