A good question.
In my opinion, this situation is one thing that limits the accuracy of
the Lens Correction Parameters ("a," "b," "c," etc.) obtained from
automatically created control point pairs.
The the vexing problem is that regions where it is *most* important to
have good values are exactly the same regions where automatic control
point generators place NO points. The problem probably doesn't occur
with lower distortion lenses, but certainly does with circular or full
frame fisheyes.
The way that I have always dealt with this is to manually add a few
control points at the sides, and particularly the corners, of
overlapping images. The manually added points plus the automatically
generated ones can produces very accurate lens parameters -- judged by
the small error numbers during optimization and the complete absence
of any visible stitching errors. But this requires manual
intervention for every single stitch.
I realize that after you have done this once, with a images from a
representative panorama, you will then probably then have a very good
starting point for future stitches. You can save the "lens" (Camera
and Lens tab), then load it for future panoramas, or save a successful
project and use it as a Template for future stitching.
But what I'd really like to see is a control point generator that
could accurately place points for images from fisheye lenses far away
from the image center.
eo
On Jul 2, 2010, at 4:39 PM, pfanous wrote:
I'm using align_image_stack. I notice that the effectiveness of the
alignment is related to how well the corner detection / control point
generation process performs. For certain images, the control point
generation is very limited.
I'm wondering if there's away to increase its effectiveness by some
means. For instance, does it use median filtering to help out the
corner detection process? If so, is there some way to increase the
radius / patch size? How can I modify the delta that it uses as a
threshold to determine if an edge is an edge?
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