JP5978809B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus.

  For example, toner images of multiple colors of cyan (C), magenta (M), yellow (Y), and black (K) can be transferred onto a sheet by transferring them over the sheet directly or via an intermediate transfer belt. An image forming apparatus that forms an image is known.

  In Patent Document 1, in such an image forming apparatus, the positional deviation of each color image (scanning position) caused by the positional deviation of the optical components constituting the light beam scanning apparatus, the deviation of the attachment of the photosensitive member, the distortion of the entire apparatus, or the like. Correction, misregistration, color misregistration, or registration misregistration) is corrected using mechanical means such as an actuator or a stepping motor, or corrected by electrical data processing without using mechanical means. Has been. In addition, it is described that a predetermined image (referred to as a registration mark or a test pattern) of each color is formed on the intermediate transfer belt and the formed registration mark is detected by a registration detection device in order to detect a positional deviation of each color image. Has been

  In Patent Document 2, a vertical cavity surface emitting laser (VCSEL) array in which a plurality of light emitting points (or light emitting elements) are two-dimensionally arranged is used as a light source, and a plurality of light output from the VCSEL array is used. An optical scanning device that improves the scanning density and speeds up exposure processing (also referred to as writing processing) of the photosensitive member by deflecting the laser beam with a polygon mirror and increasing the number of beams simultaneously scanned on the photosensitive member; An image forming apparatus having such an optical scanning device is described. In the image forming apparatus described in Patent Document 2, CMYK color system binary image data generated by processing input red (R) green (G) blue (B) color system multi-value image data is obtained. Then, the data is temporarily stored in the line buffer memory group, and then image data (also referred to as a modulation signal) corresponding to each light emitting element of the VCSEL array is simultaneously read from the line buffer memory group, and the VCSEL array is driven via the delay adjuster. To the laser drive circuit.

  Patent Documents 3 and 4 describe that image data is packed in units of a plurality of pixels (for example, 4 pixels or 8 pixels) and transferred in parallel.

JP 2000-181172 A JP 2003-255247 A JP 2004-98391 A JP 2005-268886 A

  An object of the present invention is to perform resolution conversion processing for increasing the resolution in the main scanning direction of acquired image data, and supply the image data after resolution conversion to a light emitting device having a plurality of light emitting elements to scan the image carrier. In the image forming apparatus to be performed, the capacity of the line memory for storing image data for one scanning line for each of the plurality of light emitting elements is reduced as compared with the case where the image data after resolution conversion is stored in the line memory. is there.

In order to solve the above-described problem, an image forming apparatus according to claim 1 of the present application includes an image data acquisition unit that acquires image data, and a plurality of images that are scanned in a main scanning direction that is a predetermined direction. A light-emitting device having a plurality of light-emitting elements that emit light beams, and a capacity for acquiring the image data from the image data acquisition unit and storing image data for one scanning line for each light-emitting element for all the light-emitting elements of the light-emitting device A line memory, a resolution conversion unit that reads image data for each light emitting element of the light emitting device from the line memory, and performs resolution conversion for increasing the resolution in the main scanning direction of the read image data, and the resolution conversion the image data outputted from the parts, and the main performs scanning direction of the plurality of areas each at a position displacement correction positional deviation correcting unit, image after the positional deviation correction Based on the data, the drive circuit for driving the light emitting device, wherein arranged in front of the rear stage in and the drive circuit of the positional deviation correcting unit, image data output position deviation correction from the positional deviation correcting unit And a FIFO memory for outputting the written image data to the driving circuit .

According to a second aspect of the present invention, in the aspect of the first aspect, the supply of image data from the FIFO memory to the drive circuit indicates the start of scanning of the image carrier by the light emitting device. The image data is started from the signal as a trigger, and the image data is read from the line memory to the resolution conversion unit in response to a signal indicating that the FIFO memory is free.

According to the image forming apparatus according to claim 1 of the present application, the resolution conversion process for increasing the resolution of the acquired image data in the main scanning direction is performed, and the image data after the resolution conversion is converted into a light emitting apparatus having a plurality of light emitting elements. In an image forming apparatus that supplies and scans an image carrier, the capacity of a line memory that stores image data for one scanning line for each of a plurality of light emitting elements stores image data after resolution conversion in the line memory. is reduced compared to the case, fluctuations in the output rate from the position displacement correction unit is absorbed by the FIFO memory.
According to the image forming apparatus of claim 2 of the present application, compared to the case where reading of image data from the line memory is started using a signal indicating the start of scanning of the image carrier as a trigger, the start of scanning of the image carrier is started. After the signal indicating is generated, the delay time until the image data is supplied from the FIFO memory to the driving circuit is shortened.

1 is a schematic diagram illustrating a configuration of an image forming apparatus according to an embodiment. The schematic diagram which shows the structure of a VCSEL array. FIG. 3 is a block diagram illustrating a configuration relating to misalignment detection and image data correction of the image forming apparatus according to the embodiment. 1 is a block diagram showing a functional configuration of an image processing apparatus according to an embodiment. The schematic diagram for demonstrating the resolution conversion process and the main magnification correction process. The schematic diagram which illustrates the case where the content of the main magnification correction process differs for every area | region of an image. 6 is a schematic graph showing a temporal change in the data amount of one scanning line output from the main magnification correction unit when the main magnification correction is not performed and when it is performed. 4 is a schematic graph showing a relationship between an SOS signal and an effective scanning period. The block diagram which shows the function structure of the comparative example of an image processing apparatus. The graph for demonstrating the relationship between the read start timing of the line memory in a comparative example, and the time change of the output data amount from the main magnification correction part. The schematic diagram which shows the modification of the area | region division of an image.

<Embodiment>
FIG. 1 is a diagram schematically showing a configuration of an image forming apparatus 1 according to an embodiment of the present invention. Above the image forming apparatus 1, a cover for pressing the document 2 onto the platen glass 5 and an image reading device 4 that reads an image of the document 2 placed on the platen glass 5 are disposed. The image reading device 4 irradiates light from a light source 6 onto a document 2 placed on a platen glass 5. Then, after the light reflected by the document 2 is reflected by the full-rate mirror 7 and the half-rate mirrors 8 and 9 which are mirrors, the light is guided to the image reading element 11 using a CCD (Charge Coupled Devices) through the lens 10, and the document The second image is converted into an electrical signal representing image data of each color of RGB by the image reading element 11 and output to the control unit 101.

  The control unit 101 controls each unit of the image forming apparatus 1. In addition, the control unit 101 acquires RGB image data input from the image reading device 4 or RGB image data input from an external device such as a personal computer (not shown) via a network line such as a LAN, The acquired RGB image data is subjected to processing such as conversion to CMYK four-color image data (raster data), and output to the image processing device 12.

  The image processing apparatus 12 performs processes such as binarization processing, shading correction, brightness / color space conversion, gamma correction, frame deletion, color / movement editing, and color shift correction on the CMYK image data supplied from the control unit 101. Apply. The image processing apparatus 12 sends the processed image data of each color of CMYK to the exposure apparatuses 14C, 14M, 14Y, and 14K of the image forming units 13C, 13M, 13Y, and 13K corresponding to the colors. In the drawings and the following description, a C-color image is associated with a C at the end, a M-color image is denoted with a M at the end, and a Y-color image is associated with the image. In the description, Y is added to the end of the code, and K related images are described with K added to the end of the code.

  The image forming units 13C, 13M, 13Y, and 13K are units that form CMYK toner images. The image forming apparatus 1 includes a mounting portion on which the image forming units 13C, 13M, 13Y, and 13K are mounted. The image forming units 13C, 13M, 13Y, and 13K are mounted on the image forming apparatus 1 and are imaged. The image forming apparatus 1 can be detached from the image forming apparatus 1 and is arranged in parallel in the image forming apparatus 1 at a certain interval in the horizontal direction. In the present embodiment, the four image forming units 13C, 13M, 13Y, and 13K are all configured in the same manner, and therefore, the configuration thereof will be described with the reference numerals C, M, Y, and K omitted. . The image forming unit 13 includes, as an example of an image carrier, a photosensitive drum 15 that rotates at a constant rotational speed in the direction of arrow A, and a primary charging scorotron 16 that uniformly charges the surface of the photosensitive drum 15. An exposure device 14 that exposes an image corresponding to each color on the surface of the photosensitive drum 15 to form an electrostatic latent image, and a developing device that develops the electrostatic latent image formed on the photosensitive drum 15 with toner. 17 and a cleaning device 18 for removing toner on the photosensitive drum 15.

  The exposure device 14 corresponding to each color has a laser device 19, and laser light modulated in accordance with image data sent from the image processing device 12 is output from the laser device 19. That is, the image data from the image processing device 12 serves as a modulation signal for modulating the laser beam output from the laser device 19. The laser beam output from the laser device 19 is guided by the reflecting mirrors 20 and 21 to a regular polygonal polygon mirror 22 having a plurality of reflecting surfaces on a side surface that is rotationally driven by a motor (not shown). Reflected. The light reflected by the rotating polygon mirror 22 is guided again to the photosensitive drum 15 as an image holding member through the reflecting mirror 21 and the plurality of reflecting mirrors 23 and 24, and the surface of the photosensitive drum 15 is scanned. To do. As a result, an electrostatic latent image is formed on the surface of the photosensitive drum 15. The electrostatic latent images formed on the photosensitive drums 15C, 15M, 15Y, and 15K are developed as toner images of CMYK colors by the developing units 17C, 17M, 17Y, and 17K, respectively.

  In the present embodiment, the laser device 19 is a multi-beam light emitting device having a plurality of light emitting elements capable of independently modulating each output light, such as a VCSEL array. FIG. 2 is a schematic diagram illustrating an example of a VCSEL array. The VCSEL array shown in FIG. 2 has eight laser diodes 191 (an example of a light emitting element), and these laser diodes 191 are two-dimensionally arranged in 2 rows × 4 columns.

  More specifically, the laser diodes 191 are arranged so as to be shifted in the vertical direction in FIG. 2, which is a direction corresponding to the sub-scanning direction, so that the laser beams output from the laser diodes 191 do not overlap in the sub-scanning direction. Has been. Therefore, each row of the laser diodes 191 has an inclination with respect to the horizontal direction in FIG. 2 corresponding to the main scanning direction. Further, since the laser diodes 191 are two-dimensionally arranged, the positions in the horizontal direction corresponding to the main scanning direction are different, and the distance D1 is shifted at the maximum. Therefore, when the laser diode 191 emits light at the same time, the laser beams emitted from the laser diodes 191 having different horizontal positions form an image on the photosensitive drum 15 at different positions in the main scanning direction. In order to correct such a shift in the imaging position in the main scanning direction, the image processing device 12 starts scanning the delay amount when starting supplying image data (modulation signal) to each laser diode 191 as described later. A delay circuit that adjusts the reference signal. The main scanning direction is a scanning direction of the laser beam by the rotation of the polygon mirror 22 and coincides with the direction of the rotation axis of the photosensitive drum 15. The sub-scanning direction is a direction that intersects the main scanning direction, and corresponds to the conveyance direction of the paper on which an image is formed.

  By using such a laser device 19 as a light source of the exposure device 14 for each color, a plurality of (eight in this example) laser beams are simultaneously scanned by one main scan for each color, and the surface of the photosensitive drum 15 is scanned. Thus, the electrostatic latent image is formed faster than when scanning with one laser beam. Further, for example, by adjusting the inclination angle of the VCSEL array (laser device) 19 with respect to the axial direction of the polygon mirror 22 and reducing the interval between adjacent laser diodes 191 in the direction corresponding to the sub-scanning direction, scanning in the sub-scanning direction is performed. The line density is improved. The number of laser diodes 191 included in the VCSEL array 19 is not limited to 8, and may be another number such as 16 (4 × 4 two-dimensional arrangement), 32 (4 × 8 two-dimensional arrangement), for example. Good.

  Referring to FIG. 1 again, the toner images of the respective colors formed on the photosensitive drums 15C, 15M, 15Y, and 15K are intermediate transfer members disposed below the image forming units 13C, 13M, 13Y, and 13K. Are transferred onto the intermediate transfer belt 25 by the primary transfer rolls 30C, 30M, 30Y and 30K to which a primary transfer bias is applied by a primary transfer bias power source (not shown).

  The intermediate transfer belt 25 is wound around a roll 40 to 45 with a constant tension, and is circulated and driven at a constant speed in the direction of arrow B by a roll 40 that is rotated by a motor (not shown). The As the intermediate transfer belt 25, in this embodiment, for example, a flexible synthetic resin film such as polyimide is formed in a band shape, and both ends of the synthetic resin film formed in the band shape are connected by means such as welding. Thus, an endless belt is used.

  The toner images of the respective colors transferred on the intermediate transfer belt 25 are transferred onto a recording sheet 60 as a conveyed recording medium by a secondary transfer roll 50 pressed against the roll 44 side. Hereinafter, the transfer of the toner image onto the recording paper 60 is referred to as secondary transfer. The recording sheet 60 was primarily transferred to the intermediate transfer belt 25 when it was transported between the secondary transfer roll 50 and the roll 44 provided inside the intermediate transfer belt 25. A secondary transfer bias having a polarity opposite to the polarity of the toner is applied. As a result, the electrostatic force from the intermediate transfer belt 25 toward the recording paper 60 acts on the toner on the intermediate transfer belt 25, and the toner is transferred to the surface of the recording paper 60.

  The recording paper 60 on which the toner image of each color is transferred is conveyed to the fixing device 70 by the two conveyance belts 51 and 52. The fixing device 70 fixes the toner image on the surface of the recording paper 60 by applying heat and pressure to the recording paper 60 to which the toner image is transferred. The recording paper 60 on which the toner image is fixed is discharged to a paper discharge tray 64.

  The recording paper 60 is conveyed from any of a plurality of storage units 61 to 63 that store the recording paper 60 along a paper conveyance path indicated by a broken line defined by the roll 80 and the like, and is sent onto the intermediate transfer belt 25. Is done. Further, after the toner image transfer process is completed, the photosensitive drum 15 is prepared for the next image forming process by removing residual toner, paper dust, and the like by the cleaning device 18. The belt cleaner 90 removes the toner remaining on the intermediate transfer belt 25.

  The image forming apparatus 1 according to the present embodiment performs primary transfer to the intermediate transfer belt 25 when the image forming apparatus 1 is turned on or in response to a user operation in order to prevent image color misregistration caused by changes in temperature or humidity. There is provided a function of detecting the positional deviation of the toner image and correcting image data representing the toner image of each color to be transferred to the recording paper 60 in accordance with the detected positional deviation. Hereinafter, configurations related to these functions in the image forming apparatus 1 will be described.

  FIG. 3 is a block diagram of a configuration relating to misalignment detection and image data correction in the image forming apparatus 1. As shown in FIG. 3, the image forming apparatus 1 includes a control unit 101, a storage unit 102, an operation unit 103, a communication unit 104, a pattern detector 600, an image processing device 12, an image forming unit 13, and an image reading device 4. It is configured to include.

  The control unit 101 includes a CPU (Central Processing Unit) 101A, a ROM (Read Only Memory) 101B, and a RAM (Random Access Memory) 101C. The ROM 101B stores a control program. The CPU 101A executes the control program with the RAM 101C as a working area, whereby each part of the image forming apparatus 1 is controlled, and the image forming apparatus 1 operates. For example, the control unit 101 detects the color misregistration so that each color toner image (hereinafter referred to as a test pattern) is transferred to the intermediate transfer belt 25 when the misregistration is detected. To control.

  The storage unit 102 is configured by a non-volatile storage medium, and stores various data such as image data of a test pattern (hereinafter referred to as pattern image data) used for misregistration detection processing. The operation unit 103 includes a power switch for switching on / off the power of the image forming apparatus 1 and a touch panel type display device, for example, and displays a menu screen and a message to receive an instruction from the user.

  The communication unit 104 is an interface for connecting to an external device such as a personal computer directly or via a communication network. For example, the communication unit 104 acquires image data from an external device and supplies the image data to the control unit 101.

  As shown in FIG. 1, the pattern detector 600 is disposed downstream of the image forming unit 13 in the conveyance direction of the intermediate transfer belt 25. The pattern detector 600 includes an image sensor such as a CCD that receives the reflected light of the light irradiated on the intermediate transfer belt 25, and detects a test pattern of each color transferred to the intermediate transfer belt 25. A plurality of pattern detectors 600 may be provided along the main scanning direction. The pattern detector 600 supplies information indicating the detected transfer position of each color test pattern to the image processing apparatus 12.

  As described above, the image reading device 4 acquires the RGB image data of the document designated by the user and supplies it to the control unit 101.

  For example, the image processing apparatus 12 is configured as hardware such as an ASIC (Application Specific Integrated Circuit), and performs image processing such as density adjustment on the CMYK image data supplied from the control unit 101 as described above. Further, the image processing apparatus 12 obtains the amount of misregistration of each color based on the signal from the pattern detector 600, corrects each color image data so as to reduce the amount of misregistration, and obtains the corrected image data. The image is sent to the exposure device 14 of the image forming unit 13 for each color. Hereinafter, the configuration and operation of the image processing apparatus 12 will be described in detail.

  FIG. 4 is a block diagram illustrating a configuration of the image processing apparatus 12. The image processing device 12 processes CMYK image data input from a raster data generation unit 200 described later, and supplies the processed CMYK image data to the laser drive circuit 141 of the exposure device 14. In FIG. 4, the configurations of the image processing device 12 and the exposure device 14 are shown for only one color, but the same configuration is provided for each color of CMYK.

  The raster data generation unit 200 converts RGB image data acquired from an image reading device 4 or an external device such as a personal computer via a network into CMYK image data (raster data) using any known method. The image is supplied to the image processing apparatus 12. The raster data generation unit 200 is realized by the CPU 101A of the control unit 101 executing a program. The CMYK image data input from the raster data generation unit 200 to the image processing unit 12 is, for example, multi-value image data (also referred to as multi-tone image data) with a resolution of 600 dpi. Here, the multi-value image data refers to image data in which the shade (gradation level) of each color is represented by a plurality of bits for each pixel constituting the image. For example, when the shade of each color is represented by 8 bits, Is expressed by a numerical value from “0” to “255”. The arrangement of pixels in the main scanning direction is sometimes referred to as a row, and the arrangement of pixels in the sub-scanning direction is sometimes referred to as a column.

  The image processing apparatus 12 includes an I / F (interface) unit 201, a correction processing unit 202, a line memory 203, a resolution conversion unit 204, a main magnification correction unit 205, and an output FIFO (First-In First-Out). The memory 206, the delay circuit 207, the timing signal generation unit 210, the misalignment detection unit 211, the line memory control unit 212, and the output FIFO control unit 213 are included. The correction processing unit 202, the line memory 203, the resolution conversion unit 204, and the main magnification correction unit 205 correct the CMYK image data supplied from the I / F unit 201 and process the laser light output from the laser device 19. A modulation signal generation unit 208 that generates a modulation signal for modulation is configured.

  In this example, processing upstream of the output FIFO memory 206 (processing and transfer of data) including processing in the modulation signal generation unit 208 is performed by using the first clock CLK1 having a frequency of 100 MHz generated by a clock generator (not shown) as an operating clock. The processing downstream of the output FIFO memory 206 is performed using the second clock CLK2 having a frequency of 400 MHz as the operation clock. Therefore, data writing to the output FIFO memory 206 is performed based on the first clock CLK1, and data reading from the output FIFO memory 206 is performed based on the second clock CLK2.

  The frequency of the second clock CLK2 is determined based on the resolution of image data in the main scanning direction, the length of one scanning line, the scanning speed of the laser beam in the exposure device 14 (determined by the rotational speed of the polygon mirror, etc.), and the like. The frequency of the first clock CLK1 is set as low as possible within a range that does not hinder the operation in order to reduce the circuit scale of the image processing device 12. In general, as the operation is performed with a higher frequency clock, more logic shaping buffers (inverters) are required to form each logic gate included in the image processing apparatus 12, and the circuit constituting each logic gate. Because it becomes large. In the image processing apparatus 12 of this example, image data is packed in units of a plurality of pixels (for example, 4 pixels or 8 pixels) and processed in parallel, so that an operation clock (first clock CLK1) is compared with a case where parallel processing is not performed. ) Is kept low. When packing and processing image data in units of multiple pixels, the signal lines (buses) that connect the sections have a bit width that corresponds to the data amount of the packed image data so that the packed image data can be transferred in parallel. Have For example, when image data (binary image data) in which each pixel has 1-bit data is packed and processed in units of 4 pixels, a 4-bit width bus is used.

  The timing signal generation unit 210 receives a page output signal (P_ST) for instructing image output of each page generated by the control unit 101 in response to a print instruction by a user operation on the operation unit 103 or a print request received from an external device. When input, a line synchronization signal (LS) is generated at a predetermined interval and supplied to the I / F unit 201. The I / F unit 201 transmits an image data transmission request (REQ) to the raster data generation unit 200 according to each line synchronization signal, and the raster data generation unit 200 accordingly determines the number of lines (for example, 1). ) Image data is supplied to the I / F unit 201. The I / F unit 201 transfers the image data supplied from the raster data generation unit 200 to the correction processing unit 202. As described above, the image data input from the raster data generation unit 200 to the I / F unit 201 is multi-value image data of 600 dpi, and the image data transferred from the I / F unit 201 to the correction processing unit 202 is also included. It is the same.

  The timing signal generation unit 210 determines the interval of the line synchronization signals to be generated based on the correction processing by the correction processing unit 202 described later, the writing time of the corrected image data to the line memory, and the like.

  The correction processing unit 202 binarizes the multi-value image data acquired through the I / F unit 201 by screen processing. For example, 2400 dpi bitmap halftone image data is generated for each pixel of 600 dpi multi-value (8 bits) image data input from the I / F unit 201. That is, for each pixel of the multi-value image data, 4 rows × 4 columns = 16 pixels each having 1-bit pixel data are generated. In this case, the resolution (that is, the number of pixels per unit length) is increased from 600 dpi to 2400 dpi in both the main scanning direction and the sub-scanning direction. There are many methods for generating halftone dot image data, such as a dither matrix method and an error diffusion method, and any technique may be used here.

  The correction processing unit 202 performs any known correction processing such as shading correction, brightness / color space conversion, gamma correction, frame deletion, color / movement editing, and color misregistration correction on the obtained binary image data. Apply. Note that color misregistration includes misregistration in the main scanning direction, misregistration in the sub scanning direction, misalignment in the magnification in the main scanning direction, skew misalignment, and the like. Main magnification correction, which is magnification correction, is not performed by the correction processing unit 202 but is performed by a main magnification correction unit 205 described later. The correction processing unit 202 packs the corrected binary image data in units of 4 pixels of 2 rows × 2 columns, for example, and outputs it to the line memory 203 (that is, the pixel data for 4 pixels is parallel to the line memory 203). Forwarded).

  The misregistration detection unit 211 obtains the misregistration amount by comparing the transfer position of the test pattern detected by the pattern detector 600 with the transfer position when there is no color misregistration stored in advance in a memory (not shown). The obtained positional deviation amount is supplied to the correction processing unit 202 and the main magnification correction unit 205. The correction processing unit 202 and the main magnification correction unit 205 perform the above-described correction of the binary image data so that the positional deviation amount supplied from the positional deviation detection unit 211 becomes small.

The line memory 203 is a FIFO memory that stores binary image data processed by the correction processing unit 202. The line memory 203 has a capacity capable of storing image data for one scanning line for each laser diode 191 included in the laser device 19 for all the laser diodes 191. That is, when the laser device 19 has M (8 in this example) laser diodes 191, the line memory 203 has a capacity capable of storing M rows of pixel data (pixel values) for one scanning line. For example, assuming that the scanning width (scanning line length) is 300 mm, in the case of binary image data with a resolution of 2400 dpi (that is, 1 bit per pixel),
(300 / 25.4) × 2400≈28,300 bits, and the capacity of the line memory 203 for storing data for eight scanning lines requires a capacity of about 30 k × 8 bits. The line memory 203 may have a capacity larger than this, but preferably has a capacity as small as possible for cost reduction.

  In this example, the image data packed in units of 4 pixels of 2 rows × 2 columns sequentially sent from the correction processing unit 202 is written in the line memory 203. As a result, first, image data is written to the first row and the second row, and after the data writing of the first row and the second row is finished, the image data is written to the third row and the fourth row. As described above, the image data is written every two lines. When image data for M rows is written in the line memory 203 and there is an empty output FIFO memory 206 described later, the line memory 203 outputs the image data packed in units of M rows × N1 columns to the resolution conversion unit 204. . For example, when M = 8 and N1 = 2, 8 × 2 (= 16) bit image data is transferred in parallel from the line memory 203 to the resolution conversion unit 204. N1 is a predetermined positive integer, and the ratio of the frequency of the upstream operation clock (first clock CLK1) to the downstream operation clock (second clock CLK2) of the output FIFO memory 206, and It is determined according to the resolution conversion magnification in the resolution conversion unit 204 described later. Specifically, N3 = (frequency of second clock CLK2 / frequency of first clock CLK1) / (resolution conversion magnification). In this example, since the frequency of the second clock CLK2 is 400 MHz, the frequency of the first clock CLK1 is 100 MHz, and the resolution conversion magnification is 2, N1 = 2. The line memory 203 temporarily stores image data of M rows (that is, the number of rows corresponding to the number of laser diodes 191 included in the laser device 19), and the image data of each row is simultaneously stored in a predetermined unit. By outputting, the supply of image data (modulation signal) to the M laser diodes 191 is synchronized.

  The line memory control unit 212 receives from the output FIFO memory 206 a signal (FIFO_FL) indicating whether the output FIFO memory 206 is free, the output FIFO memory 206 is free, and the line memory 203 has M rows × N1. When the image data of the pixels in the column is accumulated, the line memory 203 is controlled to output the image data of the pixels in M rows × N1 columns to the resolution conversion unit 204. The signal FIFO_FL may be, for example, a signal that becomes 1 when the output FIFO memory 206 is full and becomes 0 when there is a free space.

  The resolution conversion unit 204 performs resolution conversion for increasing the resolution in the main scanning direction (that is, the row direction) on the binary image data supplied from the line memory 203, and converts the binary image data after the resolution conversion into a main magnification. The data is output to the correction unit 205. When image data is supplied from the line memory 203 in units of pixels of M rows × N1 columns, the resolution conversion unit 204 converts the image data into image data of M rows × N2 columns (N2> N1) pixels, and after conversion The image data of M rows × N2 columns of pixels is packed and output. For example, when the resolution (in the main scanning direction and the sub-scanning direction) of the image data supplied from the line memory 203 is 2400 dpi and M = 8, N1 = 2, N2 = 4 (that is, 2 × N1), resolution conversion is performed. From the unit 204, the image data in which the resolution in the main scanning direction is doubled (that is, the resolution in the main scanning direction is increased to 4800 dpi) is packed and output in units of 8 × 4 (= 32) pixels. .

  The main magnification correction unit 205 performs main magnification correction on the image data supplied from the resolution conversion unit 204 based on the information indicating the main magnification deviation supplied from the positional deviation detection unit 211, and the corrected image data is obtained. Write to the output FIFO memory 206.

  FIG. 5 is a schematic diagram for explaining resolution conversion processing by the resolution conversion unit 204 and main magnification correction processing by the main magnification correction unit 205. In this figure, the horizontal direction represents the main scanning direction, and the vertical direction represents the sub-scanning direction. FIG. 5A shows pixels of 4 rows × 6 columns as a part of a binary image having a resolution of 2400 dpi input to the resolution conversion unit 204. In FIG. 5A, it is assumed that pixels indicated by hatching have a pixel value of 1, and pixels indicated by white have a pixel value of 0. As shown in FIG. 5B, in this example, the resolution conversion unit 204 divides one pixel into two in the main scanning direction (row direction), and the two pixels obtained by the division are the original pixels. The resolution in the main scanning direction is increased by a factor of two by having the same pixel value as that of the pixel value. That is, the resolution conversion unit 204 converts image data including pixel data of 4 rows × 6 columns into image data including pixel data of 4 rows × 12 columns. The image data with the increased resolution is supplied from the resolution conversion unit 204 to the main magnification correction unit 205.

  FIGS. 5C and 5D show correction processing for reducing the main magnification (that is, reducing the image in the main scanning direction) in the main magnification correction unit 205. When the image is reduced in the main scanning direction, the main magnification correction unit 205 performs a thinning process for deleting the number of pixels corresponding to the degree of reduction from each row. In the examples of FIGS. 5C and 5D, a process of deleting one pixel in each row is performed. In FIG. 5C, the pixel indicated by the thick frame is a pixel (operation pixel) to be deleted. By deleting these operation pixels by the main magnification correction unit 205, an image composed of pixels of 4 rows × 12 columns shown in FIG. 5C becomes 4 rows × 11 columns as shown in FIG. 5D. Is converted to an image consisting of the pixels, and the size in the main scanning direction is reduced.

  FIGS. 5E and 5F show correction processing for increasing the main magnification (that is, enlarging the image in the main scanning direction) in the main magnification correction unit 205. When enlarging an image in the main scanning direction, the main magnification correction unit 205 performs processing for inserting (adding) a number of pixels corresponding to the degree of enlargement in each row. In the example of FIGS. 5E and 5F, a process of adding one pixel in each row is performed. A pixel indicated by a thick frame in FIG. 5E is a pixel (operation pixel) into which a pixel having the same pixel value as that of the pixel is inserted to the right of the pixel. By inserting a pixel next to these operation pixels by the main magnification correction unit 205, an image composed of pixels of 4 rows × 12 columns shown in FIG. 5 (e) becomes 4 as shown in FIG. 5 (f). The image is converted to an image composed of pixels of rows × 13 columns, and the size in the main scanning direction is increased.

  It should be noted that a pixel to be deleted or inserted in each row in the main magnification correction (operation pixel) is subjected to pixel thinning (deletion) and insertion (addition) processing in the correction processing unit 202 from the binary image data to the binary image. Randomly in each row to prevent moiré from interfering with the screen processing to generate data, or disappearing of the original solid line in the image after resolution conversion, or the appearance of a line that should not have appeared. Preferably it is selected.

  As described above, in the main magnification correction, the amount of image data input to the main magnification correction unit 205 per unit time is performed because pixels are deleted or inserted in each row of the image represented by the input image data. Even if (referred to as input rate) is constant, the amount of image data (referred to as output rate) output from the main magnification correction unit 205 varies per unit time. The amount of change varies depending on main magnification correction parameters such as an image reduction ratio (that is, how many pixels are deleted in each row) and an enlargement ratio (that is, how many pixels are inserted in each row).

  Further, the “reduction” and “enlargement” of the image in the main magnification correction described above is intended to align the images of the respective colors, and thus may not be performed uniformly over the entire page. For example, when the information from the misalignment detection unit 211 indicates different misalignment amounts in a plurality of areas of the image, different corrections may be performed for each area. FIG. 6 is a schematic view illustrating the case where the content of the main magnification correction process is different for each area of the image. FIG. 6A is a schematic diagram showing an image before main magnification correction, and the image is divided into three regions (region A, region B, and region C) by a boundary line parallel to the main scanning direction. FIG. 6B shows an image obtained by correcting the size in the main scanning direction with different magnifications for the regions A, B, and C with respect to the image shown in FIG. In this example, the area A is corrected so that the size in the main scanning direction is 70% of the original size, the area B is corrected to 140%, and the area C is corrected to 90%. I am doing.

  As described above, when main magnification correction is performed with different parameters for each region (in this example, reduction rate or enlargement rate), image data is input to the resolution conversion unit 204 at a constant rate (data amount per unit time). In this case, the output rate of the converted image data output from the resolution conversion unit 204 (the amount of data output per unit time) varies depending on the region.

  FIG. 7 is a schematic graph showing temporal changes in the data amount of one scanning line output from the main magnification correction unit 205 when the main magnification correction is not performed and when the main magnification correction is not performed. FIG. 7A shows the change over time of the data amount (integrated value) of one scanning line output from the main magnification correction unit 205 when the main magnification correction is not performed on the image of FIG. Yes. The slope of the solid line in the graph of FIG. 7A corresponds to the output rate. In this case, if the input rate is constant, the output rate is also constant.

  On the other hand, FIG. 7B shows the data amount of one scanning line output from the main magnification correction unit 205 when the main magnification correction shown in FIG. 6B is performed on the image of FIG. The time change of is shown. In FIG. 7B, the solid line indicates the output data amount (integrated value) when the main magnification correction is performed, and the dotted line indicates the output data amount (integrated value) when the main magnification correction is not performed. As shown in the graph of FIG. 7B, in this case, the thinning correction was performed in which the thinning correction was performed so that the size in the main scanning direction was 70% of the original size and 90% of the original size. In region C, the output rate (ie, the slope of the solid line) is smaller than when the main magnification correction is not performed. On the other hand, in the region B where the correction in which the size in the main scanning direction is 140% of the original size (correction for inserting pixel data) has been performed, the output rate is larger than when the main magnification correction is not performed. As described above, when the main magnification correction is individually performed in accordance with the area of the image, the output rate in outputting the image data for one scanning line may vary depending on the area.

  Referring back to FIG. 4, the output FIFO memory 206 has a capacity capable of storing image data for a predetermined number N3 of pixels for each of the laser diodes 191 included in the laser device 19. In this example, the number of laser diodes 191 is M, and the stored image data is binary image data. Therefore, the output FIFO memory 206 has a storage capacity of M × N3 bits. In addition, the output FIFO memory 206 outputs the image data written by the main magnification correction unit 205 in M rows in synchronization with the second clock CLK2 while the read permission signal (RD_EN) generated by the output FIFO control unit 213 is on. The data is read while being unpacked into data for one column, and supplied to the laser drive circuit 141 as a modulation signal via the delay circuit 207. Therefore, data is read from the output FIFO memory 206 by M (8 in this example) for each read.

  The predetermined number of pixels N3 is preferably as small as possible in order to reduce the capacity of the output FIFO memory 206 and reduce the cost. However, the image data read out from the output FIFO memory 206 is read out. While the data is supplied as a modulation signal to the laser driving circuit 141 (that is, while the photosensitive drum 15 is scanned with the laser beam), the output FIFO memory 206 is set to a sufficiently large value so as not to be emptied. Selected. For example, the value of N3 is about 20.

  As described above, when the output FIFO memory 206 is vacant, the line memory control unit 212 controls the line memory 203 to output the image data of pixels of M rows × N1 columns to the resolution conversion unit 204 and output it. The resolution conversion unit 204 converts the resolution of the image data into image data of pixels of M rows × N2 columns (N2> N1), and after the main magnification correction unit 205 performs main magnification correction, the image data is written in the output FIFO memory 206. It is. Thus, the output FIFO memory 206 is maintained so as not to be empty during the read operation. Further, as described above, even when the output rate of the image data output from the main magnification correction unit 205 to the output FIFO memory 206 changes and the timing at which the output FIFO memory is vacant changes, the line memory is generated each time the vacancy occurs. The image data is read out from 203 and written to the output FIFO memory 206 through resolution conversion and main magnification correction, so that the output FIFO memory 206 is prevented from being emptied.

  After a page output signal (P_ST) instructing image output of each page is input, the output FIFO control unit 213 receives a predetermined interval from the SOS sensor 142 provided in the exposure apparatus 14 when a predetermined period elapses. The SOS (Start Of Scan) signal, which is a signal indicating the start of scanning (that is, indicating that the laser beam output from the laser device 19 is just before being irradiated on the photosensitive drum 15) is used as a reference. As described above, a read permission signal (RD_EN) for permitting data reading in the output FIFO memory 206 is generated and supplied to the output FIFO memory 206. More specifically, the output FIFO control unit 213 turns on the read permission signal in response to the acquisition of the SOS signal, and turns it off when a period corresponding to one scan elapses. As a result, the output FIFO control unit 213 instructs the output FIFO memory 206 to start and end reading. Note that the predetermined period after the page output signal is input is a period in which it is estimated that a predetermined amount of image data is written in the output FIFO memory 206. The SOS sensor 142 outputs an SOS signal to the output FIFO control unit 213 based on the scanning light of the exposure apparatus 140 detected at the predetermined position.

  The delay circuit 207 receives the image data of M rows × 1 column output from the output FIFO memory 206 and shifts the arrangement position of the M laser diodes 191 included in the laser device 19 (distance D1 shown in FIG. 2). In order to absorb this, the corresponding image data is delayed by a delay amount corresponding to the arrangement position of each laser diode 191 (also referred to as bit shift) and supplied to the laser drive circuit 141.

  The laser drive circuit 141 drives each laser diode 191 based on the image data supplied from the delay circuit 207, outputs laser light modulated based on the image data, and exposes the photosensitive drum 15.

  Here, the relationship between the SOS signal and the effective scanning period will be described with reference to FIG. The effective scanning period is a period during which an electrostatic latent image can be written on the photosensitive drum 15 by modulating the laser light applied to the photosensitive drum 15. An area of the photosensitive drum 15 that can be irradiated with laser light (that is, capable of being exposed) during the effective scanning period is referred to as an effective scanning area. By correcting the image data, the position of the image formed within the effective scanning area can be adjusted. That is, the effective scanning area defines a range in which the image position can be corrected.

  FIG. 8 is a schematic graph showing the relationship between the SOS signal and the effective scanning period. As described above, when the SOS signal is generated, the output FIFO control unit 213 turns on the read permission signal (RD_EN) accordingly, and the output FIFO memory 206 reads data and supplies it to the delay circuit 207 accordingly. However, at this time, a circuit delay occurs in processing such as data reading. The delay circuit 207 performs a process of delaying image data corresponding to each laser diode 191 with a delay amount corresponding to the arrangement position of each laser diode 191 included in the laser device 19, which corresponds to this delay amount. The period (positional deviation absorption period) is an invalid period during which an electrostatic latent image on the photosensitive drum 15 cannot be formed. Therefore, as shown in FIG. 8, after the SOS signal is generated, the period corresponding to the circuit delay until the data reading from the output FIFO memory 206 is started and the deviation of the arrangement position of the laser diode 191 are absorbed. A period after a period corresponding to the delay processing performed by the delay circuit 207 (a misregistration absorption period) has elapsed becomes an effective scanning period. Therefore, in order to widen the effective scanning period, it is preferable that the circuit delay is as small as possible.

  In the present embodiment, the line memory 203 is controlled to output image data in response to the empty space in the output FIFO memory 206, so the output FIFO memory 206 is not empty and is always in a readable state. Maintained. Therefore, there is no need to provide a delay between when the output FIFO control unit 213 receives the SOS signal and when the read permission signal is turned on (that is, when image data is read from the output FIFO memory 206). The circuit delay is reduced and the effective scanning period is extended.

  As described above, in the present embodiment, after the image data is read from the line memory 203, the main magnification correction is performed after performing the resolution conversion for increasing the resolution of the image data. Therefore, compared to the case where the resolution conversion is not performed, The accuracy of the main magnification correction is improved. Further, since the line memory 203 stores the image data before the resolution is increased, the capacity of the line memory 203 can be smaller than the case where the image data after the resolution conversion is stored in the line memory 203.

  In addition, as described above, the image data output from the main magnification correction unit 205 according to a parameter (main magnification correction parameter) such as an image area to be subjected to main magnification correction or a reduction rate or enlargement rate for each line. The output rate fluctuates. In the present embodiment, the image data output from the main magnification correction unit 205 is written in the output FIFO memory 206, and then read out from the output FIFO memory 206 and supplied to the laser drive circuit 141. Therefore, the main magnification correction unit Variations in the output rate of the image data output from 205 are absorbed by the output FIFO memory 206. Therefore, the image data is read from the output FIFO memory 206 at a constant output rate without considering the image area and the value of the main magnification parameter for each line.

<Comparative example>
In order to facilitate understanding of the operational effects of the above-described embodiment of the image processing apparatus of the present invention, a comparative example of the image processing apparatus will be described below.

  FIG. 9 is a block diagram illustrating a functional configuration of a comparative example of the image processing apparatus. In FIG. 9, the same reference numerals are given to portions common to FIG. 4, and detailed description is omitted. The main difference between the image processing apparatus 12a shown in FIG. 9 and the image processing apparatus 12 shown in FIG. 4 is that in the image processing apparatus 12a, the resolution conversion unit 204 and the main magnification correction unit 205 are located upstream of the line memory 203a. The line memory control unit 212a does not control the data reading from the line memory 203a according to the empty state of the output FIFO memory 206, but controls the SOS signal generated by the SOS sensor 142 of the exposure apparatus 14 as a reference. It is a point to do.

  The line memory 203a of the image processing unit 12a receives the image data stored in itself at a predetermined cycle during the period when the read permission signal (RD_EN) from the line memory control unit 212a is on, for example, M rows × Packing is performed in units of pixels of N4 columns, transferred in parallel to the output FIFO memory 206, and written to the output FIFO memory 206. Here, M is the number of laser diodes 191 included in the laser device 19 (that is, the number of laser beams scanned simultaneously), as in the above-described embodiment. N4 is a predetermined positive integer, and is a ratio of the frequency of the upstream operation clock (first clock CLK1) to the downstream operation clock (second clock CLK2) of the output FIFO memory 206, that is, the first The frequency may be determined as the frequency of the two clocks CLK2 / the first clock CLK1. In this example, since the frequency of the second clock CLK2 is 400 MHz and the frequency of the first clock CLK1 is 100 MHz, N4 = 4. When there is data written in the output FIFO memory 206, the output FIFO memory 206 unpacks the data into data of M rows × 1 column and outputs the data to the delay circuit 207 at a predetermined cycle based on the second clock CLK2.

  In the image processing apparatus 12a of the comparative example, the image data whose resolution has been increased by the resolution conversion unit 204 is stored in the line memory 203a, so that the line memory is compared with the line memory 203 of the image processing apparatus 12 of the above-described embodiment. 203a requires a larger capacity. For example, when the resolution conversion unit 204 converts the resolution of the image data to double in the main scanning direction, the line memory 203a of the comparative example needs twice the capacity of the line memory 203 of the embodiment. In other words, the line memory 203 of the embodiment may have a smaller capacity than the line memory 203a of the comparative example, and the cost is reduced accordingly.

  In the comparative example, the line memory control unit 212a controls data reading from the line memory 203a based on the SOS signal generated by the SOS sensor 142 of the exposure apparatus 14. Specifically, the line memory control unit 212a receives the page output signal (P_ST) for instructing the image output of each page and then stores the determined amount of image data in the line memory 203a. The read enable signal (RD_EN) of the line memory 203a is turned on at a timing set with reference to. The determination as to whether or not a predetermined amount of image data has been stored in the line memory 203a may be made by counting the number of times of writing to the line memory 203a.

  As described above, the output rate of the data output from the main magnification correction unit 205 varies depending on the content of the main magnification correction to be performed, and the data output from the main magnification correction unit 205 is written to the line memory 203a. The writing rate to the line memory 203a also varies. Accordingly, the line memory control unit 212a reads data from the line memory 203a at a constant rate in consideration of the change in the write rate to the line memory 203a (that is, the change in the output rate from the main magnification correction unit 205). It is necessary to start the reading of the line memory 203a at a timing such that the reading of data from the line memory 203a is not interrupted even if the operation is performed.

  FIG. 10 is a graph for explaining the relationship between the read start timing of the line memory 203a and the temporal change in the amount of output data from the main magnification correction unit 205 in the comparative example. In FIG. 10, the solid line indicates the output data amount (integrated value) from the main magnification correction unit 205, and the slope of this solid line corresponds to the output rate. Also, the dotted line in FIG. 10 indicates the amount of output data from the line memory 203a. Since data is read from the line memory 203a at a constant output rate, the slope of the dotted line indicating the amount of output data from the line memory 203a is constant. In FIG. 10, T1 indicates the read start timing of output data from the line memory 203a.

  At the read start timing T1, the line memory control unit 212a prevents the output data amount from the line memory 203a from exceeding the output data amount from the main magnification correction unit 205 (that is, the write data amount to the line memory 203a). It is determined. The fact that the amount of output data from the line memory 203a exceeds the amount of data written to the line memory 203a means that there is no data to be read from the line memory 203a and the image data (to be supplied to the laser drive circuit 141 via the output FIFO memory 206) This is because the modulation signal) is interrupted, and eventually a defect is generated in the formed image.

  Therefore, in the comparative example, information indicating the contents of the main magnification correction of each page (information indicating the area in the page, the reduction ratio or the enlargement ratio of each area, etc.) is sent from the main magnification correction section 205 to the line memory control section 212a. Based on the information, the line memory control unit 212a obtains the data output characteristic from the main magnification correction unit 205 by calculation, and determines the read start timing T1 according to the obtained data output characteristic. When an appropriate read start timing differs depending on each area of the image of one page, the latest read start timing may be determined as the read start timing of the line memory 203a common to each scan in the page.

  As described above, in the comparative example, since it is necessary to determine the read start timing of the line memory 203a in consideration of the content of the main magnification correction in the main magnification correction unit 205, the content of the main magnification correction is limited, An operation load for determining the read start timing may occur. On the other hand, in the above embodiment, the image data output from the main magnification correction unit 205 is written in the output FIFO memory 206, and then read out from the output FIFO memory 206 and supplied to the laser drive circuit 141. Changes in the output rate of the image data output from the main magnification correction unit 205 are absorbed by the output FIFO memory 206. Therefore, the image data is read from the output FIFO memory 206 at a constant output rate without considering the image area and the value of the main magnification parameter for each line.

  In the comparative example, the line memory control unit 212a controls data reading from the line memory 203a based on the SOS signal generated by the SOS sensor 142 of the exposure apparatus 14, and the data read from the line memory 203a. Is configured to be supplied to the laser drive circuit 141 via the output FIFO memory 206 and the delay circuit 207. Therefore, compared to the above embodiment, after the SOS signal is generated, data reading from the output FIFO memory 206 is started. The circuit delay until this time increases, and the effective scanning period shown in FIG. 8 is shortened accordingly.

<Modification>
The above embodiment may be modified as follows. The embodiments described above and the modifications described below may be implemented in combination as necessary.

(Modification 1)
In the above embodiment, the image to be corrected for main magnification is divided into three areas in the main scanning direction, and the contents of the main magnification correction are made different for each area. Or may be divided into more than three regions. Further, the boundary between the regions may not be parallel to the sub-scanning direction.

  For example, as shown in FIG. 11, the boundary between regions may be a wavy line. Alternatively, a region may be randomly determined for each row, and individual processing may be performed for each region. In these cases, the data output characteristics change for each row. However, in the image processing apparatus 12 of the above-described embodiment, the variation in the data output characteristics for each row is absorbed by the feedback control of the data amount stored in the output FIFO memory 206. The read cycle of the output FIFO memory 206 is not affected. On the other hand, in the image processing apparatus 12a of the comparative example shown in FIG. 9, it is necessary to determine the data read start timing of the line memory 203a in consideration of the data output characteristics of each row as described above. The load increases.

(Modification 2)
In the above embodiment, resolution conversion and main magnification correction are performed on the image data output from the line memory 203, but the present invention is not limited to this. In addition to or instead of the main magnification correction, other misalignment correction such as skew correction may be performed.

(Modification 3)
In the above embodiment, the line memory control unit 212 controls the line memory 203 so that data is read from the line memory 203 in accordance with information indicating that the output FIFO memory 206 is free. The invention is not limited to this. In addition to the information indicating that the output FIFO memory 206 is free, information indicating the free capacity generated in the output FIFO memory 206 is sent to the line memory control unit 212, and the line memory control unit 212 is indicated by the information. The line memory 203 may be controlled so that data is read from the line memory 203 when the free capacity of the output FIFO memory 206 becomes equal to or greater than a threshold value.

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 2 ... Original, 4 ... Image reading apparatus, 5 ... Platen glass, 6 ... Light source, 7 ... Full-rate mirror, 8, 9 ... Half-rate mirror, 10 ... Lens, 11 ... Image reading element, 12, DESCRIPTION OF SYMBOLS 12a ... Image processing apparatus, 13 ... Image forming unit, 14 ... Exposure apparatus, 15 ... Photoconductor drum, 16 ... Scorotron, 17 ... Developing device, 18 ... Cleaning device, 19 ... Laser apparatus (VCSEL array), 22 ... Polygon mirror , 20, 21 ... reflecting mirrors, 23, 24 ... reflecting mirrors, 25 ... intermediate transfer belt, 30 ... primary transfer roll, 40-45 ... roll, 50 ... secondary transfer roll, 60 ... recording paper, 51, 52 ... transporting Belt 70, fixing device 64, paper discharge tray 61-63 storage unit 80 roll, 90 cleaner for belt 101 control unit 102 storage unit 103 operation unit 04 ... Communication unit, 101A ... CPU, 101B ... ROM, 101C ... RAM, 141 ... Laser drive circuit, 142 ... SOS sensor, 191 ... Laser diode, 200 ... Raster data generation unit, 201 ... I / F unit, 202 ... Correction Processing unit 203, 203a ... Line memory, 204 ... Resolution conversion unit, 205 ... Main magnification correction unit, 206 ... Output FIFO memory, 207 ... Delay circuit, 208 ... Modulation signal generation unit, 210 ... Timing signal generation unit, 211 ... Position shift detection unit, 212, 212a ... line memory control unit, 213 ... output FIFO control unit, CLK1 ... first clock, CLK2 ... second clock, 600 ... pattern detector

Claims (2)

An image data acquisition unit for acquiring image data;
A light-emitting device having a plurality of light-emitting elements that emit a plurality of light beams that scan the image carrier in a main scanning direction that is a predetermined direction;
A line memory having a capacity for acquiring the image data from the image data acquisition unit and storing image data for one scanning line for each light emitting element for all the light emitting elements;
A resolution converter that reads out image data for each light emitting element of the light emitting device from the line memory and performs resolution conversion to increase the resolution in the main scanning direction of the read image data;
A positional deviation correction unit that performs positional deviation correction for each of the plurality of regions in the main scanning direction for the image data output from the resolution conversion unit;
A driving circuit for driving the light emitting device based on the image data after the positional deviation correction ;
Arranged after the misalignment correction unit and before the drive circuit, the misalignment corrected image data output from the misalignment correction unit is written, and the written image data is output to the drive circuit. An image forming apparatus having a FIFO memory . Supply of image data from the FIFO memory to the drive circuit is triggered by a signal indicating the start of scanning of the image carrier by the light emitting device, and reading of the image data from the line memory to the resolution conversion unit. The image forming apparatus according to claim 1 , wherein the image forming apparatus is performed in response to a signal indicating that an empty area has occurred in the FIFO memory.

Images