JP2013059938A - Apparatus, method and program for processing image - Google Patents

Abstract

An image processing apparatus for generating image data for printing, which can effectively execute correction processing for nozzle characteristics for all densities is provided.
An image processing apparatus for image data for printing converts color image data expressed in a first color space into image data expressed in a second color space of a color material used at the time of printing. And a nozzle characteristic correction unit that corrects the image data converted by the color conversion unit based on the characteristics of each nozzle that discharges the color material, and the density gradation value of each color in the first color space Is associated with the density gradation value of each color in the second color space, and a value smaller than the maximum value that the density gradation value of the second color space can take is a density of the second color space. The color conversion unit performs the conversion process according to the color conversion table that is associated with each other so as to maximize the gradation value.
[Selection] Figure 1

Description

  The present invention relates to an image processing apparatus and the like for generating image data for printing, and more particularly to an image processing apparatus and the like that can effectively execute correction processing for nozzle characteristics for all densities.

  Conventionally, an image recording apparatus such as an ink jet printer has been used for various purposes. In the printer, ink of each color, which is a color material, is ejected from a plurality of nozzles provided in the head onto a print medium such as paper, and printing is performed.

  In such an ink jet printer, it is known that defects occur in printed matter such as density unevenness due to the characteristics of each nozzle (ink discharge amount, ink discharge direction, etc.).

  In order to eliminate such problems due to the nozzle characteristics, it has been proposed to perform correction processing on image data for printing.

  Regarding the correction processing, for example, Patent Document 1 below discloses a technique for correcting the ejection ink amount of each nozzle from the output result of an unevenness detection pattern or the like.

Japanese Patent Laid-Open No. 2004-174751

  However, the image data to be corrected (before correction) is usually composed of data representing density gradation values and ink amounts, and these data can have a minimum density and a maximum density that can be output. Therefore, there is a problem that the image data representing the maximum density cannot have a value higher than that even when it is desired to make it dark based on the nozzle characteristics, and proper correction cannot be performed. Further, even in image data having a value near the maximum density, there is a case where the correction to increase the density has a small difference up to the maximum density, and the necessary correction cannot be performed, and there is a similar problem. Therefore, in the conventional correction method, there is a possibility that sufficient correction is not performed for a dark portion.

  Therefore, an object of the present invention is to provide an image processing apparatus for generating image data for printing, and capable of effectively executing correction processing for nozzle characteristics for all densities. It is.

  In order to achieve the above object, one aspect of the present invention is connectable to an image recording apparatus, and the image processing apparatus for image data for printing uses the image data expressed in the first color space as the image data. A color conversion unit that converts the image data expressed in the second color space of the color material used in the recording apparatus, and the image recording apparatus that discharges the color material into the image data converted by the color conversion unit. And a nozzle characteristic correction unit that performs correction based on the characteristics of each nozzle, and is a table in which density gradation values of each color in the first color space are associated with density gradation values of each color in the second color space. Thus, the color conversion table associated with each other is such that a value smaller than the maximum value that the density gradation value of the second color space can take becomes the maximum of the density gradation value of the second color space. The color conversion unit performs the conversion process according to

  Further, in the above invention, a preferred aspect is that the color ejected from the nozzle with respect to the same data value when instructing the image recording apparatus to perform printing based on the image data corrected by the nozzle characteristic correction unit. The amount of the material is processed in accordance with the color conversion table that is associated so that the maximum value that the density gradation value of the second color space can take is the maximum of the density gradation value of the second color space. It is characterized in that it is increased more than the case.

  In order to achieve the above object, according to another aspect of the present invention, there is provided an image processing method for printing image data, wherein the image data expressed in the first color space is converted into the second color of the color material used during printing. A color conversion step that converts the image data expressed in space, and a nozzle characteristic correction step that corrects the image data converted in the color conversion step based on the characteristics of each nozzle that discharges the color material. A table in which the density gradation value of each color in the first color space is associated with the density gradation value of each color in the second color space, and the maximum value that the density gradation value in the second color space can take The conversion process in the color conversion process is performed according to the color conversion table that is associated with each other so that a smaller value is the maximum density gradation value of the second color space. .

  In order to achieve the above object, according to still another aspect of the present invention, an image processing program for causing a computer to perform image processing of printing image data uses image data expressed in the first color space during printing. A color conversion step of converting the image data expressed in the second color space of the color material to be processed, and correcting the image data converted in the color conversion step based on the characteristics of each nozzle that discharges the color material Nozzle characteristic correction step is executed by the computer, and the density gradation value of each color in the first color space is associated with the density gradation value of each color in the second color space, the second color The color conversion step according to the associated color conversion table so that a value smaller than the maximum value that the density gradation value of the space can take becomes the maximum of the density gradation value of the second color space. Said change in Process is performed, is that.

  Further objects and features of the present invention will become apparent from the embodiments of the invention described below.

1 is a configuration diagram according to an embodiment of an image processing apparatus to which the present invention is applied. It is the figure which illustrated the correction table 128. It is the figure which illustrated the dot generation amount table 129 in the graph format. 3 is a flowchart illustrating a procedure of processing performed by a driver 12. It is a figure for demonstrating the correction process of a high concentration area | region.

  Embodiments of the present invention will be described below with reference to the drawings. However, such an embodiment does not limit the technical scope of the present invention. In the drawings, the same or similar elements are denoted by the same reference numerals or reference symbols.

  FIG. 1 is a configuration diagram according to an embodiment of an image processing apparatus to which the present invention is applied. A driver 12 shown in FIG. 1 is an image processing apparatus to which the present invention is applied, and corrects the characteristics of each nozzle provided in the printer 2 after color conversion processing to the color space of ink colors used in the printer 2 (image recording apparatus). In the color conversion process, the process is executed in accordance with a color conversion table in which a value smaller than the maximum density gradation value that the data can have is set to the maximum value. The correction process can be sufficiently executed.

  FIG. 1 functionally shows the apparatus configuration in the present embodiment. The host computer 1 is a host device of the printer 2 that gives a print instruction to the printer 2, and is configured by a personal computer, for example. Therefore, although not shown, the host computer 1 includes a CPU, RAM, ROM, HDD, display, operation device, and the like.

  The application 11 is a print request source, and there may be applications having various functions such as a text creation application and a graphic creation application. The application 11 includes a program that instructs processing contents, the CPU that executes processing according to the programs, the RAM, and the like, and outputs image data representing the printing contents when a print request is made.

  The driver 12 is a driver for the printer 2, performs image processing on the image data output from the application 11 to obtain image data (print data) for the printer 2, sends the print data to the printer 2, and This is a part that issues a print instruction for printing requested by the application 11.

  The driver 12 includes a driver program for instructing processing contents, the CPU for executing processing according to the program, various data used for processing, the RAM, and the like. The specific functional configuration and processing contents will be described later. . The driver program is stored in the HDD of the host computer 1 by being copied from a storage medium such as a CD to the host computer 1 or downloaded to the host computer 1 via a network such as the Internet. The

  The printer 2 is, for example, a line head ink jet printer that executes print processing in accordance with the print instruction of the host computer 1. As shown in FIG. 1, the printer 2 includes a controller 13 and a print execution unit 14.

  The controller 13 is a part that receives print data according to the print instruction and causes the print execution unit 14 to execute print processing according to the print data. Specifically, it is configured by a program describing processing contents, a CPU that executes processing according to the program, a RAM, a ROM that stores the program, an ASIC, and the like.

  The print execution unit 14 is a part that actually executes print processing on a print medium such as paper in accordance with an instruction from the controller 13. Here, a line head including a plurality of nozzles that eject ink that is a color material to the print medium, a transport device that transports the print medium at a predetermined speed, and the like are provided. Here, as an example, CMYK (cyan, magenta, yellow, black) four-color ink is used. Moreover, the line head is divided into a plurality of head units as an example, and these are alternately arranged in a so-called zigzag pattern.

  Next, the functional configuration of the driver 12 shown in the lower part of FIG. 1 will be described. The rasterization unit 121 is a part that performs rasterization processing on the image data output from the application 11 and generates bitmap data expressed in, for example, an RGB (red, green, blue) color space.

  The color conversion unit 122 is a part that converts the bitmap data into data expressed in the color space of CMYK, which is the color of the color material, according to the color conversion table 127. The color conversion table 127 is an LUT (look-up table) prepared in advance, and is a table in which each density gradation value of CMYK corresponding to each density gradation value of RGB is stored. The color conversion table 127 is designed for each printing condition because the color actually printed varies depending on the printing conditions such as the type of printing medium (paper type) and resolution, even with the same density gradation value. And stored in the HDD or the like. For example, a predetermined high resolution LUT and a predetermined low resolution LUT are prepared for plain paper and fine paper, respectively, and a total of four LUTs are stored.

  Further, in the color conversion table 127, for each color in the RGB color space (first color space), the density gradation value is represented by 8 bits (256 gradations) as an example, and each color is 0 to 255. Has the value of On the other hand, each color in the CMYK color space (second color space) is similarly designed to have a value of each color 0 to 255, but the maximum value of the actually stored value is the design maximum value. The value is smaller than (maximum possible value). Here, as an example, the value (242) is 95% of the design maximum value. As described above, the image processing apparatus is characterized in that the maximum value after conversion of the color conversion table 127 is smaller than the design maximum value, that is, the maximum value in a normal case. Accordingly, in any color conversion table 127, each color in the RGB space is associated with a color expressed by a density gradation value of 0 to 242 of each color of CMYK. For example, (R, G, B) = (0, 0, 0) is associated so as to be converted to (C, M, Y, K) = (0, 0, 0, 242).

  Each of these color conversion tables 127 is generated by a conventional method in which the density gradation value width of each color of CMYK is set to 0 to 242 in advance. In addition, for a table generated with the density gradation value width of each CMYK color being 0 to 255, the density gradation value of each CMYK color may be generated by 95%. The generated color conversion table 127 is stored in the same manner as the driver program described above.

  Next, the nozzle characteristic correction unit 123 is a part that corrects the bitmap data after the color conversion according to the correction table 128. Here, the correction process for the nozzle characteristics described above, that is, the correction process for suppressing a printing defect that appears due to the characteristics of each nozzle provided in the line head is executed.

  The correction table 128 is a table in which the density gradation value before correction is associated with the density gradation value after correction for each nozzle, and is prepared in advance and stored in the HDD or the like. The storage method is the same as that of the driver program described above. FIG. 2 is a diagram illustrating the correction table 128. In the table shown in FIG. 2, there are nozzle numbers (nozzles # 0 to # 1079, assuming 1080 nozzles here) in the left column, and the density level before correction of the upper end row is on the right side. The above-described corrected density gradation value corresponding to the tone value is stored.

  For example, in the nozzle of “Nozzle # 0”, when the input gradation value is “200”, it is indicated that the value should be corrected to “190”, and the bitmap after the color conversion is performed. In the data, if the value of the pixel ejecting ink from the nozzle is “200”, the value is corrected to “190” by the nozzle characteristic correcting unit 123.

  In this embodiment, as described above, the head units are arranged in a zigzag pattern, and there are overlapped portions in which some nozzles are overlapped in the width direction of the print medium between the head units. Since two sets of nozzles are provided at the same position in the direction, in other words, since two nozzles of the same color exist in the same raster, correction values for these nozzles are combined into one. It can be stored in the correction table 128. Also, as shown in FIG. 2, a plurality of correction tables 128 are prepared for each printing condition.

  The correction table 128 is generated in advance by the following preliminary work. First, in each printing condition (paper type, resolution, etc.), a printing process is actually executed using a later-described dot generation amount table 129 prepared for the printing condition. The printing process is executed for a plurality of CMYK tone values (for example, values obtained by dividing 0-255 in five stages) from low density to high density. After that, the actual density of the printed matter is measured by an optical reader or the like, and from each of a plurality of stepwise input density gradation values and actual density values obtained for each nozzle, interpolation processing is performed for each nozzle. An actual density value for each input tone value, that is, a curve indicating the relationship between the input tone value and the actual density value is obtained. Thereafter, the corrected value of the input tone value (here, the CMYK density tone value) is determined so that the curve for each nozzle matches the target curve. This input gradation value is the density gradation value before correction of the correction table 128, and the value after correction is the density gradation value after correction. In this way, the correction table 128 is generated for each printing condition. The target curve can be generated, for example, from the average density value of all nozzles that eject the same color ink.

  As for “nozzle # 1079” in FIG. 2, the density gradation value can only be a value up to 255 for the nozzle that should be corrected (increase the value) in a region where the density gradation value is large. For this reason, there is a case where a correction value for sufficiently darkening cannot be stored. That is, in the example of “nozzle # 1079”, it is desired to make the density gradation value “255” higher than the density gradation value “255”, but the corrected value is also “255”.

  Next, the dot separation unit 124 is a part that converts the corrected bitmap data into data expressed by the dot generation rate according to the dot generation amount table 129. Here, as an example, there are three sizes of small dots (S), medium dots (M), and large dots (L) that can be hit with each nozzle, and the density gradation value (0-255) before processing is set. These are converted into data of the occurrence rates of these three dots. The occurrence rate of each dot can be indicated by a value of 0-4096, for example.

  The dot generation amount table 129 is a table in which the generation rates of the three dots are associated with the CMYK density gradation values (0 to 255). The dot generation amount table 129 is prepared in advance for each of the printing conditions, and includes the HDD and the like. Stored in The storage method is the same as that of the driver program described above.

  FIG. 3 is a diagram illustrating the dot generation amount table 129 in a graph format. In the graph shown in FIG. 3, the horizontal axis indicates the density gradation value before dot separation, and the vertical axis indicates the dot occurrence rate after dot separation. Graphs S, M, and L show the occurrence rates of small dots, medium dots, and large dots, respectively. As can be seen from the figure, when the density gradation value is small, only small dots are generated, resulting in low density printing, and conversely, when the density gradation value is large, three dots including large dots are generated. Thus, printing with high density is realized.

  The dot separation process using the dot generation amount table 129 is a process for converting the input density gradation value into the amount of ink actually ejected from the nozzles. It has both the function of determining the ink amount itself (total ink amount ejected by three dots) with respect to the tone value and the function of determining how to distribute the same ink amount to the three dots. Yes.

  The straight line I in FIG. 3 determines the former ink amount. In the graph, the ink amount (expressed in% here) indicated by the straight line is expressed by ejection of small dots, medium dots, and large dots. Curves S, M, and L. FIG. 3A is for a paper type such as fine paper that does not cause a problem even if the ink amount is large, and is designed to discharge the maximum allowable ink amount of the printer 2 at the maximum density. On the other hand, (b) of FIG. 3 is for a paper type that bleeds when the ink amount is large, such as plain paper, and 70% of the maximum allowable ink amount of the printer 2 is ejected at the maximum density. Designed.

  Therefore, even if the original image data is the same, the amount of ink ejected itself changes if the printing conditions are different. In this way, the dot separation unit 124 converts the density gradation value of each color into ink amount data represented by three types of dots suitable for the printing conditions.

  Next, the halftone processing unit 125 is a part that executes so-called halftone processing and converts the data converted into the dot occurrence rate into data representing the presence or absence of each dot. As a processing method, a conventional dither method, an error diffusion method, or the like can be used.

  Next, the print data conversion unit 126 is a part that converts the data after the halftone process into the print data expressed by a command for the printer 2.

  In the driver 12 in the present embodiment having the configuration as described above, image processing is executed as follows. FIG. 4 is a flowchart illustrating a procedure of processing performed by the driver 12. Hereinafter, specific contents of the image processing will be described with reference to FIG.

  First, as described above, when the application 11 issues a print request, the image data is received by the driver 12 (step S1). At this stage, the received image data is usually in a data format expressed in units of objects such as text, graphics, and images. Therefore, the rasterizing unit 121 executes rasterization processing and converts the image data into Conversion into bitmap data (step S2). Specifically, each pixel is converted into data having density gradation values (0-255) for each color of RGB. A conventional method can be used for rasterization.

  Next, the generated bitmap data is transferred to the color conversion unit 122, and color conversion processing using the color conversion table 127 described above is executed (step S3). Specifically, the color conversion corresponding to the printing condition is selected according to the information indicating the printing condition such as the paper type and resolution selected by the user of the host computer 1 using the operation device or determined as a default value. The table 127 is selected, and data represented by (R, G, B) of each pixel is sequentially converted into data represented by (C, M, Y, K). Then, bitmap data in which each pixel is expressed by a density gradation value of each color of CMYK is generated.

  However, as described above, in each color conversion table 127, since the density gradation value of each color of CMYK takes a value of 0-242, the data of each color after conversion is a value up to 242.

  For the image data in the CMYK color space generated in this way, that is, for the image data expressed by the density gradation value of the ink color used in the printer 2, the correction processing related to the nozzle characteristics described above. Is executed (step S4). First, the nozzle characteristic correction unit 123 selects a correction table 128 corresponding to the printing condition in accordance with the information indicating the printing condition. After that, for each color data (density gradation value) of each pixel, it is determined which nozzle is used to strike, and the corrected density gradation value corresponding to the determined nozzle is the correction table 128 selected above. And processing to change the data to the extracted value. Therefore, the data expressed by (C, M, Y, K) is corrected and converted into data expressed by (C ′, M ′, Y ′, K ′). That is, appropriate image data reflecting the characteristics of each nozzle is generated.

  Here, as described above, the CMYK density gradation values input to the process are all values from 0 to 242. With this, the density gradation value can be increased even for pixels (regions) with high density. Since there is a width, it is possible to correct a nozzle that needs to be increased in density, and correction for nozzle characteristics is effective even in a region having a high density.

  FIG. 5 is a diagram for explaining the correction processing. In FIG. 5, as an example, “nozzle #n” that is the nth nozzle is taken up, and data after correction corresponding to the data before correction stored in the correction table 128 is shown. In this nozzle, the density tends to be low in the high density portion. Therefore, this correction table is created so that the density gradation value is corrected in the high density portion. However, as described above, the density gradation value cannot be corrected to a value larger than 255 near the design maximum value of 255, and the value cannot be sufficiently increased. For example, in the portion indicated by b in FIG. The value cannot be corrected sufficiently.

  Even with such correction table 128 data, as described above, since the value input to the process is up to 242 in this apparatus, data up to the point indicated by the arrow a in FIG. 5 is used. Since the portion (b) that cannot be sufficiently corrected is not used, it is possible to correct up to 255 at maximum, and to solve the problem that the high density portion is not sufficiently corrected. In other words, sufficient correction is possible for all densities.

  The determination of which nozzle to hit is performed using the processing result of a portion (not shown in FIG. 1) of the driver 12 that executes the processing.

  Next, a decomposition process for each dot is performed on the corrected data (step S5). This process is performed by the dot separation unit 124 using the dot generation amount table 129 as described above. Specifically, according to the information indicating the printing conditions, a dot generation amount table 129 corresponding to the printing conditions is selected, and (C ′, M ′, Y ′, K) is selected for each pixel with reference to the selected table. The density gradation value of ') is converted into the generated amount data (S, M, L) for each dot.

  Thereafter, the converted data is transferred to the halftone processing unit 125, where halftone processing is executed (step S6). The image data is converted into data representing the presence / absence of small, medium and large dots.

  The halftone processed data is converted into print data for the printer 2 by the print data conversion unit 126 (step S7) and transmitted to the printer 2 (step S8). Thereafter, the transmitted print data is received by the controller 13 and a printing process according to the print data is executed. That is, ink is ejected from each nozzle according to print data, and small, medium, and large dots are formed on the print medium.

  In the image processing apparatus according to the present embodiment, in the color conversion process, the density gradation value is associated with a value of 0-242 (0-95%). Therefore, the printer 2 as a whole discharges from the nozzles. In order to correct the disadvantage caused by this, the density gradation value is set to a value of 0-255 (0-100%) by color conversion processing for the same density data in the printer 2 in order to correct the disadvantage. You may make it set so that the amount of inks may increase rather than the case where it matches. For example, the voltage applied to the piezo element can be increased.

  In the case of image processing that uses a method of adjusting the total ink amount of each color in the color conversion table 127, depending on the color conversion table 127, the maximum density gradation value of CMYK is smaller than the design maximum value ( For example, it is 70%), and since it is not converted to the value of the area that cannot be sufficiently corrected as described above, such a table can be used as it is. The table to be converted to the value of the area that cannot be sufficiently corrected is recreated so that the maximum value becomes a smaller value. For example, when the maximum value is 97% of the design maximum value, it is set to 95%.

  As described above, in the driver 12 according to the present embodiment, the image data is processed so that the maximum density gradation value has a margin at the time of the color conversion process. Can be corrected, and a problem that dark portions cannot be darkened can be suppressed. Therefore, an appropriate correction process is performed for the high density region, density unevenness caused by the nozzle characteristics can be eliminated, and the print quality can be improved.

  Further, as described above, by taking measures to increase the amount of ink ejected with respect to data of the same density on the printer side, it is possible to eliminate the disadvantage that the whole becomes thin.

  In the present embodiment, the image processing apparatus is a line head printer, but the apparatus of the present invention can be applied to other types of printers as long as it is an inkjet printer.

  Further, the processing performed by the driver 12 in this embodiment can be executed by using the CPU or the memory of the controller 13 on the printer 2 side, or can be executed by being divided into the host computer 1 and the printer 2. It may be.

  The protection scope of the present invention is not limited to the above-described embodiment, but covers the invention described in the claims and equivalents thereof.

  DESCRIPTION OF SYMBOLS 1 Host computer, 2 Printer, 11 Application, 12 Driver, 13 Controller, 14 Print execution part, 121 Rasterization part, 122 Color conversion part, 123 Nozzle characteristic correction part, 124 Dot separation part, 125 Halftone processing part, 126 Print data Conversion unit, 127 color conversion table, 128 correction table, 129 dot generation amount table

Claims (4)

It is connectable to an image recording device, and is an image processing device for printing image data,
A color conversion unit that converts image data expressed in a first color space into image data expressed in a second color space of a color material used in the image recording apparatus;
A nozzle characteristic correction unit that corrects the image data converted by the color conversion unit based on the characteristics of each nozzle of the image recording apparatus that discharges the color material;
A table in which the density gradation value of each color in the first color space is associated with the density gradation value of each color in the second color space, and the maximum value that the density gradation value of the second color space can take The color conversion unit performs the conversion process according to the color conversion table that is associated with each other so that the smallest value is the maximum density gradation value of the second color space. Processing equipment. In claim 1,
When the image recording apparatus is instructed to print based on the image data corrected by the nozzle characteristic correction unit, the amount of the color material ejected from the nozzle with respect to the same data value is the second color space. The maximum value that can be taken by the density gradation value of the second color space is increased as compared with the case where processing is performed in accordance with the color conversion table that is associated with the second color space. A featured image processing apparatus. An image processing method for image data for printing,
A color conversion step of converting the image data expressed in the first color space into image data expressed in the second color space of the color material used at the time of printing;
A nozzle characteristic correction step of correcting the image data converted in the color conversion step based on the characteristics of each nozzle that discharges the color material,
A table in which the density gradation value of each color in the first color space is associated with the density gradation value of each color in the second color space, and the maximum value that the density gradation value of the second color space can take The conversion process in the color conversion step is performed in accordance with the color conversion table that is associated with each other so that the smaller value is the maximum density gradation value in the second color space. Image processing method. An image processing program for causing a computer to execute image processing of image data for printing,
A color conversion step of converting the image data expressed in the first color space into image data expressed in the second color space of the color material used at the time of printing;
Causing the computer to execute a nozzle characteristic correction step of correcting the image data converted in the color conversion step based on the characteristics of each nozzle that discharges the color material,
A table in which the density gradation value of each color in the first color space is associated with the density gradation value of each color in the second color space, and the maximum value that the density gradation value of the second color space can take The conversion process in the color conversion step is performed in accordance with the color conversion table that is associated with each other so that the smaller value is the maximum density gradation value in the second color space. Image processing program.

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