Hugin/PanoTools: skewing image, HOWTO?

Discussion in 'Digital Photography' started by Ilya Zakharevich, Dec 5, 2006.

  1. In Hugin, I know how to stitch a certain image. The result has two
    "correct" vertical lines, and one "correct" horizontal line. [Here
    "correct" stands up for "the way I like it" ;-]. The result looks
    very reasonable in equirectangular projection.

    Next, I want to "skew" the resulting image: I want to keep the horizontal
    scale the same, but *selectively* change the vertical scale: I want to
    extend the vertical size of the right edge twice, while keeping the
    vertical size of the left edge the same. (Currently the stitch is like

    | ~~--__
    |............| <--- Horizon
    | |
    | | [view in fixed-width font]
    | __--~~

    and I want it to look more rectangular.) (I do not care about
    "non-horizon horizontal lines" becoming non-horizontal; this would not
    affect the composition.)

    I can do this in two steps:

    a) Stitch to an equirectangular image;

    b) Forget that it is equirectangular, and load it into a "normal"
    image editing program; then apply "perspective correction".

    However, I notice that in AutoStitch I can do the same in one step, by
    manually tuning the "yaw angle" parameter. Is there a way to do it in
    one step in Hugin and/or PanoTools?

    Ilya Zakharevich, Dec 5, 2006
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  2. Ilya Zakharevich

    frederick Guest

    I guess that the reference to autostitch in your last sentence is a
    typo? Anyway, after playing with Hugin and others, I decided that I'd
    use autostitch and buy a copy of autopano pro (based on autostitch) when
    I struck a need that autopano couldn't meet. So far, I haven't needed
    to buy it. My experimentation with various stitching software lead me
    to believe that PTGui was the best, but that's an opinion - not based on
    spending the weeks that would be required to compare software fairly.
    I'd just use perspective correction on your stitched example. I like
    The Gimp PC tool better than PS (and not just because it's free).
    AFAIK, you can't do it with Hugin / Panotools, but I could be wrong. If
    I had to study something for a few days before using it, when there is a
    more simple, but perhaps less elegant solution, then forget it - keep it
    I'd also scale a copy the stitched image to 10%, using the rulers to set
    the PC grid noting the settings before using those settings on a full
    sized image. (Waiting for the computer to apply PC to 100mp image, when
    the result may not be spot on is a waste of time - YMMV - particularly
    if you have some supercomputer at hand) I'd consider also downloading
    Gimp 2.39 (or 2.4 if it's out now - haven't checked) because it has the
    option for Lanczos interpolation, and when I tried, it seemed a little
    better than (bi) cubic.
    frederick, Dec 5, 2006
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  3. [A complimentary Cc of this posting was sent to
    You mean in last-but-one? Then it is not.

    Changing the yaw (psi?) in autostitch changes the perspective (as if
    the projection is not equirectangular...). Maybe it is related to the
    fact that my images are rotated [obviously, changing *pitch* WILL result
    in a perspective-like changes; so maybe I was changing pitch when I
    was thinking I was changing yaw - the docs do not say in which order
    rotation and set-view-coordinates is applied]?

    Ilya Zakharevich, Dec 6, 2006
  4. Ilya Zakharevich

    frederick Guest

    I thought it was your last paragraph...
    Anyway, why not d/l autopano pro trial. Perhaps looking at
    pitch/yaw/roll settings in that (with preview gui) can enlighten you on
    what autostitch settings should be.
    frederick, Dec 6, 2006
  5. [A complimentary Cc of this posting was sent to
    I know perfectly well what autostitch settings should be, and what
    changing any of them will do. [Note that I do not know *why* it
    behaves like this... ;-]

    Remember, my original question was whether it is possible to
    reconstruct the effect with hugin (or just PTStitcher/nona/PTmender).

    Ilya Zakharevich, Dec 7, 2006
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