The present invention relates generally to image processing and information encoding and, more particularly, to printing or encoding information on printed pages together with printed images or text using combinations of the printed mark size and marking material color which are imperceptible to the human eye.
Steganography is the art and science of communicating in a way which hides the existence of the communication. In contrast to cryptography which actually encrypts or encodes a message to hide its meaning, the goal of Steganography is to hide a second message within a first, otherwise harmless message.
The word Steganography literally means covered writing as derived from Greek. It includes a vast array of methods and variations that have been used throughout history to conceal information and the very existence of a message. For example, drawings have often been used to conceal or reveal information. It is simple to encode a message by varying lines, colors or other elements in pictures. With the advent of the computer, the electronic printer and the ability to process and manipulate images and data, such methods have been taken to new dimensions.
Plain paper has long been a favored recording medium for storing and transferring human readable information. In fact, it has recently been said that paper is one of the most promising media types for new computer applications. Even given the emergence of digital-based electronic communications, such as the world wide web, paper-based communication has kept pace with digital information. Electronic document processing systems have enhanced the functional utility of plain paper and other types of hardcopy documents by enabling the application of machine readable digital data thereon. This machine readable data enables the hardcopy document to actively interact with such a document processing system in a variety of different ways when the document is scanned into the system by an ordinary input scanner. See, for example, the copending U.S. patent application Ser. No. 09/369,381 of Paul Jeran and Terry Mahoney, Ser. No. 09/369,381, filed on Aug. 5, 1999, assigned to the instant assignee, and entitled xe2x80x9cMethods of Document Management and Automated Document Tracking, and a Document Management System.xe2x80x9d Jeran et al discloses a document management system wherein a printing device is configured to print text on a document as well as to automatically print machine-readable code on the document. The document management system also includes a scanning device configured to scan documents and extract at least some information from the machine-readable code, the information thus extracted being used to manage or control the use, distribution or the like of the document.
As a general rule, digital data is recorded by writing two-dimensional marks on a recording medium using a marking material in accordance with a pattern which encodes the data either by the presence or absence of marks at a sequence of spatial locations or by the presence or absence of mark-related transitions at such locations. When the recording medium is paper, the writing is accomplished by a printing device resulting in printed text or other images on the surface of the paper which visually communicates the information to the user.
The marking of printed documents or other articles with information, such as the use of bar codes, for identification and sorting is well known. The conventional black on white bar code is useful only on areas of white or other light colored background on articles. It is further known to use fluorescent inks and other marking materials to provide bar codes or other intelligible markings on documents and the like that are virtually invisible to the unaided eye.
While the use of bar codes and other prior art methods are effective in providing machine-readable information, the presence, if not the meaning, of the information is typically discernable to the user and it requires the use of at least some surface area which could otherwise be used for text or other images. It would therefore be desirable to develop methods of providing machine-readable information which is not visually perceptible to the human eye and does not require the use of additional media surface area.
In a preferred embodiment, the present invention provides machine-readable information on a printed document in the form of printed marks which are not visually perceptible to the human eye. A combination of sufficiently small size and selected color render the printed marks visually imperceptible to the human eye, yet easily detectable by a machine such as a scanner. The printed marks are dispersed across portions or all of the printed document in selected patterns for encoding the information, such as in a bar code, or the information may merely be printed text. The marks representing the information are printed in unused blank space between or surrounding existing text and other images on the printed document thus avoiding the use of any additional surface area of the media.
The present invention may be implemented as a method of providing information on a printed page wherein a set of image elements are printed on a printed page in a selected pattern representing information to be printed on a printed page. The image elements are dispersed over at least a portion of the printed page. Each of the printed image elements is of a sufficiently small size and color to be visually imperceptible to the human eye.
In a preferred embodiment, the present invention is implemented as a method of encoding information on a page of printed text wherein a combination of size and color is selected to provide printed marks which are visually imperceptible to the human eye. A first set of data representing a printed page of text or other images is provided. The method includes identifying allowable encoding locations on the page of printed text, preferably the allowable locations will be at positions of blank space between or surrounding existing characters. A second set of data representing image elements mapped to allowable encoding locations in a selected pattern corresponding to information to be encoded on the page of printed text is generated. The first and second sets of data are then summed or otherwise combined, preferably using an AND or OR operation, to generate a third set of data representing the page of printed text modified to include the encoded information. The third set of data is then utilized to print the modified page of printed text.
Other aspects and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.