On Mon, 14 Sep 1998 19:13:04 +0200, Helmut Dersch wrote:
>Neuman-Ruether wrote:
[snip]
>> Again, we agree on the technicalities, but not on the conclusion...
[snip]

>This is a good basis to start...

>> BUT, as extremely wide angles of coverage are
>> approached (and certainly as one reaches or exceeds 180 degrees), the
>> rectangular image type suffers serious technical problems, and also
>> aesthetically appears to most people to be FAR from an accurate
>> representation of most subjects.

>Agreed. I think the problem with wide angle rectilinear images is due
>to the close viewing distance required to make them look natural:
>This in turn leads to unequal viewing distances of center vs edge,
>which is uncomfortable. And viewing the image from the
>wrong distance (as is usually done) makes them look very unnatural.
>(I have never seen people changing positions during a slide
>presentation...)

>> Here, I think, the curvature of the
>> fisheye view (though it cannot easily be used to recover "reality"
>> when viewed on a flat plane - though it works fine projected into a
>> hemisphere), better represents very wide angle views to most people
>> (since spherical perspective better approximates the familiar [if
>> unrecognized...] characteristics of the eye-view perspective - which,
>> oddly enough, most people incorrectly assume to approximate
>> rectangular perspective). Given two photographs of people and other
>> rounded objects (many near the edge of coverage) of a very wide area
>> of coverage (say, about 120 degrees horizontal...) taken with a
>> rectangular-perspective lens, and another taken with a
>> spherical-perspective lens (both taken from the same "normal"
>> reasonably distant viewpoint), I think most people would find the
>> fisheye rendition of the subject "more natural looking". Given the
>> same conditions, but substituting buildings as subject matter, and the
>> choice could go either way, depending on preference for the lesser of
>> the two ills...;-)

>Agreed, if the two ills are: viewing a flat fisheye image vs
>viewing a rectilinear image with wrong viewing distance. This
>can in fact be easily mathematically quantified: If you take a
>feature from the edge of a fisheye image and the same feature from the edge
>of an ultra-wide angle rectilinear image, then magnify them
>(which corresponds to viewing at the wrong distance), the
>fisheye-feature will match the "real view" more closely.

Well, it seems from the above that all is hunkey-dorey, untill...:

>But I strongly disagree that this has anything to do with
>the "real" eye view perspective whatever that might be. It is simple
>geometry and math, and _any_ viewer will sense this the same way.
>Even if the intermediate image representation in our retina is a
>spherical projection: A flat fisheye image viewed by another fisheye
>lens is no longer a spherical image. So how should we be able
>to recognize it as matching our own genuine projection
>characteristics?

I am mystified...;-) If we are in agreement that we see in a
modified fisheye perspective, that we can observe that perspective
and its characteristics in our own sight, that flat representations
of very wide fields of view are somewhat more naturally rendered at
the edges in fisheye perspective than in rectangular perspective
under normal viewing conditions, then, for me, the conclusions are
VERY obvious and inescapable: fisheye renditions are more
natural-looking (at least over areas limited to those practically
coverable with rectangular-perspective type lenses), and they better
approximate our own vision perspective characteristics!

I find it hard to believe that you, and another correspondent, don't
believe your own eyes...! ;-) (Though it does take a bit of practice
to be able to place one's attention somewhere other than the center
of the visual field, and to spread that attention area wide enough to
see clearly the curvature, but it can be done. Even without this
ability, though, the evidence is crushingly overwhelming regarding the
perspective type of our vision! ;-) I don't understand the resistence
to this realization...!!! ;-)