why a 3D tv? - AVS Forum
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post #1 of 13 Old 08-18-2010, 06:44 AM - Thread Starter
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hi all, i went to Best Buy yesterday and took a look at a 3D TV with the glasses and it was awsome. but why do you need a special 3D TV to be able to watch 3D content? Why can't a 3D movie (the same one that they show in theatres) be put on DVD or blu-ray as is and we just use the same glasses they gave us in the theatres and watch it on any TV?
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post #2 of 13 Old 08-18-2010, 07:09 AM
 
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Theaters for the most part use polarized light to create 3D while almost all of the new 3DTVs use active shutter glasses and frame sequential 3D
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post #3 of 13 Old 08-18-2010, 07:13 AM - Thread Starter
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but the result is the same. the 3D effects i saw on that TV yesterday at Best Buy was the same quality as I saw in the theatres. so why did they come out with new technology and have us buy a new TV if we went to see 3D content?
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post #4 of 13 Old 08-18-2010, 07:39 AM
 
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Quote:
Originally Posted by velocci View Post

but the result is the same. the 3D effects i saw on that TV yesterday at Best Buy was the same quality as I saw in the theatres. so why did they come out with new technology and have us buy a new TV if we went to see 3D content?

Existing flat panel HDTVs can't do what a 3DTV can which is to show alternating L & R eye images at 60 frames/sec per eye. This coupled with active shutter glasses, emitter and using a 3D Bluray disc and player is the only method of getting Full HD per eye.

If you used exisiting HDTV technology, you would wind up with 30 frames/sec per eye which would exhibit annoying flicker in the images.
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post #5 of 13 Old 08-18-2010, 08:06 AM
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I think he's asking why consumer TV's can't use polarized glasses instead of active shutter. The fact is that there is a lot of technology in the theatre that you are missing and don't see. In order for a consumer television to show polarized 3D, you would need a few more technologies built into the TV - namely, a polarizer and a special lenticular screen coating often referred to as a "Z" screen or similar. These are both very expensive technologies and the net result is an interlaced image instead of a full progressive image that can be achieved by a fast refresh rate and active glasses. JVC makes a pro 3D monitor that works with polarized glasses for about $6K if you really want one
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post #6 of 13 Old 08-18-2010, 08:30 AM - Thread Starter
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but in the theatres, its not a TV, its a white screen with an image being put on it. this image is blurry and when you put on those glasses, you see 3D. it has the same resolution as any other 2D movie, but its blurry. why can't you have that same blurry movie put on a DVD and play it on your TV with the same theatre glasses?
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post #7 of 13 Old 08-18-2010, 08:59 AM
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Allow me to break it down for you.

First you need to understand the very basics of 3D and how we (humans) see in 3D. This is accomplished by our two eyes, at a set distance apart, working together. We see an image from 2 slightly different viewpoints at the same time. Our brain puts the two images together and determines depth based on how far or close those same two images are from each other. We do this automatically, and we do it on a per object basis. So if you put your hand real close to your face, you'll see two of the same object (your hand), and it will be out of focus. If you pull your hand back slowly, as you focus on it you will see the two images merge into one object.

So to "trick" our brains into seeing a 2D screen as being full of 3D objects, the screen needs to somehow direct specific images at specific eyes. So you will have an image that only your left eye sees, and an image only your right eye sees. If these two images appear so fast (90 times per second or more) that we cannot tell that its two images, our brain puts it together as one image. And there you go, its just like seeing 3D in real life!

There's a few ways of getting images to only show to a specific eye. The method you see in theaters is called "polarized". To make it simple, this works by putting a filter on the projector that rotates or flips to make the light travel either horizontal or vertical once reflected off a screen. The glasses you wear in these movies have one eye that can only see horizontal light, and one eye that can only see vertical light. This is a REALLY simplified explaination. The issue with this system is you actually lose a lot of light that's being reflected back at you, because half of it is being lost in the glasses. The other problem is the mechanical motion of "flipping" the filter can cause crosstalk (when you see both images at once). The biggest reason that this isn't used in the home is because the screens that have these filters on them are usually 8 to 12 times more expensive than a normal HDTV. But the glasses are really cheap (~$1).

The method being used at home is very different. It uses a cheap screen (by comparison, at least) and expensive glasses. The HDTV only has to be able to display 120Hz, which means the TV can change the image on the screen 120 times per second. This breaks down to 60 frames per second per eye. So it shows the left eye, then the right eye in full frame, but it happens so fast it appears as one single (blurry) image. The glasses are actually are very small electronic screens themselves (LCD) that can turn clear, then totally black very fast. So it syncs to the screen so that when the left frame is shown on the screen, the right eye lens goes black. That way you only see the left frame with your left eye. Then the same happens to the right eye. This happens 120 times per second, and thus you see 3D as you would in real life. And because this is a digital process, you get less crosstalk than with polarized. But crosstalk is still present.

So there you go. I know this post is REALLY long, but its the easiest way to explain 3D in its current format. Don't even get me started on explaining autostereoscopic (3D without glasses). I don't even think I fully understand that tech yet.

And for all the 3D savvy folks reading this, please excuse the info that isn't 100% correct. I was just trying to make it easier to understand.
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post #8 of 13 Old 08-18-2010, 09:20 AM - Thread Starter
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ah, i get it now. so the 2D image you see of a 3D movie at the theatres is not the same as a normal 2D image of a 3D movie. for a 3D movie, the light actually reflects off the screen differently than that of a 2D movie. right?


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Originally Posted by White_Worm View Post

To make it simple, this works by putting a filter on the projector that rotates or flips to make the light travel either horizontal or vertical once reflected off a screen.

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post #9 of 13 Old 08-18-2010, 09:39 AM
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Awesome explanation white_worm! Where is the clapping smiley when you need it!
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post #10 of 13 Old 08-18-2010, 11:55 AM
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Quote:
Originally Posted by velocci View Post

ah, i get it now. so the 2D image you see of a 3D movie at the theatres is not the same as a normal 2D image of a 3D movie. for a 3D movie, the light actually reflects off the screen differently than that of a 2D movie. right?

That is correct, in a very simplified way. So what you're seeing is actually 2 separate 2D images at nearly the same time. This is also the reason that 3D movies in theaters have to use a silver screen (its actually woven with aluminum now). The screen needs to reflect more light than normal, because the normal amount of reflection is lost to the polarized glasses.

Interesting fact: polarized sunglasses work in a similar fashion. When sunlight comes down to earth, the waveform of the light is both horizontal and vertical. When it bounces off a surface such as metal or water, the reflected light becomes mostly vertical. Polarized sunglasses use a special filter that scatters vertical light off, while letting horizontal light in.

I might have the vertical/horizontal switched up, but you get the gist.
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post #11 of 13 Old 08-18-2010, 01:32 PM - Thread Starter
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why do those sunglasses not allow the vertical light through?

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Originally Posted by White_Worm View Post

That is correct, in a very simplified way. So what you're seeing is actually 2 separate 2D images at nearly the same time. This is also the reason that 3D movies in theaters have to use a silver screen (its actually woven with aluminum now). The screen needs to reflect more light than normal, because the normal amount of reflection is lost to the polarized glasses.

Interesting fact: polarized sunglasses work in a similar fashion. When sunlight comes down to earth, the waveform of the light is both horizontal and vertical. When it bounces off a surface such as metal or water, the reflected light becomes mostly vertical. Polarized sunglasses use a special filter that scatters vertical light off, while letting horizontal light in.

I might have the vertical/horizontal switched up, but you get the gist.

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post #12 of 13 Old 08-18-2010, 02:19 PM
 
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Quote:
Originally Posted by velocci View Post

why do those sunglasses not allow the vertical light through?

How Do Polarized Lenses Work? (Sunglasses)

http://www.allaboutvision.com/sunglasses/polarized.htm

And no - you can't use Polarized Sunglasses to watch a 3D movie, nor can you use 3D Polarized Glasses as sunglasses.
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post #13 of 13 Old 08-18-2010, 02:27 PM
 
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velocci:

They do make LCD 3DTVs that use polarized glasses instead of active shutter glasses. This is how they do it. You have to give up 50% of the vertical resolution (1080 becomes 540) to make it work

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