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

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  • Milko Amorth
    Hi Matt, ... The PTlens coefficients (a,b and c lens distortion) have been determined with the same tools, but with a specific calibration target. If you use
    Message 1 of 16 , Jun 30, 2007
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      Hi Matt,

      > But I'm confused -- are the PTlens coefficients the same as
      > used with PTgui, or is PTgui already using the same algorithm, or?
      The PTlens coefficients (a,b and c lens distortion) have been determined
      with the same tools, but with a specific calibration target.
      If you use the lens data base of ptlens in ptgui you dont have to optimize
      for them in PTgui anymore. You just have to do your FoV, d and e for your
      calibration set. In theory, if you keep your lens locked in one spot on
      your cam and you dont change your crop lines, you never have to optimize
      for those params again.......just yaw, pitch and roll of the images. That
      is an ultimate goal and not easy to achieve.....any lens mount shift will
      have to be reoptimized for d and e. If you nail this down for your set it
      is really fun to do lets say 3 or 4 shots around and only two pairs of cps
      each pair manually and see it come together faster then with any auto
      mode. Old school thinking:-))


      > www.isde5.org. I wonder if the WWPP would be interested in an
      > International Polar Year event? www.ipy.org I'm not sure what form
      > that would take, especially since most folks dont have access to the
      > poles. But perhaps either a winter event in general or a climate
      > change event of some sort? Anyway, just some thoughts.

      Join us and propose this to the members. The themes are all suggested and
      ultimately chosen by a small panel.
      If the theme is doable and has apeal for most members then it could be a
      winner....it can happen.
      The more restrictive the themes are, the less partisipation will occur,
      naturally.



      --
      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
    • Milko Amorth
      Hi John, ... Yes, and as you point out in your optimizer tutorial you must only place these points on lines that should remain straight in the selected output
      Message 2 of 16 , Jun 30, 2007
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        Hi John,

        > Also t3,t4,...tn.
        Yes, and as you point out in your optimizer tutorial you must only place
        these points on lines that should remain straight in the selected output
        projection. Another good read.
        http://www.homepage.ntworld.com/j.houghton/optitude.htm
        Thanks.

        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
      • 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 3 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 4 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 5 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 6 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 7 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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