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Discussion Starter · #1 ·
We've been looking at some big expensive LCD units for some projects at work, like this:

http://www.projectorcentral.com/proj...m?part_id=2052


and a similar (maybe almost the same unit from Eiki, the LC-X5), which have stated on:eek:ff CR of 1100:1.


Pure BS? They are monster light cannons. Is their ludicrously high brightness the secret? Curious how they would be better than my 20HD in this respect. Both are new this year.


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Well considering the lumens that these projectors put out, they ought to have even larger contrast ratios. The Sanyo with 10,000 lumens output only has a contrast ratio of 1100:1. If it's accurate, you're still talking about a black level of nearly 10 lumens, not a great black level in my book. The Epson with 1200:1 has a black level or over 4 lumens, still terrible as far as absolute black levels are concerned. Keep in mind that we are talking about contrast ratio, which means it can be improved by jacking the lumens way up (preferable for a large venue or one with poor light control), or by cutting the absolute black level, which is what we want to see happen in a controlled light environment with a limited screen size like a home theater.
 

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Sean,


From an engineering standpoint I don't see how jacking the lumens up helps them get to higher CRs. And a neutral density filter could always get your black level down to match a dimmer projector with the same CR, or beat a dimmer projector with a lower CR by having the same white level and lower black level. Also, I think people care about ft-lamberts more than lumens. The projectors can support some pretty huge screens - probably much larger than just about anybody here could put in their house. If a 10000 lumen, 1100:1 CR projector was put on a screen that was 5 times as big as a 2000 lumen, 800:1 CR projector, then the 10000 lumen projector would have a lower black level (in ft-lamberts).


I've never quite understood the reasoning that the CR is high enough, but the absolute black level is too high, when it is so easy to lower the brightness of everything. The problem comes in when the CR isn't high enough to allow a reasonable white level when you set the black level where you want. 1200:1 isn't enough, IMO, but it is better than 800:1 of other LCDs.


--Darin
 

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I'm not sure lumens have anything at all to do with contrast ratio.


CRT projectors have terrible lumen output, but can do >3000:1 contrast with ease.


Aren't we confusing too unrelated concepts? The 10,000 lumen output is the total light output of the projector. It is inaccurate to say: If 10,000 lumens, and 1000:1, then 10 lumens for black. That's not the way it works.


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Well, considering that we are talking about full on/off contrast ratio, the lumen output for black can be determined by dividing the full on/off contrast ratio by the lumen output (assuming both specifications are accurate, which may not be the case). Is this not the very definition of a ratio? If the lumen out put at black were 5 lumens and max lumen output were still 10,000, then the contrast ratio would be 2000:1.


CRT projectors can do well more than a paltry 3000:1 full on/off, but that is because their light output at black is nearly zero, not because they brute force tons of lumens at the screen. Again, this works both ways as far as increasing CR (again, full on/off).


Lumens have nothing to do with ANSI contrast ratio, true, but that hasn't been a problem for digital projectors for quite a while.


Darin, I am under the impression, perhaps mistakenly, that it is easier to increase the white level at a greater rate than the accompanying black level, but much harder to reduce the black level while holding the white level constant. Again, I may be mistaken in this perception.
 

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it is easier to get higher contrast out of a 4 x 3 panel then 16 x 9
 

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Discussion Starter · #8 ·
Quote:
Originally posted by tycoondog2
it is easier to get higher contrast out of a 4 x 3 panel then 16 x 9
Thanks! That's the info I was looking for.


Have to go take down the laundry now. The PJ is done drying it.


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"Well, considering that we are talking about full on/off contrast ratio, the lumen output for black can be determined by dividing the full on/off contrast ratio by the lumen output (assuming both specifications are accurate, which may not be the case). "



Well, you are tlaking about LUMENS, and others are talking about black levels. They are correlated, yes, but not necessarily indicative of actual performance.


As they said, the larger the screen, the less bright the image. 4 lumens spread across a 200-300" screen probably looks "more black" than 1 lumen on an 100" screen. (Because 2x diagonal = 4x surface area)
 

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My point is, that you need a lumen value to determine the black level, in ft. lamberts, on the screen. You have to keep your units of measure consistent. You can't talk about lumen output and contrast ratio and then refer to black level in ft. lamberts. No screen size was specified. If you said that this was going to be projected onto a 40' wide screen, then you'd be talking about brightness of 10 ft. lamberts and a black level of .01 ft. lamberts (assuming a 4x3 screen of 1.3 gain).


You're right, strictly speaking, of course. I'm really referring to the value of k, used in the past on this forum to describe the minimum light output of a projector as determined by dividing the light output by the CR. In the absence of a screen size, however, I equate the two terms, since you can't determine ft. lamberts without a screen size and gain. So, if it makes everyone happy, then the k of these two projectors is not terribly impressive.


Please remember, I still own a crt, so to me, a k of close to 1 lumen on projectors this bright would probably be more to my liking. That would get us .003 ft. lamberts on a 25' wide screen. Of course, it would only take a 4000:1 contrast ratio with a 5200 lumen output to get us there.
 

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The reason for the contrast ratio spec is so that users can take both lumens/ft-lamberts and black levels into account. Contrast ratio is the best indication of how good the blacks will look. Some people get turned off by the black levels in some of the light cannons, but how blacks appear to the human eye is relative to the brightness of what is around it.
 

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Quote:
Originally posted by Sean Max
Darin, I am under the impression, perhaps mistakenly, that it is easier to increase the white level at a greater rate than the accompanying black level, but much harder to reduce the black level while holding the white level constant. Again, I may be mistaken in this perception.
Sean,


I think this is somewhat true for business DLPs where they can "cheat" and use the white segment to get big CR numbers, even though you can't achieve those in their film modes. It might be true for LCDs, but I can't think of any reason. Once the optics are figured out turning the light from the lamp down to half should theoretically keep the CR the same and lower both black and white levels. Same with going with twice as bright a bulb. This of course assumes that the color balance doesn't change to the point of forcing you to recalibrate. Someone who knows more about LCDs than me might be able to point out a reason that they can get to higher CRs in these high output projectors (other than more expensive lenses).


The reason I found these CR numbers interesting is that I wonder if it means that the next batch of consumer LCDs will have these numbers. Will the PLV-80 be 1200:1 CR? More?


--Darin
 

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I always love these conversations about how ANSI contrast is more accurate than full on/full off. The argument goes something like this....."ANSI contrast better shows contrast performance in the real world where black and white will co-exist on the screen together". What hogwash. ANSI measurements are determined by IRE 100(pure white)squares placed next to IRE 0 (absolute black)squares (each black square is surrounded by white). I have NEVER seen a situation in a movie where this is going to happen. Usually movies are quite dark all around and rarely are bright scenes and dark scenes mixed where shadow detail is MEANT to be seen by the audience to begin with. It's a meaningless spec. ANSI contrast


A few people on here are correct when they say absolute black levels and gray scale reproduction is what it is all about. I believe someone on here said it's all about perceived contrast when talking about high lumen machines...HA...too funny. What perceived contrast are you talking about when you are watching the dark scenes from the Matrix? There isn't anything to contrast the black against, so the overall image looks gray at that point. I've seen video on high lumen LCD's 1000's of times and in each case, that is exactly what happens as soon as the image turns dark.
 

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Quote:
Originally posted by sphinx
I've seen video on high lumen LCD's 1000's of times and in each case, that is exactly what happens as soon as the image turns dark.
Part of my point is that the problem here is the CR, not the black level per se. The reason I say this is that if the CR were high enough you could slap a neutral density filter on there and get the black level where you wanted. With a low CR this would kill your whites, though.


I agree about the ANSI contrast once it gets above a certain level (maybe 150:1). If there is something bright on the screen then you will perceive stuff that is close to black as black. Once everything goes near black and your iris adjusts then it is a different story, though.


I think KBK is one of the rare people who keeps touting ANSI contrast as the ultimate, but he never seems to respond when people question this or give reasons that it isn't valid. We've seen the stuff about CRTs having lower ANSI contrast than digital projectors, but better on/off contrast and I've never seen KBK respond to how CRTs could be considered better at black level and shadow detail if ANSI contrast was more important than on/off.


--Darin
 

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That's because KBK is a spy sent here by an alien race to laugh at our meager understanding of physics and the properties of light. :) His entire goal is to confuse us to point that our brains lock up and an invasion will be a piece of cake. His only flaw is that he picked avsforum as a medium, thinking it would be the easiest way to infect Earthlings efficiently.
 
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