Originally Posted by Josh Z
What this tells me is that it's possible to have a great amount of offset with little 3D depth. But is the opposite also necessarily true? Can you have great 3D depth with little to no offset?.
The Glasses off test, can be used with certain caveats and is used by stereographers as a rule of thumb way on-location while watching a shot being composed. This is mostly done by stereographers with a lot of experience. Other precise methods include percentage marks either hand-drawn on the preview monitor, or teh monitor itself having them as a feature.
However, as I mentioned there are caveats. One of these caveats is the fact that many of todays movies are "hybrid" ie. a mix of CGI, green screen and live talent.
Using a process called multi-rigging, it's possible to "change" the depth (parallax offeset) of background and foreground independently and then compose for the final shot. This is done to avoid audiences going wall-eyed (eyes having to diverge) to fuse together background imagery that may have excessive (positive) parallax.
So the glasses on-off test in a movie like spiderman may not reveal the true Spatial Depth of a scene if indeed such processes were used.
However, in an un-modified scene, YES you could use the glasses off test to vaildate how much 3D there is overall in a scene
1) if there is much separation in background elements, then you can guess it's got deep 3D
2) if there is much separation in foreground, then you know theres out of screen 3D (as well as window edge violations as seen in the anaglyph image posted above)
in fact anaglyph preview gives more clues as the direction of the red-cyan fringes showing the separation reveals a lot (unless the background is light colored, in which case the color subtraction is reversed...but that's getting a bit too technical)
also, worth mentioning is that you can only tell the final depth of a scene with glasses on. It's the spatial relationship between different elements/layers in a scene that make for good 3D. That...and how the composition of the scene makes the eye travel around this volume.
So yes, in many instances, even though there's not too much separation, a well composed 3D scene is actually hiding in there!Dialog scenes
If you don't see too much separation in dialog scenes, or indeed it looks flat, you can easily see where the point of convergence is set at.
To ease cuts between different angles in a dialog scene, some stereographers/directors will make it easy and just set convergence at the so called point of interest (usually the talents face)
Many reasons are given for this, among them...
a) it's less distracting for the audience to have to make their eyes fuse imagery (we'll do that for you as James Cameron said in avatar)...rather you should be paying attention to the dialog
b) it's easier for cuts to match spatially (e.g reverse angle, over the shoulder shots etc)
There is one con to this (imho) : It's a lazy way to create 3D. It messes with the geography of the room/location where the dialog is taking place.
When your shooting overscan with Epics, a depth budget, a camera blocking script and planning... there's no reason why this practice should be.
Typically live action (sports for instance) is where you would continually converge on area of interest so cuts would be easy and not jarring on the audiences.
Oh BTW, I've not seen spiderman yet. Will do so tomorrow and then relate my experience!
P.s for a review I did on the 3D aspects of Tron, see here
'Think in 3D' now out on Amazon.
twitter: @cly3d.Edited by realvision - 7/7/12 at 3:11am