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Topic: More photos, less synthy

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normalityrelief (Over 1 year ago)
Recently I've been coming across an interesting phenomenon - I work at a (stage) theater & often carry a small P&S camera to snap as many photos of the main stage space from as many different angles providing as much detail as possible. Every now & then I upload all of the photos I've taken - including shots used in previous synths of the same space - to see how the overall virtual space (I mostly work in point-cloud view) improves as I add more perspectives to the mix. Of the four I've done, these are the results:

SDT Theater-1st
120 photos
97% synthy

Mainstage-01
544 photos
67% synthy

Mainstage-02
623 photos
68% synthy

Mainstage-03
1036 photos
55% synthy

Can anybody explain what's happening here? I plan to continue along this track, but can't seem to figure out why adding more photos make for less synthy ... synths. Remember, every synth includes the same photos from the previous.

Any thoughts??
Nathanael (Over 1 year ago)
Hi there, normalityrelief, 

The synthy score is just a measure of what percentage of your photos Photosynth was able to match to each other, or to quote Nathan Wilfert, °In geek speak: it’s the probability that one can navigate between two photos selected at random, without replacement.°. 

So, in answer to your question of why you are getting lower scores even as you add more groups of photos, the answer is simply that something about the different groups of photos is keeping Photosynth from matching them all together in the same cluster of photos. You should be able to see this when you view the different synths in 2D View (also called Grid Mode). 

As you add more and more photos and the groups do not connect to each other, the percentage of photos that belong to the same point cloud is a lower and lower percentage. 

The real question is what is so different about your batches of photos that they are not matching each other. Stage dressing? Lighting?
Nathanael (Over 1 year ago)
I am only another end user of Photosynth like yourself, but would be glad to take a look at your synths and see if I can find a reason why the photos are not matching each other, if you like, but I will need the links or collection IDs of the synths to look at them.
normalityrelief (Over 1 year ago)
That is some superb geek speak - & that answers my question exactly! Many of the photos most definitely have different stage settings, which I considered, but had hoped would be less significant in the overall outcome. Also I think I was misunderstanding how the synthiness was calculated - it would make perfect sense that adding more photos would decrease the amount the matching engine would be able to match, unless they all were of the exact same setting.

And I'd love to have someone else's perspective, especially considering that I haven't yet been able to find the time to research how synths work nearly as much as I'd like. I had them unlisted, but they're all public now, & I *think* findable here: http://photosynth.net/userprofilepage.aspx?user=normalityrelief&content=Synths

Thanks much for the input man, it's very much appreciated!
dave
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