| 摘要 |
A differential color or luminance signal is used to embed a binary message in selected stroke segments in the text of a document and for extracting a message so embedded. The bits representing the message are embedded in the stroke segments by modifying a color or luminance value of pixels in one region of a selected stroke with respect to such a value of pixels in a second region of that stroke. To determine whether a bit is embedded in a stroke segment, a value representative of the luminance or color of pixels in the one region is compared with a value representative of the luminance or color of pixels in the second region. The presence or absence of a bit is determined by whether the difference between the two values is greater than a minimum predetermined threshold.
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