

Microsoft's Photosynth Makes Photos a 3D Experience - Anon84
http://www.pcworld.com/article/150100/must_see_microsofts_photosynth_makes_photos_a_3d_experience.html

======
dats
The really impressive thing about Photosynth is how far it has come in the
last year. It used to take hours to weeks to create synths from hundreds of
pictures. The processing time is dominated by

1\. Keypoint detection (SIFT or a similar algorithm)

2\. Keypoint matching for each pair of images with approximate nearest
neighbor (ANN) search on kd-trees

3\. Structure from motion to recover rotation and the relative location of
photos

~~~
apu
Any details available on how they're speeding up each of these steps? The only
research publications I see are the original work and the new 'finding paths'
paper presented last week at Siggraph.

~~~
dats
Yeah, the papers only discuss how they combine known algorithms[1]. They could
be speeding up the process using any combination of these:

1\. Using the order of the images to reduce matching from O(N^2) to something
closer to O(N) since people are more likely to take pictures sequentially
instead of randomly. I'm going to run some tests next time I boot into
Windows.

2\. Running keypoint detection as the images are uploaded and potentially
slowing down the upload speed to make it appear more seamless.

3\. New keypoint detection algorithm for constant-time speedup. SURF, for
instance, is about 5x faster than SIFT.

4\. Using GPUs. The keypoint detection and matching steps are perfect for
running on parallel GPUs. A couple recent papers showed 10-15x speedup for
keypoint detection and KD-tree construction and search on GPUs, compared to
similarly priced CPUs.

Any other ideas?

[1] There's also a new paper called _Skeletal graphs for efficient structure
from motion_ that discusses a neat graph algorithm for the SfM step.

------
azharcs
Great work by Microsoft, has to be one of the very good products of 2008.

------
azharcs
More details on Research of Photosynth
<http://phototour.cs.washington.edu/findingpaths/>

------
cglee
Of course, Windows only...

~~~
gasull
Photosynth is a website, not a desktop app.

~~~
dats
I think he means that it's a (Windows) plugin for your browser. Both the
picture uploader and the viewer are Windows-only for now.

------
username2
Videosynth...

