JP2961953B2 - Color correction method and apparatus - 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 correction apparatus applied to a color image forming apparatus such as a color printer or a color copying machine for printing out a color image.

[0002]

2. Description of the Related Art In recent years, video printers for printing out television images and color image forming apparatuses such as color copying machines have been actively developed.

In these color image forming apparatuses, cyan C, magenta M and yellow Y, which are complementary colors of red R, green G and blue B which are three primary colors of color light, respectively.
The purpose of color reproduction is to realize the same color as the target color of each color image forming apparatus, such as a CRT and a color original, based on the subtractive color mixing principle using black K ink in some apparatuses. You.

However, the spectral absorption characteristics of ink that actually exist are broad, and do not act as ideal absorption filters for the respective color lights. That is, there is an unnecessary absorption component that absorbs even color light having a wavelength that should be completely transmitted. Due to the presence of the unnecessary absorption component, color turbidity occurs at the time of color mixing, and a color having a lower saturation and a different hue than a desired color is reproduced.

[0005] Color correction is performed for the purpose of correcting the characteristics of the real ink and performing the desired color reproduction. However, since the color reproduction using the real ink has nonlinearity,
The linear masking by the linear matrix operation, which is the most common color correction, has insufficient correction accuracy. However, if non-linear operations such as non-linear high-order masking are performed for color correction in consideration of non-linearity in color reproduction, high-precision correction is possible, but a large number of multipliers and adders are required, and color correction is performed. The circuit configuration of the device becomes extremely complicated and expensive.

Therefore, a color correction apparatus in which the color correction data resulting from the non-linear operation is stored in advance in a look-up table (LUT) and this LUT is referred to is considered. However, storing the color correction data for all the input signals in the LUT results in an enormous capacity of the LUT. For example, in an apparatus in which each of the three-color separated image signals (R, G, B) as input signals is 8 bits and the color correction data (C, M, Y) of the color correction calculation result is 8 bits, 2 ²⁴
A huge memory capacity of × 3 = 48 (M bytes) is required.

Therefore, the input color space is divided by a plurality of cubes, and only the color correction data for each vertex of the cube is represented by L.
A method has been proposed in which color correction data for an input signal stored in a UT and located in the middle of a cube is determined by interpolation.

Hereinafter, an example of the above-described conventional color correction apparatus will be described with reference to the drawings.

Before describing the configuration and operation of the conventional color correction apparatus, a method of determining color correction data used in the conventional color correction apparatus will be described with reference to FIG.

FIG. 6 shows a cube including the input signal P among a plurality of cubes that divide the input color space. The color correction data for each vertex Pk (k = 0 to 7) of the cube is LU.
T.

Since the weight from the color correction data for each vertex Pk changes according to the position of the input signal P, the color correction data (C, M, Y) for the input signal P is determined according to the position. Interpolation must be performed. Therefore, the cube is divided into eight small rectangular parallelepipeds on a plane parallel to each axis constituting the input color space passing through the input signal P, and the volume of the small rectangular parallelepiped having a diagonal relationship with each vertex Pk is represented by Vk (k = 0 7), the volume of the cube is V, and the color correction data for each vertex Pk is (Ck, M
k, Yk) to determine the color correction data (C, M, Y) for the input signal P by the calculation of (Equation 2).

[0012]

(Equation 2)

A sublimation type thermal transfer system is provided with a conventional color correction device in which the number of cubes for dividing the input color space is equivalent to the upper 5 bits of each of the input signals, and performs the sequential recording in the order of yellow, magenta, and cyan. The configuration and operation of the recording type image forming apparatus will be described.

FIG. 7 is a block diagram of a conventional image forming apparatus. In FIG. 7, 33 is counted up in synchronization with the CLK signal, and 3 corresponds to k in (Equation 2).
A counter for outputting a bit signal 31 is a high-order 5 of each of the input signals P represented by three-color separated image signals (R, G, B).
An address generation means for selecting a cube containing the input signal P by performing an operation using the bits and the output of the counter 33 and generating an address signal corresponding to each vertex of the cube, and 32 divides the input color space. Address correction means 31 for storing color correction data for each vertex of the
And an LUT memory which outputs a 2-bit COLSEL signal representing a color to be recorded among yellow, magenta, and cyan as an address and outputs 8-bit color correction data corresponding to the address. ) Is preliminarily stored as a weighting factor, the lower 3 bits of the input signal P, the output of the counter 33 are input as an address, and an 8-bit weighting factor corresponding to the address is output. The memory 35 multiplies the output of the LUT memory 32 by the output of the weight coefficient table memory 34, and further performs cumulative addition in synchronization with the CLK signal.
The multiplying and accumulating means 36 for outputting color correction data (C, M, Y) used for recording controls the amount of heat applied to an ink film (not shown), so that the color correction data (C, M) output from the accumulating and adding means 35. , Y), a recording control means for controlling the amount of heat transferred from an ink film (not shown) to an image receiving paper (not shown) by a recording control means 37, and a thermal head for performing recording. It is.

The operation of the image forming apparatus provided with the conventional color correction device configured as described above will be described below.

The operation of recording the first color, that is, the recording of yellow will be described. When the input signal P is input, the address generating means 31 performs an operation on each of the upper 5 bits of the input signal and the output of the counter 33, and sequentially outputs the address signals corresponding to the vertices P0 to P7 of the cube including the input signal P. The LUT memory 32 outputs the color correction data Y0 to Y7 according to the address signal.

On the other hand, the lower three bits of the input signal P and the output of the counter 33 are input to the weight coefficient table 34, and the weight coefficients V0 / V to V7 / V are sequentially output.

Then, the multiplying and accumulating means 35 executes the operation of (Equation 2) using the output of the LUT memory 32 and the output of the weight coefficient table 34, and outputs yellow color correction data Y for the input signal P.

The recording control means 36 controls the amount of heat of the thermal head 37 in accordance with the value of the color correction data Y output from the multiplying and accumulating means 35, and performs gradation recording on an image receiving paper (not shown).

After the above operation is performed for one yellow recording screen, the same operation is performed for magenta and cyan inks. After finishing the recording of the three color inks,
A desired full-color image is formed on a receiving paper. (JP-A-63-162248)

[0021]

However, the above-described color correction apparatus performs an interpolation operation for determining color correction data for the input signal P by multiplying the color correction data for each vertex of the cube by a weight coefficient of the volume ratio. In addition to the LUT memory for storing the color correction data, a weight coefficient memory for storing a weight coefficient for the volume ratio is required.
Table 1 shows the relationship between the number of bits on each axis representing the number of cubes that divide the input color space and the memory capacity when both the color correction data and the weight coefficient are 1-byte data.

[0022]

[Table 1]

When color correction data is determined by using an interpolation operation, an interpolation error occurs. However, in order to reduce the interpolation error and improve the interpolation accuracy, the number of cubes into which the input color space is divided is increased and stored. It is sufficient to increase the color correction data. Conversely, when the interpolation error may be large, the stored color correction data may be reduced.

However, as can be seen from Table 1, in the conventional color correction apparatus, even if the capacity of the LUT memory is reduced by reducing the number of stored color correction data, the weight coefficient memory of the weight coefficient memory is correspondingly reduced. There was a problem that the capacity increased.

The present invention has been made in view of the above problems, and provides a color correction method and a color correction apparatus which can realize an interpolation operation with a memory capacity corresponding to interpolation accuracy.

[0026]

In order to solve the above-mentioned problems, a color correction method according to the present invention provides a three-color separated image signal which is an input signal as a first axis, a second axis, and a third axis. A three-dimensional input color space consisting of each axis is divided by a plurality of rectangular parallelepipeds, color correction data for each vertex of the rectangular parallelepiped is stored in advance in storage means, and an input signal for which color correction data is to be determined from the plurality of rectangular parallelepipeds Is selected, and eight pieces of color correction data for each vertex of the selected rectangular parallelepiped are read out from the storage means, and the input color is selected by a side constituting the selected rectangular parallelepiped out of the eight pieces of color correction data. An interpolation operation using color correction data for two points facing each other across a side parallel to the first axis of the space and position information of the input signal in the selected rectangular parallelepiped in the first axis direction is performed by the selected interpolation processing. First of rectangular parallelepiped Is performed for each of the four sides parallel to the above, thereby determining the color correction data for four points located on the four sides and having the same position in the first axis direction as the input signal. Color correction data for two points of the four points that are opposed to each other across a side parallel to the second axis of the input color space with sides forming a rectangle made of four points, and an input signal in the selected rectangular parallelepiped Is performed on two sides parallel to the second axis of the rectangle by using the position information on the second axis direction of the second axis. The color correction data for two points having the same position in the direction is determined, the color correction data for the two points for which the color correction data is determined, and the third axis direction of the input signal in the selected rectangular parallelepiped. By performing an interpolation operation using the position information about is intended to determine the color correction data with respect to the input signal.

[0027]

The operation of the color correction method of the present invention will be described below.

A rectangular parallelepiped containing an input signal for which color correction data is to be determined is selected, and eight color correction data corresponding to the vertices of the selected rectangular parallelepiped are read from the storage means, and as a first step, read from the storage means. Out of the eight color correction data, color correction data for two points that oppose each other across the four sides parallel to the first axis of the input color space on the sides constituting the selected rectangular parallelepiped; By an interpolation operation using the position information on the first axis direction, it is located on four sides of a rectangular parallelepiped parallel to the first axis of the input color space,
And the position in the first axis direction is the same as the input signal 4
The color correction data for the point is determined. As a second step, of the four points for which the color correction data has been determined in the first step, the side that constitutes a rectangle made up of four points corresponds to the second axis of the input color space. By performing an interpolation operation using color correction data for two points facing each other across two parallel sides and position information of the input signal in the rectangular parallelepiped in the second axis direction, two squares parallel to the second axis of the input color space are obtained. The color correction data for two points located on the side and having the same position in the second axis direction as the input signal is determined. As a third step, the color correction data for the two points determined in the second step is determined. And color correction data for the input signal is determined by an interpolation calculation using positional information of the input signal in the rectangular parallelepiped in the third axis direction.

That is, the color correction method of the present invention does not determine the color correction data by an interpolation operation using a weight coefficient corresponding to a volume ratio stored in advance in a weight coefficient memory as in the prior art. Since the three-dimensional interpolation operation is performed by repeating the interpolation operation in each axis direction using the color correction data for the point and the position information of the input signal, the color correction data for the input signal is determined. The memory capacity is only the LUT memory for storing the color correction data, and the interpolation calculation can be realized with the memory capacity according to the interpolation accuracy.

[0030]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A color correction method according to the present invention will be described with reference to the drawings.

FIG. 4 shows a rectangular parallelepiped including the input signal P among a plurality of rectangular parallelepipeds which divide the input color space. Each vertex of the rectangular parallelepiped is represented by Pk (k = 0 to 7).

Referring to FIG. 4, the determination of the color correction data for the input signal P located at the center of the rectangular parallelepiped will be described.

Of the vertices of the rectangular parallelepiped, P0 and P1, P2 and P3, P4 and P5, and P6 and P7 are the vertices that constitute the rectangular parallelepiped and oppose each other across the side parallel to the R axis of the input color space. And the color correction data for the input signal located on the side connecting the two points is 1 in the R-axis direction of the input color space.
It can be obtained by a dimensional interpolation operation.

The interpolation of color correction data for P0 and P1 using linear interpolation as a one-dimensional interpolation will be described with reference to FIG. FIG. 5 is a diagram in which a straight line parallel to the R axis of the input color space and passing through the lattice points P0 and P1 is represented on the horizontal axis, and the color correction data of the yellow ink for the input signal is represented on the vertical axis. The color correction data of the yellow ink for P0 is Y0,
The color correction data of the yellow ink for P1 is Y1, P0
S0 represents an input signal whose position in the R-axis direction is the same as that of the input signal P, and the distance between P0 and S0 when the distance between P0 and P1 is normalized by 1 is represented by q. , And the color correction data YR0 for S0 can be obtained from FIG.

[0035]

(Equation 3)

Similarly to S0, the color correction data for S1, S2, and S3 in FIG. 4 are respectively represented by P2 and P3, P4 and P5, and P6.
, And P7, and can be obtained by one-dimensional interpolation using the position of the input signal P in the R-axis direction.

As described above, S0 and S1, S2 and S3 for which the color correction data is obtained are sides of a rectangle consisting of S0, S1, S2 and S3, with the side parallel to the G axis of the input color space interposed therebetween. The color correction data for the input signals T0 and T1, which are opposite points and are located on the sides connecting the two points, are S0, S1, and S1, respectively.
Using the color correction data for 2 and S3 and the position of the input signal P in the G axis direction, it can be obtained by one-dimensional interpolation calculation in the G axis direction of the input color space.

Further, since the straight line connecting T0 and T1 is parallel to the B axis of the input color space, the color correction data for the input signal P located on the straight line connecting the two points is the same as the color correction data for T0 and T1. It can be determined by a one-dimensional interpolation operation using the position of the input signal P in the B-axis direction.

That is, in the interpolation operation in the color correction method of the present invention, one-dimensional interpolation operation in the R-axis direction is performed using the color correction data for each vertex of the rectangular parallelepiped including the input signal P, and the result is represented by G A three-dimensional interpolation operation is performed by performing a one-dimensional interpolation operation in the axial direction, and further performing a one-dimensional interpolation operation in the B-axis direction on the result. Since the interpolation calculation is not performed using the corresponding weight coefficient, the required memory capacity is sufficient only for the memory for storing the color correction data.

Hereinafter, a color correction apparatus which realizes the color correction method of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of an image forming apparatus of a sublimation type thermal transfer recording system which includes a color correction apparatus according to an embodiment of the present invention and performs a sequential recording in the order of yellow, magenta, and cyan. The sublimation dye used in (1) has a large non-linearity of the input signal with respect to the R signal, so that a rectangular parallelepiped that divides the input color space is 2 bits parallel to the R axis, 3 bits parallel to the G axis, and parallel to the B axis. The size of each side is represented by the number of 4 bits.

In FIG. 1, 1 is the upper 6 bits of the R signal, the upper 5 bits of the G signal, and the upper 4 bits of the B signal of the 8-bit three-color separated image signal (R, G, B) which is the input signal P. Address generating means for selecting a rectangular parallelepiped including the input signal P from a plurality of rectangular parallelepipeds dividing the input color space, and outputting address signals corresponding to eight vertices of the rectangular parallelepiped. Is a LUT memory for storing color correction data for
A ROM having a capacity of 32 Kbytes for each color of magenta and cyan was used. Various methods are conceivable for obtaining the color correction data stored in the LUT memory 2. In this embodiment, the secondary masking is applied among the nonlinear high-order masking conventionally performed, and each of the rectangular parallelepipeds is previously calculated by a computer. The color correction data for the vertices was calculated and stored.

Reference numeral 3 denotes control means for outputting control signals a to f for controlling the timing of each operation of the color correction apparatus. The control means 3 counts up in accordance with the input CLK signal and controls the control signals a to c.
, And a down counter circuit that counts down according to the CLK signal and outputs control signals df.

Reference numeral 4 denotes an input of color correction data output from the LUT memory 2, and an interpolation operation in the R-axis direction of the input color space using the lower two bits of the R signal of the input signal P for the color correction data. And S0, S1, S2, S3 in FIG.
R that outputs color correction data for an input signal corresponding to
The interpolation means 5 is the output of the R interpolation means 4,
The color correction data corresponding to the input signals corresponding to 0, S1, S2, and S3 are input, and interpolation is performed in the G-axis direction of the input color space using the lower three bits of the G signal of the input signal P. G interpolation means for outputting color correction data corresponding to the input signals corresponding to T0 and T1, and 6 inputs the color correction data corresponding to the input signals corresponding to T0 and T1 in FIG. B interpolation means for performing an interpolation operation in the B-axis direction of the input color space using the lower 4 bits of the B signal of the input signal P and outputting color correction data for the input signal P; By controlling the amount of heat, the recording control means 8 performs gradation color printing in accordance with the color correction data output from the B interpolation means. Controlling the amount of ink to be transferred to the image receiving sheet, not shown, from beam, a thermal head for recording.

In the above configuration, the address generating means 1
Is a three-color separation image signal (R, G, B) which is the input signal P
The upper 6 bits of the R signal, the upper 5 bits of the G signal, and the upper 4 bits of the B signal are respectively subjected to an addition operation with the control signals a, b, and c output from the control means 3. An address corresponding to each vertex of the rectangular parallelepiped including the input signal P is output to the LUT memory 2. Specifically, the values represented by the upper 6 bits of the R signal, the upper 5 bits of the G signal, and the upper 4 bits of the B signal of the input signal P are represented by (R0, G0, B
0), the control signals a and R0, the control signals b and G0, and the control signals c and B0 are added, and a 6-bit, 5-bit, and 4-bit signal of each addition operation result is output. However, R0, G0, and B0 are 0 to 63, 0 in decimal notation, respectively.
~ 31, 0 ~ 15, and the addition result is 6
If the number is 4, 32, or 16 or more, a limiter is applied to the addition result so that the upper limit is 63, 31, or 15, respectively. The color correction data obtained in advance by calculation is such that the position of the R axis in the input color space of the vertices of the rectangular parallelepiped is A0 to A5 of the address input of the LUT memory 2, the position of the G axis is A6 to A10, and the position of the B axis is Are stored so as to correspond to A11 to A14, and the addition result of a and R0 of the address generation means 1 is stored in A0 to A5 of the address input of the LUT memory 2, and b
And the result of adding G0 to A6 to A10, and the result of adding c and B0 to A1
1 to A14, respectively, and control signals a,
Since b and c are the outputs of the up-counter circuit that counts up in synchronization with the CLK signal, the LUT memory 2 synchronizes the color correction data for each of the vertices P0 to P7 of the rectangular parallelepiped including the input signal P with the CLK signal. And output sequentially.

In this embodiment, the R interpolation means 4, the G interpolation means 5, and the B interpolation means 6 each execute a one-dimensional linear interpolation operation, and a detailed block diagram is shown in FIG.

In FIG. 2, reference numerals 21a and 21b denote latch circuits for latching the color correction data inputted to the respective interpolation means.
Since the clock input is inverted by the inverting means 22, the input signal is latched at the falling edge of the output of the control means 3.

Numeral 23 denotes a subtractor for subtracting the output of the latch circuit 21a from the output of the latch circuit 21b. Numeral 24 denotes a lower 2 bit signal for the output of the subtractor 23 in the case of the R interpolation means, and in the case of the G interpolation means. Is a multiplying means for multiplying the lower 3-bit signal by the lower 3-bit signal, and in the case of the B-interpolating means, an adder 25 for adding the output of the multiplier 24 and the output of the latch circuit 21a.

Each lower bit signal of the input signal P represents a position in the direction of each axis of the input signal P in a rectangular parallelepiped including the input signal P, and corresponds to q in FIG. Each of the interpolating means 4, 5, and 6
In each case, the interpolation operation of (Equation 3) is performed.

The operation of this embodiment will be described with reference to the timing chart of FIG. The address generating means 1 performs an addition operation on control signals a, b, and c for each of the higher-order bits of the N-th input signal for which the color correction data is to be determined, so that the address generating means 1 includes a rectangular parallelepiped including the N-th input signal. Output addresses corresponding to the vertices P0 to P7. (FIG. 3F) The LUT memory 2 outputs the color correction data Y0 to Y7 for each of the vertices P0 to P7 of the rectangular parallelepiped of FIG. 4 including the Nth input signal according to the above address.

The color correction data Y 0, Y 2, Y 4, Y 6 output from the LUT memory 2 are output at the rise of the control signal d.
1, Y3, Y5, and Y7 are the falling edges of the control signal d, and the latch circuits 21a and 21b of the R interpolation means 4 respectively.
Latched. (FIGS. 3H and I) Then, for Y0 and Y1, Y2 and Y3, Y4 and Y5, and Y6 and Y7.
Is subjected to the interpolation operation (Equation 3) using the lower 2 bits of the R signal of the Nth input signal, and new color correction data YR0, YR1, YR2, and YR3 are output. (FIG. 3
J) YR0 and YR2 output from the R interpolation unit 4 are latched by the latch circuit 21a and the latch circuit 21b of the G interpolation unit 5, respectively, at the rise of the control signal e, and YR1 and YR3 at the fall of the control signal e. . (Fig. 3L, M) and Y
Interpolation (Equation 3) is performed on R0 and YR2 using the lower 3 bits of the G signal of the Nth input signal for YR1 and YR3, and color correction data YG0 and YG1 are newly obtained. Is output. (FIG. 3N) YG0 output from the G interpolation means 5 is a rising edge of the control signal f, and YG1 is a falling edge of the control signal f.
The data is latched by the latch circuits 21a and 21b of the interpolation means 6. (P, Q in FIG. 3) Then, the interpolation operation of (Equation 3) is performed on YG0 and YG1 using the lower 4 bits of the B signal of the Nth input signal, and the interpolation operation result in the B-axis direction is obtained. Is output. (FIG. 3R) Then, the three-dimensional interpolation operation is completed by the interpolation operation in the B-axis direction, and the output of the B interpolation means 6 is controlled as the color correction data Y (N) for the Nth input signal. Give to means 7.

The recording control means 7 controls the amount of heat of the thermal head 8 in accordance with the value of the color correction data output from the B interpolation means 6, and performs gradation recording on an image receiving paper (not shown).

After the above operation is performed for one yellow recording screen, the same operation is performed for magenta and cyan inks. After finishing the recording of the three color inks,
A desired full-color image is formed on the receiving paper.

As described above, in this embodiment, the R interpolation means 4 performs the interpolation calculation in the R-axis direction on the color correction data for each vertex of the rectangular parallelepiped read from the LUT memory 2 as the storage means. G for the output of the R interpolation means 4
The interpolation means 5 performs an interpolation operation in the G-axis direction, and the B interpolation means 6 performs an interpolation operation in the B-axis direction on the output of the G interpolation means 5, thereby performing a three-dimensional interpolation operation to perform color correction on the input signal. The data is determined. Instead of determining the color correction data by interpolation using a weight coefficient corresponding to the volume ratio stored in the weight coefficient memory in advance as in the conventional example, the required memory capacity is Only an LUT memory for storing color correction data can be used, and an interpolation operation can be realized with a memory capacity corresponding to the interpolation accuracy.

In the color correction apparatus of this embodiment, the R interpolation means is configured to determine color correction data for four points in time series, and the G interpolation means is determined to determine color correction data for two points in time series. Although the configuration is such that four sets of circuits for performing one-dimensional interpolation calculation shown in FIG. 2 are provided for the R interpolation means and two sets for the G interpolation means, and each is configured to perform the interpolation calculation in parallel, It is also possible to perform an interpolation operation at high speed.

In this embodiment, the side parallel to the R axis is 2 bits, the side parallel to the G axis is 3 bits, and the side parallel to the B axis is 4 bits.
Although the input color space is divided by a rectangular parallelepiped having a size represented by each bit number of bits, the number of bits representing the length of each side is not limited to the above, and for example, each side has the same bit. It is apparent that the color correction device according to the present invention can be applied to a case where the input color space is divided by a cube represented by a number.

In this embodiment, the input signal is a three-color separated image signal (R, G, B), and the color correction data of cyan C, magenta M, and yellow Y are converted by R interpolation means, G interpolation means, and B interpolation. Although the configuration is determined by a three-dimensional interpolation operation using means, an image formation for forming a color image using four color inks of cyan, magenta, yellow, and black with respect to the three-color separated image signal of the input signal In the case of a color correction apparatus applied to the apparatus, color correction data for four inks is stored in an LUT memory as storage means, and a three-dimensional interpolation operation similar to that in this embodiment is performed on each color correction data. Should be applied.

[0058]

As described above, according to the present invention, the input color space is divided by a plurality of rectangular parallelepipeds, the color correction data for each vertex of the rectangular parallelepiped is stored in the storage means, and the two points of color correction data and the position of the input signal are stored. Since the three-dimensional interpolation calculation is executed by repeating the interpolation calculation in each axis direction using the information and the color correction data for the input signal is determined, the necessary memory capacity is an LUT for storing the color correction data. Only a memory is required, and an interpolation operation can be realized with a memory capacity corresponding to the interpolation accuracy.

[Brief description of the drawings]

FIG. 1 is a block diagram of an image forming apparatus using a color correction device according to an embodiment of the present invention.

FIG. 2 is a block diagram showing details of an interpolation means in the embodiment.

FIG. 3 is a timing chart illustrating the operation of the embodiment.

FIG. 4 is a view of a rectangular parallelepiped in an input color space for explaining an interpolation method in the color correction method of the present invention.

FIG. 5 is a diagram showing a one-dimensional linear interpolation operation for explaining an interpolation method in the color correction method of the present invention.

FIG. 6 is a diagram of a unit cube in an input color space for explaining an interpolation method of a conventional color correction device.

FIG. 7 is a block diagram of an image forming apparatus using a conventional color correction device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Address generation means 2 LUT memory 3 Control means 4 R interpolation means 5 G interpolation means 6 B interpolation means

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-4-242372 (JP, A) JP-A-4-219076 (JP, A) JP-A 4-144481 (JP, A) JP-A-3-324 13066 (JP, A) JP-A-2-226867 (JP, A) JP-A-3-57376 (JP, A) JP-A-59-210770 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H04N 1/40-1/409 H04N 1/46 H04N 1/60

Claims (3)

(57) [Claims] A first axis, a second axis, and a third axis, which are components of a three-color separation image signal that is an input signal, and a three-dimensional input color space including each axis is divided by a plurality of rectangular parallelepipeds; The color correction data for each vertex of the rectangular parallelepiped is stored in advance in the storage means, and a rectangular parallelepiped including the input signal for which the color correction data is to be determined is selected from the plurality of rectangular parallelepipeds. Data is read out from the storage means, and color correction is performed on two points of the eight color correction data, the sides forming the selected rectangular parallelepiped, which are opposed to each other across a side parallel to the first axis of the input color space. By performing an interpolation operation using data and position information of the input signal of the selected rectangular parallelepiped in the first axis direction with respect to four sides parallel to the first axis of the selected rectangular parallelepiped, Horn The color correction data for four points located on the side and having the same position in the first axis direction as the input signal is determined, and a rectangle consisting of four of the four points for which the color correction data has been determined is formed. An interpolation operation using color correction data for two points facing each other across a side parallel to the second axis of the input color space on the side to be performed, and position information on the second axis direction of the input signal in the selected rectangular parallelepiped is performed. The color correction data for two points located on the two sides and having the same position in the second axis direction as the input signal is determined by performing the processing on the two sides parallel to the second axis of the rectangle. The color correction data is determined.
A color correction method for determining color correction data for an input signal by performing an interpolation operation using color correction data for a point and position information of the input signal in the selected cuboid in the third axis direction. . 2. A component of a three-color separation image signal, which is an input signal represented by m bits (m is a natural number), is represented by a first axis.
The second axis and the third axis are used, and a three-dimensional input color space including the respective axes is defined as 2 ⁿ¹ , 2 ⁿ² , 2 ⁿ³ (n1 <m, n2 <m, n
3 <m, n1, n2, and n3 are natural numbers), store the color correction data for each vertex of the rectangular parallelepiped, and output the color correction data according to an input address. Means and upper L1 bit, L2 bit, L3 bit (L1 = mn1, L2 = mn2, L3 = mn) of m bits of each component of the input signal.
3) input, select a rectangular parallelepiped O including the input signal from the plurality of rectangular parallelepipeds, and output an address in the storage means for storing eight color correction data A for each vertex of the rectangular parallelepiped O. Means for inputting color correction data for two points in the input color space;
The color correction data for a point located on a straight line connecting the points is determined by interpolation calculation, and the interpolation calculation element to be output is one-dimensional interpolation calculation means, the eight color correction data A output from the storage means, A signal q ₁ (0 ≦ q ₁₎ representing the position of the input signal on the first axis in the rectangular parallelepiped O.
<Integer of 2 ⁿ¹ ), and among the eight color correction data A, color correction data corresponding to two points that oppose each other across the side parallel to the first axis on the side configuring the rectangular parallelepiped O; By performing an interpolation operation using the signal q _{1 on} each of four sides parallel to the first axis constituting the rectangular parallelepiped O, the position on the four sides and the position on the first axis There a first shaft interpolation operation means arranged from the one-dimensional interpolation operation unit to output four color correction data B for 4-point is q _1, the four color correction data B
And a signal q ₂ (an integer of 0 ≦ q ² <2 ⁿ² ) representing the position of the input signal with respect to the second axis in the rectangular parallelepiped O, and the four points of the four color correction data B Color correction data for two points that oppose each other across a side parallel to the second axis with sides forming a rectangle made up of:
₂ is performed on each of two sides parallel to the second axis that constitutes the rectangle, so that the position on the two sides and the position on the second axis are q ₂ The second one configured by the one-dimensional interpolation calculating means so as to output two color correction data C for a certain two points.
Axis interpolation calculating means, the two color correction data C, and a signal q ₃ (0 ≦ q ³ <2 ⁿ³ integer) representing a position of the input signal in the rectangular parallelepiped O with respect to the third axis;
A _third interpolation unit configured to perform an interpolation operation using the two color correction data C and the signal q ₃ and output color correction data D for the input signal;
A color correction device comprising: an axis interpolation unit. 3. The color correction data for two points in the input color space are represented by X1 and X2, respectively, and a signal representing the position of the input signal in the i-axis direction (i = 1, 2, 3) in the rectangular parallelepiped including the input signal. Assuming that the value is q _i (i = 1, 2, 3), the one-dimensional interpolation calculation means outputs the color correction data X3 by executing the linear interpolation calculation represented by (Equation 1). 3. The color correction device according to claim 2, wherein the color correction device is a color correction device. (Equation 1)