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

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  • Yoram Bernet
    Serge, thank you and thanks also to all the others who have been educating me on this. So ,Serge, this is really helpful, but it does change my understanding
    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
      me on this. So ,Serge, this is really helpful, but it does change my
      understanding of how this works. Let me try.



      Let's say that I have a horizontal line in the image that is significantly
      curved due to barrel distortion. I had originally, been designating point
      pairs by clicking at opposite ends of the line (for the first pair of a
      line), then at various random midpoints for subsequent pairs (thinking that
      the algorithm tries to minimize the distance of all points from the line
      designated by the first and second CPs).



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



      (Strictly speaking, I guess that what I'm calling the point of max
      distortion is actually the point of least distortion and the points near the
      edge of the image are the points of max distortion. )



      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?



      Many thanks and Happy New Year!



      Y



      -----Original Message-----
      From: PanoToolsNG@yahoogroups.com [mailto:PanoToolsNG@yahoogroups.com] On
      Behalf Of Serge Maandag
      Sent: Tuesday, January 01, 2008 12:29 PM
      To: PanoToolsNG@yahoogroups.com
      Subject: RE: FW: [PanoToolsNG] calibrating a lens/teleconverter combo using
      PTGui



      > This leads me to the question - are straight line CPs processed in pairs
      > (per the CP numbers that show up in the images)? Or - are they processed
      in
      > sets (with all CPs that have the same line number/name in the 'Type' field
      > on the table below the images members of a single set)? Is there a rule of
      > thumb regarding where to designate the 2nd CP of each pair (clearly, very
      > close causes problems - that's what caused the optimizer to say 'too good
      to
      > be true').

      Line type control points are processed as set. The way they work is as
      follows:

      You can define a line (within a panotools script) by starting it with t3, t4
      or any
      t followed by a number > 2. A line consists of 2 or more line segments. A
      line
      segment is defined by 2 coordinates, start and end of the segment.
      The optimizer will try to have all segments line up on one straight line.

      The way Joost added line type control points to PTGui might be a bit
      confusing.
      In most cases you just define 2 segments and want them to line up. In that
      case the
      logical way would be to click twice in the left pane (and thus define
      segment1) and
      then click twice in the right pane (defining segment2).

      Instead, Joost chose to have the user alternately click the left and right
      panes.
      You are doing exactly the same thing as above and in the same order, but you
      just
      keep switching panes. This means you can define more than 2 segments to
      define a
      line. This can be handy for long overhead wires. Just select the appropriate
      line in
      the "CP type" dropdown box before clicking left and right.

      To get the best results, always try to define your segments as big as
      possible. Be
      cautious though: When optimizing with line type control points, the
      optimizer aims
      to have the segments line up in the output image. Depending on the type of
      output
      projection, that may be valid or not at all!

      With rectilinear (flat) projection, all straight lines in real life are
      straight in
      the image, so it will be valid. With cylindrical or equirectangular
      projection it's
      only valid for vertical lines and for the horizon. If the line segments are
      close to
      each other it may still work or it may help to temporarily switch the output
      projection to rectilinear during the optimization.

      Serge.
      http://360photo. <http://360photo.org/> org/





      [Non-text portions of this message have been removed]
    • 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 2 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 3 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 4 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 5 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 6 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 7 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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