Lower left: Each overlapping pair of images is compared and corresponding
features are marked with control points. This allows the software to place each
image on the sphere taking into account the true focal length, barrel distortion, tilt
and shift.
Above: After alignment, the images can be assembled and previewed. The images The final panorama after some editing. The image has been cropped to eliminate
have been taken with a range of exposures so the seams are visible. An equirectan- the uninteresting wall and paving stones.
gular projection has been used to view the spherical image.
Below: Photometric optimisation matches the exposure and white balance between next screen shot, above centre) cal panorama, these have to represent
overlapping images, and corrects for camera response function and lens vignet- the software remaps the images the surface of a sphere, partial or
ting. Even without blending, the seams are not apparent. according to the desired cartographic whole. This problem is well-known
projection and then these are to cartographers who have invented
individually adjusted and blended to many different ways of achieving this.
eliminate seams (below centre). Each different cartographic
The final image can be adjusted projection has its own advantages
in the usual manner for brightness, and disadvantages depending on the
contrast, colour and sharpness before desired properties of the spheri-
final presentation as a “flat” image or cal image one wants to preserve.
else being converted to an interactive A common choice for spherical
“virtual reality” panorama (e.g. panoramas is the equirectangular
QuickTimeVR or Flash). A partial projection where the horizontal
crop of the panorama can be effec- axis on the image represents the
tive, as above. The main picture on azimuthal co-ordinate of a point
this page is cropped top and bottom. on a sphere, and the vertical
axis represents its elevation.
Cartographic projection
Equirectangular projections of
the sphere are characterised by a
An image usually consists of a rectan- width:height ratio of 2:1 represent-
gular array of pixels but for a spheri- ing 360 degrees horizontal and 180
19 photoworld
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