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1200 : 1 Eye contrast ratio  

post #1 of 6
Thread Starter 
“About 1200 to 1 contrast ratio, this is the contrast ratio of the human eyeâ€
I read this statement in Barco’s projector site.
With a near absolute black level we need a projector with a projector with 1200 lumens peak capability, here is very important the world peak, because contrast is realy important when only part of the screen is being illuminated. Ok, now what are the digital projectors that can match this requarement, let say that we can accept not perfect black level but very near and not full contrast ration but at least 1000 peak lumens. Note that peak lumen and ANSI lumens are near the same for lamp illuminated projector, not the case with crt projector wich obiusly match this requarement.
Federico
post #2 of 6
I'm really not sure what Barco is saying here, or where they received their information. Perception is way more complicated than this, and follows something called a "photopic response curve" which is influenced by both frequency and the amount of light. In other words, certain frequencies cause retinal receptor cells (rods/cones) to fire more vigorously than other frequencies at a certain light intensity. Raise the intensity, and the frequencies left out of lower light levels may cause a more intense response. It's seriously really complicated. To say "the human eye has such-and-such contrast ratio" is incredibly unscientific and questionable.

The eye is an incredible machine, capable of firing off an impulse by a single photon hitting a receptor (rod/cone). Our brains filter this so that it still only takes 9 to 5 photons over about 100ms to be perceived! A person can clearly detect the light of a candle in total darkness from literally miles away. And these cells are continuously adaptable, and therefor constantly adjust their sensitivity (with the help of your brain as well). Brightness discrimination varies between individuals as well, especially since the brain is where the discrimination occurs regardless of source neural firing.

I mean good grief. What is the contrast ratio between rods/cones not firing at all, to those being bombarded by millions of photons per ms? Yeah, you get the picture.

Personally, Barco's claim as far as human eye contrast ratio sounds like marketing material aimed at the average and unquestioning population, and is not science. But hey, I could be wrong ;-)


[This message has been edited by Skyhawk (edited 05-19-2001).]
post #3 of 6
Federico,

It all depends on how much white there is in the image.

I would say:

Bright scenes need 150:1
Normal scenes need 300:1
Dark scenes need 1000:1

These are of coarse rough estimates and they are completely subjective.

For instance, other people like the 10HT for everything but it is nowhere near the contrast ratio of film which I think is the ultimate ruler to measure performance.

One thing is for sure 1200:1 would do it for just about every scene for just about every viewer.

-Mr. Wigggles

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The Mothership is now boarding.
post #4 of 6
MrWigggles,

Just out of curiosity, why would you think the darker the scene the more contrast ratio is needed? I would have guessed that contrast discrimination would at worst remain constant, or rather be higher in low light conditions. For example, I can detect a candle from a mile away in darkness, yet cannot detect a black element the size of a candle flame from a mile away during highly lit conditions - explainable by the amount of noise all those firing rod/cones are producing to those that are not.

With my projector and dark scenes, my wish is to just have deeper blacks - even if it means I don't have to reach for the sunglasses in sunlit scenes or when a flashlight pierces the darkness.




------------------
Skyhawk
- Infocus LP350
post #5 of 6
Thread Starter 
Skyhawk, I think that you're right, that's the question: where does Barco find that information? Any way one thing is true crt looks excellent, maybe b/c the perfect black, maybe b/c the contrast or both. If you want to take a look: http://www.barco.com/projection_syst.../cinerange.asp

"Bright scenes need 150:1
Normal scenes need 300:1
Dark scenes need 1000:1"
MrWiggles, what do you mean for a bright scene? is it a scene where most parts are ilumininated? and dark scenes are the ones where there is only a small area illuminated, right?
Well that's ok with graphic of luminance that Barco shows here: http://www.barco.com/projection_syst...ces/advice.asp

Now, if we are to compare a video projector with a 35mm movie projector then the crt is not the answer b/c the movie projector has a constant light output as all other lamp based projectors, digital projectors. If this is right what we need is a digital projector with almost perfect black. I've seen that TI is announcing a new dmd device with 12 degree angle of reflexion, how will this benefit the black level issue is the question.

Federico
post #6 of 6
I think it's 100:1 contrast in a *scene* is about the limit what most people can perceive. Take your average glossy magazine, I believe it has a contrast ratio in this range and it looks plently black and white! Of course, this is the contrast ratio of the scene, it has little to do with what you would need for a projector. Dark scenes, for example don't use the projectors full contrast range (from black to white), instead it only uses a small range. Ideally contrast in the majority of dark scenes should be more than 100:1 from the lightest to darkest point in the scene.

So, what you really need is enough contrast in every scene so that you perceive the darkest value to be black (perception of "black" is really related to how bright "white" is). See, what actually happens is that your eye adapts to (roughly) the average level of illumination and you can discriminate a contrast range of roughly 100:1 around that level. Your eye is actually quite a marvelous organ it has a dynamic range of something like 10^6:1, the catch is that it can't see the range all at once one.

Regards,

Kam Fung
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