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Topic: Try to Calibrate

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wallace0314 (Over 1 year ago)
Hi, everybody,
 I use photomodeler Calibration Grid to test  photosynth and discover that there is a point in the blank of the four color points.
here is the synth:
http://photosynth.net/view.aspx?cid=47c158c9-f7e0-4bfd-94e9-56fd9a8ae57f
http://photosynth.net/view.aspx?cid=187225da-a9b7-4eb7-9430-828bccb637d9
 Is there someone who can tell me how to explain this kind of situation?
 Thanks a lot!
NateLawrence (Over 1 year ago)
Hi, Wallace,

I believe that Photosynth is treating the white space between each set of four dots as a white blob and then using the surrounding four dots of differing colours (but, more importantly, differing darknesses) in the patch of imagery which it uses to create the signature for that blob. 

I noticed that a few of the colored dots had their own point in the point cloud, but the reason that this is probably less frequent is that the only thing surrounding each coloured dot is pure white which does not make for a good signature at all.
NateLawrence (Over 1 year ago)
I don't know how familiar you are with photogrammetry and computer vision (and I am by no means an expert) but from what I gather from Wikipedia and some videos with Drew Steedly and Blaise Aguera y Arcas of the Photosynth team, gathering image features is a two step process: first detecting interest points - usually by finding corners and blobs - and, secondly, examining a square patch of imagery around that corner|blob to create a numerical signature for which is hopefully invariant to scale, illumination, etc.

Although Photosynth uses its own feature detector developed at Microsoft Research, it does follow in the footsteps of David Lowe's SIFT ( http://en.wikipedia.org/wiki/Scale-invariant_feature_transform , http://www.cs.ubc.ca/~lowe/papers/ijcv04.pdf , http://www.eecs.umich.edu/~silvio/teaching/EECS598/lectures/lecture10_1.pdf ).
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