JP2954257B2 - Color information converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention processes an image density signal (Dr, Dg, Db) representing a color-separated image density to record black, cyan, magenta or yellow. The present invention relates to a color information converter that outputs a recording density signal (Dx) representing a density.

[Conventional technology]

For example, in a color copier, spectral density data such as R (red), G (green), and B (blue) read by a color scanner is converted into C (cyan), M (magenta), and Y ( Conversion to recording density data of each color such as yellow (Y) and Bk (black) is known, and many conversion methods and conversion devices have been proposed (for example, JP-A-63-116277, JP-A-59-1984). -161979, JP-A-61-13260, Japanese Patent Application No. 63-193695, etc.). For example, JP-A-63-125054 discloses a color conversion circuit that switches a constant by a signal irrelevant to the value of an image density signal, and JP-A-63-246979 discloses a color conversion circuit for full color. A color conversion device having a circuit, a color conversion circuit for monocolor, and a circuit for selecting the output of both is disclosed. Japanese Patent Application No. 63-135833 provides a color conversion circuit for generating a constant selection signal for selecting a constant corresponding to each image density signal in accordance with the value of the image density signal.

[Problems to be solved by the invention]

It is composed of a plurality of LUTs (look-up tables) and the like described in JP-A-59-161979.
In a device having a γ conversion circuit capable of switching T, by providing an LUT for undercolor, the undercolor can be easily added. However, in such an apparatus, it has been difficult to realize it at low cost because the memory capacity for undercolor is increased accordingly. In the color information conversion disclosed in JP-A-63-116277, a process called so-called masking process is performed.
This is performed according to the following equation focusing only on the recording density of one color material.

 Dx = Kxr.Dr + Kxg · Dg + Kxb · Db (7) where Kxr, Kxg, and Kxb are constants, and x: c, m, y, and k.

However, the conventionally known circuit has a disadvantage that an under color cannot be added. Japanese Patent Application Laid-Open No. 61-13260 discloses a method in which the minimum value of image density signals (Dr, Dg, Db) representing the image densities of color separation is selected, and a black recording density is determined by a gamma conversion circuit. Have been. In this case, it is necessary to consider the unnecessary absorption components contained in the cyan, magenta, and yellow coloring materials.
Images cannot be recorded in full black. An LUT is usually used for the γ conversion process. However, since a plurality of LUTs are required to change the black recording amount pattern, the circuit becomes complicated.

In the color information conversion of Japanese Patent Application Nos. 63-135833 and 63-193695, when performing image recording using a black color material,
Since the black output starts from the gray scale density 0, it is recognized that the expression of the gradation is slightly inferior. In the color conversion circuit disclosed in JP-A-63-125054, it is not possible to select a constant in accordance with the value of the image density signal. Is insufficient in color reproducibility. The color conversion device disclosed in Japanese Patent Application Laid-Open No. 63-246979 requires a color conversion circuit for full color and a color conversion circuit for mono color, so that the circuit configuration is complicated and it is difficult to realize it at low cost. . In the color conversion circuit disclosed in Japanese Patent Application No. 63-135833, a constant is selected in accordance with the value of the image density signal. However, even when performing mono-color printing, it is necessary to prepare constants corresponding to the value of the image density signal. Therefore, in order to perform processing in which full-color recording and mono-color recording are mixed, more constants are used. The product-sum processing means is required, and it is difficult to realize the circuit at low cost.

A first object of the present invention is to realize a color information conversion device capable of adding an under color with a simple configuration at a low cost.

A second object of the present invention is to realize a color information converter capable of converting into either full black or skeleton black, with a simple configuration and at low cost.

A third object of the present invention is to provide a color conversion circuit which can correct the density addition rule non-satisfaction in full-color printing and can perform processing in which full-color printing and mono-color printing are mixed. And at low cost.

[Means for solving the problem]

In order to achieve the first object, the color information conversion apparatus according to the first aspect of the present invention processes an image density signal (Dr, Dg, Db) representing the color-separated image density to obtain black, cyan, magenta. Alternatively, a recording density signal (D
In the color information conversion device that outputs x): each of the image density signals (Dr, Dg, Db) representing the color-separated image density and each image density signal (Dr, Dg, Db) are determined. And a predetermined first set of constants (Kxr, Kxg, Kxb)
Multiplication processing means (305, 306,
307); constant signal generating means (313) for generating a signal representing a second set of constants (Kxo); and multiplication processing means (305, 30).
6,307), and means (311, 312, 315, 316) for calculating the sum (Dx) of the signal output by the constant signal generating means (313) and outputting the result.

In order to achieve the second object, the color information conversion apparatus according to the second aspect of the present invention processes an image density signal (Dr, Dg, Db) representing the color-separated image density to reduce the black recording density. In a color information converter that outputs a recording density signal (Dk) representing the image density: an image density signal (Dr, Dg,
Db), a predetermined first set of constants (Kxr, Kxg, Kx) defined for each image density signal (Dr, Dg, Db)
b) a constant selection means (3
01); a first set of constants (Kxr, Kxg, Kxb) defined for each image density signal according to the output of the constant selection means (301), and an image representing the color-separated image density Multiplication processing means (305, 306, 307) for multiplying each of the density signals (Dr, Dg, Db) and outputting the result; constant signal generation means (313) for generating a signal representing a second set of constants (Kxo) Means for calculating the sum (Dk) of the signal output from the multiplication processing means (305, 306, 307) and the signal output from the constant signal generation means (313) and outputting the result (311, 31)
2,315,316);

In order to achieve the third object, the color information conversion apparatus according to the third aspect of the present invention includes a constant (Kxr, Kxg) corresponding to each of the image density signals (Dr, Dg, Db) representing the color-separated image density. , Kx
b) a constant selection means (301) for generating a constant selection signal (SEL), and at least the constant selection signal (SE)
L) and a product-sum processing means (302 to 307, 311, 315, 316) for calculating the product sum of each of the image density signals (Dr, Dg, Db) and outputting the result. The apparatus is configured to use at least one of a full color recording area and a mono color recording area on an image (mono color recording area).
Means (106) for specifying the constant, and the constant selection means (30
1) While the image density signal (Dr, Dg, Db) is in the area specified by the specifying means (106), a first value corresponding to the value of the image density signal (Dr, Dg, Db) is provided. Constant selection signal (SEL
= REL) and one of the second constant selection signals (SEL = AREA 0 to 2) irrelevant to the value of the image density signal (second constant selection signal: SEL = AREA 0 to 2) to generate the area. While outside, means (409) for generating the other (first constant selection signal: SEL = REL) is included.

Symbols in parentheses indicate corresponding elements or corresponding signal symbols in the embodiment shown in the drawings and described later.

[Action]

According to the color information conversion device of the first aspect, the multiplication processing means (305, 306, 307) includes the image density signals (Dr, Dg, Db) representing the color-separated image densities and the respective image density signals (Dr, Db). Dg, Db)
Since the set of constants (Kxr, Kxg, Kxb) is multiplied and the result is output, the color correction corresponding to the first set of constants is performed substantially simultaneously with the color conversion, thereby simplifying the processing. , Hardware and / or processing logic is simplified. Further, the constant signal generating means (313) is provided with a second set of constants (K
xo) and means for generating and outputting signals (311, 312, 315,
316) is the sum (D) of the signal output from the multiplication processing means (305, 306, 307) and the signal output from the constant signal generation means (313).
Since x) is calculated and the result is output, the output (Dx) includes an under color corresponding to the second set of constants (Kxo). That is, undercoloring can be realized at a low cost with a simple configuration.

According to the color information conversion device of the second aspect, the processing of the first aspect is performed to obtain a recording density signal (Dk) representing the recording density of black, and the second set of constants of the first set of constants is calculated. By the combination, recording density signals (Dk) of full black and skeleton tone black can be obtained with a simple and inexpensive configuration.

According to the color information conversion device of the third aspect, for example, if the designating means (106) designates a mono-color recording area, the area (full-color recording area) outside the area (mono-color) designated by the designating means (106) Then, the means (409) for generating a constant selection signal generates a first constant selection signal, and the product-sum processing means (302 to 307, 311, 315, 316) generates image density signals (Dr, Dg, Db) representing the color-separated image density. ) And a constant corresponding to the value of the image density signal (Dr, Dg, Db) are calculated and the result is output. Therefore, the color reproducibility corrected for the density addition rule failure in full color printing is improved. Good recording color density information can be obtained.

The means (409) for generating a constant selection signal in the area (monocolor recording area) designated by the designating means (106)
Of the product-sum processing means (302 to 307, 31
1,315,316) calculates the product sum of the image density signal representing the color-separated image density and a constant irrelevant to the value of the image density signal (Dr, Dg, Db), and outputs the result. Recording color density information for recording a determined mono color can be obtained.

As described above, a constant corresponding to the value of the image density signal at the time of full-color recording, and a constant regardless of the value of the image density signal at the time of mono-color recording. A color information conversion apparatus capable of performing processing by mixing full-color recording and mono-color recording with excellent characteristics is realized at a low cost with a simple configuration.

Other objects and features of the present invention will become apparent from the following description of embodiments with reference to the drawings.

FIG. 1 is a schematic block diagram of a color copying machine incorporating an embodiment of the present invention.

In FIG. 1, reference numeral 101 denotes an image reading unit using an image sensor such as a CCD.
m (400 DPI) resolution, read as red (R), green (G) and blue (B) light quantity data, and raster scan type 8-bit image signals R, G and B Output.

Image signals R, G and B output by the image reading unit 101
Is supplied to the color correction processing unit 102 according to an embodiment of the present invention. The color correction processing unit 102 performs processing such as so-called γ correction and masking processing based on the image signals R, G, and B, and outputs cyan (C), magenta (M), yellow (Y), and black (Bk). The recording amounts of the four color materials are determined, and raster scan type 8-bit image signals C, M, Y, and Bk are output. The image signals C, M, Y and Bk output from the color correction processing unit 102 are supplied to an image recording unit 103 such as a color laser printer. Image recording unit 103
Is, for example, about 16 pixels / based on the image signals C, M, Y and Bk
An image is recorded on paper at a resolution of mm (400 DPI) using cyan, magenta, yellow and black color materials.
A timing control unit 104 outputs a synchronization signal CLK of each raster scan type image signal and an area signal AREA indicating a switching timing of a processing mode described later,
The image data is supplied to the image reading unit 101, the color correction processing unit 102, the image recording unit 103, and the like. Reference numeral 106 denotes an operation unit for inputting and displaying a processing mode and the like of the color copying machine. Reference numeral 105 denotes a system control unit, which performs input detection and display control of the operation unit 106, and according to an operation input on the operation unit 106, an image reading unit 101, a color correction processing unit 102, and an image recording unit 103.
And controls the entire color copying machine, such as outputting a signal (setting signal SET) for setting the timing control unit 104.

FIG. 2a shows the configuration of the color correction processing unit 102 according to one embodiment of the present invention.

In FIG. 2a, reference numerals 201 to 203 denote gamma conversion circuits, which perform processing such as logarithmic conversion at the same time as correcting the gradation characteristics of the image signals R, G, and B output from the image reading unit 101. Output as 8-bit image density signals Dr, Dg and Db. Each of the γ conversion circuits 201 to 203 is composed of a RAM or the like, and includes a plurality of LUTs (look-up tables).
have. These LUTs are provided for adjusting the density of the output image and switching between execution and non-execution of the negative / positive inversion process. Switching of these LUTs is performed by the area signal AREA output from the timing control unit 104. Further, the content of the LUT is rewritten according to the setting of the density adjustment, the type of processing, and the like, by the setting signal SET output from the system control unit 105. Note that the γ conversion circuit 201
203 perform a conversion such that 0 is output when the converted density value is 0, and 225 is output when the converted density value is 1.5.

Image density signals Dr and D output from γ conversion circuits 201 to 203
g and Db are input to the color conversion circuits 204 to 207, respectively. The color conversion circuits 204 to 207 include image density signals Dr, Dg, and Db.
To calculate the END (equivalent achromatic color density) of the cyan, magenta, yellow and black color materials, respectively, and output them as 8-bit recording density signals Dc, Dm, Dy and Dbk. Here, the recording density signals Dc, Dm, and Dy output from the color conversion circuits 204 to 206 correspond to the respective color materials when an image is recorded using the cyan, magenta, and yellow color materials.
Indicates END. Each of the color conversion circuits 204 to 207 includes a multiplier, an adder, a RAM, and the like, as described later, and performs processing equivalent to the following conversion processing.

Dx = Kxr · Dr + Kxg · Dg + Kxb · Db + Kxo (1) where Kxr, Kxg, Kxb are the first set of constants, Kxo is the second set of constants, x; c, m, y, k, and c Is cyan, m is magenta,
y means yellow and k means black.

A plurality of constants used for this processing are stored in the RAM, respectively.
5 is written by the setting signal SET output. These constants are switched by an area signal AREA or the like output from the timing control unit 104. In this embodiment, it is assumed that the area signals AREA input to the color conversion circuits 204 to 206 are the same signal.

The recording density signals Dc, Dm, and Dy output from the color modulation circuits 204 to 206 are respectively sent to the UCR circuits 208 to 210 and the color conversion circuit 2.
The recording density signal Dk output from 07 is input to the UCR circuits 208 to 210 and the delay circuit 211.

The UCR circuits 208 to 210 perform so-called UCR (under color removal) processing and the like, and record density signals D output from the color conversion circuit 207.
According to k, the recording density signals Dc, Dm, and Dy output from the color conversion circuits 204 to 206 are corrected, and the corrected recording density signals Dc ′,
This is a circuit that outputs Dm 'and Dy'.

The UCR circuits 208 to 210 are LUTs composed of a ROM or the like, and these LUTs perform processing equivalent to the following conversion processing.

 Dx ′ = A · (Dx−Dk) / (A−Dk) (2) where A is a constant, for example, about 2, x; c, m, y.

The delay circuit 211 is a circuit that delays the recording density signal Dk in accordance with the recording density signals for cyan, magenta, and yellow that are delayed by passing through the UCR circuits 208 to 210, and outputs the delayed recording density signal Dk. I do. Recording density signals Dc ', Dm', Dy 'output from UCR circuits 208 to 210 and delay circuit 211
Are output from the γ conversion circuit 212, respectively.
~ 215 is input.

The γ-conversion circuits 212 to 215 provide recording density signals Dc ′, Dm ′, Dy ′
And END represented by Dk, the image recording unit 103
Is corrected according to the characteristics of the image recording unit 103, and the image signals C, M, Y, and Bk of 8 bits are output from the image recording unit 103.
The γ conversion circuits 212 to 215 are similar to the γ conversion circuits 201 to 203,
Each of the LUTs has a plurality of LUTs, and these LUTs are provided for switching processing depending on the type of image such as a photo image / text image.
Area signal ARE output from timing control unit 104
Performed by A. The contents of the LUT are rewritten by the setting signal SET output from the system control unit 105.

A synchronization signal CLK (not shown) output from the timing control unit 104 is supplied to each of the circuits 201 to 215 shown in FIG. 2a, and the circuits 201 to 215 operate in synchronization with the synchronization signal CLK. I do.

In the color copier described above, cyan, magenta,
The color correction unit 102 is a type that simultaneously records four color materials of yellow and black.
The recording amounts of the four color materials of yellow and black are simultaneously obtained and output. However, the color correction unit 102 in the color copying machine of the type that records the four color materials in a sequential manner or the like,
A configuration as shown in FIG. 2b can be adopted.

In FIG. 2b, reference numerals 1101 to 1103 denote gamma conversion circuits similar to those in FIG. 2a, and image signals output from the image reading unit.
At the same time as correcting the gradations of R, G, and B, processing such as logarithmic conversion is performed, and image density signals Dr, Dg, and D of 8 bits each are obtained.
Output as b. The image density signals Dr, Dg, and Db output from the γ conversion circuits 1101 to 1103 are input to color conversion circuits 1104 to 1105 similar to FIG. 2a. Color conversion circuit 110
4, 1105 processes the image density signals Dr, Dg, and Db to obtain END (equivalent achromatic color density) of the cyan, magenta, yellow, or black color material, and obtains an 8-bit recording density signal Dc / Dm / This is a circuit that outputs as Dy and Dk. The constant used in this processing is written by the setting signal SET output by the system control unit 105 according to the color of the color material to be output. The recording density signal Dc / Dm / Dy output from the color conversion circuit 1104 is sent to the UCR circuit 1106 similar to FIG. 2a, and the recording density signal Dk output from the color conversion circuit 1105 is sent to the UCR circuit 1104.
Input to a delay circuit 1107 similar to 106 and FIG. 2a. U
The CR circuit 1106 is a circuit that performs so-called UCR (under color removal) processing and the like, and according to the recording density signal Dk output from the color conversion circuit 1105, the recording density signal Dc / Dm / Dy output from the color conversion circuit 1104.
And outputs a corrected recording density signal Dc ′ / Dm ′ / Dy ′. The delay circuit 1107 is a circuit for delaying the recording density signal Dk in accordance with the recording density signal for cyan, magenta or yellow which is delayed by passing through the UCR circuit 1106, and outputs the delayed recording density signal Dk. UC
The recording density signal Dc '/ Dm' / Dy 'output from the R circuit 1106 and the recording density signal Dk output from the delay circuit 1107 are input to the selector circuit 1108, respectively. The selector circuit 1108 controls the recording density signal Dc '/ D
m '/ Dy' or the recording density signal Dk, and outputs an image density signal Dc '/ Dm' / Dy '/ Dk.The output of the selector circuit 1108 is a gamma conversion circuit similar to that shown in FIG. 2a. Entered in 1109. The γ conversion circuit 1109 calculates the recording density signal Dc ′ / Dm ′ / D
The END represented by y ′ / Dk is corrected according to the characteristics of the gradation of each color material of the image recording unit, and an 8-bit image signal C / M / Y / Bk is output. In addition, the γ conversion circuit 1109
The contents of the LUT are rewritten by the SET output by the system control unit according to the color of the output color material. Also, the second
Each of the circuits 1101 to 1109 shown in FIG. b is supplied with a synchronization signal CLK (not shown) output from the timing control unit, and the circuits 1101 to 1109 operate in synchronization with the synchronization signal CLK.

As described above, in the color correction unit 102 embodying the present invention, the image density signals Dr,
Since Dg and Db are processed and the END of the black color material and the other (cyan, magenta and yellow) color materials are obtained in parallel, the recording density signal Dk and the other recording level signals (Dc, Dm,
The delay of Dy) is the same, and there is an advantage that a delay circuit is not required outside the color correction processing unit 102.

 FIG. 3 shows the configuration of the color conversion circuits 204 to 207.

In FIG. 3, reference numeral 301 denotes a constant selection circuit, which is a signal determined by the magnitude relationship of the image density signals Dr, Dg and Db, or a direct signal in accordance with 4 bits of the area signal AREA output by the timing control unit 104. And outputs a signal determined by the area signal AREA as a 3-bit constant selection signal SEL.

FIG. 4 shows the details of the constant selection circuit 301. The constant selection circuit 301 will be described in more detail. Reference numerals 401 to 403 denote 8-bit comparators, and input image density signals Dr, Dg, and D
Compare b with each other and output the result. That is, the comparator 401 outputs H when Dr <Db, and outputs L otherwise.
The comparator 402 outputs H when Dg <Db and outputs L otherwise, and the comparator 403 outputs H when Dr <Dg and outputs L otherwise.
Is output. Further, the outputs of the comparators 401 to 403 are EX
Via OR gates 404 and 405, NOR gates 406 and 407, and inverter 408, 3-bit related signals REL0 to REL2 become selectors.
Entered in 409. Here, the magnitude relation between the outputs of the comparators 401 to 403, the image density signals Dr, Dg and Db and the relation signal R
The relationship between EL0 and EL2 is as shown in Table 1 below.

On the other hand, the other input terminal of the selector 409 is connected to the area signal ARE.
A0 to A2 are input to the select terminal with the area signal AREA3, and the relation signals REL0 to REL2 or the area signals AREA0 to AREA2 are selected according to the area signal AREA3 and output to the D flip-flop 410. The clock terminal of the D flip-flop 410 has a pixel synchronization signal CLOCK which is one of the synchronization signals CLK.
Is input, and the D flip-flop 410 latches the signal output from the selector 409 and outputs it as a 3-bit constant selection signal SEL. The constant selection circuit 301 receives the image density signals Dr, Dg, and Db and the area signal AREA in response to the pixel synchronization signal C.
Input in synchronization with LOCK.

Referring again to FIG. 3, the constant selection signal SEL output from the constant selection circuit 301 is input to the constant memory circuits 302 to 304.

The constant memory circuits 302 to 304 store the constant Kx shown in the equation (1).
8 words x 12 bits for storing r, Kxg and Kxb respectively
The RAM is accessed by using a constant selection signal SEL as an address signal, and the selected constant is output as 12-bit constant signals Kxr, Kxg, and Kxb. In addition, 12
The bit constant signals Kxr, Kxg and Kxb are signed fixed-point signals (−8 ≦ Kxr, Kxg, Kxb <8). Further, the constant memory circuits 302 to 304 include a circuit for enabling data writing to the RAM by the setting signal SET output from the system control unit 105, and constant signals Kxr, Kxg and Kxb to be output.
Is output in synchronization with the pixel synchronization signal CLOCK.

Constant signals Kxr and Kxg output from constant memory 302 circuits to 304
And Kxb are input to multiplication circuits 305 to 307, respectively.

The other input terminals of the multiplication circuits 305 to 307 are connected to the delay circuit 30
Image density signals Dr, Dg, and Db are input through 8-310. Here, the delay circuits 308 to 310 are provided with image density signals Dr, D
A circuit for delaying g and Db, a first set of constant signals generated by a constant selection circuit 301 and a first set of constant memory circuits 302 to 304
It functions to correct the delay of Kxr, Kxg and Kxb. Multiplication circuit
Reference numerals 305 to 307 denote image density signals Dr and Dg respectively inputted.
, And Db and the first set of constant signals Kxr, Kxg, and Kxb, and outputs the upper 16 bits of the result in synchronization with the pixel synchronization signal CLOCK. The signals output from the multiplication circuits 305 to 307 are
The signals are input to adders 311 and 312. On the other hand, reference numeral 313 denotes a second set of constant memory circuits, and the second set of constants Kx shown in equation (1).
and stores the same configuration as the first set of constant memory circuits 302 to 304.

To the second set of constant memory circuits 313, of the area signals AREA, 3-bit signals (AREA4 to 6) different from the area signal input to the constant selection circuit 301 are input via a delay circuit 314, The circuit 313 uses this signal as an address signal and
A 2-bit second set of constant signals Kxo is output. The 12-bit second set of constant signals Kxo is a signed fixed-point signal (−2048 ≦ Kxo <2048). Further, the delay circuit 314
This is a circuit for correcting a delay generated in the constant selection circuit 301 and the multiplication circuit 305. The second set of constant signals Kxo output from the second set of constant memory circuits 313 is input to the adder circuit 312.

Addition circuits 311 and 312 perform addition processing on the signals output from multiplication circuits 305 to 307 and constant memory circuit 313, and output the result to addition circuit 315. The addition circuit 315 further performs addition processing on the signals output from the addition circuits 311 and 312, and outputs the result to the shaping circuit 316. The shaping circuit 316 includes an adding circuit 311,
This is a circuit for shaping the result added by 312 and 315 into 8 bits. That is, if the addition result is negative, it is replaced with 0, and if it exceeds 255, it is replaced with 255, and the 8-bit recording density signal Dx is output in synchronization with the pixel synchronization signal CLOCK.

As described above, processing equivalent to the conversion processing shown in equation (1) is performed by the color conversion circuits 204 to 207.

Next, the first set of constants Kxr, Kxg, Kxb and the second set of Kxo stored in the color conversion circuits 204 to 207 in the full color mode will be described.

The color conversion processing according to the present invention is based on so-called masking processing. However, when performing full-color processing, as shown in FIG. 5, the image densities Dr, Dg and Db
Is divided by a plane radially extending around the achromatic color axis (Dr = Dg = Db), and a constant of color conversion processing is set for each of the divided color spaces (hereinafter simply referred to as a color space).
An improvement has been made in which Kxr, Kxg, Kxb, and Kxo are defined, and color conversion processing is performed using these constants.

Color conversion constants Kxr, Kxg, Kxb, and Kxo in one color space
Is determined as follows.

As shown in FIG. 6, for example, chromatic colors P and Q (where Dr ≠ Dg or D
g ≠ Db or Db ≠ Dr) with different achromatic colors N on the achromatic axis.
1, N2 (Dr = Dg = Db) is determined, and chromatic colors P and Q and achromatic color N1,
The image densities Dr, Dg, and Db of N2, and the recording densities Dxc, Dxm, Dxy, and Dxk of the cyan, magenta, yellow, and black coloring materials that are optimal for recording the chromatic colors P, Q and the achromatic colors N1, N2 are shown. Decide. The image densities of the chromatic colors P and Q are respectively (Dpr,
Dpg, Dpb), (DQr, DQg, DQb), the image densities of the achromatic colors N1 and N2 are (DN1r, DN1g, DN1b) and (DN2r, DN2b), respectively, and the recording densities of the chromatic P and Q are ( Dpc, Dpm, Dp
y, Dpk), (DQc, DQm, DQy, DQk) and the recording densities of the achromatic colors N1 and N2 are (DN1c, DN1m, DN1y, DN1k), (DN2c, DN2
m, DN2y, DN2k), the color conversion constants Kcr to Kko in this color space are obtained by the following equation (3).

In the above, the image density and recording density of the chromatic colors P and Q and the achromatic colors N1 and N2 are determined by the image reading unit used.
Optimal values according to the spectral characteristics of the image recording unit 101 and the image recording unit 103 are obtained (for example, experimentally obtained so as to minimize the difference in color and image density between the read image and the recorded image). ),use.

Also, the four colors (chromatic colors P and Q and achromatic colors N1 and N2) used in the equation (3) are set so that they do not all exist on the same plane in the color space formed by the image densities Dr, Dg and Db. Any color can be chosen if you choose.

Also, as shown in FIG. 6, two achromatic colors N1 and N2 common to all color spaces and chromatic colors P and Q on both boundary surfaces are selected, and the chromatic colors P and Q are respectively set to adjacent colors. When used also when calculating the color conversion constant of the space, it is possible to easily prevent the color conversion processing result from being discontinuous at the boundary of the color space.

As shown in FIG. 5, in this embodiment, the achromatic axis (Dr =
Dg = Db), planes Dr = Dg, Dg = Db and Db
= Dr, the constants of the color conversion process are changed for each of the six color spaces, so that in the constant selection circuit 301 (FIGS. 3 and 4), Dr, Dg and Db A signal SE indicating the determined color space
T is generated and supplied to the constant memory circuits 302 to 304 as a constant designation signal.

Table 2 shows the recording densities Dx (x = c, m, y, k) corresponding to the image densities Dr, Dg, and Db of a total of six chromatic colors on each boundary surface and two achromatic colors common to each color space. ) Is shown. Table 3 shows the color conversion coefficients Kxr, Kxg, Kxb, and Kxo (x = c, m, y, x) in each color space obtained from the data shown in Table 2.
k) shows an example.

As shown in Table 3, the constant Kxo in the second set in each color space has the same value (0). This is because the two achromatic colors N1 and N2 are used in common for each color space when calculating the color conversion constant.

Therefore, since the constant Kxo in each color space is the same, in the embodiment shown in FIG. 3, the area signal AREA is directly used as the address signal of the constant memory circuit 313 that outputs the constant Kxo. This saves the RAM capacity of the constant memory circuit 313.

When the system control unit 105 writes the constant Kxo to the constant memory circuit 313, instead of writing the value shown in Table 3 as it is, the obtained constant is used as in the γ conversion circuits 201 to 203 described above. At 0 o'clock, the obtained constant is 1.
In case of 5, convert to 255 before writing. Similar conversion is performed below.

Next, the constants Kxr ', Kxg', Kxb 'and Kxo' stored in the color conversion circuits 204 to 207 in the mono color mode will be described.

The color conversion processing in the mono color mode is performed in the same format as the processing shown in equation (1), but the image conversion is substantially performed.
Neutral concentration D calculated from equation (4) from Dr, Dg and Db
It is based on n. Here, the neutral density Dn corresponds to a value obtained by converting the brightness of an image into a density.

Dn = Knr · Dr + Kng · Dg + Knb · Db (4) where Knr, Kng, and Knb are constants, and Knr = 0.3, Kn in the following.
It is assumed that g = 0.5 and Knb = 0.2.

The color conversion constants Kxr ', Kxg', Kxb 'and Kxo' are determined as follows.

Different neutral densities DN1 and DN2 are determined in advance, and then the recording densities of cyan, magenta, yellow, and black coloring materials that are optimal for recording colors of these neutral densities DN1 and DN2 are determined. Here, the neutral densities are the recording densities corresponding to DN1 and DN2, respectively (DN1c, DN1m, DN1y, DN1k),
Assuming that (DN2c, DN2m, DN2y, DN2k), the color conversion constants Kcr to Kko in this case are obtained by Expression (5).

here, Further, as described above, the two neutral densities DN1, DN2 and the recording densities (DN1c, DN1m, DN1) corresponding to these neutral densities
y, DN1k), (DN2c, DN2m, DN2y, DN2k), color conversion constant
By using the method for calculating Kcr to Kko, the image portion (for example, D
Not only N1 = 1.5) but also the color of the background portion (DN = 0) can be arbitrarily selected, and the image can be recorded without deteriorating the gradation, so that more various mono-color recording is possible. Such a monochromatic recording can be executed by the color conversion circuit shown in FIG. This will be clear from the description below.

Table 4 shows the neutral concentrations DN1 (= 0) and DN2 (= 1).
And corresponding examples of the recording densities Dxc, Dxm, Dxy and Dxk. Table 5 shows the results obtained from the data shown in Table 4.
Color conversion coefficients Kxr ', Kxg', Kx in mono color mode
Examples of b 'and Kxo' are shown below.

Next, an original image as shown in FIG.
The operation of the color conversion process in a case where an undercolor is added to a predetermined area as shown by a two-dot chain line and another area is recorded in monocolor will be described. FIG. 8a is a diagram showing the appearance of the operation unit 106. FIG.

Referring to FIG. 8A, the operation unit 106 includes a copy start key 801, a numeric keypad 802, and a clear / stop key.
803, an interrupt key 804, a set number display 805, a copy number display 806, and a touch panel display 807. The touch panel display 807 is provided with a panel in which a number of transparent contact detection switches are arranged on the display surface of the display, and the display unit and the input unit are integrated. Specifically, selection of various operation modes, display of input guidance associated therewith, and display of the selected mode are performed by the touch panel display. FIG. 8b shows an example of the display screen of the touch panel display 807 in a standard state. In this state, it is possible to select various operation modes such as undercolor, monocolor, and magnification. In such a display state, when the part displayed as undercolor is pressed, the display is changed to the undercolor setting state and the display screen as shown in FIG. 8c. In the under color setting state, it is possible to input the diagonal coordinates (X1, Y1) and (X2, Y2) of the rectangular area to which the under color is added, and to select the color of the under color. In other words, the diagonal coordinate value can be entered using the numeric keypad 802 after pressing the part indicated as X1, Y1, X2, Y2, and the undercolor color can be selected by pressing the displayed color name part I can do it. The setting of the under color is completed by pressing the end display section, and the cancellation of the setting of the under color is executed by pressing the cancel display section, and the display returns to the standard state. When the part displayed as monocolor is pressed in the display state as shown in FIG. 8b, the display is changed to the display screen as shown in FIG. In the mono color setting state, the diagonal coordinates (X1, Y1) (X2,
Y2) input and selection of monocolor recording colors are possible. In other words, the coordinate values of the diagonal coordinates can be input numerically using the numeric keypad 802 after pressing the portion indicated as X1, Y1, X2, Y2, and the monocolor recording color is pressed at the displayed color name portion You can choose by. The setting of the mono color is completed by pressing the end display section, and the cancellation of the setting of the mono color is executed by pressing the cancel display section, and the display returns to the standard state. In the example shown in FIG. 8d, the recording density (DN2c, DN2m, DN2y, DN2) of the neutral density DN2 in Table 4 is selected by selecting the monocolor recording color.
2k) is changed, and the recording density (DN1c, DN1m, DN1y, DN1k) of the neutral density DN1 is not changed.

On the other hand, the above-described display control and operation detection are performed by the system control unit 105. When the setting of the under color is completed, the system control unit 105
Constants Kco ″, Kmo ″, Ky predetermined in correspondence with the undercolor color selected in the operation unit 106
O ″ and Kko ″ are read from the ROM built in the system control unit 105, and written to predetermined addresses of the constant memory circuits 313 of the color conversion circuits 204 to 207 by the setting signal SET. When the setting of the mono color is completed, the constants Kcr ′ to K K which are predetermined in accordance with the mono color recording color selected in the operation unit 106 are set.
ko ′ is read from the ROM built in the system control unit 105, and the color conversion circuits 204 to 207 are
Is written to a predetermined address of each of the constant memory circuits 302 to 304, 313.

Prior to the start of the copying operation, the system control unit 105 sets constants Kcr to Kko for normal full-color copying,
The data is read from the ROM incorporated in the system control unit 105 and written into predetermined addresses of the constant memory circuits 302 to 304 and 313 of the color conversion circuits 204 to 207 by the setting signal SET.

In the following, constants Kcr to K for full color shown in Table 3 are shown.
ko is converted into each of the color conversion circuits 204 to 207 in the order shown in Table 3.
And write the constants Kco, Kmo, Kyo and Kko shown in Table 3 to the address 0 of the constant memory circuit 313, and write the constants for the mono color shown in Table 5 The constants Kcr 'to Kkb' of the constant memory circuit 30
2 to 304 are written into address 6, the monocolor constants Kco ', Kmo', Kyo 'and Kko' shown in Table 5 are written into address 1 of constant memory circuit 313, and undercolor constant Kco "is written. , Kmo ″, Kyo ″ and Kko ″ are constant memory circuits
The description will be continued assuming that data is written to address 3 of 313.
If an example of constants for realizing a light yellow (yellow) undercolor as shown in FIG. 7b is shown, Kco ″
= Kmo "= Kko" = 0, Kyo "= 0.5.

When the above writing is performed, 12-bit data (hexadecimal) as shown in FIG. 11a is stored in the RAM of the constant memory circuit 302 of the color conversion circuit 204. 12-bit data (hexadecimal) as shown in FIG. 11b is stored in the RAM 313. In the RAM address (unused part) that has no data to write,
0 is written. The system control unit 105
Further, the timing control unit 104 is set in accordance with the input coordinate values of the diagonal coordinates and the address of the constant memory circuit 313 in which the constant is written.

FIG. 9 shows the configuration of the AREA signal generating portion of the timing control unit 104. Referring to FIG. 9, reference numeral 901 denotes a main scanning direction counter circuit which counts the pixel synchronization signal CLOCK and outputs the upper bit x of the count result. The count value of the main scanning direction counter circuit 901 is cleared by a line synchronization signal LSYNC which is one of the synchronization signals CLK. A sub-scanning direction counter circuit 902 counts the line synchronization signal LSYNC, and outputs the upper bit y of the count result. Further, the count value of the sub-scanning direction counter circuit 902 is cleared by the frame synchronization signal FSYNC which is one of the synchronization signals CLK. Signal x output from main scanning direction counter circuit 901 and sub-scanning direction counter circuit 902
And y are input to the address selection circuit 903.

The address selection circuit 903 responds to a certain bit SET 0 of the setting signal SET output from the system control unit 105,
Signals x and y, or specific signal group SET 'of setting signal SET
And outputs it to the area memory circuit 904. That is, the system control unit 105 selects the setting signal SET 'when writing data to the area memory circuit 904, and selects and outputs the signals x and y when performing a copying operation.

The area memory circuit 904 is a circuit composed of a RAM or the like, and a signal output from the above-described address selection circuit 903 is a RAM.
And the data stored in the RAM is output as the area signal AREA. Further, a specific signal group SET ″ of the setting signal SET is supplied from the system control unit 105 to the RAM as a write control signal or data.

FIG. 7c shows a part of the data written in the RAM of the area memory circuit 904 (area signal AREA data commonly supplied to the color conversion circuits 204 to 207). x and y are a main scanning direction counter circuit 901 and a sub-scanning direction counter circuit 90, respectively.
2 corresponds to the output signal. (X1, y1), (x
(2, y2) indicate the positions corresponding to the diagonal coordinates of the monocolor processing area input from the operation unit 106, (x3, y3), (x
4, y4) indicates a position corresponding to the diagonal coordinates of the area to which the under color is added.

As shown in FIG. 7c, in the area (x1, y1) to (x2, y2) in which only the monocolor processing is set, data (AREA0) for selecting the RAM address 6 of the constant memory circuits 302 to 304
2 = 6, AREA3 = 1) and signals (AREA4-6 = 1) for selecting the address 1 of the RAM of the constant memory circuit 313 are written. In the areas (x3, y3) to (x4, y4) where only the undercolor is set, the constant memory circuits 302 to 304
Data {AREA 0-2 = don't care (= 0), AREA 3 = 0} for selecting RAM addresses 0 to 5 according to the image signal and a signal for selecting RAM address 3 of constant memory circuit 313 ( AREA 4-6 = 3) is written and the area (x3, y3) where the mono color processing and under color are set at the same time
In (x4, y2), the data (AREA 0 to 2 = 6, AREA 3 = 1) for selecting the RAM address 6 of the constant memory circuits 302 to 304 and the signal (AR) for selecting the RAM address 3 of the constant memory circuit 313
EA 4-6 = 3) is written, and in other areas, data {AREA 0-2 = don't care (= 0) for selecting addresses 0-5 of the RAMs of the constant memory circuits 302-304 according to image signals. ), A
REA 3 = 0} and a signal (AREA 4 to 6 = 0) for selecting the address 0 of the RAM of the constant memory circuit 313 are written.

Therefore, while processing the designated area, the desired constants are provided to the selected color conversion processing in the color conversion circuits 204 to 207, so that the predetermined area is processed as shown in FIG. 7b. It can be processed in mono color or add under color.

FIG. 10 shows the relationship between the density of the gray scale and the recording density Dk of the black color material when copying the gray scale. Next, the operation of the color conversion process when an image is recorded using skeleton black as shown in FIG. 10 will be described.

In the color conversion circuit 207 shown in FIG. 2, in order to generate the skeleton recording density signal Dk, two different gray scale densities and black color material on the relationship line shown in FIG. 10 are recorded. The density Dk may be determined and replaced with the achromatic data in Table 2. For example, the gray scale density is set to 0 and 1, and the recording density Dk of the black color material at this time is set.
Are -0.4 and 0.3, respectively, the relationship between the image density and the recording density exemplified in Table 2 can be rewritten as shown in Table 6. In this case, the constant of the color conversion process is
The values are as shown in Table 7.

Therefore, the system control unit 105 stores the constants shown in Table 7 in the respective constant memory circuits 303 of the color conversion circuits 204 to 207.
By writing to 304304,313, it is possible to copy an image in skeleton black. Further, image copying using skeleton tone black is excellent in expressing gradation, and is particularly suitable for copying a photographic image or the like.

On the other hand, the constants shown in Table 3 correspond to the full black image copying shown in FIG. Image copying in full black is suitable especially for copying a character image because black characters can be recorded using only a black color material.

Switching of the coefficients shown in Tables 3 and 7 is realized by pressing the photo display unit or the character display unit in the standard state shown in FIG. 8b. That is, when the system control unit 105 detects that the photo display unit is pressed, the system control unit 105 uses the constants shown in Table 7 when detecting the press of the character display unit, and outputs the constants shown in Table 3 when it detects the press of the character display unit. 204-207
Is written to each of the constant memory circuits 302 to 304, 313.

 Referring again to FIGS. 8a and 8b.

When the part where the color conversion is displayed is pressed in the display state as shown in FIG. 8b, the state changes to the color conversion setting state and the display screen changes to the display screen as shown in Table 9. In the color conversion setting state, the recording colors (white, red, brown, and black) are set for each original color (white, red, yellow, green, C: cyan, blue, M: magenta, black).
Orange, yellow, yellow-green, green, C, blue, M, purple, black, gray, etc.) and density (light, medium, dark) can be selected. That is, when the color name of the recording color corresponding to each document color or the density display area of the density is pressed, the color name or the density level is sequentially changed, and a desired combination can be set.

Next, an operation in a case where a white (background) portion is converted into a specific color and recorded will be described. The color conversion device 207 shown in FIG.
In order to convert a white portion to a specific color,
If the achromatic color closer to white in the table is white (Dr = Dg = Db = 0) itself, it can be replaced with the recording density itself of the desired color. For example, the white part is light yellow (Dc = Dm = Dk =
(0, Dy = 0.5), the relationship between the image density and the recording density exemplified in Table 2 can be rewritten as shown in Table 10. In this case, the constant of the color conversion process is
The values are as shown in Table 11.

The color conversion processing described above differs from the above-described under color processing in that it does not affect the recording density of chromatic colors or the other achromatic color, as is clear from Table 10.

[Effects of the Invention] As described above, according to the first and second aspects of the present invention, undercoloring can be realized at a low cost with a simple configuration, and a full black and skeleton tone black recording density signal ( Dk) can be obtained with a simple and inexpensive configuration.

According to the third aspect of the present invention, the image density signal is a constant corresponding to the value of the image density signal during full-color printing, and a constant irrelevant to the value of the image density signal during mono-color printing. A color information conversion device that is converted into a signal and that can perform processing by mixing full-color recording and monocolor recording with excellent color reproducibility is realized with a simple configuration and at low cost.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration of a color copying machine incorporating one embodiment of the present invention. FIG. 2a is a block diagram showing the configuration of the color correction processing device 102 shown in FIG. 1, that is, one embodiment of the present invention. FIG. 2b is a block diagram showing another configuration of the color correction processing device 102, that is, another embodiment of the present invention. FIG. 3 is a block diagram showing the configuration of the color conversion circuits 204 to 207 shown in FIG. 2a. FIG. 4 is a block diagram showing a configuration of the constant selection circuit 301 shown in FIG. FIG. 5 and FIG. 6 are graphs showing the area of the branch density space for explaining the content of the color correction processing of the color correction processing device 102. 7a and 7b are plan views showing an original image. FIG. 7c is a plan view showing a color correction process designation area on the document. FIG. 8a is a plan view showing the appearance of the operation unit 106 shown in FIG. 8b, 8c, and 8d are plan views of the touch panel display 807 of the operation unit 106. FIG. FIG. 9 is a block diagram showing a configuration of a part of the timing control unit 104 shown in FIG. FIG. 10 is a graph showing the relationship between the density of the gray scale and the recording density of the black color material when copying the gray scale of the original. FIG. 11a is a plan view showing an example of data written to the RAM of the constant memory circuit 302 shown in FIG. FIG. 11b is a plan view showing an example of data written to the RAM of the constant memory circuit 313 shown in FIG. 106: operation unit (specifying means) 301: constant selection circuit (constant selection means) 302 to 304: constant memory circuit 305 to 307: multiplication circuit (multiplication processing means) 313: constant memory circuit (constant signal generation means) 311,312,315 : Adder circuit, 316: shaping circuit (311, 312, 315, 316: output means) (302 to 307, 311, 315, 316: product-sum processing means) 401 to 403: comparator 409: selector (generating means) 410: D flip-flop 801: copy start key, 802 : Numeric keypad 803: Clear / Stop key, 804: Interrupt key 805: Number of sets display 806: Number of copies display 807: Touch panel display

Claims (3)

(57) [Claims] 1. A color information converter for processing an image density signal representing a color-separated image density and outputting a recording density signal representing a black, cyan, magenta or yellow recording density: Multiplication processing means for multiplying each of the image density signals representing the density and a predetermined first set of constants defined for each image density signal and outputting the result; Constant signal generating means for generating a signal representing the signal;
Means for calculating the sum of the signal output from the multiplication processing means and the signal output from the constant signal generation means and outputting the result. 2. A color information conversion apparatus for processing an image density signal representing a color-separated image density and outputting a recording density signal representing a black recording density: an image density signal representing a color-separated image density Constant selecting means for generating a signal for switching a predetermined first set of constants determined for each image density signal in accordance with the following: each image density signal in response to the output of said constant selecting means Multiplication processing means for multiplying a first set of constants determined for each of the above and each of the image density signals representing the color-separated image density and outputting the result; a signal representing a second set of constants Means for generating constant signal;
Means for calculating the sum of the signal output from the multiplication processing means and the signal output from the constant signal generation means and outputting the result. 3. A constant selecting means for generating a constant selection signal for selecting a constant corresponding to each of image density signals representing color-separated image densities, a constant corresponding to said constant selection signal and said image density. And a product-sum processing means for calculating a product sum with each of the signals and outputting the result, wherein the device specifies at least one of a full-color recording area and a mono-color recording area on an image. Means, wherein the constant selection means is configured to perform a first operation in accordance with a value of the image density signal while the image density signal is in an area designated by the designating means.
And a second constant selection signal independent of the value of the image density signal and a means for generating the other while outside the area. apparatus.