Method for embedding and extracting a spatial domain blind watermark using sample expansion
View Patent ↗Disclosed is a method for embedding and extracting a spatial domain blind watermark using a sample expansion. The sample expansion method using a sample expansion coefficient is introduced to basically improve a common disadvantage of the conventional watermarking method based on the patchwork method, for instance, the watermark is not robust against a compression attack such as JPEG. By applying the sample expansion to a sample group, the embedded watermark comes to contain a low frequency component more larger than ever, so that radio frequency component decreases as much. Thus, although the radio frequency component of the watermark is damaged by the image compression such as JPEG, it is possible to relatively reduce the damage of the watermark. Also, an adaptive watermark embedding method can be considered such that the embedded watermark value is proportional to an average value of the pixel. In order to overcome non-robustness that is a common disadvantage of the conventional methods based on the conventional patchwork method or the conventional modified patchwork method, not a single pixel but sample-expanded pixel is chosen, and there is proposed a spatial domain blind watermarking method using a watermark value that is proportional to an average value of pixel every tile.
1. A method for embedding and extracting a spatial domain blind watermark using a sample expansion in a watermarking method for embedding a watermark information for protecting a copyright of a digital image in the digital image, the method comprising the steps of:
creating a pseudo binary random number having a constant size in row and column directions and setting a sample-pair according to the pseudo binary random number;
expanding the pseudo binary random number by a constant size in the row and column directions according to a set sample expansion coefficient;
tiling the expanded sample-pair blocks at a constant number;
creating a watermark bit corresponding to the each tile and converting a polarity of the each tile according to the watermark bit information;
multiplying an average pixel value every tile with a watermark embedding intensity to compute a watermark value to be embedded; and
embedding the watermark in a pixel within the tile according to the computed watermark value and collecting a partial image in which the watermark is embedded, every tile to acquire a finally watermarked image.
2. The method of claim 1 , wherein the step of setting the sample-pair according to the pseudo binary random number block sets the sample-pair by two samples group of a bit “1” and a bit “0”.
3. The method of claim 1 , wherein the step of expanding the pseudo binary random number expands the pseudo binary random number to the constant size according to a sample expansion coefficient that is set to deal with a pixel block that is not a single pixel of 1×1 but is expanded to a size of d×d (d is a positive integer except for 1).
4. The method of claim 1 , wherein the tiling step computes the number of the tiles using a following equation:
Number of tiles=└ R/P R ′┘×└C/P C ′┘
where └*┘ is the largest integer among numbers less than the *, and P R ′ and P C ′ are indicative of sizes of the expanded block in row and column.
5. The method of claim 1 , wherein in the step of creating the watermark bit and converting the polarity of the each tile according to the watermark bit information, the watermark can be made by a pseudo binary random number generator or can be generated by allocating an arbitrary binary value.
6. The method of claim 1 , wherein the polarity of the each tile is converted into “+1” when the bit information of the each tile is “1”, and the polarity of the each tile is converted into “−1” when the bit information of the each tile is “0”.
7. The method of claim 1 , wherein in the step of computing the watermark value, the average pixel value every tile is obtained by computing an average pixel value Mi,j of an original image block with respect to all (i, j) tiles in order to decide the value of the watermark value to be embedded.
8. The method of claim 1 , wherein the step of computing the average pixel value every tile computes the watermark value every tile using a following equation:
┌k×M i,j ┐
where k is the watermark embedion intensity, M i,j is a (i, j)-th average pixel value every tile, and ┌*┐ is the smallest integer among integers less than the *.
9. The method of claim 1 , wherein the step of acquiring the watermarked image embeds the watermark into the pixel within the tile using a following equation:
E i,j =O i,j +W i,j ×┌k×M i,j ┐×P′−
where, E i,j is a tile block into which the watermark is embedded, O i,j is a partial block of an original image corresponding to a (i, j)-th tile, and W i,j is a value of (i, j) term of a block W.
10. The method of claim 9 , wherein the (i, j) term of the block W and the sample expanded block P′ have a value of “+1” or “−1”.
11. The method of claim 1 , after embedding the watermark value every tile, further comprising a step of embedding the watermark using a following equation such that the average value of the pixel every tile is not changed;
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where, Ei, j is a tile block in which the watermark is embedded, O i,j is a partial block of an original image corresponding to a (i, j)-th tile, and W i,j is a value of (i, j) term of a block W.
12. A method for embedding and extracting a spatial domain blind watermark using a sample expansion in a method for extracting a watermark information for protecting a copyright of a digital image, the method comprising the steps of:
tiling the digital image into sample-pair blocks at a constant size;
computing an average pixel value of the blocked two samples group every tile;
extracting a watermark bit every tile and determining the extracted watermark bit; and
collecting the determined watermark bits every tile and acquiring a final watermark bit block.
13. The method of claim 12 , wherein the step of computing the average pixel value of the two samples group, computes the average pixel value using a following equation:
D i,j =M 1 −M 0
Where, D i,j is the average pixel value of the two samples group, M 1 is the average pixel value of a portion which a bit of P′ is “1” with respect to all (i, j)-th tiles, and M 0 is the average pixel value of a portion which the bit of P′ is “0”.
14. The method of claim 12 , wherein the step of determining the extracted watermark bit determines the extracted watermark bit as “1” when the average pixel value of the two samples group is 0 or more, and determines the extracted watermark bit as “0” when the average pixel value of the two samples group is 0 or less.