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Divergence

by JackDesBwa 2020-05-20 08:21:05

This photo illustrates the fact, true but hardly believable for some people, that the orientations of the cameras have no importance concerning the alignment process in digital stereoscopic photography, provided that you use sufficiently efficient tools. However, it has an effect on the field of view since you can only have stereoscopic effect in the zone seen by both cameras.

Here, the scene was taken in cha-cha with voluntarily exaggerated divergence (left/right and up/down) as well as a rotation of the cameras around the optical axis. Nonetheless, the lens was moved horizontally between the two shots, which is fundamental to avoid a tilt in the final image (as would be the case with a tilted rig). The orientations of the cameras were estimated to be (8.1°, 2°, -9.1°) and (-5.8°, -4.7°, -4.3°) around each axis relative to what it would be with parallel configuration, if I interpret the data correctly.

On the top left part, we see the two original photos. The brain would clearly not be able to fuse them because of far too much divergence in all directions and because of the rotation.

In the second row, we rotate the images in 3D to counteract the tilt of the cameras. It is actually for illustrative purposes as the rectification process can work directly in projective coordinates. Furthermore, the 3D representation here is almost but not totally accurate.

Then we can project this 3D view in 2D. This creates a pair that can be fused by the brain, although with effort because there are very very much rivalries due to the different fields of view which can make it actually very hard to fuse. This is shown in the third row. Again, this step can be done directly in projective space without 3D representation.

In the fourth row, we restrict the image to the zone seen by both cameras. Without the annoying rivalries, we can easily fuse the result now.

Finally, we crop the irregular shape into a rectangular area and get the result on the right. It remains a slight error of alignment because of some manual adjustments I had to do for this educative image, but they are not really problematic. The quality of the image is not visibly altered by the process, the original photos are of medium quality (slightly blurred) in the first place.

-- 2020-05-18, LX15 cha-cha

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