JP3832519B2 - Image forming apparatus and image processing apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus such as a digital copying machine, a computer printer or a network printer, and an image processing apparatus which is an image processing unit of such an image forming apparatus.
[0002]
[Prior art]
In many image forming apparatuses such as digital copiers, computer printers, and network printers that are currently commercialized, an electrophotographic system that can obtain high-quality images at high speed as an image output unit (image output apparatus) Is widely adopted.
[0003]
In the electrophotographic system, as a developing means, insulating toner and magnetic particles are mixed and rubbed in a developing device to charge the insulating toner, and a developer is formed in a brush shape by magnetic force on the developing roll. A two-component magnetic brush developing system that develops an electrostatic latent image on a photosensitive member by supplying a developer onto the photosensitive member by rotation is widely used, particularly in color image forming apparatuses. ing.
[0004]
However, in this electrophotographic image output unit, especially the image output unit using the two-component magnetic brush development method, the output image changes from the halftone part to the background part in the sub-scanning direction due to its nonlinear and asymmetric output characteristics. When it does, the density | concentration of the rear-end part which touches the background part of a halftone part falls.
[0005]
That is, as shown in FIG. 10A, the output image is opposite to the paper feed direction orthogonal to the main scanning direction, which is the scanning direction of the light beam for forming the electrostatic latent image on the photosensitive member. When the halftone portion 1 changes to the background portion 2 in the sub-scanning direction, the density of the rear end portion 1B in contact with the background portion 2 of the halftone portion 1 decreases for the following reason.
[0006]
In the electrophotographic method using the two-component magnetic brush development method, as shown in FIG. 11, the photosensitive drum 310 is charged by the electrostatic latent image forming charger 320 by the rotation of the photosensitive drum 310 in the direction of the arrow 311. The charged photosensitive drum 310 is irradiated with laser light L modulated with an image signal, whereby an electrostatic latent image is formed on the photosensitive drum 310, and the electrostatic latent image is formed. The photosensitive drum 310 is in contact with the developer layer 337 on the surface of the developing sleeve 335 that rotates in the direction of the arrow 336 at a linear velocity that is approximately twice the linear velocity of the photosensitive drum 310, thereby The toner adheres to the latent image portion on the photosensitive drum 310, and the electrostatic latent image on the photosensitive drum 310 is developed into a toner image.
[0007]
FIG. 11A shows a moment when the latent image portion 3 of the halftone portion 1 is formed on the photosensitive drum 310 by the irradiation of the laser beam L, and the front edge 3f contacts the developer layer 337. (B) shows the moment when the portion slightly ahead of the rear edge 3b of the latent image portion 3 is in contact with the developer layer 337, and FIG. 6 (C) shows the moment when the rear edge 3b of the latent image portion 3 is the developer layer 337. Shows the moment of contact.
[0008]
The developing sleeve 335 is given a developing bias having a potential of −500 V, for example. The photosensitive drum 310 is charged to a potential of −650 V, for example, by the charger 320, and the latent image portion 3 of the halftone portion 1 is set to −200 V, for example, lower than the developing bias potential. Further, the portion 4 corresponding to the background portion 2 behind the halftone portion 1 becomes −650 V having a charging potential higher than the developing bias potential.
[0009]
When the front edge 3f of the latent image portion 3 is in contact with the developer layer 337 as shown in FIG. 11A, the toner tq present at the position Q where the photosensitive drum 310 and the developer layer 337 are in contact with each other is in the forward direction. A developing electric field is applied, and the toner tq is attracted to the surface of the developer layer 337 and adhered onto the latent image portion 3. However, when the portion 4 corresponding to the background portion 2 behind the halftone portion 1 approaches the developer layer 337 as shown in FIG. 5B, the toner tb present in the portion facing the portion 4 of the developer layer 337. However, it is moved away from the surface of the developer layer 337 by the developing electric field in the reverse direction, and enters deep into the developer layer 337.
[0010]
Then, when the developing sleeve 335 rotates in the direction of the arrow 336, the toner tb approaches the position Q where the photosensitive drum 310 and the developer layer 337 are in contact with each other, and the developer layer is caused by the low potential of the latent image portion 3. Although it moves to the surface side of 337, there is a time delay in reaching the surface of the developer layer 337. For this reason, the amount of toner deposited on the photosensitive drum 310 is reduced from the time when the portion slightly in front of the rear edge 3b of the latent image portion 3 contacts the developer layer 337 as shown in FIG. As described above, the density of the rear end portion 1B in contact with the background portion 2 of the halftone portion 1 is lowered.
[0011]
When the front of the halftone portion 1 is also a background portion, even when the front edge 3f of the latent image portion 3 is in contact with the developer layer 337 as shown in FIG. As indicated by the toner tf, the portion 5 on the photosensitive drum 310 corresponding to the front background portion is separated from the surface of the developer layer 337.
[0012]
However, due to the rotation of the developing sleeve 335 in the direction of the arrow 336, the toner tf rapidly moves away from the position Q where the photosensitive drum 310 and the developer layer 337 are in contact with each other, and the developer layer is caused by the low potential of the latent image portion 3. The toner tq attracted to the surface of 337 immediately approaches the position Q and adheres to the latent image portion 3. Therefore, even if the output image changes from the background portion to the halftone portion 1 in the sub-scanning direction, the density of the front end portion of the halftone portion 1 in contact with the background portion does not decrease.
[0013]
As described above, in the electrophotographic method using the two-component magnetic brush developing method, the output image is sub-scanned due to a partial decrease in the toner density on the surface of the developer layer 337 on the developing sleeve 335 from the average value. When the direction changes from the halftone portion 1 to the background portion 2, the density of the rear end portion 1 </ b> B in contact with the background portion 2 of the halftone portion 1 decreases. In this specification, this decrease in density is referred to as TED (Trail Edge Deletion).
[0014]
This TED can be reduced to some extent by bringing the linear velocity of the developing sleeve 335 closer to that of the photosensitive drum 310. However, even if the linear velocity of the developing sleeve 335 is equal to that of the photosensitive drum 310, it is difficult to completely eliminate the TED, and it is difficult to develop a sufficient amount of toner.
[0015]
Japanese Patent Application Laid-Open No. 5-281790 and Japanese Patent Application Laid-Open No. 6-87234 describe development means for developing a high-precision laser light scanner that writes an electrostatic latent image on a photosensitive member with laser light and developing the electrostatic latent image. The idea of adjusting the parameters to increase the contrast of the developing electric field and prevent the above-described decrease in density like TED has been shown.
[0016]
[Problems to be solved by the invention]
However, the method of increasing the contrast of the developing electric field by improving the accuracy of the laser scanner serving as the electrostatic latent image writing means leads to an increase in the size and cost of the image output unit. In addition, when the number of screen lines is increased in the image output unit in order to increase the resolution of the output image, the contrast of the developing electric field is reduced and the density reduction like TED is more likely to occur. It is difficult to achieve both high resolution and high resolution.
[0017]
In recent years, with the spread of computer printers and network printers, there is a tendency to increase the chances of printing graphic images created on a host computer such as a personal computer. In such a graphic image, compared to a natural image such as a photograph, a decrease in density like TED is easily noticeable. Therefore, in an image forming apparatus such as a computer printer or a network printer, a decrease in density such as TED becomes more problematic than an image forming apparatus such as a copying machine.
[0018]
As a method for correcting linear and symmetric output characteristics of an image output unit such as MTF characteristics, a method of correcting input image data by digital filter processing is widely used. However, in the digital filter processing, as described above, it is impossible to reduce or prevent density reduction such as TED based on the nonlinear and asymmetric output characteristics of the image output unit.
[0019]
In view of this, the present invention provides a halftone portion when the output image changes from the halftone portion to the background portion in the sub-scanning direction without increasing the size and cost of the image forming apparatus or the image output device. It is intended to prevent a decrease in density at the rear end portion in contact with the background portion.
[0020]
[Means for Solving the Problems]
The image forming apparatus of the present invention
In an electrophotographic image forming apparatus including a two-component magnetic brush developing device of a rotating developing sleeve type that holds a developer layer on the surface ,
Image acquisition means for acquiring input image data for a large number of pixels, having position information and pixel value information on a recording medium for each pixel;
Edge extraction means for extracting edge pixels in which the pixel value of the input image data changes from the intermediate pixel value to the background pixel value in the sub-scanning direction on the recording medium;
Correction means position information that the extracted edge pixels have, and on the basis of the difference between the intermediate pixel value and the background pixel value, corrects the pixel value of pixels having the intermediate pixel values of the input image data,
It is characterized by providing .
[0021]
The image processing apparatus of the present invention
Image information for forming an image on a page-by-page basis to obtain output image data to be supplied to an electrophotographic image output device having a two-component magnetic brush developer of the rotary developing sleeve type that holds a developer layer on the surface In an image processing apparatus for processing
Image acquisition means for acquiring input image data for a large number of pixels, having position information and pixel value information on a page for each pixel;
Edge extraction means for extracting edge pixels whose pixel values of the input image data change from intermediate pixel values to background pixel values in the sub-scanning direction on the page;
Correction means position information that the extracted edge pixels have, and on the basis of the difference between the intermediate pixel value and the background pixel value, corrects the pixel value of pixels having the intermediate pixel values of the input image data,
It is characterized by providing .
[0022]
[Action]
In the image forming apparatus or the image processing apparatus of the present invention configured as described above, input image data having position information and pixel value information on the recording medium or on the page for each pixel in the image acquisition means of the apparatus Or image information is input to the image acquisition means of the apparatus, and the image information is input image data having position information and pixel value information on the recording medium or page for each pixel in the image acquisition means Expanded to
[0023]
The edge extraction unit of the apparatus detects an edge pixel in which the pixel value of the input image data acquired by the image acquisition unit changes from the intermediate pixel value to the background pixel value in the sub-scanning direction on the recording medium or on the page. is, in the correction unit of the apparatus, based on the difference between the position information thereof detected edge pixels have, and said intermediate pixel value and the background pixel value, the pixel value of pixels having the intermediate pixel values of the input image data Is corrected.
[0024]
Therefore, when the output image changes from the halftone portion to the background portion in the sub-scanning direction, the pixel value of the pixel is not corrected on the recording medium at the rear end portion in contact with the background portion of the halftone portion. The pixel value of the pixel is corrected so as to prevent a decrease in density that occurs when it is output to the recording medium, and the corrected pixel value is recorded on the recording medium in the image output unit in the apparatus or the image output apparatus outside the apparatus. Will be output. Accordingly, a decrease in density at the rear end portion that contacts the background portion of the halftone portion is prevented.
[0025]
BEST MODE FOR CARRYING OUT THE INVENTION
[Example 1 ... FIGS. 1 to 5, FIG. 10]
FIG. 1 shows an overall configuration of a digital color copying machine as an example of an image forming apparatus of the present invention, which is mounted with an example of an image processing apparatus of the present invention. The image forming apparatus of this example, that is, a copying machine, includes an image input unit 100, an image processing unit 200, and an image output unit 300. In the image input unit 100, an image on a document is read by a scanner including a CCD sensor or the like at a resolution of, for example, 16 pixels / mm (400 pixels / inch), and R (red), G (green), B ( An input image signal composed of 8-bit, 256-gradation digital data is obtained for each color of (blue).
[0026]
The image processing unit 200 is an example of an image processing apparatus according to the present invention. In the image processing unit 200, Y (yellow), M, which are recording colors in the image output unit 300, from an input image signal from the image input unit 100. (Magenta), C (cyan), and K (black), an 8-bit, 256-gradation digital data image recording signal is formed for each color, and the pixel value of the image recording signal is corrected as will be described later. Is done.
[0027]
That is, FIG. 2 shows an example of the image processing unit 200, and RGB three-color signals Ri, Gi, Bi from the image input unit 100 are transmitted by the transmission neutral density conversion means 210 to signals of transmission neutral density Re, Ge, The converted neutral density signals Re, Ge, and Be are converted by the color correction means 220 into YMC three-color signals Ye, Me, and Ce, which are transmitted neutral density signals. The Ye, Me, and Ce are converted into YMC three-color signals Yei, Mei, and Cei and the black signal Kei from which the undercolor has been removed by the black plate generation undercolor removing unit 230, and the signals Yei, Mei, Cei, and Kei are The gradation is corrected by the gradation correcting means 240 and converted into an image signal composed of YMCK four-color signals Yi, Mi, Ci, and Ki.
[0028]
The signals Yi, Mi, Ci, and Ki are supplied as input image data to the data correction unit 250, and the pixel values are corrected as will be described later. In this example, a color signal Sc from an external device such as a computer is taken into the image processing unit 200 through the external device interface 260 and supplied to the data correction unit 250, which is the same as the signals Yi, Mi, Ci, and Ki. The pixel value is corrected.
[0029]
Then, YMCK four-color signals Yo, Mo, Co, and Ko whose pixel values are corrected from the data correction unit 250 are supplied to the image output unit 300 as output image data from the image processing unit 200.
[0030]
As the transmission neutral density conversion unit 210 and the gradation correction unit 240, for example, a one-dimensional lookup table is used. As the color correction unit 220, a commonly used linear masking method based on a 3 × 3 matrix operation can be used, but a non-linear masking method such as 3 × 6 or 3 × 9 may be used. Further, as the black plate generation and under color removal means 230, a skeleton UCR method that is usually used can be used. However, any other known method may be used.
[0031]
The image output unit 300 is based on an electrophotographic system and a two-component magnetic brush developing system. As shown in FIGS. 1 and 2, the image output unit 300 includes a screen generator 390, and the output image data from the image processing unit 200 has a pulse width modulated according to the pixel value by the screen generator 390. It is converted into a binary signal, that is, a screen signal.
[0032]
As shown in FIG. 1, in the image output unit 300, the laser diode 381 of the laser light scanner 380 is driven by the screen signal from the screen generator 390, and the laser light L from the laser diode 381, that is, from the laser light scanner 380. Is obtained, and the laser beam L is irradiated onto the photosensitive drum 310.
[0033]
The photosensitive drum 310 is charged by the electrostatic latent image forming charger 320, and an electrostatic latent image is formed on the photosensitive drum 310 by being irradiated with the laser light L from the laser light scanner 380. .
[0034]
The KYMC four-color developing units 331, 332, 333, and 334 of the rotary developing unit 330 are brought into contact with the photosensitive drum 310 on which the electrostatic latent image is formed, so that each color formed on the photosensitive drum 310 is obtained. The electrostatic latent image is developed into a toner image.
[0035]
Then, the sheet on the sheet tray 301 is fed onto the transfer drum 340 by the sheet feeding unit 302 and wound, and a corona discharge is applied from the back surface of the sheet by the transfer charger 341, whereby the photosensitive drum. The developed toner image on 310 is transferred onto the paper. When the output image is a multicolor image, the sheet is repeatedly brought into contact with the photosensitive drum 310 two to four times, whereby a plurality of color images in the four colors of KYMC are transferred.
[0036]
The sheet after the transfer is sent to the fixing device 370, and the toner image is fixed on the sheet by being melted by heating. After the toner image is transferred onto the sheet, the photosensitive drum 310 is cleaned by the cleaner 350 and is prepared for reuse by the pre-exposure device 360.
[0037]
Specifically, in this example, a laser beam scanner 380 having a beam diameter in the main scanning direction and a beam diameter in the sub scanning direction of 64 μm is used. Further, as the developer, a mixture of an insulating toner having an average particle size of 7 μm and magnetic particles (ferrite carrier) having an average particle size of 50 μm was used, and the toner concentration was set to 7%.
[0038]
As the magenta toner, 100 parts by weight of a polyester main binder, C.I. I. Pigment Red 57: 1 Pigment, 4 parts by weight, 4 parts by weight of a charge control agent, and an external additive were used. As the cyan toner, 100 parts by weight of a polyester main binder, C.I. I. Pigment Blue 15: 3 pigment, 4 parts by weight, a charge control agent 4 parts by weight, and an external additive were used. As the yellow toner, 100 parts by weight of a polyester main binder, C.I. I. Pigment Yellow 17 pigment, 4 parts by weight, a charge control agent 4 parts by weight and an external additive were used. As the black toner, 100 parts by weight of a polyester-based main binder and 4 parts by weight of carbon black, 4 parts by weight of a charge control agent, and an external additive were used.
[0039]
In the image forming apparatus of the above example, that is, a copying machine, when the data correction unit 250 of the image processing unit 200 does not correct pixel values, which will be described later, the screen line number of the screen generator 390 is set to 400 lines / inch. When the image changing from the halftone portion to the background portion is output in the sub-scanning direction, the density of the rear end 1B in contact with the background portion 2 of the halftone portion 1 as shown by the broken line in FIG. Decreased. In addition, it was recognized that this density reduction becomes more remarkable when the number of screen lines in the screen generator 390 is increased.
[0040]
When the laser beam scanner 380 was made to have a beam diameter of 20 μm in the main scanning direction of the laser beam L, the density reduction at the rear end 1B was reduced. However, the laser light scanner 380 is increased in size and cost. Further, when the number of screen lines is increased, even if the beam diameter of the laser beam L in the main scanning direction is reduced, the reduction in the density of the rear end 1B cannot be reduced to a level that cannot be perceived.
[0041]
However, in this example, the data correction unit 250 of the image processing unit 200 corrects the pixel value of the input image data from the gradation correction unit 240. FIG. 3 shows a specific example of the data correction unit 250. The data correction unit 250 includes an edge extraction unit 251, a characteristic description unit 252, and a pixel value correction unit 253.
[0042]
The edge extraction means 251 changes the output image from the halftone portion 1 to the background portion 2 in the sub-scanning direction from the input image data Si from the gradation correction means 240 as shown in FIG. The rear edge 1b in contact with the background portion 2 of the halftone portion 1 is extracted.
[0043]
Specifically, the edge extraction unit 251 stores the pixel values of pixels that are continuous in the sub-scanning direction in the memory, and when the pixel value exceeds a predetermined threshold value, the pixel at that point is used as the pixel of the halftone unit 1. Thereafter, the number of pixels in the sub-scanning direction that continue to be counted is counted, and the length (number of pixels) D in the sub-scanning direction of the halftone portion 1 is detected. When the value is equal to or smaller than the predetermined threshold value, the previous pixel is determined as the rear edge 1b in contact with the background portion 2 of the halftone portion 1, and the length of the halftone portion 1 in the sub-scanning direction (hereinafter, referred to as the halftone portion 1) This is called the edge length).
[0044]
Then, the edge extraction unit 251 supplies the pixel value C of the pixel determined to be the rear edge 1b to the characteristic description unit 252 and supplies the determined edge length D to the pixel value correction unit 253.
[0045]
In an electrophotographic image forming apparatus, it is generally difficult to reproduce a pixel having a halftone dot area ratio of 5% or less by an image output unit. Therefore, the threshold value in the edge extraction unit 251 is set to 5%. By setting the threshold value to 5%, all the rear edges 1b in contact with the background portion 2 of the halftone portion 1 reproduced by the image output portion 300 are detected.
[0046]
Accordingly, the halftone portion 1 here has a pixel value of 5 to 100% in the gradation step, and the background portion 2 has a pixel value of 0 to 5% in the gradation step.
[0047]
As long as the edge extraction unit 251 can detect the rear edge 1b, the edge extraction unit 251 may be one that obtains a first derivative value of an image such as a gradient by digital filter processing or another method such as pattern matching. Good.
[0048]
The characteristic description means 252 is configured by a look-up table (hereinafter referred to as LUT), and the intermediate portion when the output image changes in advance from the halftone portion 1 to the background portion 2 in the sub-scanning direction. The characteristics of the density reduction that occurs at the rear end 1B of the tone part 1 that contacts the background part 2 are described.
[0049]
As is clear from the reason why TED is generated in FIG. 11, the range of the rear end 1B where the density reduction of the halftone portion 1 occurs and the density reduction amount at the rear end 1B are as follows. It depends on the potential of the latent image portion 3 of the halftone portion 1 and the pixel value of the halftone portion 1, that is, the pixel value C of the rear edge 1 b in contact with the background portion 2 of the halftone portion 1.
[0050]
Therefore, the characteristic description means 252 is provided with a set of LUTs, and as shown in FIG. 4A, the number of correction target pixels (correction range) a for the pixel value C of the rear edge 1b is included in one LUT. In the other LUT, the correction value (halftone dot area ratio) b of the pixel value of the rear edge 1b with respect to the pixel value C of the rear edge 1b is stored in the other LUT, as shown in FIG. Is stored. The correction target pixel number a corresponds to the range of the rear end 1B in which the density reduction of the halftone portion 1 occurs, and the pixel value correction amount b corresponds to the density reduction amount at the rear edge 1b.
[0051]
The pixel value correction amount b is determined based on a partial decrease from the average value of the toner density in the developer layer of the developing sleeve of the rotary developing device 330 shown in FIG. Specifically, for each partial developer layer determined for each predetermined rotation angle in the rotation direction of the developing sleeve, it is determined based on a decrease from the average value of the toner density.
[0052]
Then, the pixel value C of the rear edge 1b supplied from the edge extraction unit 251 to the characteristic description unit 252 is supplied as an address to the set of LUTs of the characteristic description unit 252, and the rear end from the set of LUTs. The correction target pixel number a and the pixel value correction amount b corresponding to the pixel value C of the edge 1b are read, and the read correction target pixel number a and the pixel value correction amount b are supplied to the pixel value correction unit 253. Is done.
[0053]
The pixel value correction unit 253 receives the input image data from the gradation correction unit 240 when the edge length D supplied from the edge extraction unit 251 is larger than the correction target pixel number a supplied from the characteristic description unit 252. It is determined that the pixel value of Si is corrected. This is because when the edge length D, that is, the length of the halftone portion 1 in the sub-scanning direction is small, the density reduction of the halftone portion 1 does not occur. Further, the amount of density reduction at the rear end 1B of the halftone part 1 tends to change substantially linearly from the pixel at which density reduction starts to the pixel at the rear edge 1b.
[0054]
Therefore, when the pixel value correcting unit 253 determines to correct the pixel value of the input image data Si, as shown in FIG. 5, the pixel position in the sub scanning direction is set to x, and the pixel position in the sub scanning direction of the rear edge 1b is set. When xo, the linear expression
y = (b / a) × {x− (xo−a)}
= (B / a) × ( x-xo + a) (1)
Is calculated, and the calculated correction amount y is added to the original pixel value of the correction target pixel in the range of xo−a ≦ x ≦ xo.
[0055]
Therefore, when the pixel value of the input image data Si from the gradation correction unit 240 is a value as shown by the solid line in FIG. 5, the pixel value of the output image data So from the data correction unit 250 is xo−a ≦ In the range of x ≦ xo, the value is as shown by the broken line in FIG.
[0056]
Then, the output image data So with the pixel values corrected in this way is supplied to the image output unit 300 as an image recording signal from the image processing unit 200, and is output from the image output unit 300, whereby FIG. As shown by the solid line in B), the density drop at the rear end 1B of the halftone portion 1 that contacts the background portion 2 when the output image changes from the halftone portion 1 to the background portion 2 in the sub-scanning direction. Is prevented.
[0057]
FIG. 10B shows a density measurement result when a patch having an input halftone dot area ratio of 40% is output in black with a screen line number of 400 lines / inch. That is, the pixel value is not corrected by the data correction unit 250, and the solid line is the case according to the present invention, that is, the pixel value is corrected by the data correction unit 250 as described above.
[0058]
The above example is a case where the correction amount y is calculated by the linear expression expressed by the equation (1), but the correction amount y is set according to the density reduction characteristic at the rear end 1B of the halftone portion 1. You may make it calculate with another function type | formula.
[0059]
The above example is a case where the characteristic description unit 252 describes the common correction target pixel number a and pixel value correction amount b for each color of YMCK, but the correction target pixel number a and pixel value correction amount for each color. An LUT storing b may be prepared. In addition, the number of correction target pixels a and the pixel value correction amount b may be described for each number of screen lines in the image output unit 300.
[0060]
Further, when the relationship between the pixel number C and the pixel value correction amount b with respect to the pixel value C of the rear edge 1b as shown in FIG. The coefficient of the function formula may be held in the characteristic description unit 252 and the correction target pixel number a and the pixel value correction amount b may be calculated using the coefficient.
[0061]
According to this example, in an image processing apparatus that processes input image data, or in an image forming apparatus that includes such an image processing apparatus as an image processing unit, the image output device or the image output unit is increased in size and cost. Without coming, it is possible to prevent a decrease in density at the rear end portion in contact with the background portion of the halftone portion when the output image changes from the halftone portion to the background portion in the sub-scanning direction. Further, even when the number of screen lines is increased in order to increase the resolution of the output image, the above-described decrease in density can be prevented, so that the resolution of the output image can be easily increased.
[0063]
[Example 2 ... FIGS. 6 to 9 and FIG. 10]
FIG. 6 shows an overall configuration of a network printer system using an example of the image processing apparatus of the present invention and using an example of the image forming apparatus of the present invention. In this network printer system, a client device 500, a printing device 600, and another device 900 are connected to a network 400.
[0064]
The network 400 is, for example, Ethernet (trademark of Xerox, USA), and a plurality of protocols operate according to applications of the client device 500, the printing device 600, and other devices 900.
[0065]
The client device 500 includes a plurality of client devices 501, 502..., And each client device 501, 502... Includes a computer, a workstation, or the like. Print information described in a description language (hereinafter referred to as PDL) is sent out.
[0066]
This network printer system corresponds to an OPI (Open PrePress Interface: trademark of Aldus, USA) system, and print information described in PDL from the client device 500, that is, PDL commands / data includes OPI corresponding to the OPI system. Commands may be included.
[0067]
In the OPI system, a client device and a plurality of printing devices are connected via a network, and at least one of the plurality of printing devices holds high-resolution image data in a storage device, and the client device stores the high-resolution image described above. A printing device that performs editing processing using low-resolution information corresponding to data and holds high-resolution image data is a system that outputs high-resolution image data based on the print information of the page layout program from the client device. The page layout processing of image data can be performed without increasing the load on the client apparatus and without increasing the load on the client device.
[0068]
The printing apparatus 600 is an example of the image forming apparatus of the present invention. In this example, the printing apparatus 600 corresponds to the above OPI system. The printing apparatus 600 includes an image processing unit 700 and an image output unit 800. The image processing unit 700 is an example of the image processing apparatus according to the present invention. Similar to the image output unit 300 of the first embodiment, the image output unit 800 is of an electrophotographic type and of a two-component magnetic brush developing method. The image processing unit 700 and the image output unit 800 may be physically separate devices, or the image processing unit 700 may be physically incorporated into the image output unit 800 and physically formed as one device. Good.
[0069]
The other apparatus 900 is a printing apparatus other than the printing apparatus 600, a server apparatus such as a print server, a disk server, or a mail server. Each of these printing devices and server devices also includes a plurality of devices.
[0070]
The image processing unit 700 of the printing apparatus 600 includes a communication control unit 710, a main control unit 720, a magnetic disk device unit 730, a buffer memory 740, and an output unit control unit 750.
[0071]
The communication control unit 710 connects the image processing unit 700 to the client device 500 and another device 900 via the network 400, and performs communication using, for example, CSMA / CD (Carrier Sense Multiple Access / Collision Detect) used as an Ethernet control method. To control.
[0072]
Information input to the image processing unit 700 from the client device 500 or another device 900 by the communication control unit 710 is passed from the communication control unit 710 to the main control unit 720, and the main control unit 720 analyzes the communication protocol and performs PDL. The image data output by the image output unit 800 is expanded and the pixel value of the image data is corrected, and the corrected image data is written in the buffer memory 740 as will be described later. It is.
[0073]
The magnetic disk device unit 730 includes an operation system, a device driver, and an image control unit that control the entire image processing unit 700 including the communication control unit 710, the main control unit 720, the buffer memory 740, and the output unit control unit 750, and the image output unit 800. Application software is installed, and these operation systems are loaded and executed from the magnetic disk unit 730 to the main storage unit not shown in the drawing as needed.
[0074]
The high-resolution image data corresponding to the OPI system is stored in the magnetic disk device unit 730, and the high-resolution image data is transferred from the magnetic disk device unit 730 to the main control unit 720 as needed by the OPI command. Read out. The magnetic disk device unit 730 is used as a temporary data saving place when the capacity of the main storage device or the buffer memory 740 is insufficient.
[0075]
As described above, the output image data obtained by the main control unit 720 is temporarily stored in the buffer memory 740. The output unit control unit 750 controls the buffer memory 740 while communicating with the image output unit 800, whereby the output image data is read from the buffer memory 740 and sent to the image output unit 800. An output image is obtained at.
[0076]
As shown in FIG. 7, the main control unit 720 includes a communication protocol analysis control unit 721, a PDL command / data analysis unit 722, an image development unit 770, a character development unit 724, a color determination unit 725, an information combination unit 726, and a correction drawing. A communication protocol analysis control unit 721 is connected to the communication control unit 710, and a correction drawing unit 790 is connected to the buffer memory 740. In FIG. 7, the magnetic disk device unit 730 shown in FIG. 6 is omitted.
[0077]
Information input from the client device 500 or another device 900 to the communication control unit 710 as described above is input from the communication control unit 710 to the communication protocol analysis control unit 721. The information input to the communication protocol analysis control unit 721 includes print information described in PDL in which read image information and code information are mixed, that is, PDL command / data. The PDL command / data may include an OPI command.
[0078]
The communication protocol analysis control unit 721 analyzes the protocol of the input information, and transfers the PDL command / data of the input information to the PDL command / data analysis unit 722. The communication protocol analysis control unit 721 corresponds to the above-described plurality of protocols, and supports, for example, TCP / IP, AppleTalk (trademark of Apple Inc.), and IPX / SPX.
[0079]
When sending information from the image processing unit 700 to the client device 500 or another device 900, the communication protocol analysis control unit 721 controls the communication protocol according to the client device 500 or other device 900, The information is output to the communication control unit 710.
[0080]
The PDL command / data input to the PDL command / data analysis unit 722 via the communication control unit 710 and the communication protocol analysis control unit 721 is analyzed by the PDL command / data analysis unit 722. The PDL command / data analysis unit 722 analyzes a plurality of PDLs including Postscript (PostScript: trademark of Adobe Systems Inc., USA) and Interpress (InterPress: trademark of Xerox Corporation, USA) and converts them into intermediate code data.
[0081]
Information on the resolution of the image output unit 800 obtained by the PDL command / data analysis unit 722 and image shape information such as an outline, a position, and a rotation angle are passed from the PDL command / data analysis unit 722 to the image development unit 770. The image development unit 770 develops the image data output from the image output unit 800 based on these pieces of information.
[0082]
In this case, when the code data from the PDL command / data analysis unit 722 includes character information, the image development unit 770 takes out outline information from the character development unit 724 and develops image data for the character. The image development unit 770 performs processing such as data compression / expansion, image enlargement / reduction, rotation / mirroring, resolution conversion, and the like based on the code data from the PDL command / data analysis unit 722.
[0083]
The color determination unit 725 converts the image data developed by the image development unit 770 into image data for each color of YMCK based on the color information of the PDL command / data analyzed by the PDL command / data analysis unit 722. A parameter is generated, and the parameter is sent to the information combining unit 726. In the information combination unit 726, the image data developed by the image development unit 770 is converted into image data for each color of YMCK according to the parameters from the color determination unit 725.
[0084]
The image data for each color of YMCK from the information combining unit 726 is supplied to the correction drawing unit 790 as input image data, and the correction drawing unit 790 corrects the pixel value of the input image data as described later. The corrected image data for each color of YMCK is written in the buffer memory 740 as output image data. Image data is read from the buffer memory 740 for each color of YMCK, and the read image data is supplied to the image output unit 800.
[0085]
As shown in FIG. 8, the image output unit 800 includes an image signal control unit 810, a laser drive unit 820, and an image exposure unit 830. The image data read from the buffer memory 740 of the image processing unit 700 is an image signal. The laser modulation signal is converted into a laser modulation signal by the control unit 810, the laser modulation signal is supplied to the laser driving unit 820, and the laser diode 831 of the image exposure unit 830 is driven by the laser driving unit 820.
[0086]
Although omitted in FIG. 8, in the image output unit 800, the laser light from the laser diode 831 thus modulated by the laser modulation signal from the image signal control unit 810 scans the photosensitive drum. As a result, an electrostatic latent image is formed on the photosensitive drum, the electrostatic latent image is developed into a toner image by the developing device, and the toner image is transferred onto the paper by the transfer device. Is output.
[0087]
FIG. 9 shows a specific configuration of main parts such as the image development unit 770 and the correction drawing unit 790 in the main control unit 720. The image expansion unit 770 expands the code data from the PDL command / data analysis unit 722 into image data for each of three image objects of characters, lines / graphics, and a read image, and performs drawing.
[0088]
In other words, the character information is sent to the character expansion unit 724 and font-expanded to generate character bit map data, which is passed to the information combining unit 726. The read image information is subjected to image conversion processing such as resolution conversion in the read image conversion unit 771 and then transferred to the information combining unit 726.
[0089]
The information of the line / figure is subjected to coordinate conversion by the coordinate conversion unit 773 and rendered as an image described in the PDL for each thin line, line / surface drawing, and rectangle. That is, the fine line part is drawn by the fine line drawing part 774 and passed to the information combining part 726, and the line / surface drawing part is drawn by the line / surface drawing part 775 and passed to the information combining part 726. The rectangular part is drawn by the rectangular drawing part 776 and passed to the information combining part 726.
[0090]
The output of the line / surface drawing unit 775 is supplied to the edge detection unit 777. The edge detection unit 777 detects the rear edge in the sub-scanning direction of the line / surface image, and the rectangular drawing unit. The output 776 is supplied to the edge detection unit 778, and the edge detection unit 778 detects the rear edge of the rectangular image in the sub-scanning direction.
[0091]
The information combining unit 726 forms an image of one page by superimposing images for each image object, and performs processing such as color conversion on the basis of information obtained from the color determination unit 725 for each object. .
[0092]
The correction drawing unit 790 includes an edge storage unit 791, a page image unit 792, a characteristic description unit 793, a density decrease determination unit 794, and an edge redrawing unit 795.
[0093]
The edge accumulating unit 791 accumulates the rear edge information from the edge detecting units 777 and 778 of the image developing unit 770 as an edge list. In the page image unit 792, the combined page image is obtained from the information combining unit 726 and transferred to the density reduction determination unit 794 and the edge redrawing unit 795.
[0094]
Similar to the characteristic description unit 252 of the first embodiment, the characteristic description unit 793 sets the pixel value C of the rear edge for the line / surface image and the rectangular image as illustrated in FIGS. The corresponding correction target pixel number a and pixel value correction amount b are described in advance. In addition, a condition in which the density lowering occurs at the rear end in the sub-scanning direction of the line / surface image and the rectangular image is described in advance.
[0095]
In response to a request from the density reduction determination unit 794, the characteristic description unit 793 sends conditions for causing the density reduction to the density reduction determination unit 794, and the pixel value C of the rear edge is supplied from the density reduction determination unit 794. At this time, the correction target pixel number a and the pixel value correction amount b corresponding to the pixel value C are sent to the edge redrawing unit 795.
[0096]
When the page image is transferred from the page image unit 792, the density decrease determination unit 794 is based on the edge list stored in the edge storage unit 791 and the above condition obtained from the characteristic description unit 793 according to its own request. Then, the rear edge of the image that is expected to cause a decrease in density at the rear end in the sub-scanning direction is determined, and the determination result is sent to the edge redrawing unit 795.
[0097]
The edge redrawing unit 795 uses the determination result from the density decrease determination unit 794 and the correction target pixel number a and the correction amount b from the characteristic description unit 793 to display the line / line of the page image transferred from the page image unit 792. The rear end in the sub-scanning direction, which is expected to cause the density reduction of the surface image and the rectangular image, is redrawn, and the redrawn page image is transferred to the buffer memory 740. Similar to the first embodiment, the redrawing is performed by calculating the correction amount y by the linear expression expressed by the equation (1) and adding the calculated correction amount y to the original pixel value.
[0098]
Accordingly, also in this example, a decrease in density at the rear end in the sub-scanning direction of the line / surface image and the rectangular image is prevented.
[0099]
The above example is a case where each function of the correction drawing unit 790 is realized by software, but the correction drawing unit 790 may be configured by hardware having an equivalent function for speeding up.
[0100]
According to this example, in an image processing apparatus that develops image data from PDL or in an image forming apparatus that includes such an image processing apparatus as an image processing unit, the image output device or the image output unit is increased in size and cost. Without lowering the density, it is possible to prevent a decrease in density at the rear end portion of the halftone portion that contacts the background portion when the output image changes from the halftone portion to the background portion in the sub-scanning direction. Further, even when the number of screen lines is increased in order to increase the resolution of the output image, the above-described decrease in density can be prevented, so that the resolution of the output image can be easily increased.
[0101]
In particular, according to this example, there is an advantage that it is possible to surely prevent a decrease in the density of a graphics image such as a graphic image that is generated by the client device and easily causes a decrease in density.
[0103]
【The invention's effect】
According to the present invention, the halftone portion when the output image changes from the halftone portion to the background portion in the sub-scanning direction without increasing the size and cost of the image forming apparatus or the image output device. It is possible to prevent a decrease in density at the rear end portion in contact with the background portion. Further, even when the number of screen lines is increased in order to increase the resolution of the output image, the above-described decrease in density can be prevented, so that the resolution of the output image can be easily increased.
[Brief description of the drawings]
FIG. 1 is a diagram showing an overall configuration of a digital color copying machine as an example of an image forming apparatus according to the present invention.
FIG. 2 is a diagram illustrating an example of an image processing unit of the copier of FIG.
3 is a diagram illustrating an example of a data correction unit of the image processing unit in FIG. 2;
4 is a diagram illustrating an example of contents described in a characteristic description unit of the data correction unit in FIG. 3;
5 is a diagram illustrating an example of a mode in which a pixel value is corrected by a pixel value correcting unit of the data correcting unit in FIG. 3;
FIG. 6 is a diagram showing an overall configuration of a network printer system using an example of an image processing apparatus according to the present invention.
7 is a diagram illustrating an example of an image processing unit of the system of FIG. 6;
FIG. 8 is a diagram illustrating an example of an image output unit of the system of FIG.
9 is a diagram illustrating an example of a main part of a main control unit of the image processing unit in FIG. 7;
FIG. 10 is a diagram showing an aspect of concentration reduction which is a problem in the present invention and how it is prevented in the present invention.
FIG. 11 is a diagram for explaining the reason why the concentration decrease which is a problem in the present invention occurs.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Halftone part 1B Back end part 1b Back edge 2 Background part 200 Image processing part 250 Data correction part 251 Edge extraction means 252 Character description description means 253 Pixel value correction means 700 Image processing part 720 Main control part 722 PDL command / data analysis part 770 Image development unit 790 Correction drawing unit 791 Edge storage unit 792 Page image unit 793 Characteristic description unit 794 Density decrease determination unit 795 Edge redrawing unit

Claims (13)

In an electrophotographic image forming apparatus including a two-component magnetic brush developing device of a rotating developing sleeve type that holds a developer layer on the surface ,
Image acquisition means for acquiring input image data for a large number of pixels, having position information and pixel value information on a recording medium for each pixel;
Edge extraction means for extracting edge pixels in which the pixel value of the input image data changes from the intermediate pixel value to the background pixel value in the sub-scanning direction on the recording medium;
Correction means position information that the extracted edge pixels have, and on the basis of the difference between the intermediate pixel value and the background pixel value, corrects the pixel value of pixels having the intermediate pixel values of the input image data,
An image forming apparatus comprising: The image forming apparatus according to claim 1.
The correction means includes a correction target pixel determining unit that determines a correction target pixel whose pixel value is to be corrected from position information of the edge pixel and a difference between the intermediate pixel value and the background pixel value; and the intermediate pixel An image forming apparatus comprising: a correction amount determination unit that determines a pixel value correction amount for a correction target pixel determined by the correction target pixel determination unit based on a difference between a value and a background pixel value . The image forming apparatus according to claim 1.
The correction unit includes an information storage unit that stores the number of correction target pixels and a pixel value correction amount according to a difference between the intermediate pixel value and the background pixel value, and is based on information stored in the information storage unit. An image forming apparatus that determines a correction target pixel and a pixel value correction amount for each correction target pixel. The image forming apparatus according to claim 1.
2. The image forming apparatus according to claim 1, wherein the intermediate pixel value is 5 to 100% at a gradation level of the pixel value. The image forming apparatus according to claim 1.
The image forming apparatus according to claim 1, wherein the background pixel value is a minimum density value reproducible by the image forming apparatus. The image forming apparatus according to claim 1.
The image forming apparatus according to claim 1, wherein the background pixel value is 0 to 5% in a gradation step of the pixel value. The image forming apparatus according to claim 1.
The image forming apparatus according to claim 1, wherein the pixel value correction amount by the correcting unit is determined based on a partial decrease from an average value of toner density in the developer layer of the rotary developing sleeve. The image forming apparatus according to claim 7.
The pixel value correction amount in the correction unit is determined based on a decrease from the average value of the toner density for each partial developer layer determined for each predetermined rotation angle in the rotation direction of the rotary developing sleeve. An image forming apparatus. Image information for forming an image on a page-by-page basis to obtain output image data to be supplied to an electrophotographic image output device having a two-component magnetic brush developer of the rotary developing sleeve type that holds a developer layer on the surface In an image processing apparatus for processing
Image acquisition means for acquiring input image data for a large number of pixels, having position information and pixel value information on a page for each pixel;
Edge extraction means for extracting edge pixels whose pixel values of the input image data change from intermediate pixel values to background pixel values in the sub-scanning direction on the page;
Correction means position information that the extracted edge pixels have, and on the basis of the difference between the intermediate pixel value and the background pixel value, corrects the pixel value of pixels having the intermediate pixel values of the input image data,
An image processing apparatus comprising: The image processing apparatus according to claim 9.
The correction means includes a correction target pixel determining unit that determines a correction target pixel whose pixel value is to be corrected from position information of the edge pixel and a difference between the intermediate pixel value and the background pixel value; and the intermediate pixel An image processing apparatus comprising: a correction amount determination unit that determines a pixel value correction amount for a correction target pixel determined by the correction target pixel determination unit based on a difference between a value and the background pixel value . The image processing apparatus according to claim 9.
The correction unit includes an information storage unit that stores the number of correction target pixels and a pixel value correction amount according to a difference between the intermediate pixel value and the background pixel value, and is based on information stored in the information storage unit. An image processing apparatus that determines a correction target pixel and a pixel value correction amount for each correction target pixel. The image processing apparatus according to claim 9.
The image processing apparatus according to claim 1, wherein the intermediate pixel value is 5 to 100% at a gradation step of the pixel value. The image processing apparatus according to claim 9.
The image processing apparatus according to claim 1, wherein the background pixel value is 0 to 5% in a gradation step of the pixel value.

Images