JP6611503B2 - Image processing apparatus, image processing method, and program - Google Patents

Description

  The present invention relates to an image processing technique for generating image data for image formation using an electrophotographic system.

  2. Description of the Related Art Conventionally, an electrophotographic image forming apparatus that irradiates a rotating polyhedron (polygon) with laser light and exposes the photosensitive member with reflected light to form an image has been widely used. An f-θ lens, which is an optical lens, is provided between the polygon mirror and the photosensitive member. The f-θ lens has optical characteristics such as a laser beam condensing function and a distortion correcting function that guarantees temporal linearity of scanning. The laser beam that has passed through the f-θ lens is combined and scanned at a scanning speed equal to the main scanning direction, which is the longitudinal direction of the photosensitive member. However, the length of the region irradiated onto the photoconductor may deviate from an ideal scanning magnification due to a deviation in characteristics from the manufacturing error of the f-θ lens.

  Therefore, in order to correct a shift in scanning magnification in the main scanning direction, a method of inserting or deleting pixels (hereinafter referred to as pixel pieces) of less than one pixel of image data has been proposed. In Patent Document 1, when adjusting the main scanning magnification, at least one of a plurality of pixel pieces is set in advance as an extinguished pixel piece, and an extinguished pixel piece is used for a pixel at a position with a large scanning magnification. A method of deleting is disclosed. Further, in Patent Document 2, the effective image area is divided into five blocks, no pixel pieces are inserted at both ends, and one pixel piece is inserted for each pixel at both ends. A method of controlling to insert two pieces is disclosed.

JP 2014-109636 A JP-A-2005-96351

  However, in the methods described in Patent Document 1 and Patent Document 2, the position where the unlit pixel piece is inserted or deleted in each pixel is not considered. Therefore, there may be a change in the amount of blur of light that is exposed and scanned on the surface of the photoconductor depending on the insertion position of the extinguished pixel piece. As a result, the uniformity of image quality in the main scanning direction is degraded.

  Accordingly, an object of the present invention is to appropriately generate image data so that an image forming apparatus using an electrophotographic method can stably form an image.

In order to solve the above-described problems, the present invention is an image processing apparatus for generating image data for forming an image by exposing an image bearing drum by an exposure unit including laser light using an electrophotographic method. Input means for inputting data, and each pixel in the image data according to a position in the main scanning direction on the photosensitive drum when the laser light is irradiated on the photosensitive drum based on the image data The number of pixel pieces to be inserted is determined as the number of pixel pieces, and when the number of pixel pieces is one or more, the image according to the intensity distribution of the laser beam on the photosensitive drum so as to suppress the fluctuation of the scanning spot diameter for each pixel in the data, position to determine the position of inserting the pixel piece number of pixels pieces for each pixel in the image data And determining means; and generating means for generating an exposure signal for controlling the exposure unit based on the image data and the position at which the pixel piece determined by the position determining means is inserted. .

  In the present invention, image data can be appropriately generated so that an image forming apparatus using an electrophotographic system can stably form an image.

1 is a block diagram illustrating a configuration of an image processing apparatus according to a first embodiment. Block diagram showing details of image forming apparatus using electrophotography The figure which shows the outline of the optical system in an image forming apparatus The figure for demonstrating the deviation | shift amount table Diagram showing change in scan width on photoconductor The figure which shows typically the result at the time of determining a pixel piece pattern without considering a scanning spot diameter The figure explaining the pattern of a pixel piece, and the scanning spot diameter The figure which shows typically the result at the time of determining a pixel piece pattern in consideration of a scanning spot diameter The figure for demonstrating a pixel piece pattern table The figure which shows the flow of a pixel piece pattern determination process The block diagram which shows the detail of the image processing apparatus of 2nd Embodiment Diagram for explaining the blur amount table Diagram showing change in scanning spot diameter on photoconductor The block diagram which shows the detail of the image processing apparatus of 3rd Embodiment The block diagram which shows the detail of the image processing apparatus of 4th Embodiment

  Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. Note that the configurations shown in the following embodiments are merely examples, and the present invention is not limited to the illustrated configurations.

<First Embodiment>
The first embodiment includes an image forming system including an image forming apparatus that forms an image on a recording medium using an electrophotographic method, and an image processing apparatus that converts input image data into image data that can be output by the image forming apparatus. Explained as an example. FIG. 1 is a block diagram showing a detailed configuration of an image processing apparatus 1 applicable to the first embodiment. The image processing apparatus 1 and the image forming apparatus 2 are connected by an interface or a circuit. The image processing apparatus 1 is a printer driver installed in, for example, a general personal computer. In that case, each component in the image processing apparatus 1 described below is realized by a computer executing a predetermined program. However, the image forming apparatus 2 may include the image processing apparatus 1.

[Image forming apparatus and image forming]
First, the image forming apparatus 2 will be described. FIG. 2 is a block diagram illustrating a detailed configuration of the image forming apparatus 2 applicable to the first embodiment. The image forming apparatus 2 includes a CPU 201 that receives image data from the image processing apparatus 1, a RAM 202 for storing, and an HDD 203. The image forming apparatus 2 forms an image using four color materials of C (cyan), M (magenta), Y (yellow), and K (black). The image forming apparatus 2 according to the present embodiment is a tandem method, has an image forming unit corresponding to each color, and independently forms a single color image. The image forming unit mainly includes a light source, an exposure device, a photosensitive drum as an image carrier, a charging device, and a developing device. Hereinafter, image formation by electrophotography will be described.

(1) Charging Step The photosensitive drums 212, 213, 214, and 215 are charged to a predetermined potential using the chargers 216, 217, 218, and 219. The charging potentials by the chargers 216 to 219 are controlled to be a desired voltage by measuring the potentials by the electrometers 241, 242, 243, and 244 facing the photosensitive drums 212 to 215.

(2) Exposure Step The drive units 204, 205, 206, and 207 modulate image data obtained from the CPU into an exposure signal by an exposure signal generation process, and based on the exposure signal, the exposure units 208, 209, 210, and 211. Drive each one. The exposure units 208 to 211 expose the photosensitive drums 212, 213, 214, and 215 to form an electrostatic latent image on the photosensitive drum.

  FIG. 3 is a schematic diagram illustrating an optical system including a driving unit and an exposure unit. Here, an optical system including the drive unit 204 and the exposure unit 208 will be described as an example, but other drive units and exposure units have the same configuration. First, the drive unit 204 includes a laser driver 310, an intensity detection photo detector 304 (hereinafter referred to as an intensity detection PD sensor), and a beam position detection photo detector 306 (hereinafter referred to as a BD sensor). The intensity detection PD sensor 304 detects the intensity of the laser beam in order to control the exposure amount. The BD sensor 306 detects the position of the laser beam in order to control writing. The exposure unit 208 includes a light emitting element 301, a collimator lens 302, and a polygon mirror 305.

  First, the light emitting element 301 is driven to emit laser light. The laser beam is spread by the collimator lens 302 and reflected on the surface of the rotating polygon mirror 305 to expose and scan the photosensitive member. In the present embodiment, the light intensity distribution by the laser light that is exposed and scanned based on the pixel value of each pixel is referred to as a “scanning spot”. When the BD sensor detects the laser beam to be moved and scanned, a writing start signal is generated and transmitted to the CPU 201. The CPU 201 sends the image data to the laser driver 310 a predetermined time after receiving the write start signal. The laser driver 310 drives the light emitting element 301 based on an exposure signal obtained by modulating image data, and generates an electrostatic latent image on the photosensitive drum 212. Note that the laser driver 310 in this embodiment controls the driving of the laser light according to pixel piece pattern information indicating the position of the pixel piece that defines the turning on or off of the laser light of less than one pixel. Details of this will be described later.

(3) Toner Development Step The electrostatic latent image on the photosensitive drum is attached with toner by the developing devices 220, 221, 222, and 223 to generate a toner image.

(4) Transfer process By applying a voltage to the conductive rollers 224, 225, 226, and 227 as transfer means at the contact portion between the transfer belt 228 and each photosensitive drum, the toner image is transferred from the photosensitive member to the transfer belt. The primary transfer to. A color toner image is formed on the transfer belt 228 by sequentially forming CMYK toner images in synchronization. Next, by applying a voltage to the secondary transfer roller 230 at the secondary transfer nip where the recording medium 230 and the transfer belt 228 come into contact with each other, the color toner image is further transferred onto the recording medium 230.

(5) Fixing Step The recording medium on which the color toner image is formed is conveyed to the fixing unit 232. The heated fixing unit 232 applies heat and pressure to the recording medium and the toner image on the recording medium to melt and fix the toner image on the recording medium.

(6) Paper Discharge Process Finally, the recording medium on which the color image is formed is discharged from the image forming apparatus 2 through the fixing unit 232. Thus, image formation using the electrophotographic method in the image forming apparatus 2 is completed.

[Image processing device]
Each configuration in the image processing apparatus will be described. When data (hereinafter referred to as PDL data) described in a printer description language (PDL), which is an image output command, is received from a device (not shown), image data is drawn based on the PDL data. Various image processing is performed on the image data, and the image processed image data is transmitted to the image forming apparatus 2. The image processing apparatus 1 includes an image generation unit 101, a color conversion processing unit 102, a color separation image storage unit 103, a halftone processing unit 104, and a halftone image storage unit 105. The image processing apparatus 1 also includes a shift amount information storage unit 106 for each color, a pixel piece number calculation unit 107, a spot diameter correction amount calculation unit 108, a pixel piece position determination unit 109, a pixel piece position information storage unit 110, and a pixel piece position. An information storage unit 111 is included. The image processing apparatus 1 further includes a pixel piece position information adding unit 112, a transfer buffer 113, and an image data transfer unit 114.

  The image generation unit 101 rasterizes the received PDL data, and generates image data composed of R (red), G (green), and B (blue). The generated RGB image data is sent to the color conversion processing unit 102.

  The color conversion processing unit 102 converts the RGB image data received from the image generation unit 101 into data corresponding to the color material included in the image forming apparatus 2. Here, the RGB image data is converted into image data corresponding to C (cyan), M (magenta), Y (yellow), and K (black). The color conversion processing unit 102 stores image data corresponding to each CMYK in the color separation image storage unit 103.

  The halftone image processing unit 104 performs halftone processing on the color-converted image data received from the color separation image storage unit 103, and outputs halftone image data of each color obtained by the halftone processing to the halftone image storage unit 105. Output to.

  The pixel piece number determination unit 107 acquires shift amount information using a shift amount table for each CMYK held by the shift amount information storage unit 106, and inserts it to correct the scanning magnification for each pixel based on the shift amount information. The number of pixel pieces to be determined is determined. In the present embodiment, the pixel piece to be inserted is a pixel piece that does not light the laser beam. Further, 0 may be included as the number of pixel pieces.

  The spot diameter correction amount calculation unit 108 acquires the shift amount information using the shift amount table for each pixel number CMYK held by the shift amount information storage unit 106, and corrects the spot diameter for each pixel based on the shift amount information. A correction amount for calculating the value is calculated.

  The pixel piece position determining unit 109 determines the position at which the number of pixel pieces determined by the pixel piece number determining unit 107 is inserted based on the correction amount calculated by the spot diameter correction amount calculating unit 108. The pixel piece position determination unit 109 refers to the pixel piece position table held by the pixel piece position information storage unit 110. As a result, pixel piece pattern information indicating the pattern of the pixel piece that defines whether the laser light is turned on or off is generated as pixel piece pattern information for each pixel. The pixel piece (lighting pixel piece) that defines lighting here means a pixel piece for expressing the gradation of image data. Therefore, the pixel piece is turned on or off according to the pixel value of the pixel in the corresponding image data. On the other hand, the pixel piece that defines the light-off (light-off pixel piece) means a pixel piece for correcting the scanning magnification of the image data, and is a pixel piece that is always non-lighted.

  Pixel piece pattern information of each pixel obtained by the pixel piece position determining unit 109 is stored in the pixel piece pattern information storage unit 111 for each CMYK. Details of the shift amount table, the pixel piece arrangement table, and the pixel piece position determination will be described later.

  The pixel piece pattern information addition unit 112 adds pixel piece pattern information to the CMYK halftone image data stored in the halftone image storage unit 105. The halftone image data to which the pixel piece pattern information is added is output to the transfer buffer 113 and transferred to the image forming apparatus 2 by the image data transfer unit 114.

  Next, the deviation amount table will be described. FIG. 4 shows a deviation amount table. The shift amount here means the shift amount between the scanning width of each pixel in the image data in the main scanning direction and the target scanning width that should be originally handled. The horizontal axis in FIG. 4 represents the position in the longitudinal direction of the photosensitive drum, and the vertical axis represents the scanning width per pixel on the photosensitive drum. In this embodiment, the largest scanning width in the longitudinal direction of the photosensitive drum is set as the reference W.

  FIG. 5 shows an example of change in the amount of deviation when the f-θ lens is removed. Since the polygon mirror 305 moves at a constant speed, the laser beam scans from the surface of the polygon mirror 305 so as to draw an arc. In this case, the rotation speeds θa, θb, θc, and θd per unit time are θa = θb = θc = θd. At this time, if the scanning widths per unit time on the axis of the photosensitive drum surface are Xa, Xb, Xc, and Xd, respectively, the relationship is Xa> Xb, Xd> Xc. From this result, it can be seen that the scanning width per pixel on the photosensitive drum increases toward the end of the drum and decreases toward the center. If this is the case, since the scanning width of one pixel at the edge and the center of the image is different, the actual scanning width of each pixel on the photosensitive drum is, for example, a curve indicated by a solid line in FIG. Therefore, an image is formed in which the scanning width of one pixel extends at the edge of the image and is compressed at the center.

Therefore, the scanning width of one pixel is increased in a pseudo manner by inserting more extinguished pixel pieces into the pixel corresponding to the central portion in the image data. On the other hand, the extinguished pixel piece is not inserted into or deleted from the pixel corresponding to the end in the image data. Thereby, the scanning width on the photosensitive drum can be made uniform without the f-θ lens. In the present embodiment, the scan width on which the scan width on the photosensitive drum corresponding to one pixel is the largest is designed to be the target scan width W.
The dotted line in FIG. 4 is the target scanning width on the photosensitive drum for each pixel number. In the deviation amount table shown in FIG. 4 as described above, when the pixel number is input, the difference between the reference scanning width W on the photosensitive drum and the scanning width actually exposed is read as the deviation amount L. Can do.

  In this embodiment, one such shift amount table is held for each color. Since the image forming unit is designed independently for each color, the shift amount tables are different. Further, when it is known that the variation of the scanning magnification changes according to the sub-scanning direction, a plurality of deviation amount tables are held for each color, and the deviation amount table is selected according to the position in the sub-scanning direction. Also good. If it is known that the variation in scanning magnification does not change for each color, only one shift amount table common to each color may be held.

  In the present embodiment, the deviation amount table is generated based on the measurement result by measuring the scanning width per unit time when the photosensitive drum is exposed at the time of manufacture. If the fluctuation of the main scanning magnification does not greatly change from the theoretical value of the scanning width X when the f-θ lens is removed, calculation is performed based on the scanning width X per unit time at the drum longitudinal position without performing measurement. May be.

  Here, the relationship between the pixel piece to be inserted and the scanning spot diameter will be described. First, FIG. 6 is a diagram for explaining an exposure result when a pixel piece is inserted without considering the scanning spot diameter. FIG. 6A is a diagram schematically illustrating an example of a result of exposing certain image data. Here, one pixel is represented by a thick line, and is composed of four pixel pieces per pixel. Of the three consecutive pixels, the center pixel is a case where all four pixel pieces are lit pixel pieces, and the left pixel and the right pixel are cases where all four pixel pieces are non-lighted pixel pieces. The three pixels shown on the left are assumed to have a scanning magnification of 100% and a scanning width target value corresponding to one pixel. The three pixels shown in the center have a scanning magnification of 80%, and the scanning magnification is smaller than the target. Therefore, the three pixels shown in the center are adjusted so that the scanning magnification becomes pseudo wide by inserting one pixel piece into each pixel. The three pixels shown on the right have a scanning magnification of 67%, and the scanning magnification is smaller than the target. Therefore, the three pixels shown on the right are adjusted so that the scanning magnification becomes pseudo wide by inserting two pixel pieces into each pixel.

  Here, it is assumed that a pixel piece for adjusting the scanning magnification is uniformly inserted at the right end (end in the main scanning direction) of each pixel. FIG. 6B is a diagram schematically showing the result of inserting the extinguished pixel piece into the image data shown in FIG. When attention is paid to the center pixel among the three consecutive pixels, the three pixels shown on the left are not composed of pixel pieces, and thus are composed of four lit pixel pieces. In the case of the central three pixels, the pixel consists of four lit pixel pieces and one extinguished pixel piece, and in the case of the right three pixels, the pixel consists of four lit pixel pieces and two extinguished pixel pieces. At this time, since the width (scanning width) of the lit pixel piece of each pixel remains narrow in an area where the scanning magnification before correction is narrow (center 3 pixels, right 3 pixels), the scanning spot diameter is reduced. FIG. 6C is a diagram schematically illustrating an example of a scanning spot when exposure scanning is performed based on the image data illustrated in FIG. The light amount distribution indicated by a dotted line in the drawing is a light amount distribution (hereinafter also referred to as a spot shape) of a scanning spot corresponding to each lighting pixel piece. A spot shape indicated by a solid line in the drawing is a light amount distribution of an integrated scanning spot in which scanning spots corresponding to each pixel piece are integrated. Since the number of lit pixel pieces is the same, the total light amount of the integrated scanning spot in each region should be uniform. However, the integrated scanning spot diameter becomes narrower as the scanning magnification before correction becomes narrower, and the scanning spot diameter becomes larger as the scanning magnification before correction becomes wider (S1> S2> S3). As a result, in the output image formed on the recording medium, the image quality such as density, tint, sharpness, and graininess varies depending on the position in the main scanning direction.

  Therefore, in the present embodiment, in the pixel into which at least one or more extinguished pixel pieces are inserted, the insertion position is determined in consideration of the scanning spot diameter. When the scanning spot diameter is wide, the extinguished pixel pieces are inserted so that the lit pixel pieces are concentrated so that the scanning spot diameter does not widen. On the other hand, when the scanning spot diameter is narrow, the scanning spot diameter is artificially widened by inserting the extinguished pixel pieces so as to increase the dispersion of the lit pixel pieces. Thereby, the scanning spot diameter of each pixel can be formed substantially uniform.

  FIG. 7 is a graph showing the relationship between the distribution of the lit pixel pieces and the scanning spot diameter in a plurality of pixel piece patterns including four lit pixel pieces and two unlit pixel pieces. The horizontal axis represents the standard deviation ratio of the lit pixel piece arrangement (the ratio of the standard deviation to the pixel piece pattern <1> in which the extinguished pixel pieces are inserted at the ends of all the pixels). The standard deviation indicates variation from the center position of the lit pixel piece in the main scanning direction. The vertical axis represents the scanning spot diameter ratio (ratio of the pixel piece pattern <1> to the scanning spot diameter) when exposure scanning is performed based on each pixel piece arrangement pattern. The black dots in the graph indicate the correspondence between the standard deviation ratio of each pixel piece pattern and the scanning spot diameter ratio, and it can be seen that the scanning spot diameter ratio is proportional to the standard deviation ratio of the pixel piece pattern. A white point in the graph indicates a correspondence between a standard deviation ratio and a scanning spot diameter ratio in a pixel having a target scanning magnification. In order to make the scanning spot diameter uniform, exposure scanning may be performed with a pixel piece pattern close to the standard deviation ratio (= exposure width ratio 100% / 67% = 1.5) of the target pixel. In this case, the pattern with the closest standard deviation ratio is the pattern indicated by <3> in the figure.

  In other words, for a plurality of pixel pieces constituting one pixel, when there are a pixel piece that is lit and a pixel piece that is not lit, in order to widen the scanning spot diameter, the non-lighted pixel pieces are distributed over the plurality of pixel pieces. Deploy. Specifically, at least one non-lighting pixel piece is arranged at a position sandwiched between the lighting pixel pieces. Furthermore, by changing the insertion position of the non-lighted pixel piece according to the ratio of the scanning spot diameter of the target pixel and the target scanning spot diameter, it is possible to cope with a plurality of scanning spot diameters. Thus, in this embodiment, the pattern of the pixel piece corresponding to one pixel is determined according to the scanning spot diameter, and the position of the pixel piece to be inserted is determined.

  FIG. 8 is a diagram schematically showing exposure control based on image data in the present embodiment. In the area where the scanning magnification is reduced, the scanning spot diameter is obtained by inserting the extinguished pixel pieces between the lit pixel pieces (distributing the lit pixel pieces) so as to approximate the standard deviation ratio of the target pixel. Can be suppressed (S1′≈S2′≈S3 ′).

  Next, the pixel piece pattern table will be described. FIG. 9A shows a pixel piece pattern table. The pixel piece pattern table stores pixel piece pattern information Fn associated with the number Pn of unlit pixel pieces and the spot diameter correction amount Sr (standard deviation ratio). The pixel piece pattern information Fn is associated with a pixel piece pattern (FIG. 9B) indicating the arrangement of the lit and unlit pixel pieces. The laser driver 310 generates an exposure signal based on the arrangement of the extinguished pixel pieces according to the pixel piece pattern information. The pixel piece pattern table shown in FIG. 9A as described above can read the corresponding pixel piece pattern information when the number Pn of inserted pixel pieces and the spot diameter correction amount Sr are input.

  Next, details of the pixel piece pattern determination process in each pixel will be described. FIG. 10 is a diagram illustrating a flowchart of the pixel piece pattern determination process. In the pixel piece pattern determination process, pixel piece pattern information indicating a pixel piece pattern, which is used when the laser driver 310 generates an exposure signal for each pixel in the image data, is generated. Note that the case where processing is performed on cyan (C) image data will be described as an example, but the same processing may be applied to image data of other colors (M, Y, K).

  First, in step S100, a variable indicating a pixel number is initialized.

  Next, in step S101, the error amount is initialized. The error amount is an error generated when the scanning magnification in the main scanning direction is adjusted by inserting and extracting a pixel up to a pixel immediately before the target pixel. Since there is no error amount at the start of scanning for a certain main scanning line, it is initialized to zero.

  Next, in step S102, the pixel piece number determination unit 107 determines the number of extinguished pixel pieces to be inserted in order to expose the target pixel on the photosensitive drum at a target scanning magnification. The pixel piece position determining unit 109 acquires a shift amount Lk from the target scanning magnification in the main scanning line corresponding to the target pixel position k from the cyan plate shift amount table stored in the shift amount information storage unit 106. Next, the number Pn of unlit pixel pieces to be inserted is determined by the following equation (1).

if ((shift amount Lk + error amount from target scanning magnification) <(pixel piece length × 1/2))
Pn = 0
elseif ((deviation amount Lk + error amount from target scanning magnification) <(pixel piece length × 3/2))
Pn = 1
elseif ((deviation amount Lk + error amount from target scanning magnification) <(pixel piece length × 5/2))
Pn = 2
elseif ((deviation amount Lk + error amount from target scanning magnification) <(pixel piece length × (n × 2 + 1) / 2))
Pn = n
... (1)
The error generated when the exposure width in the main scanning direction is adjusted by inserting and extracting the pixel pieces up to the previous pixel is distributed to the target pixel, thereby adjusting the scanning magnification in the entire main scanning direction. Therefore, the left side of Equation (1) indicates the predicted deviation amount from the target width on the photosensitive drum and the error of the scanning width that could not be corrected by pixel piece insertion up to the immediately preceding pixel for the target pixel. It is determined that the predicted shift amount from the target position on the photosensitive drum is equal to or larger than the pixel piece length × ((n−1) × 2 + 1) / 2) and smaller than the pixel piece length × (n × 2 + 1) / 2). Then, the number Pn of unlit pixels to be inserted is acquired as n.

  In step S103, the spot diameter correction amount calculation unit 108 calculates a correction amount Sr for exposing the target pixel on the photosensitive drum with the target scanning spot diameter. First, the spot diameter correction amount calculation unit 108 acquires a deviation amount Lk from the target scanning magnification at the main scanning position k corresponding to the target pixel from the deviation amount table of the cyan plate stored in the deviation amount information storage unit 106. The correction amount Sr is calculated as the scanning spot diameter correction amount according to the following equation (2).

Sr = (W + Lk) / W (2)
W is a reference scanning width.

  Next, in step S104, the pixel piece position determining unit 109 refers to the pixel piece pattern table stored in the pixel piece pattern information storage unit 110, and based on the number of extinguished pixel pieces Pn and the spot diameter correction amount Sr. Pixel piece pattern information Fn is acquired.

  In step S105, the error amount is updated by the following equation (3).

Error amount = (deviation amount from target scanning magnification + error amount) − (pixel piece length × n) (3)
In step S106, it is determined whether or not the processing has been completed up to pixel number N in the main scanning line. If not, the process proceeds to step S111, the pixel number is incremented, and the process returns to step S102. If the pixel number N has been reached in the main scanning line, the processing of the main scanning line to be processed is terminated. The above processing is performed for all main scanning lines constituting the image data. The pixel piece arrangement determining process is thus completed.

  The pixel piece pattern information adding unit 112 reads out the pixel value (indicating the original exposure width for each pixel) of each pixel constituting the image data from the halftone image storage unit 105. Next, pixel piece pattern information is added to each pixel using the pixel piece pattern information storage unit 111 of each color, and output image data in which the pixel value and pixel piece pattern information in each pixel are stored in a predetermined format is generated. The output image data is stored in a transfer buffer 113 for sending data to the engine unit. Thereafter, the image data transfer unit 114 sends the output image data stored in the transfer buffer 113 to the image forming apparatus 2 in synchronization with the image forming timing signal transmitted from the image forming apparatus 2.

(Pixel piece pattern control)
The laser driver 310 in the image forming apparatus 2 actually controls the pixel piece pattern based on the output image data to which the pixel piece pattern information is added for each pixel. As described above, the laser driver 310 modulates the received output image data into an exposure signal, and drives the light emitting element 301. The laser driver 310 inserts an extinguished pixel piece at a position determined by the pixel piece pattern information for each pixel so as to adjust the scanning spot diameter when one pixel is exposed as shown in FIG. An exposure signal is generated with the pixel piece pattern shown. In the present embodiment, for pixels whose scanning spot diameter is enlarged, extinguished pixel pieces are inserted so that the lit pixel pieces are concentrated, and lit pixel pieces are dispersed for pixels whose main scanning spot diameter is reduced. As shown in FIG.

  As described above, in the first embodiment, the scanning width in the main scanning direction is adjusted by inserting or deleting the extinguished pixel piece for each pixel. When a pixel piece is inserted, it is inserted at a position considering the scanning spot diameter. The main scanning magnification and the spot diameter can be made uniform regardless of the position in the main scanning direction.

  In the present embodiment, the case where the f-θ lens is removed has been described as an example. However, even when the f-θ lens is attached, in reality, the fluctuation of the scanning magnification according to the position in the main scanning direction occurs. Therefore, the first embodiment can achieve the same effect even in the image forming apparatus 2 with the f-θ lens attached.

  In the present embodiment, only the case where a pixel piece is inserted (or not inserted) into each pixel has been described. Of course, in order to reduce the scanning magnification, it can be used in combination with a method of deleting pixel pieces constituting a pixel. In this case, the number of pixel pieces may be set to an integer of 0 or less, and the pixel pieces may be deleted so as to obtain a desired pixel piece pattern.

Second Embodiment
In the first embodiment, an example in which the correction amount of the scanning spot diameter is calculated based on the shift amount of the scanning width on the photoconductor for each pixel has been described. In the present embodiment, an example is shown in which a correction amount for correcting the scanning spot diameter is calculated in consideration of the difference in blurring amount (scanning spot diameter) of the light intensity distribution imaged on the surface of the photoreceptor. In addition, about the structure similar to 1st Embodiment, the same code | symbol is attached | subjected and each detailed description is abbreviate | omitted suitably.

  FIG. 11 is a block diagram showing a detailed configuration of the image processing apparatus 1 applicable to the second embodiment. The image processing apparatus 1 includes a blur amount information storage unit 201. The spot diameter correction amount calculation unit 108 obtains blur amount information using a blur amount table for each number of pixel pieces CMYK held by the blur amount information storage unit 201, and calculates a scanning spot diameter for each pixel based on the blur amount information. A correction amount for correction is calculated.

Next, the blur amount table will be described. FIG. 12 shows a blur amount table. The blur amount here means a scanning spot diameter formed on the photosensitive member in the main scanning direction. In FIG. 12, the horizontal axis represents the position in the longitudinal direction of the photosensitive drum, and the vertical axis represents the scanning spot diameter on the photosensitive drum. Here, the scanning spot diameter on the photosensitive drum refers to the diameter of a circle composed of 1 / e ² intensity points when the exposure intensity distribution is approximated by a two-dimensional Gaussian distribution, for example. In this embodiment, the largest scanning spot diameter in the longitudinal direction of the photosensitive drum is set as the reference V.

  FIG. 13 shows an example of a change in the scanning spot diameter formed on the photosensitive drum when the f-θ lens is removed. As shown in FIG. 13A, laser light (R1, R2, R3, R4, R5) is irradiated from the surface of the polygon mirror 305 toward the photosensitive drum. FIG. 13B shows the change in the diameter of the scanning spot formed on the photosensitive drum surface at this time. FIG. 13B shows an enlarged view of a region surrounded by a dotted line in FIG. When the widths D1, D2, D3, D4, and D5 of the laser beams (R1, R2, R3, R4, and R5) are substantially the same, the scanning spot diameter (S1, S2, S3, S4, and S5 on the photosensitive drum). ) Have a relationship of S1> S2> S3 and S5> S4> S3. From this result, it can be seen that when the polygon mirror 305 is arranged on a line orthogonal to the central portion of the photosensitive drum, the scanning spot diameter on the photosensitive drum becomes wider at the drum end and becomes narrower at the central portion. . If this is the case, the scanning width of one pixel at the edge and the center of the image is different, so the actual scanning spot diameter of each pixel on the photosensitive drum is not uniform, and an image with in-plane uniformity deteriorated is formed. Is done.

Therefore, the light-off pixel pieces are pseudo-expanded by inserting the light-off pixel pieces so that the light-on pixel pieces are dispersed toward the center, and conversely, the light-off pixel pieces are concentrated so that the light-on pixel pieces are concentrated toward the end. The scanning spot diameter is prevented from widening by inserting.
As a result, the scanning spot diameter on the photosensitive drum can be made uniform regardless of the blurring amount (scanning spot diameter) of the light intensity distribution imaged on the photosensitive member surface.

In the blur amount table shown in FIG. 12, when a pixel number is input, the difference between the reference spot diameter V on the photosensitive drum and the actual scanning spot diameter can be read as the blur amount M.
In this embodiment, such a blur amount table is held for each color. Since the image forming unit is designed independently for each color, the blur amount table is generally different. Furthermore, when it is known that the variation of the scanning magnification changes according to the sub-scanning direction, a plurality of shift amount tables are held for each color, and the blur amount table is selected according to the position in the sub-scanning direction. Also good. If it is known that the variation in scanning magnification does not change for each color, only one blur amount table common to each color may be held.

  In this embodiment, the blur amount table is generated based on the measurement result by measuring the scanning spot diameter when the photosensitive drum is exposed at the time of manufacture. If the fluctuation of the main scanning magnification does not greatly change from the theoretical value of the scanning spot diameter S when the f-θ lens is removed, it is calculated based on the scanning spot diameter S at the drum longitudinal position without performing measurement. Also good.

  In the pixel piece pattern determination process of the present embodiment, the spot diameter correction amount calculation unit 108 calculates a correction amount Sr for exposing the target pixel on the photosensitive drum with a target scanning spot diameter. In step S103 shown in FIG. 10, the spot diameter correction amount calculation unit 108 calculates from the target scanning magnification at the main scanning position k corresponding to the target pixel from the cyan plate displacement amount table stored in the displacement amount information storage unit 106. The shift amount Lk is acquired. Also, the blur amount Mk, which is the difference from the target spot diameter at the main scanning position k corresponding to the target pixel, is obtained from the cyan plate displacement amount table stored in the blur amount information storage unit 201. The correction ratio Sr is calculated as a scanning spot correction amount according to the following equation (4).

Sr = ((W + Lk) / W) × ((V + Mk) / V) (4)
W is a reference scanning width, and V is a reference scanning spot diameter.

  With such a configuration, an image can be formed without causing in-plane uniformity deterioration even when the amount of blur of the light intensity distribution imaged on the surface of the photoconductor is different at the main scanning position.

<Third Embodiment>
In the above-described embodiment, the number of pixel pieces and the spot diameter correction amount are calculated based on the deviation amount table measured at the time of manufacture and the blur amount table. However, if the individual differences in the amount of deviation and the amount of blur are acceptable, a table of pixel pieces and spot diameter correction amounts calculated in advance based on the average amount of deviation and amount of blur should be retained. Good. Therefore, in the present embodiment, a method of performing the pixel piece pattern determination process using the pixel piece number table and the spot diameter correction amount table will be described. FIG. 14 is a block diagram illustrating a configuration of the image processing apparatus 1 applicable to the third embodiment. The same components as those in the first embodiment are denoted by the same reference numerals and description thereof is omitted.

  The pixel piece number table storage unit 301 stores the number of pixel pieces corresponding to the position in the main scanning direction on the photosensitive drum. The spot diameter correction amount table storage unit 302 stores a correction amount corresponding to the position in the main scanning direction on the photosensitive drum.

  In the present embodiment, the number Pn of insertions of unlit pixel pieces at the pixel position k corresponding to the target pixel is acquired from the pixel piece number table 301. Further, the spot diameter correction amount Sr at the pixel position k corresponding to the target pixel is acquired from the spot diameter correction amount table storage unit 302.

  The pixel piece position determining unit 109 determines the position at which the number of pixel pieces acquired from the pixel piece number table 301 is inserted based on the correction amount acquired from the spot diameter correction amount table storage unit 302. The pixel piece position determining unit 109 refers to the pixel piece pattern table held by the pixel piece pattern information storage unit 110, determines the pixel piece pattern for each pixel, and determines the position of the pixel piece to be inserted.

  The pixel piece pattern information adding unit 112 reads pixel piece pattern information corresponding to the pixel number from the pixel piece pattern flag table for the halftone image data acquired from the halftone image storage unit 105. With this configuration, it is possible to form an image without causing in-plane uniformity degradation by simultaneously performing the pixel piece position information generation process and simultaneously performing the scanning spot diameter correction using the pixel piece pattern. .

<Fourth embodiment>
In the above-described embodiment, the method of performing the pixel piece pattern determination process by separately acquiring the number of pixel pieces and the spot diameter correction amount for each pixel has been described. In the present embodiment, a method for performing pixel piece pattern determination processing using a pixel piece pattern information table corresponding to main scanning position information without acquiring the number of pixel pieces and the spot diameter correction amount will be described. FIG. 15 is a block diagram showing a configuration of the image processing apparatus 1 applicable to the fourth embodiment. The same components as those in the first embodiment are denoted by the same reference numerals and description thereof is omitted.

  The pixel piece pattern information table storage unit 401 stores pixel piece pattern information Fn at the main scanning position on the photosensitive drum.

  In the present embodiment, the pixel piece position determining unit 109 acquires the pixel piece pattern information Fn from the pixel piece pattern information table storage unit 401 corresponding to the main scanning position information indicating the main scanning position on the photosensitive drum. With this configuration, there is no need to prepare a calculation unit and a table storage unit corresponding to the number of pixel pieces and the spot diameter correction amount, so that in-plane uniformity degradation occurs without significantly increasing the memory cost. An image can be formed without any problems.

  In the above-described embodiment, the image processing apparatus 1 has been described with the configuration in which the pixel piece pattern information is added to the halftone image data. For example, the image forming apparatus 2 may generate pixel piece pattern information and add the pixel piece pattern information to the received data.

<Other embodiments>
The present invention can also be realized by supplying a storage medium storing a computer program code of software for realizing the functions of the above-described embodiments to a system or apparatus. In this case, the function of the above-described embodiment is realized by the computer (or CPU or MPU) of the system or apparatus reading and executing the program code stored in the storage medium so that the computer can read it.

Claims (8)

An image processing apparatus for generating image data for forming an image by exposing an exposure unit including a laser beam using an electrophotographic method to expose a photosensitive drum ,
Input means for inputting image data;
The number of pixel pieces to be inserted for each pixel in the image data according to the position in the main scanning direction on the photosensitive drum when the laser light is irradiated on the photosensitive drum based on the image data. Pixel piece number determining means for determining the pixel piece number as
When the number of pixel pieces is one or more, each pixel in the image data is controlled so as to suppress variation in the scanning spot diameter for each pixel in the image data according to the intensity distribution of the laser light on the photosensitive drum. Position determining means for determining a position to insert the number of pixel pieces with respect to the number of pixel pieces;
An image processing apparatus comprising: generating means for generating an exposure signal for controlling the exposure unit based on the image data and the position at which the pixel piece determined by the position determining means is inserted.   The position determining means includes a plurality of lighting pixel pieces corresponding to the pixel value of the target pixel for the target pixel in the image data, and the pixel piece number determining means includes one or more pixel pieces, and When the intensity distribution of the laser beam at the position on the photosensitive drum corresponding to the target pixel is narrower than the target distribution, at least one new pixel is positioned between the lighting pixel pieces constituting the target pixel. The image processing apparatus according to claim 1, wherein a piece is inserted.   The position determining means includes two or more pixel pieces to be inserted by the pixel piece number determining means for the target pixel in the image data, and the laser beam at a position on the photosensitive drum corresponding to the target pixel. 2. The image processing apparatus according to claim 1, wherein when the intensity distribution is narrower than a target distribution, the image elements are inserted into pixel pieces constituting the target pixel in a distributed manner at a central position.   The position determining means has a plurality of lighting pixel pieces corresponding to the pixel value of the target pixel for the target pixel in the image data, and the number of pixel pieces to be inserted by the pixel piece number determining means is two or more, and When the intensity distribution of the laser beam at the position on the photosensitive drum corresponding to the target pixel is narrower than the target distribution, the inserted pixel pieces are continuously sandwiched between the lighting pixel pieces constituting the target pixel. The image processing apparatus according to claim 1, wherein the image processing apparatus is disposed at a position. The position determination means holds a table in which the number of pixel pieces to be inserted and the positions to be inserted are associated with each other for a plurality of positions different in the main scanning direction on the photosensitive drum , The image processing apparatus according to claim 1, wherein a position where the piece is inserted is determined. An image processing apparatus according to any one of claims 1 to 5,
By exposing unit including a laser light using an electrophotographic method exposes the photosensitive drum, the image forming apparatus and an image forming unit for forming an image on a recording medium.   A computer program that causes a computer to function as the image processing apparatus according to claim 1 by being read and executed by a computer. An image processing method for generating image data for forming an image by exposing an exposure unit including laser light using an electrophotographic method to expose a photosensitive drum ,
Enter the image data,
In accordance with the position of the photosensitive drum in the main scanning direction when the laser beam is irradiated onto the photosensitive drum based on the image data, the variation in the scanning spot diameter for each pixel in the image data is suppressed. And determining the number of pixel pieces to be inserted as the number of pixel pieces for each pixel in the image data,
When the number of pixel pieces is one or more, according to the intensity distribution of the laser light on the photosensitive drum, determine the position to insert the number of pixel pieces for each pixel in the image data,
Image processing method characterized by generating an exposure signal for based on the insertion position of the image data and the decision pixel pieces, and controls the exposure unit.

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