1、 International Telecommunication Union ITU-T T.871TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (05/2011) SERIES T: TERMINALS FOR TELEMATIC SERVICES Still-image compression JPEG-1 extensions Information technology Digital compression and coding of continuous-tone still images: JPEG File Interchang
2、e Format (JFIF) Recommendation ITU-T T.871 ITU-T T-SERIES RECOMMENDATIONS TERMINALS FOR TELEMATIC SERVICES Facsimile Framework T.0T.19 Still-image compression Test charts T.20T.29 Facsimile Group 3 protocols T.30T.39 Colour representation T.40T.49 Character coding T.50T.59 Facsimile Group 4 protocol
3、s T.60T.69 Telematic services Framework T.70T.79 Still-image compression JPEG-1, Bi-level and JBIG T.80T.89 Telematic services ISDN Terminals and protocols T.90T.99 Videotext Framework T.100T.109 Data protocols for multimedia conferencing T.120T.149 Telewriting T.150T.159 Multimedia and hypermedia f
4、ramework T.170T.189 Cooperative document handling T.190T.199 Telematic services Interworking T.300T.399 Open document architecture T.400T.429 Document transfer and manipulation T.430T.449 Document application profile T.500T.509 Communication application profile T.510T.559 Telematic services Equipmen
5、t characteristics T.560T.649 Still-image compression JPEG 2000 T.800T.829 Still-image compression JPEG XR T.830T.849 Still-image compression JPEG-1 extensions T.850T.899For further details, please refer to the list of ITU-T Recommendations. Rec. ITU-T T.871 (05/2011) i INTERNATIONAL STANDARD ISO/IEC
6、 10918-5 RECOMMENDATION ITU-T T.871 Information technology Digital compression and coding of continuous-tone still images: JPEG File Interchange Format (JFIF) Summary Recommendation ITU-T T.871 | ISO/IEC 10918-5 specifies a file format, referred to as the JPEG File Interchange Format (JFIF), for fil
7、e-based interchange of images encoded according to the JPEG image coding standard (Recommendation ITU-T T.81 | ISO/IEC 10918-1). This Recommendation | International Standard is substantially based on the JFIF version 1.02 specification that was produced in 1992. The JFIF version 1.02 specification w
8、as widely and freely circulated, and became widely recognized as a de facto standard. This Recommendation | International Standard was developed primarily to formalize the JFIF version 1.02 specification. History Edition Recommendation Approval Study Group 1.0 ITU-T T.871 2011-05-14 16 ii Rec. ITU-T
9、 T.871 (05/2011) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications, information and communication technologies (ICTs). The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is res
10、ponsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Assembly (WTSA), which meets every four years, establishes the topics for study by the
11、 ITU-T study groups which, in turn, produce Recommendations on these topics. The approval of ITU-T Recommendations is covered by 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 collabora
12、tive basis with ISO and IEC. NOTE In this Recommendation, the expression “Administration“ is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. Compliance with this Recommendation is voluntary. However, the Recommendation may contain certain m
13、andatory provisions (to ensure, e.g., interoperability or applicability) and compliance with the Recommendation is achieved when all 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
14、. The use of such words does not suggest that compliance with the Recommendation is required of any party. INTELLECTUAL PROPERTY RIGHTS 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
15、takes no position concerning the evidence, validity or applicability of claimed Intellectual Property Rights, whether asserted by 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 pr
16、operty, protected by patents, which may be required to implement this Recommendation. However, implementers are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database at http:/www.itu.int/ITU-T/ipr/. ITU 2012 All rights reserv
17、ed. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU. Rec. ITU-T T.871 (05/2011) iii Table of Contents Page 1 Scope 1 2 Normative references . 1 2.1 Identical Recommendations | International Standards 1 2.2 Paired Recommendations | I
18、nternational Standards equivalent in technical content . 1 2.3 Additional references 1 3 Definitions 1 4 Abbreviations . 1 5 Conformance 2 6 JPEG File Interchange Format (JFIF) overview . 2 6.1 JPEG compression 2 6.2 Colour space 2 6.3 JFIF APP0marker segment . 3 6.4 APP0marker used to specify JFIF
19、extensions . 3 6.5 Application marker segments used for application-specific information 3 7 Conversion to and from RGB . 3 8 Image orientation 4 9 Spatial relationship of components. 4 10 JPEG File Interchange Format (JFIF) specification . 6 10.1 JFIF file syntax 6 10.2 JFIF extension APP0marker se
20、gment . 7 10.3 JFIF extension: Thumbnail coded using JPEG encoding 7 10.4 JFIF extension: Thumbnail stored using one byte per pixel 8 10.5 JFIF extension: Thumbnail stored using three bytes per pixel 8 Bibliography 9 ISO/IEC 10918-5:2012 (E) Rec. ITU-T T.871 (05/2011) 1 INTERNATIONAL STANDARD RECOMM
21、ENDATION ITU-T Information technology Digital compression and coding of continuous-tone still images: JPEG File Interchange Format (JFIF) 1 Scope This Recommendation | International Standard specifies the JPEG File Interchange Format (JFIF). The JPEG File Interchange Format (JFIF) is a minimal file
22、format which enables the exchange of JPEG encoded images (according to Rec. ITU-T T.81 | ISO/IEC 10918-1) having 1 or 3 colour channels and 8 bits per colour channel between a wide variety of platforms and applications. This minimal format does not include some advanced features found in various oth
23、er specified file formats. The purpose of this format is to provide for a basic form of exchange of JPEG images. The optional inclusion of thumbnail images for rapid browsing is also supported. 2 Normative references The following Recommendations and International Standards contain provisions which,
24、 through reference in this text, constitute provisions of this Recommendation | International Standard. At the time of publication, the editions indicated were valid. All Recommendations and Standards are subject to revision, and parties to agreements based on this Recommendation | International Sta
25、ndard are encouraged to investigate the possibility of applying the most recent edition of the Recommendations and Standards listed below. Members of IEC and ISO maintain registers of currently valid International Standards. The Telecommunication Standardization Bureau of the ITU maintains a list of
26、 currently valid ITU-T Recommendations. 2.1 Identical Recommendations | International Standards Recommendation ITU-T T.81 (1992) | ISO/IEC 10918-1:1994, Information technology Digital compression and coding of continuous-tone still images Requirements and guidelines. 2.2 Paired Recommendations | Int
27、ernational Standards equivalent in technical content None. 2.3 Additional references Recommendation ITU-R BT.601-6 (2007), Studio encoding parameters of digital television for standard 4:3 and wide screen 16:9 aspect ratios. 3 Definitions For the purposes of this Recommendation | International Stand
28、ard, the following definitions apply. 3.1 JPEG File Interchange Format (JFIF): The interchange format specified in this Recommendation | International Standard for exchange of images encoded according to the JPEG standard (Rec. ITU-T T.81 | ISO/IEC 10918-1) having 1 or 3 colour channels and 8 bits p
29、er colour channel. 3.2 thumbnail: Reduced resolution representation of the main JPEG (Rec. ITU-T T.81 | ISO/IEC 10918-1) coded image that can be used to identify the image by its content. NOTE Thumbnails are commonly used to browse multiple images quickly using a low resolution visual representation
30、 of the images, rather than using file names or other metadata. 4 Abbreviations For the purposes of this Recommendation | International Standard, the following abbreviations apply. ApiByte i of application data APP0Application data marker, type 0 ISO/IEC 10918-5:2012 (E) 2 Rec. ITU-T T.871 (05/2011)
31、 EOI End of Image ICC International Color Consortium JFIF JPEG File Interchange Format JPEG Joint Photographic Experts Group Lf Length of frame header Lp Length of application data segment Nf Number of components in frame RGB Red, Green, and Blue (colour component values) SOF Start of Frame SOI Star
32、t of Image YCBCR Luminance (denoted as Y), Chrominance toward Blue, and Chrominance toward Red (colour component values) 5 Conformance Some requirements in this Recommendation | International Standard are expressed as format or syntax requirements rather than as software or hardware implementation r
33、equirements. Implementations fall into two categories: JFIF decoders and JFIF encoders. In order for a JFIF decoder to be considered conforming, the decoder shall not report errors when processing conforming instances of the specified format, except when forced to do so by resource exhaustion or whe
34、n the encoded image data uses non-baseline features of Rec. ITU-T T.81 | ISO/IEC 10918-1 that are not supported by the decoder. NOTE The decoder should report errors when processing non-conforming deviations from the specified format. In order for a JFIF encoder to be considered conforming, the file
35、s produced by the encoder shall be formatted as specified. 6 JPEG File Interchange Format (JFIF) overview 6.1 JPEG compression Any JPEG (Rec. ITU-T T.81 | ISO/IEC 10918-1) process is supported by the syntax of the JPEG File Interchange Format (JFIF), provided the encoded image has 1 or 3 colour chan
36、nels and 8 bits per colour channel. NOTE 1 It is strongly recommended that the JPEG baseline process, as defined in Rec. ITU-T T.81 | ISO/IEC 10918-1, be used for the purposes of file interchange. This ensures maximum compatibility among applications supporting JPEG coded images. Files conforming to
37、 the JPEG File Interchange Format shall conform to the interchange format specified in Rec. ITU-T T.81 | ISO/IEC 10918-1. The encoded image in the JPEG File Interchange Format shall have 1 or 3 colour channels and 8 bits per colour channel. Additionally, the JFIF APP0marker (see 6.4) shall be presen
38、t immediately following the SOI marker (specified in Rec. ITU-T T.81 | ISO/IEC 10918-1). NOTE 2 The interchange format specified in Rec. ITU-T T.81 | ISO/IEC 10918-1 requires that all table specifications used in the encoding process are coded in the image data prior to their use. 6.2 Colour space T
39、he colour space to be used is YCBCRas defined by Rec. ITU-R BT.601 (256 levels) but with a different scaling as specified below. If only one component is used, that component shall be the Y component channel as specified below. NOTE The colour space specification herein can provide only a basic leve
40、l of colour fidelity. The use of supplemental metadata such as an ICC profile (e.g., as specified in ISO 15076-1) may be necessary to provide a more accurate colour characterization. If three components are used, they shall be present in the image with the ordering of the components such that the fi
41、rst component is the Y channel, the second component is the CBchannel, and the third component is the CRchannel. ISO/IEC 10918-5:2012 (E) Rec. ITU-T T.871 (05/2011) 3 6.3 JFIF APP0marker segment The JFIF APP0marker segment shall immediately follow the SOI marker. The JFIF APP0marker segment is defin
42、ed as an APP0marker (specified in Rec. ITU-T T.81 | ISO/IEC 10918-1) containing the null-terminated string: “JFIF“ encoded as specified in 10.1 in the first five application data bytes of the marker segment (Api, for i = 1 to 5). Additional APP0marker segments may also be present, provided the assoc
43、iated application data bytes do not begin with this string. The JFIF APP0marker segment provides some information that is not contained in the JPEG (Rec. ITU-T T.81 | ISO/IEC 10918-1) stream, such as: version number, horizontal and vertical pixel densities (expressed in dots per inch or dots per cm)
44、, pixel aspect ratio (derived from the horizontal and vertical pixel densities), and an optional thumbnail encoded as 24-bit RGB image data. NOTE The “JFIF“ string as specified in 10.1 is encoded according to Rec. ITU-T T.50 | ISO 646. 6.4 APP0marker used to specify JFIF extensions Additional APP0ma
45、rker segment(s) can optionally be used for the JFIF extensions specified in clause 10. If used, these segment(s) must immediately follow the JFIF APP0marker segment. Decoders shall skip any unsupported JFIF extension segments and continue decoding. The JFIF extension APP0marker is identified by the
46、zero-terminated string “JFXX“ encoded as specified in 10.2 in the first five application data bytes of the marker segment (Api, for i = 1 to 5). The JFIF extension APP0marker segment contains a 1-byte code with a value specified in clause 10 that identifies the particular extension type. NOTE The en
47、coding of the “JFXX“ string as specified in 10.2 is encoded according to Rec. ITU-T T.50 | ISO 646. 6.5 Application marker segments used for application-specific information Additional APP0and other application marker segments may be used to hold application-specific information that does not affect
48、 the ability to decode or display the JFIF file segment. Application-specific marker segments must appear after the JFIF APP0and any JFIF extension APP0marker segments. Application-specific APP0marker segments shall contain application data bytes such that the initial application data bytes contain
49、a zero-terminated string value that identifies the application. For application-specific APP0marker segments, this string shall not be the zero-terminated string values “JFIF“ as specified in 10.1 or “JFXX“ as specified in 10.2, to avoid conflict with this Recommendation | International Standard. It is recommended that this string represent an organization name or company trademark. Generic strings such as “dog“, “cat“, “tree“, etc., should not be used. 7 Conversion to and from RGB The interpretat
