1、 International Telecommunication Union ITU-T T.851TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (09/2005) SERIES T: TERMINALS FOR TELEMATIC SERVICES ITU-T T.81 (JPEG-1)-based still-image coding using an alternative arithmetic coder ITU-T Recommendation T.851 ITU-T Rec. T.851 (09/2005) i ITU-T Reco
2、mmendation T.851 ITU-T T.81 (JPEG-1)-based still-image coding using an alternative arithmetic coder Summary This Recommendation defines a format for digital compression and coding of still images supporting the use of an alternative arithmetic coder called the “Q15-coder“ and an alternative baseline
3、 compared to ITU-T Rec. T.81 | ISO/IEC 10918-1 (JPEG-1). Support of the Huffman entropy coding method specified in ITU-T Rec. T.81 (JPEG-1) is not required in this Recommendation. The Q15-coder resolves the carry in the decoder instead of in the encoder, and so has a low latency compared to the QM-c
4、oder arithmetic coder incorporated in T.81, which has a potential latency of the rest of the entire entropy-coded segment. This Recommendation also specifies a DCT with input precision of 16 bits, which is greater than the precision of the T.81 (JPEG-1) DCT. Source ITU-T Recommendation T.851 was app
5、roved on 13 September 2005 by ITU-T Study Group 16 (2005-2008) under the ITU-T Recommendation A.8 procedure. Keywords Alternative baseline, Q15-coder, still-image coding, still-image compression, still images. ii ITU-T Rec. T.851 (09/2005) FOREWORD The International Telecommunication Union (ITU) is
6、the United Nations specialized agency in the field of telecommunications. The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing
7、 telecommunications on a worldwide basis. The World Telecommunication Standardization Assembly (WTSA), which meets every four years, establishes the topics for study by the ITU-T study groups which, in turn, produce Recommendations on these topics. The approval of ITU-T Recommendations is covered by
8、 the procedure laid down in WTSA Resolution 1. In some areas of information technology which fall within ITU-Ts purview, the necessary standards are prepared on a collaborative basis with ISO and IEC. NOTE In this Recommendation, the expression “Administration“ is used for conciseness to indicate bo
9、th a telecommunication administration and a recognized operating agency. Compliance with this Recommendation is voluntary. However, the Recommendation may contain certain mandatory provisions (to ensure e.g. interoperability or applicability) and compliance with the Recommendation is achieved when a
10、ll of these mandatory provisions are met. The words “shall“ or some other obligatory language such as “must“ and the negative equivalents are used to express requirements. The use of such words does not suggest that compliance with the Recommendation is required of any party. INTELLECTUAL PROPERTY R
11、IGHTS ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. ITU takes no position concerning the evidence, validity or applicability of claimed Intellectual Property Rights, whether asserted by
12、ITU members or others outside of the Recommendation development process. As of the date of approval of this Recommendation, ITU had not received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementors are cautioned that thi
13、s may not represent the latest information and are therefore strongly urged to consult the TSB patent database. ITU 2005 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU. ITU-T Rec. T.851 (09/2005) iii CONTENTS P
14、age 1 Scope 1 2 References. 1 2.1 Normative references 1 2.2 Informative references 1 3 Definitions 2 4 Abbreviations 2 5 Conventions 2 6 General 2 7 Alternative baseline 3 8 Compressed data formats 4 8.1 JPG extensions marker syntax 4 8.2 Extended DCT precision 5 8.3 Summary. 6 9 Huffman coding 6 1
15、0 Arithmetic coders 6 10.1 Encoder procedures 7 10.2 Decoder procedures 11 10.3 Probability estimation. 14 11 Encoder and decoder control procedures 16 iv ITU-T Rec. T.851 (09/2005) Introduction ITU-T Rec. T.81 | ISO/IEC 10918-1 (T.81) specifies a process for digital compression and coding of contin
16、uous-tone still images. T.81 contains two entropy coders: Huffman coding and an arithmetic coder called the “QM-coder“. The Huffman coding method is required in the T.81 baseline. For all other encoding processes (extended sequential, progressive, hierarchical, and lossless), the use of all defined
17、entropy coders is allowed. This Recommendation defines a still-image coding method based on ITU-T Rec. T.81 (JPEG-1) which makes use of an alternative arithmetic encoder called the “Q15-coder“, and defines an “alternative baseline“ compared to ITU-T Rec. T.81. In this Recommendation, support for Huf
18、fman coding is not required. NOTE Images encoded according to this Recommendation can be losslessly transcoded to or from any of the entropy coding methods of ITU-T Rec. T.81, including the baseline Huffman coding of ITU-T Rec. T.81. All decoders which support any DCT-based process defined in Table
19、1 shall also be capable of decoding bitstream conforming to the alternative baseline. Interoperability with the Huffman-based baseline of T.81 is not required by this Recommendation, but might be required by an application incorporating this Recommendation. An application specification might require
20、 a dual-mode entropy codec, or a server-based transcoding facility. ITU-T Rec. T.851 (09/2005) 1 ITU-T Recommendation T.851 ITU-T T.81 (JPEG-1)-based still-image coding using an alternative arithmetic coder 1 Scope This Recommendation is applicable to continuous-tone, greyscale or colour, digital st
21、ill-image data. According to the principles of ITU-T Rec. T.80, it enhances T.81 technologies by providing an additional arithmetic coder. This Recommendation: defines an arithmetic coder (“Q15-coder“) for use with T.81 technologies; extends the DCT input precision to 16 bits; provides an alternativ
22、e baseline in which no Huffman coding is required. The provisions of ITU-T Rec. T.81 | ISO/IEC 10918-1 shall apply to this Recommendation with the exceptions, additions, and deletions given in this Recommendation. 2 References 2.1 Normative references The following ITU-T Recommendations and other re
23、ferences contain provisions which, through reference in this text, constitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and other references are subject to revision; users of this Recommendation are therefore encouraged to i
24、nvestigate the possibility of applying the most recent edition of the Recommendations and other references listed below. A list of the currently valid ITU-T Recommendations is regularly published. The reference to a document within this Recommendation does not give it, as a stand-alone document, the
25、 status of a Recommendation. ITU-T Recommendation T.80 (1992), Common components for image compression and communication Basic Principles. ITU-T Recommendation T.81 (1992) | ISO/IEC 10918-1:1994, Information technology Digital compression and coding of continuous-tone still images: Requirements and
26、guidelines (often called “JPEG-1“). 2.2 Informative references Additional arithmetic coding references: MARKS (K.M.): A JBIG-ABIC compression engine for digital document processing, IBM J. Res. Develop., Vol. 42, No. 6, pp. 753-758, 1998. KAMPF (F.A.): Performance as a function of compression, IBM J
27、. Res. Develop., Vol. 42, No. 6, pp. 759-766, 1998. SLATTERY (M.S.) and MITCHELL (J.L.): The Qx-coder, IBM J. Res. Develop., Vol. 42, No. 6, pp. 767-784, 1998. 2 ITU-T Rec. T.851 (09/2005) 3 Definitions This Recommendation defines the following terms: 3.1 alternative baseline (sequential): A particu
28、lar sequential DCT-based encoding and decoding process specified in this Recommendation. 3.2 bit stuffing: A procedure in which the arithmetic encoder inserts a bit in the next byte into the entropy-coded segment following the generation of an encoded hexadecimal XFF byte. This procedure replaces by
29、te stuffing. 4 Abbreviations This Recommendation uses the following abbreviations: IEC International Electrotechnical Commission ISO International Organization for Standardization JPEG Joint Photographic Experts Group (The joint ITU-T | ISO/IEC committee responsible for developing joint text standar
30、ds for continuous-tone still picture coding) 5 Conventions In this Recommendation the following conventions are used: “shall“ indicates a mandatory requirement. “should“ indicates a suggested but optional course of action. “may“ indicates an optional course of action rather than a recommendation tha
31、t something take place. For the purposes of this Recommendation, the following additional symbols apply: a the ASCII text letter “a“ (X61) c the ASCII text letter “c“ (X63) JPG marker used for JPEG extensions including Q15-coding Lj length of parameters in the JPG segment for JPEG extensions 2 the A
32、SCII text number “2“ (X32) 6 General The provisions of ITU-T Rec. T.81 | ISO/IEC 10918-1 shall apply to this Recommendation with the exceptions, additions, and deletions given in this Recommendation. Every instance where an arithmetic coder is used in ITU-T Rec. T.81 | ISO/IEC 10918-1, the arithmeti
33、c coder defined in this Recommendation shall be used instead. For the purposes of this Recommendation, Table 1/T.81 | ISO/IEC 10918-1 shall be considered to be extended with the additions in Table 1 below, in which an alternative baseline and a set of alternative processes are defined. ITU-T Rec. T.
34、851 (09/2005) 3 Table 1/T.851 Summary: Essential characteristics of additional coding processes Alternative-Baseline Process (required for all DCT-based decoding processes) DCT-based process Source image: 8-bit samples within each component Sequential Q15-arithmetic coding Decoders shall process sca
35、ns with 1, 2, 3, and 4 components Interleaved and non-interleaved scans Alternative Extended DCT-based Processes DCT-based process Source image: 8-bit through 16-bit samples Sequential or progressive Arithmetic coding (Q15-coder): 4 AC and 4 DC tables Decoders shall process scans with 1, 2, 3, and 4
36、 components Interleaved and non-interleaved scans Alternative Lossless Processes Predictive process (not DCT-based) Source image: P-bit samples ( 162 P ) Sequential Arithmetic coding (Q15-coder): 4 DC tables Decoders shall process scans with 1, 2, 3, and 4 components Interleaved and non-interleaved
37、scans Alternative Hierarchical Processes Multiple frames (non-differential and differential) Uses alternate extended DCT-based or alternate lossless processes Decoders shall process scans with 1, 2, 3, and 4 components Interleaved and non-interleaved scans 7 Alternative baseline For conformance with
38、 the alternative baseline defined in this Recommendation, any DCT-based decoder shall also embody the alternative-baseline sequential decoding process. The alternative-baseline sequential process shall start with the JPG extension marker with the parameters “ac2“ (e.g., specifies use of the Q15-code
39、r). The precision P shall be 8 for the input and reconstructed samples within each component. Only one Start of Frame (SOF9) is allowed. The decoders shall process interleaved and non-interleaved scans with 1, 2, 3, and 4 components. The quantization values shall be expressed in one byte (Pq = 0). 4
40、 ITU-T Rec. T.851 (09/2005) 8 Compressed data formats Table B.1/T.81 | ISO/IEC 10918-1 shall be replaced with Table 2 above. NOTE The JPG marker has moved from under “Frame markers“, where it was listed in ITU-T Rec. T.81 | ISO/IEC 10918-1 as “reserved for JPEG extensions“, to the group of “Other ma
41、rkers“ where it now indicates “JPEG extensions“. Table 2/T.851 Marker code assignments Code Assignment Symbol Description Start Of Frame markers, non-differential, Q15-coder arithmetic coding XFFC9 XFFCA XFFCB SOF9SOF10SOF11Extended sequential DCT Progressive DCT Lossless (sequential) Start Of Frame
42、 markers, differential, Q15-coder arithmetic coding XFFCD XFFCE XFFCF SOF13SOF14SOF15Differential sequential DCT Differential progressive DCT Differential lossless (sequential) Huffman table specification XFFC4 DHT Define Huffman table(s) Q15-coder arithmetic coding conditioning specification XFFCC
43、DAC Define Q15 arithmetic coding conditioning(s) Restart interval termination XFFD0 through XFFD7 RSTm(Note) Restart with modulo 8 count “m“ Other markers XFFC8 XFFD9 XFFDA XFFDB XFFDC XFFDD XFFDE XFFDF XFFE0 through XFFEF XFFF0 through XFFFD XFFFE JPG EOI (Note) SOS DQT DNL DRI DHP EXP APPnJPGnCOM
44、JPEG extensions End of image Start of scan Define quantization table(s) Define number of lines Define restart interval Define hierarchical progression Expand reference component(s) Reserved for application segments Reserved for JPEG extensions Comment Reserved markers XFF00 through XFF99 XFFA0 throu
45、gh XFFBF RES May be generated by Q15-coder Reserved NOTE Marker which is not the start of a marker segment. 8.1 JPG extensions marker syntax The JPG marker (XFFC8) is used to specify extensions to ITU-T Rec. T.81 | ISO/IEC 10918-1. The first extension is defined as a replacement to the SOI marker an
46、d indicates that the arithmetic coding defined by Annex D/T.81 | ISO/IEC 10918-1 shall be replaced by the arithmetic coder defined in clause 10. Figure 8-1 specifies the marker segment which defines the extensions defined in this Recommendation. Table 3 gives the parameter sizes and values for the J
47、PG extensions. ITU-T Rec. T.851 (09/2005) 5 Figure 8-1/T.851 JPG extensions syntax The marker and parameters shown in Figure 8-1 are defined below. The size and allowed values of each parameter are given in Table 3. JPG: JPG extensions Marks the beginning of the parameters which define the JPG exten
48、sions. Lj: JPG extensions segment length Specifies the length of the parameters in the JPG segment shown in Figure 8-1. “ac2“: ASCII characters (X616332) Used for the Q15-coder specified in clause 10. Table 3/T.851 JPEG extensions marker (JPG) parameter sizes and values Parameter Size (bits) Value J
49、PG 16 XFFC8 Lj 16 5 a 8 X61 c 8 X632 8 X32NOTE The byte order for these fields is defined in ITU-T Rec. T.81 | ISO/IEC 10918-1. Other future extensions may change the value of Lj. If the first three bytes are “ac2“, any information following shall not change the decoding process. If the first three parameters are not “ac2“, the extension may be incompatible. In Figure B.17/T.81 | ISO/IEC 10918-1, this JPG extension mar
