PANORAMIC IMAGE PROJECTIONS

An image projection occurs whenever a flat image is mapped onto a curved surface, or vice versa, and is particularly common in panoramic photography. A projection is performed when a cartographer maps a spherical globe of the earth onto a flat piece of paper, for example. Since the entire field of view around us can be thought of as the surface of a sphere (for all viewing angles), a similar spherical to 2-D projection is required for photographs which are to be printed.

Narrow Angle of View
(grid remains nearly square)

Wider Angle of View
(grid is highly distorted)

For small viewing angles, it is relatively easy to distort this into an image on a flat piece of paper since this viewing arc is relatively flat. Some distortion is inevitable when trying to map a spherical image onto a flat surface, therefore each projection type only tries to minimize one type of distortion at the expense of others. As the viewing angle increases, the viewing arc becomes more curved, and thus the difference between panorama projection types becomes more pronounced. When to use each projection depends largely on the subject matter and application; here we focus on a few which are most commonly encountered in digital photography. Many of the projection types discussed in this tutorial are selectable as an output format for several panoramic software packages; PTAssembler allows selection of all those which are listed.