Forum : Advice & Critiques

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Topic: Synth not 360 (not including all photos)?

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larrycl (Over 1 year ago)
Hi, I realize this is a newbie question, but what did I do wrong with this synth?
http://photosynth.net/view.aspx?cid=0b53e081-790f-43b3-8569-5404547e8c55

This was a 360 degree panorama taken from the top of the Key West Lighthouse.  I tried to get overlap between the shots, as well as zooming in on interesting features.

Unfortunately, it was only rendered as 82% synthy, and a bunch of photos were not included in the set.  I'm not sure why; for example, there is a Navy ship in the main set that I would have expected to be easy to match, yet there are a number of photos including this ship that ended up not being included.

Would appreciate it if any of you could take a look and give me some advice for future synths, or perhaps some tips for re-trying this synth (such as throwing out a photo or two) to improve it.
madeeds (Over 1 year ago)
Start by shooting a panorama of the horizon.  You'll need to overlap your photos by at least 66%.  Then go back and add any off-horizon or detail shots.  Make sure that these photos also overlap your original pass by at least 66%.  As a rule, every photo must have some points that it shares with at least 2 other photos.
microwar (Over 1 year ago)
[IMG]http://i31.tinypic.com/n1awye.jpg[/IMG]
I start off with the horisont (black) and then do the rest overlapping at least it will have 3 photos overlapping, middle part will have 6 overlapping ones.

Then you can fill in the details in the image.

Like Dadeeds say. overlapping is very important. Maby not 66%. If you have a Hi res cam. 6-7 mpix ->  20% overlap shoud do it, but then you need 20% from any direction. (20%+20%+20%+20%=80% ??? lool).
OmniSynThesis (Over 1 year ago)
I have come across this problem too. I did try leaving out the non synthesized photos, but sometimes that made it even worse.
I have used my Panasonic Lumix DMC-LX2 with a full 10MB with 16:9 aspect ratio.
I wonder why the needed overlap is that much, a panorama doesn't seem to need that much of an overlap.
Nathanael (Over 1 year ago)
OmniSynThesis, whereas a panorama is just trying to line up the edges of multiple images which are shot from a single point in space (ideally with the camera's lens not even swinging through space, but rather having the camera pivot around the lens) to create a seamless image, Photosynth operates by trying to locate the same set of points from a minimum of three different perspectives, and by examining how they move in relation to each other (parallax), determine the distance between each point.

Holding the camera at arm's length while standing in one place doesn't provide very much parallax, but it's better (for a synth, not a panorama) than holding the camera close to your head and carefully turning in place.
Nathanael (Over 1 year ago)
By shooting with 60% overlap as Matt is instructing, not only will each image overlap each of its neighbours a little, but any image that I am centred on will have its left neighbour overlap its right neighbour. This means that each keypoint that is detected and tracked will appear in at least three different images, and if you are holding your camera at arm's length, then these three different shots will be taken from three different positions.

Even though, shooting a panorama is a good beginning point for a synth (to help all the close-ups know where they fit in relation to each other, most people don't bother to get any farther and really miss out on Photosynth's real capabilities.
Nathanael (Over 1 year ago)
The more parallax that you can give Photosynth, the more accurately it will estimate the distance between image keypoints, so camera motions like circling parts of the scene will provide much more of a point cloud, both because you are focusing on a single part of the scene longer, and because you are demonstrating to Photosynth in more detail how things relate in space to each other.


I should stress that for shooting a real panorama (to stitch together with a program like ICE), you want as little parallax as possible - ideally no parallax for an extremely clean stitch. This means moving the camera's lens as little as possible, using a tripod - ideally a special panorama tripod.

By contrast, shooting for a synth needs as much parallax as you can provide, with essentially no maximum number of useful angles on any single part of the scene, so moving around objects is really important.

Anyhow... I'm beginning to repeat myself, so I'll stop.
Nathanael (Over 1 year ago)
Oh, I should say one last thing though. 

Photosynth can only match images well if objects don't more than double in size in the photo's frame between the two nearest photos of it, so if you want a really far shot and a really close shot, just be sure to get some shots walking from near to far or vice versa.

It's also important to understand that the matching really needs you to take small enough steps when you're moving *around* something. The Photosynth Photography Guide suggests a safe maximum of 25 degrees difference when moving around a surface. 

For more details and tips, the Photography Guide is available here: http://photosynth.net/help.aspx#photosynthhelp

If you like to actually hear people talk about things, rather than read, then here is a video for you.

http://on10.net/blogs/nic/ShutterSpeed-EP04-The-Photosynth-Team/

If you really feel like going down the rabbit hole, click here: http://photosynth.ning.com/video/video/listTagged?tag=Synthing.Process
OmniSynThesis (Over 1 year ago)
Nathanael, you are priceless. Thank you so much for explananing Panorama versus 360 Synth. Now I understand the difference and why my 360 Synths fail; I have used Panorama technique for my 360 Synth experiments.

With your explanation I also got to understand the 'Point Cloud' and why the positioning of my highlights does not match reality on a map projection.

I watched the Photosynth Team video and learned a lot more.

I feel we need your explanation in the manual.
j889 (Over 1 year ago)
I was doing a 360 panorama, and found the best way to do it, was to take a video panorama and then using Virtual Dub turn it into a series of PNGs, delete some frames and then use the remaining images in ICE (or photosynth I guess)
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