P3D Re: Parallax tech

[Andrew Woods <andrew@xxxxxxxxxxxxxxxxxxxxx>]

Larry Berlin <lberlin@xxxxxxxxx> wrote:
> We talk about parallax in stereo images all the time, as well as a
> number of related phenomena, yet I'm unaware if there is an official
> unit of measurement for parallax in stereoscopic images?

Unfortunately, very little is officially standardised in stereoscopic imaging -
including terminology.  There are generally accepted usages of most terms
however there are sometimes exceptions and ambiguities.  This is one of the
aspects we'd like to address in the standards forum we're organising at the
forthcoming Stereoscopic Displays & Applications conference (Jan 24-26, 2000,
San Jose, CA.  http://www.stereoscopic.org  ).

BTW: I just read in Stereo World this morning, the York 2000 stereo convention's
claim to be the first stereo convention of 2000.  I guess they didn't know about
the Stereoscopic Displays & Applications conference...  ;-)

With regards to the term "parallax", I commonly use the term "Screen Parallax"
to mean the linear distance between homologous points on the screen surface
(measured in mm, cm, or inches if you prefer).  I know this doesn't apply
very well to hand held viewers or HMDs but that's a limitation of this term.

The term "disparity" is also commonly used but in my experience it is not well
defined.  It is usually expressed as an angle but I have seen it expressed as:
(a) the angle subtended by one homologous point, the midpoint between the
    observer's eyes and the other homologous point, or
(b) the angle subtended by one of the observer's eyes, the virtual image
    location of a selected stereoscopic image point, and the other eye
    of the observer.
(i.e. one measures the angle at the eyes and the other measures the angle
      in space).

Hopefully the standards forum will get the ball rolling on getting some
useful standards defined.

Cheers,
Andrew Woods.

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