Contrast Ratio to Black Levels - AVS Forum
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post #1 of 14 Old 01-29-2013, 07:04 AM - Thread Starter
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I want to know what relationship does contrast play toward black levels. Just did some research on contrast ratios. Looked up the contrast ratios for the Epsons, Sonys, and JVCs. Some reviewers states that the Epsons and Sonys have the same or better blacks than jvc, but jvc have a better contrast. Need a little education from the knowledgeable
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post #2 of 14 Old 01-29-2013, 07:33 AM
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Originally Posted by blee0120 View Post

I want to know what relationship does contrast play toward black levels. Just did some research on contrast ratios. Looked up the contrast ratios for the Epsons, Sonys, and JVCs. Some reviewers states that the Epsons and Sonys have the same or better blacks than jvc, but jvc have a better contrast. Need a little education from the knowledgeable

Sony and Epson both use a dynamic iris (DI) wihin the lens assembly of their projectors. The DI can open and close to increase or decrease the amount of light coming from the lens. During scenes in the video which are mostly dark the DI will close down and make ther overall projected image darker. This lowers the black level, but also lowers the whites and all other shades by the same amount. Such projectors have two different black levels and contrast ratios (CRs). One is the "native" values that are measured when the DI is turned off (generally with the iris locked in the full open position). The other mode used for measurements, and the only one the manufactures will use for coming up with their spec. sheets and inflated advertising claims, is with the DI engaged at its most aggressive setting. They then project a full white screen and measure the white level (the DI will automatically fully open for this signal) then they project a full black screen to measure the black level (the DI will close down to its minimum for this type of signal). This latter test will produce big numbers for the contrast ratio (CR = ratio of white level to black level) and a low value for black level. However, many users will find this most extreme setting for the DI unacceptable due to the side effects it causes. When DI is engaged a more moderate setting will generally be more acceptable for most users. The best of the sub-$5K Sony and Epson projectors have native contrast ratios in the range of 5,000:1 while Sony's flagship 1080p projecfor, model VW95es, has native CR of 10,000:1 or a little higher. These Sony and Epson projectors can achieve a realistic dynamic CR of perhaps 50,000:1 maximum using DI turned on and set to a moderate level so as to not produce too many objectionable side effects. However, projectors using DI simply will not produce overall results (in terms of image quality) equivalent to an otherwise similar performing projector that achieves a similar measured CR value, but does this without use of a DI (i.e, having a high native CR).

The JVC projectors do not need to rely on DI (and don't have one) as they have very high native CR and low black levels.

Note that all of the above dicusssion concerns On/Off Contrast Ratios, which are the only type normally specified by the projector manufacturers.

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post #3 of 14 Old 01-29-2013, 07:44 AM
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Originally Posted by blee0120 View Post

I want to know what relationship does contrast play toward black levels. Just did some research on contrast ratios. Looked up the contrast ratios for the Epsons, Sonys, and JVCs. Some reviewers states that the Epsons and Sonys have the same or better blacks than jvc, but jvc have a better contrast. Need a little education from the knowledgeable

Reference black level is a meaure that is absolute but depends on several factors including screen sze, throw distances, screen gain. It is a very small number and next to impossible to measure with porecision absent some very expensive test gear. On off contrast depends on two measurements. Peak white/divided by ref black. By holding everythibg I measured above constant, the variables cancel out. Most projectors under discussion in this thread have a peak lumens out, or lumens at 100 IRE out that are relatively the same. I don't much care if its 1500 or 500, it doesn't affect on off all that much because the lower half, the number divided into the top number, is tiny and has a much bigger effect on the value of the ratio. Its in the .0X to .00X range. But it really is impoosible to measure accurately. To get a high on off ratio, one needs a very small ref black level. In a nut shell, that's what's going on re the two numbers from which on off is calculated. If the ref black was zero, the on off result would be mathetmatically undefined since division by 0 is undefined though you might call it infinity. Note that if ref black is say .000001, the top value becomes irrelevant. Put 500 in for the 100 ire value. You get essentially 500 million to one. Put in 900 You get 900 million to one. Is there a difference? You can measure the ref black level accurately to say 4 decimal places..

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post #4 of 14 Old 01-29-2013, 07:47 AM
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Originally Posted by Ron Jones View Post

Sony and Epson both use a dynamic iris (DI) wihin the lens assembly of their projectors. The DI can open and close to increase or decrease the amount of light coming from the lens. During scenes in the video which are mostly dark the DI will close down and make ther overall projected image darker. This lowers the black level, but also lowers the whites and all other shades by the same amount. Such projectors have two different black levels and on/off contrast ratios (CRs). One is the "native" values that are measured when the DI is turned off (generally with the iris locked in the full open position). The other mode used for measurements, and the only one the manufactures will use for coming up with their spec. sheets and inflated advertising claims, is with the DI engaged at its most aggressive setting. They then project a full white screen and measure the white level (the DI will automatically fully open for this signal) then they project a full black screen to measure the black level (the DI will close down to its minimum for this type of signal). This latter test will produce big numbers for the contrast ratio (CR = white leve/black level) and a low value for black level. However, many users will find this most extreme setting for the DI unacceptable due to the side effects it causes. When DI is engaged a more moderate setting will generally be more acceptable for most users. The best of the sub-$5K Sony and Epson projectors have native contrast ratios in the range of 5,000:1 while Sony's flagship 1080p projecfor, model VW95es, has perhaps over 10,000:1 CR. These Sony and Epson projectors can achieve a realistic contrast ratio of perhaps 50,000:1 maximum using DI turned on and set so as to not produce too many objectional side effects. However, DI simply will not produce a results as good as having an equivalent projector with the equivalent native CR.

The JVC projectors do not need to rely on DI (and don't have one) as they have very high native CR and low black levels.

Hi ron. You are leaving obe important fact about DIs out. While when the iris closes all lightout is reduced by the same amount, all DIs boost the whites by changing the gamma to reduce the amount the whites are reduced. Its not perfect and peak whites will be clipped to some extent.

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post #5 of 14 Old 01-29-2013, 07:51 AM
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Reference black level is a meaure that is absolute but depends on several factors including screen sze, throw distances, screen gain. It is a very small number and next to impossible to measure with porecision absent some very expensive test gear. On off contrast depends on two measurements. Peak white/divided by ref black. By holding everythibg I measured above constant, the variables cancel out. Most projectors under discussion in this thread have a peak lumens out, or lumens at 100 IRE out that are relatively the same. I don't much care if its 1500 or 500, it doesn't affect on off all that much because the lower half, the number divided into the top number, is tiny and has a much bigger effect on the value of the ratio. Its in the .0X to .00X range. But it really is impoosible to measure accurately. To get a high on off ratio, one needs a very small ref black level. In a nut shell, that's what's going on re the two numbers from which on off is calculated. If the ref black was zero, the on off result would be mathetmatically undefined since division by 0 is undefined though you might call it infinity. Note that if ref black is say .000001, the top value becomes irrelevant. Put 500 in for the 100 ire value. You get essentially 500 million to one. Put in 900 You get 900 million to one. Is there a difference? You can measure the ref black level accurately to say 4 decimal places..

Re JVC and need. It is not debateable that higher on offs are better than lower on offs. The JVCs have good on offs but they could be better, anything could be better as far as on offs go. JVCs could have killer on offs if they would add a user selectable DI on off. For marketing reasons they don't. Its as if they are opposed to DIs because of religeous believes. Its a shame, a pure shame, that JVC doesn't provide the option of a well executed DI such as Sony's.

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post #6 of 14 Old 01-29-2013, 08:15 AM - Thread Starter
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After seeing a double stack crt, I was in awe of the fade to black scenes. I know it isn't really realistic with the JVCs or the Sony vpl 1000. The crt resolution didn't look as good as my jvcs, but it wasn't that far off. Its starting to make me give up my HP screen and lose the contrast I'm getting with the iris completely closed on a 120in screen. I have a carada 80in cinema white and I must admit that the carada looked better. It was only 80in tho.
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post #7 of 14 Old 01-29-2013, 09:04 AM
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Re JVC and need. It is not debateable that higher on offs are better than lower on offs. The JVCs have good on offs but they could be better, anything could be better as far as on offs go. JVCs could have killer on offs if they would add a user selectable DI on off. For marketing reasons they don't. Its as if they are opposed to DIs because of religeous believes. Its a shame, a pure shame, that JVC doesn't provide the option of a well executed DI such as Sony's.

I'm not sure it's a religious thing. White crush is theoretically unavoidable with even the best DI, that's fact. And when you see it, it doesn't look pretty.
DI is just a compromise which was made to prevent dark scenes to look completely awful. I don't think that's a problem for JVC.

What we really need to get infinite blacks is two-chip systems, like Carl Zeiss Velvet, which has 1.000.000:1 navite on/off plus every benefits of DLP like motion and ANSI CR.

As I read implemented in HT projector it would cost only about $50k. Which is not too much for the high-end market I think.
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post #8 of 14 Old 01-29-2013, 09:06 AM
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The higher native on/off for a projector, the easier it is to have less side effects, because the IRIS will not need to be as aggressive in the mixed dark scenes. The JVC would definitely benefit more from an IRIS and have the fewest side effects from a "best-case" IRIS between all projectors.

You can do full fade to black with some IRIS's, but it's goofy side effects. The Benq w7000 can do it if you change the MIN IRIS settings in the service menu, it does make for a good laugh if you set it that way and suddenly everyone in the room is blind. I like to tell people I can get 5,000,000:1 with this IRIS (haha, it's true).



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post #9 of 14 Old 01-29-2013, 09:19 AM
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Originally Posted by blee0120 View Post

I want to know what relationship does contrast play toward black levels. Just did some research on contrast ratios. Looked up the contrast ratios for the Epsons, Sonys, and JVCs. Some reviewers states that the Epsons and Sonys have the same or better blacks than jvc, but jvc have a better contrast. Need a little education from the knowledgeable

...just an important side note, in actual application, one must have a perfectly dark viewing environment before any projector is to be able to deliver a respectable contrast ratio. If any stray room light or reflection falls on the viewing screen, it will absolutely overwhelm and destroy the actual black level regardless of projector and regardless of CR specification. So unless you first absolutely control the room light, comparing CR specs is meaningless.

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post #10 of 14 Old 01-29-2013, 09:25 AM
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Increasing the on off will improve performance regardless of light reflecting from the screen off the adjacent surfaces and back to the screen. And will not change the on off measurement. Stray light is different. And if you are talking ANSI, light from the screen reflection back to the screen will dramatically lower measured ANSI. Rather than explain this future, read Darin's article in secrets of home Theater about 6 years back.e

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post #11 of 14 Old 01-29-2013, 09:30 AM
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Originally Posted by coderguy View Post

The higher native on/off for a projector, the easier it is to have less side effects, because the IRIS will not need to be as aggressive in the mixed dark scenes.

I agree, but the question is: would "not argressive" iris make any substantial difference? I mean, with such a high native CR? Multiplying JVC contrast with iris by 1.5 factor wouldn't make significant improvement. And multiplying by 4 or higher will bring in an artefacts.
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post #12 of 14 Old 01-29-2013, 09:35 AM
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Two reasons I think...

The JVC can take a bigger hit to the white peak without being as noticeable, because it already has such bright white peaks in dark scenes (if you compared a JVC to a DLP w/ IRIS, the main thing is the white stars are so much brighter more so than just the black level being darker itself), so part of the advantage is the white peaks can take a hit without it killing the image so fast.

It's also (presumably) not only the linear aggressiveness that can be lowered, it's the fact you can isolate the derivative curve to be MORE aggressive in MOSTLY entirely dark scenes because the fact that you already have such high white peaks it won't cause the non-linear eye response to be as sensitive to the lowering of the black levels and white levels at the same time as a side effect type thing. Just like there are sweet spots to the fully dark scenes, there are also sweet spots to starfields, the problem becomes with most projectors is that those white peaks get TOO dull TOO fast looking in darker scenes when the IRIS kicks in, but the JVC will maintain that better. The dynamic gamma response does not fully solve the IRIS problems, because the gamma tracking and IRIS tracking are rarely ever perfectly in-synch on most projectors, and also if the IRIS lowers the brightness too much, you cannot boost the gamma output level enough at all points before you run out of room. At some point it will over-compensate the gamma as well and you will get clipping or you will just lose the "sweet spot" look to the mix of dark and bright.



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post #13 of 14 Old 01-29-2013, 09:59 AM - Thread Starter
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...just an important side note, in actual application, one must have a perfectly dark viewing environment before any projector is to be able to deliver a respectable contrast ratio. If any stray room light or reflection falls on the viewing screen, it will absolutely overwhelm and destroy the actual black level regardless of projector and regardless of CR specification. So unless you first absolutely control the room light, comparing CR specs is meaningless.
assuming the projectors are in a theater friendly environment of course.
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post #14 of 14 Old 01-29-2013, 10:05 AM
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Originally Posted by mark haflich View Post

Increasing on off weill improve performance regardless of light reflecting from the screen off the adjacent surfaces and back to the screen. stray light is different. And if you are talking ANSI, light from the screen reflection back to the screen will dramatically lower measured ANSI. Rather than explain this future, read Darin's article in secrets of home Theater about 6 years back.e

...that would be applicable in a light controlled viewing environment with dark surroundings (no stray light). My point to the original poster is that unless a dark, light controlled theater room is the planned environment, projector CR specifications are relatively unimportant. In a normal living room or media room environment, with low level room light present, comparing ANSI Lumen levels between projectors would be time better spent, with regard to the relative picture contrast that would actually be enjoyed..

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