1、INTERNATIONAL TELECOMMUNICATION UNION lTU=T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU T.43 (07/97) SERIES T: TERMINALS FOR TELEMATIC SERVICES Colour and gray-scale image representations using lossless coding scheme for facsimile ITU-T Recommendation T.43 (Previously CCITT Recommendation) ITU-T
2、 T-SERIES RECOMMENDATIONS TERMINALS FOR TELEMATIC SERVICES For further details. please refer to TU-T List of Recommendations. ITU-T RECOMMENDATION T.43 COLOUR AND GRAY-SCALE IMAGE REPRESENTATIONS USING LOSSLESS CODING SCHEME FOR FACSIMILE Summary This Recommendation defines a colour data representat
3、ion method in order to make it possible to interchange colour and gray-scale image data using Recommendation T.82 coding scheme over facsimile communication services such as Group 3 and Group 4 facsimile. In this Recommendation, three types of images are treated. The first one is one bit per colour
4、CMY(K) or RGB image. The second one is palettized colour image in which palette tables are specified with CIELAB colour space defined in Recommendation T.42. The last one is continuous-tone colour and gray-scale image specified with CIELAB colour space defined in Recommendation T.42. Source ITU-T Re
5、commendation T.43 was prepared by ITU-T Study Group 8 (1 997-2000) and was approved under the WTSC Resolution No. 1 procedure on the 2nd of July 1997. Recommendation T.43 (07/97) 1 FOREWORD ITU (International Telecommunication Union) is the United Nations Specialized Agency in the field of telecommu
6、ni- cations. The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of the ITU. The ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. The World T
7、elecommunication Standardization Conference (WTSC), which meets every four years, establishes the topics for study by the ITU-T Study Groups which, in their turn, produce Recommendations on these topics. The approval of Recommendations by the Members of the ITU-T is covered by the procedure laid dow
8、n in WTSC Resolution No. 1. In some areas of information technology which fall within ITU-Ts purview, the necessary standards are prepared on a collaborative basis with IS0 and IEC. NOTE In this Recommendation, the expression “Administration“ is used for conciseness to indicate both a telecommunicat
9、ion administration and a recognized operating agency. INTELLECTUAL PROPERTY RIGHTS The ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. The ITU takes no position concerning the evidence, va
10、lidity 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, the ITU hadhad not received notice of intellectual property, protected by patents, which ma
11、y be required to implement this Recommendation. However, implementors are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database. O ITU 1997 All rights reserved. No part of this publication may be reproduced or utilized in any
12、 form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the ITU. ii Recommendation T.43 (07/97) CONTENTS 1 Scope 2 Field of application . 3 References 4 Definitions 5 Conventions 6 Image representation method . 6.1 Overview . 6.2 Colo
13、ur representation One bit per colour CMY(K) or RGB image representation Palettized colour image representation 6.2.1 6.2.2 6.2.3 Continuous-tone colour and gray-scale image representation . 7 Data structure specification BCIH structure and entry classification BCID structure and application rule for
14、 encoding scheme . Usage ofT.82 encoding scheme (JBIG) . 7.1 Overview . 7.2 7.2.1 BCIH structure 7.2.2 Definition of entries 7.3.1 Gray code conversion 7.3.2 7.3.3 Other encoding schemes . 7.3 Recommendation T.43 (07197) Page 1 1 1 1 1 2 2 2 2 3 3 4 4 5 5 5 7 8 9 11 . 111 Recommendation T.43 COLOUR
15、AND GRAY-SCALE IMAGE REPRESENTATIONS USING LOSSLESS CODING SCHEME FOR FACSIMILE (Geneva, 1997) 1 Scope This Recommendation defines colour and gray-scale image representation and their coding schemes in order to make it possible to interchange colour and gray-scale image data such as one bit per colo
16、ur CMY(K) or RGB image, palettized colour image, and/or continuous-tone colour and gray-scale image, using lossless coding scheme over a facsimile communication service such as Group 3 or Group 4 facsimile. Its purpose is to specify representation and lossless coding schemes for three types of colou
17、r and gray-scale images. The first one is one bit per colour CMY(K) or RGB image. The second one is palettized colour image. The last one is continuous-tone colour and gray-scale image. This Recommendation, together with documents such as parts of Recommendations T.4 and T.30, or T.563, T.503 and T.
18、521, will define a colour image data format that may be used by colour facsimile service and by other telematic services. In this Recommendation, the coding scheme specified in Recommendation T.82 (JBIG) is used for lossless encoding of these three types of colour and gray-scale images. Application
19、of other coding schemes are for further study. 2 Field of application This Recommendation defines a colour data representation and coding scheme which mainly enables a receiver to reproduce colour image data as specified by the sender. It is assumed that when a service is performed using this Recomm
20、endation, all non-basic features are subject to negotiation. 3 References The following ITU-T Recommendations and other references contain provisions which, througth reference in this text, constitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. A
21、ll Recom- mendations and other references are subject to revision; ail users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendations and other references listed below. A list of the currently valid ITU-T Recommendation
22、s is regularly published. - - IT-T Recommendation T.42 (1 996), Continuous-tone colour representation method for facsimile. ITU-T Recommendation T.82 (1993) I ISO/IEC 1 1544: 1993, Information technology - Coded representation of picture und audio information - Progressive bi-level image compression
23、. (Commonly referred to as JBIG standard) 4 Definitions The definitions in Recommendations T.42 and T.82 apply to this Recommendation unless explicitly amended. 4.1 Recommendation T.82, which was defined by this group. JBIG: Joint Bi-level Image Experts Group, and also shorthand for the encoding met
24、hod, described in 5 Conventions The conventions in Recommendations T.42 and T.82 apply to this Recommendation. Recommendation T.43 (07/97) 1 6 Image representation method 6.1 Overview In this Recommendation, the representation methods for three types of colour and gray-scale images that require loss
25、less coding scheme are defined. The first one is one bit per colour CMY(K) or RGB image. The second one is palettized colour image. The last one is continuous-tone colour and gray-scale image. Some of these images are electronically created under the soft-copy environment. Others may be obtained usi
26、ng scanner and image processing techniques such as the dither method. As the palettized colour image mode may require accurate reproduction in some cases, this mode has to have accurate colour reproduction possibility. Therefore, the colour palette table data of this mode are specified by the device
27、- independent interchange colour space defined in Recommendation T.42. On the other hand, one bit per colour image mode is specified mainly to reproduce colour image using primary colours. The following represents an example for the use of one bit per colour CMY(K) or RGB mode: - A sender creates or
28、 generates an original colour image with three or four colour components and one bit per colour component using scanner and image processing techniques such as dither. Each bit-plane indicates the ordoff of one of the primary colours. The sender encodes this image using lossless encoding method such
29、 as Recommen- dation T.82 (JBIG). The sender then sends the encoded data with the indication of this mode. The receiver receives the data and represents the image on the CRT (soft-copy) or printer (hard-copy) using their own primary colours. Although the sender adds the information about senders pri
30、mary colours and the receiver has high reproduction ability, the receiver may not reproduce the accurate colour image, because the tone reproduction property of the printer depends not only on primaries but also on pel recording size. The following represents an example for the use of palettized col
31、our image mode: - A sender creates an original colour image using a colour palette in which table data are specified by a specific device-dependent colour space. This colour space may depend on the primaries, white point and gamma of the senders CRT. The sender converts the device-dependent colour p
32、alette to the palette interchange colour space in which table data are specified by the device-independent colour space defmed in Recommendation T.42. The sender then sends the interchange colour palette and the image data encoded with a lossless encoding method such as Recommendation T.82 (JBIG). T
33、he receiver receives the interchange colour palette and the encoded image data. The interchange colour palette is converted to the receiver-specific colour palette, which is specified by the receivers device-dependent hard-copy or soft-copy colour space. The following represents an example for the u
34、se of lossless encoded continuous-tone colour image mode: - A sender creates or generates an original continuous-tone colour or gray-scale image in the colour space defined in Recommendation T.42. In some high-end applications, they need lossless transmission of these images. This Recommendation sup
35、ports lossless encoding of these images using, such as Recommendation T.82 (JBIG). In order to obtain high data compression ratio using the lossless encoding methods, Gray code conversion technique is introduced. 6.2 Colour representation Colour representation defines colour image specification meth
36、od. In this subclause, three types of colour representation methods are defined. 6.2.1 One bit per colour CMY(K) or RGB image representation In this mode, the colour image is treated as one bit per colour component type image using CMY(K) or RGB primaries. In one bit per colour type image in three c
37、olour primaries (CMY or RGB) or in four colour primaries (CMYK), each bit- plane expresses the following colour primaries as shown in Tables 1 to 3. 2 Recommendation T.43 (07/97) Table 1f.43 - Colour table for one bit per colour “CMYK“ image Bit-plane Bit-plane MSB Colour primaries LSB+2 LSB+l LSB C
38、olour primaries Cyan Magenta Yellow Black Table 2f.43 - Colour table for one bit per colour “CMY“ image MSB LSB+l LSB Cyan Magenta Yellow Table 3f.43 - Colour table for one bit per colour “RGB“ image I Bit-plane I Colour primaries MSB LSB+l LSB Red Green Blue 6.2.2 Palettized colour image representa
39、tion Palettized colour images are expressed by indices of 12 bits or less or optionally 13 to 16 bits. The corresponding colour information of each index is given by the colour palette table, in which each entry consists of three component colour coordinates in CIELAB colour space. Each component of
40、 the colour coordinate is represented by 8 bits or 12 bits value specified by Recommendation T.42. A colour palette example that has 236 entries and each component is represented by 8 bits precision is shown in Table 4. A colour palette example that has 128 entries and each component is represented
41、by 12 bits precision is shown in Table 5. 6.2.3 In this mode, the colour image is represented by CIELAB colour space specified in Recommendation T.42 and the gray-scale image is represented by L* component of CIELAB colour space specified in Recommendation T.42. Each component has 8 bits or less or
42、optionally 9 to 12 bits precision. The data structure for this mode is defined for lossless encoding method. In order to obtain high encoding data efficiency, Gray code conversion is used. Currently sub-sampling is not supported in this Recommendation. Continuous-tone colour and gray-scale image rep
43、resentation Recommendation T.43 (07/97) 3 STD-ITU-T RECMN T.43-ENGL 1997 W 4b2591 Ob37089 972 = Index Table 4R.43 - Colour palette table example for 236 entries and 8 bit accuracy Component values (12 bits) Component values (8 bits) I BCIH Table 5lT.43 - Colour palette table example for 128 entries
44、and 12 bit accuracy BCID Ending marker 7 Data structure specification 7.1 Overview Lossless encoding method such as JBIG can be used as a coding scheme for colour and gray-scale images. In this encoding, an image is resolved into a set of bit-planes, and each bit-plane is coded by lossless encoding
45、method. In resolving an image into bit-planes, Gray code conversion is only used for continuous-tone image. This data structure is defined as BCIE (Bit-plane Colour Image Entity) consisting of BCIH (Bit-plane Colour Image Header), BCID (Bit-plane Colour Image Data) and ending marker (XFFAB) as shown
46、 in Figure 1. 4 Figure 1T.43 -Data structure of BCIE Recommendation T.43 (07/97) STD-ITU-T RECMN T-43-ENGL 1997 = 4Bb2591 0b37090 b94 7.2 BCM structure and entry classification 7.2.1 BCIH structure The structure of BCIH (Bit-plane Colour Image Header) is specified in Figure 2. BCIH consists of Magic
47、 Number XFFAS and two or more entries. G3FAXO/G4FAXO entry and ECIH (End of Colour Image Header) entries are mandatory. Each entry consists of Entry Marker XFFE1 or XFFE3, entry length, FAX identifier n and entry data. Format of each entry is specified in the subsequent subclauses. Figure 2.43 - Dat
48、a structure of BCIH 7.2.2 Definition of entries 7.2.2.1 Entry marker The entry marker XFFE1 or XFFE3 will initiate identification of the entry. Marker XFFE1 is the same code used in JPEG colour fax as APPI and used when length indication is two octet space. Marker XFFE3 is used when length indicatio
49、n requires four octet space. Each entry is identified by the FAX identifier N. The FAX identifier N is 6 octets value X47, X3m, X46, X41, X58, Xn, where m equals 3 or 4 and n equals O to maximum XFF (255). 7.2.2.2 G3FAXOlG4FAXO entry The magic number of the BCIH and this entry uniquely identifies the image data encoded by lossless coding scheme for colour and gray-scale image FAX application. It defines the version, image size, spatial resolution, encoding method, image type, interleave and number of bits. This entry is mandatory. The data format is a
