Patent ID: 6229924
Filing Date: 2001-05-08
Classification: G06K,G06T,G10L,G11B,H04N

Abstract:
A method for adding a multibit watermark to an image comprising,generating DCT (Discrete Cosine Transform) coefficients representing said image, said coefficients being arranged in blocks, said blocks being arranged into macro blocks,each of said macro blocks containing a block one, a block two, a block three and a block four, and the coefficients in each block being arranged in rows and columns, alternate of said rows and columns being designated even and odd rows and columns, adjusting said coefficients as follows:the coefficient in block one being changed directly in response to the bits of said watermark, the bits in blocks two, three and four being changed in accordance with the following rules:Block two: invert the direction of the change if the coefficient is in an odd row,Block three: invert the direction of the change if the coefficient is in an odd row columnBlock four: invert the direction of the change if the coefficient is in an odd row or if it is in and odd column, but do no invert the direction of the change if the coefficient is in both and odd row and in an odd column,whereby the sinusoids generated by said adjustments are in phase across block boundaries in each macro block.