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Moisaicing is the process of projecting images from individual frames
on to a single image, recreating the static background in a panoramic
view, thus augmenting the video presence. Projection parameters are obtained
by reconstructing the movements of the camera during the filming.
The camera is modelled in a see-through projection, using 8 movement
parameters. Here, camera movement is mainly composed of pan and tilt,
yielding negligible values for the remaining parameters. Translational
movements of the camera are also very small compared with the depth range to
the object, and therefore a single camera model can be applied to all
regions. Displacement between adjacent frames are calculated from the
correlation of feature blocks, leading to the estimation of the camera
movements.
The panoramic view is rendered taking a reference frame that is chosen
by calculating the central position of the camera in relation to the
total span through the video clip. This reference frame is taken as
the center of the mosaic image and all other frames are projected
on its plane. The following image shows the panoramic view of the
background region from a sequence 31 frames long. In this example,
the 15th frame was found to be in the ideal projection plane for
rendering of the mosaic image.
With conventional mosaicing techniques, moving objects are extracted
by using temporal filters, but depending on the camera movement there
are cases when they can not be extracted. In the technique presented
here, object regions are segmented so that there is no dependency
to the camera movements. Therefore, the occurence of ghosts has been
greatly reduced.
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