JP2016102836A - Information processor and method for controlling the device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To address the situation in which a wrong estimated density causes wrong calibration if large change of density has occurs by cartridge replacement and the like.SOLUTION: The information processor measures the densities of a first patch and a second patch. The density of the second patch is estimated with the density variation of the first patch, and it is determined whether the difference between the measured density and estimated density of the second patch is in a predetermined range. Calibration with the estimated value is done if the difference is determined to be in the range, and usual calibration is done otherwise.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a density correction technique in an electrophotographic image forming apparatus.

  In the image forming apparatus, gamma correction (density correction) is performed based on a gamma correction table corresponding to gamma characteristics (input / output characteristics) in order to keep the print density constant. Since the gamma characteristic changes due to aging deterioration of the photosensitive drum, transfer belt, etc., parts replacement, temperature fluctuation, and other environmental changes, calibration processing for updating the gamma correction table is performed. In general, the gamma correction table is updated by outputting a plurality of patch images corresponding to a plurality of gradation data values to a transfer belt or the like, detecting the density of the output patch image with a sensor or the like, and according to the detected density value. It is done.

  In Patent Document 1, a plurality of halftone patches are measured by the first gradation expression method to measure the density fluctuation amount. A method of performing calibration with a small number of patches for different gradation expression methods by estimating the patch density of the second gradation expression method using the measured density fluctuation amount is disclosed.

JP 2009-302669 A

  In some cases, such as cartridge replacement or the like, a large density fluctuation may occur. However, in Patent Document 1, when such a large density fluctuation occurs, calibration based on an erroneous estimated density is performed.

  An information processing apparatus according to the present invention is an information processing apparatus that updates information used in gamma correction for correcting image data output from an image forming apparatus, and is based on a specific dot pattern output by the image forming apparatus. The first patch configured, the measuring means for measuring the density of each patch of the second patch configured by a different dot pattern from the first patch, and measured by the measuring means at the time of the previous update A storage unit that stores the density of the first patch, a density variation based on a difference between the density of the first patch measured by the measurement unit and the density of the first patch stored in the storage unit. The estimation means for estimating the density of the second patch, the density of the second patch measured by the measurement means, and the density of the second patch estimated by the estimation means Determining means for determining whether the difference is a value within a predetermined range; and when the determination means determines that the difference is a value within a predetermined range, the determination is based on the density of the first patch. And first update means for updating the information using the estimated value of the second patch.

  As described above, according to the present invention, the accuracy of the gamma correction table can be maintained when performing calibration with a small number of patch outputs.

1 is a block diagram of an image forming apparatus according to Embodiment 1. FIG. It is a figure which shows an example of a dot shape. It is a figure explaining the characteristic model of density fluctuation. 3 is a flowchart showing the operation of the first embodiment. FIG. 6 is a schematic diagram for explaining the operation of the first embodiment. FIG. 10 is a schematic diagram for explaining the operation of the second embodiment. 6 is a flowchart showing the operation of the second embodiment. 10 is a flowchart illustrating the operation of the third embodiment.

  Hereinafter, the present invention will be described in detail based on preferred embodiments with reference to the accompanying drawings. In addition, the structure shown in the following Examples is only an example, and this invention is not limited to the structure shown in figure.

[Example 1]
In an electrophotographic image forming apparatus, it is known that the output density for the same input image changes due to environmental changes and changes with time. In order to correct this, a density correction process is performed. Information (gamma correction table) generally used for executing density correction processing is calculated as follows. That is, by forming a plurality of patches with different gradations from low density to high density on an intermediate transfer belt, etc., measuring the density of each gradation patch with an optical sensor, etc., and obtaining an output density curve for the input image density Calculated. The patches of each gradation are formed on the intermediate transfer belt by outputting halftone image data of different gradations (that is, different dot shapes or different densities) used for printing.

  On the other hand, density fluctuations due to environmental changes and changes with time appear as fluctuations in the area ratio of dots on the recording medium. Therefore, the inventor has proposed a technique that utilizes the correlation between the dot shape and the change in the dot area by utilizing the fact that the variation rate of the dot area depends on the dot shape. According to this method, the density fluctuation rate of an arbitrary dot shape can be obtained from a certain dot shape and density fluctuation rate. That is, the density fluctuation rate of each patch for generating a gamma correction table is estimated from the density fluctuation rate of one halftone patch for density fluctuation measurement. Further, it is possible to estimate the density of each patch from the density variation rate of each patch and regenerate the gamma correction table using the estimated density of each patch. That is, the gamma correction table can be updated by measuring only one patch for density fluctuation measurement with respect to an arbitrary gamma correction table. Details of this processing will be described later.

  In this embodiment, when the density of each patch is estimated from one measurement patch as described above and the process of updating the gamma correction table using the estimated density of each patch is performed, is the estimation correctly performed? An information processing apparatus that determines the above will be described as an example. Specifically, a determination patch is output together with a measurement patch by an electrophotographic image forming process, and an estimated density value estimated based on the measurement patch and a measurement value obtained by measuring the determination patch ( To determine whether the estimation is correctly performed. Depending on the determination result, the gamma correction table is updated using the estimated density described above, or the gamma correction table is updated using a density value measured by outputting a patch of each density. Switches whether to perform processing. As a result, the accuracy of calibration is improved.

  Details of this embodiment will be described with reference to FIG. FIG. 1 is a block diagram illustrating an example of an image forming apparatus according to the present exemplary embodiment. The image forming apparatus includes a gamma correction unit 101, a dot pattern generation unit 102, a halftone processing unit 103, an image formation unit 104, a first storage unit 105, a first gamma correction table update unit 106, and a second gamma correction table. An update unit 107 is included. In addition, it includes a measurement unit 108, a concentration variation detection unit 109, a second storage unit 110, a concentration variation estimation unit 111, a determination unit 112, and a control unit 113. The dot pattern generation unit 102, the first storage unit 105, the first gamma correction table update unit 106, and the second gamma correction table update unit 107 function as an information processing apparatus. In this embodiment, a case where an information processing apparatus is built in the image forming apparatus will be described as an example.

  The gamma correction unit 101 is for correcting the output density of the above-described image forming apparatus. The gamma correction unit 101 refers to a look-up table in which output characteristics with respect to input data become linear as a gamma correction table, and Perform gamma correction. A gamma correction table used by the gamma correction unit 101 is stored in the first storage unit 105. As the first storage unit 105 storing the gamma correction table, for example, a nonvolatile memory is used.

  The dot pattern generation unit 102 generates a dot pattern constituting a patch necessary for creating a lookup table used in the gamma correction processing of the gamma correction unit 101. Then, dot pattern data in which a predetermined dot pattern is arranged in a specific area is output to the image forming apparatus 104.

  The halftone processing unit 103 multivalues (eg, binarizes) input data after gamma correction. The halftone processing unit 103 performs binarization using a technique such as a dither method or an error diffusion method. The image forming unit 104 prints the binarized data by an electrophotographic method. Further, the image forming unit 104 forms the dot pattern generated by the dot pattern generation unit 102 on a transfer belt (not shown). The measurement unit 108 measures the density of the patch on the intermediate transfer belt in the image forming unit 104. As the measurement unit 108, for example, an optical sensor or the like is used. In this embodiment, the measurement unit 108 measures the patch density of two types of patches. One is an estimation patch used for obtaining a patch density estimated value described later. The other is a determination patch for determining whether the estimated patch density value is within the allowable range.

  The density fluctuation detection unit 109 detects a patch density fluctuation between the previous density correction and the current density correction. Specifically, the density variation detection unit 109 stores the patch density of the estimation patch measured by the measurement unit 108 at the previous density correction in the second storage unit 110. Then, the density variation detection unit 109 compares the density difference between the patch density of the estimation patch measured by the measurement unit 108 at the previous density correction and the patch density of the estimation patch measured by the measurement unit 108 at the current density correction. And the concentration fluctuation rate is detected. The second storage unit 110 stores the patch density measured by the measurement unit 108.

  The density fluctuation estimation unit 111 estimates the density fluctuation rate of an arbitrary patch from the density fluctuation rate detected by the density fluctuation detection unit 109, and estimates the patch density estimated value of the arbitrary patch from the estimated density fluctuation rate. The processing of the density fluctuation estimation unit 111 will be described later.

  The first gamma correction table update unit 106 updates the gamma correction table stored in the first storage unit based on the patch density estimation values of the plurality of patches estimated by the density fluctuation estimation unit 111. That is, the first gamma correction table update unit 106 creates a gamma correction table based on the patch density estimated values of a plurality of patches estimated by the density variation estimation unit, and stores the gamma correction table in the first storage unit using the created gamma correction table. Update the stored gamma correction table. Alternatively, the first gamma correction table updating unit 106 may update the gamma correction table by correcting the value of the grid point of the gamma correction table at the previous calibration stored in the first storage unit. Good. Hereinafter, this gamma correction table update processing by the first gamma correction table update unit 106 is referred to as one-patch calibration. That is, one estimation patch is formed, the patch density is measured, the density fluctuation rate is obtained from the measured density of one estimation patch, and the gamma correction table update process using the patch density estimated value of an arbitrary patch is performed. This is called patch calibration.

  The second gamma correction table update unit 107 performs full calibration using the patch density measurement value instead of the patch density estimation value. That is, a plurality of gradation patches which are halftone images from the halftone processing unit 103 are output onto the intermediate transfer belt, and their densities are measured by the measurement unit 108. The second gamma correction table update unit 107 updates the table in the first storage unit 105 using the patch density measurement values of the plurality of gradation patches thus measured.

  The determination unit 112 compares the patch density measurement value of the determination patch measured by the measurement unit and the patch density estimation value estimated by the density variation estimation unit 111 to perform one-patch calibration or perform full calibration. Determine whether to do it. The control unit 113 controls the entire image forming apparatus so as to operate as described above.

Next, processing for obtaining the patch density estimated value in the density fluctuation estimating unit 111 will be described. The density fluctuation estimation unit 111 acquires the density fluctuation rate detected by the density fluctuation detection unit 109. If this density fluctuation rate is V _m , the density measurement value of the estimation patch measured by the measuring unit 108 is D _m , and the reference density value is _Dr , the density fluctuation rate is V _m = (D _m −D _r ) / D derived by _r . For example, the reference density value may be a patch density measurement value measured by the previous measurement unit 108 or may be a preset value.

Further, the density fluctuation estimation unit 111 acquires information indicating the shape of the dot pattern used for the estimation patch from the halftone processing unit 103 and information indicating the shape of the dot pattern of an arbitrary patch to be estimated. Here, information indicating the shape of the dot pattern is referred to as a dot shape parameter. For example, the dot shape parameter is represented by a dot area and a dot circumference in a predetermined unit region. FIG. 2 is a diagram illustrating an example of a dot shape. FIG. 2A and FIG. 2B have different dot shapes. For example, the example of FIG. 2A shows a pattern in which a predetermined unit region is a 4 × 4 pixel, and three pixels in the central portion are turned on to form one dot. In the example of FIG. 2A, the dot area as the dot shape parameter indicates the number of pixels in which dots are turned on in a predetermined unit region, and is 3. Further, the dot circumference is 1 when the length of one side of the pixel is 1, and the circumference of the edge of the entire dot in a predetermined unit region is 8. Further, the example of FIG. 2B shows a pattern in which a 2 × 2 pixel at the center is turned on to form one dot. In the example of FIG. 2B, the dot area as the dot shape parameter is 4, and the dot circumference is 8. Here, assuming that the dot shape parameter is the dot circumference / dot area, the dot shape parameter F _m of the estimation patch as shown in FIG. 2B is 8/4 = 2.

The density fluctuation estimation unit 111 obtains a density fluctuation characteristic model from the dot shape parameter F _m of the estimation patch and the density fluctuation rate V _m . Then, the density model of the arbitrary patch is estimated by applying the characteristic model of the density fluctuation to the shape parameter of the dot of another arbitrary patch.

  It has been found by the inventor's verification that there is a proportional relationship between the dot shape parameter (dot circumference / dot area) and the density fluctuation rate. Therefore, a characteristic model of density fluctuation is constructed using this proportional relationship. The density variation characteristic model is defined as V = G × F where the dot perimeter / area is the shape parameter F, the density variation rate of the image is V, and the density variation gradient is G. Here, the density fluctuation gradient G indicates the slope of a linear function established between the dot shape parameter F and the density fluctuation rate V. The density fluctuation gradient G is a parameter that changes according to the conditions under which the image forming unit 104 outputs an image. In order to construct a characteristic model of density fluctuation when the image forming unit 104 outputs an image under a certain condition, it is necessary to obtain the density fluctuation gradient G.

The calculation of the density variation characteristic model V = G × F will be described. FIG. 3 is a graph for explaining a characteristic model of density variation. In the graph shown in FIG. 3, the image forming unit 104 outputs a patch image composed of the dot pattern represented by the halftone image data shown in FIG. 2B as a measurement patch, and the measurement unit 108 measures the density. This is the result of creating a characteristic model of density fluctuation from the results. With respect to the reference density _{D r} of the patch image, when the result obtained by measurement is the concentration _{D m,} as described above, the concentration change rate _{V m} is defined in _{(D m -D r) / D} r . In the dot pattern shown in FIG. 2B, as described above, the shape parameter F _m is derived as F _m = 2 (= 8/4). From these two values, the position of P _m points associating the dot shape parameters and the concentration of the variation rate is shown as in FIG. The slope of the straight line passing through the origin at this time from the point _{P m} (gradient) is obtained as _{G = (D m -D r)} / 2D r. From the above, the characteristic model of concentration fluctuation in FIG. 3 is defined as V = (D _m −D _r ) / 2D _r × F. When the density variation characteristic model is created, the density variation rate V can be uniquely derived by inputting the dot shape parameter F of an arbitrary patch image. That is, the density variation rate V is obtained for halftone image data (patch image) representing a dot pattern composed of dots having an arbitrary dot shape. Then, by using the obtained density fluctuation rate V, it is possible to estimate the image density when an arbitrary patch image is actually output as a toner image.

  Using the method described above, the density of one estimation patch whose dot shape is known can be measured, and the halftone gamma correction table whose dot shape is known can be updated. However, since it is possible to estimate the density fluctuation from the reference density (for example, the previous measured value), the density value itself may not be estimated correctly if the reference gamma characteristics are different. For example, as described above, the gamma characteristic of the image forming apparatus may change immediately after the printer body is turned on or when the cartridge is replaced. In this case, the density fluctuation at each gradation can be estimated, but the standard density value itself may not match. Therefore, when the power is turned on or when the cartridge is replaced, a patch corresponding to each gradation of the halftone to be printed is generated and measured, and the second gamma correction table update unit must regenerate the gamma correction table. That is, it is necessary to perform full calibration. In full calibration, the gamma correction table can be updated with high accuracy, but time and toner are consumed to generate a plurality of patches, and the above-described advantage of one-patch calibration cannot be utilized.

  Therefore, in this embodiment, a determination unit 112 that determines whether or not the concentration estimation is performed correctly is provided. Hereinafter, the operation of the determination unit 112 will be described. In this embodiment, both the estimation patch and the determination patch using the halftone to be printed are generated on the intermediate belt when the power is turned on or the cartridge is replaced, and the density of these patches is measured by the measurement unit 108. taking measurement. Then, the density variation rate is detected from the current patch density measurement value and the previous patch density measurement value of the estimation patch. Then, using the detected density fluctuation rate, a patch density estimated value of the determination patch is obtained as an arbitrary patch. Then, the estimated patch density value is compared with the measured patch density value of the determination patch measured by the measurement unit 108. If the result of the comparison shows that the difference is within a predetermined range, the determination unit 112 determines that the estimation is performed correctly, estimates the patch of each density from the current estimation patch, and performs gamma estimation. Correct the table. That is, the determination unit 112 outputs a determination result to the control unit 113, and in response to this, the control unit 113 causes the first gamma correction table update unit 106 to execute one-patch calibration. On the other hand, when it exceeds the predetermined range, it is determined that the estimation is not performed correctly, and the determination unit 112 outputs the determination result to the control unit 113, and the control unit 113 receives the second determination result. The gamma correction table update unit 107 is caused to execute full calibration. That is, the control unit 113 causes the halftone processing unit 103 to generate a plurality of printing halftone patches, causes the image forming unit 104 to form a plurality of patches on the intermediate transfer belt, and causes the measurement unit 108 to measure the density of these patches. . Then, the second gamma correction table update unit 107 is caused to execute full calibration using the patch density measurement values of the plurality of patches.

  Next, details of the operation of this embodiment will be described with reference to the flowchart of FIG. When the power is turned on or the cartridge is replaced, the control of the flowchart shown in FIG. 2 is performed. Note that the processing shown in FIG. 2 is realized by the processing shown in FIG. 2 is realized by the control of the control unit 113 by a CPU (not shown) executing a program stored in a ROM or RAM (not shown).

  In step S401, the image forming unit 104 outputs the estimation patch and the determination patch on the intermediate transfer belt. Note that the estimation patch and the determination patch are preferably patches having different densities (dot patterns). In step S402, the measurement unit 108 measures the density of the estimation patch and the density of the determination patch output in step S401.

  In step S403, the density fluctuation detection unit 109 detects the density fluctuation rate using the estimation patch measured in step S402. The density fluctuation estimation unit 111 estimates the density fluctuation rate of the determination patch using the detected density fluctuation rate, and estimates the patch density estimated value of the determination patch from the estimated density fluctuation rate of the determination patch.

  In step S404, the determination unit 112 compares the estimated patch density value estimated in step S403 with the measured patch density value of the determination patch measured in step S402, and determines whether the difference is within a predetermined range. judge. If the difference is within the predetermined range, it is determined that the density estimation result using the estimation patch is correct, and the process proceeds to step S405. On the other hand, if the difference is not within the predetermined range, it is determined that the density estimation result using the estimation patch is not correct, and the process proceeds to step S406.

  Step S405 is a case where the estimated density is correct. Therefore, in step S405, the first gamma correction table update unit 106 performs one-patch calibration and updates the gamma correction table. That is, the patch density estimated value of the patch density of another gradation is estimated from the patch density measured value of the estimation patch measured in step S402. Then, the gamma correction table is updated using the patch density estimated value.

  On the other hand, step S406 is a case where the estimated density is not correct. Therefore, in step S406, the second gamma correction table update unit 107 performs full calibration and updates the gamma correction table. That is, in step S 406, the control unit 113 outputs a plurality of gradation patches on the intermediate transfer belt of the image forming unit 104 in order to remeasure patch densities of other gradations. Then, the measurement unit 108 measures the patches having a plurality of gradation densities. Then, the second gamma correction table update unit 107 updates the gamma correction table using the measured patch density values of the plurality of gradation patches.

  FIG. 5 is a diagram schematically showing the contents described in the flowchart of FIG. The horizontal axis indicates the patch input data, and the vertical axis indicates the patch density. The measured value 501 at the previous calibration is the density of the estimation patch measured at the previous gamma correction table update. The estimation patch measurement value 502 is a measurement value of the estimation patch density measured this time. These differences become density fluctuations 506. The density fluctuation 508 of the determination patch is estimated from the density fluctuation 506. A value obtained by adding the estimated density fluctuation 508 to the estimated value 509 of the determination patch at the time of the previous correction is an estimated value 503. A measurement value A504 and a measurement value B505 indicate measurement values obtained by measuring the determination patch. That is, the measured value of the patch having the same dot shape as the estimated value 503 is shown. Here, for convenience of explanation, two types of measurement values are shown, but actually obtained measurement values are either one. The measured value A504 represents an example in which the measured value A504 and the estimated value 503 are within the determination range 507. On the other hand, the measured value B505 shows an example in which the measured value B505 and the estimated value 503 are outside the determination range 507. If the result of density determination of the determination patch is within the determination range 507 as in the measurement value A, the determination result in step SS404 in the flowchart of FIG. 4 is YES, and the determination range 507 is as in the measurement value B. Otherwise, the result of step S404 is NO. In the case of the measured value B, the estimated result and the measured result are greatly different. Therefore, when the gamma correction table update process using the estimated value is performed, data that is not in the gamma characteristic of the image forming apparatus is used. Correct, and gamma correction cannot be performed correctly. Therefore, in this case, the patch density corresponding to a plurality of print dot patterns is measured again, and the second gamma correction table update unit 107 measures the gamma correction table stored in the first storage unit 105. Update based on the patch density data. That is, full calibration is performed. An example of the determination range may be that the determination range is ± 10% of the estimated concentration. However, the predetermined determination range is not limited to this, and may be determined according to the characteristics of the image forming apparatus to be applied.

  As described above, according to the present embodiment, it is possible to determine whether or not full calibration is necessary with a small number of patches when the power is turned on or the cartridge is replaced. As a result, when full calibration is not required, it is possible to update the gamma correction table without performing full calibration, which can reduce time and toner consumption for density correction. There is an effect that convenience for the user is improved. As described above, in this embodiment, the density of the halftone used for printing is estimated from the density variation of the specific patch, and it is determined whether the estimation is correctly performed by comparing a part of the estimated density with the measured density. Since full calibration is performed only when it is determined that the estimated density is not correct, the number of times of calibration can be suppressed to the minimum necessary while maintaining the accuracy of the gamma correction table. Further, since the gamma characteristic of the halftone used for printing can be estimated from the density variation of the specific patch, the number of output patches can be minimized.

[Example 2]
In the first embodiment, the method for determining whether or not full calibration is necessary with a small number of patches when the power is turned on or the cartridge is replaced has been described. In this case, an example has been described in which the density of a patch having an arbitrary dot shape is estimated from the density fluctuation obtained by measuring one type of dot shape estimation patch. The second embodiment is different from the first embodiment in that a plurality of types of dot-shaped patches are output and measured as estimation patches.

FIG. 6A is a diagram for explaining how to obtain the density variation rate of the second embodiment. The vertical axis represents density, and the horizontal axis represents dot shape parameters. The dot shape parameter is a parameter indicating the shape of the dot, and is obtained, for example, by “dot circumference / dot area” as described in the first embodiment. In the second embodiment, the image forming unit 104 outputs a plurality of types (here, two types) of dot-shaped patches, and the measurement unit 108 measures their densities. The density DA0 of the measurement value 601 at the time of the previous calibration of the estimation patch for the dot shape parameter A and the density DB0 of the measurement value 604 at the time of the previous calibration of the patch for estimation of the dot shape parameter B are respectively stored in the second storage unit 110. It is assumed that it is stored in When determining whether or not to perform full calibration in this processing, the measurement unit 108 measures the density of the dot shape parameter A estimation patch and the dot shape parameter B estimation patch. Plots of the measured values DA1 and DB1 are estimated patch measured values 602 and 605, respectively. The density fluctuation from the previous measurement to the current measurement can be calculated for each dot shape parameter. Specifically:
Density fluctuation rate of shape parameter A: C = (DA1-DA0) / DA0
Density fluctuation rate of shape parameter B: D = (DB1-DB0) / DB0
FIG. 6B is a plot of density variation rates on the vertical axis and dot shape parameters on the horizontal axis. The dot shape parameters are set so that these points lie on a straight line passing through the origin. However, since the density fluctuation rates C and D include patch measurement errors, they are not always on a straight line. Therefore, a straight line passing through the origin is drawn from the two points 607 and 608 of the density fluctuation rate C and the density fluctuation rate D using the least square method. This straight line is called a density fluctuation prediction line 609. In the first embodiment, as described with reference to FIG. 3, the example in which the density fluctuation prediction line is obtained with a straight line connecting the density and the density fluctuation rate obtained from one kind of dot shape parameter has been described. On the other hand, in Example 2, since the density fluctuation prediction line is obtained from the density fluctuation rates of the two types of dot shape parameters, the deviation of the density fluctuation prediction line due to the measurement error can be reduced. Therefore, the density fluctuation prediction of an arbitrary patch can be made more accurately.

  FIG. 7 is a flowchart showing the processing flow of the second embodiment. In step S701, the image forming unit 104 outputs a plurality of gradation estimation patches and determination patches on the intermediate transfer belt. Here, the plurality of gradation estimation patches may be patches having shapes in which dots are stably formed and having different dot shape parameters. An example is shown in FIG. 2 and will be described later. In step S702, the measurement unit 8 measures the densities of a plurality of estimation patches and determination patches on the intermediate transfer belt. In step S <b> 703, the density variation estimation unit 111 estimates the density variation of the determination patch using the density variation of the plurality of estimation patches, and estimates the density of the determination patch using the estimated density variation of the determination patch. . That is, in step S703, the density fluctuation detection unit 109 first detects density fluctuations from the measurement values of the plurality of estimation patches at the time of the previous correction and the measurement values of the plurality of estimation patches measured in step S702. Then, the density variation estimation unit 111 estimates the density of the determination patch using the density variation.

  Since the processing from step S704 to step S706 is the same as the processing from step S404 to step S406 described in the first embodiment, description thereof is omitted here.

  FIG. 2 shows a part of the estimation patch. In the case of the first embodiment, the example using the dot-shaped patch shown in FIG. 2B has been described, but in the second embodiment, the dot-shaped patch shown in FIGS. 2A and 2B is used. . 2A and 2B, each square represents one pixel, black is a pixel forming a toner image, and a collection of black pixels forms one dot. Yes. White indicates pixels that do not form a toner image. In this figure, 4 × 4 pixels indicate one predetermined area, and an actual estimation patch has a density measured by the measurement unit 108 because a plurality of predetermined areas each composed of 4 × 4 pixels are continuous both vertically and horizontally. A patch of a size that can be measured is formed. FIGS. 2A and 2B differ in dot shape parameter (connection shape of pixels forming a toner image) and also in the number of black pixels, so that the density of patches formed therefrom is also different. . However, since both have a shape of a plurality of dots, a stable toner image can be formed, and the dot shape is suitable for the estimation patch.

  As described above, according to the second embodiment, there is an effect that it is possible to more accurately determine whether or not full calibration is necessary. In the second embodiment, the example in which the number of patches having different dot shape parameters is two has been described. However, it is not necessary to limit the number of patches to two, and a density fluctuation prediction line is formed using a plurality of three or more patches. You may ask for it.

[Example 3]
In the first and second embodiments, as a determination patch, a patch density measurement value obtained by outputting and measuring one type of actually used halftone patch, and the determination patch estimated from the estimation patch An example in which the estimated patch density value is compared has been described. The third embodiment is different from the first and second embodiments in that a multi-tone halftone patch is output and measured as a determination patch. FIG. 8 is a flowchart showing the processing flow of the third embodiment.

  In step S801, the image forming unit 104 outputs one estimation patch and a plurality of gradation determination patches (that is, a plurality of determination patches) on the intermediate transfer belt. Here, as the plurality of gradation determination patches, a halftone patch having a higher density than the density of the estimation patch and a halftone patch having a lower density than the density of the estimation patch may be selected. In step S802, the measurement unit 108 measures the density of one estimation patch and a plurality of determination patches on the intermediate transfer belt. In step S803, the density fluctuation estimation unit 111 uses the density fluctuation of the estimation patch to obtain density fluctuations of the determination patch of a plurality of gradations, thereby determining the patch density and the low density of the high density judgment patch. The patch density of each patch is estimated. In step S804, the determination unit 112 compares the patch density estimated value of the high density determination patch estimated in step S803 with the patch density measurement value of the high density determination patch detected in step S802. Further, the determination unit 112 compares the patch density estimated value of the low density determination patch estimated in step S803 with the patch density of the low density determination patch detected in step S803. The comparison method is as described in the first embodiment. As a result of the comparison, when the estimated density value and the measured density value are within a predetermined range in both the low density patch and the high density patch, the process proceeds to step 805 and one-patch calibration is performed. On the other hand, in other cases, the process proceeds to step S806, and full calibration is performed. S805 and S806 are the same processes as steps S405 and S406 described in the first embodiment.

  According to the method of the third embodiment, it is possible to compare the estimated density value of the halftone patch and the measured density value in both the low density and high density gradations, so that the necessity of full calibration can be determined with higher accuracy. can do.

  In the third embodiment, an example using a halftone used for printing as a multi-gradation determination patch has been described. However, different types of halftones may be used as a multi-gradation determination patch. For example, two types of patches, a patch with a low line number screen and a patch with a high line number screen, may be used. In this case, a patch having a gradation with the same or similar input density may be used for the patch of the low line number screen and the patch of the high line number screen. In particular, this embodiment is effective when dot data with different halftones exist in the same page (when halftones are switched depending on pixel attributes).

[Example 4]
In the embodiments so far, the method for determining whether or not full calibration is necessary has been described when the power is turned on or the cartridge is replaced. In the fourth embodiment, the necessity of full calibration is determined without being limited to these timings. The timing for performing density correction calibration of the image forming apparatus can be considered when a predetermined number of sheets are printed or when the installation environment has changed significantly in addition to when the power is turned on or when the cartridge is replaced. Conventionally, one patch calibration has been performed at these timings. In the present embodiment, processing for comparing the estimated density and the measured density is performed by the method described in the first to third embodiments at the timing for determining the execution of calibration. As a result, when it is determined that full calibration is necessary, full calibration is performed instead of one-patch calibration.

Note that the predetermined timing in this embodiment may be for each page or print job. That is, it may be performed when the number of printed sheets from the previous calibration reaches a predetermined number.
According to the method of this embodiment, it is possible to determine whether full calibration is possible by measuring and comparing at least one estimation patch and one determination patch. Therefore, it is possible to determine whether or not full calibration is necessary for each page by generating and measuring a patch every time one page is printed.

  According to this method, when one-patch calibration is being performed, when full accuracy cannot be obtained with one-patch calibration due to environmental fluctuations, changes with time, etc., it is possible to perform full calibration. is there.

(Other examples)
The present invention supplies a program that realizes one or more functions of the above-described embodiments to a system or apparatus via a network or a storage medium, and one or more processors in a computer of the system or apparatus read and execute the program This process can be realized. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

DESCRIPTION OF SYMBOLS 101 Gamma correction part 102 Dot pattern generation part 103 Halftone process part 104 Image formation part 105 1st memory | storage part 106 1st gamma correction table update part 107 2nd gamma correction table update part 108 Measurement part 109 Density fluctuation | variation detection part 110 Second storage unit 111 Concentration fluctuation estimation unit 112 Determination unit 113 Control unit

Claims (13)

An information processing apparatus for updating information used in gamma correction for correcting image data output by an image forming apparatus, the first patch including a specific dot pattern output by the image forming apparatus; Measuring means for measuring the density of each patch of the second patch constituted by a different dot pattern from the first patch;
Storage means for storing the density of the first patch measured by the measurement means at the time of the previous update;
Using the density variation based on the difference between the density of the first patch measured by the measuring means and the density of the first patch stored in the storage means, the density of the second patch is estimated. An estimation means;
Determining means for determining whether the difference between the density of the second patch measured by the measuring means and the density of the second patch estimated by the estimating means is a value within a predetermined range;
When the determination unit determines that the difference is a value within a predetermined range, the information is updated using the estimated value of the second patch based on the density of the first patch. An information processing apparatus comprising update means.   When the determination unit determines that the difference is not within a predetermined range, a measurement obtained by causing the image forming apparatus to output a plurality of patches and measuring the density of the output plurality of patches by the measurement unit. The information processing apparatus according to claim 1, further comprising second update means for updating the information using a value. The measuring means measures one first patch and a plurality of second patches having different dot patterns,
Whether the difference between the density of the plurality of second patches measured by the measuring means and the density of the second patch estimated by the estimating means is a value within a predetermined range. Determine
The first update unit updates the information using an estimated value based on the density of the first patch when the determination unit determines that all the differences are values within a predetermined range. The information processing apparatus according to claim 1, wherein the information processing apparatus performs the information processing.   The information processing apparatus according to claim 1, wherein the measurement unit measures the density of one first patch and one second patch. The measuring means measures the density of a plurality of first patches having different dot patterns and one second patch,
3. The information processing apparatus according to claim 1, wherein the estimation unit estimates the density of the second patch using density fluctuations obtained from density fluctuations of the plurality of first patches. .   6. The measurement unit according to claim 5, wherein the plurality of second patches measure a patch having a higher density than the first patch and a patch having a lower density than the first patch. The information processing apparatus described. The estimation means further estimates the density of a patch composed of another dot pattern based on the density variation,
The information processing apparatus according to claim 1, wherein the first update unit updates the information based on the concentration estimated by the estimation unit.   The estimating means estimates the density fluctuation of the second patch from the density fluctuation of the first patch, and estimates the estimated density fluctuation of the second patch and the density of the second patch of the previous time. The information processing apparatus according to claim 1, wherein the density of the second patch of this time is estimated from the above. An information processing apparatus according to any one of claims 1 to 8, comprising:
An image forming apparatus for forming an image on a recording medium by an electrophotographic method,
9. The image forming apparatus according to claim 1, wherein the image forming apparatus outputs the first patch and the second patch when the image forming apparatus is powered on. 10. Information processing device. An information processing apparatus according to any one of claims 1 to 8, comprising:
An image forming apparatus for forming an image on a recording medium by an electrophotographic method,
The image forming apparatus outputs the first patch and the second patch when the cartridge of the image forming apparatus is replaced,
An image forming apparatus that executes processing by the measuring unit, the estimating unit, the determining unit, and the first updating unit. An information processing apparatus according to any one of claims 1 to 8, comprising:
An image forming apparatus for forming an image on a recording medium by an electrophotographic method,
The image forming apparatus outputs the first patch and the second patch when the number of printed sheets from the previous update of information reaches a predetermined number;
An image forming apparatus that executes processing by the measuring unit, the estimating unit, the determining unit, and the first updating unit. An information processing apparatus control method for updating information used in gamma correction for correcting image data output by an image forming apparatus, comprising: a first dot pattern configured by a specific dot pattern output by the image forming apparatus; A measurement step of measuring the density of each patch of the second patch constituted by a patch and a dot pattern different from the first patch;
An acquisition step of acquiring from the storage means the density of the first patch measured at the time of the previous update;
Estimating the density of the second patch using density variation based on the difference between the density of the first patch measured in the measurement step and the density of the first patch acquired from the storage means in the acquisition step. An estimation step to
A determination step of determining whether a difference between the density of the second patch measured in the measurement step and the density of the second patch estimated in the estimation step is a value within a predetermined range;
When the determination step determines that the difference is a value within a predetermined range, the information is updated using the estimated value of the second patch based on the density of the first patch. An information processing apparatus control method comprising: an update step.   The program for functioning a computer as each means of the information processing apparatus as described in any one of Claims 1 thru | or 9.

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