JP2011223520A - Image processing apparatus and image processing program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image processing apparatus and an image processing program that change dot recording rates of respective dots more in detail.SOLUTION: An image processing apparatus converts image data into image formation data representing whether a plurality of dots of different size are formed, pixel by pixel. The image processing apparatus comprises a dot recording rate table containing correspondence relation between a density gradation value of the image data and a dot recording rate for each of the plurality of dots, half-tone means of acquiring dot recording rates of a plurality of dots corresponding to a density gradation value for each pixel of the image data by reference to the dot recording rate table, comparing the acquired dot recording rates of the plurality of dots with a threshold of a dither matrix corresponding to the pixel, and outputting image formation data representing formation of dots corresponding to the smallest dot recording rate among dot recording rates exceeding the threshold, and dot recording rate changing means of changing the dot recording rate table in response to input indicating change in dot recording rate for each density gradation value.

Description

  The present invention relates to an image processing apparatus and an image processing program that perform halftone processing.

  In recent years, in order to enrich gradation expression, an ink jet printer capable of expressing gradation more than the binary value of dot on / off for each pixel of image data, a so-called multi-value printer is known. Such a printer, for example, realizes richer gradation expression by changing the density per unit area in multiple stages by forming dots of different sizes on a recording medium.

  In addition, when printing with the printer as described above, the image data to be printed is based on a dot recording rate table in order to determine whether or not dots of any size according to the gradation value of each pixel are formed. Halftone processing is performed. The dot recording rate table is a table in which area gradation values per unit area (hereinafter referred to as dot recording rate) of dots of each size corresponding to each gradation value that image data can take are defined.

  For example, Patent Document 1 describes halftone processing based on a dot recording rate table. In Patent Document 1, the printer driver obtains each dot recording rate corresponding to the gradation value of each pixel with reference to the dot recording rate table for each pixel of the image data, and dithers for each dot corresponding to the pixel. The formation of dots having a dot recording rate larger than the matrix threshold is determined preferentially from the large size dots.

JP 2001-158085 A

  In recent years, there is a demand to change the dot recording rate table for the purpose of adjusting the ink amount during printing, adjusting the image quality such as the granularity of the printed image, or adjusting the error of the nozzle diameter for maintenance. .

  Patent Document 1 describes that the recording rate of each dot in the dot recording rate table can be changed to “10% increase” or “10% decrease”. However, it is only described that the dot recording rate of all density gradation values that can be taken by the image data is uniformly increased or decreased, for example, adjustment of the dot recording rate of only the highlight portion having a low gradation value, It was insufficient for detailed adjustment of the image quality of the printed image.

  Therefore, an object of the present invention is to provide an image processing apparatus and an image processing program that can change the dot recording rate of each dot in more detail.

  In order to achieve the above object, according to a first aspect of the present invention, in an image processing apparatus for converting image data into image formation data representing presence / absence of formation of a plurality of dots of different sizes for each pixel, A dot recording rate table having a correspondence relationship between a density gradation value of image data and a dot recording rate, which is a ratio of an area where the dots are formed per unit area on a recording medium, for each of the plurality of dots; For each pixel of the image data, the dot recording rate of the plurality of dots corresponding to the density gradation value is acquired with reference to the dot recording rate table, and the acquired dot recording rate and the pixel of the plurality of dots are acquired. Compared with the threshold value of the corresponding dither matrix, the dot recording rate exceeding the threshold value represents the formation of dots corresponding to the smallest dot recording rate Halftone means for outputting the image formation data for each said gray scale value, having a dot recording rate changing means for changing the dot recording rate table according to the input for instructing the change of the dot recording rate.

  According to the above aspect, the image processing apparatus can change the dot recording rate for each density gradation value. Therefore, the user can adjust the image quality and ink amount of the printed image in more detail.

  According to a preferable aspect in the first aspect, the dot recording rate table includes the first dot recording rate of the first dot and the dot recording of the second dot having a smaller size than the first dot. And a second dot recording rate that is larger than the first dot recording rate, and the dot recording rate changing means responds to an input instructing the change of the first dot recording rate. The second dot recording rate is changed in addition to the first dot recording rate.

  According to this aspect, the image processing apparatus can change the dot recording rate while confirming the dot recording rate of the other dots after the change and the sum of the dot recording rates.

  According to a preferable aspect of the first aspect, the dot recording rate changing unit is configured to input based on an operation by a user of a control point on a graphic object representing a correspondence relationship between the density gradation value and the dot recording rate. Accordingly, the dot recording rate corresponding to the control point and the dot recording rate corrected by curve interpolation or linear interpolation around the control point are changed.

  According to this aspect, in accordance with the change of the control point, the image processing apparatus interpolates and corrects the dot recording rate around the control point with the curve or the straight line in addition to the dot recording rate corresponding to the control point. Therefore, the user can change the dot recording rate so that the transition becomes smooth.

  According to a preferable aspect in the first aspect, the image data has the density gradation values of a plurality of colors, and the dot recording rate changing unit changes the dot recording rate for each of the colors of the plurality of colors. To do.

  According to this aspect, the image processing apparatus can adjust the image quality of the print image and the ink amount in more detail.

  In order to achieve the above object, according to the second aspect of the present invention, a computer performs image processing for converting image data into image formation data representing the presence / absence of formation of a plurality of dots of different sizes for each pixel. In the computer-readable image processing program to be executed, for each pixel of the image data, the dot recording rate of the plurality of dots corresponding to the density gradation value is obtained with reference to a dot recording rate table, and the obtained plurality The dot recording rate of the dot is compared with the threshold value of the dither matrix corresponding to the pixel, and the image forming data representing the formation of the dot corresponding to the smallest dot recording rate among the dot recording rates exceeding the threshold value is output. For each tone process and each density gradation value, the dot recording is performed according to an input for instructing the change of the dot recording rate. A dot recording rate changing step of changing a rate table, wherein the dot recording rate table includes the density gradation value of the image data and the area where the dots per unit area on the recording medium are formed. Each of the plurality of dots has a correspondence relationship with the dot recording rate, which is a ratio.

It is a figure showing the structure of the image processing apparatus in this Embodiment. FIG. 6 is a diagram illustrating a process flow of a printer driver in the present embodiment. It is a figure showing a dot recording rate table. It is an example figure showing the change screen of a dot recording rate table. It is an example figure showing the example of a change of a dot recording rate table.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the technical scope of the present invention is not limited to these embodiments, but extends to the matters described in the claims and equivalents thereof.

  The image processing apparatus according to the present embodiment enables the dot recording rate of each of a plurality of types of dots having different sizes to be changed for each gradation value, and the image data is set to any dot based on the changed dot recording rate. The dot recording rate can be changed in more detail by converting it into image forming data representing the presence or absence of the dot formation.

  FIG. 1 is a diagram illustrating a hardware configuration example of a computer 1 that is an image processing apparatus according to the present embodiment. The computer 1 includes a CPU 11, an internal memory 12, an operation unit 13, a display unit 14, a communication interface 15, and a bus 16.

  The CPU 11 executes a program stored in the internal memory 12 and controls each component of the computer 1. The internal memory 12 includes a ROM (Read Only Memory), a RAM (Random Access Memory), and the like. The ROM is a memory that stores various programs executed by the CPU 11 and various data, and the RAM is a memory that temporarily stores programs being executed by the CPU 11 and data being calculated.

  The display unit 14 includes a liquid crystal display and displays an image corresponding to the display data supplied from the CPU 11. The operation unit 13 is configured by, for example, a keyboard and a mouse, and generates a signal corresponding to a user operation. The bus 16 is a signal line that connects the CPU 11, the internal memory 12, the operation unit 13, the display unit 14, and the communication interface 15 to each other and enables data exchange between them. In addition, the printer 2 is connected to the computer 1 via the communication interface 15.

  The printer 2 connected to the computer 1 shown in FIG. 1 is an ink jet printer. The ink jet printer according to the present embodiment can form, for example, dots having three different sizes (ink amounts) of large, medium, and small on a print medium such as paper. Ink jet printers, for example, enable the formation of dots of different sizes by changing the voltage application time to the piezo elements.

  The computer 1 having the above configuration stores the printer driver program 21 for enabling the printer 2 to print image data in the internal memory 12. The printer driver program 21 includes a halftone unit 22, a dot recording rate changing unit 23, a dot recording rate table 24, and a dither matrix 25. Details of the means 22, 23, the dot recording rate table 24, and the dither matrix 25 will be described later.

  The printer driver function is executed by the cooperation of the hardware including the above-described CPU 11 of the computer 1 and the printer driver program 21 stored in the internal memory 12. The printer driver program 21 performs predetermined image processing on image data such as an application for which a print instruction has been issued, converts the image data into printable image formation data, and transfers the image formation data to the printer 2.

  FIG. 2 is a diagram showing details of processing of the printer driver installed in the computer 1 of FIG. Below, it demonstrates based on the flowchart figure of FIG. Here, each pixel of the image data to be printed has a gradation value of 0 to 255 for each of the R, G, and B components in the RGB color space. Further, it is assumed that the resolution of the image data is converted to the printing resolution of the printer 2 by the printer driver.

  First, the printer driver performs color conversion processing of image data (S11). The color conversion process is a process of converting image data composed of R, G, and B gradation values into gradation value data of each ink color that can be printed by the printer. Assume that the ink colors of the printer 2 in this embodiment are four colors of C (cyan), M (magenta), Y (yellow), and K (black). The printer driver performs color conversion of image data composed of RGB gradation values into image data having gradation values of C, M, Y, and K colors based on a color conversion table or the like.

  Subsequently, the halftone means 22 of the printer driver performs halftone processing (S12, S13) on the image data after the color conversion processing. Halftone processing is processing for converting the gradation value of image data (in this embodiment, 256 gradations from 0 to 255) into gradation values that can be expressed by the printer. Since the printer 2 in the present embodiment can form dots of three types of large, medium, and small sizes, the halftone unit 22 converts the image data of 256 gradations to “no dot formation”. The image data is converted into four-gradation image data representing “large dot formation”, “medium dot formation”, and “small dot formation”. Specifically, it is as follows.

  First, in step S12, the halftone unit 22 refers to a dot recording rate table to be described later, and for each color (C, M, Y, K) of the image data, its gradation value (0 to 255). ), The dot recording rate (level data) of each large, medium, and small dot is acquired. In step S13, for each pixel, the halftone means 22 compares the dot level data with the threshold value of the dither matrix corresponding to the pixel, and the dot corresponding to the smallest level data among the level data exceeding the threshold value. The image formation data representing the formation of is output.

  FIG. 3 is a diagram illustrating a dot recording rate table. TBL1 and TBL2 in FIG. 3 are tables in which the dot recording rate is expressed in two forms. The horizontal axis of the dot recording rate tables TBL1 and TBL2 represents the tone value of the image data (0 to 255 in this embodiment), and the vertical axis represents the dot recording rate (0 to 100%). The dot recording rate is the ratio of the area where the dots are formed per unit area when the gradation value is expressed by the coverage per unit area by the dots on the recording medium. In the figure, the dot recording rate (LDa) for large dots is represented by a dotted line, the dot recording rate (MDa, MDb) for medium dots is represented by a solid line, and the dot recording rate (SDa, SDb) for small dots is represented by a broken line.

  The level data is a value obtained by converting the dot recording rate into the threshold value range of the dither matrix. The dither matrix 31 in this embodiment of FIG. 3 has a threshold value of 0-255. Therefore, for example, the level data when the dot recording rate is “50%” is “128”.

  The dot recording rate tables of TBL1 and TBL2 in FIG. 3 represent the same contents. In the dot recording rate table TBL1 of the first form, the dot recording rates (LDa, MDa, SDa) of each dot are individually shown, whereas in the dot recording rate table TBL2 of the second form, each dot is shown. The dot recording rates (LDa, MDb, SDb) are displayed in total.

  Specifically, in the dot recording rate table TBL2 of the second form, the dot recording rate (MDb) of medium dots is the same as the dot recording rate (LDa) of large dots in the dot recording rate table TBL1 of the first form. This is represented by the sum (MDb = LDa + MDa) of the dot recording rate (MDa). Similarly, the dot recording rate (SDb) for small dots in the dot recording rate table TBL2 is the dot recording rate (LDa) for large dots and the dot recording rate (MDa) for medium dots in the dot recording rate table TBL1 of the first embodiment. ), And the dot recording rate (SDa) of small dots (SDb = LDa + MDa + SDa).

  The dot recording rate table is designed in consideration of the granularity of the printed image, banding phenomenon, printing speed, and the like. For example, in the low gradation region, small dots are used rather than relatively large dots (large and medium dots) that are easily detected by human eyes, and the graininess (roughness) of the printed image is suppressed. In the high gradation region, dots larger than small dots are used, and the banding phenomenon (white stripes) of the printed image is suppressed. In the high gradation region, the printing speed is increased by forming a small number of dots having a larger size than forming many dots having a small size.

  The printer driver in the present embodiment makes it possible to change the dot recording rate of each dot in the dot recording rate table as described above for each gradation value. Accordingly, the user performs more detailed adjustments such as the granularity of the print image and the ink amount.

  Returning to the flowchart of FIG. 2, the halftone processing of steps S12 and S13 will be described based on the dot recording rate table TBL2 of FIG. Here, a case where a pixel having image data has, for example, n1 to n4 (TBL2 in FIG. 3) gradation values is illustrated. Further, the threshold value of the dither matrix (31 in FIG. 3) corresponding to the pixel is “50”. The halftone means 22 in the present embodiment refers to the second dot recording rate table TBL2 in FIG. 3 to obtain the level data of each dot corresponding to the gradation values (n1 to n4), and the dither matrix. Image formation data representing dot formation corresponding to the smallest level data among the level data exceeding the threshold “50” corresponding to 31 pixels is output.

  First, a case where the gradation value of the pixel is “n1” will be described. According to the dot recording rate table TBL2 in FIG. 3, the level data in the case of the gradation value “n1” is the large dot “n1L”, the medium dot “n1M”, and the small dot “n1S”. In this case, in the dot recording rate table TBL2 of FIG. 3, since the level data “n1L” of the large dot is the smallest level data exceeding the threshold “50”, the halftone unit 22 forms a large dot on the pixel. A value to be represented (“11” in the present embodiment) is stored.

  Next, a case where the gradation value of the pixel is “n2” will be described. The level data in the case of the gradation value “n2” is the large dot “n2L”, the medium dot “n2M”, and the small dot “n2S” according to the dot recording rate table TBL2. In this case, the large dot level data “n2L” does not exceed the threshold “50”, and the medium dot level data “n2M” is the smallest level data that exceeds the threshold “50”. For this reason, the halftone means 22 stores a value (“10” in the present embodiment) indicating the formation of a medium dot in the pixel.

  Similarly, the level data when the gradation value of the pixel is “n3” is the small dot “n3S”, and there is no medium / large dot level data. In this case, since the small dot level data “n3S” exceeds the threshold value “50”, the halftone means 22 stores a value (“01” in the present embodiment) representing the formation of a small dot in the pixel. .

  Further, the level data when the gradation value of the pixel is “n4” is the small dot “n4S”, and there is no medium / large dot level data. In this case, since the level data “n4S” of the small dots does not exceed the threshold value “50”, no dot is formed on the pixel. For this reason, the halftone means 22 stores a value (“00” in the present embodiment) indicating that no dot is formed on the pixel.

  In this way, the halftone processing of steps S12 and S13 is performed for each pixel of the image data, so that the image data of 256 gradations becomes “00 (no dot formation)” “11 (large dot formation). ) ”“ 10 (formation of medium dots) ”“ 01 (formation of small dots) ”is converted into image formation data of four gradations.

  For example, in the case of 4 × 4 image data 32 having the same gradation value “n2”, a halftone process based on the dot recording rate table TBL2 and the dither matrix 31 in FIG. It is converted into value image formation data. The converted image formation data 33 is printed by the printer 2 as an image 34 representing the gradation value “n2”. As described above, the threshold value of the dither matrix is designed so that, for example, a print image corresponding to image data having the same gradation value per unit area expresses the gradation value.

  Returning to the flowchart of FIG. 2, after halftone processing (S12, S13), the dot recording rate changing means 23 of the printer driver displays the dot recording rate table on the display unit 14 and accepts the change of the dot recording rate table. (S14). In addition to the dot recording rate table, the dot recording rate changing means 23 may display a preview image of the image formation data after halftone processing based on the dot recording rate table.

  FIG. 4 is a diagram showing a dot recording rate table change screen 41. In the change screen 41 of FIG. 8, a dot recording rate table 42 of the second form and a preview image 44 based on the dot recording rate table 42 are displayed. The user selects an ink color whose dot recording rate is to be changed from the list box 43 in FIG. For example, when the user selects “cyan”, the dot recording rate changing unit 23 displays a dot recording rate table 42 for dots of each size of “cyan”.

  Then, for example, in the dot recording rate table 42 of FIG. 4, the user selects an arbitrary control point 40 (42S, 42M, 42L) on the line representing the dot recording rate of each size of cyan with a mouse or the like, and performs the control. By moving the point 40 up and down, left and right, the dot recording rate corresponding to an arbitrary gradation value is changed. Note that the user may select “all colors” from the list box 43 in FIG. 4 and make the same change to the dot recording rate of each size of all colors.

  An example of changing the dot recording rate table will be described later. Returning to the flowchart of FIG. 2, when the dot recording rate table is changed (YES in S15), the halftone means 22 refers to the changed dot recording rate table and again performs halftone processing of the image data. Perform (S16, S17). Then, as shown in FIG. 4, the dot recording rate changing means 23 also displays a preview image 45 of the image formation data after halftone processing based on the changed dot recording rate table (S18).

  Thereby, the user can compare the preview image 44 based on the pre-change dot recording rate table and the preview image 45 based on the post-change dot recording rate table. The user may continue to change the dot recording rate table based on the preview image 45 based on the changed dot recording rate table. Note that the dot recording rate changing means 23 may be provided with a check box 46 that enables selection as to whether or not to display the preview image 45 based on the changed dot recording rate table, as shown in FIG.

  On the other hand, when the dot recording rate table is not changed (NO in S15) or after the preview image is displayed based on the changed dot recording rate table (S18), the printer driver accepts an image data print instruction ( S19). When the print button 47 in FIG. 4 is pressed (YES in S19), the printer driver rearranges the image formation data after the halftone process in the transfer order by the microweave process (S20), and transfers it to the printer 2. Then, the printer 2 generates a print image based on the transferred data. On the other hand, when the print button 47 is not pressed (NO in S19), the printer driver accepts a change in dot recording rate (S15).

  FIG. 5 is a diagram illustrating a modification example of the dot recording rate table. In the dot recording rate table 51 of FIG. 5, it is assumed that the control point 54 on the line 51SD representing the dot recording rate of small dots is operated downward as indicated by an arrow. In the figure, 51SD represents the dot recording rate of the small dots before the change, and 61SD represents the dot recording rate of the small dots after the change. As shown in the figure, the dot recording rate changing means 23 records not only the dot recording rate corresponding to the control point 54 but also the tone values around the control point 54 in accordance with the operation of the control point 54 by the user. The rate (line) is also changed to a value interpolated by a curve function such as a Pezier curve or a spline curve.

  As a result, the user changes the dot recording rate corresponding to the control point 54 by a simple operation of the control point 54, and smoothly changes the dot recording rate of the gradation values around the control point 54 with the change. It can be changed to change. Further, the user can arbitrarily adjust the slope of the curve by operating the control point 54.

  In this way, the image processing apparatus according to the present embodiment also uses the supplemental curve for the dot recording rate corresponding to the surrounding gradation values in accordance with the operation of the control point on the graphic object representing the dot recording rate. By making correction based on this, it is possible to smooth the transition of the dot recording rate around the control point. Accordingly, the image processing apparatus can smoothly change the dot recording rate corresponding to the gradation value even when the dot recording rate can be changed for each gradation value.

  Further, the image processing apparatus according to the present embodiment can change the degree of change of the dot recording rate for each gradation value. Thereby, the user can make a change that gradually increases the degree of increase in the dot recording rate with respect to the gradation value, for example.

  Such a change is particularly effective in a low gradation region (highlighted portion, 55 in FIG. 5), for example. For example, the user can change the dot recording rate of small dots so that it gradually increases as the gradation value is lower, thereby preventing a tone jump phenomenon in the gradation of the printed image.

  On the other hand, in the dot recording rate table 52 of FIG. 5, it is assumed that the user has changed the control point 56 on the line 52LD representing the dot recording rate of large dots downward. In the figure, the dot recording rate before the change is 52LD (large dot), 52MD (medium dot), 52SD (small dot), and the dot recording rate after the change is 62LD (large dot), 62MD (medium dot). ), 62SD (small dots). In the same figure, with the downward change of the control point 56 on the dot recording rate 52LD for large dots, the dot recording rate 62MD for medium dots and the dot recording rate 62SD for small dots that have been displayed in total are also reduced. Yes.

  As described above, the dot recording rate changing unit 23 changes the dot recording rate of the smaller size dot in conjunction with the change of the dot recording rate of the large size dot. Accordingly, the user can change the dot recording rate while confirming the dot recording rate of the other dots after the change and the sum of the dot recording rates of each dot (the density of the print image).

  Then, the user can confirm whether or not the sum of the dot recording rates is proportional to the tone value (horizontal axis), and the tone expression of the print image based on the changed dot recording rate table is It is possible to prevent discontinuity. Therefore, the dot recording rate changing means 23 prevents the gradation expression of the print image from becoming discontinuous and degrading the image even when the user can change the dot recording rate for each gradation value. be able to.

  The above change is performed, for example, when the dot recording rate of large dots in the high gradation region (57 in FIG. 5) is reduced to save the amount of ink used in the print image. Since the change in the dot recording rate in the high gradation region is not easily recognized by human eyes, the influence on the printed image due to the change is small. Therefore, the user can reduce the recording rate of large dots in a high gradation region that is an arbitrary gradation value range, and can save the amount of ink used while suppressing the influence on the image quality of the printed image.

  Further, as another modification of the dot recording rate table, the user decreases the dot recording rate of medium dots and increases the dot recording rate of small dots, for example, for a gradation value range having a medium gradation region. . Thereby, the dots formed in the gradation value range formed by mixing the small and medium dots are replaced from the medium dots to the small dots, and the granularity of the printed image is improved. In addition, by not changing the dot recording rate of the gradation value range that is not subject to change, the user can adjust the granularity of the printed image while avoiding the effect on the image quality of the gradation value range that is not subject to change. Can do.

  Further, in the above modification example, the dot recording rate changing means 23 increases the dot recording rate of small dots as much as the reduction amount in conjunction with the changing operation for decreasing the dot recording rate of medium dots. May be. Thereby, the dot recording rate changing means 23 can change the dot recording rate of each size without changing the sum of the dot recording rates.

  In this way, the image processing apparatus according to the present embodiment has a dot recording rate table, and the dot recording rate of each dot in the dot recording rate table can be changed for each gradation value, and the changed dot recording Based on the rate table, the multi-gradation image data is converted into image data having gradation values printable by the printer.

  Thereby, the user can change the dot recording rate for an arbitrary gradation value or gradation value range, and can change the degree of change of the dot recording rate for each gradation value. . As a result, the user can adjust the image quality and ink amount of the printed image in more detail, and can suppress the influence on the image quality of the gradation value range that is not subject to change of the dot recording rate.

  In the dot recording rate tables 51 and 52 of the second embodiment in FIG. 5, the dot recording rate of medium dots does not fall below the dot recording rate of large dots. Similarly, the dot recording rate of small dots does not fall below the dot recording rate of medium and large dots. Therefore, for example, the dot recording rate changing means 23 performs an operation of changing the dot recording rate of the smaller size dot below the dot recording rate of the larger size dot in the dot recording rate tables 51 and 52. Restrictions may be applied so as not to break. As a result, the image processing apparatus according to the present embodiment prevents the dot recording rate table from being changed to an illegal state even when the user changes the dot recording rate for each gradation value. be able to.

  In addition, the image processing apparatus according to the present embodiment can change the dot recording rate for each gradation value individually for each color of CMYK, for example. Accordingly, the user can change the dot recording rate for an arbitrary gradation value range of a specific ink color, for example, and can adjust the image quality and the ink amount of the printed image in more detail. .

  In the above example, the example of decreasing the dot recording rate is mainly given, but the user may make a change to increase the dot recording rate. However, if the amount of ink at the time of printing exceeds a predetermined value (hereinafter, “duty limit value”), an ink scattering phenomenon occurs at the time of printing. Therefore, for example, the dot recording rate changing unit 23 may limit the dot recording rate table so that the total ink amount based on the dot recording rate cannot be changed to exceed the duty limit value. As a result, the image processing apparatus according to the present embodiment can prevent the ink scattering phenomenon even when the user changes the dot recording rate for each gradation value.

  In the above example, the dot recording rate table (TBL2 in FIG. 3) of the second mode is changed. However, the dot recording rate changing means 23 is the dot recording rate of the first mode. The table (TBL1 in FIG. 3) may be changed. In the dot recording rate table (TBL1 in FIG. 3) of the first embodiment, it is more clearly expressed how the dot recording rate of each dot is generated with respect to the gradation value (horizontal axis). Therefore, the user can change the dot recording rate of each dot while confirming the occurrence state of the dot recording rate of each dot with respect to the gradation value.

  In the example of FIG. 5, the number of control points on the line representing the dot recording rate is one, but it may be plural. Further, in the example of FIG. 5, the example in which the dot recording rate around the control point is changed by the interpolation curve has been described, but the dot recording rate changing means 23 changes the dot recording rate around the control point by the interpolation line. May be.

  The change of the dot recording rate table is not limited to the operation of the control point as shown in FIG. 5, for example, the gradation value range to be changed and the change amount of the dot recording rate are input from the outside. May be performed. The image processing apparatus according to the present embodiment may change the dot recording rate table in advance for image data to be printed and store it together with the image data. The dot recording rate table common to the printer 2 may be changed so as to be reflected in the image data.

  The image processing apparatus according to the present embodiment exemplifies the case of generating image formation data to be provided to a printer capable of forming three types of large, medium, and small dots. The type is not limited to the above example. For example, it may be a printer capable of forming dots of a larger number of sizes, a printer capable of forming dots with different concentrations of ink, or the like.

  Further, the image processing apparatus according to the present embodiment exemplifies a case where image data to be provided to a printer capable of color printing is generated using inks of four colors C, M, Y, and K. The color is not limited to the above example. For example, the image processing apparatus generates image data to be provided to a printer that performs printing using six colors of ink including light cyan and light magenta, or generates image data to be provided to a monochrome printer. Also good.

  The image processing apparatus according to the present embodiment performs halftone processing based on the dither method. However, the image processing apparatus may perform halftone processing by applying other multilevel processing such as an error diffusion method.

  The processing of the embodiment has been described as processing of the image processing apparatus. However, the image processing is stored as a program in a computer-readable recording medium, and is performed by the computer reading and executing the program. May be.

  1 Computer, 11 CPU, 12 Internal memory, 13 Operation section, 14 Display section, 15 Communication interface, 2 Printer

Claims (5)

In an image processing apparatus that converts image data into image formation data representing the presence or absence of formation of a plurality of dots of different sizes for each pixel,
A dot recording rate table having a correspondence relationship between a density gradation value of the image data and a dot recording rate which is a ratio of an area where the dots are formed per unit area on a recording medium, for each of the plurality of dots;
For each pixel of the image data, the dot recording rate of the plurality of dots corresponding to the density gradation value is acquired with reference to the dot recording rate table, and the acquired dot recording rate and the pixel of the plurality of dots are acquired. A halftone means for outputting the image formation data representing the formation of dots corresponding to the smallest dot recording rate among the dot recording rates exceeding the threshold,
Dot recording rate changing means for changing the dot recording rate table in response to an input for instructing change of the dot recording rate for each density gradation value;
An image processing apparatus comprising: In claim 1,
The dot recording rate table includes the first dot recording rate of the first dot and the dot recording rate of the second dot having a smaller size than the first dot, which is greater than the first dot recording rate. And a second dot recording rate having a large
The dot recording rate changing means changes the second dot recording rate in addition to the first dot recording rate in response to an input instructing to change the first dot recording rate. Image processing device. In claim 1 or 2,
The dot recording rate changing unit is configured to detect the dot recording rate corresponding to the control point in response to an input based on an operation by a user of the control point on the graphic object representing the correspondence between the density gradation value and the dot recording rate. And the dot recording rate corrected by curve interpolation or linear interpolation around the control point. In any one of Claims 1 thru | or 3,
The image data has the density gradation values of a plurality of colors,
The image processing apparatus according to claim 1, wherein the dot recording rate changing unit changes the dot recording rate for each of the plurality of colors. In a computer-readable image processing program for causing a computer to execute image processing for converting image data into image formation data representing the presence or absence of formation of a plurality of dots of different sizes for each pixel,
For each pixel of the image data, refer to the dot recording rate table to obtain the dot recording rate of the plurality of dots corresponding to the density gradation value, and correspond to the acquired dot recording rate of the plurality of dots and the pixel. A halftone process for outputting the image forming data representing the formation of dots corresponding to the smallest dot recording rate among the dot recording rates exceeding the threshold,
A dot recording rate changing step for changing the dot recording rate table in response to an input for instructing to change the dot recording rate for each density gradation value;
And execute
The dot recording rate table shows a correspondence relationship between the density gradation value of the image data and the dot recording rate, which is a ratio of an area where the dots are formed per unit area on a recording medium. An image processing program characterized by having each.