rfc2301.txt

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Network Working Group                                       L. McIntyre
Request for Comments: 2301                            Xerox Corporation
Category: Standards Track                                     S. Zilles
                                                    Adobe Systems, Inc.
                                                             R. Buckley
                                                      Xerox Corporation
                                                             D. Venable
                                                      Xerox Corporation
                                                             G. Parsons
                                                       Northern Telecom
                                                            J. Rafferty
                                                   Human Communications
                                                             March 1998



                      File Format for Internet Fax


Status of this Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (1998).  All Rights Reserved.

Abstract

   This document describes the TIFF (Tag Image File Format)
   representation of image data specified by the ITU-T Recommendations
   for black-and-white and color facsimile. This file format
   specification is commonly known as TIFF-FX. It formally defines
   minimal, extended and lossless JBIG modes (Profiles S, F, J) for
   black-and-white fax, and base JPEG, lossless JBIG and Mixed Raster
   Content modes (Profiles C, L, M) for color and grayscale fax. These
   modes or profiles correspond to the content of the applicable ITU-T
   Recommendations. Files formatted according to this specification use
   the image/tiff MIME Content Type.








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Table of Contents

1. INTRODUCTION........................................................4
   1.1. Scope..........................................................5
   1.2. Approach.......................................................5
   1.3. Overview of this draft.........................................5
2. TIFF and Fax........................................................7
   2.1. TIFF Overview..................................................7
     2.1.1. File Structure.............................................7
     2.1.2. Image Structure............................................9
     2.1.3. TIFF File Structure for Fax Applications..................10
   2.2 TIFF Fields for All Fax Applications...........................11
     2.2.1. TIFF Fields required for all fax modes....................12
     2.2.2. Additional TIFF Fields required for all fax modes.........13
     2.2.3. TIFF Fields recommended for all fax modes.................15
     2.2.4. New TIFF Fields recommended for fax modes.................16
3. Minimal Black-and-White Fax Mode...................................18
   3.1. Overview......................................................18
   3.2. Required TIFF Fields..........................................18
     3.2.1 Baseline Fields............................................18
     3.2.2 Extension Fields...........................................20
     3.2.3 New Fields.................................................20
   3.3. Recommended TIFF Fields.......................................20
   3.4. End of Line (EOL) and Return to Control (RTC).................20
     3.4.1 RTC Exclusion..............................................21
   3.5. File Structure................................................22
   3.6. Minimal Black-and-White Mode Summary..........................23
4. Extended Black-and-White Fax Mode..................................24
   4.1. TIFF-F Overview...............................................25
   4.2. Required TIFF Fields..........................................26
     4.2.1. Baseline Fields...........................................26
     4.2.2. Extension Fields..........................................28
     4.2.3. New Fields................................................29
   4.3. Recommended TIFF Fields.......................................29
     4.3.1. Baseline Fields...........................................29
     4.3.2. Extension Fields..........................................29
     4.3.3. New Fields................................................29
   4.4. Technical Implementation Issues...............................30
     4.4.1. Strips....................................................30
     4.4.2. Bit Order.................................................31
     4.4.3. Multi-Page................................................31
     4.4.4. Compression...............................................31
     4.4.5. Example Use of Page-quality Fields........................32
     4.4.6. Practical Guidelines for Writing and Reading Multi-Page
            TIFF-F Files..............................................33
     4.4.7. Use of TIFF-F for Streaming Applications..................34
   4.5. Implementation Warnings.......................................34
     4.5.1. Uncompressed Data.........................................34



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RFC 2301              File Format for Internet Fax            March 1998


     4.5.2. Encoding and Resolution...................................35
     4.5.3. EOL byte-aligned..........................................35
     4.5.4. EOL.......................................................36
     4.5.5. RTC Exclusion.............................................36
     4.5.6. Use of EOFB for T.6 Compressed Images.....................37
   4.6. Example Use of TIFF-F.........................................37
   4.7. Extended Black-and-white Fax Mode Summary.....................37
5. Lossless JBIG Black-and-White Fax Mode.............................39
   5.1. Overview......................................................40
   5.2. Required TIFF Fields..........................................40
     5.2.1. Baseline Fields...........................................40
     5.2.2. Extension Fields..........................................40
     5.2.3. New Fields................................................41
   5.3. Recommended TIFF Fields.......................................41
   5.4. Lossless JBIG Black-and-White Mode Summary....................41
6. Base Color Fax Mode................................................43
   6.1. Overview......................................................43
   6.2. Required TIFF Fields..........................................43
     6.2.1. Baseline Fields...........................................43
     6.2.2. Extension Fields..........................................45
     6.2.3. New Fields................................................46
   6.3. Recommended TIFF Fields.......................................47
   6.4. Base Color Fax Mode Summary...................................47
7. Lossless Color Mode................................................49
   7.1. Overview......................................................50
     7.1.1. Color Encoding............................................50
     7.1.2. JBIG Encoding.............................................50
   7.2. Required TIFF Fields..........................................51
     7.2.1. Baseline Fields...........................................51
     7.2.2. Extension Fields..........................................52
     7.2.3. New Fields................................................53
   7.3. Recommended TIFF Fields.......................................53
   7.4. Lossless Color Fax Mode Summary...............................53
8. Mixed Raster Content Mode..........................................55
   8.1 Overview.......................................................55
     8.1.1. MRC 3-layer model.........................................55
     8.1.2. A TIFF Representation for the MRC 3-layer model...........56
   8.2. Required TIFF Fields..........................................58
     8.2.1. Baseline Fields...........................................58
     8.2.2. Extension Fields..........................................59
     8.2.3. New Fields................................................60
   8.3. Recommended TIFF Fields.......................................62
   8.4. Rules and Requirements for Images.............................62
   8.5. MRC Fax Mode Summary..........................................63
9. MIME content-type image/tiff.......................................66
   9.1 Refinement of MIME content-type image/tiff for Facsimile
       Applications...................................................66
10. Security Considerations...........................................67



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11. References........................................................67
12. Authors' Addresses................................................69
Annex A: Summary of TIFF Fields for Internet Fax .....................70
Annex B. IANA Registration for image/tiff Application Parameter
         Values used for facsimile....................................75
Full Copyright Statement..............................................77

1. Introduction

   This document describes the use of TIFF (Tag Image File Format) to
   represent the data content and structure generated by the current
   suite of ITU-T Recommendations for Group 3 facsimile. These
   Recommendations and the TIFF fields described here support the
   following facsimile modes or profiles:

      S:  minimal black-and-white mode, using binary MH compression
             [T.4]
      F:  extended black-and-white mode, using binary MH, MR and MMR
             compression [T.4, T.6]
      J:  lossless JBIG black-and-white mode, with JBIG compression
             [T.85, T.82]
      C:  lossy color and grayscale mode, using JPEG compression
             [T.42, T.81]
      L:  lossless color and grayscale mode, using JBIG compression
             [T.43, T.82]
      M:  mixed raster content mode [T.44], using a combination of
             existing compression methods

   Each profile corresponds to the content of ITU-T Recommendations
   shown and is a subset of the full TIFF for facsimile specification.

   Profile S describes a minimal interchange set of fields, which will
   guarantee that, at least, binary black-and-white images will be
   supported. Implementations are required to support this minimal
   interchange set of fields.

   With the intent of specifying a file format for Internet Fax, this
   draft:

       1.  specifies the structure of TIFF files for facsimile data,
       2.  defines ITU fax-compatible values for existing TIFF fields,
       3.  defines new TIFF fields and values required for compatibility
           with ITU color fax.

   This specification of TIFF for facsimile is known as TIFF-FX.






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RFC 2301              File Format for Internet Fax            March 1998


1.1 Scope

   This document defines a TIFF-based file format specification for
   enabling standardized messaging-based fax over the Internet. It
   specifies the TIFF fields and field values required for compatibility
   with the existing ITU-T Recommendations for Group 3 black-and-white,
   grayscale and color facsimile. TIFF has historically been used for
   handling fax image files in applications such as store-and-forward
   messaging.  Implementations that support this file format
   specification for import/export may elect to support it as a native
   format. This document recommends a TIFF file structure that is
   compatible with low-memory and page-level streaming implementations.

   Unless otherwise noted, the current TIFF specification [TIFF] and
   selected TIFF Technical Notes [TTN1, TTN2] are the primary references
   for describing TIFF and defining TIFF fields. This document is the
   primary reference for defining TIFF field values for fax
   applications.

1.2 Approach

   The basic approach to using TIFF for facsimile data is to insert the
   compressed fax image data in a TIFF file and use TIFF fields to
   encode the parameters that describe the image data. These fields will
   have values that comply with the ITU-T Recommendations. The MIME
   content type of the resulting file will be image/tiff, with an
   optional Application parameter [TIFF-REG]; see Section 9.

   This approach takes advantage of TIFF features and structures that
   bridge the data formats and performance requirements of both legacy
   fax machines and host-based fax applications. TIFF constructs for
   pages, images, and strips allow a TIFF file to preserve the fax data
   stream structure and the performance advantages that come with it. A
   TIFF-based approach also builds on an established base of users and
   implementors and ensures backward compatibility with existing TIFF-
   based IETF proposals and work in progress for Internet fax.

1.3 Overview of this draft