JPH04200170A - Color image forming device - Google Patents

Abstract

PURPOSE:To reproduce more faithful colors by using the colors within a reproduction range by applying limiters on the three primary color density signals for color mixing by a subtractive color process, executing linear masking computation, outputting ink density signals and limiting the output levels thereof. CONSTITUTION:When the three primary color density signals (DR1, DG1, DB1) of the picture elements to be recorded are inputted, 1st limiter means 1, 2, 3 apply the limiters on these signals and output the three primary color density signals (DR2, DG2, DB2). A linear masking computing means 4 subjects the three primary color density signals (DR3, DG3, DB3) to the sum of products operation with the masking coefft. and outputs the ink density signals (C1, M1, Y1). Second limiter means 5, 6, 7 apply the limiters to the ink density signals (C1, M1, Y1) and outputs the ink density signals (C2, M2, Y2) which can be respectively reproduced. A recording control means 8 executes recording by controlling the heat quantity of a head 9 according to the value of Y2.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a color image forming apparatus such as a color printer.

Conventional technology In order to perform full color recording, C (cyan) 2M (
It is necessary to perform gradation recording for each of the three primary color inks of magenta) and Y (yellow).

There are two types of gradation recording: density gradation methods that allow the density to be controlled within a single dot, as typified by the sublimation thermal transfer method and silver salt photography method, and density gradation methods, such as the melting type thermal transfer method and electrophotographic method.
It can be broadly divided into area gradation methods, which express gradations by combinations of dots using visual integration effects using dithering and density patterns.

Both systems use three primary colors of colored light (R, G.

The principle of subtractive color mixing using (C, M, Y), which is the complementary color of B), is used. In additive color mixture, only the color reproduction range of the three primary colors is a problem, and each spectral component does not affect the color reproduction range, whereas in subtractive color mixture, the spectral distribution of pigments has a large influence on color reproduction. The spectral absorption characteristics of actual inks are such that the center wavelength deviates from the ideal, and the absorption characteristics are broad, so sub-absorption exists.
A phenomenon occurs in which the hue of the recorded image changes and the saturation decreases.

Conventionally, a method called masking has been used mainly in the printing field to solve these problems.

The most commonly used method is a method using linear masking as shown in equation (1) below.

A conventional color image forming apparatus using such linear masking performs a linear masking operation on each of the input three primary color density signals (D□, DGl, D□), as shown in FIG. Ink density signal (Cr, Ml,
The linear masking calculation means 31 outputs Y r ), and the output of the linear masking calculation means 31 (CI, M I
, Yr) and outputs an ink density signal (Cz, Mz, Yz); and limiter means 32, 33.
．． The ink density signal (C2, Mz+
recording control means 35 for performing gradation color recording according to
and a head 36 that performs recording by controlling the amount of dye to be transferred using the amount of heat of the thermal head by a recording control means 35.

The limiter means 32, 33, 34 are cyan 5 magenta,
CI is the maximum density that can be reproduced using each yellow ink.
RIX+ MfillX+ Y1%aX, minimum concentration C
e + i n + M i n + Y m
i. Then, a) C18, 〈CI<CIl, when X, C2=C.

When C1≦Cll1n, C2-Cwr in CI2: C□, then Cz = Csaw) M, 4. When <M, <M,, Yamtsu time Y
2=Y.

When Y1≦Y vh i n Yz=YI1. .

When Y1≧Y□, Y2-Y,ll,1X A limiter is applied.

This conventional method uses three primary color density signals (D
After the linear masking calculation means 31 performs a linear masking calculation on Rl, D c + , D s , ), the limiter means 32, 33, and 34 add the limit according to (2) 2 to each signal to determine the ink concentration. This is a method to obtain signals (C2, M2. Y2).

Furthermore, since these limiters are determined by the maximum and minimum recordable density of each ink, a limiter will inevitably be applied even if the limiter means 32, 33 and 34 after masking are not provided. Become.

Problems to be Solved by the Invention However, in the conventional configuration described above, the ink density signals (CI, M, , Y ,)
If the color is at least 1 degree or higher for each reproducible color and is lower than the maximum reproducible density, that is, within the color reproduction range of the printer, color reproduction can be performed according to the correction accuracy of linear masking, but depending on the input signal requirements If the color to be printed exceeds the color reproduction range of the printer, one of the ink density signals (C1, M + , Y + ) resulting from the linear masking calculation will be (C,, X, M,, X, Y, , , ) or less than (C,i,, M,i., Y,i,,), and for that value, the limiter means 32, 33, 34
From now on, recording will be performed using the limited value. For this reason, there is a problem in that even though there are similar colors that can be reproduced by the printer, very different colors are reproduced.

In addition, conventional color correction methods other than those mentioned above are configured with consideration to the reproducibility of colors within the color reproduction range, so if a color outside the color reproduction range is manually created, the color that can be reproduced by the printer will not match. There was a problem in that, although there were similar colors, vastly different colors were reproduced.

The present invention has been made in view of the above-mentioned points, and provides a color reproduction system that can more faithfully reproduce colors within the color reproduction range even for signals outside the color reproduction range with a simple configuration. The purpose of the present invention is to provide an image forming apparatus.

Means to solve problems The present invention provides subtractive color mixture three primary color density signals (Dll,.

A first limiter means for applying a limiter to the ink concentration signal (CI+M,
linear masking calculation means for outputting a linear masking calculation means (Y+) and a second limiter means for limiting the output level of the linear masking calculation means, the three primary color density signals (DRI, D.ll Dm+) of the first limiter means Limiter value for each color, cyan.

The maximum recordable density of magenta and yellow is the value converted into three primary color density signals, and the ink density signals (C+, M+, Y+) of the second limiter means are
Fan limiter values for each color. Magenta.

The maximum and minimum recordable density for each color of yellow,
The present invention is characterized in that the ink density is controlled by the output (C2, M2, Yz) of the second limiter means to form an image.

Further, the present invention provides additive color mixture three primary color luminance signals (R.

A complementary color conversion means performs complementary color conversion on G and B), and three primary color density signals (DR,.

A linear masking operation is performed using the input signals (D GI , D Bl) to generate ink density signals (CI, M l , Y
The complementary color conversion means includes linear masking calculation means for outputting three primary color density signals (DRI, DGI, Dm) and second limiter means for limiting the output level of the linear masking calculation means. +) The upper limit value of the limiter for each color is the value obtained by converting the maximum recordable density of cyan, magenta, and yellow into three primary color density signals, and the three primary color density signals (D Rl, D
cl.

D, 1) Set the lower limit value of the limiter for each color to cyan,
Three primary color luminance signals (R, G,
B) It performs logarithmic conversion of the reciprocal of each color, and the incoming density signal (C, , M, . . .
Yl) The limiter values for each color are the maximum and minimum recordable densities of cyan, magenta, and yellow, and the output of the second limiter means (Cz, Mz
, 'Y2) to form an image by controlling the ink density.

Three primary color density signals (DRl, Dc1,
Dal) with respect to cyan by the first limiter means.

Maximum recordable density for each magenta and yellow ink is set to 3.
A limiter is applied to the value converted to the primary color density signal, and a linear masking calculation is performed by a linear masking calculation means to obtain an ink density signal (C+, Ml.

y+), and this ink density signal (C,, M1+
y+) is further limited by the maximum and minimum recordable densities of cyan, magenta, and yellow colors using a second limiter means to determine ink density signals (C2, M Z , Y Z ′); This ink density signal is used to control the density of each color ink to form a color image.

In addition, the input three primary color luminance signals (R, G.

B), the complementary color conversion means converts the three primary color density signals (D□
, Dc1, DIl+) The upper limit value of the limiter for each color is the value obtained by converting the maximum recordable density of cyan, magenta, and yellow into three primary color density signals, and 3
Primary color density signal (D R1, D G,, D m +
) Three primary color luminance signals (R, G, B) where the lower limit value of the limiter for each color is the value obtained by converting the minimum recordable density of each color of cyan, magenta, and yellow into a three primary color density signal.
Logarithmic conversion of the reciprocal of each color is performed, and linear masking calculation is performed by the linear masking calculation means to convert it into an ink density signal (C, , M, , Yl), and this ink density signal (C4+Ml.

cyan,
The ink density signal (
C2-, M2, Yz) are determined, and the ink density signals are used to control the density of each color ink to form a color image.

EXAMPLE Hereinafter, an example of the present invention will be described based on FIGS. 1 to 5.

FIG. 1 is a block diagram of a color image forming apparatus according to an embodiment of the present invention. In this embodiment, yellow, magenta,
An example is shown in which the present invention is applied to a color printer using a sublimation thermal transfer recording method in which cyan is recorded on image-receiving paper in a field-sequential manner. This color image forming apparatus is comprised of first limiter means 1, 2.3, linear masking calculation means 4, second limiter means 5.6.7, recording control means 8, and head 9. The first limiter means 1, 2.3 receives input three primary color density signals (D I l , D cr
, DII+) respectively to generate three primary color density signals (D RZ , D a z , D
m z ).

The linear masking calculation means 4 includes the first limiter means 1,
2. Perform linear masking calculation on the output (D R
) is output. The second limiter means 5°6.7 applies a limiter to the output (C+-Ml, Yl) of the linear masking calculation means 4 to obtain an ink density signal (Cz, M
z, Yz). The recording control means 8 is
Second limiter means5. Gradation color recording is performed using the ink density signal (C2,' Mz, Y2) which is the output of -6.7. The head 9 performs recording by controlling the amount of dye to be transferred using the amount of heat of the thermal head' by the recording control means 8.

The first limiter means 1.2.3 has cyan, magenta,
The value obtained by converting the maximum recordable density of each color of yellow into three primary color density signals is D llffimX+ DQ□X+ D
lmlX, and the value obtained by converting the recordable minimum density of each color into three primary color density signals is D R@ill + DGffiin
+D++ain, the three primary color density signals (D R
l, D GI, D m I), a) DRM, , l<D, Il<D, 1. , DR when X
2=DRI DRI≦D, lll1. When l, D12 = D l1sin Dll≧D When Rfi&X, D ax = D
When DGI DGI≦D G IIi, , D6□−D G M i n When DGI≧D GIIIIX, DG2=DG□.

c) Dgmin〈Dflll〉 Da, D when Sax
! 12=DB! When D, ≦D Il+sin, □-DBI1. When n DIll≧D
) It is composed of a ROM having the input/output characteristics shown in FIG.

In this example, DR1%iX+ DGffiaX+
Dll'11- and D I+++ir++ Dc
C
□X+ Mllllall+ YmaX and C,
, , is the value obtained by multiplying M+*in+Y*in, and this is expressed by the following equation (4).

CII□ = DRmax ao+a++aZ aff+84+as a6+a7+as a, +al+az a3+at+as a6+afu+a8 The linear masking calculation means 4 executes the linear masking calculation of the above formula (1), and in this embodiment, the ink used is used as the masking coefficients a0 to a8. Determined using the least square method to minimize the root mean square error between the required color and the color reproduced by the printer for approximately 100 representative colors extracted as evenly as possible from the color space that can be reproduced by the printer. The value of the following equation (5) was used.

The second limiter means 5, 6.7 performs the limiter of the above formula (2), and is constituted by a ROM having input/output characteristics shown in FIGS. 3(A), (B), and (C). .
Next, the principle of the present invention will be explained with reference to FIG. 4, assuming recording with two-color ink.

The input density signal (x
The result of the masking operation for (I, yl) is expressed as (x2,
yz).

The input density space consisting of xl, "l+ is a straight line Xz:
m1n+ Xz= xlIMX+ Yz= y+*
It will be divided into 9 areas by ifi + Y2'''Ymax. That is, (a) Xz≦Xll1rz yz≦ylIin
(b) Xll1*〈Xz〈xlI14X+ yz
≦)'11111(C)x1%ax≦X2.
Yz≦'l 5in(d)xz≦xlI17. yln<
yl〈Y tea (e) xlh＜xz〈YmaX, ylIII＜yl〈
l5IIX (f) XMIIX≦X2, yea=n<
Vz<YmaX (g)X2≦xlIfl'l+ Y amX≦
y2(h) X*in<X2〈XIIIIXI y
sax≦y2(1)Xll! LX≦xl yv
These are nine areas expressed by amx≦y2. Here x
, 1. , is the minimum density that can be recorded with X color ink, X 1l
aX is the maximum density that can be recorded with X color ink, y, 7 is y
The minimum density that can be recorded with color ink, yl, represents the maximum density that can be recorded with y color ink.

Among these, the color reproducible area is the straight line x2=XI6iR+ by using linear masking in this embodiment.
Xz= Xasx+ )'2= y*=n
+ y z = Y, region (e) represented by a parallelogram surrounded by □.

First, a conventional method, that is, color reproduction by applying a limiter only after performing a masking operation, will be explained.

After performing masking calculations on signals outside the color reproduction range, the limiter's action leaves the input point and forms a straight line Xz=X*
i1 Xt= XIIaX+ yz= 7a
This is equivalent to conversion to the intersection of a straight line parallel to any straight line of in+7X=Vam□ and the boundary of region (e). That is, in the conventional method, for an input signal outside the color reproduction range, a color equal to the color reproduced using the input signal at this intersection point is reproduced.

For example, the area (h) (Xmin<x, < xMmX
+)' t >7 va. ) input signal (point 13) is
The color is the same as the color reproduced using the input signal at the intersection point 14 of the straight line passing through point 13 and parallel to straight line x, ==)(, , ) and straight line 'a y z−y□.

Similarly, the area (f) (Xz〉xIIISX+
The input signal (point 18) of Vein〈y2〈yo
=x, the color is reproduced using the human input signal at the intersection point 19 with □.

The input signal (point 23) of region N) (X2>Xmmx, yz>y, □) is a straight line passing through point 23 because both X2+Xz exceed the reproducible density range)'z
= ys @ straight line parallel to x and straight line xz = X III
It is equivalently transformed to the intersection point 24 with X, and further passes through the intersection point 24 and is parallel to the straight line Xz""
It is equivalently transformed to the intersection point 25 with ax, and the color is reproduced using the input signal of the point 25.

Next, color reproduction according to the present invention will be explained.

The value obtained by converting the maximum recordable density of each color x and y into an input density signal is D X1llaXr [)ysax, and the value obtained by converting the minimum recordable density of each color into an input density signal is D
+! 1i+1+Dym1a, the effect of the limiter at the input for signals outside the color reproduction range is as follows:
A straight line parallel to the x1 axis and y1 axis, and a straight line Xl=
DXMin+ x+=D*sax+ )'t=Dy
+++i+s+)'+=Dy+*ix This is equivalent to conversion to an intersection with any of ix. Then, a masking operation and a limiter after the masking operation are applied to the input signal at this intersection, and the area (e) is
A color will be reproduced that is equal to the color that would be reproduced using an input signal on the boundary of .

For example, the input signal (point 13) in region (h) is equivalently transformed by the limiter at the input to the intersection point 15 of the straight line parallel to the y axis and the straight line Hy+=D ,
After performing the masking operation, the limiter creates a straight line that passes through point I5 and is parallel to straight line x2 = x□, and a straight line)' z =
'I*□ is equivalently transformed to the intersection point 16, and the point 1
The color is reproduced using 6 input signals.

The input signal (point 18) in region (f) is caused by the limiter at the input to pass through point 18 and form a straight line parallel to the axis
It is equivalently transformed to the intersection point 20 with DXm□, and furthermore, by masking operation, a straight line passing through point 20 and parallel to the straight line vAy z = y −□ and a straight line Xz =
It is equivalently transformed to the intersection point 21 with X□8, and the color is reproduced using the input signal of the point 2I.

Then, the input signal (point 23) of region (i) is equivalently converted to the intersection point 26 of the straight line passing through point 23 and parallel to the y1 axis and the straight line )'+=Dy□, by the limiter at the input. , the straight line passing through point 26 and parallel to the x1 axis and the straight line *Xl=Dx
It is equivalently transformed to the intersection point 25 with m□, and the color is reproduced using the input signal of the point 25.

In addition, the color that is closest within the reproduction range to the color outside the reproduction range is reproduced using the signal in area (e) where the distance between the signal outside the color reproduction range and area (e) is the smallest. It becomes a different color.

For example, the density signal closest to the input signal (point 13) of area (h) is point 17 of the perpendicular line drawn from point 13 to the straight line '/z='Jmmx, and the color closest to point I3 is point 17. 1
This is the color reproduced using 7.

Similarly, the density signal closest to the input signal (point 18) in area (f) is at point 22 of the perpendicular line drawn from point 18 to straight line Xz=X, □8, and the color closest to point 18 is This is the color reproduced using point 22.

Then, the concentration signal closest to the input signal (point 23) of area (1) is the straight line X 2 = X max and y 2 - y □ 8
The color closest to point 23 is the color reproduced using point 25.

The color reproduction according to the conventional method, the color reproduction according to the present invention, and the ideal color reproduction when a signal outside the color reproduction range is inputted are described above using the input density space. These results show that the colors reproduced by the present invention are more faithful to the colors required by the input signal than the colors reproduced by the conventional method.

Next, the case of recording with three color inks will be explained.

The input concentration space consisting of D * l + D G I I D s + is the result of the masking operation (Cz,
M z , Y z ) cZ=clI
,,l,c2=c11. X, Mz=M, ;n+ Mz=
Mmax+ Y2=Y, ;,, Yz=Ymax 6
The area is divided into 27 areas by two planes. According to the principle of the present invention, (C yor, l≦C2≦C□+
Ml@I+'≦M2≦M, ,X, Yz>YII.

The input signals (DRl, Dc1, D□) in the area of It is moved to the intersection with the plane of DBI=D1@□8, subjected to a linear masking operation, and further set by the second limiter 2 to the plane C2=CIll i Ill and the plane Mz=
The color is moved to the intersection of the straight line parallel to M, □7 and the plane Y2=YIIllX, and the color reproduced using (C2, M2, Yz), which is the result of applying linear masking to the input signal at this point. Become.

Further, the lower limit value of the input signal is O, and a signal that greatly exceeds the lower limit of the color reproduction range is not input, but the upper limit value of the input signal may be a value considerably exceeding the color reproduction range. Therefore, the effect of the limiter on the upper limit is greater than the effect of the limiter on the lower limit.

Next, the operation of the color image forming apparatus in this embodiment will be explained.

First, the operation of printing the first color, that is, yellow, will be described.

Three primary color density signals (DRl, DGl.

) is input, the first limiter means 1゜2.
3 applies the limiter of (3) 2 above, and the three primary color density signals (
D R□, DG2. DI+□) is output.

Next, the linear masking calculation means 4 calculates the three primary color density signals (
D, □, DG2, Dyl□) is subjected to a product-sum operation with the masking coefficient, and the ink density signal (c++M
1, Y+).

and ink density signals (C+, MI, Y+
), the second limiter means 5, 6.7
) type limiter is applied to output reproducible ink density signals (Cz, Mz, Yz).

Then, the recording control means 8 controls the amount of heat of the head 9 according to the value of Y2 to perform recording.

After the above operation is performed for one screen of yellow recording, the same operation is performed for magenta and cyan inks to form a desired full-color image.

As described above, the evaluation value of fidelity for color reproduction of the present invention has been evaluated based on the distance in the input density space, but the experimental results of this example were evaluated using the uniform color space, which is said to be the closest to human visual characteristics. Ta.

FIG. 5 shows the results of a color reproduction experiment for an input outside the color reproduction range of the color printer according to this embodiment, and represents the u''v'' plane of the uniform color space.

* indicates a color requested by the input signal and exceeds the color reproduction range of the color printer used in this embodiment, ◯ indicates a color reproduced by this embodiment, and △ indicates a color reproduced by a conventional method. As can be seen from this figure, in this example, even when the uniform space distance was used as the evaluation value for the required color of the input signal, it was possible to reproduce a more faithful color.

FIG. 6 is a block diagram of a color image forming apparatus according to a second embodiment of the present invention.
Complementary color conversion means 10 instead of limiter means 1, 2.3
, 11.12. Complementary color conversion means 10,
11.12 is the input additive color mixture three primary color luminance signal (
R, G, B) are subjected to complementary color conversion to generate three primary color density signals (D
R2, D c z .

D, 2) is output. The linear masking calculation means 4 includes complementary color conversion means 10. ．． 11.12 output (D, □, Da2r
A linear masking operation is performed on D a2) to output an ink density signal (C+ 9M+, Y+). The second limiter means 5, 6.7 includes the linear masking calculation means 4.
A limiter is applied to the outputs (C+, Ml, Y+) of ink concentration signals (Cz, Mz, Y2). The recording control means 8 includes a second limiter means 5.
6.7 outputs (Cz, Mz, Y2) perform gradation color recording. The head 9 performs recording by controlling the amount of dye to be transferred using the amount of heat of the thermal head by the recording control means 8.

Complementary color conversion means 10, 11.12 input R, G,
B for each color) I Q -DjljjX(R(l Q-DI
When ``''7, DJI = l og (1/R) R≦l Q-DIRmm 0) 10-"'""<G< l Q-"'"7
When Dr, = l o g (1/G)G≦1
When 0-10-11G, DG = DGmax When G≧10-"'"0, DG "DG, in C) I Q - DIIIAX (13(l Q
-Dlsin(7) (!: KiDm = l o
g (1/B) When B≦10−DIlIax, Dyr −Dm−□ When B≧10411″′”0, D++=Ds−0 −・・−−−−−(6) , and is constituted by a ROM having input characteristics shown in FIG.

The linear masking calculation means 4 executes the linear masking calculation of the above equation (1), and in this embodiment, the value of the above equation (5) is used as the masking coefficient.

The second limiter means 5, 6.7 performs the limiter described in (2) 2 above, and in this embodiment, similarly to the first embodiment, a ROM in which the above (2) 2 is made into a table is used. Its input/output characteristics are the same as those shown in FIG.

Next, the operation will be explained.

First, the operation of printing the first color, that is, yellow, will be described.

When the luminance signals (R, G, B) of the pixels to be recorded are input, the complementary color conversion means 10, 11.12 performs the conversion according to the above equation (6), and converts the three primary color density signals (D+H, De2,
Dmz) is output.

Next, the linear masking calculation means 4 generates the three primary color density signals (D
ig, Dcm, Dsz) with the masking coefficient, and the ink density signal (C.

, Ml, Y+).

Then, the ink density signals (C+, Ml, 'Y+
), the second limiter means 5, 6.7 corresponds to the above (2).
A limiter of the formula is applied, and reproducible ink density signals (Cz, Mz, Yz) are output.

Then, the recording control means 8 controls the amount of heat of the head 9 according to the value of Y2 to perform recording.

After the above operation is performed for one screen of yellow recording, the same operation is performed for magenta and cyan inks to form a desired full-color image.

In this embodiment, even when the input signal is a three-primary-color luminance signal, the same effects as in the first embodiment can be obtained, and a color more faithful to the required color can be reproduced.

In the above embodiment, the first limiter means 1゜2.3 and the second limiter means 5, 6.7 were constructed from ROM, and the linear masking calculation means 4 was constructed from a product-sum calculation circuit. It is clear that the same result can be obtained even if part or all of the process is implemented by software processing.

DETAILED DESCRIPTION OF THE INVENTION According to the present invention, as described in detail, there is provided a first limiter means for applying a limiter to the subtractive color mixture three primary color density signals (D*t, Dc+, D□), and this first limiter means. linear masking calculation means for performing a linear masking calculation using the output of as input and outputting an ink density signal (C, , Ml, Yl), and a second limiter means for limiting the output level of the linear masking calculation means, Said first
The three primary color density signals (D Rl, D
G1. D B ,) The value of the limiter for each color is a value obtained by converting the maximum recordable density of each color of magenta, magenta, and yellow into three primary color density signals, and the ink density signal of the second limiter means < c + , M l ,
y + ) The limiter values for each color are set as the highest and lowest printable densities of cyan, magenta, and yellow, and the outputs of the second limiter means (C2, M2 .
Y2) Since the configuration is such that images are formed by controlling the ink density, compared to conventional devices, the configuration is simple, just providing a limiter means for the input of the masking calculation means, and it can handle the required color of the input signal. This has the excellent effect of being able to reproduce more faithful colors using colors within the reproduction range.

In addition, the three primary color luminance signals (R, G.

A complementary color conversion means that performs complementary color conversion on B), and three primary color density signals (D, ..., DGll) which are the output of this complementary color conversion means.
DIl+) for performing a linear masking operation and outputting an ink density signal (C1, M1, Y1); and a second limiter means for limiting the output level of the linear masking operation means; The complementary color conversion means converts three primary color density signals (DRl, DGl, D
l) The upper limit value of the limiter for each color is the value obtained by converting the maximum recordable density of cyan, magenta, and yellow into three primary color density signals, and the three primary color density signals (D R1,
Dc, 1. DII+) Set the lower limit value of the limiter for each color to cyan.

Three primary color luminance signals (R, G,
B) It performs logarithmic conversion of the reciprocal of each color, and the ink density signal (CI, Ml) of the second limiter means
.
, M z , Y z ), the ink density is controlled to form an image, so if the human input signal is a luminance signal, the configuration is simple, just providing a complementary color conversion means for the human input of the masking calculation means. This has the excellent effect of being able to reproduce colors with greater fidelity by using colors within the reproduction range for the requested color of the input signal.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a color image forming apparatus according to an embodiment of the present invention, FIG. 2 is an explanatory diagram of the relationship between the input and output of the first limiter means, and FIG. 3 is the input of the second limiter means. FIG. 4 is an explanatory diagram of the relationship between input and output in the input space when two-color ink is used. FIG. 5 is an explanatory diagram of the results of color reproduction experiments for color prints.
FIG. 6 is a block diagram of a color image forming apparatus according to a second embodiment of the present invention, FIG. 7 is an explanatory diagram of the relationship between human power and output of complementary color conversion means, and FIG. 8 is a diagram of a conventional color image forming apparatus. It is a block diagram. 1.2.3--first limiter means, 4-linear masking calculation means, 5. 6. 7-Second limit/7 limit means,
8 - Recording control means, 9 Head, 10, 11.12 - Complementary color conversion means. Agent Patent Attorney Tsukasa Nakajima Figure 2 Figure 3 Figure 4 Ox1 Figure 7 DR21 Figure 8

Claims (3)

[Claims] (1) Subtractive color mixture three primary color density signals (D_R_1, D_G
A first limiter means for applying a limiter to the ink concentration signal (C_1, M_1) performs a linear masking operation using the output of the first limiter means as input.
, Y_1), and a second limiter means for limiting the output level of the linear masking calculation means, the three primary color density signals (D_R_1, D_G_1, D_B_1) of the first limiter means The limiter value for each color is a value obtained by converting the maximum recordable density of cyan, magenta, and yellow into three primary color density signals, and the ink density signal (C
_1, M_1, Y_1) Limiter value for each color,
The output of the second limiter means (C
_2, M_2, Y_2) to form an image by controlling ink density. (2) The first limiter means controls the three primary color density signals (D_R
_1, D_G_1, D_B_1) For each color, cyan,
2. The color image forming apparatus according to claim 1, wherein the lower limit value is a value obtained by converting the minimum recordable density of magenta and yellow into three primary color density signals. (3) Complementary color conversion means that performs complementary color conversion on the three primary color luminance signals (R, G, B) of additive color mixture, and the three primary color density signals (D_R_1, D_G_1, D_B) that are output from this complementary color conversion means.
__l) as an input to perform a linear masking operation and output an ink density signal (C_1, M_1, Y_1), and a second limiter means for limiting the output level of the linear masking operation means, The complementary color conversion means converts three primary color density signals (D_R_1, D_G_
1, D_B_1) The upper limit value of the limiter for each color is
Let the maximum recordable density of each color of cyan, magenta, and yellow be the value converted into the three primary color density signals, and the lower limit value of the limiter for each color of the three primary color density signals (D_R_1, D_G_1, D_B_1) for each color of cyan, magenta, and yellow. The ink density signal of the second limiter means ( C_1, M_1, Y_1) The limiter values for each color are set as the maximum and minimum printable densities of cyan, magenta, and yellow, and the ink density is controlled by the output (C_2, M_2, Y_2) of the second limiter means. What is claimed is: 1. A color image forming apparatus characterized in that the apparatus is configured to form an image by