Color copying machine provided with color correcting circuit

A color copying machine has a color correcting circuit. The color correcting circuit includes a device for generating reference pattern data on each color, a device for printing the reference pattern data generated by the generating device, a device for reading a printed result of the reference pattern data printed by the printing device, a device for measuring a color reproduction error based on the reference pattern data generated by the generating device and the printed result of the reference pattern data read by the reading device, and a device for calculating a color correction coefficient of each color based on the color reproduction error measured by the measuring device.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a color copying machine for exactly 
copying a color material on a subject paper, and more particularly to the 
color copying machine which provides a color correcting circuit. 
2. Description of the Related Art 
In recent days, a great remark has been placed on a color processing 
technique which may apply to exact color copying of a subject material or 
a display image. A color copying machine provided with such a color 
processing technique known by the inventors of the present application is 
basically arranged to a color correcting unit, an image reader, a printer, 
and a memory. In addition, some controllers for various controls may be 
included in the known copying machine. However, the description herein 
does not concern with such controllers, because they have no substantial 
concern with the present invention. 
In operation, the image reader serves to read a material to be copied. The 
reader may be arranged on the same principle as the commercially available 
color scanner. The read data about the material is corrected by the color 
correcting unit and is printed as an exact color copy by the printer. The 
printer is arranged on the same principle as the commercially available 
color printer. 
In actual, however, the known color copying machine does not enable to 
exactly copy any kind of color material. This is because though the 
principle of subtractive mixture of color stimuli is applied to the color 
development of color printing, the known copying machine does not often 
provide a capability of establishing an additive law and a multiplicative 
law which are the fundamental principles of the subtractive color mixture. 
To overcome this shortcoming, the color copying machine performs the color 
correction operation with the color correcting unit. 
As a method commonly used for the color correction, a 3.times.3 matrix 
operation represented by the following expression (1) is performed with 
respect to an input signal (r, g, b) each item standing for red, green and 
blue. 
##EQU1## 
wherein (R, G, B) represents a corrected signal and all to a.sub.33 denote 
coefficients for color correction. Those coefficients are set when 
designing or shipping the products and are constantly stored in the 
memory. 
The color correcting unit is reading the correction coefficients as 
accessing the memory so that the data is output to the printer as 
sequentially performing the operations of the expression 1. The 
color-corrected output can be obtained from the printer. 
Next, the principle of the color correction based on this method will be 
briefly described later. The subtractive mixture of color stimuli done in 
the color copying machine is arranged on the assumption that the used inks 
(cyan, magenta, yellow) have the characteristics of independently 
absorbing the red, the green and the blue. 
However, the actually used inks have their characteristics mutually 
effecting on red, green and blue. To copy each correct color on the 
principle of the subtractive color mixture, it is necessary to define a 
printing density of one ink as relating it with two other color densities. 
The expression 1 indicates such a mutual influencing relation. By 
performing the color correction by means of the expression 1 having the 
properly-defined coefficients substituted therefore, it is possible to 
eliminate the effect of one color ink on the other colors. This results in 
allowing the printed output to approximate to the printed colors used in 
the ideal inks. 
The expression 1 indicates the method for color correction based on the 
3.times.3 matrix, while the color correction may be made possible on a 
matrix containing high degree items as shown in the expression 2. 
##EQU2## 
The color correction based on the expression 2 may offer higher accuracy 
than that based on the expression 1, which has been described in Joji 
Tajima, "Color Masking (II)", Proceedings of Image Electronics, Vol. 18, 
No. 2, P. 44-48. 
In the actual color correction, the expression 1 or 2 is implemented by 
hardware or software. For the implementation, the proper digital signal 
processor (DSP) or CPU having a high capability of numerical operations is 
often used. Or, another CPU functioning as controls may be used. 
The coefficients indicated in the expressions 1 and 2 has to be set as 
considering change in a wide range such as initial design of the products, 
adjustment in shipping and maintenance for aging. For setting the 
coefficients in the former two cases, it is possible to take a 
considerably long time. But, at the maintenance stage, it is not possible 
to take a long time to terminate the work. In any of those cases, it goes 
without saying that the variation of the set values has to be lowered to a 
minimum. That is, the setting of those coefficients indicated in the 
expression 1 and 2 is required to be implemented, because they define the 
color reproduction provided by the color machine. 
For setting those coefficients, the inventors of the present application 
know that the repetition of observational evaluations or the least squares 
method has been used. 
If the repetition of observational evaluations is used for setting those 
coefficients, it may be advantageous in that the color reproduction error 
for human visual perception may be lowered to a maximum. To properly set 
the coefficients with this method, it needs to consume a quite long time. 
In addition, this setting method entails the variation resulting from the 
difference of human perceptions among inspectors, It means that this 
setting method cannot make sure of a constant color reproduction accuracy 
when changing each product model or updating each lot. 
As such, this setting method has difficulty in obtaining satisfactory 
results at the initial design, the adjustment in shipping and the 
maintenance stage. 
In the case of using the least squares for setting the coefficients, in a 
sense, the set coefficients are made non-variable and optimized. 
Now, the method of setting the coefficients on the least squares will be 
described. Concretely, the multiple regression analysis, which is one kind 
of the least squares of multiple variables, is employed in this 
description. 
The multiple regression analysis consists of numerical calculations which 
serve to define a coefficient a.sub.i for describing a depending variable 
Y according to the definition of the expression 3 by using a plurality of 
independent variables X.sub.1 to X.sub.n. 
EQU Y=a.sub.1 X.sub.1 +a.sub.2 X.sub.2 +. . . +a.sub.n X.sub.n +C (Expression 3 
) 
wherein a.sub.i denotes a coefficient against an i-th independent 
coefficient X.sub.i (i=1 to n), C denotes a constant, and n denotes a 
number of independent variables. 
Assuming that the independent variables X.sub.1 to X.sub.n denote r, g and 
b indicated in the expression 1 and Y denotes R therein, by using the 
multiple regression analysis, the coefficients a.sub.11 to a.sub.13 may be 
obtained. 
The procedure for obtaining the coefficients will be performed as follows: 
(Step 1) Measure a color sample with a colorimeter and read it from an 
image input unit. 
(Step 2) Print the color sample data and measure the printed result with 
the colorimeter. 
(Step 3) Collect a lot of pieces of measured data and perform the multiple 
regression analysis by using the measured data of the original color 
sample and the measured data of the printed result. 
(Step 4) Obtain those coefficients as changing Y to G and B. 
It is well known that the multiple regression analysis has been established 
as a numerical calculation program used in a general computer. As such, if 
several pieces of data are allowed to be collected, with this method, the 
use of this method is advantageous in that the coefficients can be defined 
at high speed and the defined coefficients are made non-variable. 
However, it has been traditionally necessary to measure a lot of color 
samples each color at one time. This results in disadvantageously 
consuming a quite long time for measuring those color samples. 
As noted above, the color correction coefficients are set in some stages 
such as the standard setting at the initial design stage of the products 
and the adjustment for the products in shipping. The foregoing known 
methods provides no capability of setting such color correction 
coefficients as achieving a high color reproduction performance for a 
quite short time. Hence, heretofore, the setting of the color correction 
coefficients is not necessarily accurate. 
Further, to correct for the aging of the product performance after 
shipping, it is preferable to reset the color correction coefficients at 
the maintenance stage of the product. The color correction coefficients 
cannot be newly rewritten in the light of the structure of the used 
memory. No disclosure has been proposed of the method for setting less 
variable and highly reliable coefficients for a short time. As such, in 
actual, the resetting of the coefficients has been made impossible. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a color copying machine 
which provides a color correcting circuit for setting less variable and 
highly reliable color correction coefficients for a short time and with 
ease. 
In carrying out the object, according to a first aspect of the invention, a 
color copying machine includes a color correcting circuit, the color 
correcting circuit having: means for generating reference pattern data 
about each color; means for printing the reference pattern data generated 
by the generating means; means for reading a printed output of the 
reference pattern data printed by the printing means; means for measuring 
a color reproduction error by comparing the reference pattern data 
generated by the generating means with the printed result of the reference 
pattern data read by the reading means; and means for calculating a color 
correction coefficient of each color based on the color reproduction error 
measured by the measuring means. 
According to a second aspect of the invention, a color copying machine 
includes a color correcting circuit, the color correcting circuit having: 
means for generating reference pattern data about each color; means for 
printing the reference pattern data generated by the generating means; 
means for reading the printed result of the reference pattern data printed 
by the printing means; means for measuring a color reproduction error by 
comparing the reference pattern data generated by the reference pattern 
data generating means with the printed result of the reference pattern 
data read by the reading means; means for converting the color 
reproduction error measured by the color reproduction error measuring 
means into a Lab color difference; and means for calculating a color 
correction coefficient about each color based on the output of the 
converting means. 
In operation, the means for generating a reference pattern data serves to 
generate the reference data for measuring a color reproduction distortion. 
The printing means serves to print the reference pattern data and add the 
color reproduction distortion when the data is printed out. The means for 
reading the printed reference pattern serves to read the printed reference 
pattern and add the color reproduction distortion obtained in reading the 
reference pattern. The comparing means serves to compare the generated 
reference pattern data with the reference pattern for measuring the color 
reproduction distortion taken between the printing means and the reading 
means. The reference pattern is arranged to contain as many colors in the 
color space as possible. Those means function as measuring the 
reproduction distortions about all the generated colors at a time. This 
results in allowing the approximate coefficients to be set for a short 
time in all the stages such as the initial design of the product, the 
adjustment in shipping, and the maintenance. 
As mentioned above, the present invention employs the reference pattern 
where a lot of colors are properly arranged. Hence, it may provide a 
capability of accurately measuring the color reproduction distortion for 
each used color. If an image reader is used as the input means, in 
particular, the measurement needs only quite a short time. Further, based 
on the measured result, the coefficients of the color correcting circuit 
are allowed to be set by using the least squares. This results in making 
it possible to set non-variable coefficients at high speed. 
In deciding the coefficients of the color correcting circuit, the color 
reproduction errors measured with respect to all the colors are converted 
to Lab color difference values for the purpose of evaluating those errors 
in proportional to the visual values. This makes it possible to set the 
coefficients as visually suitable and non-variable values at high speed. 
Those result in improving the reliability of the set values in the stages 
such as initial designing of the product and adjustment in shipping and 
reducing the adjusting time at each stage of each stage, thereby enhancing 
the performance of the product and lowering the manufacturing cost. 
Further, the coefficients at the maintenance stage for correcting the 
aging are allowed to be reset. This makes it possible to constantly keep 
each product at high performance and low cost. 
In carrying out the object, according to a third aspect of the invention, a 
color copying machine having at least an image reading unit and a printing 
unit, includes: means for generating reference pattern data about each 
color; means for converting the reference pattern data generated by the 
generating means and the data given by reading a printed output of the 
reference pattern data by the reading unit, the printed output being given 
by the printing unit, into color values based on perception 
characteristics; multiple regression analyzing means for calculating a 
color correction coefficient about each color on the basis of the data 
converted by the converting means; rewritable memory means for storing 
each color correction coefficient calculated by the multiple regression 
analyzing means; and means for performing a color correction operation 
with respect to the color correction coefficients stored in the memory 
means. 
According to a fourth aspect of the invention, a color copying machine 
having at least an image reading unit and a printing unit, includes: means 
for generating reference pattern data about each color; multiple 
regression analyzing means for calculating a color correction coefficient 
about each color by comparing the reference pattern data generated by the 
generating means with the data given by reading a printed output of the 
printing unit by the image reading unit, the printed output being given by 
the printing unit; rewritable memory means for storing the color 
correction coefficients calculated by the multiple regression analyzing 
means; and means for performing a color correction operation with respect 
to the color correction coefficients stored in the memory means. 
According to a fifth aspect of the invention, a color copying machine 
having at least an image reading unit and a printing unit, includes: a 
signal I/O unit for transferring data between an external device and the 
color copying machine itself; the printing unit or printing data received 
from the external device through the signal I/O unit.; the reading unit 
for sending the read image data to the external device through the signal 
I/O unit; a rewritable memory for storing color correction coefficients 
received from the external device through the signal I/O unit; and a color 
correction unit for performing a color correction operation with respect 
to the color correction coefficients stored in the memory. 
The reference pattern data generating means serves to generate the pattern 
used as a reference on which the color reproduction error is measured. The 
color value converting means has a basic function of converting the 
reference pattern data generated in the generator and the reference 
pattern data obtained by reading the printed result with the image reader 
provided in the copying machine into the color values based on the human 
perception. The color value converting means serves to convert the 
reference pattern data generated in the data generating means and the data 
having a color reproduction error between the printing means and the image 
reading means into the corresponding color values based on the human 
perception. 
The multiple regression analyzing unit serves to derive a regression 
coefficient between two color values converted on the perception 
characteristics for a quite short time. 
The reference pattern is configured to have a possible maximum number of 
colors in the color space. By one operation, the data about a lot of 
colors can be collected. The regression coefficients derived on this data 
represent the color reproduction distortions for a lot of colors on the 
average. This makes it possible to derive the most approximate color 
correction coefficients by minimum work and for a short time at all the 
stages such as initial design of the product, adjustment in shipping and 
maintenance of the product. 
Further, the rewritable memory means has a function storing the color 
correction coefficients derived in the multiple regression analyzing 
means. As such, the memory holds the derived color correction 
coefficients. The color correcting means serves to perform the color 
correction operation as referring to the color correction coefficients 
held in the memory unit. 
The advantages provided by the memory means and the multiple regression 
analyzing means make it possible to keep the most approximate color 
correction if the aging takes place in the shipped product. This results 
in constantly maintaining the most excellent, that is, least variable 
color reproduction performance. 
The signal I/O unit receives the reference pattern data from the external 
unit and sends it to the printing means for printing it on paper. The 
reading means serves to read the printing data and send the read data to 
the external unit through the signal I/O unit. 
The color correction coefficients derived on the read data are sent from 
the external unit to the signal I/O means. The received data is stored in 
the rewritable memory means. The color correction unit serves to perform 
the color correction by using the color correction coefficients stored in 
the memory. 
As mentioned above, the color correction coefficients are derived in the 
external unit containing the reference pattern data generating means, the 
color value converter, the multiple regression analyzing means, and the 
signal I/O means. The color copying machine receives the result and uses 
it for the color correction. This results in making the construction of 
each color copying machine simpler without having to impair the foregoing 
advantages. 
Further objects and advantages of the present invention will be apparent 
from the following description of the preferred embodiments of the 
invention as illustrated in the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
First Embodiment 
FIG. 1 is a block diagram showing a color correcting circuit according to 
the first embodiment of the invention, FIGS. 2a to 2c are graphs showing 
ideal absorption characteristics of ink, in which the axis of abscissa 
denotes a wavelength and the axis of ordinates denotes a reflective 
factor, FIGS. 3a to 3c are graphs showing actual absorption 
characteristics of ink, and FIG. 4 is a flowchart showing a method for 
defining color correction coefficients in the color correcting circuit. 
As above mentioned, the subtractive mixture of color stimulidone in the 
color copying machine is arranged on the assumption that the used inks 
(cyan, magenta, yellow) have the characteristics of independently 
absorbing the red, the green and the blue as shown in FIGS. 2a-2c, and the 
actually used inks have their characteristics mutually effecting on red, 
green and blue as shown in FIGS. 3a-3c. 
In this method, the color reproduction distortions are measured about the 
possible maximum number of colors in both of the image output by a color 
printer 3 and the image read by a color scanner 1. Then, the color 
correction coefficients are derived so that the measured distortions are 
reversely corrected. 
At first, for measuring the color reproduction distortions, a pattern 
generator 21 serves to generate the reference pattern containing a 
possible maximum number of colors in the color space. The use of such 
reference pattern makes it possible to measure the color reproduction 
distortions for all the possible colors by one simple work. For example, 
assuming that the each color data item for m, n and l colors obtained by 
dividing the rgb signal into an m stage, an n stage and an l stage is 
disposed on the plane to correspond to one pixel, or two or more pixels of 
the image, the distortions for those colors are allowed to be measured. 
One example of such a reference pattern is shown in FIG. 5. This reference 
pattern is configured as an image consisting of 512.times.512 pixels, that 
is, containing 260,000 (64.sup.3) colors. The arrangement of the reference 
pattern meeting such a condition may be considered in various ways. 
The reference pattern generated in the pattern generator 21 is output on 
paper through the effect of the color printer 3. The output reference 
pattern entails the color reproduction distortions of the color printer 3. 
The output reference pattern is read by the color scanner 1. The read 
pattern also entails the color reproduction distortions. It means that the 
reference pattern data corresponds to the generated reference pattern data 
to which the reproduction distortions of the color printer 3 and the color 
scanner 1 are added. 
The data comparator 24 compares the read reference pattern data with the 
originally generated reference pattern data so as to derive a color 
reproduction error between the color printer 3 and the color scanner 1. 
The derived color reproduction error is converted to a color reproduction 
error Lab value in a Lab converter 23. Normally, human perception for a 
color difference is variable depending on each color area. Hence, the 
coefficients derived on the color reproduction errors in the color 
correction circuit may be often variable on the variety of human 
perception. To overcome the shortcoming due to the variety of human 
perception, it is necessary to produce a color space where the perceptive 
distance between each two color areas is kept constant. This color space 
is referred to as a Lab colorimetric system (herein, `Lab` denotes an 
expression 4.) The color difference in the colorimetric system is referred 
to as a Lab color difference. 
EQU CIE (1976) L*a*b* (Expression 4) 
By converting the color reproduction error into this Lab color difference, 
it is possible to derive the color reproduction coefficients. 
This conversion can be performed on the following expression. 
##EQU3## 
A numeral 25 (see FIG. 1) denotes a color correction coefficient deriving 
unit 25, which serves to derive coefficients used in the color correction 
circuit so as to keep the color reproduction error Lab value to a minimum 
and set the color correction coefficients. To derive the minimum value, it 
is possible to used the least squares or a neural network which are not 
descriptive herein, because they have been well known. 
As described above, the coefficients of the color correction circuit can be 
obtained for a short time and with ease. 
In doing normal printing, the data read from the color scanner 1 is 
corrected in the color correcting circuit 21 by using the color correction 
coefficients. The corrected data is printed on paper through the effect of 
the color printer 3. 
Second Embodiment 
FIG. 6 is a block diagram showing a color correcting circuit according to a 
second embodiment of the invention. 
The color correcting circuit is arranged to have a color scanner 1, a color 
printer 3, and a computer. The computer includes a color correcting unit 
51, a reference pattern generator 56 for generating the reference pattern 
data, a data comparator 55 for comparing the reference pattern data read 
by the color scanner 1 with the originally generated reference pattern 
data, a color reproduction error deriving unit 54 for deriving a color 
reproduction error based on the compared data, a Lab converter 53 for 
converting the derived color reproduction error into a color reproduction 
Lab value, and a color correction coefficient unit 52 for deriving and 
setting the final color correction coefficients from the derived Lab 
values. 
The method for defining the color correction according to the second 
embodiment will be described in detail as referring to FIG. 4. 
S1: A CPU 5 controls the reference pattern data generator 56 to generate 
the reference pattern data and store it in a first frame buffer 57. 
S2: The reference pattern data is read from the first frame buffer 57 and 
is printed out by the color printer 3. 
S3: The printed reference pattern is read by the color scanner 1 and is 
stored in a second frame buffer 58. The data stored in the second frame 
buffer 58 entails the color reproduction errors caused in both the color 
printer 3 and the color scanner 1. 
S4: The data comparator 55 serves to compare the originally generated 
reference pattern data shored in the first frame buffer 57 with the 
reference pattern data obtained at the step S3 and stored in the second 
frame buffer 58 so as to derive the color reproduction error based on the 
compared result in the color reproduction error deriving unit 54. 
S5: The color reproduction error obtained at the step S4 is converted into 
the color reproduction error Lab value according to the expressions 4 and 
5. 
S6: The unit 52 serves to derive a maximum coefficient from the Lab value 
obtained at the step S5 by means of the least squares or the neural 
network and store the derived coefficient in a coefficient storage unit 
59. 
As noted above, the coefficients of the color correction circuit can be 
obtained for a short time and with ease. In doing normal printing, the 
color correcting unit 51 serves to correct the data read by the color 
scanner 1 by using the coefficients obtained by the foregoing method. 
Then, the color printer 3 serves to print out the corrected data. 
Unlike one integral device as shown in FIG. 6, as shown in FIG. 7, an 
individual color scanner 1, an individual color printer 3, and an 
individual computer 4 may be combined to configure another embodiment of 
this invention. 
Third Embodiment 
FIG. 8 is a functional block diagram showing a color copying machine 
according to a third embodiment of the invention. 
As compared to the known color copying machine as described above, a 
reference pattern data generator 101, a color value converter 102, and a 
multiple regression analyzer 103 are additionally provided. Moreover, a 
memory 104 is a rewritable type. The description will be directed to how 
the shortcomings described above are overcome by using these additional 
features. 
At first, how the color correction coefficients are derived will be 
described. FIG. 9 is a flowchart showing the method for defining the color 
correction coefficients. In general, the method according to this 
invention takes the steps of grasping a possible maximum number of 
original colors in a color space and the colors processed through the 
printer 107 and the image reader 106 by one simple work, converting those 
colors into color values based on the human perception, and deriving the 
color correction coefficients through the effect of the multiple 
regression analyzer 103. 
The concrete description will be made as referring to FIGS. 8 and 9. At a 
step 11, the pattern generator 101 serves to generate the reference 
pattern containing a possible maximum number of colors in the color space. 
The pattern generator 101 is configured of storage units such as a ROM or 
a hard desk and thus can store the generated reference pattern data. 
Assume that the image consists of 512.times.512 pixels and the number of 
quantatizing bits is 8. In the assumption, the overall volume of those 
storage units needs to be about 786,432 bytes, which are calculated by: 
EQU 512 (pixels).times.512 (pixels).times.3=786432 
The reference pattern image is an image containing a possible maximum 
number of colors in the color space. One example of the reference pattern 
image will be shown in FIGS. 10 and 11. The reference pattern image may be 
arranged in various manners. Whatever arrangements the reference pattern 
image may take, if the distribution of the colors in the color space are 
similar in respective arrangements, this invention may offer the same 
effect. 
Hence, the significant factor is the difference of the distribution of the 
colors composing an image in the color space, rather than the apparent 
arrangement. For example, the reference pattern images shown in FIGS. 12 
and 13 are apparently different from those shown in FIGS. 10 and 11. 
However, the distribution of the colors in the color space is similar in 
each reference pattern image. They are the same reference pattern images 
in light of the spirit of the invention. The image may take lots of 
arrangements. 
In such a reference pattern image, it is considered that one pixel 
corresponds to one color sample described in the known technique. The use 
of such a reference pattern image may bring about the same effect as the 
case where the coefficients are derived in the known art by using a lot of 
color samples. As another reference pattern, it is easily arranged where 
two or more pixels correspond to one color sample. 
Turning to S12, the data is printed by the printer 107 ordinarily included 
in the copying machine. At the step S13, the printed image is read by the 
normal image reader 106 included in the copying machine. These printing 
and reading operations are allowed to be handled by a user himself. 
The read data contains the originally generated reference pattern data plus 
the color reproduction distortions of the printer 107 and the image reader 
106. As such, it is expected that some difference takes place between the 
originally generated reference pattern data and the read reference pattern 
data. This difference corresponds to the color reproduction error 
appearing when normal copying is performed. 
At a step S14, the color value converter 102 serves to convert the 
originally generated reference pattern data and the read reference pattern 
data into the color values based on the human perception. This is because 
the color reproduction error is evaluated on the basis of the human 
perception. This conversion makes it possible to visually keeping the 
color reproduction error to a minimum. 
Those color values are: 
CIE (1976) L*a*b* value (Expression 7), 
CIE (1976) L*u*v* value (Expression 8) 
and Munsell value. 
Herein, the term "Lab" means the expression 7. 
For example, the conversion into the Lab value is performed on the 
following expression. 
##EQU4## 
wherein R', G'and B'denote R, G, B or r, g, b in the expression 1 or 2. 
The color value converter 102 may be easily configured of a microcomputer 
having the programmed expressions or a digital signal processor. 
At a step 15, the multiple regression analyzer 103 serves to derive the 
corrected coefficients needed for the color correction, based on the Lab 
values. 
As mentioned above, the reference pattern image is arranged so that one 
pixel corresponds to one color sample. As such, the multiple regression 
analysis is required to be performed in a manner to match the color sample 
of the originally generated reference pattern data to the corresponding 
color sample (standing the same color) of the read pattern data, both of 
which have been converted into the color values based on the perception 
characteristics in the color value converter 102. 
When the printed reference pattern is read at the step S13, the user has to 
put the printed material at a right place. This can be easily achieved by 
putting a suitable mark on the image reader 106. 
The coefficients derived by the multiple regression analyzer 103 correspond 
to the matrix coefficients shown in the expressions 1 and 2. Like the 
color value converter 102, to easily obtain the coefficients, it is better 
to arrange the multiple regression analyzer 103 by using a microcomputer 
having a programmed regression analyzing process. 
The reference pattern data generator 101, the color value converter 102, 
and the multiple regression analyzer 108 enable to do their suitable 
functions if a proper storage unit and a programmed microcomputer are used 
for composing them. Those storage unit and microcomputer are pre-built for 
controlling various operations in the known copying machine. In actual, 
therefore, the present invention may be achieved if the program for 
executing the foregoing function is newly built in the existing 
microcomputer. 
At a step 16, the resulting color correction coefficients are stored in the 
rewritable memory 104. That is, the memory 104 constantly holds the latest 
color correction coefficients. The values given in the standard state of 
the product, that is, when shipping the product may be held together with 
the coefficients in the memory 104. The memory 104 may be easily 
configured of an EEPROM or a hard disk and a rewritable type for achieving 
the object of the invention. 
As referring to FIG. 8, the operation will be more concretely described. 
The reference pattern data generated in the generator 101 is guided into 
the printer 107 and the color value converter 102. The data guided to the 
printer 107 is printed at the initial stage of the flowchart shown in FIG. 
9. The data guided to the color value convert 02 is converted into the 
color values such as the Lab values formed based on the human perception. 
The reference pattern printed in the printer 107 is read from the image 
reader 106 with a help of the user's hands. The read data is guided to the 
color value converter 102 for converting it into the color values such as 
the Lab color values formed based on the human perception. 
The two color data items converted in the color value converter 102 are 
guided into the multiple regression analyzer 103. The multiple regression 
analysis is performed in terms of the data items for deriving the color 
correction coefficients. The data about the color correction coefficients 
are guided to the memory 104 and stored in it. 
Lastly, the color correcting unit 105 performs the color correction 
operation as referring to the data held in the memory 104. When the 
material is read from the image reader 106, the read data is guided to the 
color correcting unit 102. The color correcting unit 102 serves to perform 
the color correction operation as referring to the data about the color 
correction coefficients stored in the memory 104 and then output the 
resulting data to the printer 107. 
Fourth Embodiment 
FIG. 14 shows a color copying machine according to a fourth embodiment of 
the invention. As shown, this embodiment does not have the color value 
converter 102 shown in FIG. 8. The color value converter 102 is provided 
for the purpose of evaluating the color reproduction error based on the 
human perception and defining the color correction coefficients. If, 
therefore, one of the objects of the invention, that is, "simplifying the 
adjustment and reducing the adjusting time" is considered as the most 
important factor, the color value converter 102 may be removed from the 
fourth embodiment. 
The other components of this embodiment operate in the similar manner to 
those of the third embodiment shown in FIG. 8. Hence, the description 
about those components is eliminated for avoiding the overlap. 
Fifth Embodiment 
FIG. 15 shows a color copying machine according to a fifth embodiment of 
the invention. As shown, this embodiment additionally includes a new 
signal I/O unit 108a to the pattern generator 101, the color value 
converter 102, and the multiple regression analyzer 103 described in the 
third embodiment of the invention. The signal I/O unit 108b, the pattern 
generator 101, the color value converter 102 and the multiple regression 
analyzer 103 are arranged as an external device (enclosed by a broken line 
of FIG. 15). 
Further, in addition to the memory 104, the color correcting unit 105, the 
image reader 106, and the printer 107, a signal I/O unit 108a are included 
on the side of the color copying machine so as to transfer various kinds 
of data between the external device and the color copying machine. 
The reference pattern data generator 101, the color value converter 102, 
and the multiple regression analyzer included in the external device are 
normally used in the maintenance stage after temporarily terminating the 
adjustment, that is, shipping the product. To simplify the arrangement of 
the color copying machine and lower the cost of the machine itself, it is 
possible to exclude those components from the color copying machine. 
To obtain the substantially same color correction coefficients as those 
described in terms of the third embodiment of the invention, the following 
process is required to be implemented by using the reference pattern data 
generator 101, the color value converter 102, and the multiple regression 
analyzer 103 located in the external device. 
At first, as shown in FIG. 15, the signal input/output (I/O) unit 108 on 
the side of the color copying machine is connected to the signal I/O unit 
108b on the side of the external unit. The signal I/O units 108a and 108b 
for executing an I/O of the data may be basically arranged of a standard 
interface such as RS232C, SCSI, or GP-IB. 
The signal I/O unit 108a is connected to the printer 107, the image reader 
106, and the rewritable memory 104 so that the data may be transferred 
between those components and the external device. Likewise, the signal I/O 
unit 108b is connected to the reference pattern data generator 101, the 
color value converter 102, and the multiple regression analyzer 103. 
The external device serves to send the reference pattern data from the 
reference pattern data generator 101 to the color copying machine through 
the signal I/O unit 108b. The signal I/O unit 108a receives the data. 
Then, the printer 107 serves to print the received data on paper. Next, 
the image reader 106 reads the printed image and sends the read data to 
the external device through the signal I/O unit 108a. The data is received 
by the signal I/O unit 108b and is guided to the color value converter 
102. 
The color value converter 102 serves to convert the originally generated 
reference pattern data and the data read by the image reader into the Lab 
color values. The multiple regression analyzer 103 serves to derive the 
regression coefficients based on the converted Lab color values and send 
the derived values as the color correction coefficients to the color 
copying machine through the signal I/O unit 108b. 
On the side of the color copying machine, the rewritable memory 104 stores 
the color correction coefficients sent from the external device. It is 
obvious that those coefficients are the same as those described in terms 
of the third embodiment of the invention. The color correcting unit 102 
performs the color correction based on the data stored in the memory 104. 
When the image reader 106 reads the subject material, the read data is 
guided into the color correcting unit 105. The color correcting unit 105 
performs the color correction as referring to the data about the color 
correction coefficients stored in the memory 104 and output the corrected 
data to the printer 107. 
What is required for the reference pattern data generator 101, the color 
value converter 102, and the multiple regression analyzer 103 located in 
the external device is to transfer the data between the external device 
and the color copying machine. That is, they may just have the same 
functions as those described as referring to FIG. 8. This external device 
may be arranged of a dedicated device or a notebook type hand-held 
computer. 
The color value converter 102 may be removed like the fourth embodiment of 
the invention. 
Many widely different embodiments of the present invention may be 
constructed without departing from the spirit and scope of the present 
invention. It should be understood that the present invention is not 
limited to the specific embodiments described in the specification, except 
as defined in the appended claims.