Visual Cryptography
Anyone who can clarrify this algorithm and give me some light.
And is there a method in java where I can get the left most bit of a pixel??
This shall describe the proposed watermark method to embed a watermark pattern into an image. This method is based on the simple (2, 2)-visual threshold scheme described by Naor. The owner should select an h�n black/white image as her/his watermark pattern P. In the embedding process, she/he generates the verification information from the original image based on the (2,2)-visual cryptography by defining the watermark pattern as the shared image. Virtually, the verification information is one shadow of the visual cryptography. The owner should register the watermark pattern of her-/himself and the verification information of her/his image at the notarial organization.
In the embedding processes, the owner should randomly select a number as her/his secret key, S, to embed the watermark pattern into the image M. The secret keys for different images either are equal or not. The owner should keep it secretly. We assume that the owner wants to embed the h�n watermark pattern into the image M that is a k�l 256 gray-leveled image. The owner embeds the watermark pattern P into the image M by generating the secret key, S, and the verification information, V, as the following steps.
Step E-1. Select a random number S as the secret key of the image M.
Step E-2. Use S as the seed to generate h�n different random numbers over the interval [0, k�l]. (We use Ri to denote the i-th random number.)
Step E-3. Assign the i-th pair (vi1, vi2) of the verification information V based on Table 2. (You can see this below)
Step E-4. Assemble all the (vi1, vi2) pairs to construct the verification information V.
Note that Step E-3 constructs the verification information based on the watermark pattern. The proposed method does not embed the watermark pattern into Image M or alter any pixel of Image M. information The color of the i-th pixel in watermark pattern is The left most bit of the Ri-th pixel of Image M is Assign the i-th pair, (vi1, vi2), of verification information V to be Black �1� (0, 1) Black �0� (1, 0) White �1� (1, 0) White �0� (0, 1)
This is the table
color of ith pixel of | the left most bit of the | assign i-th pair (vi1, vi2) of
watermark pattern | R-ith pixel of Image M | tion information V to be
Black "1" (0, 1)
Black "0" (1, 0)
White "1" (1, 0)
White "0" (0, 1)
And the way to encrypt the Pixel p is located at Doug Stinson's page at
http://www.cacr.math.uwaterloo.ca/~dstinson/visual.html