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Author Topic: How to capture photos for a piece of kelp?  (Read 2757 times)

VeloSteve

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How to capture photos for a piece of kelp?
« on: April 22, 2017, 05:01:44 AM »
Here's what I tried:
1) Since the kelp is flexible I hung it from the central shaft of a tripod so it could be rotated.
2) Placed my Canon 5D III with 100mm lens on another tripod
3) Arranged for the background to be a plain wall, out of focus.
4) Added some extra lighting (just household stuff)
5) Took 20 shots at fairly evenly spaced angles by rotating the shaft of the first tripod.
6) Added photos and worked down the Workflow menu.
7) A few "cameras" were "NA"

I got a model, but the software thought the camera hardly moved, so the shape was all wrong.

Next:
1) Read a tutorial
2) Removed half the photos because I just want to see if this works before spending hours.
3) Masked the remaining photos as the tutorial said.
4) Aligned photos again.

Now all but 3 cameras are NA and the model is worse.

What I did not do:
1) Add some sort of scale or markers to the sample (suggestions?)
2) Shoot from high and low angles.

Are those the best two things to try next?  Is my subject just too complicated and lacking in color contrast?  Other ideas?

Is having fixed lighting with a rotating subject a problem?  It seems that the results could be very different than having the camera itself rotate.

I'm attaching a picture to show what this thing looks like.  I downsized it here, but of course I worked with the original size in PhotoScan.

Thanks!

gary9000

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Re: How to capture photos for a piece of kelp?
« Reply #1 on: May 09, 2017, 12:16:19 PM »
Caution: Long post, more to clarify my own thoughts that applying directly to your kelp problem, and I'm really tired so please excuse any typos.

   I'm completely new to this too (just got the demo to make a decent mesh *today*), and I'm having a similar problem.

   I put a small bust on a turntable and shot a series of photos. Photoscan interpreted the camera positions as being all piled up and the result was not even vaguely related to the original object. Tried several times, all fails.

   Conclusion: Need to learn more about suitable photography, need an object with more obvious surface points for the software to match.

   Action: Watched a few tutorials. Need flatter lighting, more obvious details for the software to match up.

   Today I went outside and shot a number of small areas in open shade according to the instructions. Loaded them in and the cameras/viewpoints dispersed properly, and the result from several was a pretty decent rendition of the area, including the uncolored mesh. Not terrible for ten photos.

   Conclusion: Yes, I need to work on understanding how to produce photos acceptable to the software.

   Action: Loaded up the several other image sets and produced reasonable meshes considering the small number of photos. Conclusion verified.

   Loaded up a short run of images made on a turntable shortly after the first one. While there were some apparently excessively smooth/featureless areas, and the actual mesh had a low accuracy-of-feature level, the software did actually disperse the cameras properly and only meshed the areas that had sufficient details to match between images.

   Conclusion: Supports other conclusions. Increase resolution/polygon settings.

   I took a small painted figurine and set up the tripod, turning the figurine slightly between shots. Software stacked many of the cameras and had a difficult time matching the surface points, but I *did* end up with a gummy-looking side of the object. It's really bad, but it's quite a bit better than what I had *yesterday*.

   Conclusion: Need to take sharper macro photos, need to use a method for eliminating the background, support structures, and etc.

   Action: I'll have to make some things for that. Need a black or green screen background to make masking fast, and softbox style lighting - or a thing with which to swing the camera around in an orbit. Large white areas are a problem.

   To get to your kelp problem, is the kelp shiny? That's a bad thing, can you dull it up with talc/cornstarch/ nondairy creamer/flour/dry deoderant spray (an old standby for photographing shiny spoons), or something else?. Is there other stuff in the image that doesn't move while the kelp does? That seems to be one of the sources of camera piling, at least in my case.

   There's things in some of the tutorials about using a plain background shot as a semi-auto mask.

   It seems like the lack of contrast you mentioned might also be a problem, I'm not sure how to approach that. Now that I'm registered and can see your photo, I can see that that will probably be a very difficult subject. It might be easier to do thin slices and then group them together in a modeler.

   One of the next steps in my project direction is figuring out how to get it to handle photographs of a small sculpt in a smooth white material - which seems to be one of the worst for this. Since I can deface the thing, while needing the result to to be as smooth as possible, I plan on starting by covering a small test area with pencil marks, whether dispersed dots or a grid pattern of some sort. I can go with different forms of "structured light" if I have to, it's just a matter of dragging things around and setting it up ( as if I don't already have more to do than I can accomplish)

   Sure, I could spend about six hundred bucks and have a shop do the scan and clean it up for a rescaled output, but I'm on a pocket-change budget and besides, I still need to figure out how to get from the proposed objects to a viable model. If I can do one, I'll need to do about six more, and there will be more in the future.

   And, we have a symmetry problem, so if I can get a good model of one side of the thing, I can mirror it and have it output at a cost far less than the two weeks that have already been applied to not getting it right. I'm even working on a method of doing that mechanically with stuff I already mostly have lying around.

   I'm still working/testing in demo mode, but if I can arrive at a process that works then the software will pay for itself - at least the basic version.

   Time for me to go try to sleep. I'll be fighting this in my dreams, in a half-meshed world, always with some sort of giant spiders of some sort - the two pounders aren't a problem, it's the 300+ pounders...

   Good luck with the project,
   -Gary

jphil

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Re: How to capture photos for a piece of kelp?
« Reply #2 on: May 13, 2017, 06:22:32 AM »
Yea, I think your subject is very problematic for many reasons.

1) The surface is shiny, so the reflection will change at different angles thereby not allowing the software to identify fixed references

2) The object is soft, so there is likely to be movement between shots

3) The shapes are highly variegated, causing occlusion of surfaces at almost every angle


I think this software can do a lot of amazing things, but the type of form you are working with is near impossible without some serious equipment or an extremely creative process.

The main concept you need to keep in mind is that in order to gather 3D data from 2D sources you need to triangulate points, meaning that a point needs to be easily identifiable from at the very least 2 angles.

If you identify a point in one picture, but in the next picture it is blocked by something, the surface color changes, or it moves relative to the surface, if any of these things happen, then the capture will be flawed.

The only way I could think of capturing an organic form as complicated as seaweed you would first need to harden it so it doesn't move, or devise a rig that allows you to shoot at all angles without touching it. Second you would have to coat the surface with some kind of matte coating. And lastly you would need to take an extreme amount of photos in order to account for all the crevices/occlusion.
« Last Edit: May 13, 2017, 06:26:03 AM by jphil »

B_Free42

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Re: How to capture photos for a piece of kelp?
« Reply #3 on: May 14, 2017, 04:23:53 PM »
A few things I would suggest trying...
A. Make sure you're photographs have been 'undistorted.' My models improved by an order of magnitude once I started using Adobe Lightroom to remove lens distortion from my photos. I know Lightroom is expensive, I haven't tried the Agisoft Lens program yet. Above all this is would I work on doing first.

B. Instead of rotating the seaweed, find a room/outdoor environment big enough to move the camera instead. By rotating the seaweed the shadows it casts on itself are inevitably going to move and may be enough to prevent camera alignment.

C. Model the seaweed one portion at a time. Instead of having the whole strand fill the frame of your photograph from top to bottom,  move in closer and make the seaweed occupy most of the frame horizontally. Then work your way up or down. Photoscan should still be able to stitch the photos together with enough overlap.

Hope this helps, Cheers!

Photogrammetryfacts

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Re: How to capture photos for a piece of kelp?
« Reply #4 on: May 22, 2017, 08:00:35 PM »
Longer exposure times, overexpose the kelp by one stop or so to bring out more shadow detail.

Move the camera around the kelp.

Focus again for every shot. Autofocus works fine.

Shoot at f8-12, iso100-200

Print out some coded targets and place them around the object