JP5761279B2 - Image forming apparatus, image forming method, image forming program, and recording medium - Google Patents

Description

  The present invention relates to image formation, and more particularly to an image forming apparatus, an image forming method, an image forming program, and a recording medium for forming a multi-beam latent image.

  As the functions of the image forming apparatus are improved, the image forming speed (PPM: Prints Per Minutes) per unit time of the image forming apparatus is also increasing. In recent years, an image forming apparatus that performs multi-beam exposure using a surface emitting laser (hereinafter referred to as a VCSEL) has been proposed in order to perform higher-speed and high-definition image formation. In addition, image forming apparatuses are also provided with models that perform duplex printing in response to requests for resource saving.

For this reason, in the automatic double-sided apparatus, the time interval from the first side recording to the second side recording of the paper tends to be shortened as the image forming speed is improved. For example, as a high-speed model, there is a model that is performed within 10 seconds from the first side printing to the second side printing. This is also related to the downsizing of the image forming apparatus, and the conveyance distance from the thermal fixing corresponding to the recording on the first side of the paper to the recording on the second side tends to be short, so the paper comes off from the high temperature portion. In addition to the time interval, besides the time interval, the printing paper is placed in an environment that is thermally affected and is not easily cooled.
When double-sided recording is performed in such a state, the images printed on the first and second sides corresponding to the front and back sides of the paper have heat and humidity fluctuations when high-quality paper having a thickness of about 80 μm is used as printing paper. It has been confirmed that a magnification difference of 0.2% to 0.4% occurs.

  Conventionally, with respect to the above-described problems, Japanese Patent No. 3373266 (Patent Document 1) provides an image forming apparatus with a sub-scanning magnification changing function, and reduction by thinning out sub-scanning image data or image data. It was expanding by addition.

  Also by the method described in Patent Document 1, it is possible to eliminate the magnification difference. However, as the image to be formed becomes higher in definition, for example, in an image having periodicity in which one line is formed every five lines, density unevenness is obtained when lines are thinned out or added for magnification adjustment. It has been confirmed that global image defects such as moire and the like occur remarkably.

In order to solve the above-described problems and achieve the object, an image forming apparatus according to the present invention forms a latent image based on a light source including a plurality of laser elements and a plurality of laser beams emitted from the light source. An optical system, a resolution converter that increases the resolution of at least the pixels of the input image data in the sub-scanning direction in units of divided pixels corresponding to the spatial size of the laser beam emitted from the light source, An allocation unit that allocates channels of the plurality of laser elements that perform laser irradiation corresponding to the divided pixels with respect to the divided pixels included in the image data having the resolution, and changes to the image data to which the channels are allocated. A scaling unit that scales the image data by adding or deleting divided pixels according to a magnification command signal, and a preceding unit that scales the image data according to the image data scaled by the scaling unit And a drive control unit for drive control of the light source. The present invention also provides an image forming method, an image forming program, and a recording medium that are executed by the image forming apparatus.

  In other words, according to the present invention, the scaling process can be controlled at the level of the semiconductor laser element, and high-speed printing and high speed can be achieved when considering both-sides without causing global image deterioration such as moire caused by the scaling process. There is an effect that it is possible to provide an image forming apparatus, an image forming method, an image forming program, and a recording medium suitable for fine image formation.

1 is a diagram illustrating an embodiment of an image forming apparatus. It is a figure which shows the example in case a light source unit is comprised from a semiconductor laser array or a surface emitting laser. It is the figure which showed the schematic perspective view in case the optical apparatus containing VCSEL exposes a photosensitive drum. FIG. 2 is a schematic functional block diagram of a control unit of the image forming apparatus. It is the figure which showed the detailed functional block of GAVD. FIG. 6 is a functional block diagram of the image processing unit illustrated in FIG. 5. It is a figure which shows the example of operation | movement of an image path selector when not adding a pixel bit. It is a figure which shows the example (1st scan-3rd scan) of operation | movement of the image path selector at the time of adding a pixel bit. It is a figure which shows the example of the relationship between image data, R address, and F address. It is a figure which shows the example of the relationship between a unit pixel and a laser spot. It is a figure which shows the example at the time of making image data 4 times dense in the main scanning direction and the subscanning direction, or 4 times dense only in the subscanning direction. FIG. 6 is a diagram illustrating a flowchart of an embodiment of a scaling process executed by the image forming apparatus. It is a figure which shows the example of the image data after performing the scaling process shown in FIG. It is a figure which shows the example of the image data after performing the process which adds or deletes a line only to a subscanning direction. It is the figure which showed embodiment of the image bit process with respect to the image data of the scaling process in this embodiment. It is the figure which showed other embodiment of the image bit process with respect to the image data of the scaling process in this embodiment. It is the figure which showed other embodiment of the image bit process with respect to the image data of the scaling process in this embodiment.

  Hereinafter, although this invention is demonstrated with embodiment, this invention is not limited to embodiment mentioned later. FIG. 1 is a schematic diagram showing a mechanical configuration of the image forming apparatus according to the present embodiment. An image forming apparatus 100 according to the present embodiment includes an optical device 102 including optical elements such as a VCSEL 200 (see FIGS. 2 and 3) and a polygon mirror 102a, and an image forming unit including a photosensitive drum, a charging device, a developing device, and the like. 112 and a transfer unit 122 including an intermediate transfer belt and the like. The optical device 102 includes a VCSEL 200 as a semiconductor laser. In the embodiment shown in FIG. 1, the light beam emitted from the VCSEL 200 (not shown in FIG. 1) is once condensed by a first cylindrical lens (not shown), and then reflected by the polygon mirror 102a to the reflection mirror 102b. Deflected.

  Here, the VCSEL (Vertical Cavity Surface Emitting Laser) 200 is a surface emitting semiconductor laser in which a plurality of light sources (semiconductor lasers) are arranged in a lattice pattern on the same chip. Various techniques are known as an image forming apparatus using such a VCSEL 200, and the VCSEL 200 is incorporated in the optical device 102 of the image forming apparatus 100 according to the present embodiment with the same configuration as those known techniques. It is. FIG. 2 is a configuration diagram of the VICSEL 200 incorporated in the optical device 102 according to the present embodiment. As shown in FIG. 2, the VCSEL 200 of the present embodiment forms a semiconductor laser array in which a plurality of light sources 1001 (a plurality of semiconductor lasers) are arranged in a lattice pattern. The arrangement direction of the plurality of light sources 1001 is provided to be inclined at a predetermined angle θ with respect to the rotation axis of the polygon mirror 102a as a deflector.

  In FIG. 2, the vertical arrangement direction of the light sources is a to c and the horizontal arrangement direction is 1 to 4. For example, the upper left light source 1001 in FIG. 2 is represented as a1. When the light source 1001 is arranged with the polygon mirror angle θ, the light source a1 and the light source a2 are exposed at different scanning positions, and one pixel (one pixel) is constituted by the two light sources, that is, in FIG. Consider a case where one pixel is realized with two light sources. For example, if one pixel is composed of two light sources a1 and a2, and one pixel is composed of two light sources a3 and a4, a pixel as shown at the right end of FIG. When the vertical direction in the figure is the sub-scanning direction, it is assumed that the distance between the centers of the pixels constituted by the two light sources is equivalent to 600 dpi. At this time, the center distance between the two light sources constituting one pixel is equivalent to 1200 dpi, and the light source density is twice the pixel density. Therefore, by changing the light quantity ratio of the light source constituting one pixel, the center of gravity of the pixel can be shifted in the sub-scanning direction, and high-precision image formation can be realized.

  The image forming apparatus 100 constitutes a post-object type optical device 102 that does not use an fθ lens. In the illustrated embodiment, a number of light beams L corresponding to each color of cyan (C), magenta (M), yellow (Y), and black (K) are generated, reflected by the reflecting mirror 102b, and second cylindrical. After being condensed again by the lens 102c, the photosensitive drums 104a, 106a, 108a, 110a are exposed.

  Since the irradiation of the light beam L is performed using a plurality of optical elements as described above, timing synchronization is performed in the main scanning direction and the sub-scanning direction. Hereinafter, the main scanning direction is defined as the light beam scanning direction, and the sub-scanning direction is defined as a direction orthogonal to the main scanning direction.

  Each of the photosensitive drums 104a, 106a, 108a, and 110a includes a photoconductive layer including at least a charge generation layer and a charge transport layer on a conductive drum such as aluminum. The photoconductive layer is disposed corresponding to each of the photosensitive drums 104a, 106a, 108a, and 110a, and is charged with a surface charge by the chargers 104b, 106b, 108b, and 110b including a corotron, a scorotron, or a charging roller. Is granted.

  The electrostatic charges imparted on the photosensitive drums 104a, 106a, 108a, 110a by the respective chargers 104b, 106b, 108b, 110b are imagewise exposed by the light beam L to form an electrostatic latent image. The electrostatic latent images formed on the photoconductive drums 104a, 106a, 108a, and 110a are developed by the developing devices 104c, 106c, 108c, and 110c including a developing sleeve, a developer supplying roller, a regulating blade, and the like. Is formed.

  The developer carried on the photosensitive drums 104a, 106a, 108a, and 110a is transferred onto the intermediate transfer belt 114 that moves in the direction of arrow A by the conveying rollers 114a, 114b, and 114c. The intermediate transfer belt 114 is conveyed to the secondary transfer unit while carrying C, M, Y, and K developers. The secondary transfer unit includes a secondary transfer belt 118 and conveying rollers 118a and 118b. The secondary transfer belt 118 is conveyed in the direction of arrow B by the conveyance rollers 118a and 118b. An image receiving material 124 such as high-quality paper or a plastic sheet is supplied to the secondary transfer portion from an image receiving material storage portion 128 such as a paper feed cassette by a conveying roller 126.

  The secondary transfer unit applies a secondary transfer bias to transfer the multicolor developer image carried on the intermediate transfer belt 114 onto the image receiving material 124 held by suction on the secondary transfer belt 118. The image receiving material 124 is supplied to the fixing device 120 along with the conveyance of the secondary transfer belt 118. The fixing device 120 includes a fixing member 130 such as a fixing roller including silicone rubber, fluorine rubber, and the like, pressurizes and heats the image receiving material 124 and the multicolor developer image, and forms the printed material 132 as the image forming apparatus 100. To the outside. After the multicolor developer image is transferred, the transfer belt 114 is supplied to the next image forming process after the transfer residual developer is removed by the cleaning unit 116 including a cleaning blade.

  FIG. 3 is a schematic perspective view when the optical device 102 including the VCSEL 200 exposes the photosensitive drum 104a. The light beam L emitted from the VCSEL 200 is collected by the first cylindrical lens 202 used for shaping the light beam bundle, passes through the reflection mirror 204 and the imaging lens 206, and is then deflected by the polygon mirror 102a. . The polygon mirror 102a is rotationally driven by a spindle motor that rotates several thousand to several tens of thousands. The light beam L reflected by the polygon mirror 102a is reflected by the reflection mirror 102b and then reshaped by the second cylindrical lens 102c to expose the surface of the photosensitive drum 104a.

  In order to synchronize the scanning start timing of the light beam L in the sub-scanning direction, a reflection mirror 208 is disposed. The reflection mirror 208 reflects the light beam L to the synchronization detection device 210 including a photodiode or the like before starting scanning in the sub-scanning direction. When detecting the light beam, the synchronization detection device 210 generates a synchronization signal to start sub-scanning, and synchronizes processing such as generation of a drive control signal to the VCSEL 200.

  The VCSEL 200 is driven by a pulse signal sent from a GAVD 310, which will be described later. As will be described later, the light beam L is exposed at a position corresponding to a predetermined image bit of the image data, and an electrostatic latent image is formed on the photosensitive drum 104a. Form.

  FIG. 4 is a schematic functional block diagram of the control unit 300 of the image forming apparatus 100. The control unit 300 is configured as a scanner unit 302, a printer unit 308, and a main control unit 330. The scanner unit 302 functions as a means for reading an image. A VPU 304 that performs A / D conversion on a signal read by the scanner to perform black offset correction, shading correction, and pixel position correction, and a mainly acquired image, An IPU 306 that performs image processing for digital conversion from image data in the RGB color system to the CMYK color system. The read image acquired by the scanner unit 302 is sent to the printer unit 308 as digital data.

  The printer unit 308 includes a GAVD 310 that functions as a control unit that performs drive control of the VCSEL 200, a supply LD driver 312 that supplies the semiconductor laser element with current for driving the semiconductor laser element using a drive control signal generated by the GAVD 310, and 2 And a VCSEL 200 on which dimensionally arranged semiconductor laser elements are mounted. The GAVD 310 according to the present embodiment performs high resolution processing on the image data sent from the scanner unit 302 by dividing the pixel data into pixel data so as to correspond to the spatial size of the semiconductor laser element emitted by the VCSEL 200. To do.

  The scanner unit 302 and the printer unit 308 are connected to the main control unit 330 via the system bus 316, and image reading and image formation are controlled by commands from the main control unit 330. The main control unit 330 includes a central processing unit (hereinafter referred to as a CPU) 320 and a RAM 322 that provides a processing space used by the CPU 320 for processing. The CPU 320 can be any CPU known so far, for example, CISC (Complex Instruction Set Computer) such as the PENTIUM (registered trademark) series or its compatible CPU, RISC (Reduced Instruction Set Computer) such as MIPS, etc. Can be used. The CPU 320 receives a command from the user via the interface 328, calls a program module that executes processing corresponding to the command, and executes processing such as copying, facsimile, scanner, and image storage. Further, the main control unit 330 includes a ROM 324, and stores initial setting data, control data, programs, and the like of the CPU 320 so that the CPU 320 can use them. The image storage 326 is configured as a fixed or detachable memory device such as a hard disk device, an SD card, or a USB memory. The image storage 326 stores the image data acquired by the image forming apparatus 100 and can be used for various processes by the user. It is said.

  When the printer unit 308 is driven for the image data acquired by the scanner unit 302 to output an image as an electrostatic latent image on the photosensitive drum 104a or the like, the CPU 320 controls the main scanning direction of an image receiving material such as fine paper or plastic film. And sub-scanning position control is executed. The CPU 320 outputs a start signal to the GAVD 310 when starting scanning in the sub-scanning direction. When the GAVD 310 receives the start signal, the IPU 306 starts the scanning process. Thereafter, the GAVD 310 receives the image data stored in the buffer memory or the like, thereafter processes the received image data, and outputs the processed image data to the LD driver 312. When the LD driver 312 receives image data from the GAVD 310, the LD driver 312 generates a drive control signal for the VCSEL 200. Thereafter, the LD driver 312 sends the drive control signal to the VCSEL 200, thereby turning on the VCSEL 200. The LD driver 312 drives the semiconductor laser element using PWM control or the like. The VCSEL 200 described in the present embodiment includes 8 channels of semiconductor laser elements, but the number of channels of the VCSEL 200 is not limited.

  FIG. 5 shows more detailed functional blocks of the GAVD 310. The GAVD 310 includes a memory 340 such as a FIFO buffer that receives the synchronization signal and stores and stores image data sent from the IPU 306, and performs image processing on the image data transmitted from the IPU 306 in a first-in / first-out manner. Part 342. The image processing unit 342 reads the image data from the memory 340, performs resolution conversion of the image data, assignment of the semiconductor laser element channel, and addition / deletion of image bits (that is, correction pixels for scaling the image data). Processing (that is, image data correction processing) is executed. In the image data, a position where the photosensitive drum 104a is exposed is defined by a main scanning line address value defined in the main scanning direction and a sub scanning line address value defined in the sub scanning direction. Hereinafter, in the present embodiment, the address coordinate is an address value that gives a specific image bit when image data is designated by a main scanning line address value (R address value) and a sub scanning line address value (F address value). Define as a set of Note that these address values are determined by an address generation unit 354 as will be described later. Further, these address coordinates are determined for each pixel (that is, a pixel column) arranged in a line in the main scanning direction and the sub-scanning direction. Then, the image path selector 358 (described later) applies, for each pixel column, a pixel located at the coordinate address (that is, the pixel position) designated by the address generation unit 354 described later with the R address value and the F address value. Then, correction processing such as inserting pixel bits is performed.

  The output data control unit 344 converts the output data, which is a write signal corresponding to the image data generated by the image processing unit 342, from the F address value and the sub-scanning speed into a time-series drive pulse, and further, a synchronization detection device A synchronization control signal for giving a synchronization signal to 210 is added and generated. The generated drive control signal is transmitted to the LD driver 312 to drive a VCSEL (not shown). The output data control unit 344 receives a synchronization signal from the synchronization detection device 210 and synchronizes transmission of the drive control signal to the LD driver 312. The processing of the memory 340, the image processing unit 342, and the output data control unit 344 is synchronized with the operation clock by the PLL 346.

  FIG. 6 is a functional block diagram of the image processing unit 342 shown in FIG. The resolution conversion unit 350 divides the unit pixel of the image data acquired from the memory 340 in accordance with the number of channels and the size of the VCSEL 200 and creates divided pixels. Thereafter, a laser element channel for performing irradiation of the pixel is assigned to the divided pixel. In addition, the resolution conversion unit 350 selects 2n-fold density processing (n is a positive integer) or 2n line processing when determining resolution, and determines drive assignment of laser element channels.

  The sub-scanning scaling unit 352 includes an image path selector 358 and a shift holding memory 356. The sub-scan scaling unit 352 receives an F address and an R address used for forming an image from the address generation unit 354, and the address value to be processed adds an address value for adding or deleting an image bit. Judge whether to include. The sub-scanning scaling unit 352 generates, for example, a scaling command signal such as an addition flag or a deletion flag for the address at which the image bit is added / deleted, and passes it to the image path selector 358 and the shift holding memory 356. The shift holding memory 356 stores a shift amount for shifting an image bit, and counts and holds a scaling command signal. When the enlargement / magnification command signal is set at the time of image enlargement, the image path selector 358 sets the data of the image bit to white data, and shifts the subsequent image data by one bit. When the scaling command signal is not set, the input data from the resolution conversion unit 350 is selected and output based on the shift amount from the shift holding memory 356. In this embodiment, when the 8ch VCSEL 200 is used as a semiconductor laser, a signal indicating a position to be added / deleted and a signal indicating a shift amount are allocated for 8ch and used for driving the VCSEL 200. The calculation of addition / deletion of image bits can be configured as a dedicated module as long as it is an appropriate function unit of the image processing unit 342, or can be configured as a part of other modules. The reason for counting the magnification command signal is to specify the position at which the image bit is added at the beginning of the second scan after the image bit is added at the first scan, for example, when shifting the image bit. is there.

  The operation of the image path selector 358 will be described with reference to FIGS. The attention data 602 in FIGS. 7A and 7B represents a bit value for one pixel, and the data for one pixel is represented by sub-coordinates for 8ch. It is bit data assigned to a specific main scanning coordinate position. As the input data 600, the attention data 602 and the scaling data for designating the shift unit for sub-scanning scaling are always read from the memory 340 in the previous stage, and the same processing is performed for all the lines, and the resolution conversion unit 350 is input. At the time of unchanging magnification shown in FIG. 7A, since the magnification command signal is not set, the shift amount (shift) from the shift holding memory 356 is set to 0, and as shown in FIG. The image data 602 is transferred as output data 604 which is a write signal in this embodiment.

  Next, the operation when the magnification command signal is set will be described with reference to FIG. FIG. 7B shows a case where white is added to the sub-coordinate 1 of the attention data 602 in the first scan (A). A signal indicating the addition of an image bit is set with an address value corresponding to CH1, and the bit data of CH1 is replaced so as to correspond to a white pixel and set as data in CH1 of output data 606. Then, the count value 1 corresponding to the addition corresponding to CH1 is registered in the shift holding memory 356.

  The data of CH2 to CH7 is shifted to the sub-coordinate value with the channel shift amount minus 1 as the sub-coordinate value of the output data 606. At this time, the image path selector 358 can add image bits by assigning bit data of the channel of interest data corresponding to the channel shift amount −1 to CH2 to CH7 of the output data 606. In the output data 606, image bits corresponding to white are added to the data of interest, and used as a write signal. The output data control unit 344 converts the write signal in time series to drive the VCSEL 200 drive pulse. And image formation is performed. The above-described processing is performed in units of main scanning, data about the next pixel in the main scanning direction is sequentially read from the memory 340, and image formation is performed in the main scanning direction.

  As described above, white pixels are added in the first scan (A), and the sub-coordinate values of CH1 to CH7 in the output data 606 are shifted, so that in the second scan (B), as shown in FIG. As described above, even when no white pixel is added, the sub-coordinate values of the output data 606CH8 to CH15 are shifted by -1, and a white pixel is added in the third scan (C) as in the first scan. As shown in FIG. 7D, the sub-coordinate values of the output data 606CH16 to CH23 are shifted by -2.

  FIGS. 8A and 8B show the relationship between image data, R address, and F address, and the relationship between the unit pixel and the laser spot by the VCSEL 200. FIG. 8A illustrates the relationship between the image data and each address, and FIG. 8B illustrates the relationship between the unit pixel and the laser spot. As shown in FIG. 8A, the R address 702 determines the pixel position in the main scanning direction in the image data 700, and has a value corresponding to the writable range in the feed direction of the image receiving material. The F address 704 is a value that determines the pixel position in the sub-scanning direction in the image data 700. Corresponding to these address values, feeding in the main scanning direction and lighting control of the VCSEL 200 are performed, and the light beam scans on the photosensitive drum to form an electrostatic latent image subjected to magnification control.

  FIG. 8-2 shows a laser spot 708 that irradiates the pixel region 706. In this embodiment, the VCSEL 200 includes an 8ch semiconductor laser element. The laser spot 702 of the semiconductor laser element is configured in two rows with 4 channels per row. Further, the laser spots 702 constituting the row are arranged at intervals of 2.4 μm in the sub-scanning direction and at intervals of 30 μm in the main scanning direction. That is, the laser spot 708 illustrated in FIG. 8B irradiates the pixel region 706 with a resolution that divides the pixel region 706 into four in the sub-scanning direction, and also divides the pixel region into four in the main scanning direction. . In the embodiment of FIG. 8-2, the laser modulation pitch (beam pitch) in the sub-scanning direction is 1/4 of the pixel resolution to be read. Specifically, the pixel input resolution is 1200 dpi (dots per inch). In this case, as an effective resolution, a latent image can be formed with a beam pitch of 4800 dpi.

  FIG. 9A is a schematic diagram for explaining an example of the high resolution processing executed by the resolution conversion unit 350. The resolution conversion unit 350 converts the image data 808 having the input resolution 1200 dpi and 2 bits of the unit pixel 800 into 16 pieces of 1-bit divided pixel data 802 having the output resolution 4800 dpi shown in the example shown in FIG. By performing the conversion, high resolution processing is performed in which so-called quadruple density processing is executed in the main scanning direction and the sub-scanning direction. Each divided pixel data 802 is assigned with a channel of a semiconductor laser element in charge of exposure, and is used to generate a drive control signal.

In this embodiment, the high resolution processing is performed in which the image data 808 having the input resolution of 1200 dpi and 2 bits of the unit pixel 800 is converted into the divided pixel data 808 shown in FIG. The high resolution processing is not limited to this. For example, the resolution conversion unit 350 is configured so as to perform high resolution processing in which the image data 808 having the input resolution 1200 dpi and 2 bits of the unit pixel 800 is converted into the divided pixel data shown in FIG. 9B. Also good.
In the example shown in FIG. 9B, a resolution of 1,800 dpi is provided for the main scanning direction and 1,800 dpi for the sub-scanning direction, and the divided pixel data 804 is shown as four lines of 1200 dpi × 4 bits. . That is, the resolution conversion unit 350 is configured to perform a resolution enhancement process for converting the image data 808 having the input resolution 1200 dpi and 2 bits of the unit pixel 800 into the divided pixel data 804 in the example shown in FIG. 9B. May be. Also in this case, a channel of the semiconductor laser element in charge of exposure of each divided pixel data is assigned and provided for generating a drive control signal. 9A or 9B is preferably used in order to eliminate global image defects such as moire in the sub-scanning direction and jagged edges. be able to. Further, in the case of high resolution processing for conversion into divided pixel data shown in FIG. 9B, the number of divided pixels can be reduced to ¼, so that the subsequent processing load can be reduced. it can.

FIG. 10 shows a flowchart of an embodiment of a scaling process executed by the image forming apparatus 100.
The scaling process shown in FIG. 10 starts from step S900, and the address generation unit 354 sets an R address value in step S901. In step S <b> 902, the address generation unit 354 calculates the F address value to be added / deleted using the R address by the scaling method used in the image processing unit 342.

  In step S903, the image path selector 358 executes rewriting by incrementing or deleting the set R address value and the calculated F address value after the F address by one line, and performs the sub-scanning line corresponding to the calculated F address. An image bit is set in a pixel given by an address (R address value, F address value). That is, the image path selector 358 performs a correction process on the pixels located at the R address value and the F address value. In addition, when adding a sub-scan line, the F address value is not rewritten in descending order corresponding to the insertion of the sub-scan line, but it can also correspond to the addition of the sub-scan line. It is also possible to generate additional F address values separately using the values of the two sub-scanning lines as indexes and pass them to the output data control unit 344.

  In step S904, the image path selector 358 reads the bit data in the F address range to be processed and transfers it to the output data control unit 344. The output data control unit 344 generates a pulse signal at a timing corresponding to the pixel position and sends it to the LD driver 312 to drive the semiconductor laser element.

  In the processing in step S903, a value corresponding to 1200 dpi can be assigned for one line, but an F address value corresponding to 4800 dpi, which is the resolution in the sub-scanning direction of the VCSEL 200, is assigned in advance to the F address. By controlling the driving of the semiconductor laser element of the VCSEL 200 at the 4800 dpi level, it becomes possible to execute a higher-definition zoom control.

  In step S905, the image path selector 358 determines whether or not the transfer of the pixel data in the default F address range assigned at 1200 dpi has been completed by comparing the F address value or receiving the end character bit, and searches the sub scanning range. If it is determined that the process has been completed (yes), the address generation unit 354 sets the next R address value in step S906. Thereafter, the sub-scanning scaling unit 352 determines whether or not the scanning of the main scanning range is completed in step S907. If the scanning range in the main scanning direction has not ended (no), the process is branched to step S902, and the processes in steps S902 to S907 are repeated.

  On the other hand, if the image path selector 358 determines in step S905 that scanning of the sub-scanning range has not ended (no), the sub-scanning scaling unit 352 branches the processing of step S905 to step S902, and scans it. The processes in steps S902 to S907 are repeated until the F address value in the range ends. If it is determined in step S907 that the address range to be processed for the image receiving material has finally ended (yes), the sub-scan scaling unit 352 branches the process to step S908 and ends the process.

  Hereinafter, with reference to FIGS. 11A to 11B, the image bit processing for the image data of the scaling process in the present embodiment executed in step S903 in FIG. 10 is taken as an example of line insertion. This will be described in detail. FIG. 11A illustrates an embodiment of a scaling process according to the present embodiment, and FIG. 11B is a comparative example illustrating a conventional process for adding a sub-scan line in units of one line. The embodiment illustrated in FIG. 11A is an embodiment in the case of enlarging 6.25% in the sub-scanning direction. This 6.25% enlargement process corresponds to adding one line per 16 lines in the sub-scanning direction of 1200 dpi. At this time, as shown in FIG. 11B, the process of periodically inserting the sub-scan lines is to add 1004 and 1006 to the sub-scan lines along the same F address value at a ratio of 16: 1. As a result, image defects such as moire are caused globally.

  On the other hand, in the present embodiment illustrated in FIG. 11A, an address value for inserting an image bit into the image data 1000 is calculated by the Cycle method in the sub-scanning direction, and the image bit is added. The address value of the image bit added for a predetermined sub-scan line is expressed as (main scan address, sub-scan address) = (x, y), and the inserted image bit 1002 is shown in FIG. .

  The addition of image bits is not necessarily performed at the input resolution of 1200 dpi, and can be performed in the divided pixel order shown in FIG. The Cycle method will be described. In the Cycle method, processing for separating pixels to be inserted as much as possible is executed in order to suppress visual discomfort caused by uneven distribution of pixels into which image bits are inserted. For example, when processing for adding one line per L lines in the sub-scanning direction is performed, the enlargement ratio is {(1 + 1 / L) × 100}%.

  At this time, if the offset in the sub-scanning direction of the image bit to be added is P, the address value of the image bit inserted at the address adjacent to one line in the main scanning direction with the address value of the image bit inserted in the predetermined line as a base point The above distance D1 is given by the following equation (1).

As shown in the above formula (1), when P increases in order from 1, D1 also increases. However, if at least P is less than or equal to s qrt (L), the distance D1 between the inserted image bits is P. The bigger it gets, the bigger it gets. On the other hand, when P increases to L <2P, an image bit to be inserted into the same R address exists in the second adjacent line of the sub-scan line specified by the base address value.

That is, the standards address and the address value of the first insertion image bits, the distance between the reference address and the address value of the second insertion image bits are not allocated evenly to produce an image on irregularities in this case Become.

In the present embodiment, the criteria address and the address value of the first insertion image bit, the distance between the reference address and the address value of the second insertion image bits to insert a picture bit so that allocated evenly, As a result, unevenness in the image does not occur. Further, the address generation unit 354 calculates sqrt (L) . Then, an integer value N closest to the calculated sqrt (L) is determined, and an F address for inserting an image bit is calculated from the R address using the following equation. Hereinafter, this is referred to as a Cycle N method.

In the above formula, when addition / deletion is performed in finer units using the VCSEL 200 or the like, it is also possible to set a division magnification that is a magnification for dividing the pixels in accordance with the number of laser elements of the VCSEL 200. The division magnification can be acquired by the resolution conversion unit 350 performing high resolution conversion processing. For example, when there are four VCSELs per pixel, the same enlargement / reduction can be performed by adding one beam four times the resolution, that is, by adding the line four times with a high-definition line as a unit. A percentage can be given. ModN is an operator that calculates a remainder class of N. In the case of the above-described 16: 1 enlargement ratio, L = 16 and N = 4, and an image is generated for each of the remainders 0, 1, 2, and 3 of the R address value. The value of the F address at which the bit is inserted is periodically reset. In this case, the offset value P (that is, the shift amount of the F address value) between adjacent R address lines is N = 4. In the present embodiment, in consideration of the sub-scanning direction resolution of the VCSEL 200, for example, 1200 dpi is processed at a resolution equivalent to 4800 dpi, and higher-definition and high-precision scaling processing is performed according to the above equation (3). it can. As a result, when the processing of 16 × 4 = 64 lines is completed, the insertion processing for one line with an input resolution of 1200 dpi is completed.

  As described above, by performing the insertion processing in consideration of the resolution in the main scanning direction and the sub scanning direction, the input resolution of the image data is 1200 dpi in both the main scanning direction and the sub scanning direction, When the output resolution is 4800 dpi in both the main scanning direction and the sub-scanning direction, quadruple density image data can be acquired as shown in FIG. Further, when the output resolution is 1200 dpi in the main scanning direction and 4800 dpi in the sub scanning direction, as shown in FIG. 9B, image data that is quadruple density only in the sub scanning direction is acquired. Can do.

  FIG. 11B shows an embodiment of the image bit insertion process when the above formula (3) is used and a 16: 1 enlargement ratio is used. As shown in FIG. 11A, in the insertion of CycleN, image bits are not inserted in the same F address position along the main scanning direction, so that the periodicity is kept finer and the interval between image bits is set to a long period. It becomes possible to make it. In FIG. 11A, the address position where the image bit is inserted is shown as (R address value, F address value).

  Note that even if N is not an integer, the scaling ratio accuracy is reduced, but the scaling process is performed while eliminating the occurrence of global image defects by applying the same process. be able to.

  Further, in each of the above-described equations, the case where the resolution in the main scanning direction and the sub-operation direction are equal has been described as an example. For example, the resolution in the main scanning direction and the resolution in the sub-scanning direction as illustrated in FIG. Since the scaling factor itself does not change even when the values are different, in this case, the scaling process similar to the scaling process described above can be performed by calculating the offset value using the following formula.

In the above formula, V represents the resolution in the sub-scanning direction, and H represents the resolution in the main scanning direction. As shown in the above equation, the CycleN scaling process can be performed by calculating the offset value P in consideration of the ratio between the resolution in the main scanning direction and the resolution in the sub-scanning direction.

  For example, when the resolution in the main scanning direction is 1200 dpi, the resolution in the sub-scanning direction is 4800 dpi, and N = 4, P = 2, and the pixels are separated by 2 pixels in the main scanning direction and 8 pixels in the sub-scanning direction. On the other hand, it is possible to perform scaling processing that has been subjected to correction processing such as addition of image bits.

  In addition, when scaling processing is performed in which the resolution in the main scanning direction and the resolution in the sub-scanning direction are different as described above, the interval between one image bit and the other image bits is the resolution in the main scanning direction and the resolution in the sub-running direction. Are not equal to each other in the main scanning direction and the sub-scanning direction as in the case of the same, but adding image bits at intervals according to the respective resolutions in the main scanning direction and the sub-scanning direction. Since the correction process is performed, it is possible to appropriately prevent image deterioration due to unevenness, moire, and the like associated with the scaling process for pixels located in the main scanning direction and the sub-scanning direction.

  FIG. 12 shows another embodiment of the scaling process executed in step S903 of FIG. The embodiment shown in FIG. 12 is intended to increase the scaling ratio with high accuracy, and the offset value P of the image bit inserted between L of the sub-scan lines is changed between adjacent R address lines. Process. Specifically, the embodiment shown in FIG. 12 can be applied to a case where the scaling factor is 6.66% (corresponding to the addition of one line to 15 lines). In the first embodiment, in this case, N = 4 is adopted as the value of N, and the offset value P = 4 is held. On the other hand, in the second embodiment, since sqrt (15) = 3.87, if integer arithmetic is used, the scaling factor is sacrificed. For this reason, the latest integer value is adopted as the value of N for sqrt (15) as the value of N, and the F address value for inserting the image bit is calculated by combining the value of the offset value P ′ of (N ± 1). .

  In the embodiment to be described, since 15 = 4 × 3 + 3, the image bit is inserted with an offset value P = 4 four times during L, and the image bit insertion with the offset value P = 3 is executed once. For this purpose, various formulations can be performed. For example, the program can be easily programmed by the assembler by executing the processing of the following formula. In the following formula (5), although written in C language, a corresponding assembler can be obtained by using appropriate conversion software.

  In the above equation (5), F_addr is the address value of the sub-scan line to be added, DEV_Mag is the division ratio, N is the latest integer value for sqrt (L), and R_addr is The address value in the main scanning direction, and “%” is a remainder operator shown in C language for convenience.

  As a result of applying the above equation (5), the offset is set to an offset value P = 4 for the values of 1 and 2, and the offset value P = 3 between the remainders of 0 and 3 gives an offset sequence. (4, 4, 3, 4) can be given as In FIG. 12, the hatched sub-scan line 1100 is given an offset value P = 3 corresponding to N = 3, and pixel data can be added per 15 lines. This combination is repeated for the sub-scanning line 1102, and an image bit with an offset value P = 3 is added. Furthermore, even when another offset value P is used in combination, the above equation (5) is corrected and combined so that the offset value is distributed with an optimum offset value per set interval L. Programming and its processing can be executed.

  FIG. 13 shows another embodiment of the scaling process executed by the image processing unit 342. The scaling process shown in FIG. 13 is performed by mixing CycleN and CycleN ′ processes using different N and N ′ values in order to perform a scaling ratio {(1 + 1/15) × 100}%. For example, since the scaling ratio 1/15 adds two lines of image bits for each sub-scanning line 30, considering the elimination of overlap in the cycle switching process, the cycle 4 is set to six times ( Similar effects can be obtained by repeating Cycle 3 once for 24 lines) and the remaining lines. In FIG. 13, line insertion is executed when the F address range indicated by reference numeral 1200 is Cycle 4 and line insertion is executed when the R address range indicated by reference numeral 1202 is Cycle 3.

  FIG. 14 shows still another embodiment of the scaling process executed by the image forming apparatus 100. In the embodiment shown in FIG. 14, the image data 1300 is subjected to processing with periodicity lower than the scaling processing shown in FIGS. It is possible to prevent global image degradation such as moire from the formed line image. In the embodiment shown in Fig. 14, an image bit is added to the position where the R address is (2m + 1 (m is a positive integer) in the first line 1302 of the F address. Then, for example, 6.25% In the case of enlargement, lines 1304 and 1306 are added so that a total of 2 lines are added for 32 lines, where the added lines 1304 and 1306 are referred to as high resolution lines. By repeating until the address is reached, the scaling process can be performed while reducing global moire.

  Regarding the above processing, the following processing can be used as processing for determining the address coordinates into which the image bits are inserted.

(1) When the F address is 0, an R address corresponding to 2m + 1 (m is an integer of 0 or more) is set as an image bit insertion address.
(2) When the F address is larger than 0, according to the remainder of N, the F address corresponding to the R address is determined by the following processing.
(A) When the remainder of N is 0 for the R address to be processed, the F address value is (N, 2 × N).
(B) When the remainder of N is 1 for the R address to be processed, the F address value is (N + L, 2 × N + L).
(C) When the remainder of N of the R address to be processed is 2, the F address value is (N + 0.5L, 2 × N + 0.5L).
(D) When the remainder of N is 3 for the R address to be processed, the F address value is (4 + 1.5L, 8 + 1.5L). Thereafter, (2L × j) is set as an initial value of the next period, and an F address for inserting a sub-scan line is calculated according to (a) to (d) in accordance with the residue class for N = 4 of the R address. Note that j is a positive integer greater than or equal to 0, and is the maximum positive integer that satisfies j ≦ F / 2L.

  The F address value for inserting the sub-scan line for the recursively selected R address can be calculated as follows.

(I) When the remainder of N is 0 for the R address to be processed:
F address value = (N + 2L × j, 2N + 2L × j)
(Ii) When the remainder of N is 1 for the R address to be processed:
F address value = (N + L + 2L × j, 2N + L + 2L × j).
(Iii) When the remainder of N of the R address to be processed is 2, F address value = (N + 0.5L + 2L × j, 2N + 0.5L + 2L × j).
(Iv) When the remainder of N is 3 for the R address to be processed:
F address value = (N + 1.5L + 2L × j, 2N + 1.5L + 2L × j)

  In the embodiment shown in FIG. 14, when an R address having an even F address is set as an image bit insertion address, the processing order of (i) and (ii) is changed, and the processing order of (iii) and (iv) is changed. Can be applied. In the case of L = 16, as shown in FIG. 14, 8 pixels can be added in units of 32 lines, or 4 pixels can be added in units of 16 lines. When calculating the insertion F address of the image bit in units of 16 lines, the smaller value of the values of the above formulas (i) to (iv) is used to correspond to the remainder, and (N + 2L × j), (N + L + 2L × j), (N + 0.5L + 2L × j), and (N + 1.5L + 2L × j). Even in this case, the calculated value can be exchanged by setting the R address value of the image bit inserted when the F address value = 0 to an even number or an odd number.

  Moreover, although the case where L = 16 has been described as an example for the above-described processing, by appropriately combining the methods described in FIGS. 11A to 13, the value of N can be appropriately set regardless of the value of L. By setting, the image bits to be inserted can be appropriately dispersed. The image bit insertion process described above can also be applied to the image bit deletion process.

  In the embodiment shown in FIG. 14, after determining the address of the image data to which the image bit is added as described above, the image bit data to be inserted is transmitted to the output data control unit 344, and the output timing is supported. The generated drive control signal is generated and passed to the LD driver 312. The LD driver 312 drives the semiconductor laser element using the received drive control signal, and forms an image generated as a result of the scaling process on the image receiving material.

  As described above, the image forming apparatus of the present embodiment can control the scaling process at the level of the semiconductor laser element irradiated by the VCSEL, and does not cause global image degradation such as moire accompanying the scaling process. In addition, it is possible to provide an image forming apparatus and an image forming method suitable for high-speed image formation and relative high-speed printing compatibility with double-sided printing and apparatus miniaturization.

  Further, as described above, the image forming apparatus according to the present embodiment executes the sub-scanning magnification correction by a method with few side effects such as moire, the line size is defined at the semiconductor laser element level, and 1 Insert and delete image bits on a pixel-by-pixel basis. In the present invention, the input resolution is defined in association with the divided pixels corresponding to the beam pitch of the semiconductor laser element. A channel of a semiconductor laser element that performs irradiation is assigned to each divided pixel, and a scaling process in the sub-scanning direction is executed with a line size defined by the beam pitch of the semiconductor laser element. As the semiconductor laser element, a laser diode that irradiates a single beam can be used, or a surface emitting laser (VCSEL) that can irradiate a plurality of laser beams from a two-dimensionally expanded region is used. Can do.

  For this reason, line insertion or deletion in the sub-scanning direction can be executed as a plurality of lines having a line width smaller than the input resolution, and global image deterioration such as moire can be prevented.

  Further, the address in the image data of the image bits to be added to the inserted line is calculated using an algorithm for controlling the image bits to be added so as to be arranged as far as possible, and the image bits are added. The calculation of the image bits is performed using a residue class calculation so that a sub-scan line to be inserted or deleted provides a predetermined scaling factor based on the scaling factor. The remainder class calculation is performed using the offset value P with respect to sqrt (L) for the reference line interval L that gives a reference for the scaling factor. The proximity integer P gives an offset value for adding / deleting image bits, and is introduced as a measure for determining the distance based on the geometric mean when processing as an image space defined by the main scanning address and the sub scanning address. Is done. In the case of adding / deleting image bits, the offset value P is determined so that the added bits or deleted bits are appropriately distributed with reference to sqrt (L), and the offset value P is an integer closest to sqrt (L). And corresponding to a particular purpose, the offset value P may be equal to sqrt (L) or may be small or large.

  The image bits are inserted / removed at the position of the sub-scanning address with respect to the main scanning address calculated using the remainder class calculation, thereby providing a predetermined scaling factor. In addition, the image bits to be inserted or deleted are distributed and arranged in the sub-scanning direction so as not to cause moire, unevenness, and jagged edges in the image space by remainder calculation. The image forming apparatus prevents the image deterioration associated with the scaling process by increasing the definition of the sub-scan lines to be added / deleted and controlling the arrangement of the added image bits.

  The image forming method described above is executed by a computer installed in the image forming apparatus, described in a programming language such as an assembler or C language, and can be a computer-readable program, or a computer-readable program for recording the program. It can be stored in a recording medium.

  The image forming apparatus has been described with reference to the embodiments shown in the drawings. However, the present invention is not limited to the embodiments, and other embodiments, additions, modifications, deletions, and the like will occur to those skilled in the art. It can be changed within the range that can be performed, and any embodiment is included in the scope of the present invention as long as the operation and effect of the present invention are exhibited.

DESCRIPTION OF SYMBOLS 100 ... Image forming apparatus, 102 ... Optical apparatus, 102a ... Polygon mirror, 102b ... Reflection mirror, 102c ... 2nd cylindrical lens, 104a, 106a, 108a, 110a ... Photoconductor drum, 104b, 106b, 108b, 110b ... Charger 104c, 106c, 108c, 110c ... developer, 112 ... image forming unit, 114 ... intermediate transfer belt, 114a, 114b, 114c ... conveying roller, 118 ... secondary transfer belt, 120 ... fixing device, 122 ... transfer unit, DESCRIPTION OF SYMBOLS 124 ... Image receiving material, 130 ... Fixing member, 132 ... Printed matter, 200 ... VCSEL, control apparatus, 202 ... 1st cylindrical lens, 204 ... Reflection mirror, 206 ... Imaging lens, 208 ... Reflection mirror, 210 ... Synchronization detection apparatus, 300 ... Control unit 302 ... Scanner unit 304 ... VP 306... IPU 308 Printer unit 310 GAVD 312 LD driver 316 System bus 330 Main control unit 340 Memory 342 Image processing unit 344 Output data control unit 350 Resolution Conversion unit, 352 ... sub-scanning scaling unit, 354 ... address generation unit, 356 ... shift holding memory, 358 ... image path selector

Japanese Patent No. 3373266

Claims (6)

A light source including a plurality of laser elements;
An optical system for forming a latent image based on a plurality of laser beams emitted from the light source;
A resolution converter that increases the resolution of at least the pixels of the input image data in the sub-scanning direction in units of divided pixels corresponding to the spatial size of the laser beam emitted from the light source;
An allocating unit that allocates channels of the plurality of laser elements that perform laser irradiation corresponding to the divided pixels to the divided pixels included in the image data with high resolution;
A scaling unit that scales the image data by adding or deleting divided pixels according to the scaling command signal to the image data to which the channel is assigned,
A drive control unit for controlling drive of the light source in accordance with the image data scaled by the scaling unit;
An image forming apparatus comprising: The resolution conversion unit, the allocation unit, the scaling unit, and the drive control unit are provided in a control unit that controls the light source,
The image forming apparatus according to claim 1, wherein the control unit inputs the image data via a bus.   A position determining unit that determines a pixel position of a correction pixel to be corrected based on a position of a pixel serving as a reference for scaling the image data in the main scanning direction and a number of pixels L in the sub-scanning direction;
  The scaling unit scales the image data by adding or deleting the correction pixel at the pixel position of the image data,
  The position determination unit is configured to determine whether the position of the second correction pixel adjacent to the first correction pixel in the sub-scanning direction is based on the pixel position of the first correction pixel for which the pixel position is determined. Calculating a position shift amount as an integer closest to sqrt (L) to determine a pixel position of the second correction pixel;
  The image forming apparatus according to claim 1. An image forming method executed by an image forming apparatus comprising: a light source including a plurality of laser elements; and an optical system that forms a latent image based on a plurality of laser beams emitted from the light source,
A resolution conversion step of increasing the resolution of at least the pixels of the input image data in at least the sub-scanning direction in units of divided pixels corresponding to the spatial size of the laser beam emitted from the light source;
An assigning step of allocating channels of the plurality of laser elements that perform laser irradiation corresponding to the divided pixels to the divided pixels included in the image data with high resolution;
A scaling step for scaling the image data by adding or deleting divided pixels according to a scaling command signal to the image data to which the channel is assigned,
A drive control step for controlling drive of the light source according to the image data scaled by the scaling step;
An image forming method comprising: An image forming program for causing a computer to execute the image forming method according to claim 4 . A computer-readable recording medium on which the image forming program according to claim 5 is recorded.