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This is the place for Gigapan.com members to offer peer-to-peer support for exchanging tips, ideas, comments, etc.

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Forums » Stitch » Stitcher Errors and Ideas

 
Stitcher Errors and Ideas
bkaylor bkaylor
Total Posts: 29

I would like to see some discussion on a common error: a perfectly aligned row (or column) of photos stitched as a curve or rotated completely out of alignment.

Here’s one scenario: I shot a Dallas city-scape with a fair amount of sky between buildings. My Epic Pro took 462 photos in perfectly aligned rows and columns. All settings were manual, I had a level surface, the grid preview looked beautiful. The stitched result looked like a Picasso. Portions of buildings were turned 45 degrees, the entire top border sagged downward as if it were melting. A frustrating result after the time it took to stitch 4gigapixels.

I examined the errors by stitching small portions of the overall gigapan. I tried stitching the top row of photos by itself (~30 photos). This row was shot perfectly level thanks to the Epic Pro, but always stitched as a wide curve. Where each photo blended there was a vertical jump resulting in a saw-toothed top and bottom border.

Stitching several rows together yielded more strange results, like S-shaped curves. It seems that the Stitcher attempts alignment without regard to the horizontal (or vertical) integrity of each row. This is useful for hand-shot gigapans where photos don’t line up perfectly, but it also seems to ignore the precision and purpose of the Gigapan robotic heads.

I wonder if this could be an advanced option in the stitcher. A checkbox for “Maintain Horizontal (or Vertical) Alignment” in the case of precisely shot rows or columns. This might constrain the Stitcher to place the centerpoint of each photo in a row along the same line. Other options might prevent rotation of an image during alignment since the robotic heads provide identical camera angle in every shot. There is still some correction of lens distortion, but overall rotation may not be necessary.

These are just some thoughts, and of course user error might also be my problem. I would love to hear the developers’ thoughts on the stitching process and the variables involved.

bkaylor

Ron Schott Ron Schott
Total Posts: 89

Which version of GigaPan Stitch are you using? Can you point to the URL of the GigaPan with the problems?

Phil Hotten Phil Hotten
Total Posts: 21

I have a picture that has a part that is always misaligned no matter which version of the software I use http://gigapan.com/snapshots/280693/comments
Not what sure what the problem is though. The pictures are individually perfect, it just does not stitch right.

Paul Heckbert Paul Heckbert
Total Posts: 32

To bkaylor: The older versions of Stitch, e.g. Stitch version 1.0.x, had a “bananapan bug” that would sometimes cause the stitched result to come out curved like an arc or rainbow or banana. Perhaps that was the cause of the “stitched as a wide curve” result you saw, in some tests. That bug was fixed, as far as we know, by Stitch version 2.0, which came out in March 2012. If you share a link to your stitched result, or send a screen shot of your input image grid to customerservice@gigapansystems.com, we could take a closer look at it.

About the alignment algorithm: alignment must strike a balance between assuming regularity of pan and tilt (which usually results when using a GigaPan panohead – unless it gets bumped, or the wind is strong, or objects in the scene move, or …) and aligning image features (finding corners, spots, and other visual features in the images and aligning them). Typically these two goals pull the alignment in the same (correct) direction but occasionally there are near-periodic image features in the scene, such as windows on a skyscraper, or tiles on the roof of the Sydney opera house, that cause our current algorithm to mis-align things.

To Phil Hotten: I think the alignment problem you were suffering was due to the near-periodic (almost-repeating) image features in your input images. I couldn’t tell what version of Stitch you used there. If you have Stitch.Efx, try its Save Projected Images feature, plus Photoshop or similar image editing software, to patch that gigapan by hand.

-Paul
GigaPan Stitch Developer


Forums» Stitch » Stitcher Errors and Ideas