Re: Converging lenses (was: Window reversal); D|s-TortiO|\|s

[P3D Andrew Woods <andrew@xxxxxxxxxxxxxxxxxxxxx>]

Ivester, Paul  <ivestep@xxxxxxxxxxx> wrote:
> 
> What's all this I hear about Keystone distortion?
> 
> I looked through my pile of Keystone Views and didn't see
> any noticeable distortion at all.
> 

The two "keystones" are not related.

An image illustrating keystone distortion is on my web site.
  
To download just the image:  http://info.curtin.edu.au/~iwoodsa/keyston.gif

The effect is described in at paper titled "Image Distortions in
Stereoscopic Video Systems"
  http://info.curtin.edu.au/~iwoodsa/spie93pa.html

The text from that paper relevant to keystone distortion is as follows:

from "Image Distortions in Stereoscopic Video Systems"
> 2.5 Keystone distortion
> 
> A well know effect of the toed-in camera configuration is keystone
> distortion. Keystone distortion causes vertical parallax in the
> stereoscopic image due to the imaging sensors of the two cameras
> being located in different planes. The effect of keystone distortion
> upon the display of a grid located at the camera convergence
> distance is shown in Figure 8. In one of the cameras, the image of the 
> grid appears larger at one side than the other. In the other camera, this
> effect is reversed. This results in a vertical difference between
> homologous points which is called vertical parallax. The amount of
> vertical parallax is greatest in the corners of the image and increases
> with increased camera separation, decreased convergence distance
> and decreased focal length. In this example, a lens with a focal
> length of 3.5mm (C=1m and t=75mm) would exhibit vertical parallax
> of 8.2mm in the corner of the screen on a 16" diagonal monitor. It
> can also be seen from this diagram that horizontal parallax is also
> induced. This is the source of the depth plane curvature mentioned
> earlier. The parallel camera configuration does not exhibit keystone
> distortion.

Cheers,
Andrew.

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|  Andrew Woods   | Centre for Marine Science and Technology,      |
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