Improved contrast with backlighting? - AVS Forum
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post #1 of 9 Old 01-06-2000, 12:42 PM - Thread Starter
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I saw Man in the Moon in the theater last week. They started the trailers before dimming the lights, which were ceiling spots shining directly onto the seating area. I was surprised at how good the black levels were (not great, but pretty good). I was surprised again when the lights dimmed out and the black level seemed unchanged, but the contrast seemed worse because now the whole theater was dark.

So it seems that perceived black levels could be improved by a light source behind the plane of the screen, which would cause some contraction of the eyes' pupils, providing the rest of the room surfaces are dark so that none of that light is reflected back to the screen. Kind of the optical inverse of a LEDE (live end - dead end) listening room.

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post #2 of 9 Old 01-06-2000, 08:07 PM - Thread Starter
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Thanks for the article, Mark.

I think with the advent of brighter digital projectors, the reccommendation for backlighting for direct views could be expanded.

And I have to say, I think gray surroundings is going off the deep end; where else in life do we insist that whatever object we're looking at be surrounded by gray for proper viewing?

Noah

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post #3 of 9 Old 01-07-2000, 03:48 PM - Thread Starter
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Peter,

Thanks for the nice compliment! Psychovisual Jedi Master! Wow! It's going onto my resume immediately.

Hopefully you're in a mood to wade through my post in "Screens" (maybe when you get back from CES, or whereever you were packing for.

I'm surprised perforated screens improve contrast so much. What's the % void area?

Noah

[This message has been edited by noah katz (edited January 07, 2000).]

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post #4 of 9 Old 01-08-2000, 06:21 AM
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I don't know what you mean by "void" area; however, you should expect about an 8% reduction in reflected light from a perf. screen. Now, on the other hand, your eye cannot perceive a difference in brightness of less than about 10%. (The difference between dimming a light to 90% bright versus 100% is not realized by you ... only the power company.)

The point about lights in the room (FPTV/RPTV) is a careful balancing act between picture quality and fatigue. Any light *you* can see in the room is also being "seen" by your screen. For example, if you can stand at the screen, with the lights dimmed to "movie" level, and you can tell the walls are red, you have red reflected light on your screen as well.

The degree to which that will affect picture quality is a variable from venue to venue. If any of you have had a FPTV/RPTV calibrated, it was done with zero light in the room.

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post #5 of 9 Old 01-08-2000, 11:15 PM - Thread Starter
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I disagree with the completely dark requirement. I have a 20 feet of rope light (small bulbs embedded in clear plastic) on a dimmer which surround the perimeter of my built-in entertainment center, which protrudes from the wall 6" (light is behind the screen plane). It reduces eyestrain and makes a nice halo effect reflecting off the back wall (a decidedly non-neutral creamy yellow).

Noah

Yes, by void area I meant the area of the holes.


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post #6 of 9 Old 01-09-2000, 03:49 PM
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Did someone interpret my post to mean, no lights on in the room? Not my intent. One must be careful as to how it is done.

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post #7 of 9 Old 01-09-2000, 07:55 PM - Thread Starter
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Thanks again, Peter.

The rope light is actually an interim setup until I redo my invisible, embedded-in-the-molding sidelighting fiber optics which was supposed to do the same thing, but I was sold sub-par stuff by a place that has since disappeared.

It was supposed to be stealth backlighting; no evidence of lights until turned on and the wood glows through the paint.

Peter, did you see my post in Screens (Alternative screen materials)?

Noah

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post #8 of 9 Old 01-10-2000, 06:23 AM
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Peter:
I cannot confirm your findings regarding a perforated screen having a better image. At least not in my setup. Accidently I got at first the Audio Vision fabric instead of the Da-Mat fabric for my screen. And as I have already found out with a screen sample some time ago, the image looked worse. I cannot really define what was wrong, but the image looked kind of strange. Not as good as with my tempory setup slide screen. It looked like a lot of detail had been lost. It was also some kind of soft. I always hunted for the sharpness control of my Pioneer 717 player, but there was a considerable tradeoff here. Either a soft image or some nasty artefacts. I was far from happy. A closer inspection showed that the DLP pixels had nearly the same distance as the holes in the screen. Sometimes a complete pixel row or column hit the holes. This may have caused the loss of detail. Annother point was that I could see the perforation slightly from my normal viewing distance. This may have caused additional distraction because I am very sensitive to regular pixel structures.
Now I have replaced the screen with the non-perforated one and everything looks much much better without any electronic sharpening.

This all said, I would recommend that everyone considering an acoustically transparent screen should test at least a
screen sample with the own projector and look from normal viewing distance. A AT screen may help to increase the perceived contrast as Peter described, but it may also cause other problems depending on the projector used.

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post #9 of 9 Old 01-12-2000, 09:29 PM
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Peter:
The Da-Lite Audio Vision Screen has a similar hole layout like in the negativelightmatrix file. But in contrast to your example the ratio between hole size and pixel size is approximately 1:9 with my setup with a XGA projector. You seem to have much larger larger pixels (1:25?). This comes from using only SVGA projector, projecting a larger image, or having smaller holes. In my setup I just loose to much information when a pixel hits a hole.

Emil

[This message has been edited by Emil Naepflein (edited January 13, 2000).]
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