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.
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.
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