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Description  |
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BACKGROUND OF THE INVENTION
The present invention relates to a facsimile signal coding system which
permits the receiving station to freely select the quality of a reproduced
image, and more particularly to a facsimile signal coding system of
particular utility when employed in conversational image communication or
image data base retrieval which combines a facsimile terminal with a
display unit.
Conventional facsimile communication is paper-to-paper communication and is
usually intended to obtain a hard copy. However, there is a tendency that
the demand for image processing will be diversified in the future, but at
present, the prior art does not possess functions which cope with such a
situation.
It is considered that the diversification of facsimile communication will
involve the combined use of a facsimile terminal and a display unit for
conversational image communication and video data base retrieval. In such
conversational image communication, for realizing a smooth conversation in
the case of graphic information having a large amount of data, a
progressive coding system which provides a rough display of the entire
image on a display in as early a stage as possible and then gradually
improves the picture quality is more effective than a conventional image
coding system which successively reproduces complete pictures along
scanning lines from the top to the bottom of the image.
With the sequential progressive coding system, the receiver can decide,
from the rough display, whether the information being transmitted is
desired one, and if not, he can stop the subsequent unnecessary data
transmission. If the information is desired one, then its image quality is
improved until the receiver is satisfied, and if necessary, a hard copy of
the picture at that time can also be obtained. Thus, the progressive
coding system is a coding system that permits the selection of picture
quality, a rapid retrieval and curtailment of communication costs, and
hence is suitable for interactive image communication. Especially, the
sequential progressive coding system is effective for a graded image since
it has a large amount of information.
The quality of the graded image depends upon resolution and the number of
gradation levels. Accordingly, one possible method for progressively
improving the image quality by the progressive coding system is to
gradually enhance resolution, and the other is to gradually increase the
number of gradation levels. Conventional progressive coding systems for a
graded image employ the method of gradually increasing only the number of
gradation levels, the method of gradually improving resolution alone or a
method of simultaneously increasing the number of gradation levels and
resolution in accordance with predetermined algorithms. None of the prior
art progressive coding systems is capable of increasing the number of
gradation levels and raising resolution independently of each other.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a progressive coding
system for a graded image which is capable of increasing the number of
gradation levels and improving resolution independently of each other so
as to obviate the above defect of the prior art.
To attain the above object of the present invention, there is proposed a
graded facsimile image signal coding system, comprising means for
distributing a multi-graded facsimile picture signal, represented by
2.sup.n gradation levels, into n bit planes corresponding to n digits;
initial encoding means for detecting, from picture elements forming each
bit plane, picture elements at intervals of .DELTA.X picture elements on
every .DELTA.Y-th line and encoding the detected picture elements; and
additional coding means for further coding each one of said encoded
picture elements with reference to encoded four picture elements
positioned around said one picture element to be coded.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will be described in detail below with reference to
the accompanying drawings, in which:
FIG. 1 is a schematic perspective view for explaining the division of an
image by a bit plane system for use in the present invention;
FIGS. 2A and 2B are diagrams each explanatory of the relationship between
each plane and gradation for use in the present invention;
FIG. 3 is a block diagram illustrating an embodiment of the present
invention;
FIGS. 4, 5, 6A, 6B, 7A, 7B, 7C 7D, 8A, 8B, 8C and 8D are diagrams showing
picture element arrangement patterns for explaining the principles of
encoding for use in the present invention;
FIG. 9 is a block diagram illustrating an example of an encoding sequence
controller used in the present invention;
FIG. 10 is a block diagram illustrating an example of an encoder employed
in the present invention;
FIG. 11 is a block diagram illustrating an example of a decoder for
decoding an encoded signal according to the present invention;
FIG. 12 is a block diagram illustrating an example of a plane determination
circuit for used in the circuit depicted in FIG. 11; and
FIG. 13 is a block diagram illustrating an example of a progressive decoder
utilized in the circuit shown in FIG. 11.
DETAILED DESCRIPTION
The principle of the present invention will first be described.
Now, let it be assumed that an original image to be encoded is a multilevel
image having 2.sup.N gradation levels with each picture element
represented by N bits. The following description will be given of a case
where the value N is 4.
At first, an image of one frame is resolved by a bit plane system into four
binary image planes as depicted in FIG. 1. The value of each bit plane is
determined to be "0" (a white picture element) or "1" (a black picture
element) according to the value of the gradation of the picture element.
FIG. 2 shows two examples of this determination.
FIG. 2A is a diagrammatic representation of the value of the gradation of
the original picture element by binary signals. For instance, when the
gradation is 8, the binary signals are "0111". The bit planes 1, 2, 3 and
4 are sequentially assigned the signals, starting at the MSB, and hence
assume values "0", "1", "1", "1" and "1", respectively. However, the
method using the binary signals described above has a defect of involving
many change points.
FIG. 2B shows an example in which a binary signal is assigned to each
gradation level with a view for minimizing the number of change points in
the representation of 2.sup.4 gradation levels. This method provides for
enhanced coding efficiency.
Accordingly, the following description will be given on the assumption that
the method shown in FIG. 2B is employed.
At the receiving side the binary image can be reproduced by receiving
information of the plane 1 at first. That is, it is necessary only to
display the signals "0" and "1" corresponding to white and black picture
elements, respectively. Then, by receiving information of the plane 2 and
combining it with the already received information of the plane 1, an
image of four gradation levels can be reproduced. Let the four gradation
levels be represented by "brightness 4", "brightness 3", "brightness 2"
and "brightness 1" in order of brightness, beginning with the highest.
Thus it is necessary only to display "brightness 1" when the information
of the planes 1 and 2 is the value of "1", "brightness 2" when the
information of the plane 1 is the value of "1" and the information of the
plane 2 the "0", "brightness 3" when the information of the planes 1 and 2
is the value of "0" and "brightness 4" when the information of the plane 1
is the value of "0" and the information of the plane 2 is the value of
"1". Similarly, by receiving information of the plane 3 and combining it
with the information of the planes 1 and 2 already received, an image of
eight gradation levels can be reproduced. Furthermore, by receiving
information of the plane 4 and combining it with the already received
information of the planes 1, 2 and 3, an image of 16 gradation levels can
be reproduced. In this way, the number of gradation levels can be selected
in dependence upon to which plane information is received.
Each binary-coded plane is encoded by a progressive coding system for a
binary image described later. For convenience of description, let it be
assumed that the original picture has the resolution of sixteen picture
elements/mm. With the progressive coding system for a binary image, it is
possible to gradually improve the quality of the received image by
receiving a rough image at first and then receiving additional
information. For example, encoded information of an image with the
resolution of one picture element/mm, thinned out of the original image at
intervals of sixteen picture elements both lengthwise and breadthwise
thereof, is received at first. Next, additional information is received
for the image having the resolution of 1 picture element/mm, obtaining an
image with a resolution of 2 picture elements/mm. Furthermore, additional
encoding information is received for the image with the resolution of 2
picture elements/mm, obtaining an image having a resolution of 4 picture
elements/mm. By similar operations images with resolutions of 8 picture
elements/mm and 16 picture elements/mm can be obtained. By encoding the
original image with such a progressive coding system, the resolution of
the received image can be selected depending upon to which additional
information is received.
The number of gradation levels can be selected depending upon to which
plane information is received, and the resolution of the picture can also
be selected depending upon to which additional encoding information of the
progressive coding scheme for a binary image is received. Thus, this
system is a progressive coding scheme for a graded image which enables the
number of gradation levels and resolution to be increased independently of
each other.
The resolution and the gradation representing ability of terminals which
access an image data base center are not always common to them.
Accordingly, in case of sending the same image data, the situation may
sometimes arise where it is necessary to send an image of high resolution
to some terminals and an image of high gradation to some other terminals.
In such a case, if the conventional coding system is used, it will be
necessary to store the original image and encode it each time in
accordance with the ability of each receiving terminal. This calls for
many memories and complex processing steps. With the coding system of the
present invention, however, the process involved is simplified and the
storage capacity used is reduced by storing images in the data base
through a method described below.
Table 1 shows a method of storing encoding information of images. At first,
encoding information of an image having a resolution of 1 picture
element/mm, thinned out of the original image at intervals of 16 picture
elements lengthwise and breadthwise thereof, is stored in conjunction with
the plane 1. Next, additional encoding information is stored which is
needed for improving the 1 picture element/mm resolution of the image to 2
picture elements/mm. In a similar manner, additional encoding information
for raising the resolution of the image to 4 picture elements/mm,
additional encoding information for improving the resolution of the image
to 8 picture elements/mm and additional encoding information for raising
the resolution of the image to 16 picture elements/mm are sequentially
stored. Likewise, encoding information is stored for the planes 2, 3 and
4, as shown in Table 1.
For example, in the case of displaying on a receiving terminal an image
having a resolution of 8 picture elements/mm and 8 gradation levels, it
will suffice to receive encoding information 1, 2, 3, 4, 6, 7, 8, 9, 11,
12, 13 and 14. By displaying the received information at the receiving
terminal each time, it is possible to implement a method of providing a
general or rough display of the whole image at an early stage and then
improving its image quality as referred to previously. The order of
reception of information is not limited specifically to the encoding
information 1, 2, 3, 6, 7, 8, 9, 11, 12, 13, 14 but may also be the
encoding information 1, 6, 11, 2, 7, 12, 3, 8, 13, 4, 9, 14. In the case
of the former, an image of high resolution can be obtained at a relatively
early point of time and thereafter the gradation increases. In contrast
thereto, in the case of the latter, an image of high gradation is obtained
and then its resolution improves.
TABLE 1
______________________________________
Resolution of Image
Plane 1 Plane 2 Plane 3
Plane 4
______________________________________
1 picture element/mm
1 6 11 16
2 picture elements/mm
2 7 12 17
4 picture elements/mm
3 8 13 18
8 picture elements/mm
4 9 14 19
16 picture elements/mm
5 10 15 20
______________________________________
Next, FIG. 3 illustrates an example of the circuit arrangement for emboding
the coding system of the present invention. In the description given below
of this example the number of gradations of the original image is 16 (4
bits).
FIG. 3 shows an example of an encoding circuit. Reference numerals 1 and 2
indicate input terminals, 11 a bit distributer, 12 a table, 13 an address
control circuit, 21, 22, 23 and 24 one-frame memories, 31 an encoding
sequence controller, 41 a progressive encoder, 51 an output terminal and
61, 62, 63 and-64 gates. A detailed description will be given of
operations of the circuit depicted in FIG. 3. From the input terminal 1
signals of an original image to be encoded are sequentially received, for
each picture element, in order from left to right and top to bottom,
starting at the top left-hand corner of the original image. The input
signals are transferred to the bit distributor 11, wherein each picture
element represented by four bits is split into four 1-bit signals through
utilization of the table 2. The bit signals are provided to the one-frame
memories 21, 22, 23 and 24, respectively. The table 12 is such, for
example, as shown in Table 2. Table 2 shows signal values which are
provided to the one-frame memories for each gradation signal. For
instance, when the image received from the input terminal has a value "6",
the one-frame memories (A)21, (B)22, (C)23 and (D)24 are supplied with
signals "1", " 0", "1" and "0", respectively. The address control circuit
13 specifies the coordinates of the one-frame memories 21, 22, 23 and 24
where to store the bit signals from the bit distributer 11. In each of
one-frame memories 21, 22, 23 and 24 information of one image frame is
stored, under control of the address control circuit 13, in the same order
as that in which the signals are read out of the original picture (i.e.
from left to right and top to bottom, starting at the upper left-hand
corner of the original image. Upon completion of the information transfer
to the one-frame memories 21, 22, 23 and 24, the progressive encoder 41
starts its encoding operation. The encoding sequence controller 31 has
prestored therein the sequence of encoding from the input terminal 2. By
enabling any one of the gates 61 to 64 in accordance with the prestored
encoding sequence, the encoding sequence controller 31 selects the plane
to be encoded and at the same time controls the progressive encoder 41.
Encoded information from the progressive encoder 41 is delivered from the
output terminal 51.
TABLE 2
__________________________________________________________________________
One-Frame Memories
Gradation Signals
(Planes) 0 1 2 3 4 5 6 7 8 9 10
11
12
13
14
15
__________________________________________________________________________
A 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0
B 1 1 1 1 0 0 0 0 0 0 0 0 1 1 1 1
C 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1
D 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1
__________________________________________________________________________
A detailed description will hereinafter be given, with reference to the
drawings, of algorithms of the progressive coding system for an image
represented by the binary signals.
FIGS. 4 to 8 are diagrams conceptually showing the picture element coding
sequence according to the present invention. FIG. 4 is a diagrammatic
showing of nine lines l.sub.m to l.sub.m+2.DELTA.Y extracted from a
certain part of a picture element signal.
(i) According to the present invention, picture elements marked with double
circles, which are spaced apart .DELTA.X=2.sup.n (where n=1, 2, 3, . . . )
picture elements in a lateral direction (on scanning lines) and
.DELTA.Y=2.sup.n (where n=1, 2, 3, . . . ) picture elements in a vertical
directions, are detected, and they are linked together without being
divided for each line and encoded into run-length codes. FIG. 4 shows a
case where n=2, that is, where every four picture elements are detected on
every fourth line.
(ii) Next, picture elements marked with crosses are encoded and in this
case, the picture elements marked with double circles are referred to.
That is to say, for the encoding of the cross-marked picture elements,
four already-coded double-circled picture elements are referred to which
are spaced apart from the cross-marked picture element by .DELTA.X/2 in
the lateral direction and .DELTA.Y/2 in the vertical direction, as shown
in FIG. 5. What is intended to mean by "referred to" is to judge the
amount of information which is given to the quality of the cross-marked
picture element to be encoded. The four double-circled reference picture
elements assume the following five statuses:
Status 0: the four picture elements are all white picture elements.
Status 1: only one of the four picture elements is a black picture element.
Status 2: two of the four picture elements are black picture elements.
Status 3: three of the four picture elements are black picture elements
Status 4: the four picture elements are all black picture elements.
Of the above statuses, the cross-marked picture element in the status 2 is
considered to correspond to the contour of an image since two picture
elements are white and other two picture elements are black, and the
picture quality is greatly affected depending upon whether the
cross-marked picture element lying at the center is white or black.
Accordingly, if the cross-marked picture element in the status 2 is coded
and transmitted prior to the other picture elements, then the picture
quality at the receiving side can be markedly improved. From such a point
of view, according to the present invention, picture elements are encoded
in the order of status 2--status 3--status 1--status 4--status 0.
In the status 0 and the status 4, if an interpolation process (a sort of
prediction) is carried out at the receiving side, then it is very likely
that the cross-marked picture element is interpolated to white in the
status 0 and to black in the status 4; therefore, its encoding may also be
omitted in some cases.
The mode of encoding in a case where the double-circled picture elements
lie at the four corners of the square, as shown in FIG. 5, will
hereinafter be referred to as the mode 1, and this mode for each status N
(where N=0, . . . , 5) will hereinafter be called the mode 1-N.
(iii) Next, picture elements marked with triangles in FIG. 4 are each
encoded by referring to the double-circled and cross-marked picture
elements already encoded. In this case, the reference picture elements lie
above and below the triangle-marked picture element to be encoded and on
the right and the left thereof at distances therefrom of .DELTA.X/2 and
.DELTA.Y/2, as shown in FIG. 6. This mode of encoding will hereinafter be
referred to as the mode 2. The statuses which the reference picture
elements can assume are the same as the aforementioned statuses 0 to 4,
and the encoding sequence for the triangle-marked picture elements, taking
into account the statuses of the reference picture elements, is also the
same as described above. The mode of encoding in each status will
hereinafter be referred to as the mode 2-N (where N=0, . . . 4).
(iv) Next, picture elements marked with single circles in FIG. 4 are
encoded. FIGS. 7A to 7D show the patterns of reference picture elements in
the case of the mode 1, and the reference picture elements lie distant
.DELTA.X/2 and .DELTA.Y/2 from the single-circled picture element to be
encoded. That is to say, it is necessary only to reduce the distance of
extraction of the reference picture elements by half in the procedure of
encoding the cross-marked picture elements.
(v) Finally, blank picture elements in FIG. 4 are encoded. FIGS. 8A to 8D
show the patterns of reference picture elements in this case. In the
encoding mode 2, the distance from the picture element to be encoded to
each reference picture element is 1/2 that in the case of encoding the
triangle-marked picture element.
The encoding operations in the mode 1 and the mode 2 are repeated, with the
intervals between the reference picture elements reduced by half, as
described above. When the intervals between them becomes 2.sup.1, it means
completion of the encoding of all picture elements.
While in the example shown in FIG. 4 the values .DELTA.X and .DELTA.Y are
selected so that 2.sup.2 =4, the value n in the 2.sup.n is arbitrarily
selectable. Further, the .DELTA.X and 66 Y need not always be set to the
same value; namely, it is necessary only that when the interval between
the reference picture elements becomes 2, the interval between reference
picture in that direction be fixed to 2 and the encoding in the mode 1 and
the mode 2 be carried out until the interval between reference picture
elements in the other direction becomes 2.
Details of the above-described coding procedures are as follows:
Procedure 1-1: .DELTA.X and .DELTA.Y are determined by 2.sup.n (where n=1,
2, 3, 4, . . . )
Procedure 1-2: Letting the coordinates of picture elements be represented
by P (X..DELTA.X+1, Y..DELTA.X+1) (where X, Y=0, 1, . . . ), the picture
elements P are linked together from left to right and top to bottom
without being divided for each line, and they are encoded into run-length
codes.
Procedure 1-3: Encoding takes place in accordance with algorithms shown in
Procedures 2-1 to 2-10 described later.
Procedure 1-4: .DELTA.X is set to .DELTA.X/2, and Y is set to .DELTA.Y/2.
Procedure 1-5: If .DELTA.X and .DELTA.Y are both 1 (2 at the end of the
Procedure 1-3), then encoding is finished, and if not, the operation
proceeds to the Procedure 1-3.
Procedures 2-1 to 2-10 are as follows:
Procedure 2-1: Picture elements in the mode 1-2 are encoded. All picture
elements which are in the mode 1-2 are all linked together one after
another without being divided for each line, and they are encoded into
run-length codes. The encoding is effected on the assumption, as an
initial condition, that a black picture element in the mode 1-2 virtually
exists at the head of the picture.
Procedure 2-2: Picture elements in the mode 1-3 are encoded. All picture
elements which are in the mode 1-3 are all linked together one after
another without being divided for each line, and they are encoded into
run-length codes. The encoding is effected on the assumption, as an
initial condition, that a black picture element in the mode 1-3 virtually
exists at the head of the picture.
Procedure 2-3: Picture elements in the mode 1-1 are encoded. All picture
elements which are in the mode 1-1 are all linked together one after
another without being divided for each line, and they are encoded into
run-length codes. The encoding is effected on the assumption, as an
initial condition, that a white picture element in the mode 1-1 virtually
exists at the head of the picture.
Procedure 2-4: Picture elements in the mode 1-4 are encoded. All picture
elements which are in the mode 1-4 are all linked together one after
another without being divided for each line, and they are encoded into
run-length codes. The encoding is effected on the assumption, as an
initial condition, that a black picture element in the mode 1-4 virtually
exists at the head of the picture.
Procedure 2-5: Picture elements in the mode 1-0 are encoded. All picture
elements which are in the mode 1-0 are all linked together one after
another without being divided for each line, and they are encoded into
run-length codes. The encoding is effected on the assumption, as an
initial condition, that a white picture element in the mode 1-0 virtually
exists at the head of the picture.
Procedure 2-6: Picture elements in the mode 2-2 are encoded. All picture
elements which are in the mode 2-2 are all linked together one after
another without being divided for each line, and they are encoded into
run-length codes. The encoding is effected on the assumption, as an
initial condition, that a black picture element in the mode 2-2 virtually
exists at the head of the picture.
Procedure 2-7: Picture elements in the mode 2-3 are encoded. All picture
elements which are in the mode 2-3 are linked together one after another
without being divided for each line, and they are encoded into run-length
codes. The encoding is effected on the assumption, as an initial
condition, that a black picture element in the mode 2-3 virtually exists
at the head of the picture.
Procedure 2-8: Picture elements in the mode 2-1 are encoded. All picture
elements which are in the mode 2-1 are linked together one after another
without being divided for each line, and they are encoded into run-length
codes. The encoding is effected on the assumption, as an initial
condition, that a white picture element in the mode 2-1 virtually exists
at the head of the picture.
Procedure 2-9: Picture elements in the mode 2-4 are encoded. All picture
elements which are in the mode 2-4 are linked together one after another
without being divided for each line, and they are encoded into run-length
codes. The encoding is effected on the assumption, as an initial
condition, that a black picture element in the mode 2-4 virtually exists
at the head of the picture.
Procedure 2-10: Picture elements in the mode 2-0 are encoded. All picture
elements which are in the mode 2-0 are linked together one after another
without being divided for each line, and they are encoded into run-length
codes. The encoding is effected on the assumption, as an initial
condition, that a white picture element in the mode 2-0 virtually exists
at the head of the picture.
Next, codes for use in each encoding procedure will be exemplified. A code
assignment table for use in Procedure 1-2 is shown in Table 3.
TABLE 3
______________________________________
code
.DELTA.X .times. .DELTA.Y
white run
black run
______________________________________
16 .times. 16 WYLE 1-2
8 .times. 8 WYLE 1-2
4 .times. 4 1-2 1-2
2 .times. 2 WYLE MH(W)
______________________________________
In Table 3, MH(W) means a code for a white run of the MH coding scheme, and
WYLE known WYLE codes. Table 4 shows terminating codes of MH(W), Table 5
makeup codes and Table 6 WYLE codes.
Incidentally, 1-2 in Table 3 is a code peculiar to the present invention.
In the case of it being expressed by "N-2", when the run length is within
the range of 1 to 2.sup.N-1, an N-bit code is used, and when the run
length exceeds N.sup.N-1 +1, a required number of bits are added by steps
of two (one of which is a flag bit). Table 7 shows its example.
TABLE 4
______________________________________
Run length MH (W)
______________________________________
0 00110101
1 000111
2 0111
3 1000
4 1011
5 1100
6 1110
7 1111
8 10011
9 10100
10 00111
. .
. .
. .
60 01001011
61 00110010
62 00110011
63 00110100
______________________________________
TABLE 5
______________________________________
Run length MH (W)
______________________________________
64 11011
128 10010
192 010111
256 0110111
320 00110110
. .
. .
. .
1600 010011010
1664 011000
1728 010011011
ELO 000000000001
______________________________________
TABLE 6
______________________________________
Run length
WYLE CODE (* is a binary number
______________________________________
1 to 2 0*
3 to 6 10**
7 to 14 110***
15 to 30 1110****
31 to 62 11110*****
. .
. .
. .
______________________________________
TABLE 7
______________________________________
Run length 1-2 code (*is a binary number)
______________________________________
1 0
2 to 3 10*
4 to 7 110**
8 to 15 1110***
16 to 31 11110****
32 to 63 111110*****
. .
. .
. .
______________________________________
codes for Procedure 1-3 are used properly in accordance with the code
assignment shown in Table 8, for instance. In the table, NON means the
encoding of white of a picture signal into a "0" and black into a "1", and
the table is identical in contends with Table 1 except in this regard.
TABLE 8
______________________________________
mode
.DELTA.X .times.
white,
.DELTA.Y
black status 0 status 1
status 2
status 3
status 4
______________________________________
16 .times. 16
1-white- MH(W) 2-2 1-2 NON 1-2
16 .times. 16
1-black- 1-2 1-2 1-2 NON WYLE
16 .times. 16
2-white- MH(W) SYLE 1-2 1-2 1-2
16 .times. 16
2-black- 1-2 1-2 2-2 1-2 1-2
8 .times. 8
1-white- MH(W) 1-2 1-2 1-2 1-2
8 .times. 8
1-black- 1-2 1-2 1-2 1-2 1-2
8 .times. 8
2-white- WYLE WYLE 1-2 1-2 1-2
8 .times. 8
2-black- 1-2 1-2 1-2 2-2 WYLE
4 .times. 4
1-white- WYLE 1-2 NON 1-2 1-2
4 .times. 4
1-black- 1-2 1-2 NON 1-2 WYLE
4 .times. 4
2-white- 11-2 WYLE NON 1-2 1-2
4 .times. 4
2-black- 1-2 1-2 NON WYLE WYLE
2 .times. 2
1-white- WYLE WYLE 1-2 1-2 1-2
2 .times. 2
1-black- 1-2 1-2 1-2 WYLE 8-2
2 .times. 2
2-white- WYLE WYLE NON 1-2 1-2
2 .times. 2
2-black- 1-2 1-2 NON WYLE 11-2
______________________________________
With reference to the drawings, the encoding sequence controller 31 will
hereinafter be described in detail. FIG. 9 illustrates an example of the
circuit arrangement of the encoding sequence controller 31. Reference
numeral 81 indicates an encoding sequence controller, 182 an encoding
sequence table, 83 an encoding mode controller A which effects control for
encoding of the contents of the one-frame memory A and 84, 85 and 86
encoding mode controller for the one-frame memories B, C and D. The
encoding mode controller 83, 84, 85 and 86 each store information of the
.DELTA.X and .DELTA.Y encoding modes to thereby store the stage to which
the contents of the corresponding one-frame memory has been encoded. In
the encoding sequence table 82 is prestored the sequence of encoding
operation. An example is shown in Table 9. The encoding sequence
controller 81 instructs the encoding mode controllers 83, 84, 85 and 86
for encoding in accordance with the sequence stored in the encoding
sequence table 82. For instance, let it be assumed that the encoding
sequence table 82 has set therein such a table as shown in Table 9 and
that the encoding operation has already been completed to the encoding
sequence 10. The encoding sequence controller 81 reads the contents of the
encoding sequence 11 from the encoding sequence table 82. In order to
encode the plane C in accordance with the readout contents, the encoding
sequence controller 81 enables the gate 63 and at the same time instructs
the encoding mode controller C85 to perform encoding from status 0 to 4 in
the mode 1 with .DELTA.X=4 and .DELTA.Y=4. The encoding mode controller
C85 carries out the encoding operation as instructed by the encoding
sequence controller 81 and, upon completion of the encoding operation,
sends out an end signal to the encoding sequence controller 81. Upon
receiving the end signal, the encoding sequence controller 81 disables the
gate 63 and reads out the contents of the encoding sequence 12 from the
encoding sequence table 82 for effecting the next encoding operation. When
all the contents of the encoding sequence table 82 have all be processed
and the encoding operation of all the contents of the four one-frame
memories 83, 84, 85 and 86 has been completed, all encoding operations are
finished.
TABLE 9
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Encoding Sequence
Plane .DELTA.X
.DELTA.Y
Mode Status
______________________________________
:
10 B 4 4 2 0 to 4
11 C 4 4 1 0 to 4
12 C 4 4 2 0 to 4
14 A 2 2 1 0 to 4
:
:
______________________________________
TABLE 10
______________________________________
Plane Code
______________________________________
A 00
B 01
C 10
D 11
______________________________________
FIG. 10 illustrates an example of the encoder 41. Reference numeral 101
identifies a one-frame memory for storing an image to be encoded, 102 an
encoding mode control circuit for controlling a code, 111 a
.DELTA.X-.DELTA.Y memory for storing the values of .DELTA.X and .DELTA.Y,
112 a mode selection memory, 113 a status selection memory, 121 a
reference picture element detector for extracting the values of four
reference picture elements from the one-frame memory; 122 and 123 picture
element detectors for detecting from the one-frame memory 101 the values
of picture elements to be encoded; 131, 132, 133 and 134 memories for
storing the values of the four reference picture elements; 135 a memory
for storing the value of a picture element to be encoded; 141 a counter
for calculating the sum total of the values of the four reference picture
elements; 142 a comparator for comparing a signal from the status select
circuit 113 with the contents of the counter 141; 143, 144, 145 and 146
gate circuits; 151 a run-length encoder and 161 an output terminal.
In practice, four one-frame memories are employed as shown in FIG. 3, but
it is assumed, for convenience of description, that the one-frame memory
101 is identical with the one-frame memory (one of the one-frame memories
83 to 86) which is connected directly to one of the gates 61 to 64 which
is open at that time.
Furthermore, four encoding mode controllers are used as depicted in FIG. 9,
but it is assumed, for convenience of description, that the encoding
control circuit 102 is identical with the encoding mode control circuit
(one of the encoding mode controllers 83 to 86) which is in operation in
accordance with an encoding instruction from the encoding sequence
controller 81 at that time.
The following will describe in detail the operation of the circuit depicted
in FIG. 10. An image to be encoded is stored, as an initial state, in the
one-frame memory 101. At this time, a white picture element is represented
by a value of "0" and a black picture element by a value of "1".
Furthermore, the encoding mode control circuit 102 stores the values of
first .DELTA.X and .DELTA.Y in the .DELTA.X, .DELTA.Y memory 111, a value
of "0" in the mode selection memory 112 and a value of "0" in the status
selection memory 113.
The operation starts with the encoding by Procedure 1-2 in such a manner as
follows: The encoding mode control circuit 102 first provides a plane
indicating code to the output terminal 161. An example of plane indicating
codes are shown in Table 10. For example, in the case of encoding the
plane C at that time, a code "10" is provided. The encoding mode control
circuit 102 opens the gate 144. The content of the .DELTA.X, .DELTA.Y
memory 111 is transferred to the picture element detector 122. The picture
element detector 122 successively reads out from the one-frame memory (in
order from left to right and from top to bottom of the image frame) 101
the values of picture elements which are to be encoded by Procedure 1-2
and, transfers them to the run-length encoder 151. The run-length encoder
151 determines the use of Table 1 (the code table which is used in
Procedure 1-2), since the signals from the mode selection memory 112 and
the status selection memory 113 are both the value "0", and further, it
determines, on the basis of the values of .DELTA.X and .DELTA.Y from the
.DELTA.X, .DELTA.Y memory 111 and Table 1, which code table is to be used
for run-length encoding, thereafter encoding picture signals which are
sent from the picture element detector 122.
Upon completion of the extraction of all the picture elements to be
encoded, the picture element detector 122 provides a signal on each of
input lines P.sub.151 and P.sub.102 of the run-length encoder 151 and the
encoding mode control circuit 102. Upon reception of the signal from the
input line P.sub.151, the run-length encoder 151 performs an encoding
termination process. On the other hand, the encoding mode control circuit
102 verfies, by the reception of the signal from the input line P.sub.102,
that the encoding process by Procedure 1-2 has been finished. The encoding
mode control circuit provides the plane indicating code to the output
terminal 161. Then it closes the gate 144 and provides a "1" to the mode
selection memory 112 and a "2" to the status selection memory 113,
thereafter opening the gates 145 and 146.
By receiving the values of .DELTA.X and .DELTA.Y from the .DELTA.X,
.DELTA.Y memory 111 and a "1" from the mode selection memory 112, the
picture element detector 122 reads out picture elements of the mode 1 (see
FIG. 4) from the one-frame memory 101 in a sequential order (from left to
right and from top to bottom) and transfers them to the picture element
memory 135. By receiving the values of .DELTA.X and .DELTA.Y and a "1"
from the mode selection memory 112, the reference picture element detector
121 similarly transfers the picture element values of four picture
elements of the mode 1 (see FIG. 4) from the one-frame memory 101 in
succession to the reference picture element memories 131 to 134. The two
detectors 121 and 122 operate in synchronism with each other so that the
four reference picture elements extracted by the reference picture element
detector 121 become reference picture elements for the picture | | |
