Image forming apparatus

Abstract

To appropriately monitor color tones without using color patches.SOLUTION: An image forming apparatus comprises an image forming unit and performs color correction of the image forming unit by using image data for correction. The image forming apparatus comprises: a reading unit that reads an image on a sheet formed by the image forming unit on the basis of image data for image formation different from the image data for correction; and a color tone monitoring unit that performs first monitoring processing of comparing a value based on read image data of the first sheet on which an image is formed with a value based on read image data of the n-th sheet on which an image is formed and monitoring a color tone difference on the basis of a monitoring target, and second monitoring processing of comparing values based on read image data of a plurality of sheets on which images are formed in a constant period and monitoring a color tone difference on the basis of the monitoring target. The image forming apparatus performs first color correction of performing color correction on the basis of a comparison result of comparing the color tone difference with a predetermined threshold, and second color correction of performing color correction for every constant period or every constant number of sheets on which images are formed.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus that monitors color tones during image formation. [Background technology]

[0002] There are image forming apparatuses that have a reading unit, such as an inline sensor, connected downstream of the image forming unit that forms an image on paper, and that read the image on the paper. There are also image forming systems that have a reading device (output reading device) connected downstream of the image forming apparatus that forms an image on paper, and that read the image on the paper with the reading device.

[0003] In such image forming devices and image forming systems, predetermined patch images (correction images) are formed on paper periodically, and by reading the patch images on the paper, it becomes possible to detect and correct (calibrate) color variations (color tone differences) in the image forming device.

[0004] However, forming the patch image on paper causes problems such as paper consumption for forming the patch image and a decrease in productivity of normal image formation due to outputting the paper on which the patch image is formed. To prevent this paper waste and productivity loss, a method has been proposed in which image data for image formation is compared with scanned image data of the output on a pixel-by-pixel basis during normal image formation. This method is expected to reduce paper waste and prevent productivity loss because patch images are not formed on paper.

[0005] As for this type of technology, various related proposals have been made in the following patent documents. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-182353 Summary of the Invention [Problem to be solved by the invention]

[0007] An object of the present invention is to realize an image forming apparatus that can appropriately monitor color tones without using color patches or the like. [Means for solving the problem]

[0008] An image forming apparatus that reflects one aspect of the present invention is an image forming apparatus that has an image forming unit and performs color correction of the image forming unit using correction image data, and is equipped with a reading unit that reads an image on a sheet of paper formed by the image forming unit based on image data for image formation that is different from the correction image data, and a color tone monitoring unit that performs a first monitoring process that compares a value based on the read image data of the first sheet of paper on which an image based on the image formation image data is formed with a value based on the read image data of the nth sheet of paper on which an image based on the image formation image data is formed, and monitors the color tone difference based on a monitoring target for monitoring the color tone difference, and a second monitoring process that compares values ​​based on the read image data of multiple sheets of paper on which images are formed based on the image formation image data over a certain period of time, and monitors the color tone difference based on a monitoring target for monitoring the color tone difference, and performs a first color correction that performs color correction of the image forming unit based on the comparison result of comparing the color tone difference with a predetermined threshold, and a second color correction that performs color correction of the image forming unit over a certain period of time or for every certain number of images formed. [Effects of the Invention]

[0009] According to the present invention, it is possible to appropriately monitor color tones without using color patches or the like. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a configuration diagram showing a configuration of an embodiment of the present invention. [Figure 2] 1 is a configuration diagram showing a configuration of an embodiment of the present invention. [Figure 3] FIG. 2 is an explanatory diagram illustrating processing blocks according to an embodiment of the present invention. [Figure 4] 3 is a flowchart illustrating the operation of an embodiment of the present invention. [Figure 5] FIG. 2 is an explanatory diagram illustrating a processing state according to an embodiment of the present invention. [Figure 6] FIG. 2 is an explanatory diagram illustrating a processing state according to an embodiment of the present invention. [Figure 7] FIG. 2 is an explanatory diagram illustrating a processing state according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, with reference to the drawings, an embodiment of an image forming apparatus capable of analyzing color reproduction without being affected by unstable factors and without using color patches or the like will be described in detail. [Configuration of Image Forming Apparatus] An example of the configuration of image forming apparatus 100 will be described in detail with reference to Fig. 1 and Fig. 2. Fig. 1 is a functional block diagram showing the functions of each unit of image forming apparatus 100, and Fig. 2 is an explanatory diagram showing the mechanical components of each unit of image forming apparatus 100.

[0012] The image forming apparatus 100 is connected to a PC 20 serving as an information processing terminal via a network 30. The PC 20 creates original image data (printing data other than raster images) written in the PDL language and transmits it to the image forming apparatus 100 via the network 30. Here, the image forming apparatus 100 comprises a control unit 101 that controls each unit within the image forming apparatus 100, a communication unit 102 for communicating with other connected devices, an operation display unit 103 that displays operation inputs by a user and the status of the image forming apparatus 100, a storage unit 104 that stores various settings, a paper feed unit 105 that can feed paper stored in a paper feed tray, a transport unit 107 that transports paper within the apparatus, a printer controller 110 that RIPs original image data described in PDL from the PC 20 to create image data for image formation, and a monitor 116 that monitors color tone differences at corresponding positions between the image data for image formation and the read image data by referring to the original image data. The image forming apparatus is configured to include a monitoring setting unit 115 that sets a monitoring setting color and an ideal value of the monitoring setting color, a document reading unit 120 that reads a document, an image data storage unit 130 that stores image data and various data used in image formation, an image processing unit 140 that performs various image processing required for image formation, an image forming unit 150 that forms an image on paper based on an image formation command and image data, a fixing unit 160 that stabilizes the toner image formed on the paper with heat and pressure, a color tone monitoring unit 180 that compares pixel values ​​in the image data for image formation and the read image data to analyze color reproduction, and an output reading unit 190 that reads the image formed on the paper.

[0013] 2, the image forming unit 150 is a so-called electrophotographic image forming unit in which an electrostatic latent image formed on a charged image carrier is developed into a toner image, and the toner images of each color are superimposed on an intermediate transfer body and then transferred to paper. However, the specific configuration of the image forming unit 150 is not limited to that shown in FIG.

[0014] The output reading unit 190 reads the image formed on the paper, and is arranged downstream of the image forming unit 150 and the fixing unit 160, so that the image is read while the paper is being transported. The output reading unit 190 may be arranged in an intermediate processing device or post-processing device (not shown) connected to the downstream of the image forming apparatus 100.

[0015] [Control and setting of each part of the image forming apparatus] The color materials used for image formation in the image forming unit 150 are cyan C, magenta M, yellow Y, and black K. In this embodiment, color tone refers to a color system categorized by color brightness and saturation. In the following description, L*a*b* will simply be abbreviated as Lab.

[0016] The printer controller 110 constitutes a raster image processing section that converts original image data other than a raster image into image data for forming a raster image. The monitoring setting unit 115 sets the monitoring setting colors to include at least one of the following: a single primary color (C, M, Y, K) of the CMYK color materials used in image formation; a secondary color (R, G, B) made by combining any two of the primary colors; a tertiary color (skin color, etc.) made by combining three chromatic primary colors in a predetermined ratio; and a tertiary achromatic color (gray) made by combining three chromatic primary colors (C, M, Y) in a predetermined ratio.

[0017] It should be noted that the tertiary color such as skin color is not limited to the skin color of a specific ethnic group, but can be any skin color contained in images in the country or region where it is used. The monitoring setting unit 115 references the original image data and sets a monitoring setting color and an ideal value of the monitoring setting color when monitoring the color tone difference at corresponding positions between the image data for image formation and the scanned image data. The monitoring setting unit 115 also references the original image data and sets a monitoring setting color in a low-frequency region of spatial frequency that does not include text data. Here, the low-frequency region of spatial frequency refers to an area in an image that does not have contours or patterns and is filled with a constant color, and the specific spatial frequency can be determined arbitrarily by the image forming device manufacturer or user.

[0018] The monitoring setting unit 115 can set multiple different colors as the monitoring setting color. The monitoring setting unit 115 converts the original image data based on an ICC profile or a multidimensional LUT to set an ideal value as the monitoring setting color. The monitoring setting unit 115 sets a loose threshold or a strict threshold depending on the setting status of the monitoring setting color, i.e., whether the monitoring setting color is loose or strict. The monitoring setting unit 115 sets an appropriate threshold depending on the type of monitoring setting color. The monitoring setting unit 115 sets the monitoring setting color using the average value of colors extracted from multiple locations on the image.

[0019] The monitoring and setting unit 115 can also set the ideal value based on scanned image data obtained by scanning paper on which an image is formed based on the image data for image formation or on multiple average values ​​of the scanned image data, rather than on the original image data. The color tone monitoring unit 180 monitors the color tone difference between the value of the scanned image data of the monitored color and the ideal value at corresponding positions in the image data for image formation and the scanned image data. The color tone monitoring unit 180 monitors the color tone difference using at least one of the absolute value of the color tone difference due to changes over time or the degree of change in the color tone difference as a threshold value.

[0020] When a tertiary achromatic color is selected as the monitoring setting color, the color tone monitoring unit 180 monitors changes in hue as color tone differences. Furthermore, when a tertiary color is selected as the monitoring setting color, the color tone monitoring unit 180 determines the color in the face area recognized by face recognition processing as the tertiary color, and monitors changes in the saturation of the tertiary color as color tone differences. At this time, the image processing unit 140 executes image processing such as face recognition processing.

[0021] The color tone monitoring unit 180 monitors the color tone difference at a corresponding position in the read image data for one setting of the monitor setting color. When a spot color other than the color of the basic color material used in image formation is set as a monitoring setting color, the color tone monitoring unit 180 monitors the color tone difference of the spot color in an area containing only the spot color and no other colors. Furthermore, when the color tone difference detected by the color tone monitoring unit 180 is equal to or greater than a predetermined threshold, the control unit 101 controls the image forming unit 150 to perform color correction.

[0022] The control unit 101 performs color correction by adjusting the image forming unit 150 using read correction image data obtained by reading a sheet of paper on which a correction image has been formed in the margins of the sheet. Furthermore, the control unit 101 performs color correction of the image forming unit 150 at regular intervals or after a certain number of images have been formed, even if the color difference does not reach the threshold. Furthermore, the control unit 101 performs color correction of the image forming unit 150 at regular intervals or after a certain number of images have been formed, even if the monitor setting color does not appear.

[0023] [Operation] The operation of the image forming apparatus of this embodiment will be described below with reference to the drawings. Fig. 3 is a processing block diagram showing the data flow when color tone monitoring of this embodiment is performed. Fig. 4 is a flowchart when color tone monitoring of this embodiment is performed.

[0024] Original image data (printing data other than raster images) written in PDL language is created by the user on PC 20 (step S101 in FIGS. 3 and 4). This original image data in PDL language format is supplied to the image forming device via network 30. The user operates operation display unit 103 to instruct printer controller 110 to form an image of the original image data. Upon receiving this instruction from the user, printer controller 110 performs RIP processing on the original image data before RIP, which is described in a page description language, to generate image data (image data for image formation) for image formation in image forming unit 150 (step S102 in FIGS. 3 and 4). Then, printer controller 110 stores this image data for image formation in image data storage unit 130, and supplies it to image processing unit 140 and image forming unit 150 as necessary.

[0025] The image forming unit 150 executes image formation using the image data for image formation from the printer controller 110, forms an image on paper, and outputs a printout (step S103 in FIGS. 3 and 4). In this embodiment, the paper on which the image is formed by the image forming unit 150 is referred to as a "printout." This printout is read by the output reading unit 190 or the document reading unit 120, and read image data is generated (step S104 in FIGS. 3 and 4). The output reading unit 190 or the document reading unit 120 temporarily stores the read image data generated by reading the printout in the image data storage unit 130, and supplies it to the image processing unit 140, etc., as necessary.

[0026] The monitoring setting unit 115 refers to the original image data and sets a monitoring setting color when monitoring the color tone difference at corresponding positions between the image data for image formation and the read image data, and an ideal value of the monitoring setting color (step S105 in Figures 3 and 4). Here, the monitoring setting unit 115 refers to the input original image data and sets the monitoring setting color to include at least one of the following colors: a single primary color (C, M, Y, K) of the CMYK color materials used in image formation; a secondary color (R, G, B) combining any two of the primary colors; a tertiary color (skin color, etc. (hereinafter, specific tertiary color)) combining three chromatic primary colors in a predetermined ratio; and a tertiary achromatic color (gray) combining three chromatic primary colors (C, M, Y) in a predetermined ratio.

[0027] Tertiary achromatic colors are sensitive to changes in hue (chromaticity), and when a change occurs, it is easy to confirm which CMY color has changed. In other words, by monitoring the hue differences of tertiary achromatic colors, it is possible to grasp the fluctuations in CMY, and this can be fed back to correct CMY in the image forming unit 150. Primary colors (CMY or CMYK) and secondary colors (RGB) are useful for monitoring the highest density areas. Specific tertiary colors, such as skin tones, are sensitive to changes in hue and saturation, and it is easy to confirm changes in hue and saturation.

[0028] Additionally, the ideal value of the set monitor setting color is set in one of the following three ways. First, the monitor setting color (CMYK) is converted based on an ICC profile or multidimensional LUT and set as the ideal Lab or RGB value. Second, the actual measurement value (scanned image data: RGB) of the first printed item on which the monitor setting color appears is set as the ideal value. Third, the average value of the actual measurement values ​​(scanned image data: RGB) of the first few printed items on which the monitor setting color appears is set as the ideal value.

[0029] In order to reduce the influence of errors, the monitor setting unit 115 references the original image data and sets a monitor setting color in a low-frequency region of spatial frequency that does not include text data. In addition, the monitoring setting unit 115 can set the ideal value not based on the original image data (solid line in Figure 3) but also based on the read image data obtained by reading paper on which an image is formed based on the image data for image formation or on multiple average values ​​of the read image data (dashed line in Figure 3).

[0030] In addition, multiple different colors can be set as the monitoring setting color. Furthermore, the original image data is converted based on an ICC profile or multidimensional LUT to set an ideal value as the monitoring setting color. Furthermore, depending on the monitoring setting color setting status, a loose or strict threshold is set according to the loose or strict setting of the monitoring setting color. Furthermore, an appropriate threshold is set according to the type of monitoring setting color. Furthermore, the monitoring setting color is set using the average value of colors extracted from multiple locations on the image.

[0031] Here, the image processing unit 140 converts the image data for image formation and the scanned image data into data in a unified format that can be compared (step S106 in FIGS. 3 and 4). The image data for image formation is CMYK bitmap data, and the scanned image data is RGB bitmap data, so they cannot be compared as is. Therefore, the image processing unit 140 performs image processing to unify the data formats of the image data for image formation and the scanned image data into RGB bitmap data, Lab data, etc. In FIG. 3, "image data for image formation'" and "scanned image data'" refer to data in a consistent data format.

[0032] The color tone monitoring unit 180 monitors the color tone difference between the value of the read image data of the monitor set color and the ideal value at corresponding positions in the image data for image formation and the read image data for the monitor set color (step S107 in Figures 3 and 4). That is, the color tone monitoring unit 180 first extracts pixels in the area belonging to the set monitor color by referencing the image data for image formation and the scanned image data. To explain this in more detail, when a pixel of interest in the image data for image formation matches the setting conditions for the monitor color, the color tone monitoring unit 180 extracts the pixel of interest from the image data for image formation, and extracts a pixel in the scanned image data that is at the same position as the pixel of interest as a corresponding pixel. The corresponding pixel in the scanned image data is then compared with the ideal value of the monitor color to extract the color tone difference between the two.

[0033] The timing for monitoring the color difference is as follows: when analysis of one page of image is completed, the color difference between the scanned image data (actual measured value) of the extracted monitoring setting color and its ideal value is calculated. If the ideal value is set as an RGB value, the difference between the RGB value of the scanned image data obtained from the scanned image is compared, and if the difference is greater than or equal to a threshold, color correction is performed. If the ideal value is set as an Lab value, the RGB value of the scanned image data obtained from the scanned image is converted to Lab values ​​based on the scanner profile or multidimensional LUT, and then compared. If the difference is greater than or equal to a threshold, color correction is performed.

[0034] The color tone monitoring unit 180 monitors color tone differences using at least one of the absolute value of color tone differences due to changes over time or the degree of change in color tone difference as a threshold. When a tertiary achromatic color is selected as the monitoring setting color, the color tone monitoring unit 180 monitors changes in hue as color tone differences. When a specific tertiary color such as skin color is selected as the monitoring setting color, the color tone monitoring unit 180 defines the color within a face area recognized by face recognition processing as the specific tertiary color and monitors changes in hue and saturation of the specific tertiary color as color tone differences. In this case, the image processing unit 140 simply performs image processing such as face recognition processing to extract the above-mentioned target pixel and corresponding pixel. The color tone monitoring unit 180 monitors color tone differences at a corresponding position in the scanned image data for one setting of the monitoring setting color. When a spot color other than the color of the basic color material used in image formation is set as a monitoring setting color, the color tone monitoring unit 180 monitors the color tone difference for that spot color in an area that contains only the spot color and no other colors.

[0035] Specific examples of color tone monitoring will be described below. Here, absolute color tone monitoring and relative color tone monitoring will be described. [Example of absolute color monitoring] Image data for image formation (CMYK) → Profile → Ideal value RGB, Image data for image formation (CMYK) → Printed material reading → Actual measured value RGB, In this case, the ideal RGB values ​​are compared with the actually measured RGB values ​​to monitor the color tone difference, and when this color tone difference exceeds a predetermined threshold value, color correction, which will be described later, is performed.

[0036] [Example of relative color monitoring] · First printout; Image data for image formation #1 (CMYK) → Printed matter #1 → Printed matter #1 reading (RGB) → Ideal value Lab #1, · nth printed page (n=2,3,4,…); Image data for image formation #n (CMYK) → Printed matter #n → Printed matter #n reading (RGB) → Actual measurement value Lab #n, In this case, based on the ideal value Lab#1 generated from the measured value, the ideal value Lab#1 and the measured value Lab#n are compared, and the color tone difference for each n is monitored. When this color tone difference becomes equal to or greater than a predetermined threshold value, color correction described later is executed.

[0037] Regarding the monitoring of the color tone difference by the color tone monitoring unit 180, when the color tone difference (absolute value) ΔE simply becomes equal to or greater than a predetermined threshold value Th1 at a certain point, it is determined that the color tone monitoring result = color tone difference threshold value or more. In FIG. 5, in the part (a1), ΔE ≧ Th1. Regarding the monitoring of the color tone difference by the color tone monitoring unit 180, the color tone difference (absolute value) ΔE due to the change over time is sampled and integrated. When the color tone difference integral value ∫ΔE becomes equal to or greater than a predetermined threshold value Th2, it is determined that the color tone monitoring result = color tone difference threshold value or more. In FIG. 6, in the part (a2), ΔE ≧ Th2. In this case, even if the color tone difference ΔE itself has not reached the above-described threshold value Th1, if a certain color tone difference continues over a certain period, the necessity of executing color correction can be determined by the color tone difference integral value ∫ΔE.

[0038] Regarding the monitoring of the color tone difference by the color tone monitoring unit 180, the degree of change in the sudden color tone difference, that is, the color tone difference for each printed sheet is monitored. When the color tone difference (relative value) δE for each sheet becomes equal to or greater than a predetermined change threshold value thδ, it is determined that the color tone monitoring result = color tone difference threshold value or more. In FIG. 7, in the part (b), the color tone difference (absolute value) ΔE < Th1, but the color tone difference (relative value) δE ≧ thδ.

[0039] That is, as described above, there are three types of cases where "the color tone difference becomes equal to or greater than a predetermined threshold value". Regarding the monitoring of these color tone differences, any one of these monitoring methods such as simple color tone monitoring over time, monitoring of the color tone difference integral value over time, and sudden color tone monitoring may be used, but it is desirable to perform multiple monitoring methods. When performing multiple monitoring methods, if it is determined that even one of them is equal to or greater than the threshold value, it is desirable to proceed to execute color correction.

[0040] When the color tone difference is equal to or greater than a predetermined threshold value as a result of monitoring by color tone monitoring unit 180 (YES in S108 in FIG. 3 and step S108 in FIG. 4), control unit 101 controls image forming unit 150 to perform color correction (step S109 in FIGS. 3 and 4). That is, control unit 101 performs color correction by adjusting image forming unit 150 using read correction image data obtained by reading a sheet of paper on which a correction image has been formed in the margin of the sheet.

[0041] Then, the control unit 101 repeatedly executes the above process for all images on all sheets of paper on which images are to be formed as a series of jobs (step S110 in FIG. 4). However, it can be arbitrarily determined whether the above color tone monitoring process is executed for every single sheet of paper or every few sheets. Note that in the above embodiment, since there is no need to use a color patch or the like in color tone monitoring, productivity will not be reduced even if it is executed for every single sheet of paper on which an image is to be formed.

[0042] [Other actions (1)] Image data for image formation obtained through RIP processing may contain a certain range of perfectly matched secondary colors and tertiary achromatic colors mixed in by color management. Therefore, when processing in an actual product, it is desirable to set a threshold value that allows for color mixing in the monitoring setting colors within a range that does not affect color tone monitoring.

[0043] For example, when extracting a tertiary achromatic color (gray) as the monitoring color, if the signal values ​​of each of the YMC colors are set to 256 levels from 0 to 255, and the difference between the CMY signal values ​​is less than 3, such as (CM<±3) and (MY<±3) and (YC<±3), it is desirable to extract the color as a tertiary achromatic color. Here, the 256 levels of signal values ​​and the signal value difference of 3 are just examples, and any numerical value can be set. Note that when a certain amount of color mixing is recognized in the monitoring color, it is desirable to set a slightly looser threshold for the color tone difference in color tone monitoring, taking color mixing into consideration.

[0044] Furthermore, the tertiary achromatic color (gray) in the above embodiments does not mean a gray made only from K. Therefore, even if a gray is made by mixing K in addition to CMY, it is treated as a tertiary achromatic color. [Other actions (2)] Users use a variety of images, and it is possible that the color they want to extract may not appear as a monitored color. In this case, they can collect data over a wider range by widening the threshold (width) for extraction. However, if the threshold for extraction is widened using this method, it is desirable to lower the threshold level at which a color tone difference is detected. Furthermore, if such a measure is taken, it is desirable to notify the user via the operation display unit 103.

[0045] [Specific Example (3)] When monitoring the hue of the monitor set color for scanned image data, the target image of the scanned image data can be divided into multiple M x N areas, the average value of the monitor set color extracted from each of the multiple areas is calculated, and this average value is compared with the ideal value for monitoring. In this way, it is possible to monitor the color tone difference across the entire printed surface.

[0046] [Specific Example (4)] When monitoring the tone of the monitor set color for the scanned image data, it is also desirable to divide the target image of the scanned image data into multiple M x N areas, and perform tone monitoring of the monitor set color for the ideal value generated for each corresponding area and the pixels of the scanned image data included in the same area as the area to which the ideal value belongs. By doing so, it is possible to perform tone monitoring while eliminating the influence of in-page unevenness, which causes different densities at the center and edges of the paper.

[0047] [Specific Example (5)] It is desirable that the control unit 101 executes color correction of the image forming unit 150 at regular intervals or after a certain number of images are formed, even if the color tone difference does not reach the threshold. Here, if the monitored set color is any of a primary color (CMYK), a secondary color (RGB), a specific tertiary color such as skin color, or a tertiary achromatic color, and the monitored color tone difference is equal to or less than the threshold, it is desirable to feed back to the gamma correction the difference between the actual measurement data and its ideal value data.

[0048] [Example (6)] It is desirable that the control unit 101 executes color correction of the image forming unit 150 at regular intervals or after a certain number of image formations, even if the state in which the monitored setting color does not appear continues across multiple sheets of paper.

[0049] [Specific Example (7)] When a spot color other than the colors of the basic color materials used in image formation is used, the color tone monitoring unit 180 can also set this spot color as a monitoring set color. When a spot color is set as a monitoring set color in this way, it is desirable to monitor the color tone difference of the spot color in an area that contains only the spot color and no other colors.

[0050] For example, if the fifth color other than CMYK used in image formation is red (R), fluctuations in the fifth color can be monitored by monitoring the area consisting only of red R, which does not contain CMYK. Furthermore, if the fifth color is a transparent color (clear), an area including the clear color is excluded from the monitoring target for that monitoring color even if it matches another monitoring setting color, in order to eliminate the influence of the clear color in the scanned image data.

[0051] [Other embodiment (1)] 1 shows a state in which the printer controller 110 is built in the image forming apparatus 100, but the present invention is not limited to this. That is, the printer controller 110 may be located outside the image forming apparatus 100, and the image forming apparatus 100 may receive RIP-processed image data for image formation from the outside.

[0052] [Another embodiment (2)] In the above image forming apparatus 100, an example has been shown in which the printer controller 110 and the monitoring setting unit 115 are separate, but this is not limiting. Since both the printer controller 110 and the monitoring setting unit 115 refer to the original image data, the printer controller 110 may be configured to include the monitoring setting unit 115.

[0053] [Other embodiment (3)] The image forming apparatus 100 described above has a built-in color tone monitoring unit 180. However, it is also possible to configure a color tone monitoring device having the monitoring setting unit 115 and the color tone monitoring unit 180 outside the image forming apparatus 100. In this case, the monitoring results from the color tone monitoring device are transmitted to the image forming apparatus 100, and color correction is performed in the image forming apparatus. [Explanation of symbols]

[0054] 100 Image forming device 102 Communications Department 103 Operation display section 104 Storage section 105 Paper feed section 107 Conveyor 110 Printer Controller 115 Monitoring Settings 120 Document reading unit 130 Image data storage unit 140 Image processing section 150 Image forming unit 160 Fixing unit 180 Color tone monitoring section 190 Output reading unit

Claims

[Claim 1] An image forming apparatus including an image forming unit, the image forming unit performing color correction using correction image data, a reading unit that reads an image on a sheet formed by the image forming unit based on image data for image formation that is different from the image data for correction; a color tone monitoring unit that performs a first monitoring process that compares a value based on the read image data of a first sheet of paper on which an image based on the image formation image data has been formed with a value based on the read image data of an nth sheet of paper on which an image based on the image formation image data has been formed, and monitors color tone differences based on a monitoring target for monitoring color tone differences; and a second monitoring process that compares values ​​based on the read image data of a plurality of sheets of paper on which images have been formed based on the image formation image data over a certain period of time, and monitors color tone differences based on a monitoring target for monitoring color tone differences, A first color correction is performed to perform color correction of the image forming unit based on a comparison result obtained by comparing the color tone difference with a predetermined threshold value, and a second color correction is performed to perform color correction of the image forming unit at a predetermined interval or after a predetermined number of images are formed. An image forming apparatus characterized by:

Images