JP6772017B2 - Image processing equipment, image processing methods, image forming equipment and programs - Google Patents

Description

The present invention relates to an electrophotographic image forming apparatus and an image processing technique for processing image data used by the image forming apparatus for image forming.

Conventionally, so-called electrophotographic image forming apparatus such as a laser beam printer or a copying machine that irradiates the surface of a photosensitive drum with a laser beam to form an electrostatic latent image is known. In such an image forming apparatus, various image quality correction processes are performed on the input image data in order to improve the image quality on the recording surface. For example, in order to match the target density with the density actually printed, a gradation correction process for correcting so-called gradation characteristics (input / output characteristics) is performed. Generally, in the gradation correction processing, a gradation correction parameter (gradation correction table) is used to correct the gradation characteristic.

In such an image forming apparatus, it is desirable that the shape of the spot light (hereinafter referred to as “spot shape”) formed on the surface of the photosensitive drum is substantially circular. Further, it is desirable that the size of the spot shape (hereinafter referred to as "spot diameter") is substantially uniform regardless of the position of the surface of the photosensitive drum. Usually, the laser beam from the light source is designed to form an image with a substantially uniform spot diameter at each position on the surface of the photosensitive drum after passing through the lens. However, in recent years, for the purpose of miniaturization and cost reduction of the image forming apparatus, a lens having a characteristic that the spot diameter at each position on the surface of the photosensitive drum is not always uniform may be used. Further, even when a lens having a characteristic that the spot diameter is uniform is used, the spot diameter changes due to the influence of distortion due to manufacturing error and assembly error of parts and supports constituting the image forming apparatus. It may not be uniform.

Then, there is a problem that such non-uniformity of the spot diameter causes a difference in gradation characteristics in the main scanning direction, and the image quality on the recording surface deteriorates. In order to solve such a problem, Patent Document 1 states that a test image is formed at each position in the main scanning direction, and gradation correction is performed at each position in the main scanning direction based on the detection result of the formed test image. The technology to be performed is disclosed.

Japanese Unexamined Patent Publication No. 2015-011218

However, in the gradation correction technique described in Patent Document 1, it is necessary to install a plurality of sensors facing the intermediate transfer belt in order to detect the test image formed at each position in the main scanning direction. There is a problem that the hardware configuration of the forming apparatus becomes complicated. A complicated hardware configuration is not preferable because the manufacturing cost of the image forming apparatus increases.

The present invention has been made in view of the above problems, and an object of the present invention is to improve the image quality in the recording surface with a simple hardware configuration.

The image processing device of the present invention is an image processing device that processes image data used for image formation by an electrophotographic image forming device, and emits the light beam to a control means for controlling the output of the light beam. A setting means for setting a first light emission control parameter indicating the light emission intensity and light emission time of the light emitting means to be light-emitting, and a second light emission control parameter indicating a light emission intensity and light emission time different from the first light emission control parameter. The first gradation characteristic representing the output density with respect to the input gradation value to which the set first emission control parameter is applied at a predetermined position in the main scanning direction of the photosensitive drum, and the set second An acquisition means for acquiring a second gradation characteristic representing an output density with respect to an input gradation value to which a light emission control parameter is applied, and a first correction characteristic having an inverse characteristic of the acquired first gradation characteristic. It is characterized by having a derivation means for deriving the second correction characteristic having the inverse characteristic of the acquired second gradation characteristic.

According to the present invention, there is an effect that the image quality in the recording surface can be improved with a simple hardware configuration.

It is a block diagram of the image forming apparatus which concerns on Embodiment 1. FIG. It is a block diagram of the image forming part which concerns on Embodiment 1. FIG. It is a hardware block diagram of the image forming part which concerns on Embodiment 1. FIG. It is a functional block diagram of the image processing unit which concerns on Embodiment 1. FIG. FIG. 5 is an image diagram of a spot shape formed on a photoconductor in the first embodiment. It is an image diagram which shows the gradation characteristic concerning Embodiment 1. FIG. FIG. 5 is a schematic diagram showing a test image for detecting gradation characteristics according to the first embodiment and a sensor used for reading the test image. It is a schematic diagram which shows the outline of the gradation characteristic acquisition processing which concerns on Embodiment 1. FIG. It is a functional block diagram of the gradation correction parameter change part which concerns on Embodiment 1. FIG. It is a flowchart which shows the processing procedure which changes the gradation correction parameter which concerns on Embodiment 1. It is a figure which shows the density characteristic of the test image reading data which concerns on Embodiment 1. 6 is a graph showing gradation characteristics according to the first embodiment. It is a graph which shows the correction characteristic which concerns on Embodiment 1. It is a functional block diagram of the image processing part which concerns on Embodiment 2. FIG. It is a functional block diagram of the halftone parameter change part which concerns on Embodiment 2. FIG. It is a flowchart which shows the processing procedure which changes the halftone parameter which concerns on Embodiment 2. It is a figure which shows the image of the gradation characteristic error concerning Embodiment 2. It is a figure which shows the mathematical expression which calculates the gradation characteristic error concerning Embodiment 2. FIG. 5 is a diagram showing an example of a table in which a gradation characteristic error E and a dither matrix are associated with each other in the second embodiment. It is a figure which shows the example of the table in which the state information and the light emission control parameter are associated in Embodiment 3.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. It should be noted that the following embodiments do not limit the present invention, and not all combinations of features described in the present embodiment are essential for the means for solving the present invention. The same configuration will be described with the same reference numerals.

[Embodiment 1]
FIG. 1 is a configuration diagram of an image forming apparatus 100 according to the present embodiment. The image forming apparatus 100 shown in FIG. 1 includes an image processing unit 160 and an image forming control unit 170. Further, along the intermediate transfer belt 110, the image forming portions 150a, 150b, 150c, 150d, the sensor 180, the secondary transfer device 120, and the intermediate transfer belt cleaning device 140 are provided. Further, a fixing device 130 is arranged on the downstream side of the secondary transfer device 120.

FIG. 2 is a configuration diagram of an image forming unit 150a according to the present embodiment. The image forming unit 150a includes a photosensitive drum 151a, a charging device 152a, an exposure device 153a, a developing device 154a, a primary transfer device 155a, and a cleaning device 156a. The same applies to the image forming portions 150b, 150c and 150d.

Next, the operation of the image forming apparatus 100 will be described with reference to FIGS. 1 and 2. The image forming control unit 170 controls the image forming units 150a, 150b, 150c, and 150d based on the image data processed by the image processing unit 160, forms each color toner image on each photosensitive drum 151, and forms an intermediate transfer belt. Primary transfer to 110. The toner used in the image forming apparatus 100 is generally four colors of cyan (C), magenta (M), yellow (Y), and black (K). In the present embodiment, the image forming unit 150a uses C toner, the image forming unit 150b uses M toner, the image forming unit 150c uses Y toner, and the image forming unit 150d uses K toner. The number of colors of the toner used by the image forming apparatus 100 is not limited to four. Similarly, the number of image forming units 150 is not limited to four. For example, there may be white toner or clear toner. Further, the order of the image forming units 150 corresponding to each color is not limited to this embodiment, and may be arbitrary.

As shown in FIG. 2, the photosensitive drum 151a has an organic photoconductor layer having a negative charge polarity on the outer peripheral surface, and rotates in the direction of arrow R3. A negative electrode voltage is applied to the charging device 152a, and the surface of the photosensitive drum 151a is irradiated with charged particles to charge the surface of the photosensitive drum 151a to a uniform negative electrode potential. The exposure apparatus 153a irradiates the photosensitive drum 151a with light according to the image data. As a result, an electrostatic latent image is formed on the surface of the charged photosensitive drum 151a. The developing device 154a supplies the negatively charged toner to the photosensitive drum 151a by using a developing roller that rotates at substantially the same speed as the photosensitive drum 151a. As a result, toner adheres to the electrostatic latent image on the photosensitive drum 151a, and the electrostatic latent image is inverted and developed. The primary transfer device 155a primary transfers a toner image carried on a photosensitive drum 151a to which a positive charge is applied and is charged negatively to an intermediate transfer belt 110 that moves in the direction of arrow R1. The cleaning device 156a removes the residual toner image remaining on the photosensitive drum 151a that has passed through the primary transfer device 155a.

Up to this point, the image forming unit 150a has been described, but the same applies to the image forming units 150b, 150c, and 150d. When forming a color image, the image forming units 150a, 150b, 150c, and 150d of each color execute each step of charging, exposure, development, temporary transfer, and cleaning at a predetermined time. As a result, an image in which four color toner images are overlapped is formed on the intermediate transfer belt.

As shown in FIG. 1, the secondary transfer device 120 secondary transfers the toner image carried on the intermediate transfer belt 110 to the recording medium P moving in the direction of arrow R2. The fixing device 130 applies a process such as pressurization and heating to the recording medium P on which the toner image is secondarily transferred to fix the image. The intermediate transfer belt cleaning device 140 removes residual toner remaining on the intermediate transfer belt 110 that has passed through the secondary transfer device 120.

FIG. 3 is a block diagram showing a hardware configuration of the image processing unit 160 according to the present embodiment. The image processing unit 160 of FIG. 3 includes a CPU 161, a RAM 162, a ROM 163, a storage unit 164, an external connection interface (hereinafter referred to as “I / F”) 165, and a network I / F 166. Further, each component is communicably connected via bus 167. The CPU 161 is composed of an arithmetic circuit, and controls the image processing unit 160 in an integrated manner. The CPU 161 reads the program stored in the ROM 163 or the storage unit 164 into the RAM 162 and executes various processes. The ROM 163 has a function as a storage area and stores various programs. The storage unit 164 is a disk composed of, for example, an HDD (Hard Disk Drive), an SSD (Solid State Drive), or the like, and has a function as a storage area. The external connection I / F 165 is for connecting various devices to the information processing device. For example, a display, keyboard, mouse, etc. can be connected via an external connection I / F165. The network I / F 166 controls the input / output of data with the image formation control unit 170 based on the control of the CPU 161.

FIG. 4 is a block diagram illustrating a functional configuration of the image processing unit 160 applicable to the present embodiment. The image input unit 401 accepts input of multi-valued input image data (for example, 8 bits each for RGB) from the outside. The color separation processing unit 402 refers to the color separation table stored in the color separation table storage unit (not shown), and changes the input image data received by the image input unit 401 to the image data of each CMYK color. The gradation correction unit 403 refers to the gradation correction parameters stored in the gradation correction parameter storage unit 405 and performs gradation correction processing on the image data of each CMYK color to obtain the gradation correction data of each CMYK color. Convert. The gradation correction parameter changing unit 406 changes the gradation correction parameter stored in the gradation correction parameter storage unit 405. The halftone processing unit 404 performs halftone processing on the gradation correction data of each CMYK color, converts it into, for example, 4 bits of image signal data of each CMYK color, and outputs the data to the image formation control unit 170. The halftone processing is performed based on the dither matrix stored in the halftone parameter storage unit (not shown in the description of the first embodiment).

In such an image forming apparatus 100, it is desirable that the spot shape of the spot light formed on the surface of the photosensitive drum is substantially circular. Further, it is desirable that the spot diameter, which is the size of the spot shape, is substantially uniform regardless of the position of the surface of the photosensitive drum. Normally, the laser beam output from the light emitting unit is designed to form an image on the surface of the photosensitive drum with a substantially uniform spot diameter after passing through the lens group. However, in recent years, for the purpose of miniaturization and cost reduction of the image forming apparatus, a lens having a characteristic that the spot diameter at each position on the surface of the photosensitive drum is not always uniform may be used. Further, even when a lens having a characteristic that the spot diameter is uniform is used, the spot diameter changes due to the influence of distortion due to manufacturing error and assembly error of parts and supports constituting the image forming apparatus. It may not be uniform.

FIG. 5 is a diagram showing an image of a spot shape formed on the photosensitive drum 151 in the configuration of the exposure apparatus 153 and the photosensitive drum 151 of the present embodiment. The light emitting unit 501 is composed of one or a plurality of semiconductor laser elements. The light beam output by the light emitting unit 501 passes through a collimator lens, an aperture diaphragm, and a cylindrical lens (all not shown), is reflected on the reflecting surface of the polygon mirror 502, passes through the optical element 503, and is placed on the photosensitive drum 151. Is imaged in. The polygon mirror 502 rotates at a constant speed in the R4 direction, and the laser beam imaged on the reflecting surface is deflected and scanned in the R5 direction (main scanning direction) on the photosensitive drum 151.

Normally, the function of the optical element 503 is designed so that the laser beam is formed on the surface of the photosensitive drum 151 with a substantially uniform spot diameter. However, for the reasons mentioned above, the spot diameter may not always be uniform. For example, as shown in FIG. 5, the central portion of the photosensitive drum 151 may have a small spot diameter of 504, and the end portion of the photosensitive drum 151 may have a large spot diameter of 505. If the spot diameter is not uniform on the surface of the photosensitive drum 151, the following problems occur. In the present embodiment, as shown in FIG. 5, a case where the spot diameter is small at the central portion in the main scanning direction and the spot diameter is larger at the end portion in the main scanning direction will be described.

In such a case, the gradation characteristics of the output image will differ depending on the spot diameter at each position. Here, the gradation characteristic is a characteristic indicating the correspondence between the input gradation value and the output density. In FIG. 6A, in the present embodiment, the horizontal axis is the gradation value (input gradation value) of the image data input to the image processing unit 160, and the vertical axis is the image output from the image forming unit 150. It is an image diagram which shows the gradation characteristic as an output density. In FIG. 6A, the dotted graph line shows the gradation characteristic at the central portion in the main scanning direction, that is, at the position where the spot diameter is small, and corresponds to, for example, the small spot diameter 504 in FIG. On the other hand, the solid graph line shows the gradation characteristic at the end in the main scanning direction, that is, at the position where the spot diameter is large, and corresponds to, for example, the large spot diameter 505 in FIG.

FIG. 6B is an image diagram showing the density represented by the image data input to the image processing unit 160 and the output density of the image output from the image forming unit 150. In general, it is known that the larger the spot diameter, the more the gradation characteristic becomes the so-called "gamma-raised" state. This is due to the following reasons. When the spot diameter is large, the exposure intensity to the surface of the photosensitive drum 151 is weakened by expanding the spot diameter in the bright portion where the input gradation value is low, and as a result, the amount of toner adhering to the photosensitive drum 151 is reduced. On the other hand, in the dark portion where the input gradation value is high, the amount of toner adhering to the white portion in the electrostatic latent image formed on the surface of the photosensitive drum 151 increases as the spot diameter increases. Therefore, as shown in FIG. 6B, even if the input image data represents a uniform density in the main scanning direction, when the spot diameter is large, the output density decreases in bright areas where the input gradation value is low. , The output density increases in dark areas where the input gradation value is high. As a result, if a position having a small spot diameter and a position having a large spot diameter coexist in the same main scanning direction, density unevenness occurs in the output in the main scanning direction.

As the output density differs depending on the size of the spot diameter in this way, density unevenness occurs on the printed surface. Usually, gradation correction processing is performed in order to make the correspondence between the input gradation value and the output density a linear characteristic (linear characteristic). The gradation correction process is a process of converting input image data using a gradation correction table having characteristics opposite to those of gradation characteristics. As described with reference to FIG. 6, when the gradation characteristics are different at each position on the photosensitive drum 151, it is necessary to use a gradation correction table according to the position on the photosensitive drum 151 in order to suppress density unevenness on the printing surface. .. However, creating and holding a gradation correction table corresponding to all positions is realistic because it takes time and effort for calibration (adjustment of the gradation correction table) and the memory area for holding the gradation correction table increases. Not. Therefore, the gradation correction table optimized at some typical positions on the photosensitive drum 151 is held, and at other positions, the gradation correction table used at that position is generated from the correction table corresponding to the representative position. The technology is known. Generally, the representative positions are arranged at equal intervals on the photosensitive drum 151, and at other positions, linear interpolation is performed based on two correction tables optimized at the two nearest representative positions. A gradation correction table corresponding to the position is generated.

Further, it is known that the gradation characteristics fluctuate due to environmental changes such as temperature and humidity and the influence of deterioration of toner over time. Therefore, it is common that the gradation characteristics for each representative position are acquired at a predetermined timing and the gradation correction table is adjusted. The acquisition of the gradation characteristic for each representative position is performed by forming a test image for detecting the gradation characteristic for each representative position and reading the formed test image.

FIG. 7 is a schematic view showing a gradation characteristic detection test image (hereinafter referred to as “test image”) 710 formed when acquiring gradation characteristics and a sensor 180 used for reading the test image 710 in the present embodiment. Is. The test image 710 is composed of a plurality of gradation patches output at different densities, and FIG. 6 shows an example consisting of five gradation patches 711 to 715. The plurality of gradation patches 711 to 715 are continuously placed on the intermediate transfer belt 110 at a predetermined position (generally at the end) in the main scanning direction in the sub-scanning direction (arrow R1 direction) substantially orthogonal to the main scanning direction. Is formed. Further, the plurality of gradation patches 711 to 715 are formed based on image data (hereinafter, also referred to as "input gradation data") representing input gradation values having different densities. In the present embodiment, the gradation patches 711 to 715 are formed based on the input gradation data of 20%, 40%, 60%, 80%, and 100% densities, but other densities may be used. However, the number of gradation patches does not have to be five. As the intermediate transfer belt 110 moves, the test image 710 moves in the direction of arrow R1. The sensor 180 is installed along the path of the test image 710 so as to face the intermediate transfer belt 110, and can detect the density of each gradation patch 711 to 715 of the passing test image 710.

In the present embodiment, the outline of the process of acquiring the gradation characteristics at each position on the photosensitive drum 151 using only one sensor will be described with reference to the schematic diagram of FIG.

FIG. 8A is a diagram showing a light intensity distribution in which the horizontal axis is the size of the spot diameter 505 (FIG. 5) and the vertical axis is the amount of laser light irradiated to the photosensitive drum 151 in the present embodiment. ..

FIG. 8B shows, in the present embodiment, one pixel of image data input to the image processing unit 160, where the horizontal axis is time and the vertical axis is the emission intensity of the laser beam output from the light emitting unit 501. It is a figure which shows the light emission pattern of the corresponding light emitting part 501. As shown in the light emission pattern of FIG. 8B, the light emitting unit 501 is controlled to emit laser light at a predetermined light emission time and a predetermined light emission intensity. The light emission time and light emission intensity at this time are collectively referred to as a normal light emission control parameter.

In FIG. 8C, in the present embodiment, the horizontal axis represents the position of the laser beam irradiated to the photosensitive drum 151 corresponding to one pixel of the image data, and the vertical axis represents the amount of the laser beam irradiated to the photosensitive drum 151. The exposure amount distribution is shown. The exposure amount distribution of FIG. 8 (c) is the light intensity distribution of the spot diameter 505 at the first position (the end in the main scanning direction of the photosensitive drum 151) shown in FIG. 8 (a). It is obtained by performing the convolution calculation of the shown normal light emission control parameters.

FIG. 8D is a diagram showing a light intensity distribution in which the horizontal axis is the size of the spot diameter 504 (FIG. 5) and the vertical axis is the amount of laser light irradiated to the photosensitive drum 151 in the present embodiment. ..

In FIG. 8 (e), similarly to FIG. 8 (c), the horizontal axis is the position of the laser beam irradiated to the photosensitive drum 151 corresponding to one pixel of the image data, and the vertical axis is the laser beam irradiated to the photosensitive drum 151. The exposure amount distribution as the amount of light is shown. The exposure amount distribution in FIG. 8 (e) is the light intensity distribution of the spot diameter 504 at the second position (central portion in the main scanning direction of the photosensitive drum 151) different from the first position shown in FIG. 8 (d). , It is obtained by performing the convolution calculation of the normal light emission control parameter shown in FIG. 8 (b). As described above, even if the laser light is emitted with the same light emission pattern, the exposure amount distribution corresponding to one pixel of the image data differs depending on the size of the spot diameter. That is, it can be seen that the gradation characteristics differ depending on the position of the photosensitive drum 151 in the main scanning direction.

In the present embodiment, when acquiring the gradation characteristics, the test image 710 is formed by using the adjustment light emission control parameters shown in FIG. 8 (g) in addition to the normal light emission control parameters shown in FIG. 8 (b). To do. In FIG. 8 (f), as in FIG. 8 (c), the horizontal axis is the position of the laser beam irradiated to the photosensitive drum 151 corresponding to one pixel of the image data, and the vertical axis is the laser beam irradiated to the photosensitive drum 151. The exposure amount distribution as the amount of light is shown. The exposure amount distribution of FIG. 8 (f) is the light intensity distribution of the spot diameter 505 at the first position (the end in the main scanning direction of the photosensitive drum 151) shown in FIG. 8 (a), as shown in FIG. 8 (g). It is obtained by performing the convolution calculation of the indicated light emission control parameters for adjustment.

The light emission control parameters for adjustment in FIG. 8 (g) are the exposure amount distribution in which the light emission control parameters in FIG. 8 (b) are applied to the light intensity distribution in FIG. 8 (d) and the light intensity distribution in FIG. 8 (a). The exposure amount distribution to which the light emission control parameter of FIG. 8 (g) is applied is set to be substantially equal to. By using such an adjustment light emission control parameter, the same image formation as when the normal light emission control parameter is applied at the second position (the central portion in the main scanning direction of the photosensitive drum 151) can be formed at the first position (the first position (center portion). This can be done at the end of the photosensitive drum 151 in the main scanning direction). Then, from the test image 710 formed by this method, the gradation characteristic at the second position where the sensor 180 is not installed can be obtained.

FIG. 9 is a block diagram illustrating a functional configuration of the gradation correction parameter changing unit 406 applicable to the present embodiment. The adjustment light emission control parameter setting unit 901 sets the adjustment light emission control parameter to the test image formation control unit 903. The normal light emission control parameter setting unit 902 sets the normal light emission control parameter for the test image formation control unit 903. The test image formation control unit 903 controls the image formation unit 150 to form a test image. The test image reading data acquisition unit 904 controls the sensor 180 to acquire the test image reading data. The gradation characteristic acquisition unit 905 acquires gradation characteristic data based on the test image reading data acquired by the test image reading data acquisition unit 904. The gradation correction parameter derivation unit 906 derives the gradation correction parameter based on the gradation characteristic acquired by the gradation characteristic acquisition unit 905. The derived gradation correction parameter is output to the gradation correction parameter storage unit 405.

FIG. 10 is a flowchart showing a processing procedure for changing the gradation correction parameter in the present embodiment. As shown in FIG. 10A, the gradation correction parameter changing process of the present embodiment includes the gradation correction parameter changing process (S1010) at the first position and the gradation correction parameter changing process (S1010) at the second position. S1020) and. The process according to the flowchart shown in FIG. 10 is executed by the CPU 161 after the program code stored in the ROM 163 is expanded. The symbol S described below means a step in the flowchart. The same applies to the flowchart of FIG.

FIG. 10B is a flowchart showing a processing procedure for changing the gradation correction parameter at the first position in the present embodiment.

In S1011, the normal light emission control parameter setting unit 902 sets the light emission control parameter to "normal". The normal light emission control parameter setting unit 902 calls the normal light emission control parameter stored in the gradation correction parameter storage unit 405 and sets it in the test image formation control unit 903.

In S1012, the test image formation control unit 903 forms the test image 710. The test image formation control unit 903 controls the image formation unit 150 to form the test image 710 at the position of the intermediate transfer belt 110 corresponding to the first position.

In S1013, the test image reading data acquisition unit 904 acquires the test image reading data. The test image reading data acquisition unit 904 controls the sensor 180 to acquire the test image reading data which is the reading result of the test image 710 formed in S1012.

FIG. 11A is a diagram showing density characteristics in which the horizontal axis represents the elapsed time from the start of reading the test image 710 and the vertical axis represents the density represented by the test image reading data in the present embodiment. As described above, the test image 710 formed in S1013 is a test image formed by applying the normal light emission control parameters. Although only one test image 710 is shown in this embodiment, at least two types of test images can be obtained by changing the normal gradation correction parameter (S1010) and changing the adjustment gradation correction parameter (S1020). Will be generated. The generated test image is not limited to two types, and may be a plurality of three or more types. The density D1 in the section 1101 corresponds to the value obtained by reading the gradation patch 711 in the test image 710. Similarly, the densities D2 to D5 in the sections 1102 to 1105 also correspond to the values obtained by reading the gradation patches 712 to 715 in the test image.

Returning to the flowchart of FIG. 10 again, in S1014, the gradation characteristic acquisition unit 905 acquires the gradation characteristic based on the density characteristic of the image reading data acquired in S1013. The gradation characteristic acquisition unit 905 averages the density D1 of the section 1101 to calculate the output density d1. The density D1 in the section 1101 corresponds to a value obtained by reading the gradation patch 711 formed based on the input gradation data having a density of 20%. Similarly, the gradation characteristic acquisition unit 905 averages the densities D2 to D5 in the sections 1102 to 1105 to calculate the output densities d2 to d5, respectively. The densities D2 to D5 in the sections 1102 to 1105 correspond to the values obtained by reading the gradation patches 712 to 715 formed based on the input gradation data of the densities 40%, 60%, 80%, and 100%, respectively. .. In FIG. 12A, in the present embodiment, the horizontal axis is the gradation value (input gradation value) of the image data input to the image processing unit 160, and the vertical axis is the image output from the image forming unit 150. It is a graph which shows the gradation characteristic as an output density. In FIG. 12A, each point shows the values of the output densities d1 to d5 calculated by the gradation characteristic acquisition unit 905. The gradation characteristic acquisition unit 905 interpolates the values of the output densities d1 to d5 as necessary, and derives the gradation characteristic at the first position shown by the solid line curve in FIG. 12A.

In S1015, the gradation correction parameter derivation unit 906 derives and stores the gradation correction parameter. In the present embodiment, the gradation correction parameter is a gradation correction table used in the gradation correction processing. In FIG. 13A, in the present embodiment, the horizontal axis is the pre-correction gradation value (that is, the input gradation value) input to the gradation correction table, and the vertical axis is the corrected gradation value input to the gradation correction table. It is a graph which shows the correction characteristic as the gradation value (that is, the output gradation value). In FIG. 13 (a), the solid line curve shows the correction characteristic at the first position. The gradation correction parameter derivation unit 906 derives a correction characteristic having an inverse characteristic of the gradation characteristic acquired in S1014. That is, the gradation correction parameter derivation unit 906 derives a gradation correction table in which the pre-correction gradation value shown in FIG. 13A and the post-correction gradation value are associated with each other. By using this correction characteristic derived by the gradation correction parameter derivation unit 906 to correct the image data input to the image processing unit 160, the correspondence between the input gradation value and the output density becomes a linear characteristic. It can be roughly matched.

The gradation correction parameter storage unit 405 changes the gradation correction table stored in association with the first position to the gradation correction table newly derived in S1015 and stores it. When the derivation / storage process of the gradation correction parameter is completed (S1015), the process according to this flowchart is completed, and the process returns to the flowchart of FIG. 10A again.

FIG. 10C is a flowchart showing a processing procedure for changing the gradation correction parameter at the second position in the present embodiment.

In S1021, the adjustment light emission control parameter setting unit 901 sets the light emission control parameter to "for adjustment". The adjustment light emission control parameter setting unit 901 calls the adjustment light emission control parameter stored in the gradation correction parameter storage unit 405 and sets it in the test image formation control unit 903.

In S1022, the test image formation control unit 903 forms the test image 710. The process of S1022 is the same as that of S1012 except that the set light emission control parameters are different.

In S1023, the test image reading data acquisition unit 904 acquires the test image reading data. Similar to S1013, the test image reading data acquisition unit 904 controls the sensor 180 to acquire the test image reading data which is the reading result of the test image 710 formed in S1022.

In S1024, similarly to S1014, the gradation characteristic acquisition unit 905 acquires the gradation characteristic (FIG. 12 (b)) based on the density characteristic (FIG. 11 (b)) of the image reading data acquired in S1013.

In S1025, the gradation correction parameter derivation unit 906 derives and stores the gradation correction parameter. Similar to S1015, the gradation correction parameter derivation unit 906 derives a correction characteristic (FIG. 13 (b)) having an inverse characteristic of the gradation characteristic (FIG. 12 (b)) acquired in S1024.

The gradation correction parameter storage unit 405 changes the gradation correction table stored in association with the second position to the gradation correction table newly derived in S1025 and stores it. When the derivation / storage process of the gradation correction parameter is completed (S1025), the process according to this flowchart is completed, and the process returns to the flowchart of FIG. 10A again.

By performing the above processing, it is possible to acquire the gradation characteristics at each position using only one sensor, and the gradation correction parameters at each position can be appropriately changed. In the present embodiment, an example of changing the gradation correction parameters at two locations (first and second positions) has been described, but the gradation correction parameters at three or more locations including the first position have been described. The process of changing can be performed in the same manner. In that case, the second and third positions are different from the first position. .. .. The gradation correction parameter change processing may be performed using different light emission control parameters for adjustment corresponding to each of the positions. Further, although the configuration in which the test image (test image) 710 for detecting gradation characteristics and the sensor 180 used for reading the test image (test image) 710 are arranged at the end in the main scanning direction is described as an example, it may be arranged at other positions. Well, in that case, the same processing can be performed.

As described above, according to the image quality correction technique of the present embodiment, the gradation characteristic acquisition at each position in the main scanning direction is performed by using only one sensor. Therefore, the image forming apparatus of the present embodiment can improve the density unevenness in the recording surface with a simple hardware configuration.

[Embodiment 2]
In the first embodiment, a method of acquiring gradation characteristics different depending on each position on the surface of the photosensitive drum by using only one sensor and appropriately changing the gradation correction parameter at each position based on the acquired gradation characteristics. explained. In the present embodiment, a method of estimating the graininess that differs depending on each position on the surface of the photosensitive drum using only one sensor and selecting a dither matrix having an optimum number of lines based on the estimation result will be described. The same symbols as those in the first embodiment are added and the description thereof will be omitted.

When the spot diameter differs depending on the position on the photosensitive drum, the graininess (roughness of the output image) changes for each position in addition to the gradation characteristics. Then, at a position where the spot diameter becomes larger than a certain level, the graininess may deteriorate to an unacceptable level. At that time, there is a method of suppressing deterioration of graininess by reducing the number of lines in the dither matrix used in the halftone processing. However, when the dither matrix has a low number of lines, the repeating pattern is stronger than when the dither matrix has a high number of lines, and an image containing an unintended texture may be output. Therefore, it is not preferable to use a dither matrix with a low number of lines unnecessarily. That is, it is preferable that the number of lines is set so as to satisfy both graininess and pattern visibility at a certain level. Therefore, the image forming apparatus 100 of the present embodiment estimates the state of graininess at the position where the spot diameter is the largest (that is, the graininess is the worst) on the photosensitive drum, selects the optimum number of lines at that position, and selects the optimum number of lines. Halftone processing is performed using the dither matrix corresponding to the selected number of lines. In this embodiment as well, as shown in FIG. 5, the case where the spot diameter is small at the central portion in the main scanning direction and the spot diameter is larger at the end portion in the main scanning direction will be described. However, in the present embodiment, the sensor 180 used for reading the test image 710 is arranged so as to face a position other than the end portion in the main scanning direction. Further, in the present embodiment, the second position indicates the end of the photosensitive drum 151 in the main scanning direction, that is, the position having the largest spot diameter (that is, the worst graininess on the recording surface) on the photosensitive drum 151. ..

FIG. 14 is a block diagram illustrating a functional configuration of the image processing unit 160 applicable to the present embodiment. The halftone parameter storage unit 1401 stores a plurality of dither matrices. The halftone parameter changing unit 1402 selects one from a plurality of dither matrices stored in the halftone parameter storage unit 1401, and uses the dither matrix currently set in the RAM 162 as the selected dither matrix. Change to. The halftone processing unit 404 performs halftone processing using the dither matrix selected by the halftone parameter changing unit 1402.

FIG. 15 is a block diagram of the halftone parameter changing unit 1402 in the present embodiment. The halftone parameter selection unit 1501 selects one from a plurality of dither matrices stored in the halftone parameter storage unit 1401 based on the gradation characteristics acquired by the gradation characteristic acquisition unit 905.

FIG. 16 is a flowchart showing a processing procedure for changing the halftone parameter in the present embodiment. The processing procedure of the flowchart shown in FIG. 16 includes a processing step common to the gradation correction parameter changing process at the second position described in FIG. 10C in the first embodiment. The common processing steps are also designated by the same reference numerals as those in the first embodiment, and the description thereof will be omitted.

In S1601, the halftone parameter selection unit 1501 selects and stores halftone parameters. The halftone parameter selection unit 1501 selects one from a plurality of dither matrices stored in the halftone parameter storage unit 1401 based on the gradation characteristics acquired in S1024.

In general, there is a correlation between the deterioration of gradation characteristics and the deterioration of graininess. That is, the graininess of the output image increases as the gradation characteristics deteriorate and the so-called "gamma stands" state. Therefore, the halftone parameter selection unit 1501 of the present embodiment first determines the standing condition of the gamma, that is, the linear characteristic (ideal characteristic) which is the ideal gamma characteristic of the gradation characteristic (actual characteristic) acquired in S1024. Evaluate the error (gradation characteristic error). Next, the halftone parameter selection unit 1501 selects a dither matrix having a lower number of lines as the gradation characteristic error increases. In the present embodiment, this gradation characteristic error is calculated as the root mean square of each point error, which is an error from the ideal characteristic of the test image 710.

The processing by the halftone parameter selection unit 1501 will be described with reference to FIG. In FIG. 17A, in the present embodiment, the horizontal axis is the gradation value (input gradation value) of the image data input to the image processing unit 160, and the vertical axis is the image output from the image forming unit 150. It is a graph which shows the gradation characteristic as an output density. In the graph of FIG. 17A, the solid line curve is the gradation characteristic (actual characteristic) derived by the gradation characteristic acquisition unit 905, and the dotted straight line is the linear characteristic (ideal characteristic) which is the ideal gamma characteristic. Are shown respectively.

Further, FIG. 17B is an enlarged view showing the vicinity of the input gradation value of 20% in FIG. 17A, which is linear with the value of the gradation characteristic (output density) at the input gradation value of 20%. The error e1 (20%) from the value of the characteristic (ideal characteristic) is also described. The errors e2 (40%), e3 (60%), e4 (80%), and e5 (100%) at the input gradation values 40%, 60%, 80%, and 100% can be similarly determined. The gradation characteristic error E is the error e1 (20%), e2 (40%), e3 (60%), e4 (80%), e5 (100%) in each of these gradation values, as shown in FIG. It is calculated by a mathematical formula.

Then, the halftone parameter selection unit 1501 selects one from a plurality of dither matrices stored in the halftone parameter storage unit 1401 based on the gradation characteristic error E. The halftone parameter storage unit 1401 stores, for example, a gradation characteristic error E and a plurality of dither matrices in a table associated with each other. FIG. 19 is a diagram showing an example of a plurality of dither matrices stored in the halftone parameter storage unit 1401.

In the present embodiment, the number of dither matrices stored in the halftone parameter storage unit 1401 is 3, and Mat. 1> Mat. 2> Mat. An example with a high number of lines is shown in the order of 3. The halftone parameter changing unit 1402 selects one from a plurality of dither matrices stored in the halftone parameter storage unit 1401, and uses the dither matrix currently set in the RAM 162 as the selected dither matrix. Change to a matrix. Next, the halftone processing unit 404 performs halftone processing of the image data using the dither matrix selected by the halftone parameter changing unit 1402.

As described above, in the image forming apparatus of the present embodiment, the graininess at the position where the spot diameter is the largest (that is, the graininess on the recording surface is the worst) on the photosensitive drum is set in the main scanning direction different from the position. Estimate using only sensors provided at predetermined positions. The image forming apparatus of the present embodiment performs halftone processing of image data using a dither matrix having an optimum number of lines based on the estimation result obtained by the above method, thereby maintaining both graininess and pattern visibility. You can get a satisfactory output at the level of.

[Embodiment 3]
In the above-described embodiment, the adjustment light emission control parameter setting unit 901 calls only one adjustment light emission control parameter stored in advance in the gradation correction parameter storage unit 405 (ROM163), and the test image formation control unit 903 Set for. Similarly, in the above-described embodiment, the normal light emission control parameter setting unit 902 calls only one normal light emission control parameter stored in advance in the gradation correction parameter storage unit 405 (ROM163) to form a test image. It is set for the control unit 903. This is based on the premise that the spot diameter 505 at the first position and the spot diameter 504 at the second position are unique sizes in the image forming apparatus 100, respectively.

However, the respective spot diameters may change later depending on the operating state of the image forming apparatus 100. For example, when the environmental temperature in the environment in which the image forming apparatus 100 is installed rises, the respective spot diameters may change due to thermal expansion of the lens that transmits the laser light output by the light emitting unit 501. Even when the image forming unit 150 is continuously operated for a long time, the respective spot diameters may change due to the thermal expansion of the lens. Alternatively, when the image forming unit 150 repeatedly executes the recording operation, the surface layer of the photosensitive drum 151 may be scraped off, and the optical characteristics of the photosensitive drum 151 may be changed. In such a case, by applying the adjustment issuance control parameter at the first position, it becomes impossible to obtain gradation characteristics substantially equal to the case where the normal light emission control parameter is applied at the second position. .. As a result, the accuracy of deriving the gradation correction parameter (S1025) and the accuracy of selecting the halftone parameter (S1601) are lowered, and the image quality on the recording surface is impaired.

This embodiment has been made in view of the above problems. That is, in the present embodiment, the adjustment light emission control parameter setting unit 901 selects one from a plurality of adjustment light emission control parameters according to the operating state of the image forming apparatus 100, and causes the test image formation control unit 903 to select one. Set for. Similarly, in the present embodiment, the normal light emission control parameter setting unit 902 selects one from a plurality of normal light emission control parameters according to the operating state of the image forming apparatus 100, and the test image forming control unit Set for 903. The same symbols will be added to the same configurations as those in the above-described embodiment, and the description thereof will be omitted.

FIG. 20 is a diagram showing an example of a plurality of normal light emission control parameters and a plurality of adjustment light emission control parameters stored in the gradation correction parameter storage unit 405. The plurality of normal light emission control parameters and the plurality of adjustment light emission control parameters are stored in a table associated with the state information of the image forming apparatus 100. In the present embodiment, the number of normal light emission control parameters stored in the gradation correction parameter storage unit 405 is 3, and an example is shown in which the parameters are A1, A2, and A3, respectively. Similarly, the number of adjustment light emission control parameters stored in the gradation correction parameter storage unit 405 is 3, and an example is shown in which the parameters are B1, B2, and B3, respectively. Further, in the present embodiment, the state information of the image forming apparatus 100 is exemplified by the cumulative number of output sheets from the image forming unit 150 (printer engine). The gradation correction parameter storage unit 405 sets parameters A1 and B1 for the cumulative output number 1 to 1000, parameters A2 and B2 for the cumulative output number 1001 to 2000, and parameters after the cumulative output number 2001. A3 and B3 are stored in association with each other.

The normal light emission control parameter setting unit 902 acquires the state information of the image forming apparatus 100 monitored by the monitor unit (not shown), and one of a plurality of normal light emission control parameters is selected according to the state information. Select. The selected normal light emission control parameter is set for the test image formation control unit 903 (S1011). Next, the adjustment light emission control parameter setting unit 901 acquires the state information of the image forming apparatus 100 monitored by the monitor unit (not shown), and from among a plurality of adjustment light emission control parameters according to the state information. Select one. The selected light emission control parameter for adjustment is set for the test image formation control unit 903 (S1021).

As described above, in the present embodiment, even when each spot diameter changes afterwards, by applying an appropriate adjustment issuance control parameter, normal light emission is performed at the second position. It is possible to obtain gradation characteristics that are substantially the same as when the control parameters are applied. As a result, the image forming apparatus 100 of the present embodiment can derive the gradation characteristics at each position in the main scanning direction with high accuracy by using only one sensor, and can improve the image quality on the recording surface. In the present embodiment, an example is shown in which the light emission control parameter is selected according to the cumulative number of outputs from the image forming unit 150, but the state information of the image forming apparatus 100 is not limited to this. For example, even if the light emission control parameter is selected according to the "environmental temperature" of the environment in which the image forming apparatus 100 is installed, the "most recent continuous recording number" after the image forming unit 150 starts the recording operation, and the like. Good.

[Other Examples]
The present invention supplies a program that realizes one or more functions of the above-described embodiment to a system or device via a network or storage medium, and one or more processors in the computer of the system or device reads and executes the program. It can also be realized by the processing to be performed. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

100 ... Image forming device 160 ... Image processing unit 170 ... Image forming control unit 901 ... Light emission control parameter setting unit for adjustment 902 ... Normal light emission control parameter setting unit 905 ... Gradation characteristic acquisition unit 906 ... Gradation correction parameter derivation unit

Claims (16)

An electrophotographic image forming apparatus is an image processing apparatus that processes image data used for image forming.
For the control means for controlling the output of the light beam, the first light emission control parameter indicating the light emission intensity and the light emission time of the light emission means for emitting the light beam and the light emission intensity different from the first light emission control parameter. And a setting means for setting a second light emission control parameter indicating the light emission time and
At a predetermined position in the main scanning direction of the photosensitive drum, the first gradation characteristic representing the output density with respect to the input gradation value to which the set first emission control parameter is applied, and the set second emission control An acquisition means for acquiring a second gradation characteristic representing an output density with respect to an input gradation value to which a parameter is applied, and
It has a derivation means for deriving a first correction characteristic having the inverse characteristic of the acquired first gradation characteristic and a second correction characteristic having the inverse characteristic of the acquired second gradation characteristic. An image processing device characterized by. The exposure amount distribution obtained by performing the convolution calculation of the second emission control parameter in the light intensity distribution of the spot light corresponding to the predetermined position, and the spot light corresponding to the position different from the predetermined position. The claim is characterized in that the second light emission control parameter is set so that the light intensity distribution is substantially equal to the exposure amount distribution obtained by performing the convolution calculation of the first light emission control parameter. The image processing apparatus according to 1. A forming means for forming a first test image to which the set first light emission control parameter is applied and a second test image to which the set second light emission control parameter is applied at the predetermined position. Have more
The acquisition means is characterized in that it acquires the first gradation characteristic based on the formed first test image and the second gradation characteristic based on the second test image. Item 2. The image processing apparatus according to item 1 or 2. 1. The first aspect of the present invention is characterized in that the correction means for correcting the density of the image data corresponding to the position in the main scanning direction is further provided based on the derived first correction characteristic and the second correction characteristic. The image processing apparatus according to any one of 3 to 3. An electrophotographic image forming apparatus is an image processing apparatus that processes image data used for image forming.
For the control means for controlling the output of the light beam, the first light emission control parameter indicating the light emission intensity and the light emission time of the light emission means for emitting the light beam and the light emission intensity different from the first light emission control parameter. And a setting means for setting a second light emission control parameter indicating the light emission time and
Acquiring means for acquiring the first gradation characteristic representing the output density with respect to the input gradation value to which the set second emission control parameter is applied at a predetermined position in the main scanning direction of the photosensitive drum.
An evaluation means for evaluating the difference between the acquired first gradation characteristic and the second gradation characteristic in which the output density with respect to the input gradation value represents a linear characteristic.
An image processing apparatus including a selection means for selecting a halftone parameter to be used for halftone processing based on the result of the evaluation. The spot shape of the spot light imaged on the photosensitive drum changes according to each position in the main scanning direction, and the size of the spot shape corresponding to the predetermined position is the predetermined size in the main scanning direction of the photosensitive drum. The image processing apparatus according to claim 5, wherein the image processing apparatus is smaller than the spot shape corresponding to a position other than the position of. The selection means is characterized in that the larger the difference between the first gradation characteristic and the second gradation characteristic, the lower the number of halftone parameters is selected from a plurality of halftone parameters. The image processing apparatus according to claim 5 or 6. Further having a forming means for forming a test image to which the set second emission control parameter is applied at the predetermined position.
The image processing apparatus according to any one of claims 5 to 7, wherein the acquisition means acquires the first gradation characteristic based on the formed test image. The image processing apparatus according to any one of claims 5 to 8, further comprising a halftone processing means for executing halftone processing of the image data using the selected halftone parameter. The setting means is characterized in that one is selected from a plurality of the light emission control parameters according to the operating state of the image forming apparatus, and the selected light emission control parameters are set for the control means. The image processing apparatus according to any one of claims 1 to 9. The image processing apparatus according to claim 3 or 8, wherein the test image is composed of a plurality of gradation patches output at different densities. An image forming apparatus that forms an image based on the image data corrected by the image processing apparatus according to claim 4. An image forming apparatus that forms an image based on the image data that has been halftone processed by the image processing apparatus according to claim 9. An image processing method for image data used by an electrophotographic image forming apparatus for image forming.
For the control means for controlling the output of the light beam, the first light emission control parameter indicating the light emission intensity and the light emission time of the light emission means for emitting the light beam and the light emission intensity different from the first light emission control parameter. And a setting step to set a second light emission control parameter indicating the light emission time and
At a predetermined position in the main scanning direction of the photosensitive drum, the first gradation characteristic representing the output density with respect to the input gradation value to which the set first emission control parameter is applied, and the set second An acquisition step of acquiring a second gradation characteristic representing an output density with respect to an input gradation value to which a light emission control parameter is applied, and an acquisition step.
It has a derivation step for deriving a first correction characteristic having the inverse characteristic of the acquired first gradation characteristic and a second correction characteristic having the inverse characteristic of the acquired second gradation characteristic. An image processing method characterized by that. An image processing method for image data used by an electrophotographic image forming apparatus for image forming.
For the control means for controlling the output of the light beam, the first light emission control parameter indicating the light emission intensity and the light emission time of the light emission means for emitting the light beam and the light emission intensity different from the first light emission control parameter. And a setting step to set a second light emission control parameter indicating the light emission time and
An acquisition step of acquiring a gradation characteristic representing an output density with respect to an input gradation value to which the set second emission control parameter is applied at a predetermined position in the main scanning direction of the photosensitive drum.
An evaluation step for evaluating the difference between the acquired gradation characteristic and the second gradation characteristic in which the output density with respect to the input gradation value represents a linear characteristic.
An image processing method including a selection step of selecting a halftone parameter to be used for halftone processing based on the result of the evaluation. A program for causing a computer to function as each means of the image processing apparatus according to any one of claims 1 to 11.

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