[photo-3d] RE: Algorithm wanted

[Kenneth Luker <kluker@xxxxxxxxxxxxxxxx>]

> Bruce Springsteen wrote:
> > I'm looking for the most efficient algorithm - a set of steps - for
> > locating and aligning those vectors in an un-registered pair of images.

1. Find the most distant element that is in both photos (infinity if possible).  Use that point as a common rotation center.

2. Fix one photo in place and put a straightedge on that photo passing through the chosen distant point.  Note the point where the left side of that first photo intersects the straightedge.

3. Put a straightedge on the second photo, passing through the same two points (the rotation center and the same left point as on the first photo's left edge).

4. Compare the points where the straightedges intersect the RIGHT sides of each photo.  The straightedge will, in general, not intersect the right sides at the same point in each photo.  The two points will have some vertical difference in placement with respect to the straightedge.

5.  Rotate the first photo by some small angle and note the new left-side intersection point.  Do the same with the second photo, rotating enough to make the left-side intersection points match again.

6.  Now look at the right side intersection points again. If the two new points are less vertically separated from one another than they were on the first attempt, you rotated in the proper direction.  If they are more greatly separated vertically than before, you rotated in the wrong direction.

7.  Repeat steps 4 through 6 until the straightedge intersects common points at all three places:  left edge, rotation point, and right edge.  You now have eliminated the rotational error and found the direction of camera displacement.  You can trim top and bottom edges parallel to the straightedge.

8.  The rotation point will appear to be further left along the straightedge in one of the photos than in the other.  The photo with the rotation point farthest toward the left is the left view; the other is the right view.  (Both photos may be upside down at this point, since this algorithm doesn't presume that you knew which way was up!  Turn the mounted photos right-side up before you show anyone.)

Ken Luker