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Nathanael
(Over 1 year ago)
Minimal overlap may be inevitable, but unless I am mistaken there is a parameter in Seadragon's tools to specify the amount of overlap between tiles. Time will tell.
I tell you what. I really do wish that either the synther just had an option that allowed me to have it analyse the original photos as originally provided for image features, rather than all of this cropping nonsense. We've even seen from sneak peeks at the work that the Photosynth team is doing as well as the GRAIL lab at University of Washington, that shows that dense pointclouds are the next step before a mesh can be created and the features (whose estimated positions are what we currenly see represented by the points) can be textured onto the mesh, so we know that Photosynth of the future will certainly afford us more dense pointclouds but it's all a waiting game as of now. This ugly cropping cheat seems to be the only way to get around it for now without knowing|being a programmer.
Nathanael
(Over 1 year ago)
As observed above, the synther seems reluctant to find image features which lie on the edges of tiles. Certainly in my tests I will not (as I did in this synth) have tiles from the same image overlap in the same manner. (Multiple tilesets at the same scale from the same image = a big fat negative for real synthing. We don't want self-verifying, self-sustained features and therefore points from within the same image.) It does, however, make me wonder whether a slight amount of overlap on the edges of each tile within an image's single tileset might be useful.
I am still somewhat uncertain as to how well the individual crops will match any other photo's crops as they will all be automated and therefore cut many things in the photos in half that you would keep together if you were cropping by hand. Will finding half a surface in one tile be enough to match it to the third of same part of that same surface in another photo's tile?
Nathanael
(Over 1 year ago)
Due to Jim's experiment, though, and due to sustained interest by myself and my fellow pointcloud aficionados and fanatics, I plan to try to nail down some good, specific but generally applicable practices for choosing crop sizes, suggestions for programs to batch create tiles for a given set of images etc. during this weekend.
Using the Seadragon team's tools for converting images to Seadragon's Deep Zoom Image format should actually work, as I can specify the tile size and compression quality. Once every image is converted, I'll only need the tiles of the largest (read original) resolution from the image pyramid to combine in the synther with the original images, but that should provide an excellent demonstration of my theory, should all go well.
Nathanael
(Over 1 year ago)
I'm still a firm believer that for more *meaningful* points that actually follow things' correct shape you need more distinct perspectives on things, not the same perspective rotated around in the computer (which has its own problems like the fact that pixels can only be rotated in 90 degree increments without making an absolute mess of them), but I was happy to find something I liked about Jim's rotating.
The cropping idea has been rolling around in my brain since the first week or two that I used Photosynth, but I hadn't ever done much with it except to glue some wide shots and close ups together, even though I knew that it could make the entire pointcloud more dense if you used crops of the correct size(s). The big holdup was mainly due to the fact that I (to this day) don't know what rule the synther uses to decide whether to downsample an image before inspecting it for features... I don't know the magic number that describes that border.
Nathanael
(Over 1 year ago)
Two things were happening at once. Jim was cropping in (allowing the synther to see features it normally wouldn't by using its small versions of the original images) which is good.
He was also making Photosynth keep parts of each image that could only be found in itself. These points, although kept in the pointcloud, would never be properly arranged in 3D, because no depth could be calculated from a single image because nothing moves relative to anything else. This was bad.
I was a bit unhappy to tell him that I didn't think that the rotating could be much use. Then I got to thinking. Couldn't you use that sort of technique on things that are *meant* to be flat? Things like an information plaque, if photographed head on, could be cropped out and the crop rotated all the way around so that its part of the pointcloud would be super dense. It would be flat as that sort of technique will always give, but since the original object was flat there's no problem.
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