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1、 Reference number ISO/IEC 14492:2001/Amd.1:2004(E) ISO/IEC 2004 INTERNATIONAL STANDARD ISO/IEC 14492 First edition 2001-12-15 AMENDMENT 1 2004-12-15 Information technology Lossy/lossless coding of bi-level images AMENDMENT 1: Encoder Technologies de linformation Codage avec ou sans perte des images
2、au trait AMENDEMENT 1: Codeur Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 04/03/2007 01:25:28 MDTNo reproduction or networking permitted without license from IHS -,-,- ISO/IEC 144
3、92:2001/Amd.1:2004(E) PDF disclaimer This PDF file may contain embedded typefaces. In accordance with Adobes licensing policy, this file may be printed or viewed but shall not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In d
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6、ss given below. ISO/IEC 2004 All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or I
7、SOs member body in the country of the requester. ISO copyright office Case postale 56 CH-1211 Geneva 20 Tel. + 41 22 749 01 11 Fax + 41 22 749 09 47 E-mail copyrightiso.org Web www.iso.org Published by ISO in 2005 Published in Switzerland ii ISO/IEC 2004 All rights reserved Copyright International O
8、rganization for Standardization Provided by IHS under license with ISO Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 04/03/2007 01:25:28 MDTNo reproduction or networking permitted without license from IHS -,-,- ISO/IEC 14492:2001/Amd.1:2004(E) ISO/IEC 2004 All rights reserved
9、iii Foreword ISO (the International Organization for Standardization) and IEC (the International Electrotechnical Commission) form the specialized system for worldwide standardization. National bodies that are members of ISO or IEC participate in the development of International Standards through te
10、chnical committees established by the respective organization to deal with particular fields of technical activity. ISO and IEC technical committees collaborate in fields of mutual interest. Other international organizations, governmental and non-governmental, in liaison with ISO and IEC, also take
11、part in the work. In the field of information technology, ISO and IEC have established a joint technical committee, ISO/IEC JTC 1. International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2. The main task of the joint technical committee is to prepare In
12、ternational Standards. Draft International Standards adopted by the joint technical committee are circulated to national bodies for voting. Publication as an International Standard requires approval by at least 75 % of the national bodies casting a vote. Attention is drawn to the possibility that so
13、me of the elements of this document may be the subject of patent rights. ISO and IEC shall not be held responsible for identifying any or all such patent rights. Amendment 1 to ISO/IEC 14492:2001 was prepared by Joint Technical Committee ISO/IEC JTC 1, Information technology, Subcommittee SC 29, Cod
14、ing of audio, picture, multimedia and hypermedia information, in collaboration with ITU-T. The identical text is published as ITU-T Rec. T.88 (2000)/Amd.1. Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=IHS Employees/1111111001, User=Wing, Be
15、rnie Not for Resale, 04/03/2007 01:25:28 MDTNo reproduction or networking permitted without license from IHS -,-,- ISO/IEC 14492:2001/Amd.1:2004(E) iv ISO/IEC 2004 All rights reserved Introduction In this amendment, the following new materials are added: a) new clauses 9, 10, and 11 to describe the
16、required architecture and procedures for JBIG2 encoding; and b) a new Annex J to document optional JBIG2 encoding methods. The encoding procedures in clauses 9 and 10 are essentially the inverse of the decoding procedures already described in clauses 6 and 7 of ITU-T Rec. T.88 | ISO/IEC 14492. To si
17、mplify the required new documentation, description of each of the encoding procedures is given by referring to the corresponding decoding procedures in clauses 6 and 7, wherever applicable. Clause 11 and Annex J, however, are new material and thus contain more detailed documentation. In clause 11 (a
18、lthough the encoding complements that of clause 8 of ITU-T Rec. T.88 | ISO/IEC 14492), JBIG2 encoding architecture as well as its technical components are described, and their corresponding implementation methods are given by reference. In J.1, compliant example encoding methods are summarized in ta
19、ble form. Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 04/03/2007 01:25:28 MDTNo reproduction or networking permitted without license from IHS -,-,- ISO/IEC 14492:2001/Amd.1:2004(E
20、) ITU-T Rec. T.88 (2000)/Amd.1 (06/2003) 1 INTERNATIONAL STANDARD ITU-T RECOMMENDATION Information technology Lossy/lossless coding of bi-level images Amendment 1 Encoder 1) New clauses 9, 10, and 11 Add the following clauses: 9 Encoding procedures The encoding procedures in this clause are essentia
21、lly the inverse of the decoding procedures already described in clause 6 and will not be duplicated here. The inverse of generic region encoding is described in 6.2. The inverse of generic refinement encoding is described in 6.3. The inverse of text region encoding is described in 6.4. The inverse o
22、f symbol dictionary encoding is described in 6.5. The inverse of halftone region encoding is described in 6.6. The inverse of pattern dictionary encoding is described in 6.7. 10 Control encoding procedures The control encoding procedures in this clause are essentially the inverse of the decoding con
23、trol procedures already described in clause 7 and will not be duplicated here. The inverse of segment header syntax encoding is described in 7.2. The inverse of segment type encoding is described in 7.3. The segment types syntax for the region segment information field, symbol dictionary segment, te
24、xt region segment, pattern dictionary segment, halftone region segment, generic region, generic refinement segment, end of page segment, end of stripe segment, end of file segment, profiles segment, code table segment and extension segment are described in detail in 7.4.1 to 7.4.15 respectively. 11
25、Page break-up The page break-up (“Front end“) procedures in this clause are conceptually the inverse of the page make-up (“Back end“) procedures already described in clause 8. However, page break-up also requires additional page and document decomposition steps prior to encoding. 11.1 Page break-up
26、architecture This clause describes the JBIG2 encoder break-up defined by compliant, but optional, technical components (with a range of algorithms possible to implement each of these components). These JBIG2 page break-up components are a set of processing steps labelled: Capture, Filter, Orient (de
27、-skew), Identify, eXtract, Screen, Align (register), Match, Post-match, Dictionary (optimize), and Refine. An example sequence of this component set is illustrated in the Architectural Components figure below as the horizontal axis with abbreviated labels C F O I X S A M P D R (leading from input on
28、 the left to a compressed data stream on the right). The vertical dimension above each label represents the range of possible algorithms that may be used to implement each component. The horizontal band illustrates an example JBIG2 compliant page break-up method, using some algorithm for each archit
29、ectural component and spanning over these components. Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 04/03/2007 01:25:28 MDTNo reproduction or networking permitted without license fr
30、om IHS -,-,- ISO/IEC 14492:2001/Amd.1:2004(E) 2 ITU-T Rec. T.88 (2000)/Amd.1 (06/2003) A compliant JBIG2 encoder need not include all architectural components, nor use them in exactly the above sequence. 11.2 Page image decomposition A page image is decomposed into several groups of sub-images such
31、as marks J2, line-arts, residues and halftones. Each group is identified and then compressed using an appropriate set of processing (architectural components) from those summarized in 11.2.1 to 11.2.12. Processing may include one or more of these component techniques prior to bitstream creation. The
32、 specific algorithm selected for each processing step is left up to the implementer but compliant examples for each processing step are provided in J.1. Implementing a full combination of these components, each using a compliant example encoding method, will result in an encoder capable of producing
33、 reasonable near-lossless quality for most 300 + dpi images. 11.2.1 Capture (rasterize) Capture (rasterization) is a process by which an image source is converted into a two-dimensional bi-level raster image. This is done by mapping a region of the image source to a set of pixels of the raster image
34、, and then assigning a 1-bit colour value to each pixel. In the scope of this amendment, two types of images are defined: generated and scanned images. A generated image is an image converted from a computer-generated metafile or vector graphic (e.g., a bitmap rasterized from a document created usin
35、g a typical word processor), whereas a scanned image is an image obtained from a paper document by means of imaging hardware such as a scanner or facsimile. 11.2.2 Filter In most cases, a scanning process is noisy, and the resulting scanned image may contain random pixel values not representative of
36、 the original source. These pixels or small groups of pixels are called flyspecks. It is often desireable to remove flyspecks in a scanned image to improve compression efficiency as well as visual quality of the reconstructed image. A scanned image also contains quantization errors, i.e., identical
37、marks in the original image may be slightly different in the scanned image. Smoothing the edges of the marks helps to recover the equivalence of such identical marks in the scanned image and also improve compression efficiency. These filtering techniques are shown as a reference in J.1. Filtering is
38、 seldom required for generated images although these techniques may still be applied. 11.2.3 Orient (de-skew) A scanned image may be skewed when it is scanned or photocopied at a slight angle, and it is often beneficial to identify and adjust any skew prior to compression. In most texts, marks (char
39、acters) are aligned in straight lines, and examining the slope of these lines that align pairs of marks yields the skew angle. Several methods of de-skewing are shown as a reference in J.1. 11.2.4 Identify Identification of sub-image categories involves two processes: segmentation and classification
40、. First an image is segmented into groups of sub-mages or regions having similar characteristics. These regions (segments) are then classified into pre-defined categories such as textual data, line-art and halftones, to which appropriate compression methods are applied. ARCHITECTURAL COMPONENTS Page
41、 Break-up C F O I X S A M P D R Encoding Procedure Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 04/03/2007 01:25:28 MDTNo reproduction or networking permitted without license from
42、IHS -,-,- ISO/IEC 14492:2001/Amd.1:2004(E) ITU-T Rec. T.88 (2000)/Amd.1 (06/2003) 3 11.2.5 Extract A symbol (character) is a mark consisting of black pixels. A symbol boundary is first traced by observing the connectivity of black pixels, and the adjacent black pixels are extracted to form a symbol.
43、 Although simply extracting all the pixels confined by the boundary may work in most cases, it does not handle nested marks. Several methods are shown as a reference in J.1. 11.2.6 Screen Comparing an extracted mark against all the symbols in the dictionary is inefficient especially when the diction
44、ary size is large, and relatively complex matching criteria as described in 11.2.8 are used. Simple methods, such as restricting comparisons to only be made between marks and dictionary symbols with similar width and height, can be used to find possible matching candidates. More detailed approaches
45、are shown as a reference in J.1. 11.2.7 Align (register) Symbols are often aligned (registered) in the dictionary using the same criteria selected for the screening method in 11.2.6. When distribution of black pixels is tested against symbols in a dictionary to find matching candidates, aligning sym
46、bols along their centroids can enhance the screening rate. More detailed approaches are shown as a reference in J.1. 11.2.8 Match Marks are extracted from a region containing textual data and compared with existing symbols in a dictionary, in order to exploit any similarities between them for better
47、 compression. Basically, each mark is tested to determine whether it is similar enough to be considered a match to one of the existing symbols. One way of matching is to first obtain a difference bitmap between the mark and a symbol and test the number of black pixels in the difference bitmap to a p
48、re-defined threshold. Giving more weight to the clustered black pixels in the difference bitmap usually improves matching results. When a close match is found, a reference to the matching symbol in the dictionary is coded. When there is no close match, the extracted mark is stored as a new symbol in the dictionary. 11.2.9 Post-match Several additional criteria and processing steps may be applied to the symbol dictionary to improve image quality. A best dictionary symbol shape may be determined by examining several similar symbols, which have already passed the matchi