# Need advice on Qlab, multiple projectors



## DavidAhumada (Jan 26, 2011)

I am completely new to projections, we are attempting to use them in our spring production. I have a 18X30 blue sharkstooth scrim draped upstage. We are planing on trying rear projection, to avoid actors crossing the projector path. 

We will have three separate projectors, which will be mounted above and behind the scrim. We have tested them, and know that they are bright enough to do what we want, but now my problem is figuring out how to control them.

We are planning on projecting moving and still images of the sky: day, night, sunrise, sunset, and a storm with lightning. 

I have access to both a macbook pro, and a new Imac, and we are planning on renting the Qlab license.

How do I link the three projectors, to control them? I'm playing with the demo version of Qlab, but since it isn't the video license I can't seem to figure out what I'd need to do.

Oh, and as always. On a "limited" budget.


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## shiben (Jan 26, 2011)

DavidAhumada said:


> I am completely new to projections, we are attempting to use them in our spring production. I have a 18X30 blue sharkstooth scrim draped upstage. We are planing on trying rear projection, to avoid actors crossing the projector path.
> 
> We will have three separate projectors, which will be mounted above and behind the scrim. We have tested them, and know that they are bright enough to do what we want, but now my problem is figuring out how to control them.
> 
> ...


 
If they all need to do their thing together, you will probably need a bigger computer, or at least one with three outputs. The biggest mac pro you can get, probably. Video and stuff takes a lot of horsepower with cuelab.


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## metti (Jan 26, 2011)

While it isn't ideal, I have run three projectors off of a single Macbook Pro using a Matrox TripleHead2Go. I have done likewise with a Mac Mini so I would expect that you could do this with your new iMac and maybe with your Macbook Pro depending on how it is equipped.


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## cpf (Jan 27, 2011)

Also, it's my understanding that the "trial" version of QLab is practically fully functional except that saved "pro" cues don't get loaded from a cuefile on an unlicensed copy of the software.
You're going to need a triplehead2go-type device for sure, since both the iMac and MBP only have 1 extra screen of video output. Only the Mac Pro has space to slot in extra video cards to legitimately expand your display capacity. It _might_ actually be cheaper to rent a single, high-end projector that could fill the entire screen (assuming your layout allows for the longer throw, etc) compared to the hardware you might end up buying.


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## SHARYNF (Jan 27, 2011)

if you go to 
Matrox Graphics - Products - Which GXM is right for your Mac - Graphics eXpansion Module
you can get an idea of what options and suggestions are available from Matrox

the issue is going to be if you need the three projectors to great a seamless image, with overlap and edge blending (difficult to do, need three identical projectors and the software to do it)

I am not a mac person so have not worked with qlab. I have worked with arkaos grand vj which has a mac version and a full function demo, and has edge blending etc

GrandVJ – Eight channels VJ software for real time HD video mixing

if you do NOT need one image split over the three projectors then it is a lot easier and is more about just getting all the cues right for the video

if you can come up with a design that takes into consideration that there are three independent images and allow for a hard edge then it also is easier

Sharyn


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## museav (Jan 27, 2011)

DavidAhumada said:


> I have a 18X30 blue sharkstooth scrim draped upstage. We are planing on trying rear projection, to avoid actors crossing the projector path.
> 
> We will have three separate projectors, which will be mounted above and behind the scrim. We have tested them, and know that they are bright enough to do what we want, but now my problem is figuring out how to control them.


How do you plan to use three projectors to create an 18'x30' image? Used in a typical landscape orientation, each projector would appear to relate to an 18'x24' (4:3) or 18'x32' (16:9) image, thus three projectors would have significant, if not complete, overlap. If the intent is to use the projectors in a portrait configuration then each projected image would be 18'x13.5' (4:3) or 18'x10.125' (16:9), which seems to fit the desired overall image size better. However, using the projectors in portrait mode as well as any overlap or edge blending would likely affect the potential options for image processing. So knowing the planned approach would help.

How did you test the brightness? Was it with the actual images and some approximation of the stage lighting planned? Generally, sharkstooth scrim is not great for rear projection, when stretched for a flat surface you end up the thicker material areas separated by larger voids. So more opaque areas separated by large transparent areas rather than a translucent surface. It may appear bright but that may be because your getting much of the light from the projector passing straight through and not from the projection surface.

You mentioned the projectors being above and behind the scrim. That means a lens that allows the projector to be above the image, which eliminates most very short throw lenses. The room needed behind the projection surface goes back to the actual image size involved but with the image sizes noted above you're probably looking at a minimum of 15'-20' of throw for portrait mode and maybe 22'-30' for landscape mode. Add to that the depth of the projector and any rear clearance required for cable connections or ventilation. Also consider that there could be nothing flown or standing in the projection path or that would cast shadows. This could also relate to the first question as if the projectors are used in portrait mode then they would likely have to be mounted at, or very close to, the vertical centerline of the projected image and thus could not be above the scrim.


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## shiben (Jan 27, 2011)

cpf said:


> Also, it's my understanding that the "trial" version of QLab is practically fully functional except that saved "pro" cues don't get loaded from a cuefile on an unlicensed copy of the software.
> You're going to need a triplehead2go-type device for sure, since both the iMac and MBP only have 1 extra screen of video output. Only the Mac Pro has space to slot in extra video cards to legitimately expand your display capacity. It _might_ actually be cheaper to rent a single, high-end projector that could fill the entire screen (assuming your layout allows for the longer throw, etc) compared to the hardware you might end up buying.


 
Actually, you need to rent the video component of qlab to use it for video (or buy it). its only a dollar a day, so a pretty good deal. Audio is for the most part fully functional.


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## cpf (Jan 27, 2011)

shiben said:


> Actually, you need to rent the video component of qlab to use it for video (or buy it). its only a dollar a day, so a pretty good deal. Audio is for the most part fully functional.


 
Oh, OK, I got the all-inclusive license almost immediately so I've never tried without. I can however verify that qlab has no image blending functionality; you'd have to do whatever you needed in a Quartz comp or to the source video itself.


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## dkolenda (Jan 27, 2011)

The Matrox TripleHead2Go is definitely the way to go when you're on a tight budget. Search for refurbished units and you could save some money, too.

As long as the brightness and lenses are the same between projectors, you should be able to do a very respectable full screen image without proper image blending. Just make sure the projectors are securely locked into place after aligning them!


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## museav (Jan 27, 2011)

dkolenda said:


> The Matrox TripleHead2Go is definitely the way to go when you're on a tight budget. Search for refurbished units and you could save some money, too.
> 
> As long as the brightness and lenses are the same between projectors, you should be able to do a very respectable full screen image without proper image blending. Just make sure the projectors are securely locked into place after aligning them!


If the goal was to create a 72'x18'/96'x18' or 30'x7.5'/30'x5.625' image using three 4:3/16:9 projectors then a TripleHead2Go might be a good solution. But if the goal is to have a 30'x18' image from three projectors then I don't think the TripleHead2Go is a viable solution. Creating a 30'x18' image using three projectors would seem to require image processing that can handle overlapping images and possibly portrait mode displays.

cpf suggested trying a single projector. A single 16:9 projector, or stacked projectors for more brightness and redundancy, could provide a 32'x18' image, which is very close to the apparently desired 30'x18' image size. The positive side is that this could make the video processing much easier. The negative side is that you would require more depth behind the screen, probably 25' to 30' or more, and you would need a fairly bright projector for that image size, especially if you want to create visually impactful lightning, sunrises and sunsets.


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## metti (Jan 28, 2011)

museav said:


> But if the goal is to have a 30'x18' image from three projectors then I don't think the TripleHead2Go is a viable solution. Creating a 30'x18' image using three projectors would seem to require image processing that can handle overlapping images and possibly portrait mode displays.


 
Wanting to have overlap wouldn't mean that the TH2G isn't a viable option. It is true that you need a piece of software that supports edge blending but QLab will do that via easily available and free Quartz Composer plugins. Ive done edge blending of multiple projectors via Isadora and a TH2G with great results.


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## SHARYNF (Jan 29, 2011)

metti said:


> Wanting to have overlap would mean that the TH2G isn't a viable option. It is true that you need a piece of software that supports edge blending but QLab will do that via easily available and free Quartz Composer plugins. Ive done edge blending of multiple projectors via Isadora and a TH2G with great results.


 
AFIK inorder to make edge blending you need to have overlap 

Back to the original question. If in your design you can design a set so that there is a seam (could be a tree or ??? to allows for a hard edge then you could look at having the three images with some masking possibly work.

the size of the image and the amount of ambient light and the brightness you need are all factors that Brad has raised which really are important to make sure you have looked at to make sure that a technical solution of capability will give you the performance level you want

Sharyn


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