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OMNIFOCUSED IMAGING OF SCENES WITH LIMITED MOTION Nicam achieves omnifocus
panoramic imaging only for static scenes since the camera pans across the
visual field. As panning takes time, successive images of the same moving
object are from different effective viewpoints. Fusion of these images for
omnifocus leads to registration problems. A straightforward extension to
image dynamic scenes in omnifocus would require elimination of panning. We
have developed an intermediate solution, which retains panning but yields
objects imaged in less than perfect focus. Recall that the mosaicing the
set of images taken by Nicam as it pans requires correspondence of a scene
point across the set. The presence of moving objects upsets the
correspondence between images in the sequence, resulting in a distorted
appearance of the moving objects in the final mosaic (see part (a) of the
figure). We avoid these artifacts and create large depth of field mosaics of
scenes with moving objects. The basic idea is to combine the sequence of
images in a manner such that each entire moving object is selected from a
single best focused frame and is pasted, as it is, in the final mosaic, and
other regions are chosen and pasted similarly from those images where they
are best focused and not occluded by the moving objects. This approach
ensures that all regions, except possibly those related to moving objects,
are best focused and no artifacts due to moving objects are present. The necessary algorithms require segmenting the moving
objects in each image, selecting where is it overall in best focus, and for
each still scene point determining in which frame it is best focused. The
algorithms use a set of tests to perform the segmentation of moving objects.
The tests that we use are point intensity difference test, point correlation
test, and focus trajectory test. The point difference and point correlation
tests measure how image intensity and local texture vary over the sequence of
images (the correspondence between images is known for still scene points).
If the variation is small between adjacent frames the point is more likely to
be static. The focus trajectory test checks for variation in the focus
measure across the image sequence against expected behavior. For instance,
for a still scene point variation in focus measure is expected to be
unimodal, while for a moving scene point it will be random, since the
correspondences between images for such points are incorrect. One result thus
obtained is shown in the figure below.
(a)
(b) An omnifocus image
acquired in the presence of moving objects: (a) Nicam approach. (b) New
intermediate approach. |
