U.S. patent application number 09/757649 was filed with the patent office on 2001-07-12 for image recording method.
This patent application is currently assigned to BROTHER KOGYO KABUSHIKI KAISHA. Invention is credited to Kuno, Masashi, Nishihara, Masahiro, Ueda, Masashi.
Application Number | 20010007456 09/757649 |
Document ID | / |
Family ID | 18534808 |
Filed Date | 2001-07-12 |
United States Patent
Application |
20010007456 |
Kind Code |
A1 |
Kuno, Masashi ; et
al. |
July 12, 2001 |
Image recording method
Abstract
Of the four basic colors of cyan, magenta, yellow, and black,
each of two basic colors of cyan and magenta is expressed by two
different inks, that is, light ink and normal ink which have
different densities for the corresponding color. For each of the
basic colors of cyan and magenta, after tone correction is
performed in S2 (S108) to attain a linear input/output
characteristic, an optimum group of conversion tables T3 that
matches the user's selected set of printer characteristic is
selected in S110 from the plurality of groups of conversion tables
T3, which have been prepared in advance in correspondence with a
plurality of sets of printer characteristics. Color data Ci", Mi"
for each of the cyan and magenta basic colors is converted in S112
into color data Cl and Cn and Ml and Mn for light ink and normal
ink of the corresponding color based on the selected group of
conversion tables T3.
Inventors: |
Kuno, Masashi; (Obu-shi,
JP) ; Ueda, Masashi; (Nagoya-shi, JP) ;
Nishihara, Masahiro; (Nagoya-shi, JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
277 S. WASHINGTON STREET, SUITE 500
ALEXANDRIA
VA
22314
US
|
Assignee: |
BROTHER KOGYO KABUSHIKI
KAISHA
|
Family ID: |
18534808 |
Appl. No.: |
09/757649 |
Filed: |
January 11, 2001 |
Current U.S.
Class: |
347/15 |
Current CPC
Class: |
H04N 1/6022 20130101;
H04N 1/52 20130101; H04N 1/603 20130101; B41J 2/2056 20130101 |
Class at
Publication: |
347/15 |
International
Class: |
B41J 002/21 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 12, 2000 |
JP |
2000-6250 |
Claims
What is claimed is:
1. A method for recording a color image on a recording medium by
expressing at least one basic color using a plurality of inks that
have different densities of the corresponding color, the method
comprising the steps of: preparing a plurality of conversion
tables, each for converting color data of at least one basic color
into converted color data of the plurality of inks that have
different densities of the corresponding color, each conversion
table matching one of a plurality of sets of printer
characteristics; selecting a set of printer characteristics, with
which printing operation is desired to be performed; selecting one
conversion table from the plurality of conversion tables in
accordance with the selected set of printer characteristics;
converting, based on the selected conversion table, the color data
of each of the least one basic color into converted color data of
the plurality of inks that have different densities of the
corresponding color; and performing printing operation to record a
color image on a recording medium based on the converted color data
with the selected set of printer characteristics.
2. A method as claimed in claim 1, wherein the printer
characteristics selecting step includes the step of allowing a user
to select his/her desired set of printer characteristics.
3. A method for recording a color image on a recording medium by
expressing at least one basic color using a plurality of inks that
have different densities of the corresponding color, the method
comprising the steps of: receiving color data of at least one basic
color; converting the color data of each of at least one basic
color into converted color data of the plurality of inks that have
different densities of the corresponding color, while performing
tone correction on the color data of each of the at least one basic
color; and performing printing operation to record a color image on
a recording medium based on the converted color data.
4. A method as claimed in claim 3, wherein after performing the
tone correction on the received color data of each of the at least
one basic color, the tone-corrected color data of each of the at
least one basic color is converted into the converted color data of
the plurality of inks that have different densities of the
corresponding color.
5. A method as claimed in claim 4, further comprising the steps of:
preparing a conversion table in advance; outputting, in accordance
with the conversion table, color patches of each of the at least
one basic color onto a recording medium using the plurality of inks
that have different densities of the corresponding color; measuring
density levels of the color patches; and preparing a tone
correction table based on the measured density levels, and wherein
the tone correction performing step performs the tone correction
using the tone correction table, and the conversion step performs
the conversion operation using the conversion table.
6. A method as claimed in claim 5, wherein the tone correction
table is prepared to achieve a linear relationship between the
color data of each of the at least one basic color and density
levels to be obtained, the tone correction table being prepared by
first producing a measurement curve that represents the density
levels measured for the color patches and then by calculating a
tone correction curve based on the measurement curve and on a
predetermined linear line that represents the linear
relationship.
7. A method as claimed in claim 5, wherein the plurality of
different inks include a light ink having a predetermined density
and a normal ink having another predetermined density greater than
that of the light ink, wherein the conversion table represents, for
each of the light and normal inks, correspondence between a
plurality of sets of color data and a plurality of sets of
converted color data, the converted color data for the normal ink
having zero values in correspondence with the color data of values
smaller than a predetermined reference value, and wherein the color
patches are produced by using the conversion table to convert
several sets of color data, which include one set of color data of
the predetermined reference value, into several sets of converted
color data for each of the light and normal inks, and by producing
each of the several color patches based on the corresponding set of
converted color data for the light ink and on the corresponding set
of converted color data for the normal ink.
8. A method as claimed in claim 5, wherein a plurality of
conversion tables are prepared for a plurality of different sets of
printer characteristics, a plurality of tone correction tables
being prepared for the plurality of different sets of printer
characteristics, further comprising the steps of: selecting a set
of printer characteristics, with which printing operation is
desired to be performed; selecting one tone correction table from
the plurality of tone correction tables in accordance with the
selected set of printer characteristics, the tone correction
performing step performing the tone correction using the selected
tone correction table; and selecting one conversion table from the
plurality of conversion tables in accordance with the selected set
of printer characteristics, the conversion step performing
converting operation using the selected conversion table.
9. An apparatus for recording a color image on a recording medium
by expressing at least one basic color using a plurality of inks
that have different densities of the corresponding color, the
apparatus comprising: a table storing unit storing a plurality of
conversion tables, each for converting color data of at least one
basic color into converted color data of the plurality of inks that
have different densities of the corresponding color, each
conversion table matching one of a plurality of sets of printer
characteristics; a printer characteristics selection unit selecting
a set of printer characteristics, with which printing operation is
desired to be performed; a table selection unit selecting one
conversion table from the plurality of conversion tables in
accordance with the selected set of printer characteristics; a
conversion unit converting, based on the selected conversion table,
the color data of each of the least one basic color into converted
color data of the plurality of inks that have different densities
of the corresponding color; and a printing unit performing printing
operation to record a color image on a recording medium based on
the converted color data with the selected set of printer
characteristics.
10. An apparatus as claimed in claim 9, wherein the printer
characteristics selecting unit includes a unit allowing a user to
select his/her desired set of printer characteristics.
11. An apparatus for recording a color image on a recording medium
by expressing at least one basic color using a plurality of inks
that have different densities of the corresponding color, the
apparatus comprising: a receiving unit receiving color data of at
least one basic color; a conversion unit converting the color data
of each of at least one basic color into converted color data of
the plurality of inks that have different densities of the
corresponding color, while performing tone correction on the color
data of each of the at least one basic color; and a printing unit
performing printing operation to record a color image on a
recording medium based on the converted color data.
12. An apparatus as claimed in claim 11, wherein the conversion
unit includes: a tone correction unit performing the tone
correction on the received color data of each of the at least one
basic color; and a converting unit converting the tone-corrected
color data of each of the at least one basic color into the
converted color data of the plurality of inks that have different
densities of the corresponding color.
13. An apparatus as claimed in claim 12, further comprising a table
storing unit storing a conversion table and a tone correction
table, the tone correction table being produced based on the
conversion table by measuring density levels of color patches for
each of the at least one basic color, which are produced in
accordance with the conversion table using the plurality of inks
that have different densities of the corresponding color. wherein
the tone correction unit performs the tone correction using the
tone correction table, and the converting unit performs the
conversion operation using the conversion table.
14. An apparatus as claimed in claim 13, wherein the tone
correction table has a characteristic to attain a linear
relationship between the color data of each of the at least one
basic color and density levels to be obtained, the tone correction
table being prepared by first producing a measurement curve that
represents the density levels measured for the color patches and
then by calculating a tone correction curve based on the
measurement curve and on a predetermined linear line that
represents the linear relationship.
15. An apparatus as claimed in claim 13, wherein the plurality of
different inks include a light ink having a predetermined density
and a normal ink having another predetermined density greater than
that of the light ink, wherein the conversion table represents, for
each of the light and normal inks, correspondence between a
plurality of sets of color data and a plurality of sets of
converted color data, the converted color data for the normal ink
having zero values in correspondence with the color data of values
smaller than a predetermined reference value, and wherein the color
patches are produced by using the conversion table to convert
several sets of color, data, which include one set of color data of
the predetermined reference value, into several sets of converted
color data for each of the light and normal inks, and by producing
each of the several color patches based on the corresponding set of
converted color data for the light ink and on the corresponding set
of converted color data for the normal ink.
16. An apparatus as claimed in claim 13, wherein the table storing
unit stores a plurality of conversion tables for a plurality of
different sets of printer characteristics and a plurality of tone
correction tables for the plurality of different sets of printer
characteristics, further comprising; a printer characteristic
selection unit selecting a set of printer characteristics, with
which printing operation is desired to be performed; a tone
correction table selection unit selecting one tone correction table
from the plurality of tone correction tables in accordance with the
selected set of printer characteristics, the tone correction unit
performing the tone correction using the selected tone correction
table; and a conversion table selection unit selecting one
conversion table from the plurality of conversion tables in
accordance with the selected set of printer characteristics, the
converting unit performing converting operation using the selected
conversion table.
17. A data storage medium storing, in a manner readable by a
computer, data of a program for recording a color image on a
recording medium by expressing at least one basic color using a
plurality of inks that have different densities of the
corresponding color, the program comprising: a program of preparing
a plurality of conversion tables, each for converting color data of
at least one basic color into converted color data of the plurality
of inks that have different densities of the corresponding color,
each conversion table matching one of a plurality of sets of
printer characteristics; a program of selecting a set of printer
characteristics, with which printing operation is desired to be
performed; a program of selecting one conversion table from the
plurality of conversion tables in accordance with the selected set
of printer characteristics; a program of converting, based on the
selected conversion table, the color data of each of the least one
basic color into converted color data of the plurality of inks that
have different densities of the corresponding color: and a program
of performing printing operation to record a color image on a
recording medium based on the converted color data with the
selected set of printer characteristics.
18. A data storage medium storing, in a manner readable by a
computer, data of a program for recording a color image on a
recording medium by expressing at least one basic color using a
plurality of inks that have different densities of the
corresponding color, the program comprising; a program of receiving
color data of at least one basic color; a program of converting the
color data of each of at least one basic color into converted color
data of the plurality of inks that have different densities of the
corresponding color, while performing tone correction on the color
data of each of the at least one basic color; and a program of
performing printing operation to record a color image on a
recording medium based on the converted color data.
19. A data storage medium as claimed in claim 18, wherein after
performing the tone correction on the received color data of each
of the at least one basic color, the tone-corrected color data of
each of the at least one basic color is converted into the
converted color data of the plurality of inks that have different
densities of the corresponding color.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an image recording method
for recording color images on a recording medium by using a
plurality of colored inks that have different densities of the same
color, to express a specific basic color.
[0003] 2. Description of Related Art
[0004] In recent years, color printers have come into broad
distribution as image recording devices for recording
computer-processed images in different tones and with a plurality
of colors. Such color printers eject different colors of ink from a
recording head. Generally, color printers reproduce images using
ink of four basic colors of cyan (C), magenta (M). yellow (Y), and
black (K), which will be referred to as "normal inks"
hereinafter.
SUMMARY OF THE INVENTION
[0005] In order to improve image quality, it is conceivable that
color printers use "light ink" together with normal ink in order to
reproduce a single specific color such as cyan (C) or magenta (M).
Each light ink has a density lower than its corresponding normal
ink. In other words, light ink and, normal ink are different inks
that have different densities of the same basic color.
[0006] FIG. 1 represents how images can be reproduced using both
normal and light inks for some basic color, such as cyan (C) or
magenta (M). As shown in FIG. 1, when color data, inputted from a
computer or the like, has a small tone value, then the basic color
is reproduced using the light ink only. Variations in the tone
value of the color data can be reproduced by changing the dot
density of the light ink. Once the tone value of the color data
reaches a predetermined reference tone value ("100" in this
example), then normal ink starts being used together with light
ink. As the tone value of the color data increases further from the
reference tone value, the dot density of the light ink is gradually
reduced, while the dot density of the normal ink is gradually
increased to reproduce the desired tone of the basic color.
[0007] In order to form an image on a recording medium using light
and normal inks in the wanner described above, it is conceivable
that a light ink conversion table and a normal ink conversion table
are prepared in advance for each of the basic colors, such as cyan
(C) and magenta (M), as shown in FIGS. 2(a) and 2(b).
[0008] In order to produce the light ink conversion table and the
normal ink conversion table, the reference tone value, which
indicates when to start using normal ink, should be first
determined. It is conceivable that the reference tone value be
determined in a manner described below.
[0009] A plurality of color patches are outputted onto a recording
medium based on a plurality of tone values that differ from one
another in stepwise increments. Then, normal ink is ejected in a
predetermined dot density (for example, 1%) onto each color patch.
An operator visually observes the color patches, and selects one or
more allowable color patches where the normal ink does not give a
highly noticeable dot "rough" appearance. The operator then selects
one color patch that has been produced by the smallest tone value
among the selected one or more allowable color patches. The
operator sets, as the reference tone value, the tone value of
his/her finally-selected color patch.
[0010] Then, the conversion tables of FIGS. 2(a) and 2(b) are
prepared to represent the input/output characteristics of FIG. 1.
Based on the thus obtained conversion tables, color data inputted,
from a computer or the like, will be converted into ink data for
light ink and ink data for normal ink. Light ink and normal ink
will be selectively ejected, based on the thus obtained ink data,
to form an image on the recording medium.
[0011] It is noted, however, that the density level actually
outputted onto a recording medium changes according to various
printer characteristics, such as the type or model of the printer,
the resolution, the type of ink used, and the type of recording
medium. For example, it is assumed that dot "roughness" or light
ink "bleeding (blurring)" do not appear noticeable when a basic
color is reproduced by outputting light ink and normal ink under
some condition onto a particular kind of recording medium. However,
when printing is performed onto another kind of recording medium
with different shade, different quality, or different absorbency,
even it the printing is performed under the same condition, dot
"roughness" and/or light ink "bleeding" will possibly appear
noticeable. It therefore becomes impossible to always record images
under optimum conditions.
[0012] Additionally, when reproducing a basic color using light ink
and normal ink, as shown in FIG. 3, a point of inflection tends to
occur in the output density level of the basic color at the
reference tone level, that is, at the tone level where normal ink
starts being used. At the inflection point, the first derivative of
the output density level changes discontinuously. Such an
inflection point can result in pseudo contours in the recorded
image.
[0013] It is conceivable that, in order to suitably reproduce
colors based on color data inputted from a computer or similar
source, color correction and tons correction be performed onto the
inputted color data using previously-prepared color correction
table and tons correction table. Each of the color correction table
and tone correction table is generally provided with correction
values for some tone values, which are arranged at a fixed
interval, rather than for all the tone values. Interpolation is
therefore employed to calculate approximate correction values for
tone values with no corresponding correction values. Color
correction and tone correction are performed using the approximate
correction values. However, precision of the interpolation process
drops when the output density level for input color data includes
the inflection point as described above with reference to FIG. 3.
It becomes impossible to determine a suitable approximate
correction value, and consequently impossible to perform suitable
color correction or suitable tone correction.
[0014] It is therefore a first objective of the present invention
to provide an image recording method that enables always recording
images in a suitable condition, regardless of changes in printer
characteristics, when expressing a basic color using different inks
that have different densities of the same color.
[0015] It is a second objective of the present invention to provide
an image recording method that enables performing suitable
correction operation, without generation of pseudo contours in the
image recorded on the recording medium, when expressing a basic
color using different inks that have different densities of the
same color.
[0016] In order to attain the above and other objectives, the
present invention provides a method for recording a color image on
a recording medium by expressing at least one basic color using a
plurality of inks that have different densities of the
corresponding color, the method comprising the steps of: preparing
a plurality of conversion tables, each for converting color data of
at least one basic color into converted color data of the plurality
of inks that have different densities of the corresponding color,
each conversion table matching one of a plurality of sets of
printer characteristics; selecting a set of printer
characteristics, with which printing operation is desired to be
performed; selecting one conversion table from the plurality of
conversion tables in accordance with the selected set of printer
characteristics: converting, based on the selected conversion
table, the color data of each of the least one basic color into
converted color data of the plurality of inks that have different
densities of the corresponding color; and performing printing
operation to record a color image on a recording medium based on
the converted color data with the selected set of printer
characteristics.
[0017] As used with respect to the present invention, "printer
characteristics" refers to various conditions that influence
recorded images. Representative examples of the printer
characteristics include; the type of recording medium, the type of
ink used in the printer, the resolution of the printer, the model
or type of the printer, which determines the unique qualities of
the subject printer, and the print speed of the printer.
[0018] The printer characteristics selecting step may include the
step of allowing a user to select his/her desired set of printer
characteristics.
[0019] According to another aspect, the present invention provides
a method for recording a color image on a recording medium by
expressing at least one basic color using a plurality of inks that
have different densities of the corresponding color, the method
comprising the steps of: receiving color data of at least one basic
color: converting the color data of each of at least one basic
color into converted color data of the plurality of inks that have
different densities of the corresponding color, while performing
tone correction on the color data of each of the at least one basic
color; and performing printing operation to record a color image on
a recording medium based on the converted color data.
[0020] After performing the tone correction on the received color
data of each of the at least one basic color, the tone-corrected
color data of each of the at least one basic color may be converted
into the converted color data of the plurality of inks that have
different densities of the corresponding color.
[0021] The method may further comprise the steps of: preparing a
conversion table in advance; outputting, in accordance with the
conversion table, color patches of each of the at least one basic
color onto a recording medium using the plurality of inks that have
different densities of the corresponding color; measuring density
levels of the color patches; and preparing a tone correction table
based on the measured density levels, and wherein the tone
correction performing step performs the tone correction using the
tone correction table, and the conversion step performs the
conversion operation using the conversion table.
[0022] The tone correction table may be prepared to achieve a
linear relationship between the color data of each of the at least
one basic color and density levels to be obtained, the tone
correction table being prepared by first producing a measurement
curve that represents the density levels measured for the color
patches and then by calculating a tone correction curve based on
the measurement curve and on a predetermined linear line that
represents the linear relationship.
[0023] Here, "linear relationship" refers to when the color data of
the basic colors and the measured density levels achieve a
proportional relationship.
[0024] The plurality of different inks may include a light ink
having a predetermined density and a normal ink having another
predetermined density greater than that of the light ink. The
conversion table may represent, for each of the light and normal
inks, correspondence between a plurality of sets of color data and
a plurality of sets of converted color data, the converted color
data for the normal ink having zero values in correspondence with
the color data of values smaller than a predetermined reference
value. The color patches may be produced by using the conversion
table to convert several sets of color data which include one set
of color data of the predetermined reference value, into several
sets of converted color data for each of the light and normal inks,
and by producing each of the several color patches based on the
corresponding set of converted color data for the light ink and on
the corresponding set of converted color data for the normal
ink.
[0025] A plurality of conversion tables may be prepared for a
plurality of different sets of printer characteristics, a plurality
of tone correction tables being prepared for the plurality of
different sets of printer characteristics. In this case, the method
may further comprise the steps of selecting a set of printer
characteristics, with which printing operation is desired to be
performed; selecting one tone correction table from the plurality
of tone correction tables in accordance with the selected set of
printer characteristics, the tone correction performing step
performing the tone correction using the selected tone correction
table; and selecting one conversion table from the plurality of
conversion tables in accordance with the selected set of printer
characteristics, the conversion step performing converting
operation using the selected conversion table.
[0026] According to another aspect, the present invention provides
an apparatus for recording a color image on a recording medium by
expressing at least one basic color using a plurality of inks that
have different densities of the corresponding color, the apparatus
comprising: a table storing unit storing a plurality of conversion
tables, each for converting color data of at least one basic color
into converted color data of the plurality of inks that have
different densities of the corresponding color, each conversion
table matching one of a plurality of sets of printer
characteristics; a printer characteristics selection unit selecting
a set of printer characteristics, with which printing operation is
desired to be performed; a table selection unit selecting one
conversion table from the plurality of conversion tables in
accordance with the selected set of printer characteristics; a
conversion unit converting, based on the selected conversion table,
the color data of each of the least one basic color into converted
color data of the plurality of inks that have different densities
of the corresponding color; and a printing unit performing printing
operation to record a color image on a recording medium based on
the converted color data with the selected set of printer
characteristics.
[0027] According to another aspect, the present invention provides
an apparatus for recording a color image on a recording medium by
expressing at least one basic color using a plurality of inks that
have different densities of the corresponding color, the apparatus
comprising: a receiving unit receiving color data of at least one
basic color; a conversion unit converting the color data of each of
at least one basic color into converted color data of the plurality
of inks that have different densities of the corresponding color,
while performing tone correction on the color data of each of the
at least one basic color; and a printing unit performing printing
operation to record a color image on a recording medium based on
the converted color data.
[0028] The conversion unit may include: a tone correction unit
performing the tone correction on the received color data of each
of the at least one basic color; and a converting unit converting
the tone-corrected color data of each of the at least one basic
color into the converted color data of the plurality of inks that
have different densities of the corresponding color.
[0029] According to another aspect, the present invention provides
a data storage medium storing, in a manner readable by a computer,
data of a program for recording a color image on a recording medium
by expressing at least one basic color using a plurality of inks
that have different densities of the corresponding color, the
program comprising: a program of preparing a plurality of
conversion tables, each for converting color data of at least one
basic color into converted color data of the plurality of inks that
have different densities of the corresponding color, each
conversion table matching one of a plurality of sets of printer
characteristics; a program of selecting a set of printer
characteristics, with which printing operation is desired to be
performed; a program of selecting one conversion table from the
plurality of conversion tables in accordance with the selected set
of printer characteristics; a program of converting, based on the
selected conversion table, the color data of each of the least one
basic color into converted color data of the plurality of inks that
have different densities of the corresponding color; and a program
of performing printing operation to record a color image on a
recording medium based on the converted color data with the
selected set of printer characteristics.
[0030] According to still another aspect, the present invention
provides a data storage medium storing, in a manner readable by a
computer, data of a program for recording a color image on a
recording medium by expressing at least one basic color using a
plurality of inks that have different densities of the
corresponding color, the program comprising: a program of receiving
color data of at least one basic color; a program of converting the
color data of each of at least one basic color into converted color
data of the plurality of inks that have different densities of the
corresponding color, while performing tone correction on the color
data of each of the at least one basic color; and a program of
performing printing operation to record a color image on a
recording medium based on the converted color data.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] The above and other objects, features and advantages of the
invention will become more apparent from reading the following
description of the embodiment taken in connection with the
accompanying drawings in which:
[0032] FIG. 1 is a graph showing the relationship between input
color data and an output density level in a conceivable image
recording process, for a particular basic color that is reproduced
using two inks that have different densities of the same color;
[0033] FIG. 2(a) is a schematic view showing a light ink conversion
table which is used during the conceivable image recording
processes of FIG. 1;
[0034] FIG. 2(b) is a schematic view showing a normal ink
conversion table which is used during the conceivable image
recording processes of FIG. 1;
[0035] FIG. 3 is a graph showing one example of relationship
between input color data and an output density level obtained by
the conceivable image recording process that expresses a particular
basic color using two inks that are different densities of the same
color;
[0036] FIG. 4 is a block diagram showing an image recording system
that executes an image recording method according to is an
embodiment of the present invention;
[0037] FIG. 5(a) is a schematic flow diagram briefly showing an
image recording process performed by the system of the present
embodiment;
[0038] FIG. 5(b) is a flowchart executed by the system of the
present embodiment to attain the image recording processes of FIG.
5(a);
[0039] FIG. 6 is a schematic view showing a color correction table
used during the image recording processes;
[0040] FIG. 7 is a graph representing a measurement curve,
indicative of a relationship between color data and an output
density level, which is obtained during a process for preparing a
tone correction table, and a tone-correction curve, indicative of a
relationship between color data and color-corrected data, which is
represented by the prepared tone correction table;
[0041] FIG. 8 is a graph representing a relationship between color
data, for each of two basic colors of magenta or cyan, and
corresponding light ink data and normal ink data;
[0042] FIG. 9(a) is a schematic view showing a light ink conversion
table representing the relationship, between the color data and
light ink data, shown in FIG. 8;
[0043] FIG. 9(b) is a schematic view showing a normal ink
conversion table representing the relationship, between the color
data and normal ink data, shown in FIG. 8; and
[0044] FIG. 10 is a schematic view showing color patches produced
when preparing the light ink conversion table, the normal ink
conversion table, and the tone correction table.
DETAILED DESCRIPTION OF THE EMBODIMENT
[0045] Next, an image recording system according to an embodiment
of the present invention will be described while referring to the
attached drawings.
[0046] As shown in FIG. 4, an image recording system 100 of the
present embodiment includes a personal computer 1 and a color
printer 2. The personal computer 1 and the color printer 2 are
connected by a dedicated interface cable 3 for data
transmission.
[0047] The personal computer 1 includes a central processing unit
(CPU) 11, a read-only memory (ROM) 12, a random access memory (RAM)
13, a hard disk 14, a printer interface (I/F) 15, a cathode-ray
tube (CRT) display 16, and an input unit 18, all connected together
by a bus 17 for data transmission.
[0048] The CPU 11 is for executing various control operations and
calculation operations according to various programs stored in the
ROM 12 and according to other various programs retrieved from the
hard disk 14 and stored in the RAM 13. The ROM 12 stores the
various control programs, and also various types of data.
[0049] The RAM 13 is capable of storing the various programs
retrieved from the hard disk 14, and also various data obtained
from calculations performed by the CPU 11.
[0050] The hard disk 14 serves as an auxiliary storage unit for
storing, as files, data and programs which are not stored in main
memories such as the ROM 12 or the RAM 13. The hard disk 14 stores
an image recording process program for executing an image recording
process of the present embodiment. Thus, the hard disk 14 serves as
a data storage medium storing data of a program of the image
recording process. The hard disk 14 also stores a variety of
profiles, such as color correction tables T1 (FIG. 6). tone
correction tables T2 (FIG. 7), and conversion tables T3 (light ink
conversion tables T3l (FIG. 9(a)) and normal ink conversion tables
T3n (FIG. 9(b))). These tables T1, T2, and T3 are used during the
image recording process as will be described later.
[0051] The input unit 18 includes a mouse and a key board, with
which a user can input his/her instruction into the personal
computer 1.
[0052] The printer interface 15 is for performing two-way data
transmission between the computer 1 and the color printer 2
according to a specific transmission protocol agreed upon by the
computer 1 and the color printer 2. The CRT 16 is for displaying
various types of data in a form visually recognizable by the user
of the system 100.
[0053] The color printer 2 includes an ink-jet type print unit 21
and a PC interface 22. The print unit 21 is capable of performing
data transmission with the personal computer 1 through the PC
interface 22 and the printer interface 15.
[0054] With the above-described structure, the image recording
system 100 of the present embodiment performs an image recording
process. The image recording process will be described below
briefly with reference to FIG. 5(a).
[0055] When input color data (Ci, Mi, Yi, Ki) is prepared by an
image preparation application or the like, the input image data
(Ci, Mi, Yi, Ki) is color-corrected in S1 into color-corrected
color data (Ci', Mi', Yi', Ki'). Then, the color-corrected color
data (Ci', Mi', Yi', Ki') is tone-corrected in S2 into
color-and-tone-corrected color data (Ci", Mi", Yi", Ki"). Then, in
S3, the cyan color component. Ci" of the color-and-tone-corrected
color data (Ci", Mi", Yi", Ki") is converted into light cyan ink
data Cl and normal cyan ink data Cn. Also in S3, the magenta color
component M" of the color-and-tone-corrected color data (Ci", Mi",
Yi", Ki") is converted into light magenta ink data Ml and normal
magenta ink data Mn. Then, in S4, the light cyan ink data cl,
normal cyan ink data Cn, light magenta ink data Ml, normal magenta
ink data Mn, color-and-tone-corrected yellow data Yi" and
color-and-tone-corrected black data Ki" are binarized into
binarized color data (Clo, Cno, Mlo, Mno, Yo, Ko) in a well-known
manner, such as described in U.S. Pat. No. 5,045,952. Then, the
binarized color data (Clo, Cno, Mlo, Mno, Yo, Ko) is outputted to
the printer 2, where a desired color image is printed in S5 based
on the binarized color data (Clo, Cno, Mlo, Mno, Yo, Ko).
[0056] The print unit 21 is of a type that forms images on a
recording medium by ejecting six basic color inks of light cyan
(Cl), normal cyan (Cn), light magenta (Ml), normal magenta (Mn),
yellow (Y), and black (K) based on the binary color data (Clo, Cno,
Mlo, Mn, Yo, Ko) received from the personal computer 1. The print
unit 21 is configured to record multi-tons color images, having
density levels of 256 tones for each of four colors of cyan,
magenta, yellow, and black, by selectively ejecting dots of the six
basic color inks according to the received binary color data (Clo,
Cno, Mlo, Mno, Yo, Ko). For example, when color data Cl has a tone
level of "1" among 256 tone levels and when the color data Cl is
converted in S4 into binary color data Clo, the recording unit 21
will eject ink dots of light cyan ink at a dot recording density of
1% when receiving the binary color data Clo.
[0057] It is noted that printers of various models can, be used as
the printer 2. For example. "Epson PM7000" (trade name)
manufactured by Seiko Epson Corporation, "Epson MC7000" (trade
name) manufactured also by Seiko Epson corporation, and
"Hewlett-Packard DJ 5000" (trade name) manufactured by
Hewlett-Packard Company can be used as the printer 2. The printer 2
can be used to record images at various resolutions of: 360 dpi
(dot per inch), 720 dpi, and 1,440 dpi. The printer 2 can be used
with various types of ink, including: dye (normal), ultraviolet
ink, "Hexachrome" (trade name) manufactured by Pantone Corporation,
"Photo Ink" (trade name) manufactured by Seiko Epson Corporation,
and Hi-Fi Color (CMYK+orange/green). The printer 2 can record
images on various types of recording medium, such as coated paper,
calendered paper, film, OHP sheet, normal paper, and cloth. The
printer 2 can be used to record images at various recording speeds,
including: a one-way printing speed and a two-way printing speed.
The one-way printing speed is a printing speed, at which printing
is achieved by a print head moving in one direction only. The
two-way printing speed is a printing speed, at which printing is
achieved by a print head moving in both of two opposite
directions.
[0058] A plurality of different sets of printer characteristics are
defined so that each set of printer characteristics is defined by
one of a plurality of possible combinations of the printer model,
the resolution, the type of ink used, the type of recording medium,
and the recording speed.
[0059] A plurality of color correction tables T1 are prepared in
advance in one to one correspondence with the plurality of sets of
printer characteristics. The plurality of color correction tables
T1 are stored in the hard disk 14. Although not shown in the
drawing, when the image recording process of FIG. 5(a) is started,
a user selects one set of printer characteristics, at which he/she
desires to perform the subject image recording process. In the
color-correction process of S1, therefore, one optimum color
correction table T1 is selected from all the color correction
tables T1 in accordance with the user's selected set of printer
characteristics, and is used for the color-correction process of
S1.
[0060] A color correction table T1, for each set of printer
characteristics, is a look up table used to correct, in S1, input
color data (Ci, Mi, Yi, Ki) in order to reproduce colors faithfully
by taking into account how respective colors of cyan, magenta,
yellow, and black influence one another. As shown in FIG. 6, the
color correction table T1 includes a plurality of sets of color
data (C, M, Y, K), which are possibly inputtable to the
color-correction process of S1. The color correction table T1
includes, in correspondence with each set of color data (C, M, Y,
K) a set of color-corrected color data (C', M', Y', K'), which
should be outputted from the color-correction process of S1 in
response to the input of the subject set of color data (C, M, Y,
K).
[0061] More specifically, the color correction table T1 includes
6,561 (=9.sup.4) sets of color data (C, M, Y, K), wherein C=0, 32,
64, 96, 128, 160, 192, 224, and 255, M= 0, 32, 64, 96, 128, 160,
192, 224, and 255, Y=0, 32, 64, 96, 128, 160, 192, 224, and 255,
and K=0, 32, 64, 96, 128, 160, 192, 224, and 255. In association
with each set of color data (C, M, Y, K), the table T1 includes one
set of color-corrected color data (C', M', Y', K') that should be
outputted from the process of S1 to reproduce the corresponding
color data (C, M, Y, K). Thus, the color correction table T1 is
configured as a four-dimensional look up table, in which 6,561 sets
of color-correction data (C', M', Y', K') are stored in one to one
correspondence with the 6,561 sets of color data (C, M, Y, K).
[0062] It is noted that the color correction table T1 does not
store color-corrected color data (C', M', Y', K') for all of the
256.sup.4 sets of color data (C, M, Y, K), which have all the 256
tone values of 0, 1, 2, . . . , 254, and 255 for each color
component. However, the color correction table T1 stores
color-corrected color data (C', M', Y', K') only for the 9.sup.4
sets of color data (C, M, Y, K), which have only nine tone values
of 0, 32, 64, 96. 128. 160, 192, 224, and 255 for each color
component. Accordingly, during the image recording process (FIG.
5(a)), if input color data (Ci, Mi, Yi, Ki) matches with some set
of color data (C, M, Y, K) in the color correction table T1, the
input color data (Ci, Mi, Yi, Ki) will be directly color-corrected
into color-corrected color data (Ci', Mi', Yi', Ki') that is stored
in the color correction table T1 it correspondence with the
matching color data (C, M, Y, K). On the other hand, if the input
color data (Ci, Mi, Yi, Ki) matches with no color data (C, M, Y, K)
in the color correction table T1, then approximate color-correction
data (Ci', Mi', Yi', Ki') is calculated by interpolating several
sets of color-correction data (C', M', X', K'), which are stored in
the table T1 for several sets of color data (C, M, Y, K) that
surround the subject set of input color data (Ci, Mi, Yi, Ki).
[0063] A plurality of sets of tone correction tables T2 are
prepared in advance in one to one correspondence with the plurality
of sets of printer characteristics. The plurality of tone
correction tables T2 are stored in the hard disk 14. A set of tone
correction tables T2, for each set of printer characteristics, has
four tone correction tables T2, each being for one of the four
basic colors of cyan (C), magenta (M), yellow (Y), and black (K).
During the image recording process (FIG. 5(a)), in the tone
correction process of S2, one set of optimum tone correction tables
T2 is selected from all the sets of tone correction tables T2 in
accordance with the set of printer characteristics selected by the
user, and is used for the tone correction process of S2.
[0064] A tone correction table T2, for each color component, is
used to correct, in S2, the tone A' (=Ci', Mi', Yi', or Ki') of the
corresponding color component in the input color data (Cl', Mi',
Yi', Ki'), which has already been color-corrected in S1, into a
color-and-tone-corrected value Ai", (=Ci", Mi", Yi" or Ki") so that
processes of S2 through S5 will attain a linear "tone
characteristic". It is noted that the "tone characteristic" is
defined as the density level of an image, to be actually outputted
on the recording medium in S5, with respect to the color-corrected
tone value A' (=Ci', Mi', Yi', or Ki'). The output density is
determined by actually measuring the output image using a
calorimeter or the like.
[0065] It is assumed that when a cyan color component Ci' of
color-corrected color data (Ci', Mi', Yi', Ki') from S1 is
subjected to the processes of S2-S5, an output density level is
obtained in S5 as indicated by a one-dot-and-one-chain line in FIG.
7. In this case, a tone correction table T2 for cyan color
component should be prepared to produce an input/output
characteristic correction curve, as indicated by a broken line in
the figure, to correct for the cyan tone Ci' of the color-corrected
color data and to attain a linear input/output characteristic, as
indicated by a solid, straight line in the figure.
[0066] Thus, a tone correction table T2 for each color component A
(=C, M, Y, or K) includes a plurality of sets of color-corrected
data A' (=C', M', Y', or K'), which are outputtable from the
color-correction process of S1 and therefore inputtable to the
tone-correction process of S2. The tone correction table T2
includes, in correspondence with each set of color-corrected data
A' (=C', M', Y', or K'), a set of color-and-tone corrected data A"
(=C", M", Y", or K"), which should be outputted from the
tone-correction process of S2 in response to the input of the
subject set of color-corrected data A' (=C', M', Y', or K').
[0067] A plurality of groups of conversion tables T3 are prepared
in advance also in one to one correspondence with the plurality of
sets of printer characteristics. The plurality of groups of
conversion tables T3 are stored also in the hard disk 14. One group
of conversion tables T3, for each set of printer characteristics,
includes two sets of conversion tables T3, each set being for one
of cyan (C) and magenta (M). A set of conversion tables T3, for
each of cyan and magenta, includes two conversion tables: a light
ink conversion table T3l and a normal ink conversion table T3n.
During the image recording process (FIG. 5(a)), in the conversion
process of S3, one optimum group of conversion tables T3 is
selected from all the groups of conversion tables T3 in accordance
with the set of printer characteristics selected by the user, and
is used for the conversion process of S3.
[0068] The conversion tables T3 are prepared only for those basic
colors that are expressed using both of light ink and normal ink.
Because each color of cyan and magenta is expressed using light ink
and normal ink in this embodiment, the conversion tables T3 are
prepared only for those two colors of cyan and magenta. The
conversion tables T3 (T3l and T3n) for each of cyan and magenta
color components are used to divide, in S3, color data Ai" (=Ci" or
Mi"), which has already been color-corrected in S1 and
tone-corrected in S2, into light ink data A" (=C" or M") and normal
ink data An (=Cn or Mn) in a conversion characteristic shown in
FIG. 8. The light ink conversion table T3l and the normal ink
conversion table T3n are prepared as shown in FIGS. 9(a) and 9(b).
respectively, for each of cyan and magenta colors, to represent the
conversion characteristic of FIG. 8.
[0069] Thus, conversion tables T3n and T3l for each color component
A (=C or M) includes a plurality of sets of
color-and-tone-corrected data A" (=C" or M"), which are outputtable
from the tone-correction process of S2 and therefore inputtable to
the conversion process of S3. The light ink conversion table T3l
includes, in correspondence with each set of
color-and-tone-corrected data A" (=C" or M"). a set of light ink
data Al (=Cl or Ml), which should be outputted from the conversion
process of S3 in response to the input of the subject set of
color-and-tone-corrected data A" (=C" or M"). The normal ink
conversion table T3n includes, in correspondence with each set of
color-and-tone-corrected data A" (=C" or M"), a set of normal ink
data An (=Cn or Mn). which should be outputted from the conversion
process of S3 in response to the input of the subject set of
color-and-tone-corrected data A" (=C" or M").
[0070] It is noted that according to the conversion characteristic
of FIG. 8, in order to reproduce each of cyan and magenta colors,
when the tone value of the color-and-tone-corrected data A" (=C" or
M") is smaller than a predetermined reference tone value (128, for
example), only light ink is used to reproduce the tone by changing
the dot recording density of light ink. Normal ink starts being
used when the tone value of the color-and-tone-corrected data A"
(=C" or M") reaches the reference tone value (128). Once the
reference tone value is reached, the tone is reproduced by
gradually (linearly) reducing the dot recording density of light
ink while gradually (linearly) increasing the dot recording density
of normal ink in association with increase in the tone value of the
color-and-tone-corrected data A" (=C" or M").
[0071] The reference tone value is defined as the tone value when
normal ink starts being used. The reference tone value is
determined in a comprehensive manner, taking into account the
allowable tone values for light ink where "roughness" of dots of
normal ink do not appear noticeable and where light ink "bleeding
(blurring)" is not induced. The frequency of occurrence in
"roughness" and the frequency of occurrence in "bleeding" can
change with color, "quality," absorbency, and the like of the
recording medium, and also with a ratio between densities of the
normal ink and of the light ink. Therefore, the plurality of groups
of conversion tables T3 are prepared to match the plurality of sets
of printer characteristics, including the printer model,
resolution, the type of ink used, the type of recording medium, and
the printing speed.
[0072] Next will be described how to prepare the color correction
tables T1, the tone correction tables T2, and the conversion tables
T3 (T3n and T3l).
[0073] For each set of printer characteristics, the conversion
tables T3 (T3n and T3l). the tone correction tables T2, and the
color correction tables T1 are prepared in this order. That is, the
printer 2 is set with one set of printer characteristics, and the
tables T3, T2, and T1 are produced in this order. Then, the printer
2 is reset with another set of printer characteristics, and the
tables T3, T2, and T1 are produced again in this order. Thus, the
tables T3, T2, and T1 are repeatedly produced while changing the
printer characteristics.
[0074] First will be described how to prepare the conversion tables
T3 (T3n and T3l) for cyan color. It is noted that the conversion
tables T3 (T3n and T3l) are prepared for magenta color in the same
manner as described below for cyan color.
[0075] First, the reference tone value is set to a desirable value
("128," in this example). The reference tone value is defined as
the tone level point C", from which normal ink will be used.
[0076] Next, the value of normal ink data Cn for the reference tons
value C" of 128 is determined as a desirable value ("1," for
example). This value indicates the amount of normal ink that should
be ejected, together with light ink, to reproduce the reference
tone value C" of 128. It is noted that when the normal ink data Cn
having the value of "1" is converted into binary data Cno in S4 and
supplied to the color printer 2, the print unit 21 will eject the
normal ink at a dot recording density of 1%.
[0077] Then, the value of light ink data Cl for the reference tone
value C" of 128 is determined in a trial-and-error manner described
below. It is noted that this value indicates the amount of light
ink that should be ejected, together with normal ink, to reproduce
the reference tone value C" of 128.
[0078] First, the print unit 21 is controlled to produce a
plurality of single-color color patches by ejecting light ink on a
recording medium based on a plurality of tone levels that differ
from one another in stepwise increments. For example, nine
single-color color patches are produced for nine tone levels of 0,
32, 64, 96, 128, 160, 192, 224, and 255 as shown in FIG. 10, Wore
specifically, nine sets of light ink data Cl of 0, 32, 64, 96, 128,
160, 192, 224, and 255 are prepared, binarized in the same manner
as in the process of S4, and supplied to the printer 2. As a
result, the plurality of single-color color patches are produced by
light cyan ink in stepwisely-increasing dot recording
densities.
[0079] Then, the print unit 21 is controlled to eject normal ink,
onto each single-color color patch, based on the tone level ("1" in
this example) that is already determined for the reference tone
level C" of 128. More specifically, one set of normal ink data Cn
of 1 is prepared, binarized in the same manner as in the process of
S4, and supplied to the printer 2. As a result, each single-color
color patch is further printed with normal ink at a dot recording
density (1% in this example) that corresponds to the tone level of
"1".
[0080] Then, the plurality of single-color color patches are
visually observed by an operator to select one or more allowable
color patches where normal ink dot "roughness" appear unnoticeable.
Then, one color patch is selected that has been printed with the
lowest tone level of light ink among the selected one or more
allowable color patches. The tone level of the thus selected one
color patch is determined as the lowest allowable light ink amount
for the reference tone level C" of 128.
[0081] The print unit 21 is further controlled to produce a
plurality of mixed-color color patches by ejecting four inks of:
light cyan ink, light magenta ink, yellow ink, and black ink, at a
plurality of tone levels that are different from one another in
stepwise increments. Each color patch is produced according to the
same tone level for all of the four inks. For example, nine
mixed-color color patches are produced at nine tone levels of 0,
32, 64, 96, 128, 160, 192, 224, and 255 for each of four colors as
shown in FIGS. 10. More specifically, nine sets of color data (Cl,
Ml, Y", K"), each set of color data having the same tone values of
0, 32, 64, 96, 128, 160, 192, 224, and 255 for all the color
components, are prepared, binarized in the same manner as in the
process of S4, and supplied to the printer 2. As a result, nine
mixed-color color patches are produced by all the four inks in
stepwisely-increasing dot recording densities.
[0082] Then, the plurality of mixed-color color patches are
visually observed by the operator to select one or more allowable
color patches where no bleeding or blurring appear in cyan or
magenta light ink. One color patch is then selected that has
printed with the highest tone level among the selected one or more
allowable color patches. The tone level of the thus selected one
color patch is determined as the highest allowable light ink amount
for the reference tone level C" of 128.
[0083] When the thus determined highest allowable light ink amount
is equal to the determined lowest allowable light ink amount, the
highest or lowest allowable light ink amount is deter ed as light
ink tone data Cl that should be outputted in S3 for the reference
tone level C" of 128. Accordingly, the highest or lowest allowable
light ink amount is determined as light ink data Cl for the
reference tone C" of 128. In this example, as shown in FIGS. 8 and
9(a), light ink data Cl is determined as "255" with respect to the
reference tone value C" of 128.
[0084] On the other hand, when the determined highest and lowest
allowable light ink amounts are not equal to each other,
observations of the single-color color patches and of the
mixed-color color patches are performed again to reselect allowable
color patches in a lower precision so that the lowest and highest
allowable light ink amounts will become equal to each other.
[0085] Next, the value of light ink data Cl is determined for all
the remaining tone values C" of 0-127 and 129-255.
[0086] First, the value of light ink data Cl is determined as "0"
for color data C" of the minimum and maximum tone values of 0 and
255. Then, as shown in FIG. 8, a graph is prepared in which the
horizontal axis denotes color data C' in the range of 0 to 255, and
the vertical axis denotes light ink data and normal ink data both
in the range of 0 to 255. Then, as indicated by a broken line in
FIG. 8, a linearly increasing-and-then-decreasing line is prepared
to connect the light ink minimum-tone point (0, 0) to the light ink
reference-tone point (128, 255) and further to the light ink
maximum-tone point (255, 0). Along this linearly
increasing-and-decreasing line, the value of light ink data Cl,
defined along the vertical axis, is determined for all of the 256
color data C" of 0, 1, . . . , 255 defined along the horizontal
axis. As a result, light ink data Cl is determined as shown in FIG.
9(a) with respect to all of the tone values of 0-255 of color data
C".
[0087] Next, the value of normal ink data is determined for all of
the remaining tone values of 0-127 and 129-255 of color data C" in
a trial-and-error manner described below. It is noted that the
value of normal ink data Cn is already determined as "1" for the
reference tone value C" of 128.
[0088] First, the value of normal ink data Cn is determined as "0"
for all the tone values C" of 0-127 that are smaller than the
reference tone value 128.
[0089] Then, the value of normal ink data is determined for the
maximum tone value C" of 255 in a manner described below.
[0090] First, the print unit 21 is controlled to produce a
plurality of single-color color patches by ejecting normal ink on a
recording medium based on a plurality of tone levels that differ
from one another in stepwise increments. For example, nine
single-color color patches are produced by normal ink for nine tone
levels of 0, 32, 64, 96, 128, 160, 192, 224, and 255 as shown in
FIG. 10. More specifically, nine sets of normal ink data Cn of 0,
32, 64, 96, 128, 160. 192, 224, and 255 are prepared, binarized in
the some manner as in the process of S4, and supplied to the
printer 2. As a result, nine single-color color patches are
produced by normal ink in stepwisely-increasing dot recording
densities.
[0091] Then, the print unit 21 is controlled to eject light ink,
onto each single-color color patch, based on the tone level of
light ink that is already determined for the maximum tone level C"
of 255. In this example the tone level is already determined as "0"
for the maximum tone level C" of 255. Accordingly, each color patch
is further printed with no light ink.
[0092] Then, the plurality of single-color color patches are
visually observed by the operator to select one or more allowable
color patches where no undesirable white regions appear noticeable.
One color patch is then selected that has printed with the lowest
tone level of normal ink among the selected one or more allowable
color patches. The tone level of this color patch is determined as
the lowest allowable normal ink amount for the maximum tone level
C" of 255.
[0093] Next, the print unit 21 is controlled to produce a plurality
of mixed-color color patches by ejecting four inks of: normal cyan
ink, normal magenta ink, yellow ink, and black ink, at a plurality
of tone levels that are different from one another in stepwise
increments. Each color patch is produced according to the same tone
level for all of the four inks. For example, nine mixed-color color
patches are produced at nine tone levels of 0, 32, 64, 96, 128,
160, 192, 224, and 255 for each of the four inks as shown in FIG.
10. More specifically, nine sets of color data (Cn, Mn, Y", K"),
each set of color data having the same tone values of 0, 32, 64,
96, 128, 160, 192, 224, and 255 for all the color components, are
prepared, binarized in the same manner as in the process of S4, and
supplied to the printer 2. As a result, nine mixed-color color
patches are produced by the four inks in stepwisely-increasing dot
recording densities.
[0094] Then, the plurality of mixed-color color patches are
visually observed by the operator to select one or more allowable
color patches where no bleeding or blurring appear in the cyan or
magenta normal ink. One color patch is then selected that has
printed with the highest tone level among the selected one or more
allowable color patches. The tone level of the thus selected one
color patch is determined as the highest allowable normal ink
amount for the maximum tone level C" of 255.
[0095] When the thus determined highest allowable normal ink amount
is equal to the determined lowest allowable normal ink amount, the
highest or lowest allowable normal ink amount is determined as
normal ink tone data Cn that should be outputted from S3 for the
maximum tone level C2 of 255. Accordingly, the highest or lowest
allowable normal ink amount is determined as normal ink data Cn for
the maximum tone C" of 255. In this example, as shown in FIGS. 8
and 9(b), normal ink data Cn is determined as "255" with respect to
the maximum tone value C" of 255.
[0096] On the other hand, when the determined highest and lowest
allowable normal ink amounts are not equal to each other,
observations of the single-color color patches and of the
mixed-color color patches are performed again to reselect allowable
color patches in a lower precision so that the lowest and highest
allowable normal ink amounts will become equal to each other.
[0097] Next, the value of normal ink data Cn is determined for all
the remaining tone values C" of 129-254.
[0098] As indicated by a solid line in FIG. 8, a linearly
increasing line is produced to connect the normal ink
reference-tone point (128, 1) to the normal ink maximum-tone point
(255, 255). Along this linearly-increasing line, the value of
normal ink data Cn, defined along the vertical axis, is determined
for all of the values of color data C" of 129, 130, . . . 253, and
254, defined along the horizontal axis. Thus, the value of normal
ink data Cn with respect to all the tone values C" of 128-255 is
determined and stored as shown in FIG. 9(b).
[0099] Next will be described how to prepare the tone correction
table T2 for cyan color. It is noted that the tone correction table
T2 is prepared for magenta color in the same manner as described
below for cyan color.
[0100] First, nine sets of color data C' of 0, 32, 64, 96, 128,
160, 192, 224, and 255, which will be possibly inputted into the
tone-correction process of S2, are prepared. Each set of color data
C' is subjected to no tone-correction process of S3. As a result,
nine sets of color data C" having the some tone values 0, 32, 64,
96, 128, 160, 192, 224, and 255 are obtained. Then, the nine sets
of color data C" are subjected to the conversion process of S3. As
a result, each set of color data C" is converted into normal ink
data Cn and light ink data Cl by using the conversion tables T3n
and T3l, which are already produced in the manner described above.
Thus, nine sets of color data C' are directly converted into nine
sets of ink data (Cn, Cl).
[0101] Then, the print unit 21 is controlled by the nine sets of
ink data (Cn, Cl) to print nine single-color color patches on a
recording medium using both light and normal inks. That is, each
set of ink data (Cn, Cl) is binarized in the same manner as in the
process of S4, and supplied to the printer 2. As a result, nine
color patches are produced as shown in FIG. 10. Then, the output
density level of each color patch is measured using a colorimeter
or the like.
[0102] A graph of FIG. 7 is then prepared, in which the horizontal
axis indicates color data C' in the range of 0-255, a left-hand
vertical axis indicates the measured density levels in the range of
0-255. and a right-hand vertical axis indicates tone-corrected
levels C" of 0-255 to be obtained. Based on the measurement results
of the nine color patches, a measurement curve is prepared, as
indicated by a one-dot-and-one-chain line in the figure, to
represent the relationship between the color data C' (horizontal
axis) and the measured density values (left-hand vertical axis). A
predetermined reference line is then plotted in the same graph to
connect the minimum tone point (0, 0) and the maximum tone point
(255, 255) as indicated by a solid line in the figure. Then, as
indicated by a broken line in the same figure, a tone-correction
curve is calculated as a curve that is symmetrical to the
measurement curve with respect to the reference line. The
tone-correction curve is then set as a tone-correction table T2.
That is, along the tone-correction curve, the value of
tone-corrected data C", defined along the right-hand vertical axis,
is determined for all of the 256 values of color data C' of 0-255,
defined along the horizontal axis.
[0103] It is noted that the measurement results of the color
patches show that when color data C' is subjected to the color
reproducing characteristic of S3-S5, represented by the measurement
curve (one-dot-and-one-chain line in FIG. 7), the color data C' is
converted into the output density level plotted on the measurement
curve. The tone-correction curve (broken line in FIG. 7) is
therefore determined so that when any color data C' is actually
inputted, the color data C' will be subjected first to the tone
correction characteristic of S2, represented by the tone-correction
curve, and then to the color reproducing characteristic of S3-S5,
represented by the measurement curve, resulting in the output
density levels on the linear reference line. Accordingly,
actually-inputted color data C' will be converted through S2-S5 to
the output density levels with a linear conversion characteristic,
which is a combination of the tone correction characteristic of S2,
represented by the tone-correction curve (broken line in FIG. 7),
and the color reproducing characteristic of S3-S5, represented by
the measurement curve (one-dot-and-one-chain line in FIG. 7).
[0104] It is also noted that when preparing color patches in order
to prepare the tone correction table T2, it is desirable to produce
256 color patches based on all of the 256 different tones from 0 to
255 of color data C'. However, when only nine color patches are
produced at tone values "0", "32", . . . , and "255" that are
separated from one another by the fixed tone value of "32", then it
is preferable to produce one of the nine color patches based on the
reference tone value C' of 128 as shown in FIG. 10. When expressing
a single basic color using normal ink and light ink, a point of
inflection tends to be generated in the output density level at the
point of the reference tone value where normal ink starts being
used. Therefore, it is preferable to take into consideration the
output density level at the reference tone point in order to
perform tone correction with high precision.
[0105] Next will be described how to prepare the tone correction
table T2 for yellow color. It is noted that the tone correction
table T2 is prepared for black color in the same manner as
described below for yellow color.
[0106] The print unit 21 is first controlled according to nine sets
of color data Y' of 0, 32, 64, 96, 128, 160, 192, 224, and 255 to
produce nine color patches. More specifically, nine sets of yellow
color data Y' of 0, 32, 64, 96, 128, 160, 192, 224, and 255 are
prepared, binarized in the same manner as in the process of S4, and
are supplied to the printer 2. As a result, nine color patches are
produced by yellow ink as shown in FIG. 10. Densities of the nine
color patches are measured by the colorimeter. Because a
measurement curve (one-dot-and-one-chain line) of FIG. 7 is
produced based on the measurement results similarly as described
above for cyan ink, a predetermined reference line (solid line) and
a tone-correction curve (broken line) are determined also in the
same manner as described above. The thus obtained tone-correction
curve (broken line) is set as the tone-correction table T2 for the
yellow color.
[0107] Next will be described how to prepare the color-correction
table T1.
[0108] First, 6,561 (=9.sup.4) sets of color data (C', M', Y', K'),
which will possibly be outputted from the color-correction process
of S1, are prepared, wherein C=0, 32, 64, 96, 128, 160, 192, 224,
and 255, M=0, 32, 64, 96, 128, 160, 192, 224, and 255, Y=0, 32, 64,
96, 128, 160, 192, 224, and 255, and K=0, 32, 64, 96, 128, 160,
192, 224, and 255. The yellow component Y' of each set of color
data (C', M', Y', K') is tone-corrected into tone-corrected data Y"
in the same manner as in the process of S2 using the
tone-correction table T2 already prepared for yellow color in the
manner described above. Similarly, the black component K' of each
set of color data (C', M', Y', K') is tone-corrected into
tone-corrected data K' in the same manner as in the process of S2
using the tone-correction table T2 already prepared for black
color. The cyan component C' of each set of color data (C', M', Y',
K') is tone-corrected into tone-corrected data C" in the same
manner as in the process of S2 using the tone-correction table T2
already prepared for cyan color, and are further converted in the
same manner as in the process of S3 into light ink data Cl and
normal ink data Cn using the conversion tables T3l and T3n already
prepared for cyan color. Similarly, the magenta component M' of
each set of color data (C', M', Y', K') is tone-corrected into
tone-corrected data M" in the same manner as in the process of S2
using the tone-correction table T2 already prepared for magenta
color, and are further converted in the same manner as in the
process of S3 into light ink data Ml and normal ink data Mu using
the conversion tables T3l and T3n already prepared for magenta
color. Thus, each set of color data (C', M', Y', K') is converted
into a set of color data (Cl, Cn, Ml, Mn, Y", K"). The set of color
data (Cl, Cn, Ml, Mn, Y", K") is then binarized into binarized data
(Clo, Cno, Mlo, Mno, Yo, Ko) in the same manner as in the process
of S4, and is supplied to the printer 2. As a result, the print
unit 21 is controlled to produce 6,561 color patches. The color
patches are measured using the calorimeter in order to determine
L*a*b* color values (L, a, b), defined in the L*a*b* colorimetric
system (CIE 1976), for all the sets of original color data (C', M',
Y', K'). Interpolation calculation is performed on the measured
L*a*b* color values and the original color values (C', M', Y', K')
to determine a relationship between a plurality of Lab color values
(L, a, b) and a plurality of color values (C', M', Y', K'), which
are to be outputted from the color-correction process of S1.
[0109] Next, the relationship between color values (C, M, Y, K),
which are to be inputted to the color correction process of S1, and
L*a*b* color values (L, a, b) is determined. More specifically,
6,561 sets of color data (C, M, Y, K), which will possibly be
inputted to the color correction process of S1, are prepared,
wherein C=0, 32, 64, 96, 128, 160, 192, 224, and 255, M=0, 32, 64,
96, 128, 160, 192, 224, and 255, Y=0, 32, 64, 96, 128, 160, 192,
224, and 255, and K=0, 32, 64, 96, 128, 160, 192, 224, and 255.
Each set of color data (C, X, Y, K) is outputted, without being
subjected to any correction or conversion process, to a standard
printer to produce 6,561 color patches. The color patches are
measured by the colorimeter to obtain the L*a*b color values (L, a,
b) of the color patches. Interpolation calculation is performed on
the measured L*a*b* color values and the original color values (C,
M, Y, K) to determine a relationship between a plurality of color
values (C, M, Y, K), which are to be inputted to the
color-correction process of S1, and a plurality of Lab color values
(L, a, b). It is noted that the relationship between color data (C,
M, Y, K) and the L*a*b color values (L, a, b) can be determined
also based on a (CMYK-Lab) look up table that is supplied from
Pantone Corporation or SWOP (Standard Wet Offset Printing). As a
result, the relationship among color data (C, M, Y, K), to be
inputted to the process of S1, L*a*b* color data (L, a,. b), and
color-corrected color data (C', M', Y', K'), to be outputted from
the process of S1, is obtained. Therefore, a direct relationship
between color data (C, M, Y, K) and color-corrected color data (C',
M', Y', K') is obtained. Thus, the color correction table T1 is
obtained.
[0110] According to the present embodiment, the table T1, the
tables T2 for cyan, magenta, yellow, and black, and tables T3 (T3n
and T3l) for cyan and magenta are produced in the above-described
manner in correspondence with each of all the sets of printer
characteristics selectable by a user of the image recording system
100.
[0111] The image recording system 100 attains the image recording
process of FIG. 5(a) when the personal computer 1 performs an image
recording routine, in a manner shown in FIG. 5(b), by executing the
image recording process program stored in the hard disk 14.
[0112] The personal computer 1 starts an image recording process of
FIG. 5(b) when the user of the system 100 inputs, via the input
unit 18, his/her instruction to record input color data (Ci, Xi,
Yi, Ki), which is prepared using an image preparation application
or the like. When the image, recording process starts being
executed, the CPU first stores the input color data (Ci, Mi, Yi,
Ki) into a work area of the RAM 13 in S100.
[0113] The CPU 11 then performs in S101 an operation that enables
the user to select his/her desired set of printer characteristics,
at which the color printer 2 should perform printing operation.
[0114] More specifically, the CPU 11 controls in S101 the CRT 16 to
display five categories relating to the printer characteristics.
These categories are; printer model, ink type, recording medium
type, resolution, and print speed. Each category includes a
plurality of items prepared in advance. Examples of items for
"printer model" include: Epson PM7000, Epson MC7000, and
Hewlett-Packard DJ 5000. Examples of items for "resolution"
include: 360 dpi (dot per inch), 720 dpi, 1,440 dpi. Examples of
items for "ink type" include: dye (normal), ultraviolet ink,
"Hexachrome", "Photo Ink", and Hi-Fi Color (CMYK+orange/green).
Examples of items for "recording medium type" include: coated
paper, calendered paper, film, OHP sheet, normal paper, and cloth.
Examples of items for "print speed" include: a one-way printing
speed and a two-way printing speed.
[0115] Viewing the CRT 16, the user selects one of the items for
each category to thereby input his/her selected one set of printing
characteristics via the input unit 18.
[0116] Next, in S102, in accordance with the set of printer
characteristics, that is determined by the combination of items
selected by the user, the CPU 11 selects an appropriate color
correction table T1 from the plurality of color correction tables
T1 in the hard disk 14. The selected color correction table T1 is
copied into the RAM 13. Then, in S104, the input color data (Ci,
Mi, Yi, Ki) is color-corrected into color-corrected color data
(Ci', Mi', Yi', Ki') using the selected color correction table T1.
Thus, the color-correction process (S1 in FIG. 5(a)) is
attained.
[0117] It is noted that if input color data (Ci, Mi, Yi, Ki) is not
equal to any color data (C, M, Y, K) listed in the color correction
table T1, color-corrected color data (Ci', Mi', Yi', Ki') is
calculated by performing a linear interpolation onto several sets
of color-corrected color data (C', M', Y', K') that are listed in
the table T1 for several sets of color data (C, M, Y, K) that
surround the subject input color data (Ci, Hi, Yi, Ki).
[0118] As a result, each set of input color data (Cl, Mi, Yi, Ki)
is color-corrected into color-corrected color data (Ci', Mi', Yi',
Ki') so as to be suitably reproduced by a combination of four
colors of cyan, magenta, yellow, and black. The yellow and black
color components Yi' and Ki' of the color-corrected color data
(Ci', Mi', Yi', Ki') will be subjected to a tone correction process
so that an image finally obtained on the image recording medium
will properly have linear input/output characteristics with respect
to the color values of Yi' and Ki'. Cyan and magenta color
components Ci' and Mi' will be subjected to the tone correction
process and further to a conversion process so that an image
finally obtained on the image recording medium will properly have
linear input/output characteristics with respect to the color
values of Ci' and Mi'.
[0119] More specifically, in S106, in accordance with the set of
printer characteristics selected by the user in S101, an
appropriate set of tone correction tables T2 is selected from the
plurality of sets of color correction tables T2 in the hard disk
14. The selected set of tone correction tables T2 includes tone
correction tables T2 for all the colors of cyan, magenta, yellow,
and black. The selected set of tone correction tables T2 is copied
into the RAM 13.
[0120] Then, in S108, using the selected set of tone correction
tables T2, values of color data (Ci', Mi', Yi', Ki'), which has
already been subjected to the color correction processes of S104,
are subjected to tone correction.
[0121] During the tone correction process for the cyan component,
the value Ci' of the color-corrected input color data (Ci', Mi',
Yi', Ki') is used to refer to the horizontal axis in the
tone-correction table T2 (FIG. 7) for cyan color. Then, with
respect to the color-corrected data Ci' (horizontal axis), the
value of tone-corrected color data Ci" (right-band vertical axis)
on the tone-correction curve is obtained. Thus, a
color-and-tone-corrected color data Ci" is obtained for the
color-corrected color data Ci'. The same operation is performed for
other remaining values Mi', Yi', and Ki' by using the
tone-correction tables T2 (FIG. 7) for magenta, yellow, and black
colors. As a result, one set of color-and-tone-corrected color data
(Ci", Mi", Yi", Ki") is produced based on each set of
color-corrected color data (Ci', Mi', Yi', Ki'). Thus, the tone
correction process (S2 in FIG. 5(a)) is attained.
[0122] The values Yi" and Ki" of yellow and black color components
will be directly converted into binary data Yo and Ko as described
later. Contrarily, the value Ci" of cyan color component is further
converted into light cyan ink data Cl and normal cyan ink data Cn.
The value Mi" of magenta color component is further converted into
light magenta ink data MI and normal magenta ink data Mn.
[0123] More specifically, in S110, in accordance with the set of
printer characteristics selected by the user in S101, an
appropriate group of conversion tables T3 is selected from the
plurality of groups of conversion tables T3 in the hard disk 14.
The selected conversion table group T3 has: a light ink conversion
table T3l and a normal ink conversion table T3n for cyan color, and
a light ink conversion table T3l and a normal ink conversion table
T3n for magenta color. The selected conversion table group T3 is
copied into the RAM 13. Then, in S112, using the selected
conversion tables T3l and T3n for cyan color, the value Ci" is
converted into values Cl and Cn. Similarly, using the selected
conversion tables T3l and T3n for magenta color, the value Mi" is s
converted into values M3 and Mn.
[0124] It is noted that during the conversion process for cyan, the
value Ci" is used to refer to the horizontal axis of FIG. 8, which
is represented by the conversion tables T3l and T3n (FIGS. 9(a) and
9(b)) for cyan color. Then, with respect to the value of the
color-and-tone-corrected data Ci" (horizontal axis), a value Cl of
light ink color data (vertical axis) is obtained on the light ink
conversion line (broken line) and a value Cn of normal ink color
data (vertical axis) is obtained on the normal ink conversion line
(solid line). Thus, light ink color data Cl and normal ink color
data Cn are produced. In other words, the color-and-tone-corrected
color data Ci" is converted into ink data (Cl, Cn). The same
operation as described above is performed for magenta color
component using the conversion tables T3n and T3l for magenta
color. Thus, light cyan ink data Cl, normal cyan ink data Cn, light
magenta ink data Ml, and normal magenta ink data Mn are produced.
Thus, the conversion process (S3 in FIG. 5(a)) is attained.
[0125] The thus produced ink data Cl, Cn, Ml, and Mn is outputted
together with the color data Yi" and Ki" for yellow and black
components. Thus, a set of color data (Cl, Cn, Ml, Mn, Yi", Ki") is
obtained based on each set of original input color data (Ci, Mi,
Yi, Ki).
[0126] Then, in S114, the thus obtained color data (Cl, Cn, Ml, Mn,
Yi", Ki"). which has been subjected to the several correction and
conversion processes as described above, is subjected to a
binarization processes in the well known manner such as those
described in the U.S. Pat. No. 5,045,952. Thus, the binarization
process (S4 in FIG. 5(a)) is attained.
[0127] Then, a resultant binary signal (Cl.sub.o, Cn.sub.o,
Ml.sub.o, Mn.sub.o, Y.sub.o, K.sub.o) is outputted to the color
printer 2. The print unit 21 is controlled in S116 to print a color
image on the image recording medium based on the binary signal
(Cl.sub.o, Cn.sub.o, Ml.sub.o, Mn.sub.o, Y.sub.o, K.sub.o) at the
user's selected set of printer characteristics.
[0128] As described above, according to the present embodiment, the
plurality of groups of conversion tables T3 (T3n and T3l) that
match the plurality of sets of printer characteristics are prepared
for converting color data Ci" and Mi", in two basic colors of cyan
and magenta, into color data Cl and Cn and Ml and Mn for light ink
and normal ink. When the user sets his/her desired set of printer
characteristics for the present image recording process differently
from that used during the previous image recording process, a new
group of conversion tables T3 (T3n and T3l) that properly matches
the present printer characteristics will be used during the present
image recording process. Accordingly, the dot "roughness" of s
normal ink and the bleeding of light ink will appear unnoticeable
on the recorded images. As a result, images can always be recorded
under the optimum conditions.
[0129] According to the image recording method of the present
embodiment, color data Ci' and Mi' for the two basic colors of cyan
and magenta is subjected to tone correction in S2 (SLOB). and then
in S3 (S112), the tone-corrected color data Ci" and Mi" is
converted into color data Cl and Cn and Ml and Mn for light and
normal inks according to the conversion table T3 (T3l and T3n).
Accordingly, when an image is recorded based on the converted color
data (ink data), the image will reliably be influenced from the
tons correction operation, so that the image will have good
quality.
[0130] Furthermore, according to the embodiment, tone correction is
performed according to a tone correction table T2 that has been
prepared to adjust color data of the basic colors to have a linear
relationship with respect to output density levels. Accordingly,
the interpolation precision, at which approximate correction values
are calculated in S1 (S104) by the linear interpolation, is
improved so that further high quality can be achieved.
[0131] The color patches, produced in order to prepare the tone
correction tables T2 for the two basic colors of cyan (C) and
magenta (M), include a color patch that corresponds to the
reference tone value of 128, where a point of inflection tends to
occur in the corresponding output density level. Therefore, the
tone correction tables T2, prepared based on those color patches,
will attain tone adjustment with high precision, so that pseudo
contours are not generated in the recorded images.
[0132] While the invention has been described in detail with
reference to the specific embodiment thereof, it would be apparent
to those skilled in the art that various changes and modifications
may be made therein without departing from the spirit of the
invention, the scope of which is defined by the attached
claims.
[0133] For example, according to the embodiment, tone correction
processes of S2 (S108) and conversion processes of S3 (S112) are
performed individually after color correction processes of S1
(S104) are performed. That is, conversion processes of S3 (S112)
are performed after the tone correction processes of S2 (S108).
However, tone correction processes and conversion processes could
be performed simultaneously by merging together the tone correction
table T2 and the conversion table T3.
[0134] According to the embodiment, each of the two basic colors of
cyan (C) and magenta (M) is expressed using light and normal inks
of the same color. However, the present invention is not limited to
the case when each of the two basic colors is expressed using light
and normal inks, but could be applied to the situation where only
one of these two basic colors is expressed using light and normal
inks of the same color. Or, another basic color can be expressed
also using light and normal ink of the same color. For example,
black color may be expressed using light and normal ink of the
same, black color.
[0135] Further, the present invention is not limited to expressing
the same color using light and normal inks, that is, using two inks
with different densities. The present invention could be applied to
the situation where the same color is expressed using inks with
three or more different densities.
[0136] Also, the embodiment describes automatic selection of a
variety of tables T1-T3 based on the printer characteristics
selected by the user. However, the system can be modified so that
the user can directly select a table T1-T3 desired to be used. That
is, in each of S102, S106, and S110, the program can be designed to
allow the user to select his/her desired table.
[0137] The color correction table T1 may be produced in a manner
described in U.S. Pat. No. 4,500,919.
[0138] If the tone correction tables T2 and the conversion tables
T3 can be prepared to satisfactorily represent the variations in
the printer characteristics, a single color correction table T1 may
be prepared in correspondence with all the sets of printer
characteristics. In this case, the single color correction table T1
will be used for all the sets of printer characteristics. The
selection process of S102 is not needed.
[0139] In the above-described embodiment, the tone correction table
T2 is prepared so as to store a set of tone-corrected color data A"
(=C" or M") for each of all the 256 sets of color data A' (=C' or
M') of 0 to 255. However, the tone correction table T2 may be
prepared to store a set of tone-corrected color data A" (=C" or M")
only for several sets of color data A' (=C' or M') which are
arranged at a fixed interval of "32," for example. In this case,
interpolation calculation is employed during the tone correction
process of S2 (S108).
* * * * *