Image processing system

An image processing system for reading multi-level image data corresponding to each pixel of an input image from a multi-tone-level draft image such as a photograph and correcting a density level at each of the pixels, which is represented by the obtained image data, and outputting data representing corrected density levels. The image processing system first performs an appropriate sampling of the read image data of the pixels at a sampling rate in such a manner to enable reference to the density levels at the pixels when correcting the density levels. The sampling rate is most appropriately predetermined.

BACKGROUND OF THE INVENTION 
1. Field of The Invention 
This invention relates to an image processing system for performing a 
processing such as a tone correction on image data optically read from a 
photograph or the like and thereafter outputting processed image data. 
2. Description of The Related Art 
In recent years, with advance of image processing techniques, an image 
processing system, which can read image data of a picture or the like and 
perform various processings on the image data and also can edit the image 
data by, for example, "pasting" or placing an image represented by the 
image data on a document, has come to require a variety of functions and 
an improvement in operability. 
A conventional image processing system has a function of a tone correction, 
by which a tone of read image data is converted into another tone 
arbitrarily indicated by an operator. In such a case, a desired 
tone-correction rate or degree can be set by first displaying a curve 
graph (hereunder sometimes referred to as a tone curve or as a tone 
correction curve), in which tone levels (namely, densities) of input image 
data are plotted in abscissa (namely, in horizontal axis) and tone levels 
of output image data obtained by performing a tone correction on the tone 
of the input image data are plotted in ordinate (namely, in vertical 
axis), as illustrated in FIG. 39 and next modifying the tone curve by 
using an input means such as a mouse. In case of FIG. 39, a tone curve 1 
corresponds to a case where a tone level of output image data is equal to 
a tone level of corresponding input image data (namely, output image data 
is obtained from input image data without any conversion or modification). 
Further, as shown in FIG. 39, a tone curve 2 is entirely lower than the 
tone curve 1. Thus, in case of employing the tone curve 2, an output image 
represented by the output image data is lighter than an input image 
represented by the input image data. In contrast, a tone curve 3 is 
entirely higher than the tone curve 1. Thus, in case of employing the tone 
curve 3, an output image represented by the output image data is darker 
than an input image represented by the input image data. Further, a 
portion of an output image, which is represented by tone levels of a steep 
portion of a tone curve, is enhanced in comparison with a corresponding 
input image. Conversely, another portion of the output image, which is 
represented by tone levels of a gentle portion of the tone curve, is 
blurred or scumbled in comparison with the corresponding input image. 
To set such a tone curve, information on densities at arbitrary positions 
(namely, of arbitrary pixels) of an original image (or an input image) and 
the distribution of densities of pixels of the original image is 
necessary. Thus, in case of a conventional image processing system, 
multi-level density data (hereunder sometimes referred to as multi-level 
image data) obtained as a result of a tone correction performed on image 
data read from the original image is not only converted into binary data 
(or halftone-dot data) to be displayed on a screen of a cathode-ray-tube 
(CRT) of a display device thereof, such multi-level data itself is also 
stored in a random access memory (RAM) thereof. 
Hereinafter, a conventional image processing system will be described. 
FIG. 40 is a schematic block diagram for illustrating the configuration of 
the conventional image processing system. Reference numeral 21 designates 
a central processing unit (CPU) for controlling the system and processing 
data; 22 a RAM for storing 8-bit 256-level image data, which represents 
the density of each pixel with 256 levels, as the above described 
multi-level density data; 23 what is called a page memory for storing 
binary data converted from the multi-level image data stored in the RAM 22 
under the control of the CPU 21; 24 an image input unit for optically 
reading a draft such as a photograph, for performing a tone correction on 
the read image data and for transferring the corrected data to the RAM 22; 
25 a CRT display unit; and 26 a printer. 
FIG. 41 is a schematic block diagram for illustrating the configuration of 
the image input unit 24 of the image processing system of FIG. 40. 
Reference numeral 27 denotes a CCD image sensor (hereunder referred to as 
a CCD) for reading image data from a draft picture optically and 
outputting an analog electric signal representing the read image data; 28 
an analog-to-digital (A/D) converter for converting an analog voltage 
signal output from the CCD 27 to a digital signal; 29 a shading correction 
circuit for performing a shading correction on the digital signal; 30 a 
tone correction circuit for performing a tone correction an the signal 
according to a tone-correction rate preliminarily set by the CPU 21. 
Hereinafter, an operation of the conventional image processing system 
having the above described configuration will be described by referring to 
FIGS. 40 and 41. 
First, image data optically read by the CCD 27 and converted into an analog 
electric signal is further converted by the A/D converter 28 into an 8-bit 
(256-level) digital electric signal. Then, the digital electric signal 
undergoes a shading correction in the shading correction circuit 29. 
Subsequently, the tone correction circuit 30 performs a tone correction on 
the data represented by the signal corrected in the circuit 29 at the 
predetermined tone-correction rate. Next, the corrected data is written to 
the RAM 22. Then, the 8-bit image data stored in the RAM 22 is converted 
by the CPU 21 into binary image data (or halftone-dot image data) which is 
then displayed on the CRT display unit 25 and is also output to the 
printer 26. 
The tone-correction rate can be determined as equal to a rate desired by an 
operator by setting a tone curve used for a tone correction. In the 
conventional image processing system, the read multi-level image data 
(namely, 8-bit (256-level) image data) respectively representing 
density-levels of all pixels of a draft picture (namely, an input image) 
are stored in the RAM. For example, the stored image data are accessed for 
inquiring into the densities of desired points of the input image 
displayed on the CRT display unit and into the distribution of densities 
(namely, tone-levels) represented by the image data. Namely, the stored 
image data are referred to for setting a tone curve for a tone correction. 
The conventional image processing system, however, has a drawback in that a 
large number of bits are required for storing density data corresponding 
to each pixel and thus a storage device having a huge storage capacity is 
necessary. The present invention is created to eliminate such a drawback 
of the conventional system. 
SUMMARY OF THE INVENTION 
It is, accordingly, an object of the present invention to provide an image 
processing system which can easily obtain density data representing the 
density at each desired positions in (or of each desired pixel of) a 
multi-level draft (or input) image having three or more density-levels in 
order to modify a tone correction curve (hereunder sometimes referred to 
as a density correction curve), which represents the relation between 
input density data and output density data (namely, modified density data) 
and is necessary for performing a tone correction (hereunder sometimes 
referred to as a density correction) on image data read from the draft 
image by using a reading element such as a CCD capable of outputting a 
signal corresponding the density at each position of the draft image. 
Further, it is another object of the present invention to provide an image 
processing system which can save storage elements (thus can save storage 
areas) by storing density data of suitably selected pixels of an input (or 
draft) image as data required for obtaining density data at desired 
positions in (or density data of desired pixels of) the input image, 
instead of storing density data of all pixels of the input image. 
Moreover, it is a further object of the present invention to provide an 
image processing system which can select and store density data of pixels 
of an input image at a most suitable rate and thus have a most suitable 
storage capacity. 
To achieve the foregoing object, in accordance with an aspect of the 
present invention, there is provided an image processing system, which 
comprises reading means for outputting multi-level image data 
corresponding to a density of each of pixels, to which an image of a draft 
is partitioned, sampling means for obtaining density data by sampling the 
image data output from the reading means at a predetermined rate of the 
number of the pixels, which correspond to image data to be sampled, to 
that of all of the pixels, storing means for storing the density data 
obtained by the sampling means, image processing means for performing a 
processing on the image data output from the reading means, displaying 
means for displaying an image represented by data obtained as a result of 
the processing by the image processing means, indicating means for 
indicating a position in the image displayed by the displaying means and 
control means for reading the density data corresponding to the position 
indicated by the indicating means from the storing means and making the 
displaying means display the read density data. 
To achieve the foregoing object, in accordance with another aspect of the 
present invention, there is provided an image processing system, which 
comprises reading means for outputting multi-level image data 
corresponding to a density of each of pixels, to which an image of a draft 
is partitioned, sampling means for obtaining density data by sampling the 
image data output from the reading means at a predetermined rate of the 
number of the pixels, which correspond to image data to be sampled, to 
that of all of the pixels, storing means for storing the density data 
obtained by the sampling means, halftone-dot processing means for 
performing a halftone-dot processing, the halftone-dot processing means 
generating a halftone dot from each block composed of the pixels by 
assigning one of a plurality of binary density levels to a part of the 
pixels of each of the blocks to obtain a density to be represented by the 
corresponding block, displaying means for displaying an image represented 
by data obtained as a result of the processing by the halftone-dot 
processing means, indicating means for indicating a position in the image 
displayed by the displaying means and outputting information representing 
the indicated position and control means for making the displaying means 
display the data stored in the storing means according to the information 
representing the indicated position. 
To achieve the foregoing object, in accordance with yet another aspect of 
the present invention, there is provided a method for performing an image 
processing, comprising the steps of partitioning an image of a draft into 
a plurality of pixels, reading multi-level image data corresponding to a 
density of each of the pixels, obtaining density data by sampling the 
image data at a predetermined rate of the number of the pixels, which 
correspond to image data to be sampled, to that of all of the pixels, 
storing the density data obtained by the sampling of the image data, 
displaying an image represented by the density data, specifying an 
indicated position in the displayed image and reading the density data 
corresponding to the specified position in the displayed image and 
displaying the read density data corresponding to the specified position. 
To achieve the foregoing object, in accordance with still another aspect of 
the present invention, there is provided an image processing system, which 
comprises reading means for outputting multi-level digital image data 
corresponding to a density of each of pixels, to which an image of a draft 
is partitioned; sampling means for obtaining multi-level digital density 
data by sampling the multi-level image data output from the reading means 
at a predetermined rate of the number of the pixels, which correspond to 
multi-level image data to be sampled, to that of all of the pixels; 
storing means for storing the multi-level density data sampled by the 
sampling means; image processing means for generating a halftone-dot image 
by assigning one of binary density levels to each of the pixels having 
tone levels greater than a predetermined value corresponding to each cell 
of a halftone-dot pattern table, the tone level being represented by the 
multi-level density data corresponding to each of the pixels; displaying 
means for displaying the halftone-dot image obtained by the image 
processing means; indicating means for indicating a position in the 
halftone-dot image displayed by the displaying means; and control means 
for reading the density data corresponding to the position indicated by 
the indicating means from the storing means and making the displaying 
means display the read density data, wherein under the control of the 
control means, the display means displays a numerical value of a tone 
level represented by the read density data near the position in the 
halftone-dot image, which position is indicated by the indicating means. 
To achieve the foregoing object, in accordance with another aspect of the 
present invention, there is provided an image processing system, which 
comprises: reading means for outputting multi-level digital image data 
corresponding to a density of each of pixels, to which an image of a draft 
is partitioned; sampling means for obtaining multi-level data digital 
density data by sampling the multi-level image data output from the 
reading means at a predetermined rate of the number of the pixels, which 
correspond to multi-level image data to be sampled, to that of all of the 
pixels; first storing means for storing the multi-level density data 
sampled by the sampling means; image processing means for generating a 
halftone-dot image by producing halftone dots from each block composed of 
the pixels, the image processing means assigning one of binary density 
levels to the pixels of each block, which have tone levels greater than a 
predetermined value corresponding to each cell of a halftone-dot pattern 
table, the tone level being represented by the multi-level density data 
corresponding to each pixel; second storing means for storing halftone-dot 
data corresponding to each of the produced halftone dots; displaying means 
for displaying the halftone-dot image represented by the halftone-dot data 
stored in the second storing means; indicating means for indicating a 
position in the halftone-dot image displayed by the displaying means; and 
control means for reading the density data corresponding to the position 
indicated by the indicating means from the first storing means and making 
the displaying means display the density data stored in the first storing 
means, wherein under the control of the control means, the display means 
displays a numerical value of a tone level represented by the read density 
data near the position in the halftone-dot image, which position is 
indicated by the indicating means. 
To achieve the foregoing object, in accordance with yet another aspect of 
the present invention, there is provided a method for performing an image 
processing, which comprises the steps of: partitioning an image of a draft 
into a plurality of pixels; reading multi-level digital image data 
corresponding to a density of each of the pixels; obtaining multi-level 
digital density data by sampling the multi-level image data at a 
predetermined rate of the number of the pixels, which correspond to image 
data to be sampled to that of all of the pixels; storing the multi-level 
digital density data obtained by the sampling of the image data; 
displaying an image represented by the density data; specifying an 
indicated position in the displayed image; reading the density data 
corresponding to the specified position in the displayed image; and 
displaying the read density data near the specified position in the 
displayed image.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Hereinafter, preferred embodiments of the present invention will be 
described in detail by referring to the accompanying drawings. 
I. FIRST EMBODIMENT 
FIG. 1 is a schematic block diagram for illustrating the configuration of a 
first embodiment of (namely, an image editing system embodying) the 
present invention. Reference numeral 1 designates a CPU for controlling 
the system and processing data; 2 a magnetic disk and drive unit 
(hereunder referred to simply as a magnetic disk) for storing programs and 
data; 3 what is called a page memory (hereunder sometimes referred to as 
an image memory); 4 a memory used for displaying a graph or the like 
(hereunder sometimes referred to as a display memory); 5 a CRT display 
unit (hereunder sometimes referred to simply as a CRT); 6 an image input 
unit; 7 a printer; 8 a keyboard; and 9 a mouse for indicating a position 
on a screen of the CRT 5. 
FIG. 2 is a schematic block diagram for illustrating the configuration of 
the image input unit 8 of the image editing system of FIG. 1. Reference 
numeral 10 denotes a CPU for controlling the image input unit 6; 11 an 
image sensor (hereunder referred to as a CCD) for outputting analog 
voltage signal in response to light incident thereto by converting the 
intensity of the incident light to the magnitude of a voltage (namely, the 
level of an analog voltage); 12 an A/D converter for converting an analog 
voltage signal output from the CCD 11 to an 8-bit digital voltage signal; 
13 a shading correction circuit for correcting variation in the voltage 
signal due to a shading phenomenon occurring in a read or input image; 14 
a tone correction circuit for performing a conversion of densities 
represented by input or read image data; 15 a binarization circuit for 
converting the 8-bit digital voltage signal into a binary data signal 
representing 0 or 1 by performing halftone-dot generation processing on 
the density data represented by the 8-bit digital voltage signal, which is 
corrected by the tone correction circuit 14; 16 a counter for repeatedly 
performing a process of counting a value set by the CPU 10 and outputting 
a positive signal of a period (hereunder sometimes referred to as a 
sampling period) corresponding to a pixel sampled when the counting of 
value is completed; 17 a gate circuit for selecting digital image data in 
response to the signal output from the counter 16; 18 a buffer for storing 
the image data of 1 line selected by the gate circuit 17; 20 a 
readable/writable memory for storing the image data temporarily held in 
the buffer 18; and 19 a transfer circuit for transferring the image data 
of 1 line temporarily stored in the buffer 18 to the memory 20 in response 
to a control signal output from the CPU 10. 
Hereinafter, an image processing performed by the image editing system 
having the above described configuration will be described in detail. 
1. READING OF IMAGE DATA 
First, as shown in the flowchart of FIG. 3, the CPU 1 of the system sends a 
signal representing conditions of a reading of image data for setting a 
tone curve, as well as a reading-operation starting command, to the CPU 10 
of the image input unit 6 in step S1. Then, the image input unit 6 reads 
image data from an image and transfers the read image data to the image 
memory 3 sequentially. Thereafter, if the CPU 1 accepts a 
reading-operation terminating signal issued by the image input unit 6 in 
step S2, the CPU 101 expands or reduces the image data stored in the page 
memory 3 in accordance with the resolution of the CRT 5 in step S3. 
Subsequently, the expanded or reduced image data is written to the display 
memory 4 in step S4. The image data written to the display memory 4 is 
displayed in the CRT 5. 
Thus, the read image data is converted into binary data (or halftone-dot 
image data), which is shown of the screen of the CRT 5. In addition, the 
read multi-level image data itself is sampled at a predetermined sampling 
rate and the sampled data is stored in the memory 20. 
2. TONE CORRECTION 
In the tone correction circuit 14, a RAM having a storage area of 256 bytes 
as illustrated in FIG. 4 is provided. In the storage area of this RAM, 
tone levels (namely, density levels) represented by output image data, 
which would be obtained as a result of a tone correction, are set by the 
CPU 10 at locations thereof, the addresses of which respectively have 
values equal to tone levels represented by input image data, at the time 
of initialization of the RAM prior to the reading of the input image. 
Namely, predetermined relation between tone levels of output image data 
and tone levels of input image data (namely, the conversion relation) is 
initially established in the storage area of the RAM by the CPU 10. For 
instance, in case where the conversion relation represented by a tone 
curve of FIG. 5 is established therein, image data indicating a tone level 
of 110, which are stored at locations respectively having addresses of 100 
and 101 of the RAM of FIG. 4, are output therefrom correspondingly to tone 
levels of 100 and 101 represented by input image data. Further, in such a 
case, image data respectively indicating tone levels of 190 and 192, which 
are stored at locations respectively having addresses of 200 and 201 of 
the RAM of FIG. 4, are output therefrom respectively corresponding to tone 
levels of 200 and 201 represented by the input image data. As described 
above, a tone correction is performed according to the established tone 
curve by fetching data stored at locations of the storage area of the RAM 
respectively corresponding to addresses, which are indicated by tone 
levels represented by the input image data, and then outputting the 
fetched data as the output image data. 
3. SETTING OF TONE CURVE 
In the magnetic disk 2, a storage area having the same structure as does 
the RAM of the tone correction circuit 14 is provided as illustrated in 
FIG. 4. Further, data representing an initial conversion relation 
indicated by the initial (tentative) tone curve is stored for displaying 
the tone curve in this storage area of the magnetic disk 2. The CPU 1 
reads density data (hereunder sometimes referred to as initial value 
data), which is stored in the storage area of the magnetic disk 2 
according to the relation indicated by the initial tone curve, therefrom. 
Then the CPU 1 generates data (hereunder sometimes referred to as display 
data) representing a graph of the initial tone curve, of which the 
horizontal axis denotes the density levels (namely, addresses in the 
storage area of the magnetic disk 2) represented by input image data and 
the vertical axis designates the density levels represented by output 
image data (stored at locations having the addresses in the storage area 
of the magnetic disk 2), according to the initial value data. Further, the 
generated display data is stored in the display memory 4. Subsequently, 
the initial tone curve for a tone correction as illustrated in FIG. 5 is 
displayed on the screen of the CRT 5 according to the display data. This 
tone curve is transformed into a desired curve by using the mouse 9 and 
executing a program employing known graphic processing techniques. 
Thereafter, the CPU 1 sends coordinate data representing coordinates of 
the modified. tone curve to the CPU 10 of the image input unit 6. At that 
time, the coordinate data sent from the CPU 1 is set in the RAM of the 
tone correction circuit 14 by the CPU 10. 
4. GENERATION OF BINARY IMAGE (OR HALFTONE-DOT IMAGE) 
The binarization circuit 15 converts the multi-level image data corrected 
by the tone correction circuit 14 into binary image data (or halftone-dot 
image data). In this circuit, the density (namely, the tone level) 
represented by the density data of each pixel output from the tone 
correction circuit 14 is compared with the value set at a corresponding 
cell of the halftone-dot pattern table of FIG. 6 established therein. If 
the tone level of a pixel is larger than the value set at the 
corresponding cell of the table, the color of the pixel is determined as 
black (corresponding to a value of 1). Conversely, if the tone level of a 
pixel is smaller than the value set at the corresponding cell of the 
table, the color of the pixel is determined as white (corresponding to a 
value of 0). The same halftone-dot pattern table is repeatedly used to be 
compared with image data of pixels of the same number as of cells thereof. 
FIG. 8 illustrates the relation between each pixel of the input image and 
a corresponding cell of the halftone-dot pattern table diagramatically. As 
is apparent from this figure, each pixel of the input image is in 
one-to-one correspondence relation with a cell of the halftone-dot pattern 
table. 
Thus, to generate a halftone-dot image, halftone is approximately 
represented by regulating a rate of an area of black pixels to a unit area 
(namely, the size of the halftone-dot pattern table). Therefore, if a 
halftone-dot pattern table of a large size (namely, a halftone-dot pattern 
table having a large number of cells) is employed, an image, each of pixel 
which has many tone-levels, can be represented. In contrast, if a 
halftone-dot pattern table of a small size (namely, a halftone-dot pattern 
table having a small number of cells) is employed, only an image, each of 
pixel which has a small number of tone-levels, can be represented. 
Practically, the binarization circuit 15 has the halftone-dot pattern 
tables of various sizes. Thus a desired one of the tables can be used 
according to an indication from the CPUs 1 and 10 based on a direction 
from an operator. 
On the other hand, if the CPU 10 of the image input unit 6 receives a 
reading-operation starting command from the CPU 1 in step S11 as 
illustrated in FIG. 9, the CPU 10 sets a tone curve in the tone correction 
circuit 14 in step S12. Further, the CPU 10 starts an operation of reading 
a draft image in step S13. Then, the CPU 10 issues a sampling-operation 
starting signal to the gate circuit 17. When starting the operation of 
reading the draft picture, the draft picture is irradiated and thereafter 
light reflected by the draft picture focuses into an image on the CCD 11. 
This light is converted by the CCD 11 into an electric signal. 
Subsequently, the electric signal is further converted by the A/D 
converter 12 into an 8-bit digital signal. Thereafter, the shading 
correction circuit 13 performs a shading correction on the 8-bit digital 
signal. Further, the 8-bit image data obtained as a result of the shading 
correction is input to both of the tone correction circuit 14 and the gate 
circuit 17. 
As is shown in FIG. 7, the counter 16 outputs a signal C to the gate 
circuit 17 each time when counting a value set by the CPU 10, in 
synchronization with an outputting of the image data from the shading 
correction circuit 13 (see a fundamental clock A and a digital image 
signal B). The gate circuit 17 is enabled in response to the signal output 
from the counter 16 and samples the image data output from the shading 
correction circuit 13 at a sampling rate and writes an output signal D 
representing the sampled data to the memory 20 through the buffer 18 and 
the transfer circuit 19. At that time, the CPU 10 counts the pixels of the 
image represented by the image data input to the gate circuit 17 in step 
S15. If the CPU 10 judges in step S16 that the image data of 1 line is 
input thereto, and further judges in step S17 that not all of the image 
data has been processed, the CPU 10 instructs the gate circuit 17 to 
suspend the sampling. In response to such an instruction from the CPU 10, 
the gate circuit 17 suspends the sampling of the image data to be written 
to the memory 20. 
Even when the gate circuit 17 suspends the sampling of the image data, the 
CPU 10 counts the image data of each line by counting the pixels of the 
image data input to the circuit 17 in step S19 similarly as in steps S15 
and S16. Subsequently, if the CPU 10 judges in step S20 that not all of 
the image data have not been processed, and further judges in step S21 
that the processing of the image data of a predetermined number of lines 
stored in the counter 16 has been finished, the control procedure returns 
to step S14, whereupon the CPU 10 issues a sampling-operation starting 
signal to the gate circuit 17. As a result, with regard to a block of the 
input image data, on which a binarization is performed (namely, from which 
halftone-dot image data (or binary image data) is generated), the density 
data of each pixel thereof is "extracted" (or sampled) and stored in the 
memory 20. 
5. DISPLAYING OF DENSITY 
An operation of displaying density data is controlled by the CPUs 1 and 10 
in accordance with the flowcharts of FIGS. 10 and 11. First, if a position 
in an image displayed on the screen of the CRT 5 is indicated by using the 
mouse 9 in step S31, the CPU 1 calculates an address in the page memory 3 
(corresponding to coordinates in the read draft picture) from the 
indicated position or coordinates on the screen of the CRT 5 in step S32. 
Then, in step S33, the CPU 1 issues the CPU 10 of the image input unit 6 
with signals representing the calculated coordinates and a command 
requesting the density level corresponding to the calculated coordinates. 
Thereafter, if the CPU 1 receives image density information from the image 
input unit 6 in step S34, the density represented by the received 
information is displayed in step S35 in the vicinity of a position, which 
is indicated by a cursor, on the screen of the CRT 5 as illustrated in 
FIG. 12. 
On the other hand, as illustrated in FIG. 11, if the CPU 10 accepts 
information representing the calculated coordinates and the command 
requesting the corresponding density from the CPU 1 in step S41, the CPU 
10 computes an address of the memory 20, at which the sampled 
corresponding image data are stored, from the coordinates received from 
the CPU 1 in step S42 and subsequently, in step S43, the CPU 10 outputs 
the density data stored at the address to the CPU 1. 
6. THE RELATION BETWEEN THE SIZE OF THE HALFTONE-DOT PATTERN TABLE AND A 
SAMPLING PERIOD 
Referring now to the control procedures of FIGS. 13 and 14, the CPU 1 
receives data representing the size of the halftone-dot pattern table 
input from the keyboard 8 in step S31, the CPU 1 sends the received data 
representing the input size to the CPU 10 of the image input unit 6. On 
the other hand, if the CPU 10 receives the data indicating the size of the 
halftone-dot pattern table from the CPU 1 in step S53, the CPU 10 
establishes the received value of the size of the table in the counter 16 
in step S54. As described above, the counter 16 outputs the signal C each 
time when counting the value established by the CPU (namely, in this case, 
the value of the size of the halftone-dot pattern table) therein. The gate 
circuit 17 is enabled in response to the signal C and samples the image 
data. Therefore, the number of pixels (namely, the number of density data 
to be stored) corresponding to the sampling period is set as equal to the 
size (namely, the number of unit blocks to be converted to halftone dots) 
of the halftone-dot pattern table. 
Generally, in case where a halftone image is represented by a binary output 
device, halftone is approximately represented by effecting a halftone-dot 
generation processing similarly as in case of this embodiment. Namely, 
halftone is approximately represented by regulating a rate of an area of 
black pixels to a unit block or area composed of a plurality of pixels. 
Thus, the density of a position in an image is represented by using a 
block of a predetermined size. Therefore, in case where the density at a 
position in a halftone-dot image is obtained by indicating the position in 
the halftone-dot image and then reading the multi-level density data 
stored in a memory, it is of no significance to store plural multi-level 
data correspondingly to a unit block. 
The data output to the CRT 5 and the printer 7 is halftone-dot image data. 
It is, therefore, necessary and sufficient for knowing the density at a 
desired position in a displayed image to set the number of pixels (or 
density data) corresponding to a sampling period as equal to the size of 
the halftone-dot pattern table and to store a multi-level image data 
correspondingly to each unit block to be converted into a halftone dot. 
Namely, it is necessary and sufficient for knowing the density at a 
desired position in a draft image to set the number of the blocks as equal 
to the number of the density data to be sampled and stored. 
As stated above, in case of the first embodiment, a read multi-level image 
data is converted to binary image: data and the binary image data is 
stored in the image memory. Moreover, the read image data itself is 
sampled and the sampled data is stored in the memory. Thus, the necessary 
memory capacity can be reduced or saved. Further, the density at a 
position in the read image can easily be known and provided as reference 
data for setting a tone curve for a tone correction. 
Furthermore, in case of the first embodiment, the number of the pixels (or 
the blocks) composing the halftone-dot pattern table is set as equal to 
that of the density data corresponding to the sampling period. Thus, the 
multi-level data of the pixels of a number, which is most suitable for 
knowing the density at a desired position in the read image, can be 
sampled. 
Incidentally, the sampled multi-level image data is stored in the first 
embodiment. Thus, a roughly estimated distribution of densities of a draft 
picture can be obtained and also used as effective reference data for 
setting a tone curve for a tone correction. 
Additionally, the first embodiment is adapted to determine the sampling 
period by indicating the size of the halftone-dot pattern table. However, 
the same effects can be obtained if the first embodiment is adapted to 
determine the size of the halftone-dot pattern table from the sampling 
period. 
II. SECOND EMBODIMENT 
FIG. 15 is a schematic block diagram for illustrating the configuration of 
a second embodiment of (namely, another image editing system embodying) 
the present invention. Reference numeral 101 designates a CPU for 
controlling the system and processing data; and 106 an image input unit. 
As is apparent from a comparison between FIGS. 1 and 15, the configuration 
of the second embodiment is similar to that of the first embodiment except 
the CPU 101 and the image input unit 106. 
FIG. 16 is a schematic block diagram for illustrating the configuration of 
the image input unit 106 of FIG. 15. Reference numeral 110 denotes a CPU 
for controlling the image input unit 106; 115 a binarization circuit for 
converting the 8-bit digital signal into a binary data signal representing 
0 or 1 by performing a halftone-dot generation processing on the density 
data represented by the 8-bit digital signal, which is corrected by the 
tone correction circuit 14; 116 a counter for repeatedly performing a 
process of counting a preset value "4" and outputting a positive signal of 
a period corresponding to a pixel sampled when the counting of the value 
is completed; and 119 a transfer circuit for transferring the image data 
of 1 line temporarily stored in the buffer 18 to the memory 120 in 
response to a control signal output from the CPU 110. 
Hereinafter, an image processing performed by the image editing system 
(namely, the second embodiment) having the above described configuration 
will be described in detail. 
1. READING OF IMAGE DATA 
First, as shown in the flowchart of FIG. 17, the CPU 101 of the system 
sends a signal representing conditions of a reading of image data for 
setting a tone curve, as well as a reading-operation starting command, to 
the CPU 110 of the image input unit 106 in step S101. Then, the image 
input unit 106 reads image data from an image and transfers the read image 
data to the image memory 3 sequentially. Thereafter, if the CPU 101 
accepts a reading-operation terminating signal issued by the image input 
unit 106 in step S102, the CPU 101 expands or reduces the image data 
stored in the page memory 3 in accordance with the resolution of the CRT 5 
in step S103. Subsequently, the expanded or reduced image data is written 
to the display memory 4 in step S104. The image data written to the 
display memory 4 is displayed in the CRT 5. 
On the other hand, if the CPU 110 of the image input unit 106 receives a 
reading-operation starting command from the CPU 101 in step Sill as 
illustrated in FIG. 18, the CPU 110 sets a tone curve in the tone 
correction circuit 14 in step S112. Further, the CPU 110 starts an 
operation of reading a draft image in step S113. Then, the CPU 110 issues 
a sampling-operation starting signal to the gate circuit 17. When starting 
the operation of reading the dragt picture, the draft picture is 
irradiated and thereafter light reflected by the draft picture focuses 
into an image on the CCD 11. This light is converted by the CCD 11 into an 
electric signal. Subsequently, the electric signal is further converted by 
the A/D converter 12 into an 8-bit digital signal. Thereafter, the shading 
correction circuit 13 performs a shading correction on the 8-bit digtal 
signal. Further, the 8-bit image data obtained as a result of the shading 
correction is input to both of the tone correction circuit 14 and the gate 
circuit 17. 
As is shown in FIG. 19, the counter 116 outputs a signal C to the gate 
circuit 17 each time when counting "4" preset by the CPU 110, in 
synchronization with an outputting of the image data from the shading 
correction circuit 13 (see a fundamental clock A and a digital image 
signal B). The gate circuit 17 is enabled in response to the signal output 
from the counter 116 and samples the image data output from the shading 
correction circuit 13 at a sampling rate and writes an output signal D 
representing the sampled data to the memory 120 through the buffer 18 and 
the transfer circuit 119. At that time, the CPU 110 counts the pixels of 
the image represented by the image data input to the gate circuit 17 in 
step S115. If the CPU 110 judges in step S116 that the image data of 1 
line is input therto, and further judges in step S117 that not all of the 
image data has been processed, the CPU 110 instructs the gate circuit 17 
to suspend the sampling. In response to such sn instruction from the CPU 
110, the gate circuit 17 suspends the sampling of the image data to be 
written to the memory 120. 
Even when the gate circuit 17 suspends the sampling of the image data, the 
CPU 110 counts the image data of each line by counting the pixels of the 
image data input to the circuit 17 in step S119 similarly as in steps S115 
and S116. Subsequently, if the CPU 110 judges in step S120 that riot all 
of the image data have not been processed, and further judges in step S121 
that the processing of the image data of a predetermined number of lines 
stored in the counter 106 has been finished, the control procedure returns 
to step S114, whereupon the CPU 110 issues a sampling-operation starting 
signal to the gate circuit 17. Thus, the read image is converted into the 
binary image, which is displayed on the screen of the CRT 5, and the read 
multi-level image data is sampled at a predetermined rate and the sampled 
image data is stored in the memory 120. 
2. TONE CORRECTION 
In the tone correction circuit 14, a RAM having a storage area of 256 bytes 
as illustrated in FIG. 20 is provided. In the storage area of this RAM, 
tone levels (namely, density levels) represented by output image data, 
which would be obtained as a result of a tone correction, are set by the 
CPU 110 at locations thereof, the addresses of which respectively have 
values equal to tone levels represented by input image data, at the time 
of initialization of the RAM prior to the reading of the input image. 
Namely, predetermined relation between tone levels of output image data 
and tone levels of input image data (namely, the conversion relation) is 
initially established in the storage area of the RAM by the CPU 110. For 
instance, in case where the conversion relation represented by a tone 
curve of FIG. 21 is established therein, image data indicating a tone 
level of 110, which are stored at locations respectively having addresses 
of 100 and 101 of the RAM of FIG. 20, are output therefrom correspondingly 
to tone levels of 100 and 101 represented by input image data. Further, in 
such a case, image data respectively indicating tone levels of 190 and 
192, which are stored at locations respectively having addresses of 200 
and 201 of the RAM of FIG. 20, are output therefrom respectively 
corresponding to tone levels of 200 and 201 represented by the input image 
data. As described above, a tone correction is performed according to the 
established tone curve by fetching data stored at locations of the storage 
area of the RAM respectively corresponding to addresses, which are 
indicated by tone levels represented by the input image data, and then 
outputting the fetched data as the output image data. 
3. SETTING OF TONE CURVE 
In the magnetic disk 2, a storage area having the same structure as the RAM 
of the tone correction circuit 14 does as illustrated in FIG. 20 is 
provided. Further, data representing an initial conversion relation 
indicated by the initial (tentative) tone curve is stored for displaying 
the tone curve in this storage area of the magnetic disk 2. The CPU 101 
reads density data (namely, initial value data), which is stored in the 
storage area of the magnetic disk 2 according to the relation indicated by 
the initial tone curve, therefrom. Then the CPU 101 generates data 
(hereunder sometimes referred to as display data) representing a graph of 
the initial tone curve, of which the horizontal axis denotes the density 
levels (namely, addresses in the storage area of the magnetic disk 2) 
represented by input image data and the vertical axis designates the those 
represented by output image data (stored at locations having the addresses 
in the storage area of the magnetic disk 2), according to the initial 
value data. Further, the generated display data is stored in the display 
memory 4. Subsequently, the initial tone curve for a tone correction as 
illustrated in FIG. 21 is displayed on the screen of the CRT 5 according 
to the display data. This tone curve is transformed into a desired curve 
by using the mouse 9 and executing a program employing known graphic 
processing techniques. Thereafter, the CPU 101 sends coordinate data 
representing coordinates of the modified tone curve to the CPU 110 of the 
image input unit 106. At that time, the coordinate data sent from the CPU 
101 is set in the RAM of the tone correction circuit 14 by the CPU 110. 
4. GENERATION OF BINARY IMAGE (OR HALFTONE-DOT IMAGE) 
The binarization circuit 15 converts the multi-level image data corrected 
by the tone correcton circuit 14 into binary image data (or halftone-dot 
image data). In this circuit, the density (namely, the tone level) 
represented by the density data of each pixel output from the tone 
correction circuit 14 is compared with the value set at a corresponding 
cell of the halftone-dot pattern table of FIG. 22 established therein. If 
the tone level of a pixel is larger than the value set at the 
corresponding cell of the table, the color of the pixel is determined as 
black (corresponding to a value of 1). Conversely, if the tone level of a 
pixel is smaller than the value set at the corresponding cell of the 
table, the color of the pixel is determined as white (corresponding to a 
value of 0). The same halftone-dot pattern table is repeatedly used to be 
compared with image data of pixels of the same number as of cells thereof. 
FIG. 23 illustrates the relation between each pixel of the input image and 
a corresponding cell of the halftone-dot pattern table diagramatically. As 
is apparent from this figure, each pixel of the input image is in 
one-to-one correspondence relation with a cell of the halftone-dot pattern 
table. 
The binarization circuit 115 has 33 kinds of halftone-dot pattern tables, 
the size of which ranges from 4.times.4 to 36.times.36. Further, a desired 
one of the tables can thus be used according to an indication from the 
CPUs 101 and 110 based on a direction input from the keyboard 8 by an 
operator. 
5. DISPLAYING OF DENSITY 
An operation of displaying density data is controlled by the CPUs 101 and 
110 in accordance with the flowcharts of FIGS. 24 and 25. First, if a 
position in an image displayed on the screen of the CRT 5 is indicated by 
using the mouse 9 in step S131, the CPU 101 calculates an address in the 
page memory 3 (corresponding to coordinates in the read draft picture) 
from the indicated position or coordinates on the screen of the CRT 5 in 
step S132. Then, in step 133, the CPU 101 issues the CPU 110 of the image 
input unit 106 with singals representing the calculated coordinates and a 
command requesting the density level corresponding to the calculated 
coordinates. Thereafter, if the CPU 101 receives image density information 
from the image input unit 106 in step S134, the density represented by the 
received information is displayed in step S135 in the vicinity of a 
position, which is indicated by a cursor, on the screen of the CRT 5 as 
illustrated in FIG. 12. 
On the other hand, if the CPU 110 accepts information representing the 
calculated coordinates and the command requesting the corresponding 
density from the CPU 101 in step S141, the CPU 110 computes an address of 
the memory 120, at which the sampled corresponding image data are stored, 
from the coordinates received from the CPU 101 in step S142 and 
subsequently, in step S143, the CPU 110 outputs the density data stored at 
the address to the CPU 101. 
6. THE RELATION BETWEEN THE SIZE OF THE HALFTONE-DOT PATTERN TABLE AND A 
SAMPLING PERIOD 
As described above, generally, in case where a halftone image is 
represented by a binary output device. halftone is approximately 
represented by effecting a halftone-dot generation processing similarly as 
in case of this embodiment. Namely, halftone is approximately represented 
by regulating a rate of an area of black pixels to a unit block or area 
composed of a plurality of pixels. Thus, the density of a position in an 
image is represented by using a block of a predetermined size. Therefore, 
in case where the density at a position in a halftone-dot image is 
obtained by indicating the position in the halftone-dot image and then 
reading the multi-level density data stored in a memory, it is preferable 
to store at least a multi-level data correspondingly to a unit block. 
That such a relation holds good is necessary and sufficient for obtaining 
information on the density at a desired position in a displayed 
halftone-dot image, watching the halftone-dot image, if the number of 
blocks converted by the binarization circuit 15 into dots is equal to that 
pixels corresponding to the sampled image data in case where change in 
density represented by draft image data is gentle as illustrated in FIG. 
26. However, in a portion, in which change in density is radical as 
illustrated in FIG. 27, such as a line drawing or a contour of an image, 
there occurs a bias to black or white pixels in a unit block converted 
into a halftone dot. Thus, if only the density data of a is stored for 
such a unit block converted into a halftone dot, information on the 
density, which is entirely different from an actual or true appearance of 
such a unit block of may be obtained in case that a displayed image is 
observed and a position in the displayed image is indicated. For example, 
in case of the picture of FIG. 27, if the multi-level data, which 
indicates the density or tone-level of 230, of the pixel (a, 1) is sampled 
for a whitish unit block, only irrelevant density information is obtained 
then a position (d, 1) is indicated. 
In view of this problem and a limit to a memory capacity, it is necessary 
for obtaining relevant density information to set a sampling period as 
equal to the minimum size of the halftone-dot pattern table similary as in 
case of the second embodiment and sample a plurality of multi-level data 
correspondingly to a unit block to be converted into a halftone dot. 
As stated above, in case of the second embodiment, a read multi-lefvel 
image data is converted to binary image data and the binary image data is 
stored in the image memory. 
Moreover, the read image data itself is sampled and the sampled data is 
stored in the memory. Thus, the necessary memory capacity can be reduced 
or saved. Further, the density at a position in the read image can easily 
be known and provided as reference data for setting a tone curve for a 
tone correction. 
Furthermore, in case of the second embodiment, the number of the pixels, 
the corresponding density data of which should be sampled, is set as equal 
to or more than that of blocks converted into halftone dots. Thus, the 
multi-level data can be sampled by using only the minimum memory capacity 
required for obtaining image density information. In case of the second 
embodiment, the memory capacity required for obtaining image density 
information is 1/(4.times.4)=1/16 times that required in case of storing 
all of the multi-level data of the entire draft picture. 
Incidentally, the sampled multi-level image data is stored in the first 
embodiment. Thus, a roughly estimated distribution of densities of a draft 
picture can be obtained and also used as effective reference data for 
setting a tone curve for a tone correction. 
Additionally, in case of the second embodiment, a read multi-level image 
data is converted to binary image data and the binary image data is stored 
in the image memory. Moreover, the read image data itself is sampled at a 
sampling rate larger than a rate of the number of halftone dots to the 
number of all of the pixels, and the sampled data is stored in the memory. 
Thus, the necessary memory capacity can be reduced or saved. Further, the 
density at a position in the read image can easily be known and provided 
as reference data for setting a tone curve for a tone correction. 
III. THIRD EMBODIMENT 
FIG. 28 is a schematic block diagram for illustrating the configuration of 
a third embodiment of (namely, a further image editing system embodying) 
the present invention. Reference numeral 201 designates a CPU for 
controlling the system and processing data; and 206 an image input unit. 
As is apparent from a comparison between FIGS. 1 and 28, the configuration 
of the third embodiment is similar to that of the first embodiment except 
the CPU 201 and the image input unit 206. 
FIG. 29 is a schematic block diagram for illustrating the configuration of 
the image input unit 206 of FIG. 28. Reference numeral 210 denotes a CPU 
for controlling the image input unit 206; 215 a binarization circuit for 
converting the 8-bit digital signal into a binary data signal representing 
0 or 1 by performing a halftone-dot generation processing on the density 
data represented by the 8-bit digital signal, which is corrected by the 
tone correction circuit 14; 216 a counter for repeatedly performing a 
process of counting a preset value "36" and outputting a positive signal 
of a period corresponding to a pixel sampled when the counting of the 
value is completed; 220 a readable/writable memory for storing the image 
data selected by the gate circuit 17 and temporarily held in the buffer 
18; and 119 a transfer circuit for transferring the image data of 1 line 
temporarily stored in the buffer 18 to the memory 120 in response to a 
control signal output from the CPU 210. 
Hereinafter, an image processing performed by the image editing system 
(namely, the third embodiment) having the above described configuration 
will be described in detail. 
1. READING OF IMAGE DATA 
First, as shown in the flowchart of FIG. 30, the CPU 201 of the system 
sends a signal representing conditions of a reading of image data for 
setting a tone curve, as well as a reading-operation starting command, to 
the CPU 210 of the image input unit 206 in step S201. Then, the image 
input unit 206 reads image data from an image and transfers the read image 
data to the image memory 3 sequentially. Thereafter, if the CPU 201 
accepts a reading-operation terminating signal issued by the image input 
unit 206 in step S202, the CPU 201 expands or reduces the image data 
stored in the page memory 3 in accordance with the resolution of the CRT 5 
in step S203. Subsequently, the expanded or reduced image data is written 
to the display memory 4 in step S204. The image data written to the 
display memory 4 is displayed in the CRT 5. 
On the other hand, if the CPU 210 of the image input unit 206 receives a 
reading-operation starting command from the CPU 201 in step S211 as 
illustrated in FIG. 18, the CPU 210 sets a tone curve in the tone 
correction circuit 14 in step S212. Further, the CPU 210 starts an 
operation of reading a draft image in step S213. Then, the CPU 210 issues 
a sampling-operaton starting signal to the gate circuit 17. When starting 
the operaton of reading the dragt picture, the draft picture is irradiated 
and thereafter light reflected by the draft picture focuses into an image 
on the CCD 11. This light is converted by the CCD 11 into an electric 
signal. Subsequently, the electric signal is further converted by the A/D 
converter 12 into an 8-bit digital signal. Thereafter, the shading 
correction circuit 13 performs a shading correction on the 8-bit digtal 
signal. Further, the 8-bit image data obtained as a result of the shading 
correction is input to both of the tone correction circuit 14 and the gate 
circuit 17. 
As is shown in FIG. 32, the counter 216 outputs a signal C to the gate 
circuit 17 each time when counting "4" preset by the CPU 210, in 
synchronization with an outputting of the image data from the shading 
correction circuit 13 (see a fundamental clock A and a digital image 
signal B). The gate circuit 17 is enabled in response to the signal output 
from the counter 216 and samples the image data output from the shading 
correction circuit 13 at a sampling rate and writes an output signal D 
representing the sampled data to the memory 220 through the buffer 18 and 
the transfer circuit 219. At that time, the CPU 210 counts the pixels of 
the image represented by the image data input to the gate circuit 17 in 
step S215. If the CPU 210 judges in step S216 that the image data of 1 
line is input therto, and further judges in step S217 that not all of the 
image data has been processed, the CPU 210 instructs the gate circuit 17 
to suspend the sampling. In response to such sn instruction from the CPU 
210, the gate circuit 17 suspends the sampling of the image data to be 
written to the memory 220. 
Even when the gate circuit 17 suspends the sampling of the image data, the 
CPU 210 counts the image data of each line by counting the pixels of the 
image data input to the circuit 17 in step S219 similarly as in steps S215 
and S216. Subsequently, if the CPU 210 judges in step S220 that not all of 
the image data have not been processed, and further judges in step S221 
that the processing of the image data of a predetermined number of lines 
stored in the counter 206 has been finished, the control procedure returns 
to step S214, whereupon the CPU 210 issues a sampling-operation starting 
signal to the gate circuit 17. Thus, the read image is converted into the 
binary image, which is displayed on the screen of the CRT 5, and the read 
multi-level image data is sampled at a predetermined rate and the sampled 
image data is stored in the memory 220. 
2. TONE CORRECTION 
In the tone correction circuit 14, a RAM having a storage area of 256 bytes 
as illustrated in FIG. 33 is provided. In the storage area of this RAM, 
tone levels (namely, density levels) represented by output image data, 
which would be obtained as a result of a tone correction, are set by the 
CPU 210 at locations thereof, the addresses of which respectively have 
values equal to tone levels represented by input image data, at the time 
of initialization of the RAM prior to the reading of the input image. 
Namely, predetermined relation between tone levels of output image data 
and tone levels of input image data (namely, the conversion relation) is 
initially established in the storage area of the RAM by the CPU 210. For 
instance, in case where the conversion relation represented by a tone 
curve of FIG. 34 is established therein, image data indicating a tone 
level of 110, which are stored at locations respectively having addresses 
of 100 and 101 of the RAM of FIG. 33, are output therefrom correspondingly 
to tone levels of 100 and 101 represented by input image data. Further, in 
such a case, image data respectively indicating tone levels of 190 and 
192, which are stored at locations respectively having addresses of 200 
and 201 of the RAM of FIG. 33, are output therefrom respectively 
corresponding to tone levels of 200 and 201 represented by the input image 
data. As described above, a tone correction is performed according to the 
established tone curve by fetching data stored at locations of the storage 
area of the RAM respectively corresponding to addresses, which are 
indicated by tone levels represented by the input image data, and then 
outputting the fetched data as the output image data. 
3. SETTING OF TONE CURVE 
In the magnetic disk 2, a storage area having the same structure as the RAM 
of the tone correction circuit 14 does as illustrated in FIG. 33 is 
provided. Further, data representing an initial conversion relation 
indicated by the initial (tentative) tone curve is stored for displaying 
the tone curve in this storage area of the magnetic disk 2. The CPU 201 
reads density data (namely, initial value data), which is stored in the 
storage area of the magnetic disk 2 according to the relation indicated by 
the initial tone curve, therefrom. Then the CPU 101 generates data 
(hereunder sometimes referred to as display data) representing a graph of 
the initial tone curve, of which the horizontal axis denotes the density 
levels (namely, addresses in the storage area of the magnetic disk 2) 
represented by input image data and the vertical axis designates the those 
represented by output image data (stored at locations having the addresses 
in the storage area of the magnetic disk 2), according to the initial 
value data. Further, the generated display data is stored in the display 
memory 4. Subsequently, the initial tone curve for a tone correction as 
illustrated in FIG. 34 is displayed on the screen of the CRT 5 according 
to the display data. This tone curve is transformed into a desired curve 
by using the mouse 9 and executing a program employing known graphic 
processing techniques. Thereafter, the CPU 201 sends coordinate data 
representing coordinates of the modified tone curve to the CPU 210 of the 
image input unit 206. At that time, the coordinate data sent from the CPU 
201 is set in the RAM of the tone correction circuit 14 by the CPU 210 
4. GENERATION OF BINARY IMAGE (OR HALFTONE-DOT IMAGE) 
The binarization circuit 15 converts the multi-level image data corrected 
by the tone correcton circuit 14 into binary image data (or halftone-dot 
image data). In this circuit, the density (namely, the tone level) 
represented by the density data of each pixel output from the tone 
correction circuit 14 is compared with the value set at a corresponding 
cell of the halftone-dot pattern table of FIG. 35 established therein. If 
the tone level of a pixel is larger than the value set at the 
corresponding cell of the table, the color of the pixel is determined as 
black (corresponding to a value of 1). Conversely, if the tone level of a 
pixel is smaller than the value set at the corresponding cell of the 
table, the color of the pixel is determined as white (corresponding to a 
value of 0). The same halftone-dot pattern table is repeatedly used to be 
compared with image data of pixels of the same number as of cells thereof. 
FIG. 36 illustrates the relation between each pixel of the input image and 
a corresponding cell of the halftone-dot pattern table diagramatically. As 
is apparent from this figure, each pixel of the input image is in 
one-to-one correspondence relation with a cell of the halftone-dot pattern 
table. 
The binarization circuit 115 has 33 kinds of halftone-dot pattern tables, 
the size of which ranges from 4.times.4 to 36.times.36. Further, a desired 
one of the tables can thus be used according to an indication from the 
CPUs 201 and 210 based on a direction input from the keyboard 8 by an 
operator. 
5. DISPLAYING OF DENSITY 
An operation of displaying density data is controlled by the CPUs 201 and 
210 in accordance with the flowcharts of FIGS. 37 and 38. First, if a 
position in an image displayed on the screen of the CRT 5 is indicated by 
using the mouse 9 in step S231, the CPU 201 calculates an address in the 
page memory 3 (corresponding to coordinates in the read draft picture) 
from the indicated position or coordinates on the screen of the CRT 5 in 
step S232. Then, in step 233, the CPU 201 issues the CPU 210 of the image 
input unit 106 with singals representing the calculated coordinates and a 
command requesting the density level corresponding to the calculated 
coordinates. Thereafter, if the CPU 201 receives image density information 
from the image input unit 206 in step S234, the density represented by the 
received information is displayed in step S235 in the vicinity of a 
position, which is indicated by a cursor, on the screen of the CRT 5 as 
illustrated in FIG. 12. 
On the other hand, if the CPU 210 accepts information representing the 
calculated coordinates and the command requesting the corresponding 
density from the CPU 201 in step S241, the CPU 210 computes an address of 
the memory 220, at which the sampled corresponding image data are stored, 
from the coordinates received from the CPU 201 in step S242 and 
subsequently, in step S243, the CPU 210 outputs the density data stored at 
the address to the CPU 201. 
6. THE RELATION BETWEEN THE SIZE OF THE HALFTONE-DOT PATTERN TABLE AND A 
SAMPLING PERIOD 
As described above, generally, in case where a halftone image is 
represented by a binary output device, halftone is approximately 
represented by effecting a halftone-dot generation processing similarly as 
in case of this embodiment. Namely, halftone is approximately represented 
by regulating a rate of an area of black pixels to a unit block or area 
composed of a plurality of pixels, Thus, the density of a position in an 
image is represented by using a block of a predetermined size. Therefore, 
in case where the density at a position in a halftone-dot image is 
obtained by indicating the position in the halftone-dot image and then 
reading the multi-level density data stored in a memory, it is of no 
significance to store plural multi-level data correspondingly to a unit 
block. 
The data output to the CRT 5 and the printer 7 is halftone-dot image data. 
It is, accordingly, sufficient for knowing the density at a desired 
position in a displayed image to set the number of pixels, the 
corresponding density data of which should be sampled, as equal to or less 
than the maximum size of the halftone-dot pattern table. 
As stated above, in case of the third embodiment, a read multi-level image 
data is converted to binary image data and the binary image data is stored 
in the image memory. Moreover, the multi-level image data itself is 
sampled, and the sampled data is stored in the memory. Thus, the necessary 
memory capacity can be reduced or saved. Further, the density at a 
position in the read image can easily be known and provided as reference 
data for setting a tone curve for a tone correction. 
Furthermore, in case of the second embodiment, the number of the pixels, 
the corresponding density data of which should be sampled, is set as equal 
to or less than that of blocks to be converted into halftone dots. Thus, 
the multi-level data can be sampled by using only the minimum memory 
capacity required for obtaining image density information. In case of the 
third embodiment, the memory capacity required for obtaining image density 
information is 1/(38.times.38)=1/1296 times that required in case of 
storing all of the multi-level data of the entire draft picture. 
Incidentally, the sampled multi-level image data is stored in the first 
embodiment. Thus, a roughly estimated distribution of densities of a draft 
picture can be obtained and also used as effective reference data for 
setting a tone curve for a tone correction. 
Additionally, in case of the third embodiment, a read multi-level image 
data is converted to binary image data and the binary image data is stored 
in the image memory. 
Moreover, the multi-level image data itself is sampled at a sampling rate 
larger than a rate of the number of halftone dots to the number of all of 
the pixels, and the sampled data is stored in the memory. Thus, the 
necessary memory capacity can be reduced or saved. Further, the density at 
a position in the read image can easily be known and provided as reference 
data for setting a tone curve for a tone correction. 
While preferred embodiments of the present invention have been described 
above, it is to be understood that the present invention is not limited 
thereto and that other modifications will be apparent to those skilled in 
the art without departing from the spirit of the invention. The scope of 
the present invention, therefore, is to be determined solely by the 
appended claims.