SECURITY DOCUMENT WITH HALFTONE IMAGES AND METHOD FOR ITS MANUFACTURE

The invention relates to a method for manufacturing a security document by printing halftone images (28, 30) on opposite sides (12, 14) of a transparent region (26) of a substrate (16). Using a first and a second analog halftone image (A1, A2), it calculates a first and a second binary halftone image Bl(x, y), B2(x, y) using binary halftoning algorithms. A third binary halftone image B3(x, y) = B2(x, y) AND NOT B1(x, y) is calculated. The first binary halftone image B1(x, y) is used to generate a front-side printed image (28), and the third binary halftone image B3(x, y) is used to print the back-side printed image (30). When viewing the document from the front in reflection, the first halftone image (Al) can be seen. When viewing the document in transmission, the second halftone image (A2) can be seen.