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52217Re: Drum panorama

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  • Scott Highton
    Nov 2, 2011
      Hi Peter,

      What you're trying to do is the equivalent of a slit scan camera shooting an object on a turntable, as I believe someone else mentioned here.  In general, the narrower the slit, the better your results (unless you go to extremes and then wind up with diffraction problems... don't worry about this for the following).  This sort of work has traditionally been done with slit scan camera/turntable systems such as those available from Roundshot (both film and digital) and Panoscan.



      You can try a similar approach with a low priced digital camera, a slow moving turntable, and some automated scripts (which you'll probably have to create) in Photoshop.

      Basically, you shoot a series of images as the object rotates, then extract a center column of pixels from each image, and then stack these columns together (like books in a book case) in Photoshop to create a complete 360° flattened view.  Don't try to "stitch" these columns, but rather, simply abut them next to each other.  The more pictures you take (i.e. the smaller the rotation between each), the fewer number of pixels you'll need to extract from the center of each, and the better your resulting image assembly is likely to be.

      In a perfect world, you'd only take a single pixel column from each image (the equivalent of a single pixel wide slit or image sensor), but that could entail capturing and extracting thousands of images.

      However, you may find that you can still get great results by shooting fewer images and extracting 10, 20, or 50 pixel wide columns from the center of each.  You'll have to do your own tests to see what works for the size of the object you're shooting and the resolution of the finished image you need.  And you'll have to figure out how many shots are necessary (how much to rotate the object between each shot) for a full rotation in order to maintain the proper aspect ratio for the resulting file when the columns are all stacked together.  Use a telephoto lens for best results.


      For example, let's say you want a final image that is 3,600 pixels wide.

      If you were only going to extract a single pixel column for each source image, you'd need 3,600 images, and you'd have to rotate the object 1/10 of a degree between shots.
      If you could use 10 pixel (wide) columns instead, you'd need only 360 images where the object was rotated one degree between shots.
      If you could use 20 pixel columns, you'd need 180 images where the object was rotated two degrees between shots.
      If you could use 50 pixel columns, you'd need 72 images where the object was rotated five degrees between shots.
      Or, if you could use 100 pixel columns, you'd need only 36 images where the object was rotated 10 degrees between shots.
      You see the pattern.


      Bryan Mumford, developer of the Time Machine camera triggering and time lapse system, has a web page that discusses this approach using his Time Machine, a motorized rotary table, and a digital camera.  The Time Machine controls the rotation of the rotary table and the firing of the camera.  He calls this process "Streak Photography," and he's created some beautifully artistic results, including sequences assembled into QT movies.  The same approach should work for capturing and assembling single "unwrapped" object images.




      Should you decide that you want to pursue a "stitching" approach instead, consider using a telephoto lens and shoot the object from a distance.  This will compress the differences between high and low points on the surface of the drum and minimize visual distortion or foreshortening of the object in each source image.  Then, enter a long focal length, such as 400mm, in PTGui (you may need to override the  EXIF lens info).  That might  better help with control point generation.


      Good luck with your efforts, and please let us know about your results (post them so we can see, if possible).

      Regards,




      Scott Highton
      Author, Virtual Reality Photography
           320 pages, 300+ illustrations, $44.95
           ISBN 978-0-615-34223-8)
      Web: http://www.vrphotography.com

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