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Claims  |
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What we claim is:
1. A coding method for a facsimile signal, in which a two-level facsimile
signal obtained by scanning an original picture and successively sampling
the scanning output into picture elements is received as an input, and in
which the position of an information change picture element having changed
from one to the other of two signal levels is coded and outputted, the
improvement of the method comprising:
a first step of setting a starting picture element on a coding scanning
line to be coded from which the coding starts;
a second step of detecting first and second information change picture
elements successively following the starting picture element on the coding
scanning line;
a third step of detecting a first reference picture element which is a
first information change picture element lying after a picture element
just above the starting picture element on a reference scanning line
immediately preceding the coding scanning line and has a signal level
different from that of the starting picture element and a second reference
picture element next to the first information change picture element;
a fourth step of detecting, as a first mode, the state in which the second
reference picture element is detected spaced apart from a picture element
just above the first information change picture element by more than n (n
being an integer) picture elements;
a fifth step of detecting, as not the first mode, the state in which the
second reference picture element is not detected spaced apart from a
picture element just above the first information change picture element by
more than n picture elements;
a sixth step of comparing a first correlation between the starting picture
element and the first information change picture element and between the
first information change picture element and the second information change
picture element with a second correlation between the first information
change picture element and the first reference picture element and between
the second information change picture element and the second reference
picture element when the abovesaid state is detected as not the first
mode;
a seventh step of coding the prsence of the first and second reference
picture elements as the first mode and setting the picture element just
below the second reference picture element as the starting picture element
in the first step when the first mode is detected;
an eighth step of coding a distance between the starting picture element
and the first information change picture element and a distance betweenn
the first information change picture element and the second information
change picture element as a second mode and setting the second information
change picture element as the starting picture element in the first step
when the first correlation is higher than the second correlation;
a ninth step of coding a distance between the first information change
picture element and the first reference picture element and a distance
between the second information change picture element and the second
reference picture element is a third mode and setting the second
information change picture element as the starting picture element in the
first step when the first correlation is lower than the second
correlation; and
a tenth step of sending out the coded outputs of the seventh, eighth and
ninth steps after combining them into a composite signal.
2. A coding method for a facsimile signal according to claim 1, further
comprising:
an eleventh step of successively coding by a one-dimensional method
information change picture elements on a coding scanning line to be coded
for each predetermined length of the coding scanning line to develop one
dimensional codes and storing the one-dimensional codes;
a twelfth step of comparing the information amount of the one-dimensional
codes with the two-dimensional codes stored for each predetermined length
of the coding scanning line;
a thirteenth step of selecting said composite signal as an output when the
information amount of the one-dimensional codes is higher than the
information amount of the two-dimensional codes;
a fourteenth step of selecting the one-dimensional codes as an output when
the information amount of the one-dimensional codes is not higher than the
information amount of the two-dimensional codes; and
a fifteenth step of adding a peculiar control code to the coded output of
each of the thirteenth and fourteenth steps for sending out them after
combining into a composite transmission signal.
3. A coding method for a facsimile signal, in which a two-level facsimile
signal obtained by scanning an original picture and successively sampling
the scanning output into picture elements is received as an input, and in
which the position of an information change picture element having changed
from one to the other of two signal levels is coded and outputted, the
improvement of the method comprising:
a first step of setting a starting picture element on a coding scanning
line to be coded from which the coding starts;
a second step of detecting first and second information change picture
elements successively following the starting picture element on the coding
scanning line;
a third step of detecting a first reference picture element which is a
first information change picture element lying after a picture element
just above the starting picture element on a reference scanning line
immediately preceding the coding scanning line and has a signal level
different from that of the starting picture element and a second reference
picture element next to the first information change picture element;
a fourth step of detecting, as a first mode, the state in which the second
reference picture element is detected spaced apart from a picture element
just above the first information change picture element by more than n (n
being an integer) picture elements;
a fifth step of detecting, as not the first mode, the state in which the
second reference picture element is not detected spaced apart from a
picture element just above the first information change picture by element
more than n picture elements;
a sixth step of comparing a first correlation between the starting picture
element and the first information change picture element and between the
first information change picture element and the second information change
picture element with a second correlation between the first information
change picture element and the first reference picture element and between
the second information change picture element and the second reference
picture element when the abovesaid state is detected as not the first
mode;
a seventh step of coding the presence of the first and second reference
picture elements as the first mode and setting the picture element just
below the second reference picture element as the starting picture element
in the first step when the first mode is detected;
an eighth step of coding the distance between the starting picture element
and the first information change picture element and a distance between
the first information change picture element and the second information
change picture element as a second mode and setting the second information
change picture element as the starting picture element in the first step
when the first correlation is higher than the second correlation;
a ninth step of coding a distance between the first information change
picture element and the first reference picture element and a distance
between the second information change picture element and the second
reference picture element as a third mode and setting the second
information change picture element as the starting picture element in the
first step when the first correlation is lower than the second
correlation; and
a tenth step of temporarily stopping the two-dimensional coding operation
and coding the positions of information change picture elements of the
next coding scanning line only without referring to the positions of
information change picture elements of another scanning line when the
number of coding scanning lines has reached a preset value; and
an eleventh step of sending out the coded outputs of the seventh, eighth,
ninth and tenth steps after combining them into a composite signal.
4. A coding method for a facsimile signal according to claim 3, further
comprising:
a twelfth step of successively coding by a one-dimensional method
information change picture elements on a coding scanning line to be coded
for each predetermined length of the coding scanning line to develop
one-dimensional codes and storing the one-dimensional codes;
a thirteenth step of comparing the information amount of the
one-dimensional codes with the two-dimensional codes stored for each
predetermined length of the coding scanning line;
a fourteenth step of selecting said composite signal as an output when the
information amount of the one-dimensional codes is higher than the
information amount of the two-dimensional codes;
a fifteenth step of selecting the one-dimensional codes as an output when
the information amount of the one-dimensional codes is not higher than the
information amount of the two-dimensional codes; and
a sixteenth step of adding a peculiar control code to the coded output of
each of the fourteenth and fifteenth steps for sending out them after
combining into a composite transmission signal.
5. A coding method for a facsimile signal, in which a two-level facsimile
signal obtained by scanning an original picture and successively sampling
the scanning output into picture elements is received as an input, and in
which the position of an information change picture element having changed
from one to the other of two signal levels is coded and outputted, the
improvement of the method comprising:
a first step of setting a starting picture element on a coding scanning
line to be coded from which the coding starts;
a second step of detecting first and second information change picture
elements successively following the starting picture element on the coding
scanning line;
a third step of detecting a first reference picture element which is a
first information change picture element lying after a picture element
just above the starting picture element on a reference scanning line
immediately preceding the coding scanning line and has a signal level
different from that of the starting picture element and a second reference
picture element next to the first information change picture element;
a fourth step of detecting, as a first mode, the state in which the second
reference picture element is detected spaced apart from a picture element
just above the first information change picture element by more than n (n
being an integer) picture elements;
a fifth step of detecting, as not the first mode, the state in which the
second reference picture element is not detected spaced apart from a
picture element just above the first information change picture element by
more than n picture elements;
a sixth step of comparing a first correlation between the starting picture
element and the first information change picture element with a second
correlation between the first information change picture element and the
first reference picture element when the abovesaid state is detected as
not the first mode;
a seventh step of coding the presence of the first and second reference
picture elements as the first mode and setting the picture element just
below the second reference picture element as the starting picture element
in the first step when the first mode is detected;
an eighth step of coding a distance between the first information change
picture element and the first reference picture element as a third mode
and setting the first information change picture element as the starting
picture element in the first step when the first correlation is lower than
the second correlation;
a ninth step of newly comparing a third correlation between the starting
picture element and the first information change picture element and the
between the first information change picture element and the second
information change picture element with a fourth correlation between the
first information change picture element and the first reference picture
element and between the second information change picture element and the
second reference picture element when it is detected that the first
correlation is higher than the second correlation;
a tenth step of coding a distance between the starting picture element and
the first infformation change picture element and a distance between the
first information change picture element and the second information change
picture element as a second mode and setting the second information change
picture element as the starting picture element in the first step when the
third correlation is higher than the fourth correlation;
an eleventh step of coding a distance between the first information change
picture element and the first reference picture element and a distance
between the second information change picture element and the second
reference picture element as a third mode and setting the second
information change picture element as the starting picture element in the
first step when the third correlation is lower than the fourth
correlation; and
a twelfth step of sending out the coded outputs of the seventh, eighth,
tenth and eleventh steps after combining them into a composite signal.
6. A coding method for a facsimile signal according to claim 5, further
comprising:
a thirteenth step of successively coding by a one-dimensional method
information change picture elements on a coding scanning line to be coded
for each predetermined length of the coding scanning line to develop
one-dimensional codes and storing the one-dimensional codes;
a fourteenth step of comparing the information amount of the
one-dimensional codes with the two-dimensional codes stored for each
predetermined length of the coding scanning line; a fifteenth step of
selecting said composite signal as an output when the information amount
of the one-dimensional codes is higher than the information amount of the
two-dimensional codes;
a sixteenth step of selecting the one-dimensional codes as an output when
the information amount of the one-dimensional codes is not higher than the
information amount of the two-dimensional codes; and
a seventeenth step of adding a peculiar control code to the coded output of
each of the fifteenth and sixteenth steps for sending out them after
combining into a composite transmission signal.
7. A coding method for a facsimile signal, in which a two-level facsimile
signal obtained by scanning an original picture and successively sampling
the scanning output into picture elements is received as an input, and in
which the position of an information change picture element having changed
from one to the other of two signal levels is coded and outputted, the
improvement of the method comprising:
a first step of setting a starting picture element on a coding scanning
line to be coded from which the coding starts;
a second step of detecting first and second information change picture
elements successively following the starting picture element on the coding
scanning line;
a third step of detecting a first reference picture element which is a
first information change picture element lying after a picture element
just above the starting picture element on a reference scanning line
immediately preceding the coding scanning line and has a signal level
different from that of the starting picture element and a second reference
picture element next to the first information change picture element;
a fourth step of detecting, as a first mode, the state in which the second
reference picture element is detected spaced apart from a picture element
just above the first information change picture element by more than n (n
being an integer) picture elements;
a fifth step of detecting, as not the first mode, the state in which the
second reference picture element is not detected spaced apart from a
picture element just above the first information change picture element by
more than n picture elements;
a sixth step of comparing a first correlation between the starting picture
element and the first information change picture element with a second
correlation between the first information change picture element and the
first reference picture element when the abovesaid state is detected as
not the first mode;
a seventh step of coding the presence of the first and second reference
picture elements as the first mode and setting the picture element just
below the second reference picture element as the starting picture element
in the first step when the first mode is detected;
an eighth step of coding the distance between the first information change
picture element and the first reference picture element as a third mode
and setting the first information change picture element as the starting
picture element in the first step when the first correlation is lower than
the second correlation;
a ninth step of newly comparing a third correlation between the starting
picture element and the first information change picture element and
between the first information change picture element and the second
information change picture element with a fourth correlation between the
first information change picture element and the first reference picture
element and between the second information change picture element and the
second reference picture element when it is detected that the first
correlation is higher than the second correlation;
a tenth step of coding a distance between the starting picture element and
the first information change picture element and a distance between the
first information change picture element and the second information change
picture element as a second mode and setting the second information change
picture element as the starting picture element in the first step when the
third correlation is higher than the fourth correlation;
an eleventh step of coding a distance between the first information change
picture element and the first reference picture element and a distance
between the second information change picture element and the second
reference picture element as a third mode and setting the second
information change picture element as the starting picture element in the
first steps when the third correlation is lower than the fourth
correlation;
a twelfth step of temporarily stopping the two-dimensional coding operation
and coding the positions of information change picture elements of the
next coding scanning line only without referring to the positions of
information change picture elements of another scanning line when the
number of coding scanning lines has reached a preset value; and
a thirteenth step of sending out the coded outputs of the seventh, eighth,
tenth, eleventh and twelfth steps after combining them into a composite
signal.
8. A coding method for a facsimile signal according to claim 7, further
comprising:
a fifteenth step of successively coding by a one-dimensional method
information change picture elements on a coding scanning line to be coded
for each predetermined length of the coding scanning line to develop
one-dimensional codes and storing the one-dimensional codes;
a sixteenth step of comparing the information amount of the one-dimensional
codes with the two-dimensional codes stored for each predetermined length
of the coding scanning line;
a seventeenth step of selecting said composite signal as an output when the
information amount of the one-dimensional codes is higher than the
information amount of the two-dimensional codes;
an eighteenth step of selecting the one-dimensional codes as an output when
the information amount of the one-dimensional codes is not higher than the
information amount of the two-dimensional codes; and
a nineteenth step of adding a peculiar control code to the coded output of
each of the seventeenth and eighteenth steps for sending out them after
combining into a composite transmission signal. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
This invention relates to a coding method for efficient transmission or
storage of a binary signal, such as a two-level facsimile signal.
Heretofore, there have been proposed, as two-level facsimile signal coding
systems, (1) a run-length coding system in which a signal obtained by
scanning is converted into a time series train and then the magnitudes of
the run lengths of white and black are successively coded alternately with
each other for transmission and (2) a system in which signals of plural,
for example, two scanning lines are simultaneously coded all together. The
system (1) does not utilize at all the property that facsimile signals
have a high correlation in a direction perpendicular (vertical) to the
scanning line direction; therefore, the compression efficiency is low. The
system (2) makes use of the correlation in the vertical direction with
respect to the signals of several scanning lines to be coded at a time but
does not utilize the correlation to signals of other scanning lines;
consequently, the compression effect is higher than that in the case of
the system (1) but not sufficient.
SUMMARY OF THE INVENTION
The present inventors have proposed various two-dimensional successive
coding systems which obviate such defects of the prior art systems and
removes redundancy of a facsimile signal by a relatively small number of
memories and a simple circuit or means to thereby permit a substantial
reduction of the amount of codes or the number of bits to be sent out.
An object of the present invention is to provide a two-dimensional
successive coding method in which the amount of information or signals to
be transmitted is much more decreased, thereby to permit the reduction of
the transmission time and the number of memories for storing or processing
information.
Another object of this inventin is to provide a coding method for a
facsimile signal using a one-dimensional, two-dimensional adaptive coding
method in which the two-dimensional successive coding principle and the
one-dimensional coding principle, such as a run-length coding method, are
adaptively adopted, so that the amount of information or signals to be
transmitted is reduced, thereby to shorten the transmission time and to
lessen the influence of a transmission error.
In the present invention relating to the first object, when successively
coding the positions (hereinafter referred to as addresses) of information
change picture elements (hereinafter referred to simply as change picture
elements) of a facsimile signal, each having a binary signal level
different from that of an immediately preceding picture elements, the
number of picture elements (hereinafter referred to as a distance) between
each change picture element to be coded and a selected one of the
adjoining change picture elements on the same scanning line (hereinafter
referred to as a coding line) as the change picture element to be coded or
on a scanning line immediately preceding it (which scanning line will
hereinafter be referred as a reference line) is employed to be classified
into three modes determined by the combinations of states of the above
information change picture elements.
The present invention (relating to the second object) is based on the
principle that in the coding of a digital facsimile signal, picture signal
information of each line is coded by the one-dimensional system (for
example, a run-length coding system) and the two-dimensional system and,
for each line, the two coded signals are compared with each other, for
example, in the number of coded bits and a favorable one of them is
selected as a coded output. Let [one-dimensional] and [two-dimensional]
represent the numbers of coded bits obtained by coding a coding line by
the one-dimensional and the two-dimensional coding system, respectively.
When [one-dimensional]>[two-dimensional], the two-dimensional coding is
used as a result of a judgement that the amount of information by the
one-dimensional coding is larger than that of by the two-dimensional
coding, whereas when [one-dimensional].ltoreq.[two-dimensional], the one
dimensional coding is employed for the line to be coded as a result of a
judgement that the amount of information by the one-dimensional coding is
smaller than that by the two-dimensional coding.
BRIEF DESCRIPTION OF THE DRAWING
This invention will be described in details hereinafter with reference to
the accompanying drawings, in which:
FIGS. 1, 2, 3A and 3B, 6A, 6B, 6C, 6D, 9 and 14 show examples of facsimile
signals explanatory of the principles of this invention;
FIGS. 4A, 7A and 7B illustrate independently or jointly in block form
embodiments of this invention;
FIGS. 4B, 4C and 4D illustrate in block form specific operative examples of
circuits for use in the embodiments of FIGS. 4A, 7A and 7B;
FIGS. 5A and 8A show in block form examples of decoding apparatus for
facsimile signals encoded by the embodiments of FIGS. 4A, 7A and 7B;
FIGS. 5B, 5C and 5D show in block form specific operative examples of
circuits for use in the decoding apparatus of FIGS. 5A and 8A;
FIG. 8B is a block diagram illustrating a circuit example employed in FIG.
13;
FIGS. 10 and 11 show in block form another embodiment of this invention and
an example of the decoding apparatus corresponding thereto;
FIGS. 12 and 15 are block diagrams each illustrating another embodiment of
this invention; and
FIG. 13 is a block diagram illustrating an example of a decoding apparatus
for a facsimile signal encoded by the embodiment of FIG. 12.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
A detailed description will be given of specific operative examples of this
invention.
FIGS. 1, 2, 3A and 3B illustrate examples of facsimile signals, blank
blocks representing white picture elements and hatched blocks black
picture elements.
At first, a coding start picture element a.sub.0 and the other change
picture elements are defined as follows:
a.sub.0 : a starting picture element on the coding line L.sub.c with which
the coding starts along the scanning direction SD;
a.sub.1 : a change picture element next to a.sub.0 on the coding line;
a.sub.2 : a change picture element next to a.sub.1 on the coding line;
b.sub.1 : a first change picture element on the reference line L.sub.r
occurring after the picture element just above a.sub.0 and having a binary
signal level different from that of a.sub.0 ;
b.sub.2 : a change picture element next to b.sub.1 on the reference line.
As will hereinbelow be described, the picture elements on the coding line
and the reference line are successively collated with each other to detect
the change picture elements on the both scanning lines for coding.
(Procedure 1): In a case where the two change picture elements b.sub.1 and
b.sub.2 on the reference line are detected prior to the change picture
element a.sub.1 on the coding line (refer to FIG. 2), this state is
defined as a first mode (hereinafter referred to as the Pass mode), and a
distance b.sub.1 b.sub.2 is coded with a Pass mode code, for example,
"1110" (refer to the column of the Pass mode in Table 1), by which a
starting picture element for the next coding is set at a picture element
a'.sub.0 on the coding line just under the picture element b.sub.2.
(Procedure 2): In a case where the change picture element a.sub.1 is
detected on the coding line prior to the change picture element b.sub.2 on
the reference line (refer to FIGS. 3A, 3B), coding of distances a.sub.0
a.sub.1 and a.sub.1 a.sub.2 is defined as a second mode (hereinafter
referred to as the Horizontal mode), and this coding is achieved in
accordance with Table 1(a), and then the number of bits [a.sub.0 a.sub.1
]+[a.sub.1 a.sub.2 ] which is obtained by adding a mode code "1111" to the
coded value is prepared. In Table 1(a), MH(a.sub.0 a.sub.1) and MH(a.sub.1
a.sub.2) are values represented by MH(xy) in Table 1(b), x and y
respectively representing the front and the back picture elements in the
parentheses. At the same time, coding of distances b.sub.1 a.sub.1 and
b.sub.2 a.sub.2 is defined as a third mode (hereinafter referred to as the
Vertical mode), and the coding is provisionally effected in accordance
with Table 1(a) to obtain a bit number [b.sub.1 a.sub.1 ]+[b.sub.2 a.sub.2
]. In this case, D(n) is defined as shown in Table 1(c) following the
value n in the parenthesis.
TABLE 1
______________________________________
Elements
Mode to be coded
Code
______________________________________
Pass mode b.sub.1 b.sub.2
1110
Horizontal mode
a.sub.0 a.sub.1, a.sub.1 a.sub.2
1111 + MH(a.sub.0 a.sub.1) + MH(a.sub.1 a.sub.2)
b.sub.1 a.sub.1 = 0
0
b.sub.1 a.sub.1 = +1
100
Vertical mode
b.sub.1 a1 = -1
101
b.sub.1 a.sub.1 .ltoreq. 2
1100 + D(b.sub.1 a.sub.1 - 1)
b.sub.1 a.sub.1 .ltoreq. -2
1101 + D(.vertline.b.sub.1 a.sub.1 .vertline. -
______________________________________
1)
(a)
MH(xy) MH(xy)
xy x : white x : black n D(n)
______________________________________
0 00110101 0000110111 1 1
1 000111 010 2 01
2 0111 11 3 001
3 1000 10 4 0001
4 1011 011 5 00001
: : : : :
(b) (c)
______________________________________
In the colum of the "Vertical mode" in Table 1, "-" indicates the case of
the picture element a.sub.1 being detected before the picture element
b.sub.1 (or a.sub.2 being detected before b.sub.2), and "+" the case of
picture element a.sub.1 being detected after the picture element b.sub.1
(or a.sub.2 being detected after b.sub.2).
Next, the coded bit numbers [a.sub.0 a.sub.1 ]+[a.sub.1 a.sub.2 ] and
[b.sub.1 a.sub.1 ]+[b.sub.2 a.sub.2 ] thus obtained are compared with each
other to select any one of coding modes in accordance with the following
conditions:
[a.sub.0 a.sub.1 ]+[a.sub.1 a.sub.2 ].gtoreq.[b.sub.1 a.sub.1 ]+[b.sub.2
a.sub.2 ] (a)
In a case where this conditions is established, it is judged that high
correlation exists, respectively, between the change picture elements
a.sub.1 and a.sub.2 to be coded and reference picture elements b.sub.1 and
b.sub.2, and the distances b.sub.1 a.sub.1 and b.sub.2 a.sub.2 are coded
in the Vertical mode; thereafter a new starting picture element is shifted
to the position of the picture element a.sub.1.
For example, in the case of FIG. 3A.
[a.sub.0 a.sub.1 ]=11111011=8 bits
[a.sub.1 a.sub.2 ]=011=3 bits
[b.sub.1 a.sub.1 ]=100=3 bits
b.sub.2 a.sub.2 ]=11001=5 bits
As a consequence, the condition [a.sub.0 a.sub.1 ]+[a.sub.1 a.sub.2
].gtoreq.[b.sub.1 a.sub.1 ]+[b.sub.2 a.sub.2 ] is established, and a coded
signal of the picture elements a.sub.1 and a.sub.2 becomes "10011001".
[a.sub.0 a.sub.1 ]+[a.sub.1 a.sub.2 ]<[b.sub.1 a.sub.1 ]+[b.sub.2 a.sub.2
](b)
When this condition is set up, it is judged that high correlation exists,
respectively, between the change picture elements a.sub.1 and a.sub.2 to
be coded and the starting picture element a.sub.0 and the change picture
element a.sub.1, and it is determined to perform coding in the second
mode, that is, in the Horizontal mode; and coding of distances a.sub.0
a.sub.1 and a.sub.1 a.sub.2 is achieved following the Horizontal mode code
"1111", shifting a new starting picture element to the position of the
picture element a.sub.2.
For example, in the case of FIG. 3B,
[a.sub.0 a.sub.1 ]=11110111=8 bits
[a.sub.1 a.sub.2 ]=10=2 bits
[b.sub.1 a.sub.1 ]=11011=5 bits
[b.sub.1 a.sub.2 ]=110100001=9 bits
As a result, the condition [a.sub.0 a.sub.1 ]+[a.sub.1 a.sub.2 ]<[b.sub.1
a.sub.1 ]+[b.sub.2 a.sub.2 ] is established, and the coded outputs of the
picture elements a.sub.1 and a.sub.2 become "11110111" and "10"
respectively.
In the above description, the expressions (a) and (b) are mentioned as the
conditions for selecting the Horizontal mode and the Vertical mode, but
other conditional expressions can be used such as follows:
[a.sub.0 a.sub.1 ]+[a.sub.1 a.sub.2 ].gtoreq.[b.sub.1 a.sub.1 ]+[b.sub.2
a.sub.2 ]+m (c)
[a.sub.0 a.sub.1 ]+[a.sub.1 a.sub.2 ]<[b.sub.1 a.sub.1 ]+[b.sub.2 a.sub.2
]+m (d)
(m being an integer)
Alternatively, if use is made of the distances a.sub.0 a.sub.1, a.sub.1
a.sub.2 and b.sub.1 a.sub.1, b.sub.2 a.sub.2 before coding,
(a.sub.0 a.sub.1 +a.sub.1 a.sub.2).gtoreq.(b.sub.1 a.sub.1 +b.sub.2
a.sub.2)+m (e)
(a.sub.0 a.sub.1 +a.sub.1 a.sub.2)<(b.sub.1 a.sub.1 +b.sub.2 a.sub.2)+m (f)
(m being an integer)
Moreover, in the column of codes in Table 1, an MH code (a modified
Huffmann code, for particulars, refer to CCITT Draft Recommendation T. 4)
and a bit-by-bit code D(n) are used; but it is a matter of course that the
present invention is not limited specifically to the use of such codes and
can be achieved with ordinary variable length codes.
Besides, in (procedure 1), it is conditioned that the change picture
elements just above the picture elements a.sub.0 and a.sub.1 are not
regarded as b.sub.1 and b.sub.2 ; but the condition can be modified such
that the change picture element just above the picture element a.sub.0 or
a.sub.1 is included in b.sub.1 and b.sub.2, or that the change picture
elements are not regarded as b.sub.1 and b.sub.2 unless they are not
spaced by more than n (n being an integer) picture elements apart from the
picture elements a.sub.0 and a.sub.1.
As described in detail above, in the present invention, addresses of change
picture elements to be coded are successively coded in pairs, and in this
case, the addresses are each coded using a relative distance between the
change picture element to be coded and a selected one of the change
picture elements already coded on the coding line or the reference line.
A brief description will be made of an example of boundary conditions which
are utilized when carrying this invention into practice, although it does
not define the essence of the invention.
(1) Coding of a starting picture element on each scanning line:
A change picture element from white to black is always used as the first
change picture element on each line to be coded. Accordingly, in a case of
the first picture element being black, it is made the first change picture
element, or the first picture element is compulsorily made white.
Further, the first starting picture element a.sub.0 on each coding line is
set up at the position of the first picture element.
(2) Coding of a terminating picture element on each scanning line:
The terminating picture element (In CCITT Recommendation T. 4, one line
consists of 1728 picture elements.) of each line is coded on the
assumption that it is followed by a change picture element.
The following will describe examples of circuits for carrying this
invention into practice in accordance with the principles described above.
FIG. 4A illustrates an example of a coding apparatus. Reference numeral 1
indicates an input terminal for a sampled facsimile signal; 2 and 3
designate line memories, each storing signals of one line; 4 identifies a
memory for storing the level of starting picture element; 5 denotes an
address control circuit for controlling addresses of memories 2 and 3 and
for generating an end of line signal EOL; 6 represents an exclusive OR
(EOR) circuit; 7 shows an OR circuit; 11 and 12 refers to detectors for
change picture element of the coding line and the reference line
respectively; 21, 22, 23 and 24 indicate detectors for detecting the
change picture elements a.sub.1, a.sub.2, b.sub.1 and b.sub.2
respectively; 25 and 26 designate b.sub.1 a.sub.1 and b.sub.2 a.sub.2
direction detector 31, 32, 33 and 34 identify counters; 40 denotes a Pass
mode detector; 51, 52, 53, 54 and 55 represent coders; 60 shows a
comparator for comparing the numbers of coded bits with each other; 71,
72, 73, 74, 75 and 76 refer to gates; 81 and 82 indicate address counters;
83 identifies an a.sub.0 address register; 90 designates a signal
combiner; and 100 identifies an output terminal.
For the sake of brevity, a memory shift pulse generator, a counter clock
pulse generator, etc. are not shown; but these do not exert influence on
an understanding of the essence of the operation of the present invention.
Next, the construction and operation of this embodiment will be described
in more detail.
A facsimile signal to be coded is provided line by line from the input
terminal 1 to the coding line memory 2 for storage therein. At this time,
as a signal of a reference line, a signal of the preceding line stored in
the coding line memory 2 is transferred to the reference line memory 3 for
storage therein. The a.sub.0 memory 4 has stored therein information of
the starting picture element a.sub.0.
Reading of the coding line memory 2 and the reference line memory 3
simultaneously starts from the position of the starting picture element
a.sub.0 under the control of the address control circuit 5. The signal
read from the coding line memory 2 bit by bit is applied to the picture
element detector 11.
The change picture element detector 11 comprises an exclusive OR circuit
421 and a 1-bit memory 420, as shown in FIG. 4B, and compares the picture
element signal read out of the line memory 2 with an immediately preceding
picture element signal to provide an output "1" to the a.sub.1 detector 21
(a flip-flop) when detecting a change picture element. As a result of
this, information on a line a.sub.1p of the a.sub.1 detector 21 changes
from "0" to "1", and information on a line a.sub.1n changes from "1" to
"0".
The a.sub.2 detector 22 is a flip-flop which provides "1" on a line
a.sub.2p when a change picture element is detected by the first change
picture element detector 11 after the picture element a.sub.1 is detected
by the a.sub.1 detector 21 ("1" on the line a.sub.1p).
The output a.sub.1p from the a.sub.1 detector 21 and the output a.sub.2p
from the a.sub.2 detector 22 are applied to the a.sub.0 a.sub.1 and
a.sub.1 a.sub.2 counters 31 and 32 respectively.
The a.sub.0 a.sub.1 counter 31 starts counting of pulses from the moment
when the address control circuit 5 sets a.sub.0 and stops the counting
when receiving "1" from the output line a.sub.1p of the a.sub.1 detector
21. (As a consequence, the number of picture elements between the picture
elements a.sub.0 and a.sub.1 is counted.)
The a.sub.1 a.sub.2 counter 32 starts counting of pulses upon detection of
the picture element a.sub.1 by the a.sub.1 detector 21, that is, upon
reception of "1" on the line a.sub.1p, and stops the counting upon
reception of the signal "1" from the line a.sub.2p when the picture
element a.sub.2 is detected by the a.sub.2 detector 22. As a consequence,
the counters 31 and 32 store the count values of a.sub.0 a.sub.1 and
a.sub.1 a.sub.2 respectively, and these count values are applied to the
a.sub.0 a.sub.1 and a.sub.1 a.sub.2 coders 51 and 52.
The coders 51 and 52 perform coding in accordance with such code tables as
shown in the Horizontal mode column and the MH(xy) column of Table 1.
Next, coding of the picture element b.sub.1 is carried out in the following
way. The signal read from the reference line memory 3 bit by bit is
applied to the picture element detector 12, wherein a change picture
element is detected. On the other hand, in the exclusive OR circuit 6, it
is detected whether that information differs in code from the start
picture element a.sub.0 in the a.sub.0 memory 4 | | |
