JP5634167B2 - Image forming apparatus and image forming method - Google Patents

Description

  The present invention relates to a method for controlling coloring and gloss of specularly reflected light of a sample in an image forming method in a printing apparatus.

  In recent years, so-called photographic printing processing in which an image is recorded on photographic glossy paper in an ink jet recording apparatus has become widespread. As inks used in this photographic printing process, dye inks using dyes that are easily dissolved in water as color materials are widely used. In the dye ink, the color material dissolved in the solvent easily penetrates into the inside of the fiber of the recording medium. Accordingly, since the surface shape of the recording medium is easily maintained even after image recording, the gloss of the recording medium itself is maintained as the gloss of the recorded image. That is, if recording with a dye ink is performed on a recording medium having excellent gloss, a recorded image having excellent gloss can be obtained. Therefore, in the ink jet recording apparatus using the dye ink, it is possible to realize the glossiness to the image by improving the gloss of the recording medium itself.

  On the other hand, there is an increasing demand for improved light resistance and water resistance of printed materials (hereinafter referred to as samples). The above-described dye ink is generally known to have low light resistance, and the dye molecules of the color material are easily decomposed by light, so that the recorded image is faded. Samples printed with dye ink are generally known to have low water resistance, and when wetted with water, dye molecules that have penetrated into the fiber dissolve in water, and bleeding tends to occur in a recorded image.

  In recent years, in order to solve the light resistance and water resistance problems generated in dye inks, the use of pigment inks using pigments as coloring materials has increased. The coloring material of the pigment ink is present in the solvent as particles having a size of several tens of nanometers to several microns, unlike the dye in which it exists as a molecule. In general, since pigment ink has a larger color material particle size than dye ink, it is known that pigment ink can provide a sample having higher light resistance than dye ink.

  However, when recording is performed using pigment ink, unlike the case where recording is performed using dye ink, pigment ink tends to be deposited on the surface of the recording medium. For this reason, the surface area is rough in an image region where a large amount of pigment ink is recorded, and irregular reflection of light tends to occur on the image surface. As a result, the gloss of the image, in particular, the image clarity (corresponding to “image definition” described in JIS K 7150) is lowered, and the image is easily recognized as an undesirable image in photographic printing.

  In an ink jet recording apparatus using pigment ink, since the ink recording amount differs depending on the color and gradation to be reproduced, the structure and material of the surface of the sample are different. Then, since the surface shape is different for each color or gradation as described above, uneven glossiness occurs, and different glossiness is observed depending on the position of the image, which gives the image observer a sense of incongruity.

  Decreasing the image clarity of a printed image is not a problem limited to an inkjet recording apparatus using pigment ink, but a similar problem occurs in an electrophotographic recording apparatus in which recording is performed by fixing toner on a recording medium. . It is known that the image clarity in the electrophotographic system changes depending on the toner recording amount, fixing temperature, fixing speed, and the like.

  Further, in addition to the above-described problem of lowering of image clarity, a recording apparatus that performs recording on a recording medium with ink and toner has the following problems.

  Depending on the type of ink or toner used, a so-called bronze phenomenon may occur in which reflection with wavelength dispersion occurs due to the characteristics of the material exposed on the surface of the sample. When the bronze phenomenon occurs, specularly reflected light from the sample (and light diffused in the vicinity of the specular reflection) is colored. When the bronze phenomenon occurs, the color of the illumination image reflected on the sample is observed as a color different from the original color of the illumination, and is often recognized as an unfavorable image in photographic printing.

  In a recording apparatus that forms an image with pigment ink or toner, the structure and material of the surface of the sample differ depending on the color and gradation to be reproduced. The bronze phenomenon depends on the material of the surface of the sample, and the degree of occurrence varies depending on the structure of the surface. This surface structure is, for example, the coverage of ink that occupies the surface of the recording medium. That is, in a sample composed of a structure or material having a different surface for each color or gradation, the color of the regular reflection color differs for each color or gradation. In such a sample, the specular reflection color of the image area composed of a plurality of colors is observed as a different color depending on the position of the image, which makes the viewer feel uncomfortable.

  In order to solve the above-described problems, various techniques have been proposed. For example, a technique for recording clear ink or white ink in an area where colored ink is not recorded, or a technique for overcoating clear ink over the entire recording area is disclosed in order to suppress a decrease in glossiness (for example, , See Patent Document 1). Furthermore, in order to suppress the bronze phenomenon, a technique of overcoating yellow ink on an image is disclosed (for example, see Patent Document 2).

JP 2003-132350 A JP 2004-181688 A

  However, the above conventional techniques have the following problems. First, according to the technique described in Patent Document 1 described above, by recording clear ink or white ink in an area where colored ink is not recorded, the specular gloss (described in JIS Z 8741) is changed to color or gradation. Regardless of this, there is an effect of making uniform. However, this technique has a low effect of suppressing the image clarity deterioration, and furthermore, since the colored ink in which the bronze phenomenon occurs is exposed, the bronze suppression effect cannot be expected. In addition, when clear ink is overcoated over the entire recording area, although there is an effect of suppressing the bronze phenomenon, surface irregularities are likely to occur due to the deposition of the clear ink, resulting in a decrease in image clarity as a result. .

  Also, according to the technique described in Patent Document 2, for example, when reproducing cyan, it is necessary to use yellow ink, and recording is performed by mixing ink colors that should not be necessary for original color reproduction. Therefore, there is a problem that the saturation is lowered.

  In view of the above, an object of the present invention is to suppress coloring of specularly reflected light in an image formed using colored ink containing a pigment coloring material as much as possible.

  As a means for achieving the above object, an image forming apparatus of the present invention comprises the following arrangement.

  That is, at least two kinds of colorless inks including a plurality of colored inks including a pigment coloring material, a first colorless ink, and a second colorless ink having a higher permeability to the colored ink than the first colorless ink. An image forming apparatus that forms an image using an image, and acquires ink values for the colored ink and the first and second colorless inks for each pixel of an input image by color separation processing using a color separation table. An image that forms a color image on a recording medium by performing color separation using the ink values of the colored ink obtained by the color separation unit and the first and second colorless inks for each pixel. And the color separation table includes a colored ink containing a color material that is likely to be colored in the regular reflection light as the suppression target ink. The ink value of the first colorless ink is set to increase as the value increases, and the ink value of the second colorless ink increases as the ink value of the colored ink other than the suppression target ink increases. It is characterized by being set to.

  According to the present invention, in an image formed using colored ink containing a pigment color material, it is possible to suppress coloring of regular reflection light while suppressing a reduction in gloss as much as possible.

FIG. 2 is a block diagram showing the configuration of the image forming apparatus according to the first embodiment. FIG. 2 is a block diagram showing a configuration for creating a color separation LUT in the first embodiment; A flowchart showing color separation LUT generation processing; A diagram explaining how to create bronze information, The figure which shows the example of the bronze value in each colored ink, A conceptual diagram showing a cross-sectional structure when colorless ink is recorded on colored ink, Conceptual diagram showing the angle dependence of the reflected light intensity from the sample, A graph showing the gloss characteristics of each of the cases where the colorless ink is not recorded, the first colorless ink is recorded, and the second colorless ink is recorded; A graph showing each ink value and total recording amount according to the input signal value, total ink amount that can be recorded on the recording medium, The block diagram which shows the detailed structure of the halftone process part 104 in 2nd Embodiment, A diagram showing an example dot arrangement pattern, The figure which shows the mask pattern example of C ink, Conceptual diagram of a recording head in an inkjet printer, The figure which shows the mask pattern example of Y ink, The figure which shows the dot arrangement pattern example of each ink, Schematic diagram showing a cross section when colored ink is superimposed on the recording medium, Schematic diagram showing a cross section when colored ink and colorless ink overlap on the recording medium, The figure which shows the mask pattern example of the colorless ink produced in 2nd Embodiment, The figure which shows the mask pattern example of the colorless ink in 3rd Embodiment. The figure which shows the example which switches a mask pattern according to an input signal value, It is a figure which shows the example of a composition about two types of colorless ink in this invention.

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

<First Embodiment>
In the present embodiment, a plurality of types of colorless ink containing a colorless and transparent pigment material and having different permeability to the colored ink are superimposed on an image formed by a plurality of colored inks including a pigment color material. An example in which coloring of specular reflection light and reduction in gloss of an image are suppressed will be described. Hereinafter, the case where two types of colorless ink are used will be described as an example.

Colorless ink composition The two types of colorless inks (first and second colorless inks) used in the present embodiment will be specifically described. The two types of colorless inks used in the present embodiment are characterized in that their permeability is different from each other. FIG. 21A shows the composition of the solvent shared by the two types of colorless ink in this embodiment. Resin 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) as shown in FIG. Add aqueous solution. By this operation, a colorless ink having a relatively high permeability to the polymer A (in other words, easily penetrating into the color material) and containing no color material is produced. Further, a colorless ink having a relatively low permeability to the polymer B (in other words, easily deposited on the surface of the color material) and containing no color material is produced. Hereinafter, the colorless ink based on the polymer B is referred to as a first colorless ink, and the colorless ink based on the polymer A is referred to as a second colorless ink.

  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.

System Configuration FIG. 1 is a block diagram showing a functional configuration of the image forming system in the present embodiment. In the image input unit 101, an image to be printed is input. Here, the image forming system of the present embodiment is configured by connecting a recording device such as an ink jet printer equipped with pigment ink and a host device such as a PC that controls the recording device through a predetermined interface. Is done. However, FIG. 1 shows only the functional configuration of the system, and there is no particular limitation on which apparatus side each function is included. Normally, a printer driver runs on the operating system (OS) of the host device, and the image input unit 101 is mounted as a user interface (UI) of the printer driver. The image input unit 101 may also be configured to execute a print command by referring to the printer driver from the application after editing or processing the image with an application different from the printer driver.

  The color matching processing unit 102 performs color matching processing on the image signal of the input image input from the image input unit 101 by using a color conversion table. Generally, the color reproduction range that can be reproduced by a display device such as a display is different from the color reproduction range that can be reproduced by a recording device such as a printer. Also, the color reproduction range that can be reproduced by the recording apparatus is different. Therefore, for example, the color matching processing unit 102 converts an RGB value that is an image signal of the input image into another RGB value corresponding to the recording apparatus. Note that if the resolution of the input image cannot be handled by the printer of the image output unit 105, the color matching processing unit 102 converts this to a predetermined resolution and then performs actual color matching processing.

  The color separation processing unit 103 refers to the color separation table (LUT) holding unit 106 for the input image (RGB value) after the color matching process, and sets each color material color mounted on the printer of the image output unit 105. Conversion to signal values (for example, CMYK values, hereinafter referred to as ink values) and colorless ink signal values is performed. Next, the halftone processing unit 104 converts the ink value obtained after color matching into the number of gradations (number of bits) that can be processed by the image output unit 105. Prior to this bit conversion processing, lightness conversion processing (γ correction processing) for improving the gradation of the image printed on the recording medium may be performed. The image data whose number of bits has been converted by the halftone processing unit 104 is printed on a recording medium by the printer in the image output unit 105 to form a color image.

Color Separation LUT Creation Processing In this embodiment, in the color separation LUT that shows the relationship between input signal values such as RGB values and each ink value of colored ink, the relationship between the input signal value and the ink value of colorless ink Is also retained. Therefore, the color separation processing unit 103 refers to the color separation LUT holding unit 106, and is converted into an ink value including colorless ink. The color separation LUT is created in the color separation processing unit 103 and stored in the color separation LUT holding unit 106. Hereinafter, a configuration for creating a color separation LUT in the color separation processing unit 103 is shown in FIG. 2, and the creation processing will be described in detail.

  In FIG. 2, a color separation LUT generation unit 201 generates a color separation LUT based on the bronze information of each ink stored in advance in the color material bronze information storage unit 202, and stores this in the color separation LUT holding unit 106. To do. Note that the color separation LUT holding unit 106 holds in advance a color separation LUT that holds the relationship between the input signal value and the ink value of the colored ink. That is, the color separation LUT generation unit 201 creates a color separation LUT for colorless ink indicating the relationship between the input signal value and the colorless ink value based on the color separation LUT of the colored ink, and stores this in the color separation LUT holding unit 106. Store. In order to simplify the description of the printer of this embodiment, an example is shown in which four basic colors of C (cyan), M (magenta), Y (yellow), and K (black) are used as colored ink. In recent printers, in addition to the four color inks of CMYK, light inks such as light cyan, light magenta, and gray, and special color inks such as red, orange, green, blue, and violet may be used. Even when the light ink or the special color ink is used in the printer, the present embodiment can be similarly applied.

  FIG. 3 shows a flowchart of the color separation LUT generation process. First, in step S301, the color material bronze information for each colored ink is acquired from the color material bronze information storage unit 202. In step S302, the color separation LUT for the colored ink is acquired from the color separation LUT holding unit 106. In step S303, the color separation LUT of the colorless ink is generated based on the color material bronze information acquired in step S301 and the color separation LUT of the colored ink acquired in step S302.

  The bronze information stored in the color material bronze information storage unit 202 acquired in S301 is created in advance in a control device (not shown). Hereinafter, the creation method will be described with reference to FIG. In FIG. 4, reference numeral 401 denotes a measurement sample, which is obtained by printing colored ink to be measured on a recording medium by a printer of the image output unit 105. The recording medium for the measurement sample is not particularly limited as long as the size of the bronze with dried colored ink can be measured, and any sheet-like medium such as an OHP sheet may be used. Further, as the measurement sample, it is sufficient that the surface of the sheet-like medium is coated with ink, so that the ink does not necessarily have to be recorded by the printer. More preferably, it is preferable to record a single color ink with a predetermined recording amount on a recording medium to be actually printed using the printer of the image output unit 105.

  The regular reflection light from the measurement sample 401 when the measurement sample 401 is irradiated from a predetermined angle by the light source 402 is detected by the light receiver 403. In the light receiver 403, the specularly reflected light is detected as tristimulus values XxYxZx in the CIE XYZ color system. The control unit holds in advance the tristimulus values XsYsZs of the sample in which bronze is not generated as a reference value. Then, the saturation C * of the CIE LCh color system is obtained from the detected value XxYxZx and the reference value XsYsZs, and this saturation C * is handled as an index value (hereinafter referred to as a bronze value) representing the size of bronze. Thus, when the bronze value for each color ink is acquired, this is stored in the color material bronze information storage unit 202 as color material bronze information.

  Note that a sample free from bronzing is a sample in which the color of specularly reflected light is substantially achromatic, such as a black polished glass plate having a small refractive index wavelength dispersion. The bronze value is not limited to C * as long as it is an index value indicating the size of the bronze. For example, the mean square error of the spectral characteristic Px (λ) of the specular reflection light from the sample to be evaluated is calculated based on the spectral characteristic Ps (λ) of the specular reflection light from the reference sample such as a black polished glass plate. This may be a bronze value. Furthermore, even if a reference sample is not used, values obtained by directly detecting the spectral characteristics of the light source itself may be used as the reference values XsYsZs and Ps (λ).

  As described above, in S302, the color separation LUT of the colored ink that is held in advance in the color separation LUT holding unit 106 is acquired.At this time, based on the color material bronze information of each color ink acquired in S301, Determine the colored ink that should be bronzed. Here, FIG. 5 shows an example of the color material bronze information, that is, the actually measured bronze value, for each CMYK ink obtained in S301. The bronze value in the figure indicates that the greater the value, the greater the occurrence of bronze. Reference numeral 501 is a threshold value set in advance for determining the bronze suppression target ink. When the bronze value exceeds the threshold value, it is determined that the ink has a large bronze value, and when it falls below the threshold value, it is determined that the ink has a small bronze value. In the example shown in FIG. 5, since only the bronze value of C ink exceeds the threshold value, in this case, it is determined that the ink that should suppress bronzing is only C ink. In S302, the color separation LUT is acquired for all the colored inks including the C ink that is the target of bronzing suppression. The color separation LUT for the color ink is a LUT created in advance for the color ink so as to improve image quality items other than gloss and bronze, such as a color reproduction range, graininess, and gradation.

Colorless LUT Creation Processing for Colorless Ink Hereinafter, the color separation LUT creation processing for colorless ink in S303 will be described in detail. Prior to describing the LUT creation process, each of the two types of colorless inks (first and second colorless inks) having different characteristics as described with reference to FIG. 21 is recorded on the colored ink. A characteristic phenomenon in this case will be described with reference to FIGS. In the image formation of the present embodiment, it is premised that, after recording with colored ink, recording is performed so that colorless inks overlap.

  FIG. 6A is a conceptual diagram showing a cross-sectional structure when the first colorless ink that is relatively easily deposited on the colored ink is recorded. A colored ink layer 602 is deposited on the recording medium 601, and a first colorless ink layer 603 is deposited thereon. Black circles in the figure indicate pigment particles of colored ink. As shown in FIG. 6A, the first colorless ink layer 603 is deposited on the colored ink layer 602 to form irregularities. In this example, since the surface of the colored ink having a large bronze is covered with the colorless ink having a small bronze, the bronze can be suppressed. However, the image irregularity formed on the image surface causes the irregular reflection of light, thereby reducing the image clarity of the printed image.

  FIG. 6B is a conceptual diagram showing a cross-sectional structure when the second colorless ink that is relatively easy to penetrate into the colored ink is recorded. A colored ink layer 702 is deposited on the recording medium 701, and the second colorless ink layer 703 penetrates into the colored ink layer 702. Similar to FIG. 6A, black circles in the figure indicate pigment particles of colored ink. As shown in FIG. 6 (b), the second colorless ink easily penetrates into the colored ink, so that surface irregularities are not easily formed. In this case, since the unevenness of the image surface is small as compared with the case of FIG. 6A, the irregular reflection of light on the image surface is small, and it is possible to suppress a reduction in the image clarity of the printed image. However, since it is difficult to coat all the pigment particles of the colored ink with the second colorless ink having high penetrability, bronzes of the pigment particles themselves remain.

  Here, FIG. 7 shows the angle-dependent characteristics of reflected light intensity, which is a cause of bronzing. In FIG. 7, reference numeral 801 denotes the angle-dependent characteristic of the reflected light intensity in the printed image shown in FIG. 6A, and 802 denotes the angle-dependent characteristic of the reflected light intensity in the printed image shown in FIG. It can be seen that the characteristic 801 spreads light in the vicinity of regular reflection as compared with the characteristic 802. As described above, this is because the image surface shown in FIG. 6A is more uneven than the image surface shown in FIG. 6B, and therefore irregular reflection of light on the image surface is likely to occur. As the spread of light in the vicinity of regular reflection is larger as in the characteristic 801, the image clarity is degraded.

  For example, FIG. 8A shows a case where no colorless ink is recorded on the image formed with C ink, a case where the first colorless ink is recorded (corresponding to FIG. 6A), and a second case. An example of each image clarity measurement result when colorless ink is recorded (corresponding to FIG. 6B) is shown. CL1 and CL2 in the figure indicate the first colorless ink and the second colorless ink, respectively. That is, C + CL1 in the figure corresponds to the characteristic 801 shown in FIG. 7, and C + CL2 similarly corresponds to the characteristic 802. According to FIG. 8A, when the first colorless ink is recorded on the colored ink as described in the characteristic 801 of FIG. 7, the colorless ink is not recorded or the second colorless ink is recorded. It can be seen that the image clarity is reduced as compared with the case of the above.

  Similarly, FIG. 8B shows the case where no colorless ink is recorded, the case where the first colorless ink is recorded (corresponding to FIG. 6A), and the second on the image formed with the C ink. When the colorless ink is recorded (corresponding to FIG. 6B), an example of each bronze value measurement result is shown. According to FIG. 8B, when the first colorless ink is recorded on the colored ink, the occurrence of bronzing is compared to the case where the colorless ink is not recorded or the second colorless ink is recorded. It can be seen that is suppressed.

  As described above with reference to FIGS. 6 to 8, the first colorless ink tends to suppress the occurrence of bronze, but tends to cause a decrease in image clarity. In addition, the second colorless ink is less likely to cause image clarity deterioration, but has an insufficient bronze suppression effect. Therefore, in this embodiment, after suppressing the occurrence of bronze, the recording amount of each colorless ink is appropriately adjusted according to the color to be reproduced so as to minimize degradation of image clarity. The colorless ink recording amount control in this embodiment will be described below with reference to FIG.

  FIG. 9A is a graph showing the recording amount (ink value) of colored ink according to the input signal value. Here, an RGB value is described as an example of the input signal value, but other color space signals such as a CMYK value may be used as long as they are color signals of an image, for example. FIG. 9A shows a change in gradation from yellow (R, G, B = 255, 255, 0) to cyan (0, 255, 255) passing through green (0, 255, 0). 1101 indicates the ink value of C ink, 1102 indicates the ink value of Y ink, and 1103 indicates the total recording amount (C + Y) of colored ink. That is, the ink values 1101 and 1102 for the C and Y inks shown in FIG. 9A correspond to the color separation results for the C and Y inks in the color separation LUT for the colored ink.

  As described above, in order to suppress the generation of bronze, it is desirable to record the first colorless ink on the colored ink that is likely to generate bronze. However, when the first colorless ink is used, the image clarity is deteriorated. Will occur. Therefore, in the present embodiment, control is performed so that recording with the second colorless ink is performed for the image area recorded with the colored ink with less bronzing.

  FIG. 9B is a graph showing the recording amount (ink value) of colorless ink set in this embodiment corresponding to the recording amount of colored ink shown in FIG. 9A. In FIG. 9B, 1201 is the ink value of the first colorless ink, 1202 is the ink value of the second colorless ink, and 1203 is the total recording amount of the colorless ink. According to FIGS. 9A and 9B, the first colorless ink is overlapped with the C ink, which is likely to generate bronze, and the second colorless ink is overlapped with the Y ink, which is less likely to generate bronze. You can see that it is recorded. That is, the ink values 1201 and 1202 of the first and second colorless inks shown in FIG. 9B are the color separation results for each colorless ink in the colorless ink color separation LUT. In other words, the color separation LUT of the colorless ink is set so that the ink value of the first colorless ink increases as the C ink value that is the bronzing suppression ink increases. In addition, the ink value of the second colorless ink is set so as to increase as the colored ink value other than the suppression target ink (in this case, the Y ink value) increases.

  The increase and decrease of the colorless ink values 1201 and 1202 shown in FIG. 9 (b) correspond to the increase and decrease of the colored ink values 1101 and 1102 shown in FIG. 9 (a), but they are not the same value and are proportional to each other. Is set to This is because the upper limit of the recordable ink amount is generally determined in advance on the recording medium. FIG. 9C shows a total recording amount 1103 of colored ink, a total recording amount 1203 of colorless ink, a total ink recording amount 1301 obtained by adding both, and an upper limit 1302 of the ink amount that can be recorded on the target recording medium. It was. That is, the colorless ink total recording amount 1203 in this embodiment is set so that the maximum value of the total ink recording amount 1301 does not exceed the ink amount upper limit 1302.

  In FIGS. 9A to 9C, the gradation from yellow to cyan passing through the green has been described as an example, but in the present embodiment, each colorless ink corresponding to each RGB value is similarly applied to other gradations. Determine the amount of recording. The recording amount of each colorless ink for each RGB value determined in this way is set as the color separation LUT for each colorless ink and stored in the color separation LUT holding unit 106. The color separation LUT for each colorless ink can be held as a LUT that is independent of the color separation LUT for the colored ink, but can be combined with the color separation LUT for the colored ink to form one LUT. It is desirable to hold as.

  It should be noted that, in order to determine the colorless ink recording amount for all input signal values, a considerable number of measured values are required, depending on the step size (number of bits) of the RGB values. Therefore, the colorless ink recording amount may be obtained between the primary colors, and the corresponding colorless ink recording amount may be calculated for other RGB values by a known interpolation process such as tetrahedral interpolation. The primary colors are, for example, red, green, blue, cyan, magenta, yellow, black, and white.

  As described above, according to the present embodiment, color separation for colorless ink is performed so as to appropriately adjust the recording amounts of the first and second colorless inks that overlap the colored ink according to the color to be reproduced. Create a LUT. By determining the recording amount of colorless ink using this color separation LUT, it is possible to minimize degradation of image clarity while suppressing the occurrence of bronzing, that is, the occurrence of coloring of specularly reflected light.

Second Embodiment
Hereinafter, a second embodiment according to the present invention will be described. In the first embodiment described above, a color separation LUT for appropriately adjusting the recording amounts of the first and second colorless inks according to the colors to be reproduced is created so as to achieve both bronze and image clarity. An example is shown. In the second embodiment, as a more suitable method for achieving both bronze and image clarity, a mask pattern for setting colorless ink to be recorded for each recording position is set according to the ink type present on the outermost surface of the formed image. An example of generation is shown.

Multi-pass printing method Prior to the description of the mask pattern generation process in the second embodiment, a multi-pass printing method in an ink jet printing printer will be described.

  The recording heads in the ink jet recording system include a line type and a serial type. The line type is a recording method in which only the recording medium is moved in the sub-scanning direction using a recording head corresponding to the print area width. In addition, the serial type sequentially forms an image on a recording medium by alternately repeating the main scanning and the sub scanning while ejecting ink from a recording head having a shorter width than the line type. is there. The recording main scan is to move and scan the carriage on which the recording head is mounted with respect to the recording medium, and one recording main scan is also referred to as one pass. Further, the sub-scan refers to conveying the recording medium by a predetermined amount in a direction orthogonal to the main recording scan. In this case, the width of the area to be recorded in one recording main scan is determined by the arrangement density and the number of the plurality of ink discharge ports (hereinafter referred to as “recording elements”) constituting the recording head. Therefore, the method of forming an image in the shortest time is to advance the recording by repeating the recording main scan for the width and the sub-scan corresponding to the width.

  However, when recording is performed on a certain area of the recording medium by only one recording scan, the ink recording position varies due to manufacturing errors of nozzles that eject ink, air currents due to recording main scanning of the recording head, and the like. Occurs and the image quality deteriorates. In addition, so-called “joining lines” such as density and color differences occur at the boundaries between the recording main scans. In practice, therefore, a multi-pass printing method is often employed to further improve image quality.

  In the multi-pass printing method, N times (N ≧ 2) printing scans are performed on an image area that can be printed by one printing main scan (one pass). The amount of sub-scanning performed during each recording main scan is equivalent to the recording width of the recording elements included in each block when a plurality of recording elements arranged in the recording head are divided into N blocks. That is, an image is formed by performing N recording main scans by the recording elements included in the N blocks on the same area on the recording medium.

  When the printing element array on the printing head is divided into N blocks, the number of printing elements included in each block is generally the same, but the number is not particularly limited. For example, if the total number of printing elements is not divisible by N, the (N-1) th blocks are composed of M printing elements corresponding to the quotient of the division, and the last Nth block is Alternatively, it is possible to use L recording elements, which are the remainder that cannot be divided. Also, a method of making the recording width in the forward direction (odd number scanning) and the recording width in the backward direction (even number scanning) constant by repeating block division by repeating arbitrary M and L in order, etc. May be taken. Furthermore, for example, a recording head having 10 recording elements is divided into three recording element blocks composed of two, six, and two, and only the area recorded by two recording elements located at both ends May be recorded by two multipass recording methods. In this case, an image is formed in one recording main scan for the area recorded by the six recording elements located in the center, and the number of multi-passes may be expressed as N = 1.5. Is possible.

  As described above, in the multi-pass printing method, an image is completed by a plurality of printing main scans using different blocks, so that it is not possible to print all the recordable image data by only one printing main scan. Here, a so-called mask pattern is used to distribute the image data into blocks for each pass. This mask pattern is often determined independently of the image signal. For example, by installing an AND circuit that performs an AND operation between the mask pattern and the image signal in each printing element, each printing scan is performed. It is configured to determine whether to record a given image signal. Therefore, from the viewpoint of individual image data, the probability of printing in one printing main scan is determined by this mask pattern. That is, the image data to be recorded is thinned out to some extent by the mask pattern, and the probability of thinning out is hereinafter referred to as “thinning rate” in this specification. In other words, the “thinning rate” has the opposite meaning to the probability of printing in each printing main scan (hereinafter referred to as “printing rate”).

  Here, a specific example of the multipass recording method described above will be given. In the case of performing multipass printing four times using 100 recording elements, the recording element is divided into four blocks of 25. The amount of sub-scanning performed between each recording main scan is equivalent to 25 recording elements. Further, the mask pattern corresponding to each block in each printing main scan has a thinning rate of 75% and a printing rate of 25%. The mask patterns are complementary to each other in four blocks, and 100% recording is performed by superimposing the four mask patterns. Here, as an example, the example in which the total number 100 of printing elements is equally divided by the multipass number N = 4 is shown, but the block division in the multipass printing method is of course not limited to such a method. . As described above, the number of passes N in multipass printing need not be divisible by the total number of printing elements. If the main scanning is performed by a plurality of different blocks for the same image area, the multi-pass recording method is established.

  As described above, the reason for adopting the multi-pass printing method is to improve the image quality. According to this method, the ink printing order is controlled by controlling the mask pattern for each ink color. Is possible.

System Configuration The configuration of the image forming system in the second embodiment is basically the same as that of the first embodiment described above, but the multi-pass printing method is used for recording in the inkjet printer of the image output unit 105. For this purpose, the halftone processing unit 104 generates mask data in which a mask pattern prepared in advance for the dot arrangement is applied to each color of colored ink. The second embodiment is characterized in that the halftone processing unit 104 further creates and applies a mask pattern for colorless ink in accordance with the mask data for the colored ink.

FIG. 10 shows a detailed configuration of the halftone processing unit 104 in the second embodiment, and the operation thereof will be described. In the following description, a minimum structural unit that is an object of image processing for processing multi-value data represented by a plurality of bits is referred to as a pixel, and data corresponding to the pixel is referred to as pixel data. The image processing of multi-value data represented by a plurality of bits corresponds to color separation processing performed by the color separation processing unit 103, for example. In the color separation process according to the second embodiment, RGB 8-bit data is converted into 8-bit data of each CMYK corresponding to the colored ink installed in the printer using the color separation LUT.

  In FIG. 10, a halftone processing unit 1401 performs a process of quantizing each 8-bit data of CMYK color-separated into colored ink values by the color separation processing unit 103 into 4-bit data of CMYK. The number of bits related to quantization is not particularly limited. For example, 16-bit data of CMYK may be quantized into 5-bit data of CMYK. Hereinafter, description will be made assuming that the halftone processing unit 1401 performs quantization from 8-bit data to 4-bit data.

  The dot arrangement patterning processing unit 1402 further reduces the number of levels of CMYK data quantized to 4 bits by the halftone processing unit 1401 to 1 bit. This is because, in order to perform recording with the ink jet printer in the image output unit 105 of the second embodiment, binary (1 bit) information indicating whether to record ink is required. In the dot arrangement patterning processing unit 1402, for each pixel expressed by 4-bit data of levels 0 to 8 that is an output value from the halftone processing unit 1401, the gradation level (level 0 to 8) of the pixel is set. A corresponding dot arrangement pattern is assigned. Thereby, ON / OFF of dot arrangement is defined for each of a plurality of areas in one pixel, and 1-bit ejection data of “1” or “0” is arranged.

  Here, FIG. 11 shows an example of an output pattern for each of the input levels 0 to 8 assigned to the colored ink by the dot arrangement patterning processing unit 1402. That is, the dot arrangement patterning processing unit 1402 holds the output pattern data therein. Each level value shown at the left end in the figure corresponds to levels 0 to 8 which are output values from the halftone processing unit 1401. In addition, the area of each matrix composed of 2 vertical areas × 4 horizontal areas arranged on the right side in the drawing corresponds to an area of one pixel after halftone processing. Each area in one pixel corresponds to a minimum unit in which dot on / off is defined, and an area with a circle indicates a dot recording (dot on) area. As can be seen from FIG. 11, as the number of levels increases, the number of dots to be recorded increases one by one. By controlling the number of dots arranged according to the number of levels in this way, the density information of the original image is reflected in the printed image. In addition, (4n) to (4n + 3) shown at the upper end in the figure indicate the pixel position in the horizontal direction from the left end of the input image by substituting an integer of 1 or more for the variable n. Also, a plurality of different patterns are prepared depending on the pixel position. That is, even when the same level is input, four types of dot arrangement patterns shown in (4n) to (4n + 3) are circulated and assigned on the recording medium.

  In FIG. 11, the vertical direction is the arrangement direction of the ejection ports of the recording head, and the horizontal direction is the scanning direction of the recording head. Therefore, as described above, recording can be performed with various dot arrangements on the same level, so that the number of ejections can be distributed between the nozzles located in the upper stage and the nozzles located in the lower stage of the dot arrangement pattern, or a recording apparatus An effect of dispersing various unique noises can be obtained.

  In the dot arrangement patterning processing unit 1402, all the dot arrangements (colored dot arrangements) of the colored ink (CMYK) with respect to the recording medium are determined when the dot arrangement patterning process described above is completed.

  Next, processing in the mask data conversion processing unit 1403 will be described. With the dot arrangement patterning process described above, the presence or absence of colored ink dots for each area on the recording medium has been determined. Therefore, if this information is directly input to the drive circuit of the recording head, a desired image can be recorded. Is possible. However, since the multi-pass printing method is adopted in the ink jet printer of the second embodiment, it is necessary to convert the dot arrangement pattern of each color into data for each block. For this conversion, a mask pattern for each color previously held in the mask pattern holding unit 1405 is used, and mask data for each block is obtained after the conversion.

  In general, an ink jet printer has several hundred nozzles, but for the sake of simplicity, the ink jet printer of the second embodiment is assumed to have 16 nozzles. These nozzles are divided into, for example, first to fourth four nozzle groups as shown in FIG. 12, and each nozzle group includes four nozzles. The patterns recorded after application of the respective mask patterns by the nozzle groups are complementary to each other, and when these are superimposed, the recording of the area corresponding to the 4 × 4 area is completed. When each recording scan is completed, the recording medium is conveyed (sub-scanned) by the width of the nozzle group. Therefore, in the same area of the recording medium (area corresponding to the width of each nozzle group), an image is completed only by four recording scans (4 passes). Thus, the formation of each identical region of the recording medium by a plurality of nozzle groups by a plurality of scans has an effect of reducing variations unique to the nozzles and variations in the conveyance accuracy of the recording medium.

  The colorless ink mask pattern generation unit 1404 generates first and second colorless ink mask patterns based on the colored ink mask pattern and the colored ink dot arrangement. The colorless ink mask pattern generation process will be described in detail below.

Mask Pattern Generation Processing As described above, the printing order can be controlled by setting a mask pattern for each nozzle group for each colored ink. In the second embodiment, the colorless ink recorded on the colored ink at each pixel is controlled by generating a mask pattern for the colorless ink according to the mask data of the colored ink determined according to the input image. It is characterized by that.

  Hereinafter, a process for generating a mask pattern for colorless ink in the mask pattern generation unit 1404 for colorless ink will be described in detail. In addition, in order to improve the recording speed, so-called bidirectional printing in which recording is performed in the forward direction and backward direction of the recording main scan is also employed in printers that are currently widely used. Now, a case where printing is performed only in the forward direction will be described as an example.

  FIG. 13 is a conceptual diagram of a recording head in the ink jet printer according to the second embodiment, in which the corresponding inks are arranged in the main scanning direction so that the corresponding inks are C, M, Y, K, CL1, CL2. That is, recording is performed in the order of C, M, Y, K, CL1, and CL2. CL1 and CL2 indicate the first colorless ink that is relatively easy to deposit on the colored ink and the second colorless ink that is relatively easy to penetrate into the colored ink, respectively, as in the first embodiment. Yes. Similarly to the first embodiment, it is assumed that only the C ink has its bronze amount exceeding the threshold value, and therefore only the C ink is set as the bronze suppression target ink.

  The above-described mask pattern A shown in FIG. 12 is a mask pattern for C ink having a large bronze amount. FIG. 14 shows a mask pattern B of Y ink having a small bronze amount. These mask patterns A and B are held in the mask pattern holding unit 1405 in advance. Hereinafter, a case where the dot arrangement pattern shown in FIG. 15 is recorded by applying these mask patterns A and B will be considered. FIG. 15A shows a dot arrangement pattern for C ink, and FIG. 15B shows a dot arrangement pattern for Y ink. Here, in FIG. 15 (c), addresses of the areas shown in FIGS. 15 (a) and 15 (b) are indicated by AP, and each area is indicated by this address hereinafter. For example, an area at the position of address A is referred to as area A. FIG. 16 shows a cross section when colored inks overlap on the recording medium. In FIGS. 16A to 16D, 2101 is a recording medium, 2102, 2106, and 2107 are C ink, and 2103, 2104, and 2105 are Y ink.

  As described above, each dot arrangement pattern shown in FIGS. 15A and 15B is recorded in four passes by applying the mask patterns shown in FIGS. 12 and 14 using the C and Y inks, respectively. . Then, the overlapping order of the ink in each area in the dot arrangement pattern, that is, each dot position is controlled by the mask pattern. For example, in the area E, the order is C → Y shown in FIG. In areas B, L, and O, the order is Y → C shown in FIG. Areas D, F, K, and M are only Y as shown in FIG. 16 (b) as is clear from the dot arrangement pattern. Similarly, areas A, C, G, H, I, J, N, and P are Only C shown in FIG. Therefore, in this example, for the areas A, B, C, G, H, I, J, L, N, O, P, the outermost surface is C ink, and for the areas D, E, F, K, M, the outermost surface Becomes Y ink.

  As described in the first embodiment, in order to suppress the decrease in image clarity as much as possible while suppressing the occurrence of bronze, the colored ink having a large bronze amount is coated with the first colorless ink that is relatively easy to deposit, In this area, it is necessary to record the second colorless ink which is relatively easy to penetrate. Therefore, in the second embodiment, a mask pattern for controlling the recording position of colorless ink so that CL1 is recorded on C ink having a large bronze amount and CL2 is recorded on Y ink having a small bronze amount. Is generated.

  FIG. 17 shows a cross section when the colorless ink is superimposed on the colored ink formed on the recording medium in accordance with the colorless ink recording position control in the second embodiment. 17A to 17D correspond to FIGS. 16A to 16D, in which 2201 is a recording medium, 2202, 2206, and 2207 are C ink, and 2203, 2204, and 2205 are Y ink. In addition, 2208 and 2209 indicated by diagonal lines are CL2 ink, and 2210 and 2211 indicated by halftone dots are CL1 ink. According to FIGS. 17 (a) and 17 (b), CL2 ink is superimposed on Y ink, and according to FIGS. 17 (c) and 17 (d), CL1 ink is superimposed on C ink. I understand.

  FIG. 18A shows an example of each mask pattern of C, Y, CL1, and CL2 applied in the second embodiment. In the figure, mask patterns A and B are for C ink and Y ink, respectively, also shown in FIGS. 12 and 14, and are held in advance in a mask pattern holding portion 1405. The mask pattern C is for CL2 ink, and the mask pattern D is for CL1 ink. These are generated by the colorless ink mask pattern generation unit 1404 and stored in the mask pattern holding unit 1405. The colorless ink mask pattern generation unit 1404 determines the type of the colored ink that comes to the outermost surface of each area from the dot arrangement of the colored ink and the mask pattern, and CL1 and CL2 are superimposed on the color ink type according to the color ink type. The mask patterns C and D are appropriately created. Then, by recording CL1 and CL2 by applying the mask patterns C and D, recording in the overlapping order as shown in FIG. 17 becomes possible.

  In the second embodiment, the mask patterns C and D for colorless ink are created. However, in the mask data conversion processing unit 1403, for example, the mask pattern C is the first colorless ink in which all areas are dot-on. This is applied to a certain dot arrangement pattern. Similarly, the mask pattern D is also applied to the dot arrangement pattern of the second colorless ink in which all areas are dot-on. That is, the colorless ink mask patterns C and D created in the second embodiment are substantially equivalent to the colorless ink multi-pass dot arrangement pattern itself (corresponding to colored ink mask data).

  FIG. 18A shows an example in which CL1 and CL2 are recorded only by the fifth nozzle group. However, CL1 is applied to the area where the C ink is on the outermost surface, and CL2 is applied to the area where the Y ink is on the outermost surface. Can be recorded, the mask pattern is not limited to this example. For example, the dot-on portions of the mask patterns C and D may be created so as to be divided and recorded in the fifth nozzle group and the sixth nozzle group. Further, since it is not necessary to wait until the fifth nozzle group for the area where the color ink recording has already been completed, the mask patterns C and D for the first to fourth nozzle groups as shown in FIG. You can create it. In the example shown in FIG. 18B, since it is possible to complete recording in four passes including colorless ink, higher-speed recording is possible.

  As described above, according to the second embodiment, for each input image, the overlapping order of the colored ink for each area is determined according to the dot arrangement of the colored ink and the mask pattern, and the first order is determined according to the determination result. Each mask pattern for the second colorless ink is created. Specifically, the first colorless ink is recorded in the area where the ink having a large bronze amount is on the outermost surface, and the second colorless ink is recorded on the area where the other ink is on the outermost surface or the recording medium is exposed. Each mask pattern is created so that the colorless ink is recorded. By recording colorless ink on the input image using the mask pattern for colorless ink created in this way, the deterioration of image clarity is minimized while suppressing the occurrence of bronzing, that is, the occurrence of colored specularly reflected light. Can be fastened.

<Third Embodiment>
The third embodiment according to the present invention will be described below. In the second embodiment described above, an example in which the overlapping order of the colored ink for each area determined by the dot arrangement patterning processing unit 1402 is determined for each input image and a mask pattern of colorless ink is generated is shown. As a result, CL1 is always recorded in the area where the ink with a large amount of bronze is on the top surface, and CL2 is always recorded in the area where the other ink is on the top surface or where the recording medium is exposed. More preferable image quality can be obtained. However, since it is necessary to newly generate a mask pattern for each input image, there are problems such as a slower printing speed or more memory compared to printing using a predetermined mask pattern. is there. Therefore, in the third embodiment, although CL1 is not necessarily recorded on ink with a large bronze amount and CL2 is not recorded on other pixels depending on the input image, the same mask pattern is applied to all input images. An example in which applied image formation is performed will be described.

  The configuration of the image forming system in the third embodiment is substantially the same as that of the second embodiment described above, except that the colorless ink mask pattern generation unit 1404 is not included in the detailed configuration of the halftone processing unit 104. That is, in the third embodiment, as a mask pattern for colorless ink used in the mask data conversion processing unit 1403, one type prepared in advance is used regardless of the processing result in the dot arrangement patterning processing unit 1402. Features.

  FIG. 19A shows an example of a mask pattern used in the third embodiment. As in the second embodiment described above, the mask pattern A is C ink, the mask pattern B is Y ink, the mask pattern C is CL2 ink, and the mask pattern D is CL1 ink. According to the figure, the mask pattern A of the fourth nozzle group for the C ink to be suppressed due to the large amount of bronze is the same as the mask pattern D of the CL1 ink which is the first colorless ink that is relatively easy to deposit. It is a pattern. Although this also depends on the input image, there is a high possibility that another ink is recorded on the ink recorded in the first half of the multi-pass for the same area, and the ink recorded in the second half is This is because it is relatively easy to remain on the outermost surface. The CL2 ink mask pattern C, which is the second colorless ink that is relatively easy to penetrate, has an exclusive relationship with the CL1 ink mask pattern D.

  FIG. 19 (b) shows an example in which the pattern obtained by ORing the third nozzle group and the fourth nozzle group for C ink having a large bronze amount and the mask pattern D of CL1 ink are the same pattern. . The reason for this is that, as in the example shown in FIG. 19A, the difference in the possibility of ink remaining on the outermost surface in the first half and the second half of the multi-pass for the same area is taken into consideration. The same applies to the point that the mask pattern C of the CL2 ink has an exclusive relationship with the mask pattern D of the CL1 ink.

  Further, for example, the mask patterns shown in FIGS. 19A and 19B may be switched according to the recording amount of C ink having a large bronze amount. FIG. 20 is a graph showing the recording amount (ink value) of colored ink according to the input signal value. This figure shows the gradation change from yellow (R, G, B = 255, 255, 0) to cyan (0, 255, 255) passing through green (0, 255, 0), 2701 is the ink value of C ink. , 2702 is the ink value of Y ink. When the ink values of the C and Y inks transition in this way according to the gradation level, for example, the mask pattern to be applied is switched according to the recording amount of the C ink. That is, the mask pattern shown in FIG. 19 (a) is applied to the region A where the recording amount of C ink is relatively small, and the mask pattern shown in FIG. 19 (b) is applied to the region B where the recording amount of C ink is relatively large. Control to do. Thereby, the bronze suppression according to the input image signal can be realized.

  As described above, according to the third embodiment, the mask patterns for the first and second colorless inks are prepared in advance according to the mask pattern of the colored ink. Specifically, the first colorless ink is recorded in an area where the ink having a large amount of bronze is likely to be the outermost surface, and other ink may be the outermost surface or the recording medium may be exposed. Control is performed so that the second colorless ink is recorded in the highly characteristic area. For all input images, the colorless ink mask pattern created in this way is used in common to record colorless ink. Can be kept to a minimum.

  In the first to third embodiments described above, an example in which two types of colorless inks having different penetrability are used has been described. However, the colorless ink that can be used in the image forming apparatus of the present invention is not limited to two types, and includes a first colorless ink and a second colorless ink that is more permeable to colored inks than the first colorless ink. At least two types of colorless ink can be mounted. Also in this case, the first colorless ink is overlapped with the colored ink to be controlled for bronze, such as C ink, and the second colorless ink is overlapped with the other colored ink. An effect is obtained. Moreover, you may combine 1st Embodiment mentioned above and 2nd or 3rd embodiment suitably.

<Other embodiments>
The present invention is also 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, etc.) of the system or apparatus reads the program. It is a process to be executed.

Claims (9)

A plurality of colored inks including a pigment coloring material, and at least two kinds of colorless inks including a first colorless ink and a second colorless ink having higher permeability to the colored ink than the first colorless ink. An image forming apparatus that performs image formation,
Color separation means for acquiring ink values for the colored ink and the first and second colorless inks by color separation processing using a color separation table for each pixel of the input image;
Image forming means for forming a color image on a recording medium by performing recording with the ink values of the colored ink obtained by the color separation means and the first and second colorless inks for each pixel; Have
In the color separation table, colored ink containing a color material that is likely to be colored in regular reflection light is used as a suppression target ink, and the ink value of the first colorless ink increases as the ink value of the suppression target ink increases. The image forming apparatus is configured so that the ink value of the second colorless ink increases as the ink value of the colored ink other than the suppression target ink increases.   The color separation table is set so that the ink value of the first colorless ink is proportional to the ink value of the suppression target ink, and the ink value of the colored ink other than the suppression target ink is The image forming apparatus according to claim 1, wherein the ink values of the second colorless ink are set to have a proportional relationship.   In the color separation table, the sum of the ink values of the first and second colorless inks and the ink values of the colors of the colored inks exceeds a value corresponding to the upper limit of the amount of ink that can be recorded on the recording medium. 3. The image forming apparatus according to claim 2, wherein the ink values of the first and second colorless inks are set so as not to be present. A plurality of colored inks including a pigment coloring material, and at least two kinds of colorless inks including a first colorless ink and a second colorless ink having higher permeability to the colored ink than the first colorless ink. An image forming apparatus for forming an image by a multipass recording method,
Color separation means for obtaining an ink value for each color of the colored ink by color separation processing for each pixel of the input image;
Colored dot arrangement means for setting a dot arrangement pattern for each color of the colored ink according to the gradation level of each color indicated by the ink value of the colored ink for each pixel;
For each color of the colored ink, a mask pattern holding unit that holds a mask pattern for dividing the dot arrangement pattern for each pass in the multipass printing method ;
The overlapping order of the colored ink is determined for each dot position based on the dot arrangement pattern and the mask pattern set by the colored dot arrangement means for each color of the colored ink, and the first and Mask pattern generating means for generating a mask pattern for each of the second colorless inks;
Each color of the colored ink is converted into mask data indicating a dot arrangement pattern for each pass in the multi-pass printing method based on the dot arrangement pattern and each mask pattern held in the mask pattern holding unit, and Mask data conversion means for converting into the mask data based on the dot arrangement pattern in which all of the first and second colorless inks are dot-on and the respective mask patterns generated by the mask pattern generation means,
For each pixel, each color of the colored ink and each of the first and second colorless inks are subjected to multi-pass printing using the mask data converted by the mask data conversion unit, thereby forming a color image on the recording medium. Image forming means for forming,
The mask pattern generation means uses colored ink containing a color material that is likely to be colored in specularly reflected light as a suppression target ink, and a dot of the first colorless ink overlaps a dot that is the top surface of the suppression target ink. A mask pattern is generated for each of the first and second colorless inks so that the dots of the second colorless ink overlap the other dots. A plurality of colored inks including a pigment coloring material, and at least two kinds of colorless inks including a first colorless ink and a second colorless ink having higher permeability to the colored ink than the first colorless ink. An image forming apparatus for forming an image by a multipass recording method,
Color separation means for obtaining an ink value for each color of the colored ink by color separation processing for each pixel of the input image;
Colored dot arrangement means for setting a dot arrangement pattern for each color of the colored ink according to the gradation level of each color indicated by the ink value of the colored ink for each pixel;
For each of said first and second clear ink and the color of the colored ink, and the mask pattern holding means for holding a mask pattern for dividing the dot arrangement pattern to each path in the multi-pass recording method,
Each color of the colored ink is converted into mask data indicating a dot arrangement pattern for each pass in the multi-pass printing method based on the dot arrangement pattern and each mask pattern held in the mask pattern holding unit, and Mask data conversion means for converting into the mask data based on the dot arrangement pattern in which all of the first and second colorless inks are dot-on and the respective mask patterns held in the mask pattern holding means;
For each pixel, for each color of the colored ink and each of the first and second colorless inks, a color image is formed on a recording medium by performing multi-pass printing using the mask data converted by the mask data conversion unit. Image forming means for forming,
The mask pattern for each of the first and second colorless inks held by the mask pattern holding unit is a suppression ink using a colored ink containing a color material that is likely to be colored in the regular reflection light as the suppression target ink. The first colorless ink dot is overlapped with the dots recorded in the latter half of the multi-pass printing of the target ink, and the second colorless ink dot is overlapped with the other dots. An image forming apparatus.   The image forming apparatus according to claim 1, wherein the suppression target ink is set based on a saturation of specularly reflected light of a sample formed by each color of the colored ink. .   2. The suppression target ink is set based on a mean square error with respect to a spectral characteristic serving as a reference for spectral characteristics of specularly reflected light of a sample formed by each color of the colored ink. 6. The image forming apparatus according to any one of items 1 to 5. A plurality of colored inks including a pigment coloring material, and a first colorless ink and a second colorless ink having a higher permeability to the colored ink than the first colorless ink An image forming method in an image forming apparatus that forms an image using at least two kinds of colorless inks including:
A color separation step in which the color separation means obtains ink values for the colored ink and the first and second colorless inks by color separation processing using a color separation table for each pixel of the input image;
The image forming unit forms a color image on a recording medium by performing recording based on ink values of the colored ink obtained in the color separation step and the first and second colorless inks for each pixel. An image forming step,
In the color separation table, colored ink containing a color material that is likely to be colored in regular reflection light is used as a suppression target ink, and the ink value of the first colorless ink increases as the ink value of the suppression target ink increases. The image forming method is characterized in that the ink value of the second colorless ink increases as the ink value of the colored ink other than the suppression target ink increases.   A program for causing a computer device to function as each unit of the image forming apparatus according to any one of claims 1 to 7 when executed on the computer device.

Images