3D or not to 3D?

I remember my first modern 3D movie experience, like most people of my age it was when I saw James Cameron’s Avatar in IMAX. Beforehand, as we entered the cinema to take our seats, my friends and I were all handed what could only be described as Elton John styled giant sunglasses (IMAX, because of the size of the screen, uses glasses with a lens approx 2 inches in size for each eye, so that your entire eye’s view is covered from side to side). The movie started, the 20th Century Fox logo had a slight edge to it that was obviously from the effect, it looked different, but was not as mesmerizing as expected.

The next shot however, a scene set in a large chamber aboard a ship as people awoke from cryosleep chambers, with everyone is floating around weightless, was literally a jaw dropping moment – the image had something that I had never seen in a movie before, visual depth – the large chamber that was meant to look metres long really looked like it went back, the people floating and moving really looked like they were far away from the characters in the foreground, I was dumbstruck by just how much of a difference it made.

At later points in the movie, the jungle scenes where the characters walked had insects flying around that really looked as if they were around them, not just beside them, the jungle vistas had depth and looked as though they went on for miles and miles. Holographic displays used by the characters in a control centre really looked like a proper hologram as opposed to the regular flat image you got for anything similar before.

After being totally blown away, I wanted to know more about how it worked, the glasses (which we had to give back then – before you had to pay for them like the Real 3D systems now widespread in many cinemas) appeared to be normal, nothing special about the lenses, nothing like the gimmicky red and blue 3D glasses of old, how was it that the glasses made this work without any colour distortion? At moments when I had removed the glasses out of curiosity, the image could be made out, but appeared blurry, and switching between the two views gave me no indication as to how this technology worked.

Let’s take a look at this shall we? It all has to do with light, and the way it bounces off of objects or passes through objects due to their shapes. During a 3D projection, there are two projectors projecting different images in sync, passing them through concave and convex lenses, which curve the image slightly. This does not distort the image enough to be noticeable to the naked eye, but distorts it enough that the light that is carrying the images, is curved at opposing angles from each other.

Take a look at the following two images (click to enlarge):

At first glance, the images appear the same, but upon closer examination, there are slight differences between the two, the left image is only meant to be seen by the left eye, and vice versa with the right. Here is the same image, with an arrow showing one measurable difference. In both images, the character of Jake Sully, lying on the shelf, is identical, he is the foreground image. Everything behind him, the background image, is slight different in position, providing the difference in perspective which creates the illusion of depth.

If you look at the screen without the glasses, you see both images simultaneously, which is why you get a blurred image – on certain shots, foreground images will be perfectly clear, as in both images, they are exactly the same – but the background image will appear blurred, this is because the background images are different, and the human brain can’t distinguish between the two images being received through both eyes simultaneously.

One image is sent to your left eye and the other to your right one. How does this work? – this is where the glasses come in, acting as a filter for each eye. Anyone who has a pair of the Real 3D glasses can see this by looking closely at the glasses, hold them at an angle in the light, you will see that the light is reflected differently by each of the two lenses because, like the two projector lenses, one is curved inwards towards the eye, and the other is curved outward away from it.

This allows each eye to receive the separate images, the human brain then just does what it does naturally – it processes both the images as you would see in everyday life. Another simple way to demonstrate this is by closing one eye and picking a spot on a far wall. Hold out your arm and place your thumb in front of it to block it from view. Now close that eye and open the other one, keeping your thumb in place. You will now see your perspective has changed slightly, allowing you to see the spot on the wall with your second eye that the first one could not. 3D Televisions work in a different way, requiring a different type of glasses than those you would wear in a cinema.

To understand how this works, it helps to understand that the human eye can see on average about 18 frames a second. A normal video image usually plays back at a speed of around 24-30 frames per second (depending on broadcast signals in your region). This is what gives the impression of video as being a moving image, it’s not – it’s just that the images are updating faster than your eye can see. Another example of this is a flip book animation, each page being a single frame which when flipped through, appears to move.

If you ever see slow motion in a movie or on TV there are two types, one which will appear more jerky is where normal footage that has been filmed at 24 frames a second, is slowed down to half speed on playback, only playing back 12 frames per second. The other which will appear more fluid is where the camera has been overcranked and filmed at a much higher rate – ie -48 frames a second. When played back at normal speed – 24 frames a second, everything will appear to be moving at half the speed.

What a 3D TV does, is to alternate between the two left and right images, each having 24 frames a second, it will show them both, in all showing 48 frames a second. Again, as this is more than 18 frames which the human eye sees, to look at the TV without glasses you would see a blurry image of the two, ‘shutter’ glasses for 3DTV’s work by blocking the image in time with the TV screen alternating between the two, meaning your left eye only sees the left image, and same with your right.

Work is being done to develop 3DTVs that work without the need of shutter glasses and would work with glasses similar to the cinema versions, but these are still in the development stages.

3D is not for everyone though, for some people it simply will not work  if they only have vision in one eye, or some, due to a brain injury when they were  younger that prevents the brain from receiving both eye inputs simultaneously, such a condition is sometimes called Stereoblindness.

The problem is, that for any movie to work properly in 3D, it has to be framed to do so while filming. The example images from Avatar as shown above works because it was filmed in this way, the problem comes when studios attempt to convert a movie that was shot in 2D to make it appear 3D, often with disappointing or downright distracting effects, the reason is basically, everyone is an expert on 3D even if they don’t know it, since we all see in 3D naturally (apart from those otherwise unable), we know when something doesn’t look right, we may not be able to say exactly what it is, but we know something is wrong with what we’re seeing.

Hollywood is pushing to convert more and more movies from 2D to 3D, with Thor, Green Lantern, and Captain America being released this year after having been converted in post production. Personally I won’t see anything in 3D unless it was filmed in 3D, and even then, unless they have taken measures to ensure the cinematography and framing is designed for it, it won’t hold up. Transformers: Dark of the Moon was filmed using 3D cameras, but ultimately it’s wasted in the movie as there aren’t enough shots that are setup to take advantage of it.

Here’s hoping that 3D either dies a quick death or Hollywood gets their act together and starts figuring out what they’re doing.


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