JP7243771B2 - Image forming apparatus and image forming method - Google Patents

Description

The present invention relates to an image forming apparatus and an image forming method for monitoring color tone during image formation.

2. Description of the Related Art There is an image forming apparatus that reads an image formed on a sheet by connecting a reading section including an in-line sensor or the like to the downstream side of an image forming section that forms an image on the sheet. In addition, there is an image forming system in which a reading device (output reading device) is connected to the rear stage of an image forming device that forms an image on a sheet, and the reading device reads the image formed on the sheet.

In such image forming apparatuses and image forming systems, predetermined patch images (correction images) are periodically formed on a sheet of paper, and the patch images on the sheet of paper are read to detect color fluctuations of the image forming apparatus. It is possible to detect (color tone difference) and correct (calibrate).

However, in relation to forming the patch image on paper, there arise problems such as consumption of paper for forming the patch image and a decrease in productivity of normal image formation due to the output of the paper on which the patch image is formed.
Therefore, in order to suppress such waste of paper and decrease in productivity, a technique has been proposed in which image data for image formation and read image data of an output product are compared pixel by pixel during normal image formation. According to this method, since patch images are not formed on paper, it is expected that paper waste can be reduced and productivity can be suppressed.

As this type of technology, various related proposals have been made in the following patent documents.

JP 2014-182353 A

SUMMARY OF THE INVENTION An object of the present invention is to realize an image forming apparatus capable of appropriately monitoring color tones without using color patches or the like.

An image forming apparatus to which one aspect of the present invention is reflected is an image forming apparatus that includes an image forming unit, performs color correction of the image forming unit using correction image data, and performs color correction by the image forming unit. a reading unit for reading an image on a sheet formed based on image forming image data different from the image data for image formation, a setting unit for setting colors for monitoring color tone differences, and the sheet read by the reading unit a color tone monitoring unit that compares a value based on the read image data of and a value based on the read image data of a sheet on which an image is formed after the read sheet, and monitors a color tone difference of the set color ; Prepare.
An image forming method according to one aspect of the present invention includes the steps of: forming an image on a sheet based on image forming image data different from correcting image data used for color correction in an image forming unit; a step of reading an image on a sheet of paper on which an image is formed based on the image data for use by a reading unit ; a step of setting a color for monitoring a color tone difference; and comparing the value based on the value based on the read image data of the sheet on which the image was formed after the read sheet, and monitoring the tone difference of the set color .

According to the present invention, it is possible to appropriately monitor color tones without using color patches or the like.

1 is a configuration diagram showing the configuration of an embodiment of the present invention; FIG. 1 is a configuration diagram showing the configuration of an embodiment of the present invention; FIG. It is an explanatory view showing a processing block of an embodiment of the present invention. It is a flow chart which shows the operation of the embodiment of the present invention. FIG. 4 is an explanatory diagram showing how processing is performed according to the embodiment of the present invention; FIG. 4 is an explanatory diagram showing how processing is performed according to the embodiment of the present invention; FIG. 4 is an explanatory diagram showing how processing is performed according to the embodiment of the present invention;

Hereinafter, embodiments of an image forming apparatus capable of analyzing color reproduction without being affected by unstable factors and without using color patches will be described in detail with reference to the drawings.
[Configuration of Image Forming Apparatus]
A configuration example of the image forming apparatus 100 will be described in detail with reference to FIGS. 1 and 2. FIG. 1 is a functional block diagram showing the function of each section of the image forming apparatus 100, and FIG. 2 is an explanatory diagram showing mechanical components of each section of the image forming apparatus 100. As shown in FIG.

Image forming apparatus 100 is connected to PC 20 as an information processing terminal via network 30 . The PC 20 creates original image data (data for printing other than raster images) written in the PDL language, and transmits the data to the image forming apparatus 100 via the network 30 .
Here, the image forming apparatus 100 includes a control unit 101 that controls each unit in the image forming apparatus 100, a communication unit 102 that communicates with other connected devices, and an operation input by a user and the image forming apparatus. a storage unit 104 for storing various settings; a paper feed unit 105 capable of feeding paper accommodated in a paper feed tray; a printer controller 110 which RIP-processes original image data written in PDL from the PC 20 into image forming image data; A monitoring setting unit 115 for setting a monitoring setting color and an ideal value of the monitoring setting color when monitoring a color tone difference at a corresponding position; An image data storage unit 130 for storing data, an image processing unit 140 for executing various image processing necessary for image formation, and an image forming unit 150 for forming an image on paper based on an image forming command and image data. a fixing unit 160 for stabilizing a toner image formed on a sheet of paper with heat and pressure; and a color tone monitoring unit 180 for analyzing color reproduction by comparing pixel values between image data for image formation and read image data. , and an output reading unit 190 for reading an image formed on a sheet.

In the image forming unit 150, as shown in FIG. 2, 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 the intermediate transfer member. This is a so-called electrophotographic image forming unit in which the image is transferred to the paper after the image is formed. However, the specific configuration of the image forming section 150 is not limited to that shown in FIG.

Further, the output reading section 190 reads an image formed on the paper, is arranged downstream of the image forming section 150 and the fixing section 160, and is configured to read the image while the paper is being conveyed. there is Note that the output article reading unit 190 may be arranged in an intermediate processing device or post-processing device (not shown) connected to the rear stage of the image forming apparatus 100 .

[Control and setting of each part of the image forming apparatus]
Assume that cyan C, magenta M, yellow Y, and black K are color materials used for image formation in the image forming unit 150 . Further, in the present embodiment, the color tone refers to a system of colors divided by the lightness and saturation of the color. In the following description, L*a*b* is simply written as Lab.

The printer controller 110 constitutes a raster image processing section that converts original image data other than a raster image into raster image image forming image data.
The monitor setting unit 115 selects any single primary color (C, M, Y, K) of the CMYK color materials used for image formation, or a secondary color (R, G, B), a tertiary color (skin color, etc.) that is a combination of the three primary chromatic colors at a predetermined ratio, and a combination of the three primary chromatic colors (C, M, Y) at a predetermined ratio A monitor setting color is set to include at least one color of a tertiary achromatic color (gray).

Note that the tertiary color such as skin color is not limited to the skin color of a specific ethnic group, and may be any skin color included in the image in the country or region where the image is used.
The monitoring setting unit 115 refers to the original image data, and sets the monitoring setting color and the ideal value of the monitoring setting color when monitoring the color tone difference at the corresponding positions of the image data for image formation and the read image data. set. Also, the monitoring setting unit 115 refers to the original image data and sets the monitoring setting color in a low spatial frequency region that does not contain text data. Here, the low-frequency region of the spatial frequency means a region in which there is no contour or pattern in the image and is filled with a certain color. can be arbitrarily determined by the person or user.

In addition, the monitoring setting unit 115 can set a plurality of different colors as monitoring setting colors. Also, the monitor setting unit 115 converts the original image data based on an ICC profile or a multidimensional LUT to set ideal values as monitor setting colors. In addition, the monitoring setting unit 115 sets a loose threshold value and a strict threshold value depending on whether the monitoring setting color is set loosely or strictly according to the setting state of the monitoring setting color. Also, the monitor setting unit 115 sets a suitable threshold according to the type of monitor setting color. In addition, the monitoring setting unit 115 sets the monitoring setting color using an average value of colors extracted from a plurality of locations in the image.

In addition, the monitoring setting unit 115 sets the read image data obtained by reading the paper on which the image is formed based on the image data for image formation, not based on the original image data, or the average value of a plurality of read image data. It is also possible to set the ideal value based on The color tone monitoring unit 180 monitors the color tone difference between the value of the read image data of the monitor setting color and the ideal value at the corresponding positions of the image data for image formation and the read image data. Further, the color tone monitoring unit 180 monitors the color tone difference using at least one of the absolute value of the color tone difference and the degree of change of the color tone difference due to aging as a threshold value.

When the tertiary achromatic color is selected as the monitoring setting color, the color tone monitoring unit 180 monitors the hue change as a color tone difference. Further, when a tertiary color is selected as the monitoring setting color, the color tone monitoring unit 180 determines the color within the face region recognized by the face recognition process as the tertiary color, and determines the saturation of the tertiary color. Monitor changes as tonal differences. At this time, the image processing unit 140 executes image processing such as face recognition processing.

The color tone monitoring unit 180 monitors the color tone difference at one corresponding position of 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 for image formation is set as the monitoring setting color, the color tone monitoring unit 180 detects the color tone difference in an area containing only the spot color and not including other colors. Monitor. Further, the control unit 101 controls the image forming unit 150 to perform color correction when the color tone difference is equal to or greater than a predetermined threshold as monitored by the color tone monitoring unit 180 .

The control unit 101 performs color correction by adjusting the image forming unit 150 using the reading correction image data obtained by reading the paper on which the correction image is formed in the margin of the paper. Further, even if the color tone difference does not reach the threshold value, the control unit 101 performs color correction of the image forming unit 150 for a certain period of time or for each certain number of images formed. Further, the control unit 101 performs color correction of the image forming unit 150 for a certain period of time or for each certain number of images formed, even when the monitor setting color does not appear.

〔motion〕
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 flow of data when color tone monitoring is performed according to this embodiment. FIG. 4 is a flow chart for executing color tone monitoring according to this embodiment.

In the PC 20, the user creates original image data (data for printing other than raster images) written in the PDL language (step S101 in FIGS. 3 and 4). This PDL language format original image data is supplied to the image forming apparatus via the network 30 .
The user operates the operation display unit 103 to instruct the printer controller 110 to form the original image data. The printer controller 110 that has received this instruction from the user performs RIP processing on the original image data before RIP described in the page description language, and image data (image forming image for image formation) for forming an image in the image forming section 150 . data) is generated (step S102 in FIGS. 3 and 4). The printer controller 110 stores the image data for image formation in the image data storage unit 130, and supplies the image data to the image processing unit 140 and the image forming unit 150 as required.

The image forming section 150 performs image formation using the image data for image formation from the printer controller 110, forms an image on paper, and outputs a printed matter (step S103 in FIGS. 3 and 4). Note that, in this embodiment, a sheet of paper on which an image has been formed by the image forming section 150 will be referred to as a "printed matter." This printed matter 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 printed matter in the image data storage unit 130, and supplies the read image data to the image processing unit 140 or the like as necessary.

The monitoring setting unit 115 refers to the original image data, and sets the monitoring setting color and the ideal value of the monitoring setting color when monitoring the color tone difference at the corresponding positions of the image data for image formation and the read image data. Set (step S105 in FIGS. 3 and 4).
Here, the monitoring setting unit 115 refers to the input original image data, and selects one of the primary colors (C, M, Y, K) of the color materials C, M, Y, and K used for image formation. Secondary colors (R, G, B) that combine any two colors, tertiary colors that combine three primary colors at a predetermined ratio (skin color, etc. (hereinafter referred to as specific tertiary colors)), A monitoring setting color is set to include at least one color of a tertiary achromatic color (gray) obtained by combining three primary colors (C, M, Y) at a predetermined ratio.

Note that the tertiary achromatic color is sensitive to hue (chromaticity) change, and when it changes, it is easy to confirm which color of CMY has changed. In other words, by monitoring the color tone difference of the tertiary achromatic color, it is possible to grasp the CMY variation, and feed back the CMY correction in the image forming section 150 . Primary colors (CMY or CMYK), secondary colors (RGB) are useful for monitoring the highest density. A specific tertiary color such as skin color is sensitive to changes in hue and saturation, and it is easy to confirm changes in hue and saturation.

Also, the ideal value of the set monitor setting color is set by one of the following three types. First, monitor set colors (CMYK) are converted based on an ICC profile or multi-dimensional LUT and set as Lab or RGB ideal values. Second, the actual measurement values (read image data: RGB) of the first printed matter in which the monitoring setting color appears are taken as ideal values. Third, the ideal value is the average value of the actually measured values (read image data: RGB) of the first few prints on which the monitoring setting color appears.

In order to reduce the influence of errors, the monitor setting unit 115 refers to the original image data and sets the monitor setting color in a low spatial frequency region that does not contain text data.
In addition, the monitoring setting unit 115 does not set the ideal value based on the original image data (the solid line in FIG. 3), but rather reads the reading obtained by reading the paper on which the image is formed based on the image data for image formation. It is also possible to set the ideal value based on a plurality of average values of the image data or the read image data (broken line in FIG. 3).

Also, here, a plurality of different colors can be set as monitor setting colors. Also, ideal values are set by converting the original image data based on the ICC profile or multi-dimensional LUT as the monitoring set colors. In addition, a loose threshold value or a strict threshold value is set depending on whether the monitoring setting color is set loosely or strictly according to the setting state of the monitoring setting color. Also, a suitable threshold value is set according to the type of monitoring setting color. Also, the average value of the colors extracted from multiple locations in the image is used to set the monitoring setting color.

Here, the image processing unit 140 converts the image forming image data and the read image data into data in a standardized format that can be compared (step S106 in FIGS. 3 and 4). The image data for image formation is CMYK bitmap data, and the read image data is RGB bitmap data, which cannot be directly compared. Therefore, the image processing unit 140 executes image processing so that the image data for image formation and the read image data are aligned in data format such as RGB bitmap data or Lab data. In FIG. 3, 'image data for image formation' and 'reading image data'' mean data whose data formats are the same.

The color tone monitoring unit 180 monitors the color tone difference between the value of the read image data of the monitor setting color and the ideal value at the corresponding positions of the image data for image formation and the read image data for the monitor setting color (see FIGS. 3 and 5). step S107 in FIG. 4).
That is, the color tone monitoring unit 180 first extracts pixels in an area belonging to a monitoring setting color set by referring to the image data for image formation and the read image data. To explain this in detail, when a pixel of interest in the image data for image formation matches the setting condition of the monitor set color, the pixel of interest is extracted from the image data for image formation, and a pixel at the same position as the pixel of interest in the read image data is extracted. are extracted as corresponding pixels. Then, the corresponding pixel of the read image data is compared with the ideal value of the monitor set color to extract the color tone difference between the two.

As for the timing of monitoring the color tone difference, the color tone difference between the read image data (actually measured value) of the extracted monitor setting color and its ideal value is calculated when the analysis of the image for one page is completed. Here, when the ideal values are set by RGB values, the difference between the RGB values of the read image data obtained from the scanned image is compared, and if the difference is equal to or greater than the threshold value, color correction is performed. When the ideal values are set as Lab values, the RGB values of the read image data obtained from the scanned image are converted to Lab values based on the scanner profile or multidimensional LUT, and then compared, and the difference is greater than or equal to the threshold. If so, perform color correction.

Note that the color tone monitoring unit 180 monitors the color tone difference using at least one of the absolute value of the color tone difference and the degree of change in the color tone difference due to aging as a threshold value. When the tertiary achromatic color is selected as the monitoring setting color, the color tone monitoring unit 180 monitors the hue change as a color tone difference. When a specific tertiary color such as skin color is selected as the monitoring setting color, the color tone monitoring unit 180 determines the color in the face region recognized by the face recognition process as the specific tertiary color, and determines the specific tertiary color. Hue change and chroma change are monitored as color tone difference. At this time, the image processing unit 140 may perform image processing such as face recognition processing to extract the target pixel and the corresponding pixel described above. The color tone monitoring unit 180 monitors the color tone difference at one corresponding position of 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 for image formation is set as the monitoring setting color, the color tone monitoring unit 180 detects the color tone difference in an area containing only the spot color and not including other colors. Monitor.

A specific example of color tone monitoring will be described below. Absolute tone monitoring and relative tone monitoring are described herein.
[Specific example of absolute color tone monitoring]
・Image data for image formation (CMYK)→Profile→Ideal values RGB,
・Image data for image formation (CMYK) → read printed matter → measured values RGB,
In this case, the color tone difference is monitored by comparing the ideal values RGB and the actually measured values RGB, and when the color tone difference exceeds a predetermined threshold value, color correction, which will be described later, is performed.

[Specific example of relative color tone monitoring]
・ First page of printed matter;
Image data for image formation #1 (CMYK)→printed matter #1→printed matter #1 reading (RGB)→ideal value Lab#1,
・ n printed matter (n = 2, 3, 4, ...);
Image data for image formation #n (CMYK)→printed matter #n→printed matter #n reading (RGB)→measured value Lab#n,
In this case, the ideal value Lab#1 generated from the actual measurement value is used as a reference, and the ideal value Lab#1 and the actual measurement value Lab#n are compared to monitor the color tone difference for each n. When the threshold value is exceeded, color correction, which will be described later, is performed.

Regarding the monitoring of the color tone difference by the color tone monitoring unit 180, when the color tone difference (absolute value) ΔE becomes equal to or greater than a predetermined threshold Th1 at a certain time, it is determined that the color tone monitoring result is greater than or equal to the color tone difference threshold. In FIG. 5, ΔE≧Th1 at the portion (a1).
In monitoring the color tone difference by the color tone monitoring unit 180, the color tone difference (absolute value) ΔE due to changes over time is sampled and integrated. , color tone monitoring result=more than the color tone difference threshold value. In FIG. 6, ΔE≧Th2 at the portion (a2). In this case, even if the color tone difference ΔE itself does not reach the threshold value Th1, if the color tone difference continues for a certain period of time, the color tone difference integrated value ∫ΔE is used for color correction. Able to determine the need for execution.

In monitoring the color tone difference by the color tone monitoring unit 180, the degree of sudden change in color tone difference, that is, the color tone difference for each printed material is monitored, and the color tone difference (relative value) δE for each printed material is When it becomes equal to or greater than the change threshold thδ, it is determined that the color tone monitoring result is equal to or greater than the color tone difference threshold. In FIG. 7, in the portion (b), the color tone difference (absolute value) ΔE<Th1, but the color tone difference (relative value) δE≧thδ.

That is, as described above, there are three types of cases where "the color tone difference has become equal to or greater than the predetermined threshold value". As for the monitoring of these color tone differences, any one of temporal simple color tone monitoring, temporal color tone difference integral value monitoring, and sudden color tone monitoring may be performed, but it is desirable to perform a plurality of monitoring. Note that when performing a plurality of monitorings, it is desirable to proceed to color correction execution when even one of them is determined to be equal to or greater than the threshold value.

Control unit 101 executes color correction of image forming unit 150 when the color tone difference is greater than or equal to a predetermined threshold value as monitored by color tone monitoring unit 180 (S108 in FIG. 3, YES in step S108 in FIG. 4). (Step S109 in FIGS. 3 and 4). That is, the control unit 101 performs color correction by adjusting the image forming unit 150 using read correction image data obtained by reading a sheet on which a correction image is formed in the margin of the sheet.

Then, the control unit 101 repeatedly executes the above processing for all the images on the sheets to be image-formed as a series of jobs (step S110 in FIG. 4). However, it is possible to arbitrarily decide whether the color tone monitoring process described above is executed for each sheet of paper or for every several sheets. Note that, in the above-described embodiment, there is no need to use color patches or the like for color tone monitoring, so even if the monitoring is performed for each sheet on which an image is to be formed, productivity is not lowered.

[Other operations (1)]
In the image data for image formation obtained by the RIP process, there is a possibility that the secondary colors and tertiary achromatic colors that are completely the same are mixed within a certain range due to color management. Therefore, it is desirable to set a threshold value that allows color mixture in the monitoring setting color within a range that does not affect color tone monitoring, in terms of executing processing in an actual product.

For example, when extracting a tertiary achromatic color (gray) as a monitoring setting color, if the signal value of each color of YMC is set to 256 steps from 0 to 255, (CM<±3) and (MY< ±3) and (YC<±3), when the difference between the signal values of CMY is less than 3, it is desirable to extract the color as a tertiary achromatic color. Here, 256 levels of signal values and setting the difference of signal values to 3 are examples, and arbitrary numerical values can be determined. Note that when a certain amount of color mixture is recognized in the monitoring setting colors in this way, it is desirable to set a slightly looser threshold value for the color tone difference in color tone monitoring in consideration of the color mixture.

Further, the tertiary achromatic color (gray) in the above embodiments means that it is not gray made only from K. For this reason, even gray in which K is mixed in addition to CMY is treated as a tertiary achromatic color.
[Other operations (2)]
The images used by the user are various, and there is a possibility that the color that the user wants to extract does not appear as the monitor setting color. In that case, a wider range of data can be collected by widening the threshold (width) for extraction. However, when the threshold for extraction is widened by this method, it is desirable to lower the level of the threshold for determining that there is a color tone difference. Moreover, when such measures are taken, it is desirable to notify the user via the operation display unit 103 .

[Specific example (3) of the embodiment]
When monitoring the color tone of the monitor setting color for the read image data, the target image of the read image data is divided into a plurality of M×N areas, and the average value of the monitor setting color extracted from each of the multiple areas is obtained. Values can be monitored in comparison to ideal values. By doing so, it is possible to monitor the difference in color tone over the entire surface of the printed matter.

[Specific example (4) of the embodiment]
When monitoring the color tone of the monitoring setting color for the read image data, the target image of the read image data is divided into a plurality of M × N areas, and the ideal value generated in each corresponding area is the same as the area to which the ideal value belongs. It is also desirable to perform tone monitoring of the monitor setting color for the pixels of the read image data contained in the area. By doing so, it is possible to monitor the color tone while eliminating the influence of the in-plane unevenness that causes different densities at the center and edges of the paper.

[Specific example (5) of the embodiment]
Even if the color tone difference does not reach the threshold value, it is desirable that the control unit 101 performs color correction of the image forming unit 150 for a certain period of time or every certain number of images formed. Here, the monitoring setting color is any of primary colors (CMYK), secondary colors (RGB), specific tertiary colors such as skin tones, and tertiary achromatic colors, and the monitored color tone difference is equal to or less than the threshold. In the case of , it is desirable to feed back the difference between the measured data and the ideal value data to the gamma correction.

[Specific example (6) of the embodiment]
Even if the state in which the monitoring setting color does not appear continues over a plurality of sheets, the control unit 101 can perform color correction of the image forming unit 150 for a certain period of time or for each certain number of images formed. desirable.

[Specific example (7) of the embodiment]
When using a spot color other than the color of the basic color material used for image formation, the color tone monitoring unit 180 can set this spot color as the monitoring setting color. When a spot color is used as a monitoring setting color in this way, it is desirable to monitor the color tone difference in an area containing only the spot color and not including other colors.

For example, assuming that the fifth color other than CMYK is red (R) as the color of the color material used for image formation, an area composed only of red R that does not include CMYK is set as a monitoring target. Five color variations can be monitored.
Further, when the fifth color is a transparent color (clear), even if an area including clear matches another monitoring setting color, it is excluded from the monitoring target as the monitoring setting color. This is to exclude the effect of clear on read image data.

[Other embodiment (1)]
Although the image forming apparatus 100 shown in FIG. 1 has the printer controller 110 built therein, the present invention is not limited to this. That is, the printer controller 110 may exist outside the image forming apparatus 100, and the image forming apparatus 100 may externally receive RIP-processed image data for image formation.

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

[Other embodiment (3)]
The image forming apparatus 100 described above has a configuration in which the color tone monitoring unit 180 is incorporated. Here, it is also possible to configure a color tone monitoring device having monitor setting unit 115 and color tone monitoring unit 180 outside image forming apparatus 100 . In this case, the result of monitoring by the color tone monitoring device is transmitted to the image forming apparatus 100, and the image forming apparatus executes color correction.

100 Image forming apparatus 102 Communication unit 103 Operation display unit 104 Storage unit 105 Paper supply unit 107 Conveyance unit 110 Printer controller 115 Monitoring setting unit 120 Document reading unit 130 Image data storage unit 140 Image processing unit 150 Image forming unit 160 Fixing unit 180 Color tone Monitoring unit 190 Output reading unit

Claims (30)

An image forming apparatus that includes an image forming unit and executes color correction of the image forming unit using correction image data,
a reading unit that reads an image on a sheet formed by the image forming unit based on image forming image data different from the correction image data;
a setting unit for setting a color for monitoring the color tone difference;
A value based on the read image data of the sheet read by the reading unit is compared with a value based on the read image data of the sheet on which the image is formed after the read sheet, and the color tone difference of the set color is determined. a color tone monitoring unit for monitoring;
An image forming apparatus comprising: 2. The image forming apparatus according to claim 1, further comprising a control section that controls execution of color correction of said image forming section based on the result of monitoring the difference in color tone by said color tone monitoring section. 3. The image forming apparatus according to claim 2, wherein said control unit controls to perform color correction of said image forming unit based on the number of images formed in said image forming unit. 3. The image forming apparatus according to claim 2, wherein said control section performs control to perform color correction of said image forming section at predetermined intervals. The color tone monitoring unit compares a value based on read image data of a plurality of sheets read by the reading unit with a value of read image data of a sheet on which an image is formed after the plurality of sheets, and determines the color tone. The image forming apparatus according to any one of claims 2 to 4, wherein the difference is monitored. 6. The image forming apparatus according to claim 5, wherein the value based on the read image data of the plurality of sheets is an average value of the read image data of the plurality of sheets. 7. The image forming apparatus according to claim 1, wherein said setting unit sets a color for monitoring said color tone difference based on an image of a predetermined area. 8. The image forming apparatus according to claim 7, wherein the image of the predetermined area is an image of an area filled with a constant color. 9. The image forming apparatus according to claim 8, wherein the image of said area does not include contours. 10. The image forming apparatus according to claim 8, wherein the image of said area does not contain a pattern. 8. The image forming apparatus according to claim 7, wherein the image in the predetermined area is an image in a low spatial frequency area and does not contain text data. 7. The image forming apparatus according to claim 1, wherein said setting unit sets colors for monitoring said color tone difference based on colors extracted from images at a plurality of locations. The setting unit predetermines any single primary color of the CMYK color materials used for image formation, a secondary color combining any two of the primary colors, and three chromatic colors of the primary color. The color for monitoring the color tone difference is set to include at least one of a tertiary color combined at a ratio and a tertiary achromatic color combined at a predetermined ratio with three chromatic colors of the primary colors. 13. The image forming apparatus according to any one of 1 to 12. 14. The image forming apparatus according to claim 1, wherein said setting unit sets a plurality of different colors as colors for monitoring said color tone difference. 15. The image forming apparatus according to any one of claims 1 to 14 , wherein said color tone monitoring unit monitors changes in at least one of lightness, saturation, and hue. forming an image on a sheet based on image forming image data different from correcting image data used for color correction in the image forming unit;
a step of reading, by a reading unit, an image on a sheet on which an image is formed based on the image data for image formation;
setting a color for monitoring tonal differences;
A value based on the read image data of the sheet read by the reading unit is compared with a value based on the read image data of the sheet on which the image is formed after the read sheet, and the color tone difference of the set color is determined. a monitoring step;
An image forming method characterized by comprising: 17. The image forming method according to claim 16 , further comprising the step of performing color correction of said image forming unit based on the monitoring result of said color tone difference. 17. The image forming method according to claim 16 , wherein color correction of said image forming unit is performed based on the number of images formed in said image forming unit. 17. The image forming method according to claim 16 , wherein color correction of said image forming unit is performed at predetermined intervals. In the step of monitoring the color tone difference, a value based on read image data of a plurality of sheets of paper read by the reading unit is compared with a value of read image data of a sheet on which an image is formed after the plurality of sheets of paper. 20. The image forming method according to claim 16 , wherein the color tone difference is monitored. 21. The image forming method according to claim 20 , wherein the value based on the read image data of the plurality of sheets is an average value of the read image data of the plurality of sheets. 22. The image forming method according to any one of claims 16 to 21 , wherein in the step of monitoring the color tone difference, changes in at least one of lightness, saturation, and hue are monitored. 23. The image forming method according to claim 16, wherein a color for monitoring said color tone difference is set based on an image of a predetermined area. 24. The image forming method according to claim 23, wherein the image of the predetermined area is an image of an area filled with a constant color. 25. The method of forming an image according to claim 24, wherein the image of said area does not include contours. 26. The image forming method according to claim 24 or 25, wherein the image of said area does not contain a pattern. 24. The image forming method according to claim 23, wherein the image of the predetermined area is an image of a low spatial frequency area and does not contain text data. 22. The image forming method according to any one of claims 16 to 21, wherein colors for monitoring said color tone difference are set based on colors extracted from images at a plurality of locations. A single primary color of CMYK color materials used for image formation, a secondary color combining any two of the primary colors, and a combination of three chromatic colors of the primary colors at a predetermined ratio 29. The color for monitoring the color tone difference is set to include at least one of a secondary color and a tertiary achromatic color obtained by combining three chromatic colors of the primary color at a predetermined ratio. The image forming method according to item 1 or 1. The image forming method according to any one of claims 16 to 29, wherein a plurality of different colors are set as colors for monitoring said color tone difference.

Images