JP2017196763A - Information processing device, information processing method and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an information processing device, information processing method and program which can suppress image defect due to a scan lens having no fθ characteristic.SOLUTION: An information processing device which corrects image data printed by an image formation device with unfixed scan speed in the main-scanning direction of the laser beam on the photoreceptor surface includes insertion means which inserts pixel pieces having a length in the main-scanning direction shorter than one pixel in the number obtained in accordance with the ratio of the scan speeds in respective regions to the maximum scan speed of the scan speeds in the respective regions with respect to the image corresponding to each of the respective regions obtained by dividing the scan region of the laser beam in the main-scanning direction.SELECTED DRAWING: Figure 6

Description

  The present invention relates to a technique for performing optical writing using a laser beam in an image forming apparatus such as a laser beam printer, a digital copying machine, or a digital FAX.

  An electrophotographic image forming apparatus has an optical scanning unit for exposing a photoreceptor. The optical scanning unit emits laser light based on the image data, reflects the laser light with a rotating polygon mirror, and transmits the scanning lens to irradiate and expose the photosensitive member. The optical scanning unit forms a latent image on the photosensitive member by performing scanning by moving the laser beam spot formed on the surface of the photosensitive member by rotating the rotary polygon mirror.

  Usually, a lens having a so-called fθ characteristic is used as the scanning lens. The fθ characteristic is an optical characteristic that forms an image of the laser beam on the surface of the photoconductor so that the spot of the laser beam moves on the surface of the photoconductor at a constant speed when the rotary polygon mirror rotates at a constant angular velocity. It is. By using a scanning lens having such fθ characteristics, appropriate exposure can be performed. Patent Document 1 discloses an image forming apparatus that uses a scanning lens having fθ characteristics.

  A scanning lens having such an fθ characteristic is relatively large and expensive. Therefore, for the purpose of downsizing and cost reduction of the image forming apparatus, there is a case where a scanning lens itself is not used or a scanning lens having no fθ characteristic is used.

JP 2013-45051 A

  However, when a scanning lens that does not have fθ characteristics is used, the laser beam spot on the surface of the photoconductor does not move at a constant speed on the surface of the photoconductor. The magnification is shifted in the main scanning direction.

  SUMMARY An advantage of some aspects of the invention is that it provides an information processing apparatus, an information processing method, and a program that can suppress image defects caused by a scanning lens that does not have an fθ characteristic.

  An information processing apparatus according to the present invention is an information processing apparatus that corrects image data to be printed by an image forming apparatus in which the scanning speed of laser light on the surface of a photosensitive member in the main scanning direction is not constant. For the image corresponding to each area obtained by dividing in the scanning direction, the number of main scans determined according to the ratio of the scanning speed in each area to the maximum scanning speed among the scanning speeds in each area An insertion means for inserting a pixel piece whose length in the direction is shorter than one pixel is provided.

  According to the present invention, it is possible to suppress image defects caused by a scanning lens that does not have fθ characteristics. Thereby, it is possible to print an image with good image quality without using a scanning lens having fθ characteristics.

1 is a diagram illustrating an example of a configuration of an image forming apparatus according to a first embodiment. 1 is a cross-sectional view of an optical scanning device according to a first embodiment. It is a graph which shows the characteristic of the partial magnification with respect to the image height of an optical scanning device. It is a block diagram which shows an example of the exposure control structure in an image forming apparatus. It is a figure for demonstrating the scanning system which has the characteristic shown in FIG. It is a figure for demonstrating the pixel piece insertion process which an image modulation part performs. It is a block diagram which shows an example of the hardware constitutions of the image modulation part in a 1st Example. It is a figure for demonstrating the pixel piece insertion process of a 1st Example. It is a timing chart for demonstrating the pixel piece insertion process of a 1st Example. It is a figure for demonstrating the pixel piece insertion process which an image modulation part performs in 2nd Example. It is a block diagram which shows an example of the hardware constitutions of the image modulation part in a 2nd Example. It is a figure for demonstrating the pixel piece insertion process of a 2nd Example. It is a timing chart for demonstrating the pixel piece insertion process of a 2nd Example. It is a figure for demonstrating the pixel piece insertion process which an image modulation part performs in 3rd Example. It is a figure for demonstrating the pixel piece insertion process of a 3rd Example. It is a timing chart for demonstrating the pixel piece insertion process of a 3rd Example.

[Example 1]
<Image forming apparatus>
FIG. 1 is a diagram illustrating an example of the configuration of the image forming apparatus 9 according to the first embodiment. The laser driving unit 300 in the optical scanning device 400 serving as an optical scanning unit generates scanning light (laser light) 208 based on the image signal output from the image signal generation unit 100 and the control signal output from the control unit 1. To emit. A photosensitive drum (photosensitive member) 4 charged by a charging unit (not shown) is scanned with a laser beam 208 to form a latent image on the surface of the photosensitive drum 4. Then, toner is attached to the latent image by a developing unit (not shown) to form a toner image corresponding to the latent image. The toner image is transferred to a recording medium such as paper which is fed from the paper feeding unit 8 and conveyed to a position where the roller 5 contacts the photosensitive drum 4. The toner image transferred to the recording medium is thermally fixed to the recording medium by the fixing device 6 and is discharged out of the apparatus through the paper discharge roller 7.

<Optical scanning device>
FIG. 2 is a cross-sectional view of the optical scanning device 400 according to the first embodiment. FIG. 2A shows a main scanning section. FIG. 2B shows a sub-scan section.

  In this embodiment, the light beam (laser beam 208) emitted from the light source 401 is shaped into an elliptical shape by the aperture stop 402 and is incident on the coupling lens 403. The light beam that has passed through the coupling lens 403 is converted into substantially parallel light and is incident on the anamorphic lens 404. The substantially parallel light includes weakly convergent light and weakly divergent light. The anamorphic lens 404 has a positive refractive power in the main scanning section, and converts an incident light beam into convergent light in the main scanning section. The anamorphic lens 404 condenses the light beam in the vicinity of the deflecting surface 405a of the deflector 405 in the sub-scan section, and forms a long line image in the main scanning direction.

  The light beam that has passed through the anamorphic lens 404 is reflected by a deflecting surface (reflecting surface) 405a of a deflector (polygon mirror) 405. The light beam reflected by the deflecting surface 405 a passes through the imaging lens 406 as the laser beam 208 shown in FIG. 1 and enters the surface of the photosensitive drum 4. The imaging lens 406 is an imaging optical element. In the present embodiment, the imaging optical system is constituted by only a single imaging optical element (imaging lens 406). The scanned surface 407 is the surface of the photosensitive drum 4 on which the light beam that has passed (transmitted) through the imaging lens 406 is incident, and is scanned with the light beam. The imaging lens 406 forms an image of a light beam on the surface to be scanned 407, and a predetermined spot-like image (hereinafter simply referred to as a spot) is formed. By rotating the deflector 405 at a constant angular velocity in the direction of arrow A by a driving unit (not shown), the spot moves on the scanned surface 407 in the main scanning direction, and an electrostatic latent image is formed on the scanned surface 407. Is done. The main scanning direction is a direction parallel to the surface of the photosensitive drum 4 and orthogonal to the moving direction of the surface of the photosensitive drum 4. The sub-scanning direction is a direction orthogonal to the main scanning direction and a direction orthogonal to the optical axis of the light beam.

  A beam detect (hereinafter referred to as BD) sensor 409 and a BD lens 408 are a synchronization optical system that determines the timing for writing an electrostatic latent image on the scanned surface 407. The light beam that has passed through the BD lens 408 enters the BD sensor 409 including a photodiode and is detected by the BD sensor 409. Based on the timing when the light beam is detected by the BD sensor 409, the writing timing is controlled.

  The light source 401 is a semiconductor laser chip. The light source 401 according to the present embodiment includes one light emitting unit (a light emitting unit 11 shown in FIG. 4 to be described later). However, the light source 401 may include a plurality of light emitting units that can independently control light emission. Even when the light source 401 includes a plurality of light emitting units, a plurality of light beams generated from the respective light emitting units pass through the coupling lens 403, the anamorphic lens 404, the deflector 405, and the imaging lens 406, respectively, to the scanned surface 407. To reach. Thereby, spots corresponding to the respective light beams are formed on the scanned surface 407 at positions shifted in the sub-scanning direction.

  The optical scanning device 400 stores various optical members such as the light source 401, the coupling lens 403, the anamorphic lens 404, the imaging lens 406, and the deflector 405 in the housing (optical box) 400a. Realized.

<Imaging lens>
As shown in FIG. 2, the imaging lens 406 has two optical surfaces (lens surfaces), an incident surface (first surface) 406a and an exit surface (second surface) 406b. The imaging lens 406 scans the surface to be scanned 407 with a desired scanning characteristic with the light beam deflected by the deflection surface 405a in the main scanning section. The imaging lens 406 makes the spot of the laser beam 208 on the scanned surface 407 into a desired shape. Further, the imaging lens 406 has a conjugate relationship between the vicinity of the deflection surface 405a and the vicinity of the surface to be scanned 407 in the sub-scan section. Thereby, surface tilt is compensated (scan position deviation in the sub-scanning direction on the surface to be scanned 407 when the deflection surface 405a tilts is reduced).

  The imaging lens 406 according to the present embodiment is a plastic mold lens formed by injection molding, but a glass mold lens may be adopted as the imaging lens 406. Since the molded lens can be easily molded into an aspherical shape and is suitable for mass production, the productivity and optical performance can be improved by adopting the molded lens as the imaging lens 406.

  The imaging lens 406 does not have a so-called fθ characteristic. In other words, the imaging lens 406 has a scanning characteristic that moves the spot of the light beam passing through the imaging lens 406 at a constant speed on the scanning surface 407 when the deflector 405 rotates at a uniform angular velocity. Not. As described above, by using the imaging lens 406 having no fθ characteristic, the imaging lens 406 can be disposed close to the deflector 405 (at a position where the distance D1 is small). In addition, the imaging lens 406 having no fθ characteristics can have a smaller width (width LW) in the main scanning direction and a thickness (thickness LT) in the optical axis direction than an imaging lens having the fθ characteristics. Thereby, the housing 400a of the optical scanning device 400 can be downsized. In addition, in the case of a lens having an fθ characteristic, there may be a sudden change in the shape of the entrance surface and exit surface of the lens when viewed in the main scanning section, and good imaging performance is achieved due to such shape restrictions. It may not be obtained. On the other hand, the imaging lens 406 having no fθ characteristics can obtain good imaging performance because there are few sharp changes in the shape of the entrance surface and exit surface of the lens when viewed in the main scanning section. Can do.

  The scanning characteristic of the imaging lens 406 according to this embodiment is expressed by the following formula (1).

  In Expression (1), the scanning angle (scanning field angle) by the deflector 405 is θ, the light beam condensing position (image height) on the scanned surface 407 is Y [mm], and the axial image height. The image formation coefficient at is K [mm], and the coefficient (scanning characteristic coefficient) for determining the scanning characteristic of the imaging lens 406 is B. In this embodiment, the on-axis image height indicates the image height on the optical axis (Y = 0 = Ymin), and corresponds to the scanning angle θ = 0. The off-axis image height indicates the image height (Y ≠ 0) outside the central optical axis (when the scanning angle θ = 0), and corresponds to the scanning angle θ ≠ 0. Further, the most off-axis image height indicates the image height (Y = + Ymax, −Ymax) when the scanning angle θ is maximum (maximum scanning field angle). The scanning width W is a width in the main scanning direction of a predetermined area (scanning area) where a latent image can be formed on the surface to be scanned 407, and is represented by W = | + Ymax | + | −Ymax |. The center of the scanning area is the axial image height. In addition, the end of the scanning region is the most off-axis image height.

  Here, the imaging coefficient K is a coefficient corresponding to f at the scanning characteristic (fθ characteristic) Y = fθ when parallel light enters the imaging lens 406. In other words, the imaging coefficient K is a coefficient for making the condensing position Y and the scanning angle θ proportional to each other in the same manner as the fθ characteristic when a light beam other than parallel light enters the imaging lens 406.

  Supplementing the scanning characteristic coefficient, since equation (1) when B = 0 is Y = Kθ, it corresponds to the scanning characteristic Y = fθ of the imaging lens having the fθ characteristic used in the conventional optical scanning device. . In addition, since the equation (1) when B = 1 is Y = K tan θ, it corresponds to the projection characteristic Y = f tan θ of a lens used in an imaging device (camera) or the like. That is, by setting the scanning characteristic coefficient B in the range of 0 ≦ B ≦ 1 in the expression (1), a scanning characteristic between the projection characteristic Y = ftan θ and the fθ characteristic Y = fθ can be obtained.

  Here, when the equation (1) is differentiated by the scanning angle θ, the scanning speed of the light beam on the scanned surface 407 with respect to the scanning angle θ is obtained as shown in the following equation (2).

  Further, when the equation (2) is divided by the velocity dY / dθ = K at the on-axis image height, the following equation (3) is obtained.

Expression (3) expresses the amount of deviation of the scanning speed of each off-axis image height with respect to the scanning speed of the on-axis image height. In the optical scanning device 400 according to the present embodiment, the scanning speed of the light beam is different between the on-axis image height and the off-axis image height except when B = 0.

  FIG. 3 is a graph showing the characteristics of the partial magnification with respect to the image height of the optical scanning device 400. FIG. 3 shows the relationship between the image height and the partial magnification when the scanning position on the scanned surface 407 shown in FIG. 2 is fitted with the characteristic of Y = Kθ. Here, the partial magnification is a rate at which the image at the scanning position is deformed in the scanning direction because the scanning speed varies depending on the scanning position.

  In this embodiment, the main scanning width (scanning width W) is 210 mm. Accordingly, the center of the main scanning position at which the on-axis image height is 105 mm. Here, the main scanning start position is 0 mm and the main scanning end position is 210 mm. Further, when the imaging lens 406 has the scanning characteristic expressed by the equation (1), as shown in FIG. 3, the partial magnification decreases as the main scanning center position (axial image height) is approached. This is because the scanning speed gradually increases from the main scanning center position (axial image height) toward the main scanning end (off-axis image height). In FIG. 3, the partial magnification at the main scanning start position where the main scanning speed is the fastest in the scanning region is used as a reference (100%).

  Assuming that the partial magnification at the main scanning start position with the fastest main scanning speed is the reference (100%), in this embodiment, the partial magnification at the main scanning central position (axial image height) is 75% as shown in FIG. It is. This means that the irradiation length in the main scanning direction on the surface to be scanned 407 is 0.75 times when light is irradiated for a unit time at the center of the main scanning width. Accordingly, if the pixel width in the main scanning direction is determined at a fixed time interval determined by the period of the image clock (VCLK) described later, the pixel density differs between the on-axis image height and the off-axis image height.

  Further, as the main scanning position moves away from the main scanning center position and approaches the end (main scanning start position or main scanning end position), the scanning speed gradually increases. As a result, the time required to scan the unit length on the surface to be scanned 407 is shorter near the main scanning end than near the main scanning center. This means that when the light emission luminance of the light source 401 is constant, the total exposure amount per unit length is larger in the vicinity of the main scanning center than in the vicinity of the main scanning end. That is, when trying to print an image having the same density per pixel, the density of the image is higher near the center of the main scan than near the end of the main scan.

  Thus, in the above-described optical configuration, there is a possibility that good image quality cannot be maintained due to variations in partial magnification in the main scanning direction and variations in the total exposure amount per unit length. Therefore, in this embodiment, in order to obtain good image quality, partial magnification correction and density correction for correcting image density per unit length are performed by inserting a white pixel piece, which will be described later.

<Exposure control configuration>
FIG. 4 is a block diagram illustrating an example of an exposure control configuration in the image forming apparatus 9. The image signal generation unit 100 receives print information from a host computer (not shown) and generates a VDO signal corresponding to image data (image signal). The image signal generation unit 100 includes an image modulation unit 101 and a CPU 102. The image modulation unit 101 and the CPU 102 are connected via a CPU bus 103.

  The control unit 1 includes a CPU 2 and an IC 3 incorporating a program for controlling the CPU 2.

  When the image signal generation unit 100 is ready to output a VDO signal for image formation, the image signal generation unit 100 instructs the control unit 1 to start printing using serial communication. When the preparation for printing is completed, the control unit 1 transmits a TOP signal that is a sub-scanning synchronization signal and a BD signal that is a main-scanning synchronization signal to the image signal generation unit 100.

  When receiving the synchronization signal from the control unit 1, the image signal generation unit 100 outputs a VDO signal that is an image signal to the laser driving unit 300 at a predetermined timing.

  The laser driving unit 300 turns on and off the switch 14 in the laser driver IC 309 in accordance with the VDO signal received from the image signal generation unit 100 and causes the light emitting unit 11 to blink. In this embodiment, when the VDO signal is 1, the switch 14 is turned on, and the laser light is emitted from the light emitting unit 11. When the VDO signal is 0, the switch 14 is turned off and the laser light is not emitted from the light emitting unit 11. Thereby, the emission of laser light is turned on and off. The monitor unit 12 is a photodiode and detects the light amount of the light emitting unit 11. The laser driver IC 309 performs feedback control based on the amount of light detected by the monitor unit 12 so that the luminance of the light emitting unit 11 becomes a desired luminance. Thereby, the brightness | luminance of the light emission part 11 is adjusted automatically, and the temperature-dependent brightness fluctuation | variation is suppressed. The luminance of the light emitting unit 11 is set by the variable resistor 13. Specifically, the resistance value of the variable resistor 13 is adjusted so that the luminance of the light emitting unit 11 becomes a desired value, that is, the current value of the current supplied to the light emitting unit 11 becomes a desired value. . For example, the variable resistor 13 is adjusted at the time of factory assembly so that the illuminance at the main scanning start position on the scanned surface 407 becomes an appropriate value.

  The memory 304 is connected to the CPU 102 of the image signal generation unit 100 via a serial line or the like. The memory 304 stores partial magnification characteristic information described later. The CPU 102 of the image signal generation unit 100 reads partial magnification characteristic information from the memory 304 when the image forming apparatus 9 is activated, and stores it in the image modulation unit 101 (specifically, a partial magnification generation unit 122 described later). The image modulation unit 101 will be described later with reference to FIG.

<Characteristics of non-constant speed scanning system>
FIG. 5 is a diagram for explaining a scanning system having the characteristics shown in FIG. FIG. 5 shows the amount of light received by the scanned surface 407 when the laser driver 300 emits a small spot laser at each position in the main scanning direction in the constant speed scanning system and the non-constant speed scanning system. . Here, the constant speed scanning system is a scanning system in which a spot of laser light moves on the surface of the photoreceptor at a constant speed. The non-constant scanning system is a scanning system in which the spot of the laser beam does not move on the surface of the photosensitive member at a constant speed, and is a scanning system having the characteristics shown in FIG. In the constant speed scanning system, the intensity of light and the irradiation shape are constant regardless of the position in the main scanning direction. On the other hand, in the non-constant speed scanning system, the light intensity increases in inverse proportion to the ratio of the partial magnification, which is the ratio of the scanning speed, except for the main scanning start position and the main scanning end position, and the shape of the latent image is compressed in the main scanning direction. It will be done. Therefore, in the non-constant speed scanning system, the density is previously reduced with respect to the output image at a position other than the main scanning start position and the main scanning end position in accordance with the ratio of the partial magnification, which is the ratio of the scanning speed at each position. It is necessary to perform processing. In addition, it is necessary to perform a process of scaling (extending) the shape in the main scanning direction in accordance with the reciprocal of the partial magnification at a position other than the main scanning start position and the main scanning end position. Note that the above processing is not required at the main scanning start position and the main scanning end position.

<Contents of correction>
FIG. 6 is a diagram for explaining correction (pixel piece insertion processing described later) performed by the image modulation unit 101.

  In the present embodiment, the image modulation unit 101 performs on / off control of laser light in units of segments (hereinafter referred to as pixel pieces) obtained by dividing one pixel into 12 in the main scanning direction. One pixel may be divided into 16 or may be divided into other numbers.

  FIG. 6 shows one pixel 601 at the main scanning start position and one pixel 602 at the main scanning center position. Pixels 601 and 602 are pixels at a main scanning start position and a main scanning center position of an image (hereinafter referred to as an original image) input to the image modulation unit 101, and both are black pixels. Here, the black pixel is a pixel in which all pixel pieces constituting the pixel are black pixel pieces. A black pixel piece is a pixel piece from which laser light is emitted in a corresponding scanning section. On the other hand, a pixel in which all pixel pieces constituting the pixel are white pixel pieces is referred to as a white pixel. The white pixel piece is a pixel piece that does not emit laser light in a corresponding scanning section, that is, a pixel piece having a density of 0%.

  Pixels 611 and 612 are pixels output by the image modulation unit 101 corresponding to the pixels 601 and 602. Since the pixel 601 is a pixel at the main scanning start position, correction by the image modulation unit 101 is not applied. Therefore, the pixel 601 and the pixel 611 are the same. On the other hand, the correction by the image modulation unit 101 is applied to the pixel 602 located at the center of the main scanning. Since the partial magnification at the main scanning center position is 75%, the pixel 602 is demagnified 1.33 times by the image modulation unit 101 based on the reciprocal of the partial magnification to be a pixel 612. The 1.33 (4/3) -fold scaling is performed by inserting one pixel piece for every three pixel pieces. In normal scaling, a pixel piece having the same color and density as the adjacent pixel piece (for example, the left adjacent pixel piece in FIG. 6) is inserted in order to maintain the image density. Insert a pixel piece. When the density of the entire pixel is 100%, that is, when all the pixel pieces constituting the pixel are black pixel pieces having a density of 100%, the density of the pixel in which the white pixel piece is inserted as described above is equivalent to 75%. . The pixels 611 and 612 are transmitted to the laser driving unit 300 as image signals.

  Irradiation images 621 and 622 are latent images (irradiation images) corresponding to the pixels 611 and 612 formed on the scanned surface 407 by the laser driving unit 300. The irradiation image 621 corresponding to the pixel 611 at the main scanning start position has the same shape as the pixel 611 because the partial magnification at that position is 100%, and the intensity of the laser beam is also an appropriate value. On the other hand, the irradiation image 622 corresponding to the pixel 612 at the main scanning center position has a partial magnification of 75% at that position, and the pixel 612 has been preliminarily scaled by 1.33 times. It becomes the same shape. However, since the scanning speed at the main scanning center position is 75% of the scanning speed at the main scanning start position, the density of the black pixel piece in the irradiation image 622 is 1.33 times the density of the black pixel piece in the irradiation image 621.

  Images 631 and 632 are print images developed based on the irradiation images 621 and 622. At the main scanning start position, a laser beam having a predetermined intensity is uniformly applied to the scanned area of one pixel. Thereby, at the main scanning start position, an image (here, image 631) in which the black pixel piece irradiated with a predetermined luminance occupies 100% of one pixel is printed. On the other hand, in the main scanning center position, an image (here, image 632) in which a black pixel piece irradiated with 1.33 times the luminance of the main scanning start position occupies 75% of one pixel is printed. Therefore, the total amount of received light is the same at the main scanning center position and the main scanning start position, and the image 632 at the main scanning center position has the same density as the image 631 at the main scanning start position.

  By applying the above correction to each pixel in the entire area other than the main scanning end, an image with good image quality can be printed. In the above description, correction by inserting a white pixel piece into a black pixel is taken as an example. However, even if a white pixel piece is inserted into a white pixel, the density of the printed image does not change. Therefore, the same processing may be applied to white pixels.

<Hardware configuration>
FIG. 7 is a block diagram illustrating an example of a hardware configuration of the image modulation unit 101 in the first embodiment.

  The image modulation unit 101 inputs a 12-bit parallel signal representing one pixel of a binary image from a host computer (not shown). When the pixel is a white pixel, the parallel signal is 0 for all 12 bits. When the pixel is a black pixel, the parallel signal is all 12 bits. In this embodiment, the parallel signal is transferred from the host computer (not shown) to the image modulation unit 101 in synchronization with the image clock VCLK. The image modulation unit 101 generates an image signal (VDO signal) using the following components for the input parallel signal.

  As shown in FIG. 7, the image modulation unit 101 includes a partial magnification generation unit 122, a PS (parallel-serial) conversion unit 123, a pixel piece insertion processing unit 124, a PLL 127, a pixel piece insertion control unit 128, AND element 135.

  The PS conversion unit 123 converts the input 12-bit parallel signal into a serial signal. The serial signal is transferred in synchronization with a clock having a frequency 12 times that of VCLK (hereinafter referred to as VCLK × 12).

  The pixel piece insertion processing unit 124 performs the above-described correction (pixel piece insertion processing). In this embodiment, the pixel piece insertion processing unit 124 inserts a pixel piece in units of 1/12 pixel with respect to the pixel represented by the input serial signal. Details of the pixel piece insertion processing will be described later with reference to FIG. In this embodiment, the pixel piece insertion processing unit 124 includes a FIFO (First-In First-Out) memory. The pixel piece insertion processing unit 124 includes a write enable (WE) terminal, a read enable (RE) terminal, a write clock (WCLK) terminal, and a read clock (RCLK) terminal. The WE terminal is fixed to enable (1 in this embodiment), and the serial signal is transferred to the pixel piece insertion processing unit 124 every clock. Data transmitted by the serial signal is stored in the pixel piece insertion processing unit 124. Reading of data stored in the pixel piece insertion processing unit 124 is performed by controlling the RE terminal. The RE terminal is controlled by the pixel piece insertion control unit 128. In addition, the pixel piece insertion processing unit 124 absorbs the input and output speed differences caused by the pixel piece insertion processing. The pixel piece insertion control unit 128 selects one RE output pattern from a plurality of RE output patterns to be described later, based on the partial magnification value output from the partial magnification generation unit 122. Then, the pixel piece insertion control unit 128 cyclically outputs a signal (RE signal) based on the selected RE output pattern to the RE terminal of the pixel piece insertion processing unit 124 and the AND element 135.

<Pixel piece insertion processing>
The pixel piece insertion process will be described with reference to FIG. FIG. 8 is a diagram for explaining the pixel piece insertion processing according to the first embodiment. FIG. 8A shows partial magnification characteristic information used for the pixel piece insertion process. The partial magnification characteristic information is information indicating the partial magnification characteristic of the optical scanning device 400 and is stored in advance in the memory 304 of the laser driving unit 300. The partial magnification characteristic is measured for each individual device at the time of manufacturing the optical scanning device 400, for example. When there is little variation between individual devices, a representative partial magnification characteristic obtained by measuring any of the devices may be set in the partial magnification characteristic information without performing individual measurement. . The partial magnification characteristic information is read in advance from the memory 304 by the CPU 102 via the serial communication 307 before printing. Then, the CPU 102 sends the read partial magnification characteristic information to the partial magnification generation unit 122 of the image modulation unit 101. The partial magnification generation unit 122 holds the received partial magnification characteristic information.

  The partial magnification characteristic information includes position information of each area obtained by dividing the scanning area into a plurality of parts in the main scanning direction, and partial magnification values corresponding to each area. The partial magnification characteristic information 1200 shown in FIG. 8A is an example of partial magnification characteristic information obtained when the scanning area is divided into 23 areas in the main scanning direction. Note that the number of divisions in the main scanning direction may be other than 23, and the size of each region does not have to be constant. As the area is finely divided, the accuracy for correction is improved. Therefore, the number of divisions in the main scanning direction may be determined in consideration of required image quality and mounting complexity. As shown in FIG. 8A, the partial magnification value in the regions at both ends of the scanning region is 100 (%). Further, as shown in FIG. 8A, the partial magnification value becomes lower as it approaches the center of the scanning region.

  FIG. 8B shows an RE output pattern corresponding to each partial magnification value. As shown in FIG. 8B, in this embodiment, an RE output pattern of 32 cycles is defined for each partial magnification value. For example, a pattern “11101110111011101110111011101110” in which 0 is evenly inserted so that the number of 1 is 75% is assigned to the RE output pattern corresponding to the partial magnification value = 75%. By putting 0 in the RE output pattern in this way, the image is expanded at a rate of 32 / n (n = number of 1 included in the pattern). In other words, the rate of expanding the image is determined based on the rate of 0 (or the rate of 1) included in the RE output pattern. Here, since 1 is 24, the image is expanded to 32/24 times. In this embodiment, the ratio of 0 (or ratio of 1) included in the RE output pattern is determined according to the ratio of the scanning speed in each region to the maximum scanning speed among the scanning speeds in each region. Since the expanded image is compressed to 75% by the non-constant speed scanning system, it has a correct shape on the scanned surface 407, that is, the same shape as that before the expansion. Here, the case of the partial magnification value = 75% is taken as an example, but the correct shape can be obtained for the expanded image in the same manner for other partial magnification values. Details of the RE output pattern and pixel piece insertion processing will be described later along the timing chart of FIG.

  Note that the length of the RE output pattern is not limited to 32 bits. Different pattern lengths may be defined for each partial magnification value. Further, the longer the RE output pattern, the higher the expansion rate can be set. Therefore, the RE output pattern may be determined in consideration of required image quality and mounting complexity. Further, the RE output pattern corresponding to each partial magnification value may be hardwired in the pixel piece insertion control unit 128. Each RE output pattern may be configured to be set by a program. For example, the CPU 102 may be configured to be able to rewrite information indicating the RE output pattern stored in a storage unit (not shown) of the image signal generation unit 100 according to the program.

  FIG. 9 is a timing chart for explaining the pixel piece insertion processing of the first embodiment.

  The timing chart shown in FIG. 9 shows how the VDO signal corresponding to the pixels near the center of the main scanning is transferred. Therefore, the partial magnification value is 75% in all cycles (cycles # 1 to # 18). Therefore, the pixel piece insertion control unit 128 outputs the above-described RE output pattern “11101110111011101110111011101110” in synchronization with VCLK × 12. That is, 1 of 3 cycles and 0 of 1 cycle are repeatedly output.

  The pixel piece insertion processing unit 124 reads and outputs written image data in the next cycle when the RE signal is 1, and holds the current output when the RE signal is 0. For example, since the RE signal is 1 in cycles # 1 to # 3, the output signals in cycles # 2 to # 4 are updated. The binary signal “0, 1, 2,...” In the timing chart shown in FIG. 9 corresponds to the output value corresponding to the 0th pixel piece when the cycle # 1 is the reference, and to the first pixel piece. The output value, the output value of the second corresponding pixel piece, etc. are represented. The output value corresponding to each pixel piece is 0 or 1. Since the RE signal in cycle # 4 is 0, the output value in this cycle (the output value corresponding to the third pixel piece) is held in the next cycle (cycle # 5). As a result, one pixel piece is inserted. Similarly, in the cycles of # 8, # 12, and # 16, pixel pieces are inserted by holding the output value of the pixel piece insertion processing unit 124, respectively.

  Further, the output signal of the pixel piece insertion processing unit 124 is input to the AND element 135 shown in FIG. 6, and the AND element 135 takes a logical product of the output signal and the RE signal. Therefore, as shown in the timing chart shown in FIG. 9, the VDO signal is always 0 in cycles # 4, # 8, # 12, and # 16 in which the RE signal is 0. Thereby, a white pixel piece is inserted. In this embodiment, when the VDO signal is 0, laser light emission by the light emitting unit 11 is turned off. Therefore, 0 in the VDO signal corresponds to white in the print image.

  As described above, in this embodiment, the number of white pixel pieces corresponding to the partial magnification value of each area is inserted into each area obtained by dividing the scanning area in the main scanning direction. Thereby, in a non-constant speed system, it is possible to suppress a positional deviation or magnification of a printed image caused by a change in scanning speed without performing pulse width modulation with respect to VCLK. In addition, it is possible to suppress a change in the density of the printed image caused by a change in scanning speed without correcting the brightness of the laser beam. In addition, since a configuration (circuit or the like) for performing pulse width modulation or laser beam luminance correction is not required, the configuration of the apparatus can be further simplified.

  In the present exemplary embodiment, the configuration in which the image forming apparatus includes a configuration (image modulation unit 101) for performing pixel piece insertion processing on image data has been described. However, a configuration for performing pixel piece insertion processing of image data may be provided outside the image forming apparatus. For example, a configuration corresponding to the image modulation unit 101 can be realized by an information processing apparatus such as a PC (personal computer).

[Example 2]
In the pixel piece insertion process in the first embodiment, in the pixel piece insertion process in the first embodiment, the density change due to the change in the area ratio of the black pixel piece and the white pixel piece is the same as the change in the area ratio. It is assumed that the density change due to the change in scanning speed is equal. However, this is not always the case in the actual electrophotographic process. In other words, the density derived from the area ratio does not always match the density of the actual print image. Further, the density derived from the scanning speed does not always match the density of the actual print image. Therefore, the above premise is not necessarily established. Therefore, when the number of white pixel pieces to be inserted is changed in accordance with the change rate of the scanning speed, there is a possibility that an area where the density becomes too thin may be generated. In this embodiment, a pixel piece insertion process suitable for such an electrophotographic process will be described.

<Contents of correction>
FIG. 10 is a diagram for explaining correction (pixel piece insertion processing) performed by the image modulation unit 101 in the second embodiment.

  FIG. 10 shows one pixel 1001 at the main scanning start position and one pixel 1002 at the center position of the main scanning. Pixels 1001 and 1002 are pixels at the main scanning start position and the main scanning center position of the original image, and both are black pixels.

  Pixels 1011 and 1012 are pixels output by the image modulation unit 101 corresponding to the pixels 1001 and 1002. Since the pixel 1001 is a pixel at the main scanning start position, correction by the image modulation unit 101 is not applied. Therefore, the pixel 1001 and the pixel 1011 are the same. On the other hand, the correction by the image modulation unit 101 is applied to the pixel 1002 located at the center of the main scanning. Since the partial magnification at the main scanning center position is 75%, the pixel 1002 is scaled 1.33 times based on the reciprocal of the partial magnification, so that the pixel 1012 is obtained. The scaling of 1.33 (4/3) times is performed by inserting one pixel piece for every three pixel pieces, as in the first embodiment. At this time, the inserted pixel piece is always a white pixel piece in the first embodiment.

  In this embodiment, the image modulation unit 101 inserts pixel pieces of the same color as the image color at the position where the pixel piece is inserted, instead of the white pixel piece at a predetermined ratio. Specifically, the image modulation unit 101 inserts a pixel piece having the same color (value) as a pixel piece adjacent to each other at the insertion position (hereinafter simply referred to as an adjacent pixel piece). The predetermined ratio is generated in the print image by, for example, the relationship between the change in the scanning speed and the change in density generated in the print image, or the change in the area ratio of the black pixel piece and the white pixel piece, which is obtained in advance. It is determined based on at least one of the relationship with the change in concentration.

  By such processing, the density of the printed image is more appropriately set even in the electrophotographic process in which the density in the whole or a part of the scanning area is too low in the pixel piece insertion process of the first embodiment. It can be corrected. FIG. 10 shows an example in which the pixel piece insertion processing of this embodiment is applied to black pixels. However, even if a white pixel piece is inserted into a white pixel, the density of the printed image does not change. Therefore, the same processing may be applied to white pixels.

  By applying the correction of the present embodiment to the entire area other than the main scanning end, an image with good image quality can be printed.

<Hardware configuration>
FIG. 11 is a block diagram illustrating an example of a hardware configuration of the image modulation unit 101 in the second embodiment.

  Here, only differences from the hardware configuration in the first embodiment shown in FIG. 7 will be described. The pixel piece insertion control unit 128 of the image modulation unit 101 of this embodiment outputs a white mask pattern signal in addition to the RE output pattern. In the first embodiment, the RE signal is input to the AND element 135. That is, the position where the white mask processing is performed (the position where the white pixel piece is inserted) is determined by the RE output pattern.

  The pixel piece insertion control unit 128 selects one RE output pattern from a plurality of RE output patterns based on the partial magnification value output from the partial magnification generation unit 122, as in the first embodiment. The pixel piece insertion control unit 128 further selects one white mask pattern from the plurality of white mask patterns based on the partial magnification value output from the partial magnification generation unit 122. Then, the pixel piece insertion control unit 128 cyclically outputs a signal based on the selected RE output pattern (RE signal) and a signal based on the white mask pattern (white mask pattern signal). In this embodiment, the pixel piece insertion control unit 128 outputs the RE signal only to the pixel piece insertion processing unit 124. Then, the pixel piece insertion control unit 128 outputs a white mask pattern signal to the AND element 135 instead of the RE signal.

  The RE output pattern and the white mask pattern corresponding to each partial magnification value may be hardwired in the pixel piece insertion control unit 128. Further, each RE output pattern and each white mask pattern may be configured to be set by a program. For example, the CPU 102 may be configured to rewrite information indicating the RE output pattern and information indicating the white mask pattern stored in a storage unit (not shown) according to the program.

<Pixel piece insertion processing>
The pixel piece insertion processing of the present embodiment will be described with reference to FIG. FIG. 12 is a diagram for explaining pixel piece insertion processing according to the second embodiment. The partial magnification characteristic information shown in FIG. 12A is the same as the partial magnification characteristic information shown in FIG. That is, the number of divisions in the main scanning direction and the division method in the scanning area, and the partial magnification value corresponding to each area obtained by the division are the same as those in the first embodiment.

  FIG. 12B shows an RE output pattern and a white mask pattern corresponding to each partial magnification value.

  As shown in FIG. 12B, the RE output pattern is the same as in the first embodiment. The value for the white mask pattern is determined as follows. In this embodiment, the same pattern as the RE output pattern is assigned to the white mask pattern, and a part of the bits corresponding to 0 in the assigned pattern is set to 1. For example, as shown in FIG. 12B, the white mask pattern corresponding to the partial magnification value = 75% has 0 of the 8th bit and the 20th bit of the RE output pattern “11101110111011101110111011101110” corresponding to the same partial magnification value. Changed to 1. As a result, the number of bits having a value of 0 is smaller in the white mask pattern than in the RE output pattern. By using such a white mask pattern, the print density can be increased.

  FIG. 13 is a timing chart for explaining the pixel piece insertion processing of the second embodiment.

  The timing chart shown in FIG. 13 shows how the VDO signal corresponding to the pixels near the center of the main scanning is transferred. Therefore, the partial magnification value is 75% in all cycles (cycles # 1 to # 18). Therefore, the pixel piece insertion control unit 128 outputs the above-described RE output pattern “11101110111011101110111011101110” in synchronization with VCLK × 12. That is, 1 of 3 cycles and 0 of 1 cycle are repeatedly output.

  Since the RE signal input to the pixel piece insertion processing unit 124 is the same as that of the first embodiment, the output signal of the pixel piece insertion processing unit 124 is also the same as that of the first embodiment. However, in this embodiment, not the RE signal but the white mask pattern signal as shown in FIG. Therefore, the VDO signal output from the AND element 135 is different from that in the first embodiment. For example, in cycle # 8, the output signal of the pixel piece insertion processing unit 124 is not masked, and a value corresponding to the eighth pixel piece is output as the VDO signal. As a result, when the pixel (corresponding to cycles # 1 to # 12) including the pixel piece (eighth pixel piece) is a black pixel, the white pixel piece is reduced by one compared to the first embodiment. Therefore, the density of black pixels can be increased. When the pixel including the pixel piece (eighth pixel piece) is a white pixel, since all the pixel pieces remain as white pixel pieces, the image quality is not changed.

  As described above, in this embodiment, in the pixel piece insertion process, a part of pixel pieces selected based on a predetermined condition among the pixel pieces to be inserted are set as pixel pieces having the same color as the adjacent pixel piece. The pixel pieces other than the partial pixel pieces are white pixel pieces. Accordingly, it is possible to suppress image defects even in an electrophotographic process in which image defects may not be suppressed by the pixel piece insertion processing of the first embodiment.

[Example 3]
As described above, in the pixel piece insertion processing in the first embodiment, the density change due to the change in the area ratio between the black pixel piece and the white pixel piece, and the density change due to the change in the scanning speed at the same rate as the change in the area ratio. Are assumed to be equal. However, this is not always the case in the actual electrophotographic process.

  For example, as in the pixel piece insertion process of the first embodiment, even if a white pixel piece is inserted according to the rate of change in scanning speed, the print density may still be too high. In this embodiment, a pixel piece insertion process suitable for such an electrophotographic process will be described.

<Contents of correction>
FIG. 14 is a diagram for explaining correction (pixel piece insertion processing) performed by the image modulation unit 101 in the third embodiment.

  FIG. 14 shows one pixel 1401 at the main scanning start position and one pixel 1402 at the center of the main scanning. Pixels 1401 and 1402 are pixels at the main scanning start position and the main scanning center position of the original image, and both are black pixels.

  Pixels 1411 and 1412 are pixels output by the image modulation unit 101 corresponding to the pixels 1401 and 1402. Since the pixel 1401 is a pixel at the main scanning start position, correction by the image modulation unit 101 is not applied. Therefore, the pixel 1401 and the pixel 1411 are the same. On the other hand, the correction by the image modulation unit 101 is applied to the pixel 1402 located at the center of the main scanning. Since the partial magnification at the main scanning center position is 75%, the pixel 1402 is demagnified 1.33 times based on the reciprocal of the partial magnification to be a pixel 1412. The scaling of 1.33 (4/3) times is performed by inserting one pixel piece for every three pixel pieces, as in the first embodiment. The pixel piece inserted at this time is always white as in the first embodiment. However, in this embodiment, a process of replacing a part of a black pixel piece constituting a pixel with a white pixel piece is performed. By such processing, the density of the printed image is corrected more appropriately in the electrophotographic process in which the density is too high in all or part of the scanning area in the pixel piece insertion processing of the first embodiment. can do. FIG. 14 shows an example in which a white pixel piece is inserted into a black pixel. However, when inserting a white pixel piece into a white pixel, all the pixel pieces in the pixel are inserted. Since it is a white pixel piece, the image quality is not changed by the white mask processing.

  By applying the pixel piece insertion processing of the present embodiment to the entire area other than the main scanning end, an image with good image quality can be printed.

<Hardware configuration>
The hardware configuration of the image modulation unit 101 of this embodiment is the same as that of the second embodiment. That is, the pixel piece insertion control unit 128 of this embodiment outputs a white mask pattern in addition to the RE output pattern.

  The pixel piece insertion control unit 128 selects one RE output pattern from a plurality of RE output patterns based on the partial magnification value output from the partial magnification generation unit 122, as in the first embodiment. The pixel piece insertion control unit 128 further selects one white mask pattern from a plurality of white mask patterns based on the partial magnification value output from the partial magnification generation unit 122. Then, the pixel piece insertion control unit 128 cyclically outputs a signal based on the selected RE output pattern (RE signal) and a signal based on the white mask pattern (white mask pattern signal). As in the second embodiment, the RE output pattern and the white mask pattern corresponding to each partial magnification value may be hardwired in the pixel piece insertion control unit 128. Further, each RE output pattern and each white mask pattern may be configured to be set by a program.

<Pixel piece insertion processing>
The pixel piece insertion processing according to this embodiment will be described with reference to FIG. FIG. 15 is a diagram for explaining pixel piece insertion processing according to the third embodiment. The partial magnification characteristic information shown in FIG. 15A is the same as the partial magnification characteristic information shown in FIG. That is, the number and method of division in the main scanning direction in the scanning region and the partial magnification value corresponding to each region obtained by the division are the same as those in the first and second embodiments.

  FIG. 15B shows an RE output pattern and a white mask pattern corresponding to each partial magnification value.

  As shown in FIG. 15B, the RE output pattern is the same as in the first and second embodiments. The value for the white mask pattern is determined as follows.

  In this embodiment, the same pattern as the RE output pattern is assigned to the white mask pattern, and some of the bits corresponding to 1 in the assigned pattern are set to 0. As shown in FIG. 15B, the white mask pattern corresponding to the partial magnification value = 75% is obtained by changing 1 in the 6th and 14th bits of the RE output pattern corresponding to the same partial magnification value to 0. Becomes a white mask pattern. As a result, the number of bits having a value of 0 is greater in the white mask pattern than in the RE output pattern. By using such a white mask pattern, the printing density can be reduced.

  FIG. 16 is a timing chart for explaining the pixel piece insertion processing of the third embodiment.

  The timing chart shown in FIG. 16 shows how the VDO signal corresponding to the pixels near the center of the main scanning is transferred. Therefore, the partial magnification value is 75% in all cycles (cycles # 1 to # 18). Therefore, the pixel piece insertion control unit 128 outputs the above-described RE output pattern “11101110111011101110111011101110” in synchronization with VCLK × 12. That is, 1 of 3 cycles and 0 of 1 cycle are repeatedly output. Since the RE signal input to the pixel piece insertion processing unit 124 is the same as that of the first embodiment, the output signal of the pixel piece insertion processing unit 124 is also the same as that of the first embodiment. However, in this embodiment, not the RE signal but the white mask pattern signal as shown in FIG. Therefore, the VDO signal output from the AND element 135 is different from the first and second embodiments. For example, in cycle # 6, the output signal of the pixel piece insertion processing unit 124 is masked, and the VDO signal in the same cycle is output as 0. As a result, when the pixel (corresponding to cycles # 1 to # 12) including the pixel piece (sixth pixel piece) is a black pixel, the white pixel piece is increased by one as compared with the first embodiment. The density of black pixels can be reduced. When the pixel including the pixel piece (sixth pixel piece) is a white pixel, since all the pixel pieces remain white, the image quality is not changed.

  As described above, in this embodiment, some pixel pieces selected based on a predetermined condition among the pixel pieces constituting the pixel in the pixel piece insertion process are set as white pixel pieces. Accordingly, it is possible to suppress image defects even in an electrophotographic process in which image defects may not be suppressed by the pixel piece insertion processing of the first embodiment.

(Other embodiments)
The present invention supplies a program that realizes one or more functions of the above-described embodiments to a system or apparatus via a network or a storage medium, and one or more processors in the computer of the system or apparatus read and execute the program This process can be realized. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

  101 Image modulator

Claims (8)

An information processing apparatus for correcting image data to be printed by an image forming apparatus in which the scanning speed of the laser beam on the surface of the photoconductor is not constant,
For an image corresponding to each of the regions obtained by dividing the scanning region of the laser light in the main scanning direction, the scanning speed that is the maximum of the scanning speed in each region and the scanning speed in each region An information processing apparatus comprising: an insertion unit that inserts a number of pixel pieces whose length in the main scanning direction is shorter than one pixel, which is obtained according to the ratio of The pixel piece inserted by the insertion means is a black pixel piece or a white pixel piece,
The information processing apparatus according to claim 1, wherein the laser beam is emitted in a scanning section corresponding to the black pixel piece, and the laser beam is not emitted in a scanning section corresponding to the white pixel piece. The information processing apparatus according to claim 2, wherein all of the pixel pieces inserted by the insertion unit are white pixel pieces. Among the pixel pieces to be inserted by the insertion means, each of the partial pixel pieces selected based on a predetermined condition is determined as a black pixel piece or a white pixel piece according to the color of the image at the insertion position, The information processing apparatus according to claim 2, wherein the pixel pieces other than the partial pixel pieces are white pixel pieces. The insertion means includes
The information processing apparatus according to claim 3, wherein, for an image corresponding to each of the regions, a part of the pixel pieces selected based on a predetermined condition among the pixel pieces constituting the image is a white pixel piece. The predetermined condition is a relationship between a change in scanning speed and a change in image density caused by the change, or a relationship between a change in the area ratio of a black pixel piece and a white pixel piece and a change in image density caused by the change. The information processing apparatus according to claim 4, wherein the information processing apparatus is at least one of the information processing apparatus. An information processing method for correcting image data to be printed by an image forming apparatus in which the scanning speed of the laser beam on the surface of the photoconductor is not constant,
For an image corresponding to each of the regions obtained by dividing the scanning region of the laser light in the main scanning direction, the scanning speed that is the maximum of the scanning speed in each region and the scanning speed in each region An information processing method comprising an insertion step of inserting a number of pixel pieces whose length in the main scanning direction is shorter than one pixel, which is determined according to the ratio of   A program for causing a computer to function as the information processing apparatus according to any one of claims 1 to 6.