High ambient light level, bright projector, and gray screen. - AVS Forum
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post #1 of 24 Old 05-29-2000, 03:02 PM - Thread Starter
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To all:

I would like to put an LCD projector in a room with potentially high ambient light levels (lots of glass) and would like the best possible image without huge effort.

Since the black level will be determined by the light level, it has occurred to me that a dark/gray screen with high gain and a very bright projector might do the trick. I am considering a Mitsubishi x300 (2000 ansi lumens).

I am soliciting recommendations for the screen and comments from anyone who may have had experience with a similar scenario.

Ken Elliott

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post #2 of 24 Old 05-30-2000, 08:58 PM - Thread Starter
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Was this a dumb idea?

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post #3 of 24 Old 05-31-2000, 10:50 PM - Thread Starter
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To PANARAMAX
What is the theory behind polka dots? Or are you kidding?

Terry,
More in line with my thinking. It is well known that the eye and brain are non-linear. Your eye has an AGC and your iris in your eye sets an f-stop. Blacks hence become blacker in bright light because less light hits the retina.
The correct level of grey can be determined empirically. A raised polka dot (I publicly declare IP and patent rights if no-one has ever thought of this.) could block ambient without impacting reflected light. Another way of doing it would be a perforated black screen with white shadowed background.
Any thoughts???

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post #4 of 24 Old 05-31-2000, 10:53 PM - Thread Starter
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How about black nylon stocking material over a high reflectivity white background?

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post #5 of 24 Old 06-01-2000, 12:02 AM - Thread Starter
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Terry,
Sounds more appealing to me than special paint. I am surpised to get such a quick response from Australia. A case of night owls and early birds?

With the brightness of current projectors it can probably be thinner than that. It should be an easy experiment. Unfortunately, I am still choosing a projector.

KE

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post #6 of 24 Old 06-01-2000, 12:04 AM - Thread Starter
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Terry,
Sounds more appealing to me than special paint. I am surpised to get such a quick response from Australia. A case of night owls and early birds?

With the brightness of current projectors it can probably be thinner than that. It should be an easy experiment. Unfortunately, I am still choosing a projector.

KE

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post #7 of 24 Old 06-03-2000, 11:30 AM
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You can get some opaque black plastic (about 15 mil I think) and hang it over you windows.

What I did was buy a grommet kit and put a grommet in the top two corners of the plastic. I put loops of string in the grommets (Iused different color string for each size of window). I then put mollies or nails about six inches above and about 6 inches beyond each window in a horizontal direction. It just takes a few minutes to hang these and they do a very good job of making the room dark.

You should make sure the nails, hooks, or mollies are several inches further apart than the grommets. This will cause the weight of the plastic to put tension on it.

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post #8 of 24 Old 06-03-2000, 07:01 PM - Thread Starter
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In a pinch, I can darken. Much of the time, it will be relatively dark and obviously bright sunlight ambients will wash out everything but a 2 Mega-lumen projector.
However, I can afford a 2000 lumen LCD with resonable contrast. The question is the effective contrast ratio.
One can quite easily calculate the lux associated with the black and white levels for a known geometry. If the black level is 1 lux and the screen has a gain of 1.0, the room will have to be very dark to get good video.
If the black level is 20 lux, a certain amount of ambient can be tolerated. To appear black however, a grayer screen may be required to attenuate the whites, blacks, and ambient. I suppose one could wear sunglasses.
A figure of merit could be (white level)/(black level + ambient)= effective contrast ratio.(EFR)
A nice goal would be an EFR of >200 at an ambient light level of 50 lux.
Unfortunately, a rough estimate indicates that this requires a very bright projector with high contrast at that brightness.
The gain and construction of the screen can have a major impact on this ratio. A dark screen has the psychological impact of being black against a lighter background.
A white screen on the other hand looks white with minimal ambient.
The home theatre community is accustomed to blacked out rooms and a completely dark room is great much of the time. There are certain social situations however when this just is not feasible. Scenarios where good blacks are obtained under modest ambient levels would be nice to have.

Ken Elliott

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post #9 of 24 Old 06-05-2000, 11:40 PM - Thread Starter
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Sometimes I wonder if any one reads the screen forum. Only a few posts per day. Funny since the screen has a major impact on appearance.

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post #10 of 24 Old 06-06-2000, 05:29 AM
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As for the polka dot idea, it's been done already. The basis if that idea, and the execution of it in the form of a stocking has been done for years and has been disposed of for better solutions. Don't any of you remember the monocrome commercial enviroment monitors of 10-15 years ago? Remember the monitors with the poly-like fine weave fabric over the screen to limit the angle of view? And thus limit the ambient light problems? You can still get one for free at the local recycle places or in the dumpster at a large institution or corporation......


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post #11 of 24 Old 06-06-2000, 07:59 AM - Thread Starter
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KBK

Thanks for the reply. Please help me.

What are the "better" screen solutions that you refer to? I am assuming a 1-5 lux ambient and a 2000 lumen projector. I will be at INFOCOMM next week and can check out commercial solutions.

kelliot

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post #12 of 24 Old 06-06-2000, 05:17 PM
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I would love to help you, but I am unable to comply. This would result in something akin to a commercial post, so I have to desist. I am in the process of developing multiple custom screen paints for various projector usages, but am not quite ready to hit the market. I am looking at this point at about 4-6 different types of paint (DIY). It would be in the form of a process of appliction of specifically manufactured custom paints and would take the better part of a week to construct, but cost about 4 to 10 times less than an equivalent screen depending on your choice. It very much has the potential to outclass most commercially availible screens. But hey, I might be foolin' myself.... Reading your posts helps give me a greater understanding of the problems that are involved with the use of a modern lcd (and dlp) projector. Heck, modern projectors make screen paint design easy. It's the CRT's that are difficult to design for.

[This message has been edited by KBK (edited June 06, 2000).]

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post #13 of 24 Old 06-06-2000, 09:22 PM - Thread Starter
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Well, thanks anyhow.

After scanning the HDTV forum, CRT forum, the DLP, LCD etc. forum, and the HTPC forum as well as this forum, I have come to the conclusion that the real adventurous types reside here.

I just hope we are not all one step from loosing touch with reality.
Unfortunately, I got an engineering background. I want calculate the lux, the contrast ratios, etc.

I also know that the technology is changing radically and in a few years the paradigm for front projection could change to a real consumer product from a cave-dwellers luxury item. To do so, the ambient light issue needs a realistic ambient solution.

Good luck in your quest for the perfect paint!

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post #14 of 24 Old 06-08-2000, 07:06 PM
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Do a web search on "projection screens" and one of the sites will have a holographic material that, if I remember correctly, they claim has excellent contrast in full room light.

I was looking for rear projection, so didn't delve further.

Keep us posted on what you find out

Noah

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post #15 of 24 Old 06-08-2000, 08:52 PM
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Loosing touch with reality? It took me ten years to get back close enough to it just to make contact with the people that are at least three deviations off of the norm....just remember, "Normal is for Average". Go big or Stay Home....

As for the screen paints, I will be designing one that will be specifically designed to be used in a high ambient light condition with a high output dlp or lcd. It will be a real pain in the posterior to apply though. But it WILL work. As for rear projection, I think I found an excellent set of materials for that sort of application, and will be postiong it in a diy format as well. I just have to get the paint thing going initally and I will be able to get more materials for experimentation.

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post #16 of 24 Old 06-09-2000, 10:59 AM - Thread Starter
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No luck on the holographic screen search, lots of R&D, haven't found a product.

KBK, we are all waiting for your paint demo.


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post #17 of 24 Old 06-09-2000, 04:54 PM
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post #18 of 24 Old 06-09-2000, 06:16 PM - Thread Starter
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Looks great, if one could do something about the price.

Makes KBKs paint look cheap.

Sherman Williams must have a color ...

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post #19 of 24 Old 06-09-2000, 10:52 PM
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Interesting thread. I once built a screen for my lcd projector. I found that by painting the screen a light grey the pixel structure completly disapered on an 11 foot wide image. Amazing. Another benifit was any video noise what so ever was completly gone. A very clean picture. The darker screen color also enhances color.
This would be a better solution for the lower resolution 800x600 dlp projectors than using the cynus depixel lens.
You guys got my wheels spining again.
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post #20 of 24 Old 06-10-2000, 05:16 AM
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Alan:

So, in conclusion, what you are saying is: Use a swatch of material or wood that is painted the backdrop color of your choice. Put that in front of your projector in the operational conditions that it will operate in. Begin placing mild or light greys on the screen till you get to the point where the grey matches the 'inter-pixel' coloration level, thus eliminating this effect and making it the 'black level'? Can't see why this wouldn't work.....

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post #21 of 24 Old 06-10-2000, 10:04 AM
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KBK
Yes. It will work.
You will not need to go to dark. A light gray will do just fine. When watching the movie you will be surprised that your image will look as if it is being projected on a white screen. You will not notice any gray what so ever.
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post #22 of 24 Old 06-17-2000, 12:59 AM - Thread Starter
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I just returned from Infocomm. I was surprised at the number of projectors demo-ed under high ambient light conditions. (My guess is up to 50 lux.) The black level suffered and was typically grey as expected.
The brighter projectors are obviously better with detail.
The screen gurus at Draper, Stewart, and Dalite seemed more focussed on mounting hardware than screen material.
Of course, its got me thinking again. No great inspirations so far. I guess I need holographic paint.
Any thoughts out there on other approaches from the past?


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post #23 of 24 Old 12-13-2000, 07:57 AM - Thread Starter
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Scott,

I see that you are reviving some of the posts from the past. I am happy to see some of my dumber ideas again. Also good (or bad) to see that the basics haven't changed much.

For the record, I finally got a NEC MT1040. The purchase was motivated as a temporary solution until the G3010z or better came out. I'm glad I didn't wait. The only thing that has happened since Infocomm was the LP350. I'd be tempted to try an LP350 except for the absence of aspect ratio control in 1080i mode.

It would be good to find out more about the holographic screens.

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Ken Elliott

[This message has been edited by kelliot (edited 12-13-2000).]

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post #24 of 24 Old 12-14-2000, 05:14 AM
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Well, finally, the paint is here. Time to get some to Alan. You make the grey you want.

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