JP4720274B2 - Apparatus for simulating ink dot shape, method for simulating ink dot shape, and computer program - Google Patents

Description

  The present invention relates to a technique for simulating the shape of ink dots formed on a printed image.

  When printing an image on a printing device, color conversion processing, halftone processing, and adjacent dots are usually formed on the printing medium for gradation data representing gradation for each color component for each pixel in a dot matrix. Various image processing is performed, such as microweave processing for preventing the nozzles to be biased to the same nozzle. The image quality of the printed matter printed through such image processing greatly depends on the content of the image processing. Although this image quality can be evaluated based on various viewpoints, frequency analysis is known as a method for evaluating noise and smoothness of appearance, that is, graininess (for example, Non-Patent Document 1).

Makoto Fujino, “Japan Hardcopy '99 Proceedings”, p.291-294

  In the above-mentioned Non-Patent Document 1, it is necessary to actually print an image based on data after image processing and to scan the print result with a scanner in order to evaluate the graininess. Therefore, conventionally, there has been a demand for a method for evaluating the image quality of a printed image without actually printing the image.

  By the way, the shape of the ink dots formed on the print medium is affected by the surrounding ink dots. That is, when there are many other ink dots around the ink dot on the pixel of interest, the ink dot of that pixel of interest tends to spread over a larger range. However, in the past, the actual situation was that no consideration was given to the spread of such ink dots.

  SUMMARY An advantage of some aspects of the invention is that it provides a technique capable of appropriately predicting and simulating the spread of ink dots on a printed image.

In order to achieve the above object, an apparatus of the present invention is an apparatus that simulates the shape of ink dots formed on a print medium when printing a print image,
Reference for storing dot shape data indicating the relationship between the peripheral duty indicating the total amount of ink dots formed in the peripheral region set around the pixel of interest and the spreading shape of the ink dots formed on the pixel of interest A data storage unit;
A dot data generation unit that generates dot data indicating the ink dot formation state of each pixel on the print medium;
A dot shape calculation unit that calculates the spread shape of individual ink dots formed on the print medium according to the dot data with reference to the dot shape data;
An image quality evaluation index calculation unit for calculating an image quality evaluation index for evaluating the image quality of the print based on the spread shape of each ink dot calculated by the dot shape calculation unit;
Is provided.

According to this apparatus, since the spreading shape of each ink dot is determined according to the peripheral duty indicating the total amount of ink dots formed in the peripheral region of the target pixel, the formation state of the ink dots around the target pixel Accordingly, it is possible to appropriately predict the spreading shape of the ink dots of each pixel of interest. Also, an appropriate image quality evaluation index can be obtained by reflecting the spread of individual ink dots determined according to the ink dot amount in the peripheral area.

  It is possible to use a plurality of different size dots having different sizes in printing the print image, and the dot shape data may be created for the case where each of the plurality of different size dots is the target pixel. Good. At this time, the dot shape calculation unit may set the peripheral region for calculating the peripheral duty to a larger region as the size of the ink dot formed in the target pixel is larger.
  According to this configuration, it is possible to appropriately predict the spreading shape of individual ink dots even for a print image using a plurality of different size dots.

  The dot shape calculation unit may include an ink dot amount calculation unit that calculates the ink dot amount in the peripheral region of each ink dot using the dot data.

  If dot data is used, it is possible to know at which position in the peripheral area of each ink dot a dot is formed, so it is possible to determine the amount of ink dots in the peripheral area from the dot data. Therefore, it is possible to determine both the position where the individual ink dots are formed and the amount of ink dots in the peripheral area using the dot data.

  The dot data generation unit includes a color conversion unit that converts image data representing the print image into ink amount data, and the dot shape calculation unit includes the ink dot amount in the peripheral region of each ink dot. May be provided with an ink dot amount calculation unit that calculates the ink amount data.

  If the ink amount data is used, the ink amount in the peripheral region of each ink dot can be known, so that the ink dot amount in the peripheral region can be determined from the ink amount data.

  The dot shape data represents the spread of the ink dots in units of sub-pixels smaller than the pixels, and the dot shape calculation unit is configured to store the individual ink dots on a sub-pixel plane composed of the sub-pixels. The spread may be determined.

  According to this configuration, it is possible to accurately express the spread of individual ink dots in units of subpixels.

  The image quality evaluation index includes a granularity index indicating the granularity of the print image, and the image quality evaluation index calculation unit calculates a spatial frequency characteristic of the brightness of the print image based on the spread of the individual ink dots. The granularity index may be calculated from the spatial frequency characteristic.

  According to this configuration, the image quality of the printed image can be evaluated from the granularity index.

  The reference data storage unit further stores color value data for obtaining brightness of each sub-pixel smaller than the pixel in the range of the spread of the individual ink dots, and the image quality evaluation index calculation unit The spatial frequency characteristic of the brightness of the printed image may be calculated based on the brightness for each subpixel.

  It should be noted that the present invention can be realized in various aspects, for example, a printing image simulation method and apparatus, an image quality evaluation method and apparatus, a computer program for realizing the functions of these methods or apparatuses, The present invention can be realized in the form of a recording medium that records a computer program, a data signal that includes the computer program and is embodied in a carrier wave, and the like.

Next, embodiments of the present invention will be described in the following order.
A. First embodiment:
A-1. Configuration of print control device:
A-2. Simulation processing:
B. Other embodiments:
B-1. Correction of dot misalignment:
B-2. Determining the dot shape according to the scanning method:
B-3. Bidirectional printing and use of different size dots:
B-4. Other embodiments of dot shape data:
C. Granularity index calculation processing:
D. Variations:

A. First embodiment:
A-1. Configuration of print control device:
FIG. 1 is a block diagram showing a schematic configuration of a computer serving as a print control apparatus according to the present invention. The computer 10 includes a CPU (not shown) serving as the center of arithmetic processing, a ROM, a RAM, and the like as a storage medium, and can execute a predetermined program using peripheral devices such as the HDD 15. An operation input device such as a keyboard 12 and a mouse 13 is connected to the computer 10 via an I / O 19a, and a display 18 for display is also connected via an I / O 19b. Further, it is connected to the printer 40 via a USB I / O 19c.

  The printer 40 according to the present embodiment includes a mechanism in which an ink cartridge filled with a plurality of colors of ink can be attached and detached for each color. In this mechanism, each ink of CMYKOG (cyan, magenta, yellow, black, orange, and green) is provided. Mount the cartridge. The printer 40 can form a large number of colors by combining these ink colors, thereby forming a color image on the print medium. The printer 40 in the present embodiment is an ink jet printer, but the present invention can be applied to various printers such as a laser method in addition to the ink jet method.

  Furthermore, a configuration using six colored inks of CMYKOG is not essential, and a configuration using four colors of CMYK or seven colors of CMYKOGDY (dark yellow) may be used. Of course, other colors such as lc (light cyan) and lm (light magenta) may be used in place of the O and G inks, and dark and light inks may be used for the K ink.

  Although the configuration of the computer 10 has been described in a simplified manner, a computer having a general configuration as a personal computer can be employed. Of course, the computer to which the present invention is applied is not limited to a personal computer. Although this embodiment is a so-called desktop computer, it may be a notebook computer or a mobile computer. Further, the connection interface between the computer 10 and the printer 40 is not limited to the above, and various connection modes such as a parallel interface, a SCSI connection, and a wireless connection can be employed.

  Further, in the present embodiment, the print control apparatus is configured by the computer 10, but the print control process according to the present invention can be implemented by the program execution environment installed in the printer, and is directly connected to the printer. The image data may be acquired from a digital camera and the print control process may be performed. That is, a configuration may be employed in which the print control processing in this printer is simulated by a computer. Of course, it is possible to apply the present invention to a configuration in which a digital camera performs print control processing in a similar configuration, and various other configurations such as a configuration in which print control processing according to the present invention is performed by distributed processing. The present invention can be applied to the configuration. The present invention may be applied to a print control process in a so-called multi-function machine in which a scanner that captures an image and a printer that prints an image are integrated.

  In the computer 10 according to the present embodiment, a printer driver (PRTDRV) 30, an input device driver (DRV) 21, and a display driver (DRV) 22 are incorporated in the OS 20. The display DRV 22 is a driver that controls the display of a print target image, a printer property screen, and the like on the display 18, and the input device DRV 21 receives a code signal from the keyboard 12 and mouse 13 input via the I / O 19a. The driver accepts a predetermined input operation.

  The PRTDRV 30 can execute printing by performing predetermined processing on an image for which a print instruction has been issued from an application program (not shown) or an image of a patch described later. Furthermore, it is possible to simulate the recording state of dots formed on the print medium without performing actual printing. The PRTDRV 30 includes an image data acquisition module 31, a color conversion module 32, a halftone processing module 33, and a print data creation module 34 in order to execute printing. In addition, a simulation module 35 is provided to simulate the dot recording state.

  The image data acquisition module 31 acquires RGB data 15a from the HDD 15 and reduces or increases the number of pixels by interpolation or the like as necessary if the number of pixels is excessive or insufficient depending on the resolution when printing with the printer. It is. This RGB data is dot matrix data in which each color component of RGB (red, green, blue) is expressed by gradation to define the color of each pixel. In this embodiment, each color has 256 gradations, and conforms to the sRGB standard. The data adopts the color system that follows.

  In the present embodiment, this RGB data will be described as an example, but various data such as JPEG image data adopting the YCbCr color system and data adopting the CMYK color system can be adopted. Of course, the present invention is applied to data conforming to the Exif 2.2 standard (Exif is a registered trademark of the Japan Electronics and Information Technology Industries Association), data corresponding to Print Image Matching (PIM: PIM is a registered trademark of Seiko Epson Corporation), etc. It can also be applied.

  The color conversion module 32 refers to the LUT 15b stored in the HDD 15 and converts the RGB data color system into the CMYKOG color system. That is, the LUT 15b is a table that expresses colors by using the sRGB color system and the CMYKOG color system, associates the colors, and describes the correspondence between a plurality of colors. Accordingly, with respect to an arbitrary color expressed in the sRGB color system, the colors of the CMYKOG color system corresponding to the arbitrary color can be obtained by interpolation calculation by referring to the surrounding colors and the sRGB color defined in the LUT 15b. And color conversion can be performed. The LUT 15b has a plurality of tables prepared in advance, and is associated with each printing condition such as the type and resolution of the printing medium.

  Note that the converted CMYKOG data (also referred to as “ink amount data”) is also dot-matrix data that defines the color of each pixel by expressing each color component in gradation, and in this embodiment is 256 gradations for each color. . The halftone processing module 33 refers to the CMYKOG data, and generates halftone image data for each color in which the color of each pixel is expressed with gradations less than 256 (in this embodiment, two gradations). . Halftone image data is data indicating the formation state of ink dots for each pixel, and is also referred to as “dot data” in this specification. The print data creation module 34 receives the halftone image data, rearranges the data in the order used by the printer 40, and sequentially outputs the dot data used in one main scan to the printer 40. As a result, the printer 40 prints the image indicated by the RGB data 15a.

  The simulation module 35 receives the halftone image data, simulates the dot recording state without printing by the printer 40, and sets an image quality evaluation index IDX for evaluating the image quality of the printed image represented by these dots. This is a module that outputs to the display 18. FIG. 2 shows the internal configuration of the simulation module 35. The simulation module 35 includes an image data acquisition unit 35a, a parameter acquisition unit 35b, a sub-pixel plane formation unit 35c, a recording state data generation unit 35d, a brightness calculation unit 35e, an image quality evaluation index calculation unit 35f, and a peripheral duty calculation unit 35g. ing. The sub-pixel plane forming unit 35c, the recording state data creating unit 35d, and the peripheral duty calculating unit 35g realize a function of calculating a dot shape on the print medium. These are collectively referred to as a “dot shape calculating unit”. Can be called. The function of each part in the simulation module 35 will be described later. Various reference data (parameter data 15c, dot shape data 15d, and color value data 15e) used by the simulation module 35 will also be described below.

  FIG. 3 is a flowchart showing the overall procedure of the dot shape simulation. In step T10, prior to the simulation process (step T30 described later), dot shape data 15d and color value data 15e (FIG. 2) are created based on the measurement.

  FIG. 4 is an explanatory diagram showing how the dot shape is measured. A peripheral area SA is set around the target dot SP on the target pixel. In this example, the peripheral area SA has a size of 5 pixels × 3 pixels, but the size of the peripheral area SA can be arbitrarily set. In the present specification, “pixel” means a so-called print pixel (a pixel as a unit of a dot formation position on a print image). As will be described later, in the simulation, sub-pixels obtained by further dividing the print pixel are also used.

  In the peripheral area SA, other dots (referred to as “peripheral dots”) are formed in addition to the target dots. In the dot array used for this measurement (referred to as “measurement pattern”), the target dot is formed of black ink, and the peripheral dots are formed of yellow ink. The peripheral dots may be formed on the target pixel. 4A to 4D show cases where the number of peripheral dots is different. The number of peripheral dots can be represented by the ink duty Dy (referred to as “peripheral duty Dy”) of the peripheral dots. The peripheral duty Dy is a value representing the amount of peripheral dots formed in the peripheral area SA. In the example of FIG. 4, the peripheral duty Dy is given by a value obtained by dividing the number of peripheral dots by the number of pixels in the peripheral area SA.

  As shown in FIGS. 4A to 4D, the spread of the target dot SP depends on the peripheral duty Dy. That is, as the peripheral duty Dy increases, the target dot SP tends to spread over a larger range. This is because, even if the target dots SP are formed with the same ink amount, the ink of the target dots SP is likely to spread if there are peripheral dots. In the measurement of the dot shape, measurement patterns are respectively created under a plurality of conditions with different peripheral duties Dy, and the spread of the target dot SP on each measurement pattern is measured. This measurement can be performed by observing the measurement pattern with a microscope. Alternatively, the spread of the target dot SP can be measured by reading the measurement pattern with a scanner and analyzing the read image data. In the latter case, the reading resolution of the scanner is set to several times the resolution of the print pixel.

  This measurement of the dot shape can be executed for each of the plurality of inks used for printing as target dots. For example, when six types of inks of CMYKOG (cyan, magenta, yellow, black, orange, and green) can be used, measurement can be performed for each of these inks as target dots. Instead of this, it is also possible to actually measure only when one type of ink is the target dot, and use this measurement result for other inks.

  When printing the measurement patterns as shown in FIGS. 4A to 4D, the peripheral dots are formed with an ink different from the target dots. This is because when the same ink is used, the spread of the target dots cannot be measured. In addition, it is preferable to use the ink of the peripheral dots that is significantly different in brightness or hue from the ink of the target dots. Note that it is not necessary to create a measurement pattern for each case where all the inks other than the ink of the target dot are used as the peripheral dots. For example, the measurement pattern in which the peripheral dots are formed using one typical type of ink. Should be created.

  As the measurement pattern, it is possible to create a measurement pattern in which target dots are formed using individual ink discharge nozzles mounted on the printer 40. Alternatively, the target dot may be formed using only one representative nozzle, and the result may be applied to other nozzles. In the following example, a case will be mainly described in which measurement patterns in which target dots are formed using individual nozzles are created, and dot shape data is created for each individual nozzle.

  FIG. 5 is an explanatory diagram for explaining an example of the dot shape data 15d obtained by the measurement. The dot shape data 15d is data describing parameters for specifying the shape and size of the dot for each nozzle and for each peripheral duty Dy. In this embodiment, the dot shape is predetermined to be elliptical, and the shape and size are specified by the major axis and minor axis of the ellipse. Further, in the example shown in FIG. 5, the sizes of the first dot and the second dot and the relative distance between the two are used so that the case where the ink droplet is separated into two by the time the ink droplet reaches the printing medium from the nozzle can be dealt with. Can be described as a parameter.

  That is, the main scanning direction size (X0) and sub-scanning direction size (Y0) of the first dot and the main scanning direction size (X1) and sub-scanning direction size (Y1) of the second dot can be described. The relative distance between one dot and the second dot can be described by the distance (X2) in the main scanning direction and the distance (Y2) in the sub-scanning direction. Each parameter is described for each nozzle and each ink color, and a set of dot shape data as shown in FIG. 5 is prepared in advance for each type of print medium.

  Instead of describing each parameter of the dot shape data for each nozzle, each parameter of the dot shape data may be simply described for each ink color. In this case, it is assumed that the nozzles that eject the same ink form dots having the same shape. Further, only one piece of data common to a plurality of inks may be created as the dot shape data. In this case, each parameter of the dot shape data is described according to only the peripheral duty Dy. However, since the spread of the dots often changes depending on the ink type of the target dot, it is preferable to create dot shape data for at least each ink.

  The lower part of FIG. 5 shows the dot shape specified by each parameter of the dot shape data 15d. In the first dot and the second dot, an ellipse having a major axis or a minor axis in the scanning direction specified by the dot shape data 15d is formed to form the shape of each dot. The relative distance of each dot can be specified as the distance from the center of both. The dot shape data 15d is created by actually ejecting ink from each nozzle formed on the carriage mounted on the printer 40 and measuring the shape and size of the print medium. Is determined in units of sub-pixels (described later). Therefore, the size in each scanning direction can be uniquely specified on a sub-pixel plane described later.

  In the example shown in FIG. 5, the size of the first dot formed with nozzle number 1 for C ink is 50, and the size in the sub-scanning direction is 50. The size of the second dot is “0” in both the main scanning direction and the sub-scanning direction. For this reason, the relative distance is also “0”. In this case, the ink droplets are not separated during the flight, and one first dot is formed by one ejection of the ink droplets.

  Further, when ink droplets are ejected while moving the carriage provided in the printer 40 in the main scanning direction, the ink droplets fly while having a relative speed in the main scanning direction with respect to the printing medium, and on the printing medium in the main scanning direction. And an elliptical dot whose major axis is substantially parallel. Therefore, the dot shape is generally an ellipse having a major axis in the main scanning direction as shown in the lower part of FIG. 5, but, of course, the major axis direction is not limited, and the major axis and the minor axis are set to the same value. By doing so, it may be a circular dot. Further, the number of dot separations may be three or more, or data indicating a dot-shaped pattern itself composed of a plurality of sub-pixels may be recorded.

  FIG. 6 is an explanatory diagram for explaining an example of the color value data 15e. In the present specification, the “color value” is a value for expressing the color of a pixel or a sub-pixel, and means a value capable of obtaining at least lightness. The “color value” is also referred to as “lightness expression value”. In the present embodiment, spectral reflectance is used as the color value. Spectral reflectance is data indicating the reflectance of dots recorded on a printing medium in association with wavelengths of a plurality of lights. This reflectance is determined in advance for a state in which each color ink used in the printer 40 is ejected alone on the print medium and a state in which no ink is recorded on the print medium (line W in FIG. 6). Yes. For example, the upper part of FIG. 6 shows the spectral reflectance (R (λ)) of the C ink. Such spectral reflectance is measured in advance, and the reflectance is specified at intervals of 10 nm from a wavelength of 380 nm to 780 nm. To color value data 15e. Also for color value data, a set of data as shown in FIG. 6 is prepared in advance for each type of print medium.

  In the present embodiment, a spectral reflectance is obtained by printing a patch of a predetermined size with the maximum ink amount limit value for each print medium and measuring the color of the patch under a predetermined light source. That is, the spectral reflectance obtained in this way is the spectral reflectance when each dot is observed. Note that such a method for obtaining the spectral reflectance is an example, and a patch is printed at a predetermined ink recording rate, and the ratio between the area of the dot on the printing medium and the area of the area where the dot is not recorded is used. Thus, the spectral reflectance of each color may be calculated, and various configurations can be employed. In the present invention, it is only necessary to be able to calculate a color value (brightness in this embodiment) for each sub-pixel. In this sense, it is not essential to prepare data indicating spectral reflectance. For example, it is possible to employ a configuration in which data indicating a color value for a single color and a color value when a plurality of colors are superimposed are prepared in advance.

  Note that the color values constituting the color value data 15e may be obtained by measuring a measurement pattern (FIG. 4) created when the dot shape data 15d is measured. For example, colorimetric values (XYZ values) or optical density values are obtained by measuring a measurement pattern using a colorimeter or densitometer, and these colorimetric values or optical density values are used as color values. Is possible.

  The dot shape data 15d and the color value data 15e do not need to be separated, and the dot shape data 15d and the color value data 15e may be stored in the same data.

  When the dot shape data 15d and the color value data 15e are thus created, image data (RGB data 15a in FIG. 1) to be simulated is prepared in step T20. In step T30, simulation processing is executed.

A-2. Simulation processing:
The simulation process is performed by instructing the start of simulation on a property screen (not shown) of the PRTDRV 30. FIG. 7 is a flowchart showing this simulation process. When the simulation process is started, the user operates the mouse 13 or the like to input the printing conditions for the RGB data 15a, and the PRTDRV 30 acquires data indicating the printing conditions and accepts the printing conditions for the simulation (S100). ). At this time, data indicating printing conditions necessary for a simulation process described later is recorded in the HDD 15 as parameter data 15c.

  Here, only the printing conditions are specified for simulation, and the printing conditions are not designated for actually executing printing. In addition, all the information necessary for executing printing (for example, the mode, resolution, speed, etc. at the time of printing) can be the printing conditions, but it is not necessary for the user to select all the printing conditions. The unprinted printing conditions may be configured to use default printing conditions. When the printing conditions are determined, the image data acquisition module 31, the color conversion module 32, and the halftone processing module 33 perform respective processes according to the printing conditions.

  That is, the image data acquisition module 31 acquires the RGB data 15a and refers to the print resolution specified as the print condition. Then, the number of each pixel when the printer 40 forms an image is calculated and compared with the number of pixels of the RGB data 15a. Thus, if the number of pixels of the RGB data 15a is excessive or insufficient, the number of pixels is adjusted by interpolation processing or the like (step S105).

  The color conversion module 32 selects the LUT 15b corresponding to the type and resolution of the printing medium specified as the printing condition, and refers to the LUT 15b to determine the RGB color 15a or the color system of the data in which the number of pixels is adjusted. Conversion is performed (step S110). That is, gradation data for each color of CMYKOG (referred to as “ink amount data IAD”) is generated. The halftone processing module 33 performs halftone processing on the gradation data after the color conversion. If the halftone algorithm can be designated as the printing condition, halftone processing is performed with the designated algorithm to generate dot data indicating the dot formation state (step S115). When printing is performed instead of simulation processing, as shown by a broken line in FIG. 7, the print data creation module 34 performs the above-described processing to perform printing after the halftone processing.

  In the simulation process, after step S115, the image data acquisition unit 35a (FIG. 2) of the simulation module 35 acquires the ink amount data IAD and the dot data DD, and each module of the simulation module 35 performs step S120 and subsequent steps. Processing is performed to calculate an image quality evaluation index IDX. In the present embodiment, the image quality evaluation index IDX is calculated with reference to the parameter data 15c, the dot shape data 15d, and the color value data 15e stored in the HDD 15.

  FIG. 8 is an explanatory diagram for explaining an example of the parameter data 15c. The parameter data 15c includes data indicating printing conditions input to the user as described above and predetermined data. In the figure, the resolution in the main scanning direction (X resolution) and the resolution in the sub-scanning direction (Y resolution), the number of ink colors, and the type of printing medium acquired as the printing conditions are described.

  The X resolution and the Y resolution are data in which the resolution is specified in units such as dpi, and are 1440 dpi and 720 dpi in FIG. The number of ink colors is the number of ink colors mounted on the printer 40. In the present embodiment, each of the CMYKOG ink colors is specified by specifying six colors. Of course, the ink color itself may be specified directly. The print medium is data indicating the type of medium such as photographic paper, but the data indicating the print medium is not essential as long as a plurality of types of media are not selectable.

  In the example shown in FIG. 8, “number of subpixels / pixel” and the number of nozzles are described as predetermined data. The number of subpixels / pixel indicates the number of divisions when each pixel in the data after halftone processing is divided into smaller subpixels. In FIG. 8, each pixel is divided into 20 vertical and horizontal subpixels. It is shown that. Of course, the number of divisions may be specified by the user as a printing condition, and is not limited to 20. The number of nozzles indicates the number of nozzles formed in the carriage mounted on the printer 40 in the sub-scanning direction. In the parameter data 15c, in addition to the above examples, various data necessary for calculating the image quality evaluation index can be described, and various data can be described and used as necessary.

  In the flow shown in FIG. 7, when the image data acquisition unit 35a acquires the ink amount data IAD and the dot data DD as described above, the parameter acquisition unit 35b appropriately obtains necessary data from the parameter data 15c recorded in the HDD 15. Obtain (step S120). In this embodiment, data indicating each of X resolution, Y resolution, the number of colors, the print medium, and the number of subpixels / pixel is acquired.

  In step S130, the peripheral duty calculator 35g calculates the peripheral duty Dy of each dot represented by the dot data DD. The definition of the peripheral duty Dy is the same as that described in FIG. However, in step S130, the peripheral duty including the peripheral dots formed with the same ink as the target dot is calculated. Note that the reason why the target dots and the peripheral dots are formed with different inks in the measurement of FIG. 4 is that it is necessary to distinguish the peripheral dots from the target dots in order to measure the target dots.

  The calculation of the peripheral duty Dy can be performed by regarding each dot represented by the dot data DD as a target dot and summing the ink amounts of a plurality of inks in the peripheral area SA of the target dot. Specifically, for example, the peripheral duty Dy can be obtained by adding the ink amounts of the respective pixels in the peripheral area SA in the ink amount data IAD and subtracting the ink amount of the target dot from the total value. Instead, the peripheral duty Dy may be calculated by checking the number of peripheral dots formed in the peripheral area SA from the dot data DD. In the latter case, the ink amount data IAD is not necessary in the process of step S130.

  Next, the sub-pixel plane forming unit 35c forms a sub-pixel plane for simulating the dot recording state (step S135). That is, each pixel in the dot data DD acquired by the image data acquisition unit 35a is divided by the number of subpixels / pixel of the parameter data 15c, and a plane for simulation is formed by the subpixels obtained by the division. That is, the dot matrix of the dot data DD is changed to a dot matrix with higher resolution. Note that specific processing can be realized by defining an array so that recording state data can be specified for each pixel of the sub-pixels.

  FIG. 9 is an explanatory diagram for explaining a simulation process in the present embodiment. In the figure, the upper left shows halftone image data (dot data) after halftone processing, and a part of the sub-pixel plane is shown in the center of the figure. That is, a plane formed by a rectangle smaller than a pixel as shown in the center of the figure is considered as a sub-pixel plane. In FIG. 9, the upper left end of the sub-pixel plane is the coordinate (0, 0), the coordinate in the main scanning direction is x, and the coordinate in the sub scanning direction is y. After the subpixel plane is formed, the recording state data creation unit 35d refers to the dot shape data 15d and simulates the dot shape on the subpixel plane (step S140).

  That is, in the halftone image data after the halftone processing, whether or not to form a dot for each pixel is specified by two gradations, and therefore, from this halftone image data, the subpixel corresponding to each pixel is designated. Whether or not to form dots can be determined. Further, the printer 40 in the present embodiment drives the carriage and the paper feed roller by a specific main scanning and sub scanning control method. Therefore, it is possible to specify the nozzles that form the dots of each pixel in the halftone image data by the same processing contents as the rearrangement processing in the print data creation module 34. Therefore, by referring to the dot shape data 15d, it is possible to specify in detail the shape of the dot formed in the subpixel corresponding to each pixel. Of course, data indicating the control method may be recorded in the HDD 15 in advance, and the nozzle may be specified with reference to this data.

  In the present embodiment, the center of each pixel is set as a reference position, and the dots are arranged so that the center of the first dot corresponds to the reference position. If this process is performed on all the pixels, dots can be formed on the sub-pixel plane as shown by hatching in FIG.

  As shown in FIG. 5, in the dot shape data 15d, parameters (X0, Y0, etc.) representing the dot shape are registered for a plurality of values of the peripheral duty Dy. Accordingly, the shape of each ink dot on the sub-pixel plane is determined according to the peripheral duty Dy of each ink dot. In addition, the dot shape in the peripheral duty value that is not registered in the dot shape data 15d is estimated or interpolated from the dot shape in the registered peripheral duty value. As a result, the shape of each ink dot can be determined in consideration of the influence of the ink dots formed around the ink dot.

  As described above, when the dots are formed on the sub-pixel plane while determining the shape of the dots in detail, it is determined whether or not the process for forming the dots has been completed for all the colors obtained in step S120. In step S145), the processes in and after step S130 are repeated until it is determined that all colors have been completed. The data obtained in this way is the recording state data.

  When dots are formed on the sub-pixel plane for all colors, the brightness calculation unit 35e sets each ink so that it can be evaluated how the dots formed by each ink color are visually recognized by human eyes. The brightness in the superimposed state is calculated (step S150). That is, assuming a predetermined light source, a tristimulus value XYZ is calculated from the spectral reflectance corresponding to the print medium acquired in step S120 and the spectral sensitivity of the human eye, and further, L * a is calculated from the tristimulus value XYZ. * b * value is calculated.

  The obtained L * is the brightness, and the brightness is specified for each coordinate on the sub-pixel plane (this is expressed as L (x, y)). Since the coordinates (x, y) correspond to the same position in the sub-pixel plane for each ink color, when dots are formed on the same coordinate in the sub-pixel plane of different ink colors, the spectral of each color The brightness may be calculated using the result of multiplying the reflectances as the spectral reflectance of the subpixel. When no dot is formed at the coordinates (x, y), the lightness L (x, y) is calculated from the spectral reflectance of the print medium (the W line in FIG. 6). When the lightness L (x, y) of each sub-pixel is obtained, the image quality evaluation index calculating unit 35f calculates an image quality evaluation index for evaluating the image quality of the print image based on the lightness L (x, y) ( Step S155).

  As the image quality evaluation index, for example, a granularity index or a banding index can be used. It is also possible to use a comprehensive image quality evaluation index combining a plurality of indices. An example of a method for calculating the granularity index will be described later. The banding index is obtained, for example, by extracting the data in the v direction after the VTF processing described in FIG. 19, and is used as an index representing the streak composed of lines perpendicular to the sub-scanning direction of the printed image. can do.

  As described above, in the present embodiment, since the shape of each dot is determined according to the peripheral duty in the simulation process, it is possible to appropriately predict the spread of the ink dots on the printed image. Further, since the image quality evaluation index is calculated using the ink dot shape, it is possible to obtain a more appropriate image quality evaluation index as compared with the case where the influence of the peripheral duty is not taken into consideration.

B. Other embodiments:
B-1. Correction of dot misalignment:
In the above-described embodiment, the simulation is performed on the assumption that the ink ejected from each nozzle is recorded at the reference position. This embodiment is an embodiment when the present invention is implemented, and it may be considered that the dot formation position can be shifted from the reference position. For example, if the deviation amount that the ink ejected from each nozzle deviates from the reference dot formation position is created in advance as dot position deviation data, the dot formation position can be finely adjusted when creating the recording state data. .

  FIG. 10 is an explanatory diagram for explaining an example of the dot position deviation data. The dot position deviation data 15f is data describing deviation from the reference position in units of sub-pixels for each of a plurality of nozzles formed on the carriage. That is, even when ink droplets are ejected under the same conditions, an error occurs in the ink droplet recording position between a plurality of nozzles. Therefore, the printer 40 discharges ink from each nozzle to measure the recording position, and sets the data as the deviation amount. At this time, a recording position at a certain nozzle is set as a reference dot formation position, and a nozzle that forms a dot at the reference dot formation position has both a deviation (X) in the main scanning direction and a deviation (Y) in the sub-scanning direction. Assume that it is 0 ″. In the example shown in FIG. 10, the center of the pixel is the reference dot formation position.

  When a deviation occurs from the reference dot formation position, the sub-pixel corresponding to the deviation amount is described as dot position deviation data in the main scanning direction and the sub-scanning direction. Since the dot position deviation data 15f is described for each nozzle, the deviation is described for each ink color. This dot position deviation data 15f is recorded in the HDD 15 in advance. The configuration and processing flow for performing the simulation processing are substantially the same as those in the above-described embodiment, but the processing in the recording state data creation unit 35d is different.

  That is, in step S140, the shape of the dot formed by each nozzle is specified with reference to the dot shape data 15d, and the dot formation position is adjusted with reference to the dot position deviation data 15f. The data shown in FIG. 10 will be described as an example. In nozzle number 1, since the deviation (X) in the main scanning direction and the deviation (Y) in the sub-scanning direction are both “0”, as shown in the lower part of FIG. For ink ejected from nozzle number 1, dots are formed at the reference dot formation position.

  In nozzle number 2, the deviation (X) in the main scanning direction is “2”, and the deviation (Y) in the sub-scanning direction is “1”. Accordingly, for the dot of nozzle number 2, a dot is formed at a position P shifted by two subpixels in the main scanning direction and one subpixel in the subscanning direction from the center of the pixel that is the reference dot formation position. To do. As described above, if the dot recording state is specified while taking into account errors between the nozzles, and the image quality evaluation index is calculated based on this, it is possible to evaluate the print image quality including errors between the nozzles. Become. In addition, since the image quality evaluation index can be calculated including the error between nozzles, the image quality evaluation index is calculated for a plurality of image processes as described above, so that high image quality can be maintained even if errors are included. Possible image processing can be extracted from the plurality of image processing.

  The error that can be considered in the present invention is not limited to the error between nozzles as described above. For example, a carriage feed error may be considered. FIG. 11 is an explanatory diagram for explaining an example of dot position deviation data when feeding error is considered. The dot position deviation data 15g is data in which deviation from the reference position is described in units of sub-pixels for each main scanning frequency (pass). That is, since the carriage records dots by repeating main scanning and sub-scanning, an error occurs in the dot recording position due to a driving error when driving the carriage in the main scanning direction or a feeding error in the paper feed roller. obtain. Therefore, the printer 40 discharges ink from each nozzle to measure the recording position, and sets the data as the deviation amount. At this time, a recording position in a certain pass is set as a reference dot formation position, and a pass in which dots are formed at the reference dot formation position has both a deviation (X) in the main scanning direction and a deviation (Y) in the sub scanning direction. Assume that it is 0 ″. In the example shown in FIG. 11, the center of the pixel is the reference dot formation position.

  When a deviation occurs from the reference dot formation position, the sub-pixel corresponding to the deviation amount is described as dot position deviation data in the main scanning direction and the sub-scanning direction. The dot position deviation data 15g describes the deviation from the reference dot formation position that occurs in each pass for each ink color. The upper limit of the number of passes (#N in FIG. 11) is not particularly limited, but it is preferable to correspond to the maximum print medium size that can be printed by the printer 40. For example, the number of passes required when printing on the entire surface of an A4 size print medium is the upper limit of the number of passes.

  This dot position deviation data 15g is recorded in the HDD 15 in advance. The configuration and processing flow for performing the simulation processing are substantially the same as those in the above-described embodiment, but the processing in the recording state data creation unit 35d is different. That is, in step S140, the dot shape formed by each pass is specified with reference to the dot shape data 15d, and the dot formation position is adjusted with reference to the dot position deviation data 15g. The data shown in FIG. 11 will be described as an example. In pass number 1, since the deviation (X) in the main scanning direction and the deviation (Y) in the sub scanning direction are both “0”, as shown in the lower part of FIG. For ink ejected from pass number 1, dots are formed at the reference dot formation position.

  In pass number 2, the deviation (X) in the main scanning direction is “2”, and the deviation (Y) in the sub-scanning direction is “−1”. Therefore, for the dot of pass number 2, a dot is formed at a position P ′ shifted by two subpixels in the main scanning direction and one subpixel in the reverse direction of the subscanning from the center of the pixel that is the reference dot formation position. I will do it. As described above, it is possible to evaluate the print image quality including the error between passes by specifying the dot recording state while taking into account the error between passes and calculating the image quality evaluation index based on this. Become. In addition, since the image quality evaluation index can be calculated including the error between passes, the image quality evaluation index is calculated for a plurality of image processes as described above, so that high image quality can be maintained even if errors are included. Possible image processing can be extracted from the plurality of image processing.

  Note that the above-described nozzle error and feed error can occur simultaneously. Therefore, both the dot position deviation data 15f and 15g are prepared in advance, and the dot formation position is adjusted by adding the deviation amount indicated by the both dot position deviation data to the reference dot formation position in step S140. A configuration may be adopted. Further, in the examples shown in FIGS. 10 and 11, since the shift amount is expressed in units of sub-pixels, it is necessary to correspond to the number of divisions and resolutions for dividing the pixel into sub-pixels. If changed, the dot position deviation data corresponding to the condition is referred to. Of course, this configuration is only an example, and the amount of deviation measured as described above is described in units of length, and the amount of deviation in sub-pixel units is calculated according to the resolution and the number of pixel divisions. It may be adopted.

B-2. Determining the dot shape according to the scanning method:
In the above-described embodiment, the printer 40 that drives the carriage and the paper feed roller by the specific main scanning and sub-scanning control method (that is, the scanning method) is assumed. However, the carriage and the paper feed roller by various control methods. It is also possible to apply the present invention to the printer 40 that drives the printer. That is, if the control method is different, the nozzles and passes for forming the dots of the pixels of the same halftone image data are different. Therefore, the nozzle is specified based on the control method.

  FIG. 12 is an explanatory diagram for explaining an example of control method data indicating a control method for main scanning and sub-scanning and an arrangement of a plurality of nozzles formed on the carriage. The control method data 15h shown in the figure describes the number of nozzles and the nozzle density as the nozzle arrangement. The number of nozzles indicates the number of nozzles arranged in the sub-scanning direction in the carriage. In FIG. 12, the number of nozzles is “7” for simplicity, but there are usually more nozzles such as 180. The nozzle density indicates the density of nozzles arranged in the sub-scanning direction in dpi units. That is, the density is indicated by the number of nozzles per inch in the sub-scanning direction. In the example shown in FIG. 12, the nozzle density is not described. However, if the nozzle density is necessary to specify the nozzle, data is described here.

  In addition, the number of passes and the recording pattern can be described as a main scanning control method. The number of passes indicates how many passes one line (raster) in the main scanning direction is filled. When the recording pattern fills one raster in two or more passes, the adjacent dots are recorded in which pass. Is shown. For example, if it is defined that “0” indicates the first pass and “1” indicates the subsequent pass, and “01011010” is set as the recording pattern, it is possible to specify the pass for recording each dot. . In the example shown in FIG. 12, since the number of passes is “1”, the recording pattern is not described.

  As a sub-scanning control method, a feed amount, the number of overlap nozzles, and an overlap pattern can be described. The feed amount is data indicating the feed amount at the time of sub-scan in units of the number of rasters. That is, according to the Y resolution, the length of one raster can be determined (for example, 1/720 inch when the Y resolution is 720 dpi). The sub-scan feed amount is determined. The number of overlap nozzles is data indicating the number of nozzles when control is performed so that the same path is filled (overlap) with a plurality of nozzles formed at the upper and lower ends in the sub-scanning direction. The overlap pattern is data indicating which dot is formed at the upper end or the lower end in a certain raster. In the example shown in FIG. 12, the overlap control is not performed, and the number of overlap nozzles and the overlap pattern are not described.

  The left side of FIG. 12 illustrates control in the contents of the control method data 15h shown in the figure. The raster shown here is one line in the main scanning direction, and is shown with raster numbers in order from the top. The pass number is the number of passes. Below this number, the position of the nozzle in each pass is indicated by a solid circle, and the nozzle numbers 1 to 7 are assigned in order from the top. In this example, it is assumed that the resolution in the sub-scanning direction is 720 dpi and the nozzle density in the sub-scanning direction is 180 dpi, and the distance between each nozzle corresponds to 4 rasters.

  Since the feed amount is "5" in the control method data 15h, in the pass number 2, five rasters are fed in the sub-scanning direction. If this feed amount is repeated, there will be nozzles for recording dots on the raster with the raster number 13 or lower. Therefore, in the control according to the control method data 15h, dots are not recorded above the raster number 12, but dots are recorded below the raster number 13. Accordingly, in the uppermost raster in the halftone image data, dots are formed by the fourth nozzle.

  As described above, if the control method data 15h is used, it is possible to specify the nozzles that form the dots of each raster. Therefore, in step S140, the nozzles are specified by referring to the control method data 15h, and The dot shape is specified with reference to the dot shape data 15d. As a result, even when complex control is performed, it is possible to easily calculate the image quality evaluation index in the control method. If the control method data 15h is referred to, the pass number can be obtained as shown on the left side of FIG. 11 (that is, the number of main scans can be specified). Errors can also be taken into account. Of course, an error between nozzles can be taken into consideration with reference to the dot position deviation data 15f.

  Although omitted in FIG. 12, of course, when the number of passes is 2, the nozzles can be specified using the data indicating the recording pattern, and the overlap nozzle number and the overlap number are also used when controlling the overlap. The nozzle can be specified using the data indicating the wrap pattern. Of course, when the carriage and the paper feed roller are driven by another control method, other parameters may be described in the control method data 15h, and the dot or pass forming each dot may be specified by the control method. In other nozzle arrangements, for example, when a nozzle array is formed by arranging a large number of nozzles in the sub-scanning direction and this nozzle array is arranged in the main scanning direction and configured to eject ink of the same color, the nozzle arrangement Is described in the control method data 15h, and the dot and pass forming each dot may be specified by this data and the data indicating the control method.

B-3. Bidirectional printing and use of different size dots:
The present invention can also be applied to a printer capable of bidirectional printing and a printer capable of adjusting the ink discharge amount per time. FIG. 13 is an explanatory diagram showing data prepared in this case. As the parameter data 15c, in addition to the above parameters, data indicating whether or not to perform bidirectional printing and data indicating whether or not to adjust the ink discharge amount per time are described. In this example, the ink discharge amount per time can be adjusted in three stages (small, medium and large). Note that ink dots formed using the same ink and having different ink discharge amounts are also referred to as “different size dots”. The “size” of “different size dots” means the size of the target dot when there are no surrounding dots.

  In bidirectional printing, ink is ejected in both directions of the main scanning direction, and in unidirectional printing, ink is ejected in either direction. Therefore, the dot shape data, the color value data (spectral reflectance data), and the dot position deviation data can be different between bidirectional and unidirectional. Therefore, bidirectional data and unidirectional data are prepared in advance. With this configuration, it is possible to calculate the recording state data in both directions and unidirectional.

  Since each of the three small, medium, and large ink droplets has a different dot shape, color value, and dot formation position due to an error, the dot shape data, color value data, It is preferable to prepare and prepare misalignment data. In this case, the halftone image data (dot data) is data indicating four dot formation states of no dot, small dot formation, medium dot formation, and large dot formation, and is 2-bit data for each ink color. .

  When creating the recording status data, obtain this halftone image data, and refer to the dot shape data, color value data, and dot position deviation data according to the size of each dot. It is possible to calculate recording state data as a result of superimposing. If the image quality evaluation index is calculated based on the recording state data calculated as described above, it is possible to evaluate the image quality during bidirectional printing, and the case of using three types of ink droplets of small, medium, and large. It becomes possible to evaluate the image quality.

  FIG. 14 shows an example of a calculation method of the peripheral duty when different size dots are used. In this example, one large dot L is formed in the peripheral area SA, and two medium dots and two small dots are formed. The peripheral duty Dy is a value N (i) × Dy (i) obtained by multiplying the number N (i) of the i-th size peripheral dots by the duty conversion value Dy (i) of the i-th size peripheral dots. Given in sum. The duty conversion value Dy (i) is a larger value as the dot size is larger. For example, a value proportional to the ink ejection amount can be used as the duty converted value Dy (i).

  When using different size dots, it is preferable to create measurement patterns in which peripheral dots of various sizes as shown in FIG. 14 are formed in step T10 of FIG. However, only the measurement pattern using only dots of a specific size (for example, medium dots) as peripheral dots may be created. Also in this case, since the value of the peripheral duty Dy can be calculated by the calculation formula shown in FIG. 14, it is possible to register the dot spread depending on the peripheral duty Dy as the dot shape data 15d.

  The peripheral area SA can be set in different ranges for dots of different sizes. This is because large dots can have far-reaching effects. Therefore, in this case, it is preferable to set the size of the peripheral area SA larger as the dot size (ink discharge amount) is larger. In the case where the peripheral area SA having a different size is used for dots having different sizes, in the calculation of the peripheral duty Dy, N (i) × Dy (i) is the size of each peripheral area SA. It is preferable to use normalized values. As can be understood from these descriptions, as the peripheral duty Dy, an arbitrary one having a correlation with the total ink amount of dots recorded in the peripheral area SA can be used.

B-4. Other embodiments of dot shape data:
FIG. 15 shows another embodiment of the dot shape data 15d. The difference from the data of FIG. 5 is that a color value is added to the parameter of each dot, and the other points are the same as the data of FIG. That is, in this example, the color value data is included in the dot shape data 15d. Note that the color value shown in FIG. 15 is not the spectral reflectance (FIG. 6) but the optical density value of the dot. As the optical density value, for example, when the area of the ink dot is one pixel or more, a value equal to the optical density value of the color patch on which the ink is printed can be adopted. Further, when the area of the ink dot is less than one pixel, a value obtained by multiplying the optical density value of the color patch printed with the ink solid by the area ratio of the ink dot to one pixel can be employed.

  FIG. 16 shows still another embodiment of the dot shape data 15d. The dot shape data 15d has a configuration in which color values are registered within a range of ink dots in a subpixel array having a predetermined size composed of a plurality of subpixels. That is, in the dot shape data 15d in FIG. 16, the spread of the ink dots is represented by the outline of the subpixel in which the color value is registered. Since the dot shape data 15d can accurately describe the dot position in units of sub-pixels, the dot position deviation data 15f (FIG. 10) due to nozzle manufacturing error is not necessary. Such dot shape data 15d is preferably created for each ink, each nozzle, and each peripheral duty Dy. However, as described above, the dot shape data 15d may not be created for each nozzle, but may be created for each ink and the peripheral duty Dy.

  FIG. 17 shows another embodiment of the dot shape data 15d. This dot shape data is obtained by replacing the main scanning direction and sub-scanning direction sizes of the data in FIG. 15 with the respective size ratios, and the other points are the same as the data in FIG. In this case, the size of the ink dot when the size ratio is 1 is registered in advance elsewhere.

  As described above, various contents and data structures can be adopted as the dot shape data 15d.

C. Granularity index calculation processing:
FIG. 18 is a flowchart for calculating a granularity index as a kind of image quality evaluation index, and FIG. 19 is an explanatory diagram for explaining how the granularity index is calculated. In this embodiment, the granularity index evaluates the brightness of an image with a spatial frequency (cycle / mm). For this purpose, first, FFT (Fast Fourier Transformation) is performed on the lightness L (x, y) shown at the left end of FIG. 19 (step S200). 18 and 19, the obtained spatial frequency spectrum is shown as S (u, v). The spectrum S (u, v) is composed of a real part Re (u, v) and an imaginary part Im (u, v), and S (u, v) = Re (u, v) + jIm (u, v). It is.

  Here, (u, v) has a dimension of the inverse space of (x, y), but (x, y) is defined as a coordinate in the present embodiment, so these are converted into dimensions of the actual length. In order to make it correspond, resolution etc. must be considered. Therefore, even when evaluating S (u, v) in the spatial frequency dimension, dimension conversion is required. Therefore, first, in order to calculate the magnitude f (u, v) of the spatial frequency corresponding to the coordinates (u, v), the lowest frequency of the image to be simulated is calculated (step S205). The lowest frequency of the image to be simulated is a frequency that vibrates once in the image to be simulated, and is defined for each of the main scanning direction and the sub-scanning direction.

That is, the minimum frequency eu in the main scanning direction is X resolution / (number of pixels in the main scanning direction × 25.4), and the minimum frequency ev in the sub scanning direction is Y resolution / (number of pixels in the sub scanning direction × 25.4). Defined. The X resolution and Y resolution are the data acquired in step S120. Here, 1 inch is 25.4 mm. The number of pixels in the main scanning direction and the number of pixels in the sub scanning direction are the number of pixels of the image to be processed. Normally, a square area in the print image is not the entire print image but a processing target. Minimum frequency e _u in each scanning direction, if e _v is calculated, the spatial frequency in arbitrary coordinates (u, v) size f (u, v) is ^{_{((e u · u) 2}} + (e v・ V) ² )) It can be calculated as ^1/2 .

  On the other hand, human eyes have different sensitivities to lightness depending on the magnitude f (u, v) of the spatial frequency, and the visual spatial frequency characteristic is, for example, VTF (f) shown in the lower center of FIG. It is a characteristic. The VTF (f) in FIG. 19 is VTF (f) = 5.05 × exp (−0.138 · d · π · f / 180) × (1−exp (−0.1 · d · π · f / 180)). Here, d is the distance between the printed matter and the eyes, and f is the magnitude f of the spatial frequency. Since f is expressed as a function of the above (u, v), the visual spatial frequency characteristic VTF can be a function VTF (u, v) of (u, v).

  By multiplying the above-mentioned spectrum S (u, v) by this VTF (u, v), the spectrum S (u, v) can be evaluated in a state in which the visual spatial frequency characteristic is taken into consideration. If this evaluation is integrated, the spatial frequency can be evaluated for the entire sub-pixel plane. Therefore, in the present embodiment, processing up to integration is performed in steps S210 to S230. First, both (u, v) are initialized to “0” (step S210), and a certain coordinate (u, v The spatial frequency f (u, v) at v) is calculated (step S215). Further, the VTF at the spatial frequency f is calculated (step S220).

  When the VTF is obtained, the square of the VTF is multiplied by the square of the spectrum S (u, v), and the result is added to the variable Pow (step S225). That is, since the spectrum S (u, v) includes a real part Re (u, v) and an imaginary part Im (u, v), in order to evaluate the magnitude, first, the square of the VTF and the spectrum S ( The product of u, v) and the square is obtained and sequentially accumulated. Then, it is determined whether or not the above processing has been performed for all coordinates (u, v) (step S230), and if it is not determined that the processing has been completed for all coordinates (u, v), unprocessed The coordinates (u, v) are extracted, and the processing from step S215 is repeated. Note that, as shown in FIG. 19, the VTF suddenly decreases and becomes almost “0” as the spatial frequency increases, so by limiting the range of the coordinates (u, v) to a predetermined value or less in advance. Calculation can be performed within a necessary and sufficient range.

When the accumulation of products is completed, (Pow ^1/2 / total number of subpixels) is calculated (step S235). That is, the dimension is returned to the dimension of the spectrum S (u, v) by the square root of the variable Pow, and is normalized by dividing by the total number of sub-pixels. By this normalization, an objective index Int (FIG. 18) that does not depend on the number of pixels of the processing target image is calculated. Of course, it is only necessary to perform normalization here, so normalization may be performed by dividing by the number of pixels of the processing target image. Further, according to the standardization, it is possible to evaluate the graininess regardless of the size of the image, but if the graininess when the parameters such as image processing are changed for the image having the same number of pixels is compared, Standardization is not necessarily required.

  In the present embodiment, the graininess index is further corrected by taking into account the influence of the lightness of the entire printed matter. In other words, in this embodiment, even if the spatial frequency spectrum is the same, the printed matter gives different impressions to the human eyes when it is bright and dark, and the brighter one feels more grainy. Make corrections. For this reason, first, the lightness L (x, y) is added to all the pixels and divided by all the pixels to calculate the average lightness Ave of the entire image (step S240).

Then, the correction coefficient a (L) based on the brightness of the entire image is defined as a (L) = ((Ave + 16) / 116) ^0.8, and the correction coefficient a (L) is calculated (step S245) and the index Int Is used as the granularity index GI (step S250). The correction coefficient may be a function that increases or decreases the coefficient value according to the average brightness, and various other functions can be employed. When the granularity index GI is calculated by the above processing, the image quality evaluation index calculating unit 35f outputs a predetermined control signal via the display DRV22 and displays the granularity index GI on the display 18 (step S255).

  Since the granularity index indicates the granularity of the printed material when printing is performed using halftone image data, the granularity of the halftone image data can be evaluated without actually performing printing. In the present embodiment, in the flow shown in FIG. 18 above, the graininess index GI is displayed on the display 18 and the process is terminated. Of course, once the graininess index GI is calculated, the printing conditions are further changed. The process of accepting and calculating the granularity index GI again may be repeated. This is the same when other image quality evaluation indexes are used.

  That is, if the calculation of the image quality evaluation index is repeated while changing the above printing conditions, the image quality evaluation index under various printing conditions can be easily calculated, and the image processing that can obtain the highest image quality in the input RGB data is determined. can do. Of course, it is not essential to evaluate only the image quality, and it is also possible to determine the most preferable image processing in consideration of the expected printing speed and the like.

  For example, if image quality evaluation indices are calculated for a plurality of resolutions, it is possible to grasp the minimum necessary resolution from the viewpoint of image quality for certain halftone image data. In addition, if the image quality does not improve greatly even if it exceeds a certain resolution, unnecessary high resolution without an image quality improvement effect can be prevented, and a decrease in printing speed can be prevented. Can be optimized. Also, by preparing a plurality of LUTs and calculating the image quality evaluation index from the result of color conversion with reference to each LUT, or calculating the image quality evaluation index from the result of color conversion by a plurality of interpolation methods. It is possible to grasp the optimum color conversion method from the viewpoint of image quality or grasp the optimum color conversion method in consideration of the speed of color conversion. In addition, by calculating the image quality evaluation index from the results of processing with multiple halftone algorithms, it is possible to grasp the optimal algorithm from the viewpoint of image quality, or to understand the optimal algorithm taking into account the speed of halftone processing Etc. are possible.

D. Variations:
The present invention is not limited to the above-described examples and embodiments, and can be implemented in various modes without departing from the gist thereof. For example, the following modifications are possible.

D1. Modification 1:
In the above embodiment, the print pixel is divided into a plurality of sub-pixels. However, the print pixel may not be divided into sub-pixels. For example, the coverage of the print medium surface by ink dots can be used as a granularity index. In this case, the coverage is calculated from the predicted size of each ink dot without being divided into sub-pixels. can do.

D2. Modification 2:
In the above embodiment, the image quality evaluation index is calculated using the ink dot simulation. However, the simulation according to the present invention can be applied to purposes other than the image quality evaluation index.

FIG. 2 is a block diagram illustrating a schematic configuration of a print control apparatus. It is a block diagram which shows the internal structure of a simulation module. It is a flowchart which shows the whole procedure of dot shape simulation. It is explanatory drawing which shows the mode of a dot shape measurement. It is explanatory drawing explaining the example of dot shape data. It is explanatory drawing explaining the example of color value data. It is a flowchart which shows a simulation process. It is explanatory drawing explaining the example of parameter data. It is explanatory drawing for demonstrating a simulation process. It is explanatory drawing explaining the example of dot position shift data. It is explanatory drawing explaining the example of dot position shift data. It is explanatory drawing explaining the example of control method data. It is explanatory drawing explaining the example of data in the case of using bidirectional | two-way printing and a small medium large dot. It is explanatory drawing which shows an example of the calculation method of a periphery duty in the case of using a different size dot. It is explanatory drawing which shows other embodiment of the dot shape data 15d. It is explanatory drawing which shows other embodiment of the dot shape data 15d. It is explanatory drawing which shows other embodiment of the dot shape data 15d. It is a flowchart at the time of calculating a granularity parameter | index. It is explanatory drawing explaining a mode that a granularity parameter | index is calculated.

Explanation of symbols

10 ... Computer 12 ... Keyboard 13 ... Mouse 15 ... HDD
15a ... RGB data 15b ... Color conversion lookup table 15c ... Parameter data 15d ... Dot shape data 15e ... Color value data 15f ... Dot position deviation data 15g ... Dot position deviation data 15h ... Control method data 18 ... Display 19a ... I / O
19b ... I / O
19c: USB I / O
21 ... Input device DRV
22 ... Display DRV
DESCRIPTION OF SYMBOLS 30 ... Printer driver 31 ... Image data acquisition module 32 ... Color conversion module 33 ... Halftone processing module 34 ... Print data creation module 35 ... Simulation module 35a ... Image data acquisition part 35b ... Parameter acquisition part 35c ... Sub-pixel plane formation part 35d ... recording state data creation unit 35e ... lightness calculation unit 35f ... image quality evaluation index calculation unit 35g ... peripheral duty calculation unit 40 ... printer

Claims (9)

An apparatus for simulating the shape of ink dots formed on a print medium when printing a print image,
Reference for storing dot shape data indicating the relationship between the peripheral duty indicating the total amount of ink dots formed in the peripheral region set around the pixel of interest and the spreading shape of the ink dots formed on the pixel of interest A data storage unit;
A dot data generation unit that generates dot data indicating the ink dot formation state of each pixel on the print medium;
A dot shape calculation unit that calculates the spread shape of individual ink dots formed on the print medium according to the dot data with reference to the dot shape data;
An image quality evaluation index calculation unit for calculating an image quality evaluation index for evaluating the image quality of the print based on the spread shape of each ink dot calculated by the dot shape calculation unit;
A device comprising: The apparatus of claim 1, comprising:
It is possible to use a plurality of different size dots having different sizes in printing the print image,
The dot shape data is created for each of the plurality of different size dots as the target pixel,
The said dot shape calculation part is an apparatus which sets the said periphery area | region for calculating the said periphery duty to an area | region large, so that the size of the ink dot formed in the said attention pixel is large. The apparatus according to claim 1 or 2, wherein
The said dot shape calculation part is an apparatus provided with the periphery duty calculation part which calculates the said periphery duty in the said periphery area | region of each ink dot using the said dot data. The apparatus according to claim 1 or 2, wherein
The dot data generation unit includes a color conversion unit that converts image data representing the print image into ink amount data,
The said dot shape calculation part is an apparatus provided with the periphery duty calculation part which calculates the said periphery duty in the said periphery area | region of each ink dot using the said ink amount data. A device according to any one of claims 1 to 4, comprising:
The dot shape data represents a spreading shape of the ink dot in units of sub-pixels smaller than the pixel,
The said dot shape calculation part is an apparatus which determines the spreading | diffusion shape of the said individual ink dot on the sub pixel plane comprised by the said sub pixel. The apparatus of claim 1 , comprising:
The image quality evaluation index includes a granularity index indicating the granularity of the printed image,
The image quality evaluation index calculation unit calculates a spatial frequency characteristic of lightness of the print image based on a spread shape of the individual ink dots, and calculates the granularity index from the spatial frequency characteristic. The apparatus of claim 6 , comprising:
The reference data storage unit further stores color value data for obtaining brightness for each sub-pixel smaller than the pixel in the range of the spread shape of the individual ink dots,
The image quality evaluation index calculation unit is a device that calculates a spatial frequency characteristic of the brightness of the print image based on the brightness of each sub-pixel. A method of simulating the shape of ink dots formed on a print medium when printing a print image,
A step of preparing dot shape data indicating a relationship between a peripheral duty indicating the total amount of ink dots formed in a peripheral region set around the pixel of interest and a spreading shape of the ink dots formed on the pixel of interest When,
Generating dot data indicating an ink dot formation state of each pixel on the print medium;
Calculating a spread shape of individual ink dots formed on the print medium according to the dot data with reference to the dot shape data;
A step of calculating an image quality evaluation index for evaluating the image quality of the printing based on the spread shape of each ink dot calculated in the dot shape calculation step;
A method comprising: A computer program for executing a simulation of the shape of ink dots formed on the print medium during printing of the print image to a computer, the computer,
A dot data generation function for generating dot data indicating the ink dot formation state of each pixel on the print medium;
The dot shape data indicating the relationship between the peripheral duty indicating the total amount of ink dots formed in the peripheral region set around the target pixel and the spreading shape of the ink dots formed on the target pixel is read from the memory. A dot shape calculation function for calculating the spread shape of individual ink dots formed on the print medium according to the dot data with reference to the dot shape data;
An image quality evaluation index calculation function for calculating an image quality evaluation index for evaluating the image quality of the printing based on the spread shape of each ink dot calculated by the dot shape calculation function ;
Computer program for realizing .

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