JPH0149627B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a color inkjet recording method and apparatus for recording color images using at least one specific color (spot color) in addition to cyan, magenta, and yellow. A color inkjet recording device scans a color original image with a color scanner, measures the blue, green, and red densities of each part, and performs masking processing on these three color density signals to produce three colors of cyan, magenta, and yellow.
The ink is converted into a color density signal, and the amount of cyan, magenta, and yellow ink ejected is controlled according to the three color density signals to reproduce and record a color image. In this color inkjet recording device,
When recording specific colors that have subtle hues and continuously change density levels, such as skin tones or sky blues, the special colors must be reproduced using three inks: cyan, magenta, and yellow, so it is best to balance them at intermediate densities. The color will be distorted and the color will be slightly different. These special colors represent the skin color of a person's face, and the sky blue represents the blue sky, so their finish has a great effect on the overall image. Generally, in the printing industry, during the color separation process of an original image reading device, a special color component with certain spectral characteristics is extracted, and the remainder after removing this spectral characteristic is separated into the three primary colors of blue, green, and red, and the special color component is extracted. A 4-color color separation version including the printing plate is created. In the method for creating color separation plates described above, special color components are extracted optically in advance, so when applying this to a color inkjet recording device, the optical system, phototube, logarithmic converter, and image information processing memory are required. This has the disadvantage that an extra device is required for the spot color, which increases cost. In view of the above-mentioned problems, the present invention is a color inkjet printer that uses ink of a specific color to reproduce colors faithfully to the original color image even in images in which the density of the special color varies continuously. The object of the present invention is to provide an event recording method and apparatus. Another object of the present invention is to provide a color inkjet recording device that can easily use special color inks by adding a small amount of equipment. The present invention specifies the density levels of three specific color components to be added, that is, cyan, magenta, and yellow, and sets these density levels to cyan, magenta, and yellow.
In addition to removing it from the yellow density signal, a special color density signal is formed from the density level ratio of the three colors, and the ejection amount of the special color ink is controlled according to the obtained special color density signal. . That is, the present invention removes three special color density components from the cyan, magenta, and yellow density signals, and uses special color ink commensurate with the removed amount. The apparatus of the present invention for realizing the above recording method includes three ink ejecting means for ejecting ink of three colors cyan, magenta, and yellow in accordance with density signals, as well as ink ejecting means different from these colors. A special color ink ejecting means for ejecting ink of at least one special color; a density level removing means for removing a preset density level component corresponding to the special color from each density signal of cyan, magenta, and yellow; Said 3
spot color density detection means for removing density level components corresponding to the spot colors when the color density signals are included and generating density signals of the spot colors; control means for controlling the amount of ink ejected for the special color ejected from the special color ink ejecting means in response to the request, and controlling the amount of ink ejected for the other three colors based on the remaining density signal removed by the density level removing means; It consists of Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 shows an embodiment in which a color image is recorded in four colors, cyan C, magenta M, and yellow Y, using skin color FL as a special color. The image information recorded on the color original image is converted into cyan C, magenta M, and yellow Y density signals. These density signals are generated by 32 bits of digital signals.
Expresses intermediate tones of levels. Conventionally, the ejection amounts of three types of ink are controlled in accordance with these three types of density signals: cyan C, magenta M, and yellow Y. The present invention detects skin color from these three types of density signals.
The undercolor of the FL is removed and a density signal of the skin color FL corresponding to this is formed to enable faithful color reproduction of the skin color. Note that sky blue or the like can also be used as a special color. In the embodiment shown in FIG. 1A, the density signal of cyan C is 10 levels (001001), the density signal of magenta M is 18 levels, and the density signal of yellow Y is 25 levels. The skin color FL density level is removed from these density signals. Here, the density level of skin color and the components of cyan C, magenta M, and yellow Y are shown in Table 1.

[Table] In this first table, the 20 levels of skin color are 3 x 3
Indicates the maximum density value at which all dots with the largest particle size are recorded in the matrix of cyan C,
Corresponds to 32 levels of magenta M and yellow Y. In FIG. 1A, a skin color component with a density level of "8" indicated by diagonal lines is included. This density level "8" is C:10, M:13, Y:14, and these density levels are subtracted from each other. As a result, as shown in FIG. 1B, C:0,
Density levels (density signals) of M: 5, Y: 11, FL: 8 are obtained. Depending on these concentration levels,
A color image is recorded by controlling the ejection amount of cyan, magenta, yellow, and flesh-colored ink. FIG. 2 shows an embodiment using flesh color FL and black B as special colors. The embodiment shown in FIG. 2A has density levels of C: 21, M: 18, and Y: 25. This density level includes a black component at a density level of "10" indicated by a solid line and a skin color component at a density level of "4" indicated by a dashed-dotted line. Therefore, as shown in Figure 2B, black B and
The undercolor of skin color FL is removed, and density levels of black B and skin color FL corresponding to this are formed. Through this process, C: 6, M: 1, Y: 6, FL:
4. B: 10 density levels (density signals) are obtained,
Cyan, magenta,
A color image is reproduced by controlling the amount of ink ejected for yellow, skin color, and black. FIG. 3 shows a color inkjet recording apparatus that implements the present invention, and this recording apparatus includes a digital color scanner 10 and an image processing apparatus 1.
1 and an inkjet printer 12. The digital color scanner 10 has a rotating cylinder 1
Each part of the color original image 14 wrapped around the image sensor 3 is scanned to measure the density of the three colors of blue, green, and red. In conjunction with the rotation of the rotating cylinder 14, the feed screw shaft 1
5. The moving table 17 is moved in the axial direction of the rotating cylinder 14 by the rails 16. This moving table 17 includes an optical system 18 and a dichroic mirror 1.
9,20, these dichroic mirrors 19,
Phototubes 21, 22, and 23 each measure blue light, green light, and red light separated into three colors at 20, and a logarithmic converter 24 that logarithmically converts the color signals measured by these phototubes 21 to 23, respectively. ing. The logarithmically converted density signals of the three colors are sent to the A-D converter 25, where they are converted into digital signals, and then sent to the image processing device 11 through the signal line 26, and then sent to the internal storage device. It is stored in 28. The image processing device 11 includes a central processing unit 27,
It is composed of an internal storage device 28, a UCR circuit 29, and a table memory circuit 30. As the central processing unit 27, a commonly used mini-computer can be used, and it can control the position of the digital color scanner 10 and the inkjet printer 12, and control the position of the inkjet printer 12.
Image processing such as abstraction control of the reproduced image and color correction using nonlinear masking including quadratic terms is performed. The central processing unit 27 receives the digitized three images from the digital color scanner 10.
A color density signal and a rotation signal of the rotating cylinder 13 are input through signal lines 26 and 31, respectively. The UCR circuit 29 removes the undertone of a special color, for example, a skin color component, from the density signals of the three colors cyan, magenta, and yellow obtained by the masking process, and calculates a skin color density signal corresponding to the amount of removal. The table memory circuit 30 generates tone signals to be supplied to the inkjet printer 12 by referring to the table memory for each level of density signals of cyan, magenta, yellow, and flesh color. The inkjet printer 12 is composed of a rotating cylinder 33 wrapped around a recording paper (blank paper) 32 and a head section 34 that integrates inkjet ejection heads for each color, which are controlled by signals from the central processing unit 27. There is. Rotating cylinder 33
is rotated by a main scanning motor 36 that is controlled by a main scanning control signal transmitted from the central processing unit 27 through a signal line 35 . The head portion 34 rotates around the rotating cylinder 3 along the rail 37.
A sub-scanning motor 39 is configured to move parallel to the rotation axis of No. 3 and is controlled by a sub-scanning control signal transmitted from the central processing unit 27 via a signal line 38.
It is driven by a feed screw shaft 40 that rotates by.
The head unit 34 includes four cyan, magenta, yellow, and skin-colored inkjet ejection heads, and each head has a plurality of small head portions opening in a matrix with respect to the recording paper 32. Four colors of ink are supplied to each ejection head from a device not shown, and an amount of ink corresponding to the tone signal of the table memory circuit 30 is ejected from each small head portion through a signal line 41. That is, pixels of one color on the recording paper 32 are formed by a combination of dots arranged in a matrix.
The size and arrangement of these dots expresses the density of pixels in the reproduced image. For example, 32 levels of intermediate tones can be expressed by selecting the arrangement and size of dots in a 3 x 3 matrix. In this device, the density signals of blue, green, and red at each point written in the internal storage device 28 are read out in accordance with the position signals of each inkjet ejection head of the head section 34, and nonlinear masking processing is applied to these density signals. By controlling the head section 34 using density signals of cyan, magenta, yellow, and flesh color obtained by performing undercolor removal distribution, a reproduced image faithful to the color original image 14 can be recorded on the recording paper 32. Figure 4 shows the UCR circuit, table memory circuit,
FIG. 3 is a block diagram showing the head section in detail. Undercolor designation elements 50, 51, and 52 are provided that can designate cyan, magenta, and yellow components at arbitrary levels depending on the spot color. The determination circuit 53 determines whether each of the cyan, magenta, and yellow density signals sent from the central processing unit 27 exceeds the density level designated by the under color designation elements 50-52. The under color removal distribution circuit 54 draws an amount corresponding to the specified level with special color ink when each color exceeds the specified level, and draws the excess amount with each color ink when the specified level is not exceeded or exceeds the specified level. Each density signal is distributed by removing the undercolor as if drawing. This undercolor removal/distribution circuit 54 forms density signals for cyan, magenta, yellow, and special colors, such as skin color, and sends them to the table memory circuit 30. The table memory circuit 30 includes table memory circuits 55 to 58 for cyan, magenta, yellow, and skin color, and generates tone signals in accordance with density signals. This tone signal specifies the position, number and particle diameter of dots to be placed in a 3.times.3 dot matrix for each color. The tone signal output from the table memory circuit 30 is sent to the head section 34. This head section 34 is for cyan, magenta, yellow,
Four types of head drive circuits 59 to 62 for skin color;
Heads 63 to 6 for cyan, magenta, yellow, and skin tone, with three small heads for each color.
It consists of 6. The three small heads provided for each color are arranged in the main scanning direction, and are installed so that the ink droplets are shifted one dot at a time in the sub-scanning direction by changing the orientation, and the three small heads are arranged in the main scanning direction by the aforementioned tone signal. Record the dot line. FIG. 5 is a block diagram of an embodiment using flesh color and black as special colors. In this embodiment, an undercolor specifying element 67 for black, a discrimination circuit 68, and an undercolor removal distribution circuit 69 are added after the undercolor removal distribution circuit 54 for skin color, and cyan, magenta and magenta from which skin color components have been removed are added. By removing the black component from the yellow density signal, it is converted into cyan, magenta, yellow, and black density signals.
Here, for black, cyan, magenta,
Since the density levels of yellow are equal, only one undercolor designation element 67 is provided. The distributed cyan, magenta, yellow, skin color, and black density signals are sent to table memory circuits 55-58 and 70, respectively. The tone signals from these table memory circuits 55 to 58 and 70 drive head drive circuits 59 to 62 and 71, and the tone signals for cyan, magenta, yellow,
The amount of ink ejected from the skin color and black heads 63 to 66 and 72 is controlled. In the above embodiment, the two special colors are skin tone and black.
Although colors are used, other colors that are frequently used and express important images, such as sky blue, can also be used. In this case, in addition to sequentially performing the undercolor removal distribution for each spot color in a serial manner, it can also be performed in parallel to increase the processing speed. The present invention having the above-mentioned configuration has the following advantages: cyan, which is commonly used;
In addition to magenta and yellow, color images are recorded using special colors such as flesh-colored ink, so special colors with subtle hues and continuously changing density levels are reproduced in colors that are faithful to the original color image. can do. Furthermore, since the density signal of the special color ink is formed from the density signal of the commonly used ink, it can be easily implemented by adding only a small number of devices. Furthermore, by using this special color ink, it is possible to expand the area where color reproducibility is good.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing undercolor removal and density distribution in an example using skin color as a special color, FIG. 2 is an explanatory diagram of an example using skin color and black as a special color, and FIG.
The figure is a schematic diagram of a color inkjet recording apparatus that implements the method of the present invention, FIG. 4 is a block diagram of the main part, and FIG. 5 is a block diagram of an embodiment using skin color and black as special colors. 10...Digital color scanner, 11...
Image processing device, 12... inkjet printer, 29... UCR circuit, 30... table memory circuit, 34... head section, 50-52... undercolor designation element for skin color.

Claims (1)

[Scope of Claims] 1. A color inkjet recording method for recording a color image by controlling the ejection amount of three color inks according to density signals of cyan, magenta, and yellow, comprising: specifying a desired density level for each color, removing the specified density level from each of the three color density signals, and forming a spot color density signal from the ratio of the density levels of these three colors; A color inkjet characterized in that a color image is recorded using at least four color inks including the special color by controlling the ejection amount of the special color ink according to the obtained density signal of the special color. Recording method. 2. The color inkjet recording method according to claim 1, wherein the special color is a skin color. 3 Remove preset density level components from three ink ejecting means that eject inks of three colors, cyan, magenta, and yellow, respectively, and density signals of each color for controlling the amount of ink ejected for the three colors. density level removing means; special color ink ejecting means for ejecting special color ink corresponding to the density level component removed by the density level removing means; a special color density detection means that generates a density signal of the special color when it is detected that each of the density level components of the special color ink is included; Color inkjet recording characterized by comprising a control means for controlling the ink ejection amount of the special color and controlling the ink ejection amount of the three colors based on the remaining density signal removed by the density level removing means. Device. 4. The color inkjet recording apparatus according to claim 3, wherein the special color is a skin color.