Title: Image processing apparatus, image processing method, and storage medium for color matching
Abstract: An image processing apparatus comprises a color matching processing unit for performing color matching processing according to color reproduction characteristics of input and output devices, a color separation unit for separating image data subjected to the color matching processing, into color components corresponding to recording agents used by the output device, and a control means for controlling a method of the color matching processing and a method of the image data separation, according to a kind of input image. Thus, it is possible to perform the color matching processing and the color component separation according to the kind of input image, thereby realizing the color matching in consideration of how to use the recording agents and the satisfactory color matching according to a human's sight characteristic.
Patent Number: 6,897,988 Issued on 05/24/2005 to Saito, et al.
| Inventors:
|
Saito; Kazuhiro (Yokohama, JP);
Makita; Takeshi (Kawasaki, JP);
Matsuoka; Hirochika (Yokohama, JP)
|
| Assignee:
|
Canon Kabushiki Kaisha (Tokyo, JP)
|
| Appl. No.:
|
624376 |
| Filed:
|
July 27, 2000 |
Foreign Application Priority Data
| Jul 28, 1999[JP] | 11-213795 |
| Current U.S. Class: |
358/515; 358/1.9; 358/505; 358/523 |
| Intern'l Class: |
H04N 001/46 |
| Field of Search: |
358/515,18,505,523,113,115,518,525,522,19,500
382/167
|
References Cited [Referenced By]
U.S. Patent Documents
| 4751535 | Jun., 1988 | Myers.
| |
| 5510910 | Apr., 1996 | Bockman et al.
| |
| 5546195 | Aug., 1996 | Arai.
| |
| 5604566 | Feb., 1997 | Mano et al.
| |
| 5668890 | Sep., 1997 | Winkelman.
| |
| 5767980 | Jun., 1998 | Wang et al.
| |
| 5838333 | Nov., 1998 | Matsuo.
| |
| 5875260 | Feb., 1999 | Ohta.
| |
| 5933252 | Aug., 1999 | Emori et al.
| |
| 5949427 | Sep., 1999 | Nishikawa et al.
| |
| 6257693 | Jul., 2001 | Miller et al.
| |
| 6549654 | Apr., 2003 | Kumada.
| |
| 6608927 | Aug., 2003 | Ohta.
| |
| Foreign Patent Documents |
| 405330148 | Dec., 1993 | JP.
| |
Primary Examiner: Coles; Edward
Assistant Examiner: Gibbs; Heather D.
Attorney, Agent or Firm: Fitzpatrick, Cella, Harper & Scinto
Claims
1. An image processing apparatus comprising:
color matching processing means for performing a color matching processing of
mapping an input color signal into a color reproduction range of an output apparatus;
color separation means for separating image data, subjected to the color matching
processing, into color components corresponding to recording agents used by the
output apparatus;
setting means for setting a kind of input image;
control means for controlling a method of the color matching processing and a
method of the image data separation, according to the kind of input image set by
said setting means;
synthesis means for generating a lookup table by synthesizing output of said
color matching means and said color separation means, both controlled by said control
means; and
image processing means for converting the input color signal using the generated
lookup table.
2. An apparatus according to claim 1, wherein said control means sets a UCR (under
color removal) quantity used by said color separation means, according to the kind
of input image set by said setting means.
3. An apparatus according to claim 1, wherein said control means sets a UCR quantity
used a kind of input apparatus, a profile corresponding to the kind of output apparatus,
and a kind of a recording sheet used by the output apparatus.
4. An apparatus according to claim 1, wherein the kind of input image includes
a photograph and a graphic.
5. An apparatus according to claim 1, wherein said image processing means performs
a multidimensional interpolation processing.
6. An image processing method comprising:
a color matching processing step, of performing a color matching processing of
mapping an input color signal into a color reproduction range of an output apparatus;
a color separation step, of separating image data, subjected to the color matching
processing, into color components corresponding to recording agents used by the
output apparatus;
a setting step, of setting a kind of input image;
a control step, of controlling a method of the color matching processing and
a method of the image data separation, according to the kind of input image set
in said setting step;
a synthesis step, of generating a lookup table by synthesizing output of said
color matching processing step and said color separation step, both controlled
in said control step; and
an image processing step, of converting the input color signal using the generated
lookup table.
7. An image processing method comprising:
an obtaining step, of obtaining a color matching processing condition to realize
color matching between a first apparatus and a second apparatus; and
a generating step, of generating a multidimensional table based on the color
matching processing condition obtained in said obtaining step,
wherein the color matching processing condition of mapping a color reproduction
range of the first apparatus to a color reproduction range of the second apparatus
is obtained based on an equal-interval hue line of the Atlas of the Munsell Color
System,
wherein the color matching processing condition of each plural representative
colors is independently obtained, and
wherein the mapping condition concerning a color other than the plural representative
colors is obtained based on the color matching processing condition obtained for
the plural representative colors.
8. A method according to claim 7, wherein
an achromatic-color target value is set for each of the plural representative
colors, and
the color matching processing condition is based on the achromatic-color target
value.
9. A method according to claim 8, wherein the obtained color matching processing
condition is set as the color matching processing condition used when a kind of
input image is a photograph.
10. A method according to claim 8, wherein the plural representative colors are
red, green, blue, cyan, magenta and yellow.
11. A method according to claim 7, wherein the color matching processing condition
for one of the plural representative colors corresponding to a recording agent
used in the second apparatus is obtained based on a reproduction line of the recording
agent used in the second apparatus.
12. A storage medium which stores a program for executing an image processing
method, said program comprising:
code for an obtaining step, of obtaining a color matching processing condition
to realize color matching between a first apparatus and a second apparatus; and
code for a generating step, of generating a multidimensional table based on the
color matching processing condition obtained in said obtaining step,
wherein the color matching processing condition of mapping a color reproduction
range of the first apparatus to a color reproduction range of the second apparatus
is obtained based on an equal-interval hue line of the Atlas of the Munsell Color
System,
wherein the color matching processing condition of each plural representative
colors is independently obtained, and
wherein the mapping condition concerning a color other than the plural representative
colors is obtained based on the color matching processing condition obtained for
the plural representative colors.
13. An image processing method of mapping an input color signal into a color
reproduction range of an output device, said method comprising:
a providing step, of providing a hue line of the Atlas of the Munsell Color System;
a setting step, of setting a target color in regard to each of plural representative
colors; and
a mapping step, of mapping a color signal outside the color reproduction range
of the output device into the color reproduction range by using the hue line of
the Atlas of the Munsell Color System, provided in said providing step, and the
target color set in said setting step, both corresponding to the color signal outside
the color reproduction range of the output device.
14. A storage medium which stores a program for executing an image processing
method of mapping an input color signal into a color reproduction range of an output
device, said program comprising:
code for a providing step, of providing a hue line of the Atlas of the Munsell
Color System;
code for a setting step, of setting a target color in regard to each of plural
representative colors; and
code for a mapping step, of mapping a color signal outside the color reproduction
range of the output device into the color reproduction range by using the hue line
of the Atlas of the Munsell Color System, provided in said providing step, and
the target color set in said setting step, both corresponding to the color signal
outside the color reproduction range of the output device.
15. An image processing apparatus comprising:
an obtaining unit adapted to obtain a color matching processing condition to
realize color matching between a first apparatus and a second apparatus; and
a generating unit adapted to generate a multidimensional table based on the color
matching processing condition obtained by said obtaining unit;
wherein the color matching processing condition of mapping a color reproduction
range of the first apparatus to a color reproduction range of the second apparatus
is obtained based on an equal-interval hue line of the Atlas of the Munsell Color
System,
wherein the color matching processing condition of each plural representative
colors is independently obtained, and
wherein the mapping condition concerning a color other than the plural representative
colors is obtained based on the color matching processing condition obtained for
the plural representative colors.
16. An image processing apparatus for mapping an input color signal into a color
reproduction range of an output device, said apparatus comprising:
a providing unit adapted to provide a hue line of the Atlas of the Munsell Color
System;
a setting unit adapted to set a target color in regard to each of plural representative
colors; and
a mapping unit adapted to map a color signal outside the color reproduction range
of the output device into the color reproduction range by using the hue line of
the Atlas of the Munsell Color System, provided by said providing unit, and the
target color set by said setting unit, both corresponding to the color signal outside
the color reproduction range of the output device.
17. An image processing apparatus comprising:
a color matching processing unit adapted to perform a color matching processing
of mapping an input color signal into a color reproduction range of an output apparatus;
a color separation unit adapted to separate image data, subjected to the color
matching processing, into color components corresponding to recording agents used
by the output apparatus;
a setting unit adapted to set a kind of input image;
a control unit adapted to control a method of the color matching processing and
a method of the image data separation, according to the kind of input image set
by said setting unit,
a synthesis unit adapted to generate a lookup table by synthesizing output of
said color matching unit and said color separation unit, both controlled by said
control unit; and
a image processing unit adapted to convert the input color signal using the generated
lookup table.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to image processing apparatus and method which
perform processing concerning color matching, and a storage medium.
2. Related Background Art
A color matching method is the method to match tints of two devices (e.g., a
monitor
and a color printer each having a different color reproduction range) with each
other. When the color reproduction range of the monitor is compared with the color
reproduction range of the color printer, the color reproduction range of the monitor
is generally wider than the color reproduction range of a printing output by the
color printer, whereby a part of colors represented by the monitor can not be reproduced
by the printer.
Thus, various methods to realize color matching between the monitor and the
color printer are designed. Concretely, in these methods, in a device-independent
uniform color space such as CIE-L*a*b* color system, color gamut mapping (or color
space compression) to the color reproduced by the monitor is performed to obtain
the color reproducible by the printer, thereby realizing the color matching between
the monitor and the color printer.
As a conventional color matching method, there is designed a method which performs
compression processing without dislocating hue angles as shown in FIG. 18, a method
which performs compression processing at equal value (lightness) as shown in FIG.
19, and a method which performs compression processing toward one specific point
on an achromatic color axis as shown in FIG. 20, or the like.
In an actual processing system, when image data is subjected to color gamut mapping
pixel by pixel, an enormous processing time is necessary. Thus, a multidimensional
table in which only representative points were subjected to the color gamut mapping
is previously generated, and colors at points other than the representative points
are subjected to color processing according to multidimensional interpolation processing.
However, in the above conventional case, since the color matching is performed
in the device-independent L*a*b* color space, it is impossible to realize color
matching in consideration of how to use inks dependent on a printer (device).
Further, in such the conventional color gamut mapping as shown in FIG. 18,
in the case where the compression is performed without dislocating the hue angles
in an a*b* plane, since the uniform color space such as the L*a b* color space
does not completely reflect a human's sight characteristic, there is a problem
that an appeared tint rather changes because the compression is performed without
dislocating the hue angle. As to value (lightness) compression, in the case where
the compression is performed at the identical lightness as shown in FIG. 19, there
is an advantage that the brightness itself is maintained. However, there is a problem
that a chroma of a highlight area or a shadow area disappears extremely. Further,
in the case where the lightness compression is performed in such the manner as
shown in FIG. 20, the reproducibility of the chroma improves in comparison with
the compression method shown in FIG.
19. However, there is a problem that
unbalance of the lightness occurs due to the hue, whereby feeling of wrongness
appears in reproduction image quality.
SUMMARY OF THE INVENTION
The present invention has been made in consideration of the above programs, and
an object thereof is to realize satisfactory color matching.
An object of the first invention is to perform color matching processing and
color
component separation according to kinds of input images, thereby realizing the
color matching in consideration of how to use recording agents.
An object of the second invention is to realize satisfactory color matching according
to a human's sight characteristic.
In order to achieve the above objects, the present invention has the following structures.
The first invention is characterized by comprising:
- a color matching processing means for performing color matching processing
according to color reproduction characteristics of input and output apparatuses;
- a color separation means for separating image data subjected to the
color matching processing, into color components corresponding to recording agents
used by the output apparatus; and
- a control means for controlling a method of the color matching processing
and a method of the image data separation, according to a kind of input image.
The second invention is characterized by an image processing method which obtains
a color matching processing condition to realize color matching between a first
apparatus and a second apparatus,
- wherein the color matching processing condition that a color reproduction
range of the first apparatus is mapped to a color reproduction range of the second
apparatus is obtained based on an equal-interval hue line of the Atlas of the Munsell
Color System.
Other objects and features of the present invention will become apparent from
the following detailed description and the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram showing a structure of the first embodiment of the
present invention;
FIG. 2 is a block diagram for explaining a system environment;
FIG. 3 is a diagram for explaining a user interface of an UI (user interface)
unit 106;
FIG. 4 is a block diagram showing a structure of the second embodiment of the
present invention;
FIG. 5 is a block diagram for explaining structures of an photograph ink separation
unit and a character/graphic ink separation unit;
FIG. 6 is a flow chart for explaining processing to generate an ink separation
table for converting R, G and B data into C, M, Y and K data in the third embodiment
of the present invention;
FIG. 7 is a block diagram showing a structure of the fourth embodiment of the
present invention;
FIG. 8 is a flow chart for explaining processing to generate a color gamut mapping
table in the fourth embodiment;
FIG. 9 is a flow chart for explaining a color gamut mapping quantity determination
step S804 based on monitor and printer profiles shown in FIG. 8;
FIG. 10 is a diagram for explaining the flow chart shown in FIG. 9;
FIG. 11 is a diagram for explaining a step S904;
FIG. 12 is a diagram for explaining the step S904 of setting mapping
value (lightness) according to a kind of image set in FIG. 9, and explaining lightness
setting of a color gamut mapping quantity suitable for character and graphic in
the fifth embodiment;
FIG. 13 is a diagram for explaining six color areas in a color area judgment
step S807 shown in FIG. 8;
FIG. 14 is a diagram for explaining a mapping processing step S808 based
on two mapping points shown in FIG. 8;
FIG. 15 is a diagram for explaining the mapping processing step S808
based on the two mapping points shown in FIG. 8;
FIG. 16 is a diagram for explaining the color gamut mapping quantity determination
step S804 based on the monitor and printer profiles shown in FIG. 8, in
the sixth embodiment;
FIG. 17 is a block diagram showing a structure of the seventh embodiment;
FIG. 18 is a diagram for explaining a conventional example that compression
processing is performed without dislocating hue angles in an a*b* plane;
FIG. 19 is a diagram for explaining a conventional example that color gamut
mapping is performed at identical lightness; and
FIG. 20 is a diagram for explaining a conventional example that color gamut
mapping is performed toward one specific point on an achromatic color axis.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 2 is a block diagram for explaining one example of a system environment
to which the embodiment of the present invention is applied. In FIG. 2, numeral
205 denotes a computer which is used by a user to form a document. Numeral
204 denotes a monitor which displays the formed document. Numerals
201,
202 and
203 denote kinds of formed documents. Namely, numeral
201
denotes a character document, numeral
202 denotes a graphic document, and
numeral
203 denotes a photograph document. Numeral
209 denotes a
color printer which prints the formed document. Numerals
206,
207
and
208 denote kinds of sheets which are used in the color printer
209.
Namely, numeral
206 denotes a coated sheet, numeral
207 denotes a
dedicated sheet, and numeral
208 denotes a common sheet (or an ordinary
sheet). As for these three kinds of sheets, color reproduction ranges at the printing
time and their costs differ chiefly. Namely, the color reproduction ranges become
small in the order of the coated sheet
206, the dedicated sheet
207
and the common sheet
208, and the costs become lower in the same order.
Numeral
210 denotes a printing which was printed by the color printer
209.
The user properly uses the sheets (the coated sheet, the dedicated sheet and the
common sheet) in accordance with usage of the document composed of characters,
graphics and photographs. Even in this case, the user always expects that the printing
which has been satisfactorily color-matched with the printer is output.
(First Embodiment)
FIG. 1 is a block diagram showing a structure of the first embodiment of the
present invention. In FIG. 1, numeral
101 denotes a matching table unit
for a photograph (called a photograph matching table unit hereinafter), numeral
102 denotes a matching table unit for a character and a graphic (called
a character/graphic matching table unit hereinafter), numeral
103 denotes
an ink separation (or decomposition) unit for a photograph (called a photograph
ink separation unit hereinafter), numeral
104 denotes an ink separation
(or decomposition) unit for a character and a graphic (called a character/graphic
ink separation unit hereinafter), and numeral
105 denotes a halftone unit.
The halftone unit
105 performs processing to match the number of bits of
input data with the number of bits manageable by the printer in a halftone method
such as a dither method, an error diffusion method or the like. Numeral
106
denotes a UI (user interface) unit by which a user selects a monitor profile, a
kind of image and a sheet. Numeral
107 denotes a matching table generation
unit, numeral
108 denotes a monitor profile unit, and numeral
109
denotes a profile unit for a photograph (called a photograph profile unit hereinafter).
The photograph profile unit
109 stores profile data for the photograph according
to each sheet. Numeral
110 denotes a profile unit for a character and a
graphic (called a character/graphic profile unit hereinafter) which stores profile
data for the character and the graphic.
The user selects the monitor profile, the kind of image kind and the sheet respectively
from a monitor profile menu
301, an image kind menu
302 and a sheet
menu
303 as shown in FIG. 3, by using the UI unit
106.
For example, processing to be performed when a sRGB is selected in the monitor
profile menu
301, a photograph is selected in the image kind menu
302,
and a coated sheet is selected in the sheet menu
303 will be explained.
Such selected information is transferred to the matching table generation unit
107. In response to the transferred information, the matching table generation
unit
107 loads sRGB profile data and coated sheet profile data respectively
from the monitor profile unit
108 and the photograph profile unit
109.
Then a photograph matching table is generated in later-described color gamut mapping,
and such table data is written in the photograph matching table unit
101.
When character/graphic is selected in the image kind menu
302 of the
UI unit
106, the profile data according to the selected sheet is loaded
from the character/graphic profile unit
110 to the matching table generation
unit
107. Then a character/graphic matching table is generated in the later-described
color gamut mapping, and such table data is written in the character/graphic matching
table unit
102.
The profile data in the photograph profile unit
109 is the data which
is obtained by binarizing R′ (red), G′ (green) and B′ (blue)
data through the photograph ink separation unit
103 and the halftone unit
105, and represents a color reproduction characteristic of the result printed
by a printer engine. In the photograph profile unit
109, the profile data
is stored for each sheet. Similarly, the profile data in the character/graphic
profile unit
110 is the data which is obtained by binarizing R′,
G′ and B′ data through the character/graphic ink separation unit
104 and the halftone unit
105, and represents a color reproduction
characteristic of the result printed by a printer engine. In the character/graphic
profile unit
110, the profile data is stored for each sheet.
For example, the profile data representing the color reproduction characteristic
includes R (red), G (green), B (blue), C (cyan), M (magenta) and Y (yellow) color
reproduction range data representing color reproduction ranges of a device used
in the later-described fourth embodiment.
Next, the photograph ink separation unit
103 and the character/graphic
ink separation unit
104 will be explained with reference to FIG.
5.
It should be noted that the structure of the photograph ink separation unit
103
is the same as the character/graphic ink separation unit
104.
In FIG. 5, numeral
501 denotes a luminance/density conversion unit, and
numeral
502 denotes an UCR (under color removal) quantity unit which stores
a value to control a set UCR quantity. Numeral
503 denotes an UCR processing
unit which performs UCR processing according to the value stored in the UCR quantity
unit
502. The luminance/density conversion unit
501 converts the
R′, G′ and B′ data into C, M and Y data on the basis of following
logarithmic equations.
where α is an arbitrary real number.
The C, M and Y data are then converted according to a value μ% set to the
UCR quantity unit
502, as follows.
where β(C, M, Y, μ) is a real number which is changed according
to the values of C, M, Y and p, and by which how to apply a K ink can be set.
Here, for example, the value p % is set to be 50% in the photograph ink separation
unit
103, and the value p % is set to be 100% in the character/graphic ink
separation unit
104. Thus, it is possible to make the UCR quantity for the
photograph differ from the UCR quantity for the character and the graphic. In the
UCR quantity 100% used for the character and the graphic, a process gray based
on C, M and Y three colors is not composed, and a gray line is composed by only
the K ink. Thus, it is possible to realize the color reproduction which is not
influenced easily by a balance change of C, M and Y inks due to a change of a color
printer. On the other hand, the UCR quantity for the photograph is set to be 50%,
and β(C, M, Y, μ)=0 is set when the C, M and Y values are small, whereby
it is possible to realize ink separation that the K ink is not used to reproduce
flesh color.
Next, a flow of the image data processing using the multidimensional table
generated by the matching table generation unit
107 will be explained.
When the photograph is selected in the image kind menu
302 of the UI
unit
106, generated R, G and B photograph image data are converted into
the R′, G′ and B′ data by the photograph matching table unit
101 according to multidimensional interpolation calculation processing based
on the stored multidimensional table. Then the R′, G′ and B′
data are subjected to ink separation processing suitable for the selected photograph,
by the photograph ink separation unit
103. After then, the processed data
are binarized by the halftone unit
105, transferred to the printer engine,
and subjected to printing.
Similarly, when the character/graphic is selected in the image kind menu
302 of the UI unit
106, generated R, G and B character/graphic image
data are subjected to the multidimensional interpolation calculation processing
based on the stored multidimensional table by the character/graphic matching table
unit
102. After the multidimensional interpolation calculation processing,
the obtained R′, G′ and B′ data are subjected to ink separation
processing suitable for the character and the graphic by the character/graphic
ink separation unit
104. After then, the processed data are binarized by
the halftone unit
105, transferred to the printer engine, and subjected
to printing.
In the conventional art, when the color matching is performed, the suitable inks
are not properly used according to the kind of image, whereby proper use of the
suitable ink can not be realized according to the photograph image and the character/graphic image.
According to the present embodiment, as explained above, the color matching
units (the photograph matching table unit
101 and the character/graphic
matching table unit
102) for matching tint are disposed independently of
the ink separation units (the photograph ink separation unit
103 and the
character/graphic ink separation unit
104), and the color matching unit
and the ink separation unit are selected according to the kind of image, whereby
proper use of the suitable ink can be realized according to the kind of image.
It should be noted that the structure used in the first embodiment can of course
correspond with the monitor profile set by the user. Further, the color matching
units (the matching table units
101 and
102) are provided independently
of the ink separation units (the ink separation unit
103 and
104),
and the necessary matching tables are previously generated for a combination of
the monitor and the sheet supposed to be frequently used. Thus, by previously storing
the table for the photograph in the photograph matching table unit
101 and
previously storing the table for the character and the graphic in the character/graphic
matching table unit
102, it is possible to save the time necessary to generate
the matching table, thereby performing the printout processing at high speed.
(Second Embodiment)
In the first embodiment, the means for realizing the color matching is provided
independently of the means for realizing the ink separation, whereby the printout
processing can be performed at high speed. The second embodiment proposes to simplify
a hardware structure for reduction in costs and color reproduction equivalent to
the first embodiment.
FIG. 4 is a block diagram showing a structure of the second embodiment. In FIG.
4, numeral
401 denotes a matching synthesis table unit for a photograph
(called a photograph matching synthesis table unit hereinafter), numeral
402
denotes a matching synthesis table unit for a character and a graphic (called a
character/graphic matching synthesis table unit hereinafter), and numeral
403
denotes a matching synthesis table generation unit. It should be noted that, like
FIG. 1, numerals
105,
106,
108,
109 and
110
denote a halftone unit, a UI unit, a monitor profile unit, a photograph profile
unit and a character/graphic profile unit, respectively.
Like the matching table generation unit
107 in the first embodiment,
the matching synthesis table generation unit
403 loads monitor profile data
from the monitor profile unit
108 according to a monitor profile, an image
kind and a sheet all set in the UI unit
106. When the image kind is the
photograph and the sheet is a coated sheet, the matching synthesis table generation
unit
403 loads photograph coated sheet profile data from the photograph
profile unit
109, generates a photograph matching table in later-described
color gamut mapping, and performs processing corresponding to that of the photograph
ink separation unit
103 of FIG. 1 on the result data of this photograph
matching table, thereby generating C, M, Y and K data. Thus, it is possible to
generate a synthesis table which converts R, G and B data equivalent to those processed
in the two block systems (i.e., the photograph matching table unit
101 and
the photograph ink separation unit
103) shown in FIG. 1 into the C, M, Y
and K data. Then this synthesis table is stored in the photograph matching synthesis
table unit
401.
Similarly, when the character/graphic is selected in the image kind menu
302 of the UI unit
106, the data are loaded from the monitor profile
unit
106 and the character/graphic profile unit
110, and the loaded
data is subjected to color gamut mapping and image synthesis processing. A character/graphic
matching synthesis table which is obtained as a result of such the processing is
stored in the character/graphic matching synthesis table unit
402.
Next, a flow of image data processing in the second embodiment will be explained.
When the photograph is selected in the image kind menu
302 of the UI unit
106, the generated R, G and B photograph image data are subjected to the
multidimensional interpolation calculation processing by the photograph matching
synthesis table unit
401 on the basis of the stored synthesis table. Then
C′, M′, Y′ and K′ data subjected to the multidimensional
interpolation calculation processing are binarized by the halftone unit
105,
transferred to a printer engine, and subjected to printing. When the image data
is the character or the graphic, the same processing as above is performed by using
the character/graphic matching synthesis table unit
402.
As explained above, there is no need to provide plural tables in each of the
photograph
matching table unit
101 and the character/graphic matching table unit
102
as in the first embodiment. Also, there is no need to provide any hardware corresponding
to the photograph ink separation unit
103 and the character/graphic ink
separation unit
104 as in the first embodiment, whereby it is possible to
simplify the hardware structure of the color matching apparatus and thus reduce
the costs.
(Third Embodiment)
In the first embodiment, the hardware structures as shown in FIG. 5 are-used
for
the photograph ink separation unit
103 and the character/graphic ink separation
unit
104. However, it is possible to use a three-input and four-output table
for converting R, G and B data into C, M, Y and K data and a hardware structure
for executing multidimensional interpolation calculation.
FIG. 6 is a flow chart for explaining processing to generate a three-input and
four-output ink separation table which converts the R, G and B data into the C,
M, Y and K data. In FIG. 6, symbol S
601 denotes a start step, symbol S
602
denotes a grid data generation step of generating R, G and B grid data, symbol
S
603 denotes a luminance/density conversion step, symbol S
604 denotes
a judgment step of judging whether or not the table to be generated is for the
photograph, symbol S
605 denotes a UCR quantity setting step for a character
and a graphic, symbol S
606 denotes a UCR quantity setting step for a photograph,
symbol S
607 denotes a UCR processing step, symbol S
608 denotes a
grid data end judgment step, and symbol S
609 denotes an end step.
First, in the step S
602, values of the R, G and B data input to the
table constituting the ink separation unit are generated. For example, when grid
data is made of 17×17×17 slice, following data are sequentially generated
at intervals of 16 for each of R, G and B.
| |
| R |
G |
B |
| |
| 0 |
0 |
0 |
| 0 |
0 |
16 |
| 0 |
0 |
32 |
| . |
. |
. |
| . |
. |
. |
| . |
. |
. |
| 0 |
0 |
255 |
| 0 |
16 |
0 |
| 0 |
16 |
16 |
| . |
. |
. |
| . |
. |
. |
| . |
. |
. |
| 255 |
255 |
255 |
| |
Then, in the step S
603, the generated R, G and B data are subjected
to luminance/density conversion on the basis of the logarithmic equations (1),
(2) and (3). In these equations, it should be noted that a is an arbitrary real number.
Next, it is judged in the step S
604 whether or not the generated table
is the photograph ink separation table. If judged that the generated table is the
photograph ink separation table, then in the UCR quantity setting step S
606
a UCR quantity (μ%) for the photograph is set. Conversely, if judged that
the generated table is not the photograph ink separation table, then in the character/graphic
UCR quantity setting step S
605 a UCR quantity (μ%) for the character
or the graphic is set.
In the UCR processing step S
607, the UCR processing is performed by using
the UCR quantity (μ%) set in the step S
605 or S
606, in accordance
with the equations (4), (5), (6) and (7), thereby obtaining the C, M, Y and K data.
In the grid data end judgment step S
608, it is judged whether or not generation
of all the necessary grid data ends. If judged that the generation of the necessary
grid data does not end, the flow returns to the grid data generation step S
602
to generate next grid data. Conversely, if judged that the generation of the necessary
grid data ends, the flow advances to the end step S
609 to terminate the
generation of the three-input and four-output ink separation table which converts
the R, G and B data into the C, M, Y and K data.
The generated photograph table data is written in the table of the photograph
ink separation unit
103, and the character/graphic table data is written
in the table of the character/graphic ink separation unit
104.
According to the present embodiment, the photograph ink separation unit
103 and the character/graphic ink separation unit
104 in the first
embodiment can be realized by the three-input and four-output ink separation table
and the multidimensional interpolation calculation. Thus, the complicated hardware
structure such as a logarithmic converter necessary in the first embodiment is
not required, thereby simplifying a hardware structure and realizing cost reduction.
In the above first to third embodiments, the hardware circuits are used. The
hardware
circuit is incorporated in the color printer
209 or the computer
205
shown in FIG.
2. Concretely, this hardware circuit is incorporated in a
controller of the color printer
209 or as a printer board in the computer
205.
The present invention is not limited to the hardware circuit and can be achieved
also with software. In this case, a program which has been stored in a hard disk
in the computer and realizes the operation of each embodiment (FIGS. 1,
4
and
6) operates through an OS (operating system) and a printer driver, under
the control of a CPU.
(Fourth Embodiment)
In the fourth embodiment, the color gamut mapping used in each of the first to
third embodiments will be explained.
For example, a concrete method of the color gamut mapping which is performed
by the matching table generation unit
107 with use of the UI unit
106,
the monitor profile unit
108, the photograph profile unit
109, and
the character/graphic profile unit
110 in the first embodiment will be explained
in detail.
FIG. 7 is a block diagram showing a structure of the fourth embodiment. In FIG.
7, numeral
106 denotes the UI unit, and numeral
108 denotes the monitor
profile unit. Numeral
701 denotes a Munsell Color System data unit in which
L*a*b* data based on the Atlas of the Munsell Color System has been stored. Numeral
702 denotes a color gamut mapping quantity determination unit. Numeral
703
denotes a printer profile unit in which the data of the photograph profile unit
109 and the character/graphic profile unit
110 shown in FIG. 1 are
stored. Numeral
704 denotes a grid data generation unit, numeral
705
denotes a color space conversion unit which converts the R, G and B data into the
L*a*b* data based on the monitor profile unit
108, and numeral
706
denotes a color gamut mapping unit which performs the color gamut mapping based
on the result of the color gamut mapping quantity determination unit
702.
Numeral
707 denotes a search unit which searches the R, G and B data before
ink separation, to reproduce colors based on the L*a*b* data.
Hereinafter, the processing in the fourth embodiment will be explained
with reference to a flow chart shown in FIG.
8.
Symbol S
801 denotes a start step. Symbol S
802 denotes a step
of setting a monitor profile, an image kind and a sheet based on an instruction
from the UI unit
106. Namely, the user selects appropriate items in the
menus
301 to
303 of the UI unit
106 shown in FIG.
3
and performs the setting based on the selected items.
Symbol S
803 denotes a step of setting the printer profile based on
the set values of the image kind and the sheet. Namely, the printer profile data
corresponding to the image kind and the sheet is selected from the printer profile
unit
703.
Symbol S
804 denotes a step of determining the color gamut mapping quantity
based on the monitor profile and the printer profile. Namely, the color gamut mapping
quantity is determined based on the monitor and printer profile data set from the
monitor profile unit
108 and the printer profile unit
703 and the
data based on the Munsell Color System obtained from the Munsell Color System data
unit
701.
FIG. 9 is a flow chart for explaining in detail the color gamut mapping quantity
determination step S
804 based on the monitor and printer profiles.
In the present embodiment, the color gamut mapping quantity is three-dimensionally
determined based on six representative points of R (red), G (green), B (blue),
C (cyan), M (magenta) and Y (yellow). Hereinafter, a method to determine mapping
points after the color gamut mapping for these six points will be explained.
In FIG. 9, symbol S
901 denotes a start step of starting to determine the
color gamut mapping quantity.
Symbol S
902 denotes a step of plotting the data based on the Munsell
Color System, in the L*a*b* color space. Actually, the Munsell Color System which
is three-dimensionally composed of a value (Munsell Value), a hue (Munsell Hue)
and a chroma (Munsell Chroma) is plotted in the L*a*b* three-dimensional color
space. However, in the present embodiment, in order to simplify the explanation,
a chart in which values of the hue (Munsell Hue) and chroma (Munsell Chroma) obtained
at the certain value (Munsell Value) are plotted on an L*a*b* plane is shown in
FIG.
10.
Symbol S
903 denotes a step of plotting set sheet profile information
in the L*a*b* color space, as shown in FIG.
10. FIG. 10 shows color reproduction
ranges (or gamuts) of the coated sheet, the dedicated sheet and the common sheet.
As apparent from FIG. 10, when the coated sheet, the dedicated sheet and the common
sheet are compared with others, magnitudes of the color reproduction ranges (or
gamuts) of these sheets satisfy the relation "coated sheet>dedicated sheet>common sheet".
In steps S
904, S
905 and S
906, the mapping points after the
color gamut mapping for the six representative points of R, G, B, C, M and Y are
sequentially determined.
Symbol S
904 denotes the step of setting the mapping value according
to the set image kind. FIG. 11 is a diagram for explaining the step S
904.
FIG. 11 in which the vertical axis represents the value (L*) and the horizontal
axis represents the chroma (C*) shows the color reproduction ranges (gamuts) of
the monitor, the coated sheet, the dedicated sheet and the common sheet. For example,
the setting value of B is defined by a node (or vertex) between a straight line
connecting B with a point GB defined on the gray axis (the vertical axis) and a
color reproduction range (gamut) of the printer. Therefore, the setting value in
case of the coated sheet is defined by a point B
1, the setting value in
case of the dedicated sheet is defined by a point B
2, and the setting value
in case of the common sheet is defined by a point B
3. Other points GR, GG,
GC, GM and GY are set respectively in correspondence with R, G, C, M and Y. Thus,
the node (or vertex) between the straight line connecting the color with its corresponding
point and the color reproduction range (gamut) of the printer is defined as the
value after the mapping.
Symbol S
905 denotes the step of setting the mapping (a*b*) value along
an equal-interval hue line of the Atlas of the Munsell Color System. The processing
in the step S
905 will be explained with reference to FIG.
10. In
FIG. 10, the equal-interval hue line of the Atlas of the Munsell Color System has
been plotted in the step S
902 of plotting the data based on the Munsell
Color System in the L*a*b* color space. In the step S
905, the mapping (a*b*)
points of R, G, B, C, M and Y for the monitor are sequentially calculated and plotted
based on the color reproduction range data stored in the monitor profile. For example,
in case of B, the mapping point is plotted between points 5.0PB and 7.5PB. Thus,
the plotted line is subjected to the non-linear color gamut mapping toward an achromatic
color direction along these two equal-interval hue lines of the Munsell Color System,
and nodes B
1, B
2 and B
3 between the plotted line and the color
reproduction ranges of the coated sheet, the dedicated sheet and the common sheet
are defined as the mapping points respectively. In FIG. 10, the explanation is
performed based on a two-dimensional plane for simplification. However, in actual,
non-linear mapping is performed three-dimensionally on two a*b* planes defined
by upper and lower Munsell Values based on the value determined in the step S
904.
Symbol S
906 denotes the step of judging whether or not the determination
of the mapping points of the six points R, G, B, C, M and Y ends. If NO in the
step S
906, the flow returns to the step S
904 to define the equal-interval
hue line of the Atlas of the Munsell Color System corresponding to other points
R, G, C, M and Y and sequentially determine the (a*b*) value of the mapping point.
Conversely, if YES in the step S
906, the flow advances to a step S
907
to end the determination processing of the color gamut mapping quantity.
In steps S
805, S
806, S
807, S
808, S
809 and
S
810,
the color gamut mapping is performed in the L*a* be color space for each of the
grid points of R, G and B, based on the values set in the steps S
802, S
803
and S
804. Then the R, G and B data for realizing the L*a*b* data after the
color gamut mapping are searched, and the matching table for the photograph or
the character/graphic is generated.
Symbol S
805 denotes the step of generating R, G and B grid point data.
In this step, the data of the number of grid points (i.e., the number of slices)
are sequentially generated.
| |
| R |
G |
B |
| |
| 0 |
0 |
0 |
| 0 |
0 |
16 |
| 0 |
0 |
32 |
| . |
. |
. |
| . |
. |
. |
| . |
. |
. |
| 0 |
0 |
255 |
| 0 |
16 |
0 |
| 0 |
16 |
16 |
| . |
. |
. |
| . |
. |
. |
| . |
. |
. |
| 255 |
255 |
255 |
| |
Symbol S
806 denotes the color space conversion processing step based
on the set value of the monitor profile. In this step, the color space conversion
from the R, G and B data into the L*a*b* data is performed based on the monitor
profile data and following equations.
| |
|
| |
|
X a11 a12 a13 R |
|
| |
|
Y = a21 a22 a23 G |
(8) |
| |
|
Z a31 a32 a33 B |
| |
|
L* = 116 f(Y/Yn) - 16 |
(9) |
| |
|
a* = 500(f(X/Xn) - f(Y/Yn)) |
(10) |
| |
|
b* = 200(f(Y/Yn) - f(Z/Zn)) |
(11) |
| |
but |
| |
|
f(X/Xn) = (X/Xn)^(1/3) X/Xn > 0.008856 |
(12) |
| |
|
f(X/Xn) = 7.787(X/Xn) + 16/116 |
| |
|
X/Xn ≦ 0.008856 |
(13) |
| |
|
where a11 to a33 are coefficients which are obtained from chromaticity points
of R, G and B described in the selected monitor profile and a chromaticity point
of white, and Xn, Yn and Zn are values of XYZ tristimulus values of monitor white.
Symbol S
807 denotes the step of judging which area the (a*b*) value
subjected to the color gamut mapping in the step S
806 belongs to. Processing
of this step will be explained with reference to FIG.
13. In FIG. 13, symbols
MR, MG, MB, MC, MM and MY are obtained by plotting monitor R, G, B, C, M and Y
on an a*b* plane. Around a central point O, the above six points divides the area
into six areas. Namely, the area between O-MR and O-MM is defined as an RM area,
the area between O-MM and O-MB is defined as an MB area, the area between O-MB
and O-MC is defined as a BC area, the area between O-MC and O-MG is defined as
a CG area, the area between O-MG and O-MY is defined as a GY area, and the area
between O-MY and O-MR is defined as a YR area. For example, the step S
807
judges that the MP point belongs to the MB area as shown in FIG.
13.
Symbol S
808 denotes the step of performing the mapping processing based
on the two mapping points as the judgment result of the step S
807. As shown
in FIG. 13, the mapping processing is performed based on the mapping points of
R and M when the (a*b*) value belongs to the RM area. Similarly, the mapping processing
is performed based on the mapping points of M and B when the (a*b*) value belongs
to the MB area, the mapping processing is performed based on the mapping points
of B and C when the (a*b*) value belongs to the BC area, the mapping processing
is performed based on the mapping points of C and G when the (a*b*) value belongs
to the CG area, the mapping processing is performed based on the mapping points
of G and Y when the (a*b*) value belongs to the GY area, and the mapping processing
is performed based on the mapping points of Y and R when the (a*b*) value belongs
to the YR area.
Hereinafter, since the MP point belongs to the MB
