Image processing apparatus including binary data producing unit

An image data processing apparatus binary-codes an image signal obtained from an image sensor of the CCD type or the like so as to output a binary-coded image signal. The image signal obtained from the image sensor A/D-converted into digital image data. Based upon the digital image data, average values of luminance values of the digital image data are calculated for an array of pixels in a preselected area of the CCD. This average value is used as a threshold level for binary coding the image data for these pixels at the center portion of this preselected area. Furthermore, to detect coutours this data processing apparatus calculates a gradient in the luminance values of the pixels in a portion of the preselected area of the CCD in an X direction and a Y direction, and the gradient value is used to obtain binary-coded data in accordance with the above-described method.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a binary-coded image information producing 
apparatus used in black/white copiers, facsimiles, and other electronic 
products. 
2. Description of the Related Art 
Up to now, various methods and systems have been proposed by which 
binary-coded image information can be obtained from analog image 
information. In general, most of these binary coding methods/systems aim 
to more accurately represent an original image, by which a half tone image 
can be represented as a quasi-half tone image. 
As the above-described quasi-half tone image producing method such a 
quasi-half tone image has been represented by obtaining a binary coded 
image, while varying a dot number within a predetermined area in response 
to a tone of an original image. 
However, for some practical applications it is necessary that only a 
certain portion of interest contained in an original image must be 
duplicated as a sharp image. For instance, when the portion of interest 
photograph is only the black alpha-numeric characters included in it, 
difficulties arise in reproducing the characters well with such binary 
coding methods capable of representing a quasi-half tone image. That is, 
it is sometimes difficult to discriminatively represent these 
black-colored characters printed on the quasi-half tone image. The reasons 
are as follows. Since, as previously described, the dot quantity of the 
image is varied in accordance with the tone of the original image, there 
is no change in the dot quantities of both the characters and background 
portion in case that practically no difference exists in the tones between 
the characters and background. 
Furthermore, a tone of an area around a contour of characters and a 
background thereof is represented based upon dot quantities of these 
contour and background so that the sharpness of the character contour is 
deteriorated. In such a case, a binary coding method capable of accurately 
and sharply reproducing the alpha-numeric characters contained in an 
original image is preferable to a binary coding method which is meant to 
be capable of correctly reproducing the entire original image. 
SUMMARY OF THE INVENTION 
A primary object of the present invention is to provide a binary-coded 
image information producing apparatus capable of sharply reproducing a 
specific portion contained in an original image and, in particular, 
alpha-numeric characters and the like. 
To achieve the above-described object of the present invention, an image 
processing apparatus of the invention comprises; 
image sensing means having a plurality of photoelectric converting 
elements, for outputting electric signals of an optical image converted by 
said photoelectric converting elements; 
selecting means for selecting said electric signals produced by a 
predetermined number of said photoelectric converting elements, in 
sequence; 
arithmetic means for producing an average value of said electric signals 
selected by said selecting means; and, 
binary data producing means for producing binary data in response to at 
least one of said electric signals (at a center) of said electric signals 
selected by said selecting means with said average value produced by said 
arithmetic means as a threshold value. 
Further, the above-described object may be achieved by providing an image 
processing apparatus according to the present invention, comprising: 
image sensing means having a plurality of photoelectric converting elements 
for outputting electric signals of an optical image converted by said 
photoelectric converting elements in a predetermined order; 
difference-value signal producing means for producing difference-value 
signals according to a difference in amounts of said electric signals 
output from said image sensing means; 
first binary data output means for outputting one-leveled data of first 
binary data after said difference-value signals produced by said 
difference-value signal producing means become more than a first positive 
reference value, and for outputting another-leveled data of said first 
binary data after said difference-value signals produced by said 
difference-value signal producing means become more than a first negative 
reference value; 
second binary data output means for outputting one-leveled data of second 
binary data after said difference-value signals produced by said 
difference-value signal producing means become more than a second positive 
reference value which is less than said first positive reference value, 
and for outputting another-leveled data of said second binary data after 
said difference-value signals produced by said difference-value signal 
producing means become less than a second negative reference value which 
is more than said first negative reference value; and, 
addition means for adding said second binary data output from said second 
binary data output means, while said first binary data output means 
outputs one of one-leveled data and another-leveled data to said first 
binary data output from said first binary data output means.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Construction of Compact Copier 
In FIG. 1, there is shown a perspective view of a compact copying machine, 
or copier, the exterior of which is formed by a housing case 10. This 
housing case 10 is constructed of a photographing unit 10a and a printing 
unit 10b. A lens 11 used for a photographing operation is provided in a 
front surface of the photographing unit 10a so as to optically form an 
image to be copied. At an upper surface of this photographing unit 10a, 
there are provided: a release switch 12 for starting a photographing 
process of an image to be copied and a printing process thereof; a mode 
changing switch 13 for changing a photographing mode into a printing mode 
and vice versa; and a copy mode instruction switch 14 for selecting either 
a contour copy mode or a normal copy mode (as explained below). 
FIG. 2 illustrates an arrangement of a printer 15 employed in the printing 
unit 10b of this copying machine. A paper supply roller 16 on which a heat 
sensitive recording paper "P" has been wound is employed inside this 
printer 15. Thus, the recording paper "P" is stored on this roller 16 and 
fed out from the housing case 10 of the copying machine while being 
pinched between rotating rollers 17a and 17b. Between the rotating roller 
17a and paper supply roller 16, a thermal head 18 is provided under the 
condition that this head 18 is forcibly urged into contact with a heat 
sensitive recording surface of the recording paper "P" by a spring 19. The 
output timing of the print data by the thermal head 18 is controlled in 
accordance with a paper feed speed of the recording paper "P" defined by 
the rotating roller 17a. 
When it is desired to use the above-described compact copying machine 10 to 
duplicate an original, the mode selecting switch 13 is set to the 
photographing mode. After an image of the original is optically 
photographed while observing it through a viewfinder (not shown in the 
drawings), the release switch 12 is depressed. Then, the image to be 
copied is optically focused onto a solid-stage imaging element (will be 
discussed later) provided within the photographing unit 10a to produce an 
analog signal which is thereafter converted into digital data and stored 
in an electronic memory. Subsequently, the mode selecting switch 13 is set 
to the printing mode and the release switch 12 is depressed. Accordingly, 
the stored image data obtained of the original image with the 
photographing unit 10a are successively output to the thermal head 18 of 
the printer 15 and printed out on the recording paper "P". 
In this case, when the normal duplication (copy) mode is previously 
designated by the copy mode instruction switch 14, the image data are 
binary-coded in accordance with the density thereof and printed out on the 
recording paper "P". When the contour duplication mode is designated, the 
image data are binary-coded in such manner that the entire image region is 
subdivided into a region where a difference in the density is rapidly 
changed, and also another region having no rapidly changing density. Then, 
the image data of both regions are printed out on the recording paper "P". 
Circuit Arrangement of Compact Copier 
FIG. 3 shows an electronic circuit arrangement of the above-described 
compact copying machine. A control unit 20 is employed so as to control 
various operations of circuits thereof in response to a key operation 
signal and a switch operation signal derived from a key and switch 12, 13 
and 14. 
In the photographing mode, an optical image incident upon the photographing 
lens 11 is focused onto an image sensor 23 via a diaphragm 22. This image 
sensor 23 is, for instance, a solid-state imaging (image pickup) element 
(referred to as a "CCD") having a 1/2 inch size and 390,403 pixels 
(509.times.767 picture elements). The image sensor 23 is driven by an 
image sensor drive unit 24 into which the above-described control signal 
is supplied from the control unit 20. The diaphragm 22 is also driven by a 
diaphragm drive unit 25 into which the control signal is furnished from 
the control unit 20. An exposure calculation unit 26 is connected to these 
image sensor drive unit 24 and diaphragm drive unit 25. The function of 
this exposure calculation unit 26 is to obtain an optimum exposure value 
based upon brightness around an image to be copied (i.e., a subject to be 
imaged) which is photometric-measured by a photometric unit 27. 
Accordingly, both the above described image sensor drive unit 24 and 
diaphragm drive unit 25 drive the image sensor 23 and diaphragm 22 in 
accordance with a shutter speed and an open degree of the diaphragm which 
are set based upon the above-described optimum exposure value, and also 
automatically adjust both an exposing time for the image sensor 23 and the 
open degree of the diaphragm. 
The photographing lens 11 is driven by a lens drive unit 28. An AF control 
unit 29 is connected to this lens drive unit 28, into which the control 
signal is supplied from the control unit 20. The function of this AF 
control unit 29 is to measure an optimum focal length by utilizing, for 
instance, an ultrasonic reflection from the image to be copied. Based upon 
the measured optimum focal length, the lens drive unit 28 drives the lens 
11 and automatically adjusts the focal length. 
The image sensor 23 generates analog image signals which are output with 
levels corresponding to the densities of the focused images detected at 
each of its pixels. These are input via an amplifying/signal processing 
unit 30 to an A/D (analog-to-digital) converting unit 31. The functions of 
the above-described amplifying/signal processing unit 30 are to amplify 
the analog image signals supplied from the image sensor 23 to a 
predetermined voltage level, to remove such a frequency component higher 
than a frequency A/D-convertable in the A/D converting unit 31, and also 
to clamp the black-level voltage at a reference voltage at a negative 
voltage side of this A/D converting unit 31. The A/D converting unit 31 
converts the analog image signals input from the respective pixels of the 
image sensor 23 into 6-bit digital data. The digital image data output 
from this A/D converting unit 31 are successively supplied to a first 
image data memory unit 32 and stored therein. A memory capacity of this 
first data memory unit 32 corresponds to at least (509.times.767) of the 
image sensor 23. A write address used for this first image data memory 
unit 32 is designated via a memory control unit 34 by a DMA (direct memory 
access) control unit 33. 
In the above-described photographing mode, the image data which have been 
stored in the first image data memory unit 32, are processed in a 
calculation unit 35 to which a calculation control signal is supplied from 
the control unit 20. That is, a binary coding process for either a 
photographic density, or a contour of the image data is performed in the 
calculation unit 35 under the control of the control unit 20. Accordingly, 
the processed image data are transferred as binary coded image data having 
"1(black)" or "0 (white)" level to a second image data memory unit 36. In 
this case, both a read address and a write address for the first image 
data memory unit 32 and second image data memory unit 36 are designated 
from an address calculation unit 37 to which the control signal is 
supplied from the control unit 20. 
Binary-Coding of Imaging Area 
FIG. 4 illustrates an arrangement of pixels in the imaging area of the 
image sensor 23. It should be noted that for the sake of simple 
explanation of FIG. 4, "I" and "J" are determined as coordinates 
representative of the areas of the three pixels, and furthermore, "i" and 
"j" are determined as coordinates indicative of the respective signal 
pixels within the three pixels represented by "I" and "J". A brief review 
of binary coding based on this invention will now be provided, with a 
detailed discussion. 
As to the photographic density binary coding process of the image data 
stored in the memory unit 32, data corresponding to a 9.times.9 pixel area 
of the image sensor 23 is retrieved from the memory unit 32, and a 
calculation is performed by the calculation unit 35 to obtain an average 
value "A" of the photographic density in the 9.times.9 pixel area. The 
calculated average density calculated value "A" is used as a threshold 
value for binary coding (in a manner described below in detail) each of 
the image data in a 3.times.3 pixel area at the center of the 9.times.9 
pixel area. Thereafter, the 9.times.9 pixel area used for binary coding of 
the respective image data on the 3.times.3 pixel area at its center is 
successively moved by 3-pixel increments, first along a horizontal 
direction and then along a vertical direction of a pixel array, and the 
above-described calculation is repeated for each such 9.times.9 pixel 
area. As a result, all of the image data of all pixels except for a 
3-pixel wide strip along the periphery of the image sensor can be 
binary-coded in this way. 
With respect to the contour binary coding process for the image data, first 
of all, absolute values are calculated for a 3.times.3 pixel area from (1) 
a difference in photographic densities between the 3 pixels forming the 
left side and the 3 pixels forming the right side of the 3.times.3 pixel 
area, and (2) a difference in photographic densities between the 3 pixels 
forming the top row and the 3 pixels forming the bottom row by the 
3.times.3 pixel area. Then, these absolute values are summed with each 
other, and the resultant value is used as the density gradient value for 
the center pixel of this 3.times.3 pixel area. Subsequently, such a 
setting process of the density gradient value of the center pixel in this 
3.times.3 area is successively moved by 1 pixel increments along both the 
horizontal and vertical directions of the pixel array and the calculation 
is repeated, so that finally, the density gradient values of all the 
respective pixels except for 1 pixel wide area around the periphery of the 
entire image sensor 23 have been set. Thereafter, the density binary 
coding process described above is similarly executed on the image data 
derived by setting the density gradient values to the respective pixels. 
As a result, all of the image data except for the 1 pixel wide area around 
the periphery of the image sensor can be processed with respect to the 
contour binary coding to discern the portion of the original having the 
large density gradient from the remaining portion. 
The binary-coded image data which have been processed for either the 
density binary process or contour binary process, and stored in the second 
image data memory unit 36, are successively read out therefrom in response 
to the operation signals of the release switch 12 in the printing mode, 
and thereafter transferred to the printer control unit 38. This printer 
control unit 38 performs the temperature control of the thermal head 18 in 
response to the control signal derived from the control unit 20. The image 
data output via the printer control unit 38 are transferred to the printer 
15, and thus printed out as an image on the recording paper "P" in 
synchronism with the paper feed speed of this recording paper "P". 
Operations of Compact Copier 
Various operations of the above-described compact copying machine with the 
above-described arrangements will now be described. 
When, for instance, a three-dimensional image is copied by utilizing this 
compact copying machine, the mode selecting switch 13 is set to the 
photographing mode, and after the three-dimensional image to be copied is 
optically captured while observing this image through the viewfinder (not 
shown), the release switch 12 is depressed. Thus, this image is optically 
focused onto the image sensor 23 employed within the photographing unit 
10a, through the photographing lens 11. In this case, the automatic 
exposure control is performed by the exposure calculation unit 26 via the 
image sensor drive unit 24 and diaphragm drive unit 25. Also the automatic 
focusing control is performed by the AF control unit 29 via the lens drive 
unit 28. 
Now, it should be understood that electric charges corresponding to the 
densities of the three-dimensional image to be copied have been stored 
with respect to the respective pixels of the image sensor 23. 
When the image has been focused onto the image sensor 23, the image signals 
are sequentially output via the amplifying/signal processing unit 30. 
Then, these analog image signals are converted into the 6-bit digital 
image data, and thereafter the 6-bit digital image data are stored into 
the first image data memory unit 32. It should be noted that the digital 
image data stored into the respective memory regions of the first image 
data memory unit 32 corresponds in value to the analog charge levels 
stored into the respective pixels of the image sensor 23. 
Density Binary-Coding Process 
In case that the normal copying mode is designated by the copying mode 
instruction switch 14, the density binary coding process is carried out of 
the image data which have been derived when the original was photographed, 
and then stored into the first image data memory unit 32. FIG. 5 shows a 
flowchart for explaining the density binary-coding process of the image 
data as carried out by the calculation unit 35. At first, an 
initialization I=0, J=0 is performed with respect to the arrangement of 
the imaging area, shown in FIG. 4, corresponding to the memory area of the 
first image data memory unit 32 (step Al). It should be noted that the 
above-described "I" and "J" as represented in FIG. 4, indicate a 
coordinate of three pixels which are handled as a single unit and 
extending in the horizontal and vertical directions, respectively. Also, 
"i" and "j" (will be discussed later) represent a coordinate of each of 
pixels. Then, an average value "A" of density of a 9.times.9 pixel area is 
set equal to zero (0) and a reference position of the pixel is determined 
as i=1 and j=1 (step A2). The average density values of the respective 
3.times.3 pixel areas within the 9.times.9 pixel area are calculated under 
the condition that A=S/9+A (step A3). It should be noted that "S" 
corresponds to a total of the density data of the respective pixels within 
the above-described 3.times.3 area, and is calculated by the following 
equation (1): 
EQU S=f(I+i-1, j+j-1)+f(I+i, J+j-1)+f(I+i+1, J+j-1) +f(I+I-1, J+j)+f(+i, 
J+j)+f(I+i+1, J+J) +f(I+I-1, J+j+1)+f(I+I, J+j+1)+f(I+i+1, J+J+1) 
Thus, when the density average value "A" of the 3.times.3 area 100 
positioned at the upper and left side with respect to the 9.times.9 pixel 
area, the pixel reference position is advanced by three pixels in the I 
direction under the condition that i=i+3 (step A4). At this time, since 
i=4, a "NO" judgement is made in a step A5, and the density binary-coding 
process is again returned to step A3. At this step A3, a summation is 
carried out between the density average value S/9 of the 3.times.3 area 
101 positioned at the upper and center position of the above-described 
9.times.9 pixel area, and the average density value calculated previously 
(in this case, the average density value of the 3.times.3 area 100) under 
the condition that the pixel position of i=4 is understood as the 
reference. Thereafter, the pixel reference position is advanced by 3 
pixels in the I direction under the condition that i=i+3 (step A4). At 
this time, since i= 7, a "NO" judgement is made at the step A5. 
Accordingly, the coding process is again returned to the step A3. At this 
step A3, another summation is executed between the average density value 
"A" previously calculated and the density average value S/9 of the 
3.times.3 area 102 positioned at the upper and right position of the 
above-described 9.times.9 area under such a condition that the pixel 
position of i=7 is used as a reference. In other words, this density 
average value "A" is equal to a value obtained by adding the three density 
average values, i.e., the density average value of the 3.times.3 pixel 
areas 100, 101 and 102. 
When i=i+3 is again applied by step A4, it yields i=10. Accordingly, a 
"YES" judgement result at a step A5 causes the binary coding process to 
advance to step A6. At this step A6, the pixel reference position in the I 
direction is again returned to i=1, whereas the pixel reference position 
in the J direction is equal to j=j+3, and it is advanced by three pixels 
in the J direction. At this time, since j=4, a "NO" judgement is made at a 
step A7, and the coding process is again returned to the previous step A3. 
At this step A3, the average density value S/9 of the 3.times.3 area 103 
positioned at the center and left side of the 9.times.9 pixel area is 
summed with the addition result "A" of the density averages of the 
previously calculated areas 100, 101 and 102 under the condition that the 
pixel position of i=1 and j=4 is used as the reference. Also at the step 
A4, as i=i+3, the pixel reference position is advanced by 3 pixels along 
the I direction where a calculation is made of the average density value 
S/9 of the 3.times.3 area 104 positioned at the middle and center of the 
9.times.9 area under the condition that the pixel position of i=4, j=4 is 
used as a reference. The resultant average density value is added to the 
above-described addition result "A". 
Since the above-described steps A3 to A7 are repeatedly executed, the 
average density values of the respective 3.times.3 areas 100 to 108 which 
have been obtained by dividing the 9.times.9 area into 9 groups are 
calculated and the addition value of the average density values of these 9 
areas is given as "A". Subsequently, at a step A8, as A=A/9, the average 
density value "A" is calculated for the entire 9.times.9 area. 
In step A9, the following values are set: I=I+1, J=J+1, i=0, j=0. Then, the 
binary coding process is advanced to a step A10 in which a judgement is 
made relative to f(I+i, J+j). In other words, for I=1 and J=1, as set by 
step A9, a judgement is made whether or not the image density of a single 
pixel 109 positioned at the upper and left side of the centrally located 
3.times.3 area 104 is higher than the average density value "A" for the 
entire 9.times.9 area. Let us assume that at this step A10, a judgement is 
made "NO". In other words, it is judged that the image density of the 
single pixel 109 is thinner than the above-described average density value 
"A". Then, the density binary coding process is advanced to a step A11a, 
where the binary-coded data g(I+i, J+j) equal to "0" (white) is assigned 
to this pixel. Let us now assume that at the step A10, another judgement 
is made "YES". That is, a judgement is made that the image density of the 
single pixel 109 is darker than the above-described average density value 
"A". Then, the process is advanced to a step A11b in which binary-coded 
data g(I+i, J+j) equal to "1" (black) is assigned to this pixel. Then, the 
above-described binary-coded data "0" or "1" is written into the memory 
area corresponding to the second image data memory unit 36 (step A12). 
Thus, at a step A13, the pixel reference position i=i+1 is advanced in the 
I direction by 1 pixel, and at this time since i=1, then a "NO" judgement 
is made at a step A14, and the process is again returned to the step A10. 
Thereafter, at the steps A10 to A12, the density data on the single pixel 
110 positioned at the upper and center of the 3.times.3 pixel area with 
respect to the center of the 9.times.9 area, is binary-coded based upon 
the above-described average density value "A" in the same manner as just 
described for pixel 109, and the binary-coded data "0" or "1" assigned to 
pixel 110 is written into the second image data memory unit 36. Then, at 
the step A13, i=i+1 and at the step A14, a "NO" judgement is made. 
Accordingly, the process is returned to the previous step A10. In this 
case, the density data on the single pixel 111 positioned at the upper and 
right of the 3.times.3 area with respect to the center of the 9.times.9 
area is binary-coded based upon the above-described density average value 
"A". Furthermore, the resultant binary-coded data "0" or "1" assigned to 
pixel 111 is written into the memory area corresponding to the second 
image data memory unit 36. Subsequently, at a step A13, i is made equal to 
i+1 so that now i=3. Then a "Yes" judgement is made at step A14, and the 
process proceeds to step A15 where the pixel reference position i is 
returned to 0 and the density binary-coding process is advanced to j=j+1. 
At this time, since j=1, a "NO" judgement is made at step A16. The process 
is returned to the above step A10. As a result, the density data on the 
single pixel 112 positioned at the middle and left side of the 3.times.3 
area with respect to the center of the 9.times.9 area corresponding to the 
above i=0 and j=1, is binary-coded based upon the above-described density 
average value "A" at the step A11. At the next step A12, the binary-coded 
data assigned to pixel 112 is written in the memory area corresponding to 
the second image data memory unit 36. Thus, the above-described binary 
coding process steps A10 to A16 are repeated so that the density of each 
of the 9 pixels constituting the 3.times.3 area is binary-coded, and the 
binary coded for these pixels is successively written into the second 
image data memory unit 36. 
Then, when the above-described density binary coding process is carried out 
for single pixels 113 to 117, the processes is advanced to i=3 at a step 
A13 and j=3 at a step A15. As a consequence, "Yes" judgements are made at 
steps A14 and A16. Then, the process is advanced to step A17 where J=J-1. 
It will be recalled that the value of J was increased by 1 in step A9 for 
use in steps A10 and A11. Step A17 returns J to its previous value so that 
further processing in the same row can continue. Although the value of I 
was also increased by step A9, this is necessary in order to advance the 
processing to the next 9.times.9 pixel area for binary coding of the 
subsequent 3.times.3 pixel area. If at step A17 I does not exceed 253, a 
"NO" judgement is made at a step A18, and the process is again returned to 
the previous steps A2. 
That is, since the density binary coding process defined at the steps A2 to 
A18 is repeated, the density binary coding for the respective pixels 
within the 3.times.3 pixel area 104 with respect to the center of the 
9.times.9 pixel area is successively performed along the I direction in 3 
pixel steps, and is continued until I=254. At this time, all of the pixel 
data having the respective densities within the 3.times.3 area 104 (for 
each 9.times.9 pixel area) are binary coded for I between 1 and 254 and 
J=1, and the binary coded pixel data are stored in the second image data 
memory unit 36. Thereafter, the process is advanced to a step A19, where I 
is returned to 0 and the process is advanced to the next row J=J+1, the 
above-described processes defined at the steps A2 to A18 are repeated, and 
all of the pixel data of the 3.times.3 areas are binary-coded until J=2 
and I=1 to 254, and thus are stored in the second image data memory unit 
36. Thereafter, the return of I to 0 is repeatedly executed, and the 
advance process of J=J+1 is repeatedly performed at a step A19. When "J" 
reaches 167, a "NO" judgement is made at a step A20. As a consequence, the 
density binary coding process has been accomplished for all of the pixels 
except for the 3-pixel wide area around the periphery of the image sensor 
23, and the binary coded pixel data have been stored in the second image 
data memory unit 36. 
Even if there is a small density difference between a character and a 
background thereof, e.g., a black-colored character is written in a 
red-colored background, since the average density value of the 9.times.9 
pixel area is used as the threshold level and the respective pixels within 
the 3.times.3 pixel area which is positioned at a center of the 
above-described 9.times.9 pixel area are binary-coded in the 
above-described density binary-coding process, both the character portion 
and background portion (in particular, at the boundary portion) can be 
binary-processed as clearly different data (black or white). This is 
because the binary coding operation is performed based upon the density of 
the characters and the average density of the background portion. 
Contour Binary-Coding Process 
Under the conditions that the digital data having the values corresponding 
to the densities of the image to be copied have been written in the first 
image data memory unit 32, in case that the contour duplication mode is 
designated by a duplication mode designation switch 14, the contour binary 
coding process is performed for the image data which have been acquired 
and stored into the first image data memory unit 32. 
FIG. 6 is a flowchart for representing a contour binary-coding process of 
the image data. An initialization of i=1, j=1 is performed for the 
arrangement of the imaging area shown in FIG. 4, corresponding to the 
memory area of the first image data memory unit 32 (step B1). Referring to 
FIG. 4, the 3.times.3 pixel area 104 will be used as an example to explain 
this aspect of the invention because its pixels have been individually 
numbered. However, the same steps are carried out for each of the 9 
3.times.3 pixel areas within a 9.times.9 pixel area. A calculation is 
executed so as to, firstly, obtain a density difference .DELTA.xf(i, j) in 
the x direction between 3 pixels 109, 112 and 115 positioned at the left 
side of the 3.times.3 pixel area 104, and 3 pixels 111, 114 and 117 
positioned at the right side thereof and to, secondly, obtain a density 
difference in the y direction between 3 pixels 109, 110 and 111 positioned 
at the upper side of the same 3.times. 3 pixel area 104 and 3 pixels 115, 
116 and 117 positioned at the lower side thereof (step B2). These density 
differences in the X direction and the Y direction for this 3.times.3 
pixel area are calculated by the following equations (2) and (3): 
EQU .DELTA.xf(i,j)=f(i-1, j-1)+f(i-1, j)+f(i-1, j+1) -{f(i+1, j-1)+f(i+1, 
j)+f(i+1, j+1)} (2) 
EQU .DELTA.yf(i,j)=f(i-1, j-1)+f(i,j-1)+f(i+1, j-1) -{f(i-1, j+1)+f(i, 
j+1)+f(i+1, j+1)} (3) 
Thus, when both the density difference .DELTA.xf (i, j) in the X direction 
and the density difference .DELTA.yf (i, j) in the Y direction in the 
above-described 3.times.3 area are obtained, a value obtained by summing 
an absolute value of the density difference in the X direction with 
another absolute value of the density difference in the Y direction, is 
set to be a density gradient value of central pixel 113 of this 3.times.3 
pixel area 104. Then, the density gradient value is written into a memory 
area of the corresponding second image data memory unit 36 (steps B3 and 
B4) 
EQU g(i, j)=.vertline..DELTA.xf(i, j).vertline.+.vertline..DELTA.yf(i, 
j).vertline. (4) 
Thereafter, at a step B5, the contour binary coding process is advanced to 
a pixel reference position (i=i+1). Until this "i" exceeds 766, the 
density gradient setting process with respect to the central pixel of the 
3.times.3 area defined in the above-described steps B2 to B4 is 
successively repeated in such a manner that this process is shifted in the 
I direction by 1 pixel increments (step B6). 
Thereafter, a "YES" judgement is made at a step B6. In other words, "i" is 
equal to 767 when the density gradient value setting process for the pixel 
corresponding to (i=766, j=1) is completed. Subsequently, when the process 
is advanced to a step B7, the value of i is returned to 1, and j is 
incremented by j=j+1. At this time, since j=2, a "NO" judgement is made at 
a step B8, and thus the process is returned to a step B2. Accordingly, at 
these steps B2 to B4, the density gradient setting process with respect to 
the pixel position of (i=1, j=2) is performed. Furthermore, the process 
defined at the steps B2 to B6 is repeated so that all of the density 
gradient values are set until the pixel array in the I direction being 
equal to i=766 as j equals 2. Then, as the process defined by the steps B2 
to B8 is repeated, the density gradient setting process for the 
above-described 1 pixel increments (i=1 to 766) in the I direction is 
successively repeated in such a manner that this process operation is 
shifted by 1 pixel in the J direction. As a result, the density gradient 
setting process with respect to all of the pixels except for the 1 pixel 
area around all of the image sensor 23 is accomplished, and the resultant 
density gradient data are stored into the second image data image unit 36. 
In accordance with the above-described process operation, after the density 
gradient value setting process with respect to 1 pixel increments based 
upon the density difference within the 3.times.3 area for the photographed 
image data has been completed, the data on the image to be copied 
corresponding to this density gradient are transferred from the second 
image data memory unit 36 to the first image data memory unit 32 (step 
B9). Then, with respect to the image data to which the density gradient 
values have been set at a single pixel unit and which have been stored in 
this first image data memory unit 32, the density binary coding process 
defined in the flowchart shown in FIG. 5 is performed. As a consequence, 
both the image data having the large density gradients and the image data 
having the normal density gradient are contour-binary-coded except for the 
1 pixel wide area around the entire image, and the coded image data are 
stored into the second image data memory unit 36 (step A). 
Basic Idea of Contour Binary-Coding Process for Image Data 
Referring now to FIGS. 7A and 7B, a basic idea of a contour binary coding 
process for image data will be described. 
A region where a density gradient of image data in either the X direction, 
or Y direction is rapidly changed as is shown in FIG. 7A, is recognized as 
a density difference thereof .DELTA.x or .DELTA.y as is shown in FIG. 7B. 
This density difference data is averaged so as to produce binary-coded 
data thereof. That is to say, the data on the portion of the original in 
which the color of the image varies, read out by the image sensor 23, is 
represented as a density distribution as shown in FIG. 7A in accordance 
with the reflectance of this color. Then, a density difference as 
represented in FIG. 7B is formed based upon the above-described density 
distribution. As the density difference is binary-coded, the changing 
point of the color may be represented as black (1-level) data, whereas 
other portions may be indicated as white (0-level) data. 
As a result, this image is finally obtained as a contour image. 
It should be noted that the address control for both the first image data 
memory unit 32 and second image data memory unit 36 is carried out under 
the control of the address control unit 37 during both the density 
binary-coding process and contour binary-coding process in response to the 
control signal derived from the control unit 20. Also, the density 
calculation binary-coding process is executed in the calculation unit 35 
in response to the calculation control signal derived from the control 
unit 20. 
To print out the image data which have been processed by either the density 
binary-coding operation, or the contour binary-coding operation, and 
thereafter stored into the second image data memory unit 36, first of all, 
the mode selecting switch 13 is set to the printing mode and the release 
switch 12 is depressed. Then, the binary-coded image data of the image to 
be copied which have been stored in the second image data memory unit 36 
are read out as print data to the print control unit 38. Thus, the print 
data are sequentially transferred to the thermal head 18 in response to 
the feeding speed of the heat sensitive recording paper "P". As a result, 
the image to be copied is printed out on the recording paper "P" under the 
condition that the densities thereof are converted into black/white 
conditions, or the contour of the image is converted into the black 
condition. As previously described, since both the character portion and 
background portion can be converted into clearly different data (i.e., 
black or white data) in case that the binary coding operation is carried 
out by way of the density binary-coding process, even when both the colors 
of the characters and background are relatively equal densities with each 
other, the characters can be correctly or accurately reproduced without 
deteriorating the contour thereof as in the conventional quasi-binary 
coding operation. 
Furthermore, in case that the binary coding operation is performed by 
utilizing the above-described contour binary-coding process, since only 
the portion where the color (density) thereof is changed may be 
represented as the black data, and also the remaining same color (density) 
portion may be represented as the white data, the contours of the 
characters can be clearly represented even when both the colors of the 
characters and also background have nearly equal densities. Also in case 
that a pattern or the like constructed of a plurality of colors is 
binary-coded, the boundary portions of the respective colors are 
represented as black and also the area having the same color is 
represented as white so that the shape of the pattern can be correctly or 
accurately represented. 
Other Binary-Code Image Forming Apparatus 
FIG. 8 is a schematic block diagram of a binary coding circuit according to 
another preferred embodiment of the invention. 
An image signal which is obtained from, for instance, the image sensor 23 
of the compact copying machine shown in FIG. 3, and supplied via the 
amplifying/signal-processing unit 30, is supplied to a first differential 
circuit 100 and second differential circuit 101. 
These first and second differential circuits 100 and 101 calculate the 
differential of the above-described image signal based upon different time 
constants .tau..sub.1 and .tau..sub.2 (note .tau..sub.1 is greater than 
.tau..sub.2). 
The differential value signal output from the first differential circuit 
100 is supplied to a minus (negative) terminal of the first comparator 102 
and also a plus (positive) terminal of a second comparator 103. On the 
other hand, the differential value signal output from the second 
differential circuit 101 is supplied to a minus (negative) terminal of a 
third comparator 104 and a plus (positive) terminal of a fourth comparator 
105. 
Now, it should be noted that a binary-coding reference voltage "VH1" is 
applied to a plus terminal of the first comparator 102, and another 
binary-coding reference voltage "VL1" is applied to a minus terminal of 
the second comparator 103, a further binary-coding reference voltage "VH2" 
is applied to a plus terminal of the third comparator 104, and moreover a 
still further binary-coding reference voltage "VL2" is applied to a minus 
terminal of the fourth comparator 105. In this case, the respective 
voltage levels of these binary-coding reference voltages "VH1", "VL1," 
"VH2", and "VL2" have the following relationships: 
EQU VH1&gt;VH2&gt;0&gt;VL2&gt;VL1. 
The outputs from the first and second comparators 102 and 103 are supplied 
to a set terminal and a reset terminal of a first holding circuit 106, 
respectively. The outputs from the third and fourth comparators 104 and 
107 are furnished to a set terminal and a reset terminal of a second 
holding circuit 107, respectively. 
It should be understood that the above-described first differential circuit 
100, first and second comparators 102 and 103, and further the first 
holding circuit 106 constitute a binary-coding circuit for obtaining a 
binary output for those portions of an image signal involving changes of 
relatively large magnitude. On the other hand, the above-described second 
differential circuit 101, third and fourth comparators 104 and 105, and 
also second holding circuit 107 constitute a binary-coding circuit for 
obtaining a binary-coded output for those portions in response to an image 
signal involving changes of a relatively small magnitude. 
Then, the outputs derived from the first holding circuit 106 and second 
holding circuit 107 are supplied to an OR gate 108. An output of this OR 
gate 108 is supplied as a final binary-coded signal of this image signal 
to, for instance, the second image data memory unit 36. 
Binary-Coding Operation of second Binary Coding Circuit 
Referring now to FIGS. 9A to 9F representing output signal waveforms, a 
binary-coding operation of the above-described binary-coding circuit will 
be described. 
First, the image signal represented in FIG. 9A is supplied to the first and 
second differential circuits 100 and 101 so as to produce differential 
output signals represented in FIGS. 9B and 9D based on the respective time 
constants .tau..sub.1 and .tau..sub.2. 
Since the time constant .tau..sub.1 of the first differential circuit 100 
is large, a differential output of the image signal is obtained therefrom 
in response to the relatively large variations of the image signal. 
On the other hand, since the time constant .tau..sub.2 of the second 
differential circuit 101 is small, a differential output of the image 
signal is obtained-therefrom in response to the relatively small 
variations of the image signal. 
The output of the first differential circuit 100 is supplied to the first 
and second comparators 102 and 103, and compared with the corresponding 
reference voltage "VH1" and "VL1". The first comparator 102 outputs a low 
level signal when the above-described differential output exceeds the 
reference voltage "VH1". In other words, the image signal changes from the 
black level side to a white level side. On the other hand, the second 
comparator 103 outputs a low level signal in case that the differential 
output falls below the reference voltage VL1, namely the image signal is 
varied from the white level into the black level. 
Then, the outputs from the first and second comparators 102 and 103 are 
supplied to the first hold circuit 106. This first hold circuit 106 is set 
when the low level signal is output from the first comparator 102, and 
reset when another low level signal is output from the second comparator 
103. In other words, the first hold circuit 106 is set under the condition 
that the black level of the image signal is varied to the white level 
thereof, whereas this circuit 106 is reset under the condition that the 
white level of the image signal is changed into the black level. As a 
consequence, a roughly binary-coded image signal represented in FIG. 9C is 
obtained. 
On the other hand, the differential output from the second differential 
circuit 101 is supplied to the third and fourth comparators 104 and 105 so 
as to be compared with the corresponding reference voltages VH2 and VL2. 
It should be noted that the third comparator 104 outputs the low level 
signal when the differential output exceeds the reference voltage VH2. 
Since this differential output responds to small changes in the image 
signal and "VH2" is lower than "VH1", this differential output also 
responds to the small changes of the image signal from the black level to 
the white level. Similarly, the fourth comparator 105 responds to small 
changes of the image signal from the white level to the black level, as 
compared with the second comparator 103. 
The outputs from the third and fourth comparators 104 and 105 are supplied 
to the second hold circuit 107. As a result, the output signal represented 
in FIG. 9E of this second hold circuit 107 becomes a binary-coded signal 
in response to the small changes in the image signal. 
Thereafter, the outputs of the first and second hold circuits 106 and 107 
are supplied to the OR gate 108 so as to be added to each other. Then, the 
summed signal is output as the final binary-coded image signal shown in 
FIG. 9F. That is, the binary-coded signal output from the OR gate 108 has 
been roughly binary-coded in such a manner that this signal represents an 
original document having a large white portion. To the contrary, the 
finely binary-coded signal is produced from such as image signal having a 
large black portion. 
The above-described binary-coding circuit is useful for reading, for 
instance, such an original document having characters written on a white 
background, so that a space portion of the original document having the 
white background becomes a binary-coded output from which signal changes 
caused by the noise and smear of the original document have been cut out. 
A portion of the original document having a relatively significant black 
portion can be obtained as the binary-coded output representing the fine 
information. 
Also, the above-described binary coding circuit may be applied to, for 
instance, such an original document where a white character is drawn on a 
black background by substituting the OR gate 108 with an AND gate.