Extracting Rectilinear Images from Panoramas
Panoramic images employing cylindrical projection can
be generated in a variety of ways:
Often, perspectively corrected rectilinear partial views
of these panoramas are wanted. This article describes how these can be
extracted using free software (Panorama
Tools). Image extraction uses high quality interpolators preserving
the quality of the original photograph and making them suitable for printing.
Direct capture using scanning slit cameras (Roundshot, PanoScan,
Direct capture using Swing Lens camera (Horizon, Widelux,
Warping and stitching of normal images using software (eg
Rendering using 3d modeling software (eg Povray).
The following image is a 360° panorama generated using
the Roundshot camera equipped with a 14mm lens. (original
photograph by Julio Moya, firstname.lastname@example.org)
To extract partial views, select a viewing direction by
choosing proper yaw and pitch angles, in this case we use yaw=-115°
Then decide which field of view you wish to show: 50°
corresponds to normal vision, whereas 104° is rather wide. Finally,
you have to choose pixel dimensions for the extracted image, ie width=500
Now open the panoramic image in Photoshop, choose 'Panorama
Tools' and 'adjust'. Push 'Prefs' and select options (b) and (c). Then,
back in 'adjust', select 'extract' and 'use options', push 'set' and fill
the dialog as shown below:
Clicking 'OK' twice initiates the transformation and results
in the upper left image below. The other images were extracted using different
yaw angles, and the last image corresponds to a camera tilted down by a
pitch angle of -45°.
Notice that the lower left image runs across the seam from
left to right, and some retouching may be required before printing. Finally,
other image dimensions and fields of view are equally possible as shown
by the "portrait"-images below:
Some Additional Comments:
If the lens used for image capture shows distortions, or
if the scanning speed is not properly synchronized to the focal length
of the lens, then the extracted images will exhibit barrel or pincussion
type distortions. These can be corrected using the 'correct'-option in
the 'adjust' submenu, see above. You have to find suitable correction parameters
as outlined in this article.
For Swing-lens cameras field of view is smaller than 360°.
Typical values are 120-140°. Enter these values in the 'Panorama->HFOV'
field of the 'adjust' submenu.
Partical views can be extracted from other formats also,
eg rectilinear, fisheye and equirectangular projections. Choose the appropriate
options in the 'adjust' submenu above.
Using the interactive Panorama editing feature of 'Panorama
Tools', you can shift the viewport across the Panorama similar to an interactive
VR-viewer with the options to zoom in and out. At any time you can save
or print the current viewport. See the Readme file of 'Panorama Tools'
about this feature.
1999 © Helmut Dersch email@example.com