ELECTRONIC WATERMARK EMBEDDING METHOD AND EXTRACTION METHOD AND APPARATUS FOR THEM

摘要

A block dividing unit (41) divides a binary image into a plurality of blocks (S104). A unit for counting the number of pixels (42) calculates a number of black pixels Bi for each block Ai (S106). A calculation unit (44) calculates a remainder bi of the number of black pixels Bi with respect to a reference value p (S112). A unit for counting the number of modification pixels (45) decides whether the watermark information di to be embedded in the object block Ai is “1” or “0” (S114). When the watermark information di is decided to be “1”, the number of modification pixels ci is calculated so that the remainder bi is (3/4)p (S116). When the watermark information di is decided to be “0”, the number of modification pixels ci is calculated so that the remainder bi is (1/4)p (S118). A pixel modification unit (46) modifies the pixel value of pixels in the object block Ai (S124). Thus, it is possible to embed watermark information appropriate for an image based on a line drawing such as a cartoon.