U.S. patent application number 08/959755 was filed with the patent office on 2001-08-09 for image forming apparatus and method of correcting the characteristic of each body by printing reference pattern in the machine and reading the printed pattern again.
Invention is credited to KANAMORI, KEIKO.
Application Number | 20010012110 08/959755 |
Document ID | / |
Family ID | 17708159 |
Filed Date | 2001-08-09 |
United States Patent
Application |
20010012110 |
Kind Code |
A1 |
KANAMORI, KEIKO |
August 9, 2001 |
IMAGE FORMING APPARATUS AND METHOD OF CORRECTING THE CHARACTERISTIC
OF EACH BODY BY PRINTING REFERENCE PATTERN IN THE MACHINE AND
READING THE PRINTED PATTERN AGAIN
Abstract
An image forming apparatus which includes the input function of
taking in image data on a document by scanning and the output
function of forming an image on the basis of the image data,
includes the generating function of generating a first gradation
pattern with a plurality of density areas, a first formation
function of correcting the first gradation pattern on the basis of
a first correction data item previously stored to produce a second
gradation pattern and forming the second gradation pattern on a
first image medium by use of the output function, the taking-in
function of taking in the second gradation pattern on the first
image medium by use of the input function and outputting a third
gradation pattern, the function of creating a second correction
data item used to make a correction so that the density in each of
a plurality of density areas of the third gradation pattern may be
essentially equal to the density in each of a plurality of density
areas of the first gradation pattern, the combining function of
combining the first correction data item and the second correction
data item to generate a third correction data item, and a second
formation function of correcting the image data entered by the
input function on the basis of the third correction data item and
forming the corrected image data on a second image medium.
Inventors: |
KANAMORI, KEIKO;
(KAWASAKI-SHI, JP) |
Correspondence
Address: |
FOLEY & LARDNER
SUITE 500
3000 K STREET NW
WASHINGTON
DC
200075109
|
Family ID: |
17708159 |
Appl. No.: |
08/959755 |
Filed: |
October 29, 1997 |
Current U.S.
Class: |
358/1.9 |
Current CPC
Class: |
H04N 1/4078
20130101 |
Class at
Publication: |
358/1.9 |
International
Class: |
B41B 001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 29, 1996 |
JP |
8-286721 |
Claims
1. An image forming apparatus which includes an input function of
taking in image data on a document by scanning and an output
function of forming an image on the basis of the image data,
comprising: means for generating a first gradation pattern with a
plurality of density areas; first formation means for correcting
the first gradation pattern on the basis of a first correction data
item previously stored to produce a second gradation pattern and
forming the second gradation pattern on a first image medium by use
of the output function; means for taking in the second gradation
pattern on the first image medium by use of the input function and
generating a third gradation pattern; means for creating a second
correction data item used to make a correction so that the density
in each of a plurality of density areas of the third gradation
pattern may be essentially equal to the density in each of a
plurality of density areas of the first gradation pattern; means
for combining the first correction data item and the second
correction data item to form a third correction data item; and
second formation means for correcting the image data entered by the
input function on the basis of the third correction data item and
forming the corrected image data on a second image medium.
2. An image forming apparatus according to claim 1, wherein the
first formation means includes means for storing the first
correction data item used to correct the first gradation pattern
into the second gradation pattern so that the third gradation
pattern may be more similar to the first gradation pattern than a
fourth gradation pattern, wherein the third gradation pattern is
obtained by the input function fetching the second gradation
pattern which is obtained by correcting the first gradation pattern
on the basis of the first correction data, and the fourth gradation
pattern is obtained by the input function fetching a fifth
gradation pattern which is obtained by the output function
outputting the first gradation pattern without correction.
3. An image forming apparatus according to claim 1, wherein the
first formation means includes means for storing the first
correction data item used to correct the first gradation pattern
into the second gradation pattern so that the density in each of a
plurality of density areas of the third gradation pattern may be
close to the density in each of the plurality of density areas of
the first gradation pattern, when the input function takes in the
image of the second gradation pattern formed by the output function
and produces the fourth gradation pattern.
4. An image forming apparatus according to claim 1, wherein the
creating means includes means for creating correction data items on
density that neither the first gradation pattern nor the third
gradation pattern has, using an interpolation method on the basis
of the first gradation pattern and the third gradation pattern.
5. An image forming apparatus according to claim 1, wherein the
first formation means includes: means for selecting one of a
plurality of first correction data items previously stored to
correct the first gradation pattern according to the operator's
operation on an operation panel; and means for correcting the first
gradation pattern into the second gradation pattern on the basis of
one of the first correction data items selected by the select means
and forming the second gradation pattern on the first image medium
by use of the output function.
6. A color image forming apparatus which includes an input function
of taking in color image data on a document by scanning and an
output function of forming an image on the basis of the color image
data, the color image forming apparatus comprising: means for
generating a first color gradation pattern with a plurality of
density areas; first formation means for correcting the first color
gradation pattern on the basis of a first color correction data
item previously stored to produce a second color gradation pattern
and forming the second color gradation pattern on a first image
medium by use of the output function; means for taking in the
second color gradation pattern on the first image medium by use of
the input function and generating a third color gradation pattern;
means for creating a second color correction data item used to make
a correction so that the density in each of a plurality of density
areas of the third color gradation pattern may be essentially equal
to the density in each of a plurality of density areas of the first
color gradation pattern; means for combining the first color
correction data item and the second color correction data item to
produce a third color correction data item; and second formation
means for correcting the image data entered by the input function
on the basis of the third color correction data item and forming
the corrected image data on a second image medium.
7. An image forming apparatus according to claim 6, wherein the
first formation means includes means for storing the first color
correction data item used to correct the first color gradation
pattern into the second color gradation pattern so that the third
color gradation pattern may be more similar to the first color
gradation pattern than a fourth color gradation pattern, wherein
the third color gradation pattern is obtained by the input function
fetching the second color gradation pattern which is obtained by
correcting the first color gradation pattern on the basis of the
first color correction data, and the fourth color gradation pattern
is obtained by the input function fetching a fifth color gradation
pattern which is obtained by the output function outputting the
first color gradation pattern without correction.
8. A color image forming apparatus according to claim 6, wherein
the combining means includes means for producing the third color
correction data item composed of cyan, magenta, yellow, and black
correction data items by combining, for each color, the first color
correction data item composed of cyan, magenta, yellow, and black
correction data items with the second color correction data item
composed of cyan, magenta, yellow, and black correction data
items.
9. A color image forming apparatus according to claim 6, wherein
the first formation means includes means for storing the first
color correction data item used to correct the first color
gradation pattern into the second color gradation pattern so that
the density in each of a plurality of density areas of the third
color gradation pattern may be close to the density in each of the
plurality of density areas of the first color gradation pattern,
when the input function takes in the image of the second color
gradation pattern formed by the output function and produces the
third color gradation pattern.
10. A color image forming apparatus according to claim 6, wherein
the creating means includes means for creating color correction
data items on density that neither the first color gradation
pattern nor the third color gradation pattern has, using an
interpolation method on the basis of the first color gradation
pattern and the third color gradation pattern.
11. A color image forming apparatus according to claim 6, wherein
the first formation means includes: means for selecting one of a
plurality of first color correction data items previously stored to
correct the first color gradation pattern (P1) according to the
operator's operation on an operation panel; and means for
correcting the first color gradation pattern into the second color
gradation pattern on the basis of one of the first color correction
data items selected by the select means and forming the second
color gradation pattern on the first image medium by use of the
output function.
12. A method of correcting the gradation characteristic of an image
forming apparatus which includes an input function of taking in
image data on a document by scanning and an output function of
forming an image on the basis of the image data, the method
comprising: the step of generating a first gradation pattern with a
plurality of density areas; a first formation step of correcting
the first gradation pattern on the basis of a first correction data
item previously stored to produce a second gradation pattern and
forming the second gradation pattern on a first image medium by use
of the output function; the step of taking in the second gradation
pattern on the first image medium by use of the input function and
outputting a third gradation pattern; a step of creating a second
correction data item used to make a correction so that the density
in each of a plurality of density areas of the third gradation
pattern may be essentially equal to the density in each of a
plurality of density areas of the first gradation pattern; and a
combining step of combining the first correction data item and the
second correction data item to generate a third correction data
item.
13. An image forming method according to claim 12, wherein the
first formation step includes a step of storing the first
correction data item used to correct the first gradation pattern
into the second gradation pattern so that the third gradation
pattern may be more similar to the first gradation pattern than a
fourth gradation pattern, wherein the third gradation pattern is
obtained by the input function fetching the second gradation
pattern which is obtained by correcting the first gradation pattern
on the basis of the first correction data, and the fourth gradation
pattern is obtained by the input function fetching a fifth
gradation pattern which is obtained by the output function
outputting the first gradation pattern without correction.
14. A method according to claim 12, wherein the first formation
step includes the step of storing the first correction data item
used to correct the first gradation pattern into the second
gradation pattern so that the density in each of a plurality of
density areas of the third gradation pattern may be close to the
density in each of the plurality of density areas of the first
gradation pattern, when the input function takes in the image of
the second gradation pattern formed by the output function and
produces the third gradation pattern.
15. A method according to claim 12, wherein the creating step
includes the step of creating correction data items on density that
neither the first gradation pattern nor the third gradation pattern
has, using an interpolation method on the basis of the first
gradation pattern and the third gradation pattern.
16. A method according to claim 12, wherein the first formation
step includes: the step of selecting one of a plurality of first
correction data items previously stored to correct the first
gradation pattern according to the operator's operation on an
operation panel; and the step of correcting the first gradation
pattern into the second gradation pattern on the basis of one of
the first correction data items selected by the select means and
forming the second gradation pattern on the first image medium by
use of the output function.
17. A method of correcting the color gradation characteristic of a
color image forming apparatus which includes an input function of
taking in color image data on a document by scanning and an output
function of forming an image on the basis of the color image data,
the method comprising: a step of generating a first color gradation
pattern with a plurality of density areas; a first formation step
of correcting the first color gradation pattern on the basis of a
first color correction data item previously stored to generate a
second color gradation pattern and forming the second color
gradation pattern on a first image medium by use of the output
function; a step of taking in the second color gradation pattern on
the first image medium by use of the input function and outputting
a third color gradation pattern; a step of creating a second color
correction data item used to make a correction so that the density
in each of a plurality of density areas of the third color
gradation pattern may be essentially equal to the density in each
of a plurality of density areas of the first color gradation
pattern; a step of combining the first color correction data item
and the second color correction data item to produce a third color
correction data item; and a second formation step of correcting the
image data entered by the input function on the basis of the third
color correction data item and forming the corrected image data on
a second image medium.
18. A method according to claim 17, wherein the combining step
includes a step of producing the third color correction data item
composed of cyan, magenta, yellow, and black correction data items
by combining, for each color, the first color correction data item
composed of cyan, magenta, yellow, and black correction data items
with the second color correction data item composed of cyan,
magenta, yellow, and black correction data items.
19. A method according to claim 17, wherein the first formation
step includes a step of storing the first color correction data
item used to correct the first color gradation pattern into the
second color gradation pattern so that the third color gradation
pattern may be more similar to the first color gradation pattern
than a fourth color gradation pattern, wherein the third color
gradation pattern is obtained by the input function fetching the
second color gradation pattern which is obtained by correcting the
first color gradation pattern on the basis of the first color
correction data, and the fourth color gradation pattern is obtained
by the input function fetching a fifth color gradation pattern
which is obtained by the output function outputting the first color
gradation pattern without correction.
20. A method according to claim 17, wherein the first formation
step includes the step of storing the first color correction data
item used to correct the first color gradation pattern into the
second color gradation pattern so that the density in each of a
plurality of density areas of the third color gradation pattern may
be close to the density in each of the plurality of density areas
of the first color gradation pattern, when the input function takes
in the image of the second color gradation pattern formed by the
output function and produces the third color gradation pattern.
21. A method according to claim 17, wherein the creating step
includes the step of creating color correction data items on
density that neither the first color gradation pattern nor the
third color gradation pattern has, using an interpolation method on
the basis of the first color gradation pattern and the third color
gradation pattern.
22. A method according to claim 17, wherein the first formation
step includes: the step of selecting one of a plurality of first
color correction data items previously stored to correct the first
color gradation pattern according to the operator's operation on an
operation panel; and the step of correcting the first color
gradation pattern into the second color gradation pattern on the
basis of one of the first color correction data items selected in
the select step and forming the second color gradation pattern on
the first image medium by use of the output function.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates an image processing method of taking
in image data by, for example, reading the image on a document with
a scanner, performing a specific process on the input image data,
and then outputting the image data on paper with an electronic
photographic laser printer and an image processing apparatus, such
as a digital copying machine, using the image processing
method.
[0002] With an image processing apparatus, such as a digital
copying machine's body dealing with image data, the image data read
from a document by a reading device, such as a scanner, is
generally digitized, made multivalued, and processed according to
the purpose, and outputted on an output device, such as a laser
printer. In this case, because of the characteristics of the
scanner acting as the input device and the photosensitive member
and laser optical system in the output device, the desired result
cannot be obtained without correction.
[0003] In general, to correct the characteristic of the entire
system, including the characteristics of the scanner of the input
device and the photosensitive member and laser optical system in
the output device, a gradation correction table used to correct the
characteristic of the entire system beforehand is stored in a
memory such as a ROM. The characteristic is corrected by referring
to the table. In another approach, each image processing device's
body is forced to output a thing from which the gradation
characteristic can be known, such as a test print. The test print
is then supplied to the input device. From the inputted data, a
characteristic correction table for correcting the gradation
characteristic is formed. The gradation characteristic is corrected
to by reference to the table.
[0004] Even if the characteristics of the input device, the output
device, and the like are obtained beforehand and stored in such a
memory as a ROM and a correction is made by reference to the
correction data, it is difficult to make a correction appropriate
for each image processing apparatus because the characteristics of
the scanner, photosensitive member, and laser optical system differ
from one image processing apparatus to another.
[0005] To make a correction for each image processing apparatus,
the gradation data internally generated in the image processing
apparatus is printed at the printer section to provide a hard copy.
The hard copy is read by the same image processing apparatus that
has generated the gradation data. From the read data, the
characteristic correction data for correcting the characteristics
of the input device and output device is obtained. This approach is
very effective theoretically.
[0006] Actually, however, when data on each gradation is obtained
by generating gradation data, outputting it on the printer section
acting as the output device, and supplying the outputted gradation
data to the input device, the relationship between the gradation
data sent to the output device and that supplied to the input
device plotted on the ordinate and abscissa axes is not ideal.
Examples of the data are shown in FIGS. 9 and 10.
[0007] As shown in the examples, when the data rises sharply or the
data contains a part lying as if it were almost parallel with the
abscissa, small noise (the portion indicated by "a" in FIG. 9 or
the portion indicated by "b" in FIG. 10) may make the
characteristic correction data discontinuous or cause the reversal
of numerical values in the parts close to the abscissa and ordinate
axes.
[0008] It is very easy for a person to correct the discontinuity or
reversal of the data due to noise, while seeing it with his or her
eyes. It is very difficult, however, to do the same thing using
calculating expressions. Actually, because of such noises, the
characteristic correction data cannot be created exactly.
[0009] This causes the problem of being unable to get the linearity
as expected theoretically, even if the gradation data is corrected
for each digital copying machine.
BRIEF SUMMARY OF THE INVENTION
[0010] The object of the present invention is to provide an image
processing apparatus for and method of creating ideal
characteristic correction data and achieving high shading
reproducibility without being affected by the discontinuity of the
data and the reversal of numerical values caused by noise in
creating characteristic correction data used to correct the input
and output characteristics of the entire image processing
system.
[0011] The foregoing object is accomplished by providing an image
forming apparatus which includes the input function of taking in
image data on a document by scanning and the output function of
forming an image on the basis of the image data, the image forming
apparatus comprising: means for generating a first gradation
pattern with a plurality of density areas; first formation means
for correcting the first gradation pattern on the basis of a first
correction data item previously stored to produce a second
gradation pattern and forming the second gradation pattern on a
first image medium by use of the output function; means for taking
in the second gradation pattern on the first image medium by use of
the input function and generating a third gradation pattern; means
for creating a second correction data item used to make a
correction so that the density in each of a plurality of density
areas of the third gradation pattern may be essentially equal to
the density in each of a plurality of density areas of the first
gradation pattern; combining means for combining the first
correction data item and the second correction data item to
generate a third correction data item; and second formation means
for correcting the image data entered by the input function on the
basis of the third correction data item and forming the corrected
image data on a second image medium.
[0012] With the above configuration, the present invention produces
the following effect. To create correction data used to correct the
gradation characteristic for each model of copying machine, a
gradation pattern P1 serving as an ideal reference in a digital
copying machine is generated (see FIG. 16). The gradation pattern
P1 is corrected using a first correction data item f1 and then
printed so that it may be used to correct the deviation in the
output system including the printer section to provide an ideal
relationship between the input and the output. The printed
gradation pattern P2 is read by the scanner, which produces a third
gradation pattern P3 including the deflection in the input system
including the scanner section. Next, a second correction data item
f2 used to make a correction so that the third gradation pattern P3
may be equivalent to the first gradation pattern P1 acting as the
original reference. Specifically, a combination data is obtained on
the basis of the prepared first correction data f1 and the made
second correction data f2. The combination of correction data items
f1 and f2 is determined to be a third correction data item f3 used
to correct the deflection in the entire machine of the model. In an
ordinary process, a document image is inputted and corrected using
the third correction data item. This removes the deflection in both
of the input system including the scanner section and the output
section including the printer section, or the deflection in the
entire machine. Therefore, it is possible to provide a digital
copying machine that makes a correction, taking into account the
deflection in the machine itself, and reproduces the gradation
density of the image of the document with fidelity.
[0013] The foregoing object is also accomplished by providing a
method of correcting the gradation characteristic of an image
forming apparatus which includes the input function of taking in
image data on a document by scanning and the output function of
forming an image on the basis of the image data, the method
includes the step of generating a first gradation pattern with a
plurality of density areas; a first formation step of correcting
the first gradation pattern on the basis of a first correction data
item previously stored to produce a second gradation pattern and
forming the second gradation pattern on a first image medium by use
of the output function; the step of taking in the second gradation
pattern on the first image medium by use of the input function and
generating a third gradation pattern; a step of creating a second
correction data item used to make a correction so that the density
in each of a plurality of density areas of the third gradation
pattern may be essentially equal to the density in each of a
plurality of density areas of the first gradation pattern; and a
combining step of combining the first correction data item and the
second correction data item to generate a third correction data
item.
[0014] Like the image forming apparatus, the method of correcting
the gradation characteristic of the present invention makes it
possible to provide an image forming apparatus capable of
reproducing a gradation image with fidelity by making the second
correction data f2 and composing the first and second correction
data f1, f2.
[0015] Additional objects and advantages of the invention will be
set forth in the description which follows, and in part will be
obvious from the description, or may be learned by practice of the
invention. The objects and advantages of the invention may be
realized and obtained by means of the instrumentalities and
combinations particularly pointed out in the appended claims.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0016] The accompanying drawings, which are incorporated in and
constitute a part of the specification, illustrate presently
preferred embodiments of the invention, and together with the
general description given above and the detailed description of the
preferred embodiments give below, serve to explain the principles
of the invention.
[0017] FIG. 1 is a side view of the internal configuration of a
digital copying machine according to a first embodiment of the
present invention;
[0018] FIG. 2 is a schematic block diagram of the digital copying
machine of FIG. 1;
[0019] FIG. 3 is a block diagram of the image processing
section;
[0020] FIG. 4 is a flowchart to help explain a characteristic
correction method in the image processing section;
[0021] FIG. 5 shows an example of a gradation pattern outputted on
paper to provide a hard copy;
[0022] FIG. 6 shows a first correction data item used to correct
the gradation characteristic of the gradation pattern;
[0023] FIG. 7 is a drawing to help explain an area where the value
of each gradation in the inputted gradation pattern is sampled;
[0024] FIG. 8 shows the relationship between the value of each
gradation in the resulting gradation pattern when the hard copy
obtained by correcting the characteristic of the gradation pattern
internally generated in the image processing section is supplied to
the scanner section and the value of each gradation in the
gradation pattern generated in the image processing section;
[0025] FIG. 9 shows a problematic data item in the relationship
between the internally generated gradation pattern and the
resulting gradation pattern obtained when the outputted gradation
pattern is supplied to the input device;
[0026] FIG. 10 shows another problematic data item differing from
that of FIG. 9 in the relationship between the internally generated
gradation pattern and the resulting gradation pattern obtained when
the outputted gradation pattern is supplied to the input
device;
[0027] FIG. 11 is a side view of the internal configuration of a
digital color copying machine according to a second embodiment of
the present invention;
[0028] FIG. 12 is a block diagram of the digital color copying
machine;
[0029] FIG. 13 is a block diagram of the color image processing
section of the digital color copying machine;
[0030] FIG. 14 is a flowchart to help explain a method of
correcting the characteristic in the second embodiment;
[0031] FIG. 15 shows an example of a color gradation pattern
outputted on paper to provide a hard copy;
[0032] FIG. 16 is a conceptual diagram to help explain the
principle of the present invention; and
[0033] FIG. 17 shows an example of the display of the operation
panel on which the desired correction data item is to be
selected.
DETAILED DESCRIPTION OF THE INVENTION
[0034] Hereinafter, referring to the accompanying drawings,
embodiments of the present invention will be explained.
[0035] 1. Configuration
[0036] FIG. 1 shows the internal configuration of a digital copying
machine as an example of an image processing apparatus according to
a first embodiment of the present invention. The digital copying
machine is, for example, a composite copying machine having three
functions: the function of a copying machine, that of a facsimile,
and that of a printer.
[0037] In FIG. 1, a scanner section 4 acting as an input device and
a reading device and a printer section 6 acting as an output device
and an image forming device are provided in the apparatus body
10.
[0038] On the top of the apparatus body 10, there is provided a
document table 12 composed of a transparent glass on which a
document D to be read is placed. On the top of the apparatus body
10, too, there is provided an automatic document feed 7
(hereinafter, abbreviated as ADF) that automatically feeds the
document D onto the document table 12. The ADF 7 is provided on the
document table 12 so that it can open and close and also functions
as a document weight that forces the document D to come in close
contact with the document table 12.
[0039] The ADF 7 is composed of a document tray 8 in which the
document D is set, an empty sensor 9 for sensing the presence or
absence of a document, a pickup roller 14 for picking up the
document D sheet by sheet from the document tray 8, a paper feed
roller 15 for transporting the picked-up document D, an aligning
roller pair 16 for aligning the leading edge of the document D, and
a transport belt 18 provided in a manner that covers almost all the
top of the document table 12. A plurality of documents D set in the
document tray 8 face up is picked out, starting with the bottommost
page, or the last page. The picked-out page is positioned in place
by the aligning roller pair 16 and then transported by the
transport belt 18 to a specific position on the document table
12.
[0040] In the ADF 7, at the end of the opposite side of the
aligning roller pair 16 across the transport belt 18, a reversing
roller 20, a non-reversing roller 21, a flapper 22, and a discharge
roller 23 are provided. The document D from which the image data
has been read by the scanner section 4 is transported by the
transport belt 18 from the top of the document table 12 and
discharged onto a document discharge section 24 on the top of the
ADF 7 via the reversing roller 20, flapper 22, and discharge roller
23. To read the reverse side of the document D, switching the
flapper 22 causes the reversing roller 20 to reverse the document D
transported by the transport belt 18. Thereafter, the transport
belt 18 carries it to a specific position on the document table
12.
[0041] The scanner section 4 provided in the apparatus body 10
includes an exposure lamp 25 serving as a light source that
illuminates the document D on the document table 12 and a first
mirror 26 for reflecting the reflected light from the document D in
a specific direction. The exposure lamp 25 and first mirror 26 are
provided on a first carriage 27 provided below the document table
12. The first carriage 27 is provided so as to move in parallel
with the document table 12. The first carriage is moved back and
forth below the document table 12 by a driving motor via a toothed
belt (not shown).
[0042] Below the document table 12, a second carriage 28 is
provided so as to move in parallel with the document table 12. On
the second carriage 28, a second and third mirrors 30 and 31 that
reflect, in that order, the light from the document D reflected by
the first mirror 26 are provided at right angles to each other. The
second carriage 28 is moved by the toothed belt driving the first
carriage so that it may follow the movement of the first carriage
27 in such a manner that it moves in parallel with the document
table 12 at a speed half that of the first carriage.
[0043] Below the document table 12, there are provided an image
forming lens 32 for concentrating the reflected light from the
third mirror 31 on the second carriage 28 and a CCD line sensor 34
acting as a photoelectric conversion device for receiving the
reflected light converged by the image forming lens 32 and
converting it photoelectrically. The image forming lens 32 is
provided in a plane including the optical axis of the light
reflected from the third mirror 31 in such a manner that it can
move via a driving mechanism. The movement of the image forming
lens enables the reflected light to form an image at the desired
magnification. Then, the line sensor 34 converts the incident
reflected light photoelectrically and outputs the electric signal
corresponding to the read document D.
[0044] The printer section 6 includes a laser exposure device 40
acting as a latent image forming device. The laser exposure device
40 comprises a semiconductor laser oscillator 41 acting as a light
source, a polygon mirror 36 serving as a scanning member for
continuously deflecting the laser light emitted from the
semiconductor laser oscillator 41, a polygon motor 37 acting as a
scanning motor for rotating the polygon mirror 36 at the specified
number of revolutions explained later, and an optical system 42 for
deflecting the laser light from the polygon mirror 36 and directing
it to the photosensitive drum 44. The laser exposure device 40
having such a construction is fixed to a support frame (not shown)
of the apparatus body 10.
[0045] The semiconductor laser oscillator 41 is turned on and off
according to image data on the document D read by the scanner
section 4 or data on the document transmitted or received by
facsimile. The laser light is directed to the photosensitive drum
44 via the polygon mirror 36 and optical system 42. Exposing and
scanning the peripheral surface of the photosensitive drum 44, the
laser light forms an electrostatic latent image on the peripheral
surface of the photosensitive drum 44.
[0046] The printer section 6 also has the fully rotary
photosensitive drum 44 acting as an image-retaining member provided
almost in the center of the apparatus body 10. The peripheral
surface of the photosensitive drum 44 is exposed and scanned by the
laser light from the laser exposure device 40, thereby forming the
desire latent image. Around the photosensitive drum 44, there are
provided, in this order, an electrification charger 45 for
electrifying the peripheral surface of the photosensitive drum 44
with a specific charge, a developing unit 46 acting as a developing
device for supplying toner acting as a developer to the
electrostatic latent image formed on the photosensitive drum 44 to
develop the image with the desired image density, a peeling charger
47 for peeling from the photosensitive drum 44 a paper sheet P
serving as an image forming medium supplied from a paper feed
cassette explained later, a transfer charger 48 for transferring
the toner image formed on the photosensitive drum 44 to the paper
sheet P, a peeling claw 49 for peeling the paper sheet P from the
peripheral surface of the photosensitive drum 44, a cleaning device
50 for removing the remaining toner from the peripheral surface of
the photosensitive drum 44, and a discharger 51 for discharging the
peripheral surface of the photosensitive drum 44.
[0047] In the lower part of the apparatus body 10, an upper-stage
paper feed cassette 52, a middle-stage paper feed cassette 53, a
lower-stage paper feed cassette 54 are stacked one on top of
another in a removable manner. In each of the paper feed cassettes
52 to 54, sheets of paper P of different sizes are loaded. On the
side of these paper feed cassettes 52 to 54, a large-capacity
feeder 55 is provided. The large-capacity feeder 55 houses sheets
of paper P of a frequently used size, for example, about 3000
sheets of paper of size A4. Above the large-capacity feeder 55, a
paper feed cassette 57 also serving as a manual feed tray 56 is
provided in a detachable manner.
[0048] In the apparatus body 10, a transport path 58 extends from
each of the paper feed cassettes 52 to 54 and the large-capacity
feeder 55 and passes through the transfer section between the
photosensitive drum 44 and the transfer charger 48. At the end of
the transport path 58, a fixing device 60 with a fixing lamp 60a is
provided. In the sidewall of the apparatus body 10 facing the
fixing device 60, an outlet 61 is formed. In the outlet 61, the
single-tray finisher 150 is installed.
[0049] In the vicinity of not only the upper-stage paper feed
cassette 52, middle-stage paper feed cassette 53, and lower-stage
paper feed cassette 54 but also the large-capacity feeder 55, there
is provided a pickup roller 63 for picking up paper sheets P one by
one from the paper feed cassettes 52, 54, 57 or large-capacity
feeder 57. In the transport path 58, there are provided a large
number of paper feed roller pairs 64 for transporting the paper
sheet P picked up by the pickup roller 63 over the transport path
58.
[0050] In the transport path 58, a resist roller pair 65 is
provided on the upstream side of photosensitive drum 44. The resist
roller pair 65 corrects the inclination of the picked-up paper
sheet P aligns the leading edge of the toner image on the
photosensitive drum 44 with the leading edge of the paper sheet P.
The resist roller pair then supplies the paper sheet P to the
transfer section at the same speed as the moving speed of the
peripheral surface of the photosensitive drum 44. In front of the
resist roller pair 65, or on the side of the paper feed roller 64,
a pre-aligning sensor 66 for sensing the arrival of the paper sheet
P is provided.
[0051] The paper sheet P picked up one by one by the pickup roller
63 from one of the paper feed cassettes 52 to 54, 57 or the
large-capacity feeder 55 is sent to the resist roller pair 65 by
the paper feed roller pair 64. Then, the leading edge of the paper
sheet P is positioned in place by the resist roller pair 65 and
thereafter the sheet is sent to the transfer section.
[0052] In the transfer section, the developer image, or the toner
image, formed on the photosensitive drum 44 is transferred onto the
paper sheet P by the transfer charger 48. The paper sheet P on
which the toner image has been transferred is peeled from the
peripheral surface of the photosensitive drum 44 by the action of
the peeling charger 47 and peeling claw 49. The peeled sheet is
transferred to the fixing device 60 via a transport belt 67 forming
part of the transport path 52. After the fixing device 60
melt-fixes the developer image onto the paper sheet P, the sheet P
is passed through the outlet 61 by a paper feed roller pair 68 and
a discharge roller pair 69 and is delivered onto a finisher
150.
[0053] Below the transport path 58, an automatic reversing device
70 for reversing the paper sheet P passed through the fixing device
60 and sending back the sheet to the resist roller pair 65. The
automatic reversing device 70 includes a temporal accumulation
section 71 for temporarily accumulating the paper sheets P, a
reversing path 72 that branches off the transport path 58 and that
reverses the paper sheet P passed through the fixing device 60 and
directs it to the temporal accumulation section 71, a pickup roller
73 for picking up the paper sheets P one by one from the temporal
accumulation section 71, and a paper feed roller 75 for supplying
the picked-up paper sheet P to the resist roller pair 65 via the
transport path 74. At the branching section between the transport
path 58 and the reversing section 72, an apportioning gate 76 for
apportioning the paper sheet P to the outlet 61 or to the reversing
path 72.
[0054] To copy the document on both sides of paper, the paper sheet
P passed through the fixing device 60 is directed by the
apportioning gate 76 to the reversing path 72. Then, the sheet is
temporarily accumulated in the temporal accumulation section 71
with the back of the sheet upward. Thereafter, the sheet is sent by
the pickup roller 73 and paper feed roller pair 57 to the resist
roller pair 65 via the transport path 74. After the paper sheet P
is positioned in place by the resist roller pair 65, it is sent
back to the transfer section, which transfers the toner image onto
the back of the paper sheet P. Then, the paper sheet P is delivered
to the finisher 150 via the transport path 58, fixing device 60,
and discharge roller 69.
[0055] The finisher 150 staples the delivered documents in units of
a copy and accumulates them. Each time a sheet of paper P to be
stapled is delivered from the outlet 61, a guide bar 151 moves the
sheet to the side on which it is to be stapled and aligns it. After
all the sheets have been delivered, a paper clamp arm 152 holds
down a copy of paper sheets P delivered and a stapler unit (not
shown) staples it.
[0056] Thereafter, the guide bar 151 goes down and the stapled
paper sheets P are delivered in units of a copy by a finisher
discharge roller 155 to a finisher delivery tray 154. How much the
finisher delivery tray 154 goes down is determined to some extent
by the number of paper sheets P discharged. Each time a copy of
document is delivered, the tray goes down stepwise. The guide bar
151 for aligning the discharged paper sheet P is located at such a
height as prevents the bar from coming into contact with the
stapled paper sheets P on the finisher delivery tray 154.
[0057] The finisher delivery tray 154 is connected to a shift
mechanism (not shown) that shifts the documents copy by copy (for
example, in four directions: the front, the rear, the right, and
the left) in the sort mode.
[0058] In the upper part of the front of the apparatus body 10,
there is provided an operation panel (not shown) is provided which
not only is used to enter various copy conditions and instructions
including a copy start instruction to start a copy operation but
also displays operation statuses.
[0059] FIG. 2 is a schematic block diagram of the digital copying
machine of FIG. 1. In FIG. 2, the control system is composed of
three CPUs (central processing units): a main CPU 91 in a main
control section 90, a scanner CPU 100 in the scanner section 4, and
a printer CPU 110 in the printer section 6.
[0060] The main CPU 91 performs two-way communication via the
printer CPU 110 and a common RAM 95. The main CPU 91 gives an
operation instruction and the printer CPU 110 returns a condition
status. The printer CPU 110 and scanner CPU 110 perform serial
communication. The printer CPU 110 gives an operation instruction
and the scanner CPU 100 returns a condition status.
[0061] The operation panel 80 has various operation keys 81, a
liquid-crystal display section 82, and a panel CPU 83 to which
these are connected. The operation panel is connected to the main
CPU 91.
[0062] The control section 90 comprises the main CPU 91, a ROM 92,
a RAM 93, an NVRAM 94, the common RAM 95, an image processing
section 96, a page memory control section 97, a page memory 98, a
printer controller 99, and a printer font ROM 121.
[0063] The main CPU 91 supervises the entire control. The ROM 92
stores control programs and the like. The RAM 93 stores data
temporarily.
[0064] The NVRAM (nonvolatile RAM) 94 is a nonvolatile memory
backed up by a battery (not shown) and is designed to retain the
stored data even when the power supply is turned off.
[0065] The common RAM 95 is used to perform two-way communication
between the main CPU 91 and the printer CPU 110.
[0066] The page memory control section 97 writes image data into or
reads image data from the page memory 98. The page memory 98 has an
area that can store pages of image data. The page memory is capable
of storing, page by page, the data obtained by compressing the
image data from the scanner section 4.
[0067] The printer font ROM 121 stores the font data corresponding
to the print data. Using the font data stored in the printer font
ROM 121, the printer controller 99 develops the print data from an
external apparatus 122, such as a personal computer, into image
data with the resolution specified by the print data.
[0068] The scanner section 4 comprises a scanner CPU 100 for
supervising the entire control, a ROM 101 for storing control
programs and the like, a RAM 102 for storing data, a CCD driver 103
for driving the line sensor 34, a scanning motor driver 104 for
controlling the rotation of the scanning motor that moves the
exposure lamp 25 and mirrors 26, 27, 28, and an image correcting
section 105.
[0069] The image correcting section 105 comprises an A/D conversion
circuit for converting the analog signal from the line sensor 34
into a digital signal, a shade correcting circuit for correcting
the fluctuation of the threshold level of the output signal from
the line sensor 34 due to changes in the ambient temperature, and a
line memory for temporarily storing the digital signal subjected to
shade correction at the shade correcting circuit.
[0070] The printer section 61 comprises a printer CPU 110 that
controls the entire control, a ROM 111 for storing control programs
and the like, a RAM 112 for storing data, a laser driver 113 for
driving the semiconductor laser oscillator 41, a polygon motor
driver 114 for driving the polygon motor 37 in the laser exposure
device 40, a transport control section 115 for controlling the
transport of the paper sheet P over the transport path 58, a
process control section 116 for controlling the process of
performing electrification, development, and transfer using the
electrification charger 45, developing unit 46, and transfer
charger 48, a fixing controller 117 for controlling the fixing
device 60, and an option control section 118 for controlling an
option.
[0071] The image processing section 96, page memory 98, printer
controller 99, image correcting section 105, and laser driver 113
are connected to each other with an image data bus 120.
[0072] The image processing section 96 corrects the gradation
characteristic (or the density characteristic) of the image data
read by the scanner section 4. The image processing section
comprises, for example, an internal pattern generating section 131
acting as a gradation pattern generating device for generating
gradation patterns changing stepwise, a correction data select
section 132 for selecting either the gradation pattern generated at
the internal pattern generation section 131 or the image data
inputted by the scanner section 4 and outputting the selected one,
a characteristic correction data creation section 133 for creating
characteristic correction data from the gradation pattern inputted
by the scanner section 4, and a characteristic correcting section
134 for correcting the gradation of the image data selected at the
correction data select section 132.
[0073] 2. Principle
[0074] With the above-described configuration, a characteristic
correcting method for each machine of the present invention is
carried out so that each of the density gradations may have an
ideal density value in the digital copying system. The method is
based on the principle explained below. FIG. 16 is a diagram to
help explain the principle of the present invention.
[0075] In FIG. 16, after a first reference gradation pattern P1 (in
the ideal form) generated in an image forming apparatus 501 is
corrected on the basis of a first correction data item f1 to
correct the deflection in the output system including the printer
section, it is printed as a second reference gradation pattern P2
(S503). Then, the printed second reference gradation pattern P2 is
read by the scanner section, which supplies the read pattern P2 as
a third reference gradation pattern P3 including the deflection in
the input system to the copying machine. The third reference
gradation pattern P3 is corrected on the basis of a second
correction data item f2 so that the third reference gradation
pattern P3 may approach to the first reference gradation pattern P1
(in the ideal form). As a result, the third reference gradation
pattern P3 takes the ideal value close to that of the first
reference gradation pattern P1. In other words, such a second
correction data item f2 as causes the third reference gradation
pattern P3 to approach to the ideal first reference gradation
pattern P1 is determined (S505).
[0076] Finally, a combination of the first correction data item f1
and second correction data item f2 is used as a correction value
for use in a normal image forming process.
[0077] That is, a third correction data item f3 used to correct the
deflection in the entire machine is created by combining the second
correction data item f2 used to correct the deflection in the input
system including the scanner and the first correction data item f1
used to correct the deflection in the output system including the
printer section. In an ordinary process, the original document
image D1 is read by the scanner section. Then, the image D2
including the deflection in the input system is corrected on the
basis of the third correction data item f3 used to correct the
defection in the entire machine. After the third correction, the
image D3 is formed. Printing the image D3 on the printer section
provides a printed image D1' with a density distribution closest to
that of the original document image D1 (S507). The reason is that
the third correction data item f3 has a value used to correct the
deflections in the input system and output system. This enables the
image characteristic of the inputted original document image D1 to
be reproduced with fidelity in printing.
[0078] Accordingly, the character correcting method offers a step
of correcting the first standard pattern P1 with the first
correction data f1, and then data shown in FIGS. 9 and 10 would be
corrected to the data shown 8. Therefore, it produces the image
forming apparatus less affected by noise and realizes more precise
calculation for the correction data.
[0079] 3. First Embodiment
[0080] The characteristic correcting method in the image processing
section 96 operating on the aforementioned principle will be
explained in detail by reference to the flowchart of FIG. 4.
[0081] Explanation will be given on the assumption that the
multivalued level in inputting image data is expressed in eight
bits and the multivalued level in outputting image data is
expressed in seven bits.
[0082] First, when the operator sets, for example, the
characteristic correction data creation mode by operating a
specific key on the operation panel 80 and enters an operation
start instruction, the internal pattern generating section 131
generates a gradation pattern P1 that changes stepwise (S11). The
generated gradation pattern P1, together with the one f1 of a
plurality of correction data items (f1, f1-2, f1-3, . . . )
selected by the data select signal given from the main CPU 91, is
sent to the characteristic correcting section 134.
[0083] In a method of selecting a correction data item, the
operator selects the best correction data item from the select
screen on the operation panel shown in FIG. 17.
[0084] The characteristic correcting section 134 corrects the
gradation pattern P1 from the internal pattern generating section
131 by use of the selected characteristic correction data item
(referred to as the first correction data item fl) and sends the
corrected gradation pattern P2 to the printer section 6 (S13). The
printer section 6 prints the corrected gradation pattern from the
characteristic correcting section 134 on the paper sheet P as a
hard copy (S15).
[0085] Instead of selecting one of a plurality of characteristic
correction data items, one characteristic correction data item may
be given beforehand and the gradation pattern be corrected using
the characteristic correction data item without the select
process.
[0086] FIG. 5 shows an example of the gradation pattern P2 of the
outputted hard copy. The numerals (0, 2, 5, . . . , 170, 255) in
the figure represent the density values of the individual
patterns.
[0087] The first correction data f1 set in the characteristic
correcting section 134 is, for example, a correction curve as shown
in FIG. 6. Specifically, it is characteristic correction data on a
correction curve where the relationship between the signal before
correction and the signal in the portion corresponding to each
output signal after the input is almost linear, when the gradation
characteristic of the hard copy outputted from the printer section
6 is supplied from the scanner section 4.
[0088] As described above, before the gradation pattern from the
internal pattern generating section 131 is outputted in the form of
a hard copy, part of the characteristic is corrected and outputted.
This corrects the characteristic of the system to some extend, not
all of the characteristic though. As a result, the characteristic
of the outputted hard copy approaches to a linear one.
[0089] Then, the hard copy outputted from the printer section 6 is
set in the scanner section 4. The scanner section 4 reads the
gradation pattern P2 of the hard copy to produce a gradation
pattern P3 (S17). The inputted gradation pattern P3 is sent to the
characteristic correction data creation section 133. The
characteristic correction data creation section 133 finds the value
of each gradation by sampling a data item for each gradation of the
gradation pattern. Hereinafter, a data sampling method and a method
of finding the value of each gradation will be explained.
[0090] The gradation pattern generated at the internal pattern
generating section 131 is, for example, a pattern where an image
signal changes in the feed direction stepwise as shown in FIG. 5.
Explanation will be given using a case where the number of stages
at which the pattern changes is seventeen.
[0091] The internal pattern generating section 131 generates each
gradation pattern P1 in the form of data items changing at regular
intervals: 0, 10, 20, 30, 40, 50, 60, 70, 80, 90, A0, B0, C0, D0,
E0, F0, FF (hex). The data items are corrected at the
characteristic correcting section 134 and outputted on the printer
section 6. The gradation pattern P2 internally generated,
corrected, and outputted is taken in again by the scanner section 4
as described above. The scanner section samples the inputted
gradation pattern P3 gradation by gradation.
[0092] To find the value of each gradation, for example, a highly
stable portion is sampled in the area shown in FIG. 7. Since the
peripheral part of each gradation lacks stability, the area
expressed by range X (x2-x1) and range Y (y2-y1) is sampled with a
sampling pitch of p (that is, sampling is done at a rate of one
sample every a p number of pixels). The value of the relevant
gradation is determined by dividing the sum total of sample pixel
values by the sum total of sample pixels. The portion where
sampling is done for each gradation can be changed arbitrarily and
set in the desired area.
[0093] Next, using the value of each gradation thus obtained, the
characteristic correction data item f2 is determined. When the
abscissa represents the value of each gradation pattern P1
generated at the internal pattern generating section 131 and the
ordinate represents the value of each gradation obtained through
calculations after the scanner section 4 takes in the hard copy P2
from the printer section 6, there is an almost linear relationship
between the input and the output as shown in FIG. 8.
[0094] That is, the second characteristic correction data item f2
is found which makes the inputted gradation pattern P3 have an
almost linear relationship between the input and the output as the
gradation pattern P1 generated at the internal pattern generating
section 131. Therefore, the correction process can bring back the
inputted gradation pattern P3 into the state of the originally
generated gradation pattern P1 on the basis of the second
characteristic correction data item f2.
[0095] When the characteristic correction data item f2 is found on
the basis of an almost linear curve, that is, a curve having no
nonlinear portions, defective data items resulting from the
discontinuity of data and the reversal of numerical values due to
noise can be eliminated, which makes the system less affected by
noise.
[0096] Since the obtained relationship between the input and the
output is represented by the data items skipping at regular
intervals, not all the data items expressed in 8 bits (i.e., 256
values expressed in 8 bits), missing data items are interpolated by
the following method. The number of data items interpolated need
not be larger than the number of data items set in the
characteristic correction section 134. For example, even if the
input image data contains 8 bits, it is enough to interpolate as
many data items as there are 128 values in 7 bits provided that the
output image data contains 7 bits. An interpolation method is, for
example, one of the following ordinary approaches:
[0097] Linear interpolation
[0098] Spline interpolation
[0099] Interpolation by a method of least squares
[0100] The missing data items are found by using one of these. For
the curve representing the relationship between the input and the
output obtained from the acquired data items, a curve contrasting
with a straight line
y=x
[0101] is found. The curve is determined to be a characteristic
correction data item (referred to as a second correction data item
f2). If a curve representing the relationship between the input and
output obtained by interpolation is C, the second correction data
item f2 can be found as follows:
f2[n]=i
[0102] (n =0, 1, 2, . . . , 127)
[0103] where i fulfills the following expression
i.ltoreq.C[i]<i+1
[0104] (n =0, 1, 2, . . . , 127)
[0105] f2: a second correction data item
[0106] C: a curve representing the relationship between the input
and the output.
[0107] After the second correction data item f2 has been
determined, a combination (referred to as a third correction data
item f3) of the first correction data item f1 used for
interpolation when the printer section 6 outputs a gradation
pattern and the second correction data item f2 found from the
relationship between the input data and the output data is stored
as a usually used characteristic correction data item in a memory
section, such as the NVRAM in the characteristic section 134. An
example of a method of finding the third correction data item f3
will be shown below.
f3[n]=f2[f1[n]]
[0108] (n =0, 1, 2, . . . , 127)
[0109] f1: a first correction data item
[0110] f3: a third correction data item
[0111] Then, the process of creating the characteristic correction
data item f3 has finished. The created characteristic correction
data item f3 (or the third correction data) is used in an actual
image process. Specifically, in an actual image process, the image
data read from the document D by the scanner section 4 is sent to
the characteristic correcting section 134 via the correction data
select section 132 that has selected the input image data from the
scanner section 4 under the direction of the data select signal
from the main CPU 91. Using the characteristic correction data item
f3 (or the third correction data item) stored in a memory section,
such as the NVRAM, the characteristic correcting section 134
corrects the gradation characteristic of the inputted image data
and sends the corrected data as the output image data to the
printer section 6 or the page memory 98.
[0112] As explained above, the discontinuity of data items or the
reversal of numerical values is not corrected through complicated
calculations. Instead, characteristic correction data items are
found at two stages using the previously given characteristic
correction data item so that even if the discontinuity of data
items or the reversal of numerical values takes place, it may be
suppressed to the extent that it has no adverse effect on the
creation of the characteristic correction data items. Use of a
combination of the characteristic correction data items of two
different stages enables the difference between machines to be
absorbed and makes the machine less affected by noise. This
provides the characteristic correction data items as expected.
[0113] Therefore, the gradation characteristic of the input image
data from the scanner section 4 is corrected using the thus
obtained characteristic correction data items. This provides a
copied image whose subtle half tone portions are optimized with a
constantly stable picture quality.
[0114] 4. Second Embodiment
[0115] A color image forming apparatus according to a second
embodiment of the present invention will be explained in detail by
reference to the accompanying drawings.
[0116] FIG. 11 is a side view of the internal configuration of a
digital color copying machine according to a second embodiment of
the present invention. FIG. 12 is a block diagram of the digital
color copying machine. FIG. 13 is a block diagram of the color
image processing section of the digital color copying machine. FIG.
14 is a flowchart to help explain a characteristic correction
method in the second embodiment. FIG. 15 shows an example of a
color gradation pattern printed on paper to form a hard copy.
[0117] In FIG. 11, a digital color copying machine 200 is composed
of a scanner section 201 acting as a reading device and a printer
section 202 acting as an image forming apparatus.
[0118] The scanner section 201 for reading the image on a document
has a document table cover 203 on its top. The scanner section also
has a document table 204 that is made of transparent glass and
faces the document table cover 203 in the closed state. A document
D is set on the document table. Below the document table 204, there
are provided an exposure lamp 205 for illuminating the document D
on the document table 4, a reflector 206 for gathering the rays of
light from the exposure lamp 205 on the document D, and a first
mirror 207 for deflecting the reflected light from the document D
to the left in the figure. The exposure lamp 205, reflector 206,
and first mirror 207 are fixed to a first carriage 208. The first
carriage 208 is connected to a pulse motor (not shown) via a
toothed belt (not shown). The first carriage receives the driving
force of the pulse motor and moves in parallel with the document
table 204.
[0119] In the figure, to the left of the first carriage 208, that
is, in the direction in which the light reflected by the first
mirror 207 is directed, a second carriage 209 is provided so as to
move in parallel with the document table 204 via a driving
mechanism (not shown), such as a toothed belt and a DC motor. On
the second carriage 209, a second mirror 211 for deflecting
downward the reflected light from the document D directed by the
first mirror 207 and a third mirror 212 for deflecting the
reflected light from the second mirror 211 to the right in the
figure are provided at right angles to each other. The second
carriage 209 follows the movement of the first carriage 208 in such
a manner that it moves in parallel with the document table 204 at a
speed half that of the first carriage 208.
[0120] In a plane including the optical axis of the light reflected
via the second carriage 209, there is provided an image forming
lens 213 for concentrating the reflected light from the second
carriage 209 to form an image at a specific magnification. In a
plane crossing at almost right angles with the optical axis of the
light passed through the image forming lens 213, there is provided
a CCD image sensor (photoelectric conversion element) 215 that
converts the reflected light converged by the image forming lens
213 into an electric signal, or image data.
[0121] When the light from the exposure lamp 205 is gathered by the
reflector 206 on the document D on the document table 204, the
reflected light from the document D passes through the first mirror
207, second mirror 211, third mirror 212, and image forming lens
213 and strikes the CCD image sensor 215, which converts the light
into image data.
[0122] The printer section 202 has a first to fourth image forming
sections 210y, 120m, 210c, and 210k that produce images separated
into the individual color components on the basis of a known
subtractive color mixing method, that is, a yellow (hereinafter,
referred to as y) image, a magenta (hereinafter, referred to as m)
image, a cyan (hereinafter, referred to as c) image, and a black
(hereinafter, referred to as k) image.
[0123] Below the image forming sections 210y, 210m, 210c, and 210k,
there is provided a transport mechanism 220 including a transport
belt 221 for transporting each color image formed at the
corresponding image forming section in the direction of arrow a in
the figure. The transport belt 221 is stretched between a driving
roller 291 rotated in the direction of arrow a by a belt motor (not
shown) and a driven roller 292 separated a specific distance apart
from the driving roller 291. The transport belt is moved endlessly
at a constant speed in the direction of arrow a. The image forming
sections 210y, 210m, 210c, and 210k are arranged in series in the
direction in which the transport belt 221 transports the image.
[0124] The image forming sections 210y, 210m, 210c, and 210k
include photosensitive drums 261y, 261m, 261c, and 261k,
respectively, acting as image retaining members. Each of the drums
is formed so that its outer peripheral surface can rotate in the
same direction at the position where it is in contact with the
transport belt 221. A drum motor (not shown) for rotating each
photosensitive drum at a specific circumferential speed is
connected to each photosensitive drum.
[0125] The axes of the photosensitive drums 261y, 261m, 261c, 261k
are arranged at regular intervals in such a manner that they cross
at right angle with the direction in which the image is transported
by the transport belt 221. In the following explanation, the
direction of the axis of each photosensitive drum is determined to
be the main scanning direction (a second direction) and the
direction in which the photosensitive drum is rotated, or the
direction (the direction of arrow a in the figure) in which the
transport belt 221 rotates is determined to be the feed direction
(a first direction).
[0126] Around the photosensitive drums 261y, 261m, 261c, 261k,
charging devices 262y, 262m, 262c, 262k and discharging devices
263y, 263m, 263c, 263k extending in the main scanning direction,
development rollers 264y, 264m, 264c, 264k, lower stirring rollers
267y, 267m, 267c, 267k, and upper stirring rollers 268y, 268m,
268c, 268k extending in the main scanning direction, transfer
devices 293y, 293m, 293c, 293k extending in the main scanning
direction, and cleaning blades 265y, 265m, 265c, 265k and waste
toner collecting screws 266y, 266m, 26c, 266k extending in the main
scanning direction are arranged in that order in the direction in
which the photosensitive drum rotates.
[0127] Each transfer device is provided in a position where it
presses the transfer belt 221 against the corresponding
photosensitive drum, that is, inside the transport belt 221. The
exposure point in the exposure device explained later is formed on
the outer peripheral surface of the photosensitive drum between
each charging device and the corresponding development roller.
[0128] Below the transport mechanism 220, there are provided paper
feed cassettes 222a, 222b that house a plurality of sheets of
recording paper P acting as image forming mediums to which the
image formed by the image forming sections 210y, 210m, 210c, 210k
is transferred.
[0129] At one end of each of the paper feed cassettes 222a, 222b
and on the side closer to the driven roller 292, there are provided
pickup rollers 223a, 223b that pick up, one by one, the sheets of
recording paper P housed in the paper feed cassettes 222a, 222b,
starting with the one at the top. Between the pickup rollers 223a,
223b and the driven roller 292, there is provided a resist roller
224 for aligning the leading edge of the recording paper sheet P
taken out of the paper feed cassettes 222a, 22b with the leading
edge of the y toner image formed on the photosensitive drum 261y of
the image forming section 210y. The toner images (m, c, k) formed
on the other photosensitive drums 211y, 211m, 211c are supplied to
the respective transfer positions in synchronization with the
transfer timing of the recording paper sheet P transported over the
transport belt 221.
[0130] An adsorption roller 226 that gives a specific amount of
adsorbability to the recording paper sheet P transferred with a
specific timing via the resist roller 224 is provided between the
resist roller 224 and the first image forming section 210y and near
the driven roller 292, specifically on the outer peripheral surface
of the driven roller via the transport belt 221. The axis of the
adsorption roller 226 is arranged in parallel with the axis of the
driven roller 292.
[0131] At one end of the transport belt 221 and near the driving
roller 291, specifically on the outer peripheral surface of the
driving roller 291 via the transport belt 221, there is provided a
position shift sensor 296 for sensing the position of the image
formed on the transport belt 221 is provided a specific distance
apart from the driving roller 291. The position shift sensor 296 is
composed of a transmitting type or a reflecting type of
photodetector.
[0132] Above the peripheral surface of the driving roller 291 and
on the transfer belt 221 on the downstream side of the position
shift sensor 96, there is provided a transfer belt cleaning device
295 that removes the toner adhering onto the transfer belt 221 or
paper dust of the recording paper sheet P.
[0133] In the direction in which the recording paper sheet P
transported via the transport belt 221 and separated from the
driving roller 291 is further transported, there is provided a
fixing device 280 that melts the toner image transferred to the
recording paper sheet P by heating the sheet P at a specific
temperature and fixes the toner image on the sheet P. The fixing
unit 280 is composed of a heat roller pair 281, oil applying
rollers 282, 283, a web take-up roller 284, a web roller 285, and a
web pressing roller 286. The toner image formed on the recording
paper sheet P is fixed on the sheet, which is discharged by a
delivery roller pair 287.
[0134] The exposure device 250 that forms a color-separated
electrostatic latent image on the outer peripheral surface of each
of the photosensitive drums has a semiconductor laser 260. The
emission of light of the semiconductor laser is controlled on the
basis of the image data items (y, m, c, k) of the respective colors
into which the image is separated at the image processing device
explained later. On the optical path of the semiconductor laser
260, there are provided, in this order, a polygon mirror 251 that
is rotated by a polygon motor 254 and reflects and scans the laser
beam and f .theta. lenses 252, 253 for correcting the focal point
of the laser beam reflected by the polygon mirror 251 to form an
image are provided.
[0135] Between the f .theta. lens 253 and each of the
photosensitive drums 261y, 261m, 261c, 261k, there are provided
first deflecting mirrors 255(y, m, c, k) for deflecting the laser
beam of each color passed through the f .theta. lens 253 toward the
exposure position on the corresponding photosensitive drum and
second and third deflecting mirrors 256(y, m, c) and 257(y, m, c)
that further deflect the laser beams deflected by the first
deflecting mirrors 255y, 255m, 255c. After being deflected by the
first deflecting mirror 255k, the laser beam for black is directed
to the photosensitive drum 261k without passing through another
mirror.
[0136] Regarding the color image forming device 200, the block
diagram of its electrical instrumentation is the same as that in
the monochrome digital copying machine of FIG. 2. Therefore,
explanation of that part will not be given.
[0137] The characteristic structure of the color image processing
in the image processing section 96 will be described by reference
to FIG. 12. As shown in FIG. 14, the image processing section 96
includes an adjustment interpolation section 301. The image
processing section also includes a color conversion section 305, an
ACS 303, a macro recognition section 309, and a recognition memory
311 each connected to the adjustment interpolation section. The
image processing section further includes a background removing
section 313, a histogram forming section 315, a
background/character level detector 317, an LPF 319, an HEF 321, a
character emphasizing section 323, and a micro recognition section
325, which are connected to the color conversion section, ACS,
macro recognition section, and recognition memory. The image
processing section 96 still further includes a combining section
327 that receives and combines the output of the LPF 319 and that
of the character emphasizing section 323, an enlargement/reduction
section 329 that enlarges and reduces the combined image, a black
character forming section 333 and an inking section 331 each
connected to the enlargement/reduction section, a selector 335 that
selects one of the outputs of the black character forming section
and the inking section, a y correction section 337, a data
processing section 339, a screen processing section 341, and a
pulse-width converter 343 that receives the output of the screen
processing section 341. A DM 340 is connected to the data
processing section 339.
[0138] The image processing section 96 has an optional section 345.
The optional section 345 includes an HDD 347, a variable-length
compression section 349 connected to the HDD, and a PM 357. The
optional section also includes an error diffusion section connected
to the PM and a YIQ converter 353 and a CMY converter 355 each
connected to the enlargement/reduction section 329. A printer I/F
361 is connected to the CMY converter 355 via the PM 357. A scanner
I/F 363 is connected to the data processing section 339. A printer
I/F 365 is connected to the screen processing section 341 via a
smoothing section 359.
[0139] Hereinafter, the function of each of the above-described
sections will be explained in detail. In FIG. 12, the adjustment
interpolation section 301 compensates for the position shift by
interpolating the necessary data items in the image on the basis of
the amount of shift. Specifically, in the enlargement and reduction
functions, the main scanning operation is carried out by a digital
process and the feed operation is performed by changing the moving
speed of the scanner carriage. In the case of a structure using an
RGB 3-line CCD sensor (with an 8-line pitch), there is no problem
with a magnification of .times.1 or integral multiples. At
magnitudes other than these, a position shift takes place in the
feed direction between R, G, and B. The position shift is corrected
at the adjustment interpolation section 301.
[0140] The ACS 303 judges whether the document is a color document
or a monochrome document. Specifically, the ACS makes the judgment
during pre-scanning and switches between the color process and the
monochrome process in a regular scanning.
[0141] In the color conversion section 305, although the scanner
input signal is RGB, the printer signal is CMYK. Therefore, the
conversion of color signal is necessary. In the color conversion,
the RGB signal is converted into a CMY signal. The K signal is
generated at the inking section 331. Color adjustment according to
the user's taste is made by changing the parameters of color
conversion.
[0142] The monochrome forming section 307 generates a monochrome
signal from the RGB color signal in the monochrome copy mode.
[0143] The background removing section 313, histogram forming
section 315, background/character level detector 317 remove the
background of a document, such as the background of a newspaper.
The histogram forming section creates a color density histogram of
the document. From the values in the histogram, the color level of
the background and the level of the characters are sensed. On the
basis of the sensed levels, the background removing section 313
removes the background portions and outputs the character portions
more densely.
[0144] The macro recognition section 309 judges the photograph area
and the character area in the document. The macro recognition
section judges the areas in broad perspective on the basis of the
run image in the page memory. The run image has been obtained by
pre-scanning the document.
[0145] The micro recognition section 325 judges the photograph area
and the character area in the document. It makes a judgment
referring to a local area with a size of about 3.times.3
pixels.
[0146] The LPF 319, HPF 321, and character emphasizing section 323
perform a spatial filter process, including noise removal, moir
removal, and edge emphasis, and an emphasizing process of the
character portions. The filter parameter is set for each area on
the basis of the micro recognition data.
[0147] The enlargement/reduction section 329 performs an
enlargement and reduction process in the main scanning
direction.
[0148] The YIQ conversion section 353, error diffusion section 351,
and CMY conversion section temporarily store the image in a memory
in electronic sorting or in an image rotation process and reads the
necessary part from the memory. Since it is necessary to read any
area of the image or to read the image at a constant rate, a
fixed-length compression/expansion process is needed. Use of a YIQ
signal reduces the redundancy of color components and error
diffusion helps maintain the gradation, while reducing the number
of bits used.
[0149] The variable-length compression section 349 stores the image
in an HDD when the electronic sorting function cannot get a
sufficient memory capacity from only the page memory. Since there
is a limit to the access speed of the HDD, the variable-length
compression is effected at as high a compression efficiency as
possible.
[0150] The inking section 331 generates a K signal from CMY,
whereas the color conversion section 305 converts RGB into CMY.
[0151] The black character forming section 333 creates a black
character. Since writing a black character all in black provides a
high-quality picture in terms of color and resolution as compared
with a stack of C, M, and Y, the micro recognition signal is used
to switch between the inking and the formation of a black
character.
[0152] The y correcting section 337 corrects the y characteristic
of the printer. The y correction section sets a y table for each of
C, M, Y, and K.
[0153] The data processing section 339 performs a gradation
process, including error diffusion. The data processing section
converts the 8-bit input signal into a signal containing about 4
bits without degrading the gradation.
[0154] In the case of a quadruple tandem printer, each color has a
different recording phase. Therefore, the DM (direct memory) 340 is
used to delay the image of each color so that each color may have
the same phase.
[0155] The screen processing section 341 inclines the screen of
each color to suppress the occurrence of moir or color errors. In
the case of a quadruple tandem printer, the direct output of each
color causes moir or color errors because of a slight skew of each
color or an error in the magnification. The screen processing
section suppresses this.
[0156] Because the signal level and recording density in the image
processing are not liner, the pulse-width converter 343 converts
the pulse width by controlling the pulse driving time of the laser
modulation section to achieve a linear characteristic.
[0157] With the above-described configuration, the color
characteristic correction data is created according to the
flowchart of FIG. 13.
[0158] A internal color pattern generating section 431 for
generating a reference color image pattern CP1 is connected to the
color correction data select section 432, which is connected to a
color characteristic correcting section 434. The color correction
data select section 432 receives the data select signal from the
main CPU 91. The output of a color characteristic correction data
forming section 433 for acquiring the image data from the scanner
section 4 and creating the characteristic correction data is
supplied to a color characteristic correcting section 434. The
output of the color characteristic correcting section 434 is
supplied to the y correcting section 337.
[0159] The operation of creating the color characteristic
correction data in the second embodiment of the present invention
will be described by reference to the flowchart of FIG. 14.
[0160] The operation of creating the color characteristic
correction data is basically the same as in the above-described
monochrome digital image forming apparatus. In FIG. 14, when the
operator operates a specific key on the operation panel 80, this
causes the characteristic correction data creation mode to be
selected and an operation start instruction to be inputted. As a
result, the internal color pattern generating section 431 generates
a color gradation pattern CP1 whose density changes stepwise (S31).
The generated color gradation pattern CP1, together with one
correction data item Cf1 selected from a plurality of correction
data items (Cf1, Cf1-2, Cf1-3, . . . ) according to the data select
signal supplied from the main CPU 91, is sent to the color
characteristic correcting section 434.
[0161] The operator enters the correction data item from the
operation panel of FIG. 17 as in the monochrome digital image
forming apparatus.
[0162] The color characteristic correcting section 134 corrects the
color gradation pattern CP1 from the internal color pattern
generator 431 using the given correction data item Cf1 and sends
the corrected color gradation pattern CP2 to the printer section 6
(S33). The printer section 6 prints the corrected color correction
pattern CP2 from the color characteristic correcting section 434 on
a sheet of paper P to provide a hard copy (S35).
[0163] FIG. 15 shows an example of a hard copy of the color
correction pattern CP2. Since the hard copy is a color image, it
has the gradation image of each of cyan C, magenta M, yellow Y, and
black K.
[0164] The first color correction data item Cf1 used in the color
characteristic correcting section 134 is used to correct the degree
of the deflection of the color signal to the printer. Therefore,
the first color correction data item Cf1 is divided into color
correction data items about cyan C, magenta M, yellow Y, and black
K. The supplied image signal is corrected using the color
correction data item Cf1 to produce a color correction pattern CP2.
Supplying the color correction pattern CP2 to the printer provides
a substantially linear characteristic, although the deflection of
the characteristic of the printer system is not complete. That is,
the correction corresponds to the case where the deflected curve of
FIG. 6 is corrected to a linear one in the monochrome digital image
forming apparatus, except that the color correction is made for
each of the four color signals.
[0165] The color hard copy CP2 outputted from the printer section 6
is set in the scanner section 4, which reads it as the color
correction pattern CP3 of the color hard copy (S37). The value of
each gradation of the read color gradation pattern CP3 is found by
sampling data on each gradation of the gradation pattern. The
process is carried out for each of cyan C, magenta M, yellow Y, and
black K.
[0166] A concrete method of determining the value of each gradation
is almost the same as in the monochrome digital image forming
apparatus.
[0167] Next, using the determined value of the gradation of each
color, the second color characteristic correction data item Cf2 is
found. The second color characteristic correction data item Cf2 is
a correction data item used to correct the deflection including the
deflection in the scanner section 4 to achieve a near-perfect
linearity as in the monochrome digital image forming apparatus.
This is basically the same as with the curve of FIG. 8 having a
corrected linearity in the monochrome digital image forming
apparatus.
[0168] A method of finding the second color characteristic
correction data Cf2 is basically the same as in the interpolation
process in the monochrome digital image forming apparatus, except
that the interpolation process is carried out for each of cyan C,
magenta M, yellow Y, and black K (S19).
[0169] After the second color characteristic correction data item
Cf2 has been obtained, the first color characteristic correction
data item Cf1 used in the correction when the printer section 6
outputted the color gradation pattern CP1 is combined with the
second color characteristic correction data item Cf2 for each of
cyan C, magenta M, yellow Y, and black K to produce a third color
characteristic correction data item Cf3. This is stored as a
normally used characteristic correction data item in the memory
section, such as an NVRAM, in the characteristic correcting section
434 (S41). The method of creating the third color characteristic
data item is the same as in the monochrome digital image forming
apparatus.
[0170] The first, second, and third correction data items of the
invention are, for example, the digital density correction data
items corresponding to the digital density data items at 256 stages
in a one-to-one ratio according to the deflection of the printer
system (or the scanner system). For example, the correction data
item "48" corresponds to the digital density data "50" and the
correction data item "49" corresponds to the digital density data
item "51". The finest correction data items are the digital
correction density data items "1" to "253" corresponding to the
digital density data items "0" to "255" in a complete one-to-one
ratio.
[0171] These correction data items may correspond to the digital
density data items in a more rough ratio, for example, in a
three-to-one ratio, instead of a complete one-to-one ratio. The
correction data items may be function data items expressed by a
suitable function. In the case of the color digital copying
machine, the correction data items are prepared for each of cyan C,
magenta M, yellow Y, and black K.
[0172] As described above, with the present invention, the
characteristic correction data items are prepared at two stages to
correct the deflection for each copying machine body. The
correction data item at the first stage is used to correct the
deflection in the output system including the printer section. The
correction data item at the second stage is used to correct the
deflection in the input system including the scanner section. These
two types of correction data items are combined to generate a third
correction data item for the entire system. The third correction
data item is set as a correction data item for use in ordinary
image processing. This makes it possible to provide an image
forming apparatus capable of correcting the deflection for each
copying machine and realizing an ideal linear relationship (see
FIG. 8) between the input and the output as expected at the design
stage.
[0173] Accordingly, it is possible to provide an image processing
method and image processing apparatus that are capable of creating
characteristic correction data items as expected without being
affected by the discontinuity of data items and the reversal of
numerical values due to noise, when characteristic correction data
items for correcting the input and output characteristics of the
entire system for each copying machine are created.
[0174] Furthermore, it is possible to provide a monochrome or color
digital copying machine with a very high reproducibility of density
that causes the shading image of the read document to be reproduced
with fidelity by the density correction process.
[0175] Additional advantages and modifications will readily occurs
to those skilled in the art. Therefore, the invention in its
broader aspects is not limited to the specific details and
representative embodiments shown and described herein. Accordingly,
various modifications may be made without departing from the spirit
or scope of the general inventive concept as defined by the
appended claims and their equivalents.
* * * * *