| If you project a grid of parallel lines, each dark-bright-border acts
as light knife. However there is a ambuguity which line is seen by the
pixels of the camera. This ambiguity is solved by the Coded Light Approach
(CLA) .
CLA is an absolute measurement method, requiring only a small number
of images to obtain a full depth-image. This is can be achieved with
a sequence of projections using a grid of switchable lines (light or
dark). All the lines are numbered from left to right. The numbers are
encoded with the so called 'Gray-Code'. Despite its name, the Gray-Code
is a binary code. In this code adjacent lines differ by exactly one
bit leading to good fault tolerance. Using a special line projector,
with, say 640 switchable lines, all lines may be encoded with ten bits.
This can be encoded in ten images within half a second. One bit of
all lines is projected at a time. A bright line represents a binary
'zero' a dark line a 'one'. All object points illuminated by the same
switchable line see the same sequence of bright and dark illuminations.
This information is extracted from the video-images by binarisation.
This binary image is added to a so-called bit-plane stack. After ten
binarisations the bit-plane stack contains the full gray-code of the
corresponding line in the projector.
Using look-up-tables standard video framegrabbers a full 3-D image
can be generated within one or some few seconds in a very reliable
manner
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