Digital image watermarking apparatus and method
First Claim
1. A method for embedding watermark into a digital image having a luminance component, comprising:
- (a) transforming said luminance component into coefficients of a frequency domain having a first frequency area and a second frequency area;
(b) generating a replacement coefficient from a coefficient of said first frequency area and said watermark;
(c) replacing a coefficient of said second frequency area with said replacement coefficient, whereby said watermark is embedded into said digital image;
(d) transforming said digital image embedded with said watermark into an inverse frequency domain;
(e) transforming the luminance component of the digital image embedded with said watermark into the coefficients of the frequency domain;
(f) generating a watermark for authentication;
(g) extracting said watermark embedded in said digital image by using the coefficients of said first and second frequency domains; and
(h) authenticating said digital image by finding a correlation of said extracted watermark and said watermark for authentication, wherein (h) comprises;
(h1) finding the maximum peak value and the position of said maximum peak value from the correlation between said extracted watermark and said watermark for authentication;
(h2) finding the 4th moment from said correlation;
(h3) judging that said extracted watermark is same with said watermark for authentication in case where said 4th moment is over a predetermined critical value, the maximum peak value of said correlation is over a predetermined critical value, and the position of the maximum peak value of the extracted watermark and the watermark for authentication are the same.
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Abstract
The present invention relates to a digital image watermarking apparatus and method. Luminance component of a digital image are transformed into coefficients of a frequency domain, and watermark is generated by encrypting a user key and generating pseudo random number from encrypted user key. Then, a replacement coefficient generated from a coefficient of a first frequency area and the watermark is replaced with a coefficient of a second frequency area so that the watermark is embedded into the digital image. The embedded watermark is extracted at an authenticating apparatus and the digital image is authenticated by finding the correlation between the extracted watermark and watermark for authentication.
33 Citations
14 Claims
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1. A method for embedding watermark into a digital image having a luminance component, comprising:
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(a) transforming said luminance component into coefficients of a frequency domain having a first frequency area and a second frequency area; (b) generating a replacement coefficient from a coefficient of said first frequency area and said watermark; (c) replacing a coefficient of said second frequency area with said replacement coefficient, whereby said watermark is embedded into said digital image; (d) transforming said digital image embedded with said watermark into an inverse frequency domain; (e) transforming the luminance component of the digital image embedded with said watermark into the coefficients of the frequency domain; (f) generating a watermark for authentication; (g) extracting said watermark embedded in said digital image by using the coefficients of said first and second frequency domains; and (h) authenticating said digital image by finding a correlation of said extracted watermark and said watermark for authentication, wherein (h) comprises; (h1) finding the maximum peak value and the position of said maximum peak value from the correlation between said extracted watermark and said watermark for authentication; (h2) finding the 4th moment from said correlation; (h3) judging that said extracted watermark is same with said watermark for authentication in case where said 4th moment is over a predetermined critical value, the maximum peak value of said correlation is over a predetermined critical value, and the position of the maximum peak value of the extracted watermark and the watermark for authentication are the same. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. An apparatus for embedding a watermark into a digital image having a luminance component, comprising:
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a frequency domain transformer for transforming said luminance component into coefficients of a frequency domain having a first frequency area and a second frequency area; a watermark generator for generating said watermark; a replacement coefficient generator for generating a replacement coefficient from a coefficient of said first frequency area and said watermark; a replacing device for replacing a coefficient of said second frequency area with said replacement coefficient, whereby said watermark is embedded into said digital image; an inverse frequency domain transformer for transforming said digital image embedded with said watermark into an inverse frequency domain; a frequency domain transformer for transforming the luminance component of the digital image embedded with said watermark into coefficients of the frequency domain; a watermark generator for generating watermark for authentication; a watermark extractor for extracting said watermark embedded into said digital image by using the coefficients of said first and second frequency domains; and a correlation computation device for authenticating said digital image by finding a correlation between said extracted watermark and said watermark for authentication, wherein the correlation computation device finds the maximum peak value and the position of said maximum peak value from the correlation between said extracted watermark and said watermark for authentication, finds the 4th moment from said correlation, and judges that said extracted watermark is same with said watermark for authentication in case where said 4th moment is over a predetermined critical value, the maximum peak value of said correlation is over a predetermined critical value, and the position of the maximum peak value of the extracted watermark and the watermark for authentication are the same. - View Dependent Claims (13, 14)
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Specification