CA1114493A - Method and device for transmitting facsimile picture signals - Google Patents
Method and device for transmitting facsimile picture signalsInfo
- Publication number
- CA1114493A CA1114493A CA274,945A CA274945A CA1114493A CA 1114493 A CA1114493 A CA 1114493A CA 274945 A CA274945 A CA 274945A CA 1114493 A CA1114493 A CA 1114493A
- Authority
- CA
- Canada
- Prior art keywords
- run
- length
- storage element
- value
- shift register
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
- H04N1/41—Bandwidth or redundancy reduction
- H04N1/411—Bandwidth or redundancy reduction for the transmission or storage or reproduction of two-tone pictures, e.g. black and white pictures
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
- H04N1/41—Bandwidth or redundancy reduction
- H04N1/411—Bandwidth or redundancy reduction for the transmission or storage or reproduction of two-tone pictures, e.g. black and white pictures
- H04N1/413—Systems or arrangements allowing the picture to be reproduced without loss or modification of picture-information
- H04N1/419—Systems or arrangements allowing the picture to be reproduced without loss or modification of picture-information in which encoding of the length of a succession of picture-elements of the same value along a scanning line is the only encoding step
Abstract
ABSTRACT:
With the facsimile transmission of pictures the run run-lengths (plurality of successive picture elements of the same luminance value) are often transmitted in coded form to save transmission time and transmission bandwidth respectively. Herein the shortest run-length is often allocated to the shortest code word. In accordance with the invention every run length having the value 1 is either extended to the value 2 or suppressed and the shortest code word is then allocated in a corresponding manner to the run-length 2. As a result the total length of the transmitted code words for a document is considerably reduced. Extension is done such that one picture element is extended to the left to the detriment of the preceding run-length having the opposite luminance value provided this preceding run-length still contains thereafter at least two picture elements and that in the other case one picture element is extended to the right to the detriment of the next run-length provided the latter retains at least the value 2 and that otherwise the run-length having the value 1 is suppressed. It is true that the resolution is slightly reduced, however only for the very thin lines which is fully acceptable and in many cases hardly noticeable..
With the facsimile transmission of pictures the run run-lengths (plurality of successive picture elements of the same luminance value) are often transmitted in coded form to save transmission time and transmission bandwidth respectively. Herein the shortest run-length is often allocated to the shortest code word. In accordance with the invention every run length having the value 1 is either extended to the value 2 or suppressed and the shortest code word is then allocated in a corresponding manner to the run-length 2. As a result the total length of the transmitted code words for a document is considerably reduced. Extension is done such that one picture element is extended to the left to the detriment of the preceding run-length having the opposite luminance value provided this preceding run-length still contains thereafter at least two picture elements and that in the other case one picture element is extended to the right to the detriment of the next run-length provided the latter retains at least the value 2 and that otherwise the run-length having the value 1 is suppressed. It is true that the resolution is slightly reduced, however only for the very thin lines which is fully acceptable and in many cases hardly noticeable..
Description
~49L:~
The invention relates to a method ~or transmitting facsimile picture signals obtained from an element-by-element scanning of an original by allocating code numbers to the pluralities of successive element:s having the same luminence value (1 run-length), and to a device suitable therefor.
Such methods for data compression by means o codin~
are used in facsimile systems to save transmission band-width or transmission time are known. A coding method may be used which operates with a ternary intermediate coding and which ~urnishes optimum results ~or many documents.
Depending on the contents of the document to be transmitted, (for example a weather map), other methods are, however, possible which yield still slightly better results, the differences being, however, relatively small. A method which is generally used and which accomplishes a consider-able reduction in the transmission bandwidth or transmission time by means of a particularly ingenuous coding only may, consequently, not be expected.
It is therefore an object of the invention to provide a method with which the signals to be transmitted are so processed prior to coding that in the subsequent coding shoxter code words, at least on an average, occur.
According to the invention this is realized because each run-length having the value 1 is extended to the run-length ~ ~ .
P~ 73 23-~1977 ~ 3 having ~he value 2~ or~ should this result in a xelati~e shift of the extended run-length by more than one picture element~ is suppressed ancl that when allocating code numbers only the converted run-lengths are taken into account and that at the receiver end the recovered, converted run-lengths are dir~ctly released.
As with most documents the short-run-lengths occur most frequently a considex;able improvement o~ the data com-pression can be obtained in this manner as the code words for the short~run-lengths are still further compressed by the method according to the invention. Namely, in many coding methods the number o~ bits in the code word exceed ~or short run-lengths the number of picture elements to be coded, for example~ with said coding ~et ~ s with ternary intermediate coding the run-length 1 is represented by 1.6 bits, the run-length 2 and 3 by 3.2 bits and the run-length 4 by 4 A 8 bits In these cases the code word was longe~ than the run-length itself. By means of the method according to , the invention no code word is allocated anymore to the run-length 1 J as this run-length is no longer included in the coding action but the run-length 2 is allocated to the ; shortest code word eto. so that, for example, with ternary intermediate coding all run-lengths having the value 2n(n = 1, 2, 39~..) can be represented by 1.6 bits less. In this man~er substantially all code words become shorter than the run-length itselfO
The inorease in the grain size which is caused by extending a length~1 is acceptable in substantially all : . ~ :
~ ~3~
:: .: :
:
~ :
,- . . : :
cases and is often even hardly noticea~le. It was namely found that a document which, for example, contains a machine-written text and which therefore imposes already certain requirements on the resolution of the scanning and recording arrangement can be represented, even at an element density of only four elements per mm at the record-ing side by run-length the shortest of which consists for both luminance values of two picture elements. Extending the run-length 1 should not be confused with an increase of the grain size of the total scan to double the value, that is to say to half the scanning density, for the odd run-length from the value 3 upward are retained. Further-more, scanning a line having a width b, if it is located between two scanning points which ara spaced from one another at a distance b furnishes already, depending on the setting of the threshold value of the scanning device a run-length 0, 1 or 2. So ext~nding the run-length 1 to the value 2 acts to a certain degree as changing the thres-hold value of the scanning device.
It is known in principle to extend short signals in ~he scanning of documants. However, this always refers to a continuous scanning without clock control, the length of the picture signals from a given minimum value being transmitted in analog form and directly. Consequently these methods operate with analog means and a coding of the sig-nals to be transmitted is not provided.
:
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.
P~JD 7~-073 23~2--1977 ~ n accordance with Qn e~lbodiment o~ the Method according to the invention extending the run length having the value 1 can be per~ormed because each run-length having the value 1 is extended with the last picture el~ment of the preceding run-length having the other luminance value~
provided the preceding run-Length retains, wllen converted, at least the value 2 and, otherwise is extended with the ~irst picture element of the next following run~lcngth having the other luminance value provided the following run-length, when converted~ retains at least the valuo 2 and9 is completely suppressed. In this manner it is accomplished that extending the run-length having the value 1 to the detriment of a preceding or next run-length takes place only then when these connecting run-lengths retain at least $he value 2.
Performing the method according to the invention can be done by a substantially dircct conversion o~ the conditions indicated with the method in a loglc switching network in conformity with the rules of the switchlng algebra.
To check whether the preceding and the ~ollowing run-length retains at lea~t the value 2 a shi~t register can be provided ~or both of them.
An embodiment of $he invention will be further , , , explained with re~erence to the drawing, in which-` ' ~igure 1 is a block diagram of a device for per-`~ 25 ~orming the method according to the in~ention, ~ igure 2 shows the succession o~ logic signals in various points o~ the block diagram according to ~igure 1 at a variable succession of scanning signals, ::
, ::
.
P~ID 76-o73 23-2-l 977 1, ~igure 3 is an extensive circuit ~iagram of the block diagram of Figure 1.
The scanned picture si~nal is applied in Figure 1 to the first storage element P2 of a shi~t register SR1~ In the embodiment shown here the shift register SR1 comprises only three stages~ storage elements P2 9 P1 and P0 respecti~ely~
as only these three stages are necessary for converting the run-length 1. Each ti~le a new picture signal is applied to the storage element P2 the contents of all storage elements are simultaneously transferred one step to the right. The outputs of the storage elements P2, P1 and P0 are connected to inputs - of a s~Yitching network SW.
The output of the switching ~etwork SW leads to the first storage element U0 of a shift register SR2 which, in this example~ comprises two ~urther storage elements U1 and U2 which is sufficient for controlling the conversion of the run-length having the value 1. A clock signal CP is applled for controlling the storage elements P2, P1, P09 U1 . and U2~ whereas the storage element U0 is controlled by an `20 inverse clock s:ignal CP. The outputs o~ the second and the . third storage element U1 and U2 respectively are also con-I nected to inputs of the switching network SW and the output . .
~ of the last storage element U2 is connected to a coder K. In ~ ~ .
the coder X code words are allocated in accordance with one of the prior art methods to the run-lengths supplied by the , shi~t register SR2~ which code words are then transferred . to the reoeiYer (not shown in the drawing) and reconverted : into the run-lengths applied to the coder K at the *ransmitter ~ ~ .
:
6_ , . .
Pl-~ 76-o73 23~-1977 side and directly released.
The switching network SW consists of three sub_ switching networks SN1, SN2 a.nd SN3 which each consist of logic switching elementsO ~'or the various input signals these sub-switching networks suppl.y the output signals indicated in the following table:
- TABLE
SN1 - L .for U1 ~ U2 SN1 - 0 for U1 = U2 SN2 = L for U1 = P0 - P1 = P2 SN2 = 0 for . ~.all other cases SN3 = U1 for SN1 = L
SN~ P0 for SN1 = 0 SN2 = L
SN3 = P0 for SN1 = 0 - S~2 = 0 It should be born in mind that owing to *he control . with *he clock signals ~P and CP the out;put of the third sub-switching network SN3 is at the same ti~e the input of the first storage element U0 of the second shift register SR2. ..
The meaning of these signals is further explained herebelow~
If the contents of the storage elements U1 and U2 is di~ferent, it is a must that the output signal of the second storage element U1 is supplied to the first storage element U0 of the second shift register SR2~ to a~bid tha-t the contents of this storage element differs from its neighbour U1 for :; ' this would mean t,hat a run-Iength with the value 1 is supplied : ~ .
` : ' . . :
. .
P~ID 76~o73 ~3~2-1977 to the coder K. This condition is recognized by the sub-switching network SN1 (Ul ~ U2 results in SN1 = L) and the third sub-switching network SN3 is controlled in a corres-ponding manner (SN1 = L results in SN3 = U1) as indioated in the table so that the actual value of the next picture element which is stored in the last storage element P0 of the first shi~t register SR1 is suppressed. This condition has priority to all other conditions for therea~ter changing the contents of the shift register SR2 is no longer possible. This results in the fact that any possible run-length with the value 1 is extended *o the right to the detriment of the nei~hbouring next picture element, The sub-switching network SN2 checks the condltion whether the storage element P1 o~ the first shift register SR1 contains a run-length having the value 1 (P2 and P0 both differ from P1) and whether at least the run-length 2 (P0 =
U1) precedes this run-length 1. As this condition (U1-P0=P1 =
P2 results in SN2 = L) only becomes effectiYe when the first sub-switching network SN1 h~s the~output signal 0~ so U1 =
U2, it is ':herewlth established that a run-length of at least 3 precedes the run-length 1 in the storage element P1.
So~ in this oase the run-length 1 may be extended to the .. . .
~; left to the detriment of the preceding run-length which ~ is achievecL because $he third sub-switching network SN3 sup-;~ 25 plies at its output the in~erted output signal of the last storage element P0 of the first shift register SR1 (SN1 = 09 SN2 = L results in SN3 = P0) for with this condition this ;~ is just the non-in~erted ~alue o~ the last but one storage ' , :., :~ .
. . ..
P~ 76-o~3 23--2~1977 element Pl When neither the first SNl nor the second sub-switching networ~~SN2 supplies an output signal L (SNl = 0, SN2 = 0) the possibility does not exist that in the second shift register SR2 a run-length 1 is present which must be extended to the right or in the first shift register SRl a run-length 1 which must be extended to the left, so that consequently the scanned signal which has arived in the last storage element P0 can be directly taken over in the first storage element U0 of the second shift register (SNl - 0 , SN2 = 0 results in SN3 = P0).
The operation of the switching device of ~igure 1 will be described with reference to the time diagram in~
~igure 2 which shows the variation for a randomly scanned signal sample, wherein the black elements in an original to be transmitted are represented in the first line of the diagram by means of crosses. The subsequent lines represent ihe - contents of the storage elements of the first and the second shift register SR1 and SR20 Tlle last lines represent the output signals of the first and the second sub-switching network SNl and SN2 whereas the output signal of the third sub-; ~ switching network SN3 is equal to the contents of the first storage element U0 of the second shift register SR2. T~e solid .
.
crosses below the signal SN2 represent the black elements ~hich correspond to the output signal U2 and which are printed ~ 25 : out in a recei~er. For comparison the dashed orosses in ;~ Fi~ure 2 represent the bl~ck elements of the original to be transmitted~ a delay of four elements being present which is produced b~ the device according to ~igure 1, The digits in .
~ ~igure 2 represent a few o~ the columns.
, g_ , :
P~ID 76-o73 4'~3 At the beginning of the scan (at the beginning of a line) the storage elements U1 and U2 are adjusted to a given value (0) which corresponds to the background of the document which is normall~ white. The contents of the storage elements P0~ P1 and P2 directly ~ollow'~rom the scanned signals, wherein, owing to the direction of shift to the right in the shi~t register SR1 the s~orage element P0 con-tains the signal ~hich was scanned first and the other storage elements the corresponding subsequent signals. This means in the diagra'm of Figure 2, at the chosen time axis t, that with the three signal rows P0, P1 and P2 a shift upwards to the right takes place and with the three signal rows U0 to U2 a shift each time downwards to the right.
In the'co~umn 3 neither of the sub-swit¢hing net-1~ works SN1 and SN2 furn~shes a signal as ¢an be easily checked, ' ' so that U0 directl~ takes o~er the state of P0~ (U0 = P0 = L).
In this respect attention should be paid to the ~act that the storage element U0 owing to the use of the in~erse block signal CP is not wxitten in before the other signals in this column~ particularly on the outputs oP the sub-switching ~ ~ .
networks SN1, SN2 and SN3 ha~e assumed the right position.
' ' In oolumn 4 the contents of U1 and U2 are different ' so that U~ ta~es over the contents of U1 (=L) so that it is certain no-run-length 1 can be produced in the second shift 25 ' register SR10 However,~as the scanned succession of signals indeed contains in this place a run-length exceeding 1 (P0 ie also equal to L) the soanned succession of signals is not changed thereby. The same applies for column 6~ where :, ~
.. .
: . ' ~ PIlD 76-o73 ,, , , _ 23-2-'l977 4 ~ 3 the ~irst white signal (U1 = 0) is au-toma-tically extended by another white element (U0 - U1), the scanned signal (P0 = 0) having, however the same value in spite thereof~
. A change does not occur until in oolumn 7. ~rom the contents of P0, P1 and P2 it can be deduced that the ~irst shift register SR1 contains a black run length having the value 1 (O,L90). At the same time it can be deduced ~rom the corresponding contents (0) o~ U2~ ~1 and P0 that this run-le,ngth i.s preceded by a white run length having the value 3.
This causes the sub-switching network SN2 to supply a signal L so that the inverted contents o~ P0, that is to say the contents of P1 - L~ is *~ken over in U0. Herewith this black-run-length having the value 1 is completed with an element on the le~t-hand side9 that is to say to the detriment of the ,5 preceding whlte run-length having the value 3. By way Or illustration re~erence is made to the solid and dashed crosses in Figure 2 at the columns 7 to 10 inclusive. In column 8 bhe same takes place as in the columns 4 and 67 that is to say the complementary picture element of column 7 is extended by ~: 20 the following pictu~e element which, however~ again corres-ponds to the scanned signal so that again no change occurs.
A rollowing special ~eature occurs'in column 10, whtch ollows a white run-length having the value 1, which in the ,~ , , .
original signal pattern occurs in column 7. Owing to the devlating oontents o~ U1 a~d U2 and the signal L obtained thereby at the out'put'of the ~irst sub-switching network : SN1 ~he contents o~ U1 (= 0) is here taken over in U0 although the scanned signal in this place has~the opposite ::
, : ~ : :: :
'-.
.
PlrD 7G-073 23-2~19~
value (P0 = L). So thc white run-leng~th having the value 1 ~U1 = 0 bet~een U2 = P0 = L) is here completed with one picture clement to the right (U0 becomes 0)~ tha-t is to say to the detriment of a ~ollowing run-length as the preoeding r~n-length only has the value 2 and, consequently~ cannot be shortened, it being irrelevant i~ this prcced:ing run-length has the values 2 owing to a corresponding, scanned signal or as the result of an extension. Here is shown the advantage o~ the measure to per~orm an extension~ i~ possible, ~irst to the detrimcnt of the preceding run-length ~or in t}Lis manner two successive run-lengths having the value 1 and a dif~erent signal value can be extended and consequently retained. Extending the white run-length to the right, per-~ormed in the column 10 (and recorded in the columns 11 and 12) oauses the next black run-length to be shifted to the right~ also oyer one picture element7 in the case this run-length should have the value 2 and this also applies ~or all immediately following run-lengths until a run-length occurs which exceeds 2. In the example o~ ~igure 2 this is already the next black run-length itsel~ (columns 12, 13 and 14) so that shi~`ting ends at the end o~ this run-length.
In column 16 a shi~t to the le~t of a black run-length having the value 1 occurs again (U0 becomes L)~ which takes plaoè in the same manner as the shi~t lll the column 7 and which ~urnishes the crosses at the columns 1S and 19.
; : :
; In llke manner the next white run-Iength having in cclumn 17 P0 - L~ P1 = 0~ P2 = L and U1 ~ U2~ is shifted one place to the right which results on recording in the white run-length - ~ , 12_ P~ID 7G - o ~3 23 -2~1977 ...
in the columns 20 and 21. ~n col-~mn 18~ ho~ever, a black run-length having thevalue 1 is presen-t in the scanned signal (P1 _ L, P0 = P2 = 0). This run-length cannot af~ect column 19 as extending the preceding white run-length has priority as U1 ~ U2. An ex-tension to the right is also im-possible as then a shift over more than one place would occur so that the scanned signal values P1 = L in the column 18 is suppressed in column 19 where U0 = U1 = 0, Also the sub-sequent white run-length having the value 1 is suppressed namely owing to the fact that therea~`ter aga~n a black run-length having the value 1 follows. The latter is again extended to the left (crosses at the columns 22 and 23) for then the preceding white run-length in the succession of output signals which reaches as fas as column 19 retains at 1~ least the value 2 which~ consequently~ is still permissible.
~he subsequent short white run length is again extended by one place to the right etc. So, in this manner, a scanned sucoession of signals having successi~e run-lengths of the value 1 is converted into a succession of signals having suocessive run-lengths of the value 2 and a corresponding half-rate occurrence of th-e signal values so that the succession ~ se ls retained albeit~ by necessity, with only half the resolutlon.
igure 3 shows the details of the switching arrange-m~nt o~ Figure~1. The two-shift registers SRI and SR2 com-; prise storaee elemsnts which are designed as D-~lip.flops, which transfer the signaI at the input D to the outputs Q and Q under the control of~a clock signal to be supplied to . ~
~, .
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,,~
:
~ ~ .
;, ~ .. ~ ., :, .
P~l]) 7G-o73 clock il1pUtS T, Herewith the storage elements P2, P1 and PO as well as U1 and U2 receive the same clock signal CP9 while a dela.yed and the in~erse clock signal CP respect.ively are supplied to storage elcment UO. The switching network SW is again divided into three sub-swi.-tching network.s SN1 SN2 and SN3 to obtain a better comparison to the block diagram of Figure 1. The sub-switohing network SN1 should supply a signal L, when the contents of the storage elements U1 and U2 is dif~erent. This is accomplished by the exclusive OR-gate G1, which is connected to the output Q o~ these storage elements. The signal L at the output of the exclusive OR-gate G1 ef'~ects that in the sub-switching network SN3 the output Q of the storage element U1 is con~ected via the AND-gate G6 and the OR gate G9 to -the input D of storage element UO, while at the same time the ~ND gates G8 and G7 and consequently the other input o~ the OR gate G9 are blocked through the invertor I1.
The sub-switching network SN2 comprises the two . AND gates G2 and G3 the inputs o~ which are each connected to similar outputs of the storage elements P2~ PO and U1 and to the opposite output o~ the storage element P1r The out-puts o~ these AND-gates are combined in the OR-gate G4 whose ~ output consequently represents the output o~ the second ;~ sub-switching network SN2. When the OR gate G4 supplies a signal L and the e~clusive OR~gate G1 simult~neously the signal O *he AND gate G7 is released, which gate connects .
the output Q o~ the storage element PO to the input D of the storage element UO. When~ on the contrary, the -two : : ~
~ 1 4-~: .
, . . .. . ... ~ . . . . .. . . . . . .
P~ 76-o73 23 2-1~77 ~ 3 logic switching elements Gi and G1~ supply the signal O the AND.-gate G8 is released through the invertors Il and I2 ~ihich AND-gate then connects the output Q of the storage element PO to the input D of the storage element UO. In this manner all conditions for the switching ne-twork SW are taken into account, In conformity wit:h the known rules of -the switching algebra the switching network described can be simplified in various manners~ depending on the ~act whether the maximum number Or consecutively connected logic switching elements~ the number o~ swl-tching elernents themselves or the inputs thereof should be reduced to a minimum.
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The invention relates to a method ~or transmitting facsimile picture signals obtained from an element-by-element scanning of an original by allocating code numbers to the pluralities of successive element:s having the same luminence value (1 run-length), and to a device suitable therefor.
Such methods for data compression by means o codin~
are used in facsimile systems to save transmission band-width or transmission time are known. A coding method may be used which operates with a ternary intermediate coding and which ~urnishes optimum results ~or many documents.
Depending on the contents of the document to be transmitted, (for example a weather map), other methods are, however, possible which yield still slightly better results, the differences being, however, relatively small. A method which is generally used and which accomplishes a consider-able reduction in the transmission bandwidth or transmission time by means of a particularly ingenuous coding only may, consequently, not be expected.
It is therefore an object of the invention to provide a method with which the signals to be transmitted are so processed prior to coding that in the subsequent coding shoxter code words, at least on an average, occur.
According to the invention this is realized because each run-length having the value 1 is extended to the run-length ~ ~ .
P~ 73 23-~1977 ~ 3 having ~he value 2~ or~ should this result in a xelati~e shift of the extended run-length by more than one picture element~ is suppressed ancl that when allocating code numbers only the converted run-lengths are taken into account and that at the receiver end the recovered, converted run-lengths are dir~ctly released.
As with most documents the short-run-lengths occur most frequently a considex;able improvement o~ the data com-pression can be obtained in this manner as the code words for the short~run-lengths are still further compressed by the method according to the invention. Namely, in many coding methods the number o~ bits in the code word exceed ~or short run-lengths the number of picture elements to be coded, for example~ with said coding ~et ~ s with ternary intermediate coding the run-length 1 is represented by 1.6 bits, the run-length 2 and 3 by 3.2 bits and the run-length 4 by 4 A 8 bits In these cases the code word was longe~ than the run-length itself. By means of the method according to , the invention no code word is allocated anymore to the run-length 1 J as this run-length is no longer included in the coding action but the run-length 2 is allocated to the ; shortest code word eto. so that, for example, with ternary intermediate coding all run-lengths having the value 2n(n = 1, 2, 39~..) can be represented by 1.6 bits less. In this man~er substantially all code words become shorter than the run-length itselfO
The inorease in the grain size which is caused by extending a length~1 is acceptable in substantially all : . ~ :
~ ~3~
:: .: :
:
~ :
,- . . : :
cases and is often even hardly noticea~le. It was namely found that a document which, for example, contains a machine-written text and which therefore imposes already certain requirements on the resolution of the scanning and recording arrangement can be represented, even at an element density of only four elements per mm at the record-ing side by run-length the shortest of which consists for both luminance values of two picture elements. Extending the run-length 1 should not be confused with an increase of the grain size of the total scan to double the value, that is to say to half the scanning density, for the odd run-length from the value 3 upward are retained. Further-more, scanning a line having a width b, if it is located between two scanning points which ara spaced from one another at a distance b furnishes already, depending on the setting of the threshold value of the scanning device a run-length 0, 1 or 2. So ext~nding the run-length 1 to the value 2 acts to a certain degree as changing the thres-hold value of the scanning device.
It is known in principle to extend short signals in ~he scanning of documants. However, this always refers to a continuous scanning without clock control, the length of the picture signals from a given minimum value being transmitted in analog form and directly. Consequently these methods operate with analog means and a coding of the sig-nals to be transmitted is not provided.
:
~ 4 ~
:
:~
.. . . . .. . ~ :
.
P~JD 7~-073 23~2--1977 ~ n accordance with Qn e~lbodiment o~ the Method according to the invention extending the run length having the value 1 can be per~ormed because each run-length having the value 1 is extended with the last picture el~ment of the preceding run-length having the other luminance value~
provided the preceding run-Length retains, wllen converted, at least the value 2 and, otherwise is extended with the ~irst picture element of the next following run~lcngth having the other luminance value provided the following run-length, when converted~ retains at least the valuo 2 and9 is completely suppressed. In this manner it is accomplished that extending the run-length having the value 1 to the detriment of a preceding or next run-length takes place only then when these connecting run-lengths retain at least $he value 2.
Performing the method according to the invention can be done by a substantially dircct conversion o~ the conditions indicated with the method in a loglc switching network in conformity with the rules of the switchlng algebra.
To check whether the preceding and the ~ollowing run-length retains at lea~t the value 2 a shi~t register can be provided ~or both of them.
An embodiment of $he invention will be further , , , explained with re~erence to the drawing, in which-` ' ~igure 1 is a block diagram of a device for per-`~ 25 ~orming the method according to the in~ention, ~ igure 2 shows the succession o~ logic signals in various points o~ the block diagram according to ~igure 1 at a variable succession of scanning signals, ::
, ::
.
P~ID 76-o73 23-2-l 977 1, ~igure 3 is an extensive circuit ~iagram of the block diagram of Figure 1.
The scanned picture si~nal is applied in Figure 1 to the first storage element P2 of a shi~t register SR1~ In the embodiment shown here the shift register SR1 comprises only three stages~ storage elements P2 9 P1 and P0 respecti~ely~
as only these three stages are necessary for converting the run-length 1. Each ti~le a new picture signal is applied to the storage element P2 the contents of all storage elements are simultaneously transferred one step to the right. The outputs of the storage elements P2, P1 and P0 are connected to inputs - of a s~Yitching network SW.
The output of the switching ~etwork SW leads to the first storage element U0 of a shift register SR2 which, in this example~ comprises two ~urther storage elements U1 and U2 which is sufficient for controlling the conversion of the run-length having the value 1. A clock signal CP is applled for controlling the storage elements P2, P1, P09 U1 . and U2~ whereas the storage element U0 is controlled by an `20 inverse clock s:ignal CP. The outputs o~ the second and the . third storage element U1 and U2 respectively are also con-I nected to inputs of the switching network SW and the output . .
~ of the last storage element U2 is connected to a coder K. In ~ ~ .
the coder X code words are allocated in accordance with one of the prior art methods to the run-lengths supplied by the , shi~t register SR2~ which code words are then transferred . to the reoeiYer (not shown in the drawing) and reconverted : into the run-lengths applied to the coder K at the *ransmitter ~ ~ .
:
6_ , . .
Pl-~ 76-o73 23~-1977 side and directly released.
The switching network SW consists of three sub_ switching networks SN1, SN2 a.nd SN3 which each consist of logic switching elementsO ~'or the various input signals these sub-switching networks suppl.y the output signals indicated in the following table:
- TABLE
SN1 - L .for U1 ~ U2 SN1 - 0 for U1 = U2 SN2 = L for U1 = P0 - P1 = P2 SN2 = 0 for . ~.all other cases SN3 = U1 for SN1 = L
SN~ P0 for SN1 = 0 SN2 = L
SN3 = P0 for SN1 = 0 - S~2 = 0 It should be born in mind that owing to *he control . with *he clock signals ~P and CP the out;put of the third sub-switching network SN3 is at the same ti~e the input of the first storage element U0 of the second shift register SR2. ..
The meaning of these signals is further explained herebelow~
If the contents of the storage elements U1 and U2 is di~ferent, it is a must that the output signal of the second storage element U1 is supplied to the first storage element U0 of the second shift register SR2~ to a~bid tha-t the contents of this storage element differs from its neighbour U1 for :; ' this would mean t,hat a run-Iength with the value 1 is supplied : ~ .
` : ' . . :
. .
P~ID 76~o73 ~3~2-1977 to the coder K. This condition is recognized by the sub-switching network SN1 (Ul ~ U2 results in SN1 = L) and the third sub-switching network SN3 is controlled in a corres-ponding manner (SN1 = L results in SN3 = U1) as indioated in the table so that the actual value of the next picture element which is stored in the last storage element P0 of the first shi~t register SR1 is suppressed. This condition has priority to all other conditions for therea~ter changing the contents of the shift register SR2 is no longer possible. This results in the fact that any possible run-length with the value 1 is extended *o the right to the detriment of the nei~hbouring next picture element, The sub-switching network SN2 checks the condltion whether the storage element P1 o~ the first shift register SR1 contains a run-length having the value 1 (P2 and P0 both differ from P1) and whether at least the run-length 2 (P0 =
U1) precedes this run-length 1. As this condition (U1-P0=P1 =
P2 results in SN2 = L) only becomes effectiYe when the first sub-switching network SN1 h~s the~output signal 0~ so U1 =
U2, it is ':herewlth established that a run-length of at least 3 precedes the run-length 1 in the storage element P1.
So~ in this oase the run-length 1 may be extended to the .. . .
~; left to the detriment of the preceding run-length which ~ is achievecL because $he third sub-switching network SN3 sup-;~ 25 plies at its output the in~erted output signal of the last storage element P0 of the first shift register SR1 (SN1 = 09 SN2 = L results in SN3 = P0) for with this condition this ;~ is just the non-in~erted ~alue o~ the last but one storage ' , :., :~ .
. . ..
P~ 76-o~3 23--2~1977 element Pl When neither the first SNl nor the second sub-switching networ~~SN2 supplies an output signal L (SNl = 0, SN2 = 0) the possibility does not exist that in the second shift register SR2 a run-length 1 is present which must be extended to the right or in the first shift register SRl a run-length 1 which must be extended to the left, so that consequently the scanned signal which has arived in the last storage element P0 can be directly taken over in the first storage element U0 of the second shift register (SNl - 0 , SN2 = 0 results in SN3 = P0).
The operation of the switching device of ~igure 1 will be described with reference to the time diagram in~
~igure 2 which shows the variation for a randomly scanned signal sample, wherein the black elements in an original to be transmitted are represented in the first line of the diagram by means of crosses. The subsequent lines represent ihe - contents of the storage elements of the first and the second shift register SR1 and SR20 Tlle last lines represent the output signals of the first and the second sub-switching network SNl and SN2 whereas the output signal of the third sub-; ~ switching network SN3 is equal to the contents of the first storage element U0 of the second shift register SR2. T~e solid .
.
crosses below the signal SN2 represent the black elements ~hich correspond to the output signal U2 and which are printed ~ 25 : out in a recei~er. For comparison the dashed orosses in ;~ Fi~ure 2 represent the bl~ck elements of the original to be transmitted~ a delay of four elements being present which is produced b~ the device according to ~igure 1, The digits in .
~ ~igure 2 represent a few o~ the columns.
, g_ , :
P~ID 76-o73 4'~3 At the beginning of the scan (at the beginning of a line) the storage elements U1 and U2 are adjusted to a given value (0) which corresponds to the background of the document which is normall~ white. The contents of the storage elements P0~ P1 and P2 directly ~ollow'~rom the scanned signals, wherein, owing to the direction of shift to the right in the shi~t register SR1 the s~orage element P0 con-tains the signal ~hich was scanned first and the other storage elements the corresponding subsequent signals. This means in the diagra'm of Figure 2, at the chosen time axis t, that with the three signal rows P0, P1 and P2 a shift upwards to the right takes place and with the three signal rows U0 to U2 a shift each time downwards to the right.
In the'co~umn 3 neither of the sub-swit¢hing net-1~ works SN1 and SN2 furn~shes a signal as ¢an be easily checked, ' ' so that U0 directl~ takes o~er the state of P0~ (U0 = P0 = L).
In this respect attention should be paid to the ~act that the storage element U0 owing to the use of the in~erse block signal CP is not wxitten in before the other signals in this column~ particularly on the outputs oP the sub-switching ~ ~ .
networks SN1, SN2 and SN3 ha~e assumed the right position.
' ' In oolumn 4 the contents of U1 and U2 are different ' so that U~ ta~es over the contents of U1 (=L) so that it is certain no-run-length 1 can be produced in the second shift 25 ' register SR10 However,~as the scanned succession of signals indeed contains in this place a run-length exceeding 1 (P0 ie also equal to L) the soanned succession of signals is not changed thereby. The same applies for column 6~ where :, ~
.. .
: . ' ~ PIlD 76-o73 ,, , , _ 23-2-'l977 4 ~ 3 the ~irst white signal (U1 = 0) is au-toma-tically extended by another white element (U0 - U1), the scanned signal (P0 = 0) having, however the same value in spite thereof~
. A change does not occur until in oolumn 7. ~rom the contents of P0, P1 and P2 it can be deduced that the ~irst shift register SR1 contains a black run length having the value 1 (O,L90). At the same time it can be deduced ~rom the corresponding contents (0) o~ U2~ ~1 and P0 that this run-le,ngth i.s preceded by a white run length having the value 3.
This causes the sub-switching network SN2 to supply a signal L so that the inverted contents o~ P0, that is to say the contents of P1 - L~ is *~ken over in U0. Herewith this black-run-length having the value 1 is completed with an element on the le~t-hand side9 that is to say to the detriment of the ,5 preceding whlte run-length having the value 3. By way Or illustration re~erence is made to the solid and dashed crosses in Figure 2 at the columns 7 to 10 inclusive. In column 8 bhe same takes place as in the columns 4 and 67 that is to say the complementary picture element of column 7 is extended by ~: 20 the following pictu~e element which, however~ again corres-ponds to the scanned signal so that again no change occurs.
A rollowing special ~eature occurs'in column 10, whtch ollows a white run-length having the value 1, which in the ,~ , , .
original signal pattern occurs in column 7. Owing to the devlating oontents o~ U1 a~d U2 and the signal L obtained thereby at the out'put'of the ~irst sub-switching network : SN1 ~he contents o~ U1 (= 0) is here taken over in U0 although the scanned signal in this place has~the opposite ::
, : ~ : :: :
'-.
.
PlrD 7G-073 23-2~19~
value (P0 = L). So thc white run-leng~th having the value 1 ~U1 = 0 bet~een U2 = P0 = L) is here completed with one picture clement to the right (U0 becomes 0)~ tha-t is to say to the detriment of a ~ollowing run-length as the preoeding r~n-length only has the value 2 and, consequently~ cannot be shortened, it being irrelevant i~ this prcced:ing run-length has the values 2 owing to a corresponding, scanned signal or as the result of an extension. Here is shown the advantage o~ the measure to per~orm an extension~ i~ possible, ~irst to the detrimcnt of the preceding run-length ~or in t}Lis manner two successive run-lengths having the value 1 and a dif~erent signal value can be extended and consequently retained. Extending the white run-length to the right, per-~ormed in the column 10 (and recorded in the columns 11 and 12) oauses the next black run-length to be shifted to the right~ also oyer one picture element7 in the case this run-length should have the value 2 and this also applies ~or all immediately following run-lengths until a run-length occurs which exceeds 2. In the example o~ ~igure 2 this is already the next black run-length itsel~ (columns 12, 13 and 14) so that shi~`ting ends at the end o~ this run-length.
In column 16 a shi~t to the le~t of a black run-length having the value 1 occurs again (U0 becomes L)~ which takes plaoè in the same manner as the shi~t lll the column 7 and which ~urnishes the crosses at the columns 1S and 19.
; : :
; In llke manner the next white run-Iength having in cclumn 17 P0 - L~ P1 = 0~ P2 = L and U1 ~ U2~ is shifted one place to the right which results on recording in the white run-length - ~ , 12_ P~ID 7G - o ~3 23 -2~1977 ...
in the columns 20 and 21. ~n col-~mn 18~ ho~ever, a black run-length having thevalue 1 is presen-t in the scanned signal (P1 _ L, P0 = P2 = 0). This run-length cannot af~ect column 19 as extending the preceding white run-length has priority as U1 ~ U2. An ex-tension to the right is also im-possible as then a shift over more than one place would occur so that the scanned signal values P1 = L in the column 18 is suppressed in column 19 where U0 = U1 = 0, Also the sub-sequent white run-length having the value 1 is suppressed namely owing to the fact that therea~`ter aga~n a black run-length having the value 1 follows. The latter is again extended to the left (crosses at the columns 22 and 23) for then the preceding white run-length in the succession of output signals which reaches as fas as column 19 retains at 1~ least the value 2 which~ consequently~ is still permissible.
~he subsequent short white run length is again extended by one place to the right etc. So, in this manner, a scanned sucoession of signals having successi~e run-lengths of the value 1 is converted into a succession of signals having suocessive run-lengths of the value 2 and a corresponding half-rate occurrence of th-e signal values so that the succession ~ se ls retained albeit~ by necessity, with only half the resolutlon.
igure 3 shows the details of the switching arrange-m~nt o~ Figure~1. The two-shift registers SRI and SR2 com-; prise storaee elemsnts which are designed as D-~lip.flops, which transfer the signaI at the input D to the outputs Q and Q under the control of~a clock signal to be supplied to . ~
~, .
~ -13-: : , .. :
,,~
:
~ ~ .
;, ~ .. ~ ., :, .
P~l]) 7G-o73 clock il1pUtS T, Herewith the storage elements P2, P1 and PO as well as U1 and U2 receive the same clock signal CP9 while a dela.yed and the in~erse clock signal CP respect.ively are supplied to storage elcment UO. The switching network SW is again divided into three sub-swi.-tching network.s SN1 SN2 and SN3 to obtain a better comparison to the block diagram of Figure 1. The sub-switohing network SN1 should supply a signal L, when the contents of the storage elements U1 and U2 is dif~erent. This is accomplished by the exclusive OR-gate G1, which is connected to the output Q o~ these storage elements. The signal L at the output of the exclusive OR-gate G1 ef'~ects that in the sub-switching network SN3 the output Q of the storage element U1 is con~ected via the AND-gate G6 and the OR gate G9 to -the input D of storage element UO, while at the same time the ~ND gates G8 and G7 and consequently the other input o~ the OR gate G9 are blocked through the invertor I1.
The sub-switching network SN2 comprises the two . AND gates G2 and G3 the inputs o~ which are each connected to similar outputs of the storage elements P2~ PO and U1 and to the opposite output o~ the storage element P1r The out-puts o~ these AND-gates are combined in the OR-gate G4 whose ~ output consequently represents the output o~ the second ;~ sub-switching network SN2. When the OR gate G4 supplies a signal L and the e~clusive OR~gate G1 simult~neously the signal O *he AND gate G7 is released, which gate connects .
the output Q o~ the storage element PO to the input D of the storage element UO. When~ on the contrary, the -two : : ~
~ 1 4-~: .
, . . .. . ... ~ . . . . .. . . . . . .
P~ 76-o73 23 2-1~77 ~ 3 logic switching elements Gi and G1~ supply the signal O the AND.-gate G8 is released through the invertors Il and I2 ~ihich AND-gate then connects the output Q of the storage element PO to the input D of the storage element UO. In this manner all conditions for the switching ne-twork SW are taken into account, In conformity wit:h the known rules of -the switching algebra the switching network described can be simplified in various manners~ depending on the ~act whether the maximum number Or consecutively connected logic switching elements~ the number o~ swl-tching elernents themselves or the inputs thereof should be reduced to a minimum.
~: .
, ':
. ~ '': :
' .'. ,; " . :, .. ' , .~ ' , . :' .
. :~ . . : : . ; .
Claims (4)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS
1. A method for transmitting facsimile picture signals obtained from an element-by-element scanning of an original by allocating code numbers to the pluralities of successive picture elements having the same luminance value, comprising the steps of:
extending each run-length having the value 1 to the run-length having the value 2;
suppressing any extended run-length if said extension results in a relative shift of the extended run-length by more than one picture element and allocating code numbers only to the converted run-lengths; and directly releasing recovered, converted run-lengths at the receiving end.
extending each run-length having the value 1 to the run-length having the value 2;
suppressing any extended run-length if said extension results in a relative shift of the extended run-length by more than one picture element and allocating code numbers only to the converted run-lengths; and directly releasing recovered, converted run-lengths at the receiving end.
2. The method as claimed in claim 1, further comprising the steps of:
extending each run-length having the value 1 with the last picture element of the preceding run-length having the other luminance value, if the preceding run-length retains, when converted, at least the value 2; and, otherwise extending each run-length having the value 1 with the first picture element of the next following run-length having the other luminance value, provided the follow-ing run-length, when converted, retains at least the value 2;
and, otherwise suppressing any extended run-length if the following run-length, when converted, has a value less than 2.
extending each run-length having the value 1 with the last picture element of the preceding run-length having the other luminance value, if the preceding run-length retains, when converted, at least the value 2; and, otherwise extending each run-length having the value 1 with the first picture element of the next following run-length having the other luminance value, provided the follow-ing run-length, when converted, retains at least the value 2;
and, otherwise suppressing any extended run-length if the following run-length, when converted, has a value less than 2.
3. A device for carrying the method as claimed in Claim 2 into effect, characterized in that a first shift register having at least three series-connected storage elements consecutively records the digitalized luminance values of the scanned picture element and shifts its cont-ents one storage element further upon scanning each new picture element, that a second shift register having at least three series-connected storage elements shifts its contents upon scanning of each new picture element, the out-put of the last storage element being connected to a device for allocating code numbers, that the input of the first storage element of the second shift register is connected to the output of a switching network, whose inputs are con-nected to the outputs of the last three storage elements of the first shift register and of the second and third storage element of the second shift register and which at the output, a) supplies the same signal as the output of the second storage element of the second shift register, if the output signals of the second and the third storage element of the second shift register deviate from one another, b) supplies the inverted output signal of the last storage element of the first shift register when the output signal of this storage element is equal to that of the last but two storage element of the first shift register and of the second shift register and at the same time deviates from the output signal of the second storage element of the first shift reg-ister, c) supplies the same signal as the output of the last storage element of the first shift register at all other combinations of the output signals of these storage elements.
4. A device as claimed in Claim 3, characterized in that the switching network consists of three sub-switching networks the first sub switching network of which is con-nected to the outputs of the second and third storage ele-ment of the second shift register and supplies a first signal when the two storage elements have different output signals and the second sub-switching network is connected to the last three storage elements of the first shift reg-ister and to the second storage element of the second shift register and supplies a first signal when the output signal of the last storage element but one of the first shift register simultaneously deviates from all other connected output signals, and the third sub-switching network is connected to the outputs of the two first switching networks as well as of the last storage element of the first shift register and of the second storage element of the second shift register and at the output, a) supplies the first output signal of the second storage element when the first sub-switching network supplies the first signal, b)supplies the inverted output signal of the last storage element when only the second sub-switching network supplies the first signal, c) supplies the output signal of the last storage element when neither the first nor the second sub-switching network supplies the first signal.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE19762615486 DE2615486C2 (en) | 1976-04-09 | 1976-04-09 | Method and arrangement for the transmission of facsimile image signals |
| DEP.2615486.9 | 1976-04-09 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1114493A true CA1114493A (en) | 1981-12-15 |
Family
ID=5974924
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA274,945A Expired CA1114493A (en) | 1976-04-09 | 1977-03-28 | Method and device for transmitting facsimile picture signals |
Country Status (7)
| Country | Link |
|---|---|
| JP (1) | JPS52123819A (en) |
| AU (1) | AU508389B2 (en) |
| CA (1) | CA1114493A (en) |
| DE (1) | DE2615486C2 (en) |
| FR (1) | FR2347843A1 (en) |
| GB (1) | GB1539858A (en) |
| NL (1) | NL7703685A (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3232370C2 (en) * | 1982-08-31 | 1984-10-25 | Siemens AG, 1000 Berlin und 8000 München | Method for operating an image copier and image copier for carrying out this method |
| US5033105A (en) * | 1987-08-11 | 1991-07-16 | Apple Computer | Video compression algorithm |
| GB2208059B (en) * | 1987-08-11 | 1991-09-25 | Apple Computer | Video compression algorithm |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3585504A (en) * | 1968-10-07 | 1971-06-15 | British Telecommunications Res | Electrical signalling system |
| US3700797A (en) * | 1969-12-31 | 1972-10-24 | Electronic Image Systems Corp | Facsimile noise deletion and coding system |
| JPS5242607B2 (en) * | 1973-04-12 | 1977-10-25 | ||
| DE2440768C3 (en) * | 1974-08-26 | 1982-03-18 | Philips Patentverwaltung Gmbh, 2000 Hamburg | Method and apparatus for data compression for the facsimile transmission of graphic information |
| DE2450073A1 (en) * | 1974-10-22 | 1976-05-06 | Licentia Gmbh | Predistortion circuit for video signal coding - supplied from facsimile image scanner and its clock pulse source |
-
1976
- 1976-04-09 DE DE19762615486 patent/DE2615486C2/en not_active Expired
-
1977
- 1977-03-28 CA CA274,945A patent/CA1114493A/en not_active Expired
- 1977-04-05 NL NL7703685A patent/NL7703685A/en not_active Application Discontinuation
- 1977-04-06 JP JP3860077A patent/JPS52123819A/en active Pending
- 1977-04-06 GB GB1455677A patent/GB1539858A/en not_active Expired
- 1977-04-07 FR FR7710606A patent/FR2347843A1/en active Granted
- 1977-04-12 AU AU24173/77A patent/AU508389B2/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| NL7703685A (en) | 1977-10-11 |
| AU508389B2 (en) | 1980-03-20 |
| FR2347843B1 (en) | 1982-06-18 |
| DE2615486C2 (en) | 1983-12-08 |
| DE2615486A1 (en) | 1977-10-20 |
| FR2347843A1 (en) | 1977-11-04 |
| JPS52123819A (en) | 1977-10-18 |
| AU2417377A (en) | 1978-10-19 |
| GB1539858A (en) | 1979-02-07 |
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