Re:Errors fixed, thanks for the help!

[P3D Larry Berlin <lberlin@xxxxxxxxx>]

>Date: Wed, 11 Jun 1997
>From: P3D  Adam L. Beckerman  writes:
>
>
>	Greg W. has informed me that I had made a few faux-paux 
>in the stereo of my house (1.  vertical misalignment -- presumably 
>because of the shoot-step-shoot method, and ...........
>................  I'll get the hang of this soon enough...
>

****  You're doing great for starters! You mention misalignment due to the
method of side stepping. All such stereo pairs can suffer several different
types of distortions, and misalignments. It's easy in the computer to fix
vertical alignment, but more difficult to adjust for rotation or distortions
caused by slightly misaligned camera angles.

The best method is to open the image in a graphics program that provides
rulers. Drag the ruler to several obvious points in the image pair and note
ahead of time how much discrepancy exists between each of these places. Of
particular importance is to compare object points in the foreground with
points in the background. If the camera rotates, this is where most of the
changes will occur.

Sometimes the repair is to slide one image up or down a few pixels to
correct the alignment. Other times, one image will actually be slightly
shorter than the other. By carefully selecting most of the shorter image you
can then stretch the image a little bit until test points indicate that it
matches up. If there are still discrepancies (vertical alignment of
features), especially between the background and foreground, it is necessary
to select these specific areas very carefully using a feathered edge
selection area. Then stretch or move the selected areas without affecting
the unselected areas. If you aren't sure what you're doing, make several
copies of your image before you start. That way you can keep playing around
until you're satisfied, and not mess up your original.

I've had to *repair* this type of thing even in slide bar images. It doesn't
take much movement of the camera to cause small amounts of this kind of
problem. They are typical in varying amounts in most hand-held single camera
stereo images, which is why it's considered such a difficult method.

Another thing, it matters how you intend to view the images. Side by sides
are more lax because your eyes can make up for a range of problems, with
varying degrees of headachy side effects. Anaglyphs are more critical
because the images are appreciably in the same space. JPS images for LCS
viewing are even more critical. Similar is probably true of slides intended
for projection.

Bottom line is have fun!  :-)

Larry Berlin

Email: lberlin@xxxxxxxxx
http://www.sonic.net/~lberlin/
http://3dzine.simplenet.com/


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