JP2007174379A - Image processor, and its control method and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image processor capable of decreasing a frequency of calibration data generation without impairing precision of gray scale correction processing. <P>SOLUTION: The image processor which adjusts the formation density of an image forming apparatus forming an image by performing gray scale correction processing based upon calibration data acquires the formation density that the image forming apparatus has for a predetermined input value in timing to the past generation of calibration data, holds the formation density as reference density, makes the image forming apparatus to form a pattern image including a patch image of the density corresponding to the predetermined input value, acquires the formation density of the formed patch image as comparison density, and determines the timing where the calibration data should be generated again based upon the density difference between the comparison density and reference density. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image processing apparatus that adjusts the formation density of an image forming apparatus that forms an image by performing gradation correction processing based on calibration data, a control method thereof, and a program.

  When an image forming apparatus (such as a copier or a printer) forms an image on a medium such as paper based on image data, the image forming apparatus forms an image on the medium according to a pixel value or the like of the image data. The density of each color such as the toner amount of each color is controlled, and an image of a color corresponding to the image data is formed on the medium. In order to realize such control, for example, the image processing apparatus connected to the image forming apparatus sets the pixel value (input value) of the image data on the medium in the standard state of the image forming apparatus based on a conversion table held in advance. Is converted into a density value (output instruction value) that can realize the target value (standard density value) of the density formed in the above. The output instruction value obtained by the conversion is output to the image forming apparatus, thereby instructing the density of the image to be formed. Thus, the image forming apparatus can adjust the toner amount and the like based on the output instruction value, and can form an image having a standard density according to the input value of the image data.

  However, since the state of the image forming apparatus generally fluctuates depending on the use environment, changes with time, etc., the formation density actually formed on the medium may deviate from the standard density value even using the conversion table. Therefore, there is a technique for executing a gradation correction process for adjusting a density value using calibration data in an image processing apparatus. According to this technique, the image processing apparatus generates calibration data reflecting the engine characteristics and the like of the image forming apparatus in advance. Then, a gradation correction process is performed to correct the output instruction value obtained by converting the input value of the image data using the conversion table described above based on the calibration data, and the value obtained by the correction is corrected. By outputting the post-instruction value, control is performed to adjust the toner amount of the image forming apparatus. Thus, the image processing apparatus can cause the image forming apparatus to form an image in accordance with the engine characteristics of the image forming apparatus at the time of calibration data generation.

  The image processing apparatus performs calibration data generation processing for generating calibration data by the following method, for example. That is, a calibration image including a predetermined output instruction value is formed on the image forming apparatus, and the formation density of the formed calibration image is acquired. Calibration data can be generated based on the correspondence between the output instruction value obtained in this way and the actual formation density. As a method of acquiring the formation density of the calibration image formed on the medium, for example, there is a method of causing the scanner image to read the calibration image and acquiring the read density as the formation density (see, for example, Patent Document 1). ). However, according to this method, since the obtained formation density is affected by the reading characteristics of a scanner or the like, the formation density by the image forming apparatus may not be obtained with high accuracy.

Therefore, when it is desired to generate calibration data with higher accuracy, the following method may be used. In other words, by measuring the formation density of the image formed according to the maximum value of the output instruction value with a measuring instrument such as a colorimeter or spectrophotometer, first the output instruction that realizes the maximum formation density value in the standard state Perform correction to determine the value. Thereafter, correction is performed to determine an output instruction value that realizes a formation density value less than the maximum formation density value by a scanner or the like.
Japanese Patent Application Laid-Open No. 07-222013

  However, the method of the above conventional example takes time and effort for the user as compared with the case where the calibration image generation process is performed by simply reading the calibration image by a scanner or the like. Also, since the calibration data generation process takes time, the image forming apparatus cannot be used during that time, which is inconvenient. Therefore, there is a demand for reducing the frequency of performing such calibration data generation processing. Nonetheless, if you continue to use calibration data generated in the past without performing calibration data generation processing for a long time, the engine characteristics of the image forming apparatus change over time, so the desired gradation The correction process cannot be performed.

  The present invention has been made in view of the above circumstances, and one of its purposes is an image processing apparatus capable of reducing the frequency of calibration data generation processing without impairing accuracy of gradation correction processing, a control method thereof, and To provide a program.

  An image processing apparatus according to the present invention for solving the above-described problems is an image processing apparatus that adjusts the formation density of an image forming apparatus that forms an image by performing gradation correction processing based on calibration data. A reference density holding unit that acquires a formation density formed by the image forming apparatus with respect to a predetermined input value at a timing when the calibration data is generated in the past, and holds the density as a reference density; Comparison density acquisition means for forming a pattern image including a patch image having a density corresponding to a predetermined input value and acquiring the formation density of the formed patch image as a comparison density; and the density of the comparison density and the reference density Timing determining means for determining a timing at which the calibration data should be regenerated based on the difference. To.

  Thus, by determining the timing for regenerating calibration data based on the density difference between the comparative density and the reference density, it is possible to determine the desired timing for regenerating calibration data, and the accuracy of gradation correction processing is not impaired. The frequency of calibration data regeneration can be reduced within the range.

  Further, in the image processing apparatus, the comparison density acquisition unit forms the pattern image including a plurality of patch images having a density corresponding to the same input value, and sets a comparison density corresponding to each of the plurality of patch images. The timing determination unit may acquire the timing at which the calibration data should be reproduced based on the density difference between the comparative densities acquired in association with each of the plurality of patch images.

  According to another aspect of the present invention, there is provided a control method for an image processing apparatus for adjusting a forming density of an image forming apparatus that forms an image by performing gradation correction processing based on calibration data using a computer. A method of obtaining a formation density formed by the image forming apparatus with respect to a predetermined input value at a timing when the calibration data is generated in the past, and holding the obtained density as a reference density; and the image formation Causing the apparatus to form a pattern image including a patch image having a density corresponding to the predetermined input value, obtaining the formation density of the formed patch image as a comparison density, and the density of the comparison density and the reference density Determining when to regenerate the calibration data based on the difference, and That.

  The program according to the present invention is a program for controlling an image processing apparatus that adjusts the formation density of an image forming apparatus that forms an image by performing gradation correction processing based on calibration data. At a timing when the calibration data is generated, a reference density holding unit that acquires a formation density formed by the image forming apparatus with respect to a predetermined input value and holds it as a reference density, and the predetermined input value to the image forming apparatus Based on the density difference between the comparison density and the reference density, and a comparison density acquisition unit that forms a pattern image including a patch image having a density corresponding to the density and acquires the formation density of the formed patch image as a comparison density , A timing determination means for determining a timing at which the calibration data should be regenerated, and a computer Characterized in that to function.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. An image processing apparatus 10 according to an embodiment of the present invention is a print server or the like, for example, and includes a control unit 11, a storage unit 12, and an interface unit 13 as shown in FIG. The image processing apparatus 10 is connected to the image forming apparatus 20 and the image reading apparatus 30.

  Here, the control unit 11 is a CPU or the like, and operates according to a program stored in the storage unit 12. The contents of the processing executed by the control unit 11 in the present embodiment will be described in detail later.

  The storage unit 12 is a computer-readable storage medium that holds a program executed by the control unit 11, and includes at least one of a memory element such as a RAM or a ROM, a disk device, or the like. The storage unit 12 also operates as a work memory for the control unit 11.

  The interface unit 13 transmits and receives data between the image forming apparatus 20 and the image reading apparatus 30. In particular, by outputting image data of a predetermined pattern image to the image forming apparatus 20, the image forming apparatus 20 is caused to form a pattern image. The image data of the pattern image read by the image reading device 30 is received and output to the control unit 11.

  The image forming apparatus 20 is a printer or a copier, for example, and forms an image on a medium based on the control of the image processing apparatus 10. Here, as an example, the image forming apparatus 20 is an apparatus that forms an image using toners of four colors of cyan (C), magenta (M), yellow (Y), and black (K).

  The image reading device 30 is a scanner, for example, and reads an image formed on a medium based on the control of the image processing device 10.

  Note that the image processing apparatus 10 may be configured integrally with at least one of the image forming apparatus 20 and the image reading apparatus 30. In this case, all or a part of each part constituting the image processing apparatus 10 described above may be shared with the image forming apparatus 20 or the image reading apparatus 30, and the interface part 13 may not be provided.

  The image processing apparatus 10 controls the image forming apparatus 20 to form an image on a medium based on a user instruction or the like. As a specific example, the control unit 11 of the image processing apparatus 10 acquires image data that is an object of image formation, and stores pixel values (for example, luminance values of RGB) of each pixel included in the image data. 12 is converted into respective density values (output instruction values) of CMYK based on a predetermined conversion table (color conversion profile) stored in FIG. Here, the output instruction value is a value for instructing the density of an image to be formed to the image forming apparatus 20. Further, the output instruction value obtained by the conversion based on the color conversion profile is a value corresponding to the formation density of an image formed by the image forming apparatus 20 in a predetermined standard state.

  Further, the control unit 11 performs gradation correction processing based on calibration data generated by processing to be described later. Specifically, the control unit 11 further converts the output instruction value described above based on the calibration data stored in the storage unit 12 to obtain a corrected output instruction value (post-correction instruction value). Then, by outputting the corrected instruction value to the image forming apparatus 20 via the interface unit 13, it is possible to cause the image forming apparatus 20 to form an image having a gradation corresponding to the image data.

  Next, reference density acquisition processing executed by the control unit 11 when generating the calibration data described above will be described with reference to the flowchart of FIG.

  First, the control unit 11 performs calibration data generation processing by a predetermined method (S1). As an example, the control unit 11 performs calibration data generation processing by the following method. That is, the image forming apparatus 20 is caused to form a calibration image on a medium using calibration image data including a predetermined input value. Then, for example, when the measuring instrument connected to the image processing apparatus 10 via the interface unit 13 reads the density of the formed calibration image, the control unit 11 acquires the read formation density value. Accordingly, the control unit 11 can generate calibration data based on the correspondence relationship between the output instruction value for the image forming apparatus 20 corresponding to the input value and the actually formed density value. Further, if necessary, the calibration data may be generated using the formation density value obtained by the image reading device 30 reading the calibration image, in addition to the formation density value obtained by the measuring instrument.

  Next, the control unit 11 causes the image forming apparatus 20 to form a predetermined pattern image (S2). As a specific example, the control unit 11 uses, for example, pattern image data including a plurality of rectangular regions (patch images) having a density (color component value) corresponding to a predetermined input value as illustrated in FIG. A pattern image is formed on 20. Here, the difference in the pattern of the rectangular area in the figure represents the difference in the color component value for each patch image. The pattern image data may be the same as or different from the calibration image data used in the process of S1.

  Further, the pattern image may be an image including all patch images having input values corresponding to the CMYK component colors used by the image forming apparatus 20, or one of the plurality of component colors specified by the user. The image may include only a patch image corresponding to the component color of the part. By forming a pattern image including only part of the component color patch images in this way, it is detected by simple processing that a difference in density of the formation density has occurred with respect to the component color emphasized by the user, as will be described later. be able to. This makes it possible to determine the timing for regenerating calibration data so that high-accuracy gradation correction processing can be performed for the component colors emphasized by the user.

  Furthermore, the pattern image may include a plurality of patch images having input values corresponding to a certain color component value. In this way, a plurality of patch images (same color patch images) having a density corresponding to the same input value are formed and included in one pattern image, and the formation densities of the plurality of same color patch images are acquired by processing to be described later. Thus, the occurrence of density unevenness in one image can be detected later.

  Subsequently, the control unit 11 acquires the pattern image formed by the process of S2 by causing the image reading device 30 to read the pattern image (S3).

  Further, the control unit 11 performs a color conversion process for converting the pixel value of the image data representing the density of each patch image included in the pattern image read in the process of S3 into a color component value in a predetermined color space. Then, the density (reference density) of each reference patch image is acquired (S4). As the predetermined color space, for example, a CIE Lab color space can be used. At this time, the color conversion process may be performed after correcting the pixel value of the image data read using the calibration data generated for the scanner. The control unit 11 averages the color component values in a predetermined color space obtained by color conversion of pixels included in each patch image, for example, so that the color component values (in the predetermined color space ( For example, reference density data represented by L *, a *, b *) can be obtained.

  Next, the control unit 11 associates the information specifying each patch image included in the pattern image acquired in the process of S3 with the reference density calculated in the process of S4 for each patch image, and stores the storage unit 12 is held by being stored (S5). As information for specifying each patch image, for example, a patch image identifier, coordinate information indicating a position in image data, or the like can be used. Thereby, the memory | storage part 12 memorize | stores the data of a reference | standard density as represented by FIG. 4 as an example.

  Next, a timing determination process for determining the timing for performing the calibration data generation process using the reference density data held by the above-described reference density acquisition process according to a user instruction or the like is based on the flowchart of FIG. I will explain. The user may execute this timing determination process at a regular timing such as daily or weekly, or before performing image formation that requires reproduction of image data color with high accuracy. It may be executed.

  First, the control unit 11 causes the image forming apparatus 20 to form a predetermined pattern image (S11). As the predetermined pattern image, the same pattern image used in the reference density acquisition process is usually used. Note that the pattern image does not necessarily have to be the same as the pattern image used in the reference density acquisition process, but at least a patch image having a density corresponding to an input value that is the same as the predetermined input value that is the target of the reference density acquisition The image data must be included.

  Subsequently, the control unit 11 acquires the pattern image formed by the process of S11 by causing the image reading device 30 to read the pattern image (S12).

  Further, the control unit 11 sets the pixel value of the image data representing the density of each patch image included in the pattern image read in the process of S12 in a predetermined color space in the same procedure as the process of S4 in the reference density acquisition process. By performing a color conversion process for converting into color component values in, the density (comparative density) of each patch image to be compared with the reference density is acquired (S13). For example, when the CIE Lab color space is used as the predetermined color space, data of comparative densities represented by three color component values of L *, a *, and b * is obtained for each patch image as in the case of the reference density. be able to.

ここで、ΔＥが濃度差であり、Ｌ０、ａ０、ｂ０は基準濃度のＣＩＥ Ｌａｂ色空間におけるそれぞれの色成分値、またＬ１、ａ１、ｂ１は比較濃度のＣＩＥ Ｌａｂ色空間におけるそれぞれの色成分値を表している。 Next, the control unit 11 calculates, for each patch image, a density difference between the comparison density acquired in the process of S13 and the reference density stored in the storage unit 12 by the reference density acquisition process (S14). For example, when the reference density and the comparative density value are calculated using the CIE Lab color space as the predetermined color space, the control unit 11 can calculate the density difference by the following formula.

Here, ΔE is the density difference, L0, a0, b0 are the respective color component values in the reference density CIE Lab color space, and L1, a1, b1 are the respective color component values in the CIE Lab color space of the comparative density. Represents.

  Further, the control unit 11 calculates the density difference between the comparison densities acquired in the process of S13 for each of the plurality of patch images having the density corresponding to the same input value included in the pattern image (S15). Note that the density difference between the comparative densities can also be calculated by the same procedure as that for calculating the density difference between the reference density and the comparative density in the process of S14. The density difference calculated in the process of S15 represents the difference in formation density that occurs within the range of one formed image with respect to the input value of the same image data. When the density difference has a large value, the image forming apparatus This means that density unevenness is generated in the formed image by 20. For example, in the case where the pattern image as in the example of FIG. 3 is used, it is assumed that both the patch image P1 and the patch image P2 are regions composed of pixels having an input value corresponding to a color component value of 100% cyan. In this case, the density difference is calculated using the color component values Lc1, ac1, bc1 representing the comparative density of the patch image P1 and the color component values Lc2, ac2, bc2 representing the comparative density of the patch image P2.

  Subsequently, based on the density difference calculated in S14 and S15, the control unit 11 next executes calibration data generation processing to determine the timing for regenerating calibration data (S16). For example, if one of the density differences calculated in S14 and S15 exceeds a predetermined reference value T1, it is determined that the calibration data should be regenerated immediately. In addition, when all the density differences are equal to or less than the predetermined reference value T1, and there is a density difference exceeding the second predetermined reference value T2 smaller than T1, within a predetermined period (for example, within one week). It is determined that the calibration data should be regenerated. Further, when all the density differences are equal to or smaller than the reference value T2, it is determined that the gradation correction process using the calibration data is performed with a desired accuracy, and the process is terminated.

  As the predetermined reference value, a common value may be used for all patch images or a set of patch images of the same color, or a different value preset for each patch image may be used. These predetermined reference values may be individually designated by the user. Further, when the number of patch images exceeding the reference value exceeds a predetermined number, it is determined that the calibration data should be regenerated, for example, the number of patch images or sets of patch images satisfying a predetermined condition. Based on this, it may be determined that the calibration data should be regenerated.

  When it is determined that the calibration data should be regenerated immediately or within a predetermined period as a result of the process of S16, the control unit 11 displays the fact on a display unit (not shown), for example. Notify

  In the above description, the density difference between the reference density of each patch image and the comparison density, and the density difference between the comparison densities for the set of patch images of the same color are used independently of each other. Although it is determined that the timing at which regeneration should be performed, the control unit 11 may determine the timing at which calibration data should be regenerated by using both in combination. For example, instead of the determination using a predetermined reference value, the next calibration is performed based on an average value Tm obtained by averaging T values obtained by a predetermined function T = f (ΔE) using each density difference ΔE as a variable. The timing at which the operation data should be regenerated may be determined within Tm days or the like.

  In the above description, the reference density is held in the storage unit 12 of the image processing apparatus 10, but the embodiment of the present invention is not limited to this. For example, the image processing apparatus 10 may transmit a reference density and a comparative density acquired via a communication network to a server machine of a service provider that performs a calibration service. In this case, the server machine determines and outputs the timing at which the calibration data should be regenerated using the transmitted reference density and comparison density. The service provider can provide a service for regenerating calibration data to the user of the image forming apparatus 20 at a desired timing for the user based on the output result.

  According to the present embodiment described above, by determining the timing at which calibration data should be regenerated based on the density difference between the comparison density and the reference density, it is possible to determine the desired calibration data regeneration timing, The frequency of regenerating calibration data can be reduced within a range that does not impair the accuracy of the tone correction process. Further, by determining the calibration data regeneration timing using the density difference between the comparative densities for the same color patch image, the calibration data is taken into consideration in consideration of density unevenness occurring in the formed image of the image forming apparatus 20. The timing of the regeneration process can be determined.

1 is a block diagram illustrating a schematic configuration of an image processing apparatus according to an embodiment of the present invention. It is a flowchart showing an example of the reference | standard density | concentration acquisition process performed by the image processing apparatus which concerns on embodiment of this invention. It is a figure showing an example of the pattern image which the image processing apparatus which concerns on embodiment of this invention forms. It is a figure showing an example of the data of the reference density held by the image processing apparatus according to the embodiment of the present invention. It is a flowchart showing an example of the timing determination process performed by the image processing apparatus which concerns on embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Image processing apparatus, 11 Control part, 12 Storage part, 13 Interface part, 20 Image forming apparatus, 30 Image reading apparatus.

Claims (4)

An image processing apparatus that adjusts the formation density of an image forming apparatus that forms an image by performing gradation correction processing based on calibration data,
A reference density holding unit that acquires a formation density formed by the image forming apparatus with respect to a predetermined input value at a timing when the calibration data is generated in the past, and holds the density as a reference density;
Comparison density acquisition means for causing the image forming apparatus to form a pattern image including a patch image having a density corresponding to the predetermined input value, and acquiring the formation density of the formed patch image as a comparison density;
Timing determining means for determining a timing at which the calibration data should be regenerated based on a density difference between the comparison density and the reference density;
An image processing apparatus comprising: The image processing apparatus according to claim 1.
The comparison density acquisition unit forms the pattern image including a plurality of patch images having a density corresponding to the same input value, acquires a comparison density in association with each of the plurality of patch images,
The image processing apparatus according to claim 1, wherein the timing determination unit determines a timing at which the calibration data is to be reproduced based on a density difference between the comparative densities acquired in association with each of the plurality of patch images. An image processing apparatus control method for adjusting a formation density of an image forming apparatus that forms an image by performing gradation correction processing based on calibration data using a computer,
Obtaining a formation density formed by the image forming apparatus with respect to a predetermined input value at a timing when the calibration data is generated in the past, and holding the obtained density as a reference density;
Causing the image forming apparatus to form a pattern image including a patch image having a density corresponding to the predetermined input value, and obtaining a formation density of the formed patch image as a comparison density;
Determining a timing at which the calibration data should be regenerated based on a density difference between the comparison density and the reference density;
An image processing method comprising: A program for controlling an image processing apparatus that adjusts the formation density of an image forming apparatus that forms an image by performing gradation correction processing based on calibration data,
A reference density holding unit that acquires a formation density formed by the image forming apparatus with respect to a predetermined input value at a timing when the calibration data is generated in the past, and holds the density as a reference density;
A comparison density acquisition unit that causes the image forming apparatus to form a pattern image including a patch image having a density corresponding to the predetermined input value, and acquires a formation density of the formed patch image as a comparison density; and Timing determining means for determining a timing at which the calibration data should be regenerated based on a density difference from the reference density;
A program characterized by causing a computer to function.

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