on/off CR vs ANSI CR? - AVS Forum
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post #1 of 10 Old 01-27-2005, 07:49 AM - Thread Starter
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Can someone explain the difference between on/off CR and ANSI CR for me? Or point me to where I can figure it out.

Thanks,
Scott
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post #2 of 10 Old 01-27-2005, 01:13 PM
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Pretty simple. On/off CR is the greatest difference in lumen levels from a fully white image and a fully black image. (literally as bright as the projector can go to as dark as it can go). *** edited to include the caveat: when properly calibrated as it should be for optimal viewing. Of course, you could also measure the 'out of the box' values.***

ANSI CR is a measurement taken from a specific screen which is divided into 16 squares. The 4 x 4 grid has alternating black and white squares and the CR is measured as the difference between the average lumens measured from the centers of the white squares to the average lumens measured from the centers of all the black squares.

On/off CR gives you the greatest possible difference between the brightest and darkest a projector can project between different frames whilst ANSI CR gves you the greatest difference within a single frame/image. All projector manufacturers list on/off CR. And while projectors can achieve a 5000:1 on/off CR or higher, ANSI CR is not only limited by the projector and technology but the surrounding environment too. With white walls and a white ceiling, it is pretty much impossible to reach even 100:1 ANSI CR because the reflected light from the brightest parts of the image will wash out the darkest. To enjoy maximum ANSI CR, you would have to blackout the room to not only cut out ambient light, but to absorb ambient light reflections off the screen from being reflected back to the screen.
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post #3 of 10 Old 01-27-2005, 01:23 PM - Thread Starter
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Thank you. Perfectly clear now. Best, Scott
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post #4 of 10 Old 01-27-2005, 01:50 PM
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Quote:
Originally posted by djbluemax1
Pretty simple. On/off CR is the greatest difference in lumen levels from a fully white image and a fully black image. (literally as bright as the projector can go to as dark as it can go).
Just wanted to clarify a couple of things. The on/off CR that most of us care about and discuss around here is calibrated. So, not the brightest the projector could go if colors where blown out. Some manufacturers do a better job of specing with a home theater setup than others. JVC even exceeds their CR spec for the HD2K at d65. Also, magazines and many of us measure 100 IRE to 0 IRE with video signals (some room for above white), so this can also affect the numbers and means that it often isn't even as bright as the projector could go at d65.

And nobody with a multi-position iris specs on/off as the brightest the projector can go with the iris open and the dimmest it can go with the iris closed unless it is dynamic. The brightest to dimmest would be pretty much irrelevant if that can't do it during movies without intervention and they would get trashed for that. The ratio between the brightest that the Sharp 12k can go with bulb on high and brightest iris choice is probably 15k:1 or so to the dimmest, but it is speced at 5500:1 because it can't do that other range without changing settings.

But the basic point is the same.

--Darin

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post #5 of 10 Old 01-27-2005, 02:09 PM - Thread Starter
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Well hell. So much for understanding perfectly :D. Now I'm not sure.

To put it into my words to see if I understand. You are saying that when the PJ is calibrated, it's likely less bright than out of the box when the colors are likely maxed (and not balanced/wrong). And that what we all care about is a brightness measurment taken AFTER it's calibrated - that is, what's the PJ's brightness when it's colors are properly adjusted.

I'm not sure I'm following "above white" comment. Do you mean the "whiter than whites" that are above that "reference white" digital 235? So you are saying many of you and the magazines measure the projectors display with a 100IRE pattern displayed (which should corelate to a digital input of 235 if I understand that right) and that the PJ still may go brighter in reality (236-254).

To give it some real world grasp, take a simple fixed IRIS DLP front projector (i.e. Optoma H77, Sim2300E). I have Cliff Plavin's OpticONE at my house today. I (could) have decent Extech light meter if required. Presume I am able to calibrate it to D65 (big presumption :D). How does one measure the ANSI CR literally? Or is it possible with those tools.

Thanks,
Scott
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post #6 of 10 Old 01-27-2005, 02:54 PM
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Oops, I amend my point. Yes, the ANSI CR and on/off CR are the maximum differences measured when the projector is calibrated to D65. All else is correct.

As for measuring it with the OpticOne and light meter. No problems. just calibrate for D65 with the OpticOne and after it has been fully calibrated, you can then measure the brightest test screen at the calibrated settings and the darkest to measure the on/off CR. Using the ANSI checkerboard pattern that should come with AviaPro will then allow you to measure the centers of the white boxes and the centers of the black boxes, to get the average difference for ANSI CR.

Still simple :)

Measuring the 0 - 100IRE range makes it easier since both screens are included in Avia Pro but it is not necessarily the absolute on/off CR range especially if the source can potentially include material with higher/lower values.
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post #7 of 10 Old 01-27-2005, 02:59 PM
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Scott,

It sounds like you have it. I was referring to 235 (or 100 IRE with video levels) and leaving some room to not crush everything above that.

I don't know if any things other than AVIA Pro and Colorfacts have ANSI checkerboards. Basically, you just want a 4x4 checkerboard of 0 IRE and 100 IRE. To do the test technically correct you have to measure all 16 rectangles and then invert the black and white in the checkboard, but most people either do just one set of measurements or do some kind of modified ANSI CR where they only measure some (like WSR only measuring the middle rectangles).

--Darin

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post #8 of 10 Old 01-27-2005, 03:09 PM - Thread Starter
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Got it. Thanks guys. Scott
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post #9 of 10 Old 01-27-2005, 03:12 PM
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Even the normal Avia disc has the ANSI checkerboard but a lot of times, people get the OpticOne with AviaPro which has even more patterns and includes the ANSI checkerboard. Can't remember if DVE has the ANSI checkerboard pattern.

Scott,
Did the OpticOne you've got come bundled with AviaPro?
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post #10 of 10 Old 01-27-2005, 03:18 PM - Thread Starter
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No, I kinda went a back way. I got mine without AviaPro via a "private one time opportunity". May get AP later, but my regular Avia and DVE will work for grayscale, contrast and brightness AFAIK. And I believe both compainies are aobut to release new discs. Avia an update to the consumer version, and DVE-Pro at around $150, I heard both things third hand so cannot vouch for them. I thought I'd save the cost of the AP and wait for one of those new discs or maybe a signal generator instead.

S
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