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RE: FW: [PanoToolsNG] calibrating a lens/teleconverter combo using PTGui

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  • Serge Maandag
    ... Yes, totally. ... No, The three coefficients a, b and that the panotools optimizer uses can only correct barrel and pincushion distortion. The two line
    Message 1 of 13 , Jan 1, 2008
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      > Serge, thank you and thanks also to all the others who have been educating
      > Now based on what you're saying, it seems that I should do this differently.
      > Specifically - it seems that I should designate the first point at one end
      > of the line (say the left) and the second point at a point (probably roughly
      > midway between the two ends of the image) at which the line is maximally
      > distorted. That does it for the first pair. For the second pair, I should
      > designate a point at the opposite far end of the line (the right) and the
      > second point of the pair near to the second point of the first pair (the
      > point of maximum distortion). - Is this correct?

      Yes, totally.

      > Wouldn't I then want to
      > proceed by designating lots of subsegments along the line that I eventually
      > want rendered straight?

      No, The three coefficients a, b and that the panotools optimizer uses can only
      correct barrel and pincushion distortion. The two line segments are enough info for
      the optimizer to do that. Subsegments would only be useful to fix a wobbly line. But
      that wouldn't be possible anyway with only a,b and c.

      The less segments you define, the less confusing it is to the optimizer. If I have
      to correct a barrel shaped box, I define a line (consisting of 2 line segments) on
      each side of the box.

      > Another question - once I correct for barrel distortion, using this method,
      > the nextproblem that shows up is perspective distortion (even though I've
      > used a PC lens, there is some perspective distortion due to not having the
      > sensor plane exactly parallel to the subject). To fix this, I'd like to be
      > able to designate certain line segs and say "these should all be horizontal"
      > and other segs and say "these should all be vertical". Is this done using
      > the horizontal and vertical line types in the dialog box (t1 and t2)? Can I
      > correct for both barrel distortion and perspective distortion in the same
      > step or do you recommend doing so iteratively?

      Correct and yes, the optimizer can do it in one go. There are occasions where the
      optimizer goes haywire, but that rarely happens. If it does, you'll notice. Then you
      can always:

      - set t1/t2 points
      - optimize yaw pitch and roll
      - remove the the t1/t2 points and set line type points
      - turn off yaw pitch and roll optimization
      - optimize a, b and c (or at least b)

      Happy newyear to you to!

      Serge.
      http://360photo.org/
    • Erik Krause
      ... Sorry, this is wrong. The use of three coefficients (a, b and c) was especially necessary to allow the correction of wavy (or wobbly) distortion as well.
      Message 2 of 13 , Jan 4, 2008
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        Serge Maandag-3 wrote:
        >
        >> Wouldn't I then want to
        >> proceed by designating lots of subsegments along the line that I
        >> eventually
        >> want rendered straight?
        >
        > No, The three coefficients a, b and that the panotools optimizer uses can
        > only
        > correct barrel and pincushion distortion. The two line segments are enough
        > info for
        > the optimizer to do that. Subsegments would only be useful to fix a wobbly
        > line. But
        > that wouldn't be possible anyway with only a,b and c.
        >
        > The less segments you define, the less confusing it is to the optimizer.
        > If I have
        > to correct a barrel shaped box, I define a line (consisting of 2 line
        > segments) on
        > each side of the box.
        >

        Sorry, this is wrong. The use of three coefficients (a, b and c) was
        especially necessary to allow the correction of wavy (or wobbly) distortion
        as well. Wavy distortion is a mixture of barrel and pincushion distortion in
        different distances to the image center. For details see
        http://wiki.panotools.org/Wavy_distortion

        To correct for this kind of distortion you need more than two pairs of
        control points on each line and you need lines in different distances from
        the center. The optimizer will not be confused at all, since there isn't a
        possibility of false local minima.

        best regards


        -----
        Erik Krause
        http://www.erik-krause.de
        --
        View this message in context: http://www.nabble.com/RE%3A-FW%3A-calibrating-a-lens-teleconverter-combo-using--PTGui-tp14569835p14615206.html
        Sent from the PanoToolsNG mailing list archive at Nabble.com.
      • Serge Maandag
        ... Thanks for the update, Erik. I kind of always pictured pincushion distortion as bulgy in the middle and pointy in the corners, but it occurs to me that
        Message 3 of 13 , Jan 4, 2008
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          > Sorry, this is wrong. The use of three coefficients (a, b and c) was
          > especially necessary to allow the correction of wavy (or wobbly) distortion
          > as well. Wavy distortion is a mixture of barrel and pincushion distortion in
          > different distances to the image center. For details see
          > http://wiki.panotools.org/Wavy_distortion

          Thanks for the update, Erik.

          I kind of always pictured pincushion distortion as bulgy in the middle and pointy in
          the corners, but it occurs to me that this is in fact a combination of barrel
          distortion and pincushion distortion. More than this can't be correct by the
          optimizer, though.

          Luckily pincushion distortion is more rare than barrel distorion. Especially on wide
          angle lenses.

          Serge.
        • Yoram Bernet
          Folks: I was struggling with using the straight line control points to remove barrel distortion from a single image. I posted some questions to this list and
          Message 4 of 13 , Jan 24, 2008
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            Folks:



            I was struggling with using the straight line control points to remove
            barrel distortion from a single image. I posted some questions to this list
            and got lots of helpful answers. Also - Erik - thanks for updating the
            tutorial.



            However, i'm still not getting the results that I hoped for. I shot a close
            up of a model using the Canon 24 mm tilt/shift lens. I used vertical shift.
            I'm trying to correct for barrel distortion.



            Please see the following illustration for reference
            www.yorambernet.com/Panotools/panotools.jpg. There are three images in the
            illustration: on the top left is my uncorrected image. On the top right is
            the corrected image and on the bottom, a snapshot of the PTGui 'Control
            Points' screen, showing the control points (CPs) that I used. I set CP pairs
            on three important lines and grouped them in the CP dialog box as new lines
            3, 4 and 5. On the top two images (corrected and uncorrected, I've inserted
            four light blue reference lines that are perfectly straight. The lower three
            of these correspond to the lines that I am trying to straighten and help to
            illustrate the degree to which the straightening worked.



            In particular - it appears that the line defined by CP pairs 0, 1 and 2 is
            substantially improved. However, the line defined by CP pairs 3, 4, 5, 6, 7
            and 8, while improved, is far from perfect. The barrel distortion seems to
            be much improved near the middle of the line, but not near the ends. The
            ends still curve significantly away from the reference line.



            I tried optimizing for 'b' only and I tried optimizing for 'a', 'b' and 'c'.
            I tried defining fewer CP pairs along each line and more CP pairs along each
            line. I was unable to get results better than those illustrated in the
            reference image. That said, I also tried optimizing for vertical shift (VS).
            It seems to me that the first time I tried optimizing for VS as well as for
            'b', I did get a much better result. Thinking that this might have been the
            key, I went back and defined additional CP pairs, hoping to get perfect
            results. I again optimized for 'b' and for 'VS'. This time I got 'too good
            to be true' from the optimizer and the resulting image was just a black
            canvas. I tried again and again to reproduce the promising results that I
            thought I had obtained by optimizing for 'VS' as well as for 'b', but every
            time, got 'too good to be true'.



            So - here are my questions:

            1. Am I asking for too much? Is this as good as it gets?
            2. Is it possible to optimize for VS (without having recorded how many
            mm of shift were actually used)? Could I in fact have got much better
            results on one of the optimization runs when I selected 'VS' but for some
            reason am simply unable to reproduce it?
            3. How do I optimize for VS?
            4. How do I get better results?



            Many thanks for any assistance/insight!



            BTW - on the reference image of the CP dialog box, several CPs overlap. So,
            for example, on the right pane, CPs 0 and 1 overlap and therefore, CP 0 on
            the right pane is not visible.



            Yoram

            -----Original Message-----
            From: PanoToolsNG@yahoogroups.com [mailto:PanoToolsNG@yahoogroups.com] On
            Behalf Of Erik Krause
            Sent: Friday, January 04, 2008 4:18 AM
            To: PanoToolsNG@yahoogroups.com
            Subject: RE: [PanoToolsNG] FW: calibrating a lens/teleconverter combo using
            PTGui





            Serge Maandag-3 wrote:
            >
            >> Wouldn't I then want to
            >> proceed by designating lots of subsegments along the line that I
            >> eventually
            >> want rendered straight?
            >
            > No, The three coefficients a, b and that the panotools optimizer uses can
            > only
            > correct barrel and pincushion distortion. The two line segments are enough
            > info for
            > the optimizer to do that. Subsegments would only be useful to fix a wobbly
            > line. But
            > that wouldn't be possible anyway with only a,b and c.
            >
            > The less segments you define, the less confusing it is to the optimizer.
            > If I have
            > to correct a barrel shaped box, I define a line (consisting of 2 line
            > segments) on
            > each side of the box.
            >

            Sorry, this is wrong. The use of three coefficients (a, b and c) was
            especially necessary to allow the correction of wavy (or wobbly) distortion
            as well. Wavy distortion is a mixture of barrel and pincushion distortion in
            different distances to the image center. For details see
            http://wiki. <http://wiki.panotools.org/Wavy_distortion>
            panotools.org/Wavy_distortion

            To correct for this kind of distortion you need more than two pairs of
            control points on each line and you need lines in different distances from
            the center. The optimizer will not be confused at all, since there isn't a
            possibility of false local minima.

            best regards

            -----
            Erik Krause
            http://www.erik- <http://www.erik-krause.de> krause.de
            --
            View this message in context: http://www.nabble.
            <http://www.nabble.com/RE%3A-FW%3A-calibrating-a-lens-teleconverter-combo-us
            ing--PTGui-tp14569835p14615206.html>
            com/RE%3A-FW%3A-calibrating-a-lens-teleconverter-combo-using--PTGui-tp145698
            35p14615206.html
            Sent from the PanoToolsNG mailing list archive at Nabble.com.





            [Non-text portions of this message have been removed]
          • Erik Krause
            ... Sorry for taking me so long. I missed your post because of the entirely new subject in an older thread... [...] ... No. ... Check vertical shift on the
            Message 5 of 13 , Jan 27, 2008
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              On Thursday, January 24, 2008 at 17:20, Yoram Bernet wrote:

              > However, i'm still not getting the results that I hoped for. I shot a
              > close up of a model using the Canon 24 mm tilt/shift lens. I used
              > vertical shift. I'm trying to correct for barrel distortion.

              Sorry for taking me so long. I missed your post because of the
              entirely new subject in an older thread...

              [...]
              > 1. Am I asking for too much? Is this as good as it gets?

              No.

              > 2. Is it possible to optimize for VS (without having recorded how many
              > mm of shift were actually used)? Could I in fact have got much better
              > results on one of the optimization runs when I selected 'VS' but for some
              > reason am simply unable to reproduce it?

              Check "vertical shift" on the optimizer tab page and optimize again.
              Be prepared that your result slips out of center. Hence you might
              need to use a larger output field of view. You can adjust this in the
              pano editor (ctrl+e). It could well be, that the PTGui optimizer
              won't give you good results. If this is the case, use panotools
              optimizer.

              Using a shift lens is a classical case of center of distortion not
              beeing in the image center. However, panotools should handle this
              case properly, but if you use shift and lens correction optimization
              together, the optimizer might find a false minimum. In this case you
              might want to tune your control points and/or use more lines.

              Please not, that if you deselect a parameter for optimization, this
              won't reset the value. You must set these parameter manually to zero
              on lens settings tab.

              best regards

              Erik Krause
              http://www.erik-krause.de
            • Rick Drew
              I received a few emails asking about my home-made camera warmer / jacket for shooting outdoors in winter. My current one was constructed from a fleece hat I
              Message 6 of 13 , Jan 27, 2008
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                I received a few emails asking about my home-made camera warmer / jacket for
                shooting outdoors in winter. My current one was constructed from a fleece
                hat I purchased at WalMart for $2.00. Cutting and sewing took about two
                hours. I added photos to flickr.com - keyword rickscamerahat .



                http://flickr.com/search/?q=rickscamerahat
                <http://flickr.com/search/?q=rickscamerahat&w=22793959%40N06>
                &w=22793959%40N06



                Hope it helps.



                Rick Drew



                PS - I used it yesterday. In the morning the wind-chill was 3 degrees
                Fahrenheit. One battery lasted for 911 photos!



                [Non-text portions of this message have been removed]
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