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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.
BRIEF DESCRIPTION OF THE DRAWINGS
The above-described object and features of the present invention may be
understood by the following descriptions with reference to the
accompanying drawings, in which:
FIG. 1 is a perspective view of a compact copier employing a binary coding
circuit according to a preferred embodiment of the present invention;
FIG. 2 is a front view, partially in sectional view of the compact copier
shown in FIG. 1;
FIG. 3 is a schematic block diagram showing the internal arrangement of the
compact copier shown in FIG. 1 including its structural components and
circuitry;
FIG. 4 schematically illustrates a pixel arrangement of the image sensor
shown in FIG. 3;
FIG. 5 is a flowchart for explaining a binary coding operation of
concentration performed by the circuit shown in FIG. 3 to determine
photographic density;
FIG. 6 is a flowchart for explaining a binary coding operation effected by
the circuit shown in FIG. 3 to determine contour;
FIGS. 7A and 7B schematically illustrate a basic idea relating to the
binary coding operation of the contour detection carried out in the
compact copier represented in FIG. 1;
FIG. 8 is a schematic block diagram of a circuit arrangement of another
binary coding circuit according to a second preferred embodiment of the
present invention; and,
FIGS. 9A to 9F are signal waveform graphs for representing output waveforms
of major circuit portions in the binary coding circuit shown in FIG. 8.
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 phtographing 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 A1). 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):
##EQU1##
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 104 is binary-coded, and
the binary coded data 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 process 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):
##EQU2##
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).
g(i, j)=.vertline..DELTA.xf(i, j).vertline.+.vertline..DELTA.yf(i,
j).vertline. equation (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 prin | | |
