JP2013011740A - Image processing apparatus, and manufacturing method of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce bleeding of an image edge that occurs in a fixing step during electrophotographic process.SOLUTION: An image processing apparatus performs the following steps of: converting image data into a color material amount signal representing the amount of a color material (S801); detecting an edge area of an image, which has a direction orthogonal to a conveyance direction of a recording medium, from the color material amount signal (S802); obtaining fixing force in fixing a toner image formed based on the color material amount signal onto the recording medium (S803); and correcting the value of the color material amount signal corresponding to pixels situated downstream in the conveyance direction in the edge area depending on the fixing force (S804).

Description

  The present invention relates to image processing for forming an image by an electrophotographic process.

  In an electrophotographic image forming apparatus such as a laser beam printer or a copying machine, an image is generally formed through a plurality of processes such as charging, exposure, development, transfer, and fixing. In other words, the surface of the photoconductor is uniformly charged by the charging process, and an exposure unit including a laser light source scans and exposes the surface of the photoconductor with a laser beam corresponding to the input image signal, and electrostatically forms on the photoconductor. A latent image is formed. Next, a toner image is generated by developing the electrostatic latent image on the photoconductor by development processing, and the toner image on the photoconductor is transferred to a recording medium by transfer processing. Then, the toner image is fixed on the recording medium by the fixing process, and the image formation is completed.

  In such an electrophotographic process, blurring of the image edge according to the paper feeding direction may occur, and the sharpness of the image may be reduced.

  One of the causes of blurring of the image edge is a phenomenon in which when toner is transferred from the intermediate transfer member 101 to the recording medium 102, the toner that has moved to the surface of the recording medium 102 jumps and the toner scatters. FIG. 1 schematically shows toner scattering.

  Further, on the upstream side in the conveyance direction of the recording medium 102, the surface of the recording medium 102 and the surface of the intermediate transfer member 101 cannot be said to be sufficiently parallel. As a result, the phenomenon that toner transfer to the recording medium 102 is delayed and the toner image stretched to the upstream side in the transport direction from the desired position is transferred (post-drawing) can also cause blurring of the image edge. one of.

  FIG. 2 schematically shows the backward pulling. FIG. 2A shows a state where the toner image on the intermediate transfer body 101 is transferred to the recording medium 102 by the transfer process. The toner image reaches the surface of the recording medium 102 on the downstream side in the transport direction. However, since the surfaces of the recording medium 102 and the intermediate transfer member 101 are not parallel, the toner image does not reach the surface of the recording medium 102 on the upstream side in the transport direction. As a result, as shown in FIG. 2B, the toner image is stretched upstream in the transport direction.

  As a solution to these problems, a method has been proposed in which an edge region of an image is specified and the pixel value of the edge region is reduced to prevent toner scattering (see Patent Document 1). In addition, a method has been proposed in which the amount of toner in pixels other than the edge region is reduced to prevent post-drawing that occurs during transfer (see Patent Document 2).

  According to the techniques proposed in Patent Documents 1 and 2, toner scattering and post-drawing in transfer processing can be suppressed. However, blurring of the image edge also occurs in the fixing process.

  The occurrence of blurring of the image edge in the fixing process will be described with reference to FIG. FIG. 3A shows a state in which toner is transferred onto the recording medium 102 in the order of yellow Y, cyan C, and yellow Y. The recording medium 102 is conveyed to the fixing unit 104 by the conveyance belt 103. The fixing unit 104 heats and pressurizes the toner transferred and placed on the recording medium 102. At that time, the toner is crushed toward the upstream side in the transport direction, and as a result, as shown in FIG. 3 (b), the toner after fixing rides on the adjacent toner and the upstream end of the image in the transport direction. In this case, the toner is stretched to the white portion of the paper, and blurring of the image edge occurs.

JP 11-034401 A JP 2006-159624 A

  An object of the present invention is to reduce blurring of an image edge that occurs in a fixing step in an electrophotographic process.

  The present invention has the following configuration as one means for achieving the above object.

  The image processing according to the present invention converts image data into a color material amount signal representing a color material amount, and detects an edge region of the image having a direction orthogonal to the conveyance direction of the recording medium from the color material amount signal. And a color material amount signal corresponding to a pixel located downstream of the edge region in the transport direction according to a fixing force when fixing a toner image formed based on the color material amount signal to the recording medium. It is characterized by correcting the value.

  According to the present invention, it is possible to reduce blurring of an image edge that occurs in a fixing step in an electrophotographic process.

FIG. 6 is a diagram schematically illustrating toner scattering. The figure which shows backdrawing typically. FIG. 6 is a diagram for explaining occurrence of blurring of an image edge in fixing processing. FIG. 3 is a schematic diagram illustrating the principle of suppressing blurring of an image edge according to an embodiment. FIG. 3 is a diagram illustrating a configuration example of an image forming unit of the image processing apparatus according to the embodiment. 1 is a block diagram illustrating a configuration example of an image processing apparatus according to an embodiment. FIG. 3 is a diagram illustrating a configuration example of a print job. The flowchart explaining the process of an image process part. The figure which shows an example of a color separation LUT. The figure which shows an example of a fixing force table. The flowchart explaining the detail of the process which specifies an edge area | region. The figure which shows an example of a Sobel filter. The figure explaining the detail of a filter process. 9 is a flowchart for explaining details of processing for correcting a color material amount signal. FIG. 5 is a diagram illustrating an example of a relationship between an edge pixel and a color material amount correction region. FIG. 6 is a diagram illustrating an example of laser driving by an exposure unit according to the second embodiment. The flowchart explaining the process of an image process part. The figure which shows an example of a pulse width control mask. The figure which shows the relationship between a pulse width control mask, the image signal after a halftone process, and a ternary image signal. The figure explaining the pulse width control by an exposure part.

  Hereinafter, image processing according to an embodiment of the present invention will be described in detail with reference to the drawings.

[principle]
In the image processing according to the embodiment, an edge region in which bleeding of an image orthogonal to the transport direction is likely to occur is specified, and the amount of toner on the downstream side in the transport direction with respect to the specified edge region is reduced.

  FIG. 5 is a schematic diagram for explaining the principle of suppressing blurring of an image edge according to the embodiment. FIG. 4A shows a state in which toner is transferred in the order of yellow Y, cyan C, and yellow Y onto the recording medium 102 by the image processing of the embodiment, and the toner amount of each dot shown in FIG. In comparison, the toner amount of each dot is reduced. If the fixing process is performed in such a state, even if the toner is crushed toward the upstream side in the conveyance direction, as shown in FIG. Reduced. In addition, the rate at which the toner is stretched to the white portion of the paper at the image end on the upstream side in the transport direction is reduced, and bleeding of the image edge can be suppressed.

[Image forming unit]
FIG. 5 shows a configuration example of the image forming unit of the image processing apparatus according to the embodiment.

  The image forming unit includes a cleaner 16 that removes toner remaining on the surface of the photosensitive drum 11 around the photosensitive drum 11 that is an image carrier, and a charging unit 12 that uniformly charges the surface of the photosensitive drum 11 after cleaning. , An exposure unit 13 and a developing unit 14 for developing the electrostatic latent image are provided.

  The exposure unit 13 includes a laser light source 31, a polygon scanner 32, and an f-θ lens 33. The developing unit 14 includes toner cartridges 4C, 4M, 4Y, and 4K for the respective colors. The toner image on the surface of the photosensitive drum 11 is transferred to the intermediate transfer drum 51 of the transfer unit 15.

  In the configuration shown in FIG. 5, when the photosensitive drum 11 and the intermediate transfer drum 51 are rotated four times, a four-color toner image is superimposed on the surface of the intermediate transfer drum 51, and then the toner image is transported on the transport belt 52. To the recording medium S to be transferred. Then, the recording medium S is sent to the fixing unit 71, and the toner image is fixed to the recording medium S.

[Device configuration]
A configuration example of the image processing apparatus according to the embodiment will be described with reference to the block diagram of FIG.

  The data input unit 601 is, for example, a serial bus interface such as USB or a network interface, and inputs image data to be printed from various external devices. The data input unit 601 may be a card reader, and can input image data recorded on a memory card as image data to be printed.

  The setting unit 602 includes an operation input unit such as a touch panel and a keyboard. The user operates the operation input unit to instruct the type of recording medium used for printing, the orientation of the recording medium, the print image quality, and the like. The setting unit 602 outputs to the image processing unit 603 a print job that includes print information indicating user instructions and image data to be printed.

FIG. 7 shows a configuration example of a print job. As shown in FIG. 7, the print information includes recording medium information indicating the type of the recording medium, basis weight information indicating the weight per 1 m ^{2 of} the recording medium, printing information indicating the size and orientation of the recording medium, and the print quality. Etc. are included. Examples of the recording medium include plain paper, glossy paper, coated paper, and matte paper.

  In the following description, the direction of the recording medium is referred to as “lateral direction” when the long side of the recording medium is parallel to the transport direction, and “vertical direction” when the short side of the recording medium is parallel to the transport direction. Further, when the print quality indicates image quality priority, “image quality priority mode”, which is a print mode for slowing the conveyance speed of the recording medium, is set. Further, when the print quality indicates speed priority, a “speed priority mode” that is a print mode for increasing the conveyance speed of the recording medium is set.

  The data input unit 601 and the setting unit 602 can be configured as a printer driver. In such a configuration, the data input unit 601 and the setting unit 602 exist in a computer device such as a personal computer, and the image processing unit 603 and subsequent units exist in the image processing apparatus.

  As will be described in detail later, the image processing unit 603 determines a color material amount signal (CMYK value) indicating the color material amount to be recorded on the recording medium based on the print information and image data included in the print job. Next, based on the determined color material amount signal and the orientation of the recording medium, an edge region where blurring of an image is likely to occur in the fixing process is specified. Then, when fixing the color material of the pixel located downstream in the conveyance direction of the specified edge region, a force for fixing the color material generated by heat and pressure to the recording medium (hereinafter, fixing force) is acquired, The color material amount signal is corrected based on the fixing power.

  The image processing unit 603 outputs the corrected color material amount signal to the exposure unit 13 (see FIG. 5) of the image forming unit 604, and executes an image forming process. The print information included in the print job is separately supplied to a control unit (not shown) of the image forming unit 304, and the control unit controls the image forming process.

  The image processing unit 603 can also be realized by supplying a program for realizing an image processing function described later to a computer device such as a one-chip microcontroller.

[Image processing unit]
The processing of the image processing unit 603 will be described with reference to the flowchart of FIG.

  The image processing unit 603 performs color separation processing to display RGB information of each pixel indicated by the image data of the print job, color separation data CMYK (color material amount signal) corresponding to a combination of toners for reproducing the color represented by each pixel. (S801). Note that the image processing unit 603 performs color separation processing using a color separation look-up table (LUT) indicating the correspondence between RGB values and CMYK values together with an interpolation operation. FIG. 9 shows an example of the color separation LUT. FIG. 9 shows an example of a LUT that outputs 8-bit CMYK values for each color with respect to 8-bit RGB values. However, the RGB depth and CMYK value can be set to any bit depth, for example, 4-bit CMYK values for each color. May be output.

  Next, as will be described in detail later, the image processing unit 603 uses an Sobel filter corresponding to the CMYK amount and the direction of the recording medium indicated by the print information, and has an edge region having a direction orthogonal to the conveyance direction of the recording medium. Is identified (S802).

  Next, the image processing unit 603 refers to a fixing force table indicating the relationship between the print information and the fixing force, and acquires the fixing force based on the printing information (S803). FIG. 10 shows an example of the fixing force table. The example of FIG. 10 shows the fixing force corresponding to the paper type (type of recording medium), basis weight, and printing mode of the recording medium.

  The fixing force depends on heat and pressure in the fixing process. Therefore, for example, for each model of the image processing apparatus, the fixing force corresponding to the combination of the paper type, basis weight, and print mode of the recording medium is measured, and the fixing force table is created in advance. It is also possible to use a fixing force table indicating the fixing force for one type of information, such as a fixing force table indicating the fixing force for the paper type or a fixing force table indicating the fixing force for the print mode.

  Next, the image processing unit 603 corrects the color material amount signal of the pixel located downstream in the transport direction with respect to the specified edge region according to the fixing force based on the ease of bleeding of the specified edge region ( S804).

  Next, the image processing unit 603 performs halftone processing on the corrected color material amount signal to generate, for example, 1-bit CMYK data of each color, and image signals corresponding to the CMYK data are sequentially formed in the image forming unit 604. To the exposure unit 13 (see FIG. 5) (S805).

Specification of Edge Region Details of the processing for specifying the edge region (S802) will be described with reference to the flowchart of FIG.

  The image processing unit 603 determines the orientation of the recording medium from the print information (S1001), selects the vertical sobel filter for the vertical direction (S1002), and selects the horizontal sobel for the horizontal direction. A filter is selected (S1003). FIG. 12 shows an example of a Sobel filter. FIG. 12A shows a sobel filter for a vertical direction, and FIG. 12B shows a sobel filter for a horizontal direction. The filter size is not limited to 3 × 3, but may be 5 × 5, or an edge detection filter such as a Prewitt filter may be used instead of the Sobel filter.

  Next, the image processing unit 603 selects one of the color materials (S1004), and applies the selected Sobel filter to the image data corresponding to the selected color material (S1005).

  Details of the filter processing will be described with reference to FIG. Each pixel in FIG. 13 represents a pixel, the pixel 1201 is located at the upper left end (0, 0) of the image, and the pixel 1202 is located at the lower right end (W, H) of the image. When the 3 × 3 Sobel filter shown in FIG. 12 is used, the filtering process starts from the pixel 1208 and its surrounding eight pixels, proceeds in the order indicated by the arrows in FIG. 13, and ends at the pixel 1204 and its surrounding eight pixels.

When the selected color material is cyan C, the image data after filtering is Cf. Similarly, magenta M is Mf, yellow Y is Yf, and black K is Kf. If the vertical Sobel filter shown in FIG. 12A is selected and the coordinates of the pixel of interest are (x, y), the image data after the filter processing is expressed by the following equation.
Xf (x, y) = -X (x-1, y-1) + X (x + 1, y-1)
+ -2X (x-1, y) + 2X (x + 1, y)
+ -X (x-1, y + 1) + X (x + 1, y + 1)… (1)
Where Xf is Cf, Mf, Yf or Kf,
The bit depth of Xf shall be equal to the bit depth of input data X.
1 ≦ x ≦ W-1, 1 ≦ y ≦ H-1.

  Next, the image processing unit 603 determines whether or not the filter processing has been applied to the image data of all the color materials (S1006), and if there is image data of unapplied color materials, the processing returns to step S1004.

  When the filter processing is applied to the image data of all the color materials, the image processing unit 603 causes edge blurring due to the fixing processing based on the image data after the filter processing indicating the degree of change in the color material amount of each color material. A determination value indicating an easy pixel is determined (S1007).

The image processing unit 603 calculates the total change amount T of the color material amount in each pixel from the image data after the filter processing according to Expression (2), and determines whether or not the pixel is likely to cause edge bleeding according to Expression (3). A determination value E (x, y) indicating is determined.
T (x, y) = | Cf (x, y) | + | Mf (x, y) | + | Yf (x, y) | + | Kf (x, y) |;… (2)
;
if (T (x, y) <Th)
E (x, y) = '0';
else
E (x, y) = '1';… (3)

  In other words, a pixel whose total change amount T is larger than the threshold Th is recorded as '1' in the determination value E (x, y) as a pixel in which edge bleeding is likely to occur, and a pixel other than that is determined as the determination value E (x, y). Record '0' in The threshold value depends on the bit depth of the image data after filtering, but is set to “128” in the case of 8 bits. Note that the threshold value Th may be decreased when the print mode of the print information indicates image quality priority, and the threshold value Th may be increased when speed priority is indicated.

Correction of Color Material Amount Signal Details of the processing for correcting the color material amount signal (S804) will be described with reference to the flowchart of FIG.

  The image processing unit 603 acquires a determination value E (x, y) indicating whether or not the pixel is likely to cause edge bleeding (S1501), and searches for the pixels in the order illustrated in FIG. 13 to easily cause edge bleeding. One (hereinafter referred to as edge pixel) is selected (S1502). Then, the color material amount of a plurality of pixels (for example, eight pixels, hereinafter referred to as a color material amount correction region) located downstream in the transport direction of the selected edge pixel (target edge pixel) is acquired (S1503).

  FIG. 15 shows an example of the relationship between the edge pixel and the color material amount correction region. FIG. 15A shows the relationship between the target edge pixel 1601 and the color material amount correction area 1602 when the orientation of the print information recording medium indicates the vertical direction. FIG. 15B shows the relationship between the target edge pixel 1601 and the color material amount correction area 1602 when the orientation of the print information recording medium indicates the horizontal direction. When the target edge pixel 1601 is near the edge of the image, the color material amount correction region 1602 may be a region narrower than eight pixels, for example. Further, when the print mode of the print information indicates image quality priority, the color material amount correction area 1602 may be widened, and when the speed priority is indicated, the color material amount correction area 1602 may be narrowed.

  Next, the image processing unit 603 compares the total color material amount Ad of the color material amount correction area 1602 with the total color material amount Ai of the target edge pixel 1601, and the target edge pixel 1601 is blurred by the fixing process. It is determined whether or not it occurs (S1504). If Ad <Ai, it is determined that the amount of color material to be crushed by the fixing process is small and no edge blur occurs, and the process proceeds to step S1506.

When Ad ≧ Ai, the image processing unit 603 determines a determination value indicating whether or not the color material amount correction area 1602 includes a thin line area having a color different from the preceding and succeeding pixels in the transport direction (S1505). In other words, the pixels in the color material amount correction region 1602 are scanned in the transport direction in order from the pixels close to the target edge pixel 1601, and the total between the target pixel and each of the two adjacent pixels adjacent to each other in the direction orthogonal to the transport direction. The color material amount difference D1 is calculated by Equation (4).
D1 = √ (ΣΔX1 ² + ΣΔX2 ² ) / 2… (4)
Here, ΔX1 is the difference in the amount of color material between the target pixel and one edge direction adjacent pixel,
ΔX2 is the difference in color material amount between the target pixel and the other edge direction adjacent pixel,
X is C, M, Y, K.

The image processing unit 603 further calculates a total color material amount difference D2 between the target pixel and an adjacent pixel located upstream in the conveyance direction (adjacent pixel in the conveyance direction) by Expression (5).
D2 = √ (ΣΔX ² )… (5)
Here, ΔX is the difference in the amount of color material between the target pixel and the adjacent pixel in the transport direction,
X is C, M, Y, K.

The image processing unit 603 determines a determination value Fi that indicates whether or not to correct the color material amount signal for each pixel in the color material amount correction region 1602 by Expression (6).
if (D1 ≤ Th1 && D2 ≥ Th2)
Fi = 0;
if (D1> Th1 || D2 <Th2)
Fi = 1;… (6)
i is the pixel distance.

  The pixel distance i corresponds to the pixel number counted from the side closer to the target edge pixel. When the color material amount correction area is eight pixels, the pixel distance i = 1 of the pixel closest to the target edge pixel is set to the target edge pixel. The pixel distance i = 8 of the farthest pixel.

  That is, if the thin line extending in the edge direction, the image processing unit 603 has a sufficiently small color material amount difference D1 from the adjacent pixels in the edge direction (close to the color) and the color material amount of the adjacent pixels in the transport direction. The difference D2 is sufficiently large (the color is different). Therefore, for example, a threshold value Th1 = Th2 = 10 is set, and if D1 ≦ Th1 and D2 ≧ Th2, it is determined that the target pixel is in the thin line region (Fi = 0). When D1> Th1 or D2 <Th2, it is determined that the target pixel is not in the thin line region (Fi = 1).

Next, the image processing unit 603 corrects the color material amount signal of each pixel in the color material amount correction region 1602 by Expression (7) (S1506).
Xi _dst = Xi _src -k (P × Fi / i) (7)
Here, Xi _src is the color material amount signal before correction of the i-th pixel,
Xi _dst is the color material amount signal after correction of the i-th pixel,
X is C, M, Y, K,
P is fixing power,
k is a predetermined coefficient.

  Next, the image processing unit 603 determines whether or not the processing of steps S1502 to S1505 has been performed for all edge pixels (S1507). If there is no unprocessed edge pixel, the color material amount correction processing is terminated. If there is an unprocessed edge pixel, the process returns to step S1502, and the processes from step S1502 to S1505 are repeated for the next edge pixel.

  In this manner, the value of the color material amount signal of the pixel in the color material amount correction area downstream of the conveyance direction of the edge area orthogonal to the conveyance direction is reduced, and sharpness is deteriorated due to edge bleeding occurring in the fixing process. Reduce.

  In the above description, the example in which the fixing force corresponding to the paper type, basis weight, and print mode of the recording medium is acquired has been described. However, the color material amount signal may be corrected with the fixing force constant. Alternatively, the value of the color material amount signal on the downstream side in the conveyance direction of the edge region may be reduced without acquiring the fixing force. Further, if attention is focused only on reducing the occurrence of edge blurring, the value of the color material amount signal of the pixel located downstream in the conveyance direction of the edge region may be set to zero.

  The image processing according to the second embodiment of the present invention will be described below. Note that the same reference numerals in the second embodiment denote the same parts as in the first embodiment, and a detailed description thereof will be omitted.

  In the first exemplary embodiment, an edge region where edge bleeding is likely to occur due to the fixing process is identified according to the conveyance direction of the recording medium, and the color material of the pixel in the color material amount correction region located downstream in the conveyance direction of the edge region The value of the quantity signal was reduced to prevent sharpness degradation. In the second embodiment, an example will be described in which the exposure time of the pixels in the color material amount correction region located downstream in the conveyance direction is reduced by laser beam pulse width control to prevent the sharpness from being deteriorated.

  An example of laser driving by the exposure unit 13 according to the second embodiment will be described with reference to FIG. Note that the scanning direction of the laser beam is a main scanning direction orthogonal to the transport direction (sub-scanning direction). FIG. 16 (a) shows laser drive by the exposure unit 13 of Example 1 that does not perform pulse width control. That is, there are two laser drive states, laser drive (exposure) and laser non-drive (not exposure). For this reason, the color material supplied downstream in the conveyance direction of the edge region facilitates edge bleeding in the fixing process.

  FIG. 16B shows a laser drive example of the second embodiment in which the pulse width control is performed to narrow the pulse width in the downstream area in the conveyance direction of the edge area. In this way, the exposure amount is reduced in the downstream area of the edge area in the transport direction, the supply amount of the color material is reduced, and the blurring of the edge is suppressed in the fixing process.

  The processing of the image processing unit 603 will be described with reference to the flowchart of FIG. Note that the processing in steps S801 and S802 is substantially the same as the processing in the first embodiment shown in FIG. 8, and detailed description thereof is omitted.

  The image processing unit 603 creates a pulse width control mask based on the specified edge region information (S811). That is, an area located downstream in the conveyance direction of the edge area is specified, and a signal for performing laser driving with a narrow pulse width (hereinafter, narrow pulse width driving) is recorded in the pulse width control mask. In other areas, a signal for performing laser driving with a pulse width normally used (hereinafter referred to as normal pulse width driving) is recorded in a pulse width control mask.

  FIG. 18 shows an example of a pulse width control mask. In FIG. 18, an area surrounded by a broken line indicates an edge area. A hatched area downstream in the conveyance direction of the edge area indicates an area using narrow pulse width driving, and the other area indicates an area using normal pulse width driving.

  Next, the image processing unit 603 performs halftone processing on the CMYK data to generate, for example, 1-bit CMYK data for each color (S812). Then, for example, from a CMYK data of 1 bit for each color and a pulse width control mask, a ternary image signal having three values of a signal indicating non-laser driving, a signal indicating narrow pulse width driving, and a signal indicating normal pulse width driving is generated. (S813). The ternary image signal is output to the exposure unit 13 (see FIG. 5) of the image forming unit 604 in the surface order.

  FIG. 19 shows the relationship between a pulse width control mask, an image signal after halftone processing, and a ternary image signal. The pulse width control mask (FIG. 19A) shows normal pulse width driving and narrow pulse width driving across the edge region. The image signal after the halftone process (FIG. 19B) shows an on dot that supplies a color material and an off dot that does not supply a color material. The ternary image signal (FIG. 19C) is generated from the pulse width control mask and the image signal after the halftone process. The ternary image signal indicates non-laser driving for off dots, normal pulse width driving for on dots upstream in the transport direction of the edge region, and narrow pulse width driving for on dots downstream in the transport direction of the edge region. Indicates.

  The pulse width control by the exposure unit 13 will be described with reference to FIG. The exposure unit 13 compares the ternary image signal (level V) input from the image processing unit 603 with the triangular wave signal (level S), and causes the laser light source 31 to emit light during a period corresponding to V <S. Is generated. The laser light source 31 emits light according to the laser driving pulse, and the photosensitive drum 11 is exposed and scanned by the laser light whose pulse width is controlled according to the ternary image signal.

  In this way, the amount of color material to be supplied is reduced by reducing the exposure time in the area downstream of the conveyance direction of the edge area orthogonal to the conveyance direction, and the reduction in sharpness due to edge bleeding that occurs in the fixing process is reduced. To do.

[Modification]
In the second embodiment, the fixing force may be acquired similarly to the first embodiment, and the pulse width corresponding to the fixing force may be set. For example, in order to realize a pulse width corresponding to the two-stage fixing force, the image signal supplied to the exposure unit 13 may be made quaternary. For example, in the example shown in FIG. 20, the level “01” is unused, but a two-stage pulse width corresponding to the fixing force may be defined by the levels “01” and “10”. Similarly, in order to realize a pulse width corresponding to three or more stages of fixing power, the image signal supplied to the exposure unit 13 may be set to five or more values.

  Further, in Example 2, if attention is focused only on reducing the occurrence of edge bleeding, normal pulse width driving is performed in the normal area, and laser is not driven in the downstream area in the transport direction of the edge area. Good. Alternatively, an edge region may be detected from the image signal after halftone processing, and a pulse width control mask may be generated corresponding to one dot of the image signal after halftone processing.

  In the above-described embodiment, an image processing apparatus that primarily transfers a toner image formed on the photosensitive drum 11 to the intermediate transfer drum 51 and then secondary-transfers the toner image on the intermediate transfer drum 51 to a recording medium will be described. did. However, the present invention is also applicable to an image processing apparatus that transfers a toner image formed on the photosensitive drum 11 directly to a recording medium.

  In the above-described embodiment, the image processing apparatus has been described in which four-color toner development is sequentially performed by the developing unit 14 and transferred to the intermediate transfer drum 51 material. However, the present invention is applicable to a tandem image processing apparatus having the same basic configuration but having a charging unit, a photosensitive drum, an exposure unit, and a development unit for each color. Of course, the present invention can also be applied to an image processing apparatus that forms a monochrome image with a single color toner.

[Other Examples]
The present invention can also be realized by executing the following processing. That is, software (program) that realizes the functions of the above-described embodiments is supplied to a system or apparatus via a network or various storage media, and a computer (or CPU, MPU, etc.) of the system or apparatus reads the program. It is a process to be executed.

Claims (9)

Conversion means for converting the image data into a color material amount signal representing the color material amount;
Detecting means for detecting an edge region of an image from the color material amount signal having a direction orthogonal to a conveyance direction of the recording medium;
The value of the color material amount signal corresponding to the pixel located downstream in the transport direction of the edge region is determined according to the fixing force when fixing the toner image formed based on the color material amount signal to the recording medium. An image processing apparatus comprising correction means for correcting.   2. The image processing apparatus according to claim 1, wherein the fixing force is determined based on a type, basis weight, and print mode of a recording medium indicated by print information input together with the image data. The correction means determines whether or not blurring of an edge occurs in the edge pixel in the fixing from the value of the color material amount signal of a plurality of pixels located downstream in the transport direction of the edge pixel included in the edge region. Means for determining whether
3. The correction according to claim 1, wherein when it is determined that blurring of the edge occurs, correction is performed to reduce the value of the color material amount signal of the plurality of pixels according to the fixing force. Image processing device. In the case where it is determined that blurring of the edge occurs, the correction unit determines whether or not there is a pixel in a thin line region having a different color from the preceding and following pixels in the transport direction in the plurality of pixels. Having means,
4. The image processing apparatus according to claim 3, wherein a value of the color material amount signal of a pixel in the thin line area included in the plurality of pixels is not corrected. An image processing apparatus that forms an image by scanning an image carrier with laser light,
Conversion means for converting the image data into a color material amount signal representing the color material amount;
Detecting means for detecting an edge region of an image from the color material amount signal having a direction orthogonal to a conveyance direction of the recording medium;
A creation means for creating a pulse width control mask for narrowing a pulse width of the laser beam to a pulse width that is normally used in a region downstream of the edge region in the transport direction;
An image processing apparatus comprising: generating means for generating at least a ternary color material amount signal from the color material amount signal and the pulse width control mask.   6. The detection unit according to claim 1, wherein the detection unit specifies the edge region using an edge detection filter corresponding to a direction of a recording medium indicated by print information input together with the image data. Image processing apparatus. An image processing method of an image processing apparatus having a conversion unit, a detection unit, and a correction unit,
The converting means converts the image data into a color material amount signal representing the color material amount,
The detection means detects an edge region of an image having an orientation orthogonal to the conveyance direction of the recording medium from the color material amount signal;
A color material corresponding to a pixel located downstream of the edge region in the transport direction according to a fixing force when the correction unit fixes a toner image formed based on the color material amount signal to the recording medium. An image processing method comprising correcting a value of a quantity signal. An image processing method for an image processing apparatus, which includes a conversion unit, a detection unit, a creation unit, and a generation unit, and forms an image by scanning an image carrier with laser light,
The converting means converts the image data into a color material amount signal representing the color material amount,
The detection means detects an edge region of an image having an orientation orthogonal to the conveyance direction of the recording medium from the color material amount signal;
The creation means creates a pulse width control mask for narrowing the pulse width of the laser light in a region downstream of the edge region in the transport direction from a pulse width that is normally used;
The image processing method, wherein the generation unit generates at least a ternary color material amount signal from the color material amount signal and the pulse width control mask.   7. A program for causing a computer to function as each unit of the image processing apparatus according to claim 1.

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