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

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  • 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 1 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 2 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 3 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 4 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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