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Re: [PanoToolsNG] Re: optimizing a 10.5mm lens in PTgui

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  • Milko Amorth
    Hi Serge, ... Sure, good enough for the pano fit in eq/cyl projection. Try these values for a pano twice the resolution or try a calibration grid target with
    Message 1 of 16 , Jun 30, 2007
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      Hi Serge,

      > For this second scenario you don't need horizontal/vertical line control
      > points,
      > because it does not matter whether the scene is tilted or not. As long
      > as the
      > average control point distance is low, you've got a good calibration
      > that you can
      > use on single images from then on.
      Sure, good enough for the pano fit in eq/cyl projection. Try these values
      for a pano twice the resolution or try a calibration grid target with
      rectlinear projection and you will see it is just an approximation.


      I just did a test run with 2 calibration grid images using the auto align
      of ptgui beta and ptgui optimizer.
      The optimizer does not care if the images are side by side or in line.
      It placed 28 cps nicely spread on the outside of the grid with a minimum
      of 0,0000031 and a maximum of 0,00185 source pixel distance. It produced
      a=0,012160; b=-0,012329; c=0,014578 and tagged this is too good to be true.
      Perfect overlap and match of both images, but still showing some barrel
      distortion and perspective shifts.

      After that, i just applied the calibrated values for this lens from the
      data base, which are different (a=0,01309 b=-0,03639 c=0).
      and no distortion what so ever, but still the perspective shift. Only
      after setting t1 and t2 I got it perspectively correct. After reoptimizing
      with the previous values and the new t1 and t2 I got quite close but not
      perfect. Applying the data base lens coefficients again......voila. Nice
      grid. A good lens calibration takes time and away the guessing
      game.....and it needs true lines. Luckily you only have to do it once for
      your set.


      Cheers, Milko



      --
      Milko Amorth
      360° Immersive Imaging
      Photographic Virtual Reality
      VRCanada.ca
      604.561.5101

      PhotoScrapbook at Flickr.com/photos/vrdundee
      Skype me @ vrdundee
      Member of IVRPA.org
      Contributor to the World Wide Panorama Project
    • Serge Maandag (yahoo)
      ... Milko, I think we re trying to say the same. I was going for images with lots of detail and thus tons of control points. That s the dirt ugly way. You re
      Message 2 of 16 , Jul 2, 2007
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        > I just did a test run with 2 calibration grid images using the auto align
        > of ptgui beta and ptgui optimizer.
        > The optimizer does not care if the images are side by side or in line.
        > It placed 28 cps nicely spread on the outside of the grid with a minimum
        > of 0,0000031 and a maximum of 0,00185 source pixel distance. It produced
        > a=0,012160; b=-0,012329; c=0,014578 and tagged this is too good to be true.
        > Perfect overlap and match of both images, but still showing some barrel
        > distortion and perspective shifts.

        Milko,

        I think we're trying to say the same. I was going for images with lots of detail and
        thus tons of control points. That's the dirt ugly way. You're going for the clean
        optimize grid way. That saves you a lot of control points and is intuitive.

        My only point was that you don't necessarily have to work with t1/t2 points to
        determine lens error parameters. But that's mere theory. Using t1/t2 points does
        make it easier and more transparent though. As long as you don't forget to optimize
        y,p,r too :)

        Doing a 360 is the best way to determine the lens FoV though..

        Serge.
      • matt_nolan_uaf
        Serge and Milko, Thanks for your input. A few follow up questions. - Milko, what sort of target did you use for calibration? A sheet of graph paper, or
        Message 3 of 16 , Jul 2, 2007
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          Serge and Milko,

          Thanks for your input. A few follow up questions.

          - Milko, what sort of target did you use for calibration? A sheet of
          graph paper, or something more sophisticated?

          - If I understand correctly, the t1 and t2 lines are used more to
          correct shift than to calibrate the lens? I tried using these only,
          and got strange results, but I didnt fool with it very much.

          - What exactly is the 'optimizer' doing? Is it changing control
          points to match better, or just using what exists and coming up with
          the best lens parameters? Is there a way to 'force' some control
          points to have higher priority in optimization?

          - Is the field of view for the 10.5 mm lens changing? I didnt think
          so, so shouldn't I force PTgui to use the correct values to help it
          optimize shifts? Does anyone know the correct value? Or does this
          vary slightly with each lens? What are others getting?

          BTW, I was able to 'successfully' use PTgui on single images at a
          wedding over the weekend. I saved the lens parameters found by a 360
          panorama, and then applied it to single frames. I tried calibrating
          using just pairs, but as I said the results were wierd, and the
          panorama did well enough for my eyes in this application. In the
          future I'd like to calibrate for real. It's really wild how much
          shifting can be done in PTgui. You can see a few pics here
          http://www.uaf.edu/water/faculty/nolan/temp/belfair/belfair.htm

          Cheers,
          Matt



          --- In PanoToolsNG@yahoogroups.com, "Serge Maandag (yahoo)"
          <yahoo@...> wrote:
          >
          > > I just did a test run with 2 calibration grid images using the
          auto align
          > > of ptgui beta and ptgui optimizer.
          > > The optimizer does not care if the images are side by side or in
          line.
          > > It placed 28 cps nicely spread on the outside of the grid with a
          minimum
          > > of 0,0000031 and a maximum of 0,00185 source pixel distance. It
          produced
          > > a=0,012160; b=-0,012329; c=0,014578 and tagged this is too good
          to be true.
          > > Perfect overlap and match of both images, but still showing some
          barrel
          > > distortion and perspective shifts.
          >
          > Milko,
          >
          > I think we're trying to say the same. I was going for images with
          lots of detail and
          > thus tons of control points. That's the dirt ugly way. You're going
          for the clean
          > optimize grid way. That saves you a lot of control points and is
          intuitive.
          >
          > My only point was that you don't necessarily have to work with
          t1/t2 points to
          > determine lens error parameters. But that's mere theory. Using
          t1/t2 points does
          > make it easier and more transparent though. As long as you don't
          forget to optimize
          > y,p,r too :)
          >
          > Doing a 360 is the best way to determine the lens FoV though..
          >
          > Serge.
          >
        • Serge Maandag (yahoo)
          ... Don t know about Milko, but I used the tiled wall in my bathroom :) ... No. The t1 and t2 parameters are mainly to tell the optimizer: This point should be
          Message 4 of 16 , Jul 2, 2007
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            > - Milko, what sort of target did you use for calibration? A sheet of
            > graph paper, or something more sophisticated?

            Don't know about Milko, but I used the tiled wall in my bathroom :)

            > - If I understand correctly, the t1 and t2 lines are used more to
            > correct shift than to calibrate the lens? I tried using these only,
            > and got strange results, but I didnt fool with it very much.

            No. The t1 and t2 parameters are mainly to tell the optimizer: This point should be
            straight above or straigth next to the other point. Normally you use them on
            horizons or on doorframes. But when you're calibrating your lens it means you are
            searching for parameters that make straight lines in the real world seem straight in
            your photo. Since t1 and t2 control points are all about straight lines, they come
            in handy to do the actual calibration.


            > - What exactly is the 'optimizer' doing? Is it changing control
            > points to match better, or just using what exists and coming up with
            > the best lens parameters? Is there a way to 'force' some control
            > points to have higher priority in optimization?

            First of all, the optimizer does what you're telling it too. You will have to tell
            it what parameters can be played with to reach the ultimate goal: control points in
            multiple images that, on the 3d globe, exactly fall in the same place. You can
            compare it to the "goal seek" function in Microsoft Excel.

            Before you press "optimize", you will have set an input (format and position) and an
            output (format and position). The optimizer will determine how good the control
            points will match if the input image is warped to the output format and position. If
            it's not a perfect match, it will repeatedly change parameters like yaw and roll to
            see if the result gets better. It will stop when it has found the parameters that
            give the best match.

            > - Is the field of view for the 10.5 mm lens changing? I didnt think
            > so, so shouldn't I force PTgui to use the correct values to help it
            > optimize shifts? Does anyone know the correct value? Or does this
            > vary slightly with each lens? What are others getting?

            Not much, that's for sure. There's probably some variation when you focus
            differently. Whether the aperture setting has any influence, I don't know. I always
            optimize the field of view along in my 360 panoramas anyway. There will be some
            variation between 2 lenses for sure, but for single images that's not going to hurt
            you.

            > I tried calibrating using just pairs, but as I said the results
            > were wierd,

            they shouldn't be. Perhaps you forgot to optimize a variable or you did not place
            your control points optimally. If you place the image and the .pts online, we can
            have a look..

            Serge.
          • Milko Amorth
            Hi Matt, hi Serge, ... Tiles are great if you can trust your tiler ;-) I do use my tiled shower to do a precise script for close-ups under 10 feet. In general
            Message 5 of 16 , Jul 5, 2007
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              Hi Matt, hi Serge,

              > Don't know about Milko, but I used the tiled wall in my bathroom

              Tiles are great if you can trust your tiler ;-) I do use my tiled shower
              to do a precise script for close-ups under 10 feet.
              In general you need a true grid to fill your view finder and be at least
              10 feet away or more. Highrise buildings make the best target when you
              have one opposite and can shoot with the horizon in the center. Laser
              levels can help as well. For normal lenses I have a grid map pano on the
              wall made of chart paper.

              Like Serge said, the optimizer will do what you tell it to do. Remember,
              it does not look at the picture but the coordinates you set (Xpixel and
              Ypixel).

              Happy stitching,
              Cheers, Milko


              --
              Milko Amorth
              360° Immersive Imaging
              Photographic Virtual Reality
              VRCanada.ca
              604.561.5101

              PhotoScrapbook at Flickr.com/photos/vrdundee
              Skype me @ vrdundee
              Member of IVRPA.org
              Contributor to the World Wide Panorama Project
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