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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 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 2 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 3 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 4 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 5 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 6 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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