JP4898293B2 - Image forming apparatus, image forming method, and program - Google Patents

Description

The present invention, images forming apparatus and images forming method for forming the images, as well, and a program for executing the image forming method in a computer.

  2. Description of the Related Art Conventionally, as a color image forming apparatus using an electrophotographic system, there is an apparatus that performs development for each color using a plurality of developing units for one photoconductor. In this color image forming apparatus, a method of forming a full color image by superposing and forming a color image on a single transfer sheet by repeating the exposure-development-transfer process a plurality of times is generally used. .

Japanese Patent Application Laid-Open No. 64-40956 JP-A-8-85237 JP-A-11-266360

  However, in the above-described method, it is necessary to repeat the image forming process three to four times (when black is used) in order to obtain one print image, which has a drawback that it takes time. As a method for compensating for this defect, there is a method in which a plurality of photoconductors are used to sequentially superimpose the obtained images for each color on a transfer paper and perform a full color print by one paper passing.

  According to this method using a plurality of photoconductors, the throughput can be greatly shortened. On the other hand, transfer of each color is caused by the positional accuracy and diameter deviation of each photoconductor, the optical system positional accuracy, etc. There has been a problem of color misregistration due to misregistration on paper. This makes it 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 paper or a conveyance belt forming a part of a transfer unit, detected, and the optical path of each optical system is detected based on this result. Or a method of correcting the image writing position of each color (see Patent Document 1). However, this method 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. However, in order to do this, 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 frequently correcting the optical path of the optical system.

  Second, it is possible to correct the misalignment of the left end and the upper left by correcting the image writing position, but it can correct the tilt of the optical system or the magnification shift due to the optical path length shift. There is a problem that it cannot be done.

  Thirdly, since the condition of the toner varies depending on the process state (operating environment state of the color image forming apparatus) such as temperature, humidity, and remaining toner amount that changes with time, the image is reproduced with high image quality depending on the process condition. It becomes difficult.

  Further, in Patent Document 2, the output coordinate position of the image data for each color is automatically converted into a position where the registration deviation is corrected, and the position of the light beam modulated based on the converted image data of each color is expressed as a color signal. It is disclosed that correction is performed with an amount smaller than the minimum dot unit.

  However, in the configuration of Patent Document 2, the halftone dot reproducibility of the intermediate gradation image is deteriorated by correcting the output coordinate position of the image data for each color with respect to the image subjected to the intermediate gradation processing. There is a problem in that color unevenness may occur and moire may become apparent. An example of this will be described with reference to FIG.

FIG. 1 is a schematic view showing density unevenness.
An input image 101 shown in FIG. 1A is an image having a constant density value. FIG. 1B shows an image (image after color misregistration correction processing) 102 after performing a certain color misregistration correction processing on the input image 101. When the image 102 is actually printed, the input image 101 is an image having a constant density value because the relationship between the image density value and the toner density with respect to the image density value is not linear as shown in FIG. Nevertheless, an image with a non-constant density value is printed. When such a non-uniform density value is periodically repeated, moire becomes obvious and there is a problem that a good color image cannot be obtained.

  Further, Patent Document 3 discloses a method of identifying a mesh line area and performing correction less than a pixel unit without performing edge enhancement on the mesh line area. However, the method of Patent Document 3 has a problem in that moire becomes obvious due to halftone processing such as halftone processing on the corrected pixel, and a good color image cannot be obtained.

The present invention has been made in view of the above problems, it is dependent on the reproducibility of the image to the operating environmental conditions (process state) without not a Re to eliminate the moire caused by the correction, the good images images forming device for realizing the acquisition, and to provide the images forming method, and a program.

Images forming apparatus of the present invention processes the input image, image by by exposing the image bearing member to form a latent image based on the input image after the process, developed by the developer the latent image an image forming apparatus for forming a detects an operating environment in the image forming apparatus, and the operation environment detecting means for outputting an operation environment information based on the result of the detection, the sub-scanning line of exposure in the image forming apparatus and Figure been amount storage means for storing a displacement amount in the scanning direction, it said not a Re based on the amount Re not obtained from the amount storage means, a correction amount calculation means Re without calculating the correction amount Re not a, the shift correction amount based on a first correction means for correcting the sub scanning direction of displacement of the pixel unit with respect to the input image, detecting means for detecting an edge portion of the input image, an edge by the detecting means of the input image first image detected as part Against over data, according to the correction coefficient based on the error correction amount, and a second correction means for correcting the sub scanning direction deviation of less than the pixel unit is not detected as an edge part by the detecting means of the input image for the second image data, it possesses a halftone processing unit that performs halftone processing, the said second correction means, based on the operating environment information, the correction coefficient based on the error correction amount Adjust .
The image forming method of the present invention processes an input image, exposes an image carrier based on the input image after the processing to form a latent image, and develops the latent image with a developer to form an image. An image forming method in an image forming apparatus to form, an operating environment detecting step for detecting an operating environment in the image forming apparatus and outputting operating environment information based on a result of the detection, and scanning of exposure in the image forming apparatus A deviation amount storing step for storing a deviation amount of the line in the sub-scanning direction in a deviation amount storage means; a deviation correction amount calculating step for calculating a deviation correction amount based on the deviation amount obtained from the deviation amount storage means; A first correction step for correcting a shift in the sub-scanning direction in pixel units with respect to the input image based on the shift correction amount; and a detection step for detecting an edge portion of the input image by a detection unit; A second correction unit that corrects a shift in a sub-scanning direction less than a pixel unit according to a correction coefficient based on the shift correction amount with respect to the first image data detected as an edge portion by the detection unit in the input image; A correction step; and a halftone processing step for performing a halftone process on the second image data that is not detected as an edge portion by the detection means in the input image, and the second correction step includes: The correction coefficient based on the shift correction amount is adjusted based on the operating environment information.
The program of the present invention processes an input image, exposes the image carrier based on the input image after the processing to form a latent image, and forms the image by developing the latent image with a developer. An operating environment detection step for causing a computer to execute an image forming method in an image forming apparatus, detecting an operating environment in the image forming apparatus, and outputting operating environment information based on a result of the detection, and the image A deviation amount storing step for storing a deviation amount in the sub-scanning direction of an exposure scanning line in the forming apparatus in a deviation amount storage means, and a deviation correction for calculating a deviation correction amount based on the deviation amount obtained from the deviation amount storage means. An amount calculation step, a first correction step for correcting a shift in the sub-scanning direction in pixel units with respect to the input image based on the shift correction amount, and an input image edge A detection step of detecting a portion by a detection means, and for the first image data detected as an edge portion by the detection means in the input image, less than a pixel unit according to a correction coefficient based on the shift correction amount A second correction step for correcting a shift in the sub-scanning direction; and a halftone processing step for performing halftone processing on the second image data that is not detected as an edge portion by the detection means in the input image. The second correction step adjusts the correction coefficient based on the shift correction amount based on the operating environment information.

According to the present invention, without being dependent on the reproducibility of the image to the operating environmental conditions (process state), not a Re to eliminate the moire caused by the correction, it is possible to obtain good images.

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

(First embodiment)
FIG. 2 is a schematic sectional view mainly showing a mechanical configuration of the color image forming apparatus according to the first embodiment. For example, the color image forming apparatus 1 according to the first embodiment corresponds to the case of a four-drum type color laser beam printer.

  As shown in FIG. 2, the color image forming apparatus 1 has a transfer material cassette 53 mounted on the lower right side of the apparatus. Transfer materials such as transfer paper set in the transfer material cassette 53 are taken out one by one by a paper feed roller 54 and fed to the image forming unit 11 by a pair of transport rollers 55-a and 55-b. Here, the color image forming apparatus 1 according to the present embodiment includes four image forming units 11-C, 11-Y, 11-M, and 11-K.

  The transfer material conveyance belt 10 that conveys the transfer material is stretched flat in the transfer material conveyance direction (from right to left in FIG. 2) by a plurality of rotating rollers (56, 58, etc.). The transfer material is electrostatically attracted to the transfer material conveyance belt 10. Further, facing the belt conveying surface of the transfer material conveying belt 10, the image forming unit 11 is provided with four photosensitive drums 14 as linear image bearing members in a straight line. Specifically, as shown in FIG. 2, the image forming unit 11 includes the photosensitive drums 14-C corresponding to the image forming units 11-C, 11-Y, 11-M, and 11-K. 14-Y, 14-M and 14-K are provided.

  The image forming unit 11 is provided with a developing unit 52. Specifically, as shown in FIG. 2, the image forming unit 11 includes development units 52-C, 52 corresponding to the image forming units 11-C, 11-Y, 11-M, and 11-K. -Y, 52-M and 52-K are provided. Each developing unit 52 includes cyan (CYAN), 14-Y yellow (YELLOW), 14-M magenta (MAGENTA), and 14-K black (BLACK) of the corresponding photosensitive drum 14-C. ) Color toner, charger and developer.

  A predetermined gap is provided between the charger and the developer in the housing of each of the developing units 52-C, 52-Y, 52-M, and 52-K. Through this gap, the peripheral surface of each photosensitive drum 14 is uniformly charged with a predetermined charge from each exposure unit 51 formed of a laser scanner. Then, the peripheral surface of the photosensitive drum 14 charged by each exposure unit 51 is exposed according to the image information to form an electrostatic latent image. Then, each developing device transfers the toner to the blackout portion of the electrostatic latent image and develops a toner image (development). As shown in FIG. 2, the image forming unit 11 includes exposure units 51-C and 51-Y corresponding to the image forming units 11-C, 11-Y, 11-M, and 11-K. , 51-M and 51-K. Each exposure unit 51-C, 51-Y, 51-M, and 51-K includes a laser 12 for exposing each photosensitive drum 14.

  A transfer member 57 is disposed in the image forming unit 11 across the conveyance surface of the transfer material conveyance belt 10. Specifically, as shown in FIG. 2, the image forming unit 11 includes transfer members 57-C, 57- corresponding to the image forming units 11-C, 11-Y, 11-M, and 11-K. Y, 57-M and 57-K are provided. The toner image formed (developed) on the peripheral surface of each photosensitive drum 14 is absorbed by the charge generated on the transferred transfer material by the transfer electric field formed by the corresponding transfer member 57. It is transferred to the transfer material surface.

  The transfer material onto which the toner image has been transferred is discharged out of the apparatus by a pair of paper discharge rollers 59-a and 59-b. The transfer material conveyance belt 10 is an intermediate transfer belt having a configuration in which each toner of cyan (CYAN), yellow (YELLOW), magenta (MAGENTA), and black (BLACK) is temporarily transferred and then secondarily transferred to the transfer material. It doesn't matter.

  The controller 15 in FIG. 2 controls the overall operation of the color image forming apparatus according to the present embodiment.

FIG. 3 is an image diagram for explaining the shift of the main scanning line scanned on the photosensitive drum 14 which is an image carrier.
Reference numeral 301 in FIG. 3 is an image showing an ideal main scanning line, and scanning is performed perpendicularly to the rotation direction of the photosensitive drum 14. Reference numeral 302 in FIG. 3 denotes an actual main scanning line in which the positional accuracy and the diameter of the photosensitive drum 14 are shifted, the inclination is increased to the right due to the positional accuracy of the optical system in the exposure unit 51 of each color, and the curvature is generated. It is an image showing. When such an inclination or curvature of the main scanning line exists in the image forming unit 11 of any color, color misregistration occurs when a plurality of color toner images are collectively transferred to the transfer material.

  In the present embodiment, the point A that is the scanning start position of the printing area in the main scanning direction (laser scanning direction: x direction) is used as a reference point. Then, the shift amount in the sub-scanning direction between the ideal main scanning line 301 and the actual main scanning line 302 is measured at a plurality of points (point B, point C, point D) with the point A as a reference point. And it divides | segments into several area | regions (area | region 1 between Pa-Pb, area | region 2 between Pb-Pc, and area | region 3 between Pc-Pd) for every point which measured the measured deviation | shift amount, and between each point The slope of the main scanning line in each region is approximated by straight lines (Lab, Lbc, Lcd) connecting the two. That is, in this embodiment, the input image is divided into blocks (regions 1 to 3), and color misregistration correction processing can be performed on each block.

  Therefore, when the difference in displacement amount between the points (m1 in the region 1, m2-m1 in the region 2, m3-m2 in the region 3) is a positive value, the main scanning line in the corresponding region is raised to the right. It indicates that it has a slope, and when it is a negative value, it indicates that it has a downward slope.

  FIG. 4 is a block diagram showing a functional configuration of the controller 15. Specifically, FIG. 4 shows the configuration of the controller 15 for performing the color misregistration correction processing for correcting the color misregistration caused by the inclination and curvature of the scanning line described above and image formation performed in the present embodiment. The structure of the part 11 is shown.

  The image forming unit 11 actually performs a printing process based on the image bitmap information generated by the controller 15. The color misregistration amount storage units 403-C, 403-M, 403-Y, and 403-K of the image forming unit 11 store the main scan line misregistration amount for each area described above for each corresponding color. . In the present embodiment, the amount of deviation in the sub-scanning direction between the ideal main scanning line 301 and the actual main scanning line 302 measured at a plurality of points described with reference to FIG. The information is stored in each color misregistration amount storage unit 403 as information to indicate. In this embodiment, the color misregistration amount storage unit 403 is configured in the image forming unit 11. However, for example, the color misregistration amount storage unit 403 may be configured in the controller 15.

  FIG. 5 is a diagram illustrating an example of information stored in the color misregistration amount storage unit 403. In this embodiment, each color misregistration amount storage unit 403 stores information related to the ideal main scanning line 301 and information related to the actual misregistration amount of the main scanning line 302. The information related to the amount of deviation is not limited to that shown in FIG. 5 as long as the actual inclination and curvature characteristics of the main scanning line 302 can be identified.

  The information stored in the color misregistration amount storage unit 403 is stored in advance as information unique to the apparatus by measuring the misregistration amount in the manufacturing process of the apparatus. Alternatively, a detection mechanism for detecting the shift amount is provided in the apparatus itself, and a predetermined pattern for measuring the shift amount is formed for each color image carrier (photosensitive drum 14), and the detection mechanism detects the shift amount. It may be configured to store the amount of deviation.

  Next, the operation of the controller 15 to perform the printing process by correcting the image data so as to cancel out the shift amount of the main scanning line stored in the color shift amount storage unit 403 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) or the like, and outputs it as RGB data for each dot.

  The color conversion unit 405 converts the RGB data output from the image generation unit 404 into CMYK space data that can be processed by the image forming unit 11 and stores the data in the bitmap memory 406 described later for each color.

  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.

  The color misregistration correction amount calculation means 407 corresponds to each color misregistration amount storage means 403-C, 403-M, 403-Y and 403-K, and each color misregistration correction amount calculation means 407-C, 407-M, 407-. Y and 407-K are provided. The color misregistration correction amount calculation means 407-C, 407-M, 407-Y and 407-K are respectively stored in the corresponding color misregistration amount storage means 403-C, 403-M, 403-Y and 403-K. A color misregistration correction amount is calculated based on information relating to the scan line misregistration amount. Specifically, each color misregistration correction amount calculation means 407-C, 407-M, 407-Y and 407-K correspond to the coordinate information in the main scanning direction designated by the color misregistration correction means 408 for each dot. The color misregistration correction amount in the sub-scanning direction is calculated and output to the color misregistration correction means 408.

  Here, when the coordinate data in the main scanning direction is x (dot) and the color misregistration correction amount in the sub-scanning direction is Δy (dot), the calculation formulas of the respective regions shown in FIG. 3 are shown below. At this time, the printing density is set to 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))
Here, L1, L2, and L3 are distances (unit: mm) in the main scanning direction from the printing start position to the left ends of the regions 1, 2, and 3, respectively. Further, m1, m2, and m3 are deviation amounts between the ideal main scanning line 301 and the actual main scanning line 302 at the left ends of the region 1, the region 2, and the region 3, respectively.

  The color misregistration correction unit 408 corresponds to each color misregistration correction amount calculation unit 407-C, 407-M, 407-Y and 407-K, and each color misregistration correction unit 408-C, 408-M, 408-Y, 408. -K is provided.

  The color misregistration correction unit 408 corrects color misregistration due to inclination and distortion of the main scanning line based on the color misregistration correction amount calculated for each dot by the color misregistration correction amount calculation unit 407. Specifically, the color misregistration correction unit 408 adjusts the output timing of the bitmap data stored in the bitmap memory 406 and the exposure amount for each pixel based on the color misregistration correction amount by the color misregistration correction amount calculation unit 407. Make adjustments to correct color misregistration. The color misregistration correction unit 408 in the present embodiment prevents color misregistration (registration misregistration) when each color toner image is transferred to a transfer material (transfer medium).

Next, the internal configuration of the color misregistration correction unit 408 will be described with reference to FIG.
FIG. 8 is a block diagram showing an internal configuration of the color misregistration correction unit 408.
As shown in FIG. 8, the color misregistration correction unit 408 includes a coordinate counter 45, a coordinate conversion unit (first correction unit) 41, a line buffer 42, an edge pattern storage unit 46, an edge detection unit 43, and a gradation correction unit ( (Second correction means) 44. The line buffer 42 has window data 42a.

  The coordinate counter 45 outputs the coordinate position data in the main scanning direction and the sub-scanning direction for performing color misregistration correction processing to the coordinate conversion means 41 and simultaneously outputs the coordinate position data in the main scanning direction to the gradation correction means 44.

  The coordinate conversion unit 41 corrects the integer part of the correction amount Δy based on the coordinate position data in the main scanning direction and the sub-scanning direction from the coordinate counter 45 and the correction amount Δy obtained from the color misregistration correction amount calculation unit 407. Processing, that is, reconstruction processing in the sub-scanning direction in units of pixels is performed.

  The edge detection unit 43 compares the n × m window data 42a obtained from the line buffer 42 with the edge pattern information stored in the edge pattern storage unit 46, thereby detecting the edge portion of the image to be detected. Do.

  The edge detection means 43 indicates whether it is the image data of the edge part or the image data of the non-edge part by attribute data in the subsequent stage.

  The gradation correction unit 44 applies the correction amount Δy to the image data detected as the edge portion by the edge detection unit 43 based on the coordinate position data in the main scanning direction from the coordinate counter 45 and the correction amount Δy. Performs correction processing after the decimal point. Here, the gradation correction unit 44 performs the correction process by adjusting the exposure ratio of dots before and after the sub-scanning direction in less than a pixel unit. At this time, the gradation correction unit 44 uses the line buffer 42 for referring to the dots before and after in the sub-scanning direction.

  For image data that is not an edge portion (non-edge portion) detected by the edge detection unit 43, it is determined that there is no need to correct a color shift less than a pixel, and gradation correction by the gradation correction unit 44 is performed. Simplify the process as not being performed.

FIG. 6 is an image diagram for explaining the operation of correcting the shift amount of the integer part of the color shift correction amount Δy in the coordinate conversion means 41.
As shown in FIG. 6A, the coordinate conversion unit 41 uses the bitmap memory 406 in accordance with the value of the integer part of the color misregistration correction amount Δy obtained from the information about the 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 are offset.

  For example, if the coordinate position in the sub-scanning direction from the coordinate counter 45 is the n line shown in FIG. 6B, the coordinate position in the main scanning direction is x, and the x coordinate in the main scanning direction is as shown in FIG. In the area [1] shown, the color misregistration correction amount Δy is 0 or more and less than 1. When the n-th line data is reconstructed, the coordinate conversion unit 41 performs a coordinate conversion process for reading the n-th line data from the bitmap memory 406.

  In the area [2] shown in FIG. 6A, the color misregistration correction amount Δy is 1 or more and less than 2. When the n-th line data is reconstructed, the coordinate conversion unit 41 reads the image bit map at the position offset from the number of one sub-scanning line, that is, the coordinates for reading the n + 1-th line image data from the bitmap memory 406. Perform the conversion process.

  Similarly, the coordinate conversion means 41 is on the (n + 2) th line from the bitmap memory 406 in the area [3] shown in FIG. 6A, and n + 3 from the bitmap memory 406 in the area [4] shown in FIG. A coordinate conversion process for reading out the data of the line is performed. With the above method, reconstruction processing in the sub-scanning direction is performed in units of pixels. FIG. 6C shows an exposure image when the image carrier (photosensitive drum 14) is exposed to an image that has been subjected to color misregistration correction processing in pixel units by the coordinate conversion means 41. FIG.

  FIG. 7 is an image diagram for explaining an operation performed by the gradation correction unit 44 to correct a color shift of less than a pixel unit. Specifically, FIG. 7 shows an operation for correcting the shift amount of the color shift correction amount Δy after the decimal point. The correction of the color misregistration correction amount Δy after the decimal point is performed by adjusting the exposure ratio of dots before and after the sub-scanning direction.

  FIG. 7A shows an image of a main scanning line having an upward slope. FIG. 7B shows a bitmap image of a horizontal straight line before gradation correction. FIG. 7C shows a correction image for the bitmap image of FIG. 7B for canceling the color shift due to the inclination of the main scanning line shown in FIG. 7A. In order to realize the correction image of FIG. 7C, the exposure amount adjustment for dots before and after in the sub-scanning direction is performed.

FIG. 7D shows the relationship between the color misregistration correction amount Δy and the correction coefficient for performing gradation correction. In FIG. 7D, k is the integer part of the color misregistration correction amount Δy (the fractional part is rounded down) and indicates the correction amount in the sub-scanning direction in units of pixels. In FIG. 7D, β and α are correction coefficients for performing correction in the sub-scanning direction less than a pixel unit, and the information below the decimal point of the color misregistration correction amount Δy is applied to dots before and after in the sub-scanning direction. Represents the distribution of exposure dose. Specifically, α represents the distribution rate of preceding dots, and β represents the distribution rate of subsequent dots. The distribution ratios α and β are as shown in FIG.
α = Δy−k
β = 1−α
Is calculated by

  FIG. 7E shows a bitmap image that has been subjected to tone correction for adjusting the exposure ratio of dots before and after in the sub-scanning direction in accordance with the correction coefficient shown in FIG. FIG. 7F shows an exposure image when the gradation-corrected bitmap image is exposed on the image carrier (photosensitive drum 14), and the inclination of the main scanning line is canceled and a horizontal straight line is displayed. Will be formed.

Next, returning to the description of FIG. 4, the process detection means (operation environment detection means) 401 will be described.
In the present embodiment, the controller 15 includes process detection means 401-C, 401-M, 401-Y, and 401 corresponding to the color misregistration correction means 408-C, 408-M, 408-Y, and 408-K. -K is provided. Each process detection unit 401 detects an operating environment in the color image forming apparatus 1 and outputs operating environment information based on the detection result to an exception processing unit 409 described later.

  In the color image forming apparatus (color printer) 1, density control is executed in order to keep the density at which each color image is output (printed). However, since execution of the density control consumes time and toner, the density control is frequently performed. Can not be executed.

  Therefore, in the present embodiment, a form in which the blend value is changed according to the environmental change of the color image forming apparatus 1 is shown. The environmental change here is a change in temperature and humidity in the vicinity of the transfer material that affects the electrophotographic process. In general, in an electrophotographic process, if a transfer material (paper) has a high resistance value, toner is hardly transferred. The resistance value of the transfer material (paper) changes depending on the amount of moisture contained in the transfer material. When the humidity decreases, the amount of water contained in the transfer material decreases, the resistance value of the transfer material increases, and the toner becomes difficult to transfer. Further, when the temperature is increased, the moisture contained in the transfer material is diffused, the resistance value of the transfer material is increased, and the toner is hardly transferred. When the toner becomes difficult to be transferred, the toner image becomes small even if the exposure amount is the same. Conversely, in an environment where the toner is difficult to transfer, the exposure amount must be increased in order to maintain the toner image. That is, when the humidity in the vicinity of the transfer material decreases or the temperature in the vicinity of the transfer material increases, it is necessary to increase the blend value related to the density of each color image. By detecting the temperature and humidity in the vicinity of the transfer material with a monitor or the like by each process detection unit 401, an optimum blend value can be obtained.

Next, the exception processing unit 409 and the halftone processing unit 410 of FIG. 4 will be described.
In this embodiment, the controller 15 includes exception processing units 409-C, 409-M, 409-Y, and 409 corresponding to the color misregistration correction units 408-C, 408-M, 408-Y, and 408-K. -K is provided. Similarly, halftone processing means 410-C, 410-M, 410-Y and 410-K are provided corresponding to the color misregistration correction means 408-C, 408-M, 408-Y, and 408-K. Yes. In the following, an example in which processing is performed in the order of halftone processing → color misregistration correction processing on the input image, and processing in the order of color misalignment correction processing → halftone processing is performed on the input image. Will be described.

  FIG. 9 is a schematic diagram illustrating an example when color misregistration correction processing is performed after halftone processing is performed on an input image. FIG. 9A shows an input image having a constant density of 50%.

  When halftone processing is performed on the input image shown in FIG. 9A using a certain 4 × 4 halftone pattern, the image shown in FIG. 9B is obtained. If the image shown in FIG. 9B is an image to be obtained and an image equivalent to this image is obtained even after performing the color misregistration correction process, it can be said that the color misregistration correction process can be realized without image deterioration.

  Here, FIG. 9C shows an image obtained when ½ pixel color shift correction is performed in the upward direction (vertical direction) on the image after the halftone process shown in FIG. 9B. . As can be seen from FIG. 9C, by performing the color misregistration correction processing on the image after the halftone processing shown in FIG. 9B, the halftone image halftone dot reproducibility deterioration is caused by the halftone processing. ing.

  FIG. 10 is a schematic diagram illustrating an example in which halftone processing is performed after performing color misregistration correction processing on an input image. FIG. 10A shows an input image, which is an image having a constant density (50%), as in FIG. 9A described above.

  FIG. 10B shows an image obtained when ½ pixel color misregistration correction processing is performed in the upward direction (vertical direction) on the input image shown in FIG. By performing the color misregistration correction process, an image having a density of 25% is generated on the upper and lower one lines 100a and 100b.

  FIG. 10C shows an image obtained when halftone processing is performed on the image after the color misregistration correction processing shown in FIG. In the image shown in FIG. 10C, an image having a density of 25% is generated in the upper and lower one lines 100a and 100b in the color misregistration correction process in FIG. 10B, and therefore the upper and lower one lines 100a and 100b are shown in FIG. The image is different from (b). However, with respect to other parts other than the upper and lower one lines 100a and 100b, an image similar to that shown in FIG. 9B is obtained, and the halftone dot of the halftone image as shown in FIG. 9C is obtained. There is no deterioration.

  FIG. 11 is a schematic diagram illustrating an example in which halftone processing is performed after performing color misregistration correction processing on an input image. FIG. 11A is an input image, and FIG. 11B is an image after the coordinate conversion process is performed on the input image shown in FIG. FIG. 11C is an image after color misregistration correction processing is performed on the image shown in FIG. 11B, and FIG. 11D is a half view on the image shown in FIG. It is an image after performing tone processing.

  When halftone processing is performed after performing color misregistration correction processing, when attention is paid to the edge portion of the image, as shown in FIG. 11D, the edge portion of the image follows the halftone pattern by halftone processing. As a result, tone correction is invalidated. As a result, gaps and discontinuities occur in the edge portion, and a jaggy image is formed. Processing procedures for preventing this jaggy are shown in FIGS.

FIG. 12 is a flowchart illustrating a processing method of the color image forming apparatus according to the first embodiment. Here, FIG. 12 shows a process from the edge detection process in the color image forming apparatus according to the first embodiment.
First, in step S121 in FIG. 12, the coordinate conversion means 41 performs coordinate conversion to perform correction processing for color misregistration of pixels or more.

  Subsequently, in step S122, the coordinate conversion unit 41 stores the image data subjected to the coordinate conversion in step S121 in the line buffer.

  Subsequently, in step S123, the edge detection unit 43 determines whether or not the image data to be processed, which is stored in the line buffer 42, is the image data of the edge portion.

  When it is determined in step S123 that the image data is the edge portion, in step S124, the gradation correction unit 44 performs gradation correction processing on the edge portion image data to obtain a color less than the pixel. Deviation correction processing is performed. Subsequently, in step S125, the exception processing unit 409 operates the operating environment from the process detection unit 401, which is different from the halftone processing in step S126, on the edge portion image data subjected to the gradation correction processing in step S124. Perform exception handling based on information. At this time, the exception processing unit 409 uses the halftone pattern for the edge portion to compensate for dots after halftone processing different from the halftone processing in step S126 or after the halftone processing in step S126. Etc. may be performed.

  On the other hand, if it is determined in step S123 that the image data is not edge portion image data, then in step S126, halftone processing is performed on the non-edge portion image data.

  After the processing of step S125 or S126 is completed, the pulse width modulation is performed by the pulse width modulation unit 411 in FIG. 4 based on the image data obtained by the exception processing unit 409 and the halftone processing unit 410, and a binary value is obtained. It is converted into a laser drive signal. That is, the pulse width modulation unit 411 modulates the pulse width of the light beam in the laser 12 of the exposure unit 51 on the basis of the image data obtained by the exception processing unit 409 and the halftone processing unit 410, and the light beam Correct the amount of light.

  Here, the pulse width modulation unit 411 corresponds to the color misregistration correction units 408-C, 408-M, 408-Y, 408-K, and the like, and the pulse width modulation units 411-C, 411-M, 411- Y, 411-K are provided. Thereafter, a binary laser drive signal is supplied from the pulse width modulation means 411 to each exposure unit 51-C, 51-Y, 51-M and 51-K, and each exposure unit is based on the supplied laser drive signal. Thus, each photosensitive drum 14 is exposed. Thereafter, the processing in the flowchart is terminated.

Next, operations in steps S123 to S126 surrounded by a broken line in FIG. 12 will be described in detail with reference to FIG.
FIG. 13 is a flowchart showing specific processing of steps S123 to S126 of FIG. FIG. 13 shows a flowchart of processing when the output blending MAX value is changed in the edge pattern.

  In step S131, the edge detection unit 43 determines whether or not the image data (pixel) to be processed, which is stored in the line buffer 42, is the image data (pixel) of the edge portion. The process in step S131 corresponds to the process in step S123 of FIG.

  If it is determined in step S131 that the image data is not the edge portion image data, then in step S132, halftone processing is performed on the non-edge portion image data (pixels). The process in step S132 corresponds to the process in step S126 of FIG.

  On the other hand, when it is determined in step S131 that the image data (pixel) is an edge portion, in step S133, the edge detection unit 43 adds the operating environment information by the process detection unit 401 for each pixel. At this time, the operating environment information in the present embodiment is information relating to changes in temperature and humidity in the vicinity of the transfer material detected by the process detection unit 401. The process in step S133 is included in the process in step S123 of FIG. 12, for example.

  Subsequently, in step S134, the gradation correction unit 44 performs a normal blending process (gradation correction process) on the edge image data (pixels). The process in step S134 corresponds to the process in step S124 in FIG.

  Subsequently, in step S135, the exception processing unit 409 determines whether or not to change the blend value related to the density of each image data (pixel) based on the operating environment information added in step S133. If the blend value is changed as a result of this determination, then in step S136, the exception processing means 409 increases the density of the image data (pixel) based on the operating environment information added in step S133. Judge whether to thin. As a result of this determination, if the image data (pixel) density is to be output lightly, in step S137, the exception processing means 409 performs blending processing with the MAX value decreased. On the other hand, as a result of the determination in step S136, if the image data (pixel) density is to be output high, in step S138, the exception processing unit 409 performs a blending process in which the MAX value is increased. The processing in steps S135 to S138 corresponds to the processing in step S125 in FIG.

  FIG. 14 is a schematic diagram illustrating gradation correction processing performed in the color image forming apparatus according to the first embodiment. FIG. 14A shows information related to the correction amount, and FIG. A bitmap image after gradation correction processing is shown, and an exposure image is shown in FIG.

  Image data (pixels) determined to be output with a high density in step S136 of FIG. 13, for example, if the region 140 is composed of three pixels surrounded by a dotted line in FIG. Calculation is performed as shown in FIG. Compared with FIG. 7D, the correction value of the three pixel regions 140 is greatly calculated, so that the reproducibility of the halftone line that is difficult to reproduce when 50% is achieved can be improved.

(Second Embodiment)
In the first embodiment, the blending control is performed based on the operating environment information in the environmental change such as the temperature and humidity near the transfer material obtained from the process detection unit 401. However, the operating environment in other operating environments is used. The blend value may be changed from the information.

Therefore, in the second embodiment, an example in which the blend value is changed according to the change in the film thickness of the photosensitive drum 14 is shown.
The thickness of the photosensitive drum 14 is reduced according to the number of prints of the transfer material. When the film thickness of the photosensitive drum 14 is reduced, the potential is less likely to decrease due to exposure, and as a result, it is difficult for toner to get on the photosensitive drum 14. If the toner hardly gets on the photosensitive drum 14, the toner image becomes small even if the exposure amount is the same. Therefore, it is necessary to increase the blend value when the film thickness of the photosensitive drum 14 becomes thin. Therefore, in the second embodiment, the film thickness of the photosensitive drum 14 is detected by counting the number of prints of the transfer material by the process detection unit 401, and the exception processing unit 409 is optimal according to the detection result. Perform blending process with blend value.

  2, 4 and 8 constituting the color image forming apparatus according to each of the above-described embodiments, and steps of FIGS. 12 and 13 showing the processing method of the color image forming apparatus are the RAM and ROM of the computer. This can be realized by operating the program stored in the memory. This program and a computer-readable storage medium storing the program are included in the present invention.

  Specifically, the program is recorded in a storage medium such as a CD-ROM, or provided to a computer via various transmission media. As a storage medium for recording the program, a flexible disk, a hard disk, a magnetic tape, a magneto-optical disk, a nonvolatile memory card, and the like can be used in addition to the CD-ROM. On the other hand, as the transmission medium of the program, a communication medium in a computer network (LAN, WAN such as the Internet, wireless communication network, etc.) system for propagating and supplying program information as a carrier wave can be used. In addition, examples of the communication medium at this time include a wired line such as an optical fiber, a wireless line, and the like.

  In addition, the function of the color image forming apparatus according to each embodiment is realized by executing a program supplied by the computer, and an OS (operating system) or other application in which the program is running on the computer. When the functions of the color image forming apparatus according to each embodiment are realized in cooperation with software, etc., or all or part of the processing of the supplied program is performed by a function expansion board or a function expansion unit of the computer. Such a program is also included in the present invention when the functions of the color image forming apparatus according to each embodiment are realized.

It is the schematic which shows density | concentration unevenness. 1 is a schematic cross-sectional view showing mainly a mechanical configuration of a color image forming apparatus according to a first embodiment. FIG. 4 is an image diagram for explaining a shift of a main scanning line scanned on a photosensitive drum which is an image carrier. It is a block diagram which shows the functional structure of a controller. It is a figure which shows an example of the information memorize | stored in a color shift amount memory | storage means. FIG. 10 is an image diagram for explaining an operation of correcting the shift amount of the integer part of the color shift correction amount Δy in the coordinate conversion means. It is an image figure for demonstrating the operation | movement which correct | amends the color shift below a pixel unit which a gradation correction | amendment means performs. It is a block diagram which shows the internal structure of a color shift correction | amendment means. It is the schematic which shows an example at the time of performing a color shift correction process after performing a halftone process with respect to an input image. It is the schematic which shows an example at the time of performing a halftone process after performing a color shift correction process with respect to an input image. It is the schematic which shows an example at the time of performing a halftone process after performing a color shift correction process with respect to an input image. 3 is a flowchart illustrating a processing method of the color image forming apparatus according to the first embodiment. It is a flowchart which shows the specific process of step S123-S126 of FIG. FIG. 3 is a schematic diagram illustrating gradation correction processing performed in the color image forming apparatus according to the first embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Color image forming apparatus 10 Transfer material conveyance belt 11 Image forming part 12 Laser 14 Photosensitive drum 15 Controller 41 Coordinate conversion means (1st correction means)
42 Line buffer 42a Window data 43 Edge detection means 44 Gradation correction means (second correction means)
45 Coordinate counter 46 Edge pattern storage unit 51 Exposure unit 52 Development unit 53 Transfer material cassette 54 Paper feed rollers 55-a, 55-b Transport rollers 56, 58 Rotating rollers 57 Transfer members 59-a, 59-b Paper discharge rollers 401 Process detection means (operating environment detection means)
403 Color shift amount storage unit 404 Image generation unit 405 Color conversion unit 406 Bitmap memory 407 Color shift correction amount calculation unit 408 Color shift correction unit 409 Exception processing unit 410 Halftone processing unit 411 Pulse width modulation unit

Claims (8)

An image forming apparatus that processes an input image, exposes an image carrier based on the processed input image to form a latent image, and develops the latent image with a developer to form an image. ,
Detecting an operating environment of the image forming apparatus, and the operation environment detecting means for outputting an operation environment information based on the result of the detection,
And Figure been amount storage means for storing the sub-scanning direction shift amount of the scanning line of exposure in the image forming apparatus,
Based on the amount Re not obtained from the not a Re amount storage means, a correction amount calculation means Re without calculating the correction amount Re not a,
First correction means for correcting a shift in the sub-scanning direction in pixel units with respect to the input image based on the shift correction amount ;
Detecting means for detecting an edge portion of the input image;
A second correction unit that corrects a shift in a sub-scanning direction less than a pixel unit according to a correction coefficient based on the shift correction amount with respect to the first image data detected as an edge portion by the detection unit in the input image ; Correction means;
Halftone processing means for performing halftone processing on second image data that is not detected as an edge portion by the detection means in the input image;
I have a,
It said second correction means, the operating environment based on the information, the shift correction value wherein the images forming apparatus characterized by adjusting a correction coefficient based on. The second correction means includes
When the operating environment information is information indicating that the density corresponding to the first image data should be increased, the latent image with respect to the first image data in which the shift in the sub-scanning direction less than the pixel unit is corrected is corrected. Correction according to the correction coefficient so as to increase the exposure amount in image formation,
When the operating environment information is information indicating that the density corresponding to the first image data should be reduced, the latent image with respect to the first image data in which the shift in the sub-scanning direction less than the pixel unit is corrected is corrected. The image forming apparatus according to claim 1, wherein correction is performed according to the correction coefficient that reduces an exposure amount in image formation . The image forming apparatus according to claim 1, wherein the first image data is processed in the order of correction by the first correction unit and correction by the second correction unit. The operating environment detection means detects changes in temperature and humidity in the vicinity of a transfer material for transferring the developed image.
The second correction unit performs correction by changing the correction coefficient related to the density corresponding to the first image data in accordance with changes in temperature and humidity detected by the operating environment detection unit. The image forming apparatus according to any one of claims 1 to 3. The operating environment detecting means detects the film thickness of the image carrier,
The second correction unit performs correction by changing the correction coefficient relating to the density corresponding to the first image data in accordance with the film thickness of the image carrier detected by the operating environment detection unit. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. 6. The apparatus according to claim 1, further comprising a plurality of image carriers corresponding to the respective colors, and exposing each of the image carriers to form a latent image corresponding to each color. Image forming apparatus. Image formation in an image forming apparatus that processes an input image, exposes the image carrier based on the input image after the processing to form a latent image, and develops the latent image with a developer to form an image A method,
An operating environment detection step of detecting an operating environment in the image forming apparatus and outputting operating environment information based on a result of the detection;
A shift amount storing step of storing a shift amount in the sub-scanning direction of the scanning line of exposure in the image forming apparatus in a shift amount storage unit;
A deviation correction amount calculating step for calculating a deviation correction amount based on the deviation amount obtained from the deviation amount storage means;
A first correction step for correcting a shift in a sub-scanning direction in units of pixels with respect to an input image based on the shift correction amount;
A detection step of detecting an edge portion of the input image by a detection means;
A second correction unit that corrects a shift in a sub-scanning direction less than a pixel unit according to a correction coefficient based on the shift correction amount with respect to the first image data detected as an edge portion by the detection unit in the input image; A correction step;
A halftone processing step of performing a halftone process on second image data that is not detected as an edge portion by the detection means in the input image;
Have
The image forming method according to claim 2, wherein the second correction step adjusts the correction coefficient based on the shift correction amount based on the operating environment information. Image formation in an image forming apparatus that processes an input image, exposes the image carrier based on the input image after the processing to form a latent image, and develops the latent image with a developer to form an image A program for causing a computer to execute a method,
An operating environment detection step of detecting an operating environment in the image forming apparatus and outputting operating environment information based on a result of the detection;
A shift amount storing step of storing a shift amount in the sub-scanning direction of the scanning line of exposure in the image forming apparatus in a shift amount storage unit;
A deviation correction amount calculating step for calculating a deviation correction amount based on the deviation amount obtained from the deviation amount storage means;
A first correction step for correcting a shift in a sub-scanning direction in units of pixels with respect to an input image based on the shift correction amount;
A detection step of detecting an edge portion of the input image by a detection means;
A second correction unit that corrects a shift in a sub-scanning direction less than a pixel unit according to a correction coefficient based on the shift correction amount with respect to the first image data detected as an edge portion by the detection unit in the input image; A correction step;
A halftone processing step of performing a halftone process on second image data that is not detected as an edge portion by the detection means in the input image;
To the computer,
The second correction step adjusts the correction coefficient based on the shift correction amount based on the operating environment information.

Images