Forum : Technical Preview

Get all your questions answered about our latest Photosynth Technical Preview.

Topic: Missing Sequence Frames

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KrisClarke (Over 1 year ago)
Hi all, I have just started playing with Photosynth and I am really loving the features of the Tech Preview 3D. I seem to be having a few problems though. I have made several attempts to create walks, but after the processing I seem to be missing some start and end frames, quite a few. I have taken the images with a DSLR, dropped them into the ADD PHOTOS, selected the WALK option and uploaded. Why do these frames disappear in the end sequence. Is there something I am missing (apart from frames)? 

Your help would be very welcome!

NateLawrence (Over 1 year ago)
Hi, Kris, 

Using Photosynth (the 2008 original or the Tech Preview) or other photogrammetry applications, you will often find (especially when you're new to shooting 3D photo collections) that the automated image matching is not always able to connect all the photos.

In the original Photosynth's case, you could switch to 2D view and see all of the photos that you had uploaded and which different groups of photos connected to each other and which ones (if any) hadn't connected to any others.

With the Tech Preview, any photo that isn't connected to the largest group of matched photos simply isn't shown. 

When you're signed into the account you used to upload the photos and look at one of your own synths, you can click the Info icon in the lower left corner of the synth viewer and you will be told how many images out of the total uploaded were used and you can also get hints as to why the images that didn't match failed to be matched.
Joscelin.Trouwborst (Over 1 year ago)
If I recall correctly, there is a note from the PhotosynthTeam somewhere to shoot more densely at beginning and end of walks and walls. I think it was about a smoother viewing experience. Maybe it helps in this respect too.
HGREGG (Over 1 year ago)
I have experienced *exactly* the same thing. Some of the files I tried to upload were rejected because they were 'in a different aspect ratio' - when I looked at the 'rejected' photos (at start and end of a sequence) they were portrait instead of landscape!! I resolved it (in Windows explorer) by rotating all the images clockwise all the files and then anticlockwise. Then they weren't rejected. 

I think it ay be a bug in the uploader. Try checking before you upload, if there are any messages about 'rejected' photos.
NateLawrence (Over 1 year ago)
@HGREGG, the upload screen warning you if your photos have different zoom levels or different aspect ratios isn't what Kris is reporting above, but even if it were, the warning wouldn't stop you from uploading the images.

What Kris is experiencing is something like this. (I'm making up numbers for the example.)
1) Add 50 photos to create a walk from.
2) All 50 photos successfully upload.
3) Photosynth examines all 50 photos for image features, tries to match those features, and does some triangulation to try to determine where each point which has been identified in three or more images is in 3D, relative to other observed points.
4) Some of the images can't be matched to the others (perhaps the first 8 images in filename order, four more sprinkled throughout the group of 34 photos which did match, and the last 4 photos alphanumerically).
5) This results in a synth with 34 images, which may confuse the synth author as to where their other photos are.
NateLawrence (Over 1 year ago)
@Joscelin, it's only Wall synths that I remember the Photosynth team suggesting shooting more photos at the end of, but in any case having more than you need and being able to leave some out is better than getting home and discovering that you didn't shoot enough overlap to link the photos.

Here's the direct quote from: 
1) the Photosynth 2 Expert Shooting Guide: (Page 4: Wall Tips)
"Shoot a few extra photos at each end of the wall (beyond the normal three-view overlap)."

Photosynth Blog Post: 'Capture like a pro (Part 5): Wall tips'
"As well as making sure that each point in the scene appears in at least 3 separate images, shoot a few extra photos at each end of the wall. In other words, have a four- or even five-view overlap for some features near the very beginning and the end of the sequence. This should remove any jerky behavior you may otherwise see at the very beginning and end of walls."
NateLawrence (Over 1 year ago)
Photosynth 2 Frequently Asked Questions #15:
"Shoot a few extra photos at each end of the wall (beyond the normal three-view overlap)."


In general, the same old rules apply as to whether Photosynth will be able to match your images.
:: Make sure you see every point you want reconstructed from a minimum of three different points of view.
:: Make sure you don't move too far toward or away from a subject between any two of three such photos.
:: Make sure you don't move too far around something between any two of three such photos.
:: Make sure that what you're photographing has some visual texture that Photosynth can track (like corners + blobs).

That said, there are a few times when I have uploaded some photos which I thought met these criteria which Photosynth didn't match.

One small spin of mine has all photos match in Photosynth 1 but Photosynth 2 omitted three of the input photos in the middle of the reconstruction.
KrisClarke (Over 1 year ago)
I appreciate all of your comments and suggestions. As a beginner, I have experimented with this tool to find out a solution. It would seem that the omitted frames where due to lower frequency shots on turns and corners. If I shoot more during these movement's, photosynth will include them. It's just coincidence that I was cornering at the start and end of my test walks.

Once again thanks for your help.
HGREGG (Over 1 year ago)
Thanks for all the info Nate - very helpful. Sorry if I confused things for you KrisClarke.
NateLawrence (Over 1 year ago)
@Kris, spot on as far as turning/panning. 

If you look at the Photosynth team's guidelines for Photosynth 2 Panning synths in the video tutorial or shooting guide (or panning within Photosynth 1 synths ) they ask for something like 70% overlap between images when turning, just to ensure that they see image features enough times to get them into the reconstruction. 

Even if you are shooting a Walk synth, rather than a Panning synth, any panning that you do will be well served by handling turns in a Walk with the same care. 

In general, though, the guidance for Walk synths in Photosynth 2 is to not turn in place but to change bearing gradually as you continue to move forward, if you must change directions.

With your aerial synths, I suspect this will solve itself naturally, but keep it in mind if you shoot on the ground in future.
NateLawrence (Over 1 year ago)
@H Gregg, no worries. ツ 

Photosynth 1 didn't mind mixing and matching aspect ratios, but because Photosynth 2 keeps the viewer the same aspect ratio as the input photos, there's too many empty holes around the borders of the photos for a good viewing experience if we switch between landscape and portrait in Photosynth 2.

JPG orientation is an interesting thing to deal with.
Most modern cameras have the ability to record an orientation flag to indicate whether the Top, Bottom, Left, or Right edge of an image is 'Up' but many cameras still store the actual pixels of the image sideways or upside down if that is how the camera was held while taking the photo, and rely on image viewing software to read the orientation flag and display the photo right side up.
NateLawrence (Over 1 year ago)
In cases of software which does not read the orientation flag, you will see the image data as it is actually stored. 
Prior to Windows 8, I don't believe that Windows Explorer did read this orientation flag in the photos' EXIF metadata, so you saw the image as the information was saved.

Photosynth, however, does read this orientation information in order to display photos right side up whose image data may be stored on its side.

In some cases, this may mean that if you took some shots in portrait and some in landscape, even if you haven't rotated them to all be right side up in Windows Explorer's thumbnail view (so they are all technically saved in landscape view and thus the same aspect ratio), Photosynth's upload page will read the orientation metadata and realize that some of them are intended to be viewed in portrait and will likely protest that they are different aspect ratios at that point.

In any case, further discussion probably deserves its own thread. ツ
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