Standardization activities on multimedia coding in ISO

Signal Processing : Image Communication 1 (1989) 3-16

3Elsevier Science Publishers B .V .

STANDARDIZATION ACTIVITIES ON MULTIMEDIA CODING IN ISO

Hiroshi YASUDAConvenor ISO-IEC/JTCI/SC2:WG8, Visual Media Laboratory, NTT Human Interface Laboratories . 1-2356, Take,Yokosukashi, Kanagawaken 238-03, Japan

Received 15 June 1988

Abstract . This paper first explains the organization of ISO and its background . Then it describes the standardization activitieson picture and audio information coding (i .e . multimedia information coding) that take place in ISO/JTCI/SC2 : WG8. Anoverview of recent WG8 activities is given, including discussions on the identification mechanism for different coding methods,the photographic compression coding algorithm and also starting activities on coding of hi-level images, moving pictureimages and audio, together with the cooperative relations with CCITT .

Keywords . Still picture coding, standardization

1 . Introduction

ISO (International Standardization Organiza-tion) is a non-government organization that has aconsultative status within the United NationsEconomic and Social Council . Its aim, as describedin Article 2 of its Constitution, is "to promote thedevelopment of standards in the world with a viewto facilitating international exchange of goods andservices and to developing cooperation in thesphere of intellectual, scientific, technological, andeconomic activity" .

ISO consists of a General Assembly, a Council,a set of Consultative Committees, a CentralSecretariat and a set of Technical Committees(TC) . Each TC is subdivided in a number of Sub-committees (SC) and these in a number of WorkingGroups (WG) . These TCs, SCs and WGs have thetask of providing proposals of standards which areadopted as International Standards (IS) after avoting procedure by 74 member organizationsgoing through the stages of Draft Proposals (DP)and Draft International Standards (DIS) .

Among many TCs, TC97 has been dealing withstandardization activities on all fields of data pro-

cessing. In recent years, however, there has beensome overlapping of activities between ISO andIEC (International Electrotechnical Commission) .Thus JTCI (Joint Technical Committee 1) has beenformed to take care of the common ISO and IECdata processing competences which were underthe old TC97 of ISO . Subcommittee 2 (SC2) ofJTCI deals with "Character Set and InformationCoding". Working Group 8 (WG8) of SC2 is incharge of "Coded Representation of Picture andAudio Information" .

This paper describes the current and plannedactivities of WG8, which reflect the increasingdemand for worldwide multimedia coding stan-dards, starting from the history of WG8 activitieswhich are summarized in Tables 1 and 2. Con-sidering the nature of this special issue, the iden-tification mechanism and the photographic codingalgorithm standardization activities are describedin greater detail .

2. Overview of WG8 activities

The task of WG8 is best explained by consider-ing a bit stream generated according to IS 2022

4

H. Yasuda / Standardization activities on multimedia coding

Table 1

Outline of standardization activities in WGS

Year

Activities

September 1982

WG8 (Coded Representation of Pictures) was established in ISO/TC97/SC2-

--April 1984

Videotex Coding, Computer Graphics Coding were generally discussed in WG8 .

April 1984

SC2 Plenary in Kyoto, Japan . Color coding algorithm standardization came up to the table of WG8 .

December 1984

Adaptive Block Truncation Coding was proposed as a promising candidate for Color Picture Coding .Activities on CG Coding is progressing with works in SC21/ WG2 (CGM) .

April 1985

Coding of Audio Information became NWI . WG8 has started this activity .Coding Method Identification work has also started .Basic Structure of Standards which will be generated by WG8 is decided .

Following DP's were decided.DPXI

Identification MechanismDPX2 part I

Basic Coding PrinciplesDPX2 part 2

Coding Principles Specific to Photographic Coding and Photographic Coding opcode tablesDPX2 part 3

Coding Principles Specific to Computer Graphics Coding and Computer Graphics Codingopcode tables

DPX3

Photographic Coding FunctionalitiesDPX4

Musical Note Coding

-March 1986

ABTC was tested in ESPRIT 563 project . It was proved that picture quality of ABTC was not satisfactory atrates less than 2 bit/ pel .

March 1986

New algorithms were proposed, and standardization procedure was reexamined . DCT gave higher efficiencyand PCS gave new feature of progressive build-up .

July 1986 CCITT SGVIII NIC members attended to ISO WG8 Meeting . It was found that both parties were aimingalmost at the same goal, thus joint study was recommended . DPXI and DPX2 have got ISO number 9281 and9282 respectively . Drafts were almost completed (for DPX2 part I only) .

November 1986 DP9281 and DP9282/1 were completed and sent for DP voting . First Joint Photographic Experts Meeting(JPEG) was held (CCITT SGVIII NIC and ISO/TC97/SC2/ WG8) . Roles of both parties and time table to getstandard was decided . Goal would be the end of 1987 .

March 1987 DP9281 and DP9282/ 1 were approved by DP voting . Taking into account comments attached to voting, DISof both standards were drafted and sent to DIS voting . Studies on Incremental Coding and Color List Codingwere started to be included in 9282 . Worldwide announcement was made to encourage new algorithm proposals .12 algorithms were proposed from North America, Europe and Japan. Evaluation Method for preselectionprocedure in June was decided . Three level picture quality (0.25 b/p, 0.75 b/p or 1 .0 b/p, 4 .0 b/p), 7 technicalfeatures and complexity/real time decoding were the main points to he evaluated .

June 1987 DIS voting on DP9281 and DP9282/ 1 has taken place . Step Incremental Coding, Zone Coding and DifferentialChain Coding were proposed as candidate for standard and discussion continued . Working drafts for AudioCoding, Musical Note Coding were prepared and discussed. Preselection was carried out among 10 algorithms(2 were withdrawn by proposers) . Combined evaluation gave high marks to ADCT proposed by ESPRIT andABAC proposed by IBM . Some methods proposed from Japan showed high picture quality. From these results,three groups were organized to refine algorithms toward final selection : OCT group based on ADCT, predictivegroup based on ABAC and Japanese group based on GBTC, PCS and CVQ . Because of the shortage of time,schedule was changed, final selection would be January 1988 . This deadline was decided because of CCITT'srequirement toward the end of period . October meeting was planned to decide evaluation method .

Oct.-Dec. 1987 Two meetings for photographic coding were held to decide upon evaluation method . Test picture was newlyselected to avoid statistical unfairness caused by small samples . Four lower rates, 0 .083, 0.25, 0.75, 2 .25 wereselected . To prove real-time decoding feature, real-time demonstration machines should be prepared . However,concerning technical features and complexity, a clear way to evaluate was not decided . There was an opinionto postpone final selection meeting, but enthusiasm of the members made us rush into the final selection meeting .

signal Processing ImageCamminimlian

[5] . Escape codes are used there to extend thebasic character set to other sets . The same concept,with different escape codes, is used to revert to thebasic character set.

In order to introduce new media based on pic-ture and audio in the bit stream, there is a needto define an identification mechanism of the codingmethods of the different media . DIS 9281 [3] isthe solution to the problem for visual media . Thishas been produced by WG8 and will now be stan-dardized. The features of this mechanism aredescribed in Fig . 1 .

Blocks of picture information are called pictureentities (PE) and are composed of a picture controlentity (PCE), corresponding to the escape codesof IS 2022 and a picture data entity (PD) contain-


5

January 1988 D1S9281 and DIS9282/1 were approved . Revised ADCT, Revised ABAC and Combined BSPC (GBTC+PCS)were proposed . Full static subjective test was carried out by 30 members . Although evaluation methods werenot clear, members felt no big difference among the three algorithms on the points of technical features andcomplexity . Results of subjective tests showed that ADCT got the highest marks at every rate . Because of thissituation, all members agreed to make ADCT as the first candidate for the standard . Also all members agreedto make efforts to refine ADCT within a short time .

May 1988

New organization of WG8 for efficient activities of DAPA (Digital Audio and Picture Architecture) has beenapproved with following : 4 subworking groups and RAG for IS9281,JPEG: Joint Photographic Experts Group for still picture coding algorithm .JBIG: Joint Ri-level Image Experts Group for progressive bi-level coding algorithm .MPEG: Moving Picture Expert Group for moving picture coding algorithm .CCEC : Computer Graphics Expert Group for coding principle .

Through the discussions, completion of DP for Photographic Coding Algorithm by 1989 and 2 year activitiesfor first targets of JBIG were approved .

Table 2

Convenors and Chairmen of WG8

ing the actual picture data . PCEs have a furtherstructure comprising :

• a picture coding delimiter (PCD), given bythe escape sequence 01/11 .07/00 according to IS2375 [6] ;

•

a coding method identifier (CMI), indicatinga standardized picture coding algorithm ;

• a length indicator (LI), depending on theactual coding method and giving the length in bytesof the picture data may also be present .

The availability of an agreed switching mecha-nism and of the way to code the different mediawill enable the implementation of a full-fledgedmultimedia system for telecommunication andworkstation applications .

The recognition of this need has led WG8 toVol. 1, No . 1, June 1989

WG8 Convenor Dr. Zaki Muscati (1982-1985)Dr. Hiroshi Yasuda (1985-

)CGEG Chairman Mr. Bernard Trocherie (1986-

)JPEG Chairman Mr. Graham P. Hudson (1986-1988)

Mr. Gregory Wallace (1988-

)JBIG Chairman Dr. Yasuhiro Yamazaki (1988-

)MPEG Chairman Dr. Leonardo Chiarigtione (1988-

)NIC Special Rapporteur Mr. Manfred Wortitzer (1984-1987)

Dr. Istvan Sebestyen (1987-

)

6

leading


I

FSC 2/5 Fp i

ESC 2/54/01

ISO 2022

Other ISOgraphiccharactercodingsystems

Picture coding environment

i

PPicture

CEc ontrolelement

PD Picturedata

Pictire

codingPCD coding CMI method

delimiter )

identifier.LI'length

dicator

start a comprehensive project called "DigitalAudio and Picture Architecture" (DAPA) whichforesees :

• the extension of DIS 9281 to deal with allmedia in a way to cope with all possible applica-tions (e.g. interactive retrieval of multimedia infor-mation from digital storage media) ;

•

coded representation of color/multilevel stillpicture (e.g . photovideotex) ;

• coded representation of bilevel pictures (e .g .retrieval of facsimile pages from large documentdata bases) ;Signal Processing: Image Communicmion

Identification

OP 9281 PcDCMIcFo

PCD CMI(ps) PCD CMI(Gsi PDD CMI(Fs

VPhoto- Cmputerh,graphic

graphic 1

Picture coding methods DP 9282

Otherpicturecodingsystems

L J

Illustration of the picture codingenviroment

PPicture

CEe ontnelelement

PO

Picturedata

Picture PresentationData Element

The presence of LI depends onthe value of CMI

Fig . 1 . Structure of picture presentation data element .

• coded representation of moving pictures (e .g .interactive search or access of entertainment oreducational moving picture information) ;

•

coded representation of computer-generatedgraphics (e.g . Graphic Kernel System-GKS) ;

• coded representation of audio (e.g. syntheticor natural speech accompanying any one of theabove media) .The definition of the coding methods of the

different media is at different levels ofdevelopment .

Still color/ multilevel picture coding will soon

reach the stage of DP and will be dealt with atlength in the following paragraph .Work on computer-generated graphics has

already produced DIS 9282/1 [3], which deals withsuch coding principles as OP-code table structureand coordinate representation . Additional workon incremental coding and color list coding is inprogress.

Coding of bilevel pictures has started recently .The target is to define a coding algorithm typicallyfor 400X400 DPI resolution which performs atleast as well as the current MMR of Group IVfacsimile of CCITT [1] with the additional featureof progressive update . A "Call for Proposals ofAlgorithms" has been issued and distributed to

rI ISO/IEC/JTCI/SC2/WGBi Coded Representation

I I

Digital Audio and PictureI of Picture and Audio

A

ecture DAPA/I Information

I

LJ

DAPAArchitecture

11Technique 1


GraphicsCoding(CGEG)

CCITT SG VIIITerminalCharacteristics and

)Protocols

L.--- •J

L-,,-- 11

ColorStatic

Picture

Joint P ographicExpertGroup(JPEG)

Static PictureCoding

0-

ISO National Member Bodies . This will be fol-lowed by tests and eventual adoption of a standardalgorithm .

Coding of moving pictures has also been started .A lot of work in this area has already been carriedout in CCITT, CCIR and CMTT . A standard forDAPA, however, has to provide some featureswhich were not so important for telecommunica-tion and broadcasting applications. Some of theseare :

•

greater importance of decoding in manyapplications ;

•

decoding in fast forward mode in digitaltapes ;

•

decoding in reverse playback .

Joint ai-levelImageGroup(JBIG)

New Image Communication- Group (NIC)-/RICA/

I

AudioCoding

BinaryStaticPicture

Videotex

Fac mile

Document

Phototele-

Telecon-Architecture

graphy

ferencing

RICAP ;L

J

CCITT SGI : Audiovisual Services (AVS)•

Videophone Service (VPS)•

Teleconference Service (TCS)-Audiographic conferenc service (AGCS)-Videoconference service (VCS)

Moving Pic-ture Coding

Expert Group

CCITT SG XV :Videophone and Vi-deoconference So,-vice ;AudlovisualService Infrastmc-ture

Fig . 2 . Organization of standardization work for still and moving images by CCITT and TSO .

7

Val . 1 . No.1,June 1999

8

They constitute a real challenge to providealgorithms which have to maintain the efficiencyof the traditional algorithms and to cope with thesenew requirements .

Audio coding work to date has been dealingwith synthesized music note coding . There areplans to develop standards for coding of speech,taking into account existing CCITT and CCIRrecommendations and de-facto industrial stan-dards .

The existence of some parallel activities in otherstandardization bodies such as the CCITT hasalready been mentioned . After analyzing differen-ces and commonalities, decisions were made to setup joint ISO-CCITT Committees for the areas ofmajor overlaps . Figure 2 gives the current statusof the ongoing cooperations .

3. Photographic coding algorithm

3.1. Summary of activities on the photographiccoding algorithm

In June 1987, using KTAS's image processingfacilities in Copenhagen, ten different techniqueswere tested by JPEG for subjective quality, com-plexity and technical features . Three techniqueswere chosen as a basis for further development bygroups of international experts . These were a trans-form technique-Adaptive Discrete Cosine Trans-form (ADCT)-submitted by the ESPRIT 563-PICA project; a predictive technique-AdaptiveBinary Arithmetic Coding (ABAC)-contributedby IBM; and a third hybrid technique from theJapanese Natural Image Standardization (NIS)Group-Block Separated Progressive Coding(BSPC).

For the final subjective testing held atCopenhagen in January 1988, results were pro-duced for five test pictures at compressions of 2 .25,0.75, 0.25 and 0 .083 bit/pixel. Results of excep-tionally good quality were shown for all the fivepictures at 0.75 bit/pixel .

The very low 0.083 bit/pixel compression pro-vides a first crude impression of a picture in less


than half a second on the ISDN (64 kbit/s) andin less than 3 seconds at 9 .6 kbit/s on the PSTN .This 4 kbytes of data can produce reduced-sizepictures that can be used for browsing or searchinga database .

To show the practical implementability of thetechniques, the developers demonstrated proto-type terminals operating at 64 kbit/s from picturedatabases . Economic hardware decoders weredemonstrated for ADCT and BSPC . ABAC wasdecoded by software in an IBM PC-AT. It isbelieved that for the first time ADCT was alsoshown being decoded at 64 kbit/s by software .This was achieved with a CAF 80386-based PC .

The results of the subjective tests are now beinganalyzed and the technical features and complexityary to be scrutinized . The ADCT technique willnow be refined and a draft standard will be pro-duced by the end of February 1989 .

3.2. Requirements for compression algorithm

During the preliminary selection process in June1987, requirements were identified that had to besatisfied by candidate algorithms, as shown inTable 3. In preparation for the final selection, theserequirements were intensively reexamined, and the

Table 3Requirements and their weightings

Parameters of the technique Weighting

Subjective quality of each stage of the progressivebuild-up

1st stage 102nd stage 253rd stage 5%

Decode complexity 15%Encode complexity 10%

Sequential build-up 3%Progressive build-up, more than 4 stages 3%Adaptivity 3%Compatibility 3%Error propagation 3%Reversibility 3%Special features 3%

following points were decided to be the mostimportant .

A. Static subjective qualityIt was decided to perform a static subjective test

at four compression rates with an initial stage testat less than 0.1 bit/pixel ; 0 .08 was chosen becauseit was 1/3 x 0.25 . As it is very difficult to distinguishbetween 4.0 bit/pixel during the preselection tests,it was decided to hold the 4th stage test at 2 .25bit/pixel, which is 3 x 0 .75 . The subjective testingswere weighted in two different ways : flat (25%,25%, 25%, 25%) to meet NIC criteria and skewed(10%, 15%, 60%, 15%) to meet WG8 require-ments .

For the static subjective testing it was decidedto use five non-standard (and not previously used)test pictures .

B. Dynamic subjective quality and real timedecodability

The subjective quality of the progressive build-up in real time to the 2.25 bit/pixel stage will bejudged for all test pictures. The decode displaytime must be within ni,50% of the nominal 64 kbit/ svalue for the subjective test . The display screenshould be initially set to gray and go to black whenthe first bit of data is received . Timing will stopwhen the end of the stage is seen from the screento be complete. Figure 3 shows the dynamicfeatures described above.

DATA TRANSMISSION

0 .25

0 .75

2

+0 .5

DISPLAY

Fig . 3 . Progressive build-up process .

C. Technical featuresSequential build-up . Sequential build-up is a

mandatory requirement. For a sequential build-upeach pixel should be set to its final value in one


9

write operation. Pixels should appear on the dis-play from left to right and from top to bottom . Toprovide sequential build-up, a terminal is likely torequire a display buffer, and this may be up toabout 16 full resolution display lines . The pictureachieved at a given compression value for asequential build-up should be identical to that fora progressive build-up .

Progressive build-up . It was agreed that it shouldbe mandatory to be able to provide a progressivebuild-up with more than 20 stages .

Real-time encoding/decoding synchronism .Documentary evidence must be provided statinghow real-time encoding can be achieved . It isrequired that an encoder can begin to transmit datafor the initial stages before the later stage of infor-mation is received. This property is referred to asencoder/decoder synchronism .

Resolution/level range . How the techniquewould be adapted for higher resolutions and highernumbers of levels should he documented . Themechanism by which an editor is able to changethe bit rate or picture quality of a stage must bedocumented.

Reversibility. The final stage should be reversible,i .e . free from information losses . Also, the totalnumber of information bits used to achieve finalstage should be small . A compression ratio of 1/2,namely 8 bit/pixel, is desired .

Unified coding feature . A wide application rangeis desired . Especially the capability of binary cod-ing by the same algorithm is a strong requirement .

3 .3. Outline of proposed Adaptive Discrete CosineTransform (ADCT)

A. Basic coding methodFigure 4 shows a block diagram of the ADCT

basic coding method .

Image 2-0OCT

Linear

EntropyCuantizatipn

Coding

ouantaationMetre

VLC Tables

Fig. 4 . Basic coding method of ADCT.VoL .I, No- I, June 1989

Code

1 0


(a) Transformation . A two-dimensional Dis-crete Cosine Transform is applied to 8 x 8 blocksof pixels .

(b) Linear quantization. After transformation,the coefficients are quantized linearly, using aquantization step dependent on the spectral posi-tion of the coefficient to be quantized . These quan-tization steps are given by the quantization matrix,which has been derived from a psychovisualexperiment for minimization of the visible quanti-zation error .

(c) Entropy coding . The content of the block istransmitted by sending information on the valueand the position of the coefficients . For this pur-pose the transformed-quantized block is describedby a one-dimensional scan . The DC coefficientsare treated separately and they are represented inDPCM with the previous block and encoded usingone-dimensional VLC tables. AC coefficient rela-tive positions and number of bits to representsubsequent AC value are encoded using two-dimensional VLC tables .

(d) Transmission sequence for progressive build-up. The coded data are transmitted in the followingway for progressive build-up: DC luminancecoefficients ; DC U chrominance coefficients ; DC Vchrominance coefficients ; two first AC luminancecoefficients ; AC U chrominance coefficients ; AC V

Signal Processing: Image Con'eu,islue

ENCODER

Channel

4-DiCT

(0-8)0 .08

IDCTI

1,2I.

0

6

DCTIDCT

0 .17( .25)

0 .50( .75)

1 .502 .25)

note : "DCT" and "IDCT"=Basic CodingMethod

Fig. 5 . Progressive structures of ADCT .

chrominance coefficients ; rest of AC luminancecoefficients .

(e) Adaptability. As a standard, sets of pre-defined quantization matrices and VLC tables areused as default values . However, for particularapplications and images, the bit rate and picturequality can be adjusted to nearly any desired valueby scaling the quantization matrix . Furthermoreby generating and sending VLC tables which suitto the input image, coding performance can beimproved.

B. Wideband progressive build-upWideband progressive build-up from a very low

bit rate to a high bit rate can be performed by thehierarchical structure shown in Fig . 5. First, theinyage is low-pass filtered and subsampled, forexample by 4 :1, in both directions, to give areduced image of 1/16 . Such a reduced image isthen encoded by the basic coding methoddescribed above. The decoded image (1/16) isinterpolated by 1 :4 to give the full-size image fordisplay. Secondly, the difference between the sub-sampled image by 2 :1 (1/4) and the 1 :2upsampled image of decoded 1/4 image isencoded. By repeating this process, for example,progressive build-up from 0 .08 to 0 .25 bit/pixel isrealized. Finally, reversibility can be obtained by

DECODER

accumulate bit rate


Table 4Evaluation results-Mean values for static assessments of algorithm ADCT (variances areshown in parentheses)

lossless entropy coding of the differential imagebetween the original and the latest decoded image .

Reproduced pictures are shown in Figs . 7-10 .Subjective evaluation results are summarized inTable 4 and Fig . 6. The table shows that ADCTachieves almost perfect picture quality at the rateof 2 .25 bit/pixel . Also it shows that picture qualityat the rate of 0 .75 bit/pixel is surely acceptable .

SubjectiveQualityRating

0.08

0.25bit/pixel

i

Mixed CompressionsMixed PicturesCompare With Original

0 .75

2 .25Compression

Fig . 6 . Subjective testing results for the final selection .

Lossless characteristics of the algorithm are alsoshown in Table 5. It proves the acceptable com-pression ratio even in the lossless stage .

4 . ConclusionStandardization activities on multimedia coding

in ISO have been described . For the photographiccoding algorithm standard, basic ADCT wasalready decided and through DAPA stan-dardization activity this and other newly comingstandardized coding methods will be widelyapplied in the multimedia communication and

11

Vol . I, No, 1, June 1989

Test picture Level (bit/pixel) WG8 NIC

0.08 0 .25 0 .75 2.25

BARBARA-2 1 .80 5 .20 9 .00 10.0 7 .86 6 .50(1 .57) (2 .16) (2 .05) (0 .09)

COLD-HILL 3 .00 6 .20 9 .80 10.0 8 .61 7.25(1 .57) (3 .09) (0.52) (0.15)

HOTEL 1 .60 5 .00 9.20 10 .00 7 .93 6.45(1 .00) (3 .56) (1 .51) (0.09)

GIRL&TOYS 1 .40 5.00 9.80 10 .0 8 .27 6.55(3 .23) (3 .52) (0.64) (0.01)

BALLOONS 2.40 6.69 9 .90 10 .0 8 .68 7 .25(1 .78) (3 .73) (0.35) (0.15)

Mean 2.04 5 .62 9 .54 10 .0 8 .27 6 .80

storage field .

Table 5

Ratio of reversible stage

Test picture ABAC ADCT BSPC

BARBARA-2 9 .30 9 .74 9 .59GOLD-HILL 8 .73 9 .22 9 .10HOTEL 8 .73 9 .26 9 .05GRI&TOYS 6.52 6 .98 6 .85BALLOONS 8.24 8 .71 8 .61

Mean 8.24 8 .71 8 .61

Signal Processing: Image Communkarion

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Acknowledgement

[2] DIS 9281 : Information Processing-Identification of pic-

The author would like to thank all those who

ture coding methods, 1988 .

have attended WGS meetings and have contributed

[3] DIS 9282-1 : Information Processing-Coded representa-tion of pictures-Part 1 : Encoding principles for picture

to the activities described above .

representation in a 7 or 8 bit environment, 1987 .[4] GP . Hudson e t a l ., Sp ec i al Sess i on for Still Pi ct ure St and ar-

di zat i on, PCS '88, Turin, Italy, 12-14 Sept . 1988 .[5] IS 2022: Information Processing-ISO 7-bit and 8-bit

References

coded character sets-Code extension techniques, 1986 .[6] IS 2375 : Data Processing-Procedure for registration of

escape sequences, 1985 .[1] CCITT Recommendation T .6 : Facsimile coding schemes

[7] H. Yasuda et al ., Special Session for Video Coding Stan-and coding control functions for Group 4 facsimile

dards, Globecom 88, Holliwood, FL, USA, 28 Nov .-1 Dec .apparatus .

1988 .

Signal Processing : Image Communireiion

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Standardization activities on multimedia coding in ISO