Patent ID: 6973195

Claim:
A method of embedding digital watermark information in a color image, said method comprising the steps of: providing a color signal transformation matrix and an inverse color signal transformation matrix, the color signal transformation matrix transforming image data in a first colormetric system, which expresses a predetermined color space by a combination of plural parameters, into image data in a second colorimetric system, which expresses the predetermined color space by a combination of other plural parameters, the inverse color signal transformation matrix carrying out inverse of the transformation; adjusting the color signal transformation matrix by either adding a digital watermark matrix to or subtracting a digital watermark matrix from the color signal transformation matrix, the digital watermark matrix including an arbitrary numerical value of real number x, which represents the digital watermark information, as an entry of the digital watermark matrix and satisfying a condition that a sum respective entries in each row and in each column is substantially equal to zero; transforming the image data in the first colormetric system into image data in the second colormetric system with the adjusted color signal transformation matrix; and inversely transforming the resulting image data in the second colormetric system, which is obtained by the transformation, into the image data in the first colormetric system with the inverse color signal transformation matrix, so as to embed the digital watermark information into the color image.