JP2004112343A - Image processing apparatus and method, and image processing system - Google Patents

Abstract

In a conventional calibration, a reading range is set without considering an edge effect of a patch. Therefore, a patch density is obtained including a high density portion due to an edge effect, and an optimum calibration result is not always obtained. I couldn't get it.
A calibration target printer selected by a server outputs a chart image composed of a plurality of single tone patches on a recording medium (S41). After setting a certain area as the read size, the chart image is read at the read size by the scanner (S44), and the server creates a calibration table based on the obtained patch data of a plurality of gradations (S47). Then, the calibration table is downloaded to the target printer (S48).
[Selection] Figure 2

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image processing apparatus and method, and an image processing system, and more particularly, to an image processing apparatus and method capable of performing stable color reproduction, and an image processing system.
[0002]
[Prior art]
In general, it is known that printing characteristics of a printer may change depending on environmental conditions such as temperature and humidity of an environment in which the printer is used. In addition to such environmental conditions, printing characteristics may change after a certain period of use.
[0003]
For example, in the case of an electrophotographic printer, the photosensitive characteristics of the photosensitive drum change due to aging due to the above environmental conditions and use, and as a result, printing characteristics such as gradation characteristics observed in a printed image or the like are reduced. It changes from what you want. In an ink jet printer, for example, a change in the print characteristics described above occurs due to a change in the discharge characteristics of the print head.
[0004]
As a method for coping with such a change in print characteristics, a calibration method is known. This calibration is performed not only for the change in the printing characteristics of the individual printers as described above, but also for the printing between the printers in an information processing system in which a plurality of printers are connected via a network. Even when the difference (variation) in the characteristics becomes a problem, the process is executed to reduce the variation.
[0005]
Generally, in calibration, first, in order to obtain printing characteristics of a printer, a calibration chart including a plurality of patch units is output, and the calibration chart is read by a scanner. Thereafter, for each patch unit in the read calibration chart, average luminance data within a predetermined reading range is obtained. Thereafter, the read luminance data is converted into density data, a desired calibration table is created from the density data, and the calibration table is applied to a printer to obtain a calibrated print result. it can.
[0006]
[Problems to be solved by the invention]
In the calibration shown in the above conventional example, it is assumed that the density in each patch unit constituting the calibration chart is uniform. However, in a general printer, it is known that the density at the peripheral portion of the patch may be higher than the density at the central portion due to a phenomenon called “edge effect”.
[0007]
In the above-mentioned conventional calibration, since the reading range is set without considering such an edge effect, a patch density is obtained including a high density portion due to the edge effect, and an optimum calibration result is not always obtained. I couldn't do that.
[0008]
SUMMARY An advantage of some aspects of the invention is to provide an image processing apparatus, an image processing method, and an image processing system capable of performing optimal calibration in consideration of an edge effect in a calibration chart. The purpose is to:
[0009]
[Means for Solving the Problems]
As one means for achieving the above object, the image processing system of the present invention has the following configuration.
[0010]
That is, an image processing system in which a server device, a scanner, and an image forming device are connected via a network, wherein the server device includes a plurality of single tone patches output from the image forming device onto a recording medium. Reading size setting means for setting a region where the density is substantially uniform in the patch as a reading size, and instructing the scanner of the reading size information with respect to the chart image comprising: Patch data acquisition means for acquiring patch data of a plurality of gradations obtained by reading based on information, and correction data creation means for creating color correction data for the image forming apparatus based on the patch data, Correction data transfer means for transferring the color correction data to the image forming apparatus. Characterized in that it.
[0011]
More specifically, the reading size setting means sets, as a reading size, an area excluding a high density portion caused by an edge effect of the image forming apparatus from an outer peripheral portion of the patch.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.
[0013]
<First embodiment>
[System Configuration] FIG. 1 is a diagram showing a configuration of an image processing system according to the present embodiment. In FIG. 1, reference numeral 1 denotes a server PC connected to a network 5, on which software for realizing the present system is installed.
[0014]
Reference numeral 2 denotes a printer connected to the network 5, which is a target of correction (calibration) in the present system. The printer 2 is configured to perform printing according to instructions from a plurality of PCs connected to the network 5. The printer 2 further includes a calibration data storage unit 21 therein, and downloads and stores calibration data, which will be described later, from the PC 1.
[0015]
Here, a scanner 3 for measuring the calibration chart output from the printer 2 is connected to the server PC 1, but it is of course possible to use the scanner 3 for other purposes such as document input.
[0016]
Reference numeral 4 denotes a client PC connected to the network 5, which performs creation, editing, and printing instructions of desired print data. In general, calibration for the printer 2 is performed by the server PC 1 by the system administrator, and normal printing of print data is performed by the client PC 4.
[0017]
In the printer 2 of the present embodiment, stable color reproduction is always possible by performing calibration based on calibration data created as described later. Hereinafter, a method of creating calibration data according to the present embodiment will be described with reference to the flowchart of FIG.
[0018]
Output of Printer Chart First, in step S41, the server PC 1 instructs the printer 2 to output a calibration chart, that is, printer chart data via the network 5, and the printer 2 outputs the printer chart. Here, it is assumed that a plurality of printers are connected to the network 5. In this case, it is necessary to specify a printer to be calibrated in advance in accordance with network management rules. A detailed description of the identification method is omitted.
[0019]
FIG. 3 is a diagram showing an example of the printer chart output in step S41. As shown in the figure, the printer chart of this embodiment has a data section 62 for detecting the density characteristic of the printer within one page 61 of A4 size. A total of 1024 patch units that are divided are prepared. In the horizontal direction of the data section 62, patch units are arranged for cyan (C), magenta (M), yellow (Y), and black (K), which are the basic colors of the printing toner. The numerical value described in each patch unit indicates a subscript of the array, and the relationship between the subscript of the array and the actual data value is configured as shown in the table of FIG. That is, the patch unit in the present embodiment is composed of single-color, single-tone data. For example, the actual output data value with respect to the array 0 in FIG. , 255 for array 63. In this embodiment, it is assumed that the system is an 8-bit system for each color of CMYK. Therefore, an example in which a numerical value of 0 to 255 is used as the output data value is shown. The output data value in the correspondence table shown in FIG.
[0020]
In the printer chart shown in FIG. 3, four patch units each corresponding to 32 gradations of arrays 0 to 31 belonging to the highlight side are arranged, and the arrays 33, 35, 37,. . , 61, and 63 are arranged in eight patch units each for 16 gradations. In the present embodiment, the difference in the number of gradations between the highlight side and the shadow side is that more detailed gradation information is required on the highlight side of the present system than on the shadow side. That's why. The reason why the number of patch units arranged on the shadow side is larger than that on the highlight side is that there is a tendency that the input values in the scanner vary more on the shadow side than on the highlight side.
[0021]
Reference numeral 63 shown in FIG. 3 is mounting direction discrimination information for notifying the user of the direction in which the chart 61 is mounted on a document table of a scanner described later by the arrow shape. Note that identification information (in this example, “B”) indicating that the chart 61 is for correcting the printer 2 is written in the mounting direction determination information 63. Reference numerals 64, 65, and 66 are registration marks for detecting whether the chart 61 is normally placed on the document table of the scanner. Details of the processing for detecting the registration marks 64, 65, 66 will be described later.
[0022]
Here, the density unevenness in each patch unit in the printer chart will be described with reference to FIG. In the figure, reference numeral 20 denotes a certain patch unit. The output within the patch unit 20 should ideally be output with a uniform density. However, in a printer such as an electrophotographic system, a density increase called an edge effect occurs in the periphery of the patch. Many of the edge effects are due to the development process, but will not be described in detail here.
[0023]
The upper part of FIG. 5 is a graph showing the change in density in the horizontal direction at the center of the patch unit 20, with the ordinate indicating the density and the abscissa indicating the coordinates in the patch width direction. According to the graph, it is understood that the edge effects 21 and 22 occur in the peripheral portion of the patch 20.
[0024]
The printer chart 61 shown in FIG. 3 is output from the printer 2 according to the instruction from the PC 1 as described above. The chart may be generated based on the information according to an instruction from the PC 1, or the chart may be generated by transmitting the chart configuration information from the PC 1 to the printer 2. The chart configuration information depends on the command system of the printer 2, but is not particularly limited here.
[0025]
When the output of the printer chart from the scan printer 2 is completed, it is determined in step S42 in FIG. 2 whether or not the scanner 3 constituting the present system has already been corrected. For example, the scanner is corrected in step S43. Here, the details of the scanner correction will not be particularly described.
[0026]
In step S44 after the scanner 3 is corrected, the above-described printer chart is measured using the scanner 3. Scanning by the scanner 3 is usually performed via a scanner driver configured on the server PC1, and for example, setting of a scan resolution, designation of an input area, and the like are performed.
[0027]
In the present embodiment, an RGB signal value (luminance value) within a predetermined “reading range” is read in each patch unit of the printer chart, and the value is returned to the PC 1.
[0028]
Hereinafter, the setting process of the reading range in the patch unit according to the present embodiment will be described with reference to the flowchart of FIG.
[0029]
First, in step S31, a total average value of luminance values in the outermost contour of the patch is calculated, and this is set to N (0). Next, in step S32, the initial value 0 is substituted for the variable i. Next, in step S33, it is determined whether or not the variable i has exceeded 1/2 of the patch width. If the variable i has exceeded, the process ends. If not, the process proceeds to step S34.
[0030]
In step S34, the total average value of the luminance values in the rectangle inside the pixel by i pixels from the outermost contour of the patch is calculated, and this is set to N (i). Then, in step S35, N (i) is compared with the total average value N (i-1) of the luminance values of the rectangle which is already calculated and which is one pixel outside the rectangle of N (i).
[0031]
Here, while the reading range includes the edge effect, N (i) and N (i-1) do not match, so the variable i is incremented in step S36, and the process returns to step S33. On the other hand, if N (i) and N (i-1) match in step S35, it is determined that the reading range does not include the edge effect, and the process proceeds to step S37, where the valid "reading range" Is determined to be within a value obtained by subtracting 2 * i from the patch width.
[0032]
In the server PC1, the average luminance value within the "read range" of the patch unit is input from the scanner 3, and based on the arrangement of each patch unit in the printer chart, the average (for 32 gradations) of four places is highlighted on the highlight side. On the shadow side, an RGB signal value of 48 gradations for each color of CMYK is obtained by calculating an average of eight places (for 16 gradations) on the shadow side. Here, by referring to a luminance / density conversion table (not shown) indicating the correspondence between the RGB luminance signal of the scanner 3 and the CMYK density signal of the printer 2 prepared in advance by the scanner correction, the luminance signal of the 48 gradations is obtained. A density characteristic value (CMYK value) of 48 gradations can be obtained.
[0033]
When the scanning of the printer chart shown in step S44 of FIG. 2 is completed, next, in step S45, it is determined whether or not the scanned printer chart is correct. That is, in this case, since the purpose is to correct the printer 2, it is determined whether or not the scanned chart is the chart for the printer 2. This is performed, for example, by detecting the lower left registration mark 65 shown in FIG. 3, and then detecting the upper left registration mark 64. If the registration mark detection fails, an error display is performed in step S46.
[0034]
Next, in step S47, a calibration table is created in the server PC1. Hereinafter, the process of creating the calibration table in the present embodiment will be described with reference to FIG.
[0035]
FIG. 7A is a diagram showing density characteristic values of 48 gradations obtained by the preceding scanning process. FIG. 3 shows an input / output relationship curve, which is obtained by interpolation calculation based on values for 48 gradations. Although only one color is described here, the same process is actually performed for each of CMYK colors.
[0036]
Here, a linear curve as shown in FIG. 7C is defined in advance as an ideal value of the density characteristic. Therefore, in order to bring the current density characteristic shown in FIG. 7A closer to the ideal characteristic shown in FIG. 7C, based on the characteristic shown in FIG. 7B corresponding to the inverse function of FIG. Calculate the calibration table. That is, by performing correction based on the characteristic shown in FIG. 7B with respect to the characteristic shown in FIG. 7A, the ideal characteristic shown in FIG. 7C is obtained as a result.
[0037]
Next, in step S48, the calibration table created by the server PC1 is downloaded to the printer 2 and stored in the calibration data storage unit 21. At this time, as in the case of the chart output described above, the printer to be downloaded is specified on the assumption that a plurality of printers are connected on the network 5. Note that commands related to download depend on the command system of the printer, but detailed description is omitted here.
[0038]
FIG. 8 is a flowchart illustrating a download data receiving process in the printer 2. First, it is determined in step S70 whether data has been received. If it has not been received, step S70 is repeated. If it has been received, the received data is analyzed in step S71. The analysis result is determined in step S72. If the received data is a calibration download command, the flow advances to step S73 to store the calibration data in the calibration data storage unit 21 as described above. On the other hand, if it is determined that the received command is not the calibration download command, a process corresponding to the received data is performed in step S74.
[0039]
Calibration Process The calibration process in the printer 2 will be described below.
[0040]
Normally, print data is sent from the application on the PC 1 to the printer 2 via the printer driver on the PC 1. In the printer 2, the analysis of the print data, the configuration of the page layout, the image processing, the print processing, and the like are performed in the above-described step S74 of FIG.
[0041]
FIG. 9 shows a flowchart of the calibration process in the printer 2. First, in step S110, color fine adjustment processing such as luminance correction and contrast correction is performed on the input signals RGB. Next, in step S111, a color matching process for matching the color of the monitor with the color of the printer print is performed. Next, in step S112, a luminance / density conversion process of converting the luminance RGB as the input signal into the density CMYK as the print signal of the printer is performed. Then, in step S113, a calibration process is performed. That is, the CMYK 8-bit multi-level signal is used as an input / output signal, and the output characteristics are corrected to be linear using the calibration table data stored in the calibration data storage unit 21. Next, in step S114, the CMYK 8-bit signal after the calibration is converted into a signal conforming to the output system, for example, binarized into a CMYK 1-bit signal.
[0042]
Thereby, the gradation characteristic of the output signal of each color in the present embodiment can be made linear.
[0043]
[User Interface] An example of a user interface (UI) related to calibration in the server PC 1 will be described below with reference to FIGS. Note that the calibration data creation system according to the present embodiment is realized as a type of application on the PC 1.
[0044]
FIG. 10 is a diagram illustrating a UI screen transition example according to the present embodiment. When the application is started, first, a main screen is displayed in step S801. FIG. 11 shows an example of the main screen. Basically, the other screens are shifted to other related screens by pressing the “next”, “return”, “cancel”, and “help” buttons as in FIG. In the main screen of FIG. 11, three types of selection menus, "new measurement", "open existing measurement data file", and "delete download data" are prepared.
[0045]
If “new measurement” is selected and “next” is pressed, the process proceeds to step S802. In step S802, the chart is output to the printer 2. Then, in step S805, the scanner 3 is corrected by the server PC 1 as described above, and then a brightness / density conversion table unique to the scanner 3 is created. Then, in step S807, the scanner 3 measures the chart using the luminance-density conversion table. In step S808, calibration is applied, that is, calibration data is created and downloaded to the printer 2 (S47 and S48 in FIG. 2).
[0046]
Note that a button for shifting to step S809 is prepared in the UI of step S808. When the user presses the button and the process advances to step S809, a screen that allows the storage of the measurement data is displayed, and the user can instruct to save the scan data measured in step S807. The scan data storage file can be used in a process using existing measurement data described later. After step S809, the process returns to step S808, and then a process end screen is displayed in step S810. If "end application" is specified on the screen, the process ends. If "return to main screen" is specified, the process returns to step S801.
[0047]
When "Open measurement data" is selected on the main screen of step S801 and "Next" is pressed, a measurement data instruction screen of step S803 is displayed. Here, when the “reference” button is pressed, the screen shifts to the measurement data reading screen in step S806, and a search for detailed measurement data is enabled. The measurement data read here is the data file saved in step S809 described above. Then, in step S808, calibration is applied. Since the subsequent processing is as described above, the description will be omitted.
[0048]
When "delete download data" is selected and "next" is pressed on the main screen in step S801, the calibration data stored in the calibration data storage unit 21 of the printer 2 is deleted in step S804. Note that this deletion processing is performed based on an instruction by a command from the server PC1 to the printer 2, but this command is not particularly mentioned here. Then, the process proceeds to the processing end screen of step S810.
[0049]
As described above, in the present embodiment, it is necessary to specify a target printer on the assumption that a plurality of printers are connected on the network 5, but this is specifically described. Is performed on the UI during the printing process of the printer chart in step S802 in FIG. That is, the application issues a chart output instruction and downloads calibration data to the designated printer.
[0050]
[Summary] As described above, according to the present embodiment, calibration data can be created and downloaded to the printer 2 according to an instruction from the server PC 1. Color printing can be performed.
[0051]
Further, by reading a range without density unevenness due to an edge effect or the like from the calibration chart output by the printer, and creating calibration data based on the read data, the influence of the edge effect is eliminated, and a higher level is achieved. Accuracy calibration data can be created.
[0052]
Therefore, highly accurate calibration can be realized using an existing device without using an expensive densitometer or the like.
[0053]
In the present embodiment, an example is shown in which a color laser beam printer (LBP) is used as a printer device constituting the system. However, the present invention can be similarly applied to a printer device using another printing method such as an ink jet printer. . Further, the connection form and the protocol in the network are not particularly described in detail, but any embodiment can be similarly implemented.
[0054]
[Other embodiments]
The present invention can be applied to a system including a plurality of devices (for example, a host computer, an interface device, a reader, a printer, etc.), but may be a device including one device (for example, a copying machine, a facsimile machine, etc.). May be applied.
[0055]
Further, an object of the present invention is to provide a storage medium storing a program code of software for realizing the functions of the above-described embodiments to a system or an apparatus, and a computer (or CPU or MPU) of the system or apparatus to store the storage medium. Needless to say, this can also be achieved by reading out and executing the program code stored in the.
[0056]
In this case, the program code itself read from the storage medium realizes the function of the above-described embodiment, and the storage medium storing the program code constitutes the present invention.
[0057]
As a storage medium for supplying the program code, for example, a floppy (registered trademark) disk, hard disk, optical disk, magneto-optical disk, CD-ROM, CD-R, magnetic tape, nonvolatile memory card, ROM, or the like is used. I can do it.
[0058]
When the computer executes the readout program code, not only the functions of the above-described embodiments are realized, but also an OS (Operating System) running on the computer based on the instruction of the program code. It goes without saying that a case where a part of the actual processing is performed and the function of the above-described embodiment is realized by the processing is also included.
[0059]
Further, after the program code read from the storage medium is written into a memory provided on a function expansion board inserted into the computer or a function expansion unit connected to the computer, the function expansion is performed based on the instruction of the program code. It goes without saying that a CPU or the like provided in the board or the function expansion unit performs part or all of the actual processing, and the processing realizes the functions of the above-described embodiments.
[0060]
【The invention's effect】
As described above, according to the present invention, optimal calibration can be performed in consideration of an edge effect in a calibration chart.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of an image processing system according to an embodiment of the present invention.
FIG. 2 is a flowchart illustrating calibration data creation processing according to the present embodiment.
FIG. 3 is a diagram illustrating an example of a printer chart according to the embodiment.
FIG. 4 is a diagram showing a relationship between subscripts and actual data values in a patch data array.
FIG. 5 is a diagram for explaining an edge effect in the embodiment.
FIG. 6 is a flowchart illustrating a process of setting an effective reading range within a patch unit according to the embodiment.
FIG. 7 is a diagram illustrating a calibration table according to the embodiment.
FIG. 8 is a flowchart showing a calibration data receiving process in the printer of the embodiment.
FIG. 9 is a flowchart illustrating a calibration process in the printer of the embodiment.
FIG. 10 is a diagram illustrating an example of a UI screen transition according to the embodiment.
FIG. 11 is a diagram illustrating an example of a main screen according to the present embodiment.
[Explanation of symbols]
1 server PC
2 Printer 3 Scanner 4 Client PC
5 Network 21 Calibration data storage

Claims (12)

Chart output means for outputting a chart image composed of a plurality of single tone patches on a recording medium,
Reading size setting means for setting, as the reading size, an area having substantially uniform density in the patch;
A reading unit that obtains patch data of a plurality of gradations by reading the chart image based on the reading size;
Correction data creating means for creating color correction data based on the patch data,
An image processing apparatus comprising: 2. The image processing apparatus according to claim 1, wherein the reading size setting unit sets an area excluding an outer peripheral portion of the patch as a reading size. The image processing apparatus according to claim 2, wherein the reading size setting unit sets an area excluding a high density portion in an outer peripheral portion of the patch as a reading size. 2. The image processing apparatus according to claim 1, further comprising a correction unit configured to perform color correction of the image data using the color correction data. 4. The image processing apparatus according to claim 3, further comprising an image forming unit that forms an image based on the image data after the color correction by the correction unit. An image processing system in which a server device, a scanner, and an image forming device are connected via a network,
The server device,
For a chart image composed of a plurality of single tone patches output on a recording medium from the image forming apparatus, an area where density is substantially uniform in the patch is set as a read size, and the read size information is sent to the scanner. Reading size setting means for instructing;
Patch data obtaining means for obtaining a plurality of gradation patch data obtained by reading the chart image based on the read size information in the scanner,
Correction data creating means for creating color correction data for the image forming apparatus based on the patch data,
Correction data transfer means for transferring the color correction data to the image forming apparatus;
An image processing system comprising: 7. The image processing system according to claim 6, wherein the reading size setting unit sets an area excluding an outer peripheral portion of the patch as a reading size. 8. The image processing apparatus according to claim 7, wherein the reading size setting unit sets, as a reading size, an area excluding a high density portion caused by an edge effect of the image forming apparatus from an outer peripheral portion of the patch. system. The server device further includes:
A selecting unit for selecting an image forming apparatus to be subjected to color correction from the plurality of image forming apparatuses connected to the network,
7. The image processing system according to claim 6, wherein the correction data creation unit creates the color correction data for the image forming apparatus selected by the selection unit. A chart output step of outputting a chart image composed of a plurality of single tone patches on a recording medium,
A reading size setting step of setting, as a reading size, an area having substantially uniform density in the patch;
By reading the chart image based on the read size, a reading step of obtaining patch data of a plurality of gradations,
A correction data creating step of creating color correction data based on the patch data,
An image processing method comprising: 10. A program which, when executed on a computer, causes the computer to operate as a server device in the image processing system according to claim 6. A recording medium on which the program according to claim 11 is recorded.

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