I hate contrast ratio. It's a stupid and pretty much useless measurement. It's up there on the list with horsepower as a useless number that tells you next to nothing about actual performance. "My SUV has 300 horsepower!" yeah, and a 0-60 time pushing double digits. Congratulations. Hmm, bad example. 0-60 is a useless number too, but that's a different conversation.

Full on/full off contrast ratio, at least as far as we do it, is measured with a 100-IRE field and a 0-IRE field only after the display has been calibrated. The most notable reason why contrast ratio is a useless statistic is that you can only compare this number to other displays we've measured. There is no set way to measure contrast ratio, so everyone else's numbers are going to be different. But even take our own numbers. When are you ever going to see, or need to see, the difference between a full white screen and a completely black screen? Oh, right. Isn't that why there's ANSI contrast ratio?

ANSI contrast ratio has eight black boxes and eight white boxes arranged on screen in a checkerboard pattern. Even this, though, is flawed. The average picture level of a TV show or DVD movie isn't anywhere near the 50% APL that the ANSI contrast tests. Some research has shown that the APL of most TV shows is less than 20% APL.

So how about a test that uses the ANSI checkerboard, but has white boxes that are, say, 40-IRE. This would average out to an overall picture level of 20%, around what most television programs are. A realistic representation of the contrast ratio you're likely to see when actually watching the display. We could still print the black level and the light output (of course).

A good idea? Maybe. It would just barely be more useful than any of the other contrast ratio specs, as you'd still only be able to compare it to other displays we've measured. Also, how much different would it be than the numbers we already print? If you take the ANSI contrast ratio as a worst case scenario, and the full on/full off contrast ratio as a best case, you're getting a pretty good representation of what's going on with the projector. What is more useful is the black level and light output numbers anyway.

Of course, this doesn't solve the problem of not being able to compare anyone else's numbers to ours or ours to theirs. That seems to be a problem for another time.

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Reader Comments

Posted 12/2/2005 at 21:22 — By ChrisWiggles

Your comments about on/off contrast are flat wrong. on/off CR in *addition* to ANSI on/off CR combine to give you the performance in instantaneous (in-scene) CR across various APL. At low APL, on/off CR is hugely important, at high APL ANSI CR is hugely important. Your blog entry has been linked to AVS forum, which is what brought this to my attention. Your tirade against on/off CR is misinformed and will profoundly misinform your readers. I hope you will withdraw your entry or correct it.

Posted 12/3/2005 at 21:56 — By Geoffrey Morrison

You�re missing the point completely. If you read the post I�m saying the full on/full off number is what is useless. I get hundreds of emails about people wanting to know if Projector A with a 4000:1 contrast ratio is better than Projector B with 3000:1. These numbers, by themselves, offer very little into the actual performance of the projector. What is more important is the actual black level and light output numbers, in foot-lamberts or lumens or whatever. Let me specify. Would you rather have:

TV1 with 50 ft-l and 0.05 ft-l
Or
TV2 with 20 ft-l and 0.02 ft-l ?

Take your pick, the point is you can�t tell there�s a difference because as far as each company and the public is concerned, they are the �same� at 1000:1.

Posted 12/3/2005 at 22:24 — By ChrisWiggles

I'm sorry if I "missed the point" in your statements, but the on/off CR number is anything but useless. Yes, some on/off CR numbers are meaningless when done inaccurately or manipulated by manufacturers, but good on/off CR numbers are important because on/off CR itself is fundamentally important. " the point is you can�t tell there�s a difference because as far as each company and the public is concerned, they are the �same� at 1000:1." Well, the on/off CR number makes no attempt to quantify light output, it quantifies white:black, and that is it. That's why you have a light output number in addition to on/off CR. You can't berate a specification for not quantifying something it's not supposed to capture in the first place. split post continues below

Posted 12/3/2005 at 22:28 — By ChrisWiggles

"What is more important is the actual black level and light output numbers, in foot-lamberts or lumens or whatever" This is silly to me. You can't measure the "black level" of a projection display because *that's* a meaningless quantity: it depends on screen size, gain etc. Rather, that's why we use light output, which you can figure out foot lamberts for your screen, then on/off CR gives you your black level. These two specs give you so much information, it seems very bizarre that you would suggest measuring black level and white level for one specific system which gives you the information in so much more complicated a way, and further it hinges on your ability to accurately measure the black level at the screen which is often not possible. A checkerboard at 40IRE is likewise less useful than 100IRE standard ANSI checkerboard, because anything less than 100IRE and the measurement hinges on the gamma. So it seems to me you are advocating using profoundly *less* useful measures than we have now.

Posted 12/3/2005 at 22:40 — By ChrisWiggles

And then there are statements like these in your original posting, which really mislead your readers: "When are you ever going to see, or need to see, the difference between a full white screen and a completely black screen? Oh, right. Isn't that why there's ANSI contrast ratio? " When are you ever going to look at a checkerboard in real video either? Or gray fields for grayscale? This is a hugely misleading statement, and horribly dangerous because readers will come away thinking that ANSI is somehow better a measure than on/off when they are two *completely different* measurements! I shouldn't have to explain to you why accurate and linear grayscale is important, nor why on/off CR is important, nor why ANSI CR is important, and why they're all very different things, and why all of them use completely "useless" images that we'll never see in real life. You never listen to frequency sweeps in music either, but you wouldn't claim such a ridiculous thing that FR is a "useless statistic."

Posted 12/3/2005 at 23:38 — By Geoffrey Morrison

The problem here is that we�re arguing two different things. In reality, we actually agree on most points. You�re saying that CR needs some other measurement to be useful, and with that additional information it is a useful tool. I am saying, well, the exact same thing. How we go about getting that second piece of information may differ, but that�s a whole other argument (see the next paragraph). My 40/0 measurement was merely a philosophical exercise. Nowhere do I say that�s what we�re going to do or what should be done. Read the second to last paragraph again.

If you are specifying light output, you should also specify the screen (size and gain) that light output is measured on. Once you specify screen size, figuring out what the projector will roughly produce on a different screen is just math. We feel this gives our readers a better example of what the display is doing. An argument of lumens v. foot-lamberts is a long one, and one I�m not going to get in to (for now. . .).

Posted 12/3/2005 at 23:40 — By Geoffrey Morrison

Also, I was hoping this would provoke some spirited debate. It�s good to hear both sides of an intelligent argument. So thank you for that Chris.

Posted 12/4/2005 at 0:19 — By ChrisWiggles

Then I guess I don't really get your point. In measuring a projector, you're measuring a projector not a screen. Measuring footlamberts off the screen is a very strange thing to do rather than just lumens off the projector, on/ff, and ANSI. You can do all that with no screen at all. Why complicate things by inserting a screen into the equation. With these 3 specs, you can calculate white level and black level with any screen you want. Otherwise, basically you're just making it more complicated than it needs to be. If all I have is footlambert measurements, I need to do the reverse calculation with the screen information to get my lumens and on/off numbers, and then go to a screen of my choice. This seems irrationally complex.

Posted 12/4/2005 at 0:24 — By ChrisWiggles

(sorry, wordy!) If there's any 3 fundamentally important measurements here with regards to light (disregarding color for a moment), there's nothing that gives you more information than 1)lumens 2) on/off CR and 3) ANSI CR. You can calculate everything from these. You can even calculate what a checkerboard at *any* IRE will look like if you also have gamma, which would need to be measured to compare a checkerboard of anything other than 100IRE anyway, for that to have more than isolated relevance to a single display. So there is really nothing in my opinion that gets away from the importance of these fundamental measurements. Yes, there are other things that are also interesting to measure in addition to these, but there is no way that I could ever accept an argument that on/off CR or ANSI CR are unimportant. The only exception is where on/off CR is infinite, in which case it is not on/off CR that has lost importance, rather bothering to measure/quantify infinity loses relevance. likewise, thanks.

Posted 12/9/2005 at 20:101 — By jimed1

So then, what is most important, contrast ratio, or black level? I think a lot of the public conception is that in order to decern the details in dark/shadowy scenes, a televisions CR must be high. I for one also thought that this was also directly related to the tv's ability to produce blacker blacks. So when I am looking at the new RPTV's, I take note of the contrast ratio because I am assume the higher the CR, the better the black level will be. Am I wrong? Until recently, I didn't think the blacks on any of the mirco-display RPTV's was very good. The newer sets seem to be able to show black a lot better.

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I AM ABOUT TO PURCHASE MY FIRST HDTV IN ABOUT A 32" SIZE MODERATE PRICE RANGE AND HAVE BEEN COMPARISON SHOPPING FOR ALMOST 6 MONTHS BUT AM STILL CONFUSED. IS 800:1 CONTRAST RATIO GOOD ENOUGH OR DO I NEED 1000:1, 3000:1, OR MAYBE 4000:1. THANKS, ROOKIE, DEZRA

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