A 2d commercials director in the world of stereo 3d.

As my training continues I seem to understand less and less...
There is so much in Stereoscopy that seems to be counter intuitive when you have spent the last 20 years working in 2d. So far my position on the interocular is that you should approach each job differently.
I have read conflicting articles and been given conflicting advice, and I realise that the distance between the cameras is critical to the amount of '3dness' on the shot and how much of the shot will be usable or rather 'fuse-able'.
This is my take on I-O or if you prefer I-A so far... I'm not saying it is right - it just what I have learned so far.
Don't Shoot The Messenger.
The average distance between the human eyes is 64mm (2.5 inches for those that still use imperial). If you hold a coffee cup up in front of you at arms length and concentrate on the cup. You can see the front and a little of each side of the cup. If you could have a drink of some magic potion that would make you grow into a giant - say 12 feet tall - double your size in all dimensions you would hold that cup in front of you and be able to see that little bit more around each side of the cup. So if you shoot with your cameras say 130mm (5 inches) apart then you are replicating the view of that 'giant' person. Which means that the cup will look small, half the size. Or put another way, from the perspective of the cameras the cup has shrunk... So when you show these images in 3d the amount of 'depth' in the picture of the cup would indicate to your brain that you have turned into a giant, or more reasonably this is a smaller cup than 'normal' because you can see as much of the cup as you would have, had it been half the size! Stay with me, I did some tests and am happy to email them over... reg@shoot3d.tv. I bought 2 identical cups - one large and one small and took some very accurate still photos (based on the above) and compared the results - then I made 3d photos and showed them to a group of friends - there were no size cues in the pictures - just the stereo photo's of the cups. Without fail I could 'make' the big cup look smaller in 3d by using a larger interocular IO than is natural. So the 'Hyper Stereo' stuff that you may have read or come across is REAL. Then I found out that some of my sample viewers have enhanced 'stereo-acuity' (ability to judge / perceive 'depth' - relative size and geometry - based on interpretation of vertical disparities).
Now - where does this lead me. If you have seen any of the Sky TV 3d coverage of the UK football (Soccer) matches in 3d then those of you with high stereo-acuity may have found the 3dness a bit strange - and giving you the sensation that you were watching 'miniature' sized men running round a field! This is because some of the cameras had quite a large interocular. The view is generally that you can 'get away' with this in sport.

Here's a thought...
If you were shooting a commercial in stereo 3d, you have 2 guys, one with an aftershave product that is supposed to make him more attractive to the girls, then you might make him slightly 'larger' (hypostereo) by moving the cameras closer than the human IO (say by 10mm) and shoot the other guy in your commercial who is the 'loser' wearing the 'nobrand' aftershave - well, you could shoot him with a slightly larger I-O`(hyperstereo), again say 10mm - this might psychologically give an advantage to the 'hero'. I'll try it out and let you know if I get a script in for a 3d commercial.

Biology + Psychology + Technology = 3d

The eyes are NOT film cameras. So stop trying to 'think' like a camera when you are trying to visualize a shot or a frame or a scene... This is the first major hurdle when you are a 'died in the wool' time-served 2d director such as me. 13 years in London, 2 years in the States, 6 months in Belfast, 6 months in Cardiff, 4 years in Manchester. That all adds up to 20 years of years 'thinking in 2d'!
To create good watchable stereo 3d that doesn't pull your eyeballs out of their sockets, you cannot rely solely on the Technology. You have to begin with 'how we see' and how the brain uses 'what we see' and combines that information with a whole load of other factors before you even get a camera out of the case...
At this point in the blog I should bring into the frame my new best friends. Dr Bernie Harper and Rob Black. They are from Liverpool University Psychology Dept and they eat, sleep, drink, walk, talk, 3d! They think and communicate only in 3d! It took some adjustment from them to be able to talk to a numpty director like me and start to explain and unravel some of the complexities of stereo 3d. Dr Harper (Bernie to his friends) has been 'doing' 3d research for 10 years and knows more about 3d than is good for the mortal man... Rob Black on the other hand is a Perception Specialist / Consultant and he can show you things in 1d, 2d and 3d that you never knew existed! So Liverpool University, has a world renowned psychology dept. and I would have access to some of their greatest minds to help me learn about 3d. I was psyched
Who was it that said? : "I could teach you everything there is to know about 3d in an afternoon, but it would take you a lifetime to understand it." Sorry if that is a bad quote, but it make the point. It is such a complex area that if you fancy having a go then good luck. Throw yourelf into it and prepare to fail! And understand you cannot 'fix it in post' - It doesn't work like that!

What is Native Screen Pixel Parallax? NPP

What is Native Pixel Parallax?
Well, put simply - this is the concept that by basically using some maths, you can calculate 'what works' in pixels on your screen.
Explanation: When we shoot 3d with two cameras, it is the vertical disparities (the differences) between left and right camera that the brain 'sees' and then tries to 'fuse' the images and create an artificial state of mind that makes us 'see' depth or '3d'. So the distances between those cameras should be equivalent to or near to the natural 'interocular' which is about 65mm. (2 and a half inches in old money...). If the disparities are too much then it gives you a headache and makes watching a 3d sequence a very uncomfortable experience, in some cases if the disparities are too extreme it will mean there is no picture for the brain to fuse and it just shuts down any attempt to 'fuse' for depth.
Now here is the problem, if you shoot your 3d footage and for whatever reason you have had to shoot at a larger than 65mm interaxial, you may well end up with some stereo footage that 'works' on a small computer screen, but will not work on a large 3dhd plasma - or possibly, you may have a sequence that works on a 46" 3dhd plasma - and equally it won't work on a 30 foot cinema screen.
So some of the world's Stereographers have come up with a plan. They have come up with a numeric chart of 3d 'depth' that allows for average screen sizes and average distances from the screen. Obviously this isn't a perfect science, but it's a start... (Note to reader: It's quite hard 'blogging' about stereo 3d production, because not all the experts agree on certain principles... They all seem to have a different viewpoint to the same problems. So my position is try and be polite and take on board everyone's views and then when I am in the position of filming use the different advice as required....)
So here are some of the maths involved. You decide.
A 30 foot cinema screen = 360 inches (30 x 12inches) Human interocular = 2.5 inches
2.5 as a percentage of 360 = 0.7 percent - Now take that as a percentage of the resolution (2K)
then you end up with 14pixels. So any disparities larger than 14 pixels would represent an unnatural disparity which we have trouble fusing...(Based on 2k resolution on a 30 foot wide cinema screen)
Now try a 46" plasma. Width is less than 46" (The manufacturers get that measurement by measuring diagonally corner to corner of the screen) The width is about 40 inches so if we do the same thing and take
2.5" as a percent of 40" we end up with roughly 6 percent. If the Pixel resolution of the screen is 1920 x 1080
then 6 percent of 1920 should give you about 115 pixels. So theoretically you shouldn't go over 115 pixels on a 46" screen.
Simples?
When we look at 'Infinity' our eyes are parallel and anything we see across the depths will have 2.5" disparity.
The thing is when you 'scale' an image down (less than life size) to fit onto the 46" screen, then surely the disparities would be scaled down, or we are 'seeing' something totally unnatural?
If we only ever filmed Ortho stereoscopically (all measurements = real life) and then we only ever viewed our material back at life size on a large cinema screen - everything would be fine. A 6 foot man would be 6 foot tall and the disparities would be the same as real life - nothing over 2.5".
In reality we have to shoot for a range of different screen sizes - therein lie the problems. My conclusion is that whatever size screen you are shooting for always try and get the cameras as close to a natural condition as possible. If you are 'over' or 'under' the magic 2.5" then some post production can correct some a percentage of error.
Finally, you may deliberately shoot over or under for a special effect! But try not to blow the viewers mind! I am learning by trial and error. Everyday I shoot some more stuff and then work it out.