Facsimile (or fax) technology is one of the most widely used forms of communication between companies and individuals. Notwithstanding the continuous growth of the popularity of email communications, the fax still holds a strong position as a reliable means of communication. It is presently estimated that more companies in the world have a fax number than an email address.
Among the advantages of fax communications are immediate delivery of documents, ability to transmit graphical documents, interoperability of fax devices throughout the world, improved security over email, and easy to use.
Traditional fax technology utilizes Public Switched Telephone Network (PSTN), also called Global Switched Telephone Network (GSTN), to transfer data between fax devices. Traditional fax devices comply with a variety of protocols, among which are: T.4—“Standardization of Group 3 Facsimile Apparatus for Document Transmission”, ITU-T (CCITT), July 1996; T.6—“Facsimile Coding Schemes and Coding Control Functions for Group 4 Facsimile Apparatus”, ITU-T (CCITT), November 1988; and T.30—“Procedures for Document Facsimile Transmission in the General Switched Telephone Network”, ITU-T (CCITT), July 1996; all are hereby incorporated in their entirety by reference.
Internet Fax (I-Fax) is a term used to describe extensions of the traditional fax technology that allow the use of the Internet for fax transmission. Examples of I-Fax are fax-over-IP and fax-through-email. Among the standards recommended for use in I-Fax are: T.37—“Procedures for the transfer of facsimile data via store-and-forward on the Internet”, ITU-T (CCITT), June 1998; T.38—“Procedures for real-time Group 3 facsimile communication over IP networks”, ITU-T (CCITT), 1998; F.185—“Internet facsimile: Guidelines for the support of the communication of facsimile documents”, ITU-T (CCITT), 1998; RFC 2301—“File Format for Internet Fax”, IETF, March 1998; RFC 2302—“Tag Image File Format (TIFF)—image/tiff MIME Sub-type Registration”, IETF, March 1998; RFC 3191—“Minimal GSTN address format in Internet Mail”, IETF, October 2001 (obsoletes RFC 2303, March 1998; updates RFC 2846, June 2000); RFC 3192—“Minimal FAX address format in Internet Mail”, IETF, October 2001 (obsoletes RFC 2304, March 1998; updates RFC 2846, June 2000); RFC 3965—“A Simple Mode of Facsimile Using Internet Mail”, IETF, December 2004 (obsoletes RFC 2305, March 1998); RFC 2306—“Tag Image File Format (TIFF)-F Profile for Facsimile”, IETF, March 1998; RFC 2542—“Terminology and Goals for Internet Fax”, IETF, March 1999; and RFC 3297—“Content Negotiation for Messaging Services based on Email”, IETF, July 2002; all are hereby incorporated in their entirety by reference.
Advanced capabilities of Internet Fax, such as color fax transmissions, are described, inter alia, in RFC 2531—“Content Feature Schema for Internet Fax”, IETF, March 1999 and RFC 2532—“Extended Facsimile Using Internet Mail”, IETF, March 1999; all are hereby incorporated in their entirety by reference.
In a conventional fax-through-email system, a fax service provider receives a fax transmission over the PSTN, converts the received fax transmission to a computer-readable file, e.g. TIFF or PDF (Portable Document Format), and forwards the file to the intended fax recipient via email. If a user sends a fax, the user provides document(s) to be faxed to the fax service provider via email, website, or software. The documents typically are computer-readable files. The fax service provider converts the document(s) to a faxable format (typically 1-bit black and white images), and transmits them to the recipient over the PSTN.
Presently, the majority of fax devices only support transmission of 1-bit black and white (monochrome) images. Thus, black and white faxes constitute the vast majority of all faxes transmitted. If the user's files to be faxed contain colors or shades of gray (hereinafter, the term color includes shades of gray), the colors will be typically converted to 1-bit black and white for compatibility with the majority of fax devices. At present, colors are either converted to black or dithered. Dithering is a method of simulating colors by producing black dots/pixels to represent brightness of the original color (similar to halftoning in newspaper photographs). Dithering will transform light colors to fewer dots with larger distances between them. The darker colors will be represented by more dots positioned closer to each other (additionally the size of the dots may be increased).
Various algorithms have been developed to produce a dithered image that more closely resembles the original image. Among them are error diffusion (dispersion, distribution) algorithms, which dither the image by diffusing the quantization error of a pixel to its neighboring pixels (e.g. the Floyd-Steinberg dithering algorithm).
Various colors with the same or similar brightness may look the same after dithering. Referring to FIG. 1, three elements of document A having various colors (represented by different line patterns) may look virtually undistinguishable after dithering in document B. Similarly, a fax document with a colored text on a colored background may become unreadable if the brightness of the text color is similar to the brightness of the background color (FIGS. 6 and 7).
Therefore, new methods, apparatus, software, and systems are needed to provide document optimization prior to their conversion to black and white. Additionally, new methods, apparatus, software, and systems are needed to provide document optimization for use in fax technology.