Cryptography Reference
In-Depth Information
2
4
3
5
2
4
3
5
;
1
1
1
1
1
0
1
0
T
2
T
2
=
=
1
0
0
1
1
1
1
1
2
4
3
5
2
4
3
5
:
1
1
1
1
1
1
1
1
T
3
=
T
3
=
1
0
1
0
1
0
0
1
T
1
; T
2
, and
T
3
we obtain the basis matrix S
0
Concatenating the matrices
2
4
3
5
;
1
0
1
1
1
1
1
0
1
0
1
1
S
0
=
1
1
1
0
1
0
1
1
1
1
1
0
T
1
; T
2
, and
T
3
we obtain the basis matrix
whereas, concatenating the matrices
S
1
2
4
3
5
:
1
0
1
1
1
1
0
1
1
0
1
1
S
1
=
1
1
0
1
1
0
1
1
1
1
0
1
The pixel expansion of the above construction is m =
P
X2
0
2
jXj1
= 6.
9.3 Almost Ideal Contrast VCS with Reversing
In order to improve the contrast in VCSs, Viet and Kurosawa [13] introduced
another noncryptographic operation, called reversing, which can be used by
participants in the reconstruction phase. Such an operation, which can be
easily performed by many copy machines, is applied to a transparency and
creates another transparency in which black pixel
s
are reversed to white pixels
and viceversa. In the following, we will denote by t, the transparency obtained
after applying the reversing operation to the transparency t.
Viet and Kurosawa [13] showed how to construct a (
Qual
;
Forb
)-VCS with
reversing, where black pixels are perfectly reconstructed, whereas, white pixels
are almost perfectly reconstructed. The idea behind their construction is to
run several times the distribution phase of a (
Qual
;
Forb
)-VCS with a perfect
reconstruction of black pixels. The larger the number c of runs, the better the
contrast of the resulting VCS with reversing. In particular, Viet and Kuro-
sawa showed that if the contrast of the underlying VCS is q < 1, then the
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