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GeorgeBevan

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Everything posted by GeorgeBevan

  1. Thanks for posting this! A nice wrapper on ImageJ is Fiji: http://fiji.sc/ It conveniently keeps all the plug-ins up do date and allows you to add new plug-ins directly (i.e. you don't have to download and then install the jar files). Has anyone had much experience with RawTherapee as a free and open source way to import and convert RAW files? http://rawtherapee.com/
  2. I've actually used the Paul Buff triggers quite a bit. They're very sturdily constructed and reliable. Their range is also excellent. I generally recommend the cheapest version to students, but the more expensive ones have a very similar functionality to the Pocket Wizards. It looks as if they would integrate very nicely with the Einstein lights.
  3. Carla, Are you guys using the Paul Buff solution to remotely control the Einstein or are you using Pocket Wizards? It looks like a really nice strobe! George
  4. Kathryn, In my experience working in Jordan with Rock Art the AlienBees 1600 is the way to go. I just checked the Paul Buff website and it seems that it is still manufactured. I would consider also using a different reflector than the one provided, like the 11-inch long-throw (a relatively inexpensive item). We used two of the Vagabond Lithium units in our work, each with two battery packs. Generally they performed well with the temperature approaching 50 celsius. Naturally a good set of neutral density filters (or a single variable neutral density filter) will be absolutely necessary for this sort of outdoor work in a very bright environment. For holding the spheres in place I would strongly recommend the Manfrotto "Magic Arms". Our monopods were also Manfrotto. I'll be very interested to hear how your field work goes. We faced very considerable challenges doing RTI in remote areas. George
  5. One of the problems we've found with very close-range photogrammetry is that the focal length of the lens is usually too long to produce good base-to-distance ratios. We routinely use the Nikon 60mm macro for close-in photogrammetry, but the accuracy can suffer when the base-distance ratio is out towards 1:7-1:10. You also get razor-thin depth of field with this sort of work (perhaps not a problem with a painting). With higher resolution cameras you can pull out a bit farther with a wide angle lens, like a 28mm can get roughly the same results in terms of point density but with more accuracy (better base-distance ratios). Do you have any sense how many points Arc3D is generating per inch? I haven't used that tool in quite a while. The free and inexpensive photogrammetry packages, like Arc3D, My3DScanner and 123D Catch seem to all do camera calibration by a sort of brute-force method. Under optimal conditions Agisoft can produce some nice results, although once again it does not allow access to low level calibration. There's a new incarnation of Bundler, called the SFMToolkit, that looks quite powerful: http://www.visual-experiments.com/demos/sfmtoolkit/ Thanks for these really interesting posts, Taylor.
  6. This looks to be a very useful tool! Thanks for sharing. Out of curiosity, how did the photogrammetry of the painting turn out? What software were you using to build your models?
  7. It would seem to me that the best way to accomplish change detection quantitatively would be to use photogrammetry. At present I know of no tools for comparing sets of surface normals generated by RTI (provided they are even registered textel for textel) before and after a particular conservation treatment. In theory if the one of the images used for the photogrammetry capture were also the same as one of the images used for the RTI capture (i.e. you did an RTI at one of the positions where you captured a stereo pair) the resulting epipolar image (one corrected for the position of the camera and the distortion of the lens) from the photogrammetry could be used to match the textels of the RTI to 3d points in space. I know Diego Nehab put some scripts up online that he used in his 2005 paper where he used photometric stereo to correct the normals on range maps, but I don't think they would be usable "out of the box" to do this. I can explain further if you want. Just my two cents... This is a very complicated problem and one that the community should discuss at length. It would be great if we had freely available codes for extracting the numbers from an RTI, i.e. to would convert the RTI to an array of surface normal vectors that we could then process quantitatively. I've done this a bit in Matlab with mixed success. The open source statistical computing language R might be the best package with which to create such tool.
  8. GeorgeBevan

    Tripods

    Mike, This is a good question. For inexpensive tripods our group likes Induro, particularly their largest aluminum tripod, the AT413: http://www.indurogear.com/products_details_AT413.html#5 The centre column is threaded at both ends and can be reversed. It also comes with metal spikes in case you're shooting outdoors. Usually they can had for around $220, a real bargain in terms of tripods. IMHO getting a really good ball-head for the tripod is almost as important as the tripod itself...those can be seriously pricey.
  9. I suppose if you use a minimally distorting lens (~50mm prime) and a scale bar in the RTI, you could take snapshot of the RTI and then scale the snapshot in Photoshop of ImageJ. That would allow you to do some in-plane measurements of features you see in the RTI, but certainly not depth. This is a decent video on how to set custom scale in an image: http://tv.adobe.com/watch/no-stupid-questions-with-colin-smith/setting-a-custom-scale-and-measuring-in-photoshop-cs5-extended/ Of course if the measurements are not along a plane parallel to the image plane then there will be increasing inaccuracy in the measurements the longer they are. Are you interested in measuring in the XY plane or depth? Just my two cents.
  10. We recently used the Singh-Ray Vari-ND in the desert for a shoot of petroglyphs (http://singh-ray.com/varind.html). To get good exposure in full sun the Vari-ND must be advanced such that the filter is virtually opaque...this can create some real problems establishing a good exposure/focus if you don't have a laptop (we use Zaccuto EVF + Z-Finder for off-camera exposure checks instead of the LCD on the back of the camera because it's usually not visible in bright sun). Shooting RTIs of rock art in full sun can be a real challenge! While there is a danger of the Vari-ND filter changing position during a shoot a small piece of tap can put your mind a rest. Bringing lots of filters into the field, especially if you need to hike in and are working in rugged conditions, can be a real hassle.
  11. Hi Anna, We did some sterling silver spoons to identify the hallmarks last year that were not quite as shiny as yours, but still quite lustrous. The HSH was rather impressive when we reprocessed it. It seems to me that the technique Kathryn Piquette and Lindsay MacDonald used to extract a surface profile from the RTI may be the sort of thing you're looking for to identify the slight curvature. It's about mid-way down on her blog: http://kathrynpiquette.blogspot.ca/ Hopefully Kathryn will see this post and enlighten us on how she and Lindsay did it. It's amazing work! Dynamic relighting in the RTIViewer is great for revealing high-frequency textures like fine scratches, but isn't always the best for very low frequency ones (the slight convexity extending across the entire image). Traditionally a 3D scan would be how this sort of feature would be studied, but Algorithmic Rendering of RTIs appears to be the way to go. I'm sure Carla and Marlin will have a lot to add about that. George
  12. Just to add to Marlin's post...sometimes additional customs declarations will be required even if an ATA Carnet is in place. In Jordan, where we work, an additional advance declaration must be made to the Department of Antiquities for gear, especially gear being shipped separately. Do Marlin and others have suggestions about sending equipment on separately by courier? We had a bad experience with FedEx but that may not be shared by others. Luggage restrictions on airlines have made it increasingly difficult to do international photographic work.
  13. I'll add another thought for the Nikon shooters...the Solmeta Geotaggers can also functino as radio frequency shutter releases: http://www.solmeta.com/Product/show/id/14 We just got the N2 Pro for our field work. It's really nice to have high accuracy GPS (~2m), a heading information (it has a triple axis compass) as well as a full GPS logging unit that replaces the hand-held. That we can also use it to release the trigger for RTI is icing on the cake.
  14. I just wanted to add that we now have a PTM viewer running on iPhone and iPad. It's pretty quick (written in Objective C) but only has the Specular Enhancement filter at the moment. At the present it's focused mainly at museum display presentation. I will keep the forum posted as this tool develops. If there were more available information on the HSH algorithm we could add that as well. Our recent experience with the iPhone 5 shows us that the latest hardware can handle it.
  15. No problem! Keep us posted how things turn out.
  16. Kathryn, I`m really intrigued by Lindsay`s surface profiles (I think you put them up on your blog). Will Lindsay be publishing the algorithm he used to extract the profile from the surface normals? I'd love to test the accuracy of these profiles against another profilometry technique. Amazing stuff!!
  17. One other thing on light sources...you`ll want to find a bare Quartz or Xenon flash bulb since they generate a lot of UV light (as well as IR). A Canon speedlight will have extensive UV blocking in it, as well most modern studio strobes, like the AlienBees. Tungsten and Deuterium bulbs also generate a lot of UV but they heat up very quickly and can be dangerous to use. We use three Vivitar 285 HV flashes (1970s vintage design) with the UV filters cut out to get enough UV light in. Quantum also makes newer flash units that can provide good UV and IR light sources: http://www.qtm.com/index.php/products/qflash/uv-ir-flash Just be warned that Quantum are quite expensive. At present UV LEDs can`t generally provide enough light for reflected UV photography, IMHO.
  18. Kathryn, Did you end up getting the D800EÉ We`ve just started using a couple D800s for photogrammetry but haven`t done any RTI with the yet. .
  19. We do reflected UV photography routinely using a converted camera. The problem is that the type of glass most commercial camera lenses are made out of block a lot of UV (it's not just the coatings). To get good UV transmission rather expensive Quartz-Fluorite lenses are required. There are a few on the market but they're extremely expensive...we like the Jenoptik 60mm: http://www.jenoptik-inc.com/coastalopt-standard-lenses/uv-vis-nir-60mm-slr-lens-mainmenu-155.html It's also fully focus corrected across the UV and IR range so you don't have to refocus once you bring up the opaque filter. Also...for reflected UV photography with a converted camera the Baader 2" U-filter (the "Venus" filter) is a must: http://www.company7.com/baader/options/u-filter.html
  20. We routinely use a remote shutter release for our RTI captures (we almost never use a laptop in the field). In the case of Nikon shooting I would suggest against either ML-3 or ML-L3 (yes they are TWO Nikon remote shutter releases). The latter, the ML-3 will work with "pro" bodies like the D700, D300s and D800, while the ML-3 will work with the built in IR sensor of bodies like the D7000 or D5100. The ML-3 is very expensive ($250) and not worth it. In any case, both use an IR trigger that is not suitable for RTI because the remote must be pointed directly at the infrared receiver. The range of even the ML-3 is only about 1-2m. The remote I currently recommend for Nikon is the Phottix Cleon II: http://www.phottix.com/en/wireless-remotes/phottixr-cleon-ii.html The Phottix is Radio Frequency, not IR, and so does not need a direct line of sight between the remote and the receiver. It's also a lot cheaper than a Pocket Wizard (incidentally, we have not had good experiences with the Nikon version of the Pocket Wizard).
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