JP2012205124A - Printing system, printing method, and program - Google Patents

Abstract

Printing is performed with an appropriate gradation value even for a medium whose type is unknown.
Light scattering characteristics of a target medium that is an unknown medium are measured (step S1). The measured light scattering characteristics and the light scattering characteristics of a plurality of known dedicated media are compared, and a dedicated medium having similar light scattering characteristics to the target medium is selected (step S2). A conversion table corresponding to the selected dedicated medium is acquired and set in the conversion table of the target medium (step S3). The input data is converted using the set conversion table (step S4). Print data is printed on the target medium (step S5).
[Selection] Figure 1

Description

  The present invention relates to a printing system, a printing method, and a program, and more particularly to a technique for printing on an unknown medium with appropriate gradation values.

  In a printing apparatus, processing for converting input data into print data is performed using a conversion table according to the printing medium for the purpose of guaranteeing color reproducibility or making the color unevenness unique to the printing apparatus inconspicuous. . Accordingly, there is a problem in that the conversion process cannot be appropriately performed on a recording medium whose type is unknown, and printing suitable for the recording medium cannot be performed.

  In response to this problem, Patent Document 1 inputs an ejection limit value that can be ejected per unit area by printing a pattern for setting an ejection limit value on paper and making the user visually recognize the degree of bleeding of the printed pattern. A technique for selecting a paper conversion table having an ejection limit value close to the input ejection limit value using correspondence data indicating the relationship between the paper type and the ejection limit value is disclosed. According to this technique, even if the type of medium is unknown, a conversion table for media having similar injection limit values can be used.

JP 2009-220356 A

  However, in the technique described in Patent Document 1, since the user needs to visually recognize the degree of pattern bleeding, the conversion table cannot be automatically selected.

  Furthermore, when the technique described in Patent Document 1 is applied to the color conversion table, an appropriate medium cannot be selected if the injection limit value is close, and color reproduction accuracy may be insufficient.

  The present invention has been made in view of such circumstances, and a printing system, a printing method, and a program capable of easily and accurately converting gradation values in a color space of image data printed on a medium whose type is unknown. The purpose is to provide.

  In order to achieve the above object, a printing method according to the present invention includes a measuring step for measuring light scattering characteristics of a print target medium, and a plurality of known light characteristics stored in the measured light scattering characteristics and light scattering characteristics storage means. A specific step of comparing a light scattering characteristic of the dedicated medium to identify a dedicated medium having a light scattering characteristic similar to the print target medium, and a conversion table storage in which conversion tables of the plurality of known dedicated media are stored A conversion table acquisition step of acquiring a conversion table corresponding to the specified dedicated medium, a data acquisition step of acquiring input data to be printed, and an image processing step of generating print data from the input data. An image processing step of converting the gradation value of the input data using the acquired conversion table, and printing for printing on the print target medium based on the print data Characterized in that a degree.

  According to the present invention, it is possible to easily and accurately convert a gradation value in a color space of image data printed on a medium whose type is unknown.

Flow chart showing print processing Diagram showing an example of a light scattering characteristic measuring instrument Top view of transmissive rectangular wave chart Diagram showing image detection results Diagram showing the behavior of light when the target medium is irradiated with light Diagram showing the shape of each function The figure which expanded a part of detected image, and the figure which shows the result of sampling processing Graph showing an example of measured light scattering characteristics of the target medium Diagram showing an example of correspondence between each dedicated medium and its light scattering characteristics The figure which shows an example of a response | compatibility with each exclusive medium and its conversion table Flow chart showing conversion table setting processing when using large classification together Diagram showing an example of correspondence between each dedicated medium and its light scattering characteristics Graph showing an example of light scattering characteristics and reflectance Diagram showing an example of a light scattering characteristic measuring instrument Diagram showing image detection results Configuration diagram showing overall configuration of inkjet recording apparatus Schematic configuration diagram of inkjet head Partial enlarged view of inkjet head Plan view showing nozzle arrangement of sub head Block diagram showing system configuration of inkjet recording apparatus

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[First Embodiment]
FIG. 1 is a flowchart showing print processing according to the present embodiment. In this specification, a medium whose conversion table is unknown is called a target medium (print target medium), and a medium whose conversion table is known is called a dedicated medium.

  The outline of the printing process of this embodiment will be described. First, the light scattering characteristic of the target medium is measured (step S1), and the light scattering characteristic of the dedicated medium is compared with the measured light scattering characteristic. The dedicated medium closest to is selected (step S2). Next, the conversion table for the selected dedicated medium is set as the conversion table for the target medium (step S3). The input data is converted by the set conversion table (step S4), and finally the print data is printed on the target medium based on the converted data (step S5).

  Details of each step will be described below.

<< Measurement of Light Scattering Characteristics of Target Medium (Step S1) >>
First, the light scattering characteristics of the target medium are measured with a dedicated measuring instrument. FIG. 2 is a schematic diagram showing an example of this light scattering characteristic measuring instrument.

  As shown in FIG. 2, the light scattering characteristic measuring instrument 10 receives a light source 30 that irradiates light to the target medium 20, a transmission rectangular wave chart 40 that is in close contact with the surface of the target medium 20, and reflected light from the target medium 20. The high-resolution image detector 50 to measure is comprised.

  The light source 30 includes a light emitter such as a fluorescent lamp or an LED, and irradiates the target medium 20 with a predetermined amount of light from, for example, an angle of 45 degrees.

  The transmission type rectangular wave chart 40 is a measurement chart in which a plurality of rectangular patterns 44 are formed at a predetermined interval on a transparent member 42 such as a glass substrate (see FIG. 3). The pattern 44 is deposited with a metal such as chromium. The shape and arrangement of this pattern are not limited to the example in FIG. 3, and may be determined as appropriate.

  The high-resolution image detector 50 has a number of image sensors such as CCDs arranged two-dimensionally, and detects the reflected light distribution of the target medium 20 as two-dimensional data. Note that the two-dimensional data may be detected by arranging the image sensors in a line and relatively moving the target medium 20 and the line-shaped image sensor.

  In the light scattering characteristic measuring instrument 10 configured as described above, the light source 30 irradiates the target medium 20 with light in a state where the transmission rectangular wave chart 40 is in close contact with the target medium 20.

  A predetermined pattern 44 is formed on the transmissive rectangular wave chart 40 as described above. Therefore, the light from the light source 30 is not transmitted in the region where the pattern 44 is formed, and the light from the light source 30 is transmitted in the region where the pattern 44 is not formed.

  The light that has passed through the transmissive rectangular wave chart 40 is reflected by the target medium 20 and is transmitted through the transmissive rectangular wave chart 40 again and emitted.

  The high resolution image detector 50 detects the target medium 20 including the region of the transmission type rectangular wave chart 40. FIG. 4 is a diagram schematically showing a result of image detection by the high resolution image detector 50.

Here, the extending direction of the pattern 44 of the transmission type rectangular wave chart 40 (Y ₁ direction), and the high-resolution image detector 50 of the two-dimensional array of Y-direction of the image pickup element (Y ₂ direction), but about twice Each is arranged to have a slope of.

<< Light scattering characteristics >>
A region 52 in FIG. 4 is a region where the transmission type rectangular wave chart 40 is in close contact. Therefore, the region where the pattern 44 is formed does not transmit light and is measured darkly. On the other hand, in the region between the patterns 44 where the pattern 44 is not formed, the light reaches the target medium 20 and the light is scattered inside the target medium 20, whereby the edge portion is measured to be blurred or slightly dark. Qualitatively, this blur condition indicates the light scattering characteristic of the target medium 20.

  Next, a method for quantifying the blur condition will be described. FIG. 5 is a diagram showing the behavior of light when the transmission rectangular wave chart 40 is brought into close contact with the target medium 20 and light is irradiated from above. In the figure, x indicates a spatial position, and will be described in one dimension for simplicity.

The intensity of the irradiated light is i ₁ (x). This i ₁ (x) first passes through the transmissive rectangular wave chart 40. Here, when the transmittance of the transmission-type rectangular wave chart 40 is τ (x), the intensity i ₂ (x) after transmission is

It is expressed. Further, τ (x) can be approximated as follows.

  In Equation 2, n is an integer greater than or equal to 0, and a is the period of the pattern 44. That is, in Equation 2, light is completely blocked (transmittance is 0) in the region where the pattern 44 of the transmission type rectangular wave chart 40 is formed, and all light is transmitted in the region where the pattern 44 is not formed ( The transmittance is 1).

Next, the light intensity i ₂ (x) obtained through the transmission-type rectangular wave chart 40 is incident on the target medium 20 and is scattered by the point spread function PSF _p (x) inside the target medium 20. . Further, the light is reflected by the reflectance r _p of the target medium 20, and the light intensity changes to i ₃ (x) expressed by the following equation.

  In Equation 3, * represents a convolution integral.

The light intensity i ₃ (x) emitted from the target medium 20 passes through the transmission rectangular wave chart 40 again. At this time, the light intensity changes to i ₄ (x) represented by the following equation.

Next, assuming that the intensity distribution i ₁ (x) of the incident light is constant regardless of the spatial position x, the relative reflectance r _{1_3} (x) from i ₁ (x) to i ₃ (x) is

It can be expressed as. Modulation transfer light scattering of the target medium 20 is an index indicating quantitatively function MTF _p (u) is defined by the absolute value of the Fourier transform of the point spread function PSF _p (x), the left side and r _p number 5 And by performing Fourier transform on both sides, the following equation 6 can be obtained.

Here, u represents the spatial frequency, R _{1_3} (u) represents the Fourier transform of r _{1_3} (x), and T (u) represents the Fourier transform of τ (x). However, this method has the following problems. That is, the light intensity measured by the high-resolution image detector 50 i ₃ instead _{(x), i 3 (x} ) is i ₄ after passing through the rectangular wave chart layer again (x). Therefore, the numbers 5 and 6 cannot be used directly.

_Consider the relative reflectance r _{1 — 4} (x) from i ₁ (x) to i ₄ (x). This relative reflectance r _{1_4} (x) is expressed by the following equation.

However, even if the Fourier transform is applied to Equation 7, it is mathematically impossible to analytically solve MTF _p (u) as in Equation 5 → Expression 6. Therefore, r _{1_4} (x) to r _{1_3} (x) are approximated by the following equation.

FIGS. _6A to 6C are diagrams respectively showing the shapes of functions of τ (x), r _{1_3} (x), and r _{1_4} (x). r _{1_3} (x) and as can be seen when r _{1_4} comparing (x), a half cycle of the r _{1_4} (x) has the same shape as r _{1_3} (x), the remainder of the half cycle becomes 0 Yes. Therefore, the half period phase shift r _{1_4} to (x), by further applying what the shape is turned upside down on a portion of the 0 component of r _{1_4} (x), to restore the shape of the r _{1_3} (x) be able to. This is expressed by Equation 8 as a mathematical expression.

As described above, first, r 1 — ₄ (x) is restored from r 1 — ₄ (x) according to _Equation 8, and then _Equations 5 and 6 are used to obtain MTF _p (u) indicating the light scattering degree of the target medium 20. Can be calculated.

Next, a method for obtaining r 1 — ₄ (x) from the measurement image shown in FIG. 4 will be described. FIG. 7A is an enlarged view of a part of the detected image shown in FIG. Reference numeral 56 shown in FIG. 7A indicates a sampling point measured by the image sensor of the high resolution image detector 50. Here, in order to simplify the description, the arrangement of the sampling points 56 is assumed to have a very low resolution.

  In the example shown in FIG. 7A, there are 85 sampling points 56 of 5 rows × 17 columns. Therefore, an image of 85 pixels composed of the light intensity detected by each sampling point 56 is measured.

  Here, a light intensity image is acquired in advance by measuring a complete diffuse reflection surface such as a standard white plate by the high resolution image detector 50. By dividing the light intensity image obtained as shown in FIG. 7A by this light intensity image, the light intensity image can be converted into a reflectance image.

Next, for example, a pixel in the third row from the top can be extracted from the obtained reflectance image and defined as r 1 — ₄ (x). However, r 1 — ₄ (x) obtained in this way is low-resolution data with very rough sampling. Therefore, by using the data in the first, second, fourth, and fifth lines as well as the third line, the r _{1_4} (x) data is made to have a higher resolution as shown in the graph of FIG. 7B. Perform a premium (pre-sampling process).

In order to perform this extra, and an extended direction of the pattern 44 of the transmission type rectangular wave chart 40 (Y ₁ direction), the high-resolution image detector 50 of the two-dimensional array of Y-direction of the image pickup element (Y ₂ direction) Are tilted in advance by about 2 to 3 degrees (see FIG. 4). The x coordinate of the increased data can be determined from the sampling density of the high-resolution image detector 50 (imaging element arrangement pitch) and the inclination of the pattern 44 of the transmission type rectangular wave chart 40.

  In this way, by slightly tilting the pattern 44 of the transmission type rectangular wave chart 40, even when the resolution of the high-resolution image detector 50 is not so high, the sampling data is increased by performing the pre-sampling process, and the light scattering characteristics are improved. Measurement accuracy can be improved. Further, by setting the inclination to an amount of about 2 to 3 degrees, it is possible to improve the sampling data extra efficiency.

If r _{1_4} (x) can be _obtained in this way, then r _{1_4} (x) is restored from r _{1_4} (x) using _Equation 8, and then the light scattering characteristics of the medium are shown using _Equations 5 and 6. MTF _p (u) can be calculated.

  Strictly speaking, the MTFp (u) obtained in this way is influenced by the modulation transfer function of the high-resolution image detector 50 itself, and is a light scattering characteristic of a pure medium in a physical sense. Absent. However, in this embodiment, since the light scattering characteristics of the target medium and the dedicated medium are all measured by the same high resolution image detector 50, the high resolution image detector is used for comparing the measured light scattering characteristics. The influence of 50's own modulation transfer function can be ignored. Thus, since it is not necessary to separately measure the modulation transfer function of the high-resolution image detector 50 itself, the light scattering characteristic measuring instrument 10 can be simply constructed.

If it is desired to compare the light scattering characteristics measured by different image detectors, the modulation transfer function MTF _system (u) of the high-resolution image detector 50 is separately measured, and MTFp (u) is calculated as MTF _system (u ) Is defined as the light scattering characteristic of the medium, and the light scattering characteristics of the medium obtained by removing the influence of the modulation transfer function of the image detector thus obtained can be compared.

  In addition, strictly speaking, the light scattering characteristic measured by the light scattering characteristic measuring instrument 10 causes boundary multiple reflection at the boundary of the transmission-type rectangular wave chart 40 in close contact with the target medium 20, but is shown in FIG. Since the boundary surface multiple reflection is not considered in the behavior of light, it is not a light scattering characteristic of a pure medium in a physical sense. However, in this embodiment, since the light scattering characteristics of the target medium and the dedicated medium are all measured by the same light scattering characteristic measuring instrument 10, when comparing the measured light scattering characteristics, the interface multiple reflection is used. You can safely ignore the effect.

  The light scattering property of the medium can be considered as a physical quantity that explains the optical dot gain that strongly affects the color reproducibility of the printed matter. The optical dot gain is an apparent increase in the area ratio of ink dots due to light scattering inside the medium. Therefore, the conversion table can be set with high accuracy by using the light scattering characteristic in this way.

FIG. 8 is a graph showing an example of MTF _p (u), which is the measured light scattering characteristic of the target medium 20, and similarly shows the MTF _p (u) of the dedicated media A and B. Here, the horizontal axis is plotted as the spatial frequency, and the vertical axis is plotted as the modulation ratio between input and output. The smaller the ratio of modulation at each spatial frequency, the stronger the degree of light scattering.

<< Select a dedicated medium whose light scattering characteristics are closest to the target medium (step S2) >>
FIG. 9 is a diagram illustrating an example of correspondence between each dedicated medium and its light scattering characteristics. These light scattering characteristics are obtained by measuring and storing each dedicated medium by the high resolution image detector 50 in advance through experiments or the like. In FIG. 8 shown above, the light scattering characteristics of the dedicated media A and B are plotted as an example.

Here, first, the degree of difference between the light scattering characteristics of each dedicated medium and the light scattering characteristics of the target medium 20 is evaluated. The degree of difference can be evaluated by, for example, a weighted sum of squares of distances for each spatial frequency of the two light scattering characteristics. As in the present embodiment, in the case of using the MTF _p (u) to the light scattering properties dissimilarity E _s can be calculated by Equation 9 shown below.

Here, p1 indicates a dedicated medium, and p2 indicates a target medium. MTF _{p1, i} indicates the value of the i-th MTF when MTF _p1 (u) is divided into n pieces of data discretely on the spatial frequency axis. That is, i represents the spatial frequency, and MTF _{p1, i−} MTF _{p2, i} represents the difference between the MTF of the dedicated medium and the target medium at the same spatial frequency. Here, a _i indicates a weight whose value range is [0-1].

In this way, by using the weighted sum of squares, for example, it is possible to perform adjustment such as decreasing the weight as the frequency becomes higher. Therefore, it is possible to evaluate accurately dissimilarity E _s.

As the weight a _i , for example, a visual contrast sensitivity function indicating a spatial frequency characteristic of human vision may be used. Thus, human becomes possible to evaluate and close when observing the medium, as a result, it is possible to evaluate accurately dissimilarity E _s.

Thus, to calculate the degree of difference E _s per-only media, finally, dissimilarity E _s to select the smallest only medium. As described above, since the selection can be automatically performed, not only the processing speed increases, but even a user who is not familiar with image quality evaluation can easily set the conversion table.

<< Set Conversion Table of Selected Dedicated Medium as Target Medium (Step S3) >>
FIG. 10 is a diagram illustrating an example of a correspondence between each dedicated medium and its conversion table. For each dedicated medium, a conversion table suitable for the dedicated medium is set in advance. Here, the conversion table for the dedicated medium selected above is set as the conversion table for the target medium 20. As the conversion table to be set, for example, there is a color conversion table for converting the first color space data to the second color space data, and an unevenness correction conversion table for correcting the density value of the data.

  In this way, by acquiring the light scattering characteristics of the target medium, specifying a dedicated medium with similar light scattering characteristics, and setting the conversion table of the specified dedicated medium as the conversion table of the target medium, printing on the target medium is performed. The conversion table can be set easily and with higher accuracy without performing it.

<< Convert Input Data with Set Conversion Table (Step S4) >>
Next, image data to be printed on the target medium is acquired, and print data is generated from the image data. At this time, the gradation value of the input data is converted based on the conversion table set as described above. As a result, color conversion processing and unevenness correction processing suitable for the target medium can be performed.

<< Printing Print Data on Target Medium (Step S5) >>
The print data generated in this way is printed on the target medium. As a result, printing is performed with gradation values and densities suitable for the target medium.

  As described above, according to the printing process of the present embodiment, the gradation value in the color space of the image data printed on the medium of unknown type can be converted into the gradation value suitable for the unknown medium. As a result, it is possible to print with a gradation value suitable for the unknown medium.

<< Accuracy improvement by introducing target medium type selection step >>
The setting of the conversion table may use not only the degree of difference in the light scattering characteristics of the medium but also a large classification according to the medium type. For example, if the medium is paper, it can be classified into glossy paper, matte paper, uncoated paper, etc. in advance to reduce the load of the light scattering characteristic difference calculation process, and the conversion table with high accuracy. Can be set.

  FIG. 11 is a flowchart showing conversion table setting processing when the large classification is used together.

  First, the user selects the type of the target medium 20 (step S11). For example, a list of medium types may be displayed on the display unit, and the list can be selected from the list. As the type of the target medium 20, in the case of paper, gloss paper, matte paper, uncoated paper, or the like can be considered.

  The major classification of the target medium 20 may be automatically classified by reading information such as a bar code arranged on the paper feed tray instead of being selected by the user.

  Next, the light scattering characteristic of the target medium 20 is measured (step S12). This step is the same as step S1 in the flowchart shown in FIG.

  Next, a dedicated medium having a light scattering characteristic closest to the light scattering characteristic measured in step S12 is selected from the same type of dedicated medium as the target medium 20 (step S13).

  FIG. 12 is a diagram illustrating an example of the correspondence between each dedicated medium and its light scattering characteristics. As shown in the figure, each dedicated medium is classified in advance by its type. Therefore, a dedicated medium having the light scattering characteristic closest to the target medium 20 may be selected from the same types of dedicated media as the type selected in step S11.

  For example, when the user selects gloss paper in step S11, the light scattering characteristics of each dedicated medium of gloss paper are compared with the light scattering characteristics of the target medium 20 measured in step S12, and the light scattering characteristics are the best. A dedicated medium close to the target medium 20 is selected.

  Finally, the conversion table of the selected dedicated medium is set as the conversion table of the target medium 20 (step S14), and when the print data is generated from the input data, the gradation value of the input data is converted using the conversion table. Then, the print data is printed on the target medium (step S16). This process is also the same as steps S3 to S5 in the flowchart shown in FIG.

  As described above, the target medium and the dedicated medium are roughly classified according to the medium type, and the degree of difference between the target medium and the light scattering characteristic of the target medium is compared with the light scattering characteristic of the dedicated medium of the same medium type. A conversion table can be set.

<< Improvement of accuracy by using reflectance >>
In setting the conversion table, the difference in reflectance of the medium may be used in addition to the difference in light scattering characteristics of the medium. By adding the difference in reflectance to the comparison in this way, the conversion table can be set with high accuracy even if the target medium is a special medium having a low reflectance (dark).

When the reflectances of the dedicated medium and the target medium are r _p1 and r _p2 , respectively, the reflectance difference degree E _r is expressed by the following formula 10.

  Further, when using the difference in light scattering characteristics and the difference in reflectance, the overall difference E can be defined as a weighted sum as shown in Equation 11 below, for example.

Here, b _s and b _r indicate weights whose value ranges are [0-1], respectively. In this way, the total difference E with each dedicated medium is calculated, and the conversion table for the dedicated medium having the smallest total difference E may be set as the conversion table for the target medium. Further, by using the weight, it is possible to set the conversion table with higher accuracy.

  A region 54 in FIG. 4 can be used to measure the reflectance (whiteness) of the target medium 20. The standard white plate is measured in advance by the high-resolution image detector 50, the measurement image shown in FIG. 4 is divided by the standard white plate image, and the average value of the area 54 of the divided image is calculated to obtain the reflectance of the medium. Can be acquired. In this way, since both the light scattering degree and the reflectance can be calculated from a single image as shown in FIG. 4, the measurement data amount can be shortened compared to the case where each is separately measured. There are advantages such as a reduction in size and a reduction in the size of the measuring instrument.

  FIG. 13 is a graph showing an example of light scattering characteristics and reflectance. Here, the plot for the DC component with a spatial frequency of 0 indicates the reflectance of the medium.

<< Improvement of accuracy by using color information >>
The high-resolution image detector 50 may be a monochrome image sensor, but may be a color image sensor in which color filters are arranged for each pixel. By using a color image sensor, the reflectance of each color component can be separately measured. In this way, by adding the degree of difference in color information to the comparison, it is possible to set a conversion table with high accuracy even for a special target medium having color.

In the case of using an RGB three-primary-color imaging device as an example, the target medium 20 is photographed, the average intensity value is calculated for each channel, and the light intensity of each channel of the dedicated medium and the target medium is represented by c _{p1, r} , C _{p1, g} , c _{p1, b} , c _{p2, r} , c _{p2, g} , c _{p2, b} , the color information dissimilarity E _c is expressed by Expression 12 shown below.

  When the difference degree of the light scattering characteristic and the difference degree of the color information are used, the overall difference degree E can be defined by a weighted sum as shown in the following Expression 13, for example.

Here, b _s and b _c indicate weights whose value ranges are [0-1], respectively. In this way, the total difference E with each dedicated medium is calculated, and the conversion table for the dedicated medium having the smallest total difference E may be set as the conversion table for the target medium. Further, by using the weight, it is possible to set the conversion table with higher accuracy.

  Here, the case where an RGB three-primary-color image sensor is used has been described as an example. However, for example, color information is obtained by increasing a color channel to perform so-called multiband imaging, or spectral reflectance is measured to obtain color information. You may get.

[Second Embodiment]
FIG. 14 is a diagram illustrating an example of a light scattering characteristic measuring instrument according to the second embodiment. As shown in the figure, the light scattering characteristic measuring instrument 12 is a lens that irradiates the target medium 20 with light, a light source 30 for condensing the light from the light source 30, and irradiating the surface of the target medium 20 with a minute dot image. 60 and a high-resolution image detector 50 that measures the reflected light of the target medium 20.

  In the light scattering characteristic measuring device 12 configured as described above, the lens 60 collects the light emitted from the light source 30 and irradiates the target medium 20 with a minute point image.

  The high resolution image detector 50 detects the target medium 20 including the area of the minute dot image. FIG. 15 is a diagram schematically showing a result of image detection by the high resolution image detector 50. 58 in the figure is a region in which the minute dot image projected on the target medium 20 is blurred due to the light scattering characteristics of the target medium 20.

  By detecting the spread distribution of the region 58, performing two-dimensional Fourier transform on the detected distribution, and calculating the absolute value thereof, the light scattering characteristic of the target medium 20 similar to that in FIG. 8 can be obtained. As described above, by using the minute point image, it is not necessary to closely attach the transmission type rectangular wave chart 40 to the target medium 20, and the measuring instrument can be configured in a simple manner.

  Instead of condensing the light from the light source 30 with the lens 60, a laser light source capable of projecting a minute dot image may be used as the light source 30. In this case, the lens 60 can be omitted.

[Configuration of image forming apparatus]
Next, an image forming apparatus to which the above-described light scattering characteristic measuring instrument is applied will be described.

<< Description of Overall Configuration of Inkjet Recording Apparatus >>
FIG. 16 is a configuration diagram showing the overall configuration of the ink jet recording apparatus according to the present embodiment. The ink jet recording apparatus 310 shown in the figure forms an image on a recording surface of a recording medium 314 based on predetermined image data using an ink containing a color material and an aggregating treatment liquid having a function of aggregating the ink. This is a two-liquid aggregation type recording apparatus.

  The ink jet recording apparatus 310 mainly includes a paper feeding unit 320, a processing liquid application unit 330, a drawing unit 340, a drying processing unit 350, a fixing processing unit 360, and a discharge unit 370. Transfer cylinders 332, 342, 352, and 362 are provided as means for delivering the recording medium 314 conveyed upstream of the processing liquid application unit 330, the drawing unit 340, the drying processing unit 350, and the fixing processing unit 360. As means for conveying the recording medium 314 while holding it in the coating unit 330, the drawing unit 340, the drying processing unit 350, and the fixing processing unit 360, impression cylinders 334, 344, 354, and 364 having drum shapes are provided. .

  The transfer cylinders 332, 342, 352, 362 and the impression cylinders 334, 344, 354, 364 are provided with grippers 380 A, 380 B that hold the front end (or rear end) of the recording medium 314 at predetermined positions on the outer peripheral surface. It has been. The structure for holding the tip of the recording medium 314 in the gripper 380A and the gripper 380B and the structure for transferring the recording medium 314 between the other impression cylinder or the gripper provided in the transfer cylinder are the same, and The gripper 380 </ b> A and the gripper 380 </ b> B are arranged at symmetrical positions that are moved 180 ° in the rotation direction of the pressure drum 334 on the outer peripheral surface of the pressure drum 334.

  When the transfer cylinders 332, 342, 352, 362 and the impression cylinders 334, 344, 354, 364 are rotated in a predetermined direction with the gripper 380 A, 380 B holding the leading end of the recording medium 314, the transfer cylinders 332, 342 are rotated. , 352, 362 and the impression cylinders 334, 344, 354, 364, the recording medium 314 is rotated and conveyed along the outer peripheral surface.

  In FIG. 16, only the grippers 380 </ b> A and 380 </ b> B provided in the pressure drum 334 are denoted by reference numerals, and the other gripper and transfer cylinder grippers are omitted.

  When the recording medium (sheet) 314 stored in the paper feeding unit 320 is fed to the processing liquid application unit 330, the aggregation process is performed on the recording surface of the recording medium 314 held on the outer peripheral surface of the impression cylinder 334. A liquid (hereinafter simply referred to as “treatment liquid”) is applied. The “recording surface of the recording medium 314” is an outer surface in a state where the impression cylinders 334, 344, 354, and 364 are held, and is a surface opposite to a surface held by the impression cylinders 334, 344, 354, and 364. It is.

  Thereafter, the recording medium 314 to which the aggregation processing liquid has been applied is sent to the drawing unit 340, and color ink is applied to the area of the recording surface to which the aggregation processing liquid has been applied, thereby forming a desired image.

  Further, the recording medium 314 on which the image of the color ink is formed is sent to the drying processing unit 350, where the drying processing unit 350 performs the drying process, and after the drying process, the recording medium 314 is sent to the fixing processing unit 360 to perform the fixing process. Applied. By performing the drying process and the fixing process, the image formed on the recording medium 314 is hardened. In this manner, a desired image is formed on the recording surface of the recording medium 314. After the image is fixed on the recording surface of the recording medium 314, the image is conveyed from the discharge unit 370 to the outside of the apparatus.

  Hereinafter, each part (the paper feed unit 320, the processing liquid application unit 330, the drawing unit 340, the drying processing unit 350, the fixing processing unit 360, and the discharge unit 370) of the ink jet recording apparatus 310 will be described in detail.

<< Paper Feeder >>
The paper feed unit 320 is provided with a paper feed tray 322 and a feed mechanism (not shown), and the recording medium 314 is configured to be fed from the paper feed tray 322 one by one. The recording medium 314 sent out from the paper feed tray 322 is positioned by a guide member (not shown) so that the leading end is positioned at a gripper (not shown) of the transfer drum (paper feed drum) 332 and temporarily stops.

  The light scattering characteristic measuring instrument 10 is arranged on the upper part of the recording medium 314 in this state. A transmissive rectangular wave chart 40 is brought into close contact with the recording medium 314 whose conveyance has been stopped by a chart driving mechanism (not shown), and light is emitted from the light source 30. The reflected light is measured by the high resolution image detector 50, so that a conversion table for the recording medium 314 is set. Here, it is also possible to apply the light scattering characteristic measuring instrument 12 that does not use the transmission rectangular wave chart 40.

  If the recording medium 314 is known in advance, measurement by the light scattering characteristic measuring instrument 10 (or 12) may not be performed.

(Processing liquid application part)
The processing liquid coating unit 330 includes a pressure drum (processing liquid drum) 334 that holds the recording medium 314 delivered from the paper feed cylinder 332 on the outer peripheral surface and transports the recording medium 314 in a predetermined transport direction, and a processing liquid drum. And a processing liquid coating device 336 that applies the processing liquid to the recording surface of the recording medium 314 held on the outer peripheral surface of 334. When the processing liquid drum 334 is rotated counterclockwise in FIG. 16, the recording medium 314 is rotated and conveyed in the counterclockwise direction along the outer peripheral surface of the processing liquid drum 334.

  The processing liquid coating device 336 shown in FIG. 16 is provided at a position facing the outer peripheral surface (recording medium holding surface) of the processing liquid drum 334. As a configuration example of the processing liquid coating device 336, a processing liquid container in which the processing liquid is stored, a pumping roller that is partially immersed in the processing liquid in the processing liquid container, and pumps up the processing liquid in the processing liquid container, and a pumping roller An embodiment including an application roller (rubber roller) that moves the pumped processing liquid onto the recording medium 314 is exemplified.

  In addition, there is provided an application roller moving mechanism that moves the application roller in the vertical direction (the normal direction of the outer peripheral surface of the treatment liquid drum 334), and a configuration in which collision between the application roller and the grippers 380A and 380B can be avoided. preferable.

  The treatment liquid applied to the recording medium 314 by the treatment liquid application unit 330 contains a color material flocculant that aggregates the color material (pigment) in the ink applied by the drawing unit 340, and the treatment liquid is applied on the recording medium 314. And the ink come into contact with each other, the separation of the color material and the solvent in the ink is promoted.

  The treatment liquid application device 336 is preferably applied while measuring the amount of the treatment liquid applied to the recording medium 314, and the film thickness of the treatment liquid on the recording medium 314 is determined by the ink droplets ejected from the drawing unit 340. It is preferable to make it sufficiently smaller than the diameter.

<< Drawing part >>
The drawing unit 340 holds an impression cylinder (drawing drum) 344 that holds and conveys the recording medium 314, a sheet pressing roller 346 for bringing the recording medium 314 into close contact with the drawing drum 344, and an inkjet that applies ink to the recording medium 314. Heads 348M, 348K, 348C, and 348Y are provided. The basic structure of the drawing drum 344 is the same as that of the processing liquid drum 334 described above, and a description thereof is omitted here.

  The sheet pressing roller 346 is a guide member for bringing the recording medium 314 into close contact with the outer peripheral surface of the drawing drum 344, faces the outer peripheral surface of the drawing drum 344, and delivers the recording medium 314 between the transfer drum 342 and the drawing drum 344. The recording medium 314 is disposed on the downstream side in the conveyance direction of the recording medium 314 from the position, and further on the upstream side in the conveyance direction of the recording medium 314 than the inkjet heads 348M, 348K, 348C, and 348Y.

  The recording medium 314 transferred from the transfer drum 342 to the drawing drum 344 is pressed by the sheet pressing roller 346 when being rotated and conveyed with the leading end held by a gripper (reference number omitted), and the outer periphery of the drawing drum 344. Adhere to the surface. After the recording medium 314 is brought into close contact with the outer peripheral surface of the drawing drum 344 in this way, the recording medium 314 is sent to the print area immediately below the ink jet heads 348M, 348K, 348C, 348Y without being lifted from the outer peripheral surface of the drawing drum 344. It is done.

  The inkjet heads 348M, 348K, 348C, and 348Y correspond to inks of four colors, magenta (M), black (K), cyan (C), and yellow (Y), respectively, and the rotation direction of the drawing drum 344 (see FIG. 16 (counterclockwise direction in FIG. 16) in order from the upstream side, and the ink discharge surfaces (nozzle surfaces) of the inkjet heads 348M, 348K, 348C, and 348Y are opposed to the recording surface of the recording medium 314 held by the drawing drum 344. To be arranged. Note that the “ink ejection surface (nozzle surface)” is a surface of the inkjet heads 348M, 348K, 348C, and 348Y that faces the recording surface of the recording medium 314, and is a nozzle that ejects ink (described later in FIG. 19). This is a surface on which 328 is attached.

  In addition, the inkjet heads 348M, 348K, 348C, and 348Y shown in FIG. In such a manner, it is arranged to be inclined with respect to the horizontal plane.

  The inkjet heads 348M, 348K, 348C, and 348Y are full-line heads having a length corresponding to the maximum width of the image forming area in the recording medium 314 (the length in the direction orthogonal to the conveyance direction of the recording medium 314). The recording medium 314 is fixedly installed so as to extend in a direction orthogonal to the conveyance direction of the recording medium 314.

  On the nozzle surfaces of the inkjet heads 348M, 348K, 348C, and 348Y, nozzles for ejecting ink are formed in a matrix arrangement over the entire width of the image forming area of the recording medium 314.

  When the recording medium 314 is transported to the printing area immediately below the inkjet heads 348M, 348K, 348C, 348Y, the image data is converted into the area where the aggregation processing liquid of the recording medium 314 is applied from the inkjet heads 348M, 348K, 348C, 348Y. Based on this, ink of each color is ejected (droplet ejection).

  When ink droplets of the corresponding color ink are ejected from the inkjet heads 348M, 348K, 348C, 348Y toward the recording surface of the recording medium 314 held on the outer peripheral surface of the drawing drum 344, processing is performed on the recording medium 314. The liquid and the ink come into contact with each other, and an aggregation reaction of the color material (pigment-based color material) dispersed in the ink or the color material (dye-based color material) to be insolubilized appears, and a color material aggregate is formed. As a result, movement of the color material in the image formed on the recording medium 314 (dot misalignment, dot color unevenness) is prevented.

  Further, since the drawing drum 344 of the drawing unit 340 is structurally separated from the processing liquid drum 334 of the processing liquid application unit 330, the processing liquid does not adhere to the inkjet heads 348M, 348K, 348C, and 348Y. In addition, the cause of abnormal ink ejection can be reduced.

  In this example, the configuration of CMYK standard colors (four colors) is illustrated, but the combination of ink colors and the number of colors is not limited to this embodiment, and light ink, dark ink, and special colors are used as necessary. Ink may be added. For example, it is possible to add an inkjet head that discharges light-colored ink such as light cyan and light magenta, and the arrangement order of the color heads is not particularly limited.

<< Dry processing section >>
A drying processing unit 350 holds a recording medium 314 after image formation and conveys a pressure drum (drying drum) 354, and a solvent drying device 356 that performs a drying process for evaporating water (liquid component) on the recording medium 314. It has. The basic structure of the drying drum 354 is the same as that of the processing liquid drum 334 and the drawing drum 344 described above, and a description thereof is omitted here.

  The solvent drying device 356 is a processing unit that is disposed at a position facing the outer peripheral surface of the drying drum 354 and evaporates moisture present in the recording medium 314. When ink is applied to the recording medium 314 by the drawing unit 340, the liquid component (solvent component) of the ink and the liquid component (solvent component) of the processing liquid separated by the aggregation reaction between the processing liquid and the ink are placed on the recording medium 314. Since it remains, it is necessary to remove such a liquid component.

  The solvent drying device 356 performs a drying process for evaporating the liquid component existing on the recording medium 314 by heating with a heater, blowing with a fan, or a combination thereof, and a process for removing the liquid component on the recording medium 314. Part. The amount of heating and the amount of air supplied to the recording medium 314 are appropriately set according to parameters such as the amount of moisture remaining on the recording medium 314, the type of the recording medium 314, and the conveyance speed (interference processing time) of the recording medium 314. Is done.

  When the drying process is performed by the solvent drying device 356, the drying drum 354 of the drying processing unit 350 is structurally separated from the drawing drum 344 of the drawing unit 340, so that the inkjet heads 348M, 348K, 348C, and 348Y. In this case, it is possible to reduce the cause of abnormal ink ejection due to drying of the head meniscus by heat or air blowing.

  In order to exhibit the cockling correction effect of the recording medium 314, the curvature of the drying drum 354 is preferably 0.002 (1 / mm) or more. In order to prevent the recording medium from being curved (curled) after the drying process, the curvature of the drying drum 354 is preferably set to 0.0033 (1 / mm) or less.

  In addition, a means (for example, a built-in heater) for adjusting the surface temperature of the drying drum 354 may be provided, and the surface temperature may be adjusted to 50 ° C. or higher. By performing heat treatment from the back surface of the recording medium 314, drying is promoted and image destruction during the subsequent fixing process is prevented. In such an embodiment, it is more effective to provide means for bringing the recording medium 314 into close contact with the outer peripheral surface of the drying drum 354. As an example of means for closely attaching the recording medium 314, vacuum adsorption, electrostatic adsorption, and the like can be given.

  The upper limit of the surface temperature of the drying drum 354 is not particularly limited, but from the viewpoint of safety of maintenance work such as cleaning ink adhering to the surface of the drying drum 354 (preventing burns due to high temperatures). It is preferably set to 75 ° C. or lower (more preferably 60 ° C. or lower).

  The recording medium 314 is held on the outer peripheral surface of the drying drum 354 configured as described above so that the recording surface of the recording medium 314 faces outward (that is, in a state where the recording surface of the recording medium 314 is convex). By performing the drying process while rotating and transporting, drying unevenness due to wrinkling and floating of the recording medium 314 is surely prevented.

<< Fixing processing section >>
The fixing processing unit 360 includes a pressure drum (fixing drum) 364 that holds and conveys the recording medium 314, a heater 366 that heats the recording medium 314 that has been subjected to image formation and from which the liquid has been removed, and the recording And a fixing roller 368 that presses the medium 314 from the recording surface side. The basic structure of the fixing drum 364 is the same as that of the processing liquid drum 334, the drawing drum 344, and the drying drum 354, and a description thereof is omitted here. The heater 366 and the fixing roller 368 are disposed at a position facing the outer peripheral surface of the fixing drum 364, and are sequentially disposed from the upstream side in the rotation direction of the fixing drum 364 (counterclockwise direction in FIG. 16).

  In the fixing processing unit 360, the recording surface of the recording medium 314 is subjected to preliminary heating processing by the heater 366 and fixing processing by the fixing roller 368. The heating temperature of the heater 366 is appropriately set according to the type of recording medium, the type of ink (the type of polymer fine particles contained in the ink), and the like. For example, a mode in which the glass transition temperature and the minimum film forming temperature of the polymer fine particles contained in the ink are considered.

  The fixing roller 368 is a roller member for heating and pressurizing the dried ink to weld the self-dispersing polymer fine particles in the ink to form a film of the ink, and is configured to heat and press the recording medium 314. The Specifically, the fixing roller 368 is disposed so as to be in pressure contact with the fixing drum 364 and constitutes a nip roller with the fixing drum 364. As a result, the recording medium 314 is sandwiched between the fixing roller 368 and the fixing drum 364 and nipped at a predetermined nip pressure, and the fixing process is performed.

  As an example of the configuration of the fixing roller 368, there is an embodiment in which the fixing roller 368 is configured by a heating roller in which a halogen lamp is incorporated in a metal pipe such as aluminum having good thermal conductivity. By heating the recording medium 314 with such a heating roller, when thermal energy equal to or higher than the glass transition temperature of the polymer fine particles contained in the ink is applied, the polymer fine particles are melted to form a transparent film on the surface of the image. Is done.

  When pressure is applied to the recording surface of the recording medium 314 in this state, the polymer fine particles melted into the unevenness of the recording medium 314 are pressed and fixed, and the unevenness of the image surface is leveled, so that preferable glossiness can be obtained. A configuration in which a plurality of fixing rollers 368 are provided in accordance with the thickness of the image layer and the glass transition temperature characteristics of the polymer particles is also preferable.

  The surface hardness of the fixing roller 368 is preferably 71 ° or less. By making the surface of the fixing roller 368 softer, a follow-up effect can be expected with respect to the unevenness of the recording medium 314 caused by cockling, and uneven fixing due to the unevenness of the recording medium 314 can be more effectively prevented. .

  In the ink jet recording apparatus 310 illustrated in FIG. 16, an inline sensor 382 is provided at the subsequent stage (downstream side in the recording medium conveyance direction) of the processing area of the fixing processing unit 360. The inline sensor 382 is a sensor for reading an image formed on the recording medium 314 (or a check pattern formed in a blank area of the recording medium 314), and a CCD line sensor is preferably used.

  In the ink jet recording apparatus 310 shown in this example, the presence or absence of ejection abnormality of the ink jet heads 348M, 348K, 348C, and 348Y is determined based on the reading result of the inline sensor 382 (details will be described later). Further, the inline sensor 382 may include a measuring unit for measuring a moisture amount, a surface temperature, a glossiness, and the like. In such an embodiment, parameters such as the processing temperature of the drying processing unit 350, the heating temperature of the fixing processing unit 360, and the pressurizing pressure are appropriately adjusted based on the moisture content, surface temperature, and gloss reading result, and the temperature inside the apparatus. The control parameter is adjusted as appropriate in accordance with the change and the temperature change of each part.

<< Discharge unit >>
As shown in FIG. 16, a discharge unit 370 is provided following the fixing processing unit 360. The discharge unit 370 includes an endless conveyance belt 374 wound around the stretching rollers 372A and 372B, and a discharge tray 376 that stores the recording medium 314 after image formation.

  The recording medium 314 after the fixing process sent out from the fixing processing unit 360 is transported by the transport belt 374 and discharged to the discharge tray 376.

<< Description of structure of inkjet head >>
FIG. 17 is a schematic configuration diagram of an ink jet head applied to the present invention. FIG. 17 is a view of the recording surface of the recording medium as viewed from the ink jet head (a plan perspective view of the head). In addition, since the inkjet heads 348M, 348K, 348C, and 348Y shown in FIG. Collectively, it is described as “inkjet head 348”.

  The ink-jet head 348 shown in the figure forms a multi-head by connecting n sub-heads 348-i (i is an integer from 1 to n) in a line. Each sub head 348-i is supported by head covers 349A and 349B from both sides of the inkjet head 348 in the short direction. It is also possible to configure a multi-head by arranging the sub-heads 348 in a staggered manner.

  As an application example of a multi-head configured by a plurality of sub-heads, a full-line head corresponding to the entire width of a recording medium can be given. The full-line head has a plurality of nozzles (corresponding to the length (width) in the main scanning direction of the recording medium along the direction (main scanning direction) orthogonal to the moving direction (sub-scanning direction) of the recording medium. In FIG. 19, a reference numeral 108 is attached for illustration. An image can be formed over the entire surface of the recording medium by a so-called single-pass image recording method in which the inkjet head 348 having such a structure and the recording medium are scanned only once relatively to perform image recording.

  FIG. 18 is a partially enlarged view of the inkjet head 348. As shown in the figure, the sub head 348 has a substantially parallelogram-shaped planar shape, and an overlap portion is provided between adjacent sub heads. The overlap portion is a connecting portion of the sub heads, and is formed by nozzles in which dots adjacent to the sub heads 348-i (horizontal direction in FIG. 17, main scanning direction X shown in FIG. 18) belong to different sub heads. The

  FIG. 19 is a plan view showing the nozzle arrangement of the sub head 348-i. As shown in the figure, each sub head 348-i has a structure in which nozzles 328 are arranged two-dimensionally, and a head including such a sub head 348-i is a so-called matrix head.

  In the sub head 348-i shown in FIG. 19, a large number of nozzles 328 are arranged along a column direction W that forms an angle α with respect to the sub-scanning direction Y and a row direction V that forms an angle β with respect to the main scanning direction X. The substantial nozzle arrangement density in the main scanning direction X is increased. In FIG. 19, nozzle groups (nozzle rows) arranged along the row direction V are denoted by reference numeral 328V, and nozzle groups (nozzle rows) arranged along the column direction W are denoted by reference numeral 328W. ing.

  In this matrix arrangement, when the interval between adjacent nozzles in the sub-scanning direction is Ls, in the main scanning direction, each nozzle 328 is substantially equivalent to a linear arrangement with a constant pitch P = Ls / tan θ. It can be handled.

  In the ink jet head 348 having the structure shown in FIGS. 17 to 19, the nozzle 328 has a row direction V that forms an angle β with the main scanning direction X and a column direction that forms an angle α with respect to the sub-scanning direction Y as shown in FIG. 19. The high-density nozzle head of this example is realized by arranging a large number in a lattice pattern with a constant arrangement pattern along W.

<< Explanation of control system >>
FIG. 20 is a block diagram illustrating a system configuration of the inkjet recording apparatus 310. As shown in FIG. 20, the inkjet recording apparatus 310 includes a communication interface 440 and a system control unit 442, and overall control of each unit of the apparatus is performed by the system control unit 442.

  The communication interface 440 is an interface unit (image input unit) that receives image data sent from the host computer 454. As the communication interface 440, a serial interface such as USB (Universal Serial Bus), IEEE 1394, Ethernet (registered trademark), a wireless network, or a parallel interface such as Centronics can be applied. In this part, a buffer memory (not shown) for speeding up communication may be mounted.

  The system control unit 442 includes a central processing unit (CPU) and its peripheral circuits, and functions as a control device that controls the entire inkjet recording apparatus 310 according to a predetermined program, and also functions as an arithmetic device that performs various calculations. To do. Further, it generates control signals for controlling the conveyance control unit 444, the image processing unit 446, the head driving unit 448, and the like, and functions as a memory controller for the image memory 450 and the ROM 452. Furthermore, the light scattering characteristic of the target medium is measured based on the measurement result of the light scattering characteristic measuring instrument 10, and a conversion table is set.

  The image processing unit 446 is a processing block that performs predetermined processing on the image data, and includes a processor having an image processing function. The image data sent from the host computer 454 is taken into the inkjet recording apparatus 310 via the communication interface 440 and temporarily stored in the image memory 450. The image memory 450 is a storage unit that stores an image input via the communication interface 440, and data is read and written through the system control unit 442. The image memory 450 is not limited to a memory made of a semiconductor element, and a magnetic medium such as a hard disk may be used.

  The image memory 450 stores programs executed by the CPU of the system control unit 442 and various data necessary for control (including data for ejecting test charts, abnormal nozzle information, and the like). The image memory 450 may be a non-rewritable storage means or a rewritable storage means such as an EEPROM.

  The ROM 452 stores a program executed by the CPU of the system control unit 442, and includes a program that executes the printing process shown in the flowchart of FIG.

  The ROM 452 also functions as a light scattering characteristic storage unit and a conversion table storage unit, and the correspondence between each dedicated medium shown in FIGS. 9 and 12 and its light scattering characteristic, and each dedicated medium and its conversion table shown in FIG. Is stored.

  A temporary storage unit (not shown) is used as a temporary storage area for image data and various data, and is also used as a program development area and a calculation work area for the CPU.

  The image processing unit 446 performs various processing and correction processes for generating a droplet ejection control signal from image data (multi-valued input image data) in the image memory, under the control of the system control unit 442. It functions as a signal processing means. A droplet ejection control signal (ink ejection data) generated by the image processing unit 446 is supplied to the head driving unit 448.

  That is, the image processing unit 446 includes functional blocks such as a density data generation unit, a correction processing unit, and an ink ejection data generation unit. Each of these functional blocks can be realized by ASIC, software, or an appropriate combination.

  The density data generation unit is a signal processing unit that generates initial density data for each ink color from input image data, and includes density conversion processing (including UCR processing and color conversion) and, if necessary, pixel number conversion processing. I do. The correction processing unit is a processing unit that performs density correction calculation using the density correction coefficient, and performs non-ejection correction processing and unevenness correction processing. For these processes, a conversion table stored in the ROM 452 is used as appropriate. If it is an unknown medium, the conversion table of the dedicated medium set based on the said embodiment is applied.

  The ink ejection data generation unit is a signal processing unit including a halftoning processing unit that converts the corrected image data (density data) generated by the correction processing unit into binary or multivalued dot data. Multi-value processing is performed. Various known means such as an error diffusion method, a dither method, a threshold matrix method, and a density pattern method can be applied as the halftone processing means. In the halftone process, generally, gradation image data having an M value (M ≧ 3) is converted into binary or multi-value gradation image data smaller than M. In the simplest example, the image data is converted into binary (dot on / off) dot image data. However, in the halftone process, the dot size type (for example, large size, medium size, small size) is used as in the above embodiment. Multi-level quantization corresponding to three types such as size can be performed.

  The image processing unit 446 is provided with an image buffer memory (not shown), and image data, parameters, and other data are temporarily stored in the image buffer memory when the image processing unit 446 processes image data. Note that the image buffer memory may be attached to the image processing unit 446 or may be used as the image memory. Further, the image processing unit 446 may be integrated with the system control unit 442 and configured with one processor.

  The ink discharge data generated by the image processing unit 446 (ink discharge data generation unit) is given to the head drive unit 448, and the ink discharge operation of the inkjet head 348 is controlled.

  The head drive unit 448 functions as a unit that controls the ejection drive of the inkjet head 348 and includes a drive waveform generation unit that generates a drive signal waveform for driving an actuator corresponding to each nozzle 328 of the inkjet head 348. The signal output from the drive waveform generator may be digital waveform data or an analog voltage signal.

  An overview of the flow of processing from image input to print output is as follows. Image data to be printed is input from the outside via the communication interface 440 and stored in an image memory. At this stage, for example, RGB multi-valued image data is stored in the image memory.

  In the ink jet recording apparatus 310, a pseudo continuous tone image is formed by changing the droplet ejection density and dot size of fine dots with ink (coloring material) to the human eye. It is necessary to convert to a dot pattern that reproduces the gradation (shading of the image) as faithfully as possible. Therefore, the original image (RGB) data stored in the image memory is sent to the image processing unit 446 via the system control unit 442, and is processed by the density data generation unit, the correction processing unit, and the ink ejection data generation unit. Converted to dot data for each ink color.

  At this time, color conversion processing, pixel number conversion processing, and γ conversion processing are performed on the original image data as necessary. A conversion table corresponding to the type of medium is used for these conversion processes. When the recording medium 314 is an unknown medium, a conversion table set based on the measurement result of the light scattering characteristic measuring instrument 10 is applied.

  Note that a mode using a conversion table corresponding to the type of medium is also possible for the non-ejection correction process and the unevenness correction process described above.

  As described above, the image processing unit 446 performs processing for converting the input RGB image data into dot data of four colors of M, K, C, and Y. The dot data thus generated by the image processing unit 446 is stored in the image buffer memory. This dot data for each color is converted into MKCY droplet ejection data for ejecting ink from the nozzles of the inkjet head 348 and printed, ink ejection data (dot timing for each nozzle and the dot size for each drive timing ( Discharge amount)) is confirmed.

  The head drive unit 448 outputs a drive signal for driving the actuator 132 corresponding to each nozzle 328 of the inkjet head 348 in accordance with the print content based on the ink ejection data and the drive signal (drive waveform). The head drive unit 448 may include a feedback control system for keeping the head drive conditions constant.

  In this way, the drive signal output from the head drive unit 448 is applied to the inkjet head 348, whereby ink is ejected from the corresponding nozzle 328. An image is formed on the recording medium 314 by controlling ink ejection from the inkjet head 348 in synchronization with the conveyance speed of the recording medium 314.

  As described above, based on the ink ejection data and the drive signal waveform generated through the required signal processing in the image processing unit 446, the ejection amount and ejection timing of the ink droplets from each nozzle via the head driving unit 448 are determined. Control is performed. Thereby, a desired dot size and dot arrangement are realized.

  The inline detection unit 470 illustrated in FIG. 20 is a functional block that provides information related to abnormal nozzles to the system control unit 442 through reading of nozzle detection patterns, processing of read data, and processing of determination of abnormal nozzles. The inline detection unit 470 includes the inline sensor 382 illustrated in FIG.

  The system control unit 442 performs various corrections on the ink jet head 348 based on information on the abnormal nozzle obtained from the inline detection unit 470 and other information, and also performs cleaning operations such as preliminary ejection, suction, and wiping as necessary ( Nozzle recovery operation) is performed.

  Although not shown, a maintenance processing unit including members necessary for head maintenance such as an ink receiver, a suction cap, a suction pump, and a wiper blade is provided as means for executing the cleaning operation.

  In addition, an operation unit as a user interface is provided, and the operation unit includes an input device 468 and a display unit (display) 466 for an operator (user) to perform various inputs. The input device 468 can employ various forms such as a keyboard, a mouse, a touch panel, and buttons. By operating the input device 468, the operator can perform input of printing conditions, selection of image quality mode, input / editing of attached information, information search, selection (classification) of the type of recording medium 314, and the like. Various types of information such as input contents and search results can be confirmed through display on the display unit 466. The display unit 466 functions as a means for displaying a warning such as an error message in addition to displaying a list of types of recording media.

  The ink jet recording apparatus 310 of the present embodiment has a plurality of image quality modes, and the image quality mode is set by a user's selection operation or by automatic selection by a program. The criterion for determining an abnormal nozzle is changed according to the output image quality level required in the set image quality mode. The higher the required quality, the more severe the criteria.

  Information relating to printing conditions in each image quality mode and abnormal nozzle determination criteria is stored in the image memory 450.

  Here, the embodiment in which the target medium is applied to paper has been described as a mode for carrying out the invention. However, the recording medium of the present invention is not limited to paper, and the light scattering characteristics of the target medium are known. Any medium that can compare the light scattering characteristics of the dedicated medium may be used. For example, it can be applied to tarpaulin, reboard, PET, PVC (polyvinyl chloride), back lit, aluminum composite plate and the like.

[Appendix]
As will be understood from the description of the embodiment described in detail above, this specification includes disclosure of various technical ideas including the invention described below.

  (Invention 1): The measurement step of measuring the light scattering characteristic of the print target medium is compared with the measured light scattering characteristic and the light scattering characteristics of a plurality of known dedicated media stored in the light scattering characteristic storage means. The specified target medium from the specifying step of specifying a dedicated medium having light scattering characteristics similar to those of the print target medium and the conversion table storage means storing the conversion tables of the plurality of known dedicated media. A conversion table acquisition step of acquiring a conversion table, a data acquisition step of acquiring input data to be printed, and an image processing step of generating print data from the input data, wherein the acquired conversion table is used to An image processing step for converting a gradation value of input data, and a printing step for printing on the print target medium based on the print data .

  According to the first aspect, the gradation value in the color space of the image data printed on the medium whose type is unknown can be easily and accurately converted from the viewpoint of color reproducibility.

  (Invention 2): The printing method according to Invention 1, wherein the measuring step measures the light scattering characteristic based on a modulation transfer function.

  This makes it possible to set an appropriate dedicated medium conversion table.

  (Invention 3): In the printing method of Invention 1 or 2, the light scattering characteristic is a characteristic with respect to a spatial frequency, and the specific step weights each spatial frequency and compares the light scattering characteristic.

  This makes it possible to set an appropriate dedicated medium conversion table.

  (Invention 4): The printing method according to any one of Inventions 1 to 3, further comprising a medium type acquisition step of acquiring a medium type of the print target medium, wherein the specifying step includes: A dedicated medium having light scattering characteristics similar to those of the print target medium is specified from among the dedicated media of the same medium type as the acquired medium type.

  This makes it possible to set an appropriate dedicated medium conversion table.

  (Invention 5): In the printing method of Invention 4, the medium type includes gloss paper, matte paper, and uncoated paper.

  Since the types of media can be classified in advance into glossy paper, matte paper, and uncoated paper, the processing load for comparing light scattering characteristics can be reduced, and an appropriate conversion table for dedicated media can be set. .

  (Invention 6): In the printing methods of Inventions 1 to 5, the measurement step measures the reflectance of the print target medium, and the specifying step is stored in the measured reflectance and reflectance storage means. A dedicated medium having a reflectance similar to that of the print target medium is specified based on the reflectance of a plurality of known dedicated media.

  By using the reflectivity in this way, an appropriate conversion table for a dedicated medium can be set even if the print target medium is a special medium having a low reflectivity.

  (Invention 7): In the printing methods of Inventions 1 to 5, the measuring step measures color information of the print target medium, and the specifying step is stored in the measured color information and reflectance storage means. A dedicated medium having color information similar to the print target medium is specified based on color information of a plurality of known dedicated media.

  By using color information in this way, an appropriate conversion table for a dedicated medium can be set even if the print target medium is a special medium having a tint.

  (Invention 8): In the printing method of Invention 6 or 7, the specifying step is characterized in that the light scattering characteristic and the reflectance or color information are weighted and compared.

  By weighting in this manner, an appropriate dedicated medium conversion table can be set.

  (Invention 9): In the printing method according to any one of Inventions 1 to 8, in the measurement step, a transmission chart is closely attached to the print target medium, the transmission chart is irradiated with light, and the reflected light is reflected. The light scattering characteristic of the print target medium is measured by detecting light.

  Thereby, the light-scattering characteristic of a printing target medium can be measured appropriately.

  (Invention 10): In the printing method according to any one of Inventions 1 to 8, the measurement step irradiates a surface of the print target medium with a minute point image, and detects a point spread distribution of the minute point image. The light scattering characteristic of the print target medium is measured.

  Thereby, the light-scattering characteristic of a printing target medium can be measured appropriately.

  (Invention 11): Measuring means for measuring the light scattering characteristics of the print target medium, light scattering characteristic storage means for storing the light scattering characteristics of a plurality of known dedicated media, the measured light scattering characteristics and the plurality of known And a conversion table storing a plurality of known dedicated medium conversion tables, and specifying means for identifying a dedicated medium having a light scattering characteristic similar to that of the print target medium. Storage means, conversion table acquisition means for acquiring a conversion table corresponding to the specified dedicated medium from the conversion table storage means, data acquisition means for acquiring input data to be printed, and generating print data from the input data Image processing means for converting the gradation value of the input data using the acquired conversion table, and the mark based on the print data. Printing system comprising the printing unit for printing on the target medium.

  According to the eleventh aspect, the gradation value in the color space of the image data printed on the medium whose type is unknown can be easily and accurately converted from the viewpoint of color reproducibility.

  (Invention 12): The measurement function for measuring the light scattering characteristics of the print target medium is compared with the measured light scattering characteristics and the light scattering characteristics of a plurality of known dedicated media stored in the light scattering characteristic storage means. The specific function for specifying a dedicated medium having a light scattering characteristic similar to that of the print target medium, and conversion table storage means in which conversion tables of the plurality of known dedicated media are stored correspond to the specified dedicated medium. A conversion table acquisition function for acquiring a conversion table, a data acquisition function for acquiring input data to be printed, and an image processing function for generating print data from the input data, using the acquired conversion table An image processing function for converting gradation values of input data and a printing function for printing on the print target medium based on the print data are executed by a computer. Printing program.

  The technical idea of the present specification includes a program for causing a computer to execute the above functions.

  DESCRIPTION OF SYMBOLS 10 ... Light scattering characteristic measuring device, 20 ... Target medium (print target medium), 30 ... Light source, 40 ... Transmission-type rectangular wave chart, 42 ... Transparent member, 44 ... Pattern, 50 ... High-resolution image detector, 56 ... Sampling Point, 58 ... Minute point image area, 60 ... Lens, 442 ... System control unit, 446 ... Image processing unit, 452 ... ROM, 466 ... Display unit, 468 ... Input device

Claims (12)

A measurement process for measuring the light scattering characteristics of the print target medium;
A specification for identifying a dedicated medium having similar light scattering characteristics to the print target medium by comparing the measured light scattering characteristics with the light scattering characteristics of a plurality of known dedicated media stored in the light scattering characteristic storage means. Process,
A conversion table acquisition step of acquiring a conversion table corresponding to the specified dedicated medium from a conversion table storage means in which a plurality of known dedicated medium conversion tables are stored;
A data acquisition process for acquiring input data to be printed;
An image processing step of generating print data from the input data, the image processing step of converting the gradation value of the input data using the acquired conversion table;
A printing step of printing on the print target medium based on the print data;
A printing method characterized by comprising:   The printing method according to claim 1, wherein the measuring step measures the light scattering characteristic based on a modulation transfer function.   The printing method according to claim 1, wherein the light scattering characteristic is a characteristic with respect to a spatial frequency, and the specifying step weights each spatial frequency and compares the light scattering characteristic.   A medium type acquisition step of acquiring a medium type of the print target medium, wherein the specifying step includes, among the plurality of known dedicated media, the print target from among the dedicated media of the same medium type as the acquired medium type; The printing method according to claim 1, wherein a dedicated medium having light scattering characteristics similar to the medium is specified.   The printing method according to claim 4, wherein the medium type includes gloss paper, matte paper, and uncoated paper. The measurement step measures the reflectance of the print target medium,
The specifying step specifies a dedicated medium having a reflectance similar to that of the print target medium based on the measured reflectance and the reflectances of a plurality of known dedicated media stored in a reflectance storage unit. The printing method according to any one of claims 1 to 5, wherein: The measurement step measures color information of the print target medium,
The specifying step specifies a dedicated medium having color information similar to the print target medium based on the measured color information and color information of a plurality of known dedicated media stored in the reflectance storage unit. The printing method according to any one of claims 1 to 5, wherein:   The printing method according to claim 6 or 7, wherein the specifying step compares the light scattering characteristic and the reflectance or color information by weighting.   The measurement step measures light scattering characteristics of the print target medium by bringing a transmission chart into close contact with the print target medium, irradiating the transmission chart with light, and detecting reflected light of the irradiated light. The printing method according to claim 1, wherein the printing method is performed.   The measuring step includes measuring a light scattering characteristic of the print target medium by irradiating a surface of the print target medium with a minute point image and detecting a point spread distribution of the minute point image. Item 9. The printing method according to any one of Items 1 to 8. Measuring means for measuring the light scattering characteristics of the print target medium;
Light scattering characteristic storage means for storing light scattering characteristics of a plurality of known dedicated media;
A specifying means for comparing the measured light scattering characteristics and the light scattering characteristics of the plurality of known dedicated media to identify a dedicated medium having similar light scattering characteristics to the print target medium;
Conversion table storage means in which conversion tables of the plurality of known dedicated media are stored;
Conversion table acquisition means for acquiring a conversion table corresponding to the specified dedicated medium from the conversion table storage means;
Data acquisition means for acquiring input data to be printed;
Image processing means for generating print data from the input data, the image processing means for converting the gradation value of the input data using the acquired conversion table;
Printing means for printing on the print target medium based on the print data;
A printing system comprising: A measurement function to measure the light scattering characteristics of the print target medium;
A specification for identifying a dedicated medium having similar light scattering characteristics to the print target medium by comparing the measured light scattering characteristics with the light scattering characteristics of a plurality of known dedicated media stored in the light scattering characteristic storage means. Function and
A conversion table acquisition function for acquiring a conversion table corresponding to the specified dedicated medium from a conversion table storage means in which a plurality of known dedicated medium conversion tables are stored;
A data acquisition function for acquiring input data to be printed;
An image processing function for generating print data from the input data, the image processing function for converting the gradation value of the input data using the acquired conversion table;
A print function for printing on the print target medium based on the print data;
A printing program that causes a computer to execute.