how to rotate image so that image is perfectly level

Discussion in 'Digital Photography' started by bucky3, Jul 11, 2009.

  1. bucky3

    bucky3 Guest

    When hand shooting, it is not possible to have the camera perfectly
    level all the time. Often, the images may be 1-2 degrees off, so I
    need to correct the rotation of the image. (If you use the pitch/roll/
    yaw analogy, I'm only correcting for roll.)

    Sometimes, it's pretty easy to figure out exactly how much to rotate
    it, because you can rotate the image so that all the vertical edges
    are perfectly straight up and down, or all the horizontal edges are
    perfectly straight across. But sometimes, due to perspective, vertical
    or horizontal edges should NOT be straight up/down or across, or the
    edges aren't parallel. Then I struggle with the rotation correction.

    Are there any rules/techniques to figure out the proper rotation
    correction needed? I don't have much grasp of perspective, so I was
    trying to learn about it in hopes that it would help:
    http://wiki.panotools.org/Perspective_correction
    http://wiki.blender.org/index.php/Doc:Manual/Render/Camera/Perspective
     
    bucky3, Jul 11, 2009
    #1
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  2. bucky3

    Ray Fischer Guest

    bucky3 <> wrote:
    >When hand shooting, it is not possible to have the camera perfectly
    >level all the time. Often, the images may be 1-2 degrees off, so I
    >need to correct the rotation of the image. (If you use the pitch/roll/
    >yaw analogy, I'm only correcting for roll.)
    >
    >Sometimes, it's pretty easy to figure out exactly how much to rotate
    >it, because you can rotate the image so that all the vertical edges
    >are perfectly straight up and down, or all the horizontal edges are
    >perfectly straight across. But sometimes, due to perspective, vertical
    >or horizontal edges should NOT be straight up/down or across, or the
    >edges aren't parallel. Then I struggle with the rotation correction.
    >
    >Are there any rules/techniques to figure out the proper rotation
    >correction needed?


    Yep. Adjust until it looks right.

    In my book, if the photo _is_ correct but _looks_ crooked then that's
    a problem. I'm interested in the esthetics more than then technical
    accuracy.

    > I don't have much grasp of perspective, so I was
    >trying to learn about it in hopes that it would help:
    >http://wiki.panotools.org/Perspective_correction
    >http://wiki.blender.org/index.php/Doc:Manual/Render/Camera/Perspective


    Urg. Well, it depends on the tools you have. I use photoshop and it
    lets you draw a quadrilateral that it uses to correct the perspective.
    Line up the edges with straight lines in the scene and it does the
    rest. Other tools tend to work similarly. When you don't have
    straight edges in the scene then you have to resort to some guesswork.
    Adjust until it looks right.

    --
    Ray Fischer
     
    Ray Fischer, Jul 11, 2009
    #2
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  3. bucky3

    Scott W Guest

    On Jul 11, 8:16 am, bucky3 <> wrote:
    > When hand shooting, it is not possible to have the camera perfectly
    > level all the time. Often, the images may be 1-2 degrees off, so I
    > need to correct the rotation of the image. (If you use the pitch/roll/
    > yaw analogy, I'm only correcting for roll.)
    >
    > Sometimes, it's pretty easy to figure out exactly how much to rotate
    > it, because you can rotate the image so that all the vertical edges
    > are perfectly straight up and down, or all the horizontal edges are
    > perfectly straight across. But sometimes, due to perspective, vertical
    > or horizontal edges should NOT be straight up/down or across, or the
    > edges aren't parallel. Then I struggle with the rotation correction.
    >
    > Are there any rules/techniques to figure out the proper rotation
    > correction needed? I don't have much grasp of perspective, so I was
    > trying to learn about it in hopes that it would help:http://wiki.panotools.org/Perspecti...ndex.php/Doc:Manual/Render/Camera/Perspective


    Vertical edges in the center of the image should be vertical in the
    photo. The
    edges to the sides will slope in or out depending on if the camera was
    pointed up or down.

    Scott
     
    Scott W, Jul 11, 2009
    #3
  4. bucky3

    bucky3 Guest

    On Jul 11, 12:10 pm, Scott W <> wrote:
    > Vertical edges in the center of the image should be vertical in the
    > photo. The
    > edges to the sides will slope in or out depending on if the camera was
    > pointed up or down.


    Thanks, that's the kind of rule I was looking for.

    Does it also apply that horizontal edges in the center of the image
    should be straight across in the photo too?
     
    bucky3, Jul 11, 2009
    #4
  5. bucky3

    PatM Guest

    On Jul 11, 3:31 pm, bucky3 <> wrote:
    > On Jul 11, 12:10 pm, Scott W <> wrote:
    >
    > > Vertical edges in the center of the image should be vertical in the
    > > photo.  The
    > > edges to the sides will slope in or out depending on if the camera was
    > > pointed up or down.

    >
    > Thanks, that's the kind of rule I was looking for.
    >
    > Does it also apply that horizontal edges in the center of the image
    > should be straight across in the photo too?


    The rule of thumb is to just make it look right, but sometimes you
    need precision. In that case, things should go out straight and level
    from the center of the picture (unless you don't want that for
    artistic reasons). If you need precision, you need to use something
    that you know is level and/or straight. That leaves the edge of the
    box the photo is in or the edge of the monitor. They are about the
    only "true" reference points because they are generated independently
    of the image. Sometimes you can align with the edge by moving the
    picture and sometimes you need to break out an (old school) ruler and
    measure from the edge of something.

    Good luck with it.
     
    PatM, Jul 11, 2009
    #5
  6. bucky3

    bucky3 Guest

    On Jul 11, 12:31 pm, bucky3 <> wrote:
    > Does it also apply that horizontal edges in the center of the image
    > should be straight across in the photo too?


    OK, I think I figured out the answer to this question. The answer is
    no, horizontal edges to do not need to be level in the center of the
    image because I am allowing for the camera to be tilted up or down.

    The only time that horizontal edges will be straight in the center of
    the image is if the camera is not tilted up or down (i.e. the camera
    is at the same height as the edge).
     
    bucky3, Jul 11, 2009
    #6
  7. bucky3

    Ray Fischer Guest

    Savageduck <savageduck@{REMOVESPAM}me.com> wrote:
    >On 2009-07-11 12:06:10 -0700, (Ray Fischer) said:
    >
    >> bucky3 <> wrote:
    >>> When hand shooting, it is not possible to have the camera perfectly
    >>> level all the time. Often, the images may be 1-2 degrees off, so I
    >>> need to correct the rotation of the image. (If you use the pitch/roll/
    >>> yaw analogy, I'm only correcting for roll.)
    >>>
    >>> Sometimes, it's pretty easy to figure out exactly how much to rotate
    >>> it, because you can rotate the image so that all the vertical edges
    >>> are perfectly straight up and down, or all the horizontal edges are
    >>> perfectly straight across. But sometimes, due to perspective, vertical
    >>> or horizontal edges should NOT be straight up/down or across, or the
    >>> edges aren't parallel. Then I struggle with the rotation correction.
    >>>
    >>> Are there any rules/techniques to figure out the proper rotation
    >>> correction needed?

    >>
    >> Yep. Adjust until it looks right.
    >>
    >> In my book, if the photo _is_ correct but _looks_ crooked then that's
    >> a problem. I'm interested in the esthetics more than then technical
    >> accuracy.
    >>
    >>> I don't have much grasp of perspective, so I was
    >>> trying to learn about it in hopes that it would help:
    >>> http://wiki.panotools.org/Perspective_correction
    >>> http://wiki.blender.org/index.php/Doc:Manual/Render/Camera/Perspective

    >>
    >> Urg. Well, it depends on the tools you have. I use photoshop and it
    >> lets you draw a quadrilateral that it uses to correct the perspective.
    >> Line up the edges with straight lines in the scene and it does the
    >> rest. Other tools tend to work similarly. When you don't have
    >> straight edges in the scene then you have to resort to some guesswork.
    >> Adjust until it looks right.

    >
    >In Photoshop one of the easiest ways to deal with this issue is to use
    >the Lens Correction filter.


    There are several ways to do anything in Photoshop. I cited that
    method because it corresponds to a mention on the wiki page he cited.

    Which is moot if he doesn't have Photoshop.

    But a useful tip regardless. I'm still learning about how to do
    things in Photoshop.

    >This is found in filters-->distort-->Lens Correction.
    >Here you have tools for leveling, correcting barrel & pincushion
    >distortion, CA, Vignetting, Vertical & Horizontal perspective.


    --
    Ray Fischer
     
    Ray Fischer, Jul 11, 2009
    #7
  8. bucky3

    nospam Guest

    In article <4a58e2a2$0$1652$>, Ray Fischer
    <> wrote:

    > >Are there any rules/techniques to figure out the proper rotation
    > >correction needed?

    >
    > Yep. Adjust until it looks right.
    >
    > In my book, if the photo _is_ correct but _looks_ crooked then that's
    > a problem. I'm interested in the esthetics more than then technical
    > accuracy.


    agreed.

    > Urg. Well, it depends on the tools you have. I use photoshop and it
    > lets you draw a quadrilateral that it uses to correct the perspective.
    > Line up the edges with straight lines in the scene and it does the
    > rest. Other tools tend to work similarly. When you don't have
    > straight edges in the scene then you have to resort to some guesswork.
    > Adjust until it looks right.


    another way in photoshop is to use the ruler tool and drag it along an
    edge that should be horizontal or vertical, then in the image menu,
    pick rotate canvas/arbitrary and the angle to make it level will be
    pre-filled.
     
    nospam, Jul 11, 2009
    #8
  9. Oh what the hell ... <> wrote:
    >I'm SO sick to death


    That would be great. Unfortunaly I'm afraid that's only an empty promise
    again.


    jue
     
    Jürgen Exner, Jul 11, 2009
    #9
  10. bucky3

    Paul Furman Guest

    Re: |GG| Re: how to rotate image so that image is perfectly level

    bucky3 wrote:
    > bucky3 wrote:
    >
    >> Does it also apply that horizontal edges in the center of the image
    >> should be straight across in the photo too?

    >
    > OK, I think I figured out the answer to this question. The answer is
    > no, horizontal edges to do not need to be level in the center of the
    > image because I am allowing for the camera to be tilted up or down.
    >
    > The only time that horizontal edges will be straight in the center of
    > the image is if the camera is not tilted up or down (i.e. the camera
    > is at the same height as the edge).


    Google '3-point perspective' to get a better sense of how it works. If
    the horizontal is the edge of a building viewed on a diagonal, then you
    can't/don't need to straighten it.

    Here's a 4-point perspective just to confuse you:
    http://www.termespheres.com/mh-page2.html
    -figure 2
    :)

    Scott's advice is good: hold vertical in the center. Sometimes that's
    still hard to judge if you have a building viewed at an angle and no
    windows in the middle. In that case visualize sketching more windows on
    the wall, all going to the same vanishing point as the outside edges...
    or even go ahead & sketch that on another layer. Then use vertical guide
    lines, in photoshop: control-click-drag guides off the rulers to match
    against subject geometry. It helps to have a couple of these guides
    dragged out near the available verticals, then match & balance till it
    makes sense with the vanishing point.

    Another approach in photoshop is free transform. Control-a then
    control-t and control-click & drag the corner grips one by one till it
    looks right. That can be used to fake things and avoid cropping too much
    off or to make it 'look right' for odd situations where you align
    properly & it still looks wrong. That also potentially gets you into
    perspective correction territory <g>.

    --
    Paul Furman
    www.edgehill.net
    www.baynatives.com

    all google groups messages filtered due to spam
     
    Paul Furman, Jul 11, 2009
    #10
  11. bucky3

    Guest

    On Sat, 11 Jul 2009 11:16:02 -0700 (PDT), bucky3 <>
    wrote:

    >When hand shooting, it is not possible to have the camera perfectly
    >level all the time. Often, the images may be 1-2 degrees off, so I
    >need to correct the rotation of the image. (If you use the pitch/roll/
    >yaw analogy, I'm only correcting for roll.)
    >
    >Sometimes, it's pretty easy to figure out exactly how much to rotate
    >it, because you can rotate the image so that all the vertical edges
    >are perfectly straight up and down, or all the horizontal edges are
    >perfectly straight across. But sometimes, due to perspective, vertical
    >or horizontal edges should NOT be straight up/down or across, or the
    >edges aren't parallel. Then I struggle with the rotation correction.
    >
    >Are there any rules/techniques to figure out the proper rotation
    >correction needed? I don't have much grasp of perspective, so I was
    >trying to learn about it in hopes that it would help:
    >http://wiki.panotools.org/Perspective_correction
    >http://wiki.blender.org/index.php/Doc:Manual/Render/Camera/Perspective



    I see photography as a art using science. As such there are
    no rules and what is correct is up to the artist and is not set by
    rules. If it looks right to you, it is right, YOU are the artist.

    Others (and I for some uses) see photography as a science.
    From those situations you need to determine what exactly are you
    looking for and do the measuring and adjusting.
     
    , Jul 12, 2009
    #11
  12. bucky3

    brian brown Guest

    "bucky3" <> wrote in message
    news:...
    > On Jul 11, 12:10 pm, Scott W <> wrote:
    > > Vertical edges in the center of the image should be vertical in the
    > > photo. The
    > > edges to the sides will slope in or out depending on if the camera was
    > > pointed up or down.

    >
    > Thanks, that's the kind of rule I was looking for.
    >
    > Does it also apply that horizontal edges in the center of the image
    > should be straight across in the photo too?



    Not necessarily. There can be a big difference. With most buildings, telegraph
    poles and other man made objects it can usually be assumed that all the
    vertical edges will be true verticals. Or at least they were intended
    or built that way.

    One of my favourite subjects is photographing buildings on riverbanks
    from the opposite side of the river. This usually gives an uninterrupted
    view and such buildings can be interesting.

    Sometimes however its impossible to shoot the building I'm interested in directly
    across the river, there may be trees or another building on this side blocking
    the view. So its necessary to shoot at a slight angle. For the purposes of
    argument lets call "the horizon" the line where the water meets the bank
    or embankment on the other side. Now unless my eyeline and the lens centre
    is dead level with that "horizon" on the far bank which it can't be because
    I'd be up eyes in water myself, then because I'm shooting at an angle
    that "horizon" will in fact slope slightly depending on the angle.
    The same applies when trying to shoot a panorama of an opposite riverbank
    when there's any sort of bend in the river. Its impossible to preserve the
    horizontals and they often end up looking odd. And its impossible to fix
    because if you get the bank truly horizontal in the shot then the buildings
    will be out. There are plenty of other examples.

    The verticals however are never a problem. Without a rising front - a lens that
    can be raised parallel to the picture plane you'll get falling verticals at the
    edges of the shot with tall buildings whatever you do. But these are a doddle
    to fix with perspective tools.


    michael adams

    ....
     
    brian brown, Jul 15, 2009
    #12
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