JP5847046B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus.

  In an electrophotographic printing system, the amount of toner on the high density side increases due to the edge effect on the high density side of the edge of the toner image, and the density on the low density side of the edge of the toner image decreases due to the halo effect. It is known that the toner amount on the side decreases (for example, see Patent Documents 1 to 3).

  In particular, since the edge effect at the rear end of the image in the sub-scanning direction is relatively strong, a certain printing apparatus corrects the toner amount by adjusting the exposure amount only at the rear end of the image in the sub-scanning direction (for example, Patent Document 1).

JP 2005-303882 A JP 2010-050708 A JP 2009-118378 A

  However, the techniques described in Patent Documents 1 to 3 described above compensate for one of the increase in the toner amount due to the edge effect and the decrease in the toner amount due to the halo effect. It is difficult to satisfactorily compensate for the decrease in toner amount by the same calculation method. In other words, an attempt to compensate for an increase in toner amount due to the edge effect and a decrease in toner amount due to the halo effect by different calculation methods increases the circuit scale, which is not preferable.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus that satisfactorily compensates for an increase in toner amount due to an edge effect and a decrease in toner amount due to a halo effect by a similar calculation method. To do.

  In order to solve the above problems, the present invention is configured as follows.

An image forming apparatus according to the present invention includes an end detection unit that detects an end at which peripheral pixels arranged in a predetermined direction have a predetermined gradation difference pattern, and a predetermined range in the predetermined direction from the end. For each pixel of interest, the sum of the pixel values of a predetermined first reference pixel region ahead of the pixel of interest in the predetermined direction and a predetermined second reference pixel region behind the pixel of interest in the predetermined direction And an end correction unit that specifies a correction amount for adjusting the toner amount of the target pixel based on the difference from the sum of the pixel values of the target pixel and corrects the pixel value of the target pixel with the correction amount. The gradation difference pattern relates to a forward reference pixel arranged in front of the gradation difference pattern attention pixel and a backward reference pixel arranged behind the gradation difference pattern attention pixel, and the forward reference pixel has a predetermined high density range. The predetermined low density range is specified for the backward reference pixel. Then, the edge detection unit detects, as an edge, a gradation difference pattern target pixel whose peripheral pixels satisfy the gradation difference pattern. The end correction unit sets the above-described correction amount as the negative value of the absolute value according to the above-described difference when the above-described difference is negative, and the above-described correction when the above-described difference is positive. The amount is set to a positive value of an absolute value corresponding to the difference, and the edge correction unit identifies the correction amount based on the difference based on a predetermined function or lookup table, and the function or look The characteristics of the uptable are non-linear.

  Thereby, according to the gradation distribution in the vicinity of the edge, an increase in the toner amount due to the edge effect and a decrease in the toner amount due to the halo effect are satisfactorily compensated by the same calculation method. Further, the toner amount can be selectively adjusted with respect to the end portion existing in a predetermined direction.

  In addition to the image forming apparatus described above, the image forming apparatus according to the present invention may be configured as follows. In this case, the above-described predetermined range is set in front of or behind the end portion according to the above-described gradation difference pattern.

  Thereby, the toner amount adjustment on the high density side (that is, compensation for the edge effect) and the toner amount adjustment on the low density side (that is, compensation for the halo effect) can be selectively performed.

  In addition to the image forming apparatus described above, the image forming apparatus according to the present invention may be configured as follows. In this case, the first reference pixel region and the second reference pixel region are symmetric with respect to the target pixel described above.

  Thereby, the distribution pattern of the correction amount in the predetermined direction is similar between the high density side and the low density side of the end portion.

  In addition to the image forming apparatus described above, the image forming apparatus according to the present invention may be configured as follows. In this case, the predetermined direction is the main scanning direction or the sub-scanning direction.

  In addition to the image forming apparatus described above, the image forming apparatus according to the present invention may be configured as follows. In this case, the image forming apparatus controls the end portion by controlling the photosensitive member, the exposure device that forms an electrostatic latent image on the photosensitive member, the developing device that develops the electrostatic latent image with toner, and the exposure device. And an exposure control unit that forms an electrostatic latent image based on the pixel value corrected by the correction unit.

  According to the present invention, in the image forming apparatus, an increase in the toner amount due to the edge effect and a decrease in the toner amount due to the halo effect are compensated well by the same calculation method.

FIG. 1 is a side view showing a part of a mechanical internal configuration of an image processing apparatus according to an embodiment of the present invention. FIG. 2 is a diagram showing a configuration example of the exposure apparatus and peripheral circuits in FIG. FIG. 3 is a block diagram showing the configuration of the image processing unit in FIG. FIG. 4 is a diagram illustrating an example of a gradation difference pattern. FIG. 5 is a diagram illustrating an example of image data including an image rear end portion in the sub-scanning direction. FIG. 6 is a diagram showing the end portions detected in the image data shown in FIG. 5 with the gradation difference pattern shown in FIG. 4A by the end detection portion shown in FIG. FIG. 7 is a diagram illustrating an example of a filter for designating a range for density correction in the edge detection unit illustrated in FIG. 3. FIG. 8 is a diagram illustrating an example of data indicating the density correction range specified by the edge detection unit illustrated in FIG. 3. FIG. 9 is a diagram illustrating an example of a filter including a first reference pixel region and a second reference pixel region used by the edge correction unit illustrated in FIG. FIG. 10 shows a correction amount obtained by applying the filter shown in FIG. 9A to the density correction range of image data shown in FIG. 5 (the range of value 1 in FIG. 8) by the edge correction unit shown in FIG. It is a figure which shows a1-a5. FIG. 11 is a diagram illustrating an example of a density correction range when density correction is performed on the low density side of the end portion. 12 shows a correction amount obtained by applying the filter shown in FIG. 9A to the density correction range of image data shown in FIG. 5 (the range of value 1 in FIG. 11) by the edge correction unit shown in FIG. It is a figure which shows b1-b5. FIG. 13 is a diagram illustrating an example of a correspondence relationship between the output value of the filter illustrated in FIG. 9 and the density correction amount.

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

  FIG. 1 is a side view showing a part of a mechanical internal configuration of an image processing apparatus according to an embodiment of the present invention. This image processing apparatus is an image forming apparatus having an electrophotographic printing function, such as a printer, a facsimile machine, a copying machine, or a multifunction machine.

  The image processing apparatus of this embodiment has a tandem color developing apparatus. The color developing device includes photosensitive drums 1a to 1d, exposure devices 2a to 2d, and developing devices 3a to 3d. The photoconductor drums 1a to 1d are four-color photoconductors of cyan, magenta, yellow, and black. The exposure apparatuses 2a to 2d are apparatuses that form electrostatic latent images by irradiating the photosensitive drums 1a to 1d with laser light. The exposure apparatuses 2a to 2d are laser scanning units having a laser diode that is a light source of laser light and optical elements (lens, mirror, polygon mirror, etc.) that guide the laser light to the photosensitive drums 1a to 1d.

  Further, around the photosensitive drums 1a to 1d, a charger such as a scorotron, a cleaning device, a static eliminator and the like are arranged. The cleaning device removes residual toner on the photosensitive drums 1a to 1d after the primary transfer, and the static eliminator neutralizes the photosensitive drums 1a to 1d after the primary transfer.

  Each of the developing devices 3a to 3d is mounted with a toner cartridge filled with toners of four colors of cyan, magenta, yellow and black, and the toner is supplied from the toner cartridge and constitutes a developer together with the carrier. The developing devices 3a to 3d form toner images by attaching the toner to the electrostatic latent images on the photosensitive drums 1a to 1d.

  The photosensitive drum 1a, the exposure device 2a, and the developing device 3a develop magenta, and the photosensitive drum 1b, the exposure device 2b, and the developing device 3b develop cyan, the photosensitive drum 1c, and the exposure device. Yellow development is performed by the device 2c and the developing device 3c, and black development is performed by the photosensitive drum 1d, the exposure device 2d, and the developing device 3d.

  The intermediate transfer belt 4 is an annular image carrier that contacts the photosensitive drums 1a to 1d and primarily transfers the toner images on the photosensitive drums 1a to 1d. The intermediate transfer belt 4 is stretched around the driving roller 5 and circulates in the direction from the contact position with the photosensitive drum 1d to the contact position with the photosensitive drum 1a by the driving force from the driving roller 5.

  The transfer roller 6 brings the conveyed paper into contact with the intermediate transfer belt 4 and secondarily transfers the toner image on the intermediate transfer belt 4 to the paper. The sheet on which the toner image has been transferred is conveyed to the fixing device 9 and the toner image is fixed on the sheet.

  The roller 7 has a cleaning brush, and the cleaning brush is brought into contact with the intermediate transfer belt 4 to remove the toner remaining on the intermediate transfer belt 4 after the transfer of the toner image onto the paper.

  The sensor 8 is a sensor used for toner density adjustment, and irradiates the intermediate transfer belt 4 with a light beam and detects the reflected light. When adjusting the toner density, the sensor 8 irradiates a predetermined region of the intermediate transfer belt 4 with a light beam, detects reflected light (measurement light) of the light beam, and outputs an electrical signal corresponding to the light amount.

  FIG. 2 is a diagram showing a configuration example of the exposure apparatus 2a and peripheral circuits in FIG. 2 exposes the photosensitive drum 1a to form an electrostatic latent image, and the exposure devices 2b to 2d for the photosensitive drums 1b to 1d have the same configuration.

  In FIG. 2, the exposure apparatus 2 a includes a laser diode 11, an optical system 12, a polygon mirror 13, an optical sensor 14, a driver circuit 15, an exposure control unit 16, and an image processing unit 17.

  The laser diode 11 is a light source that emits a laser beam. The optical system 12 is various lens groups disposed between the laser diode 11 and the polygon mirror 13 and / or between the polygon mirror 13 and the photosensitive drum 1a and the optical sensor 14. For the optical system 12, an fθ lens or the like is used.

  The polygon mirror 13 is an element having an axis perpendicular to the axis of the photosensitive drum 1a, a cross section perpendicular to the axis being a polygon, and a side surface being a mirror. The polygon mirror 13 rotates about its axis, and scans the light beam emitted from the laser diode 11 along the axial direction (main scanning direction) of the photosensitive drum 1a.

  The optical sensor 14 is a sensor that receives light scanned by the polygon mirror 13 to generate a main scanning synchronization signal. When light is incident, the optical sensor 14 induces an output voltage corresponding to the amount of light. The optical sensor 14 is disposed at a predetermined position on the line where light is scanned, and is used to detect the timing at which the light spot passes through the position.

  The driver circuit 15 causes the laser diode 11 to emit light according to the drive signal while synchronizing in the main scanning direction based on the main scanning synchronization signal of the optical sensor 14.

  Further, the exposure control unit 16 outputs a drive signal corresponding to the value of the image data having a predetermined number of gradations from the image processing unit 17 to control the light amount of the exposure apparatus 2a. That is, the exposure control unit 16 controls the amount of light incident on the photosensitive drum 1a (the amount of light of each pixel).

  Further, the image processing unit 17 uses the same number of gradations (for example, 16 gradations) as the number of gradations (for example, 16 gradations) that can be formed on the photosensitive drum 1a by the exposure apparatus 2a from multi-gradation (for example, 256 gradations) image data. Image data is generated, and density correction is performed to compensate for the increase and decrease in toner consumption due to the edge effect and halo effect.

  FIG. 3 is a block diagram showing a configuration of the image processing unit 17 in FIG. Note that the processing by the image processing unit 17 shown in FIG. 3 is performed on the image data of each color corresponding to the four colors of toner. The image processing unit 17 includes an image data processing unit 31, an image output direction determination unit 32, an intermediate gradation processing unit 33, an end detection unit 34, an end correction unit 35, and a data selection unit 36.

  The image data processing unit 31 performs various processes such as color conversion and resolution conversion on the image data.

  Further, the image output direction determination unit 32 specifies the orientation (landscape or portrait) of the image to be printed from the print settings or the like, and outputs the image data to the subsequent stage in the order of the pixels according to the orientation of the image.

  Further, the intermediate gradation processing unit 33 performs gradation processing such as screen processing from the original multi-gradation (256 gradations) image data (that is, 8-bit image data) with the number of gradations capable of forming an image. Generate image data.

  Further, the end detection unit 34 detects an end in a predetermined direction (main scanning direction and / or sub-scanning direction) and a gradation difference pattern specified in advance, and a range of pixels for which density correction is performed (hereinafter referred to as density). Specify the correction range. Specifically, the end detection unit 34 detects an end (pixel) in which the peripheral pixels arranged in the predetermined direction have a predetermined gradation difference pattern, and the predetermined pixel from the end in the predetermined direction. The number range is set as the density correction range.

  In this embodiment, the density correction range is set in front of or behind the end in the predetermined direction according to the gradation difference pattern.

  The end correction unit 35 corrects the value of a pixel in the density correction range in the image data in order to compensate for the increase and decrease in the toner amount due to the edge effect and / or the halo effect. Specifically, the edge correction unit 35 corrects the pixel value for each pixel (target pixel) in the density correction range. Then, the end correction unit 35 adds the sum of the pixel values of the predetermined first reference pixel area ahead of the target pixel in the predetermined direction and the predetermined second reference behind the target pixel in the predetermined direction. Based on the difference from the sum of the pixel values in the pixel area, a correction amount for adjusting the toner amount of the target pixel is specified, and the pixel value of the target pixel is corrected with the correction amount.

  In this embodiment, the first reference pixel region and the second reference pixel region are symmetric with respect to the target pixel described above.

  Further, the data selection unit 36 selects the output (corrected pixel value) of the end correction unit 35 for the pixel corrected by the end correction unit 35, and performs correction by the end correction unit 35. For pixels that have not been detected, the output (uncorrected pixel value) of the intermediate gradation processing unit 33 is selected, and the selected pixel value is output to the exposure control unit 16.

  Next, the operation of the image forming apparatus will be described.

  The edge detection unit 34 detects one or a plurality of specific image edges (for example, an image rear edge) in the image data output from the intermediate gradation processing unit 33, and a density correction range corresponding to the edge. Is specified.

  FIG. 4 is a diagram illustrating an example of a gradation difference pattern. The gradation difference pattern shown in FIG. 4A is for detecting the rear end portion of the image in the sub-scanning direction. In the gradation difference pattern shown in FIG. 4A, a predetermined high density range is designated for the forward reference pixel 52 arranged in front of the target pixel 51 in the sub-scanning direction, and from the target pixel 51 to the rear in the sub-scanning direction. A predetermined low density range is designated for the rearward reference pixels 53 arranged. In other words, the pixel of interest 51 in which the surrounding pixels satisfy this gradation difference pattern in the image data is detected as an end (image rear end in the sub-scanning direction). The gradation difference pattern shown in FIG. 4B is for detecting the image front end in the sub-scanning direction. Further, the gradation difference patterns shown in FIGS. 4C and 4D are for detecting the image side edge in the main scanning direction.

  A gradation difference pattern corresponding to an end portion to be subjected to density correction is appropriately used.

  FIG. 5 is a diagram illustrating an example of image data including an image rear end portion in the sub-scanning direction. In the example shown in FIG. 5, the pixel value on the high density side at the end is 16, and the pixel value on the low density side at the end is 1.

  FIG. 6 is a diagram showing the end portions detected in the image data shown in FIG. 5 with the gradation difference pattern shown in FIG. 4A by the end detection portion 34 shown in FIG. As shown in FIG. 6, the value of the pixel at the end (that is, the pixel of interest that satisfies the gradation difference pattern shown in FIG. 4A) is set to 1.

  FIG. 7 is a diagram illustrating an example of a filter for designating a range for density correction in the edge detection unit 34 illustrated in FIG. 3. FIG. 7A shows a filter for the rear end of the image. FIG. 7B shows a filter for the image front end, and FIGS. 7C and 7D show a filter for the image side end.

  In the filter shown in FIG. 7A, N reference pixels ahead of the target pixel 61 in the sub-scanning direction are used, and this filter is applied to the edge detection result (for example, the data shown in FIG. 6). The When the value of the pixel corresponding to at least one pixel of the reference pixel is 1 in the detection result of the end portion, the value of the target pixel 61 is set to 1, and the value of the pixel corresponding to all the reference pixels Is 0, the value of the target pixel 61 is set to 0.

  FIG. 8 is a diagram illustrating an example of data indicating the density correction range specified by the edge detection unit 34 illustrated in FIG. 3. For example, when the filter shown in FIG. 7A is applied to the edge detection result shown in FIG. 6, the value in the range of (N + 1) pixels from the edge becomes 1, as shown in FIG. The values in other ranges are 0. In this data, a pixel whose value is 1 is a target for density correction.

  Next, the edge correction unit 35 performs density correction of the image data for the density correction range designated by the edge detection unit 34. For this density correction, a filter corresponding to the target end is used.

  FIG. 9 is a diagram illustrating an example of a filter including a first reference pixel region and a second reference pixel region used by the edge correction unit 35 illustrated in FIG. FIG. 9A is a diagram illustrating an example of a filter including a first reference pixel region and a second reference pixel region that are used at ends (image rear end and image front end) in the sub-scanning direction. FIG. 9B is a diagram illustrating an example of a filter including a first reference pixel region and a second reference pixel region used at an end portion (image side end portion) in the main scanning direction.

  A filter shown in FIG. 9A is used for density correction of the rear end portion of the image. A region of (Z × X) pixels adjacent to the target pixel 71 in the sub-scanning direction is a first reference pixel region 72, and a filter coefficient of each pixel in the first reference pixel region 72 is −1. A region of (Z × X) pixels adjacent to the target pixel 71 in the rear in the sub-scanning direction is a second reference pixel region 73, and the filter coefficient of each pixel in the second reference pixel region 73 is 1. The That is, the difference between the sum of the pixel values in the first reference pixel area 72 and the sum of the pixel values in the second reference pixel area 73 of the image data (for example, FIG. 5) is the output value of this filter (that is, the target pixel). 71).

  The Z is N + 1. Further, this filter can be used for both the high density side and the low density side of the rear end portion of the image.

  Note that the filter shown in FIG. 9A can also be used for density correction for the front edge of the image. In the case of using the front end portion of the image, the sign of the result of the filter operation may be reversed.

  FIG. 10 shows a correction obtained by applying the filter shown in FIG. 9A to the density correction range of image data shown in FIG. 5 (the range of value 1 in FIG. 8) by the edge correction unit 35 shown in FIG. It is a figure which shows quantity a1-a5. The absolute values of the correction amounts a1 to a5 increase as they approach the edge, and increase as the gradation difference at the edge increases. In this example, the correction amounts a1 to a5 are as follows.

a1 = −375 × W1
a2 = −300 × W1
a3 = −225 × W1
a4 = −150 × W1
a5 = −75 × W1

  Here, W1 is a predetermined coefficient, and is set in advance so as to be a correction amount for appropriately compensating for the edge effect based on experiments or the like.

  In the above example, the high density side of the end is corrected, but the low density side can be similarly corrected.

  FIG. 11 is a diagram illustrating an example of a density correction range when density correction is performed on the low density side of the end portion. The density correction range shown in FIG. 11 is obtained by applying the filter shown in FIG. 7B to the edge detection result shown in FIG.

  FIG. 12 shows a correction obtained by applying the filter shown in FIG. 9A to the density correction range (the range of value 1 in FIG. 11) of the image data shown in FIG. 5 by the edge correction unit 35 shown in FIG. It is a figure which shows quantity b1-b5. The absolute values of the correction amounts b1 to b5 increase as they approach the edge, and increase as the gradation difference at the edge increases. In this example, the correction amounts b1 to b5 are as follows.

b1 = 375 × W2
b2 = 300 × W2
b3 = 225 × W2
b4 = 150 × W2
b5 = 75 × W2

  Here, W2 is a predetermined coefficient, and is set in advance to be a correction amount that appropriately compensates for the halo effect based on experiments or the like.

  Then, the data selection unit 36 outputs the pixel value output from the edge correction unit 35 to the exposure control unit 16 for the density correction range, and is output from the intermediate gradation processing unit 33 for the other range. The pixel value to be output to the exposure control unit 16 as it is.

  As described above, according to the above-described embodiment, the edge detection unit 34 detects an edge where peripheral pixels arranged in a predetermined direction have a predetermined gradation difference pattern, and the edge correction unit 35 For each target pixel within a predetermined range in the predetermined direction from the end portion, the sum of pixel values of a predetermined first reference pixel area ahead of the target pixel in the predetermined direction, and in the predetermined direction A correction amount for adjusting the toner amount of the target pixel is specified based on the difference from the sum of the pixel values of the predetermined second reference pixel region behind the target pixel, and the pixel of the target pixel is determined based on the correction amount. Correct the value.

  Thereby, according to the gradation distribution in the vicinity of the edge, an increase in the toner amount due to the edge effect and a decrease in the toner amount due to the halo effect are satisfactorily compensated by the same calculation method. Further, the toner amount can be selectively adjusted with respect to the end portion existing in a predetermined direction.

  The above-described embodiments are preferred examples of the present invention, but the present invention is not limited to these, and various modifications and changes can be made without departing from the scope of the present invention. is there.

  For example, in the above-described embodiment, the end correction unit 35 calculates the correction amount by multiplying the difference by a coefficient that differs according to the predetermined direction and / or the gradation difference pattern. It may be. That is, different values may be used for the above-described coefficients W1 and W2.

  In the above embodiment, the correction amount may be specified based on a predetermined function or LUT (Look-Up Table) from the output value of the filter shown in FIG. In that case, for example, as shown in FIG. 13, the function or the characteristics of the LUT may be nonlinear (eg, exponential).

  In the above-described embodiment, the density correction for the rear end portion of the image has been described as an example. For other end portions, a gradation difference pattern, a filter, or the like corresponding to the end portion is used. Similar density correction can be performed.

  The present invention is applicable to, for example, an electrophotographic image forming apparatus.

1a to 1d Photosensitive drum (an example of a photosensitive member)
2a to 2d Exposure device 3a to 3d Development device 16 Exposure control unit 34 End detection unit 35 End correction unit 72 First reference pixel region 73 Second reference pixel region

Claims (5)

In an electrophotographic image forming apparatus,
An edge detection unit that detects edges in which peripheral pixels arranged in a predetermined direction have a predetermined gradation difference pattern;
For each target pixel within a predetermined range in the predetermined direction from the end portion, a sum of pixel values of a predetermined first reference pixel area that is ahead of the target pixel in the predetermined direction, and in the predetermined direction A correction amount for adjusting the toner amount of the target pixel is specified based on a difference from a sum of pixel values of a predetermined second reference pixel region behind the target pixel, and the target amount is determined by the correction amount. An edge correction unit for correcting the pixel value of the pixel;
With
The gradation difference pattern relates to a forward reference pixel arranged in front of a gradation difference pattern attention pixel and a rear reference pixel arranged behind the gradation difference pattern attention pixel. A density range is specified, and a predetermined low density range is specified for the backward reference pixel,
The edge detection unit detects the gradation difference pattern target pixel in which the peripheral pixels satisfy the gradation difference pattern as the edge,
When the difference is negative, the end correction unit sets the correction amount as a negative value of an absolute value according to the difference, and when the difference is positive, The absolute value is positive according to the difference,
The end correction unit specifies the correction amount from the difference based on a predetermined function or a lookup table,
The characteristic of the function or the lookup table is non-linear;
An image forming apparatus.   The image forming apparatus according to claim 1, wherein the predetermined range is set in front of or behind the end portion according to the gradation difference pattern.   The image forming apparatus according to claim 1, wherein the first reference pixel area and the second reference pixel area are symmetrical with respect to the target pixel. The predetermined direction, the image forming apparatus according to any one of claims 1 to 3, characterized in that the main scanning direction or sub-scanning direction. A photoreceptor,
An exposure device that forms an electrostatic latent image on the photoreceptor;
A developing device for developing the electrostatic latent image with toner;
An exposure control unit that controls the exposure apparatus to form the electrostatic latent image based on the pixel value corrected by the edge correction unit;
The image forming apparatus according to any one of claims 1 to 4, characterized by further comprising a.

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