Correcting this misconception might not bring any practical advantages, but still, I see so many people making this mistake, so I'll correct it anyway (assuming I'm correct, of course).

I have become aware to this misconception after I received an answer for the following question:

Why does a projector with native 500:1 On/Off contrast ratio, doesn't necessarily have an ANSI contrast of 500:1, rather usually the ANSI contrast is much lower than the On/Off contrast. I mean, if the ratio between a 100% white panel, and a 0% white panel, is 500:1, then why can't it hold between two opposite squares in the checkerboard test ?, if you take out the negative effects that the room adds to the ANSI contrast, I simply saw no reason why it shouldn't be identical to the On/Off contrast value.

The answer that I received for this question, was the following:

This is because of light scatter, mostly. Light is bouncing off different internal areas of the projector all the way from the display chip to the external lens and the bright parts are "polluting" the dark parts.

Now, this answer led me to become aware to the following misconception:

The native On/Off contrast ratio of today's best LCD projectors, is something around 1000:1 (a value very low in comparison to the better DLPs).

In order to deal with this inefficiency of LCD projectors, they all come with dynamic iris, that can increase the On/Off contrast to around 10,000:1, or even more.

In any case, when people talk about the On/Off contrast ratio of LCD projectors with dynamic irises, they frequently say that the dynamic iris trick has limits, and the limits can be easily seen when there is a bright and dark area in the same image, since then the iris opens completely, and the true native contrast of the projector can be seen, which translates to very grey blacks.

In my opinion, this is exactly where the misconception happens, it seems to me that people get confused between On/Off contrast, and ANSI contrast.

I don't argue the fact that in an image with dark and bright areas, LCD projectors fail to give a convincing picture, but what I'm saying is, that it has *nothing* to do with a limitation of using a dynamic iris.

Why ?, because this part-dark-part-bright image, is a measure of ANSI contrast, and not On/Off contrast, and dynamic iris was never meant to be a cure for bad ANSI contrast.

A good LCD projector still has a native contrast ratio of1000:1, and if even 50% of it would have stayed as ANSI contrast (meaning an ANSI contrast of 500:1), then that type of part-dark-part-bright image, would have looked great (even with the iris open). But, LCD projectors have a limitation not only in native On/Off contrast, but also in ANSI contrast, and hence such images look lousy, but still, my point is that this is not a weakness of the dynamic iris, because it was never meant to be a cure for bad ANSI contrast.

To conclude: my claim is that in a part-dark-part-bright image, when the dynamic iris of an LCD projector opens, and reveals grey blacks, this is not a limitation of bad native On/Off contrast (and hence not a limitation of the dynamic iris, which only meant to tackle the On/Off contrast), rather it's a limitation of ANSI contrast, another department where LCD projectors are weak.

If I'm correct in what I said, then a consequence should be that for a DLP projector with dynamic iris (set up in a room that can handle the ANSI contrast that the DLP can produce), when the dynamic iris opens in a part-dark-part-bright image, we won't observe lighter colored blacks (as with LCDs), since the high ANSI contrast will jump in and help.

I don't have a DLP unit with dynamic iris, so I can't confirm what I just said.

This is where we need Darin to step in.

I think what you're not taking into account is that ANSI contrast is measured using a 50/50 white / black pattern. Where washed out blacks or dull whites with low native CR panels is evident is when you have a large amount of black, and small patches of bright white, or what I've found to be worse, large areas black and near black, with small quadrants of medium high picture level. In this case, the iris either has to stop down to make the blacks look black, or open up to make the whites or medium content bright ... thus revealing the native CR of the panel.

I have 2 budget digital PJ's, the HD1000 and Epson400. We've recently been watching Firefly on both of them. Aside from the space scenes, there are lots of scenes that are mostly dark, and medium bright patches ( things like faces ). This is what I've found to be most challenging to both pj's. The Mits edges out the Epson in this particular type of content for blacks, but not by a lot. I'm sure the HD3000 would do a better job.

We watched an episode in our CRT theatre, and the difference was night and day. Even though the Barco has very low ANSI, these types of scenes rendered an image I found to be far, far superior as far as blacks. So, my findings is that the on/off does play a part in instantaneous contrast.

No expert here. Just what I've observed.

Jonathan

We watched an episode in our CRT theatre, and the difference was night and day. Even though the Barco has very low ANSI, these types of scenes rendered an image I found to be far, far superior as far as blacks. So, my findings is that the on/off does play a part in instantaneous contrast.

Good point. It means something in my understanding is still missing.

I can settle the CRT phenomena (i.e that part-dark-part-bright images can look good with a pj that has high On/Off but low ANSI) in the following way:

It could be that both DLP (the better units) and CRT projectors can show good quality part-dark-part-bright images, but do achieve it differently:

The important thing about part-dark-part-bright images, is to show a very good black level. If the black levels at these images can remain solid, then it doesn't really matter how bright will the whites be, since the brain will compensate. This explains why CRTs give good results in such images.

DLPs can't make CRT blacks, but *can* make the white squares of the checkerboard, very high in intensity, and this gives the ability to trick the brain into thinking you are watching good blacks in such scenes (since in comparison to the bright whites, the grey blacks seem very dark).

LCD projectors fall between the chairs in part-dark-part-bright images, because on one hand they lack high native On/Off contrast, so once the dynamic iris opens in such mixed image, the black levels are not good, and on the other hand, they also don't have high ANSI contrast, so the brain can't even be tricked to think that the blacks are very dark. So, what you get is grey blacks and muddied image.

If I am correct about what I said here, then I guess there wasn't a misconception to begin with, since very high native On/Off contrast, CAN make a part-dark-part-bright image, look good. BUT, what I add here, is that this is not the only way to achieve this goal, and DLPs can achieve it through high ANSI contrast (which tricks the brain to think that the blacks are good in part-dark-part-bright images).