| 摘要 |
A method of embedding watermark data into a two-color (binary) image includes assessing the suitability of each of several candidate pixels to embed a bit of watermark data. This is done by identifying candidate pixels for which one pixel directly above the candidate pixel and one pixel directly below the candidate pixel have different colors; and one pixel immediately to the left of the candidate pixel and one pixel immediately to the right of the candidate pixel have different colors. In one embodiment, only a single candidate pixel in each 2x2 block is identified as flippable. The "flippability" of each candidate pixel may be determined based on a relationship of coefficients computed from a binary wavelet transform or binary lifting transform formed from the image. Data may be embedded by inverting selected candidate pixels. A recipient of the document may similarly assess which block contain the watermark data, by assessing the suitability of each 2x2 block in the document to embed such data. Conveniently, watermark data may be extracted without further information about the data's location within a document.
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