JP7361513B2 - Image forming apparatus, its control method, and program - Google Patents

Description

The present invention relates to an image forming apparatus, a control method thereof, and a program.

In an electrophotographic image forming apparatus, an image is formed using toner. Furthermore, in the case of an MFP, a scanner is mounted, and there are mainly two types of scanners (reading devices). One is a scanner that fixes a document while reading it, and the other is a scanner that uses an ADF (Auto Document Feeder) to move and read the document. The latter scanner is capable of automatically transporting multiple documents and reading them in succession. Furthermore, by providing a dedicated device for reading the back side of a document in the ADF, it becomes possible to read both the front and back sides of the document at the same time.

However, in the above configuration, a difference may occur in the acquired signal values due to individual differences between the front-side scanner and the back-side scanner and deterioration over time. In that case, when a front-side scanner and a back-side scanner scan an original of the same color, the originals will be read in different colors, causing a problem.

In order to solve the above problem, Patent Document 1 describes a calibration technology that corrects the difference in signal values obtained when the same document is read by a front-side scanner and a back-side scanner. Proposed. Specifically, a chart for correcting the difference is outputted by a printer, the outputted chart is read by a front side scanner and a back side scanner, and the difference is calculated to calculate a correction value.

Patent No. 4642871

However, the above conventional technology has the following problems. In order to reduce costs, the performance of backside scanners that are used less frequently may be degraded. For example, a 600 dpi scanner may be used for the front side, while a 300 dpi scanner may be used for the back side. If the number of lines in a chart used to correct differences in signal values obtained by a scanner is high, moiré may occur with a scanner having a low resolution. In the above example, there is a possibility that moiré does not occur with a 600 dpi scanner, but moire does occur with a 300 dpi scanner. In such a case, in the conventional technique described above, the acquired signal value changes depending on whether or not moire occurs, and an accurate correction value cannot be calculated, which may result in a decrease in correction accuracy.

Furthermore, in the case of a monochrome MFP equipped with a color scanner, the correction chart cannot be output in color, so it is necessary to use a chart output by another color printer. In this case, since it is difficult to control the number of lines of other color printers using a monochrome MFP, there is a problem in that moiré is more likely to occur and there is an increased possibility that correction accuracy will decrease.

The present invention has been made in view of at least one of the above-mentioned problems, and regardless of the reading accuracy of the front side scanner and the back side scanner of the original, the signal value when reading the same original side is A mechanism for suitably correcting the difference is provided.

The present invention provides an image forming apparatus, for example, including a first reading device for reading the front side of a document, and a first reading device for reading the back side of the document at a resolution lower than the resolution at which the first reading device reads the front side of the document. A second reading device for reading, and each of the first reading device and the second reading device is used to read the forming surface of the sheet on which the chart is formed, and the reading signal of the chart read by each reading device is read. an acquisition means for acquiring a difference in the feature amount of the read signal of the chart, and a moire determination means for determining whether moire has occurred in the chart according to the difference in the feature amount of the read signal of the chart acquired by the acquisition means; The present invention is characterized by comprising a correction means for correcting a color conversion parameter used to read a document and generate image data by the first reading device or the second reading device according to the judgment result by the moire judgment means. .

According to the present invention, it is possible to suitably correct the signal value difference when reading the same document surface, regardless of the reading accuracy of the front side scanner and the back side scanner of the document.

FIG. 1 is a configuration diagram of a system according to an embodiment. FIG. 1 is a configuration diagram of a scanner according to an embodiment. FIG. 3 is a diagram showing a flow of image processing according to an embodiment. FIG. 3 is a diagram illustrating a flow of a color conversion parameter generation process of a scanner according to an embodiment. FIG. 3 is a diagram illustrating an example of a chart according to an embodiment. FIG. 3 is a diagram illustrating the cause of moire according to an embodiment. FIG. 3 is a diagram showing in detail the flow of moiré determination processing according to an embodiment. FIG. 3 is a diagram illustrating a flow of a process of correcting color conversion parameters of a scanner according to an embodiment. FIG. 3 is a diagram illustrating an example of a UI that displays that data has been removed according to an embodiment. FIG. 3 is a diagram showing the flow of moiré determination processing and scanner color conversion parameter correction processing according to an embodiment. FIG. 3 is a diagram illustrating an example of a UI that displays the fact that processing has been interrupted and the reason thereof according to an embodiment.

Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the claimed invention. Although a plurality of features are described in the embodiments, not all of these features are essential to the invention, and the plurality of features may be arbitrarily combined. Furthermore, in the accompanying drawings, the same or similar components are designated by the same reference numerals, and redundant description will be omitted.

Note that a multifunction peripheral (digital multifunction peripheral/MFP/Multi Function Peripheral) will be described as an example of the image forming apparatus according to the embodiment. However, the scope of application is not limited to multifunction peripherals, and may be any image forming apparatus equipped with a reading device (scanner).

<First embodiment>
Below, a first embodiment of the present invention will be described. In this embodiment, moire is determined when scanning a chart for correcting the signal value difference between the front side reading device (first reading device) and the back side reading device (second reading device) of the document. A method for removing the influence of moiré will be explained.

<System configuration>
First, the configuration of the system in this embodiment will be explained with reference to FIG. An MFP (Multi-Function Printer) 101 that uses black (hereinafter abbreviated as K) toner is connected to other network compatible devices via a network 119. A PC 120, which is an information processing device, is connected to an MFP 101, which is an image forming device, via a network 119. Print data is transmitted to the MFP 101 and SFP 123 via the printer driver 122 according to instructions from the CPU 121 in the PC 120 .

The MFP 101 will be explained in detail. The MFP 101 includes a controller 102, a display device 110, a scanner 111, an input device 112, a storage device 113, a printer 114, and a network I/F 118. The network I/F 118 communicates with external devices via the network 119 and receives print data and the like. The controller 102 includes at least a CPU 103, a renderer 106, and an image processing unit 108. The interpreter 104 of the CPU 103 interprets the PDL (page description language) portion of the received print data and generates intermediate language data 105. Subsequently, the renderer 106 generates raster image data 107 from the generated intermediate language data 105. Further, the image processing unit 108 performs image processing on the raster image data 107 and the scan image 109 read by the scanner 111. Details of the image processing unit 108 will be described later.

A printer 114 connected to the controller 102 is a printer serving as an image forming unit that forms output data on a sheet such as paper using K toner. The printer 114 includes a CPU 116, a paper feeding section 115 that is controlled by the CPU 116 and that feeds paper, and a paper ejection section 117 that ejects the paper on which output data has been formed. The display device 110 is a UI (user interface) that displays instructions to the user and the status of the MFP 101. The scanner 111 is a scanner (reading device) including an ADF (Auto Document Feeder). The scanner 111 irradiates a bundle of original images or a single sheet of original images with a light source (not shown), and forms a reflected image of the original onto a solid-state image sensor such as a CCD (Charge Coupled Device) sensor using a lens. Then, a raster image reading signal is obtained as a color scan image 109 from the solid-state image sensor. Details of the scanner 111 will be described later.

The input device 112 is an interface for receiving input from a user. Note that a part of the input device may be realized as a touch panel type input device, and in that case, the part is provided integrally with the display device 110. The storage device 113 stores data processed by the controller 102, data received by the controller 102, and the like.

An SFP (Single-Function Printer) 123 that uses cyan, magenta, and yellow (hereinafter abbreviated as C, M, and Y) toners in addition to K can communicate with other network-compatible devices via the network 119 similarly to the MFP 101. connected to. The SFP 123 includes a controller 124 that generates and processes data, a printer 125, a display device 126, an input device 127, and a storage device 128. Unlike the MFP 101, the printer 125 is an image forming unit that can form output data as a color image on paper using C, M, Y, and K toners. In this embodiment, the MFP 101 will be described as an image forming apparatus that forms a monochrome image using K toner, but this is not intended to limit the invention; It may be configured to form an image. In this embodiment, only an example will be described in which when the MFP 101 cannot form a color image, a color chart output from another image forming apparatus is used to correct the signal value of the reading device. That is, the image forming apparatus of the present invention can also correct the signal value of the reading device using the color chart output by the image forming apparatus itself.

<Scanner configuration>
Next, with reference to FIG. 2, the configuration of the scanner 111 according to this embodiment will be described. Reference numeral 201 denotes a document table, and inside the document table 201, a reading device (first reading device) 204 for the front side (one side) of the document is provided. The reading device 204 can read the original on the original table. Further, a conveyance path for conveying a sheet of paper 206, which is a document, to the document table 201 is provided. Reference numeral 205 denotes a back side reading device (second reading device) for reading the back side (the other side) of the paper 206 that is transported on the transport path.

The reading device 204 has a built-in light source and a solid-state image sensor, and when the light source illuminates the document, the reflected light passes through the glass stand 203 and forms an image on the solid-state image sensor. Obtain the image reading signal. Paper 206 is conveyed to glass stand 203 by rollers 202 . When conveying the paper, the reading device 204 is fixed, and light is irradiated from a light source onto the paper that has reached the position of the reading device 204, and a reflected image is formed on a solid-state image sensor. The reading device 205 is a device for reading the back side of a sheet, and its position is fixed. Similar to the reading device 204, light is irradiated to the paper position that has been reached, and a reflected image is formed on a solid-state image sensor. The reading device 205 differs from the reading device 204 in that it irradiates the back surface of the paper 206 with light. In this way, by providing two types of reading devices 204 and 205, it is possible to simultaneously read the front and back sides of a sheet (original) in one conveyance.

Since the reading device 204 and the reading device 205 are independent devices, they can be devices with different performances. For example, the reading device 204 for the back side is expected to be used less often than the reading device 204 for the front side, and is generally a cheaper reading device with lower resolution. In this embodiment, it is assumed that the reading device 204 can acquire image data at a resolution of 600 dpi, and the reading device 205 can acquire image data at a resolution of 300 dpi. Naturally, the present invention is not intended to be limited to these performances; for example, the reading device for the back side may have a higher resolution, and even if the same resolution is used in the two reading devices. , the present invention can be applied.

<Image processing>
Next, with reference to FIG. 3, the flow of the image processing unit 108 according to this embodiment will be described. FIG. 3 shows the flow of image processing performed on the raster image data 107 and images read by the scanner 111. The processing described below is realized by executing an ASIC (Application Specific Integrated Circuit) not shown in the image processing unit 108. Note that the image processing unit 108 may be controlled by the CPU 103 without intending to limit the present invention. Further, this flowchart is executed when print data is transmitted from the PC 120 via the driver 122 or when a copy operation is performed using the scanner 111, display device 110, and input device 112.

First, in S301, the image processing unit 108 determines whether the image data is scanned image data. If it is not scanned image data, it is determined that it is raster image data 107 generated when print data is transmitted from the PC 120 via the driver 122, and the process advances to S312. On the other hand, if it is determined that the data is scanned image data (read signal), the process advances to S302.

In S302, the image processing unit 108 determines that a copy operation has been performed using the scanner 111, the display device 110, the input device 112, etc., and scans the scan image data (read signal) read by the reading device 204 for the front side of the document. Determine whether or not. If the scan image data is for the front surface, the process advances to S303; otherwise, the process advances to S306.

In S303, the image processing unit 108 executes color conversion processing. Here, RGB image data dependent on the reading device 204 is converted to device-independent RGB image data using a three-dimensional LUT (Look Up Table, hereinafter abbreviated as 3D-LUT), which is a color conversion parameter. . Subsequently, in S304, the image processing unit 108 executes character determination processing. Here, edges of the image and the like are detected to generate character determination data. Next, in S305, the image processing unit 108 performs filter processing on the RGB image data, and proceeds to S310. Here, the generated character determination data is used to perform different filtering processes for character parts and other parts.

On the other hand, if it is determined in S302 that the scan image data is not the scan image data read by the front side reader 204, it is determined that the scan image data is the scan image data read by the back side reader 205, and in S306, the image processing unit 108 , performs color conversion processing. Here, the 3D-LUT is used to convert RGB image data dependent on the reading device 205 into RGB image data independent of the device. Since the reading device is different, a 3D-LUT different from that in S303 is used. Subsequently, in S307, the image processing unit 108 performs character determination processing, and in S308, performs filter processing. Furthermore, in S309, the image processing unit 108 executes resolution conversion processing, and proceeds to S310. This is because the reading device 205 reads at a resolution of 300 dpi, so the resolution is converted to 600 dpi in order to match the resolution with the reading device 204.

In S310, the image processing unit 108 executes background removal processing to remove the background color component. Subsequently, in S311, the image processing unit 108 executes monochrome conversion processing to convert the RGB image data into gray luminance data. In S312, the image processing unit 108 executes a brightness density conversion process using a one-dimensional LUT (Look Up Table, hereinafter abbreviated as 1D-LUT), and converts the K density image data from the gray brightness image data. generate. Then, in S313, the image processing unit 108 corrects the gradation characteristics of K using the 1D-LUT. Finally, in S314, the image processing unit 108 executes image forming processing using screen processing, generates a binary K image, and ends the processing.

Here, in the above image processing, color conversion processing is performed in S303 and S306 according to the characteristics of the reading device 204 and the reading device 205, so in principle, the same signal value is output when the same document is read. It is something that will be done. However, the signal value of the scan image data obtained by the reading device may change due to individual differences in the reading device or deterioration over time, and differences may occur from one reading device to another. The MFP 101, which is an image forming apparatus according to the present embodiment, executes processing to correct these 3D-LUTs (color conversion parameters) used in color conversion processing in order to reduce the difference.

<Color conversion parameter generation process>
Next, with reference to FIG. 4, the processing procedure of the scanner color conversion parameter generation process in this embodiment will be described. The correction processing of the color conversion parameters of the scanner is controlled by the CPU 103 of the controller 102. The processing described below can be realized, for example, by the CPU 103 reading a program stored in a memory such as the storage device 113 into a RAM (not shown) and executing the program. Further, the color conversion parameters created by executing this flowchart are stored in the storage device 113.

In S401, the CPU 103 reads the surface of the chart formed on the sheet using the front surface reader 204. Details of the chart will be described later using FIG. 5. In S402, the CPU 103 uses the back side reading device 205 to read the formed side of the same chart as the chart read in S401.

Next, in S403, the CPU 103 executes moiré determination processing. Details of the moire determination process will be described later using FIG. 7. Finally, in S404, the CPU 103 uses the moiré determination result to execute correction processing for the color conversion parameters of the scanner used in S303 or S306. Details of the scanner color conversion parameter correction process will be described later using FIG. 8.

<Chart>
Next, with reference to FIG. 5, a chart formed on a sheet according to this embodiment and a plurality of patches included in the chart will be described. 501 in FIG. 5A shows an example of a chart including a plurality of patches. A plurality of patches printed on the chart 501 including the patch 502 are composed of a mixed color that is a combination of C, M, Y, and K. Note that the chart is formed on a sheet by an external device different from the MFP 101, for example, the SFP 123.

The chart 501 needs to be a mixture of colors, and since the MFP 101 according to this embodiment has a configuration in which color printing is not possible, for example, a chart output from an SFP 123 capable of color printing is used. The chart is not limited to SFP123, and a chart output by a printing device capable of outputting in other colors may be used. Of course, if the MFP 101 has a configuration capable of color printing, the MFP 101 may output the image.

A patch is a region consisting of a specific combination of identical signal values. The patches on the chart 501 are arranged so that they are evenly spaced to human vision when measured with a measuring device.

A specific example is shown in FIG. 5(b). The Lab color space 503 is a color space associated with human visual characteristics, and is composed of three-dimensional axes of L*, a*, and b*. 504 to 508 indicate patch data of the chart 501, which is obtained by measuring the chart 501 output by the printer 114 with a measuring device (in this case, the reading devices 204 and 205).

As shown in FIG. 5(b), the data in the chart 501 is arranged evenly in the Lab color space, so it is arranged evenly with respect to human vision. In this way, by arranging the patches so that they are even with respect to human vision, it becomes possible to correct all color spaces with a limited number of patches.

<Cause of moire>
Next, with reference to FIG. 6, the cause of moire occurring during scanning will be explained. FIG. 6(a) shows the relationship between a 600 dpi reading device and a chart output on a 190 line screen. A 600 dpi reading device has a sampling frequency of 600 dpi, and the Nyquist frequency is half that, 300 dpi. If the number of lines in the scanned document is higher than the Nyquist frequency, aliasing (noise) will occur, causing moiré. If the number of lines of the scanned document is lower than the Nyquist frequency, folding does not occur, and moiré does not occur.

In the example of FIG. 6A, a region 601 is a region in which moire does not occur, and a region 602 is a region in which moire occurs. When the number of lines on the chart is 190, the dpi is 190 dpi, which is lower than the Nyquist frequency, so no moiré occurs. In the example of FIG. 6A, the number of lines 603 on the chart is in the area 601, so no moiré occurs.

FIG. 6(b) is a diagram showing the relationship between a 300 dpi reading device and a chart output on a 190 line screen. A 300 dpi reading device has a sampling frequency of 300 dpi, and the Nyquist frequency is half that, 150 dpi. If the number of lines in the scanned document is higher than the Nyquist frequency, aliasing will occur, causing moiré. If the number of lines in the scanned document is lower than the Nyquist frequency, folding does not occur, and moiré does not occur. In the example of FIG. 6(b), a region 604 is a region in which moire does not occur, and a region 605 is a region in which moire occurs. When the number of lines on the chart is 190, the dpi is 190 dpi, which is higher than the Nyquist frequency, increasing the possibility that moiré will occur. In the example of FIG. 6B, the number of lines 606 on the chart is in the area 605, so there is a high possibility that moiré will occur.

Here, even with the same 190-line patch, moiré may not occur depending on the combination of signal values and colors. For example, since high-density data is hardly subjected to screen processing, it does not have a frequency characteristic like 606 in FIG. 6. Even in charts with the same number of lines, there are patches in which moire occurs after reading and patches in which moire does not occur, depending on the resolution of the reading device. As described above, even if the chart (original) is the same, moiré occurs if the relationship with the resolution of the reading device changes, and the moiré causes a difference in signal values. As a result, one patch may be read without moiré while the other patch may be read with moiré, reducing the accuracy of the scanner's process of correcting color conversion parameters. . In the configuration of this embodiment, in the example of FIG. 6, moire may not occur in the 600 dpi reading device 204, and moire may occur in the 300 dpi reading device 205.

<Moiré determination process>
Next, with reference to FIG. 7, the processing procedure of the moiré determination process (S403) according to the present embodiment will be described. The processing described below can be realized, for example, by the CPU 103 reading a program stored in a memory such as the storage device 113 into a RAM (not shown) and executing the program.

In S701, the CPU 103 focuses on the patch of the chart read by the front side reading device 204, and obtains a variance value that is a characteristic amount of the read signal in the patch area. In the example of FIG. 5, attention is paid to 502, which is one of the patches included in the chart 501, and the dispersion value of the read signal within the region of patch 502 is obtained. In this embodiment, dispersion values are obtained for each of the R, G, and B signal values in the read signal and are summed. The dispersion value is not limited to this embodiment, and any signal value may be used. For example, an RGB image may be converted into a gray image, and a variance value may be determined for the gray image. Subsequently, in S702, the CPU 103 focuses on the patch of the chart 501 read by the back side reading device 205, and obtains the dispersion value of the read signal in the patch area.

Next, in S703, the CPU 103 compares the dispersion value of the front surface and the dispersion value of the back surface. When moire does not occur, the data within the region is uniform, so the variance values are similar. If moiré occurs in one of the reading devices, the data within the area is no longer uniform, so the dispersion values for the front and back surfaces are different, resulting in a difference.

In S704, the CPU 103 determines whether the difference in the variance values compared in S703 is larger than a threshold value. Here, the threshold value is obtained in advance from the difference in variance values between those with and without moiré. If it is determined in S704 that the difference in variance values is greater than the threshold, the process advances to S705, and if not, the process advances to S706. In S705, the CPU 103 determines that the patch has moiré, and proceeds to S706. Specifically, here, the CPU 103 stores information regarding the patch determined to have moire in a memory such as a RAM. On the other hand, if the difference in the variance values is less than or equal to the threshold in S704, the process proceeds to S706 without determining that the patch is a moiré occurrence patch.

In S706, the CPU 103 determines whether all patches have been processed. If there are any unprocessed patches, the process returns to S701 and repeats the processes from S701 onwards. On the other hand, if it is determined in S706 that all patches have been processed, the process ends.

In this embodiment, the dispersion value is used as the feature quantity of the read signal to determine moire, but this is not intended to limit the present invention, and moire may be determined using other feature quantities. For example, the frequency characteristics of the patch areas may be quantified and compared.

<Color conversion parameter correction processing>
Next, the color conversion parameter correction process (S404) of the scanner according to the present embodiment will be described with reference to FIG. The processing described below can be realized, for example, by the CPU 103 reading a program stored in a memory such as the storage device 113 into a RAM (not shown) and executing the program.

In step S<b>801 , the CPU 103 executes color conversion processing for the front side reader on the image read by the front side reader 204 . Here, the same processing as in S303 above is executed. Subsequently, in S802, the CPU 103 acquires the average signal value of each patch of the chart read by the front side reader 204. Since the patch is composed of a plurality of pixels, the average value of the read signal is obtained.

Next, in S803, the CPU 103 executes color conversion processing for the back side reading device on the image read by the back side reading device 205. Here, the same processing as S306 is executed. Subsequently, in S804, the CPU 103 acquires the average signal value of each patch of the chart read by the back side reading device 205.

Next, in S805, the CPU 103 obtains the difference between the average signal values of the front and back patches. Subsequently, in S806, the CPU 103 uses the determination result of the moire determination process in S403 to determine whether moire has occurred. For example, the CPU 103 determines whether moiré has occurred by reading the determination result in S705 from a memory such as a RAM. If it is determined that moire is occurring, the process advances to S810, and if it is determined that moire is occurring, the process advances to S807.

In S807, the CPU 103 removes the data of the patch where moiré has occurred. Subsequently, in S808, the CPU 103 performs interpolation calculation using the data of the patch in which no moiré has occurred, and generates data of the removed patch. An example is shown in FIG. 5(b). For example, when the patch 504 is removed, the CPU 103 performs an interpolation calculation using surrounding data such as a patch 505, a patch 506, a patch 507, and a patch 508 to generate data.

Next, in S809, the CPU 103 displays a UI indicating that the data has been removed on the display device 110, and proceeds to S810. Here, an example of the UI will be explained using FIG. 9. A message 902 is displayed on the UI 901, indicating that since some data in the patch has a defect, the data in the patch has been removed and correction processing has been performed. In this embodiment, an example in which a UI is displayed is shown, but a configuration in which the UI is not displayed may also be used.

Returning to the explanation of FIG. Finally, in S810, the CPU 103 uses the difference between the obtained average signal values to adjust the color conversion parameters used in S303 or S306 so that the difference is minimized, that is, the precipitous difference is eliminated. to correct. Note that only the color conversion parameters of the 3D-LUT used for the back surface used in S306 may be corrected. This is because the resolution of the reading device 205 is set lower among the reading devices 204 and 205 according to this embodiment, so the signal value generated when reading is performed using the reading device 205 with a lower resolution. This is to correct the color conversion parameters so as to eliminate the difference. Of course, there is no intention to limit the present invention, and one or both of the color conversion parameters used in the reading devices 204 and 205 may be corrected depending on the respective resolutions.

As described above, the image forming apparatus according to the present embodiment includes a first reading device for the front side of a document and a second reading device for the back side of the document. The present image forming apparatus reads the forming surface of the sheet on which the chart is formed using each of the first reading device and the second reading device, and calculates the difference in the feature amount of the read signal of the chart read by each reading device. get. The image forming apparatus also determines whether moiré has occurred in the chart, based on the difference in the feature amount of the acquired chart reading signal. Furthermore, the image forming apparatus corrects the color conversion parameters used to read the document and generate image data using the first reading device or the second reading device, according to the determination result. As a result, according to the present embodiment, it is possible to suitably correct the signal value difference when reading the same document surface, regardless of the reading accuracy of the front side scanner and the back side scanner of the document.

<Second embodiment>
A second embodiment of the present invention will be described below. In the first embodiment described above, when correcting the signal value difference between the front side reading device and the back side reading device, it is determined whether or not moire has occurred for each patch from the read image data, and We have described a method for reducing the effect of such a problem by removing it and performing interpolation calculations, if any. However, if there are many patches with moiré, it becomes difficult to generate data by interpolation calculation, and even if correction data is created, the accuracy decreases, and the signals of the front and back reading devices are lower than before correction. The difference in values may become large. Therefore, in this embodiment, based on the above situation, a configuration will be described in which correction processing is stopped when the number of patches in which moiré has occurred is large, thereby preventing creation of correction data with low accuracy.

<Color conversion parameter correction processing>
Next, with reference to FIG. 10, the scanner color conversion parameter correction process according to this embodiment will be described. The processing described below can be realized, for example, by the CPU 103 reading a program stored in a memory such as the storage device 113 into a RAM (not shown) and executing the program. Note that the process flow from S1001 to S1010 is the same as the process flow from S801 to S810 in FIG. 8, and therefore the description thereof will be omitted.

If it is determined in S1006 that moire has occurred, the process advances to S1007, and the CPU 103 removes the data of the moire-generated patch. Subsequently, in S1011, the CPU 103 determines whether the number of removed patches is equal to or greater than a predetermined threshold. Here, the threshold value is determined in advance by removing and interpolating a specific number of patches and verifying accuracy. That is, when performing interpolation by removing the number of patches less than the threshold, the threshold is determined in advance through verification so that accuracy can be maintained when correcting the signal difference between the two reading devices.

If it is determined in S1011 that the number of removed patches is less than the threshold value, the process advances to S1008, and the CPU 103 generates data by interpolation calculation. On the other hand, if it is determined in step S1011 that the number of removed patches is equal to or greater than the threshold value, the process advances to step S1012, where the CPU 103 displays a UI indicating that the correction has been canceled on the display device 110, and cancels the correction process.

An example of the UI is shown in FIG. The UI 1101 is displayed on the display device 110 including a message 1102. This makes it possible to notify the user that the process has been interrupted and the cause thereof. As a result, since the chart used cannot correct the signal difference between the two reading devices, it is possible to prompt the user to prepare a chart with a lower number of lines, for example.

As described above, the image forming apparatus according to the present embodiment stops the color conversion parameter correction process when the number of patches removed due to the occurrence of moiré exceeds a predetermined threshold. Further, according to the present embodiment, a user interface notifying the user to that effect is displayed. As a result, if there are many patches in which moiré has occurred, correction processing is interrupted and the cause is indicated to the user, thereby making it possible to prevent creation of correction data with low accuracy.

<Other embodiments>
The present invention provides a system or device with a program that implements one or more of the functions of the embodiments described above via a network or a storage medium, and one or more processors in the computer of the system or device reads and executes the program. This can also be achieved by processing. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

The invention is not limited to the embodiments described above, and various changes and modifications can be made without departing from the spirit and scope of the invention. Therefore, the following claims are hereby appended to disclose the scope of the invention.

101: MFP, 102: Controller, 103: CPU, 104: Interpreter, 105: Intermediate language data, 106: Renderer, 107: Raster image data, 108: Image processing unit, 109: Scan image data, 110: Display device, 111 : Scanner, 112: Input device, 113: Storage device, 114: Printer, 115: Paper feed section, 116: CPU, 117: Paper ejection section, 118: Network I/F, 119: Network, 120: PC, 121: CPU, 122: Driver, 123: SFP, 124: Controller, 125: Printer, 126: Display device, 127: Input device, 128: Storage device

Claims (14)

An image forming apparatus,
a first reading device for reading the surface of the document;
a second reading device for reading the back side of the original at a resolution lower than the resolution at which the first reading device reads the front side of the original;
Using each of the first reading device and the second reading device to read a forming surface of a sheet on which a chart is formed, and obtaining a difference in feature amount of the read signal of the chart read by each reading device. means and
moire determining means for determining whether or not moire has occurred in the chart according to a difference in the feature amount of the read signal of the chart acquired by the acquiring means;
The present invention is characterized by comprising a correction means for correcting a color conversion parameter used to read a document and generate image data by the first reading device or the second reading device according to the judgment result by the moire judgment means. Image forming device. the chart is formed into a sheet including a plurality of patches;
The correction means is
Using each of the first reading device and the second reading device, a color conversion process was performed on the read signal of each patch when the forming surface of the sheet was read, and color conversion process was performed for each patch. Obtain the average value of each subsequent read signal,
Obtaining the difference between the average values by each reading device for each patch,
The image forming apparatus according to claim 1, wherein the color conversion parameter is corrected so as to eliminate the difference obtained for each patch. The correction means is
The read signal of the patch determined to have moire by the moire determining means is removed, the read signal of the removed patch is interpolated using the read signal of the patch without moire, and then the color The image forming apparatus according to claim 1 or 2, wherein the image forming apparatus corrects a conversion parameter. 4. The image forming apparatus according to claim 3, further comprising display means for displaying a user interface that notifies the user when the read signal of the patch has been removed. The correction means is
5. The image forming apparatus according to claim 4, wherein the correction of the color conversion parameter is stopped when the number of patches from which the read signal has been removed exceeds a predetermined threshold. 6. The image forming apparatus according to claim 5, wherein the display means displays a user interface that notifies you when the correction of the color conversion parameter is stopped by the correction means. image processing means for performing color conversion processing on a read signal obtained when a document is read using the first reading device or the second reading device, using the color conversion parameter corrected by the correction means;
The image forming apparatus according to any one of claims 1 to 6, further comprising an image forming unit that forms an image on a sheet using the read signal processed by the image processing unit. 8. The image forming apparatus according to claim 1, wherein the feature amount is a dispersion value in a read signal for each patch. 8. The image forming apparatus according to claim 1, wherein the feature amount is a frequency characteristic of a read signal for each patch. 10. The image forming apparatus according to claim 1, wherein the first reading device reads one side of the original, and the second reading device reads the other side of the original. The first reading device is provided inside the document table, and reads the surface of the document on the document table;
The image forming apparatus according to any one of claims 1 to 10, wherein the second reading device reads the back side of the original. 12. The image forming apparatus according to claim 1, wherein the chart is formed on the sheet by an external device different from the image forming apparatus. Image formation comprising: a first reading device for reading the front side of the original; and a second reading device for reading the back side of the original at a resolution lower than the resolution when the first reading device reads the front side of the original. A method for controlling a device, the method comprising:
The acquisition means uses each of the first reading device and the second reading device to read the forming surface of the sheet on which the chart is formed, and obtains the feature amount of the read signal of the chart read by each reading device. an acquisition step of acquiring the difference;
a moire determining step in which the moire determining means determines whether moire has occurred in the chart according to the difference in the feature amount of the read signal of the chart acquired in the acquiring step;
The correction means includes a correction step of correcting a color conversion parameter used for reading a document and generating image data with the first reading device or the second reading device, according to the determination result of the moiré determination step. A method for controlling an image forming apparatus, characterized in that: Image formation comprising: a first reading device for reading the front side of the original; and a second reading device for reading the back side of the original at a resolution lower than the resolution when the first reading device reads the front side of the original. A program for causing a computer to execute each step in a method for controlling an apparatus, the control method comprising:
The acquisition means uses each of the first reading device and the second reading device to read the forming surface of the sheet on which the chart is formed, and obtains the feature amount of the read signal of the chart read by each reading device. an acquisition step of acquiring the difference;
a moire determining step in which the moire determining means determines whether moire has occurred in the chart according to the difference in the feature amount of the read signal of the chart acquired in the acquiring step;
The correction means includes a correction step of correcting a color conversion parameter used for reading a document and generating image data with the first reading device or the second reading device, according to the determination result of the moiré determination step. A program featuring.

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