JP6711584B2 - Image forming apparatus, image forming method, and printed matter - Google Patents

Description

The present invention relates to an image forming apparatus and an image forming method using inks having different transmittances.

There are various recording systems as a recording device that records an image on a sheet-shaped recording medium such as paper or film, and an inkjet recording system is known as one of the recording systems. Various recording agents have been proposed in recent years for recording apparatuses to which the inkjet recording method is applied. A pigment ink is a typical example of the recording material.

In the pigment ink, the coloring material is present in the recording material as particles having a size of about several tens of nanometers. Since the pigment ink has a large particle size of the coloring material, the ink hardly penetrates into the recording medium, and the ink is fixed on the surface of the recording medium. In the pigment ink, the previously printed color material is fixed on the surface of the recording medium, and the color material printed after a short time is fixed on the previously printed color material. As described above, in the pigment ink, it is easy to determine whether the pigment ink is arranged in the upper layer or the lower layer on the recording medium according to the fixing order.

It is known that a pigment ink has two phenomena of coloring with specular reflection light. Specifically, it is known that a bronze phenomenon and a thin film interference phenomenon occur.

The bronze phenomenon is, for example, a region in which cyan ink is often used as a color material arranged in an upper layer, and specular reflection light is colored magenta. This bronzing phenomenon occurs due to the wavelength dependence of the refractive index of the pigment ink arranged in the upper layer on the recording medium, and is caused by the pigment ink coloring material itself.

The thin film interference phenomenon is an optical thin film phenomenon that occurs when a pigment ink having a high transmittance (for example, a transparent ink) has a film thickness of 2 μm or less and is fixed on the upper layer. In the optical thin film phenomenon, the saturation and hue with a specular reflection color change depending on the film thickness. The thin film interference phenomenon reduces the coloring (whitening) by increasing the thickness of the ink film (to 2 μm or more) or making the ink film thickness nonuniform (increasing the film thickness variation). Is known to do.

Patent Document 1 proposes a technique for reducing the above two specular reflection light coloring phenomena (a bronze phenomenon and a thin film interference phenomenon). In Patent Document 1, by forming an ink (transparent coloring material) having a small wavelength dependency of the refractive index and a high transmittance in the upper layer of the image, regular reflection coloring due to the bronzing phenomenon is reduced. Furthermore, the film thickness is controlled by controlling the color material amount of the ink (transparent color material) having high transmittance in the pixel of interest and the color material amount of ink (transparent color material) having high transmittance in the peripheral pixels of the pixel of interest. It causes non-uniformity and produces various colors locally. When this local light is viewed globally, various colors are blended and the thin film interference phenomenon is observed to approach white light, and as a result, specular reflection coloring due to the thin film interference phenomenon is reduced.

JP2012-90105A

However, according to the method described in Patent Document 1 described above, the film thickness of the ink (transparent color material) having a high transmittance arranged in the upper layer of the image is made uneven, and the roughness of the image surface becomes large. However, the gloss uniformity (particularly the gloss clarity and gloss image clarity) is reduced.

An image forming apparatus according to the present invention is an image forming apparatus that forms an image using at least a first color material and a second color material having different transmittances, and has a transmittance higher than that of the second color material. Recording means for recording the first color material having a high temperature on at least a part of the surface of the recording medium, and the film thickness of the first color material recorded on the recording medium is composed of a plurality of dots. varied so that a pattern, the amplitude pattern 30n m or more, and a control means for the normal direction of the inclination of the surface of said pattern for controlling said recording means so as not to exceed 0.5 °, It is characterized by having.

According to the present invention, the coloring of specular reflection can be reduced while the gloss uniformity (in particular, gloss image clarity) is improved.

It is a figure which shows the relationship between the film thickness of a transparent ink, and saturation (C*). FIG. 3 is a block diagram showing the configurations of an image processing apparatus and an image forming apparatus. FIG. 3 is a diagram showing a configuration of a recording head. It is a figure which shows the relationship between the normal line direction of the transparent ink on the image surface, and the regular reflection direction of light. It is a figure which shows the model of the period for making the normal direction (normal vector angle) on an image surface 0.5 degree, and making a film thickness distribution difference 180 nm. It is a figure which shows the spatial frequency characteristic of vision. 6 is a diagram showing a flow of processing in Embodiment 1. FIG. It is a figure for explaining the outline of color separation processing. FIG. 6 is a diagram showing details of a dot data generation unit in the first embodiment. It is a figure which shows the example of multi-pass printing. It is a figure which shows an ink value division ratio. It is a figure which shows the recording amount data setting table. It is a figure which shows the outline of a recording amount data setting process. It is a figure which shows the position of the color separation data cut-out position cut (k) according to a scanning number. It is a figure showing a transition for controlling a cycle of a change in film thickness of transparent ink so as to be a lens shape with a cycle of 40 µm to 320 µm. 6 is a flowchart showing the processing of the control unit in the first embodiment. It is a figure which shows C threshold-value matrix Th_c and T threshold-value matrix Th_t. It is a figure for demonstrating the data stored in a storage buffer. FIG. 7 is a diagram showing a dot data generation result for each scan number of cyan ink and ink having high transmittance (transparent ink). FIG. 6 is a diagram showing a relationship between an upper layer and a lower layer in accumulated dot data of a cyan ink and an ink (transparent ink) having a high transmittance in Example 1. It is a figure which shows the optical microscope image measured in order to verify the film thickness change period of the formed transparent ink. FIG. 8 is a diagram showing a configuration of a dot data generation unit in a modified example of the first embodiment. FIG. 9 is a diagram showing N-valued data and a pass mask in a modified example of the first embodiment. 7 is a flowchart showing a process of a control unit in a modified example of the first embodiment. It is a figure which shows the dot data when the injection amount of transparent ink differs. FIG. 9 is a diagram showing a relationship between upper layers and lower layers in accumulated dot data of cyan ink and ink having high transmittance (transparent ink) in Example 2; FIG. 13 is a diagram showing a relationship between upper layers and lower layers in accumulated dot data of cyan ink and ink having high transmittance (transparent ink) in Example 3;

Hereinafter, the present invention will be described in detail based on its preferred embodiments with reference to the accompanying drawings. The configurations shown in the following embodiments are merely examples, and the present invention is not limited to the illustrated configurations.

[Example 1]
In this embodiment, an ink having a relatively low transmittance and an ink having a relatively high transmittance are used. Here, an example in which an ink having a relatively low transmittance is relatively likely to cause the bronzing phenomenon, and an ink having a relatively high transmittance is relatively unlikely to cause the bronzing phenomenon is shown. In addition, an example in which an ink having a relatively low transmittance is unlikely to cause a thin film interference phenomenon, and an ink having a relatively high transmittance is relatively likely to cause a thin film interference phenomenon is shown.

Further, in this embodiment, as the ink having a relatively high transmittance, an ink having an average film thickness of 2 μm or less is used. Further, in this embodiment, at least a part of the ink having a relatively high transmittance (transparent ink) is fixed on the upper layer of the ink having a relatively low transmittance (color ink). At that time, the uniformity of gloss (especially gloss image clarity) is improved by increasing the nonuniformity (variation) of the film thickness of the ink having high transmittance while keeping the inclination of the image surface normal direction small. , Reduce the coloring of specular reflection.

By setting the cycle of film thickness change at this time to 40 μm or more, the inclination of the image surface in the normal direction is reduced. Further, by taking into account the visual spatial frequency characteristics, the period of film thickness change is set to 320 μm or less, so that local light of various colors is made inconspicuous. By doing so, the coloring of specular reflection can be reduced while the gloss uniformity (in particular, gloss image clarity) is improved. Details will be described later.

Hereinafter, an ink having a relatively high transmittance is referred to as a transparent ink for convenience, and an ink having a relatively low transmittance is referred to as a color ink (cyan, magenta, yellow, black ink). Therefore, it should be understood that transparent ink refers to an ink having a relatively high transmittance. That is, as long as the transmittance is higher than that of the color ink described later, an ink that is slightly cloudy or colored, or a yellow ink that has a higher transmittance than a black ink is also called a transparent ink. You can

The control of the transparent ink in this embodiment is applied to the region where the average film thickness is 2 μm or less. The reason is that the thin film interference phenomenon occurs when the average thickness of the transparent ink is 2 μm or less. FIG. 1 shows the relationship between the film thickness of the transparent ink and the color saturation (C*) of regular reflection light in the thin film interference phenomenon.

The horizontal axis of FIG. 1 is the average film thickness of the transparent ink, and the vertical axis is the color saturation (C*) of the specular reflection light caused by the thin film interference phenomenon. The saturation C* is the saturation according to the International Commission on Illumination CIE L*a*b*, and is defined by C*=sqrt(a*^2+b*^2), and the smaller the saturation C*, the lower the coloring. Indicates. Here, it can be seen from FIG. 1 that when the average film thickness of the transparent ink is 2 μm or more, the saturation C*≦3. C* is replaced by the color difference ΔE from the achromatic color, but since the Class A tolerance specified by the Japan Color Research Institute (the color difference that people hardly feel) is ΔE≦3, the average film thickness is When the thickness is 2 μm or more, it can be said that the condition that the specular reflection coloring due to the thin film interference phenomenon is not visually recognized. In other words, if the average film thickness is 2 μm or more, even if the nonuniformity (variation) in the film thickness of the transparent ink is reduced, the regular reflection coloring is not visually recognized, and therefore the nonuniformity (variation) in the film thickness increases. Therefore, the control described in this embodiment is not necessary. In other words, when the average film thickness is 2 μm or less, the specular reflection coloring due to the thin film interference phenomenon is visually recognized, so that the unevenness (dispersion) of the film thickness as described in this embodiment is increased. Control is needed. Therefore, the present embodiment has an effect of reducing the specular reflection coloring by increasing the nonuniformity (variation) of the film thickness under the condition that the average film thickness of the transparent ink is 2 μm or less.

Further, as the transparent ink used in this embodiment, an aqueous ink containing a relatively small amount of resin (polymer) will be described as an example. In a water-based ink, in order to disperse and stabilize a polymer in an ink liquid, it is necessary to add a resin (polymer) in a nanometer order particle state. In the water-based ink, water is vaporized during the fixing of the ink, so that the additives finally fixed are mainly the polymer. Therefore, the average thickness after fixing is 2 μm or less. However, when placed in a region where the amount of transparent ink is large, the average film thickness may exceed 2 μm. In that case, it is not necessary to control the transparent ink in this embodiment. Further, the present embodiment is applicable to the case where the average film thickness is 2 μm or less for other ink types other than the water-based ink. Generally, in the case of solvent-based ink, UV-curable ink, etc., the transparent ink is often 2 μm or more, but if the solvent-based ink or UV-curable ink of 2 μm or less is used, It is possible to apply the control described in.

FIG. 2 is a block diagram showing the configurations of the image processing apparatus and the image forming apparatus applicable to the first embodiment. In FIG. 2, the image processing apparatus 200 and the image forming apparatus 250 are connected by an interface or a circuit. A system including the image processing apparatus 200 and the image forming apparatus 250 is referred to as an image forming system. The image processing apparatus 200 is, for example, a printer driver installed in a general personal computer. In that case, each unit in the image processing apparatus 200 described below is realized by a computer executing a predetermined program. However, the image forming apparatus 250 may include the image processing apparatus 200.

The image processing apparatus 200 stores, in the input image buffer 202, color image data to be printed (hereinafter, color input image data) input from the input terminal 201. The color input image data is composed of three color components of red (R), green (G) and blue (B).

The color separation processing unit 203 decomposes the stored color input image data into data corresponding to the ink formation amount of the color material color included in the image forming apparatus 250. In this color separation processing, the color separation processing unit 203 refers to the color separation lookup table (LUT) 204. The color material colors in this embodiment are cyan (C), magenta (M), yellow (Y), and black (K), as well as transparent or CMYK ink (T) ink having a low density. There are 5 types including.

The dot data generation unit 205 converts data corresponding to the ink formation amount of the color material color into dot data for each scan. The dot data is data in which the printing position for each scan is described according to each ink color.

The storage buffer 206 stores dot data for each scan corresponding to each ink. The stored dot data for each scan is output from the output terminal 207 to the image forming apparatus 250.

The image forming apparatus 250 moves the recording head 251 in the vertical and horizontal directions relative to the recording medium 252 based on the dot data of each color and each scan received from the image processing apparatus 200 to form an image on the recording medium. Form. Here, the recording head 251 is of an inkjet type and has one or more recording elements (nozzles). The head controller 254 controls the moving unit 253 to move the recording head 251. The transport unit 255 transports the recording medium under the control of the head control unit 254. At this time, the amount of ink ejected from the recording head is about 2 to 4 picoliters so that the dot diameter is about 20 to 30 μm on the recording medium.

The ink color selection unit 256 selects the ink corresponding to the dot data to be printed from the inks mounted on the recording head 251 based on the dot data for each scan corresponding to each color formed by the image processing apparatus 200. To do.

3A and 3B are diagrams showing a configuration example of the recording head 251. In this embodiment, as described above, in addition to four types of cyan (C), magenta (M), yellow (Y), and black (K), the density is low for transparent or CMYK ink (high transmittance). Five types of ink including (T) ink are mounted on the recording head 251.

Note that FIG. 3A shows a configuration in which the nozzles are arranged in a row in the direction in which the recording medium is conveyed (main scanning direction) for simplification of description, but the number and arrangement of the nozzles are as follows. It is not limited to the example. For example, nozzles having the same density but the same color but different ejection amounts may be provided, or a plurality of nozzles having the same ejection amount may be provided. Further, the nozzles may be arranged in zigzag. In FIG. 3A, the nozzles corresponding to each ink color are arranged at the same sub-scanning position, but they may be arranged at different positions as shown in FIG. 3B.

In this embodiment, the cyan ink and the transparent ink are used to increase the non-uniformity (variation) of the film thickness of the transparent ink while reducing the roughness of the image surface, thereby achieving the gloss uniformity (particularly the gloss). An example of reducing the coloring of specular reflection while improving the image clarity) will be described. The regular reflection color is the regular reflection color caused by both the bronze phenomenon and the thin film interference phenomenon.

Specifically, at least a part of the transparent ink is fixed on the upper layer of the cyan ink. At that time, the unevenness (variation) of the film thickness of the ink having high transmittance (transparent ink) is increased while keeping the inclination of the image surface in the normal direction small, and thus the gloss uniformity (especially the gloss image) is obtained. The coloring of specular reflection is reduced while improving the property). In order to increase the nonuniformity (variation) of the film thickness while keeping the inclination of the image surface in the normal direction small, it is necessary to have a relatively long-period structure as shown in FIG. 4A and 4B have the same degree of film thickness nonuniformity (dispersion), but FIG. 4B having a structure with a relatively short period shows the inclination in the normal direction of the surface. Changes greatly depending on the location, the direction of reflected light changes. As a result, the gloss uniformity, particularly the gloss image clarity, which is the gloss definition, is reduced. On the other hand, compared to FIG. 4B, FIG. 4A has a structure with a relatively long period, so that the inclination of the surface in the normal direction can be reduced. This maintains the gloss uniformity, especially the gloss image clarity.

The inventor previously conducted a subjective evaluation (sensory evaluation) on the relationship between the angle of the normal direction and the gloss image clarity, which is the degree of gloss, and found that the surface normal direction was 0.5 degrees or less. It has been found that if there is, good gloss image clarity is maintained.

In addition, the inventor previously conducted a subjective evaluation (sensory evaluation) analysis on the relationship between the non-uniformity of the transparent ink film thickness and the gloss coloring due to the thin film interference phenomenon. As a result, if the difference between the minimum value and the maximum value in the film thickness distribution is 180 nm (nanometers) or more, various colors are generated in Newton ring shape. It was found that macroscopic observation of these various colorings offsets each other, resulting in good gloss coloring (white specular reflection light). Although the difference is set to 180 nm or more here, it may be set to 180 nm or less as long as the coloring can be reduced so that the specularly reflected light becomes white, and the effect of whitening the specularly reflected light is obtained at 60 nm or more in the above analysis. I know I can be. Further, theoretically, the upper limit of the difference is 1440 nm when the period with specular reflection color is 320 μm.

FIG. 5 shows an example in which the structure of the transparent ink having good gloss image clarity and gloss coloration was analyzed from the results of the above analysis. Assuming that a sawtooth-shaped transparent ink film thickness distribution is given, FIG. 5 shows a cycle of the film thickness distribution for making the angle of the image surface normal direction 0.5 degree and the film thickness distribution difference about 180 nm. It is the example which verified the conditions of. It can be seen from FIG. 5 that a period of 40 μm (micrometer) or more is required to satisfy the film thickness distribution difference of 180 nm. Therefore, in this embodiment, the range of the cycle of the thickness change of the transparent ink is set to 40 μm or more in order to improve the gloss uniformity (in particular, gloss image clarity) and reduce the coloring of regular reflection.

However, that is not the case if the range of the cycle of the change in the thickness of the transparent ink is 40 μm or more. Although the specular reflection has relatively low contrast, it is visually detected when the structure has a long period. Therefore, the period is set so that it is not detected based on the spatial frequency response of vision (visual periodic response). Preferably. The visual spatial frequency response needs to be high frequency (short cycle) because it has a sensitive sensitivity at low frequency (long cycle) as shown in FIG.

Therefore, when the inventor conducted an experiment in advance on whether or not the frequency (period) with specular reflection color was detected, the spatial frequency was about 3.1 [cycles/mm] or more at the observation distance of 300 mm (millimeter) of the clear visual distance. If so, the result was that it was not detected. About 3.1 [cycles/mm] or more means 320 μm cycle or less in terms of cycle conversion.

Based on the above analysis and experimental results, in order to reduce the coloring of specular reflection while improving the gloss uniformity (especially gloss image clarity), the cycle of the thickness change of the transparent ink is set to 40 μm to 320 μm. Preferably.

On the other hand, for inks with low transmittance such as cyan and black inks, if the cycle of film thickness change is made large, the deterioration of graininess can be easily visually recognized, so the above control is not performed.

Hereinafter, a control method and a processing method in this embodiment for setting the cycle of the film thickness change within the above range will be described. First, the processing in the image processing apparatus 200 and the image forming apparatus 250 applicable to this embodiment will be described with reference to the flowchart of FIG. 7. The resolution of control and processing in this embodiment is 1200 dpi (one pixel is about 20 μm square). In the flowchart of FIG. 7, the processes of steps S701 to S707 are performed by the image processing apparatus 200, and the processes of steps S751 to S753 are performed by the image forming apparatus 250. The flowchart shown in FIG. 7 is realized by the CPU executing a program stored in, for example, a ROM or an HDD (not shown) and temporarily read in the RAM.

First, in step S701, the image processing apparatus 200 inputs multi-tone input image data from the input terminal 201 and acquires the input image data. The acquired input image data is stored in the input image buffer 202. Here, the input image data is composed of three color components of red (R), green (G), and blue (B).

In step S<b>702, the color separation processing unit 203 uses the color separation LUT 204 to separate the input image data from the RGB values that make up the input image data into CMYK and transparent ink T color values. In the present embodiment, each pixel data after the color separation processing is handled as a floating point value having 0 to 255, but conversion to a higher gradation number may be performed.

As described above, the recording head 251 in this embodiment holds five types of ink. Therefore, the RGB color input image data is converted into image data of each 5 planes of each CMYKT plane. FIG. 8 shows input/output of data in the color separation processing unit 203. The input image data of each color of R, G, B is converted into the image data after color separation corresponding to each color of CMYKT by the following formula with reference to the LUT 204 for color separation.
C=C_LUT_3D(R, G, B) (1)
M=M_LUT_3D(R,G,B) (2)
Y=Y_LUT_3D(R, G, B) (3)
K=K_LUT_3D(R,G,B) (4)
T=T_LUT_3D(R,G,B) (5)

Here, each function defined on the right side of Expressions (1) to (5) corresponds to the content of the color separation LUT 204. The color separation LUT 204 determines the output value of each ink from the three input values of red, green and blue. In the present embodiment, since the configuration is provided with the five types of CMYKT inks, the LUT configuration is obtained in which five output values are obtained from three input values. With the above processing, the color separation processing in this embodiment is completed.

The following steps S703 to S707 perform processing for each color. Here, an example of the cyan ink (C) and the transparent ink (T) will be described, but the same processing is performed for the other three types of color materials, magenta (M), yellow (Y), and black (K). I do. Steps S703 to S705 are processes in the dot data generation unit 205. FIG. 9 is a diagram showing details of the dot data generation unit 205. The dot data generation unit 205 has a setting unit 901 and a control unit 951.

Next, in step S703, the dot data generation unit 205 sets a scan number and a scan position. Specifically, the scan number and scan position setting unit 902 included in the setting unit 901 of the dot data generation unit 205 sets the scan number k and cut(k) indicating the Y coordinate as the scan position in the color separation data. To do. cut(k) is the scanning position of the color separation data at the scanning number k, and corresponds to the upper end coordinate of the nozzle. The initial value of the scan number k is 1, and is incremented by 1 for each processing loop. That is, steps S703 to S707 are processes for the scan number k, the value of k is updated in step S707 described later, and the same process is repeated.

Here, the scanning position Y coordinate cut in the color separation data is taken as an example of the case of four-pass printing including 16 nozzle rows and forming an image by four scans on the same main-scan recording area on the image. The setting method of (k) will be described.

Generally, in the case of four-pass printing, as shown in FIG. 10A, at the initial value (k=1) of the scan number, image formation is performed using only the lower end ¼ of the nozzle, and the scan number k= In No. 2, paper is fed by 1/4 of the nozzle length for scan number k=1, and then image formation is performed. Further, when the scanning number k=3, the image is formed after the paper is fed by the nozzle length ¼ for the scanning number k=2. By repeating such image formation and paper feed, the final output image is formed. Therefore, when the scan number k=1, the scan position cut(1)=−12 corresponding to the nozzle upper end coordinates. When k=4, the scan position cut(4)=0 corresponding to the upper end coordinate of the nozzle.

When the scan position cut(k) of a certain ink color in the color separation data described above is generalized, the number of nozzle rows: Nzzl, the number of passes: Pass, and the scan number: k are given by the following equation.
cut(k)=−Nzzl+(Nzzl/Pass)×k (6)

FIG. 10A is a diagram showing an example of image formation in four-pass printing when all nozzles are used. It is also possible to form an image with the same paper feed amount (nozzle length 1/4 minute) as in the above example, without using all the nozzles. For example, in FIG. 10B, the same dot arrangement as in FIG. 10A is performed by using only the nozzles at the lower end 1/2, and the image is fed while the paper feed amount nozzle length 1/4 is fed. An example of forming In the example of FIG. 10B, the number of nozzles used is half that in FIG. 10A, but since the amount of paper feed is the same, an image is substantially formed by two-pass printing. Therefore, the printing amount (dot number) per pass is also doubled. Further, in the example of FIG. 10B, the printing order is such that an image is formed in the printing of the previous two scans of the four scans.

Next, in step S704, the setting unit 901 sets the print amount and print order for each nozzle for each scan. Specifically, the print amount data setting unit 903 of the setting unit 901 uses the print amount data setting table 904 to set print data for each scan indicating the print amount and print order for each nozzle for each scan. .. That is, print data indicating the print amount and print order of each nozzle at the time of the kth scan is set.

In this embodiment, as shown in FIG. 10B, an example in which the printing order and the printing amount are set without using all the nozzles is shown. Specifically, the color ink is formed first using the lower half nozzles used in the preceding scanning, and the transparent ink is formed later using the upper half nozzles used in the latter scanning. As a result, at least a part of the transparent ink is fixed on the upper layer of the color ink.

Next, the recording amount and the recording order for realizing the formation of the color ink first by using the nozzles at the lower end ½ and the subsequent formation of the transparent ink by the nozzles at the upper end ½ as described above. A method of setting will be described. In this embodiment, when the paper feed amount nozzle length is 1/4, the ink value division ratio as shown in FIG. 11 is given. The ink value division ratio is a Duty division ratio. FIG. 11 shows ink value division ratios for cyan ink (C) and transparent ink (T), respectively. The vertical axis in FIG. 11 represents the nozzle position, and the horizontal axis represents the ink value division ratio. In this embodiment, regarding the ink value division ratio, a case is considered in which cyan ink is set to the lower half nozzle and transparent ink is set to the upper half nozzle.

In FIG. 11, for example, D_c(3) indicates the ink value division ratio in the nozzle of the cyan ink nozzle position 3, and D_t(3) indicates the ink value division ratio in the nozzle of the transparent ink nozzle position 3. It is assumed that the nozzle position at the upper end is 0. The ink value division ratio of cyan ink is set for each four nozzles so that D_c(3), D_c(7)=0.0, D_c(11), and D_c(15)=0.5. The values for 16 nozzles in which dots are connected discontinuously are shown. The ink value division ratio of the transparent ink is set to every 4 nozzles so that D_t(3), D_t(7)=0.5, D_t(11), and D_t(15)=0.0, and The values for 16 nozzles in which dots are connected discontinuously are shown.

The values of D_c(3), D_c(7), D_c(11), D_c(15), D_t(3), D_t(7), D_t(11), and D_t(15) are calculated as follows. The numerical value is set to 1.0.
D_c(3)+D_c(7)+D_c(11)+D_c(15)=1.0 (7)
D_t(3)+D_t(7)+D_t(11)+D_t(15)=1.0 (8)

The ink value division ratios of the cyan ink in FIG. 11 are D_c(3)=D_c(7)=0.0 and D_c(11)=D_c(15)=0.5. It means that it is formed at a ratio of 0.5 using a /2 nozzle. That is, for the color separation data, the ink amount based on the 2-pass printing in which the printing is performed twice with the ink value division ratio of 0.5 on the same paper surface area is set.

Further, since the ink division ratios D_t(3)=D_t(7)=0.5 and D_t(11)=D_t(15)=0.0 of the transparent ink in FIG. It means that it is formed at a ratio of 0.5 using two nozzles. That is, for the color separation data, the ink amount based on the 2-pass printing in which the printing is performed twice with the ink value division ratio of 0.5 on the same paper surface area is set. Regarding this ink value division ratio, assuming that the ink value division ratio of cyan ink is D_c and the ink value division ratio of transparent ink is D_t, the function relating to the nozzle position ny is as follows.
D_c(ny)=0.0 (9)
D_t(ny)=0.5 (10)
“In addition, (0≦ny<Nzzl/2)”
D_c(ny)=0.5 (11)
D_t(ny)=0.0 (12)
“In addition, (Nzzl/2≦ny<Nzzl)”

In this embodiment, the ink value division ratios of the other three colors (YMK) are D_y, D_m, and D_k, and the same ink value division ratio as D_c is given. That is, it is assumed that the ink amount based on the 2-pass printing using the lower half nozzles is set.

When the ink value division ratios of the above equations (9) to (12) are set, the print data setting table 904 is set based on the relationship between the nozzle position and the print amount data set value as shown in FIG. The print data setting table is a table that is set based on the above-described ink value division ratio, and by integrating the values of the color separation data and this print data setting table 904, as will be described later, The ink recording amount data of the nozzle is derived. In the present embodiment, as will be described later, two types of ink recording amount data of each nozzle in each scan, upper recording amount data and lower recording amount data, are derived. Then, in the N-value conversion process (halftone process) described later, the N-value conversion process of each ink recording amount data is performed. Then, after that, the dot data is generated using the data obtained by subtracting the lower dot data corresponding to the lower recording amount data from the upper dot data corresponding to the upper recording amount data. The reason for performing such processing is to make it difficult for dots to be formed at the same position in each scan when printing a certain area by a plurality of scans. As described above, in the present embodiment, the cycle of the thickness change of the transparent ink is set in the range of 40 μm to 320 μm. Therefore, while controlling so that dots are not formed at the same position in each scan as much as possible, a process of forming dots is performed so that the cycle of the film thickness change is within the range of 40 μm to 320 μm in one scan.

Here, the details of the recording data setting table 904 for setting the upper recording amount data and the lower recording amount data which are the sources of such upper dot data and lower dot data will be described. In the LUT 1201 for setting the print amount data of cyan ink in FIG. 12, the vertical axis represents the nozzle position and the horizontal axis represents the value in the print data setting table. In the transparent ink print data setting table 1202, the vertical axis represents the nozzle position and the horizontal axis represents the values in the print data setting table. Further, in FIG. 12, two types of tables are set as the cyan ink print data setting table: a lower table for lower print amount data and an upper table for upper print amount data. In FIG. 12, the lower table is the data indicated by the dotted line 1203, the white diamond 1204, and the black diamond 1205. The upper table is the data indicated by the solid line 1206, the white quadrangle 1207, and the black quadrangle 1208. Similarly, for transparent ink, a print data setting table including an upper table and a lower table is set. Here, the white rhombus 1204 and the white quadrangle 1207 are examples not including the value, and the black rhombus 1205 and the black quadrangle 1208 are examples including the value. For example, the lower table of the nozzle number 7 in the cyan ink recording data setting table 1201 indicates 1.0 instead of 0.5.

Here, assuming that the lower table of the cyan ink print data setting table 904 shown in FIG. 12 is U_C_LUT(ny) and the upper table is O_C_LUT(ny), the table is generated according to the following rules. As described above, D_c is the ink value division ratio, ny is the nozzle position, and Nzzl is the number of nozzle rows. When the value of D_c() exceeds the number of nozzle rows, the value becomes 0.
U_C_LUT(ny)=D_c(ny+Nzzl/4)
+D_c (ny+2×Nzzl/4)+D_c (ny+3×Nzzl/4)
...(13)
O_C_LUT(ny)=D_c(ny)+D_c(ny+Nzzl/4)
+D_c (ny+2×Nzzl/4)+D_c (ny+3×Nzzl/4)
...(14)
“In addition, (0≦ny<Nzzl)”

That is, the value of the lower table U_C_LUT for cyan ink is
(When 0≦ny<4) U_C_LUT(ny)=1.0
(When 4≦ny<8) U_C_LUT(ny)=1.0
(When 8≦ny<12) U_C_LUT(ny)=0.5
(When 12≦ny<16) U_C_LUT(ny)=0.0 (15)

The upper table of cyan ink, the value of O_C_LUT is
(When 0≦ny<4) O_C_LUT(ny)=1.0
(When 4≦ny<8) O_C_LUT(ny)=1.0
(When 8≦ny<12) O_C_LUT(ny)=1.0
(When 12≦ny<16) O_C_LUT(ny)=0.5 (16)
Becomes

Here, as described above, when the dot data is generated, a value obtained by subtracting the lower data from the upper data is used. That is, when this cyan ink table is used, the dot data becomes 0 between nozzle row numbers 0 to 7. That is, for cyan ink data, dots are not formed at the upper end nozzle. On the other hand, between the nozzle row numbers 8 to 15 at the lower end, the color separation data is converted into the ink recording amount data with the value 0.5 set by the ink value division ratio. At this time, by subtracting the lower data from the upper data, it is possible to prevent dots from being formed at the same position as the position formed by the previous scan.

The transparent ink lower table, U_T_LUT(ny), upper table, and O_T_LUT(ny) are similarly given.
That is, the value of the transparent ink lower table U_T_LUT is
(When 0≦ny<4) U_T_LUT(ny)=0.5
(When 4≦ny<8) U_T_LUT(ny)=0.0
(When 8≦ny<12) U_T_LUT(ny)=0.0
(When 12≦ny<16) U_T_LUT(ny)=0.0 (17)

The value of O_T_LUT, the transparent ink upper table, is
(When 0≦ny<4) O_T_LUT(ny)=1.0
(When 4≦ny<8) O_T_LUT(ny)=0.5
(When 8≦ny<12) O_T_LUT(ny)=0.0
(When 12≦ny<16) O_T_LUT(ny)=0.0 (18)
Becomes

Since dots are formed by the upper end nozzles of transparent ink, the values of the lower end nozzle row numbers 8 to 15 used in the preceding pass are set to 0 in both the upper table and the lower table.

In step S704, the recording amount data setting unit 903 uses the recording data setting table 904 to convert the image data after each color separation into upper recording amount data and lower recording amount data.

A method of determining the upper recording amount data and the lower recording amount data will be described with reference to FIG. Here, it is assumed that the value of the color separation data of cyan ink is 128 (128/255≈50%) at all addresses (pixels). Further, the value of the color separation data of the transparent ink, at least a part of which should be fixed on the upper layer of the cyan ink, is 128 (128/255≈50%) at all addresses (pixels). The color-separated image data T of the transparent ink is a value converted by the equation (5).

As shown in FIG. 13, when the cyan ink color separation data 1301 is given, the cyan ink recording amount data 1302 of each nozzle in the k-th scan is the value of the color separation data 1301 and the recording amount data setting table 1201. Calculated by accumulating. In FIG. 13, the cyan ink recording amount data 1302 includes lower recording amount data U_c 1303 and upper recording amount data O_c 1304. Further, as shown in FIG. 13, the transparent ink recording amount data 1306 of each nozzle in the k-th scan when the transparent ink color separating data 1305 is given is the value of the transparent ink color separating data 1305 and the recording amount data setting table. It is obtained by integration with 1202. In FIG. 13, the recording amount data 1306 of transparent ink includes lower recording amount data U_t1307 and upper recording data O_t1308. For other colors, the print amount data is derived by the same process as the print amount data for cyan ink.

Details of FIG. 13 will be described below. Regarding the scan data of cyan ink, two print amount data of cyan ink lower print amount data U_c1303 and cyan ink upper print amount data O_c1304 are set. The two print amount data U_c and O_c are calculated from the U_C_LUT, which is a lower table of the cyan ink print amount setting table 1201, and the O_C_LUT, which is a higher table, as in the following equations.
U_c (nx, ny) =
C(nx,ny+cut(k))×U_C_LUT(ny) (19)

O_c(nx,ny)=
C(nx,ny+cut(k))×O_C_LUT(ny) (20)

Here, C(nx, ny+cut(k)) is the color separation value of the cyan ink C at the XY coordinates (nx, ny+cut(k)) shown in equation (1).

Further, regarding the recording amount data of the transparent ink, two recording amount data of the transparent ink lower recording amount data U_t1307 and the transparent ink upper recording amount data O_t1308 are set. The two transparent ink recording amount data U_t and O_t are calculated from the U_T_LUT, which is a lower table of the recording amount data setting table, and the O_T_LUT, which is an upper table, according to the following equations.
U_t(nx,ny)=
T(nx,ny+cut(k))×U_T_LUT(ny) (21)

O_t(nx,ny)=
T(nx,ny+cut(k))×O_T_LUT(ny) (22)

Here, T(nx, ny+cut(k)) is the color separation value of the transparent ink T at the XY coordinates (nx, ny+cut(k)) shown in equation (5).

In the present embodiment, when the corresponding nozzle has coordinates outside the area of the image Y address, the print data is set to 0. For example, at scan number k=1, the image Y address becomes negative at the upper end 3/4 of the nozzle row, so 0 is substituted for both the upper scan data and lower scan data, and a significant value is substituted for the lower end ¼ of the nozzle row. To be done. Since the color separation data cutout position cut(k) is determined by the scan number k, the scan data is determined as shown in FIG. 14 when the scan numbers k=1 to 4. FIG. 14 shows that when the scanning is repeated while the paper is being fed, the image is formed in the area A by four scannings with the scanning numbers k=1 to 4.

FIG. 14 shows print amount data (lower print amount data U_c, upper print amount data O_c) for the nozzle position of each scan number of cyan ink, and print amount data (lower print amount data for the nozzle position of each scan number of transparent ink). U_t, upper recording amount data O_t). The print amount data corresponding to each print scan of cyan ink is determined by the product of the image data after color separation and the print amount data setting table 904, as in Expressions (19) and (20). Further, the print amount data corresponding to each print scan of the transparent ink is determined by the product of the image data after color separation and the print amount data setting table 904, as in Expressions (21) and (22). Note that, in FIG. 14, for convenience of description, an example of scan numbers 1 to 4 has been described, but in step S704, the process is performed for each scan number. For example, the process of the first loop corresponds to scan number 1. The recording amount data of each nozzle is obtained.

As described above, the print amount and print order setting for each scan in step S704 in the present embodiment is completed.

Returning to FIG. 7, the description of the flowchart will be continued. Next, in step S705, the dot data generation unit 205 generates dot data based on the recording amount data set in step S704. Specifically, the control unit 951 in the dot data generation unit 205 generates dot data by using the upper recording amount data and the lower recording amount data of each color.

The control unit 951 of this embodiment performs different processing for the ink T (transparent) having a relatively high transmittance and the ink C (cyan) having a low comparative transmittance, which are arranged in the upper layer. The feature of the transparent ink (T) treatment of the present embodiment is that the film thickness non-uniformity is maintained while keeping the inclination of the image surface in the direction of the normal line small while setting the cycle of the film thickness change of the transparent ink to 40 μm or more and 320 μm or less. increase. This improves the gloss uniformity, especially the gloss image clarity, while reducing the coloring of specular reflection light due to the bronze phenomenon and the thin film interference phenomenon.

Specifically, regarding the transparent ink, dots are set at adjacent positions such that a plurality of droplets of the transparent ink in the same scan come into contact with each other, thereby making the droplets identical on the recording medium. The unit of this identification is 40 μm to 320 μm. FIG. 15(a) (1501 to 1506) shows the identification by the contact of the liquid droplets. First, in the same scan, a plurality of dots are set at adjacent positions where a plurality of liquid droplets contact each other, and ink liquid is ejected from the recording head 251 (1501). Next, the ink droplets come into contact with each other on the recording medium to form large ink droplets (1502). The formation of ink droplets within the same scan is completed, and the ink is solidified and fixed over time (1503). Since the uniformed droplets have a large discharge amount, the nonuniformity of the film thickness increases. Since the time until this fixing is long, which is several hundred milliseconds, the same occurs at the position where the droplets contact each other in the same scan. That is, in the next scan, at the adjacent positions of the dots in the previous scan, the same ink droplets due to contact between ink droplets do not occur (1504, 1505). Finally, by making the same by contacting the liquid droplets by a plurality of scans, the cycle of film thickness change is controlled so as to form a lens shape having a cycle of 40 μm to 320 μm (1506 ).

As a result, by increasing the non-uniformity (variation) of the thickness of the transparent ink while keeping the inclination of the image surface in the normal direction small, the gloss uniformity (particularly the gloss image clarity) is improved, Reduces the coloring of specular reflections. As described above, the nonuniformity of the thickness of the transparent ink is analyzed by a subjective evaluation (sensory evaluation) that the specular reflection light looks white when the difference between the thin part and the thick part is 180 nm (nanometer) or more. I understand. Therefore, it is desirable that the thickness be 180 nm or more, but sometimes 180 nm cannot always be realized depending on the composition of ink droplets and the like. In that case, it is desirable to increase the nonuniformity of the film thickness as much as possible.

In this way, by setting the cycle of the change in the thickness of the transparent ink to 40 μm to 320 μm, the inclination of the image surface in the normal direction is reduced (corresponding to reducing the roughness of the image surface), and the gloss uniformity ( In particular, the gloss image clarity) is improved. Further, by covering the transparent ink on the color ink such as cyan ink, the bronzing phenomenon of the color ink represented by cyan ink is reduced. Further, the thin film interference phenomenon is reduced by making the film thickness of the transparent ink nonuniform (to 180 nm or more as much as possible).

On the other hand, with respect to color inks having a low transmittance, such as cyan and black inks, a decrease in graininess can be easily visually recognized by increasing the cycle of film thickness change. Therefore, control like transparent ink is not performed.

The control as described above is performed when the dot data is generated based on the recording amount data. It should be noted that this recording amount data is data including two types of upper recording amount data and lower recording amount data as described above.

The control unit 951 in this embodiment will be described below. FIG. 9 shows a configuration of the control unit 951 applicable to this embodiment, and FIG. 16 shows a flowchart of the control unit 951.

The flowchart shown in FIG. 16 will be described below. In step S1601, the control unit 951 converts the cyan ink upper recording amount data O_c into an N-value. The N-value conversion unit 953 compares the upper recording amount data O_c of cyan ink with the C threshold matrix 952. An example of the C threshold matrix 952 is shown in FIG. The C threshold matrix 952 is a threshold matrix used in the N-value conversion unit 953 when performing N-value conversion processing on the cyan recording amount data. Each threshold of the C threshold matrix 952 corresponds to a pixel in the cyan recording amount data. The N-value conversion unit 953 compares the pixel value representing the upper recording amount data for each pixel with the threshold value Th_c in the C threshold matrix 952 to obtain the upper dot data.
When O_c <Th_c, Out_O_c=0 (23)
When Th_c≦O_c, Out_O_c=1 (24)

The output value obtained as a result is the upper dot data Out_O_c of cyan ink. In the above example, the C threshold matrix 952 is an example in which each pixel has one threshold value. It is possible to binarize 0, 1 if there is one threshold value for each pixel, but of course, N-1 threshold values may be used for each pixel. In this case, N-value conversion is possible.

Next, in step S1602, the control unit 951 converts the cyan ink lower recording amount data U_c into an N-value. The N-value conversion unit 954 compares the lower recording amount data U_c of cyan ink with the threshold Th_c of the C threshold matrix 952.
When U_c <Th_c, Out_U_c=0 (25)
When Th_c≦U_c, Out_U_c=1 (26)

The output value obtained as a result is the lower dot data Out_U_c of cyan ink.

In addition, it is preferable that the C threshold matrix 952 of cyan ink having a relatively low transmittance has a blue noise characteristic in which the dot arrangement is easily dispersed from the viewpoint of graininess. Further, in the present embodiment, the C threshold matrix 952 uses the same threshold matrix for each color and each scanning number, but may have different threshold matrices.

Next, in step S1603, the subtractor 955 subtracts the lower dot data from the upper dot data of the cyan ink to generate cyan ink binary data.
Out_c=Out_O_c-Out_U_c (27)

The cyan dot data Out_c calculated by the above processing is the cyan dot data per scan.

In the above equation (27), the cyan ink binary data Out_c is generated from the difference between the N-valued result Out_O_c of the upper recording amount data O_c of cyan ink and the N-valued result Out_U_c of the lower recording amount data U_c. .. However, the method of generating Out_c is not limited to this calculation.
For example, when the upper recording amount data O_c is equal to or larger than the threshold Th_c and the lower recording amount data U_c is smaller than Th_c, Out_c=1 may be set, and otherwise, Out_c=0 may be set. That is, the same result is obtained even if Out_c=1 under the condition of U_c<Th_c≦O_c and Out_c=0 under the other conditions.

In step S1604, the control unit 951 converts the transparent ink upper recording amount data O_t into an N-value. The N-value conversion unit 957 compares the upper recording amount data O_t of the transparent ink with the threshold Th_t of the T threshold matrix 956. The T threshold matrix 956 is shown in FIG. The T threshold matrix 956 is a threshold matrix used in the N-value conversion unit 957 during the N-value conversion process of transparent ink. Each threshold of the T threshold matrix 956 corresponds to a pixel in the transparent ink recording amount data. The N-value conversion unit 957 compares the pixel value representing the upper recording amount data for each pixel with the threshold Th_t in the T threshold matrix 956 to obtain the upper dot data.
When O_t <Th_t, Out_O_t=0 (28)
When Th_t≦O_t, Out_O_t=1 (29)

The output value obtained as a result is the upper dot data Out_O_t of the transparent ink. In the above example, the T threshold matrix 956 may use N-1 threshold values for each pixel, as in cyan. In this case, N-value conversion is possible.

Next, in step S1605, the transparent ink lower recording amount data U_t is N-valued. The N-value conversion unit 958 and the lower-level recording amount data U_t of the transparent ink are compared with the threshold Th_t of the T threshold matrix 956.
When U_t <Th_t, Out_U_t=0 (30)
When Th_t≦U_t, Out_U_t=1 (31)

The output value obtained as a result is the lower dot data Out_U_t of the transparent ink. In addition, in this example, the example in which the dot data of the transparent ink is generated after the dot data of the cyan ink is described, but the generation order of the data is not limited to this. Further, the processing may be performed in parallel.

As described above, when arranging at least a part of the transparent ink on the upper layer, the film thickness non-uniformity is increased by setting the cycle of the film thickness change to 40 μm to 320 μ or less. In order to do as described above, in the present embodiment, regarding the transparent ink, by setting a plurality of dots at the adjacent positions where a plurality of droplets in the same scan come into contact with each other, the droplets are made uniform on the recording medium. Let The unit of this identification is 40 μm to 320 μm.

When the resolution in the present embodiment is 1200 dpi, one pixel is approximately 20 μm. Therefore, in the present embodiment, the dot setting at the adjacent position where a plurality of droplets contact each other is 2×2 pixels or more in scanning to 16×16 or less. To

In order to perform the above control, it is preferable that the T threshold matrix 956 has an arrangement property such that the dot arrangement within the scan is fixed to 2×2 pixels or more within the scan to 16×16. In the present embodiment, the T threshold matrix 956 uses the same threshold matrix for each scan number, but may be different threshold matrices that satisfy the condition that the cycle of film thickness change is 40 μm to 320 μ or less.

Next, in step S1606, the subtractor 959 subtracts the lower dot data from the upper dot data of the transparent ink to generate transparent ink binary data.
Out_t=Out_O_t-Out_U_t (32)

Through the above processing, the transparent dot data Out_t calculated is transparent dot data per scan.

In the above formula (32), the binary data Out_t of the transparent ink is generated from the difference between the N-valued result Out_O_t of the upper recording amount data O_t of transparent ink and the N-valued result Out_U_t of the lower recording amount data U_t. .. However, the method of generating Out_t is not limited to this calculation.
For example, when the upper recording amount data O_t is equal to or larger than the threshold Th_t of the T threshold matrix 956 and the lower recording amount data U_t is smaller than Th_t, Out_t=1 may be set, and otherwise, Out_t=0 may be set. That is, similar results are obtained even if Out_t=1 under the condition of U_t<Th_t≦O_t and Out_t=0 under the other conditions.

In step S1607, it is determined whether the above-described steps S1601 to S1606 have been performed up to addresses (0, 0) to (W-1, Nzzl-1) within the band. If there is an unprocessed area, the process returns to step S1601. Repeat the process. By performing such processing, the dot arrangements of the cyan and transparent ink dot data Out_c, Out_t are determined. Note that W is the image size of the input image. For other colors, magenta Out_m, yellow Out_y, and black Out_k are generated by the same processing as the cyan dot data, and the dot data formed by each print scan is determined. With the above processing, the dot control processing in step S705 shown in FIG. 7 ends.

As described above, the dot control processing at the scan number k=1 is completed, and as a result, the dot data formed by one head operation for each color is stored in the storage buffer 206 for each color.

Next, in step S706, the image processing apparatus 200 outputs the band-shaped dot data stored in the storage buffer 206, which corresponds to the number of nozzles (Nzzl) in the vertical direction and the X size (W) of the image in the horizontal direction. The image is output from the terminal 207 to the image forming apparatus 250.

FIG. 18 shows the dot data stored in the storage buffer 206 when the scan number k=4 for cyan and transparent ink. Black dots in FIG. 18 are pixels in which dots are formed, and white dots are pixels in which dots are not formed. That is, in contrast to cyan ink, dots are formed in the transparent ink above the nozzles. This is because at least a part of the transparent ink is formed on the upper layer of the cyan ink as shown in FIG.

In step S751, the image forming apparatus 250 acquires the dot data transferred from the image processing apparatus 200. Next, in step S752, the image forming apparatus 250 starts the printing operation based on the dot data acquired in step S751. Specifically, the ink color selection unit 256 of the image forming apparatus 250 selects an ink color that matches the dot data acquired in step S751, and the printing operation is started. In step S752, while the recording head 251 moves from the left to the right with respect to the recording medium, each nozzle is driven at a constant drive interval to perform one main scan for recording an image on the recording medium. Further, when the main scanning is completed, the sub-scanning, which is the scanning in the vertical direction with respect to the main scanning, is performed once. In step S753, the image forming apparatus 250 repeats the processing of steps S751 and S752 until the printing processing of all data is completed.

Next, the description returns to the processing of the image processing apparatus 200. In step S707, the image processing apparatus 200 determines whether or not all scanning has been completed. When it is finished, the series of image forming processes is completed, and when it is not finished, the process returns to step S703, the scan number k to be processed is incremented, and the processes from step S703 are repeated. With the above, all the processes are completed.

Here, FIGS. 19 and 20 show an example of the data in the middle of the calculation of the dot data generation unit 205 of the cyan ink and the transparent ink described above and the result thereof.

In FIG. 19, cyan ink upper dot data Out_O_c1902 is obtained based on the cyan ink upper recording amount data O_c1901 of scan number 1. Further, the cyan ink lower dot data Out_U_c1904 is obtained based on the cyan ink lower recording amount data U_c1903 of scan number 1. As a result, the cyan dot data Out_c1905 is obtained from the equation (27).

On the other hand, the transparent ink upper dot data Out_O_t1907 is obtained based on the transparent ink upper recording amount data O_t1906 of the scan number 1. Further, the transparent ink lower dot data Out_U_t1909 is obtained based on the transparent ink lower print amount data U_t1908 of the scan number 1. As a result, the transparent ink dot data Out_t 1910 is obtained from the equation (32).

Further, cyan ink upper dot data Out_O_c1912 is obtained based on the cyan ink upper recording amount data O_c1911 of scan number 2. Further, cyan ink lower dot data Out_U_c1914 is obtained based on the cyan ink lower recording amount data U_c1913 of scan number 2. As a result, the cyan ink dot data Out_c1915 is obtained from the equation (27).

Further, the transparent ink upper dot data Out_O_t1917 is obtained based on the transparent ink upper recording amount data O_t1916 of scan number 2. In addition, the transparent ink lower dot data Out_U_t1919 is obtained based on the transparent ink lower recording amount data U_t1918 of scan number 2. As a result, the transparent ink dot data Out_t 1920 is obtained from the equation (32). Thereafter, dot data is similarly obtained for scan numbers 3 and 4.

It should be noted that, for example, the upper print amount data O_c1901 of the scan number 1 of cyan ink and the lower print amount data U_c1913 of the scan number 2 of cyan ink are the same data. That is, in the scan number 2 of cyan ink, cyan ink dot data Out_c1915 is obtained by subtracting cyan ink lower dot data Out_U_c1914 from cyan ink upper dot data Out_O_c1912. This means that control is performed so that dots are not formed in scan number 2 at the same positions where dots were formed in scan number 1. Similarly for the transparent ink, in the scan number 4, control is performed so that no dot is formed in the scan of the scan number 4 at the same position where the dot is formed in the scan number 3.

When these processes are repeated, the dots obtained in each scan and finally obtained are as shown in FIG. The dot data 2001 of FIG. 20 is the dot data of the cyan ink and the transparent ink obtained at each scan number, and the cumulative dot data 2002 is the cyan ink (C) and the transparent ink (formed by the corresponding scan number). It is the cumulative dot data of T). Further, in the accumulated dot data 2002, T is on the same cell and C is on the same cell, the cyan ink and the transparent ink overlap, and the transparent ink (T) is the upper layer and the cyan ink (C) is the lower layer. It has become.

From the cumulative dot data, it is understood that, in the cyan ink and transparent ink dot data, the transparent ink is the upper layer and the cyan ink is the lower layer in the region where the overlap occurs.

In addition, in the above-mentioned example, an example in which the entire transparent ink is fixed to the upper layer of the cyan ink is shown, but it is not always necessary that all of the transparent ink is fixed to the upper layer. Is also good.

As described above, when arranging at least a part of the transparent ink on the upper layer, the film thickness non-uniformity is increased by setting the cycle of film thickness change to 40 μm to 320 μ or less. In order to do as described above, in the present embodiment, regarding transparent ink, a plurality of dots are set at adjacent positions such that the droplets in the same scan come into contact with each other, so that the droplets are made identical on the recording medium. The unit of this identification is 40 μm to 320 μm.

As described above, according to the present embodiment, regarding transparent ink, a plurality of dots are set at adjacent positions such that a plurality of droplets of the transparent ink in the same scan come into contact with each other, and thus the droplets are formed on the recording medium. Make them identical. At this time, the droplets of the transparent ink are made uniform by setting the cycle to be 40 μm to 320 μm or less.

As a result, by increasing the non-uniformity (variation) of the film thickness of the ink having high transmittance (transparent ink) while keeping the inclination of the image surface in the normal direction small, the gloss uniformity (especially gloss image clarity) can be improved. ) Can be reduced and the coloring of specular reflection can be reduced.

In the above example, the transparent ink is formed later than the color ink by the dither processing for each scan. At this time, with respect to the transparent ink, dots were arranged at adjacent positions such that a plurality of droplets contact each other within the same scan.

However, even if the error diffusion process is performed for each scan, the same control as described above is possible. At this time, in order to arrange the dots at the adjacent positions where a plurality of droplets in the same scan come into contact with each other, the output feedback type error diffusion method, which is the dot concentration control of the error diffusion method, may be used. .. The output feedback type error diffusion method is described in the following document, for example. ``Modern Digital Halftoning (Signal Processing and Communications)'' by Daniel L. Lau, Gonzalo R. Arce
The measurement of the period of change in the thickness of the transparent ink in this embodiment can be easily verified by using an optical microscope. FIG. 21 shows an example of observing the distribution of transparent ink formed on paper with an optical microscope under epi-illumination. It can be seen from FIG. 21 that the interference fringes are observed as a circle. The interval of the interference fringes of this circle is the period of change in the thickness of the transparent ink. FIG. 21 shows an example in which a plurality of dots are set at adjacent positions such that the liquid droplets come into contact with each other in the same scanning so that the cycle of thickness change of transparent ink is 160 μm (1200 dpi, size of 8×8 in the same scanning). is there. As described above, the verification of whether the cycle of the change in the thickness of the transparent ink is 40 μm to 320 μ or less can be measured from the actually prepared sample.

In the above-described embodiments, in order to increase the non-uniformity of the transparent ink film thickness, an example in which the period of the transparent ink film thickness change is set in the range of 40 μm to 320 μm in all regions on the image surface is shown. .. However, due to the dot arrangement, it may not be possible to set the cycle of film thickness change in the range of 40 μm to 320 μm in all regions.

In that case, even in a part of the area, the cycle of the change in the thickness of the transparent ink may be set to be 40 μm to 320 μm. That is, the film thickness change period may be set to a range of 40 μm to 320 μm only in some regions, and the film thickness change period of the remaining regions may be set to 20 μm.

As described above, even if the period of the change in the thickness of the transparent ink in a part of the area is set to 40 μm to 320 μm, an ink (transparent ink) having a high transmittance can be obtained while keeping the inclination of the image surface in the normal direction small. It has a sufficient effect to increase the nonuniformity (variation) of the film thickness. This reduces coloring of specular reflection while improving gloss uniformity (especially gloss image clarity).

In addition, setting the cycle of the change in the thickness of the transparent ink to be 40 μm to 320 μm in some areas also includes the following states.

For example, the ink dots when the ink droplets are fixed on the paper surface may not be one, but may be formed as two or more separated ink dots. This occurs because the droplets are separated into a plurality of droplets and are formed on the paper surface during the ink ejection process. Of the two or more separated ink dots, the dot smaller than the main droplet dot that originally landed is called a satellite dot. The satellite dots may be formed at a great distance (100 microns or more in some cases) from the main droplet. When the main droplet dots and the satellite dots are formed far apart from each other, there is a high possibility that the inks do not contact each other and are not made identical. However, even if the main droplet dot and the satellite dot do not contact and are not made identical, since the satellite dot is smaller than the main droplet dot, the influence on the inclination of the image surface in the normal direction is minor. is there.

That is, even if the satellite dots are not the same, if the cycle of the thickness change of the main droplet is 40 μm to 320 μm, the cycle of the thickness change of the transparent ink is 40 μm to some areas. It is included in that it is 320 μm.

Further, in the above-described embodiment, the example in which the size is the same in the range of 40 μm to 320 μm is shown, but the size may be different for each place. For example, one region may be 40 μm in size and the adjacent region may be 80 μm.

Further, in the above-mentioned embodiment, an example of forming a square of 40 μm to 320 μm has been shown, but the square need not be a square. For example, a certain region may be a rectangle having a length of 40×width of 80 μm, and a certain region may be a rectangle having a length of 100×width of 40 μm. Further, it may have a non-rectangular shape such as a circle or an ellipse.

<Modification>
In the above example, the dither processing for each scan and the scan data control in which the transparent ink is formed later than the color ink in the scan data are used to enable the transparent ink to be the upper layer and the dot concentration degree control. ..

However, it is also possible to use a known mask disassembly process (so-called pass mask) as a method of controlling the dot data for each scan in which dots of transparent ink are formed later than color ink. The dot data control for mask decomposition will be described with reference to the block in FIG. Note that this modification is the dot data control processing in the dot data generation unit 205 in FIG. 1, and the flowchart uses FIG. 7 as in the first embodiment. Further, in this modified example, the steps other than steps S704 to S705 in FIG.

First, in step S704, the setting unit 901 sets a mask pattern indicating the print amount and print order for each nozzle for each scan using the pass mask 2201. FIG. 23 shows a pass mask PsMsk_c2301 for cyan ink and a pass mask PsMsk_t2302 for transparent ink. White pixels in the pass mask mean non-printing and a pixel value is 0, black pixels mean printing and a pixel value is 1.

For example, in the cyan ink pass mask 2301, only the lower half nozzles are used, and an image is formed while the paper is fed by 1/4 of the paper feed amount nozzle length. Further, in the pass mask 2302 of the transparent ink, only the upper half nozzle is used, and the image is formed while the paper is fed by 1/4 of the paper feed amount nozzle length.

In the example of FIG. 23, since the number of nozzles used is half with the pass masks of cyan ink and transparent ink, an image is formed by substantially two-pass printing. In the example of the pass mask of cyan ink, the image is exclusively formed in the printing of the previous two scans of the four scans. On the other hand, in the example of the pass mask of transparent ink, an image is formed in the printing of the latter two scans of the four scans. Therefore, the cyan ink is first formed on the recording medium, and the transparent ink is formed on the cyan ink. Although not shown, other color inks such as magenta, yellow, and black are formed on the recording medium before the transparent ink, using only the nozzles at the lower end 1/2 as in the cyan ink. Let's decide.

As described above, the print amount and print order setting for each scan in step S704 in the present modification is completed.

Next, in step S705, the control unit 951 in the dot data generation unit 205 performs N-value conversion from the color separation data of each color, and further generates dot data for each scan using the pass mask described above.

Also in the control unit 951 of this modification, the processing is different between the ink T (transparent) having a relatively high transmittance and the ink C (cyan) having a relatively low transmittance, which are arranged in the upper layer. However, the feature of the transparent ink (T) treatment in this modification is that the film thickness variation period is 40 μm or more and 320 μm, and the unevenness of the film thickness is increased while the inclination of the image surface in the normal direction is reduced. There is no change in making it happen. As a result, the uniformity of gloss, in particular the gloss image clarity, is improved and the coloring of specular reflection due to the bronze phenomenon and the thin film interference phenomenon is reduced.

The control unit 951 in this modification will be described below. 22 shows a configuration of a control unit 951 applicable to this modification, and FIG. 24 shows a flowchart of the control unit 951.

In step S2401, the control unit 951 N-values the CMYK color separation values calculated by the equations (1) to (4). Regarding the N-value conversion of the cyan ink, the N-value conversion section 2203 uses the C threshold matrix Th_c 2202 to perform the N-value conversion. The C threshold matrix 2202 is the same as that shown in FIG. The threshold value corresponds to the pixel in the cyan color separation data C (equation (1)). Therefore, the N-valued unit 2203 calculates the N-valued data by comparing the pixel value representing the cyan color separation data for each pixel with the threshold Th_c in the C threshold matrix 2202.
When C <Th_c, N_Out_c=0 (33)
When Th_c≦C, N_Out_c=1 (34)

The output value obtained as a result is N-valued data N_Out_c of cyan ink. Note that, in the above example, an example of binarization of 0 and 1 is shown, but when the C threshold matrix Th_c uses N−1 thresholds for each pixel, N binarization is possible. Further, although the cyan ink is N-valued in the above example, the N-values of other MYKs are also implemented.

Next, in step S2402, the color separation value T (transparent ink) calculated by equation (5) is N-valued. Regarding N-value conversion of the transparent ink, the N-value conversion section 2211 uses the T threshold matrix 2210 to perform N-value conversion. The T threshold matrix 2210 is the same as that shown in FIG. The threshold value corresponds to the pixel in the transparent ink color separation data T (Equation (5)). Therefore, the N-valued unit 2211 compares the pixel value representing the transparent ink color separation data for each pixel with the threshold Th_t in the T-threshold matrix 2210 to calculate the N-valued data.
When T <Th_t, N_Out_t=0 (35)
When Th_c≦T, N_Out_t=1 (36)

The output value obtained as a result is N-valued data N_Out_t of the transparent ink. Also for transparent ink, when N-1 threshold values are used for each pixel in the T threshold matrix 2210, N-value conversion is possible.

Next, in step S2403, the mask decomposition unit 2212 performs mask decomposition of the N-valued data using the pass mask 2201 to generate dot data for each scan.

The cyan ink pass mask PsMsk_c2301 is represented by binary values 0 and 1, and the transparent ink pass mask PsMsk_t2302 is also represented by binary values 0 and 1. At this time, the path decomposition is expressed by the following logical product.
Out_c =
N_Out_c(nx,ny+cut(k))∩PsMsk_c(nx%Msk_x,ny)
...(37)
Out_t =
N_Out_t(nx,ny+cut(k))∩PsMsk_t(nx%Msk_x,ny)
(38)
(∩: means logical product)

Note that cut(k) in the XY coordinates (nx, ny+cut(k)) of equations (37) and (38) is the scanning position at the scanning number k shown in equation (6). Further, ny is 0≦ny<Nzzl (the number of nozzles), and nx is the X coordinate of the original input image.

Further, Msk_x is the horizontal size of the pass mask, and nx% Msk_x means nx is the remainder of the X coordinate of the original N-valued image and Msk_x. That is, the pass mask is repeatedly used in the horizontal direction.

Here, Out_c and Out_t are dot data for one scan of cyan and transparent ink. Here, N_Out_c takes a value of 0 or 1, and PsMsk_c takes a value of 0 or 1. At this time, Out_c is calculated by the logical product ∩ so that it takes any value of 0 and 1. The rules are as follows.
N_Out_c:0, PsMsk_c:0 ⇒ Out_c:0
N_Out_c:0, PsMsk_c:1 ⇒ Out_c:0
N_Out_c:1, PsMsk_c:0 ⇒ Out_c:0
N_Out_c:1, PsMsk_c:1 ⇒ Out_c:1
...(39)

The transparent ink Out_t is also calculated by the logical product ∩ according to the same rule.

When the resolution in this modification is 1200 dpi, one pixel is about 20 μm. At that time, in order to set the cycle of the change in the thickness of the transparent ink to 40 μm to 320 μ or less, a pass mask is required to set a plurality of dots at adjacent positions so that the liquid droplets come into contact with each other in the same scan and to make the liquid droplets identical. Is. The unit of the pass mask for this identification must be 40 μm to 320 μm.

Therefore, in this modification, as shown in FIG. 23, the pass mask PsMsk_t 2302 is set so that units of 2×2 pixels or more (40 μm or more) to 16×16 pixels or less (320 μm or less) are formed in the same scan. It

Next, in step S2404, the processes of steps S2401 to S2403 described above are performed up to addresses (0, 0) to (W-1, Nzzl-1) in the band. As a result, the dot data Out_c and Out_t of the cyan and transparent ink are determined. Note that W is the image size of the input image. For other colors, magenta Out_m, yellow Out_y, and black Out_k are generated by the same processing as the cyan dot data, and the dot data formed by each print scan is determined. With the above, the dot control processing in step S705 ends.

As described above, the dot control processing at the scan number k=1 is completed, and as a result, the dot data formed by one head operation for each color is stored in the storage buffer 206 for each color. After that, the image formation is completed by the same steps as steps S706 to S708 of the first embodiment.

In this modification, the dot data stored in the storage buffer 206 at the scan number k=4 for cyan and transparent ink is the dot data shown in FIG. 18 as in the first embodiment.

Further, the dot data in the middle of the dot data generation unit 205 of cyan ink and transparent ink also becomes the dot data shown in FIG.

Further, in the present modification, even if the amount of transparent ink ejected is changed to some extent, it is possible to make the transparent ink droplets the same by using a pass mask that sets 2×2 pixels or more to 16×16 or less in the scan. For example, as shown in FIG. 25, with respect to N-valued data 2501 with a large amount of transparent ink after N-valued, dot data 2502 generated by a pass mask in which 8×8 droplets contact each other. Indicates. On the other hand, with respect to the N-valued data 2503 with a small amount of transparent ink ejected after the N-valued, dot data 2504 generated by a pass mask in which 8×8 droplets come into contact with each other. At this time, in the dot data 2502 in the case where the ejection amount after N-value conversion is large, the ink in the 8×8 unit area is in contact. Also in the dot data 2504 in the case where the ejection amount after the N-value conversion is small, the ink in the 8×8 unit area contacts. This is because the dot size of the transparent ink on the inkjet type recording medium has a dot size (30 μm or more) larger than the 1200 dpi resolution of 20 μm. It is not always necessary that all dots be formed at all adjacent pixel positions. For example, even in-scan dot data such as dot data 2504 in which white pixels are inserted, the dot size is large, so the recording medium The above identification phenomenon occurs. In the case of the dot data 2504, the amplitude of the change in the transparent ink film thickness is slightly smaller than that of the dot data 2502. However, the dot data 2502 and the dot data 2504 are the same in that the cycle of film thickness change is 160 μm.

As described above, according to the present modified example, with regard to transparent ink, by setting a plurality of dots at adjacent positions so that the droplets in the same scan come into contact with each other, a pass mask that makes the droplets the same on the recording medium is formed. use.

At this time, the unit of the equalization is set to 40 μm to 320 μm so that the cycle is set to 40 μm to 320 μm or less, and the droplets of the transparent ink are identified.

Specifically, when the resolution is 1200 dpi, one pixel is about 20 μm. Therefore, the dot setting at the adjacent position where a plurality of transparent ink droplets in the same scan contact each other is 2×2 pixels in the scan. The pass mask is set to the range of 16 to 16 or less.

As a result, by increasing the non-uniformity (variation) of the film thickness of the ink having high transmittance (transparent ink) while keeping the inclination of the image surface in the normal direction small, the gloss uniformity (especially gloss image clarity) can be improved. ) Can be reduced and the coloring of specular reflection can be reduced.

[Example 2]
In the above-described first embodiment, an example has been described in which a plurality of dots are set at adjacent positions such that the liquid droplets of the transparent ink in the same scan come into contact with each other to make the liquid droplets identical on the recording medium. The unit of this identification is 40 μm to 320 μm or less. As a result, by increasing the non-uniformity (variation) of the film thickness of the ink having high transmittance (transparent ink) while keeping the inclination of the image surface in the normal direction small, the gloss uniformity (especially gloss image clarity) can be improved. ) Has been improved and the coloring of specular reflection is reduced.

In this embodiment, the ejection amount of the transparent ink droplets is set to be larger than the ejection amounts of the other ink colors, and the dots are set so that the transparent ink droplets do not contact each other. Specifically, the recording head 251 is set so that the discharge amount of the transparent ink is 40 μm to 320 μm in terms of the dot diameter size on the recording medium. When inkjet glossy paper is used as a general recording medium, the ejection amount is set to about 7 picoliters to several hundred picoliters in order to set the dot diameter size on the recording medium to 40 μm to 320 μm. The ink colors (CMYK) other than the transparent ink are ejected in an amount of about 2 to 4 picoliters so that the dot diameter is about 20 to 30 μm on the same recording medium as in Example 1.

Using the recording head 251 described above, the control unit 951 of the present embodiment performs different processing for the ink T (transparent) having a relatively high transmittance and the ink C (cyan) having a relatively low transmittance, which are arranged in the upper layer. Let The characteristic of the transparent ink (T) treatment of the present embodiment is the same as that of the first embodiment, in which the cycle of the change in the thickness of the transparent ink is set to 40 μm or more and 320 μm or less, and the inclination of the image surface in the normal direction is kept small, Increase the non-uniformity of. This improves the gloss uniformity, especially the gloss image clarity, while reducing the coloring of specular reflection light due to the bronze phenomenon and the thin film interference phenomenon.

Specifically, since the discharge amount of the transparent ink of this embodiment is large, the number of dots for discharging the transparent ink is reduced as compared with other ink colors. Furthermore, it is set discretely so that the plural droplets of the transparent ink in the same scan do not contact each other. The transition until the droplets are fixed at this time is shown in FIG. 15B (1507 to 1512).

First, dots are set so that the droplets do not come into contact with each other in the same scan even if the droplets have a large ejection amount, and the ink liquid is ejected from the recording head 251 (1507). Next, a single large ink drop is formed on the recording medium (1508). The droplets are set so that the dot diameter at this time is 40 μm to 320 μm.

The formation of ink droplets within the same scan is completed, and the ink is solidified and fixed over time (1509). After being solidified (fixed), the non-uniformity of the film thickness increases because the ejection amount is large. Since the time until this solidification (fixing) is several hundred milliseconds at the longest, in the next scan, ink droplets do not come into contact with each other at the positions adjacent to the dots in the previous scan (1510, 1511). By forming a plurality of scans so that the liquid droplets do not come into contact with each other, the cycle of film thickness change is controlled so as to form a lens shape having a cycle of 40 μm to 320 μm (1512).

As a result, by increasing the nonuniformity (variation) of the thickness of the transparent ink (transparent ink) while keeping the inclination of the image surface in the normal direction small, the gloss uniformity (particularly the gloss image clarity) is improved. While still improving, the coloring of specular reflection is reduced. As described above, the nonuniformity of the thickness of the transparent ink is analyzed by a subjective evaluation (sensory evaluation) that the specular reflection light looks white when the difference between the thin part and the thick part is 180 nm (nanometer) or more. I understand. Therefore, it is desirable that the thickness be 180 nm or more, but sometimes 180 nm cannot always be realized depending on the composition of ink droplets and the like. In that case, it is desirable to increase nonuniformity as much as possible.

With respect to the above-described processing, the dots obtained by each scan of cyan ink and transparent ink and finally obtained are as shown in FIG. The dot data 2601 in FIG. 26 is dot data of cyan ink and transparent ink obtained at each scan number, and the accumulated dot data 2602 is cyan ink (C) and transparent ink (T ) Is cumulative dot data. In addition, in the cumulative dot data 2602, T is on the upper side and C is on the lower side, the cyan ink and the transparent ink overlap, and the transparent ink (T) is the upper layer and the cyan ink (C) is the lower layer. It has become. From the cumulative dot data, it is understood that, in the cyan ink and transparent ink dot data, the transparent ink is the upper layer and the cyan ink is the lower layer in the region where the overlap occurs.

Further, in FIG. 26, the number of transparent inks (T) is small and the interval between the transparent inks is 40 μm or more. Even with the above settings, since the dot size of the transparent ink on the recording medium is set to 40 μm to 320 μm or less, most of the paper surface can be covered.

The dot data described above can be created by the dithering process in the control unit 951 of FIG. 9 of the first embodiment, or can be created by the pass mask in the control unit 951 of FIG. 22 of the modification of the first embodiment. ..

As described above, according to this embodiment, the ejection amount of the transparent ink droplets is set to be larger than the ejection amounts of the other ink colors, and further, the dot setting is performed so that the transparent ink droplets do not contact each other. ..

Specifically, the recording head 251 is set so that the discharge amount of the transparent ink is 40 μm to 320 μm in terms of the dot diameter size on the recording medium.

As a result, by increasing the non-uniformity (variation) of the film thickness of the ink having high transmittance (transparent ink) while keeping the inclination of the image surface in the normal direction small, the gloss uniformity (especially gloss image clarity) can be improved. ) Can be reduced and the coloring of specular reflection can be reduced.

[Example 3]
In Examples 1 and 2 described above, the cycle of the film thickness change was set to 40 μm to 320 μm or less by the ink having the same size or a large discharge amount due to the contact of the transparent ink droplets in the same scan. As a result, by increasing the non-uniformity (variation) of the film thickness of the ink having high transmittance (transparent ink) while keeping the inclination of the image surface in the normal direction small, the gloss uniformity (especially gloss image clarity) can be improved. ) Was improved and the coloring of specular reflection was reduced.

In this embodiment, first, a layer is formed in which the minimum period of change in the thickness of the transparent ink is shorter than 40 μm. At this time, the layer is formed so as to include a periodic component of 40 μm to 320 μm as a global change of the thickness of the transparent ink. After that, a plurality of dots are set at adjacent positions where droplets in the same scan of the transparent ink come into contact with each other, and the droplets are made uniform on the recording medium. By this identification, the periodic component of the transparent ink that is shorter than 40 μm that is initially formed is removed.

The CMYKT ink in this embodiment has a discharge amount of about 2 to 4 picoliters such that the dot diameter is about 20 to 30 μm on the same recording medium as in the first embodiment.

In order to realize the above, the control unit 951 of the present embodiment makes the processing different between the ink T (transparent) having a relatively high transmittance and the ink C (cyan) having a relatively low transmittance, which are arranged in the upper layer.

Also in this embodiment, the transparent ink is formed on the upper layer of the cyan ink. For this transparent ink, first, a layer is formed in which the minimum cycle of film thickness change is shorter than 40 μm. At this time, the layer is formed so as to include a periodic component of 40 μm to 320 μm as a global change of the film thickness. After that, a plurality of dots are set at adjacent positions where droplets in the same scan of the transparent ink come into contact with each other, and the droplets are made uniform on the recording medium. By this identification, the periodic component of the transparent ink that is initially formed and is shorter than 40 μm is removed.

As a result, as in Examples 1 and 2, the period of change in the thickness of the transparent ink is set to 40 μm or more and 320 μm or less, and the unevenness of the film thickness is increased while the inclination of the image surface in the normal direction is kept small. This improves the gloss uniformity, especially the gloss image clarity, while reducing the coloring of specular reflection light due to the bronze phenomenon and the thin film interference phenomenon.

The transition until the droplet is fixed at this time is shown in FIG. 15C (1513 to 1518).

First, dots are set so that the liquid droplets do not contact each other in the same scan, and the ink liquid is ejected from the recording head 251 (1513, 1514). At this time, since the dot diameter on the recording medium becomes 20 to 30 μm, the minimum cycle of the change in the thickness of the transparent ink becomes a cycle shorter than 40 μm (1515).

Next, by overlapping these dots, a layer is formed so as to include a periodic component of 40 μm to 320 μm as a global change in the thickness change of the transparent ink (1516).

After that, a plurality of dots are set at adjacent positions where the liquid droplets in the same scan of the transparent ink contact each other, and the liquid droplets are made to be the same on the recording medium (1517). By this identification, the periodic component of the transparent ink that is initially formed and is shorter than 40 μm is removed. Thus, the cycle of film thickness change is controlled so as to form a lens shape having a cycle of 40 μm to 320 μm. (1518).

As a result, by increasing the nonuniformity (variation) of the thickness of the transparent ink (transparent ink) while keeping the inclination of the image surface in the normal direction small, the gloss uniformity (particularly the gloss image clarity) is improved. While still improving, the coloring of specular reflection is reduced. As described above, the nonuniformity of the thickness of the transparent ink is analyzed by a subjective evaluation (sensory evaluation) that the specular reflection light looks white when the difference between the thin part and the thick part is 180 nm (nanometer) or more. I understand. Therefore, it is desirable that the thickness be 180 nm or more, but sometimes 180 nm cannot always be realized depending on the composition of ink droplets and the like. In that case, it is desirable to increase nonuniformity as much as possible.

With respect to the above processing, the dots obtained by each scan of cyan ink and transparent ink and finally obtained are as shown in FIG. The dot data 2701 in FIG. 27 is dot data of cyan ink and transparent ink obtained at each scan number, and the accumulated dot data 2702 is cyan ink (C) and transparent ink (T) formed by the corresponding scan number. ) Is cumulative dot data. Further, in the cumulative dot data 2702, in the same cell where T is above and C is below, the cyan ink and the transparent ink overlap, the transparent ink (T) is the upper layer, and the cyan ink (C) is the lower layer. It has become. That is, the cells in the order of T and C from the top mean that T is the upper layer and C is the lower layer. Furthermore, from the top, the masses indicated in the order of T, T, and C mean that there are three layers, and that T is the upper layer, middle layer, and C is the lower layer.

From the cumulative dot data, it is understood that, in the cyan ink and transparent ink dot data, the transparent ink is the upper layer and the cyan ink is the lower layer in the region where the overlap occurs.

In FIG. 27, the cyan ink (C) is formed at the scan number k=1 (first pass). On the other hand, transparent ink is formed at scan numbers k=2 (second pass) and k=3 (third pass). In the second pass and the third pass, the dot data formed by the transparent ink (T) in the same scan is not set to the adjacent position in most of the vertical, horizontal, and diagonal directions. That is, in the same scan, most of the liquid droplets do not come into contact with each other, so that the same ink does not occur on the recording medium. As a result, a layer is formed in which the minimum cycle of film thickness change is shorter than 40 μm.

Further, during the scanning of the second pass and the third pass, there are dots in which the transparent inks overlap each other. That is, the nonuniformity of the transparent ink film thickness increases. At this time, the layer is formed so as to include a periodic component of 40 μm to 320 μm as a global change of the film thickness.

As a result of the scanning of the second and third passes, a layer having a minimum thickness change period of a period shorter than 40 μm, and a layer including a periodic component of 40 μm to 320 μm is formed as a global change of the film thickness change. It

Finally, in the scanning of the fourth pass, the transparent ink is formed at the position adjacent to the pixel including the diagonal direction. As a result, the transparent ink droplets in the same scan come into contact with each other, so that the periodic component formed earlier than 40 μm is removed. As a result, a lens-shaped layer having a period of 40 μm to 320 μm is finally formed as a period of film thickness change.

The above-mentioned dot data can be generated by dither processing by the control unit 951 of FIG. 9 of the first embodiment or by pass decomposition using a pass mask by the control unit 951 of FIG. 22 of the modification of the first embodiment. Further, it can be created by a combination of the above-mentioned dither processing and path decomposition using a path mask. For example, the second to third passes may be generated by pass decomposition using a pass mask, and the fourth pass may be generated by dither processing.

As described above, according to the present embodiment, first, a layer having a cycle of film thickness change shorter than 40 μm is formed. At this time, the layer is formed so as to include a periodic component of 40 μm to 320 μm as a global change of the film thickness. After that, dots are set at adjacent positions where the transparent ink droplets contact each other in the same scan, and the droplets are made to be the same on the recording medium. By this homogenization, the periodic component of the transparent ink which is shorter than 40 μm and which is previously formed is removed.

As a result, by increasing the non-uniformity (variation) of the film thickness of the ink having high transmittance (transparent ink) while keeping the inclination of the image surface in the normal direction small, the gloss uniformity (especially gloss image clarity) can be improved. ) Can be reduced and the coloring of specular reflection can be reduced.

Further, in the above-described third embodiment, the non-uniformity of the film thickness of the transparent ink is controlled by controlling the dot data in scanning. For example, in the second pass and the third pass, the nonuniformity of the film thickness is increased, and in the fourth pass, a fine periodic component having a period of 40 μm or less formed earlier is removed. However, with respect to the above, the same effect can be obtained by using at least two kinds of transparent inks having different ink compositions. For example, in the second pass and the third pass (preceding pass), the transparent ink including the period in which the film thickness change is shorter than 40 μm or the period in which the thickness is 40 μm to 320 μm in the first transparent ink which is relatively easily roughened. Form the layers. After that, by forming a transparent ink layer using a second transparent ink that is relatively easy to be smoothed, which is different from the first transparent ink that is likely to be uneven in the fourth pass (subsequent pass), it is shorter than 40 μm. Remove the cycle. In this way, by making the ink type different, the nonuniformity (variation) of the film thickness of the ink having high transmittance (transparent ink) is increased while the inclination of the image surface in the normal direction is kept small. As a result, coloring of specular reflection can be reduced while improving gloss uniformity (particularly gloss image clarity).

<Modification>
In each of the above-described embodiments, an image processing apparatus using a serial inkjet recording method, in which a recording head having a plurality of nozzles arranged in a predetermined direction is scanned a plurality of times on a recording medium in a direction intersecting the nozzle arrangement direction. Explained. However, the processing of each of the above-described embodiments can be applied to an inkjet recording method having a plurality of full line heads for the same color. In that case, the order in which the transparent ink is formed is set last. Furthermore, the dot data corresponding to each scan may be replaced with the dot data formed by each head.

Further, it can be applied to a recording apparatus (for example, a thermal transfer method or an electrophotographic method) that performs recording according to a method other than the inkjet method. In this case, the nozzles that eject ink droplets correspond to the recording elements that record dots and the laser light emitting elements.

The present invention supplies a program that implements one or more functions of the above-described embodiments to a system or apparatus via a network or a storage medium, and one or more processors in a computer of the system or apparatus read and execute the program. It can also be realized by the processing. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

202 input image buffer 203 color separation processing unit 204 color separation LUT
205 dot data generation unit 206 storage buffer

Claims (14)

An image forming apparatus for forming an image using at least a first color material and a second color material having different transmittances,
Recording means for recording the first color material having a higher transmittance than the second color material on at least a part of the surface of the recording medium,
The film thickness of the first color material recorded on the recording medium is changed so as to form a periodic pattern composed of a plurality of dots, the amplitude of the pattern is 30 nm or more, and the pattern of the surface of the pattern is changed. Control means for controlling the recording means such that the inclination in the line direction is 0.5 degrees or less;
An image forming apparatus comprising: The image forming apparatus according to claim 1, wherein the amplitude of the pattern is 90 nm or more. The image forming apparatus according to claim 1, wherein a cycle of the pattern is 40 μm or more and 320 μm or less. 4. The control unit controls the recording unit so that the amplitude of the pattern is 90 nm or more in a region where the average film thickness of the first color material is 2 μm or less. The image forming apparatus according to any one of claims. 5. The recording means records the first color material on the predetermined area by a plurality of scans after the scan for recording the second color material on the predetermined area. The image forming apparatus according to claim 1. 6. The control unit acquires data indicating a region in which dots of the first color material are formed, and controls the recording unit based on the acquired data. The image forming apparatus according to item. 7. The image forming apparatus according to claim 6, wherein the control unit acquires data that is generated based on dither processing and that sets the period of the pattern to 40 μm or more and 320 μm or less. 7. The image forming according to claim 6, wherein the control unit acquires data for making the cycle of the pattern 40 μm or more and 320 μm or less, which is generated based on the process using the pass mask. apparatus. 9. The control unit controls the cycle of the pattern by contacting a plurality of liquid droplets in the same print scan on the print medium, according to claim 1. Image forming apparatus. 9. The image forming apparatus according to claim 1, wherein the control unit controls the cycle of the pattern according to the size of a single droplet on the recording medium. The control unit records the first color material so as to form a pattern including a cycle shorter than 40 μm, and then contacts the plurality of droplets on the recording medium to make the cycle of the pattern 40 μm or more. The image forming apparatus according to claim 1, wherein the thickness is 320 μm or less. The control unit controls the recording of the first color material so that a pattern including a cycle shorter than 40 μm is formed in the first scan in the same area, and further, the control is performed more than in the first scan. 12. The image forming apparatus according to claim 11, wherein the period of the pattern is set to 40 μm or more and 320 μm or less by contacting a plurality of liquid droplets on the recording medium in the second scanning performed later. .. A printed matter formed by recording at least a first color material and a second color material having different transmittances on a recording medium,
A first color material having a higher transmittance than the second color material is recorded on the second color material,
The film thickness of the first color material recorded on the recording medium changes as a periodic pattern composed of a plurality of dots, the amplitude of the pattern is 30 nm or more, and the surface of the pattern has a normal direction. A printed matter having an inclination of 0.5 degrees or less. An image forming method for forming an image using at least a first color material and a second color material having different transmittances,
A recording step of recording the first color material having a higher transmittance than the second color material on at least a part of the surface of the recording medium,
The film thickness of the first color material recorded on the recording medium in the recording step is changed so as to form a periodic pattern composed of a plurality of dots, and the amplitude of the pattern is 30 nm or more, and the pattern A control step of controlling so that the inclination of the surface in the normal direction is 0.5 degrees or less;
An image forming method comprising: