JP4420457B2 - Image forming apparatus, control method therefor, computer program, and storage medium - Google Patents

Description

  The present invention relates to an image forming apparatus, and more particularly, to an image forming apparatus capable of correcting a positional shift generated in an image forming unit.

  2. Description of the Related Art Conventionally, as a method for obtaining a full color image of an image forming apparatus using, for example, an electrophotographic method, an image forming apparatus including one photoconductor and a plurality of developing units corresponding to each toner color has a certain toner color. A method of fixing and forming a color image on the transfer paper by repeating the process of exposing and developing the photoconductor using a developing device corresponding to the above, and transferring to the transfer paper for each toner color. It has been known.

  According to this method, in order to obtain one printed image, it is necessary to repeat the image forming process a plurality of times, and there is a drawback that it takes time to form an image.

  In order to make up for this drawback, there is a method of using a plurality of photoconductors for each toner color and sequentially superimposing the visualized images obtained for each toner color on a transfer paper to obtain a full color print by one pass. Are known. According to this method, the time required for image formation can be greatly shortened. On the other hand, due to the positional accuracy and diameter deviation of each photoconductor, the optical system positional accuracy deviation, etc. There is a problem in that it is difficult to obtain a high-quality full-color image.

  As a configuration for preventing this misalignment, a test toner image is formed on a transfer paper or a transport belt for transporting the transfer paper, detected, and the optical path of each optical system is corrected based on the detection result. In addition, a configuration for correcting the writing start position of each toner color image is known (Patent Document 1).

Further, a positional shift of each toner color is detected by a method similar to the configuration disclosed in Patent Document 1, a coordinate conversion equation is derived based on the detected value of the positional shift, and a coordinate is converted using this coordinate conversion equation. A configuration for outputting image data while performing conversion is known (Patent Document 2). Furthermore, when the dot position coordinate after coordinate conversion includes a value after the decimal point, the amount of toner is reduced around the location where the point is ideally located to form a dot, thereby causing streak spots due to quantization errors. A configuration that prevents generation is known (Patent Document 2).
Japanese Patent Application Laid-Open No. 64-40956 JP-A-8-85237

  However, the method disclosed in Patent Document 1 has the following problems. 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, and the position of the test toner image. 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 positional deviation by correcting the optical path of the optical system. In addition, by correcting the image writing position, it is possible to correct the positional deviation at the writing position, but it is not possible to correct the tilt of the optical system or the magnification deviation due to the optical path length deviation. There is.

  The method disclosed in Patent Document 2 has the following problems. That is, according to the configuration in which the image data is output while performing the coordinate conversion, it is possible to deal with a global positional shift, but streaks due to the quantization error occur. In addition, when the dot position coordinate after coordinate conversion includes a value after the decimal point, according to the configuration in which the dot is formed by reducing the amount of toner around the place where the point is ideally located, the streak due to the quantization error is to some extent. Although it is possible to prevent spots, it is necessary to finely control the toner coating amount in order to obtain a good image. However, in order to finely control the toner application amount, it is necessary to increase the number of bits allocated to one pixel of the image data. For this reason, this configuration requires a large-capacity memory for storing image data, leading to an increase in manufacturing cost of the apparatus.

  Note that the above-described problems of the prior art are the same when a monochrome image is formed.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a technique capable of obtaining a good image without requiring a large-capacity memory even in a configuration in which positional deviation occurs in an image forming unit.

In order to achieve the above object, an image forming apparatus according to the present invention comprises the following arrangement. That is,
An image forming apparatus including an image forming unit that forms an image on a recording medium,
An image memory for holding a plurality of pixels information,
Storage means for storing correction information relating to positional deviation correction of the image formed by the image forming unit;
Conversion means for converting the coordinates of the read address of the image memory based on the correction information stored in the storage means, and sequentially reading the pixel information based on the converted address information;
Holding means for holding the pixel information converted by the conversion means, pixel information for performing gradation correction processing, and pixel information preceding at least one line with respect to the pixel information for performing gradation correction processing ;
According to the correction amount of correction less than a pixel unit of the correction information, correction coefficients for pixel information to be subjected to gradation correction processing and pixel information preceding at least one line from the pixel information to be subjected to the gradation correction processing are respectively calculated. A calculation means;
Pixel information corresponding to the position of the pixel information to be subjected to gradation correction processing among the pixel information to be subjected to gradation correction held in the holding means and the pixel information preceding the one line held in the holding means. Tone correction means for correcting color misregistration less than a pixel by increasing each bit width and multiplying the pixel information with the increased bit width by the corresponding correction coefficient and then adding them ,
Halftoning means for performing halftoning on the pixel information whose bit width has been subjected to gradation correction in the gradation correction means is increased.

  According to the present invention, it is possible to provide a technique capable of obtaining a good image without requiring a large-capacity memory even in a configuration in which positional deviation occurs in the image forming unit.

  Embodiments according to the present invention will be described below in detail with reference to the accompanying drawings. However, the constituent elements described in this embodiment are merely examples, and are not intended to limit the scope of the present invention only to them.

[Physical configuration of image forming apparatus]
FIG. 1 is a schematic sectional view showing an outline of a physical configuration of an image forming apparatus corresponding to the present embodiment, and corresponds to, for example, a four-drum type color laser beam printer. In this image forming apparatus, a transfer paper cassette 53 is mounted at the lower right side of the main body apparatus. Transfer paper (transfer material, transfer medium, recording paper) as a recording medium set in the transfer paper cassette 53 is taken out one by one by a paper feed roller 54, and an image is taken by a pair of transport rollers 55-a and 55-b. It is fed to the area where the forming unit is located. In the area where the image forming unit is arranged, a transfer conveyance belt 10 as a conveyance means for conveying the transfer paper is stretched flat by a plurality of rotating rollers in the transfer paper conveyance direction (from right to left in FIG. 1). In the most upstream part, the transfer conveyance belt 10 is electrostatically adsorbed. The photosensitive drums 14-C, 14-Y, 14-M, and 14-K (hereinafter collectively referred to as 14) as four drum-shaped photosensitive members (image bearing members) facing the belt conveyance surface. ) Are arranged in a straight line.

  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, the color component C will be described.

  The C-color image forming unit contains 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 device 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. Thus, a charged state different from the non-exposed portion, that is, an electrostatic latent image is generated in the scanned and exposed portion. The developing device 52-C transfers the toner to the electrostatic latent image to make a visible image (toner image; development).

  A transfer member 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 member 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.

  As described above, the photosensitive drum 14, the exposure unit 51, the developing device 52, and the transfer member 57 integrally form an image forming unit, and each of the image forming units includes C, Y, M, and K. Installed for each basic color. It goes without saying that the image forming unit inputs a drive signal and forms a single color image on the transfer paper based on the drive signal. Note that the transfer conveyance belt 10 may be configured as an intermediate transfer belt having a configuration in which toners of basic colors of C, Y, M, and K are temporarily transferred and then secondarily transferred onto a transfer sheet. In addition, if the configuration is such that a plurality of image forming units are juxtaposed, transfer paper is conveyed between the image forming units, and a monochromatic image is superimposed on the transfer paper, a configuration using a laser beam printer as in this embodiment is used. For example, an ink jet printer may be used.

[Color shift model]
FIG. 2 is an image view showing a shift of the main scanning line formed by scanning on the photosensitive drum 14. 301 is an image of an ideal main scanning line, and scanning is performed perpendicularly to the rotation direction (Y 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 of the right-up due to the positional accuracy of the optical system in the exposure unit 51 of each basic color and the curvature are generated. It is an image. When such an inclination or curvature of the main scanning line exists in any of the basic color image stations, color misregistration (position misregistration, registration misalignment) occurs when a plurality of color toner images are collectively transferred to the transfer paper. Will occur. In the present embodiment, in the main scanning direction (X direction), an ideal main scanning line at a plurality of points (point B, point C, point D) with the point A serving as the scanning start position of the print area as a reference point. The amount of deviation in the sub-scanning direction (Y direction) between 301 and the actual main scanning line 302 is measured, and a plurality of regions (region 1 between Pa-Pb and region 1 between Pb-Pc) for each point where the amount of deviation is measured. 2 and Pc-Pd is divided into regions 3), and the inclination of the main scanning line in each region is approximated by straight lines (Lab, Lbc, Lcd) connecting the points. In the example of FIG. 2, the deviation amounts are measured at the respective points Pb, Pc, and Pd, and the deviation amounts are m1, m2, and m3, respectively. Therefore, when the difference in the amount of deviation 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 illustrated in FIG. In the XY plane, it indicates that it has an upward slope, and when it is a negative value, it indicates that it has a downward slope.

[Functional configuration of image forming apparatus]
Next, functions of the image forming apparatus corresponding to the present embodiment will be described with reference to FIG. FIG. 3 is a functional block diagram of the image forming apparatus corresponding to the present embodiment for explaining the operation of color misregistration correction processing for correcting color misregistration caused by the inclination and curvature of the scanning line.

  In FIG. 3, reference numeral 401 denotes a printer engine, which performs print processing based on image bitmap information generated by the controller 402, specifically based on a drive signal input from a PWM 410 described later.

  Reference numerals 403C, 403M, 403Y, and 403K (hereinafter collectively referred to as 403) are color misregistration amount storage units for each basic color, and store information on the main scanning line color misregistration for each area described above for each basic color. To do. In the present embodiment, the difference between the actual main scanning line 302 and the ideal main scanning line 301 described with reference to FIG. 2, that is, the main scanning direction ( The width in the X direction and the shift amount in the sub-scanning direction (Y direction) are stored in the color shift amount storage unit 403 as information indicating the inclination and curvature of the main scanning line.

  FIG. 4 is a diagram exemplarily showing information stored in the color misregistration amount storage unit 403. Regions 1 to 3 in FIG. 4 correspond to the regions in FIG. For example, the widths of the regions 1 to 3 in FIG. 4 are the widths of the regions 1 to 3 in FIG. 2, that is, the x coordinate difference of (Pa, Pb), the x coordinate difference of (Pb, Pc), and (Pc, Pd). Respectively corresponding to the x coordinate difference. Further, the shift amounts of the regions 1 to 3 in FIG. 4 are the shift amounts of the regions 1 to 3 in FIG. 2, that is, the y coordinate difference of (Pa, Pb), the y coordinate difference of (Pb, Pc), (Pc, It corresponds to the y coordinate difference of Pd).

  In this embodiment, the color misregistration amount storage unit 403 stores the misregistration amount between an ideal main scanning line and an actual main scanning line as information on color misregistration. The information is not limited to this as long as it is information (for example, the actual main scanning line inclination, end point coordinates, etc.) that can derive the inclination and curvature characteristics of the scanning line. The information stored in the color misregistration amount storage unit 403 may be stored in advance as information unique to the image forming apparatus by measuring the misregistration amount in the manufacturing process of the apparatus. The forming apparatus itself is provided with a detection mechanism for detecting the shift amount, a predetermined pattern for measuring the shift is formed for each basic color photoconductor drum 14, and the shift amount detected by the detection mechanism is determined. The configuration may be such that it is memorized.

  Next, an operation of performing printing processing by correcting image data so as to cancel out the main scanning line shift amount stored in the color shift amount storage unit 403 in the controller 402 will be described.

  The image generation unit 404 generates raster image data that can be printed from print data received from a computer device (not shown) and outputs the image data for each dot as RGB (Red, Green, Blue) data. Reference numeral 405 denotes a color conversion unit that converts RGB data output from the image generation unit 404 into CMYK space data that can be processed by the controller 402 and stores the data for each basic color in a bitmap memory (image memory) 406 described later. To do. The bitmap memory 406 temporarily stores raster image data to be printed, and is 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 (hereinafter collectively referred to as 407) are color misregistration correction amount calculation units, and each dot is based on information such as a main scanning line misregistration amount accumulated in the color misregistration amount storage unit 403. Each time, a color misregistration correction amount in the sub-scanning direction corresponding to coordinate information in the main scanning direction designated from a color misregistration amount correcting unit 408 described later is calculated and output to the color misregistration amount correcting unit 408, respectively.

  The color misregistration correction amount calculation unit 407 derives a color misregistration correction amount in the sub-scanning direction by executing, for example, the following calculation. That is, 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 formula of each region based on FIGS. The following calculation assumes that the print density is 600 dpi.

Region 1: Δy1 = x * (m1 / L1)
Region 2: Δy2 = m1 * 23.622 + (x−L1 * 23.622) * ((m2−m1) / (L2−L1))
Region 3: Δy3 = m2 * 23.622 + (x−L2 * 23.622) * ((m3−m2) / (L3−L2))
As shown in FIG. 2, L1, L2, and L3 are distances (unit: mm) in the main scanning direction from the print start position to the left ends of the regions 1, 2, and 3. m 1, m 2, and m 3 are deviation amounts between the ideal main scanning line 301 and the actual main scanning line 302 at the left ends of the regions 1, 2, and 3.

  Reference numerals 408C, 408M, 408Y, and 408K (hereinafter collectively referred to as 408) denote color misregistration amount correction units. In order to correct the color misregistration due to the inclination and distortion of the main scanning line, the color misregistration amount calculation unit 407 performs dot correction. Based on the color misregistration correction amount calculated every time, the output timing of the bitmap data stored in the bitmap memory 406 and the exposure amount for each pixel are adjusted, and the toner image of each basic color is transferred. This prevents color misregistration when transferred to paper.

  Next, the color misregistration amount correction unit 408 will be described with reference to FIG. FIG. 7 is a block diagram schematically showing the configuration of the color misregistration amount correction unit 408.

  As shown in FIG. 7, the color misregistration correction unit 408 includes a coordinate counter 801, a coordinate conversion unit 802, a line buffer 803, and a gradation correction unit 804. The coordinate counter 801 outputs the coordinate position data in the main scanning direction and the sub-scanning direction in which color misregistration correction processing is performed to the coordinate conversion unit 802, and at the same time, converts the coordinate position data in the main scanning direction into the color misregistration amount calculation unit 407, And output to the gradation correction unit 804. A coordinate conversion unit 802 as a conversion unit is based on the coordinate position data in the main scanning direction and the sub-scanning direction input from the coordinate counter 801 and the correction amount Δy obtained from the color misregistration correction amount calculation unit 407. Correction processing for the integer part of Δy, that is, reconstruction processing in the sub-scanning direction in units of pixels is performed. A gradation correction unit 804 as an acquisition unit is based on the coordinate position data in the main scanning direction from the coordinate counter 801 and the correction amount Δy, and correction processing below the decimal point of Δy, that is, before and after the sub scanning direction in less than a pixel unit. Correction is performed by adjusting the exposure ratio of dots. The gradation correction unit 804 uses a line buffer (holding unit) 803 for referring to dots before and after in the sub-scanning direction.

  As described above, the color misregistration amount correction unit 408 includes a coordinate conversion unit 802 that performs a correction process on the integer part of the correction amount Δy obtained from the color misregistration correction amount calculation unit 407, that is, a reconstruction process in the sub-scanning direction in units of pixels. , Δy, and a gradation correction unit 804 that performs correction by adjusting the exposure ratio of dots before and after the sub-scanning direction in less than a pixel unit, and the gradation correction unit 804 is sub-scanning. A line buffer is used to refer to dots before and after the direction.

  Next, processing of the coordinate conversion unit 802 of the color misregistration amount correction unit 408 will be described with reference to FIG. FIG. 5 is a diagram schematically showing an operation content in which the coordinate conversion unit 802 corrects the shift amount of the integer part of the color shift correction amount Δy.

  As shown in FIG. 5A, the coordinate conversion unit 802 stores the bitmap memory 406 in accordance with the value of the integer part of the color misregistration correction amount Δy obtained from the color misregistration information of the main scanning line approximated by a straight line. The coordinates in the sub-scanning direction (Y direction) of the accumulated image data are offset. For example, as shown in FIG. 5B, if the coordinate position in the sub-scanning direction from the coordinate counter 801 is n, and the coordinate position in the main scanning direction is X, the area A in the X coordinate in the main scanning direction In this case, since the color misregistration correction amount Δy is 0 or more and less than 1 and the offset amount is 0, when reconstructing the nth line data, the nth line data is read from the bitmap memory. In the region B, when the color misregistration correction amount Δy is 1 or more and less than 2 and the data of the nth line is reconstructed, the image bit map at the position where the number of one sub-scanning line is offset, that is, n + 1 lines from the bitmap memory A coordinate conversion process for reading eye data is performed. Similarly, coordinate conversion processing is performed in order to read data of the (n + 2) th line in the area C and n + 3th line in the area D. Through the above processing, reconstruction processing in the sub-scanning direction in units of pixels is performed.

  FIG. 5C shows an exposure image when image data that has been subjected to color misregistration correction in pixel units by the coordinate conversion unit 802 is exposed on the photosensitive drum 14. Even when the main scanning direction is deviated obliquely during image formation, by executing the reconstruction process in the sub-scanning direction as described above, the image of the straight line on the transfer paper is made close to the original image. Can be formed.

  Next, processing in which the gradation correction unit 804 performs correction by adjusting the exposure ratio of dots before and after the sub-scanning direction in less than a pixel unit will be described with reference to FIG. FIG. 6 is a diagram schematically showing the content of an operation for correcting the color misregistration performed by the gradation correcting unit 804 in less than a pixel unit, that is, correcting the color misregistration correction amount Δy after the decimal point. Correction of the shift amount after the decimal point is performed by adjusting the exposure ratio of dots before and after in the sub-scanning direction.

  FIG. 6A exemplarily shows an image of a main scanning line having an upward slope. FIG. 6B is a bitmap image of a horizontal straight line before gradation correction, that is, the original image, and FIG. 6C is for canceling the color shift due to the inclination of the main scanning line in FIG. 4B is a corrected bitmap image after gradation correction of the bitmap image exemplified in (b). The corrected bitmap image of (c) is ideal when the amount of tilt deviation is given by (a), for example. The gradation correction unit 804 is close to the correction bitmap image by adjusting the exposure amount for the regular grid points and further the toner application amount in order to form an image close to the correction bitmap image of (c). Form an image.

In order to realize the correction image of (c), the exposure amount adjustment of dots before and after in the sub-scanning direction is performed. FIG. 6D is a table showing the relationship between the color misregistration correction amount Δy and the correction coefficient for performing gradation correction. 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.
α = Δy−k
β = 1−α
Is calculated by α represents the distribution ratio for the scanning dot, and β represents the distribution ratio for the subsequent dot.

  FIG. 6E schematically shows a gradation-corrected bitmap image for adjusting the exposure ratio of dots before and after in the sub-scanning direction based on α and β as correction coefficients in (d). FIG. FIG. 6F shows an exposure image of the bitmap image with the gradation corrected on the photosensitive drum 14, and the inclination of the main scanning line is canceled out by the bitmap image with the gradation corrected, thereby forming a horizontal straight line. It shows how it is being done.

  Again, the gradation correction process will be described with reference to FIG. First, the coordinate conversion unit 802 reconfigures the image data input from the bitmap memory 406 to correct the color misregistration amount in units of pixels based on the correction amount acquired from the color misregistration correction amount calculation unit 407. Specifically, the coordinates of the read address of the bitmap memory 406 are converted based on the correction amount acquired from the color misregistration correction amount calculation unit 407, and the image data is read based on the converted address information. In this way, for example, dots arranged in the main scanning direction (corresponding to, for example, the right direction in FIG. 5B) in the oblique basis system as illustrated in FIG. 5C and FIG. 6F. The pixel information corresponding to is sequentially acquired from the bitmap memory 406. Then, the reconstructed image data is transferred to the line buffer 803. Also, the coordinate conversion unit 802 obtains the values of α and β by the above-described calculation from Δy acquired from the color misregistration correction amount calculation unit 407 and outputs the values to the gradation correction unit 804.

  The color misregistration amount correction unit 408 is configured to receive the value of the correction amount Δy from the color misregistration correction amount calculation unit 407 each time pixel information for one dot is output to the halftone processing unit 409, for example. Alternatively, the value of the correction amount Δy for one line may be received from the color misregistration correction amount calculation unit 407 in advance of processing, and the processing may be advanced based on this value.

  In the above description, the coordinate conversion unit 802 calculates α, β and the like from the correction amount Δy. However, the color misregistration correction amount calculation unit 407 includes the color misregistration amount storage unit 403 from the correction amount Δy. A configuration may be adopted in which β and the like are obtained, and α, β, and the like are output based on requests from the components of the color misregistration correction unit 408. Also in this case, for example, the color misregistration correction unit 408 may acquire α and β for one line from the color misregistration correction amount calculation unit 407 in advance of processing, or for one dot. You may make it acquire whenever it processes about this pixel information.

  The line buffer 803 temporarily buffers (holds and stores) image data of a predetermined row because the gradation correction unit 804 needs to refer to pixel values before and after the sub-scanning direction when generating correction data. Storage device. In the present embodiment, the data amount to be buffered is one line (row) of image data for simplification of description, but data of two or more lines may be buffered.

  The line buffer 803 includes a FIFO (First In First Out) buffer 806 that stores data for one line of the preceding line, and a register 805 that holds pixel data of coordinates for performing gradation correction processing. The pixel data stored in the register 805 is output to the gradation correction unit 804 and is also stored in the FIFO buffer 806 and used to generate correction data for the next line.

  The gradation correction unit 804 has x (dot) coordinates in the main scanning direction, Pn (x) (pixel data on the nth line) pixel data input from the register 805, and Pn− pixel data input from the FIFO buffer 806. If 1 (x) (pixel data on the (n−1) -th line), the following arithmetic processing is performed to generate correction data.

P′n (x) = Pn (x) * β (x) + Pn−1 (x) * α (x)
However, as described above, the values of α and β are acquired from the coordinate conversion unit 802. The gradation correction unit 804 outputs the value of P′n (x) obtained by the above calculation to the halftone processing unit 409 as an image bitmap in which the amount of color misregistration less than a pixel unit in the sub-scanning direction is corrected.

  When the halftone processing units 409C, 409M, 409Y, and 409K (collectively referred to as 409) receive image data that has undergone color misregistration correction from the tone correction unit 804 (color misregistration correction unit 480), the predetermined halftone processing is performed. Halftone processing is performed using the pattern, and the processed image data is output to PWM (Pulse Wide Modulation) units 410C, 410M, 410Y, 410K (hereinafter collectively referred to as 410).

  When the PWM unit 410 receives the image data subjected to the halftone process, the PWM unit 410 performs a pulse width modulation process on the image data and outputs it to the printer engine 401 as a drive signal. Based on the received drive signal, the printer engine 401 executes exposure processing, development processing, transfer processing to transfer paper, and the like on the photosensitive drum 14.

  In the present embodiment, the gradation correction unit 804 performs bit expansion of input image data in addition to the above processing, and outputs the image data subjected to bit expansion to the halftone processing unit 409 and the PWM unit 410. This makes it possible to form a fine image. The processing of the gradation correction unit 804 and its effect will be described in detail with reference to FIG. FIG. 8 shows that a better image can be obtained by assigning many bits to the number of bits of data output from the bitmap memory when performing gradation correction and performing color shift correction. It is a schematic diagram for demonstrating.

  In the example of FIG. 8, each pixel of the image data input to the gradation correction unit is represented by 2 bits. In FIG. 8, FIG. 8 (a) shows an image of a main scanning line having an upward slope. FIG. 8B is a bitmap image of a horizontal straight line before gradation correction, and FIG. 8C is a diagram for canceling color misregistration due to the inclination of the main scanning line in FIG. ) Is a corrected bitmap image. In order to realize the corrected bitmap image of FIG. 8C, the exposure amount adjustment of dots before and after the sub-scanning direction is performed. FIG. 8D shows a list of Δy and the values of k, α, and β corresponding to Δy, and the values of α and β are the above-described equations (α = Δy−k, β = 1-α).

  The gradation correction unit 804 performs color misregistration correction for less than a pixel unit based on the correction coefficient illustrated in FIG. Further, processing for extending the bit width of each pixel is performed. The effect of the process of extending the bit width will be described with reference to FIGS. 8 (e), (f), (g), and (h).

  8E shows a case where each pixel after gradation correction is expressed by 2 bits, and FIG. 8F shows a case where each pixel after gradation correction is expressed by 4 bits. A bit map image on the drum 14 is schematically shown.

  The correction coefficients illustrated in FIG. 8D are divided into 10 gradations in total, but in FIG. 8E, only 2 gradations are expressed because the number of bits (bit width) is only 2 bits. Therefore, it is necessary to express the calculated correction value by rounding it down to 4 gradations. In this case, an exposure image on the photosensitive drum 14 is as shown in FIG.

  On the other hand, since the number of bits is expanded to 4 bits in FIG. 8F, the value of each pixel can be expressed up to 16 gradations. For this reason, it is possible to reduce the rounding error of the correction coefficient obtained in FIG. In this case, the exposure image on the photosensitive drum 14 is as shown in FIG. As apparent from the comparison with FIG. 8 (g) of 2 bits, a more precise and good image can be obtained.

  Information on how much the number of bits per pixel is expanded is stored in a predetermined storage device, and the gradation correction unit 804 refers to this information at the time of bit expansion, and based on this information, the bit The extension process shall be controlled. In the above description, the input is 2 bits, but the same effect can be obtained even if the number of bits allocated to one pixel is increased by using the same configuration.

  As described above, the gradation correction unit 804 expands the bit width (number of bits) per pixel and then outputs data to the halftone processing unit, so that even in an environment where there is a color shift for each image forming unit. A precise and detailed image can be formed. In the above configuration, since the gradation correction unit 804 performs a process of expanding the bit width of each pixel, the bit width of each pixel of the image data input to the color misregistration correction unit may be normal. Therefore, according to the above configuration, a precise and detailed image can be formed without increasing the capacity of the storage device such as the bitmap memory 406 and the line buffer 803.

[Other Embodiments]
In the above configuration, information about how much the number of bits per pixel is expanded is stored in a predetermined storage device, but the embodiment of the present invention is not limited to such a configuration. For example, an instruction input device that functions as a user interface that can be operated by a user is provided, and an instruction input such as how many times the number of bits is expanded is received via the instruction input device. You may make it control hit bit extension. With such a configuration, the user can easily set the fineness and precision of image formation according to the application and purpose.

  As described above, the exemplary embodiments of the present invention have been described in detail. However, the present invention can take an embodiment as, for example, a system, an apparatus, a method, a program, or a storage medium. You may apply to the system comprised from an apparatus, and may apply to the apparatus which consists of one apparatus.

  The present invention can also be achieved by supplying a program that realizes the functions of the above-described embodiment directly or remotely to a system or apparatus, and the computer of the system or apparatus reads and executes the supplied program code. Including the case where it is achieved.

  Therefore, since the functions of the present invention are implemented by a computer, the program code installed in the computer is also included in the technical scope of the present invention. That is, the present invention includes a computer program itself for realizing the functional processing of the present invention.

  In that case, as long as it has the function of a program, it may be in the form of object code, a program executed by an interpreter, script data supplied to the OS, or the like.

  As a recording medium for supplying the program, for example, floppy (registered trademark) disk, hard disk, optical disk, magneto-optical disk, MO, CD-ROM, CD-R, CD-RW, magnetic tape, nonvolatile memory card ROM, DVD (DVD-ROM, DVD-R) and the like.

  As another program supply method, a client computer browser is used to connect to an Internet homepage, and the computer program of the present invention itself or a compressed file including an automatic installation function is downloaded from the homepage to a recording medium such as a hard disk. Can also be supplied. It can also be realized by dividing the program code constituting the program of the present invention into a plurality of files and downloading each file from a different homepage. That is, the present invention includes a WWW server that allows a plurality of users to download a program file for realizing the functional processing of the present invention on a computer.

  In addition, the program of the present invention is encrypted, stored in a storage medium such as a CD-ROM, distributed to users, and key information for decryption is downloaded from a homepage via the Internet to users who have cleared predetermined conditions. It is also possible to execute the encrypted program by using the key information and install the program on a computer. In addition to the functions of the above-described embodiments being realized by the computer executing the read program, the OS running on the computer based on the instruction of the program is a part of the actual processing. Alternatively, the functions of the above-described embodiment can be realized by performing all of the processes.

  Furthermore, after the program read from the recording medium is written in a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer, the function expansion board or The CPU or the like provided in 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 schematic cross-sectional view showing an outline of a physical configuration of an image forming apparatus corresponding to the present embodiment. FIG. 4 is an image diagram showing a shift of a main scanning line formed by scanning on a photosensitive drum. 2 is a functional block diagram of an image forming apparatus corresponding to the present embodiment. FIG. 6 is a diagram exemplarily showing information stored in a color misregistration amount storage unit. FIG. It is the figure which showed typically the operation | movement content which a coordinate conversion part correct | amends the deviation | shift amount of the integer part of color shift correction amount (DELTA) y. It is the figure which showed typically the operation content of the color misregistration correction for less than the pixel unit which a gradation correction | amendment part performs. FIG. 3 is a block diagram schematically illustrating a configuration of a color misregistration amount correction unit. It is the figure which showed typically the process which allocates many bits with respect to the bit number of the data output from the bitmap memory when performing gradation correction.

Claims (10)

An image forming apparatus including an image forming unit that forms an image on a recording medium,
An image memory for holding a plurality of pixels information,
Storage means for storing correction information relating to positional deviation correction of the image formed by the image forming unit;
Conversion means for converting the coordinates of the read address of the image memory based on the correction information stored in the storage means, and sequentially reading the pixel information based on the converted address information;
Holding means for holding the pixel information converted by the conversion means, pixel information for performing gradation correction processing, and pixel information preceding at least one line with respect to the pixel information for performing gradation correction processing ;
According to the correction amount of correction less than a pixel unit of the correction information, correction coefficients for pixel information to be subjected to gradation correction processing and pixel information preceding at least one line from the pixel information to be subjected to the gradation correction processing are respectively calculated. A calculation means;
Pixel information corresponding to the position of the pixel information to be subjected to gradation correction processing among the pixel information to be subjected to gradation correction held in the holding means and the pixel information preceding the one line held in the holding means. Tone correction means for correcting color misregistration less than a pixel by increasing each bit width and multiplying the pixel information with the increased bit width by the corresponding correction coefficient and then adding them ,
An image forming apparatus comprising: halftoning means for performing halftoning on the pixel information whose bit width has been subjected to gradation correction in the gradation correction means. A plurality of the image forming units are provided corresponding to basic colors, and each of the image forming units forms an image of the basic color corresponding to the recording medium,
A plurality of the storage means, the conversion means, the holding means, the gradation correction means, and the halftoning means are provided corresponding to the basic colors, respectively.
Further, the recording medium includes a conveying unit that conveys the recording medium between the plurality of image forming units and forms the basic color image on the recording medium in a superimposed manner using the plurality of image forming units. The image forming apparatus according to claim 1. The image forming unit includes:
A photoreceptor that forms an electrostatic latent image based on irradiation of a light beam;
Exposure means for irradiating the photoreceptor with a light beam;
Developing means for developing a toner image on the photosensitive member by transferring a monochromatic toner to the photosensitive member on which the electrostatic latent image is formed based on irradiation of a light beam from the exposing unit;
The image forming apparatus according to claim 1, further comprising: a transfer unit that transfers the toner image developed on the photoconductor to the recording medium. Furthermore, an input means for inputting increase information relating to the increase in the bit width,
The image forming apparatus according to claim 1, wherein the gradation correction unit increases a bit width of each pixel based on the increase information. A method for controlling an image forming apparatus including an image forming unit that forms an image on a recording medium,
Based on the correction information related to the positional deviation correction of the image formed by the image forming unit, the coordinates of the read address of the image memory holding a plurality of pixel information are converted, and the pixel information is converted based on the converted address information. A conversion process for sequentially reading
A the pixel information converted in said converting step, the pixel information for performing tone correction processing, to hold the holding means and the pixel information preceding least one line to pixel information to be grayscale correction Holding process;
According to the correction amount of correction less than a pixel unit of the correction information, correction coefficients for pixel information to be subjected to gradation correction processing and pixel information preceding at least one line from the pixel information to be subjected to the gradation correction processing are respectively calculated. A calculation process;
Pixel information corresponding to the position of the pixel information to be subjected to gradation correction processing among the pixel information to be subjected to gradation correction held in the holding means and the pixel information preceding the one line held in the holding means. A gradation correction step for correcting color misregistration of less than a pixel by increasing each bit width, multiplying the pixel information with the increased bit width by the corresponding correction coefficient, and then adding the correction coefficient ;
And a halftoning step of performing halftoning on the pixel information in which the bit width subjected to gradation correction in the gradation correction step is increased. A plurality of the image forming units are provided corresponding to basic colors, and each of the image forming units forms an image of the basic color corresponding to the recording medium,
A plurality of the storage means and the holding means are provided corresponding to the basic colors,
The conversion step, the holding step, the gradation correction step, and the halftoning step are executed for each basic color,
The image forming apparatus further includes a conveying step of conveying the recording medium between the plurality of image forming units and forming the basic color image on the recording medium in a superimposed manner using the plurality of image forming units. The method of controlling an image forming apparatus according to claim 5. The image forming unit includes:
A photoreceptor that forms an electrostatic latent image based on irradiation of a light beam;
Exposure means for irradiating the photoreceptor with a light beam;
Developing means for developing a toner image on the photosensitive member by transferring a monochromatic toner to the photosensitive member on which the electrostatic latent image is formed based on irradiation of a light beam from the exposing unit;
The image forming apparatus control method according to claim 5, further comprising: a transfer unit that transfers the toner image developed on the photoconductor to the recording medium. And an input step for inputting increase information regarding the increase in the bit width,
The image forming apparatus control method according to claim 5, wherein the gradation correction step increases a bit width of each pixel based on the increase information.   A computer program for causing a computer to execute the method for controlling an image forming apparatus according to claim 5.   A computer-readable storage medium storing the computer program according to claim 9.

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