Image watermarking based on sequency and wavelet transforms
First Claim
1. A method for embedding a binary watermark image into a gray scale host image comprising the steps of:
- discrete wavelet transforming the host image;
discrete binary wavelet transforming the watermark image;
for each sub-band subb selected from the set of LL, LH, HL and HH of a first predetermined transform level of the host image and a second predetermined transform level to the watermark imagethresholding and binarizing data elements of the corresponding sub-band of the discrete wavelet transformed host image,comparing sequencies of thresholded and binarized data elements of the discrete wavelet transformed host image with sequencies of the discrete wavelet transformed watermark image to form a watermarking sequency mask,forming watermarked wavelet domain data by combining data elements of the corresponding sub-band of the discrete wavelet transformed host image with data elements of the corresponding sub-band of the wavelet transformed watermark image as filtered by the watermarking mask, andinverse discrete transforming the watermarked wavelet domain data thereby forming a watermarked host image.
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Abstract
This invention is a new approach for the image watermarking in the wavelet transform domain based on sequency of the host and watermark image. For each sub-band a first transform level of the host image is thresholded and binarized. Sequencies of thresholded and binarized data host image are compared with sequencies of the discrete wavelet transformed watermark image to form a watermarking sequency mask. The watermarked wavelet domain data is formed by combining data elements of the discrete wavelet transformed host image with corresponding data elements of the wavelet transformed watermark image as filtered by the watermarking mask. A reverse process can extract the watermark with a high degree of accuracy even after attack upon the watermarked host image.
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Citations
16 Claims
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1. A method for embedding a binary watermark image into a gray scale host image comprising the steps of:
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discrete wavelet transforming the host image; discrete binary wavelet transforming the watermark image; for each sub-band subb selected from the set of LL, LH, HL and HH of a first predetermined transform level of the host image and a second predetermined transform level to the watermark image thresholding and binarizing data elements of the corresponding sub-band of the discrete wavelet transformed host image, comparing sequencies of thresholded and binarized data elements of the discrete wavelet transformed host image with sequencies of the discrete wavelet transformed watermark image to form a watermarking sequency mask, forming watermarked wavelet domain data by combining data elements of the corresponding sub-band of the discrete wavelet transformed host image with data elements of the corresponding sub-band of the wavelet transformed watermark image as filtered by the watermarking mask, and inverse discrete transforming the watermarked wavelet domain data thereby forming a watermarked host image. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. The method of extracting a watermark from a watermarked host image comprising the steps of:
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discrete wavelet transforming said watermarked image, for each sub-band subb selected from the set including LL, LH, HL and HH of said first predetermined transform level of the watermarked host image calculating a weight factor Ŝ
as follows;
Ŝ
(Ĥ
—
Rsubb(i,j)=(2*√
{square root over (Ksubb*abs(Ĥ
—
Rsubb(i,j)))}+Ĝ
subb(i,j),where;
Ĝ
subb(i,j)={2*√
{square root over (max(Ĥ
—
Rsubb(i,j)*Ksub)}+ε
};Ĥ
_Rsubb(i,j) is the autocorrelation of the pixel(i,j) of the wavelet transformed host image sub-band Ĥ
_subb;and ε
is a predetermined constant,determining individual pixels (i,j) of an extracted wavelet domain watermark image from Msubb(i,j), Nsub(i,j), Rsub(i,j) and Dsubb as follows;
If ((Dsubb>
0 AND Msubb<
Dsubb>
Nsubb) OR (Dsubb<
0 AND Rsubb<
Dsubb>
Nsubb)
Then Ŵ
_subb(ƒ
subb(i),j)=1
Else Ŵ
_subb(ƒ
subb(i),j)=0where;
inverse discrete binary wavelet transforming the extracted wavelet domain watermark image thereby forming an extracted watermark image.- View Dependent Claims (14, 15, 16)
where;
H_Rsubb(i,j) is the autocorrelation of the pixel(i,j) of the wavelet transformed host image sub-band H_subb.
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15. The method of claim 13, wherein:
ε
is equal to 5.
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16. The method of claim 13, further comprising:
reverse pseudo randomizing rows of the extracted wavelet domain watermark image using a pseudo randomization key before inverse discrete binary wavelet transforming the extracted wavelet domain watermark image.
Specification