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Re: Can't do perspective correction

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  • Carl von Einem
    Hi Leonard, ... Time to switch to the latest (pre-) release: in your case
    Message 1 of 3 , Apr 30, 2009
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      Hi Leonard,

      Leonard Evens wrote:
      > I am using hugin 0.7.0 under Fedora Linux 9.

      Time to switch to the latest (pre-) release:
      in your case <http://wiki.panotools.org/Hugin_Compiling_Fedora>

      > I want to correct horizontal perspective on an image. I followed the
      > instructions in the hugin tutorial at
      > hugin.sourceforge.net/tutorials/architectural/en.shtml
      > But it doesn't work and nothing I try works. I picked three horizontal
      > lines at the top middle and bottom of the building. I get curved lines
      > in the preview even though I've chosen rectilinear. I've tried all the
      > possible options.

      Rectilinear output should work. The tutorial defines three vertical
      lines (shown as a blue, green and red pair). Poles for road signs can
      often be used for those, also the edge of a building from the roof to
      the ground level.

      You seem to have used several horizontal lines. Only set those on the
      actual horizon! They are useful e.g. to level a wavy horizon when you
      shoot a panorama from a beach.

      > I've attached the image file.

      You should upload that to your webspace (or something like flickr.com)
      and post the URL here.

      > Actually I know quite a lot about it
      > The picture was taken with a 4 x 5 view camera with a 75 mm lens with
      > minimum distortion. I used a panoramic head and swung to the left 15
      > degrees (yaw -15). I used a rise which translates into a vertical
      > displacement of about 229 pixels. Is there some way to incorporate
      > that information to produce the result I want?

      4" x 5" (about 100 x 125 mm) with a 75 mm lens lead to a fov of roughly
      67 degrees (short side) and 79 degrees (long side).

      You should carefully optimize for shift (distance of image center from
      the optical axis, 'e' = vertical and 'd' = horizontal) and shear (often
      introduced by scanners, 't' = vertical and 'g' = horizontal, values in
      pixels). Don't optimize all of them at once...

      > This image is one half of a two image panaorama with the other half
      > turned 15 degrees to the right. I did manage to use hugin to merge
      > these after some effort, but the resulting image still needed some
      > horizontal perpective correction.

      Hugin can correct correct all of that in the same project. Just add your
      vertical lines and optimize not only yaw, pitch , roll and fov, but also
      d/e and g/t as described above.

      Hope that helps,
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