| Stitching Panoramas |
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The process of stitching separate exposures made by a conventional "flat back" camera (i.e. one designed to maintain rectilinear perspective) essentially consists of two stages, though you would not normally be aware of this if you were using one of the more "automatic" software packages like those supplied with digital cameras. The first stage involves remapping the rectilinear images into cylindrical perspective as shown below. This appears to introduce barrel distortion but is really a "correction". If the images had been taken with a "swing lens" camera, the film plane would have been curved and this is the sort of image that would have been recorded. In order to perform the remapping the software needs to know the focal length of the lens, or more specifically its horizontal field of view. If a digital camera has been used the software can obtain this from the EXIF data, otherwise it must be entered manually.
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remap |
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rectilinear perspective |
cylindrical perspective |
The second stage is the actual stitching. The separate images are aligned either automatically or with some manual intervention and a composite image is formed. PT Assembler outputs a layered file in Photoshop psd format. This allows maximum flexibility in positioning of the joints and in blending the images together. The people on the right of this third image moved before I took the fourth shot, but fortunately they were in the overlapping area so I could choose which "version" to use in the final panorama. I suspect that a fully automatic stitching program would have made a mess of this. The final panorama is shown below.
Click here to see the QTVR movie
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The final Panorama |
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