Affine transformation - under which circumstances, is it applicableto photo images

Discussion in 'Math Research' started by Avi, Sep 11, 2009.

  1. Avi

    Avi Guest

    Hello,

    Under which circumstances, would affine transformation be applicable
    to undistort an image?
    I know that projective transformation is the correct approach to
    undistort an image from a pinhole camera. However, I find that affine
    transformation is frequently used.
    Affine transformation, preserves parrallel lines which avoids
    correcting projective distortions that are usually seen in an
    photograph image (e.g. parallel lines meet at the horizon).
    Would the approximation be applicable if, e.g. the perspective
    distortion is samll (e.g. the horizon is located far from the photo's
    boundaries)?
    What are other conditions that make the approximation of affine
    transformation applicable?

    Regards,
    Avi
     
    Avi, Sep 11, 2009
    #1
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  2. You can use an affine transformation (actually, just a simple
    rotation) to correct tilt, and of course to crop and/or scale the
    image.

    Also, a projective transformation can be locally approximated by an
    affine one, so I suppose one could use an affine transformation to
    correct perspective distortion in a small part of the image without
    significant errors. However, the situations where this would actually
    be useful seem rather limited to me: in most cases either the error
    would be noticeable or the approximate transform itself would be close
    to identity. Easier to just do a proper projective transformation,
    IMO.
     
    Ilmari Karonen, Sep 20, 2009
    #2
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