JP5649371B2 - Image forming apparatus and image forming method - Google Patents

Description

  The present invention relates to an image forming apparatus and an image forming method for forming a color image using a colored ink containing a pigment color material and a colorless ink.

  As an ink used in an ink jet recording apparatus, a dye ink using a dye that dissolves in water as a coloring material is widely used. In the dye ink containing water as a main component, the color material dissolved in the solvent easily penetrates into the fiber of the recording medium. Accordingly, the surface shape of the recording medium is easily maintained even after the image is recorded, and the gloss of the recording medium is maintained as the gloss of the image. In other words, a combination of a recording medium having excellent gloss and a dye ink forms an image having excellent gloss. Therefore, a user of an ink jet recording apparatus using a dye ink can obtain a printed matter having a desired glossiness by selecting a recording medium having the desired glossiness.

  On the other hand, there is a demand for improving the light resistance and water resistance of printed matter. In the dye ink, the dye molecules of the coloring material are decomposed by light, and the color of the image is easily faded. In addition, when wetted with water, dye molecules that have penetrated into the fiber dissolve in water, and bleeding tends to occur in the image. That is, printed matter using dye ink generally has poor light resistance and water resistance.

  In order to solve the problems of light resistance and water resistance in the printed matter of dye ink as described above, in recent years, development of pigment ink using a pigment as a coloring material has been advanced. Unlike a dye ink in which a dye is present as a molecule in the solvent, the color material of the pigment ink is present in the solvent as particles having a diameter of several tens to several hundreds of nanometers. That is, since the color material particles of the pigment ink are larger than the dye molecules of the dye ink, a printed matter with high light resistance can be obtained. In addition, since the pigment has a property that does not dissolve in water, the pigment ink is superior to the dye ink in terms of water resistance.

  When recording is performed using the pigment ink, the pigment particles hardly penetrate into the recording medium and are deposited on the surface of the recording medium. For this reason, the fine shape (smoothness) of the image surface differs between the recording area where the pigment ink is recorded and the non-recording area where recording is not performed.

  In addition, the amount of color material used varies depending on the density and color of the image formed on the recording medium, and the area where the pigment covers the recording medium changes. Since the reflectance of the pigment and the reflectance of the recording medium are different, a difference in gloss occurs due to the difference in the area where the pigment covers the recording medium.

  As described above, in the recording using the pigment ink, the glossiness varies depending on the density and color of the image, and therefore, different areas with different glossiness are mixed in one image. That is, the gloss area observed as glossy and the matte area observed as non-gloss are mixed in one image, and such a change in gloss is recognized as “gloss unevenness”. In particular, when a photographic image is printed, uneven gloss is recognized as an image defect.

  Therefore, in order to reduce the occurrence of uneven glossiness due to the use of pigment ink, a method of forming an image using a colorless ink not containing a color material has been proposed. For example, a technique has been proposed in which the discharge amount of colored ink and colorless ink is adjusted so that the adhesion amount per unit area of the resin component derived from the pigment ink is uniform over the entire recording area of the recording medium. (For example, refer to Patent Document 1). In addition, a technique has been proposed in which the discharge amounts of colored ink and colorless ink are adjusted so that the glossiness in the recording area is substantially uniform (see, for example, Patent Document 2).

JP 2006-272934 JP JP 2007-276482 JP

  However, the conventional method of reducing gloss unevenness derived from pigment ink using colorless ink can make the gloss uniform, but depending on the type of ink and printing conditions, the reflected light at the ink layer boundary Interference may occur. When such interference occurs, the specularly reflected light from the recording surface is colored differently depending on the gradation of the image and is visually noticeable. In particular, coloring of specular reflection light is conspicuous in an area formed by bright ink such as yellow ink and colorless ink. Such a phenomenon is caused by thin film interference caused by a difference in refractive index between the color material layers including the air layer, and a color to be attached is determined according to the thickness of the color material layer. Hereinafter, the color that appears with the specularly reflected light due to such thin film interference is referred to as “interference color”.

  FIG. 1 is a schematic diagram illustrating the principle of generation of interference colors. When an image is formed with pigment ink, light 1003 reflected on the surface of the color material layer 1001 recorded on the recording medium 1002 as reflected light from the image, and the surface of the recording medium 1002 after passing through the color material layer 1001 There is light 1004 that is reflected from and emitted from the color material layer 1001. The optical path length of the light 1004 is longer than that of the light 1003 because it passes through the color material layer 1001. Due to the phase shift of the light based on this optical path length difference, so-called interference occurs in which specific wavelengths intensify or weaken the intensity, and the reflected light is colored, that is, an interference color is generated. To do.

  Therefore, in the present invention, when forming an image using colored ink and colorless ink containing a pigment color material, the effect of reducing uneven glossiness is maintained, and further, coloring to regular reflection light by using colorless ink is reduced. The purpose is to do.

  As a means for achieving the above object, the present invention comprises the following arrangement.

  That is, an image forming apparatus that forms an image using a plurality of colored inks including a pigment color material and a plurality of kinds of colorless inks having different refractive indexes, and performs color separation processing on input color image data. Then, for each pixel of the color image data, a colored ink driving amount for each color of the colored ink and a colorless ink total driving amount obtained by totaling the driving amount for each of the colorless ink are used for the colored ink driving for each color. Color separation means for setting the sum of the amount and the total amount of colorless ink to be constant in all pixels of the color image data, and colorlessness for each of the plurality of types of colorless ink in the total amount of colorless ink to be applied Each of the colorless ink placements so that the ratio of ink placement is random for each pixel. An amount setting unit for setting an amount; and for each pixel of the color image data, for each color of the plurality of colored inks, recording is performed by the amount of the colored ink set by the color separation unit, and the plurality of types Each of the colorless inks includes an image forming unit that forms a color image on a recording medium by performing recording with the colorless ink driving amount set by the driving amount setting unit.

  According to the present invention, when an image is formed using a colored ink and a colorless ink containing a pigment coloring material, the effect of reducing uneven glossiness is maintained, and further, coloring to specular reflection light by using a colorless ink is achieved. It becomes possible to reduce.

Schematic diagram explaining the generation principle of thin film interference, FIG. 2 is a block diagram illustrating a configuration example of an image forming apparatus according to the first embodiment. FIG. 3 is a diagram illustrating a configuration example of a recording head in the first embodiment. 6 is a flowchart showing image forming processing in the first embodiment; A block diagram showing an example of color separation processing in the first embodiment, The figure explaining the clear ink placement amount setting process in the first embodiment. The figure which shows the change of the interference color when the thickness of a color material layer changes in 1st Embodiment, The figure which shows the structural example of the image forming apparatus in 2nd Embodiment. The figure which shows an example of the two-dimensional implantation amount ratio map in 2nd Embodiment, FIG. 10 is a diagram illustrating a configuration example of a recording head according to a third embodiment. The figure explaining the clear ink placement amount setting process in 3rd Embodiment, Schematic diagram of clear ink recorded in the first embodiment, The figure which shows the composition example of a solvent shared by two types of clear inks, It is a figure which shows the example of a composition of two types of polymers from which a refractive index differs.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The following embodiments do not limit the present invention related to the scope of claims, and all combinations of features described in the present embodiments are essential to the solution means of the present invention. Not necessarily.

<First Embodiment>
System Configuration In the present embodiment, interference colors generated in an image formed by a plurality of colored inks (hereinafter referred to as color inks) including a pigment color material are used as a plurality of types of colorless inks (hereinafter, referred to as color inks) having different refractive indexes. An example of reduction using a clear ink) is shown. In the following, a case where two types of clear ink are used will be described as an example.

  FIG. 2 is a block diagram illustrating an example of the configuration of the image forming system according to the present embodiment, in which 2 is an image processing apparatus and 3 is a printer. The image processing apparatus 2 can be implemented by a printer driver installed in a general personal computer, for example. In that case, each part of the image processing apparatus 2 described below is realized by a computer executing a predetermined program. As another configuration, for example, the printer 3 may include the image processing device 2.

  The image processing apparatus 2 and the printer 3 are connected by a circuit or a printer interface. The image processing apparatus 2 inputs color image data to be printed from the input terminal 201 and stores the color image data in the image buffer 202. The color separation processing unit 203 color-separates the input color image data into data indicating the hit amount for each ink color provided in the printer 3. At this time, the color separation LUT 204 is referred to. Here, the ink colors are five colors obtained by adding clear ink to each color of CMYK, and the total amount of the two types of clear ink is determined as the amount of ink to be applied for the clear ink. Next, the clear ink placement amount setting unit 205 sets the placement amounts of the two types of clear ink using random numbers. Next, the halftone processing unit 206 converts the multi-gradation values (three gradations or more) into binary image data for a total of six ink colors obtained by adding two types of clear ink to each color of CMYK. The halftone image storage buffer 207 stores binary image data of each ink color obtained by the halftone processing unit 206, and the stored binary image data is output from the output terminal 208, and the printer 3 Is input via the input terminal 301.

  In the printer 3, the binary image data of each color formed by the image processing apparatus 2 is formed on the recording medium by moving the recording head 302 vertically and horizontally relative to the recording medium 303. The recording head 302 is a head that performs ink jet recording, and has a plurality of recording elements (nozzles). The moving unit 304 moves the recording head 302 under the control of the head control unit 305. The transport unit 306 transports the recording medium 303 under the control of the head control unit 305. Further, the ink color and ejection amount selection unit 307 is configured so that the ink color mounted on the recording head 302 and the head based on binary image data of each color including two types of clear ink formed by the image processing apparatus 2 The ink color and the discharge amount are selected from the ink discharge amounts that can be discharged. At this time, the driving order is controlled so that the clear ink becomes the surface layer.

  FIG. 3 is a diagram illustrating a configuration example of the recording head 302. In this embodiment, in addition to the four color inks of cyan (C), magenta (M), yellow (Y), and black (K), two types of clear inks (CL1, CL2) having different refractive indexes are combined. Assume that a total of six colors of ink are mounted on the recording head 302. Note that the recording head 302 of the present invention is not limited to the configuration shown in FIG. 3, and for example, inks having different densities such as light cyan, light magenta, and gray, or special color inks such as red and green may be mounted. Further, nozzle rows having the same color but different ejection amounts may be provided, and the nozzle arrangement is not necessarily linear. For example, the nozzles may be arranged in a zigzag manner. In the example shown in FIG. 3, the ink color is arranged in a line in the head movement direction, but it may be arranged in a line in the paper transport direction.

Image Forming Process Hereinafter, the image forming process in the image processing apparatus 2 of the present embodiment will be described with reference to the flowchart of FIG.

  First, in S 401, multi-tone color input image data is input from the input terminal 201 and stored in the image buffer 202. As input image data, color image data is constructed by three color components of red (R), green (G), and blue (B).

  In step S <b> 402, the color separation processing unit 203 performs color separation processing using the color separation LUT 204 on the multi-tone color image data stored in the image buffer 202. As a result, the input RGB data is a total of 5 colors for each color ink (C, M, Y, K) and 2 types of clear ink (CL1, CL2). Is converted to At the time of this color separation, as described above, for the clear ink, not the two types of driving amounts are determined, but the total driving amount of the two types of clear ink is determined. For this reason, in this embodiment, the input RGB data is color-separated into a total of five planes, that is, four planes indicating the amount of each CMYK color ink applied and a plane indicating the total amount of two types of clear ink applied. It is assumed that the ink ejection amount is expressed as 8-bit data of 0 to 255, for example. However, the representation of the ink ejection amount is not limited to 8 bits, and may be represented by 16 bits or a real number.

Here, the color separation processing in the present embodiment will be described with reference to FIG.

In FIG. 5, the color separation processing unit 203 refers to the color separation LUT 204, so that the input RGB data includes each color ink placement amount (colored ink placement amount) and the total amount of two types of clear ink placement (colorless ink). The state of color separation is shown in (total driving amount). Here, it is assumed that the pixel position in the image of the input image data is represented by coordinates (i, j). The conversion from the input image data R, G, B at the coordinates (i, j) to the ink amount data C, M, Y, K for each color ink and the total amount data CL for clear ink is expressed by the following equation (1). It is represented by

C (i, j) = C_LUT_3D (R (i, j), G (i, j), B (i, j))
M (i, j) = M_LUT_3D (R (i, j), G (i, j), B (i, j))
Y (i, j) = Y_LUT_3D (R (i, j), G (i, j), B (i, j)) (1)
K (i, j) = K_LUT_3D (R (i, j), G (i, j), B (i, j))
CL (i, j) = CL_LUT_3D (R (i, j), G (i, j), B (i, j))
Each function defined on the right side of the equation (1) corresponds to the color separation LUT 204. The color separation LUT 204 is a table that determines the output signal value of each ink color for the three input values of R, G, and B. In this embodiment, from the three input values of R, G, and B, C, M, The LUT configuration obtains output values for 5 planes of Y, K, and CL. Note that, as the color separation LUT 204, in order to reduce the occurrence of uneven glossiness in the entire image area, the clear ink total driving amount CL is set so that the adhesion amount of all ink is always constant. It should be noted that an optimal value for the total ink adhesion amount may be determined based on experiments, for example, and is not particularly defined.

  Returning to FIG. 4, when the color separation processing into a total of five planes is completed in S402, next, in S403, the clear ink placement amount setting unit 205 uses the clear ink total placement amount CL, and each of the two types of clear ink placement amounts. Set (colorless ink shot amount). In the present embodiment, the total amount of each clear ink is always kept at the total amount CL of clear ink determined in step S402, and the ratio of the amount of each clear ink is controlled to be random for each pixel. And Although specifically described later, in this embodiment, a random number is generated for each pixel, and based on the random number, the total amount of ink CL to be ejected is distributed to the amount of ink CL1 and CL2 for each clear ink.

  When the amount of ink for each ink is set, the halftone corresponding to the amount of ink for each ink obtained from the color separation processing unit 203 and the amount setting unit 205 for clear ink in the halftone processing unit 206 in S404. Process. As a result, the ink ejection amount data expressed in 8 bits in multiple values is converted into binary image data corresponding to two levels indicating dot on / off. The binary image data of each ink after the halftone process is stored in the halftone image storage buffer 207 in S405. For example, a known error diffusion method is used as the halftone process in the present embodiment. However, the halftone processing applicable to this embodiment is not limited to the error diffusion method, and binarization may be performed by threshold processing using a dither matrix, for example. Further, a process for giving some complementary relationship or correlation between the binary image data of each ink may be performed.

  In the present embodiment, the multi-value data of each color is calculated so that the ink adhesion amount for each pixel is constant in all pixels in the image in S403, but halftone processing is performed on this. Therefore, although the ink adhesion amount for each pixel in the output image is not constant, the average ink adhesion amount in units of a predetermined peripheral region is kept uniform throughout the entire image.

  In S406, the binary image data after halftone processing stored in the halftone image storage buffer 207 is output from the output terminal 208 in an arbitrary size such as the entire image or the bandwidth of the unit recording area, and is input from the input terminal 301. Input to printer 3. In S407, the printer 3 forms an image based on the binary image data after the halftone process. That is, the ink color and discharge amount selection unit 307 selects an ink color and discharge amount that match the binary image data, and starts the printing operation. In this printing operation, the recording head 302 scans the recording medium 303 from left to right (main scanning), and drives each nozzle at a constant driving interval to record an image on the recording medium. By repeating such main scanning on the recording medium at a timing when the recording medium 303 is conveyed by a predetermined amount in the sub-scanning direction, recording is performed on the entire area of the image.

  Thus, a series of image forming processes for multi-tone color input image data is completed. In the printed matter formed by the above processing, uneven gloss is reduced by controlling the ink adhesion amount to be constant throughout the entire image, and the generation of interference colors resulting from the use of clear ink is suppressed. Is done.

Clear ink placement amount setting process The clear ink placement amount setting process in S403 will be described in detail below. As described above, in the present embodiment, based on the clear ink total ejection amount CL, the ejection amount ratio of each of the two types of clear ink is controlled so that the total amount is maintained at CL and the ejection amount ratio is random. Specifically, a random number is generated for each pixel, and based on the random number, the total amount CL of the clear ink is distributed to the amounts CL1 and CL2 of the clear ink. In this embodiment, an example in which the amount of two types of clear ink is changed based on a random number is shown, but any method can be used as long as the amount of two types of clear ink can be changed randomly. Also good.

  Of the two types of clear ink at the coordinates (i, j) in the image, one clear ink placement amount is CL1 (i, j), and the other clear ink placement amount is CL2 (i, j). In this case, CL1 (i, j) and CL2 (i, j) are respectively set by the following equations using a random number Rnd (i, j) of 0 or more and 1 or less generated for each pixel.

CL1 (i, j) = CL (i, j) × Rnd (i, j) (2)
CL2 (i, j) = CL (i, j) × (1−Rnd (i, j)) (3)
By setting CL1 and CL2 in this way, it is possible to randomly change the values of CL1 and CL2 for each pixel. Note that the relationship expressed by the following equation always holds between CL1 and CL2.

CL1 (i, j) + CL2 (i, j) = CL (i, j) (4)
In this embodiment, the random number Rnd (i, j) generated for each pixel is a uniform random number that is not correlated or related to the value generated in the adjacent pixel, or a pseudo-random number that can be regarded as a uniform random number. Suppose that Further, for example, the spatial frequency characteristic between random numbers generated in adjacent pixels may be a random number having a so-called blue noise characteristic in which a power spectrum is small in a low frequency region and a power spectrum is large in a high frequency region. Any method may be used as a method for generating a random number having such a blue noise characteristic. For example, a known polar alternating random number can be used to generate a random number.

  Here, the clear ink placement amount setting process in the clear ink placement amount setting unit 205 will be described in detail with reference to FIG. FIG. 6 shows an example in which the clear ink placement amount is set for a one-dimensional signal consisting of 10 points in the image. Note that, when the present invention is applied to actual image formation, settings are made for a planar image, that is, a two-dimensional signal, but for the sake of simplicity of explanation, the description will be made using a one-dimensional signal. In the setting example shown in FIG. 6, 10 points are indicated by coordinates i (i = 1 to an integer of 1 to 10), and the clear ink total shot amount CL is set to 128 for each of the 10 points, and CL1 and CL2 at each point Are set to 128 in total. First, 601 is a random number generated at each point, that is, at each coordinate. In the present embodiment, the random number indicates a ratio of the amount of clear ink to be applied. Reference numeral 602 denotes the result of calculating CL1 (i, j) of each pixel according to the above equation (2). For example, since the generated random number is 0.90 at the point where the coordinate i = 1, the ratio of 0.90 out of the total driving amount 128, that is, 115 is set as CL1. Similarly, 603 is the result of calculating CL2 (i, j) of each pixel according to the above equation (3), and CL2 is 13 at the point where the coordinate i = 1. As a result, the sum (115 + 13) of CL1 and CL2 for the point at the coordinate i = 1 becomes equal to the total amount (128) of clear ink. In FIG. 6, the sum of CL1 and CL2 at each coordinate is shown at 604, but the value is equal to 128 which is the total driving amount CL at all coordinates.

  In this way, when setting the amount of each clear ink to be applied, the random amount generated for each pixel can be used, so that the ratio of the amount of clear ink to be applied can be changed randomly for each pixel. Although FIG. 6 shows an example in which the total amount CL of clear ink for 10 points is uniform, for example, when the color ink and the clear ink are overlapped, the total amount CL of clear ink is naturally applied to the entire image. It is not uniform. In this embodiment, a random ink is used to set the ratio of the amount of clear ink to be random regardless of the total amount CL of clear ink.

Effect of Clear Ink Amount Control As described above, in the present embodiment, the total amount of the two types of clear ink having different refractive indexes is maintained at the total clear ink amount CL determined by the color separation processing unit 203. On the other hand, the ratio of the amount of clear ink applied is changed for each pixel. Hereinafter, effects obtained by randomly changing the ratio of the amount of clear ink applied to each pixel in this manner will be described in detail.

  First, as shown in FIG. 1, an image is generated by light 1003 reflected from the surface of the color material layer 1001 and light 1004 reflected from the surface of the recording medium 1002 after passing through the color material layer 1001 and emitted from the color material layer 1001. An interference color different from the original color is generated. This interference color is due to a phenomenon in which reflected light is colored due to interference occurring at a specific wavelength due to a phase shift of light based on the optical path length difference between the two lights. Therefore, the wavelength at which interference occurs changes according to the optical path length difference between the two lights, and the color as the interference color also changes.

  FIG. 7 shows the change in interference color when the thickness of the color material layer changes. FIG. 7 shows a case where the thickness of the color material layer 1001 is changed from 100 to 300 nm at intervals of 20 nm when the refractive index of the air layer is 1, the refractive index of the color material layer 1001 is 1.5, and the incident angle is 45 degrees. The chromaticity of the interference color is plotted on the a * b * plane in CIEL * a * b * space. As can be seen from FIG. 7, when the optical path length difference changes due to the change in the thickness of the color material layer 1001, the interference color that is generated changes variously. In particular, the fact that the locus of interference color change is obtained as a circle on the a * b * plane means that interference colors of all colors have occurred.

  FIG. 12 shows a schematic diagram formed on the recording medium 1002 so that the two types of clear inks 1201 and 1202 overlap at different rates for each pixel and the total thickness is the same according to this embodiment. . Since the two types of clear inks 1201 and 1202 used in this embodiment have different refractive indexes, when they are formed to overlap each other, there is interface reflection in which a part of incident light is reflected at the boundary surface. Occur. Then, the reflected light on the surface of the upper clear ink 1202 and the light reflected and emitted from the boundary surface between the upper clear ink 1201 and the lower clear ink 1202 interfere with the light incident on the image, thereby causing interference. Color is generated. At this time, since the optical path length difference is determined by the thickness of the clear ink 1202 recorded on the upper layer, the color of the generated interference color is also determined by the thickness of the clear ink 1202. Since the amount of each of the clear inks 1201 and 1202 in the present embodiment varies depending on the pixel, the thickness of the clear ink 1202 is random for each pixel, that is, the optical path length difference is random for each pixel. Therefore, as described with reference to FIG. 7, various interference colors are generated according to the optical path length difference.

  Although not shown in FIG. 12, the light that is not interface-reflected between the clear inks 1201 and 1202 is transmitted through the clear ink 1202 and reflected at the lowermost surface, and is further transmitted through the clear ink 1201 and emitted. To do. The optical path length at that time is calculated as the sum of the values obtained by multiplying the refractive index by the thickness for each of the clear inks 1201 and 1202. Therefore, when the amount of clear ink 1201 and 1202 is randomly changed for each pixel, the optical path length of the reflected light transmitted through the clear ink 1201 is also random for each pixel, and various interference colors are generated. .

  FIG. 12 shows an example in which the total ejection amount of the clear inks 1201 and 1202 for each pixel is uniform, but in this embodiment, as described above, each clear ink is independent of the total ejection amount CL of the clear ink. Is set to be random. Thus, for example, even when the total amount of clear ink applied varies from pixel to pixel in a region where the clear ink is superimposed on the color ink, the reflected light from the top surface, the boundary surface, and the bottom surface of the two types of clear ink As a result, the optical path length difference is random for each pixel. Therefore, various interference colors are also generated in this region.

  By the way, in general, the human eye cannot discriminate the color change of one dot size of the printer, and actually perceives an average color of a plurality of dots. Therefore, when interference colors of various colors are generated for each pixel as described with reference to FIG. 12, the user's eyes perceive white as the average color of the various colors. Therefore, in this embodiment, by performing image formation in which the ratio of the two types of clear ink placement is controlled to be random for each pixel, coloring of specular reflection light due to generation of interference light is reduced as a result. .

  Note that changing the thickness of the ink layer for each pixel can be realized by changing the amount of ink applied for each pixel even when only one type of clear ink is used, for example. However, if the amount of only one type of clear ink applied is changed for each pixel, the ink adhesion amount cannot be kept constant over the entire recording area, and hence uneven glossiness cannot be reduced. End up. Therefore, in the present embodiment, the clear ink placement amount for each pixel, which is necessary for making the ink adhesion amount constant throughout the entire image, is determined as the total placement amount of two types of clear ink, and the clear ink placement amount for each clear ink is determined by the pixel. Control to change the driving amount ratio. As a result, according to the present embodiment, it is possible to further suppress interference colors while suppressing uneven gloss due to the use of pigment ink.

  Note that, as described above, halftone processing is performed on multi-value data indicating the amount of each clear ink shot calculated in the present embodiment. Therefore, although the ink adhesion amount for each pixel in the output image is not constant, the average ink adhesion amount in units of a predetermined peripheral area is kept uniform throughout the entire image. An inhibitory effect is obtained. Similarly, each set amount for each clear ink is binarized. However, since the ratio is random throughout the entire image, the occurrence of interference colors is also suppressed.

Clear ink composition Here, the clear ink used in the present embodiment will be specifically described. The two types of clear ink used in the present embodiment are characterized in that their refractive indexes are different from each other. FIG. 13 shows the composition of the solvent common to the two types of clear ink in this embodiment. As shown in FIG. 14, an aqueous resin solution obtained by neutralizing each of two types of polymers (Polymers A and B) having different compositions with an alkali (such as an aqueous potassium hydroxide solution) is added to the solvent. By this operation, a clear ink having a relatively high refractive index and no color material is produced for the polymer A, and a clear ink having a relatively low refractive index and no color material for the polymer B. Is created. The polymer A or B may contain a small amount of, for example, general carbon black as a coloring material to form a thin gray ink. In this case, the content ratio of the color material may be set to a content ratio of 0.2% or less for the thin gray ink, for example, when the black ink contains 3.5% of carbon black. When used as a light gray ink, it is used in the same manner as a light ink in a printer equipped with a well-known dark and light ink of the same hue. Further, the content ratio of the color material for the light gray ink is not limited to this value, and may be a content ratio that does not make the background color turbid when the gray ink is printed on the background. The increase / decrease amount of the color material such as carbon black is adjusted by increasing / decreasing pure water.

As described above, according to the present embodiment, when an image is formed using a color ink including a pigment color material and a plurality of clear inks having different refractive indexes, the amount of all ink adhered is almost uniform over the entire image. In addition, control is performed so that the ratio of the amount of clear ink applied becomes random. As a result, it is possible to further suppress the interference color generated by using the clear ink without reducing the effects obtained by using the clear ink, such as reducing uneven gloss caused by using the pigment ink. <Second Embodiment>
Hereinafter, a second embodiment according to the present invention will be described. In the first embodiment described above, a method has been described in which random numbers are generated for each pixel, and the ratio of the amount of each of the plurality of clear inks is determined. The second embodiment shows an example in which a map of a predetermined size in which a shot amount ratio based on a random number is two-dimensionally arranged is stored in a memory in advance, and a shot ratio for a pixel position in an image is read from the memory. Hereinafter, the second embodiment will be described on the assumption that two types of clear ink are used as the plurality of clear inks having different refractive indexes.

  FIG. 8 shows a configuration example of the image forming system in the second embodiment. In FIG. 8, the same components as those in FIG. 2 in the first embodiment described above are denoted by the same reference numerals and description thereof is omitted. In other words, the second embodiment is characterized in that a two-dimensional hit amount ratio storage unit 801 that can be referred to from the clear ink hit amount setting unit 205 is provided.

2D Imprint Amount Ratio Hereinafter, only processing in the two-dimensional impact amount ratio storage unit 801 and the clear ink impact amount setting unit 205 will be described. First, in the two-dimensional driving amount ratio storage unit 801, real values that are two-dimensionally arranged in a total of W × H, which is W in the horizontal direction and H in the vertical direction, are stored in advance as a driving amount ratio map. Keep it. FIG. 9 shows an example of a driving amount ratio map stored in the two-dimensional driving amount ratio storage unit 801. The driving amount ratio map composed of W × H real values corresponds to W × H pixel regions. Here, the two-dimensional real value recorded as the driving amount ratio is a two-dimensional random number indicating the driving amount ratio of the clear ink as in the first embodiment, and each of the values is a value of 0 or more and 1 or less. Shall be taken. However, the storage format of the shot amount ratio does not necessarily need to be a real number of 0 or more and 1 or less. May be stored as an 8-bit integer value. In that case, when using the shot ratio in the clear ink shot amount setting unit 205 described later, each shot ratio can be divided by 255 to be used as a real value between 0 and 1. Further, the real value held as the driving amount ratio map does not necessarily need to be based on a random number, and any real value may be arranged in an arbitrary pattern.

  The two-dimensional random number used as the implantation amount ratio map may be a uniform random number having no correlation between adjacent random numbers or a pseudo-random number that can be regarded as a uniform random number, as in the first embodiment described above. For example, a random number having a blue noise characteristic. At this time, not only the spatial frequency characteristic of the two-dimensional implantation amount ratio of W × H becomes the blue noise characteristic, but also when the two-dimensional implantation amount ratio is periodically arranged in a tile shape, the spatial frequency characteristic is It is desirable to have blue noise characteristics.

Clear ink placement amount setting Next, clear ink placement amount setting processing in the second embodiment will be described. The clear ink placement amount setting unit 205 determines the placement amounts CL1 and CL2 of the two types of clear ink from the clear ink total placement amount CL determined by the color separation processing unit 203. In the second embodiment, CL1 and CL2 are determined using a driving amount ratio map stored in the two-dimensional driving amount ratio storage unit 801.

  The clear ink placement amount setting unit 205 first obtains a placement rate corresponding to the position (coordinates) of the target pixel to be processed in the image from the two-dimensional placement amount ratio storage unit 801. When the coordinates of the pixel of interest are (i, j), out of the shot amount ratios stored in the two-dimensional shot amount ratio storage unit 801, coordinates calculated by the following formulas (5) and (6) (n, The implantation amount ratio R (n, m) stored in m) is acquired. In equations (5) and (6), “%” represents the remainder operation, that is, “a% b” represents “the remainder obtained when a is divided by b to make the quotient an integer”. To do.

n ＝ i ％ W ・ ・ ・ (5)
m = j% H (6)
Subsequently, from the clear ink total driving amount CL (i, j) at the coordinates (i, j), the respective driving amounts CL1 (i, j) and CL2 (i, j) of the two types of clear ink are expressed by the following formulas: Calculate according to (7) and (8).

CL1 (i, j) = CL (i, j) × R (n, m) (7)
CL2 (i, j) = CL (i, j) × (1−R (n, m)) (8)
Thus, the clear ink placement amount setting process in the second embodiment is completed. Since the subsequent processing is the same as that of the first embodiment described above, description thereof is omitted.

  As described above, according to the second embodiment, a two-dimensional shot amount ratio map for a plurality of clear inks is created in advance, so that a random number is not generated for each pixel, as in the first embodiment. It is possible to suppress the generation of interference colors.

<Third Embodiment>
The third embodiment according to the present invention will be described below. In the first embodiment described above, an example using two types of clear inks having different refractive indexes has been shown. However, in the third embodiment, an example using three or more types of clear inks is shown.

  Since the configuration of the image forming system in the third embodiment is the same as that of FIG. 2 in the first embodiment described above, description thereof is omitted. However, the operation of the clear ink placement amount setting unit 205 and the configuration of the recording head 302 are different from those of the first embodiment, and the characteristic operations of the third embodiment will be described below.

  First, FIG. 10 shows a configuration example of the recording head 302 in the third embodiment. The recording head 302 according to the third embodiment is assumed to be equipped with three types of clear inks (CL1, CL2, CL3) having different refractive indexes in addition to the four color inks of CMYK.

Clear ink placement amount setting Next, clear ink placement amount setting processing in the third embodiment will be described. The clear ink placement amount setting unit 205 determines the placement amounts CL1, CL2, and CL3 of each of the three types of clear ink from the clear ink total placement amount CL determined by the color separation processing unit 203. At this time, while the sum of the three types of clear ink is always kept at CL, the ratio of the amount of clear ink applied is changed according to the coordinates in the image. Therefore, in the third embodiment, a random number is generated for each pixel, and the three types of clear ink ejection amounts are determined based on the random number. In the third embodiment, an example in which the amount of three types of clear ink applied is changed based on a random number is shown. It may be used.

  Hereinafter, the total amount of clear ink applied CL (i, j) at the coordinates (i, j) indicating the pixel position in the image, CL3 (i, j), CL2 ( i, j) and CL3 (i, j). First, a random number Rnd1 (i, j) is generated in which the minimum value is 0 and the maximum value is RNDMAX1 expressed by the following equation (9).

RNDMAX1 = 2/3 (9)
Then, CL1 (i, j) is calculated from the following equation (10) using the random number Rnd1 (i, j).

CL1 (i, j) = CL (i, j) × Rnd1 (i, j) (10)
Next, in order to set CL2 (i, j) and CL3 (i, j), a random number Rnd2 (i, j) is further generated. The random number Rnd2 (i, j) is a random number whose minimum value is 0 and whose maximum value is RNDMAX2 (i, j) represented by the following equation (11).

RNDMAX2 (i, j) = 1−Rnd1 (i, j) (11)
Then, using Rnd2 (i, j), CL2 (i, j) is calculated from the following expression (12), and CL3 (i, j) is calculated from the expression (13).

CL2 (i, j) = (CL (i, j) −CL1 (i, j)) × Rnd2 (i, j) (12)
CL3 (i, j) = (CL (i, j) −CL1 (i, j)) × (1−Rnd2 (i, j)) (13)
As described above, the driving amount of each of the three types of clear ink in the third embodiment is determined.

  Here, the clear ink placement amount setting process in the third embodiment will be described in detail with reference to FIG. FIG. 11 shows an example in which the clear ink placement amount is set for a one-dimensional signal composed of 10 points in the image. When the present invention is applied to actual image formation, settings are made for a planar image, that is, a two-dimensional signal. However, for the sake of simplicity of explanation, the description will be made using a one-dimensional signal. In the setting example shown in FIG. 11, 10 points are indicated by coordinates i (i = 1 to an integer of 1 to 10), and the clear ink total shot amount CL is set to 128 for each of the 10 points, and CL1 and CL2 at each point. , CL3 is set so that the total is 128. First, 1101 and 1102 are random numbers Rnd1 and Rnd2 generated at each point, that is, at each coordinate. 1103 is a result of calculating CL1 (i, j) of each pixel according to the above equation (10), and similarly, 1104, 1105 is calculated according to the above equations (12), (13) CL2 (i, j), CL3 (i, j). Reference numeral 1106 indicates the total sum of CL1, CL2, and CL2 at each coordinate. The value is equal to 128, which is the total driving amount, at all coordinates.

  In this way, by setting the ejection amount of each of the three or more types of clear ink using different random numbers, it is possible to randomly change the ejection amount ratio of each clear ink for each pixel.

  Note that the driving amount determination method according to the third embodiment can be generalized when the number of clear inks is N. The n-th (1 ≦ n ≦ N−1) clear ink is applied using a random number Rndn (i, j) where the minimum value is 0 and the maximum value is RNDMAXn expressed by the following equation (14). It can be determined from the following equation (15).

RNDMAXn = 2 × (1−Σ (1 ≦ m ≦ n) Rndn (i, j)) / (N−n + 1) (14)
CLn (i, j) = (CL (i, j) −Σ (1 ≦ m ≦ n) CLm (i, j)) × Rndn (i, j) (15)
Further, the final Nth clear ink placement amount CLN (i, j) is calculated by the following equation (16).

CLN (i, j) = CL (i, j) −Σ (1 ≦ m ≦ N-1) CLm (i, j) (16)
As described above, it is possible to randomly change the ejection ratio of each clear ink for each pixel by determining the ejection amount of each of N types of clear inks having different refractive indexes. Further, the sum of all the clear ink placement amounts is always equal to the clear ink total placement amount CL set by the color separation processing unit 203. However, as the number of clear inks used increases, the effect of reducing the coloring of interference colors can be obtained. However, the number of clear inks to be used may be determined in consideration of the balance with the load of the configuration.

  As described above, according to the third embodiment, even when three or more types of clear ink are mounted, the clear ink is set for each pixel while maintaining the total amount of clear ink set in the color separation process. It is possible to change the driving amount ratio. As a result, it is possible to further suppress the interference color generated by using the clear ink without reducing the effects obtained by using the clear ink, such as reducing uneven gloss caused by using the pigment ink. .

  Note that the first to third embodiments described above are not necessarily applied to the entire formed image, and may be applied only to, for example, gradations in which interference colors are conspicuous. Furthermore, each embodiment may be applied only to an ink layer of a specific color in which interference colors are likely to occur, such as yellow ink.

  In the first to third embodiments described above, an example in which the ratio of the amount of clear ink applied is random for each pixel has been described. However, it is not always necessary to change the clear ink ejection amount ratio for each pixel, and it may be changed for each region of a predetermined size including a plurality of pixels. In this case, for example, based on the color separation results for each pixel, the total amount of clear ink to be applied is determined for each region, and one random number is assigned to each region, so that the ratio of the amount of clear ink to be applied is determined for each region. Just do it. However, it is necessary to set the size of the region so small that the color cannot be identified by human eyes. For example, it is possible to obtain the same effect as in the case of controlling each pixel by setting the ratio of the amount of clear ink to be applied using a common random number within a region composed of 4 pixels of 2 horizontal pixels × 2 vertical pixels. it can.

  The present invention can also be realized by executing the following processing. That is, software (program) that realizes the functions of the above-described embodiments is supplied to a system or apparatus via a network or various storage media, and a computer (or CPU, MPU, or the like) of the system or apparatus reads the program. It is a process to be executed.

Claims (7)

An image forming apparatus that forms an image using a plurality of colored inks including a pigment coloring material and a plurality of kinds of colorless inks having different refractive indexes.
Colorless ink obtained by performing color separation processing on the input color image data and summing up the amount of colored ink applied for each color of the colored ink and the amount of applied ink for each of the colorless ink for each pixel of the color image data Color separation means for setting a total shot amount so that the sum of the colored ink shot amount and the colorless ink total shot amount for each color is constant in all pixels of the color image data;
An amount setting unit that sets the amount of colorless ink applied so that the ratio of the amount of colorless ink applied for each of the plurality of types of colorless ink in the total amount of colorless ink is random for each pixel;
For each pixel of the color image data, for each color of the plurality of colored inks, recording is performed with the colored ink ejection amount set by the color separation means, and for each of the plurality of types of colorless ink, the ejection amount is performed. An image forming apparatus comprising: an image forming unit that forms a color image on a recording medium by performing recording with the colorless ink driving amount set by a setting unit.   The hit amount setting means generates a random number for each pixel of the color image data, and uses the random number to calculate a ratio of the colorless ink hit amount for each of the plurality of types of colorless ink in the colorless ink total hit amount. The image forming apparatus according to claim 1, wherein the image forming apparatus is determined. Furthermore, it has a driving amount ratio storage means for storing a two-dimensional array of driving amount ratios set at random for each pixel in advance,
The driving amount setting unit acquires a driving amount ratio corresponding to the pixel from the two-dimensional array stored in the driving amount ratio storage unit, and uses the acquired driving amount ratio, the plurality of types of colorless inks. The image forming apparatus according to claim 1, wherein a colorless ink driving amount is set for each of them. The color separation means takes the color image data as input, and outputs data indicating the total amount of colored ink applied for each color of the colored ink and the total amount of ink applied for the colorless ink. using the table, the image forming apparatus according to any one of claims 1 to 3, characterized in that the color separation process. And a halftone processing unit for performing a halftone process on the colored ink driving amount set by the color separation unit and the colorless ink driving amount set by the driving amount setting unit,
Said image forming means, said the halftone processing in the halftone processing unit, according to any one of claims 1 to 4, characterized in that the recording by the color ink ejection amount and the colorless ink applying amount Image forming apparatus. An image forming apparatus that includes a color separation unit, a driving amount setting unit, and an image forming unit, and performs image formation using a plurality of colored inks including a pigment color material and a plurality of types of colorless inks having different refractive indexes. A control method,
The color separation means performs a color separation process on the input color image data, and for each pixel of the color image data, the amount of colored ink applied for each color of the colored ink and the ink applied for each of the colorless ink A color separation step for setting a total amount of colorless ink that is a sum of the amounts, so that the sum of the amount of colored ink and the amount of colorless ink that is applied for each color is constant for all pixels of the color image data;
The hit amount setting unit sets the respective colorless ink hit amounts so that the ratio of the colorless ink hit amount for each of the plurality of types of colorless ink in the colorless ink total hit amount is random for each pixel. A driving amount setting step;
The image forming means records, for each pixel of the color image data, for each color of the plurality of colored inks according to the amount of colored ink applied set by the color separation means, and the plurality of types of colorless inks. A control method comprising: an image forming step of forming a color image on a recording medium by performing recording with the colorless ink driving amount set by the driving amount setting means for each of them. A program for causing a computer to execute the control method according to claim 6 .

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