P3D Re: 3D realism and focus cues

[roberts@xxxxxxxxxxxxxxxxx (John W Roberts)]

>Date: Mon, 19 Jan 1998 12:12:49 -0700
>From: michaelk@xxxxxxxxxxxxxxxxxx (Michael Kersenbrock)
>Subject: P3D Re: 3D realism and focus cues

>> If all scenes are bright-sunlight scenes, and if everything is kept pretty far
>> away from the camera, then assuming no change in focus with distance is a
>> pretty good approximation. But those conditions do not always hold.

>But if true, then the situation of everything being simultaneously in focus 
>is a "natural" and therefore acceptable thing for a stereo photograph
>to have, 

To make an analogy, I could say that most birds fly, and a bird is a kind of
animal, so a flying animal is a natural and acceptable thing for a stereo
photograph to have. But since pigs don't fly, a stereo photograph of a flock
of durocs flying in a graceful "V" formation will still look somewhat odd.
(Come to think of it, even a photo of a duck hovering in midair as it sips
nectar from a flower won't look quite right. :-) *Some* animals fly, and
similarly everything being simultaneously in focus is a natural thing for 
*some* stereo photographs to have. 

>and therefore defocussing where one isn't looking shouldn't
>necessarily be an improvement, even for particular stereo photographs
>where one's eye would be defocussed in the not-looked at areas.

I'm not prepared to agree with that, without considerable further evidence.
Decoupling of convergence and accommodation (and changes in focus of specifie
objects with changes in convergence) in stereo photographs is admittedly
more subtle than pigs versus birds, but it's still significant enough to be
one of the safety concerns for VR systems. For certain kinds of 3D photos,
it's one area in which stereo photos depart from accurate depiction of a
real scene.

That doesn't mean we should all throw out our stereo cameras, but I don't
think we should dismiss it as a possible area for future improvement.

John R


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