JP6666932B2 - Image forming device - Google Patents

Description

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

  2. Description of the Related Art In an image forming apparatus using an electrophotographic system, density stability and gradation stability of an output image are required. Therefore, Patent Documents 1 and 2 stabilize the quality of an image by forming a test pattern on an image carrier, reading the density of the formed test pattern with a sensor or the like, and adjusting image forming conditions and generating a gradation correction table. It discloses a configuration for causing the above.

JP-A-04-267272 JP-A-06-198973

  The density of the image formed by the image forming apparatus depends on the amount of charge of the developer itself in addition to image forming conditions such as a development contrast potential. For example, if the consumption amount of the developer increases due to the use situation of the user, the developer in the developing unit is used for image formation without being sufficiently frictionally charged. In this case, the density of the formed image becomes high. Conversely, when the consumption amount of the developer decreases due to the usage situation of the user, the charge amount of the developer in the developing unit is increased more than expected due to frictional charging. In this case, the density of the formed image is low. Here, for example, if the charge amount of the developer in the developing unit continues to increase, the output image data value with respect to the input image data value of the gradation correction table continues to be increased by density control in order to compensate for the decrease in density. However, the output image data value has a maximum value. Therefore, when the charge amount of the developer in the developing unit continues to increase, the gradation correction table generated in the density control converts all input image data values equal to or more than a predetermined value into the maximum value of the same output image data value. There is a possibility that it will be. In this case, the gradation cannot be maintained. When the charge amount of the developer in the developing unit continues to decrease, the output image data value with respect to the input image data value of the gradation correction table continues to be reduced by the density control. In this case, jaggies may occur in the line portion of the formed image.

  SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and provides an image forming apparatus that can maintain gradation and quality of an image.

According to one aspect of the present invention, an image forming apparatus that forms an image on a recording material is controlled by a converting unit that converts image data based on a gradation correction table, and is controlled by an image forming condition. an image forming unit, an image bearing member for bearing a measurement image formed by the image forming unit, the measurement image on the image carrier measurement for forming a based-out before SL image to image data Measuring means, and while the image forming means continuously forms a plurality of images, causing the image forming means to form a plurality of measurement images, and causing the measuring means to form the plurality of images on the image carrier. the measurement image is measured, the generating the gradation correction table on the basis of the measurement results of the plurality of measurement images measured by the measuring means, before Symbol plurality of measurement image measured by the measuring means Measurement result And a control means for determining the image forming condition based on said control means, for forming repeatedly the plurality of measurement images to the image forming means, during the continuous image formation of said image forming means Each time a predetermined number of recording materials are passed, the image forming means forms the plurality of measurement images, and the control means controls the maximum density of the predetermined measurement images among the plurality of measurement images. Using a predetermined measurement result instead of the measurement result, the predetermined measurement result and the measurement result of another measurement image having a lower density than the predetermined measurement image in the plurality of measurement images. and generates the tone correction table based on said image forming means said plurality of measurement images and change the pre-Symbol image forming conditions upon forming the next time, after the plurality of measurement images are formed From the plurality Image formation by said image forming means before the titration, an image is formed next, said plurality of measurement images is performed while the image forming conditions when formed, the plurality of measurement images are formed The image formation by the image forming unit after the plurality of measurement images are formed next time is performed using the tone correction table generated this time by the control unit , and the image forming condition is The tone correction table is different from the tone correction table.

  According to the present invention, it is possible to maintain gradation and quality of an image.

FIG. 1 is a schematic configuration diagram of an image forming apparatus according to an embodiment. FIG. 4 is a diagram illustrating a test pattern according to an embodiment. 9 is a flowchart of tone correction control according to one embodiment. FIG. 4 is a diagram showing a test pattern formed by gradation correction control according to one embodiment. FIG. 4 is a diagram illustrating a relationship between an input image data value and a target density according to one embodiment. 9 is a flowchart of correction control of a gradation correction table according to one embodiment. FIG. 2 is a diagram illustrating an image formed according to an embodiment. FIG. 9 is a diagram illustrating an example of a gradation correction table obtained by performing correction only based on a detection result of a formed image. FIG. 6 is an explanatory diagram of a replacement process according to one embodiment. 9 is a graph illustrating an inverse conversion table according to an embodiment. 7 is a graph showing a gradation correction table after correction according to one embodiment. 9 is a flowchart of correction control of a gradation correction table according to one embodiment.

  Hereinafter, exemplary embodiments of the present invention will be described with reference to the drawings. The following embodiments are for the purpose of explanation, and do not limit the scope of the present invention to the embodiments. In the following drawings, components not necessary for the description of the embodiment are omitted from the drawings.

<First embodiment>
FIG. 1 is a configuration diagram of the image forming apparatus 100 according to the present embodiment. In the image forming apparatus 100 shown in FIG. 1, yellow, magenta, cyan, and black image forming units PY, PM, PC, and PK are arranged along the intermediate transfer belt 6. The photoconductor 1Y of the image forming unit PY is an image carrier, is driven to rotate in the direction of the arrow in the figure, and is charged to a predetermined potential by the charging unit 2Y. The exposure unit 3Y scans and exposes the photoconductor 1Y with light to form an electrostatic latent image on the surface of the photoconductor 1Y. The developing unit 4Y supplies a yellow toner (developer) to the electrostatic latent image on the photoconductor 1Y by outputting a developing bias to visualize the electrostatic latent image as a toner image. The primary transfer roller 7Y outputs a primary transfer bias to transfer the toner image formed on the photoconductor 1Y to the intermediate transfer belt 6. Further, the image forming section PY includes a density sensor 12Y for detecting the density of the toner image formed on the photoconductor 1Y. The density sensor 12Y irradiates the photoreceptor 1Y with light, for example, and detects the density based on the reflected light.

  The image forming units PM, PC, and PK and the image forming unit PY have the same configuration except that the color of the toner used is different. Therefore, the description of the image forming units PM, PC, and PK is omitted. In the following description, when it is not necessary to distinguish colors, reference numerals excluding characters Y, M, C, and K are used. It should be noted that a multicolor toner image is formed on the intermediate transfer belt 6 by superimposing and transferring the toner images formed on the photoconductor 1 of each image forming unit to the intermediate transfer belt 6.

  The intermediate transfer belt 6 is stretched by three rollers 61, 62 and 63, and is driven to rotate in the direction of arrow R2 in the figure. The recording material P taken out of the cassette 65 is conveyed by a pair of rollers 66 and 67 toward a secondary transfer portion T2 composed of a roller 63 and a secondary transfer roller 64. The toner image transferred to the intermediate transfer belt 6 is transferred to the recording material P at the secondary transfer portion T2. Thereafter, the recording material P is heated and pressurized in the fixing unit 11 to fix the toner image on the recording material P and is discharged out of the apparatus.

  The light source 103 of the reading unit 216 irradiates the recording material placed on the document table 102 with light, and the CCD sensor 105 receives the reflected light to read the image of the recording material. The image data read by the CCD sensor 105 is subjected to predetermined image processing by a reader image processing unit 108 and a printer control unit 109. The image forming apparatus 100 according to the present embodiment can also print image data received via a telephone line (FAX) and image data received from a computer via a network in addition to the image read by the reading unit 216. It is configured to do so. Further, the operation unit 20 includes a display unit 218 for the user to operate the image forming apparatus 100 and to display the state of the image forming apparatus 100 to the user. The control unit 110 generally controls the image forming operation of the image forming apparatus 100, and includes a CPU 111, a RAM 112, and a ROM 113. The control unit 110 determines and acquires density information of the toner image formed on the photoconductor 1 based on a signal from the density sensor 12. The CPU 111 controls the image forming apparatus 100 using the programs and various data stored in the ROM 113 and using the RAM 112 as a work area. Further, the image forming apparatus 100 includes an environment sensor 30 that obtains environmental information in the image forming apparatus, for example, one or both of temperature and humidity and notifies the control unit 110 of the information.

  Subsequently, the density control according to the present embodiment will be described. The density control according to the present embodiment includes tone correction control for generating a tone correction table (γLUT) and correction control for the tone correction table for correcting the tone correction table generated by the tone correction control. I have. The density control is performed for each color. In the present embodiment, tone correction control is executed by a user operation or by satisfying a predetermined condition. In the gradation correction control, a toner image is formed on a recording material and fixed, and the fixed toner image is read by the reading unit 216 to determine image forming conditions relating to density. In this gradation correction control, image forming conditions for forming an image having a target maximum density (hereinafter, referred to as a maximum density condition value) and image data to be input in order to realize the target density. Is generated. Further, a test pattern R shown in FIG. 2A is formed on the photoconductor 1 at the determined maximum density condition value using the generated gradation correction table. In this embodiment, as shown in FIG. 2A, the test pattern R is an image pattern including ten types of densities (tones) including a solid image (maximum density image). However, other gradation numbers may be used. The image forming apparatus 100 measures the density of the test pattern R by the density sensor 12, and the correspondence between the value of the image data used to form the test pattern R and the density formed on the photoconductor 1 by the value. Is obtained.

  Thereafter, each time a predetermined number of sheets are passed during continuous image formation, the image forming apparatus 100 performs correction control of the gradation correction table (hereinafter, simply referred to as correction control). In the correction control, a test pattern Q shown in FIG. 2B is formed on the photoconductor 1, and the density of the test pattern Q is detected by the density sensor 12 to correct the gradation correction table. Note that, in the correction control, the test pattern Q is formed on the surface of the photoconductor 1 during the formation of the toner image to be printed, as shown in FIG. Input values used to form the test pattern Q are stored in the ROM 113 or the RAM 112. In this embodiment, the input values used to form the test pattern Q are five different values including the maximum value of the image data value. That is, the test pattern Q is a pattern including images of five different densities (tones) including a solid (maximum density) image. However, other gradation numbers may be used.

  First, the details of the gradation correction control will be described with reference to FIG. In step S10, the control unit 110 forms a test pattern on the recording material using image data having a value indicating the maximum density. FIG. 4A is an example of a test pattern formed in S10. The test pattern shown in FIG. 4A is formed, for example, when the input image data value is represented by 8 bits, with 255 representing the maximum density being used as the input value and changing the image forming conditions relating to the density. is there. In the following description, the exposure amount is the image forming condition that is changed to control the density, but other image forming conditions related to the density, for example, the developing bias and other values that change the developing contrast such as the charging bias are changed. It may be in a form to be performed. Furthermore, a mode in which a plurality of image forming conditions relating to density are changed may be used. The user sets the recording material on which the test pattern is formed in the reading unit 216, and in S11, the control unit 110 causes the reading unit 216 to read the test pattern and detects the density. In step S12, the control unit 110 determines the maximum density condition value based on the detected density, that is, the value of the image forming condition for setting the toner image formed with the maximum input value to the target maximum density. As described above, in this example, the image forming condition is the exposure amount.

  Subsequently, in S13, the control unit 110 forms a test pattern for gradation correction on the recording material. FIG. 4B is an example of the test pattern formed in S13. The test pattern shown in FIG. 4B is formed by a plurality of values selected from 0 to 255, for example, when the input image data value is 8 bits. The user sets the recording material on which the test pattern is formed in the reading unit 216, and in S14, the control unit 110 causes the reading unit 216 to read the test pattern and detects the density. The control unit 110 generates a tone correction table in S15 based on the detected density. Thereafter, the control unit 110 forms the test pattern R shown in FIG. 2A on the photoconductor 1 in S16, and detects the density by the density sensor 12 in S17. The control unit 110 generates target density information which is a correspondence relationship between the input value used for image formation in S16 and the density of each image of the test pattern R formed with the input value detected in S17, and S18 Is stored in the RAM 112. FIG. 5 shows the relationship between the value of the input image data obtained by interpolating the target density information stored in S18 and the density of the image formed on the photoconductor 1. Hereinafter, the detected density of each image of the test pattern R detected in S17 is referred to as a target density corresponding to the input value used to form each image. Further, the detected density of the solid image of the test pattern R is called a target maximum density.

  Next, the correction control of the gradation correction table according to the present embodiment will be described with reference to FIG. As described above, the correction control is executed every time a predetermined number of sheets are passed during continuous image formation. When the correction control is started, the control unit 110 changes the image forming condition regarding the density, that is, the exposure amount in the present embodiment, in S20, if the process of S27 in FIG. 6 is performed in the previous correction control. If the process of S27 in FIG. 6 has not been performed in the previous correction control, the image forming condition relating to the density is not changed. The details of the process of S27 and the change of the exposure amount in S20 will be described later. Subsequently, the control unit 110 forms the test pattern Q shown in FIG. 2B on each photoconductor 1 in S21, and detects the density of each image of the test pattern Q formed by the density sensor 12 in S22. The test pattern Q is formed using a gradation correction table stored in the RAM 112.

  Subsequently, in S23, the control unit 110 determines whether or not the detected maximum density of the test pattern Q, that is, the target maximum density is higher than the detected density of the solid image of the test pattern Q. Here, when the detected maximum density is higher than the target maximum density, the output image data value for the maximum value of the input image data value in the gradation correction table is changed to a smaller value to obtain an image of the target maximum density. Will be. However, if the output image data value with respect to the maximum value of the input image data value in the gradation correction table is excessively lowered, jaggies may occur as shown in FIG. There is. Therefore, in this case, the control unit 110 determines whether or not the maximum value (output maximum value) of the output image data of the gradation correction table (γLUT) can be further reduced in S24. Specifically, in the present embodiment, it is determined whether or not the output maximum value of the gradation correction table to be corrected is already equal to or less than the first threshold, and if it is equal to or less than the first threshold, it can be further reduced. It is determined that it cannot be performed, and the process of S27 is executed. On the other hand, if it is not less than or equal to the first threshold, the process of S28 is executed. For example, if the gradation correction table converts an 8-bit input image data value into a 10-bit output image data value, 800 can be used as the first threshold value, for example.

  If S23 is "No", the control unit 110 determines in S25 whether the detected maximum density of the test pattern Q is lower than the target maximum density. Here, when the detected maximum density is lower than the target maximum density, the output image data value for the maximum value of the input image data value in the gradation correction table is changed to a larger value to obtain an image of the target maximum density. Will be. However, if the output image data value with respect to the maximum value of the input image data value in the gradation correction table is excessively increased, the gradation correction table has characteristics as shown by the solid line in FIG. 8, and the gradation cannot be maintained near the maximum density. there is a possibility. The dotted line in FIG. 8 indicates a gradation correction table that can maintain gradation. Therefore, in this case, the control unit 110 determines whether the maximum value (output maximum value) of the output image data of the gradation correction table (γLUT) can be further increased in S26. Specifically, in the present embodiment, it is determined whether or not the maximum output value of the gradation correction table to be corrected is already equal to or greater than the second threshold value. It is determined that it cannot be performed, and the process of S27 is executed. On the other hand, if it is not equal to or greater than the second threshold, the process of S28 is executed. For example, when the gradation correction table is for converting an 8-bit input image data value into a 10-bit output image data value, for example, 1023 can be used as the second threshold value.

  Subsequently, the process in S27 will be described with reference to FIG. 9A and 9B, reference numeral 81 denotes a detection result of the density of the solid image of the test pattern Q, and reference numeral 83 denotes four other images (hereinafter, referred to as intermediate density images). 3) shows the result of detecting the concentration. The dotted lines in FIGS. 9A and 9B indicate the relationship between the input image data value indicated by the target density information and the density. For example, if the current output maximum value of the gradation correction table is already equal to or smaller than the first threshold value in S24 of FIG. 6, in S27, the detected density 81 of the solid image of the test pattern Q shown in FIG. The target density is changed to the target maximum density indicated by reference numeral 82. However, the predetermined density may be lower than the detected density and equal to or higher than the target maximum density. Similarly, in S26, if the current maximum output value of the gradation correction table is already equal to or greater than the second threshold, in S27, reference is made to the detected density 81 of the solid image of the test pattern Q shown in FIG. The target maximum density indicated by 82 is changed. However, the predetermined density may be higher than the detected density and equal to or lower than the target maximum density.

  Subsequently, the processing in S28 of FIG. 6 will be described. When S27 is not executed, the control unit 110 sets the measured value of the test pattern Q as the processing value, and when S27 is executed, the control unit 110 processes the solid image density by replacing the measured value with a predetermined density. The processing values are plotted as shown in FIG. 9 and linearly interpolated between the values. Then, the processing values are inversely transformed with respect to the target density information indicated by the dotted lines in FIGS. 9A and 9B to generate an inverse transformation table. FIG. 10 is a graph showing the input image data values and the output image data values indicated by the inverse conversion table. The dotted line in FIG. 10 shows the inverse conversion table when each processing value is the same as the target density information, that is, on the dotted line in FIG. 9, and the input image data value and the output image data value are the same value. On the other hand, the solid line in FIG. 10 shows an example of the inverse conversion table when the processing value is higher than the target density as shown in FIG. In the solid line in FIG. 10, the output image data value is converted to a value smaller than the input image data value in order to bring the obtained density closer to the target density.

  In step S28, the control unit 110 updates the gradation correction table (γLUT) held by the RAM 112 using the inverse conversion table. The dotted line in FIG. 11 is a graph showing the gradation correction table before correction, and the solid line is a graph showing the gradation correction table after correction when the inverse conversion table is the solid line in FIG. It is. For example, the gradation correction table after correction is obtained by multiplying the output image data value corresponding to the same input image data value in the gradation correction table before correction and the inverse conversion table and dividing by the input image data value. Desired. The control unit 110 saves the corrected gradation correction table in the RAM 112 and ends the correction control. At this time, whether or not the process of S27 has been executed for the next correction control is also stored in the RAM 112. After completing the correction control, the control unit 110 forms an image using the gradation correction table stored in the RAM 112.

  When the process of S27 is executed, the solid image of the test pattern Q is corrected not in the actual detection result but in the gradation correction table on the assumption that the predetermined density is the detection result. Therefore, the density of the image formed using the gradation correction table corrected in this manner is shifted from the target density near the maximum density. Therefore, in the present embodiment, when the process of S27 is performed, the image forming condition relating to the density, which is the exposure amount, is changed in the present embodiment. Specifically, as shown in FIG. 9A, when it is determined that the density of the image to be formed is higher than the target maximum density but the output maximum value of the gradation correction table cannot be reduced, the exposure amount To reduce the density of the image actually formed with the same input image data value. Similarly, as shown in FIG. 9B, if it is determined that the density of the image to be formed is lower than the target maximum density but the maximum output value of the gradation correction table cannot be increased, the exposure amount is increased. Then, the density of an image actually formed with the same input image data value is increased. However, if the exposure amount is changed after execution of S27 in a certain correction control, subsequent image formation is performed under image formation conditions different from those when the test pattern Q was formed in S21, and the image to be formed is The density will deviate from the target density. Therefore, in the present embodiment, the control unit 110 stores that the process of S27 has been executed, and changes the exposure amount in S20 when the correction control is next executed, that is, before forming the test pattern Q. I do. The change amount is increased or decreased in units of a predetermined amount.

  In order to confirm the effect of the present embodiment, continuous printing of 10,000 sheets is performed, and the gradation correction table is corrected using only the actual detection result of the test pattern Q, as shown in FIG. The comparison was made with the case where the gradation correction table was corrected. When the gradation correction table is corrected using only the actual detection result of the test pattern Q, jaggies occur as shown in FIG. On the other hand, when the gradation correction table was corrected according to FIG. 6, jaggies did not occur, as shown in FIG. 7B.

  As described above, an allowable range is set for the output image data value with respect to the maximum value of the input image data value of the gradation correction table, and the control unit 110 determines whether the corrected output image data value of the gradation correction table is outside the allowable range. Determine whether or not. When determining that the test pattern Q is outside the allowable range, the control unit 110 changes the detected density of the image having the maximum density of the test pattern Q to a predetermined density. Further, when the detected density of the image having the maximum density of the test pattern Q is changed to the predetermined density, the image forming conditions relating to the density are changed when the correction control of the next tone correction table is executed. With this configuration, the deviation of the formed image density from the target density can be reduced.

<Second embodiment>
In the first embodiment, only the detection result of the solid image of the test pattern Q is changed in the correction control. Further, when the solid image detection result is changed, the exposure amount is changed at the start of the next correction control. However, if the image density to be formed continues to decrease and the decrease in the image density is greater than the change in the exposure amount, the output is performed when the input image data value is equal to or more than a predetermined value as shown by the solid line in FIG. There is a possibility that the image data values will be corrected to the same gradation correction table. In this case, the gradation cannot be maintained. In the present embodiment, the detection result is changed not only for the solid image of the test pattern Q but also for the intermediate density image. The image for which the detection result is changed may be all images of the test pattern Q or an image having a predetermined density or more. In the present embodiment, all five images of the test pattern Q are to be changed.

  FIG. 12 is a flowchart of the correction control of the gradation correction table according to the present embodiment. FIG. 12 is obtained by replacing S23 to S27 in FIG. 6, and S20 to S22 and S28 are the same as those in FIG. In FIG. 12, i is an index for distinguishing five images of the test pattern Q. Ri is the detected density of the image i in S22, and Ti is the target density corresponding to the input value of the image data used to form the image i. Further, Oi is an output image data value of the gradation correction table for an input image data value used to form the image i. Further, Th1i and Th2i are the lower limit and the upper limit of the allowable range of the output image data value of the gradation correction table with respect to the input image data value used to form the image i. Th1i and Th2i for the intermediate density image are, for example, 0.8 times the output image data value for the input image data value used to form the image i and 1.times. In the gradation correction table generated by the gradation correction control. It can be determined as twice. Note that Th1i and Th2i for the solid image are the same as in the first embodiment. The control unit 110 executes each process of FIG. 12 for each image i. With this configuration, it is possible to prevent a situation where the correction of the halftone portion of the gradation correction table is continued and the gradation cannot be maintained.

<Third embodiment>
In the first embodiment and the second embodiment, the value of the exposure amount changed in S20 of FIG. 6 is a predetermined value. However, if the characteristic change of the image forming apparatus is large and cannot be compensated for by the exposure amount changed in S20, the density deviation may become too large. In the present embodiment, the exposure amount changed in S20 in FIG. 6 is made variable. Hereinafter, how to determine the exposure amount to be changed will be described. The other processes of the present embodiment are the same as those of the first embodiment and the second embodiment.

First, the control unit 110 calculates the rate of change of the detected density 81 of the solid image of the test pattern Q with reference to the target maximum density 82 as shown in FIGS. 9A and 9B.
Change rate = (detection density / target maximum density−1) × 100
Then, as the absolute value of the change rate increases, the exposure amount to be changed is increased. For example, if the absolute value of the rate of change is within 10%, the reference amount is the same as in the first embodiment. If the absolute value of the rate of change is greater than 10% and equal to or less than 20%, the reference amount is doubled. If the absolute value is larger than 30%, it can be set to three times the reference amount. The control unit 110 obtains the exposure amount to be changed in S27 in FIG. 6 or S37 in FIG. 12 and stores it in the RAM 112, and when executing the correction control of the next gradation correction table, the RAM 112 in S20 in FIG. The amount of exposure is increased or decreased based on the value held in.

  As described above, by determining the change amount of the exposure amount in accordance with the characteristic change of the image forming apparatus, the gradation of the image to be formed can be maintained and the density can be made closer to the target density.

[Other Embodiments]
The present invention is also realized by executing the following processing. That is, software (program) that realizes the functions of the above-described embodiments is supplied to a system or apparatus via a network or various storage media, and a computer (or CPU, MPU, or the like) of the system or apparatus reads the program and reads the program. This is the process to be performed.

  110: control unit, 1: photoconductor, 12: density sensor

Claims (9)

An image forming apparatus that forms an image on a recording material,
Conversion means for converting the image data based on the gradation correction table;
Is controlled based on the image forming condition, and an image forming means for forming a based-out before Symbol image on the converted image data by said converting means,
An image carrier that carries the measurement image formed by the image forming unit;
Measuring means for measuring the image for measurement on the image carrier,
While the image forming unit is continuously forming a plurality of images, the image forming unit is configured to form a plurality of measurement images, and the measurement unit is configured to display the plurality of measurement images on the image carrier. was measured, based on the based on the measurement result of the measured plurality of measurement image by the measuring means generates the tone correction table, the measurement result before Symbol the plurality of measurement images measured by the measuring means Control means for determining the image forming conditions by
The control unit is configured to cause the image forming unit to repeatedly form the plurality of measurement images, so that each time a predetermined number of recording materials are passed during continuous image formation of the image forming unit, the image forming unit Forming a plurality of measurement images,
The control means uses a predetermined measurement result instead of the measurement result of the predetermined measurement image having the maximum density among the plurality of measurement images, and uses the predetermined measurement result and the plurality of measurement images. wherein the predetermined measurement image and generates the gradation correction table on the basis of the measurement result of the low concentration of other measurement image, formed next to the image forming means of the plurality of measurement images among images change the previous Symbol image forming conditions at the time of,
Image forming, the image forming when the plurality of measurement images are formed by the image forming means from after the plurality of measurement images are formed until the plurality of measurement images are formed next It is performed under the conditions,
The image formation by the image forming unit after the plurality of measurement images are formed until the plurality of measurement images is formed next time uses the tone correction table generated this time by the control unit. Done,
The image forming apparatus according to claim 1, wherein the image forming condition is different from the gradation correction table. The measurement unit outputs a measurement value that changes according to the density of the measurement image of each of the plurality of measurement images,
Before SL control means either generates the tone correction table based on the measured value of the predetermined measurement value and the other measurement image of the measurement image, the predetermined concentration as a measurement result to a predetermined Using a substitute value corresponding to the measurement result of the measurement image of the above, whether to generate the gradation correction table based on the substitute value and the measurement value of the other measurement image, the predetermined measurement image The image forming apparatus according to claim 1, wherein the determination is made based on the measured value of (a). The measurement unit outputs a measurement value that changes according to the density of the measurement image of each of the plurality of measurement images,
Before SL control unit determines whether to generate the tone correction table using the measured value of the predetermined measurement value and the other measurement image of the measurement image,
The control means, when not generating the gradation correction table using the measurement value of the predetermined measurement image and the measurement value of the other measurement image, as a predetermined measurement result, a predetermined density 2. The tone correction table according to claim 1, wherein the tone correction table is generated based on the alternative value and the measurement value of the another measurement image using an alternative value corresponding to a measurement result of the measurement image. 3. The image forming apparatus as described in the above. The tone correction table is a one-dimensional table that converts an input value of image data into an output value,
The control unit causes the conversion unit to convert the measurement image data based on the gradation correction table, and causes the image forming unit to form the plurality of measurement images based on the converted measurement image data. ,
The control unit is configured to control the predetermined measurement image based on a measurement value of the predetermined measurement image and a conversion result of a predetermined input value in the one-dimensional table used to form the plurality of measurement images. 4. The image forming apparatus according to claim 3 , wherein it is determined whether or not to generate the gradation correction table using a measured value of an image and a measured value of the other measurement image. 5. The control unit is configured such that, when the density of the predetermined measurement image is higher than a predetermined density, and the conversion result of the predetermined input value is smaller than a threshold, the measurement value of the alternative value and the measurement value of the another measurement image are used. The image forming apparatus according to claim 4 , wherein the tone correction table is generated based on the following. The control unit is configured such that, when the density of the predetermined measurement image is lower than a predetermined density, and the conversion result of the predetermined input value is larger than a threshold value, the substitute value and the measurement value of the another measurement image are compared with each other. The image forming apparatus according to claim 4 , wherein the tone correction table is generated based on the following. The predetermined input value of the conversion result, an image forming apparatus according to claim 5 or 6, characterized in that a conversion result corresponding to the maximum input value in the one-dimensional table. The image forming unit includes a photoconductor, an exposing unit that exposes the photoconductor to form an electrostatic latent image, and a developing unit that develops the electrostatic latent image on the photoconductor.
Wherein the image forming conditions, the image forming apparatus according to any one of claims 1 to 7, characterized in that it comprises an exposure intensity of the exposure means. The image forming unit includes a photoconductor, an exposing unit that exposes the photoconductor to form an electrostatic latent image, and a developing unit that develops the electrostatic latent image on the photoconductor.
Wherein the image forming conditions, the image forming apparatus according to any one of claims 1 to 7, characterized in that it comprises a developing bias of the developing unit.