JP6410087B2 - Image forming method, image forming apparatus, and printed matter production method - Google Patents

Description

  The present invention relates to an image forming method, an image forming apparatus, and a printed matter production method.

  In recent years, there has been an increasing demand for high image quality and high stability in an electrophotographic process for image formation. It is already known that deterioration factors in image formation occur at the latent image stage before development.

  In image formation, a technique is disclosed in which when the input image area is smaller than a predetermined value, the exposure energy per unit pixel is larger than the exposure energy per unit pixel when writing a solid image (for example, Patent Document 1). reference.).

  In addition to the line width correction, pattern matching is performed with a detection pattern of 1 × 4 pixels on the horizontal attention line and the diagonal attention line having a width of 2 pixels, and the brightness of one pixel is increased. A technique for performing luminance modulation is disclosed (for example, see Patent Document 2).

  Furthermore, a technique for reducing the potential difference between the high density region and the low density region of the edge portion by increasing the exposure intensity of the edge portion to the low density region is disclosed (for example, see Patent Document 3).

  Furthermore, a technique is disclosed in which light energy exposed from each light source is corrected to be uniform by thinning out or adding exposed pixels (see, for example, Patent Document 4).

  An object of the present invention is to provide an image forming method capable of forming an image having a high resolution of a latent image MTF (Modulation Transfer Function).

The present invention relates to a method of forming an electrostatic latent image corresponding to an image pattern by an exposure step of exposing the surface of the image carrier with light according to an image pattern including an image portion and a non-image portion. The section is composed of a plurality of pixels, and each of the pixels in the image section is collated with an image pattern in the vicinity of the pixel and a collation pattern composed of a plurality of pixels. Among them, at least a pixel at the boundary with the non-image part is set as a non-exposure pixel, and among the pixels constituting the image part, at least a pixel adjacent to the non-exposure pixel is a predetermined light output value necessary for exposing the image part. When a determination is made that a high-power exposure pixel is exposed with light having a higher light output value, and the collation pattern is a symmetric two-dimensional array and the image pattern has a portion that matches the collation pattern, versus Determination is performed on the pixels of the image portion corresponding to the pixels on the axis, and the number of pixels on one side of the two-dimensional array is determined by the number of pixels in one continuous column determined as non-exposure pixels and the high output exposure pixels. It is at least twice the sum of the number of pixels determined in one continuous column .

  According to the present invention, an image having a high latent image MTF resolution can be formed.

1 is a central sectional view showing an embodiment of an image forming apparatus according to the present invention. It is a schematic diagram which shows the corotron type charging device of the said image forming apparatus. FIG. 2 is a schematic diagram illustrating a scorotron charging device of the image forming apparatus. It is a schematic diagram which shows the optical scanning device which comprises the said image forming apparatus. It is a schematic diagram which shows the light source of the said optical scanning device. It is a schematic diagram which shows another embodiment of the light source of the said optical scanning device. 2 is a block diagram illustrating an image processing unit of the image forming apparatus. FIG. It is a block diagram which shows the image processing unit with which the said image processing part is provided. It is a block diagram which shows the optical writing output part with which the said image processing part is provided. It is a schematic diagram which shows a mode that the image part of image data is exposed by the predetermined | prescribed light output value required in order to be exposed. It is a schematic diagram which shows the exposure method which the said image formation method performs. It is a schematic diagram which shows another embodiment of the exposure method which the said image formation method performs. It is a schematic diagram which shows another embodiment of the exposure method which the said image formation method performs. It is a graph which shows the relationship between the spatial frequency and the latent image MTF by the difference in the exposure method. (A) standard exposure, (b) exposure method according to the present invention, (c) another embodiment of the exposure method according to the present invention, and (d) yet another embodiment of the exposure method according to the present invention. It is a schematic diagram which shows the exposure pattern when applied to a line pattern. (A) Schematic diagram showing exposure pattern 400a in FIG. 15 (a), (b) Schematic diagram showing exposure pattern 400b in FIG. 15 (b), (c) Exposure shown in FIGS. 15 (a) and (b). It is the schematic diagram which piled up the pattern. It is a graph which shows the latent image electric field strength distribution of the exposure pattern of FIG. It is a schematic diagram which shows the collation pattern which the said image forming method uses. It is a schematic diagram which shows a mode that the said image formation method determines an exposure pattern with a collation pattern. It is a schematic diagram which shows a mode that the exposure pattern of another image data is determined with the said collation pattern. 3 is a flowchart of an exposure method performed by the image forming method. It is a schematic diagram which shows the mode of embodiment which the said image forming method performs both-ends folding processing by a collation pattern. When the both-end folding processing is applied to line pattern image data of (a-1) 9 dots wide, (a-2) 10 dots wide, (a-3) 11 dots wide, and (a-4) 12 dots wide It is a schematic diagram which shows the exposure pattern. (A-1) to (a-4) are image data, and (b-1) to (b-4) are exposure patterns (a-1) to (a-4), respectively. It is a schematic diagram which shows an exposure pattern when the said both-ends folding process is applied to the image data of a 6 dot width line pattern. It is a schematic diagram which shows a mode that the exceptional process was performed to the image data of the said 6 dot width line pattern. (A) Image data, (b) State of exception processing, (c) State of performing both-end folding processing after exception processing. It is a flowchart of the said exception process. It is a flowchart which performs a data storage process only once and determines an exposure pattern. (A) It is a schematic diagram which shows a mode that the exposure pattern of the said image data was determined based on an example of image data, (b) the said flowchart. (A) One-dimensional array collation pattern, (b) Two-dimensional array collation pattern, (c) Another embodiment of two-dimensional array collation pattern, (d) Further implementation of two-dimensional array collation pattern It is a schematic diagram which shows the form. It is a flowchart which determines an exposure pattern using the collation pattern of a one-dimensional arrangement | sequence, and the collation pattern of a two-dimensional arrangement | sequence. It is a schematic diagram which shows a mode that the exposure pattern of the said image data was determined based on the flowchart of FIG. (A) The figure explaining 1 dot folding processing, (b) The figure explaining 2 dot folding processing, (c) The figure explaining 3 dot folding processing, (d) The figure explaining 4 dot folding processing. (A) The figure which shows a mode that 2-dot folding process is performed to the image data of a 5-dot width line pattern, (b) The figure which shows a mode that 1-dot folding process is performed to the image data of a 3-dot width line pattern. It is a schematic diagram which shows the flow which performs a 1-4 dot folding process. It is a schematic diagram which shows the exposure pattern of the character image by the exposure method of this Embodiment. It is a schematic diagram which shows the exposure pattern of the outline character image by the exposure method of this Embodiment. It is a center sectional view showing an example of an electrostatic latent image measuring device. It is sectional drawing of the vacuum chamber apparatus with which the said image forming apparatus is provided. It is a schematic diagram which shows the relationship between an acceleration voltage and electrification. It is a graph which shows the relationship between an acceleration voltage and a charging potential.

  Embodiments of an image forming method and an image forming apparatus according to the present invention will be described below with reference to the drawings.

● Image forming device ●
First, an image forming apparatus according to the present invention will be described.

  The image forming apparatus according to the present invention is a laser printer 1000, for example.

  A laser printer 1000 shown in FIG. 1 includes a charging device 1031, an optical scanning device 1010, a developing device 1130, a transfer device 1033, and a cleaning unit 1035 around the photosensitive drum 1030 along the rotational direction of the photosensitive drum 1030. Are arranged in the order.

  The charging device 1031 performs a charging process. The optical scanning device 1010 performs an exposure process. The developing device 1130 executes a developing process. The transfer device 1033 performs a transfer process. The cleaning unit 1035 executes an electrophotographic process.

  Further, a charge removal unit 1034 is disposed between the transfer device 1033 and the cleaning unit 1035.

  The developing device 1130 includes a toner cartridge 1036 and a developing roller 1032 that causes the toner supplied from the toner cartridge 1036 to adhere to the surface of the photosensitive drum 1030 and visualizes the latent image on the surface of the photosensitive drum 1030 with the toner. .

  The transfer device 1033 transfers the toner image on the surface of the photosensitive drum 1030 to the recording paper 1040 drawn from the paper supply tray 1038 by the paper supply roller 1037. The leading edge of the recording paper 1040 is positioned by the registration roller 1039 and is conveyed to the fixing device 1041 in synchronization with the toner image on the surface of the photosensitive drum 1030. The recording paper 1040 on which the toner image is fixed by the fixing device 1041 is sent out to the paper discharge tray 1043 by the paper discharge roller 1042.

  The laser printer 1000 includes a communication control device 1050 and a printer control device 1060.

  The communication control device 1050 controls bidirectional communication with a host device (for example, an information processing device such as a personal computer) via a network or the like.

  The printer control apparatus 1060 includes a CPU (Central Processing Unit) (not shown) and a ROM (Read Only Memory). The printer control device 1060 includes a RAM (Random Access Memory) and an A / D (Analog / Digital) converter. The printer control device 1060 comprehensively controls each unit in response to a request from the host device and sends image information from the host device to the optical scanning device 1010.

  The ROM stores a program written in a code readable by the CPU and various data used when executing this program.

  The RAM is a temporarily writable memory for work of the CPU.

  The A / D converter converts an analog signal into a digital signal.

  The photosensitive drum 1030 is a latent image carrier of a cylindrical member, and a photosensitive layer is formed on the surface thereof. That is, the surface of the photoconductor drum 1030 is a scanned surface. The photosensitive drum 1030 is rotated in the direction of the arrow in FIG. 1 by a drive mechanism (not shown).

  The charging device 1031 uniformly charges the surface of the photosensitive drum 1030. For the charging device 1031, for example, a contact-type charging roller that generates less ozone, or a corona charger that uses corona discharge can be used.

  As shown in FIG. 2, the charging device 1031 may be a corotron charging device.

  As shown in FIG. 3, the charging device 1031 may be a scorotron charging device. Further, the charging device 1031 may be a roller type charging device (not shown).

  The components of the laser printer 1000 described above are housed in predetermined positions inside the printer housing 1044.

  Returning to FIG. 1, a process for obtaining an output image in an electrophotographic image forming apparatus such as a copying machine or a laser printer will be described.

  The optical scanning device 1010 scans and exposes the surface of the photosensitive drum 1030 charged by the charging device 1031 with a light beam modulated based on image information from the printer control device 1060. The optical scanning device 1010 forms an electrostatic latent image corresponding to image information on the surface of the photosensitive drum 1030.

  The electrostatic latent image formed by the optical scanning device 1010 moves in the direction of the developing device 1130 as the photosensitive drum 1030 rotates. Details of the optical scanning device 1010 will be described later.

  The toner cartridge 1036 stores toner (developer). The toner is supplied from the toner cartridge 1036 to the developing device 1130.

  The developing device 1130 causes the toner supplied from the toner cartridge 1036 to adhere to the latent image formed on the surface of the photosensitive drum 1030, and visualizes the electrostatic latent image. An image to which toner is attached (hereinafter also referred to as “toner image”) moves in the direction of the transfer device 1033 as the photosensitive drum 1030 rotates.

  Recording paper 1040 is stored in the paper feed tray 1038. A paper feed roller 1037 is disposed in the vicinity of the paper feed tray 1038.

  The paper supply roller 1037 takes out the recording paper 1040 from the paper supply tray 1038 one by one. The recording paper 1040 is sent out from the paper feed tray 1038 toward the gap between the photosensitive drum 1030 and the transfer device 1033 in accordance with the rotation of the photosensitive drum 1030.

  A voltage having a polarity opposite to that of the toner is applied to the transfer device 1033 in order to electrically attract the toner on the surface of the photosensitive drum 1030 to the recording paper 1040. With this voltage, the toner image on the surface of the photosensitive drum 1030 is transferred to the recording paper 1040. The recording paper 1040 on which the toner image is transferred is sent to the fixing device 1041.

  In the fixing device 1041, heat and pressure are applied to the recording paper 1040, whereby the toner is fixed on the recording paper 1040. Here, the recording paper 1040 on which the toner is fixed is sent to a paper discharge tray 1043 via a paper discharge roller 1042, and is sequentially stacked on the paper discharge tray 1043 to produce printed matter.

  The neutralization unit 1034 neutralizes the surface of the photosensitive drum 1030.

  The cleaning unit 1035 removes the toner remaining on the surface of the photosensitive drum 1030 (residual toner). The surface of the photosensitive drum 1030 from which the residual toner has been removed returns to a position facing the charging device 1031.

  In the image forming apparatus according to the present invention, an electrostatic latent image is formed by a charging device, an optical scanning device as an exposure device, a photoconductor, and an image processing unit for converting an image pattern into light output. .

  As described above, in the electrophotographic system, the photosensitive member, which is one of the latent image carriers, is uniformly charged in the charging step. In the electrophotographic system, the photosensitive member is irradiated with light in the exposure process to partially release charges. By doing so, in the electrophotographic system, an electrostatic latent image can be formed on the photoreceptor.

Configuration of Optical Scanning Device Next, the configuration of the optical scanning device 1010 will be described.

  As shown in FIG. 4, the optical scanning device 1010 includes a light source 11, a collimating lens 12, a cylindrical lens 13, a mirror 14, a polygon mirror 15, and a first scanning lens 21. The optical scanning device 1010 includes a second scanning lens 22, a mirror 24, a synchronization detection sensor 26, and a scanning control device (not shown).

  The optical scanning device 1010 is assembled at a predetermined position of the optical housing 381 shown in FIG.

  In the following description, the direction along the longitudinal direction (rotation axis direction) of the photosensitive drum 1030 is defined as the Y-axis direction of the XYZ three-dimensional orthogonal coordinate system, and the direction along the rotation axis of the polygon mirror 15 is defined as the Z-axis direction. The direction perpendicular to both the Y axis and the Z axis is taken as the X axis direction.

  In the following description, the direction corresponding to the main scanning direction of each optical member is referred to as “main scanning corresponding direction”, and the direction corresponding to the sub scanning direction is referred to as “sub scanning corresponding direction”.

  As the light source 11, a semiconductor laser (LD: Laser Diode), a light emitting diode (LED: Light Emitting Diode), or the like can be used.

  In FIG. 5, the light source 11A is a semiconductor laser array configured by arranging four semiconductor lasers 11A-k as a multi-beam light source. Further, the light source 11 </ b> A is disposed perpendicular to the optical axis direction of the collimating lens 12.

  In FIG. 6, a light source 11B is a vertical cavity surface emitting laser (VCSEL) having a light emitting portion disposed on a plane including the Y-axis direction and the Z-axis direction, for example, with a wavelength of 780 nm. .

  The light emitting units are arranged so that the intervals between the light emitting units are equal when all the light emitting units are orthogonally projected onto a virtual line extending in the sub-scanning corresponding direction. The “light emitting part interval” refers to the distance between the centers of two light emitting parts.

  The light source 11B has a plurality of light emitting units. For example, the light source 11B includes a total of twelve light emitting units 11B-k, three in the horizontal direction (main scanning direction and Y-axis direction) and four in the vertical direction (sub-scanning direction and Z-axis direction).

  When applied to the optical scanning device 1010, the light source 11B can simultaneously scan four vertical scanning lines by scanning with three light emitting units arranged in the horizontal direction on one scanning line.

  Returning to FIG. 4, the collimating lens 12 is disposed on the optical path of the light emitted from the light source 11 and refracts the light into parallel light or substantially parallel light.

  The cylindrical lens 13 focuses light that has passed through the collimating lens 12 only in the Z-axis direction (sub-scanning direction) in the vicinity of the deflection reflection surface of the polygon mirror 15.

  The cylindrical lens 13 forms an image of the light 19 emitted from the light source 11 as a long line image in the main scanning direction (Y-axis direction) in the vicinity of the reflection surface of the polygon mirror 15.

  The mirror 14 reflects the light imaged through the cylindrical lens 13 toward the polygon mirror 15.

  The optical system disposed on the optical path between the light source 11 and the polygon mirror 15 is also called a pre-deflector optical system.

  The polygon mirror 15 is a polygon mirror that rotates around a rotation axis that is orthogonal to the longitudinal direction (rotation axis direction) of the photosensitive drum 1030. Each mirror surface of the polygon mirror 15 is a deflection reflection surface.

  The polygon mirror 15 rotates at a desired speed at a constant speed by applying an appropriate clock to a motor unit (not shown) by a driving IC (Integrated Circuit) (not shown).

  When the polygon mirror 15 is rotated at a constant speed in the direction of the arrow by the motor unit, a plurality of light beams reflected by the deflecting reflection surface are respectively deflected and deflected at a constant angular velocity.

  The first scanning lens 21, the second scanning lens 22, the mirror 24, and the synchronization detection sensor 26 constitute a scanning optical system 20. The scanning optical system 20 is disposed on the optical path of the light deflected by the polygon mirror 15.

  The first scanning lens 21 is disposed on the optical path of the light deflected by the polygon mirror 15.

  The second scanning lens 22 is disposed on the optical path of the light that passes through the first scanning lens 21.

  The mirror 24 is a long plane mirror, and bends the optical path of light through the second scanning lens 22 in a direction toward the photosensitive drum 1030.

  In other words, the light deflected by the polygon mirror 15 is applied to the photosensitive drum 1030 via the first scanning lens 21 and the second scanning lens 22, thereby forming a light spot on the surface of the photosensitive drum 1030.

  The light spot on the surface of the photosensitive drum 1030 moves along the longitudinal direction of the photosensitive drum 1030 as the polygon mirror 15 rotates. The moving direction of the light spot on the surface of the photosensitive drum 1030 is the “main scanning direction”, and the rotation direction of the photosensitive drum 1030 is the “sub-scanning direction”.

  The synchronization detection sensor 26 receives light from the polygon mirror 15 and outputs a signal (photoelectric conversion signal) corresponding to the amount of received light to the scanning control device. The output signal of the synchronization detection sensor 26 is also referred to as “synchronization detection signal”.

  In the optical scanning device 1010, a plurality of lines on the surface to be scanned of the photosensitive drum 1030 are simultaneously scanned by scanning with one deflection reflection surface of the polygon mirror 15. Print data for one line corresponding to each light emitting unit is stored in the buffer memory in the image processing unit 7 that controls the light emission signal of each light emitting unit.

  The print data is read for each deflecting and reflecting surface of the polygon mirror 15, and the light beam flashes in accordance with the print data on the scanning line on the photosensitive drum 1030 as the latent image carrier, and according to the scanning line. An electrostatic latent image is formed.

  As shown in FIG. 7, the image processing unit 7 includes an image processing unit (IPU) 101, a controller unit 102, a memory unit 103, an optical write output unit 104, and a scanner unit 105. Prepare.

  The controller unit 102 receives image data from the IPU 101 and performs processing such as rotation, repeat, aggregation, compression and decompression on the image data. The controller unit 102 outputs the processed image data to the IPU 101 again.

  The memory unit 103 stores various data and prepares a lookup table for calling as necessary.

  The optical writing output unit 104 performs light modulation of the light source 11 according to the lighting data by the control driver, and forms an electrostatic latent image on the photosensitive drum 1030.

  The optical writing output unit 104 determines an exposure pattern by time-intensive exposure described later based on an input signal from a gradation processing unit 101f described later. The optical writing output unit 104 forms an electrostatic latent image based on the exposure pattern.

  By determining the exposure pattern by the optical writing output unit 104, the exposure pattern can be determined after various image processing described later by the image processing unit 101. That is, an effective exposure pattern can be determined by time-intensive exposure described later.

  The formed electrostatic latent image forms an image on a recording sheet by the above-described developing device 1130, transfer device 1033, and the like.

  The scanner unit 105 reads an image and generates image data such as RGB (Red Green Blue) data based on the image.

  As shown in FIG. 8, the image processing unit 101 includes a density conversion unit 101a, a filter unit 101b, a color correction unit 101c, a selector unit 101d, a gradation correction unit 101e, and a gradation processing unit 101f. I have.

  The density conversion unit 101a converts RGB image data from the scanner unit 105 into density data using a look-up table, and outputs the density data to the filter unit 101b.

  The filter unit 101b performs image correction processing such as smoothing processing and edge enhancement processing on the density data input from the density conversion unit 101a, and outputs the result to the color correction unit 101c.

  The color correction unit 101c performs color correction (masking) processing on the density data that has been subjected to image correction processing.

  Under the control of the image processing unit 101, the selector unit 101d performs any of C (Cyan), M (Magenta), Y (Yellow), and K (Key Plate) on the image data input from the color correction unit 101c. Choose. The selector unit 101d outputs the selected C, Y, M, and K data to the gradation correction unit 101e.

  The gradation correction unit 101e stores C, M, Y, and K data input from the selector unit 101d in advance. The tone correction unit 101e sets a γ curve that provides linear characteristics with respect to input data.

  The gradation processing unit 101 f performs gradation processing such as dither processing on the image data input from the gradation correction unit 101 e and outputs a signal to the optical writing output unit 104.

Optical writing output unit The optical writing output unit 104 drives and controls the light source. The optical writing output unit 104 is a control device that drives an LD, for example.

  As shown in FIG. 9, the optical write output unit 104 includes a reference clock generation circuit 422, a pixel clock generation circuit 425, a light source modulation data generation circuit 407, a light source selection circuit 414, a write timing signal generation circuit 415, and a synchronization timing signal generation. A circuit 417 is provided.

  Note that the arrows in FIG. 9 indicate the flow of typical signals and information, and do not represent the entire connection relationship of each block.

  The reference clock generation circuit 422 generates a high-frequency clock signal that serves as a reference for the entire optical writing output unit 104.

  The pixel clock generation circuit 425 mainly includes a PLL (Phase Locked Loop) circuit. The pixel clock generation circuit 425 generates a pixel clock signal based on the synchronization signal s19 and the high frequency clock signal from the reference clock generation circuit 422.

  The pixel clock signal has the same frequency as the high-frequency clock signal and the phase matches the synchronization signal s19.

  The pixel clock generation circuit 425 can control the writing position for each scan by synchronizing the image data with the pixel clock signal.

  The pixel clock signal is supplied to the light source driving unit 410 as one piece of driving information, and is also supplied to the light source modulation data generation circuit 407. The pixel clock signal supplied to the light source modulation data generation circuit 407 is supplied to the light source driver 410 as a clock signal of the write data s16.

  The light source selection circuit 414 is a circuit used when there are a plurality of light sources, and outputs a signal designating the selected light emitting unit. The output signal s14 of the light source selection circuit 414 is supplied to the light source driving unit 410 as one piece of driving information.

● Exposure method ●
Next, an exposure method in the embodiment of the image forming method according to the present invention will be described.

  In the image forming method according to the present embodiment, the light output waveform used for latent image formation is a predetermined light output value necessary for obtaining a target image density for an image portion including a line image or a solid image. This is a waveform for exposing the photoconductor for time.

  The image portion is a portion that includes a plurality of pixels and forms an image by attaching toner in the image pattern. The non-image portion is a portion where no image is formed without attaching toner in the image pattern.

  In the following description, the target image density is referred to as “target image density”. In the following description, a predetermined light output value necessary for obtaining a target image density is referred to as a “target exposure output value”. A predetermined time during which the entire pixel of the image portion is exposed with the target exposure output value to obtain the target image density is referred to as “target exposure time”.

  In the following description, an exposure method in which exposure is performed for a target exposure time with a target exposure output value is referred to as “standard exposure”. In the present embodiment, a solid image refers to an image area having a larger area than a line image.

  In the following description, “time concentrated exposure” (TC (Time Concentration) exposure) refers to exposing a photoconductor for an exposure time shorter than the target exposure time with a light output value (first light output value) stronger than the target exposure output value. Also called).

  As shown in FIG. 10, the exposure method by standard exposure (hereinafter referred to as “exposure method 1”) is the target exposure output value as described above for one pixel (dot) image portion including a line image and a solid image. In this method, the photosensitive member is exposed for the target exposure time. Here, the horizontal axis represents time, and the vertical axis represents the amount of light. The target exposure output value is set to a light output value of 100%, and the target exposure time is set to a duty ratio of 100%.

  As shown in FIG. 11, the exposure method by TC exposure in this embodiment (hereinafter referred to as “exposure method 2”) has a light output value of 200% of the target exposure output value and a duty ratio of 50 with respect to the target exposure time. The photoreceptor is exposed at%. Assuming that the width of the image portion is 1, the width of the section to be exposed is 4/8 pixels.

  As shown in FIG. 12, the exposure method by TC exposure in this embodiment (hereinafter referred to as “exposure method 3”) has a light output value of 400% of the target exposure output value and a duty ratio of 25 with respect to the target exposure time. The photoreceptor is exposed at%. If the width of the image portion is 1, the width of the section to be exposed is 2/8 pixel.

  FIG. 13 is a schematic diagram showing still another embodiment of the image forming method according to the present invention. In this exposure method (hereinafter referred to as “exposure method 4”), the photosensitive member is exposed with a light output value of 800% of the target exposure output value and a duty ratio of 12.5% with respect to the target exposure time. If the width of the image portion is 1, the width of the section to be exposed is 1/8 pixel.

  In the exposure methods 2 to 4 described above, the pulse width is narrower than that of the exposure method 1. In other words, in exposure methods 2 to 4, since the latent image formed becomes smaller when exposed with the same light amount as exposure method 1, the light amount is controlled according to the pulse width so that the integrated light amount at the time of latent image formation is equal. doing.

  That is, in the exposure method using TC exposure, exposure is performed with a strong light quantity with a short pulse width compared to the exposure method using standard exposure.

  In the above description, in each of the exposure methods 2 to 4, the light output value is set so that the integrated light amount is constant, but the light output value in the image forming method according to the present invention is limited to this. It is not a thing.

  FIG. 14 is a graph showing the measurement result of the latent image MTF in the vertical direction when the beam spot diameter used for exposure is 70 μm in the main scanning direction × 90 μm in the sub-scanning direction. The horizontal axis represents the spatial frequency, and the vertical axis represents the latent image MTF. In the exposure methods 2 to 4, the latent image MTF has a higher value than the exposure method 1 up to a high frequency band.

  Exposure methods 2 to 4 can stably form a latent image having a smaller diameter as compared with exposure method 1. In particular, the exposure method 4 having the shortest pulse width among the exposure methods 2 to 4 is suitable for stably forming a small-diameter latent image.

  Moreover, since exposure methods 2 to 4 perform exposure with a shorter pulse width and stronger light intensity than exposure method 1, the latent image resolution is improved. That is, according to the exposure methods 2 to 4, a latent image having a small diameter can be stably formed as compared with the exposure method 1 used in the conventional image forming method.

  The exposure method by TC exposure in the image forming method according to the present invention is superior to the case where exposure is performed by a conventional exposure method with a small beam spot diameter when importance is attached to stability of a latent image in a high frequency region, that is, a small diameter. There is. Here, the optimum beam spot diameter due to the difference in the output image is determined by the latent image MTF at the maximum spatial frequency required for the output image.

  The exposure method by TC exposure is characterized in that the width of the latent image electric field vector is narrower than other means. That is, it means that the resolution is improved while the latent image electric field vector is increased.

  Further, in the image forming method according to the present invention, unlike the case where exposure is performed by controlling the light source by power modulation or pulse width modulation, the integrated light quantity is equivalent to the case where exposure is performed with the target exposure output value. For this reason, in the image forming method according to the present invention, the toner adhesion amount and the overall image density are substantially the same as when the exposure is performed with the target exposure output value.

As described above, in the case of PM (Pulse Modulation) modulation that can irradiate a light output value P1 that is larger than the target exposure output value P0 when the solid image density is formed, the ratio TCR of the light output value is TCR = P1 / P0
It is defined as

  In this case, the exposure method in the present embodiment compresses the width of the vertical line to 1 / TCR and performs exposure with a light output value stronger than the target exposure output value at the time of solid image density. By doing in this way, according to the exposure method in the present embodiment, an image with a high MTF resolution can be formed.

  In the exposure method according to the present embodiment, a narrow range of an image portion that forms an image in an image pattern is concentrated and exposed with intense light. In this way, the exposure method according to the present embodiment improves the fidelity of an output image pattern having a small size smaller than the beam diameter size (the influence of the beam diameter size cannot be ignored), and also reduces the image pattern. It can be adjusted to a desired image density.

  That is, according to the exposure method according to the present embodiment, it is possible to form an image that achieves both a fine-size image pattern formation and a desired image density.

  The exposure method according to the present embodiment can be easily applied to an arbitrary image pattern without performing special processing such as edge detection and character information recognition.

  Therefore, according to the exposure method of the present embodiment, an image pattern can be generated even when object information cannot be obtained from a computer when image data is converted into light source modulation data.

  In addition, according to the exposure method of the present embodiment, it is possible to form an image that achieves both a fine-size image pattern formation and a desired image density without corresponding image data and light source modulation data for each character. it can

  The exposure method according to the present embodiment uses PM + PWM modulation in which PM modulation and PWM (Pulse Width Modulation) modulation are combined. According to the exposure method according to the present embodiment, the integrated light amount of the image pattern at the time of exposure can be set to the same value as that of the standard exposure by using TC exposure in which the maximum light output is intentionally increased.

  Here, according to the exposure method of the present embodiment, the resolution of the image pattern can be increased without changing the image density of the image pattern by forming a deep latent image.

  In the exposure method according to the present embodiment, the light output value is set so that one or more pixels (pixel group) in the image portion at the boundary between the image portion and the non-image portion included in the image pattern are non-exposed pixels. Set. Here, the non-exposed pixel group in the image portion at the boundary between the image portion and the non-image portion included in the image pattern is referred to as a non-exposed pixel group. In addition, the exposure method according to the present embodiment adds light output values to the pixel groups adjacent to the non-exposed pixel group (near the non-exposed pixel group) and light outputs to the non-exposed pixel group. Exposure with output value.

  That is, the sum of the values obtained by subtracting the predetermined light output value from the light output value of the light exposed to the high output exposure pixel is obtained by subtracting the light output value of the light exposed to the non-exposed pixel from the predetermined light output value. Equal to the sum of values.

  By doing so, an exposure pattern with a high latent image MTF resolution can be formed.

Example of Line Image Formation Next, an example of determining an exposure pattern of a line image by the exposure method in the present embodiment will be described. The exposure pattern is a pattern of light output values of exposure for each dot of pixels corresponding to image data.

  In the following description, the Y-axis direction (main scanning direction) in the figure is the horizontal direction, and the Z-axis direction (sub-scanning direction) is the vertical direction.

  FIG. 15A shows an exposure pattern 400a of a line image by standard exposure. The exposure pattern 400a includes an exposure pixel group 411 and a non-exposure pixel group 412. The exposure pixel group 411 is a pixel group subjected to standard exposure. The non-exposed pixel group 412 is a pixel group that is not exposed. The exposure pixel group 411 matches the image portion of the line image. The non-exposure pixel group 412 matches the non-image part of the line image.

  FIG. 15B shows an exposure pattern 400 b in which one dot at the boundary between the image portion and the non-image portion of the line image is a high output exposure pixel group 443. FIG. 15C shows an exposure pattern 400c in which two dots at the boundary between the image portion and the non-image portion of the line image are the high output exposure pixel group 443. Further, FIG. 15D shows an exposure pattern 400d in which the three dots at the boundary between the image portion and the non-image portion of the line image are the high output exposure pixel group 443.

  The high output exposure pixel group 443 is a pixel group that is subjected to TC exposure with the first light output value.

  The exposure patterns 400a to 400d shown in FIGS. 15A to 15D all have a minimum pixel of 4800 dpi and a spatial frequency of 6 c / mm. The exposure patterns 400a, 400b, 400c, and 400d form a thick vertical line (a line in the Z-axis direction) for every 8 × 8 dots (equivalent to 600 dpi).

  That is, the exposure pattern 400a shown in FIG. 15A includes an exposure pixel group 411 and a non-exposure pixel group 412 composed of two 600 dpi vertical lines. Here, the size of one pixel is about 5 μm.

  In the exposure method according to the present embodiment, in the exposure pattern 400b, a pixel group at the boundary between the image portion and the non-image portion 412 (for example, a plurality of pixels in which one pixel in the Y-axis direction is arranged in one column in the Z-axis direction). The light output value is set so that the (image) becomes the non-exposed portion 441.

  Then, a pixel group at the boundary between the image portion and the non-image portion (for example, a plurality of pixel groups in which one pixel in the Y-axis direction is arranged in one column in the Z-axis direction) is set as the high-power exposure pixel group 443.

  If the magnification ratio of the TC exposure with respect to the standard exposure is 2, the high-power exposure pixel group 443 is exposed with twice the light output. At this time, since the non-exposed portion 441 is not exposed, the integrated light quantity of the entire exposure pattern 400b is the same as that of the exposure pattern 400a.

  Note that the number of pixels of the non-exposure pixel group 441 and the high-power exposure pixel group 443 can be set to an arbitrary number of pixels in the main scanning direction or the sub-scanning direction.

  In the exposure pattern 400c, the widths in the Y-axis direction of the non-exposure pixel group 441 and the high-power exposure pixel group 443 are each two pixels. The exposure pattern 400d is set so that the width in the Y-axis direction of each of the non-exposure pixel group 441 and the high-power exposure pixel group 443 is 3 pixels.

  In FIG. 16, the horizontal axis represents dots in the Y-axis direction in FIG. 15, and the vertical axis represents the light output value for each dot. The numerical value in the dot indicates a multiple of the light output value. That is, “0” is a non-exposure pixel (light output value is 0), “1” is an exposure pixel, “2” is a high output exposure pixel whose light output value is twice that of the exposure pixel, and “x” is An arbitrary pixel is shown.

  As shown in FIG. 16A, the exposure pattern 400a by the standard exposure is exposed with a uniform light output value in which the multiple of the light output value of all dots is 1 in the Y-axis direction.

  On the other hand, as shown in FIG. 16B, in the exposure pattern 400b by TC exposure, the pixel (boundary pixel) at the boundary between the image portion and the non-image portion becomes a non-exposed pixel. The multiple of the value is 0 (light output value is 0). In the exposure pattern 400b, since the pixels at the boundary between the image portion and the non-image portion are a high output exposure pixel group, the multiple of the light output value of the high output exposure pixel group is two.

  As shown in FIG. 16C, when the waveform (a) of the light output value by the standard exposure is compared with the waveform (b) of the light output value by the TC exposure, the pixels at both ends of the waveform (a) by the standard exposure are compared. In the waveform (b) by TC exposure, it becomes a non-exposed pixel.

  Then, the light output value of the non-exposure pixel group of the waveform (a) by the standard exposure is added to the light output value of the high output exposure pixel group corresponding to both ends of the waveform (b) by the TC exposure. That is, the high output exposure pixel group is a process in which the light output value at the end portion of the image pattern is folded back inward and raised.

  FIG. 17 shows a latent image electric field intensity distribution of an image pattern by standard exposure, and a latent image electric field intensity distribution of an image pattern by TC exposure in which two dots are replaced with a non-exposure pixel group and a high-power exposure pixel group.

  Comparing the latent image electric field intensity distribution of the standard exposure and the latent image electric field intensity distribution of the TC exposure, the width of the peak portion of the electric field intensity is narrower and the gradient of the electric field intensity change is larger in the TC exposure (the edge is steep). Therefore, it can be seen that clearer image formation is possible.

  Here, a process of adding only one dot is a 1-dot processing mode, and a process of adding 2 dots is a 2-dot processing mode. Hereinafter, different mode names are used depending on the number of dots to which the light output value is added to other dots. The above is an example of the 2-dot processing mode.

Image data and collation pattern collation Here, an exposure pattern determination flow by TC exposure will be described. The image forming apparatus 1000 determines an exposure pattern by TC exposure (hereinafter referred to as “TC exposure pattern”) by comparing a plurality of verification patterns stored in advance in the optical writing output unit 104 with image data.

  As shown in FIG. 18, the matching pattern 200 is an array having binary values of 0 or 1 for each pixel. The collation pattern is, for example, a square having 11 pixels vertically and 11 pixels horizontally. The pixel at the center of the matching pattern 200 is the target position 210.

  The collation pattern 200 is collated with image data. The arrangement of the collation pattern 200 and the arrangement of the image data are collated, and the same arrangement as the collation pattern 200 is searched for in the image data. When the same arrangement as the collation pattern 200 is detected in the image data, the pixel of the image data corresponding to the target position 210, that is, the exposure intensity of the target pixel is determined.

  Note that the number of pixels of the matching pattern 200 is not limited to the above. In FIG. 18, the collation pattern 200 is a two-dimensional array having a plurality of pixels vertically and horizontally, but may be a one-dimensional array.

  As the number of pixels of the collation pattern 200 increases, various patterns can be extracted, so that the exposure intensity can be determined more precisely. However, as the number of pixels of the matching pattern 200 increases, the number of gates increases and the responsiveness decreases.

  FIG. 19 shows a state in which an exposure pattern for TC exposure is determined in the 2-dot processing mode for the target pixel 211 of the image data corresponding to the target positions 210a to 210d by the matching patterns 201a to 201d.

  The collation patterns 201a to 201d are one-dimensional arrays “01111 ×” from the left. “X” indicates an arbitrary value.

  The target position 210a of the matching pattern 201a is the fifth pixel from the left. The attention position 210b of the matching pattern 201b is the fourth pixel from the left. The attention position 210c of the matching pattern 201c is the third pixel from the left. The target position 210d of the matching pattern 201d is the second pixel from the left.

  The image data in FIG. 19 is assumed to have the same arrangement as the collation patterns 201a to 201d.

  When the collation pattern 201a is detected, the exposure intensity of the target pixel 211a is determined to be “2”. When the collation pattern 201b is detected, the exposure intensity of the target pixel 211b is determined to be “2”.

  When the collation pattern 201c is detected, the exposure intensity of the target pixel 211c is determined to be “0”. When the collation pattern 201d is detected, the exposure intensity of the target pixel 211d is determined to be “0”.

  By collating the collation patterns 201a to 201d with the image data, the TC exposure pattern corresponding to the image data is determined to be “00022x”.

  This processing is also referred to as “left folding processing” because the left end of the image data is a non-exposed pixel and the end of the exposure pixel exposed by TC exposure is a high output exposure pixel group adjacent to the non-exposed portion.

  FIG. 20 is a schematic diagram in which the process for determining an exposure pattern as described above is applied to a two-dimensional image. In FIG. 20A, image data 500a is an image portion that is exposed with a uniform light output value, and a portion outside the frame of the image portion is a non-image portion.

  FIG. 20B shows an exposure pattern 500b after collation patterns 201a to 201d are collated with image data 500a. FIG. 20C shows an exposure pattern 500c after collation patterns 201a 'to 201d' obtained by reversing the left and right of the collation patterns 201a to 201d with the exposure pattern 500b.

  This processing is also referred to as “right folding processing” because the right end of the image data is a non-exposure pixel and the right end portion of the exposure pixel by TC exposure adjacent to the non-exposure portion is a high output exposure pixel group.

  FIG. 20D shows the exposure pattern 500d after the collation pattern obtained by rotating the collation patterns 201a to 201d by 90 degrees is collated with the exposure pattern 500c. The rotated collation patterns 201ar to 204dr are “01111 ×” from the top.

  This processing is also referred to as “upward folding processing” because the upper end of the image data is a non-exposure pixel and the end of the exposure pixel exposed by TC exposure is a high-power exposure pixel group adjacent to the non-exposure portion.

  At this time, when the exposure intensity of the target pixels 211ar to 211dr is the maximum light output, the intensity before matching of the matching pattern is used as it is. That is, the light output values of the pixels in the region 500d-1 and the region 500d-2 are “2” before collation of the collation patterns 201ar to 204dr.

  Here, assuming that the maximum light output is “2”, the light output values of the pixels in the region 500d-1 and the region 500d-2 are “2” even after the collation of the collation patterns 201ar to 204dr.

  Note that the exposure pattern 500d has a shape different from that of the original image data, and has protrusions formed by regions 500d-1 and 500d-2 at the top and bottom. However, the size of the exposure pattern at the end is sufficiently smaller than the beam size. Therefore, images corresponding to the region 500d-1 and the region 500d-2 are not formed.

  FIG. 20E shows an exposure pattern 500e after collation patterns 201ar 'to 204dr' obtained by inverting the collation patterns 201ar to 204dr with the exposure pattern 500d. Also in this case, when the exposure intensity of the target pixels 211ar ′ to 211dr ′ is the maximum light output, the intensity before matching of the matching pattern is used as it is as the exposure intensity.

  This processing is also referred to as “lower folding processing” because the lower end of the image data is a non-exposed pixel, and the lower end of the exposure pixel exposed by TC exposure is a high output exposure pixel group adjacent to the non-exposed portion.

  FIG. 21 is a flowchart illustrating the processing flow of FIG. By collating the original image data (original image) 500a with the collation patterns 201a to 201d, the “left folding process” is performed, and the exposure pattern 500b is determined (step S11).

  The exposure pattern 500b determined by the “left folding process” is saved by the process of “data storage 1” (step S12).

  By collating the exposure pattern 500b with the collation patterns 201a 'to 201d', the "right folding process" is performed, and the exposure pattern 500c is determined (step S13).

  The exposure pattern 500c determined by the “right turn processing” is stored by the “data storage 2” processing (step S14).

  By collating the exposure pattern 500c with the collation patterns 201ar to 201dr, the “upward folding process” is performed, and the exposure pattern 500d is determined (step S15).

  The exposure pattern 500d determined by the “upward folding process” is saved by the process of “data storage 3” (step S16).

  By collating the exposure pattern 500d with the collation patterns 201ar 'to 201dr', "down folding process" is performed, and the exposure pattern 500e is determined (step S17).

  The exposure pattern 500e determined by the “lower folding process” is saved by the process of “data storage 4” (step S18).

  The optical writing output unit 104 forms an electrostatic latent image on the latent image carrier by exposing each pixel with the exposure intensity of the exposure pattern 500e.

  In the process of FIG. 21, the folding process is performed in the order of left, right, top, and bottom, but may be performed in a different order.

  By processing in this way, an image with a high latent image MTF resolution can be formed. Further, by using the collation pattern, the light output value can be determined without performing a simple operation such as addition processing or multiplication processing on the circuit, so that the processing speed can be increased.

[Both-end Folding Processing] Next, “both-end folding processing” for simultaneously determining the left and right end or upper and lower end exposure patterns will be described.

  As shown in FIG. 22, the exposure pattern is determined by collating the image data with the eight types of collation patterns 201a to 201d and 201a 'to 201d'. Thereafter, data storage processing is performed. In other words, the “data storage 1” and “data storage 2” processes are performed in the exposure pattern determination flow described in FIG. 21, whereas the data storage process is performed once in the both-end folding process.

  That is, the number of times data is stored in the both-end folding process is half that of the decision flow described in FIG.

  FIG. 23 is a schematic diagram in which both-end folding processing is applied to a line pattern. It shows a state in which the both-end folding processing is appropriately performed for a line having a line pattern width of 9 dots or more.

  When applied to a dot-shaped pattern, upper and lower both-end folding processing can be performed in addition to the left and right both-end folding processing described above. At that time, either the left and right both-end folding processing or the top and bottom both-end folding processing may be performed first.

  In the flow described with reference to FIG. 21, the collation patterns 201a 'to 201d' when performing the right folding process are collated with the exposure pattern 500b after the left folding process. On the other hand, when the left and right both-end folding processing is performed, the collation patterns 201a to 201d and 201a 'to 201d' are all collated with the image data 500a. Therefore, the right turn-back process can be performed without storing the exposure pattern 500b after the left turn-back process.

  From the viewpoint of processing speed in the image forming apparatus, it is desirable that the exposure pattern determination flow be completed within one clock per pixel. The flow of storing and calling data a plurality of times slows down the processing speed of the circuit or requires a huge amount of memory.

  According to the both-end folding processing, by simultaneously determining the exposure intensities at both ends, it is possible to reduce the number of times of data storage compared to the exposure pattern determination flow described with reference to FIGS.

● Exception handling (1)
Next, exception processing performed before both-end folding processing will be described.

  FIG. 24 shows an exposure pattern 226 when both-end folding processing is performed in the 2-dot processing mode on the image data 225 which is a 6-dot line pattern.

  The integrated value of the light output value when normal exposure is performed on the image data is 600%. On the other hand, the integrated value of the exposure intensity corresponding to the exposure pattern 226 is 400%. As described above, the integrated value of the total light output value becomes lower than the integrated value of the normal exposure by the both-end folding processing. Therefore, when the exposure pattern 226 is exposed, the image has a low density and a blurred image.

  Therefore, a pixel that erroneously becomes a non-exposure pixel in both-end folding processing is converted into a high-power exposure pixel by exception processing. The exceptional process is a process for determining a pixel to be converted into a high-power exposure pixel by collating a collation pattern different from the both-end folding process with image data, for example.

  In the exception processing, the width of the image portion of the image data is less than twice the sum of the number of pixels for converting the exposure pixel to non-exposure in the both-end folding processing and the number of pixels for converting the exposure pixel to a high output exposure pixel. It may be performed when the number of exposure pixels is reached.

  In both-end folding processing in the 2-dot processing mode, the non-exposure pixel is 2 dots and the high-power exposure pixel is 2 dots, so the sum of the number of pixels is 4 dots. Therefore, exception processing is performed when the width of the image portion of the image data is less than 8 dots.

  FIG. 25A shows image data 225 that is a 6-dot line pattern. The collation pattern used in the exception processing corresponds to the image data 225. That is, the collation pattern used in exception processing is “x01111110x” from the right.

  As shown in FIG. 25B, the pixel 225a of the second dot from the right in the image portion is determined as “2”, that is, a high-power exposure pixel by the exception process, and the post-processing pattern 227 is determined.

  As shown in FIG. 25C, both-end folding processing is performed on the post-processing pattern 227. At this time, the both-end folding processing is not performed for the pixel whose light output value is determined by the exception processing. Therefore, the light output value of the pixel 225a remains “2”.

  The integrated value of the light output value corresponding to the exposure pattern 228 after the both-end folding processing is 600%. That is, by performing exceptional processing, it is possible to perform both-end folding processing without reducing the integrated value of the light output value.

  In the above description, the folding process in one direction is performed. However, an exception process may be performed in which the exposure patterns at the left end and the right end, or the upper end and the lower end are simultaneously determined. Exception processing that simultaneously determines the left and right exposure patterns is referred to as “left / right exception processing”. Exception processing that simultaneously determines the upper and lower exposure patterns is called “upper and lower exception processing”.

  As shown in FIG. 26, first, left and right exception processing is performed for each pixel of the original image (step S21).

  For pixels for which the light output value has not been determined in the left / right exception processing, the left / right both-end folding processing is performed (step S22). Thereafter, data storage processing is performed (step S23).

  For the pixel for which the light output value is determined in the left / right exception process, the data storage process is performed without performing the left / right end folding process (step S23).

  Next, an up / down exception process is performed on the exposure pattern stored in step S23 (step S24).

  For pixels for which the light output value has not been determined in the up / down exceptional process, the upper / lower end folding process is performed (step S25). Thereafter, data storage processing is performed (step S26).

  For the pixel for which the light output value is determined in the upper and lower exception processing, the data storage processing is performed without performing the upper and lower end folding processing (step S26).

  By performing exceptional processing, it is possible to realize high-quality image formation without fading even for narrow images.

● Exception handling (2)
Next, another embodiment of exception processing in the image forming apparatus according to the present invention will be described focusing on the differences from the above-described embodiment. The present embodiment has been described so far in that it uses a one-dimensional array matching pattern for left and right folding processing and exception processing, and uses a two-dimensional array matching pattern for upper and lower folding processing and exception processing. Different from form.

  Exception processing using a two-dimensional array verification pattern is particularly useful in an exposure pattern determination flow in which data storage processing is performed only once.

  FIG. 27 shows an exposure pattern determination flow 27 in which data storage processing is performed only once.

  First, left and right exception processing is performed for each pixel of the original image (step S31).

  For the pixels for which the light output value has not been determined in the left / right exception processing, the left / right both-end folding processing is performed (step S32).

  Next, an up / down exception process is performed on the pixels for which the light output value has not been determined in the left and right end folding processing (step S33).

  The upper and lower edge folding processing is performed on the pixels for which the light output value has not been determined in the upper and lower exception processing (step S34). Thereafter, a data storage process is performed (step S35).

  For the pixel for which the light output value is determined in the left / right exception processing, the left / right both-end folding processing, or the upper / lower exception processing, the data storage processing is performed without performing the subsequent processing (step S35).

  Here, a description will be given of an exposure pattern obtained when the determination flow 27 is executed using a one-dimensional array verification pattern for all processes.

  As shown in FIG. 28 (a), an image portion that is formed in a corner or T-shape will be described.

  A one-dimensional matching pattern as shown in FIG. 29A is used for the upper and lower end folding processing.

  FIG. 28B shows an exposure pattern after performing both-end folding processing using a one-dimensional matching pattern in FIG. A pixel group 281 surrounded by a thick frame is a non-exposed pixel. Therefore, the integrated value of the light output value of the entire exposure pattern is 13% lower than the integrated value of the light output value of the normal exposure.

  The reason why the integrated value of the light output value is reduced is that the collation pattern is collated with the image data in the left and right both-end folding processing and the top and bottom both-end folding processing.

  The pixel group 281 does not match the matching pattern in the left and right both-end folding processing. Therefore, the light output value after the left and right end folding processing is 1. Thereafter, the pixel group 281 is determined as a non-exposure pixel in the upper and lower end folding processing.

  As a correct process, when an exposure pixel is converted to a non-exposure pixel, an exposure pixel adjacent to the pixel group to be converted is converted to a high-power exposure pixel, so that the integrated value of the exposure intensity is constant before and after the process. .

  When only the upper and lower end folding processing is performed, the pixel group 281 and the pixel group 282 become non-exposure pixels, and the pixel group 283 is converted into high-power exposure pixels. However, in this example in which the left and right both-end folding processing is performed before the upper and lower both-end folding processing, the matching pattern of the pixel group 282 and the pixel group 283 is matched by the left and right both-end folding processing, and the light output value is determined. Pixel group.

  Therefore, even if the pixel group 281 is a non-exposure pixel, pixels adjacent to the pixel group to be converted are not converted to high-power exposure pixels. That is, the pixel group 281 does not need to be converted into non-exposed pixels.

  In such a case, by using a two-dimensional array collation pattern for the upper and lower both-end folding processing, it is possible to prevent non-exposed pixels from being used when adjacent pixels are not converted into high-power exposed pixels.

  Specifically, the collation pattern of the two-dimensional array is an array of “1” on the left and right of the pixel adjacent to the pixel of interest by the number of pixels in the processing direction of the pixels whose light output values are determined by the upper and lower both-end folding processing. A matching pattern with

  In other words, the collation pattern of the two-dimensional array is a pattern in which the target pixel is arranged on the symmetry axis. The number of pixels on one side of the two-dimensional array is at least twice the sum of the number of pixels in one continuous column determined as a non-exposure pixel and a high-power exposure pixel.

  FIG. 29B shows a two-dimensional array verification pattern 291 used for upper and lower end folding processing when one pixel is a non-exposure pixel and one adjacent pixel is a high output exposure pixel. Therefore, two rows of “1” arrays are arranged on the left and right of the pixel adjacent to the target pixel 291a.

  FIG. 29C shows a matching pattern 292 used when two pixels are non-exposed pixels and two adjacent pixels are high-power exposed pixels. Accordingly, four rows of “1” arrays are arranged on the left and right of the pixel adjacent to the target pixel 292a.

  FIG. 29D shows a matching pattern 293 used when three pixels are non-exposed pixels and three adjacent pixels are high-power exposure pixels. Accordingly, six rows of “1” arrays are arranged on the left and right of the pixels adjacent to the target pixel 293a.

  As shown in FIG. 30, the decision flow 30 uses a one-dimensional array verification pattern in the left and right exception processing and the left and right end folding processing. A two-dimensional array matching pattern is used in the vertical exception processing and vertical folding processing.

  First, left and right exception processing is performed for each pixel of the original image (step S41).

  Left and right both-end folding processing is performed for the pixels for which the light output value is not determined in the left and right exception processing (step S42).

  Next, an up / down exception process is performed on the pixels for which the light output value has not been determined in the left and right end folding processing (step S43).

  Upper and lower both-end folding processing is performed for the pixels for which the light output value has not been determined in the upper and lower exception processing (step S44). Thereafter, a data storage process is performed (step S45).

  For the pixel for which the light output value has been determined in the left / right exception processing, the left / right both-end folding processing, or the top / bottom exception processing, the data storage processing is performed without performing the subsequent processing (step S45).

  FIG. 31 shows an exposure pattern after execution of a decision flow 27 including upper and lower both-ends folding processing using the matching pattern 291 with respect to FIG. It can be seen that the light output value of the pixel group 281 'is determined to be 1.

  In this way, by using a one-dimensional array matching pattern for the left and right both-end folding processing and using a one-dimensional array matching pattern for the upper and lower both-end folding processing, an exposure pattern is correctly determined even for a complex image. be able to. By this method, it is possible to make the total amount of light added by high exposure equal to the total amount of light subtracted by exposure.

● Exposure method (2)
Next, another embodiment of the exposure method in the image forming method according to the present invention will be described focusing on the difference from the example of the exposure method described above.

  In the exposure method according to the present embodiment, the number of pixels used as non-exposure pixels or high-power exposure pixels depends on the performance of the image forming apparatus, the image area in the image pattern, and the form of the image pattern (black characters, white characters, line types). , Depending on the shape of the figure).

  FIG. 32 is a schematic diagram illustrating an example of an addition process of light output values of an exposure pattern. As shown in the figure, in the exposure method according to the present embodiment, 1 to 4 dots of the exposure pattern of an image formed at 4800 dpi are set as non-exposed pixels, and the light output value is added to other pixels.

  FIG. 32A shows an example of addition in the 1-dot processing mode. FIG. 32B shows an example of addition in the 2-dot processing mode. FIG. 32C shows an addition example in the 3-dot processing mode. Furthermore, FIG. 32D shows an example of addition in the 4-dot processing mode.

  As shown in FIGS. 32A to 32D, with respect to an arbitrary number of exposure pixels arranged symmetrically, whether or not there is an exposure pixel at a corresponding position when folded around the virtual axis of symmetry. Match. Thus, by adding the light output value to the pixel on the opposite side of the symmetry axis, the numerical value of the light output value of the pixel on the opposite side becomes “2”.

  FIG. 33 is a schematic diagram showing another addition process.

  FIG. 33A shows the addition processing in the 3-dot processing mode. FIG. 33B shows another addition process in the 3-dot processing mode.

  As shown in FIGS. 33 (a) and 33 (b), the exposure method according to the present embodiment is different from the above-described addition processing of light output values of the exposure pixels arranged symmetrically. The addition process can also be performed when there is no exposure pixel at the position corresponding to the center of the image.

  That is, in the exposure method according to the present embodiment, when the addition process is performed, if the exposure pixel on the addition side is already a pixel after the addition of the light output value, the addition process is performed only on the exposure pixels that can be added. It can be performed.

  Specifically, as shown in FIGS. 33A and 33B, when the folding process cannot be performed in the 3-dot processing mode, the folding process can be performed in the 2-dot processing mode or the 1-dot processing mode.

  As described above, according to the exposure method according to the present embodiment, it is possible to appropriately perform processing so as not to add again to the pixel to which the light output value is added.

  In addition, regarding the folding processing with a smaller number of pixels than the designated processing mode, the processing may be performed in order from the folding processing with the larger number of pixels. The light source driving unit 410 includes a selector 34 that selects a processing mode.

  As shown in FIG. 34, when the 4-dot processing mode is set, the selector 34 first selects the 4-dot processing mode. The light source driving unit 410 performs collation with the collation pattern for the 4-dot processing mode. When the pattern matches the collation pattern, the return processing in the 4-dot processing mode is performed.

  Next, the selector 34 selects the 3-dot processing mode. The light source driving unit 410 performs collation with the collation pattern for the 3-dot processing mode. When the pattern matches the collation pattern, the return processing in the 3-dot processing mode is performed. The same applies to the 2-dot processing mode and the 1-dot processing mode.

  In this way, by performing processing in turn for the number of pixels smaller than the designated processing mode, a high-quality image can be formed even in a portion where the number of pixels in the image portion is small and the designated folding processing cannot be performed. Can do.

  In the image forming method according to the present invention, it is possible to select at least two types of image quality, that is, the first image quality (normal image quality mode) and the second image quality. The first image quality is image quality by standard exposure.

  According to the exposure method according to the embodiment described above, the second image quality is obtained from the first light output value for at least a pixel group at the boundary with the non-exposed portion among the pixels constituting the pixel of the image portion. Also, the image quality is exposed with a high light output value.

[Example of Forming Character Image] Next, an example in which the exposure method according to the present embodiment is applied to a character image of minute size (3 points) will be described.

  FIG. 35 is a schematic diagram showing an exposure pattern of a character image by the exposure method of the present embodiment. FIG. 5A shows an exposure pattern of the “image” character determined in the 2-dot processing mode. FIG. 4B shows an exposure pattern for standard exposure.

  FIG. 36 is a schematic diagram showing an exposure pattern of a white character image by the exposure method of the present embodiment. FIG. 36A shows a white exposure pattern of characters “Picture” at the time of standard exposure. FIG. 36B shows an exposure pattern determined in the 4-dot processing mode.

  The exposure method according to the present embodiment can be applied not only to normal colored characters but also to color reversal characters (outlined characters).

  According to the exposure method according to the present embodiment, when object information cannot be obtained from the information processing apparatus when converting from image data to light source modulation data, there are various such as a character image, a reversed character image, a dither, and a line image. An exposure pattern of a simple image can be generated.

  The exposure method according to the present embodiment can further improve the effect by properly using the exposure pattern processing mode according to the characteristics of the image data.

  In general, the white characters shown in FIG. 36 are affected by exposure at the periphery, so the electric field strength of the white background is small, and the white background is likely to be buried in the coloring. For this reason, in the exposure method according to the present embodiment, it is desirable to increase the light output value by time-intensive exposure by setting a large number of pixels in the high-power exposure pixel group and the non-exposure part.

  The exposure method according to the present embodiment reduces the number of pixels in the high-power exposure pixel group and the non-exposure part when textures or artifacts appear in the dither part such as halftones due to interference with other processes. Also good. If the number of pixels to be added is 1 dot, that is, the 1-dot processing mode, there is almost no demerit by the exposure method according to the present embodiment, and an effect of reducing a weak electric field can be obtained.

  Therefore, when the exposure method according to the present embodiment can identify black characters, white characters, and dither by tag information that identifies the type (character or line) of the target to be added to the high-power exposure pixel group. The number of pixels in the high output exposure pixel group and the non-exposure portion can be appropriately aligned.

  As a specific example, if it is a normal character or a line drawing, a tag is attached in advance to the pixel on the exposure side at the boundary between the image portion and the non-image portion. On the other hand, in the case of a reversed character or a reversed line drawing, a tag is attached to the non-exposure side pixel at the boundary between the image portion and the non-image portion, and other dithers and the like are the same as when no dither is attached.

  Then, for each tagged image, black characters and black lines are set in advance as a 3-dot processing mode, white characters and white lines are set as a 4-dot processing mode, and dither is set as a 2-dot processing mode.

  The light source modulation data generation circuit 407 described in FIG. 9 detects the boundary pixel between the image portion and the non-image portion of the exposure pattern, and the tag is set to 0 from the tag bit (information specifying the attribute of the image pattern) of the boundary pixel. 1 is detected.

  When the tag bit is 1, the light source modulation data generation circuit 407 determines that it is a black character or a black line and executes the 3-dot processing mode.

  Next, when the tag bit is 0, the light source modulation data generation circuit 407 determines a white character and a white line, and executes the 4-dot processing mode.

  If the tag bit is neither 0 nor 1, the light source modulation data generation circuit 407 determines that it is a dither part and executes the 2-dot processing mode.

  As described above, the exposure method according to the present embodiment recognizes a normal character, an inverted character, or a dither portion based on information provided from the controller side, such as an image pattern of the received image or a tag bit of the image. Then, an optimal number of folded pixels is set according to each image.

  According to the exposure method according to the present embodiment, the light output value of TC exposure can be increased or decreased, so that the best image that maximizes the capability of the image forming apparatus can be provided.

Next, the configuration of the electrostatic latent image measuring apparatus capable of confirming the state of the electrostatic latent image formed by the exposure method according to the present embodiment will be described.

  An electrostatic latent image measuring device 300 shown in FIG. 37 includes a charged particle irradiation system 400, an optical scanning device 1010, a sample stage 401, a detector 402, an LED 403, a control system (not shown), a discharge system, and a driving system. It has a power supply.

  The charged particle irradiation system 400 is disposed in the vacuum chamber 340. The charged particle irradiation system 400 includes an electron gun 311, an extraction electrode 312, an acceleration electrode 313, a condenser lens 314, a beam blanker 315, and a partition plate 316. The charged particle irradiation system 400 includes a movable diaphragm 317, a stigmator 318, a scanning lens 319, and an objective lens 320.

  In the following description, the optical axis direction of each lens will be referred to as a c-axis direction, and two directions orthogonal to each other in a plane orthogonal to the c-axis direction will be described as an a-axis direction and a b-axis direction.

  The electron gun 311 generates an electron beam as a charged particle beam and irradiates the vacuum sample stage unit 384.

  The extraction electrode 312 is disposed on the −c side of the electron gun 311 and controls the electron beam generated by the electron gun 311.

  The acceleration electrode 313 is disposed on the −c side of the extraction electrode 312 and controls the energy of the electron beam.

  The condenser lens 314 is disposed on the −c side of the acceleration electrode 313 and focuses the electron beam.

  The beam blanker 315 is disposed on the −c side of the condenser lens 314, and turns on / off the electron beam irradiation.

  The partition plate 316 is disposed on the −c side of the beam blanker 315 and has an opening at the center.

  The movable diaphragm 317 is disposed on the −c side of the partition plate 316 and adjusts the beam diameter of the electron beam that has passed through the opening of the partition plate 316.

  The stigmator 318 is disposed on the −c side of the movable diaphragm 317 and corrects astigmatism.

  The scanning lens 319 is disposed on the −c side of the stigmator 318 and deflects the electron beam via the stigmator 318 in the ab plane.

  The objective lens 320 is disposed on the −c side of the scanning lens 319 and converges the electron beam that passes through the scanning lens 319. The electron beam passing through the objective lens 320 passes through the beam emission opening 321 and is irradiated on the surface of the sample 323.

  A driving power supply (not shown) is connected to each lens.

  Charged particles are particles that are affected by an electric field or magnetic field. For example, an ion beam may be used as the beam for irradiating the charged particles instead of the electron beam. In this case, a liquid metal ion gun or the like is used instead of the electron gun.

  The sample 323 is a photoconductor, and has a conductive support, a charge generation layer (CGL), and a charge transport layer (CTL).

  The charge generation layer contains a charge generation material (CGM) and is formed on the surface on the + c side of the conductive support. The charge transport layer is formed on the + c side surface of the charge generation layer.

  When the sample 323 is exposed in a state where the surface (+ c side surface) is charged, light is absorbed by the charge generation material of the charge generation layer, and positive and negative charge carriers are generated. One of these carriers is injected into the charge transport layer and the other into the conductive support by an electric field.

  The carriers injected into the charge transport layer move to the surface of the charge transport layer by an electric field, and are combined with the charge on the surface and disappear. As a result, a charge distribution, that is, an electrostatic latent image is formed on the surface of the sample 323 (the surface on the + c side).

  The optical scanning device 1010 includes a light source, a coupling lens, an aperture plate, a cylindrical lens, a polygon mirror, a scanning optical system 393, and the like. The optical scanning device 1010 also has a scanning mechanism (not shown) for scanning light in a direction parallel to the rotation axis of the polygon mirror.

  The scanning optical system includes a light source unit, a scanning lens, an optical deflector, and the like. The optical deflector is, for example, a polygon scanner 390.

  The polygon scanner 390 is provided on a horizontal translation table 392 together with the optical housing 381.

  The light emitted from the optical scanning device 1010 irradiates the surface of the sample 323 through the reflection mirror 372, the external light shielding cylinder 385, the labyrinth 386, the light shielding member 387, the internal light shielding cylinder 388, and the glass window 368.

  The irradiation position of the light emitted from the optical scanning device 1010 on the surface of the sample 323 is along two directions orthogonal to each other on a plane orthogonal to the c-axis direction due to deflection by the polygon mirror and deflection by the scanning mechanism. Change.

  At this time, the change direction of the irradiation position due to deflection by the polygon mirror is the main scanning direction, and the change direction of the irradiation position due to deflection by the scanning mechanism is the sub-scanning direction. Here, the a-axis direction is set to the main scanning direction, and the b-axis direction is set to the sub-scanning direction.

  As described above, the electrostatic latent image measuring device 300 can two-dimensionally scan the surface of the sample 323 with the light emitted from the optical scanning device 1010. That is, the electrostatic latent image measuring apparatus 300 can form a two-dimensional electrostatic latent image on the surface of the sample 323.

  As shown in FIG. 38, the optical scanning apparatus 1010 is provided with an incident window through which light flux can enter the inside of the vacuum chamber 340 at a position of 45 degrees with respect to the vertical axis of the vacuum chamber 340. . That is, the scanning optical system 393 is disposed outside the vacuum chamber 340.

  With this configuration, vibrations and electromagnetic waves generated by the polygon mirror drive motor are unlikely to affect the trajectory of the electron beam. That is, the influence of vibrations and electromagnetic waves from the polygon mirror on the measurement result can be suppressed.

  The detector 402 is disposed in the vicinity of the sample 323 and detects secondary electrons from the sample 323.

  The LED 403 is disposed in the vicinity of the sample 323 and emits light that illuminates the sample 323. The LED 403 is used to erase charges remaining on the surface of the sample 323 after measurement.

  Note that the optical housing 381 that holds the scanning optical system 393 may be configured such that the entire scanning optical system 393 is covered with the cover 391 so that external light (harmful light) that enters the vacuum chamber is blocked.

  In the scanning optical system 393, the scanning lens has fθ characteristics. That is, when the optical polarizer rotates at a constant speed, the light beam moves at a substantially constant speed with respect to the image plane. In the scanning optical system, the beam spot diameter can also be scanned substantially constant.

  In the electrostatic latent image measuring apparatus 300, the scanning optical system is arranged away from the vacuum chamber. Therefore, there is little influence caused by directly propagating vibration generated when driving an optical deflector such as the polygon scanner 390 to the vacuum chamber 340.

  Anti-vibration means such as a damper may be provided between the vibration isolation table 382 that holds the scanning optical system 393 and the structure 383. By providing the vibration isolating means, vibration transmitted to the vacuum champ 340 can be further reduced.

  By providing the scanning optical system 393, the electrostatic latent image measuring device 300 can form an arbitrary latent image pattern including a line pattern in the bus line direction of the photosensitive member.

  In order to form a latent image pattern at a predetermined position, a synchronization detection sensor 26 that detects a scanning beam from the light deflection unit may be provided.

  The shape of the sample 323 may be a flat surface or a curved surface.

  By adding the scanning mechanism as described above, an arbitrary latent image pattern including a line pattern can be formed in the bus line direction of the photoreceptor.

● Method of electrostatic latent image measurement Next, a method of electrostatic latent image measurement will be described.

  FIG. 39 is a schematic diagram showing the relationship between the acceleration voltage and the charging potential. First, in the electrostatic latent image measurement, the electrostatic latent image measurement device 300 irradiates the sample 323 of the photosensitive member with an electron beam.

  As an acceleration voltage | Vacc | which is a voltage applied to the acceleration electrode 313, a voltage higher than a voltage at which the secondary electron emission ratio in the sample 323 becomes 1 is set. By setting the acceleration voltage in this way, in the sample 323, the amount of incident electrons exceeds the amount of emitted electrons, so that electrons are accumulated in the sample 323 and charge up occurs. As a result, in the electrostatic latent image measuring apparatus 300, the surface of the sample 323 can be uniformly charged with a negative charge.

  As shown in FIG. 39, there is a certain relationship between the acceleration voltage and the charging potential. For this reason, the electrostatic latent image measuring device 300 can form a charged potential similar to that of the photosensitive drum 1030 in the image forming apparatus 1000 on the surface of the sample 323 by appropriately setting the acceleration voltage and the irradiation time. it can.

  Since the larger irradiation current can reach the target charging potential in a shorter time, the irradiation current is set to several nA here.

  Thereafter, in the electrostatic latent image measuring apparatus 300, the amount of incident electrons in the sample 323 is set to 1/100 to 1/1000 times so that the electrostatic latent image can be observed.

  In the electrostatic latent image measuring device 300, the optical scanning device 500 is controlled to optically scan the surface of the sample 323 two-dimensionally to form an electrostatic latent image on the sample 323. The optical scanning device 500 is adjusted so that a light spot having a desired beam diameter and beam profile is formed on the surface of the sample 323.

The exposure energy required for forming the electrostatic latent image is determined by the sensitivity characteristic of the sample, but is usually about ² to 10 mJ / m ² . For samples with low sensitivity, the required exposure energy may be 10 mJ / m ² or more. The charging potential and necessary exposure energy are set in accordance with the photosensitive characteristics of the sample and process conditions. The exposure conditions of the electrostatic latent image measuring device 300 are the same as the exposure conditions adapted to the image forming apparatus 1000.

  By calculating the environment of the electrostatic field and the electron trajectory in advance and correcting the detection result based on the calculation result, the profile of the electrostatic latent image can be obtained with high accuracy.

  As described above, by using the electrostatic latent image measuring device 300, the electric charge distribution, surface potential distribution, electric field intensity distribution, and electric field intensity in the direction perpendicular to the sample surface can be accurately measured. Can be sought.

● Effect ●
As described above, according to the exposure method according to the present embodiment, the following effects can be obtained.

  According to the exposure method according to the present embodiment, an effect equivalent to that of space-concentrated exposure (beam diameter reduction) can be obtained by performing TC exposure in which exposure is performed with a strong light output in a short time. According to the exposure method according to the present embodiment, an electrostatic latent image having a small area and a depth can be formed, so that a high-resolution image can be formed.

  By using the collation pattern, the exposure pattern can be determined without performing simple operations such as addition processing and multiplication processing, and the processing speed can be increased.

  By using a two-dimensional array collation pattern for at least the up-and-down folding process, it is possible to process a plurality of pixels at the same time in a minimum of one clock, and the processing speed can be greatly improved.

  By performing the exception process before the folding process, it is possible to realize high image quality without drowning even for a narrow image.

  According to the exposure method according to the present embodiment, conditions such as the processing mode can be properly used according to the image and environmental conditions.

  In the exposure method according to the present embodiment, exposure pixels are concentrated on the inner side (center portion) of input image data, and exposure is performed with a light output value stronger than that of standard exposure. Thereby, according to the exposure method according to the present embodiment, an image faithful to the target image can be output at a desired image density even with a fine image pattern.

  According to the exposure method according to the present embodiment, TC is applied to various image patterns by increasing the light output value of the exposure unit pixel using the pixel serving as the boundary between the image unit and the non-image unit as a high output exposure pixel group. Exposure can be applied.

  According to the exposure method according to the present embodiment, when the light output value of the high output exposure pixel group exceeds a predetermined maximum light output value, the light output value is distributed to adjacent image pixels for exposure. Thereby, according to the exposure method according to the present embodiment, even when the maximum light output value cannot be set high, the image density can be maintained and high image quality can be realized.

  The exposure method according to the present embodiment converts a pixel of an image part at the boundary between an image part and a non-image part into a non-exposure pixel, and simultaneously outputs a light output value comparable to the non-exposure pixel to a high-power exposure pixel group The exposure is performed by adding to the pixels of the image portion adjacent to. By doing in this way, according to the exposure method concerning this Embodiment, TC exposure can be applied to various image data, such as a character image, a reverse character image, a dither, and a line image.

  According to the exposure method according to the present embodiment, when the light output value of the high-power exposure pixel group exceeds the maximum light output value, the light output value is not added, so that it is not necessary to perform exception processing, and the simple TC exposure can be applied to various images with simple processing.

  According to the exposure method of the present embodiment, when adding a light output value to a high output exposure pixel group, if the high output exposure pixel group has already added a light output value, the addition is possible. Since the processing is performed for the number of pixels, TC exposure can be performed under optimum conditions.

  In the exposure method according to the present embodiment, the light source modulation data generation circuit 407 recognizes the state of the image based on information provided from the controller side, such as an image processing circuit or a tag bit, and is optimal for each image. Sets the number of folded pixels. Thereby, according to the exposure method according to the present embodiment, it is possible to provide the best image that maximizes the capability of the image forming apparatus.

  According to the exposure method according to the present embodiment, the dot pattern is improved by reducing the weak electric field region, such as the dither portion, where the image patterns are adjacent to each other and there are many regions where the latent image electric field tends to be small. Can be made.

  According to the exposure method of the present embodiment, since the image quality of the image is improved at the electrostatic latent image stage, it is possible to stably realize a high quality image of a minute character image, particularly a reversed character image.

  Since the exposure method according to the present embodiment is a simple method, various images can be processed at high speed.

  According to the exposure method of the present embodiment, the integrated light quantity of the standard exposure and the TC exposure can be matched by intentionally increasing the maximum light output value using PM + PWM modulation. An image can be formed to increase the resolving power.

  According to the image forming apparatus according to the present embodiment, it is possible to provide a high-density and high-quality image forming apparatus by developing and visualizing the exposure method according to the present embodiment.

  The image forming apparatus according to the present embodiment is particularly suitable for an image forming apparatus equipped with a multi-beam scanning optical system such as a VCSEL.

DESCRIPTION OF SYMBOLS 100 Image processing apparatus 101 Image processing unit 104 Optical writing output part 300 Electrostatic latent image measuring device 410 Light source drive part 1000 Laser printer (image forming apparatus)
1010 Optical scanning device (electrostatic latent image forming device)
1030 Photosensitive drum (image carrier)

JP 2005-193540 A JP 2008-153742 A JP 2012-15864 A JP 2007-190787 A

Claims (11)

A method of forming an electrostatic latent image corresponding to the image pattern by an exposure step of exposing the surface of the image carrier with light corresponding to an image pattern including an image portion and a non-image portion,
The image portion is composed of a plurality of pixels.
Each of the pixels in the image portion is collated with an image pattern in the vicinity of the pixel and a matching pattern composed of a plurality of pixels, whereby at least the non-pixels among the pixels constituting the image portion. The pixel at the boundary with the image part is a non-exposed pixel,
A high-power exposure pixel in which at least a pixel adjacent to the non-exposure pixel among pixels constituting the image portion is exposed with light having a light output value higher than a predetermined light output value necessary for exposing the image portion. and to determine is executed,
The collation pattern is a symmetric two-dimensional array, and when the image pattern has a portion that matches the collation pattern, the determination is performed on the pixels of the image portion corresponding to the pixels on the symmetry axis of the collation pattern. The number of pixels on one side of the two-dimensional array is the sum of the number of pixels in one continuous column determined as the non-exposure pixel and the number of pixels in one continuous column determined as the high-power exposure pixel. More than twice
An image forming method. A method of forming an electrostatic latent image corresponding to the image pattern by an exposure step of exposing the surface of the image carrier with light corresponding to an image pattern including an image portion and a non-image portion,
The image portion is composed of a plurality of pixels.
Each of the pixels of the image portion includes an image pattern in the vicinity of the pixel and a one-dimensional array verification pattern composed of a plurality of pixels , the relative of the verification pattern of the one-dimensional array and the image pattern By comparing the position with a first direction that is one of the four directions of up, down, left, and right , at least a pixel that is at the boundary with the non-image portion is a non-exposed pixel among the pixels constituting the image portion. age,
A high-power exposure pixel in which at least a pixel adjacent to the non-exposure pixel among pixels constituting the image portion is exposed with light having a light output value higher than a predetermined light output value necessary for exposing the image portion. and to determine is executed,
With respect to the image pattern for which the determination has been performed, an image pattern in the vicinity of the pixel and a collation pattern of the one-dimensional array have a relative position of the collation pattern of the one-dimensional array and the image pattern. Collating in a second direction different from the first direction among the four directions, and determining the light output value of the pixels constituting the image portion,
An image forming method. When the number of pixels in one continuous column of the image portion is less than twice the sum of the number of pixels to be the non-exposure pixel and the number of pixels to be the high output exposure pixel, A process for making a portion of the high-power exposure pixels a part is performed before the determination.
The image forming method according to claim 1 or 2 . A method of forming an electrostatic latent image corresponding to the image pattern by an exposure step of exposing the surface of the image carrier with light corresponding to an image pattern including an image portion and a non-image portion,
The image portion is composed of a plurality of pixels.
Each of the pixels in the image portion is collated with an image pattern in the vicinity of the pixel and a matching pattern composed of a plurality of pixels, whereby at least the non-pixels among the pixels constituting the image portion. The pixel at the boundary with the image part is a non-exposed pixel,
A high-power exposure pixel in which at least a pixel adjacent to the non-exposure pixel among pixels constituting the image portion is exposed with light having a light output value higher than a predetermined light output value necessary for exposing the image portion. and to determine is executed,
When the number of pixels in one continuous column of the image portion is less than twice the sum of the number of pixels to be the non-exposure pixel and the number of pixels to be the high output exposure pixel, A process for making a portion of the high-power exposure pixels a part is performed before the determination.
An image forming method. Each of the pixels of the image portion is collated with a plurality of the collation patterns, whereby the determination is executed.
The image forming method according to claim 1 . The collation pattern is a symmetric two-dimensional array, and when the image pattern has a portion that matches the collation pattern, the determination is performed on the pixels of the image portion corresponding to the pixels on the symmetry axis of the collation pattern. Is executed,
The image forming method according to claim 3 or 4 . The sum of values obtained by subtracting the predetermined light output value from the light output value of light exposed to the high output exposure pixel is the light output value of light exposed to the non-exposed pixel from the predetermined light output value. Equal to the sum of the subtracted values,
The image forming method according to claim 1. An image forming apparatus that forms an electrostatic latent image corresponding to the image pattern by exposing the surface of the image carrier with light according to an image pattern including an image portion and a non-image portion,
A light source for irradiating the light;
A light source driving unit that generates a light source driving current for driving the light source;
An optical system for guiding the light emitted from the light source to the image carrier;
Having
The image portion is composed of a plurality of pixels.
The light source driving unit is
For each of the pixels constituting the image portion, at least the non-image portion of the pixels constituting the image portion by collating an image pattern in the vicinity of the pixel with a matching pattern composed of a plurality of pixels. And identify the pixel at the boundary of
A high-power exposure pixel in which at least a pixel adjacent to the non-exposure pixel among pixels constituting the image portion is exposed with light having a light output value higher than a predetermined light output value necessary for exposing the image portion. And make a decision
Driving the light source with an output value corresponding to the identified high-power exposure pixel and the non-exposure pixel ,
The collation pattern is a symmetric two-dimensional array, and when the image pattern includes a portion that matches the collation pattern, the light source driving unit is configured to store the image portion corresponding to the pixel on the symmetry axis of the collation pattern. The determination is performed on the pixels, and the number of pixels on one side of the two-dimensional array is determined as the number of pixels in one continuous column determined as the non-exposure pixel and the continuous 1 determined as the high output exposure pixel. More than twice the sum of the number of pixels in the column,
An image forming apparatus. An image forming apparatus that forms an electrostatic latent image corresponding to the image pattern by exposing the surface of the image carrier with light according to an image pattern including an image portion and a non-image portion,
A light source for irradiating the light;
A light source driving unit that generates a light source driving current for driving the light source;
An optical system for guiding the light emitted from the light source to the image carrier;
Having
The image portion is composed of a plurality of pixels.
The light source driving unit is
For each of the pixels of the image portion, at least the non-image portion of the pixels constituting the image portion by collating an image pattern in the vicinity of the pixel with a matching pattern composed of a plurality of pixels. And identify the pixel at the boundary of
  A high-power exposure pixel in which at least a pixel adjacent to the non-exposure pixel among pixels constituting the image portion is exposed with light having a light output value higher than a predetermined light output value necessary for exposing the image portion. And make a decision
  Driving the light source with an output value corresponding to the identified high-power exposure pixel and the non-exposure pixel,
  When the number of pixels in one continuous column of the image portion is less than twice the sum of the number of pixels to be the non-exposure pixel and the number of pixels to be the high output exposure pixel, Performing a process of making a part of the high-power exposure pixels a part before the determination;
Image forming apparatus. A method for producing a printed matter comprising a step of forming an electrostatic latent image corresponding to the image pattern by exposing the surface of the image carrier with light according to an image pattern including an image portion and a non-image portion. ,
The image portion is composed of a plurality of pixels.
Each of the pixels constituting the image portion is collated with an image pattern in the vicinity of the pixel and a matching pattern composed of a plurality of pixels, so that at least the non-image among the pixels constituting the image portion. The pixel at the boundary with the part is a non-exposed pixel,
A high-power exposure pixel in which at least a pixel adjacent to the non-exposure pixel among pixels constituting the image portion is exposed with light having a light output value higher than a predetermined light output value necessary for exposing the image portion. And the decision
The collation pattern is a symmetric two-dimensional array, and when the image pattern has a portion that matches the collation pattern, the determination is performed on the pixels of the image portion corresponding to the pixels on the symmetry axis of the collation pattern. The number of pixels on one side of the two-dimensional array is the sum of the number of pixels in one continuous column determined as the non-exposure pixel and the number of pixels in one continuous column determined as the high-power exposure pixel. More than twice
Print production method. A method for producing a printed matter comprising a step of forming an electrostatic latent image corresponding to the image pattern by exposing the surface of the image carrier with light according to an image pattern including an image portion and a non-image portion. ,
The image portion is composed of a plurality of pixels.
Each of the pixels constituting the image portion is collated with an image pattern in the vicinity of the pixel and a matching pattern composed of a plurality of pixels, so that at least the non-image among the pixels constituting the image portion. The pixel at the boundary with the part is a non-exposed pixel,
A high-power exposure pixel in which at least a pixel adjacent to the non-exposure pixel among pixels constituting the image portion is exposed with light having a light output value higher than a predetermined light output value necessary for exposing the image portion. And the decision
When the number of pixels in one continuous column of the image portion is less than twice the sum of the number of pixels to be the non-exposure pixel and the number of pixels to be the high output exposure pixel, A process for making a portion of the high-power exposure pixels a part is performed before the determination.
Print production method.