초록 ▼

Embedding a watermark in an image by changing selected DCT coefficients in the blocks and macro blocks of coefficients which represent the image. The changes in the blocks that comprise each macro block are done in a coordinated manner so that the phase of the watermark signal is preserved across th

Embedding a watermark in an image by changing selected DCT coefficients in the blocks and macro blocks of coefficients which represent the image. The changes in the blocks that comprise each macro block are done in a coordinated manner so that the phase of the watermark signal is preserved across the block boundaries. By preserving the phase across block boundaries, a detectable grid is formed which can be used as an orientation and scaling grid. Furthermore, by preserving the phase across block boundaries the visual artifacts introduced by the watermark are minimized. The bit rate of the image signal is preserved by maintaining a count (referred to as the cumulative change count) that represents the amount that the bit rate has been increased by changes in coefficients less the amount that the bit rate has been decreased by changes in the coefficients. If at any time the cumulative change count exceeds a pre-established limit, coefficient changes that decrease the cumulative change count continue; however, coefficient changes that increase the cumulative change count are suspended. The suspension of coefficient changes that increase the cumulative change count continues until the cumulative change count falls below the pre-established limit.

대표청구항 ▼

[ We claim:] [1.]1. 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 o

[ We claim:] [1.]1. 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.