| 摘要 |
Improved data embedding and extracting techniques provide a way to embed and extract messages in text sections of documents during copying. Extracted text pixels are grouped together to form text lines of the document. From this formation, a document layout is constructed that is used to embed the message in the text pixels. Each text line is partitioned into blocks, and those of which contain a certain threshold percentage of text pixels are identified as valid. Each valid block is used to embed one bit of information by labeling text pixels of that block with a certain predetermined color. The embedding of bits in valid blocks in a particular text line is done in a column-wise raster order. Only one message character (which may be comprised of multiple bits) is embedded in a particular text line, although that character may be embedded multiple times in the same line if there are enough valid blocks. Extracting a message so embedded involves forming a first representation of the document in which pixels are classified to locate blocks of pixels in which data is embedded, forming a second representation of the document to extract text lines and identify text pixels. These two representations are compared to identify clusters of color-labeled pixels in each text line to determine the location of embedded bits of the message. The clusters in each text line are sorted in accordance with the predetermined embedding order and converted into a sequence of bits which are decoded to determine the message character embedded in each text line.
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