JP2018165051A - Image forming apparatus and image forming apparatus control method - Google Patents

Abstract

An image forming apparatus capable of performing gradation correction with high accuracy while maintaining user convenience. An image forming apparatus includes: an image forming unit that forms an image on an intermediate transfer belt based on a predetermined gradation correction table; a density sensor that measures a density of an image formed on the intermediate transfer belt; The image forming unit 5 forms a test image including a plurality of test images having different densities in the main scanning direction of the intermediate transfer belt, and generates a gradation correction table based on the test image measurement result by the density sensor 117. A printer controller 10. [Selection] Figure 2

Description

  The present invention relates to density control of an image formed by an image forming apparatus.

  An electrophotographic image forming apparatus forms an image by scanning a photoconductor with a laser beam. The image forming apparatus includes an exposure unit that emits laser light. The exposure device irradiates a photoconductor whose surface is uniformly charged with a laser beam corresponding to an image signal representing an image to be formed. An electrostatic latent image is formed on the photosensitive member by irradiation with laser light. By developing the electrostatic latent image with toner, a toner image is formed on the photoreceptor. The toner image is transferred to the sheet. The image forming apparatus includes a fixing device. The fixing device fixes the toner image on the sheet by heating and pressing the sheet on which the toner image is transferred. Thus, an image is formed on the sheet.

  In an image forming apparatus, color variations may occur in an image formed due to environmental changes such as temperature and humidity, changes with time of the apparatus, performance deterioration of parts, and the like. The image forming apparatus performs density gradation correction in order to suppress color variation and form an image with stable image quality. The density gradation correction is generally performed by forming a measurement image including a color test image for measuring gradation on a sheet. The image forming apparatus creates a correction table from the measurement result of the color test image by the densitometer and the colorimeter and preset target data, and corrects the density gradation by correcting the image signal according to the correction table. Do.

  In order to perform highly accurate density gradation correction, it is necessary to consider the influence of density unevenness and color unevenness in the measurement image when creating the correction table. The influence of these unevennesses is generally greater in the main scanning direction in which the laser beam scans the photoconductor than in the sub-scanning direction. Density unevenness in the main scanning direction is, for example, unevenness in the amount of laser light such as aberration of the lens constituting the optical system that guides the laser light to the photoreceptor, distortion of the lens, inclination of the mounting position of the exposure device, and change in the laser optical path length. There is a cause. Further, density unevenness in the main scanning direction may be caused by sensitivity unevenness of the photosensitive member or charging unevenness of the photosensitive member.

  In order to reduce density unevenness, density unevenness correction in the main scanning direction is performed. Density unevenness correction in the main scanning direction is performed by using a sheet in which an image forming range in the main scanning direction is divided into a plurality of blocks and a measurement image including a reference test image for measuring density unevenness is formed on these blocks. Done. Based on the measurement result of the reference test image for each block, the laser light quantity is adjusted so that the density difference for each block is eliminated.

In general, after density unevenness correction in the main scanning direction is performed, density gradation correction is performed in the same procedure. Density unevenness correction and density gradation correction are performed using different measurement images. Therefore, the user needs to print the measurement image and measure the measurement image twice for the density unevenness correction and the density gradation correction. This becomes a factor of a decrease in user convenience.
Further, when the measurement image for density unevenness correction and the measurement image for density gradation correction are printed separately, a difference occurs in the printing conditions of the image forming apparatus. For this reason, the result of density unevenness correction cannot be accurately reflected in the density gradation correction, and the accuracy of density gradation correction is reduced.

  Therefore, a measurement image including a reference test image for density unevenness correction and a color test image for density gradation correction is formed on one sheet, and density unevenness correction and density gradation correction in the main scanning direction are performed simultaneously. A technique to do this has been proposed. Patent Document 1 describes an image forming apparatus that prints a measurement image in which a plurality of color test images and a plurality of reference test images are arranged on the same main scanning line, and measures the density of the printed measurement image. Yes. This image forming apparatus performs density unevenness correction in the main scanning direction using the measured densities of the plurality of reference test images, and performs density gradation correction using the measured densities of the plurality of color test images. Patent Document 2 describes an image forming apparatus that corrects density unevenness in all gradation regions by creating a gradation correction table for each position in the main scanning direction and the sub-scanning direction.

JP 2009-192896 A JP 2013-44990 A

  There are multiple causes of density unevenness in the main scanning direction, and the degree of influence varies depending on the density range. For this reason, the image forming apparatus of Patent Document 1 can correct density unevenness in the density region of the reference test image for correcting density unevenness in the main scanning direction, but cannot accurately correct density unevenness in the density region where the reference test image is not formed. . In the image forming apparatus of Patent Document 2, the correction value of each density is obtained from a reference test image in which the density is changed stepwise, and density unevenness at each density level can be corrected. However, since the number of reference test images used for correction increases, it is necessary to print the measurement images on a plurality of sheets, which reduces user convenience. In addition, since the measurement image is printed in a plurality of sheets, the gradation correction table creation accuracy decreases according to the accuracy of the printing conditions of the image forming apparatus at the time of printing.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus capable of performing gradation correction with high accuracy while maintaining user convenience.

  An image forming apparatus according to the present invention includes a conversion unit that converts image data based on a plurality of conversion conditions, and a laser based on the image data converted by the conversion unit to form an electrostatic latent image on a photosensitive member. An exposure unit that emits light, and the laser beam scans the photoconductor along a predetermined direction to expose the photoconductor; a developing unit that develops the electrostatic latent image formed on the photoconductor; An intermediate transfer member to which a plurality of measurement images formed on the photosensitive member are transferred by the exposure unit and the developing unit; a measurement unit that measures the plurality of measurement images transferred to the intermediate transfer member; First conversion means for generating correction data based on the measurement result of the measurement means; and the plurality of conversion conditions based on the measurement result of the measurement means and the correction data generated by the first generation means. A plurality of measurement images based on first measurement images formed based on the first image data and second image data different from the first image data. And the second measurement image is formed between the second measurement image and another second measurement image in the predetermined direction, and the second measurement image is formed. The image for use is formed between the first image for measurement and the other image for first measurement in the predetermined direction, and the first generation unit is configured to output the measurement result of the second image for measurement and the other first measurement image. Based on the measurement results of the two measurement images, the correction data of the first measurement image and the correction data of the other first measurement image are generated, and the first generation means is configured to generate the first measurement image. Based on the measurement result of the image and the measurement result of the other first measurement image, the first The correction data of the measurement image and the correction data of the other second measurement image are generated, and the second generation unit is configured to measure the measurement result of the first measurement image and the correction data of the first measurement image. Based on the above, the conversion condition corresponding to the position where the first measurement image of the photoconductor is formed is generated, and the second generation unit generates the measurement result of the other first measurement image and the other Based on the correction data of the first measurement image, a conversion condition corresponding to a position where the other first measurement image of the photoconductor is formed is generated, and the second generation unit is configured to generate the second measurement unit. Based on the measurement result of the second measurement image and the correction data of the second measurement image, a conversion condition corresponding to a position where the second measurement image is formed on the photoconductor is generated, and the second The generation means includes the measurement result of the other second measurement image and the other second measurement image. Based on the correction data of the regular image, a conversion condition corresponding to a position where the other second measurement image of the photoconductor is formed is generated.

  According to the present invention, it is possible to generate a gradation correction table with high accuracy while maintaining user convenience.

1 is a configuration diagram of an image forming apparatus. Explanatory drawing of a printer controller. Explanatory drawing of the function of an image process part. Explanatory drawing of the gradation correction value with respect to the input signal in a main scanning position. The flowchart showing the process which produces a gradation correction table. (A), (b) is an illustration figure of a test image. Explanatory drawing of interpolation of correction data. Explanatory drawing of correction data. Explanatory drawing of the preparation method of a gradation correction table. FIG. 6 is a view showing another test image. FIG. 6 is a view showing another test image. Explanatory drawing of correction data. Explanatory drawing of interpolation of correction data. FIG. 4 is an exemplary diagram of a sheet on which a test image is formed. FIG. 6 is an exemplary diagram of another sheet on which a test image is formed.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

<First Embodiment>
FIG. 1 is a configuration diagram of the image forming apparatus 100. The image forming apparatus 100 includes a printer 101, an image reading unit 2, and an operation unit 3.

  The printer 101 includes four image forming units 120, 121, 122, and 123 that form an image for each color component. The image forming unit 120 forms a yellow image. The image forming unit 121 forms a magenta image. The image forming unit 122 forms a cyan image. The image forming unit 123 forms a black image.

  The image forming units 120, 121, 122, and 123 have the same configuration. Hereinafter, the configuration of the image forming unit 120 that forms a yellow image will be described. The description of the configuration of the other image forming units 121, 122, and 123 is omitted. The photosensitive drum 105 is a photosensitive member having a photosensitive layer on the surface, and is charged by the charger 111 while rotating. The photosensitive drum 105 is scanned by a laser from the exposure device 108 controlled based on the image data. By scanning with the laser beam, an electrostatic latent image is formed on the photosensitive drum 105. The developing device 112 develops the electrostatic latent image using a developer containing toner and a magnetic carrier. As a result, a toner image is formed on the surface of the photosensitive drum 105. The toner image on the photosensitive drum 105 is transferred onto an intermediate transfer belt 106 that is an intermediate transfer member.

  The charger 111 functions as a charging unit that charges the photosensitive drum 105. The exposure device 108 functions as an exposure unit that exposes the photosensitive drum 105 based on image data in order to form an electrostatic latent image on the photosensitive drum 105. The developing device 112 functions as a developing unit that develops the electrostatic latent image on the photosensitive drum 105 with toner.

  The sheet 110 accommodated in the container 113 is conveyed toward the transfer roller 114 so that the timing coincides with the toner image carried on the intermediate transfer belt 106. The transfer roller 114 transfers the toner image carried on the intermediate transfer belt 106 to the sheet 110. The transfer roller 114 functions as a transfer unit that transfers the toner image formed on the photosensitive drum 105 to the sheet 110. Alternatively, the transfer roller 114 functions as a transfer unit that transfers the toner image transferred to the intermediate transfer belt 106 to the sheet 110. The sheet 110 on which the toner image is transferred is conveyed to the fixing devices 150 and 160.

  The fixing devices 150 and 160 heat and press the toner image transferred to the sheet 110 to fix it on the sheet 110. The fixing device 150 includes a fixing roller 151, a pressure belt 152, and a sensor 153. The fixing roller 151 includes a heater for applying heat to the sheet 110. The pressure belt 152 brings the sheet 110 into pressure contact with the fixing roller 151. The sensor 153 detects that the sheet 110 has passed the fixing position of the fixing device 150. The fixing device 160 is disposed downstream of the fixing device 150 in the conveyance direction of the sheet 110. The fixing device 160 gives gloss to the toner image on the sheet 110 that has passed through the fixing device 150. The fixing device 160 includes a fixing roller 161 having a heater, a pressure roller 162, and a sensor 163 for detecting that the sheet 110 has passed the fixing position of the fixing device 160.

  When the image is fixed on the sheet 110 or the image is fixed on thick paper in the mode for giving gloss, the printer 101 conveys the sheet 110 that has passed through the fixing device 150 to the fixing device 160. When fixing an image on plain paper or thin paper, the printer 101 conveys the sheet 110 that has passed through the fixing device 150 along a conveyance path 130 that bypasses the fixing device 160. As a result, the sheet 110 such as thin paper is discharged from the printer 101 without being conveyed to the fixing device 160.

  Whether the sheet 110 is conveyed to the fixing device 160 or the sheet 110 is conveyed around the fixing device 160 is controlled by switching the flapper 131.

  The flapper 132 is a guide member that guides the sheet 110 to either the transport path 135 or the transport path 139 to the outside. The sheet 110 transported along the transport path 135 is transported to the reversing unit 136. When the reverse sensor 137 provided in the transport path 135 detects the trailing edge of the sheet 110, the transport direction of the sheet 110 is reversed.

  The flapper 133 is a guide member that guides the sheet 110 to either the transport path 138 for forming a double-sided image or the transport path 135. The sheet 110 conveyed along the conveyance path 138 is conveyed again to the transfer roller 114. When the double-sided printing mode is executed, after the image is fixed on the first surface, the sheet 110 is switched back by the reversing unit 136 and conveyed to the transfer roller 114 along the conveying path 138. An image is formed on the surface.

  A color sensor 200 that measures the density of the measurement image on the sheet 110 is disposed in the conveyance path 135. When the execution of density stabilization control is instructed from the operation unit 3 or an external computer, the image forming apparatus 100 uses the color sensor 200 to execute maximum density adjustment control and gradation adjustment control.

  The flapper 134 is a guide member that guides the sheet 110 to the conveyance path 139. For example, when the sheet 110 is discharged face down, the flapper 134 guides the sheet switched back in the reversing unit 136 to the conveyance path 139. The sheet 110 conveyed along the conveyance path 139 is discharged outside the printer 101.

  Around the intermediate transfer belt 106, a density sensor 117, a position detection sensor 115, and a position detection sensor 116 are provided. The density sensor 117 measures a test image on the intermediate transfer belt 106. Six density sensors 117 are provided along a direction orthogonal to the direction in which the intermediate transfer belt 106 conveys an image. The density sensor 117 may be an area sensor such as CIS. The position detection sensor 115 detects whether an image on the intermediate transfer belt 106 has passed a predetermined position. The position detection sensor 116 detects whether or not the sheet 110 has reached the standby position.

  FIG. 2 is an explanatory diagram of the printer controller 10 that controls the image forming apparatus 100. The control unit 11 includes a CPU (Central Processing Unit), a RAM (Random Access Memory), and the like. The control unit 11 controls the operation of each unit of the image forming apparatus 100 by reading and executing the computer program stored in the storage unit 12. For example, the control unit 11 controls an image forming operation by the printer 101. The image forming unit 5 corresponds to the image forming units 120, 121, 122, and 123 described above.

  The storage unit 12 stores various computer programs, parameters used for executing processes, and the like. The memory control unit 13 controls input / output of image data to the image memory 14. The image memory 14 is a temporary memory for storing images, and is composed of a DRAM (Dynamic RAM) or the like.

  FIG. 3 is an explanatory diagram of main functions of the image processing unit 15. The image processing unit 15 performs image processing on the image data (digital image signal).

  The shading correction unit 251 corrects the reading error of the image reading unit 2 with respect to the red (R), green (G), and blue (B) digital image signals transferred from the image reading unit 2. The color conversion unit 252 performs color conversion on the digital image signal subjected to shading correction. The color conversion unit 252 converts red (R), green (G), and blue (B) digital image signals into yellow (Y), magenta (M), cyan (C), and black (K) image signals. . The generated image signals of Y, M, C, and K are transferred to the γ correction unit 255 for each color. The γ correction unit 255 converts the image signal based on the conversion condition so that the gradation characteristic of the printer 101 becomes an ideal gradation characteristic. The γ correction unit 255 converts the image signal using a gradation correction table indicating the correspondence between the input value and the output value of the image signal as the conversion condition. The halftone processing unit 256 performs pseudo halftone processing on the image signal output from the γ correction unit 255. The halftone process is performed by a method such as a dither matrix method or an error diffusion method. The halftone processing unit 256 transfers the image signal to the exposure device 108. The exposure device 108 controls blinking of the laser beam based on the image signal.

<Tone correction table creation process>
A method of creating a gradation correction table for each main scanning position using a test image that is a measurement image for creating a gradation correction table will be described. The gradation correction table for each main scanning position created here is a table representing the relationship between the address of the main scanning position X and the gradation correction value Out for the input image signal I as shown in FIG. The main scanning position corresponds to a position in a predetermined direction (main scanning direction) in which the laser beam from the exposure device 108 scans the photosensitive drum 105. In other words, the direction orthogonal to the rotation direction of the photosensitive drum 105 corresponds to the predetermined direction (main scanning direction). Hereinafter, a direction orthogonal to the main scanning direction is referred to as a sub-scanning direction. The main scanning position is divided into, for example, eight areas as shown in FIG. A region from one end of the photosensitive drum 105 to a predetermined length in the main scanning direction is defined as a main scanning position G0. A region adjacent to the main scanning position G0 is the main scanning position G1. Similarly, the photosensitive drum 105 includes main scanning positions G2, G3, G4, G5, G6, and GMAX along the main scanning direction. The main scanning position GMAX corresponds to a region from the other end of the photosensitive drum 105 to a predetermined length in the main scanning direction.

  FIG. 5 is a flowchart showing a process for creating a gradation correction table for each main scanning position. The control unit 11 invalidates the density unevenness correction process (S1). The control unit 11 controls the image forming unit 5 to form a test image (S2). The image signal of the test image (test image signal) is stored in the storage unit 12 or the image memory 14 in advance. The control unit 11 reads the image signal of the test image and inputs it to the image forming unit 5 via the image processing unit 15. The image forming unit 5 forms a test image based on the test image signal.

  FIG. 6 is an exemplary view of a test image. FIG. 6A shows a conventional test image, and FIG. 6B shows a test image of this embodiment. The test image is a plurality of test images in which the density Lk (k = 0, 1, 2, 3, 4, 5, 6, 7, 8, 9) is changed stepwise in a predetermined direction, here the main scanning direction. Consists of. In the figure, image signal values indicating the density of each pixel are shown. That is, the test signal having the density Lk indicates the image signal value Lk. In this example, the density range is a minimum value 0 to a maximum value 255. The image signal value Lk of the test image is any one of L0 = 0, L1 = 26, L2 = 52, L3 = 78, L4 = 104, L5 = 130, L6 = 156, L7 = 182, L8 = 208, and L9 = 255. Is set. Therefore, this test image includes a test image having image signal values Lk for 10 gradations.

  As shown in FIGS. 6A and 6B, the test image is arranged at a position to be a sampling point. Sampling points are provided side by side in the main scanning direction. The position of the sampling point in the main scanning direction is indicated by a main scanning position X (X = G1, G2, G3, G4, G5, G6). The position of the image edge in the main scanning direction is indicated by X = G0, GMax. If the size of the test image is reduced, the detection accuracy of the test image is lowered. Therefore, the number of test images that can be formed on one test image is limited. In the present embodiment, one test image has 6 sections in the main scanning direction and 5 sections in the sub-scanning direction, and a total of 30 test images are formed. A conventional test image is formed so that each test image in the main scanning direction has the same density. On the other hand, the test images of the present embodiment are formed so that every other test image in the main scanning direction has the same density.

  The controller 11 controls the density sensor 117 to measure the density of the test image formed on the intermediate transfer belt 106 (S3). The concentration sensor 117 inputs the measurement result to the control unit 11. The control unit 11 performs an operation for converting the acquired measurement result into a color density. The control unit 11 treats this calculated value as the detected density value. The control unit 11 interpolates correction data (interpolation data) for creating a gradation correction table at the main scanning position X where the test image is not actually formed, using the detection result of the density value of the test image (S4). ).

  FIG. 7 is an explanatory diagram of interpolation of correction data for creating a gradation correction table at the main scanning position X. In this figure, black circles indicate actual measurement values of the test image, and white circles indicate interpolation values from unevenness of the density profile in the main scanning direction. For example, the interpolation processing is performed by linear interpolation using the density values of known test images in the vicinity, but may be other interpolation processing. There are six main scan positions of the test image, X = G1, G2, G3, G4, G5, and G6. The controller 11 creates correction data for all main scanning position addresses from one end of the photosensitive drum 105 to the other end by interpolation processing.

  In general, the change in density unevenness in the main scanning direction is smaller than the change in gradation characteristics. The gradation characteristics change rapidly depending on the usage environment of the image forming apparatus 100, changes with time, and deterioration of member performance with time. For this reason, it is difficult to obtain the density characteristic with respect to the input image signal value I with high accuracy from the detection result of few gradations. The density unevenness in the main scanning direction does not change abruptly because it is caused by unevenness in the amount of laser light, sensitivity of the photosensitive drum 105, uneven charging, and the like. Therefore, the density unevenness in the main scanning direction can be obtained by interpolation from the measurement results at a plurality of positions without actually measuring all the positions in the main scanning direction. In the present embodiment, a gradation correction table for each main scanning position is created with high accuracy while suppressing the number of test images using the difference between the above gradation characteristics and density unevenness characteristics in the main scanning direction. .

  Here, FIG. 8 is an explanatory diagram of correction data obtained from the test images of FIGS. 6A and 6B. In the figure, black circles indicate actual measurement values of the test image. White circles indicate the correction data interpolated in the process of S4. When a test image having the same image signal value is formed for each main scanning position in order to create a gradation correction table for each main scanning position, conventionally, for example, a test image having 5 gradations has been formed. This is because the density of the test image includes an error of density unevenness in the main scanning direction. If a test image is formed for each main scanning position, the gradation characteristics can be corrected to the ideal gradation characteristics with high accuracy even if density unevenness occurs. However, in the above-described configuration, a plurality of test images must be formed in order to correct a wide range of gradation characteristics from low density to high density in the sub-scanning direction. In the test image of this embodiment, the density unevenness in the main scanning direction is predicted from the measurement result of the test image formed in the adjacent region, so that the number of test images that can be formed in the predetermined region in the sub-scanning direction is increased. Can do. With the above-described configuration, the number of test images that can be formed in a predetermined region is five, whereas according to this configuration, the number of test images that can be formed in a predetermined region is ten.

  Returning to the description of FIG. When the interpolation processing is completed, the γ correction unit 255 of the image processing unit 15 creates a gradation correction table for each main scanning position X (S5). FIG. 9 is an explanatory diagram of a method for creating a gradation correction table. In FIG. 9, an approximate curve of density detected from the test image is represented by a one-dot chain line. This approximate curve shows the density characteristics of the test image (toner image) detected at the main scanning position X. A solid line represents a density characteristic as a target value. The broken line is a curve that is symmetrical with the approximate curve detected from the test image with respect to the density characteristic as the target value. This broken line is a gradation correction curve and corresponds to the gradation correction table. The γ correction unit 255 repeatedly performs a process for obtaining such a gradation correction table for each main scanning position X.

  The density characteristic as a target value represented by a solid line is a straight line having an inclination “1” such that the density value of the output image is the same as the input image signal value I. That is, the density characteristic as the target value indicates a density characteristic in which, if the image signal value of the image is Ln, the density detected from the toner image formed by the image signal value is also Ln.

  In the above example, as shown in FIG. 6B, the test image has a configuration in which every other test image having the same density is arranged in the main scanning direction. The test image only needs to have a plurality of test images having the same density in the main scanning direction. FIG. 10 is a diagram illustrating another test image. In this test image, every two test images having the same density are arranged in the main scanning direction.

  The image forming apparatus 100 of the first embodiment configured as described above can increase the number of gradations of correction data when creating a gradation correction table for each main scanning position. For example, in the conventional test image of FIG. 6A, the number of gradations is “5”. On the other hand, in the test image of the present embodiment in FIG. In the test image of another example of the present embodiment in FIG. 10, the number of gradations is “15”. As a result, a gradation correction table can be created with high accuracy with a small number of test images.

  Further, since the density unevenness correction and the density gradation correction in the main scanning direction can be performed with one test image, the burden on the user is reduced as compared with the case where the density unevenness correction and the density gradation correction are performed separately. it can. Compared with the case where the measurement image for creating the gradation correction table is divided into a plurality of sheets and printed, it is possible to prevent the accuracy of the printing conditions of the image forming apparatus when printing the measurement image.

Second Embodiment
In the first embodiment, when the correction data of the gradation correction table is generated, the measurement result of the test image having the same density in the main scanning direction is generated by interpolation. For this reason, it is necessary to form a plurality of test images having the same density in the main scanning direction. In the second embodiment, a plurality of test images having the same density are not formed in the main scanning direction. In the second embodiment, correction data for creating a gradation correction table is created for each main scanning position from the measurement result of the density of one test image by using the measurement result of the test image having a close density. Since the configuration of the image forming apparatus in the second embodiment is the same as that of the first embodiment, description of the configuration is omitted.

  FIG. 11 is an exemplary diagram of a test image that is a measurement image for creating correction data in the second embodiment. As the test image, only one test image having a different density in the main scanning direction is formed. FIG. 12 is an explanatory diagram of correction data obtained from the test image of FIG. In the figure, black circles indicate actual measurement values of the test image. White circles indicate interpolation values from uneven density profiles in the main scanning direction. A triangle indicates a correction value from unevenness of the density profile in the main scanning direction. FIG. 13 is an explanatory diagram of interpolation of correction data for creating a gradation correction table in the main scanning direction.

  In the second embodiment, as shown in FIG. 12, the correction data of the image signal value Lk−1 = 162 is interpolated using the density profile in the main scanning direction of the image signal value Lk = 182. That is, from the measured density (measured value of the density signal value Lk-1 at the main scanning position G3) and the density profile, the main scanning direction (G1, G2, G4, G5, G6) of the image signal value Lk-1 = 162. ) Is interpolated for each position.

  In the image forming apparatus of the second embodiment configured as described above, even when a plurality of test images having the same density are not formed in the main scanning direction, correction data for creating a gradation table for each main scanning position Can be created. That is, a test image that is a measurement image for generating image forming conditions such as a gradation correction table may be formed with at least one of a plurality of test images arranged in the main scanning direction having different densities.

<Third Embodiment>
The plurality of test images described in the first embodiment has a configuration in which every other test image having the same density is arranged in the main scanning direction. That is, the plurality of test images described in the first embodiment have different image signal values for forming adjacent test images in the main scanning direction. For this reason, the plurality of test images described in the first embodiment have different densities in adjacent test images in the main scanning direction. The image forming apparatus described in the present embodiment forms a part of test images adjacent in the main scanning direction based on the same image signal value. Therefore, the test image described in the present embodiment includes test images having different densities adjacent in the main scanning direction and test images having the same density adjacent in the main scanning direction.

  Note that the configuration of the image forming apparatus according to the present embodiment is the same as that of the first embodiment, and thus the description of the configuration is omitted. In the following description, the main scanning positions G0 to GMAX are referred to as regions G0 to GMAX. Here, one area is divided into a plurality of main scanning positions X. Therefore, the γ correction unit 255 converts the image data based on the gradation correction table for each main scanning position.

  Furthermore, the test image described in the present embodiment is formed on a sheet and is read by the image reading unit 2. That is, the control unit 11 according to the present embodiment controls the image reading unit 2 to acquire read data of a plurality of test images formed on the sheet, and corresponds to the main scanning position based on the acquired read data. A gradation correction table to be generated is generated.

  FIG. 14 is an exemplary view of a sheet on which a plurality of test images are formed. The plurality of test images shown in FIG. 14 have 11 gradations. The plurality of test images include image signal values “0”, “24”, “48”, “72”, “96”, “120”, “144”, “168”, “192”, “216”, and It is formed based on “255”. In the plurality of test images shown in FIG. 14, image signal values for forming the test image are described. Note that the density of the test image formed based on the image signal value “255” is higher than the density of the test image formed based on the image signal value “0”.

  As shown in FIG. 14, the areas G1, G3, and G5 on the sheet are based on the image signal values “0”, “48”, “96”, “144”, “192”, and “255”. A plurality of test images are formed. As shown in FIG. 14, a plurality of test images are formed in the areas G2, G4, and G6 on the sheet based on the image signal values “24”, “72”, “120”, “168”, “216”, and “255”. The A plurality of test images having the same density are formed on the sheet output from the image forming apparatus 100 in the main scanning direction.

  The main scanning positions P1, P2, P3, P4, P5, and P6 shown in FIG. 14 correspond to sampling points for measuring the test image. A broken line connecting the centers of the plurality of test images formed in the region G1 is a virtual line connecting sampling points of the plurality of test images formed in the region G1. The virtual line coincides with the main scanning position P1. Although there are sampling points in the areas G0 and GMAX, they are omitted from FIG.

  Further, if the size of the test image is reduced, the test image detection accuracy is lowered. Therefore, the number of test images that can be formed on one sheet is limited. The number of test images formed on one sheet by the image forming apparatus 100 described in the present embodiment is 36. In the test image formed on one sheet described in the present embodiment, adjacent test images in the main scanning direction are formed based on different image signal values.

  As shown in FIG. 14, the position where the test image having the image signal value “255” is formed on one sheet is a position different in the main scanning direction and a position overlapping in the sub scanning direction. The test image having the image signal value “255” is used by the user to visually recognize density unevenness in the main scanning direction. Further, the test image having the image signal value “255” is also used to generate a gradation correction table.

  The plurality of test images shown in FIG. 14 are formed by, for example, the black image forming unit 123. Therefore, the color of the plurality of test images shown in FIG. 14 is black. Read data (measurement data) of a plurality of test images shown in FIG. 14 is used to create a black gradation correction table. The image forming apparatus 100 according to the present embodiment forms test images on four sheets, for example, in the gradation correction table creation process.

  Similar to the processing described in the first embodiment, the control unit 11 uses the detection result of the density value of the test image to create a gradation correction table at the main scanning position X where no test image is actually formed. Correction data (interpolation data) is created. Here, a process of generating a gradation correction table for the main scanning position P4 will be described. In the following description, a test image based on the image signal value “72” is referred to as a first test image. The test image having the image signal value “168” is referred to as a second test image. The test image having the image signal value “48” is referred to as a third test image. The test image having the image signal value “144” is referred to as a fourth test image.

  The control unit 11 interpolates the measurement data (density) of the third test image formed in the region G3 and the measurement data (density) of the third test image formed in the region G5, and performs third calculation in the region G4. Interpolation data (density) of the test image (image signal value “48”) is obtained. Next, the control unit 11 interpolates the measurement data (density) of the fourth test image formed in the region G3 and the measurement data (density) of the fourth test image formed in the region G5, and performs the calculation in the region G4. Interpolation data (density) of the fourth test image (image signal value “144”) is obtained. Then, the control unit 11 converts the measurement data of the first test image and the measurement data of the second test image formed in the region G4, the interpolation data of the third test image and the interpolation data of the fourth test image in the region G4. Based on this, a gradation correction table corresponding to the main scanning position P4 is generated.

  Next, processing for generating a gradation correction table for the main scanning position P5 will also be described. The control unit 11 interpolates the measurement data (density) of the first test image formed in the region G4 and the measurement data (density) of the first test image formed in the region G6, and performs the first calculation in the region G5. Interpolation data (density) of the test image (image signal value “72”) is obtained. Next, the control unit 11 interpolates the measurement data (density) of the second test image formed in the region G4 and the measurement data (density) of the second test image formed in the region G6, and performs the calculation in the region G5. Interpolation data (density) of the second test image (image signal value “168”) is obtained. Then, the control unit 11 converts the measurement data of the third test image and the measurement data of the fourth test image formed in the region G5, the interpolation data of the first test image and the interpolation data of the second test image in the region G5. Based on this, a gradation correction table corresponding to the main scanning position P5 is generated.

  Note that the control unit 11 uses the gradation correction table corresponding to an arbitrary main scanning position between the main scanning position P4 and the main scanning position P5, and the measurement data of the plurality of test images formed in the area G4 and the area G5. It may be determined based on the measurement data of a plurality of test images formed in the above. For example, the control unit 11 uses the measurement data of the first test image formed in the region G4 as the interpolation data of the first test image corresponding to an arbitrary main scanning position between the main scanning position P4 and the main scanning position P5. And the interpolation data of the first test image in the region G5 are obtained by interpolation calculation. Similarly, the control unit 11 obtains interpolation data of a plurality of test images at an arbitrary main scanning position, and generates a gradation correction table corresponding to the arbitrary main scanning position based on these interpolation data.

  FIG. 15 is an exemplary view of another sheet on which a plurality of test images are formed. The plurality of test images shown in FIG. 15 have 11 gradations. The plurality of test images include image signal values “0”, “24”, “48”, “72”, “96”, “120”, “144”, “168”, “192”, “216”, and It is formed based on “255”. In the plurality of test images shown in FIG. 15, image signal values for forming the test image are described.

  As shown in FIG. 15, the areas G1, G4, and G5 on the sheet are based on the image signal values “0”, “48”, “96”, “144”, “192”, and “255”. A plurality of test images are formed. As shown in FIG. 15, regions G2, G3, and G6 on the sheet have a plurality of values based on image signal values “24”, “72”, “120”, “168”, “216”, and “255”. The test image is formed. A plurality of test images having the same density are formed on the sheet output from the image forming apparatus 100 in the main scanning direction.

  The control unit 11 uses the detection result of the density value of the test image to create correction data (interpolation data) for creating a gradation correction table at the main scanning position X where no test image is actually formed. For example, the control unit 11 interpolates the density of the test image having the image signal value “96” formed at the main scanning position P1 and the main scanning position P4, and the image signal value at the main scanning position P2 is “96”. ”Is obtained. The control unit 11 then determines the main scanning position P2 based on the actual measurement values of the plurality of test images formed at the main scanning position P2 and the interpolation data of the test image having the image signal value “96” at the main scanning position P2. A gradation correction table corresponding to is generated.

  Further, the control unit 11 interpolates the density of the test image having the image signal value “96” formed at the main scanning position P1 and the main scanning position P4, and the image signal value at the main scanning position P3 is “96”. ”Is obtained. Then, the control unit 11 determines the main scanning position P3 based on the actual measurement values of the plurality of test images formed at the main scanning position P3 and the interpolation data of the test image having the image signal value “96” at the main scanning position P3. A gradation correction table corresponding to is generated.

  The image forming apparatus 100 of the third embodiment configured as described above can increase the number of gradations of correction data when creating a gradation correction table for each main scanning position. As a result, according to the image forming apparatus of the third embodiment, it is possible to form a test image based on different image signal values in the main scanning direction and generate a gradation correction table corresponding to the main scanning position with high accuracy. it can.

  Further, since the density unevenness correction and the density gradation correction in the main scanning direction can be performed with one test image, the burden on the user is reduced as compared with the case where the density unevenness correction and the density gradation correction are performed separately. it can. Compared with the case where the measurement image for creating the gradation correction table is divided into a plurality of sheets and printed, it is possible to prevent the accuracy of the printing conditions of the image forming apparatus when printing the measurement image.

  The image forming apparatus 100 according to the first, second, and third embodiments forms a plurality of test images using only a predetermined color toner on one sheet. However, the image forming apparatus 100 may form a test image using, for example, two or more colors of toner on one sheet. For example, the image forming apparatus 100 forms a yellow test image group, a magenta test image group, a cyan test image group, and a black test image group on one sheet 110. The control unit 11 generates a gradation correction table for yellow based on the read data (measurement data) of the yellow test image group, and the magenta floor based on the read data (measurement data) of the magenta test image group. A tone correction table is generated. Similarly, the control unit 11 generates a cyan gradation correction table based on the read data (measurement data) of the cyan test image group, and black based on the read data (measurement data) of the black test image group. A tone correction table is generated.

As described above, according to the first, second, and third embodiments of the present invention, it is possible to generate a gradation correction table with high accuracy while maintaining user convenience.
The present invention is not limited to the above-described embodiment, and can be implemented in various forms. For example, in the above-described embodiment, the CPU of the printer controller 10 reads out a program from the storage unit 12, expands it in the RAM, and executes it. However, if necessary, the program may be received from an external device or an external recording medium and expanded in the RAM.

The first, second, and third embodiments described above are for more specifically explaining the present invention, and the scope of the present invention is not limited to these examples. Various forms without departing from the gist of the present invention are also included in the present invention, and for example, a part of each of the above-described embodiments may be appropriately combined.
Note that the control of various processes described in the present embodiment can be operated by installing a process control program (computer program) in a computer. It goes without saying that a storage medium in which a processing control program is recorded so as to be executable by a computer is also included in the scope of the present invention.

Claims (17)

A rotating photoreceptor,
Conversion means for converting image data based on a plurality of conversion conditions corresponding to a plurality of positions in a predetermined direction orthogonal to the rotation direction of the photoconductor;
An exposure unit that exposes the photoconductor based on image data converted by the conversion unit to form an electrostatic latent image on the photoconductor;
Developing means for developing the electrostatic latent image on the photoreceptor to form an image;
Control means,
The control means includes
Controlling the photoconductor, the exposure unit, and the developing unit to form a first test image and a second test image in a first region including a first position among the plurality of positions;
Forming a third test image and a fourth test image in a second region different from the first region in the predetermined direction including the second position of the plurality of positions;
Forming another first test image and another second test image in the first region and a third region different from the second region in the predetermined direction including a third position among the plurality of positions; ,
Another third test image and another fourth test in a fourth area different from the first area, the second area, and the third area in the predetermined direction including the fourth position among the plurality of positions. Image and form
The first test image, the second test image, the third test image, the fourth test image, the other first test image, the other second test image, and the other output from a predetermined sensor Obtaining measurement data relating to a plurality of test images including a third test image and the other fourth test image, and generating the plurality of conversion conditions based on the measurement data;
The control means includes
Forming the third test image, the other third test image, the fourth test image, and the other fourth test image in the first region;
Forming the first test image, the other first test image, the second test image, and the other second test image in the second region;
The third test image, the other third test image, the fourth test image, and the other fourth test image are not formed in the third region, and the first test image and the other are not formed in the fourth region. The first test image, the second test image, and the other second test image are not formed.
Image forming apparatus. The range in which the first test image is formed in the first region and the range in which the other first test image is formed in the third region overlap in the rotation direction,
The range in which the second test image is formed in the first region and the range in which the other second test image is formed in the third region overlap in the rotation direction.
The image forming apparatus according to claim 1. The range in which the third test image is formed in the second region and the range in which the other third test image is formed in the fourth region overlap in the rotation direction,
A range in which the fourth test image is formed in the second area and a range in which the other fourth test image is formed in the fourth area overlap in the rotation direction.
The image forming apparatus according to claim 2. The range in which the first test image is formed in the first region and the range in which the third test image is formed in the second region overlap in the rotation direction,
The range in which the second test image is formed in the first region and the range in which the fourth test image is formed in the second region overlap in the rotation direction,
The image forming apparatus according to claim 3. The control means forms the first test image based on a first image signal value, forms the other first test image based on the first image signal value,
The control means forms the second test image based on a second image signal value, forms the other second test image based on the second image signal value,
The control means forms the third test image based on a third image signal value, forms the other third test image based on the third image signal value,
The control means forms the fourth test image based on a fourth image signal value, forms the other fourth test image based on the fourth image signal value,
The first image signal value, the second image signal value, the third image signal value, and the fourth image signal value are different from each other,
The image forming apparatus according to claim 1. The first position is between the second position and the fourth position in the predetermined direction;
The second position is between the first position and the third position in the predetermined direction,
The image forming apparatus according to claim 1. The first region is adjacent to the second region in the predetermined direction;
The image forming apparatus according to claim 1, wherein the first area is adjacent to the fourth area in the predetermined direction. The second region is adjacent to the third region in the predetermined direction,
The image forming apparatus according to claim 1. The control means includes first measurement data related to the first test image, second measurement data related to the second test image, third measurement data related to the third test image, and other third data related to the other third test image. A first conversion condition corresponding to the first position is generated based on measurement data, fourth measurement data related to the fourth test image, and other fourth measurement data related to the other fourth test image. To
The image forming apparatus according to claim 1. The control means determines first interpolation data based on the third measurement data and the other third measurement data, and performs second interpolation based on the fourth measurement data and the other fourth measurement data. Determining data, and generating the first conversion condition based on the first measurement data, the second measurement data, the first interpolation data, and the second interpolation data,
The image forming apparatus according to claim 9. The control means includes third measurement data related to the third test image, fourth measurement data related to the fourth test image, first measurement data related to the first test image, and other first related to the other first test image. Generating a second conversion condition corresponding to the second position based on measurement data, second measurement data relating to the second test image, and other second measurement data relating to the other second test image; To
The image forming apparatus according to claim 9. The control means determines third interpolation data based on the first measurement data and the other first measurement data, and performs fourth interpolation based on the second measurement data and the other second measurement data. Determining data, and generating the second conversion condition based on the third measurement data, the fourth measurement data, the third interpolation data, and the fourth interpolation data,
The image forming apparatus according to claim 11. The control means includes: other first measurement data relating to the other first test image; other second measurement data relating to the other second test image; third measurement data relating to the third test image; A third transformation corresponding to the third position based on other third measurement data relating to the third test image, fourth measurement data relating to the fourth test image, and other fourth measurement data relating to the other fourth test image. Generating a condition,
The image forming apparatus according to claim 11. The developing means develops the electrostatic latent image using a predetermined color toner,
The first test image, the second test image, the third test image, and the fourth test image are formed using the toner of the predetermined color,
The other first test image, the other second test image, the other third test image, and the other fourth test image are formed using the toner of the predetermined color,
The image forming apparatus according to claim 1. Further comprising transfer means for transferring the image formed on the photoreceptor to a sheet;
The sensor reads the plurality of test images transferred to the sheet by the transfer unit, and transfers the measurement data to the control unit.
The image forming apparatus according to claim 1. A transfer body onto which the image formed on the photoreceptor is transferred;
Transfer means for transferring the image transferred to the transfer body to a sheet, and
The sensor measures the plurality of test images transferred to the transfer body, and outputs the measurement data to the control means.
The image forming apparatus according to claim 1. A rotating photoreceptor, conversion means for converting image data based on a plurality of conversion conditions corresponding to a plurality of regions in a predetermined direction orthogonal to the rotation direction of the photoreceptor, and forming an electrostatic latent image on the photoreceptor An image forming apparatus control method comprising: an exposure unit that exposes the photoconductor based on the converted image data; and a developing unit that develops the electrostatic latent image on the photoconductor. ,
Forming a first test image and a second test image in a first region including a first position of the plurality of positions;
Forming a third test image and a fourth test image in a second region different from the first region in the predetermined direction including the second position of the plurality of positions;
Forming another first test image and another second test image in the first region and a third region different from the second region in the predetermined direction including a third position among the plurality of positions; ,
Another third test image and another fourth test in a fourth area different from the first area, the second area, and the third area in the predetermined direction including the fourth position among the plurality of positions. Image and form
The first test image, the second test image, the third test image, the fourth test image, the other first test image, the other second test image, the other outputted from a predetermined sensor Measurement data relating to a plurality of test images including the third test image and the other fourth test image,
Generating the plurality of conversion conditions based on the measurement data;
Forming the third test image, the other third test image, the fourth test image, and the other fourth test image in the first region;
Forming the first test image, the other first test image, the second test image, and the other second test image in the second region;
Forming the third test image, the other third test image, the fourth test image, and the other fourth test image in the third region;
The first test image, the other first test image, the second test image, and the other second test image are not formed in the fourth region.
A method for controlling an image forming apparatus.