Thursday, December 15, 2011

Photographic Purity– (Building a Panoramic)

We've seen that distortion is built into the process of producing a conventional photographic image. If we take a few regular photographs from the same location, slightly rotating the camera for each frame, we effectively cover a greater field of view with the shots. If the shots slightly overlap each other at the sides, we ought to be able to easily combine  them to produce a single wide-angle image.

Unfortunately, this process will not work because the built-in distortion of the camera lens causes all features in the view to change shape when the camera points in a different direction. When a particular feature is on the right side of the field of view it's one shape, and when on the left side of the field of view it's a slightly different shape. So, when the right side of the first image is overlaid on the left side of the second image, the shapes do not match. This results in either ghost images, missing information, or otherwise mismatched overlaps in the final pano image.

For a proper, undistorted blending of conventional camera shots into a wide angle panorama, the built-in distortion of a standard camera lens must be eliminated, or at least minimized. Once the distortion has been removed the separate frames may be simply overlaid on each other, with the overlapping parts of the images matching well and the images blending into one.
Panoramic sequence of nine frames that have been geometrically remapped to remove camera lens distortion

In the days before modern digital computing, this distortion elimination was nearly an impossible task. Now, this process has become not only possible but even fairly simplistic to the user. Although it seems easy from the outside of the computer, there are actually many billions of calculations and transformations being carried out for a single panorama to be compiled.

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