How much ANSI contrast is enough? How much is too much? - AVS Forum
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post #1 of 13 Old 04-06-2008, 06:51 PM - Thread Starter
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post #2 of 13 Old 04-07-2008, 09:30 AM
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sounds like the contrast is up to high, white shouldn't bloom, the minute pure white against a black, blooms or glows or somehow alters geometry it's too much.

In the lightpole example it's the camera's job to capture the halo, then the data fed to the TV will reproduce it evenly. It is not the TV's job to say oh here is a bright source against dark, I'll put a hallo on this white.

I take it you own a CRT and are having this issue. The remedy is to turn your contrast down.

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post #3 of 13 Old 04-07-2008, 12:33 PM
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I still say what you are seeing is too much brightness, and commercial theaters are not known for their accuracy.

FOr these light blooms there are three different placed it could happen
the source - film, file (digital theater) or DVD
the reproduction - the projecter, lcd, crt
the eye - If the reproduction is accurate, but their is more light coming into your eye, it could be percieving the bloom.

Honestly I'm leading towards your eyes being oversensitive to bright lights in dark enviroments.

Once you get whatever you want, if you calibrate it for overall brightness things won't bloom. Granted this effects contrast, but it's not really contrasts fault as contrast is basically a fraction where the numerator is the brightness and black level is the denominator. What I mean is a 1000:1 contrast ratio is very different with a 120cd/m white and a 0.12 black and a 500cd/m white and a 0.5 black. Both have 1000:1 contrast, but they are actually very different. Alot of displays have an easier time increasing brightness to net a higher contrast ratio even if that makes the brightness too bright.

just tune down whatever display to 25-30ftl and I think you'll be fine (even if that means going from a 750:1 to a 250:1 contrast ratio).

Thinking in terms of contrast ratio isn't very helpful since most displays are overbright. Almost everything needs to be turned down to get the correct brightness level, then you are stuck with whatever your black level is. But puttin a sticker on a TV that says 0.08cd/m black level isn't nearly as sexy as 5000:1 dynamic contrast ratio.

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post #4 of 13 Old 04-07-2008, 01:07 PM
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Speaking about theatres and contrast: what is/was normal contrast ratios in
cinema theatres? I recall hearing about low contrast, 300-500 ANSI,
can't remember if that was with traditional projectors or newer digital ones.
Anyone know the facts?
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post #5 of 13 Old 04-07-2008, 01:47 PM
 
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http://www.quantel.com/resource.nsf/Files/Digital_Film/$FILE/Digital_Film.pdf
Quote:


Modern camera negative stock will have almost a 10-stop exposure range representing a 500:1 brightness range. Generally, black to white on the print corresponds to a scene contrast of 200:1

Printed films rarely show a full 10 stops of dynamic range, even if the negative film can handle it. They're bleach bypassed, processed, etc. to about 7-8 stops at most (plus a smooth knee).

Edit: need to copy and past url
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post #6 of 13 Old 04-07-2008, 02:36 PM
 
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.The CRT will, just like in real life. Is that a good thing?

No. That's one of CRT's main weaknesses. CRTs have low ANSI contrast, and this spill dramatically reduces the instantaneous contrast across a single image especially in mixed scenes, and often this also negatively impacts shadow detail visibility. This is why if you compare a digital like a DLP with high ansi but low on/off and a CRT with enormous on/off but low ANSI, there is no easy answer as to which provides better blacks or better contrast overall since it will heavily depend on the APL of the scene. Also, don't take this as a CRT-bash, I am a CRTer myself, but it's always important to understand the strenghts and benefits of various displays, and this is a CRT's main weakness.

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In real life when a bright light is in darkness you see glare, if you turn on more lights the light no longer glares because you've equalized the lighting. I think this is what high ANSI display devices are doing. Therefore the DLP and plasma are not showing what the director filmed? It'd be like wearing polarized glasses and looking into a stream to see the fish. Sure you can now see the fish, but the rest of the world has become polarized too. At what point does ANSI contrast become more than real life and change what the director filmed?

No consumer display currently on the market that I am aware of can exceed the capabilities of the human eyes in this regards. They cannot exceed what the director intended at all. Light spill is a strong negative in a projection system since it obscures detail that should be visible. If the director wants to mimic veiling glare, it can be done in many ways, and you can see this in many film shots especially where lights are being shined directly into the camera. Having bad light spill in the projection system basically forces this to happen all the time regardless of the intent of the director. Very bad.

The only display I have ever seen that can exceed the eye's abilities is the Brightside HDR, which has something like 20,000:1 ANSI contrast. Yes, that is the correct amount of zeros, and yes I do mean ANSI (checkerboard) contrast.
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post #7 of 13 Old 04-07-2008, 02:39 PM
 
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Quote:
Originally Posted by rickardl View Post

Speaking about theatres and contrast: what is/was normal contrast ratios in
cinema theatres? I recall hearing about low contrast, 300-500 ANSI,
can't remember if that was with traditional projectors or newer digital ones.
Anyone know the facts?

It's going to depend a lot on the theater, the optics, and how clean the light path is. For a lot of mainstream crappy theaters, I'd bet it's fairly low, probably lower than 300-500:1, which is actually fairly high. With a really good film presentation, it's probably a good bit higher than that, but sadly that's the exception rather than the norm these days.
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post #8 of 13 Old 04-07-2008, 03:06 PM
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EDIT: since the article referenced apparently was in error, I have removed the quotes and URL to it.
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post #9 of 13 Old 04-07-2008, 08:39 PM
 
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Quote:
Originally Posted by rickardl View Post

I found this article about contrast, "The Contrast Ratio Game " which mentions:
at any given instant, the eye can possibly see over a range of 400 to 800:1 in contrast detection
...
Do not get carried away with big contrast numbers - the eye dynamic response is the limiting factor.

Similarly important is the fact that the presence of even a minimal amount of ambient light would make a home theater projector with a high contrast ratio rating behave the same as one with a much lower rating.

...
you need to view the image in a completely darkened room to be able to perceive the marginal difference between a 2000:1 and a 500:1 contrast ratio.

Interesting indeed...
http://www.practical-home-theater-gu...ast-ratio.html

That article is completely wrong. Stunningly wrong. Amazingly wrong.

The claim of a max of 400:1 to 800:1 has no citation whatsoever, and once again ignorantly conflates the maximum range of contrast that the eye can see across a single scene with the Contrast Sensitivity Function, which is a measure of the exact opposite, which is how LITTLE a luminance delta the eye can see. It's no surprise that the rest of the article is equally misinformed or ill-informed, despite good intent.

Sad that this stuff still gets paraded around. They actually call a 2,000:1 contrast ratio a "high contrast ratio projector" which is silly.

The human eye in a single scene can see about 5 orders of magnitude(100,000:1), and way way more than that with time and movement of the eye.

I hate to be impatient with stuff like this that gets paraded around the forums, but we've been through this time and again.

Again I link to Darin's excellent contrast ratio article found here:
http://www.hometheaterhifi.com/volum...06-part-1.html

The claims that the eye is a limiting factor is completely ridiculous and easily disproven with an easy test that ANYONE can test in their own theater. Put up a checkerboard pattern, and then stick your hand in the dark square: can you see a shadow on the screen? If yes, then you can definitely see well beyond the capability of the projector's ANSI contrast performance in your system.

That article is BS, pure and simple.
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post #10 of 13 Old 04-08-2008, 10:53 AM
 
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Quote:
Originally Posted by rickardl View Post

EDIT: since the article referenced apparently was in error, I have removed the quotes and URL to it.

The article is not very far from accepted empirical data on the subject matter. Even Wikipedia could have answered your query rickardl!

http://en.wikipedia.org/wiki/Dynamic_range
"Equally a person can see objects in starlight (although colour differentiation is reduced at low light levels) or in bright sunlight, even though on a moonless night objects receive 1/1,000,000,000 of the illumination they would on a bright sunny day: that is a range of 90dB.

The eyes take time to adjust to different light levels and the dynamic range of the human eye without any adjustment of the pupil is only approximately 30dB.

For example a good quality LCD display has a dynamic range of around 1000, or 30dB (commercially the dynamic range is often called the "contrast ratio" meaning the full on/full off contrast ratio), and some of the latest CMOS image sensors now have dynamic ranges of 110dB, compressing the range into a range, near 30dB, that the human eye may understand.

Knowing that the display does not have a huge dynamic range, the program makers do not attempt to make the nighttime scenes millions of times less bright than the daytime scenes, but instead use other cues to suggest night or day: a nighttime scene will contain duller colours and will often be lit with blue lighting, which reflects the way that the human eye sees colours at low light levels."
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post #11 of 13 Old 04-09-2008, 09:10 AM
 
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Please feel free to ignore everything thomas has to say.
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post #12 of 13 Old 04-09-2008, 09:15 AM
 
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Chris this article may require cleanup to meet Wikipedia's quality standards.
Please improve this article IF you can! (July 2006)

http://en.wikipedia.org/wiki/Dynamic_range

Good luck in advance
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post #13 of 13 Old 04-09-2008, 03:26 PM
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I think we've discuessed this to the point that we've answered the original posters question.

It's unlikely that ANSI contrast will be more than on/off, have ansi and on/off being equal is optimal.

When looking at light blooms, the contrast ratio (either on/off or ansi) is not generally the issue, but overall light output.

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