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Re: Can't do perspective correction

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  • John Houghton
    Leonard, You need to take account of the lens shift by including the lens parameter vertical shift (e) in your custom optimization parameters. Assign two
    Message 1 of 3 , Apr 30, 2009
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      Leonard, You need to take account of the lens shift by including the lens parameter vertical shift (e) in your custom optimization parameters. Assign two pairs of horizontal line (t2) control points on each of your selected horizontal features. Also assign some vertical line (t1) control points on some verticals. Optimize y,p,r on all images together with the lens parameters b and e. (You can initialize e to your estimated value). If things go awry and you get a blank output area, temporarily change the output projection to equirectangular with 360x180 fov. That will show you the entire spherical stitching surface and your image should be visible somewhere provided the lens fov has not been optimized to 0 degrees.

      BTW, this forum does not support attachments.

      John
    • Carl von Einem
      Hi Leonard, ... Time to switch to the latest (pre-) release: in your case
      Message 2 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:
        <http://panospace.wordpress.com/downloads/>
        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,
        Carl
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