EP O 1 _9 291  B1
gefofe deScfibing the ffst embod_iment of the present inventìon, the two-d.imensional coding SCheme
of the CCITT Recommendation T.4, as a typical coding scheme, is deSCfibed hefe__naftef.                 _
The followjng Table 1 shows the nNo-d_imensional code table of the CCITT ReCOmmendatiOn T.4. _  _
It is noted that.                                C 5A 5C 6A  d 6C       d
5     - _in the case that the f_irst and second scan lineS in the Fi9S. 3AI 4A, 4,  ,  C,   danC   COFreSPdOnt
to the Fefefence and coding lines.in Fig. 2,.respectiveIY, the Chan9in9 elementS  1 an   2 COf FeSPOn  '
,Jb,'' and ''a,'', respectively, and                         C  A 5C 6A  d 6C       d
- _in the caSe that the second and third SCan l__neS in the Fi9S. 3A, 4A, 4, 5,  ,   an   COFreSPdOn
to the fefe Fence and cod_ing l_ines in Fig. 2, respectively, the changin9 elementS C2 and Cs COffeSPOn  tO
Io  ''b,'' and ''a,'', reSpe CtiVeIY.                  f   d.     _  b _   th  h   .   l   nt
Nen e.g. referr.ing to F_ig. 3A, the inventiOn deteCtS a iFSt  _StanCe  12  e  een  e C and9dl_9 e em_e
C, in the f_i Fst scan l_ine and the changing element C2 in the SeCOnd SCan line, and aISO a SeCOn  i StanCe  2S
be_een the changing element C, in the second scan line and the Chan9in9 element Cs in the thi Fd SCan
l.ine. The above ope Fation is Shown in blocks 1 through 5 in Fig. 1. The OPe FatiOn Sta FtS at bIOCk 1. BIOCk 2
_5  sto Fes thfee Scan lines into a thfee line buffer not shown. Block 3 dete CtS the bOUnda_ 31 betWeen the
changing element C, and the nen white element. Block Q detects the boundafY 32 be_een the Chan9in9
element C, and the nen white element. The boundary 31 relates to the bOUnda_ 32. AISO, bIOCk 4 dete CtS
the distance _,,. glock 5 detects the boundary 33 which _is related to the bOUnda_ 32. AISO, bIOCk 5 dete CtS
the di StanCe _z3.                         .    h  h  th  f    l  3 < __  _ <  AND 3 <
2o     The operation proCeedS to block 6, The bIOCk 6 detefmineS W et eF  e OfmU ad    1z. h Kh  d  .  d
__,,l < x is satisfied, or not. As explained below the vaIUe Of ''X'' iS Sele Cted __n aCCOfda6nCCehW_t t e  e'f''t'h
.image f.idelity. If l_,2l _ 3 or l_23l _ 3, aS iS the CaSe in the FigS. 4A, 4C, 5A, 5C, 6A an   I t e anSWef O  e
block 6 _is NO and the operat_ion proceedS to bIOCk 8.                   d      f h
The distance l_,,l as well as l_23l in the Figs. 4A, 4C, 5AI 5C, 6A and 6_ C C_OFFe_SPO_n S tO One dO t e 'aSe'f
2_  _a,b,_ = 1, la,b, l = 2 and la,b,l = 3 shown in the Table 1 D lf the di StanCe _,2 Or _2s COFfeSPOn.S tO ''d' 't
the th Fee cases, the __nvention, at bIOCk 8, Fe-a FfangeS Of COnVeftS the Of_19_lnal blt Pa_efnS OCF 16mga9ed 6a Da
shown _in the F.igs. 4A, 4C. 5A, 5C, 6A and 6C to the bit patterns ShoWn in F__9S. 4B, 4D, 5g, 5,   an   ,
respectively.
The nen Table 2 ShoWS the b._t COnVefSiOn pe_Ormed in bIOCk 8.
30                              TBb_e Z             __
D_etance _ l 2 or _23                    '  _ew D1etance
35              l                  $          O    (_IGS.  _A-_D)
_             2                  $          l    (_IGS _  _A-__)
''            - 3           _      _$    _     _ _.   (_IGg_,__6A-6D)     .
The reasons for perform__ng the above convefsions are.
_    (a) The numbers of bìts of the code words for the cases a,b, = O and a,b, = 1 are ''one b_it'' and ''three
bitS'', FeSpe CtiVely, aS ShoWn in Table 1, Wh._le the nUmber Of bitS Of COde WOfdS fOF the CaSeS a,b, _ 2 and
a,b, -- 3 a Fe ''S._X b._tS'' and ''SeVen b._tS'', and
(bl The above conversion of the distanc in accordance with the _invention does not adverselv a_ect the
image fidel__ty of the original image data with a f_ine resolution, e.g., of 8 pelslmm. In other words, the
_o  or._ginal._mage._s ma._ntained even._f the distance is converted.
The Figs. QA through 6D will be described in more detail later on.
If the formula 3 < l_,2l < x AND 3 < l_z3l < x is satisfiedl the operation proceeds to block J via the YES
path. The value ofx is selected in advance,._n accordance w_ith the _image fidelity which one des_ires. In other
words. the value x is the upper lim'it for do._ng the pre-process. _i.e. for not necessarily keep._ng the orig._nal
_5  image._nformation with.in the converted image data. In the exemplary case, the value of x is selected to be
''6''. F__g. 3A ShoWS one CaSe p FodUCing_a YE_ S fFOm bloCk 6_, Wh_ efein the VaIUe Of _,2 iS ''4'' and the VaIUe Of
_23.is '_5''. Thenl block 7 determ.ines if _,2 is larger than _23. For the exemplary bit pattern shown in Fig.
3A. the block 7 produces a NO outeut. and the operation proceeds to block 1 O. Then the orig._nal._mage data
Of Fig. 3A._S Fe-affanged to fedUCe the d__Stan Ce _,2 to the VaIUe ''3''. The Fe-a Ffanged image data iS ShoWn __n
60  F._g. 3B. It._S n Oted _hat the tOtal length Of _,2 and _23 in the Original image data iS mainta__ned after the
.   conversion, as._t should be to keep the image fidelitv of the or_iginal data.
_            When l_,2l is Iarger than l_23_I the YES ou_put _is producedl and the operati_on p_ roceeds to block 9. NO
eXample fOf the prO_eSS inCIUd_Ing bloCk 9 iS ShOWn_ in t_he fig_ureS_. In bIOCk 91 _23 Of the OFiginal bi_level
image data iS reduced to ''3''I but the total length of _,2 and _23 _in the original image data is ma_inta_ined
65  in the re-arranged._mage data.            4                               .