3D TV - why can't all TV's show 3d films?

[Rob_T]

Disclaimer: I am technically totally ignorant.


Went to the cinema with wife and sprogs at the weekend to see Dispicable Me in 3D which was mildly entertaining.

You get given these glasses to put on. If you don't put them on the screen is a slight blur of overlapping images. When they're on you get 3D. Simples.

So simple question. Why can't broadcasters just broadcast the same 'blurred images to your TV? Put the glasses on and hey presto?

Why can't you buy DVD's with the same blurry images and Robert's your fathers brother?

It surely cannot be that simple, or is it? Have I just uncovered the scam of the decade?

As an example (albeit simple) I've got this app on my iphone for some flight game with '3D mode' which basically produces this blurred image. Put on the 3D specs that came with my son's spiderman comic and it's in 3D.

What point am I missing here?

[Plotloss]

The fact that to display two images you need to transmit two subtley different frames, the glasses then decode the overlay and create the 3D image.

You can do 3D on a 2D set like you have been able to do for the last 20 years by using the filtered glasses.

[Rob_T]

but surely the image is the image. so you're not transmitting multiple images, it's just one... this is my whole problem. you can transmit anything. and even if transmission is a problem, why can't you simply buy a 3d DVD of eg Dispicable Me and watch it in glorious 3D on a standard set? The image is the image is the image so to speak!

[mrmr96]

Rob_T said:

Question about 3D in the cinema.

Two things at play here:
1. Stereoscopic vision.
2. Polarising light.

I will explain both!
1. Stereoscopic vision.
This means that each eye sees a slightly different image of the world, because they are a few inches appart. So when something is nearby your eyes have to converge to look at it (eg looking at the tip of your nose causes you to go 'cross eyed'.) When things are far appart your eyes diverge (relativly) and are looking almost parrallel as you look at the horizon. Your brain can measure the divergence/convergence of different parts of the image and work out the distance. (You also use focal distance and scale to judge distance, but that's not how 3D screens work.)

So to see in 3D you need a different image for each eye, with each object slightly offset the correct amount to take account of your eye viewing it from a slightly different angle. Film makers create the two images using 3D cameras (with 2 lenses and two sensors) or using computer animation where a scene is 'rendered' using a virtual camera, and then again using the virtual camera in a slightly different position.

Next is the question of how to get one image to each eye correctly, the cinema uses polarised light:

2. Polarising light.

Light waves vibrate in different planes. Unpolarized light vibrates in all planes.

You can polarize light by passing it though a very narrow slot, so that all the light is blocked, appart from the bit vibrating in the same direction as the slot, generally either 'up and down' or 'side to side'. You can make a polarising filter using a 'comb' of slots very close together. This means all the light passing through is going in the same direction (up/down or side to side).

If the light meets another filter in the same orientation, it will pass through. If it meets a filter at 90 degrees (i.e. up down light hitting a side to side filter) then it is blocked as it can't fit through the slots.

At the cinema they have two projectors, each showing an image desgined for only one eye. Each projector has a polarised filter on it, one set at 'up down' the other turned 90 degrees to side to side. It means that the light destined for each eye is polarised differently. The glasses you wear also have a polarising filter, one eye up down, the other side side. The light for the 'correct' eye passes through the glasses. The light for the 'wrong eye' is blocked by the glasses. Hence each eye sees only one of the two images with the glasses on, but with the glasses off you see both.

3D TV's use a host of different technologies, one prolific type being shutter type. In this case the TV shows the 'left eye' and 'right eye' images on the same screen in quick succession and the glasses you wear are electric and have a shutter that blocks and opens each eye at the right time, so each eye only sees the right image. It happens really fast so you don't notice it.

Edited by mrmr96 on Monday 1st November 15:18

[Plotloss]

No because it's stereoscopic 3D, two images are being transmitted at once.

The HDMI cable carries two images up it etc etc.

[mrmr96]

Rob_T said:

but surely the image is the image. so you're not transmitting multiple images, it's just one...

Incorrect. At the cinema there are two images from separate projectors, one polarised 'up down' the other 'side side'. Without the glasses you can see both. With the glasses you can only see one with each eye. Each image is slightly different and must be delivered to the correct eye in order for your brain to combine them into one and create the illusion of 3D.

[Rob_T]

mrmr96 said:

Rob_T said:

but surely the image is the image. so you're not transmitting multiple images, it's just one...

Incorrect. At the cinema there are two images from separate projectors, one polarised 'up down' the other 'side side'. Without the glasses you can see both. With the glasses you can only see one with each eye. Each image is slightly different and must be delivered to the correct eye in order for your brain to combine them into one and create the illusion of 3D.

ok, thank you, but answer me this.

if i were to take a sophistacted video camera into the cinema, set it up on a tripod etc etc and record the image displayed on the cinema screen. let us assume the quality of the recording is perfect. why can i not then play back my recording on my tv at home, put the 3d glasses on and have the exact same effect?

[Blue Meanie]

I presume by recording it you lose any of the polarity qualities.

[mrmr96]

Rob_T said:

mrmr96 said:

Rob_T said:

but surely the image is the image. so you're not transmitting multiple images, it's just one...

Incorrect. At the cinema there are two images from separate projectors, one polarised 'up down' the other 'side side'. Without the glasses you can see both. With the glasses you can only see one with each eye. Each image is slightly different and must be delivered to the correct eye in order for your brain to combine them into one and create the illusion of 3D.

ok, thank you, but answer me this.

if i were to take a sophistacted video camera into the cinema, set it up on a tripod etc etc and record the image displayed on the cinema screen. let us assume the quality of the recording is perfect. why can i not then play back my recording on my tv at home, put the 3d glasses on and have the exact same effect?

As said above you will lose the polarisation of the light. The camera will only pick up frequency mix (hue and saturation) and intensity (brightness). The TV you play it out from will not polarise the light. You would see on your TV effectively the exact same as in the cinema when not wearing glasses, i.e. both images overlapping. Because the light from the TV isn't polarised the glasses won't 'work' because they will both let through the same light - i.e. that blurred image.

Short answer is: When you put the glasses on in front of your TV you would still see the two images overlapped, just as when you looked at the screen in the cinema without any glasses at all, because there is nothing about the light from the TV which distinguishes the image destined for the left eye from the one destined for the right eye. (i.e. they are both made of unpolarised light.)

Edited by mrmr96 on Monday 1st November 16:04

[paulrockliffe]

There are a few different technologies around, but the one you refer to where you have two slightly different pictures alternating on each refresh could work in theory with any TV. The problem is that the glasses need to be synchronised with the tv's refresh. I'd imagine that is something that could be done though, if there was a solid business case for it.

[noodleman]

mrmr96 said:

Rob_T said:

Question about 3D in the cinema.

Two things at play here:
1. Stereoscopic vision.
2. Polarising light.

I will explain both!
1. Stereoscopic vision.
This means that each eye sees a slightly different image of the world, because they are a few inches appart. So when something is nearby your eyes have to converge to look at it (eg looking at the tip of your nose causes you to go 'cross eyed'.) When things are far appart your eyes diverge (relativly) and are looking almost parrallel as you look at the horizon. Your brain can measure the divergence/convergence of different parts of the image and work out the distance. (You also use focal distance and scale to judge distance, but that's not how 3D screens work.)

So to see in 3D you need a different image for each eye, with each object slightly offset the correct amount to take account of your eye viewing it from a slightly different angle. Film makers create the two images using 3D cameras (with 2 lenses and two sensors) or using computer animation where a scene is 'rendered' using a virtual camera, and then again using the virtual camera in a slightly different position.

Next is the question of how to get one image to each eye correctly, the cinema uses polarised light:

2. Polarising light.

Light waves vibrate in different planes. Unpolarized light vibrates in all planes.

You can polarize light by passing it though a very narrow slot, so that all the light is blocked, appart from the bit vibrating in the same direction as the slot, generally either 'up and down' or 'side to side'. You can make a polarising filter using a 'comb' of slots very close together. This means all the light passing through is going in the same direction (up/down or side to side).

If the light meets another filter in the same orientation, it will pass through. If it meets a filter at 90 degrees (i.e. up down light hitting a side to side filter) then it is blocked as it can't fit through the slots.

At the cinema they have two projectors, each showing an image desgined for only one eye. Each projector has a polarised filter on it, one set at 'up down' the other turned 90 degrees to side to side. It means that the light destined for each eye is polarised differently. The glasses you wear also have a polarising filter, one eye up down, the other side side. The light for the 'correct' eye passes through the glasses. The light for the 'wrong eye' is blocked by the glasses. Hence each eye sees only one of the two images with the glasses on, but with the glasses off you see both.

3D TV's use a host of different technologies, one prolific type being shutter type. In this case the TV shows the 'left eye' and 'right eye' images on the same screen in quick succession and the glasses you wear are electric and have a shutter that blocks and opens each eye at the right time, so each eye only sees the right image. It happens really fast so you don't notice it.

Edited by mrmr96 on Monday 1st November 15:18

Thanks. That's a nice explanation of polarised light.

[MaximumJed]

paulrockliffe said:

There are a few different technologies around, but the one you refer to where you have two slightly different pictures alternating on each refresh could work in theory with any TV. The problem is that the glasses need to be synchronised with the tv's refresh. I'd imagine that is something that could be done though, if there was a solid business case for it.

Agreed, I was discussing this recently and I think a box that interrupts the HDMI signal and provides the sync for the glasses can't be that difficult a piece of tech seeing as it is effectively already built into most 3D TVs. It would need some way to calibrate the lag between it and the screen rendering, but someone clever could work that part out surely? Then all you need is a 120Hz or better screen, a box and some glasses.

[bholleran]

MaximumJed said:

paulrockliffe said:

There are a few different technologies around, but the one you refer to where you have two slightly different pictures alternating on each refresh could work in theory with any TV. The problem is that the glasses need to be synchronised with the tv's refresh. I'd imagine that is something that could be done though, if there was a solid business case for it.

Agreed, I was discussing this recently and I think a box that interrupts the HDMI signal and provides the sync for the glasses can't be that difficult a piece of tech seeing as it is effectively already built into most 3D TVs. It would need some way to calibrate the lag between it and the screen rendering, but someone clever could work that part out surely? Then all you need is a 120Hz or better screen, a box and some glasses.

They are due to release this for projectors, so it should also be possible for TV's (This might even do it)

http://www.optomaeurope.com/projectordetailshccs.a...