Title: Image reading apparatus
Abstract: An image reading device includes a light irradiation device that moves and scans a document while irradiating the light on the document table, a color CCD sensor which reads the reflecting light of the light from the light irradiating device and photoelectric converts it into plural color signals, and a correction device which executes the shading correction of plural color signals that are photoelectric converted by the color CCD sensor and at the same time, executes the color balance correction and the stray light correction. Further, at the same time with the shading correction executed using white document data comprising R, G, B signals of a white document in color equipment to the shading correction plate that are read and photoelectric converted by the color CCD sensor as desired values for the shading correction, this image reading device executes the color balance correction and the stray light correction.
Patent Number: 6,958,834 Issued on 10/25/2005 to Ide
| Inventors:
|
Ide; Naoaki (Shizuoka-ken, JP)
|
| Assignee:
|
Kabushiki Kaisha Toshiba (Tokyo, JP);
Toshiba Tec Kabushiki Kaisha (Tokyo, JP)
|
| Appl. No.:
|
613868 |
| Filed:
|
July 11, 2000 |
| Current U.S. Class: |
358/505; 358/461; 358/504; 358/518 |
| Intern'l Class: |
H04N 001/46 |
| Field of Search: |
358/504,505,518,461,474,115,500
|
References Cited [Referenced By]
U.S. Patent Documents
| 4608595 | Aug., 1986 | Nakayama et al.
| |
| 5077605 | Dec., 1991 | Ikeda et al.
| |
| 5216498 | Jun., 1993 | Matsunawa et al.
| |
| 6198841 | Mar., 2001 | Toyama et al.
| |
| 6597472 | Jul., 2003 | Suzuki et al.
| |
| 6785026 | Aug., 2004 | Terajima et al.
| |
| 2003/0016881 | Jan., 2003 | Matsuura.
| |
| Foreign Patent Documents |
| 6-57050 | Jul., 1994 | JP.
| |
Primary Examiner: Wallerson; Mark
Attorney, Agent or Firm: Foley & Lardner LLP
Claims
1. An image reading device comprising:
light irradiating means for scanning a surface of a document on a document table
while irradiating the surface with light;
color photoelectric conversion means for reading light reflected from the surface
of the document, as reflected light, and photoelectric converting the reflected
light into plural color signals;
white reference means provided at the side of the document table for being read
and photoelectric converted by the color photoelectric conversion means;
storage means for storing signal data comprising plural color signals that are
photoelectric converted by the color photoelectric conversion means and white document
data comprising plural color signals that are read and photoelectric converted
by the color photoelectric conversion means from a white document in color equivalent
to the white reference means placed on the document table; and
correction means for executing a color balance correction and a stray light correction
simultaneously with an execution of a shading correction based on the signal data
and the white document data stored in the storage means,
wherein the correction means executes the stray light correction by correcting
a difference between the signal data and the white document data which are stored
in the storage means.
2. The image reading device according to claim 1, wherein the correction means
executes the shading correction and at the same time, the stray light correction
by setting the white document data stored in the storage means as desired values
and executes the white balance correction by correlating the white reference means
with the white reference data comprising plural color signals that are read and
photoelectric converted by the color photoelectric conversion means and the white
document data stored in the storage means.
3. The image reading device according to claim 2, wherein the correction means
further executes the correction of uneven density in the moving and scanning direction
of the light irradiating means simultaneously with the other corrections.
4. The image reading device according to claim 3, wherein the storage means stores
sub-scanning data comprising plural color signals that are plural positions in
the moving and scanning direction of a uniform density image document placed on
the document table read and photoelectric converted by the color photoelectric
conversion means; and
the correction means executes the uneven density correction by executing the
color balance correction by setting the sub-scanning data stored in the storage
means as desired values for the color balance correction.
5. The image reading device according to claim 4, wherein the sub-scanning data
comprises a mean value of plural pixels at plural positions in the moving and scanning direction.
6. An image reading device comprising:
a light irradiating device configured to scan a surface of a document while irradiating
the document with light;
a color CCD sensor configured to read light reflected from the surface of the
document, as reflected light, and photoelectric convert the reflected light into
plural color signals;
a white shading correction plate provided at the side of the document table to
be read and photoelectric converted by the color CCD sensor;
a storage device configured to store signal data comprising plural color signals
that are photoelectric converted by the color CCD sensor and white document data
comprising plural color signals that are read and photoelectric converted by the
color CCD sensor from a white document in color equivalent to the white shading
correction plate placed on the document table; and
a correction device to execute a color balance correction and a stray light correction
simultaneously with an execution of a shading correction based on the signal data
and the white document data stored in the storage device,
wherein the correction device executes the stray light correction by correcting
a difference between the signal data and the white document data which are stored
in the storage device.
7. The image reading device according to claim 6, wherein the correction device
executes the shading correction and at the same time, the stray light correction
simultaneously by setting the white document data stored in the storage device
as desired values and executes the color balance correction by correlating the
white reference data comprising plural color signals that are the shading correction
plate read and photoelectric converted by the color CCD sensor with the white document
data stored in the storage device.
8. The image reading device according to claim 7, wherein the correction device
further executes the uneven density correction in the moving and scanning direction
of the light irradiating device simultaneously with the other corrections.
9. The image reading device according to claim 8, wherein the storage device
stores plural color signals that are plural positions in the moving and scanning
direction of an uniform density image document placed on the document table, read
and photoelectric converted by the color CCD sensor, and
the correction device executes the uneven density correction by executing the
color balance correction using the sub-scanning data stored in the storage device
as desired values for the color balance correction.
10. The image reading device according to claim 9, wherein the sub-scanning data
comprises a mean value of plural pixels at plural positions in the moving and scanning direction.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image reading device for reading a document
placed on a document table with a color CCD sensor.
2. Description of the Related Art
In a color image reading device that is used as an input portion of a color printer
or a terminal of a personal computer, even when an image in uniform density is
read, an image information that is output from an image reading device may cause
uneven color density depending on pixels due to the lack of optical uniformity
as non-uniform illuminance of a light illuminating the document surface, variance
of characteristic of a color CCD sensor, decrease in the lightness of the visual
field of a lens when reading the light reflected on a document and converting into
image data by a color CCD sensor.
In order to compensate an uneven illuminance caused by the optical factors mentioned
above, so far a white shading correction plate, etc. provided at the side of a
document table is read bad photoelectric converted into image data and the white
reference is judged from this image data whenever reading a document and based
on this white reference, the shading correction is executed to correct the document
read data.
Further, in a color CCD sensor, when reading a color image by dividing it
into plural colors, the read data may become uneven for each color because there
is a difference in spectral sensitivity characteristics of R (Red), G (Green) and
B (Blue) filters. Therefore, in order to compensate the sensitivity difference
in R, G and B filters, the shading correction is so far executed so far based on
a white reference and at the same time, the color balance correction is executed
so as to improve color reproducibility as disclosed in Japanese Patent Publication
No. 6-57050.
However, the above-mentioned shading correction and the color balance correction
are so far executed by reading the reflected light on the shading correction plate
provided at the side of a document table and using this read value as the white
reference. Actually, however, the illuminance of the light irradiating the shading
correction plate is not always agree with the illuminance of the light irradiating
a document placed on a document table. Therefore, when the shading correction is
executed based on the shading correction plate as the white reference, the color
balance does not agree with that at the document table and a delicate color difference
is produced when reproducing an image by a printer, etc. Further, the shading correction
plate is actually not pure white and therefore, the sensitivity difference of the
RGB filters cannot be corrected.
On the other hand, the optical system for irradiating a document generally moves
for scanning on a rail mounted in the main body of an image reading device and
therefore, the accuracy control of the rail is required in order to obtain an image
of high reproducibility. However, the maintenance of highly accurate control is
difficult and actually, the quantity of reflecting light from the document surface
varies depending on the tilt of the rail in the sub-scanning direction and the
uneven image density is generated from the fluctuation in the quantity of light
and a good image reproducibility is prevented.
Accordingly, for an image reading device, it is desirable not only to
execute the shading correction and the color balance correction of image data but
also to correct a delicate color difference caused due to a difference in illuminance
at the positions of the shading correction plate and the document table. It is
further desirable to obtain a full color image of high color reproducibility by
correcting the color balance so as not to produce uneven density in the sub-scanning
direction when reproducing an image irrespective of distortion of the rail supporting
the scanning movement of the optical system to irradiate a document.
SUMMARY OF THE INVENTION
An object of the present invention is to obtain image data of good color reproducibility
by correcting image data so as to correct color differences that are caused due
to a difference in illuminance even when illuminance in irradiation at the position
of the shading correction plate differs form that of the document table when correcting
the shading and the color balance of image data.
Another object of the present invention is to obtain image data of good color
reproducibility by correcting image data so as to obtain good density reproducibility
irrespective of fluctuation in quantity of reflecting light in the overall area
in the sub-scanning direction due to the distortion of the optical system at the
time of scanning movement to irradiate a document.
According to the present invention, an image reading device comprising:
a light irradiating means for moving and scanning while irradiating the light to
a document table; a color photoelectric conversion means for reading the reflecting
light of the light from the light irradiating means for the photoelectric conversion;
and a correction means for executing the shading correction and at the same time,
the color balance correction and the stray light correction of plural color signals
that are photoelectric converted by the color photoelectric conversion means.
Further, according to the present invention, an image reading device comprising:
a light irradiating device for moving and scanning the document table while irradiating
the light; a color CCD sensor for reading the reflected light of the light from
the light irradiating device and photoelectric converting to plural color signals;
and a correcting device for executing the shading correction, color balance correction
and stray light correction of plural color signals that are photoelectric converted
by the color CCD sensor is provided.
Further, according to the present invention, an image reading device comprising:
a light irradiating means for moving and scanning a document table while irradiating
the light; a color photoelectric conversion means for reading the reflected light
of the light from the light irradiating means and photoelectric converting into
plural color signals; and a correcting means for correcting uneven density of plural
color signals photoelectric converted by the color photoelectric conversion means
in the moving and scanning direction of the light irradiating means is provided.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagram schematically showing a structure of a color scanner and
illuminance in the sub-scanning direction of the color scanner in a first embodiment
of the present invention;
FIG. 2 is a block diagram showing an image signal processing system of a color
scanner in the first embodiment of the present invention;
FIG. 3 is a spectral sensitivity characteristic diagram of a color filter used
by a color CCD sensor 11 in the first embodiment of the present invention;
FIG. 4 is a diagram showing white document reading values, shading correction
plate reading values, stray light correction desired values, and stray light+color
balance desired value used for RGB shading correction in the first embodiment of
the present invention;
FIG. 5 is a schematic diagram showing the time of reading a uniform density
image document by a color scanner in a second embodiment of the present invention;
FIG. 6 is a diagram showing fluctuation in quantity of incident light to a color
CCD sensor in the sub-scanning direction in the second embodiment of the present invention;
FIG. 7 is a diagram showing a desired value for a color balance correction in
the sub-scanning direction in the second embodiment of the present invention;
FIG. 8 is a schematic diagram showing measuring points on a document table in
the second embodiment of the present invention;
FIG. 9 is a plan view showing measuring points on the document table in the
second embodiment of the present invention;
FIG. 10 is a diagram showing fluctuation in the actual quantity of incident
light to the color CCD sensor in the sub-scanning direction in the second embodiment
of the present invention; and
FIG. 11 is a diagram showing a desired value for the color balance correction
in the sub-scanning direction actually executed in the second embodiment of the
present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Preferred embodiments of the present invention will be described below
in detail referring to the attached drawings.
FIG. 1 schematically shows a structure of a color scanner
10, which is
an image reading device in a first embodiment of the present invention, equipped
with a color CCD sensor
11, and is used in combination with a digital color
printer
1. Above the color CCD sensor
11, a document table
12
comprising a transparent glass plate is provided.
Below the document table
12, there is provided an optical system
13
to irradiate a document G placed on the document table
12 and project the
reflecting light from the document G to the color CCD sensor
11. The optical
system
13 comprises a reflector
14, a lamp
17 of which light
is condensed to a sub-reflector
16 and illuminates the document G, first
through third mirrors
18,
20 and
21, a filter
22, and
a lens
23.
The reflector
14, the sub-reflector
16, the lamp
17 and
the mirror
18 are mounted on a first carriage
24, and the second
and the third mirrors
20 and
21 are mounted on a second carriage
26. The first carriage
24 and the second carriage
26 are driven
by a motor
30 that is controlled by a control board
28 and reciprocates
on a rail
27.
The lamp
17 is a linear shaped halogen lamp and the illuminated light
is reflected on the reflector
14 and the sub-reflector
16 and is
applied to the document G at the optimum light quantity distribution. The light
irradiated from the lamp
17 and reflected on the surface of the document
G is reflected on the first through third mirrors
18,
20 and
21,
and after cutting the infrared rays by the filter
22, applied to the color
CD sensor
11 through the lens
23. The color CCD sensor
11
photoelectric converts the incident and reflected light from the document G into
color signals of R(Red), G (Green) and B (Blue). These R, G and B signals are transferred
to the digital color printer
1 after the signal processing by the control
board
28.
On the document table
12, there is provided a document table cover
13
to press the document G so as to closely fit to the document table
12.
At the side of the document table
12, there is arranged a white shading
correction plate
32 that is illuminated by the lamp
17 and read by
the color CCD sensor
11. The shading correction plate
32 is a white
reference plate for the shading correction to correct the uneven luminous intensity
distribution of the lamp
17 and the uneven sensitivity of the color CCD
sensor
11.
Even when an image in a uniform density is read, the output signal fluctuates
depending on pixels due to such fluctuations in the optical system as non-uniform
illuminance of light applied to the document surface, fluctuation in characteristic
of a CCD sensor, decrease in brightness of the peripheral visual field of a lens.
The shading correction is a method to obtain an image in a uniform density by correcting
such fluctuation.
The shading correction is executed based on the white reference data and the
black reference data. When the shading correction plate
32 (the white reference)
is read, the quantity of light is attenuated at pixels at both ends of the main
scanning direction, as shown by the illuminance plot (a) in FIG. 1. So, the shading
correction is executed for every RGB signals according to a ratio between a difference
of read image data of RGB signals that are input signals from the document G and
the white reference data and a difference between the white reference data and
the black reference data that is a dark environment read before lighting the lamp
17.
The shading correction is executed as shown in the following shading correction
formula (1):
(where, K: Coefficient of Correction, SIG: Read Image Data, BK: Black Reference
Data, WH: White Reference Data)
FIG. 2 is a block diagram showing an image signal processing system of the color
scanner
10. The image data read by the color CCD sensor
11 is divided
into R, G, B colors by a color filter
33 having spectral sensitivity characteristics
shown in FIG. 3 and photoelectric converted to analog signals. The analog converted
image data is input into an A/D converter
36 via an amplifier
34
and converted into digital signals.
Next, the digital converted image data is input into a shading correction ASIC
37, that is a correcting means, wherein the color balance correction and
the stray light correction are executed simultaneously with the execution of the
shading correction. The shading correction ASIC
37 is controlled by a CPU
38. Further, an EEPROM
40 is connected to the CPU
38. This
EEPROM
40 stores a white document read values (RW, GW, BW) that are the
white document data obtained when adjusting the color scanner
10 and become
desired values for the RGB shading correction.
After the correction by the shading correction ASIC
37, the image data
is input to a registration ASIC
41 and after correcting the out of read
phase caused by the arrangement of the color CCD sensor
11, output to the
digital color printer
1. Because all of the shading correction, color balance
correction and stray light correction of the image data are completed at the time
when the image data is output to the digital color printer
1 from the color
scanner
10, the color correction only is made at the time when an image
is developed subsequently in the digital color printer
1 and a full color
image of good color reproducibility is easily obtained.
Next, the image data correction by the shading correction ASIC
37 will
be described in detail. The shading correction ASIC
37 executes the shading
correction of a digital converted image data output from the A/D converter
36
according to the shading correction formula (1). At the same time, in order to
correct a difference in spectral sensitivity characteristics of the color filter
33, the shading correction ASIC
37 adjusts the gain of the amplifier
34 so that the read values (RS, GS, BS) of the shading correction plate
32 become the same as the white document read values (RW, GW, BW) that are
the desired values for the RGB stray light correction.
The RGB stray light correction is executed in order to correct a difference between
RGB signals obtained by reading a white document (not shown) comprising a document
in colors equivalent to the shading correction plate
32 placed on the document
table
12 in advance and RGB signals obtained by reading the shading correction
plate
32 at its mounted position when adjusting the color scanner
10.
In other words, the RGB stray light correction is to correct the read values (RS,
GS, BS) of the shading correction plate
32 so as to substitute them with
the white document read values (RW, GW, BW) on the document table
12. Because
of this RGB stray light correction, the desired value optimized at the reading
position of the shading correction plate
32 is set for R, G and B, individually.
This desired value is equivalent to the coefficient of correction K of the shading
correction formula (1). When this correction is executed, a difference of RGB signals
when reading a white reference document with RGB signals when reading the shading
correction plate
32 is corrected and converted into color balanced values.
When further described in detail, as shown in FIG. 1, at the shading correcting
position where the shading correction plate
32 is read by the color scanner
10, the light irradiated from a lamp
17a is reflected on a
shading correction plate
32a, further reflected on first through
third mirrors
18a,
20a,
21a, and is incident
into the color CCD sensor
11. On the other hand, at the position of the
document table
12, the light irradiated from a lamp
17b is
reflected on the surface of the document table
12, further reflected on
first through third mirrors
18b,
20b,
21b
and is incident into the color CCD sensor
11.
As a result, the illuminance in the sub-scanning direction of the arrow mark x
of the scanning direction of first and second carriages
24,
26 fluctuates
as shown by the solid line (a). At the reading position of the shading correction
plate
32 of the color scanner
10, the stray light is produced by
the atmospheric influence at the end surface of the document table
12 and
around the shading correction plate
32 and its illuminance differs from
illuminance on the document table. Therefore, for instance, assuming that the illuminance
at the reading position of the shading correction late
32 is higher than
the illuminance on the document table
12 as shown by the solid line (a)
in FIG. 1, when the stray light correction is not executed, for the document data
reflected from the document G on the document tale
12, an image data that
is darker than the image output for displaying an original image density of the
document G is produced and image reproducibility by the digital color printer
1
is impaired.
Accordingly, the shading correction ASIC
37 executes the shading
correction using the white document read values (RW, GW, BW) read at the position
of the document table
12 as desired values for the shading correction and
at the same time as the shading correction, executes the stray light correction
for correcting a difference in illuminance between the reading position of the
shading correction plate
32 and the surface of the document table
12.
Further, the color balance for correcting a difference of spectral sensitivity
characteristics of the color filter
33 of the color CCD sensor
11
varies according to a difference in illuminance between the reading position of
the shading correction plate
32 and the surface of the document table
12
and full color image reproducibility is impaired. Therefore, the shading correction
ASIC
37 executes the color balance correction by taking the correlation
between the white document values (RW, GW, BW) read on the surface of the document
table
12 and the read values of the shading correction plate
32 (RS,
GS, BS) as desired values for the color balance correction and executes the stray
light correction and the color balance correction simultaneously with the execution
of the shading correction.
For desired values of the RGB stray light correction and the color balance correction
that are executed simultaneously with the shading correction, based on a color
filter of B (Blue) of low relative sensitivity, RGB radios (RS/BS, GS/BS, BS/BS)
that are color balances are obtained from read values (RS, GS, BS) of the shading
correction plate
32 and the white document read values (RW, GW, BW) are
used as absolute values because these white document read values are the desired
values for the shading correction. That is, (Stray Light+Color Balance Desired
Values) become (RS/BS)×BW, (GS/BS)×BW, BW as shown in FIG. 4.
The color scanner
10 in a structure as described above reads a white document
and sets desired values for the shading correction at the time of its shipment
or when adjusting the fluctuated characteristics of the optical system
13
at the time of replacement of a lamp for the maintenance. That is, a white document
values (RW, GW, BW) read with the color CCD sensor
11 by placing the white
document on the document table
12 are stored in the EEPROM
40.
Hereafter, when starting to read a document G on the document table
12,
for setting white reference data for the shading correction, the reading operation
of the shading correction plate
32 is first executed and read values (RS,
GS, BS) of the shading correction plate are read.
On the other hand, the CPU
38 calls out the white document read values
(RW, GW, BW) of the EEPROM
40 and from these values and the shading correction
plate read values (RS, GS, BS) read from the shading correction ASIC
37,
sets the shading correction values so that they become the above-mentioned (Stray
Light+Color Balance Desired values) (RS/BS)×BW, (GS/BS)×BW, BW and sets
the shading correction ASIC
37 so as to execute the stray light correction
and the color balance correction at the same time of the execution of the shading correction.
Then, when the document G is scanned and a document image is read, image data
separated into spectral components of RGB by the color CCD sensor
11 and
then, subject to the color balance correction and the stray light correction after
digital conversion via the amplifier
34 and A/D converter
36 by the
shading correction ASIC
37. Then, after the out of phase of reading due
to the arrangement of the color CCD sensor
11 is corrected by a registration
ASIC
41, the image data is output to the digital color printer
1
jointly to the address/data bus from the CPU. Thus, the digital color printer
1
forms a full color image using this image data.
When constructed as described above, the image reading device is able to execute
the color balance correction and the stray light correction simultaneously with
the execution of the shading correction of image data by making white document
read values (RW, GW, BW) that are read from a white document placed on the document
table
12 as desired values for the shading correction and is also able to
execute the shading correction of image data and at the same time the color balance
correction and the stray light correction and correct a delicate color difference
caused by a difference in illuminance between the reading position of the shading
correction plate
32 and the surface of the document table
12.
Accordingly, when image data with the color balance correction and the
stray light correction made simultaneously with the shading correction as described
above is input to the digital color printer
1, it becomes possible for the
digital color printer
1 to easily reproduce a good color reproducible and
high definition full color image. Furthermore, all of the shading correction, the
color balance correction and the stray light correction can be executed within
the color scanner
10. Accordingly, when the image data output from the color
scanner
10 after completing all the shading correction, the color balance
correction and the stray light correction is used, it becomes possible to suppress
fluctuation of a reproduced image caused by the fluctuation in characteristic at
the image forming apparatus side such as image forming terminals, etc. of a printer/a
personal computer, and form a full color image in uniform quality.
Next, a second embodiment of the present invention will be described. This
second embodiment is to correct irregular density caused by fluctuation in quantity
of light due to the slip of the carriage in the sub-scanning direction when reading
a document. Therefore, in this second embodiment the same component elements as
those described in the first embodiment are assigned with the same reference numerals
and the detailed explanation thereof will be omitted.
The optical system
13 which irradiates the light to the document G on
the document table
12 of the color scanner
10 and projects the reflected
light from the document G to the color CCD sensor
11 is installed on the
first and second carriages
24,
26 and scans on the rail
27.
Therefore, the horizontal degree of the optical system
13 to an image surface
of the document G is decided by accuracy of the rail
27. Normally, even
when the assembling accuracy and the installing condition of the rail are set rigidly,
it is difficult to completely eliminate the horizontal distortion and this horizontal
distortion appears as an uneven image density.
FIG. 6 is a diagram showing the fluctuation in quantity of light incident into
the color CCD sensor
11 in the sub-scanning direction of the arrow x that
is the scanning direction of the first and second carriages
24,
26
when the color scanner
10 reads the document G, and for instance, an example
wherein the illuminance dropped at the rear end of the scanning is shown. The dotted
line A in FIG. 6 shows a value when the image data was not corrected against the
fluctuation in quantity of light and the solid line B shows a value after the image
data was corrected against the fluctuation in quantity of light.
That is, if a desired values of the color balance correction in the sub-scanning
direction at the shading correction by the shading correction ASIC
37 was
set constant as shown by the dotted line C in FIG. 7, the quantity of light of
the image data output to the digital color printer
1 after read by the color
scanner
10 and the shading correction, the color balance correction and
the stray light correction were executed drops as shown by the dotted line A in
FIG. 6, and when an image is formed by the digital color printer
1, the
uneven density is produced. In this case, therefore, as shown in the solid line
D in FIG. 7, when a desired values for the color balance correction in the sub-scanning
direction in the shading correction is increased corresponding to decrease in quantity
of light, drop of the quantity of light of the image data output to the digital
color printer
1 side is prevented as shown by the solid line B in FIG. 6.
When further described in detail, an image document H in uniform density is
placed in advance on the document tale
12 when adjusting the color scanner
10 as shown in FIG. 5 and this image document H in uniform density is read
at plural measuring points J
1-J
3, K
1-K
3 and L
1-L
3;
total 9 points in the matrix shape on the document table
12; 3 point in
the main scanning direction, 3 points in the sub-scanning direction as shown in
FIG. 8. This read uniform density image data is stored in the EEPROM
40.
At each of total 9 measuring points on the document table
12, image data
of 80×80 pixels shown in FIG. 9 is read and an average is obtained and a correction
value is obtained from this average value.
Then, to make the uniform density image data in the sub-scanning direction
at each of the measuring points stored in the EEPROM
40 as desired values
for the color balance correction by the shading correction ASIC
37, a coefficient
of correction corresponding to drop in quantity of light is calculated in the CPU
38 and a coefficient of correction K for correcting quantity of light in
the sub-scanning direction is obtained. On the other hand, the RGB image data from
the color CCD sensor
11 of the document G read on the document table
12
is applied with the shading correction, the stray light correction and the color
balance correction by the shading correction ASIC
37 and at the same time,
a coefficient of correction for the color balance correction is changed at an interval
when the data is read at the observing points J
1-J
3, K
1-K
3
and L
1-L
3 in the sub-scanning direction and the uneven density is corrected.
As a result, a coefficient of correction is adjusted for every observing point
J, K and L in the sub-scanning direction and therefore, when desired values for
the color balance correction in the sub-scanning direction at the time of the shading
correction are increased gradually corresponding to the decrease in quantity of
light, the quantity of light of the image data output to the digital color printer
1 is gradually corrected as shown by the solid line E in FIG. 10. Hereafter,
based on the image data of which out of phase is corrected by the registration
ASIC
41, a full color image in nearly uniform density corrected from uneven
density is formed in the digital color printer
1.
According to this second embodiment, when white document read values (RW,
GW, BW) are set as desired values for the shading correction and further, image
data in uniform density of a image document H on the document table
12 that
are read at plural measuring points J
1-J
3, K
1-K
3 and
L
1-L
3 are set as desired values for the color balance correction,
the color balance correction and the stray light correction can be made simultaneously
with the shading correction of image data, and further, uneven density caused from
fluctuation of quantity of light in the sub-scanning direction can be corrected.
In other words, a delicate color difference of image data caused by a difference
in illumination between the reading position of the shading plate
32 and
the surface of the document table
12 can be corrected and the uneven density
in the sub-scanning direction caused from the horizontal distortion of accuracy
of the rail
27 also can be corrected.
Therefore, when the image data processed with the color balance correction
and the stray light correction simultaneously with the shading correction and further,
the uneven density correction in the sub-scanning direction is input into the digital
color printer
1, it becomes possible to easily reproduce a good color reproducible
and high definition full color image in the digital color printer
1. Furthermore,
all of the shading correction, the color balance correction, the stray correction
and the uneven density correction can be made within the color scanner
10.
Therefore, when the image data output from the color scanner
10 after completing
all the shading correction, the color balance correction, the stray light correction
and the uneven density correction is used, it becomes possible to suppress the
fluctuation of a reproduced image caused from the fluctuation of characteristics
at an image forming apparatus side such as an image forming terminal, etc. of a
printer/a personal computer and form a full color image in uniform quality.
Further, the present invention is not restricted to the above-mentioned
embodiments but can be deformed variously within the scope of the present invention.
For instance, by forming a black reference plate near the white reference shading
correction plate, the shading correction plate before reading a document and the
black reference plate are read and the read data may be used as the data for the
shading correction. Further, it is optional to input the data read by the image
reading device and processed for correction to a color printer that is a computer
terminal through the communication line without inputting directly to an image
forming apparatus or once store in a page memory, etc. and read out as necessary.
Further, the number of pixels that are read at the measuring points in the
second embodiment is not restricted if an accurate measurement is possible.
As described above in detail, according to the present invention, when a white
document placed on the document table is read by a photoelectric conversion means
and using white document data comprising R, G, B color signals that are obtained
from this white document as desired values for the shading correction, the shading
of image data is corrected, the color balance correction and the stray light correction
can be made simultaneously with the shading correction. Accordingly, when reading
a document, a satisfactory color reproducible image data is obtained without causing
a delicate color difference and using this image data, it becomes possible to easily
reproduce a good reproducible full color image of high definition.
Further, all of these shading correction, the color balance correction and
the stray light correction can be executed within the image reading device. Accordingly,
when the image data output from an image reading device after the above-mentioned
correction/corrections is used, it becomes possible to suppress fluctuation of
reproduced image caused by a difference in characteristic at the image forming
apparatus side and a full color image in uniform quality can be reproduced irrespective
of difference in characteristic of an image forming apparatus.
Further, according to the present invention, when plural positions in the
sub-scanning direction of a uniform density image document that is placed on the
document table are read by the photoelectric conversion means and the shading of
the image data is compensated using sub-scanning data comprising plural R, G, B
color signals obtained from the uniform density image document as desired values
for the color balance correction, it is possible to correct the uneven density
in the sub-scanning direction simultaneously with the execution of the shading
correction, the color balance correction and the stray light correction. Accordingly,
when reading a document, a good color reproducible image data is obtained without
causing uneven density in the sub-scanning direction and using such image data,
a good color reproducible high definition full color image can be easily reproduced
in an image forming apparatus.
Furthermore, all of the shading correction, the color balance correction,
the stray light correction and the uneven density correction can be executed within
the apparatus. Accordingly, when the image data that is output from the image reading
device after completing the shading correction, the color balance correction, the
stray light correction and the uneven density correction is used, it becomes possible
to suppress fluctuation of a reproduced image due to a difference in characteristics
of an image forming apparatus side and to reproduce a full color image in more
uniform quality irrespective of a difference in characters of an image forming apparatus.
*
