JP2006297633A - Image forming apparatus, its control method, computer program and storage medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide images reduced in image quality degradation by solving moire which may be possibly generated by color shift correction. <P>SOLUTION: A color shift correction amount is operated on the basis of a color shift amount obtained from a color shift amount storage part of each image forming part. Coordinates conversion is carried out by using the operation result, whereby the color shift correction of a pixel unit is executed. A characteristic of the image of a processing object is detected. Density conversion correction of correcting the color shift smaller than the pixel unit is carried out according to the detected characteristic. Moreover, halftone processing or exception treatment is selectively carried out according to the detected characteristic. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, a control method thereof, a computer program, and a storage medium.

  Conventionally, as a color image forming apparatus using an electrophotographic method, a single photoconductor is developed with each color using a plurality of developing devices, and the exposure-development-transfer process is repeated a plurality of times. In general, a method is used in which a color image is formed on a transfer paper by being superimposed and fixed to obtain a full color image.

  According to this method, in order to obtain one printed image, it is necessary to repeat the image forming process 3 to 4 times (when black is used), and there is a drawback that it takes time. As a method for compensating for this defect, there is a method of using a plurality of photoconductors and sequentially superimposing the visualized images obtained for the respective colors on the transfer paper to obtain a full color print by one paper passing. According to this method, the throughput can be significantly shortened. On the other hand, the color due to the positional deviation of each color on the transfer paper due to the positional accuracy and diameter deviation of each photoconductor, the optical system positional precision deviation, etc. Due to the problem of displacement, it was difficult to obtain a high-quality full-color image.

  As a method for preventing this color misregistration, for example, a test toner image is formed on a transfer belt or a conveyance belt forming a part of transfer means, and this is detected, and each optical system is detected based on this result. In this method, there are the following problems, such as correcting the optical path and correcting the image writing position of each color (see Patent Document 1).

  First, in order to correct the optical path of the optical system, it is necessary to mechanically operate a correction optical system including a light source and an f-θ lens, a mirror in the optical path, etc., and align the position of the test toner image. However, for this purpose, a highly accurate movable member is required, resulting in an increase in cost. Furthermore, since it takes time to complete the correction, it is impossible to perform correction frequently, but the optical path length deviation may change with time due to the temperature rise of the machine. It is difficult to prevent color misregistration by correcting the optical path of the optical system.

  Second, by correcting the image writing position, it is possible to correct the displacement of the left end and upper left, but it is possible to correct the tilt of the optical system and the magnification shift due to the deviation of the optical path length. There are problems such as not.

  Further, the output coordinate position of the image data for each color is automatically converted into an output coordinate position in which the registration deviation is corrected, and the position of the modulated light beam is converted into the color signal based on the converted image data of each color. A configuration has also been proposed in which correction is performed with an amount smaller than the minimum dot unit (see Patent Document 2). However, by correcting the output coordinate position of the image data for each color with respect to the image that has been subjected to the intermediate gradation processing, the reproducibility of the halftone dots of the intermediate gradation image is deteriorated, resulting in color unevenness and moire. There is a problem that it may become apparent.

  An example is shown in FIG. The input image 101 is an image having a constant density value. When an image 102 having undergone a certain color misregistration correction is actually printed on the input image 101, the relationship between the image density value and the toner density with respect to the image density value is not linear. Regardless of the image having the density value, when the image after color misregistration correction is printed, an image having a non-constant density value is printed. When such a non-uniform density value is periodically repeated, moire becomes obvious, and a good color image cannot be obtained.

Furthermore, as the printing speed increases, the photosensitive member scanned by the laser beam moves by a predetermined amount according to the printing conditions during the laser scanning time without stopping while the laser beam is scanned. ing. If the scanning directions of the lasers of the respective colors are the same, the inclination of the scanning line due to the amount of movement does not matter. However, between colors that start scanning from the opposite direction, depending on the amount of movement of the photoconductor, color unevenness, etc. It becomes a factor causing image quality degradation. Further, the amount of movement may vary depending on conditions such as the print medium, and correction cannot be performed by a single process.
Japanese Patent Application Laid-Open No. 64-40956 JP-A-8-85237

  As described above, conventionally, it has been difficult to eliminate the moire that may be caused by the color misregistration correction and provide an image with little image quality deterioration.

  Accordingly, an object of the present invention is to eliminate moire that may occur due to color misregistration correction and to provide an image with little image quality deterioration.

  In order to solve the above problems, the present invention provides an image forming apparatus including an image carrier, an exposure unit that exposes the image carrier, and a developing unit that visualizes the electrostatic latent image generated by the exposure with a recording material. A color misregistration amount storage unit that stores color misregistration amount information indicating a deviation amount of an exposure position in a sub-scanning direction when exposing the image carrier while scanning in the main scanning direction. And color misregistration correction amount computing means for computing a color misregistration correction amount for correcting the misregistration amount in the sub-scanning direction based on the color misregistration amount, and image data composed of a plurality of pixel data is stored. The image data storage means and the coordinates of the read address of the image data storage means are converted on the basis of the color shift amount in units of pixels among the color shift correction amounts, and the image data storage means according to the converted address information Coordinate conversion means for reading pixel data of the pixel of interest, and the pixel data read from the image data storage means by the coordinate conversion means based on a color shift amount less than a pixel unit among the color shift correction amounts. Density conversion means for converting pixel density, halftone processing means for performing halftone processing of the pixel data whose density has been converted by the density conversion means, and exceptional processing of the pixel data whose density has been converted by the density conversion means An exception processing means for detecting the characteristics of image data composed of pixels in a predetermined area centered on the target pixel, out of the image data stored in the image data storage means, and the exception processing and the A process determining means for determining which of the halftone processes to select, and the exception processing based on the determination in the process determining means And an output means for selecting a processing result of either one of the means and the halftone processing means and outputting the result as an exposure control signal of the exposure unit.

  The present invention for solving the above-described problems further includes an image carrier, an exposure unit that exposes the image carrier, and a developing unit that visualizes the electrostatic latent image generated by the exposure with a recording material. An image forming apparatus having an image forming unit having a color for storing color misregistration amount information indicating a misregistration amount in the sub-scanning direction of an exposure position when exposing the image carrier while scanning in the main scanning direction. Image data composed of a misregistration amount storage unit, a color misregistration correction amount calculating unit that calculates a color misregistration correction amount for correcting the misregistration amount in the sub-scanning direction based on the color misregistration amount, and image data The first image data storage means for storing the image and the coordinates of the read address of the first image data storage means are converted on the basis of the color shift amount in pixel units among the color shift correction amounts, and after the conversion According to the address information Read out the image data from the image data storage means and store it in the second image data storage means; read out the pixel data of the pixel of interest from the second image data storage means; Among them, density conversion means for converting pixel density based on a color shift amount less than a pixel unit, halftone processing means for performing halftone processing of image data density-converted by the density conversion means, and density in the density conversion means An image composed of exception processing means for performing exception processing on the converted pixel data, and pixels in a predetermined area centered on the target pixel among the image data stored in the second image data storage means A process determining unit that detects data characteristics and determines which of the exception process and the halftone process to select; and Output means for selecting one of the processing results of the exception processing means and the halftone processing means based on the determination, and outputting the selected result as an exposure control signal of the exposure unit, wherein the predetermined area is the coordinate conversion means Is set so as to cancel the address conversion based on the color shift amount in pixel units.

  According to the present invention, it is possible to eliminate moiré that may occur due to color misregistration correction and to provide an image with little image quality deterioration.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[First Embodiment]
FIG. 2 is a schematic cross-sectional view illustrating the configuration of the image forming apparatus showing the embodiment of the present invention. As shown in the figure, this embodiment has a structure of a four-drum type color laser beam printer.

  In this image forming apparatus, a transfer material cassette 53 is mounted on the lower part of the right side surface of the main body apparatus. The recording media (recording paper, transmission sheet, etc.) set in the transfer material cassette 53 are taken out one by one by the paper feed roller 54 and fed to the image forming unit by the pair of transport rollers 55-a and 55-b. . In the image forming unit, a transfer conveyance belt 10 that conveys a recording medium is stretched flat in a recording medium conveyance direction (from right to left in FIG. 2) by a plurality of rotating rollers. At the most upstream portion of the transfer conveyance belt 10, the recording medium is electrostatically attracted to the transfer conveyance belt 10. Further, four photosensitive drums 14-C, Y, M, and K serving as drum-shaped image bearing members are arranged in a straight line so as to face the belt conveyance surface to constitute an image forming unit (here. C represents cyan, Y represents yellow, M represents magenta, and K represents black.)

  Since the image forming unit for each color component is different only in the color of the toner to be mounted and there is no structural difference, only the color component C will be described (hereinafter, unless otherwise specified, only C is used for other elements). The same applies to the case of picking up and explaining.)

  The C-color image forming unit stores a charger 50-C for uniformly charging the surface of the photosensitive drum 14-C, C-color toner, and an electrostatic latent image generated on the photosensitive drum 14-C. It has a developing device 52-C for developing (developing) a visible image and an exposure unit 51-C. A predetermined gap is provided between the developing unit 52-C and the charger 50-C. On the photosensitive drum 14-C whose surface is uniformly charged by the charger 50-C, the laser beam from the exposure unit 51-C made of a laser scanner is scanned and exposed in the direction perpendicular to the drawing through the gap. . As a result, the scanning exposed portion is charged differently from the non-exposed portion, and an electrostatic latent image is generated. The developing device 52-C transfers the toner to the electrostatic latent image to make a visible image (toner image; development).

  A transfer portion 57 -C is arranged across the conveyance surface of the transfer conveyance belt 10. The toner image formed (developed) on the peripheral surface of the photosensitive drum 14-C is charged and adsorbed onto the conveyed recording medium by the transfer electric field formed by the transfer unit 57 corresponding to the toner image. Transferred onto the medium surface. By performing the above-described processing for the other color components Y, M, and K in the same manner, the C, M, Y, and K color toners are successively transferred to the recording medium. Thereafter, each color toner on the recording medium is melted and fixed by the fixing device 58, and is discharged out of the apparatus by a pair of paper discharge rollers 59-a and 59-b.

  The above is an example of transferring a toner image of each color component onto a recording medium. However, a configuration may be employed in which after the toner image of each color component is transferred onto the transfer conveyance belt, the toner image generated on the transfer conveyance belt is transferred again to the recording medium (secondary transfer). The transfer belt in this case is called an intermediate transfer belt.

  FIG. 3 is an image diagram for explaining the shift of the main scanning line scanned on the photosensitive drum 14-C (which may be M, Y, or K) which is an image carrier. The horizontal direction in the figure indicates the scanning direction of the laser beam, and the vertical direction indicates the rotation direction of the photosensitive drum (also the conveyance direction of the recording medium).

  In FIG. 3, reference numeral 301 denotes an ideal main scanning line, and scanning is performed perpendicularly to the rotation direction of the photosensitive drum 14. Reference numeral 302 denotes an actual main scanning line in which the positional accuracy and the diameter of the photosensitive drum 14 are shifted and the inclination is increased due to the positional accuracy of the optical system in each color exposure unit 51-C, and the curvature is generated. It is an image. Here, the main scanning line represents an exposure position when the photosensitive drum 14 as an image carrier is exposed while being scanned in the main scanning direction. When such an inclination or curvature of the main scanning line exists in an image forming unit of any color, color misregistration occurs when a plurality of color toner images are collectively transferred to a transfer medium.

  Therefore, in the present embodiment, in the main scanning direction (X direction) orthogonal to the rotation direction of the photosensitive drum 14, a plurality of points (point B, point C) are set with the point A serving as the scanning start position of the printing area as a reference point. , Point D), the amount of deviation in the sub-scanning direction between the ideal main scanning line 301 and the actual main scanning line 302 is measured. A direction that corresponds to the rotation direction of the photosensitive drum 14 and is orthogonal to the main scanning direction is referred to as a sub-scanning direction. And it divides | segments into several area | region (The area between Pa-Pb is the area | region 1, the area between Pb-Pc is the area | region 2, and the area between Pc-Pd is the area | region 3) for every point which measured the deviation | shift amount. Then, the inclination of the main scanning line in each region is approximated by straight lines (Lab, Lbc, Lcd) connecting the points.

  Therefore, if the difference in the amount of displacement between points (m1 for region 1, m2-m1 for region 2, m3-m2 for region 3) is a positive value, the main scanning line of the corresponding region is positive (right in the figure). It indicates that it has a slope of (up). On the other hand, when the difference in the amount of deviation is a negative value, it indicates that it has a negative (lower right in the figure) slope.

  Next, FIG. 1 is a diagram illustrating an example of the configuration of a printer engine and a controller of an image forming apparatus corresponding to the present embodiment. The operation of the color misregistration correction process for correcting color misregistration caused by the inclination and curvature of the scanning line will be described below with reference to FIG.

  In FIG. 1, reference numeral 401 denotes a printer engine that actually performs a printing process based on image bitmap information generated by the controller 402. The controller 402 is accommodated in the substrate and is electrically connected to the printer engine 401 when accommodated in the apparatus.

  Reference numerals 403C, 403M, 403Y, and 403K denote color misregistration amount storage units for each color, and write and hold the misregistration amount information for each image forming unit for each color in the apparatus manufacturing stage. As an example, it may be realized by a writable non-volatile memory such as an EEPROM. In the drawing, a color misregistration amount storage unit is provided for each color component. However, since the amount of information to be stored is sufficiently small, the color misregistration amounts of all color components may be stored in one memory element. .

  The color misregistration amount storage units 403C, M, Y, and K corresponding to the present embodiment are sub-scans of the actual main scanning line 302 measured at a plurality of points and the ideal main scanning line 301 described in FIG. The direction shift amount is stored as information indicating the inclination and curvature of the main scanning line. The engine profile 412 stores configuration information related to printing in the printer engine. The engine profile 412 is also composed of a nonvolatile writable memory.

  In order to make the description easy to understand, the following description will be made excluding the engine profile 412, and thereafter, the correction process using the engine profile 412 will be described in detail.

  FIG. 5 is a diagram illustrating an example of information stored in the color misregistration amount storage unit 403C (the same applies to M, Y, and K, but stored information varies depending on individual differences). In FIG. 5, L1 to L3 and m1 to m3 have the same meanings as in FIG.

  In this embodiment, the amount of deviation between the ideal main scanning line 301 and the actual main scanning line 302 is stored in the color misregistration amount storage units 403C, M, Y, and K. However, the information stored in the color misregistration amount storage units 403C, M, Y, and K is not limited thereto as long as the actual inclination and curvature characteristics of the main scanning line 302 can be identified.

  In addition, the information stored in the color misregistration amount storage units 403C, M, Y, and K can be stored in advance as device-specific information by measuring the amount of misregistration in advance in the device manufacturing process as described above. . On the other hand, the apparatus itself is equipped with a detection mechanism for detecting the amount of deviation, a predetermined pattern for measuring the deviation is formed for each color image carrier, and the amount of deviation detected by the detection mechanism. It is also possible to adopt a configuration for storing.

  Next, the controller 402 performs the printing process by correcting the image data so as to cancel out the deviation amounts of the main scanning lines stored in the color deviation amount storage units 403C, M, Y, and K.

  The image generation unit 404 generates raster image data that can be printed from print data (PDL data, image data, etc.) received from a computer device (not shown) and the like, and RGB data (256 gradations of 8 bits each). Is output for each dot. Since this process is known, a more detailed description is omitted.

  The color conversion unit 405 converts the RGB data from the image generation unit 404 into CMYK space data (each 8 bits) that can be processed by the engine 401 (implemented by LOG conversion and UCR processing). The bitmap memory 406 accumulates CMYK space data for each color. The bitmap memory 406 temporarily stores raster image data to be printed. Further, it can be realized as a page memory for storing image data for one page or a band memory for storing data for a plurality of lines.

  Reference numerals 407C, 407M, 407Y, and 407K denote color misregistration correction calculation units provided for the respective colors, and information on the amount of misregistration in the sub-scanning direction of the main scanning line accumulated in the color misregistration amount storage units 403C, M, Y, and K. Based on the above, the color misregistration correction amount in the sub-scanning direction corresponding to the coordinate information in the main scanning direction designated from the color misregistration correction units 408C, M, Y, and K described later is calculated for each dot. The calculated correction amount is output to each of the color misregistration correction units 408C, M, Y, and K (note that the engine profile 412 is excluded here).

  Here, when the coordinate data in the main scanning direction is x (dots) and the color misregistration correction amount in the sub-scanning direction is Δy (dots), the calculation formulas of the respective regions based on FIG. 3 are shown below. In the following, Ldot represents the size of one dot (the unit is “mm / dot”).

Region 1: Δy1 = x * (m1 / L1) (0 ≦ x <L1)
Region 2: Δy2 = m1 / Ldot + (x- (L1 / Ldot)) * ((m2-m1) / (L2-L1)) (L1≤x <L1 + L2)

Region 3: Δy3 = m2 / Ldot + (x- (L2 / Ldot)) * ((m3-m2) / (L3-L2)) (L1 + L2≤x≤L1 + L2 + L3)
In the above, L1, L2, and L3 represent distances (unit: mm) in the main scanning direction from the print start position to the left end of the regions 1, 2, and 3. m1, m2, and m3 represent deviation amounts (unit: mm) in the sub scanning line direction between the ideal main scanning line 301 and the actual main scanning line 302 at the left end of the region 1, region 2, and region 3, respectively. After determining Δy, the value of x is determined when Δy reaches one dot to be reproduced by printing, and the vertical reading position in the coordinate conversion unit in the color misregistration correction unit 408C is changed for each value. I will do it.

  On the other hand, as shown in FIG. 13, the engine profile data as configuration information relating to printing stored in the engine profile 412 from the engine 401 side includes offset information from the reference point in the paper size and the beam of each color in the engine. The scanning direction, the scanning amount of the scanner, the number of beams used, and the like are included.

  Next, the scanning exposure direction of the laser beam and the amount of inclination corresponding to the number of scanning exposure beams will be considered with reference to FIG.

  FIG. 14A shows an example in which one dot is recorded in the sub-scanning direction in one scan and the magenta and cyan scanning directions are reversed. FIG. 14B shows a case where 2 dots are recorded in the sub-scanning direction in one scan, and FIG. 14C shows a case where 4 dots are recorded in the sub-scanning direction in one scan.

  An example of FIG. 14A will be described. The positions where image formation starts are magenta dots 4m and cyan dots 4c, which do not match each other. This is because the scanning directions are reversed between magenta and cyan. The locus of dots formed in one scan is as shown by line 1401 for magenta and line 1402 for cyan. The dots 4m 'and 4c' on each line indicate arbitrary magenta and cyan dots formed within one scanning period. In this manner, magenta dots are formed on the line 1401 and cyan dots are formed on the line 1402.

  In FIG. 14A, the movement amount for one main scan (that is, the section in which dots are recorded in one main scan) is represented by Lmax. Further, the amount of deviation in the sub-scanning direction from the recording position of the dot 4m (4c) at the start of dot recording to the recording position of the dot at the end of one main scan is represented by mdot. From these Lmax and mdot, the slopes of the lines 1401 and 1402 can be obtained as mdot / Lmax.

  Next, FIGS. 14B and 14C each show a case where 2 dots and 4 dots are recorded in the sub-scanning direction within one main scanning period, respectively. At this time, the amount of deviation in the sub-scanning direction from the recording position of the dots 4mb and 4mc (4cb and 4cc) at the start of dot recording to the recording position of the dot at the end of one main scan is 2 *, respectively. Expressed in mdot, 4 * mdot. Therefore, the slopes of the lines 1403 and 1404 can be obtained as 2 * mdot / Lmax. Further, the slopes of the lines 1405 and 1406 can be obtained as 4 * mdot / Lmax.

  That is, when the number of beams used in one main scan (the number of dots recorded in the sub-scan direction in one main scan) is n, the inclination can be expressed as n * mdot / Lmax. Further, assuming that the shift direction in FIG. 3 is positive, the calculation is performed with the sign of the forward sign being negative and the sign of the reverse sign being positive, and adding a slope count.

  Next, the case where the printing speed changes due to the difference in the rotational speed of the photosensitive drum will be discussed with reference to FIG.

  FIG. 15A shows a case similar to FIG. 14A. FIG. 15B shows a case where recording is performed at 1/2 times speed. In the case of (b), the rotational speed of the photosensitive drum 14 is 1/2 the normal speed. Therefore, the amount of movement of the photosensitive drum when the main scanning is performed twice coincides with one main scanning at the normal printing speed. Therefore, the slopes of the lines 1501 and 1502 can be obtained by further multiplying the slope coefficient obtained according to the number of beams n in FIG. 14 by 1/2.

  On the other hand, when the printing speed is double speed (normal double speed, which is the rotation speed of the photosensitive drum 14), the photosensitive drum 14 moves by two normal scans in one main scan. Therefore, the slopes of the lines 1503 and 1504 can be obtained by further doubling the slope coefficient obtained according to the number of beams n in FIG.

  As described above, when the printing speed becomes k times, the inclination can be expressed as k * n * mdot / Lmax based on the number of beams n and the printing speed k.

Therefore, the shift amount Δy in all regions including the color shift amount and the engine profile is Δy = −x * k * n * mdot / Lmax + x * (m1 / L) (0) when the main scanning direction is Forward. ≦ x <L)
-x * k * n * mdot / Lmax + m1 / Ldot + (x−L / Ldot) * (m2 / L) (L ≦ x <2L)
-x * k * n * mdot / Lmax + (m1 + m2) / Ldot + (x-2L / Ldot) * (m3 / L) (2L≤x≤3L)
When the main scanning direction is Reverse Δy = x * k * n * mdot / Lmax + x * (m1 / L) (0 ≦ x <L)
x * k * n * mdot / Lmax + m1 / Ldot + (x−L / Ldot) * (m2 / L) (L ≦ x <2L)
x * k * n * mdot / Lmax + (m1 + m2) / Ldot + (x-2L / Ldot) * (m3 / L) (2L≤x≤3L)
It becomes.

  Here, when printing on a recording medium, it is necessary to offset the recording start position according to the size of the recording medium such as recording paper. For this reason, the value “y” used for the coordinate conversion processing in the sub-scanning direction of the image starts from the value “yobj” at the offset position. The correction amount in the sub-scanning direction at the offset position can be calculated by the equation for obtaining y.

  The offset position is determined based on the size of one dot. That is, coordinate conversion in the sub-scanning direction is performed by the quotient value obtained when yobj is divided by the dot size. Therefore, even if yobj is a size that cannot be divided by the size of 1 dot, recording cannot be performed at a desired recording position unless coordinate conversion is performed by the quotient value.

  In this coordinate conversion, first, there is a method of calculating the conversion amount based on the value of the quotient as the coordinate conversion initial value of the color misregistration amount calculation unit 407C. As another method, there is a method in which the reading timing in the sub-scanning direction is adjusted. Since the offset value itself is a constant value and common (fixed) during the printing process for the same recording medium, the coordinate conversion initial value in the color misregistration amount calculation unit 407C is set to 0 and obtained by calculation. If the timing is adjusted based on the conversion amount, coordinate conversion can be substantially performed. In the description of the color misregistration amount calculation unit 407C described below, a case where the former is adopted among the above two methods will be described.

  Next, the configuration of the color misregistration amount calculation unit 407C will be described with reference to FIG. In addition, processing in the color misregistration amount calculation unit 407C will be described with reference to the flowchart of FIG.

  In FIG. 16, reference numeral 1620 denotes an offset value storage unit. A CPU (not shown) of the image forming apparatus transmits offset data stored in the engine profile 412 to the offset value storage unit 1620 as offset data 1610. The transmitted offset data 1610 is written in synchronization with an offset write signal 1601 that controls the write timing. The offset data 1610 stored at this time corresponds to O1, O2, and O3 in FIG.

  An adder 1621 adds the offset value stored in the offset value storage unit 1620 and the coordinate data 1602 of the target pixel to be processed, and outputs a coordinate address 1603 to the selector 1622. The coordinate data 1602 here is provided from the color misregistration correction unit 408C. The color misregistration correction unit 408C supplies the coordinate data 1602 to be processed to the color misregistration calculation unit 407C in order to acquire the color misregistration correction amount (table data 1609) necessary for coordinate conversion from the correction calculation table 1623. .

  Next, reference numeral 1622 denotes a selector that selects either the table reference address 1605 or the coordinate address 1603 output from the adder 1621 according to the mode control signal 1606. Here, the table reference address 1605 is supplied from the CPU when the CPU writes or reads data in the correction calculation table 1623. The mode control signal 1606 is transmitted from the CPU. For example, when it is “1”, the table reference address 1605 is selected, and when it is “0”, the coordinate address 1603 is selected.

  When the table address 1604 of the correction calculation table 1623 is output from the selector 1622, table data 1609 corresponding to the table address 1604 is output from the correction calculation table 1623. The output from the correction calculation table 1623 is supplied to the color misregistration correction unit 408C. Note that when writing the table data 1609 to the correction calculation table 1623, the writing data 1608 is input from the CPU and writing is performed in synchronization with the writing control signal 1607.

  Next, in FIG. 17, in step S1701, the color misregistration amount calculation unit 407C acquires the color misregistration amount from the color misregistration amount storage unit 403C. Also, an engine profile is acquired from the engine profile storage unit 412. In step S 1703, correction data (X address offset value, Y address offset value, weighting coefficients α and β, which will be described later) based on these profiles are added in consideration of the print mode (recording paper size, transport direction, printing speed, etc.). In step S1704, the calculated data is written in the corresponding address position of the correction calculation table 1623. Thus, the calculation of the table data in the correction calculation table is performed according to the state of the printer engine 401. It may be executed when the image forming apparatus is activated or when the printing speed is changed, and the result is stored in the correction calculation table 1623.

  In step S1705, it is determined whether the print mode has been changed. If it is determined that the print mode has been changed (“YES” in step S1705), the processing from step S1703 is executed again. That is, the correction table 1623 is updated. On the other hand, if it is determined that the print mode has not been changed (“NO” in step S1705), it is determined in step S1706 whether or not printing has started, and it is detected that printing has started (step S1706). In step S1707, the offset data 1610 is read into the offset value storage unit 1620. In step S1708, coordinate data 62 is acquired.

  The offset data 1610 and the coordinate data 1620 are output to the adder 1621, and a coordinate address 1603 is generated in step S1709. The coordinate address 1603 is supplied to the selector 1622. Similarly, the selector 1622 is supplied with a table reference address 1605 from the CPU. The selector 1622 selects either the coordinate address 1603 or the table reference address 1605 based on the mode control signal 1606, and outputs the table address 1604 in step S1710.

  In step S 1711, table data 1609 corresponding to the table address 1604 input from the selector 1622 is output from the correction calculation table 1623. In step S1712, it is determined whether or not printing is finished. If printing is not finished ("NO" in step S1712), the process proceeds to step S1708, and if printing is finished ("YES" in step S1712), step The process proceeds to S1705 and the process is repeated.

  Next, the color misregistration amount correction unit 408C in FIG. 1 will be described. The color misregistration correction unit 408C is based on the color misregistration correction amount calculated and output for each dot from the color misregistration amount calculation unit 407C in order to correct the color misregistration due to the inclination and distortion of the main scanning line. The adjustment of the output timing of the bitmap data stored in the memory and the adjustment of the exposure amount for each pixel are performed. This prevents color misregistration (registration misalignment) when each color toner image is transferred to a transfer medium. The color misregistration correction unit 408C receives image data to be processed from the bitmap memory. Further, table data 1609 that is the color misregistration correction amount of each pixel is input from the color misregistration amount calculation unit 407C.

  An example of a specific configuration of the color misregistration correction unit 408C is as shown in FIG. Here, the color misregistration correction unit 408C includes a coordinate counter 801, a coordinate conversion unit 802, a line buffer 803, a smoothing determination pattern storage unit 805, a smoothing determination unit 806, a density conversion unit 807, a halftone processing unit 808, and an exception. A processing unit 809 and a selector 810 are included.

  Here, the coordinate counter 801 outputs the coordinate position data in the main scanning direction and the sub-scanning direction in which the color misregistration correction processing is performed to the coordinate conversion unit 802 and the density conversion unit 807. Further, the coordinate counter 801 outputs the coordinate data 1602 to the color misregistration amount calculation unit 407C.

  The coordinate conversion unit 802 is based on the coordinate position data in the main scanning direction and the sub-scanning direction from the coordinate counter 801 and the table data 1609 (corresponding to the correction amount Δy) obtained from the color misregistration amount calculation unit 407C. Correction processing of the integer part of the above, that is, reconstruction processing in the sub-scanning direction in units of pixels.

  The line buffer 803 is a line unit memory that stores image information before the color misregistration correction processing from the bitmap memory 406.

  The smoothing determination pattern storage unit 805 stores a window pattern of a predetermined size used in the smoothing determination unit 806. The smoothing determination unit 806 compares the window data 804 obtained from the line buffer 803 with the smoothing determination pattern stored in the smoothing determination pattern storage unit 805. Based on this comparison, image features are extracted, and density conversion processing to be performed by the density conversion unit 807 is selected.

  The window 804 shown in FIG. 8 describes a case of a size of 3 × 5, but the window size is not limited to this. Considering the detection of a thin line, which will be described later, it is desirable to set a window area that is equal to or larger than the above value.

  The density conversion unit 807 performs correction processing after the decimal point of Δy based on the coordinate position data in the main scanning direction from the coordinate counter 801 and the correction amount Δy provided as the table data 1609 for the target image, that is, the pixel Correction is performed by adjusting the exposure ratio of dots before and after the sub-scanning direction in less than a unit. This adjustment amount is determined by the smoothing determination unit 806. The density conversion unit 807 uses a line buffer 803 for referring to dots before and after in the sub-scanning direction.

  A halftone processing unit 808 performs halftone processing on the image data whose density has been converted by the density conversion unit 807. An exception processing unit 809 performs exception processing on the image data whose density has been converted by the density conversion unit 807. A selector 810 selects an output from either the halftone processing unit 808 or the exception processing unit 809 according to a selection signal from the smoothing determination unit 806 and supplies the selected output to the transfer buffer 410C.

  The flow of processing in the color misregistration correction unit 408C is as shown in the flowchart of FIG.

  In FIG. 12, in step S1201, the image data read from the bitmap memory 406 is stored in the line buffer 803. In step S1202, the coordinate conversion unit 802 performs coordinate conversion on the image data in the window 804 read from the line buffer 803, corrects color misregistration of one line or more, and converts the correction result into a density conversion unit. Output to 807.

  In step S1203, the smoothing determination unit 806 compares the image data in the window 804 read from the line buffer 803 with the smoothing determination pattern stored in the smoothing determination pattern storage unit 805. Then, the feature of the image information is extracted, and a correction amount table based on the feature is determined. Also, it is determined whether to select halftone processing or exception processing.

  In the subsequent step S1204, the density conversion unit 807 executes density conversion processing using the correction amount table designated by the smoothing determination unit 806. Further, in step S1205, it is determined whether to perform halftone processing in accordance with a selection instruction from the smoothing determination unit 806. If halftone processing is selected (“YES” in step S1205), halftone processing is executed in step S1206. On the other hand, if halftone processing is not selected (“NO” in step S1205), exception processing is executed in step S1206. Hereinafter, the process in each step will be specifically described.

  Next, processing for correcting the shift amount of the integer part (color shift amount in units of pixels) of the color shift correction amount Δy in the coordinate conversion unit 802 will be described with reference to FIG.

  In the coordinate conversion unit 802, first, as shown in FIG. 6A, according to the value of the integer part of the color misregistration correction amount Δy obtained from the color misregistration amount of the main scanning line approximated by a straight line, The coordinates in the sub-scanning direction (Y direction) of the image data stored in the map memory 406 are offset.

  For example, as shown in FIG. 6B, when the coordinate position in the sub-scanning direction from the coordinate counter 801 is n, if the coordinate position in the main scanning direction is X, the area 601 in the X coordinate in the main scanning direction Then, the color misregistration correction amount Δy is 0 or more and less than 1. Therefore, when reconstructing the nth line data, the nth line data is read from the bitmap memory. In the area 602, the color misregistration correction amount Δy is 1 or more and less than 2. Therefore, when the n-th line data is reconstructed, a coordinate conversion process for reading the data of the (n + 1) -th line from the bitmap memory 406, that is, the position where the number of sub-scanning lines is offset is performed. Similarly, in the area 603, coordinate conversion processing is performed to read data in the n + 2 line and in the area 604, data in the n + 3 line.

  With the above method, coordinate conversion processing in the sub-scanning direction is performed in units of pixels. FIG. 6C shows an exposure image obtained by exposing the image carrier to the image data that has been subjected to the color shift correction for each pixel by the coordinate conversion unit 802 in this way.

  Next, correction of color misregistration less than a pixel unit in the density conversion unit 807 will be described with reference to FIG. In the density conversion unit 807, the amount of shift after the decimal point of the color shift correction amount Δy (color shift amount less than a pixel unit) is corrected. This correction is realized by adjusting the exposure ratio of the front and rear dots in the sub-scanning direction to achieve pixel density dispersion.

  FIG. 7A shows an example (701) of a main scanning line having a positive inclination (inclination in the Y direction in FIG. 3). Here, a case where a shift of 1 dot occurs in the sub-scanning direction every time four dots advance in the main scanning direction is shown. FIG. 7B shows a horizontal straight-line bitmap image 702 before density conversion. FIG. 7C shows a bitmap image 703 after correction when correction for canceling color misregistration due to the inclination of the main scanning line in FIG. 7A is performed. In order to realize such an image 703, it is necessary to adjust the exposure amount of dots before and after in the sub-scanning direction.

  FIG. 7D shows a relationship (correction amount table) 704 between the color misregistration correction amount Δy and the correction coefficient for performing density conversion. Here, k is an integer part of the color misregistration correction amount Δy (the fractional part is rounded down), and represents the correction amount in the sub-scanning direction in units of pixels. β and α are correction coefficients for performing correction in the sub-scanning direction less than a pixel unit, and represent the distribution ratio of the exposure amount of dots before and after the sub-scanning direction based on information below the decimal point of the color misregistration correction amount Δy. It is calculated by β = Δy−k, α = 1−β. Here, α represents the distribution rate of the preceding dots (dots formed earlier), and β represents the distribution rate of the subsequent dots (dots formed later). In this way, the pixel density of each dot is dispersed in the sub-scanning direction based on the values of α and β.

  FIG. 7E shows a bitmap image 705 that has been subjected to density conversion for adjusting the exposure ratio of dots before and after the sub-scanning direction in accordance with the correction coefficient of FIG. FIG. 7F shows an exposure image 706 on the image carrier of the bitmap image whose density has been converted, and the inclination of the main scanning line is canceled and a horizontal straight line is formed.

  An example of the density conversion process shown in FIG. 7 corresponds to a general image. On the other hand, a case where density conversion processing is performed on a line formed with a width of 1 dot will be described with reference to FIG. When a line formed with a width of 1 dot is reproduced by being dispersed in the upper and lower dots, if the upper and lower dots are set to 1, the density of one dot cannot be expressed due to the relationship of dot connection. Therefore, as shown in FIG. 18, in the correction amount table 1804, it is preferable to set the coefficient so that the number is slightly larger than 1, which is a predetermined multiple of the pixel density. In the case of FIG. 18, the conversion amount of density conversion is 1.2 in total. This makes it possible to express the density for one dot.

  In addition, in pattern data in which the presence / absence of dots is repeated in units of dots, when the density conversion is performed and the pixel density is dispersed, the original pattern may be lost. Therefore, as shown in FIG. 19, in the correction amount table 1905, the coefficient α is fixed to 1 and β is fixed to 0, respectively, the coefficient is set so as not to cause density dispersion, and the original image data is output as it is. Thereby, the image quality by conversion and correction can be minimized.

  The processing in the density conversion unit 807 has been described above with reference to FIGS. 7, 18, and 19. Among these, there are three types of correction amount tables (704, 1804, and 1904), but what kind of correction amount table is used for density conversion processing is extracted by the smoothing determination unit 806 to extract the feature of the image information. And can be determined based on the characteristics. The processing in the smoothing determination unit 806 will be described later with reference to FIG.

  Next, processing in the halftone processing unit 808 in FIG. 8 will be described. The halftone processing unit 808 performs conversion processing (halftone processing) for maintaining the gradation expression of the image while reducing the number of bits of the input multivalued image information. By changing the cell size for halftoning according to the type of image information, an appropriate image reproduction is possible.

  The order in which halftone processing and color misregistration correction processing are performed on the input image also affects image reproducibility. Hereinafter, an example of a processing result when the input image is processed in the order of halftone processing → color misregistration correction and when the input image is processed in order of color misregistration correction → halftone processing, This will be described with reference to FIGS.

  First, FIG. 9 is an example in which processing is performed in the order of halftone processing → color misregistration correction on an input image. Reference numeral 900 shown in the figure is an input image having a constant density of 50%. When this image is subjected to halftone processing using a 4 × 4 halftone pattern, an image 901 is obtained. This image 901 is an originally obtained image. Even after color misregistration correction is performed, if an image equivalent to this image is obtained, it can be said that color misregistration correction can be realized without image deterioration. Here, the image 902 is obtained when the half-tone processed image 901 is subjected to the 1/2 pixel color shift correction in the upward direction (vertical direction) in FIG. As can be seen from the figure, when color misregistration correction is performed on the image after the halftone processing, the halftone dot halftone dot reproducibility deterioration is caused by the halftone processing.

  On the other hand, FIG. 10 shows an example when the input image is processed in the order of color misregistration correction → halftone processing. The reference numeral 1000 shown in the figure is an input image, which is an image having a constant density (50%), similar to the image 900 described above. An image 1001 is obtained when ½ pixel color shift correction is performed on the input image 1000 in the upward direction (vertical direction) in FIG.

  By performing such color misregistration correction, an image having a density of 25% is generated in the upper and lower line portions. An image 1002 is a result of performing the halftone process on the image after the color misregistration correction. In the image 1002, an image having a density of 25% is generated for one line at the upper end and the lower end. Therefore, the upper and lower lines are different from the image 1000, but the other parts are similar to the image 901. The halftone dots of the halftone image as seen in the image 920 are not observed.

  As described above, in the case of an image without an edge such as the image 900 and the image 1000, it is possible to suppress image degradation by performing halftone processing on the image subjected to color misregistration correction.

  On the other hand, there are the following problems in the edge portion of an image that changes sharply with respect to the surrounding density, such as characters and line drawings. For example, as shown in FIG. 11, when coordinate conversion is performed on the input image 1101, the converted image is as indicated by 1102. On the other hand, when density conversion processing is performed using a predetermined correction amount table, the converted image is as indicated by 1103. When halftone processing is performed on this image 1103, the processed image is as indicated by 1104.

  In the image 1104, since the edge portion is formed according to the halftone pattern, the result of the density conversion is invalidated, and a gap or discontinuity occurs in the edge portion. As a result, jaggies occur at image edge portions such as characters and line drawings. In addition, the image may be distorted due to the characteristics of the image information.

  In order to prevent such an adverse effect, the smoothing determination unit 806 detects the feature of the image information in addition to the processing of determining the correction amount table at the time of the density conversion, and the halftone processing unit corresponding to the feature detects the feature of the image information. It is necessary to make settings.

  Hereinafter, the process of the smoothing determination unit 806 corresponding to the present embodiment will be described.

  FIG. 20 shows an example of a specific configuration of the smoothing determination unit 806. In FIG. 20, reference numerals 2001 (ac) denote comparators, which are predetermined smoothing patterns 2005 (ac) stored in the smoothing determination pattern storage unit 805 and images output from the line buffer 803. When the pattern is matched with the data, the correction amount table corresponding to the comparator 2001 (ac) and halftone processing / exception processing are selected.

  Reference numeral 2002 denotes a target pixel to be processed, and pixels existing in a predetermined area centered on the target pixel are read from the line buffer 803 as pixels constituting the window 804.

  Reference numeral 2003 denotes a binarization processing unit that converts multi-value image data of the window 804 read from the line buffer 803 into binarized data. As a method of binarizing image information, there are a method of binarizing with the most significant bit and a method of binarizing by obtaining an average value in adjacent pixels and comparing it with the average value. The binarization processing result is input to the comparator 2001 (ac).

  2005 (ac) is a smoothing determination pattern read from the smoothing determination pattern storage unit. The smoothing determination patterns are respectively input to the comparators 2001 (a to c) and compared with the binarized image data.

  An example of the smoothing determination pattern is as shown in FIG. In FIG. 24, a 3 × 3 pattern will be described as an example of the smoothing determination pattern. Even if the window size is 3 × 5, it may be determined whether or not there is a pattern that matches the 3 × 3 pattern with the target pixel 2002 as the center.

  24A shows an example of a pattern in a case where a line having a width of 2 dots or more including the target pixel 2002 is configured. When an input pattern that matches such a smoothing determination pattern is detected in the binarized data by the comparator 2001a, as a correction amount table used for density conversion, for example, as shown in FIG. Such a correction amount table 704 is selected. Also, halftone processing is selected from halftone processing and exception processing.

  Further, (b) shows an example of a pattern in a case where a 1-dot width line including the target pixel 2002 is configured. When an input pattern that matches such a smoothing determination pattern is detected in the binarized data by the comparator 2001b, as a correction amount table used for density conversion, for example, as shown in FIG. Such a correction amount table 1804 is selected. Also, exception processing is selected from halftone processing and exception processing. The exception processing here includes the following processing, for example. In the first place, the main purpose of the halftone process is to match the bit width processed by the PWM unit in the subsequent stage with the input bit width while maintaining the gradation of the image as much as possible. Therefore, the halftone process is not performed as an exception process, and the ratio of density conversion by the density conversion unit 807 is made the same as the bit width input to the PWM by the process of integrating the maximum value of the PWM by the bit slice process or the like. Can be executed.

  Furthermore, (c) shows an example of a pattern when pixels in the window 804 form a predetermined pattern. When an input pattern that matches the input smoothing determination pattern is detected in the binarized data by the comparator 2001c, as a correction amount table used for density conversion, for example, as shown in FIG. Such a correction amount table 1904 is selected. Of the halftone processing and exception processing, exception processing is also selected here.

  A smoothing determination unit 2006 outputs a predetermined correction amount table to the density conversion unit 807 in response to an output from the comparator 2001, and a selection signal indicating which halftone / exception processing is selected. Is output to the selector 810. If the comparator 2001 does not detect any match with any smoothing determination pattern, FIG. 19D and halftone processing are selected as the correction amount table.

  As described above, the image data after color misregistration correction output from the color misregistration correction unit 408C is subjected to pulse width modulation in the PWM processing unit 411C through the transfer buffer 410C and converted into a binary laser drive signal. It is supplied to the exposure unit 51-C and exposed from the exposure unit. Thereby, an electrostatic latent image can be generated on the photosensitive drum 14.

  As described above, according to the image forming apparatus corresponding to the present embodiment, according to the image characteristics, the correction amount table is selected to perform the density conversion process, and whether to perform the halftone process is selected. Can be implemented. As a result, it is possible to provide an image with little image quality degradation and to perform processing at high speed.

  More specifically, the present invention calculates the color misregistration correction amount based on the color misregistration amount obtained from the color misregistration amount storage unit for each image forming unit, and performs coordinate conversion using the calculation result to change the color of each pixel. Deviation correction can be performed. Further, it is possible to detect a feature of an image to be processed and perform density conversion correction for correcting a color shift less than a pixel unit according to the detected feature. Further, halftone processing or exception processing can be selectively performed according to the detected feature. As a result, each color image is output to a position that cancels the registration deviation caused by the mechanical arrangement deviation of the optical scanning system, and the arrangement can be corrected with a value smaller than the minimum coordinate unit in the main scanning direction. Therefore, it is possible to output a color image without color shift at high speed without deterioration.

  In addition, by adopting a configuration in which the calculation processing of the correction amount taking into account the engine characteristics is made common, the development efficiency can be improved and the overall cost can be reduced.

[Second Embodiment]
In the first embodiment, after color conversion is performed in the color conversion unit 405, image data is once stored in the bitmap memory 406, and then coordinate conversion is performed in the color misregistration correction unit 408. On the other hand, in the present embodiment, a case will be described in which coordinate transformation is performed at the stage of development in a bitmap memory.

  FIG. 21 is a diagram showing an example of the configuration of the printer engine and controller of the image forming apparatus corresponding to the present embodiment. 21 is different from FIG. 1 in that a coordinate conversion unit 2109 is arranged in the preceding stage of the bitmap memory 2106.

  In the coordinate conversion unit 2109, as described with reference to FIG. 8, an integer of the correction amount Δy for the pixel to be processed based on the table data 1609 (corresponding to the correction amount Δy) obtained from the color misregistration amount calculation unit 407C. Partial correction processing, that is, reconstruction processing in the sub-scanning direction in units of pixels is performed, and the processing result is written in the bitmap memory 2106.

  The state written in the bitmap memory 2106 at this time is as indicated by 2302 in FIG. As described above, according to the present embodiment, the correction process for the integer part of the correction amount Δy in the sub-scanning direction is completed at the time of writing to the bitmap memory 2106. Accordingly, the color misregistration correction unit 2108C performs density conversion and the like based on the deviation amount of the decimal part of the correction amount Δy.

  A specific configuration of the color misregistration correction unit 2108C is as shown in FIG. In FIG. 22, seven stages of line buffers are prepared. However, the number of stages is not limited. That is, in the present embodiment, the minimum number of line memories used in the line buffer 2203 is the number of lines in the window used for the smoothing determination process + 2 (in the case of FIG. 22, 5 + 2 = 7).

  In the present embodiment, when the image data is read into the line buffer 2203 as described above, the shift amount of the integer part of the correction amount Δy is reflected. Therefore, when the smoothing determination unit 2206 performs a comparison process with the smoothing determination pattern, it is necessary to change the shape of the window according to the shift amount of the integer part and cancel the shift amount. For example, consider a case where the inclination of the main scanning line in this embodiment is shifted by 1 dot in the sub-scanning direction when the dot advances by 4 dots in the main scanning direction as indicated by 2301 in FIG. In this case, a window that includes a shift of one dot in the sub-scanning direction is set in consideration of the shift amount. That is, in the image 2302 in FIG. 23, a window is set like an area surrounded by a dotted line 2308. On the other hand, a normal window 2307 is set for an area not including a shift in the sub-scanning direction.

  The subsequent processing is the same as that described with reference to FIG.

  As described above, in the present embodiment, when the image data after color conversion is written in the bitmap memory, a part of the correction process in the sub-scanning direction can be performed, and then the density conversion process can be performed.

[Other Embodiments]
Note that the present invention can be applied to a system including a plurality of devices (for example, a host computer, an interface device, a reader, and a printer), and a device (for example, a copying machine and a facsimile device) including a single device. You may apply to.

  Another object of the present invention is to supply a storage medium (or recording medium) in which a program code of software that realizes the functions of the above-described embodiments is recorded to a system or apparatus, and the computer (or CPU or Needless to say, this can also be achieved by the MPU) reading and executing the program code stored in the storage medium. In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiments, and the storage medium storing the program code constitutes the present invention. Further, by executing the program code read by the computer, not only the functions of the above-described embodiments are realized, but also an operating system (OS) running on the computer based on the instruction of the program code. It goes without saying that a case where the function of the above-described embodiment is realized by performing part or all of the actual processing and the processing is included.

  Furthermore, after the program code read from the storage medium is written into a memory provided in a function expansion card inserted into the computer or a function expansion unit connected to the computer, the function is based on the instruction of the program code. It goes without saying that the CPU or the like provided in the expansion card or the function expansion unit performs part or all of the actual processing and the functions of the above-described embodiments are realized by the processing.

1 is a block diagram illustrating an outline of a configuration of a controller and an engine unit of an image forming apparatus corresponding to a first embodiment of the present invention. 1 is a block diagram illustrating an example of a configuration of an image forming apparatus corresponding to an embodiment of the present invention. FIG. 6 is a diagram for explaining a shift of a main scanning line on a photosensitive drum corresponding to the embodiment of the present invention. It is a figure for demonstrating the density nonuniformity in the image formation process corresponding to embodiment of this invention. It is a figure which shows an example of the information memorize | stored in the color shift amount memory | storage part corresponding to embodiment of this invention. It is a figure for demonstrating the operation | movement which correct | amends the deviation | shift amount of a subscanning direction based on the integer part of the color deviation correction | amendment amount corresponding to embodiment of this invention. It is a figure for demonstrating the process in a density | concentration conversion part corresponding to embodiment of this invention. It is a block diagram which shows an example of a structure of the color shift correction | amendment part corresponding to the 1st Embodiment of this invention. It is a figure for demonstrating the result of having processed the input image in order of the halftone process and the color shift correction. It is a figure for demonstrating the result of having performed the process in order of color shift correction and a halftone process to the input image. It is a figure for demonstrating the result of having performed the halftone process to the edge image which performed color shift correction. It is a flowchart corresponding to an example of the process in the color shift correction | amendment part corresponding to embodiment of this invention. It is a figure which shows an example of the engine profile data corresponding to embodiment of this invention. It is a figure which shows the relationship of the dot color, the scanning direction, and main scanning line at the time of changing the number of dots recorded by 1 scan corresponding to embodiment of this invention. FIG. 6 is a diagram illustrating a relationship between a dot color, a scanning direction, and a main scanning line when a recording speed is changed according to the embodiment of the present invention. It is a figure which shows an example of a structure of the color shift amount calculating part corresponding to embodiment of this invention. 6 is a flowchart corresponding to an example of processing in a color misregistration amount calculation unit corresponding to the embodiment of the present invention. It is a figure for demonstrating the density conversion process with respect to a thin line image corresponding to embodiment of this invention. It is a figure for demonstrating the density conversion process with respect to the image which has a repeating pattern corresponding to embodiment of this invention. It is a block diagram which shows an example of a structure of the smoothing determination part corresponding to embodiment of this invention. FIG. 5 is a block diagram illustrating an outline of a configuration of a controller and an engine unit of an image forming apparatus corresponding to a second embodiment of the present invention. It is a block diagram which shows an example of a structure of the color shift correction | amendment part corresponding to the 2nd Embodiment of this invention. It is a figure for demonstrating the density | concentration conversion process corresponding to the 2nd Embodiment of this invention. It is a figure which shows an example of the smoothing determination pattern corresponding to embodiment of this invention.

Claims (16)

An image forming apparatus having an image bearing member, an exposure unit that exposes the image bearing member, and an image forming unit that has a developing unit that visualizes an electrostatic latent image generated by exposure with a recording material,
Color misregistration amount storage means for storing color misregistration amount information representing the amount of deviation of the exposure position in the sub-scanning direction when exposing while scanning the image carrier in the main scanning direction;
Color misregistration correction amount calculating means for calculating a color misregistration correction amount for correcting the misregistration amount in the sub-scanning direction based on the color misregistration amount;
Image data storage means for storing image data composed of a plurality of pixel data;
Based on the color misregistration amount of the color misregistration correction unit, the coordinates of the read address of the image data storage unit are converted, and the pixel data of the pixel of interest from the image data storage unit is converted according to the converted address information. Coordinate conversion means for reading;
Density conversion means for converting pixel density based on a color shift amount less than a pixel unit among the color shift correction amounts for the pixel data read from the image data storage means by the coordinate conversion means;
Halftone processing means for performing halftone processing of the pixel data subjected to density conversion in the density conversion means;
Exception processing means for performing exception processing of the pixel data subjected to density conversion in the density conversion means;
Of the image data stored in the image data storage means, the feature of the image data composed of pixels in a predetermined area centered on the target pixel is detected, and either the exception processing or the halftone processing is performed. Processing determining means for determining whether to select;
And an output unit that selects one of the processing results of the exception processing unit and the halftone processing unit based on the determination by the processing determination unit and outputs the selected result as an exposure control signal of the exposure unit. Forming equipment. An image forming apparatus having an image bearing member, an exposure unit that exposes the image bearing member, and an image forming unit that has a developing unit that visualizes an electrostatic latent image generated by exposure with a recording material,
Color misregistration amount storage means for storing color misregistration amount information representing the amount of deviation of the exposure position in the sub-scanning direction when exposing while scanning the image carrier in the main scanning direction;
Color misregistration correction amount calculating means for calculating a color misregistration correction amount for correcting the misregistration amount in the sub-scanning direction based on the color misregistration amount;
First image data storage means for storing image data composed of a plurality of pixels;
Based on the color misregistration amount in pixel units out of the color misregistration correction amount, the coordinates of the read address of the first image data storage means are converted, and from the first image data storage means according to the converted address information. Coordinate conversion means for reading image data and storing it in second image data storage means;
Density conversion means for reading pixel data of the pixel of interest from the second image data storage means, and converting pixel density based on a color shift amount less than a pixel unit among the color shift correction amounts;
Halftone processing means for performing halftone processing of the image data subjected to density conversion in the density conversion means;
Exception processing means for performing exception processing of the pixel data subjected to density conversion in the density conversion means;
Of the image data stored in the second image data storage means, the feature of the image data composed of pixels in a predetermined area centered on the target pixel is detected, and the exception processing and the halftone processing A process determining means for determining which one to select,
Based on the determination in the processing determination unit, the output unit for selecting one of the processing results of the exception processing unit and the halftone processing unit and outputting as an exposure control signal of the exposure unit,
The image forming apparatus according to claim 1, wherein the predetermined area is set so as to cancel address conversion based on a color shift amount in pixel units in the coordinate conversion unit. The processing determining means further determines a coefficient for performing the pixel density conversion based on the characteristics of the image data,
3. The image formation according to claim 1, wherein the density conversion unit performs pixel density conversion based on a color shift amount less than a pixel unit among the color shift correction amounts using the coefficient. apparatus.   The image forming apparatus according to claim 3, wherein the coefficient is a coefficient for dispersing the pixel density in the sub-scanning direction.   The image forming apparatus according to claim 3, wherein the coefficient is a coefficient for dispersing the pixel density of a predetermined magnification in the sub-scanning direction.   The image forming apparatus according to claim 3, wherein the coefficient is a coefficient for preventing the pixel density from being dispersed in the sub-scanning direction. The process determining means includes a pattern image storage means for storing a predetermined pattern image,
The feature is detected by comparing image data composed of pixels in a predetermined region centered on the pixel of interest with the pattern image. The image forming apparatus described. An image bearing member, an exposure unit that exposes the image bearing member, and an image forming unit that has a developing unit that visualizes the electrostatic latent image generated by the exposure with a recording material. A method of controlling an image forming apparatus including a color misregistration amount storage unit that stores color misregistration amount information representing a deviation amount of an exposure position in a sub-scanning direction when performing exposure while scanning in a scanning direction,
A color misregistration correction amount calculating step for calculating a color misregistration correction amount for correcting the misregistration amount in the sub-scanning direction based on the color misregistration amount;
A storage step of storing image data composed of a plurality of pixel data in an image data storage unit;
Based on the color misregistration amount in the color misregistration correction amount, the coordinates of the read address of the image data storage unit are converted, and the pixel data of the pixel of interest is obtained from the image data storage unit according to the converted address information. A coordinate transformation process to read,
A density conversion step of converting pixel density based on a color shift amount less than a pixel unit among the color shift correction amounts for the pixel data read from the image data storage unit in the coordinate conversion step;
A halftone processing step of performing halftone processing of the pixel data whose density has been converted in the density conversion step;
An exception processing step for performing exception processing of the pixel data whose density has been converted in the density conversion step;
Among the image data stored in the image data storage step, the feature of the image data composed of pixels in a predetermined area centered on the target pixel is detected, and either the exception processing or the halftone processing is performed. A process decision step for deciding whether to select;
And an output step of selecting a processing result in one of the exception processing step and the halftone processing step based on the determination in the processing determination step and outputting the selected result as an exposure control signal of the exposure unit. Control method of forming apparatus. An image bearing member, an exposure unit that exposes the image bearing member, and an image forming unit that has a developing unit that visualizes the electrostatic latent image generated by the exposure with a recording material. A method of controlling an image forming apparatus including a color misregistration amount storage unit that stores color misregistration amount information representing a deviation amount of an exposure position in a sub-scanning direction when performing exposure while scanning in a scanning direction,
A color misregistration correction amount calculating step for calculating a color misregistration correction amount for correcting the misregistration amount in the sub-scanning direction based on the color misregistration amount;
A storage step of storing image data composed of a plurality of pixels in the first image data storage unit;
Based on the color misregistration amount of the color misregistration correction unit, the coordinates of the read address of the first image data storage unit are converted, and from the first image data storage unit according to the converted address information. A coordinate conversion step of reading the image data and storing it in the second image data storage unit;
A density conversion step of reading pixel data of the pixel of interest from the second image data storage unit, and converting pixel density based on a color shift amount less than a pixel unit among the color shift correction amounts;
A halftone processing step of performing halftone processing of the pixel data whose density has been converted in the density conversion step;
An exception processing step for performing exception processing of the pixel data whose density has been converted in the density conversion step;
The image data stored in the second image data storage unit detects a feature of image data composed of pixels in a predetermined area centered on the target pixel, and the exception processing and the halftone processing A process decision step for deciding which one to select,
Based on the determination in the processing determination step, comprising selecting an processing result of any of the exception processing step and the halftone processing step, and outputting as an exposure control signal of the exposure unit,
The control method for an image forming apparatus, wherein the predetermined area is set so as to cancel address conversion based on a color shift amount in pixel units in the coordinate conversion step. In the process determining step, a coefficient for performing the pixel density conversion is further determined based on the characteristics of the image data,
10. The image according to claim 8, wherein in the density conversion step, pixel density conversion based on a color misregistration amount less than a pixel unit among the color misregistration correction amounts is performed using the coefficient. Control method of forming apparatus.   The image forming apparatus control method according to claim 10, wherein the coefficient is a coefficient for dispersing the pixel density in the sub-scanning direction.   The method of controlling an image forming apparatus according to claim 10, wherein the coefficient is a coefficient for dispersing the pixel density of a predetermined magnification in the sub-scanning direction.   The image forming apparatus control method according to claim 10, wherein the coefficient is a coefficient for preventing the pixel density from being dispersed in the sub-scanning direction.   The process determination step detects the feature by comparing image data composed of pixels in a predetermined region centered on the pixel of interest with a predetermined pattern image. 14. A method for controlling an image forming apparatus according to any one of 8 to 13.   15. A computer program for causing a computer to execute the image forming apparatus control method according to claim 8.   A computer-readable storage medium storing the computer program according to claim 15.

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