Digital archiving of hard-back literature becomes in-
creasingly an essential part of the work of libraries and
museums. Although for this purpose the modern com-
puter technology accomplishes already major premises,
the status quo of the scanner technology is not satisfy-
ing. In particular it is hardly possible to get distortion-
free copies from thick books without damaging them.
This represents currently for digitalisation of valuable
historical books a large problem. In addition, a full au-
tomated character recognition in the area of book crease
is often impossible. Removing the projective distor-
tion in a two-dimensional image of a three-dimensional
warped surface is a very common problem. There are
many different approaches. But either in case of pure
software solutions the exactness and reliability are not
particulary high or the techniques are costly concerning
the additional hardware and provide only low resolu-
tions in the copy of documents due to the exclusive use
of matrix cameras.
Our contribution to handling the problem of dewarp-
ing is the development of a hardware extension for a
top view scanner. This kind of book scanner captures
a copy of the book page from above and from a cer-
tain distance. Through the use of a line camera with
an appropriate stripe lighting it is possible to receive
an evenly sharp and well illuminated two-dimensional
image. However, we get inevitably a distorted copy in
consequence of the projective geometry of the scanner
and the warped surface of the page. Using an addi-
tional camera we capture during the scanning process
an image sequence of the moving stripe lighting of the
scanner. From this image sequence we calculate a 3-
d surface reconstruction of the warped page through a
new method which is a further development of light sec-
tioning. By combining the surface reconstruction and
the original scanner image we can calculate a nearly
distortion-free copy of the book page.

(Contact: Prof. Al-Hamadi)