200 CHAPTER 6 Advanced Techniques
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The same features in Autopano Pro are available in PTGui—one of the
pioneers of panorama technology.
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Hugin, which doesn’t lack in power, is the free Open Source alternative
for panorama stitchers. It supports HDR panorama stitching and can
also be used for nonpanoramic purposes, such as perspective correction
of architectural shots.
All panorama stitchers allow you to choose among different projections. A
projection is responsible for how the image pixels are mapped onto the
viewing surface—i.e., how they are projected. All programs support at least
rectilinear, cylindrical, and spherical projection. Some of them support
many more and even rather exotic projections.
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The rectilinear projection simply projects the whole panorama onto a
flat surface. Because this leads to strong distortions towards the edges
of the image (similar to a photo taken with an ultra-wide-angle lens),
the maximum angle of field should be limited to 120°.
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The cylindrical projection projects the panorama onto the inside of a
cylinder that is then unrolled onto the viewing surface. This projection
and its variants (e.g., Miller projection) are best suited when you want to
print panoramas with a wide angle of field.
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The spherical or equirectilinear projection projects the panorama onto
the inside of a sphere that is then unrolled onto the viewing surface.
This projection is typically used for spherical panoramas viewed on a
computer display using interactive viewers.
Viewers for spherical panoramas are available as a Java applet or as a Flash
application. Apple Quicktime can show panoramas, too. Among the Java-
based viewers, the free PTViewer is interesting. It can handle cylindrical and
spherical projections and also display true HDR panoramas (see next sec-
tion) with the full contrast range. When the user changes the angle of view,
the viewer will adapt to the brightness of the scene, much as the human
eye would do. For Flash, there are many commercial offerings for panorama
viewers plus the notable exception of the panoSalado viewer that comes
for free.
6.2 HDR Panoramas
We have already mentioned one of the problems in panorama photogra-
phy: the large scene contrast. When the sun is shining and the angle of
view is 180° or greater, you will have images that are shot with the sun in
the back and images shot straight into the sun. But contrast at night can
also be too high for a classical exposure.
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