Methods and apparatus for watermarking digitally printed documents
US7307761B2 · kind B2 · utility
Assignee
Inventor
Key dates
| Filing date | Dec 12, 2002 |
| Grant date | Dec 11, 2007 |
| Priority date | — |
| Expiry date | Sep 19, 2025 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04N2201/0082
- WIPO fieldAudio-visual technology
- WIPO sectorElectrical engineering
Abstract
A form of stochastic random distribution is used to print an invisible watermark using a typical, e.g. 600 dpi, printer. The watermark contains such information as “Do Not Copy,” or other such information. While the watermark is not visible on a first generation version of a document that is printed, various techniques are used to print the watermark in such a way that it becomes readily apparent when the first generation document is photocopied. The preferred embodiment of the invention is concerned with a technique for improving such techniques, for example so that gray levels are improved to address variations from printer to printer. Another preferred embodiment of the invention is also concerned with a technique for performing error diffusion watermarking without the need for performing a calibration step.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.