JP6300886B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to gradation control of an image forming apparatus such as a copying machine or a printer.

  Patent Document 1 discloses an image processing coefficient for converting an input density to an output density by forming a plurality of measurement images (patch images) each having a different gradation and detecting the density of the patch image. An image forming apparatus for determining the image is disclosed. Here, the image processing coefficient is gradation correction data used for gradation correction at the time of image formation. Japanese Patent Application Laid-Open No. 2004-133260 proposes that when updating an image processing coefficient, a patch image is formed using the image processing coefficient before the update.

JP2011-257598A

  For example, it is assumed that when the input density is 100%, an image processing coefficient that makes the output density smaller than 100% is created. In this case, when the patch image is formed using the image processing coefficient before update, the maximum density patch image to be formed is formed by an image signal having a density of less than 100%. Here, it is assumed that the maximum density of the patch image formed at this time is less than the target maximum density. In this case, the gradation correction data in the range from the maximum density of the patch image to be formed to the target maximum density, that is, the image processing coefficient, indicates the relationship between the density of the patch image to be formed and the density of the used image signal. It is determined by extrapolation of the data shown. In this case, the image processing coefficient in the high density region from the maximum density of the patch image to be formed to the target maximum density may lose accuracy.

  The present invention provides an image forming apparatus capable of accurately determining an image processing coefficient even in a high density region.

According to an aspect of the present invention, an image forming apparatus includes: a conversion unit that converts image data based on gradation correction conditions; an image formation unit that forms an image based on image data converted by the conversion unit; An acquisition unit that acquires read data of the measurement image output from the reading device; and the image forming unit that forms a plurality of measurement images based on the measurement image data, and the plurality of the plurality of measurement images acquired by the acquisition unit anda updating means for updating the tone correction condition on the basis of the read data of the measurement image, the plurality of measurement images include a first measurement image and a second measurement image, the measurement The image data includes a first image signal value that is not converted based on the gradation correction condition by the conversion unit to form the first measurement image, and the conversion to form the second measurement image. hand Wherein and a second image signal value converted based on the tone correction condition, the concentration of the first measurement image is characterized by darker than the concentration of said second measurement image by.

  The high density image for measurement is prevented from being formed, and thus the accuracy of the image processing coefficient in the high density area is improved.

1 is a configuration diagram of an image forming apparatus according to an embodiment. 10 is a flowchart of patch image formation processing according to an embodiment. The figure which shows the patch image by one Embodiment. The figure which shows the image processing coefficient by one Embodiment. FIG. 5 is a diagram illustrating a relationship between a density indicated by image data of a patch image according to an embodiment and a density of an image signal output to an image forming unit. The figure which shows the relationship between the input density which the image data of the patch image by one Embodiment shows, and the density of the image formed. 5 is a flowchart of image processing coefficient determination processing according to an embodiment. The figure which shows the relationship between the through characteristic and image processing coefficient by one Embodiment. The comparison figure with a prior art. 1 is a configuration diagram of an image forming apparatus according to an embodiment. The flowchart of the solid density adjustment process by one Embodiment.

  Hereinafter, exemplary embodiments of the present invention will be described with reference to the drawings. In the following drawings, components that are not necessary for the description of the embodiments are omitted from the drawings.

<First embodiment>
FIG. 1 is a configuration diagram of an exemplary image forming apparatus according to the present embodiment. First, the configuration of an image forming unit will be described. The charging unit 2 charges the surface of the photoreceptor 1 that rotates in the direction of the arrow in the drawing. The primary current generator 109 supplies a current for charging the photosensitive member 1 to the charging unit 2. The exposure unit 3 exposes the surface of the photoreceptor 1 with a laser beam corresponding to the image to be formed to form an electrostatic latent image on the photoreceptor 1. The exposure driving unit 106 generates a signal for controlling the emission of laser light from the exposure unit 3 and outputs the signal to the exposure unit 3. A developing bias is applied from the developing bias generator 110 to the developing roller of the developing unit 4, and the developing unit 4 supplies toner, which is a developer contained therein, to the photosensitive member 1 by this developing bias, and the photosensitive member. The electrostatic latent image 1 is developed with toner and visualized. The transfer unit 6 transfers the toner image formed on the photoreceptor 1 to the recording material 8 conveyed by the roller 5 or the like. The transfer current generator 111 is for supplying a transfer current to the transfer unit 6. The separation unit 7 separates the recording material 8 from the photoreceptor 1, and the recording material 8 onto which the toner image has been transferred is then conveyed by a conveyance mechanism (not shown), and the toner image is fixed in a fixing unit (not shown). It is discharged out of the device. On the other hand, the toner that is not transferred by the transfer unit 6 and remains on the photoreceptor 1 is removed by the cleaning unit 9, and the pre-exposure unit 10 neutralizes the residual potential of the photoreceptor 1. The above is the description of the image forming unit.

  The CPU 101 is a control unit of the image forming apparatus and controls the primary current generation unit 109, the exposure drive unit 106, the development bias generation unit 110, the transfer current generation unit 111, and the like. The image forming apparatus shown in FIG. 1 forms a single color image, but may be a color image forming apparatus that uses a plurality of colors. The reading unit 103 reads an image of a recording material using, for example, a CCD or the like under the control of the CPU 101, and acquires image data indicating the density of the read image. Furthermore, the operation unit 102 is an interface for a user of the image forming apparatus to give an operation instruction to the image forming apparatus. Furthermore, the storage unit 104 is a storage device and stores various data. The storage unit 104 may be a single storage device or may include a plurality of storage devices.

  Next, a flow of processing when an image read by the reading unit 103 is formed by the above-described image forming unit will be described. When receiving an image formation instruction from the operation unit 102, the CPU 101 controls the reading unit 103 to read an image formed on the recording material and acquire image data corresponding to the image formed on the recording material. The storage unit 104 holds information indicating image processing coefficients that are gradation correction data. The CPU 101 converts the density of the read image data based on the image processing coefficient held by the storage unit 104 to generate an image signal. That is, the CPU 101 performs gradation correction on the read image data based on the image processing coefficient. Subsequently, the CPU 101 performs dither processing on the image signal after gradation correction based on information indicating the dither filter held by the storage unit 104. As the dither processing, a known systematic dither method or a minimum average error method can be used. The CPU 101 outputs the image signal after the dither processing to the exposure driving unit 106 as exposure data, and the exposure driving unit 106 drives the exposure unit 3 according to the exposure data to form an electrostatic latent image on the photoreceptor 1. . Thereafter, an image is formed on the recording material 8 by the processing already described.

  An example of the image processing coefficient stored by the storage unit 104 is shown in FIG. The input in FIG. 4A is the input density, that is, the density indicated by the image data before correction, and this value is obtained when the target maximum density (hereinafter referred to as the target maximum density) is 100%. Is. The output in FIG. 4A is the output density, that is, the density after gradation correction, and corresponds to the density of the image signal output to the image forming unit for image formation. Note that the maximum value of the density of the image signal, that is, 100%, is an arbitrary standard considering the characteristics of the image signal and the characteristics of the image forming unit, and the value of the output density is based on this standard. In the image processing coefficient of FIG. 4A, for example, an image having a target maximum density, that is, an input density of 100% is converted into an image signal indicating a density of 81%. By dithering the image signal indicating the density of 81% and supplying the image signal to the exposure driving unit 106, an image having a target maximum density is formed from the characteristics of the image forming apparatus at that time. Conversely, the image processing coefficient in FIG. 4A shows that when an image is formed based on an image signal indicating 100% density, an image having a density higher than the target maximum density is formed.

  In the present embodiment, in order to update or generate the image processing coefficient held by the storage unit 104, a patch image that is a measurement image including a plurality of gradations is formed. In the present embodiment, as shown in FIG. 3, twelve different gradation patch images # 1 to # 12 are used. Patch image data including density information of each patch image for forming the patch images # 1 to # 12 is stored in the storage unit 104 in advance. In this embodiment, the data of patch image # 1 indicates 0% density, and the patch image data of patch images # 2 to # 10 are 10%, 20%, 30%, 40%, 50%, Assume that the concentrations are 60%, 70%, 80%, and 90%. It is assumed that the patch image data of patch image # 11 has a density of 99%, and the patch image of patch image # 12 has a density of 100%.

  The update processing of the image processing coefficient is executed by two processes: a patch image forming process and an image processing coefficient determination process. Hereinafter, the patch image forming process will be described with reference to FIG. In S10, the CPU 101 acquires patch image data from the storage unit 104, and acquires image processing coefficients from the storage unit 104 in S11. Here, the image processing coefficient held by the storage unit 104 is generated by the previous update processing of the image processing coefficient. Note that the image processing coefficient used in the update process of the first image processing coefficient is set in the storage unit 104 in advance.

  The CPU 101 corrects the image processing coefficient acquired in S11. 4A shows an example of the image processing coefficient acquired from the storage unit 104, and FIG. 4B shows the corrected image processing coefficient obtained by correcting the image processing coefficient shown in FIG. . As shown in FIG. 4, the correction is performed by changing the output for 100% density input of the image processing coefficient acquired from the storage unit 104 to 100%. In step S13, the CPU 101 corrects the patch image data using the corrected image processing coefficient. FIG. 5 shows the relationship between the input density indicated by the patch image data of each patch image shown in FIG. 3 and the output density subjected to gradation correction using the corrected image processing coefficient shown in FIG. 4B. In S14, the CPU 101 performs dither processing on the image signal indicating the output density after gradation correction, and forms a patch image on the recording material 8 in S15.

  FIG. 6 is a plot of the relationship between the input density when forming a patch image, that is, the density of patch image data held by the storage unit 104 and the image density of the image formed on the recording material 8. The solid line indicates the target density with respect to the input density. The image density is a reflection density measured using a spectral densitometer type 504 manufactured by X-rite. In the present embodiment, since the patch image is formed using the image processing coefficient created in the previous image processing coefficient update process, the density interval of the formed image is also substantially constant. Image processing coefficients other than the density of the image to be formed are determined by interpolation processing. However, since the patch interval is formed by correcting the gradation using the image processing coefficient, the density interval of the formed image becomes substantially constant. The accuracy of processing will be improved.

  However, for example, the maximum density of output may be limited by using image processing coefficients. For example, in the image processing coefficient of FIG. 4A, the maximum value of the density of the image signal output to the image forming unit is 81%. Therefore, in the present embodiment, in order to form at least one patch image with a 100% density image signal regardless of the image processing coefficient, the image processing coefficient is corrected when the patch image is formed.

  Subsequently, an image processing coefficient determination process will be described with reference to FIG. First, in S20, the CPU 101 uses the reading unit 103 to read the patch image formed on the recording material 8 by the forming process of FIG. 2, and in S21, acquires image data indicating the density. The user sets the recording material 8 on which the patch image is formed on the reading unit 103. In S22, the CPU 101 determines the relationship between the density of the image signal output to the image forming unit for forming each patch image, that is, the density shown in the output column of FIG. 5 and the density of each patch image acquired in S21. Create the through characteristics shown. Note that the density of an image formed by an image signal having a density other than the density in the output column in FIG. 5 is obtained, for example, by linearly complementing the relationship between the density in the output column in FIG. 5 and the density of the formed image. Thereby, for example, a through characteristic indicating the relationship between the density of the image signal in increments of 1% and the density of the formed image is generated.

  In S23, the CPU 101 normalizes the through characteristic with the target maximum density. That is, for example, the target maximum density is set to 100%, and the density of the formed image is specified as a ratio with respect to the target maximum density. For example, the target maximum density is 1.5, and this value is stored in the storage unit 104 in advance.

  Subsequently, the CPU 101 acquires target gradation data from the storage unit 104 in S24, and determines an updated image processing coefficient to be used for subsequent image formation in S25. FIG. 8 is an explanatory diagram for determining the image processing coefficient in S25. Reference numeral 80 in FIG. 8 is a through characteristic, reference numeral 81 is an image processing coefficient to be determined, and reference numeral 82 indicates a target gradation indicated by the target gradation data.

  For the through characteristic 80, the horizontal axis in FIG. 8 represents the density of the image signal output to the image forming unit, and the vertical axis represents the formed image density. The formed image density is shown as a ratio based on the target maximum density. Further, the density of the image signal is 100% based on an arbitrary standard determined in consideration of the characteristics of the image signal and the characteristics of the image forming unit. The black circles are the actually used image signal and the actually formed image density, and the other portions are obtained by interpolation processing. For example, FIG. 8 shows that when the density of the image signal is 100%, an image having a density of about 102% of the target maximum density is formed. Further, with respect to the target gradation, the horizontal axis in FIG. 8 represents the input density, that is, the density indicated by the image data before gradation correction, and the vertical axis represents the image density to be formed. The input density and the density of the image to be formed are shown as a ratio based on the target maximum density. For example, FIG. 8 shows that if the input density is 100%, an image having the same density as the target maximum density should be formed. Further, with respect to the image processing coefficient 81, the horizontal axis in FIG. 8 represents the input density, and the vertical axis represents the output density used as the density of the image signal. The image processing coefficient 81 is determined by inversely transforming the through characteristic 80 with respect to the target gradation. For example, the image processing coefficient in FIG. 8 indicates that 100% input density is converted to 91% output density, but if the density of the image signal is 91% due to the through characteristics, the target is actually the target. An image having the same density as the maximum density is formed. That is, by using the image processing coefficient 81 in FIG. 8, an image having a target maximum density is formed with image data having a density of 100% as indicated by the target gradation. In step S26, the CPU 101 stores the image processing coefficient determined in step S25 in the storage unit 104, thereby ending the image processing coefficient update process. The image processing coefficient stored in S26 is then used for gradation correction in normal image formation.

  9A shows through characteristics when a patch image is formed using the image processing coefficient of FIG. 4A as it is, and FIG. 4B shows the image processing coefficient of FIG. 4A. This is a through characteristic when a patch image is formed after correction. In the image processing coefficient of FIG. 4A, the maximum density of the image signal is 81%, and the image density at this time is approximately 96% of the target maximum density. Therefore, the density of the image signal for forming an image of about 96% to 100% of the target maximum density must be determined by extrapolation from data on the lower density side than the target maximum density. As indicated by the white square in FIG. 9A, the density of the image signal for achieving the target maximum density is determined to be 87% by extrapolation interpolation. On the other hand, in the present embodiment, a patch image is formed with an image signal having a density of 100%, and therefore the image processing coefficient can be accurately determined by interpolation using the formed patch image. it can. For example, as indicated by a white square in FIG. 9B, in this embodiment, the density of the image signal for setting the target maximum density is determined to be 91%. Note that when the patch image is formed by changing the density of the image signal in units of 1%, the density of the image signal for achieving the target maximum density is 90%. Therefore, as compared with using the image processing coefficient of FIG. 9A as it is, the present embodiment improves the density error of the image signal for forming the image of the target maximum density. This means that when converted to the reflection density, the density error of the maximum density image to be formed is improved by about 0.03. Therefore, with the configuration of this embodiment, it is possible to stably reproduce the image density in the high density region, and it is possible to improve the reproducibility of characters and the quality of solid density.

<Second embodiment>
Subsequently, the second embodiment will be described with a focus on differences from the first embodiment, and re-explanation of the contents described in the first embodiment will be omitted. In the present embodiment, the density of an image formed when the density of the image signal is 100% is adjusted by changing the image forming conditions. In this embodiment, the exposure intensity is used as the image forming condition, but any parameter that can control the density of the formed image can be used. Note that the image density formed by changing the exposure intensity changes because the contrast potential changes and the amount of toner attached to the electrostatic latent image changes. FIG. 10 is a configuration diagram of the image forming apparatus according to the present embodiment. The difference from the first embodiment is that the storage unit 104 holds solid image data for forming a patch image used for the solid density adjustment process and information indicating the exposure intensity determined by the solid density adjustment process. It is that you are. Note that the solid image data indicates 100% density.

  FIG. 11 is a flowchart of the solid density adjustment process. When receiving an instruction to start solid density adjustment from the operation unit 102, the CPU 101 acquires solid image data from the storage unit 104 in S30. In step S32, the CPU 101 forms a solid patch image on the recording material based on the solid image data with a predetermined exposure intensity. At this time, tone correction is not performed by the image processing coefficient. Alternatively, as in the first embodiment, when the input density is 100%, an image processing coefficient modified so as to be converted to an output density of 100% is applied. Further, the predetermined exposure intensity can be an arbitrary initial value, for example, the minimum settable intensity range. In S <b> 32, when the recording material is set on the reading unit 103 by the user, the CPU 101 reads a solid image formed on the recording material. In S33, the CPU 101 determines whether the density of the solid image read in S32 is equal to or higher than the target maximum density. If the density of the solid image is equal to or higher than the target maximum density, the CPU 101 stores the exposure intensity used for forming the solid image in S31 in the storage unit 104 in S34 and ends the solid density adjustment process. On the other hand, if the density of the solid image is less than the target maximum density, the CPU 101 increases the exposure intensity by a predetermined amount and repeats the process from S31.

  Thereafter, the CPU 101 uses the exposure intensity stored in S34 to perform the image processing coefficient update processing described in the first embodiment. With this configuration, the maximum density of the patch image formed by the update processing of the image processing coefficient is equal to or higher than the target maximum density, and thus it is possible to perform gradation correction by interpolation in a necessary density range.

  <Other embodiments>

  In the above embodiment, the image processing coefficient is corrected so that the input density of 100% of the image processing coefficient is converted to the output density of 100%. However, if the image processing coefficient is converted to a density that is higher than the maximum value of the output density of the image processing coefficient and equal to or less than the maximum value of the density of the image signal to the image forming unit, the extrapolation interpolation interval is shortened, and the accuracy of the interpolation processing is improved. be able to. Specifically, for example, in the case of the image processing coefficient in FIG. 4A, 100% input density may be converted to an output density greater than 81% and less than 100%. Each embodiment can be configured to be performed only when the maximum value of the output density of the image processing coefficient is already smaller than the maximum value of the density of the image signal, that is, 100%.

  In the above embodiment, patch image data corresponding to each patch image is stored in the storage unit 104, and tone correction is performed on all patch image data using image processing coefficients. For this reason, the output density with respect to the input density of 100% of the image processing coefficient is corrected to a density higher than the maximum value of the output density of the image processing coefficient so that the patch image showing the density of 100% is not converted to a low density. It was. This is a patch image (first measurement image) converted to a density higher than the maximum value of the output density of the image processing coefficient regardless of the image processing coefficient, and a patch whose gradation is corrected according to the image processing coefficient. This means that two types of patch images of the image (second measurement image) are used. Accordingly, the image processing coefficients are not corrected, and the patch images are prepared in two groups of the first image data corresponding to the first patch image and the second image data corresponding to the second patch image. It can also be set as the structure to carry out. In this case, the first image data is formed as an image signal as it is without performing gradation correction. On the other hand, the second image data is subjected to gradation correction using the image processing coefficient stored in the storage unit 104 without correction, and image formation is performed. At this time, the density of the first patch image is, for example, 100%, which is the maximum value of the density of the image signal. However, for example, a plurality of patch images in a high density region such as 80% or more or 90% or more can be prepared as the first patch image. Also in this configuration, it is possible to shorten the section for performing extrapolation when determining the image processing coefficient while forming images with substantially equal density on the recording material 8 using the image processing coefficient.

  Further, in the above embodiment, a patch image is formed on a recording material that is an image carrier and is read by the reading unit 103. However, a patch image formed on another image carrier such as an intermediate transfer member The reading may be performed by a reading unit such as a sensor provided facing the carrier.

  The present invention can also be 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. It is a process to be executed.

  1: Photoconductor, 2: Charging unit, 3: Exposure unit, 4: Development unit, 6: Transfer unit, 101: CPU, 103: Reading unit, 104: Storage unit

Claims (11)

Conversion means for converting image data based on gradation correction conditions;
Image forming means for forming an image based on the image data converted by the converting means;
An acquisition means for acquiring read data of the measurement image output from the reading device;
Update means for causing the image forming means to form a plurality of measurement images based on the measurement image data, and updating the gradation correction conditions based on the read data of the plurality of measurement images acquired by the acquisition means And having
The plurality of measurement images include a first measurement image and a second measurement image,
The measurement image data includes a first image signal value that is not converted by the conversion unit based on the gradation correction condition to form the first measurement image, and a second measurement image. A second image signal value converted based on the gradation correction condition by the conversion means,
The image forming apparatus according to claim 1, wherein the density of the first measurement image is higher than the density of the second measurement image . The image forming apparatus according to claim 1, wherein the gradation correction condition is data for correcting a gradation of an image formed by the image forming unit.   The image forming apparatus according to claim 1, wherein the reading device reads the measurement image formed on the recording material by the image forming unit. An intermediate transfer member to which the plurality of measurement images formed by the image forming unit are transferred;
The image forming apparatus according to claim 1, wherein the reading device reads the plurality of measurement images transferred onto the intermediate transfer member. Conversion means for converting image data based on gradation correction conditions;
Image forming means for forming an image based on the image data converted by the converting means;
An acquisition means for acquiring read data of the measurement image output from the reading device;
Update means for causing the image forming means to form a plurality of measurement images based on the measurement image data, and updating the gradation correction conditions based on the read data of the plurality of measurement images acquired by the acquisition means And having
The plurality of measurement images include a first measurement image and a second measurement image,
The measurement image data includes a first image signal value that is not converted by the conversion unit based on the gradation correction condition to form the first measurement image, and a second measurement image. A second image signal value converted based on the gradation correction condition by the conversion means,
The image forming apparatus according to claim 1, wherein the first image signal value is a value such that a density of the first measurement image is higher than a density of the second measurement image. The image forming apparatus according to claim 5, wherein the first image signal value is higher than the second image signal value. 7. The image forming apparatus according to claim 5, wherein the gradation correction condition is data for correcting gradation of an image formed by the image forming unit. The image forming apparatus according to claim 5, wherein the reading device reads the measurement image formed on the recording material by the image forming unit. An intermediate transfer member to which the plurality of measurement images formed by the image forming unit are transferred;
The image forming apparatus according to claim 5, wherein the reading device reads the plurality of measurement images transferred onto the intermediate transfer member. The plurality of measurement images include a plurality of second measurement images,
10. The first image signal value is a value such that the density of the first measurement image is higher than the density of any one of the plurality of second measurement images. The image forming apparatus according to any one of the above. The image forming apparatus according to claim 5, wherein the first image signal value is a maximum value among a plurality of image signal values included in the measurement image data.

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