JP2875451B2 - Color signal conversion method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color signal conversion method for converting a signal of a first color signal system into a signal of a second color signal system.

[0002]

2. Description of the Related Art As a color signal system, there are a BGR signal system which is representative of additive color mixture and a YMCK signal system which is representative of subtractive color mixture. In the printing plate making process, the BGR signal
In some cases, conversion to a K signal needs to be performed. If such color signal conversion is performed by a table memory recorded in a ROM, high-speed conversion can be performed. However, for example, an 8-bit BGR signal is converted to an 8-bit YMC
When converting to a K signal, the memory capacity of the table memory is a huge amount of 64 Mbytes.

Therefore, usually, a YMCK signal for only the upper bits (for example, 4 bits) of the BGR signal is stored in a table memory. The upper bit of the BGR signal is converted into a YMCK signal by the table memory, and the lower bit (for example, 4 bits) of the BGR signal is used to interpolate the YMCK signal output from the table memory to obtain the final YMCK signal. Is generated. An example of such a color signal conversion method is described in Japanese Patent Publication No. 58-16180. In this method, the color solid of the BGR signal is divided into a plurality of tetrahedrons, and interpolation is performed in the tetrahedron. The interpolation formula is represented by a linear expression of lower bits of three color signals x, y, and z (this corresponds to the BGR signal in the above example), as shown in Expression (III) of the publication. There is an advantage that calculation can be performed easily and at high speed.

[0004]

However, in the conversion method described above, there are many cases where the ideal interpolation formula cannot be expressed by the linear expression of the lower bits of the three color signals. In such a case, there is a problem that the difference between the actual interpolation result and the ideal interpolation result becomes considerably large.

The present invention has been made to solve the above-mentioned problems in the prior art. Even when an ideal interpolation formula cannot be expressed by a linear expression of lower bits of a plurality of color signals, An object of the present invention is to provide a color signal conversion method capable of obtaining a good conversion result.

[0006]

In order to solve the above-mentioned problems, a method according to the present invention is a color signal conversion method for converting a plurality of signals of a first color signal system into signals of a second color signal system. (A) obtaining a basic value of a signal of the second color signal system according to a value of a predetermined upper bit of a plurality of signals of the first color signal system; Determining whether or not the values of the upper bits of at least two signals of the color signal system are equal to each other, and selecting one of predetermined first and second interpolation formulas according to the determination result; c) generating the signal of the second color signal system by interpolating the basic value using the value of a predetermined lower bit of the plurality of signals of the first color signal system according to the selected interpolation formula. And the first and second interpolation formulas are the first and second interpolation formulas.
Equal to the value of the upper bit of multiple signals of the color signal system
If there is no, the first interpolation formula gives a good interpolation result.
The higher order of at least two signals of the first color signal system
When the values of the bits are equal to each other, the second interpolation formula is
It is characterized by providing a good interpolation result .

[0007]

In the case where there is no value equal to the value of the upper bits of the plurality of signals of the first color signal system, the first interpolation formula gives a good interpolation result, and at least two signals of the first color signal system are obtained. When the values of the upper bits are equal to each other, the second interpolation formula gives a good interpolation result. Therefore, a better conversion result can be obtained by determining whether or not the values of the upper bits of the first color signal system are equal to each other and selecting an interpolation formula according to the determination result.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the following, two interpolation equations will be described first.
Then, a color signal conversion method using these interpolation formulas and a device for implementing the method will be described.

A. Bilinear method (first interpolation formula): There is a bilinear method as a first method for interpolating a basic value of a color signal. Although the actual color conversion from the BGR signal to the YMCK signal is performed in the BGR coordinate system, it is a three-dimensional conversion. Here, for simplicity, the two-dimensional bilinear method will be described first.

FIG. 1 is a conceptual diagram showing an interpolation operation by a two-dimensional bilinear method. Here, it is assumed that a conversion value U is obtained in an XY coordinate system. Square PaPbP
cPd is a standardized square with one side length of 1,
The color conversion values U at the vertices Pa, Pb, Pc, Pd are Ua, Ub, Uc, Ud, respectively. FIG. 2 is a graph in which the converted value U is plotted on the vertical axis.

In the bilinear method, an arbitrary point Q ( X, Y )
Is given by the following equation (1).

(Equation 1) Here, Sa, Sb, Sc, and Sd are the areas of four regions separated by two straight lines passing through the point Q and parallel to the X axis and the Y axis, as shown in FIG. Where subscripts a, b, c
, D are assigned to vertices facing each region. The areas Sa, Sb, Sc, and Sd are respectively given by the following equation (2).

(Equation 2)

The right side of Equation 1 is rewritten as Equation 3 below.

(Equation 3) Here, k0 to k3 are coefficients. That is, in the two-dimensional bilinear method, interpolation is performed using an interpolation formula including quadratic terms related to X and Y.

[0013] In the bi-linear method, as shown in FIG. 2, X
Spatial point corresponding to an arbitrary point Q on the Y plane Qu (X, Y,
UQ) is, spatial point Pua corresponding to four vertexes Pa -PD square (X a, Y a, Ua ) ~Pud (X d, Y d, U
In the case where d) exists on a smoothly connected curved surface, an accurate converted value UQ can be obtained. Here,
A curved surface connected to a plane is defined as a plane and a curved surface
The transformation value UQ is directly proportional to X or Y
Means a surface that can be expressed in a form similar to
For example, a curved surface represented by
Continued curved surface ". _{UQ = K 0 + K 1 ·} X + K 2 · Y + K 3 · XY _{Here, K 0, K 1, K} 2, K 3 are coefficients. However,
Even if the surface cannot be expressed by this equation,
For surfaces that are similar to
Curved surface ".

FIG. 3 is a conceptual diagram showing an interpolation operation by the three-dimensional bilinear method.
It is assumed that the signal is converted into a K signal. The cube of FIG. 3 is a standardized unit cube having one side length of 1,
Points Pa to Ph are vertices. The coordinate axis is BGR
The lower four bits of the signal are shown as signals BL, GL, and RL. Each vertex of the unit cube is defined by the upper 4 bits of the BGR signal. At each vertex, the upper 4 bits of the BGR signal are converted to the basic value of the YMCK signal. YMC
Considering first the Y signal among the K signals, the value after interpolation of the Y signal at an arbitrary point Q (BL, GL, RL) in the unit cube is given by the following equation 4 by the bilinear method.

(Equation 4) Here, Va to Vh are the volumes of eight rectangular parallelepipeds separated by three planes passing through the point Q and perpendicular to the BL, GL, and RL axes. However, the suffixes a to h are assigned to vertices facing the respective rectangular parallelepipeds. The volumes Va to Vh are respectively given by the following Expression 5.

(Equation 5) If the upper 4 bits of the BGR signal are regarded as an integer part, the lower 4 bits of signals BL, GL, RL can be regarded as a decimal part.

In equation (5), (1-BL), (1-G
L) and (1-RL) are represented by symbols with BL, GL, and RL with an overline (bar), respectively.
Can be rewritten as

(Equation 6)

As described above, in the bilinear method,
(1) Each vertex Pa to Ph of the unit cube including an arbitrary point Q
After converting the signal values of the upper 4 bits of the BGR signal to obtain basic values Ya to Yh of the Y signal, (2) the signal values BL, 4 of the lower 4 bits of the BGR signal corresponding to the point Q,
By interpolating these basic values using GL and RL, the final Y signal at point Q is obtained. YMC
The same applies to other signals of the K signal system.

As can be seen from Equation 6, the three-dimensional bilinear method uses an interpolation formula including a third-order term related to the lower bit signals BL, GL, and RL.

B. Tetrahedral division method (second interpolation formula): As a second method for interpolating the basic values of color signals, there is a tetrahedron division method described in Japanese Patent Publication No. 58-16180. Here, for the sake of simplicity, first, a description will be given of a triangulation method corresponding to a two-dimensional tetrahedron division method.

FIG. 4 is an explanatory diagram showing a division method by the triangulation method. Here, it is assumed that a conversion value U is obtained in an XY coordinate system. In the triangulation method, a square PaPbPcPd is divided into two triangles PaPbPc and PaPdPc by a diagonal line passing through the origin Pa, and the interpolation formula changes depending on which triangle contains the point Q to be interpolated. When the point Q is included in the first triangle PaPbPc, interpolation is performed according to the following equation (7).

(Equation 7)

On the other hand, when the point Q is included in the second triangle PaPdPc, interpolation is performed according to the following equation (8).

(Equation 8) Equations 7 and 8 are derived as follows. First, the point
If Q is included in the triangle PaPbPc, the complement of the point Q
The intermediate value UQ can be obtained by the following equation. UQ = Sa.times.Ua + Sb.times.Ub + Sc.times.Uc (7a) where Sa, Sb and Sc are weighting factors and the triangle P
When the area of aPbPc is “1”, the triangle PbP
The area of cQ, triangle PcPaQ, and triangle PaPbQ
Each is represented. Triangle PbPcQ, Triangle PcPa
Q, the respective areas Sa, Sb, S of the triangle PaPbQ
c becomes Sa = (1-X) Sb = (X-Y) Sc = Y. By substituting these into equation (7a), equation 7 is obtained.
Can be On the other hand, when the point Q is included in the triangle PaPdPc,
In this case, the interpolation value UQ of the point Q can be obtained by the following equation.
Can be. UQ = Sa'.times.Ua + Sd.times.Ud + Sc'.times.Uc (8a) where Sa ', Sd, Sc' are weighting factors and triangular.
When the area of the form PaPdPc is "1", the triangle P
Area of dPcQ, triangle PcPaQ, triangle PaPdQ
Respectively. Triangle PdPcQ, Triangle Pc
Areas Sa ′ and S of PaQ and triangle PaPdQ
d, Sc 'is, Sa' a = (1-Y) Sd = (Y-X) Sc '= X. By substituting these into equation (8a), equation 8 is obtained.
Can be Note that the right side of Expressions 7 and 8 can be generally expressed as Expression 9.

(Equation 9) Thus, in the triangulation method, a first-order interpolation formula for X and Y is used.

FIG. 5 is a graph showing the distribution when the conversion value U is set on the vertical axis. In the triangulation method, as shown in FIG. 5, the conversion value U is set on a diagonal line connecting the points Pa and Pc.
Is 0, an accurate interpolation result can be obtained. In particular, when the spatial point Qu corresponding to the point Q exists on the triangles Pa, Pub, Pc or on other triangles Pa, Pud, Pc, an accurate interpolation value UQ can be obtained. In addition,
Points Pua to Pud in FIG. 5 are similar to points Pa to
The spatial point corresponding to Pd.

FIG. 6 is an explanatory diagram showing a method of dividing a unit cube by a three-dimensional tetrahedron dividing method. The interpolation formula for obtaining the Y signal at an arbitrary point Q (BL, GL, RL) in the unit cube is as follows: The point Q is included in any of the six tetrahedrons T1 to T6 in FIGS. Depends on These six tetrahedrons T1 to T6 represent three surfaces of a unit cube including two coordinate axes by two diagonal lines passing through the point Pa.
This is a tetrahedron composed of each of six right-angled isosceles triangles formed by dividing into two right-angled triangles and a vertex Pg. As another definition of the six tetrahedrons T1 to T6, the origin Pa of the BLGLRL coordinate system and the origin P
It is also possible to regard the vertex Pg as a tetrahedron having the four vertices of the vertex Pg opposing a and the other two points adjacent to each other among the remaining six vertices of the unit cube.

Which of the six tetrahedrons T1 to T6 contains an arbitrary point Q in the unit cube is determined by the following equation (10).
Is determined according to

(Equation 10) The interpolation formula for each of the tetrahedrons T1 to T6 is represented by the following formula 11.

[Equation 11]

As described above, in the tetrahedral division method, similarly to the bilinear method, (1) the signal values of the upper 4 bits of the BGR signal are converted at each of the vertices Pa to Ph of the unit cube including an arbitrary point Q. And the basic values Ya to Y of the Y signal
h, (2) the lower 4 bits of the BGR signal corresponding to point Q
The final Y signal at point Q is obtained by interpolating these base values using the bit signal values BL, GL, RL. The same applies to other signals of the YMCK signal system.

As can be seen from Equation 11, the tetrahedron division method uses a first-order interpolation formula for the lower bit signals BL, GL, and RL.

C. Comparison between bilinear method and tetrahedral division method:
The bilinear method uses the lower bit signals BL and G of the BGR signal.
Since a cubic interpolation formula (Equation 6) for L and RL is used, and a tetrahedral division method uses a primary interpolation formula (Equation 11), the interpolation result is generally better with the bilinear method. Is obtained. However, as shown below, the tetrahedron division method may obtain a better interpolation result in some cases.

FIG. 7 is a diagram showing an example of the distribution of the true value of the conversion value U with respect to the XY coordinates. When the values (circled) at the four corners in FIG. 7 are interpolated by the tetrahedral division method,
The same interpolation result as the true value is obtained. On the other hand, when the values at the four corners are interpolated by the bilinear method, the result shown in FIG. 8 is obtained. FIG.
As can be understood by comparing the diagonal interpolation result with the true value in FIG. 7, an interpolation error occurs in the bilinear method. As described above, when the distribution of the true conversion result has a shape as shown in FIGS. 5 and 7, a better interpolation result is obtained by the tetrahedral division method than by the bilinear method. This reason
The reason is that in the space shape having a curved surface as shown in FIG. 5 or FIG.
And the boundary of the division by the tetrahedral division method
This is because the world is close.

D. Relationship between BGR signal and YMCK signal:
Assuming that the dynamic range of the BGR signal is 100, the YMC signals Yi, Mi, Ci for the ideal ink
Is given by the following Equation 12.

(Equation 12) FIG. 9 is an explanatory diagram showing the relationship of Expression 12.

Since the ink actually has turbidity, the YMC signals Yr, Mr, and Cr for the actual ink are given by the following equation (13).

(Equation 13) Here, the functions fy, fm and fc are correction terms for correcting the difference between the ideal ink and the actual ink.

Incidentally, in the conversion from the BGR signal to the YMCK signal, the concept of the primary color component is often used. The signal value of the primary color component is given by Equation 14 below.

[Equation 14] Here, the operator MIN indicates an operation that takes the minimum value in parentheses. As can be seen from the condition of Expression 14, the three primary color component signals Y1st, M
Only one of 1st and C1st is obtained. For example, FIG.
In the example, the primary color component signal Y1st (= GB) of the Y plane is obtained, and the other primary color component signals M1st and C1st both become "0".

FIG. 10 shows the primary color component signal Y1st of the Y plane.
It is explanatory drawing which shows the distribution shape of (= GB). The distribution shape of the primary color component signal Y1st is a plane inclined with the straight line of G = B as a fold. This primary color component signal Y1s
The distribution shape of t is similar to the distribution shape of FIG. That is, in both cases, the height on the diagonal is 0, and there is a plane inclined on one side from the diagonal, and a plane with a height of 0 on the other side.

When the relationship between the BGR signal and the YMCK signal was actually examined in detail, the upper four
When the values of the bits are substantially equal to each other, it has been found that the correction term fy of the equation (13), which is a conversion equation corresponding to the actual ink, has a function shape close to the primary color component signal Y1st. From this, it can be considered that the distribution of the Y signal Yr for the actual ink has a shape as shown in FIG. 11, for example. In addition, the shape of a portion before a diagonal line connecting points represented by G = B is omitted.

Since the converted Y signal Yr has a distribution shape as shown in FIG. 11, when GU = BU holds,
An interpolation method suitable for the distribution shape shown in FIG. 5, that is, a better interpolation result is obtained by performing interpolation using the tetrahedron division method.
On the other hand, when GU is not equal to BU, a better interpolation result can be obtained by performing interpolation by the bilinear method using a higher-order interpolation formula than by the tetrahedral division method. The same applies to the M signal, C signal, and K signal. The reason is as follows.
Can be. In general, two of the three color signals
Distribution of the true conversion result when the upper bits of
Is a "non-smooth surface" as shown in FIG.
There are many. As described above, as shown in FIG.
The spatial shape including the "non-curved surface" is calculated by the tetrahedron division method
Because it changes rapidly near the boundary of the split, it is bilinear
The tetrahedral division method can obtain better interpolation results than the tetrahedral division method.
In the direction. On the other hand, of the three color signals,
When there is no curve, the surface showing the distribution of the true transformation result is
In many cases, it will be a “smooth surface”, so in this case
The bilinear method tends to obtain good interpolation results.

From the above considerations, in this embodiment, the BGR
If at least two of the upper four bits of the signals BU, GU, and RU are equal to each other, the tetrahedron division method (Equation 1)
Interpolation is performed according to 1), and if there is no equivalent among BU, GU, and RU, interpolation is performed by the bilinear method (Equation 4 or 6), whereby a better interpolation result can be obtained as a whole. .

E. Configuration of Apparatus: FIG. 12 is a block diagram showing the configuration of a color signal conversion apparatus that performs color signal conversion by applying this embodiment. This device includes a bilinear interpolation circuit 20, a tetrahedral interpolation circuit 30, an upper bit signal comparison circuit 40, and a selection circuit 50. The bilinear interpolation circuit 20 and the tetrahedral interpolation circuit 30 provide upper bit signals BU, GU, RU of the BGR signal and lower bit signals BL, BL,
The converted Y signals YQ1 and YQ2 are output based on GL and RL, respectively. However, here, the two types of interpolation circuits 20 and 30 are provided with lower bit signals BL, GL and RL, respectively.
In addition to the interpolation for the upper bits BU,
A table for obtaining basic values for GU and RU is also included.

The upper bit signal comparing circuit 40 detects whether or not there is any of the upper bit signals BU, GU, and RU equal to each other, and outputs a 1-bit selection signal Sw in accordance with the result. When there are equal bits among the upper bit signals BU, GU, and RU, the selection signal Sw goes high, and the selection circuit 50 selects and outputs the output signal YQ2 of the tetrahedral interpolation circuit 30 in response to this. . On the other hand, if none of the upper bit signals BU, GU, and RU are equal to each other, the selection signal Sw goes to the L level, and the selection circuit 50 outputs the output signal YQ1 of the bilinear interpolation circuit 20 accordingly.
And outputs it as the converted Y signal Yr.

The bilinear interpolation circuit 20 and the tetrahedral interpolation circuit 30 are supplied with a 2-bit ink selection signal Ss, and YMC is selected according to the value of the ink selection signal Ss.
The other signals of the K signal system are bilinear interpolation circuits 20 and 4
It is output from each of the planar interpolation circuits 30.

FIG. 13 is a block diagram showing the internal configuration of the bilinear interpolation circuit 20. Bilinear interpolation circuit 20
Represents an address conversion circuit 22, a table memory 24,
A load value ROM 26 and a product-sum operation circuit 28 are provided.

The address conversion circuit 22 outputs the upper bit signal B
U, GU, and RU, the eight vertices Pa to P in the unit cube shown in FIG. 3 in synchronization with the 3-bit vertex selection signal Sv.
Outputs the coordinate values of h sequentially. The coordinate values of the vertices Pa to Ph are as follows: Pa (BU, GU, RU), Pb
(BU + 1, GU, RU), Pc (BU + 1, GU +
1, RU), Pd (BU, GU + 1, RU), Pe (B
U, GU, RU + 1), Pf (BU + 1, GU, RU +
1), Pg (BU + 1, GU + 1, RU + 1), Ph
(BU, GU + 1, RU + 1).

The coordinate values output from the address conversion circuit 22 are given to the table memory 24 as addresses. In accordance with the address, the table memory 24 sequentially outputs the basic values Ya to Yh of the Y signal at the vertices Pa to Ph. When the ink selection signal Ss specifies magenta, cyan, or black ink other than yellow, the table memory 24 outputs the basic value of the color signal according to the specification.

On the other hand, the load value ROM 26 synchronizes with the 3-bit vertex selection signal Sv and outputs the lower bit signals BL and GL.
, RL, the load values Va to Vh of Equation 4 are sequentially output. The 3-bit vertex selection signal Sv is a signal that changes cyclically from “000” to “111”. Also,
The values of the load values Va to Vh are given by Expression 5.

The product-sum operation circuit 28 includes the table memory 24
And the load values ROM
By taking the product of the load values Va to Vh output from 26 and sequentially adding them, the operation of Expression 4 is performed, and the Y signal YQ1 at the point Q is output.

FIG. 14 is a block diagram showing the internal configuration of the tetrahedron interpolation circuit 30. The tetrahedral interpolation circuit 30 includes a coefficient output circuit 32, an area determination ROM 34, a selection circuit 36
And a product-sum operation circuit 38.

The area determination ROM 34 stores the lower bit signal B
Receiving L, GL, and RL, it outputs a 3-bit area determination signal Sr indicating which of the six tetrahedrons T1 to T6 shown in FIG. 6 contains the point Q (BL, GL, RL).

The coefficient output circuit 32 includes an area determination ROM 34
And an upper bit signal B
In accordance with U, GU, and RU, the coefficients for the lower bit signals BL, GL, and RL in Expression 11 are output. For example, when the point Q is included in the first tetrahedron T1, the coefficients Ya,
(Yb-Ya), (Yc-Yb) and (Yg-Yc) are output. The 2-bit control signal Sc supplied to the coefficient output circuit 32 is a signal that changes cyclically from “00” to “11”, and the coefficient output circuit 32 synchronizes the control signal Sc with the coefficients one by one. Output sequentially.

The selection circuit 36 responds to the control signal Sc by
The four input signals "1", BL, GL, and RL are output in this order. The product-sum operation circuit 38 receives the outputs of the coefficient output circuit 32 and the selection circuit 36 and executes the operation of Expression 11;
A Y signal YQ2, which is a conversion result at point Q, is output.

When the Y signals YQ1 and YQ2 are output from the bilinear interpolation circuit 20 and the tetrahedron interpolation circuit 30, respectively, one of them is selected by the selection circuit 50 shown in FIG. 12 and output as the converted Y signal Yr. Is done.

According to the color conversion apparatus shown in FIGS. 12 to 14, when any two of the upper bit signals BU, GU, and RU are equal to each other, interpolation is performed by the tetrahedral division method. Since the interpolation is performed by the interpolation method, a better interpolation result can be obtained as compared with the case where the interpolation is performed by one of the methods.

The present invention is not limited to the above embodiment, but can be implemented in various modes without departing from the gist of the invention. For example, the following modifications are possible.

(1) Expression 11 which is an interpolation expression in the tetrahedral division method can be generally expressed as Expression 15 below.

(Equation 15) Here, Wa to Wh are load values for the basic values Ya to Yh. For example, the load values Wa to Wh for the tetrahedron T1 in Expression 11 are given by Expression 16 below.

(Equation 16)

Equation 15 has the same function form as Equation 4 which is an interpolation equation of the bilinear method. That is, if Equation 4 is used in the bilinear method and Equation 15 is used in the tetrahedral division method, both values are the basic values Ya to Yh and the load values Va to Vh.
Alternatively, a converted Y signal can be obtained by a product-sum operation with Wa to Wh.

FIG. 15 is a block diagram showing the configuration of a color signal conversion device that performs interpolation according to such an operation method. This device uses a bilinear interpolation circuit 20 shown in FIG.
In addition to the circuit elements 22, 24, 26, and 28, and the upper bit signal comparison circuit 40 shown in FIG. 12, a load value ROM 60 that outputs load values Wa to Wh for the tetrahedral division method,
It has a configuration in which an inverter 62 is added.

The selection signal Sw output from the upper bit signal comparison circuit 40 is used as it is as the load value R for the bilinear method.
The load value ROM for the tetrahedral division method is input to the enable terminal of the OM 26 and inverted by the inverter 62 to be used.
60 are input to the enable terminal. As a result, only one of the outputs of the two load value ROMs 26 and 60 is given to the product-sum operation circuit 28 in accordance with the selection signal Sw.

The color signal conversion device shown in FIG.
A good interpolation result similar to that of the device shown in FIG. 2 can be obtained. The color signal conversion device of FIG. 15 has advantages that the circuit configuration can be simplified and the number of circuit elements used can be reduced as compared with the device of FIG.

(2) In the above embodiment, the upper bit signal B
Although U, GU, RU and the lower bit signals BL, GL, RL are each 4-bit signals, the number of these bits can be set arbitrarily.

(3) In the above embodiment, the apparatus for converting the BGR signal system to the YMCK signal system has been described. However, the present invention relates to the conversion between the BGR signal system or the YMCK signal system and another color signal system. In addition, the present invention can be applied to conversion between the other color signal systems.

[0057]

As described above, according to the color signal conversion method of the present invention, even when an ideal interpolation formula cannot be expressed by a linear expression of the lower bits of a plurality of color signals, a satisfactory interpolation formula can be obtained. There is an effect that a conversion result can be obtained.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing an interpolation operation by a two-dimensional bilinear method.

FIG. 2 is a graph showing a distribution of converted values in a bilinear method.

FIG. 3 is a conceptual diagram showing an interpolation calculation by a three-dimensional bilinear method.

FIG. 4 is an explanatory diagram showing a division method in the triangulation method.

FIG. 5 is a graph showing a distribution of interpolation values in the triangulation method.

FIG. 6 is an explanatory diagram showing a division method in a tetrahedron division method.

FIG. 7 is a diagram showing an example of a true value distribution of a conversion value U with respect to XY coordinates.

FIG. 8 is a view showing a result of interpolating values at four corners in FIG. 7 by a bilinear method.

FIG. 9 is an explanatory diagram showing a relationship between a BGR signal and a YMCK signal of ideal ink.

FIG. 10 is an explanatory diagram showing a distribution shape of a Y color primary color component signal.

FIG. 11 is a graph showing a distribution shape of a Y signal for actual ink.

FIG. 12 is a block diagram showing the overall configuration of a color signal conversion device as an embodiment of the present invention.

FIG. 13 is a block diagram showing an internal configuration of a bilinear interpolation circuit.

FIG. 14 is a block diagram showing an internal configuration of a tetrahedral interpolation circuit.

FIG. 15 is a block diagram showing the configuration of another embodiment of the color signal conversion device.

Claims (1)

(57) [Claims] 1. A color signal conversion method for converting a plurality of signals of a first color signal system into signals of a second color signal system, comprising: (a) converting a plurality of signals of the first color signal system; Obtaining a basic value of the signal of the second color signal system according to a value of a predetermined upper bit; and (b) values of the upper bits of at least two signals of the first color signal system are equal to each other. Judging whether or not the first color signal system includes a plurality of first color signal systems according to the selected interpolation formula. Generating the signal of the second color signal system by interpolating the basic value using a value of a predetermined lower bit of the signal of the first and second signals , wherein the first and second interpolation expressions are: A plurality of the first color signal systems
If there is no value equal to the value of the upper bit of the signal
The first interpolation formula gives a good interpolation result, and the first color signal
The values of the upper bits of at least two signals of the
If they are equal, the second interpolation formula gives a good interpolation result
A color signal conversion method , characterized in that :