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Cake Monster - How to find the reasons for Zephyr rejecting images?

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  • Cake Monster - How to find the reasons for Zephyr rejecting images?

    I took these before using Zephyr, and sadly the Monster is no more.

    http://untamed.co.uk/miscImages/cakeMonster.zip

    There's 19 images - of which none were useable!
    I've been left guessing what's wrong, and was looking for some log files or something?

    They were taken with a Samsung S7 phone, so the barrel / pin-cushioning may be an issue.
    The backgrounds are blurred - and I know Zephy uses them for accurate angle detection.

    So I masked the cake in all the images - and used these masked cakes instead.
    This upped the included images to 3 or 4 useable ones, but all showing the same bit of cake...


    They're highish res, and they look in focus - for the most part.
    Would this program here be useable in Zephy? : https://www.3dflow.net/camera-calibr...ased-for-free/
    (EDIT:: Ah, calibrations in the program now, those links are dead.)

    What have I missed?

    Many thanks for any help you can spare! I need it. =)
    Last edited by SarahC; 2018-03-19, 10:17 AM.

  • #2
    Hi Sarah,

    it looks like you post processed your data somehow - this should be avoided for a whole lot of reasons, including, but not only, the fact that all the exif data have been removed. This does not allow zephyr to check if there is a pre-calibration for your camera, as it does not know which camera has been used. This is usually not a problem, as zephyr is autocalibrated, but you need enough images of a well textured subject for that. You can try running a calibration with lapyx, which is now included in zephyr with the same phone and then use that calibration for your dataset.

    Your subject is not very textured and there isn't a lot of overlap so that's another thing that makes this reconstruction very challenging.

    Next time you may also try to put a newspaper under the subject if you don't want to do a full 360° reconstruction, as it will at least help in the SfM phase. Try also to take sharper images if possible a good idea for quick capture using a phone is also to shoot a movie (here is a great tutorial by 3dscanexpert.com https://3dscanexpert.com/free-3d-sca...eo-smartphone/ )

    In short:

    - bake a new cake monster
    - take more pictures if possible, and try keeping more overlap between the images
    - do not edit your pictures in photoshop or other 3rd party software

    hope this helps!

    Comment


    • SarahC
      SarahC commented
      Editing a comment
      Hi Andrea!

      Thank you!
      More cake will be in my future, I'm sure.

      Your advice has helped greatly! I've been practicing with lots of pictures of my keyring on various surfaces, small aperture, background where possible, and with good illumination.

      I see that with the program giving me the ability to chop some of the polygons out of the surface - I don't even need a blank table for it to go on.

      Thinking back - That photoset was made for a "Carve voxels using shapes silhouette" process of an old program. Which ironically appears to be the exact opposite of what works well with Zephyr (which loves the detail to get the angles from the SIFT and RANSAC process?).

      I've been looking through the video's 3DF's posted about making good images too - lots of good tips there.



      One little last question, more of a "What do you think this could be"? My keyring - I get bad results with extreme closeups, most pictures get rejected.

      I'm guessing the backgrounds too blurry? My phone camera doesn't let the aperture be changed. Or the pixel size is too small on the phone?

      I've got a 7D Mark 2 to try properly this weekend. I'll stick it on manual white balance, an aperture of f 36 with a proper static lighting setup, ISO 100, handheld but with a shutter of about 1/90, and image stabilizing.

      Is there anything I should take into account for extreme closeups? For example a small money pile covering most of the camera frame, where there wont be much distant background (which I guess is used for accurate angle calculations?)

  • #3
    HI Sarah,

    fun fact, in the Pro/Aerial version we also have a shape from silhouette algorithm, but it's mostly used for completely transparent subjects (i.e. a bottle of water)

    SIFT is a specific algorithm that some other competitors use, but we don't. All our technology is proprietary and in-house built, but of course there are some some similarities

    It's hard to tell without seeing the images, but i guess your kerying is very uniform? Uniform colors are hard. Anyways, if you're doing extreme closeup, the difficulty lays in having sharp images.

    if you have questions feel free to ask!

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