CN1163424A - Image forming device - Google Patents

Abstract

An object of the present invention is to reduce the number of line buffers used for processing with a mask size of (n x n) in filter processing of an image processing device. In the image processing part 37, the input image from the scanning part 1 passes through the low-pass filter (LPF) 51 and the range correction part 52 performs range correction, and passes through the high-pass filter connected in parallel with the low-pass filter (LPF) 51. (HPF) 53 multiplies the coefficient of the parameter K with a multiplier 54, adds the above-mentioned corrected result and the multiplied result with an adder 55, and passes through an enlargement/reduction unit 56, a gamma correction unit 57, and an error variance processing unit. After 58, enter the printing part 2.

Description

image forming equipment

The present invention relates to an image forming apparatus such as a digital copying machine which reads a document image, performs image processing on the read image by an image processing device, and forms an image on copy paper.

In recent years, digital copiers, facsimiles, and other image forming apparatuses have spread rapidly. In such a digital office machine, an image processing device for outputting an image input from a scanner with high quality is indispensable. In digital copiers and image input and output devices called facsimiles, degradation of the MTF (Modulation Transfer Function) characteristics of the reading optical system and ghosting due to band limitation due to digital sampling usually occur during input. Distortion, degradation in the imaging system and degradation of various spatial frequencies such as digital moiré will occur during output.

Therefore, in the image processing apparatus, MTF correction must be performed. Such MTF correction is called filtering processing, and is further divided into low-pass filtering (hereinafter referred to as LPF) for suppressing moiré and the like, and high-pass filtering (hereinafter referred to as HPF) for emphasizing character edges and the like.

In the past, from the perspective of the overall flow of image processing, the LPF and HPF are serial, that is, the input image is first processed by LPF, and then the range correction processing and HPF processing for correcting the contrast of the image are performed in order. Process them one by one.

Generally, the filter processing of digital copiers in facsimile and the like is realized by two-dimensional digital filter processing in the main scanning and sub-scanning directions. That is, the filtering process is realized by multiplying a local area composed of a pixel to be processed (pixel of interest) and its surrounding pixels by a coefficient corresponding to each pixel position.

Therefore, when processing is performed with a mask size of (n×n), a line buffer of n lines is required for processing in the sub-scanning direction.

However, when performing filter processing by the conventional method, since serial processing is performed, (3×3) LPF processing and HPF processing are performed, and a line buffer of 2 lines for a total of 4 lines is required for each.

As described above, in the filter processing of the image processing device, when the mask size of (n×n) is used for processing, the processing of the sub-scanning square noise requires a line buffer of n lines, and the filtering is performed by the conventional method. In processing, since serial processing is performed, for example, (3×3) LPF and HPF processing are performed, and a line buffer of 2 lines for a total of 4 lines is required for each.

Therefore, an object of the present invention is to provide an image forming apparatus capable of reducing the number of line buffers used when processing with a mask size of (n×n) in filter processing of an image processing device.

The image forming apparatus of the present invention includes: a reading device for reading a document image; a first filter processing device for filtering image information read by the reading device; connected in parallel with the first filter processing device, The 2nd filter processing device that carries out filter processing to the image information read by above-mentioned reading device; an image processing means for performing various image processing on the result added by the adding means; and an image forming means for forming an image based on the image information processed by the image processing means.

The image forming apparatus of the present invention includes: a reading device for reading a document image; performing low-pass filtering of image information within a prescribed range including a pixel of interest in the image information read by the reading device The first processing device for processing; the correction device for performing image contrast correction on the result processed by the first processing device; in parallel with the first processing device, to carry out the attention included in the image information read by the above-mentioned reading device A second processing device for high-pass filter processing of image information within a specified range of pixels; a multiplication device that multiplies the processing result of the second processing device by a predetermined coefficient; An adding device for adding the results corrected by the correcting device; an image processing device for performing various image processing based on the result added by the adding device; and forming an image based on the image information processed by the image processing device image forming device.

The image forming method of the present invention is characterized in that the original image is read, and low-pass filtering and high-pass filtering of image information within a predetermined range including the pixel of interest in the read image information are performed in parallel. processing to form an image.

The image processing device of the present invention includes: a first processing device that performs filtering processing of image information within a specified range including a pixel of interest in an image to be processed; A second processing device for filtering image information within a predetermined range of the pixel of interest in the image to be processed; and adding the result of processing by the second processing device to the result of processing by the first processing device Addition device.

The image processing device of the present invention includes: a first processing device that performs filtering processing of image information within a predetermined range including a pixel of interest in an image to be processed; A correction device for image contrast correction; a second processing device that performs filtering processing of image information within a specified range including a pixel of interest in an image to be processed in parallel with the first processing device; the second processing device multiplication means for multiplying the result processed by the processing means by a predetermined coefficient; and addition means for adding the result multiplied by the multiplication means and the result corrected by the correction means.

The image processing device of the present invention includes: a first line buffer for temporarily storing input image information; a second line buffer for temporarily storing image information output from the first line buffer; The image information output from the buffer, the image information output from the first line buffer, and the input image information are filtered for image information within a predetermined range including the pixel of interest in the image to be processed. The low-pass filter of processing; The range correction device that the processing result of this low-pass filter is carried out the contrast correction of image; Parallel connection with above-mentioned low-pass filter, according to the image information output from above-mentioned 2nd line buffer and from A high-pass filter for filtering image information within a predetermined range including a pixel of interest in the image to be processed on the image information output from the first line buffer and the input image information; multiplication means for multiplying the result of the filter processing by a predetermined parameter K; and addition means for adding the result multiplied by the multiplication means and the result corrected by the range correction means.

The image processing device of the present invention includes: a first line buffer for temporarily storing input image information; a second line buffer for temporarily storing image information output from the first line buffer; The image information output from the buffer, the image information output from the first line buffer, and the input image information are filtered for image information within a predetermined range including the pixel of interest in the image to be processed. The low-pass filter of processing; The range correction device that the processing result of this low-pass filter is carried out the contrast correction of image; Parallel connection with above-mentioned low-pass filter, according to the image information output from above-mentioned 2nd line buffer and from A high-pass filter for filtering image information within a predetermined range including a pixel of interest in the image to be processed on the image information output from the first line buffer and the input image information; Multiplication means for multiplying the result of filter processing by a predetermined parameter K; addition means for adding the result multiplied by the multiplication means and the result corrected by the above-mentioned range correction means; and amplifying or Image processing device for image processing such as reduction, gamma correction, error variance, etc.

The image processing method of the present invention is characterized in that low-pass filter processing and high-pass filter processing are performed in parallel on image information within a predetermined range including a pixel of interest among read image information.

FIG. 1 is a block diagram showing the structure of an image processing unit in a digital copying machine according to the present invention.

Fig. 2 is a schematic sectional view of a digital copying machine of the image processing apparatus of the present invention.

FIG. 3 is a schematic configuration diagram of a control system of the digital copying machine shown in FIG. 2 .

Fig. 4 is a circuit diagram of an image processing unit in Fig. 1 .

Fig. 5 is a diagram showing pixel values in pixels of a partial area (3 x 3) in image data.

FIG. 6 is a diagram showing coefficients of a low-pass filter.

FIG. 7 is a diagram showing coefficients of a high-pass filter.

Fig. 8 is a circuit diagram of a conventional image processing unit.

Fig. 9 is a graph showing image evaluation results when the value of the parameter K is changed.

Fig. 10 is a diagram showing coefficients of LPF and HPF.

An embodiment of the present invention will be described below with reference to the drawings.

2 is a cross-sectional view of an example of the internal structure of a digital copying machine as an image processing apparatus according to an embodiment of the present invention.

That is, the digital copying machine has a scanner unit 1 for optically reading image data of an original O, and a printer unit 2 for outputting the image read by the scanner unit 1 onto copy paper P which is a recording material.

In the scanner section 1, an original document to be copied is placed on the original document table 3, and the original document O placed on the original document table 3 is illuminated by a fluorescent lamp 4 as a light source extending in the sub-scanning direction. The reflected light of the illuminated original O is photoelectrically converted by the CCD sensor 5 as a photoelectric conversion element, and image data in the reflected light is converted into an image signal.

On the side of the above-mentioned fluorescent lamp 4, a reflector 6 for effectively focusing the illumination light from the fluorescent lamp 4 on the above-mentioned original O is arranged, and between the above-mentioned fluorescent lamp 4 and the above-mentioned CCD sensor 5, a mirror 6 is arranged to change the direction from the above-mentioned original O A plurality of mirrors 7, 8, 9 for the optical path through which light from the CCD sensor 5, that is, reflected light from the original O passes, and a lens 10 for focusing the reflected light on the light collecting surface of the CCD sensor 5, etc.

The optical system for guiding the reflected light from the exposure lamp 4 and the original O to the CCD sensor 5 is provided on the carriages 11 and 12, and is moved in the main scanning direction by a pulse motor not shown in the figure. The area of the original O in the sub-scanning direction is illuminated with the fluorescent lamp 4, and the area in the sub-scanning direction of the original O is sequentially illuminated by moving the carriages 11, 12 in the main scanning direction, so that the entire area of the original O is illuminated by the fluorescent lamp 4. .

A document cover 13 for bringing the original O into close contact with the document platform 3 is arranged on the upper part of the document platform 3 . The platen of the document O can be replaced with, for example, an SDF (semi-automatic document feeder) or an ADF (automatic document feeder) according to the size or copying capacity of the digital copier.

On the image forming section as the printing section 2, there is provided a cylindrical photosensitive drum 14 which is charged in a desired electric potential while being rotated in a desired direction by a motor not shown in the figure. After the laser beam irradiates the photosensitive drum 14 , the potential of the area irradiated by the laser beam changes, and an electrostatic latent image is formed on the photosensitive drum 14 .

Around the photosensitive drum 14 is arranged a charging device 15 that charges the photosensitive drum 14 with a desired potential; a laser device 16 that outputs a laser beam modulated according to image data to the photosensitive drum 14; agent, the developing device 17 that develops the electrostatic latent image formed on the photosensitive drum 14 by the laser beam from the laser device 16; the visualized toner on the photosensitive drum 14 developed by the developing device 17 For example, a copying device 18 for copying on copy paper P, which is a recording material supplied from a recording material supply section described later;

The above-mentioned laser device 16 is composed of the following components: a semiconductor laser oscillator 24 that generates a laser beam; and a multi-faceted laser beam that is supplied from the semiconductor laser oscillator 24 through a collimator lens not shown in the figure into beams of each row. reflective mirror 25; fθ lens 26 that changes the laser beam of each row from the polygonal reflective mirror 25 into parallel light; a thin reflective mirror 27 that reflects the parallel light from the lens 26 onto the above-mentioned photosensitive drum 14; and makes the above-mentioned A mirror motor 28 rotates the polygon mirror 25 .

On the downstream side of the peeling device 19 along the rotation direction of the photosensitive drum 14, a cleaning device 20 is arranged for removing the remaining toner on the surface of the photosensitive drum 14, and simultaneously to form the next image by the laser beam. The change in potential generated on the photosensitive drum 14 is eliminated.

Between the developing unit 17 and the copying unit 18 is arranged a recording material feeding unit 21 for feeding copy paper P for copying the toner image formed on the photosensitive drum 14 to the copying unit 18 .

In the direction in which the copy paper P on which the toner image has been copied by the copy unit 18 is separated from the photosensitive drum 14, a fixing device 22 for fixing the toner image on the copy paper is provided. Between the fixing device 22 and the copying device 18 is disposed a transport device 23 for feeding the copy paper P to the fixing device 22 .

FIG. 3 is a block diagram of an example of a control system of the copier in FIG. 2 .

In FIG. 3 , a main control unit 31 that generally controls the digital copying machine is connected to a calculation unit 44 that performs various calculations, and four sub-control units 32 to 34 that perform various controls.

The main control unit 31 is also connected to an operation panel 35 for performing various image processing instructions, an area management unit 36 for managing the image processing area, and for improving the image quality of the imported image data and storing the image data. The image processing section 37, which is an image processing means, is used for editing, processing of image data, etc., and controls them.

The sub-control unit 32 is connected with the light source control unit 40 for controlling the light intensity of the fluorescent lamp 4, the mechanism drive unit 42 for driving the mechanical input unit mechanism 41 such as the paper feeding mechanism shown in FIG. The A/D converter 43 converts the analog image data converted by the CCD sensor 5 into digital data signals and controls them.

The sub-control part 33 is connected with the image expansion part 45 which expands and stores the image data after editing or processing in order to form an image. ) The image output unit 46 that outputs a pulse signal (image data for the printer unit 2) as a laser modulation signal, and the mechanism drive of the output unit mechanism 48 that drives a drive system such as a motor and a solenoid in the laser device 16 Section 49, and control them.

The sub-control unit 34 is connected to the data transmission and reception unit 50, and controls data transmission and reception with external devices.

In the above-mentioned digital copying machine, the original O is illuminated by the fluorescent lamp 4, and the light reflected from the original O is imaged on the CCD sensor 5 and converted into an analog electric signal. The analog image signal is converted into a digital signal by the A/D conversion unit 43 and output to the image processing unit 37 .

In the image processing section 37, filtering processing of image data from the scanning section 1, enlarging/reducing processing in the main scanning direction, gradation processing, and the like are performed.

FIG. 1 shows the internal structure of an image processing unit 37 as an image processing device.

The image processing section 37 consists of a low-pass filter (hereinafter referred to as LPF) 51 that suppresses the moiré of the image data read by the scanning section 1; a range correction section 52 that corrects the deviation of the CCD sensor 5; and is connected in parallel with the LPF 51 Connect, highlight the high-pass filter (hereinafter referred to as HPF) 53 of the edge of the image character etc. read with scanning section 1; Multiplier 54 from the image data of HPF53 is multiplied by the parameter K described later; The adder 55 that adds the image data from the range correction section 52 to the image data from the multiplier 54; the enlargement/reduction section 56 that enlarges or reduces the image data from the adder 55; A gamma correction unit 57 for various gamma corrections; and an error variance processing unit 58 for performing error variance processing on the image data from the gamma correction unit 57 are constituted.

FIG. 4 is an example of a circuit for performing processing of LPF 51 and HPF 52 having a mask size of (3×3) constituting image processing unit 37 shown in FIG. 1 . The data used here are all 8 bits.

That is, two rows of line buffer (LD1) 61 and line buffer (LD2) 62 for taking in image data from scanning unit 1 are provided in image processing unit 37 having a mask size of (3×3). buffer. The range correction unit 52 is connected to a range correction reference correction value calculation unit 60 that calculates a range correction reference correction value based on image data from the scanner unit 1 .

Next, the processing operation of the image processing unit 37 of the present invention will be described using an example of a circuit having a mask size (3×3) as shown in FIG. 4 configured in this way.

First, image data input from the scanner unit 1 is temporarily taken into the line buffers 61 and 62 .

As shown in FIG. 5, the pixel value in the local area (3×3) pixel in the image data synchronously input from the prescribed clock pulses from the line buffers 61, 62 is assumed to be f(i-1, j -1), f(i, j-1), f(i+1, j-1), f(i-1, j), f(i, j), f(i+1, j), f (i-1, j+1), f(i, j+1), f(i+1, j+1), then as the processing result l( i, j) can be represented by the following formula.

I(i,j)=La ^* f(i,j)+Lb ^* [f(i,j-1)+f(i,j+1)]+Lc ^* [f(i-1,j)+ f(i+1, j)]+Ld ^* [f(i-1, j-1)+f(i+1, j-1)+f(i-1, j+1)+f(i+ 1,j+1)]

The coefficients La, Lb, Lc, and Ld in this formula are the coefficients of the (3×3) LPF 51 shown in FIG. 6, and the following conditions must be met in order not to change the local average density before and after the treatment.

La+2 ^* Lb+2 ^* Lc+4 ^* Ld＝1

Next, in order to perform image contrast correction on the result of processing by the LPF 51, the range correction processing is performed by the range correction unit 52, and this value is r(i, j).

The processing of the HPF 53 is performed in parallel with the processing of the LPF 51 and the range correction processing of the range correction unit 52 . The processing of HPF53 is the same as the processing of LPF51, is to pass the value f(i-1, j-1), f(i-1, j-1), f (i, j-1), f(i+1, j-1), f(i-1, j), f(i, j), f(i+1, j), f(i-1, j+1), f(i, j+1), f(i+1, j+1) and coefficients Ha, Hb, Hc, Hd are multiplied.

Specifically, the processing result h(i, j) of the HPF 53 for the pixel f(i, j) to be noted can be represented by the following equation.

h(i,j)=Ha ^* f(i,j)+Hb ^* [f(i,j-1)+f(i,j+1)]+Hc ^* [f(i-1,j)+ f(i+1, j)]+Hd ^* [f(i-1, j-1)+f(i+1, j-1)+f(i-1, j+1)+f(i+ 1,j+1)]

The arrangement of the coefficients Ha, Hb, Hc, and Hd of the HPF53 is shown in FIG. 7 . By multiplying the processing result of HPF53 by the parameter K, the strength of the highlighted edge can be changed. That is, the larger the value of the coefficient, the stronger the degree of edge protrusion, so an optimum value can be set according to the MTF characteristic of the scanning unit 1 and the like.

The results of such parallel calculations are checked by the following equation, and the result f(i, j) is subjected to the enlarging/reducing process shown in FIG. 1 and then printed out.

    f(i,j)=r(i,j)+h(i,j)×K

According to the method explained above, by providing a buffer of 2 lines, the filter processing of the mask size (3×3) pixels can be realized.

By the way, when the processing shown in FIG. 8 is performed according to the conventional method, in order to process the HPF 53 on the range correction result, it is necessary to have two lines of the line buffers 63 and 64 for temporarily inputting the range correction result, and to fetch the result initially by The line buffers 61 and 62 of the image input from the scanning unit 1 are line buffers of 2 lines, a total of 4 lines.

On the other hand, in the present invention, the line buffer can be reduced by two lines by performing the processing of the LPF51 and the HPF53 in parallel.

In the past, after the processing of the LPF51 and the processing of the range correction part 52 are performed on the input image, the processing result of the processing is then processed by the HPF51. Unlike this, since the processing of the HPF53 is performed on the input image in the present invention, Therefore, compared with the past, the degree of protruding edges has been enhanced. As a result, moiré easily occurs, but by setting an optimum parameter K that can change the intensity of processing by the HPF53, the above-mentioned interference can be dealt with.

Fig. 9 shows the image evaluation results when the value of the parameter K is changed. When K=1.3 in the existing method, the reproducibility of small characters and suppress moiré interference are all good, and when K=1.3 in the present invention, obtain very strong prominent edge, until making value drop to K It was confirmed by simulation that the same image as before can be obtained even when ϕ = 0.6.

In the case of the present invention, the change of the image is slightly larger corresponding to the change of the value of the parameter K, so it is necessary to set the accuracy of the parameter K to be finer than before.

The coefficients shown in FIG. 10( a ) are used for the LPF 51 in this embodiment, and the coefficients shown in FIG. 10( b ) are used for the HPF 53 .

From the point of view of reproducibility of small characters and suppression of moiré, it is explained that the value of K=0.6 is preferable for the parameter K, but the value of K varies somewhat with the selection of different coefficients of LPF51 and HPF53.

For example, when the coefficient of the HPF53 is changed as shown in FIG. 10(c), since the edge is more prominent than in the above-mentioned embodiment, the appropriate value of the parameter K becomes lower. Therefore, it is necessary to select an appropriate value of the parameter K according to the values of the coefficients of LPF51 and HPF53.

In the embodiment, the case of the mask size (3×3) was described, but the size is not limited to (3×3), and the size can be freely set. Usually when the mask size is (n×n), the line buffer needs n-1 lines, only half of the original is enough.

In addition, the configuration of the coefficients is not limited by this embodiment, and all coefficient values within the size of the mask can be changed.

As described above, according to the embodiment of the present invention, line memory can be reduced by performing LPF processing and HPF processing on an input image from a scanner in parallel.

In addition, in terms of image quality, by optimizing the value of the parameter K of the HPF, the same image as conventional images can be obtained.

As described above, according to the present invention, it is possible to provide a line buffer capable of reducing the mask size (n x n) in the filter processing of the image processing apparatus.

Claims (8)

1. An image forming apparatus, characterized in that it comprises: a reading device for reading a document image; a first filter processing device for filtering image information read by the reading device; and the first The filter processing device is connected in parallel, and the second filter processing device that performs filter processing on the image information read by the above-mentioned reading device; the processing result of the second filter processing device is added to the processing result of the above-mentioned first filter processing device adding means; image processing means for performing various image processing based on the result of addition by the adding means; and image forming means for forming an image based on the image information processed by the image processing means. 2. An image forming apparatus, characterized in that it comprises: a reading device for reading an image of an original document; and performing an image within a prescribed range including a pixel noticed in image information read by the reading device A first processing device for low-pass filtering processing of information; a correction device for performing image contrast correction on the result of processing by the first processing device; parallel to the first processing device, performing image processing including reading by the reading device A second processing device for high-pass filter processing of the image information within the specified range of the pixel noticed in the image information; a multiplication device that multiplies the processing result of the second processing device by a predetermined coefficient; The addition device that adds the result of the result and the result corrected by the above-mentioned correction device; the image processing device that performs various image processing according to the result added by the addition device; and according to the image processed by the image processing device An image forming apparatus for forming an image from image information. 3. An image forming method, characterized in that the steps of: reading a document image, and performing low-pass filtering of image information within a prescribed range including a pixel of interest in the read image information in parallel processing and high-pass filtering to form an image. 4. An image processing device, characterized in that it includes: a first processing device for filtering image information within a predetermined range including a pixel of interest in a processing target image; and the first processing device A second processing device that performs filtering processing of image information within a predetermined range including the pixel of interest in the image to be processed in parallel; and processes the result processed by the second processing device with the first processing device Adding means for summing the results. 5. An image processing device, characterized in that it includes: a first processing device for filtering image information within a prescribed range including a pixel of interest in an image to be processed; A correction device for correcting the contrast of the image as a result of the processing; a second processing device for performing filtering processing of image information within a predetermined range including the pixel of interest in the processing target image in parallel with the above-mentioned first processing device ; multiplication means for multiplying the result processed by the second processing means by a predetermined coefficient; and addition means for adding the result multiplied by the multiplication means and the result corrected by the correction means. 6. An image processing device, characterized in that comprising: a first line buffer temporarily storing input image information; a second line buffer temporarily storing image information output from the first line buffer; The image information output from the second line buffer, the image information output from the first line buffer, and the input image information are processed within a predetermined range including the pixel of interest in the image to be processed. A low-pass filter for filter processing of image information; a range correction device for image contrast correction for the processing result of the low-pass filter; Image information, image information output from the first line buffer, and input image information are subjected to high-pass filtering for filtering image information within a predetermined range including the pixel of interest in the image to be processed. multiplier; multiplication means for multiplying the result processed by the high-pass filter by a predetermined parameter K; and addition means for adding the result multiplied by the multiplication means and the result corrected by the above-mentioned range correction means. 7. An image processing device, characterized in that comprising: a first line buffer temporarily storing input image information; a second line buffer temporarily storing image information output from the first line buffer; The image information output from the second line buffer, the image information output from the first line buffer, and the input image information are processed within a predetermined range including the pixel of interest in the image to be processed. A low-pass filter for filter processing of image information; a range correction device for image contrast correction for the processing result of the low-pass filter; Image information, image information output from the first line buffer, and input image information are subjected to high-pass filtering for filtering image information within a predetermined range including the pixel of interest in the image to be processed. device; the multiplication device that multiplies the result of this high-pass filter processing by a predetermined parameter K; the addition device that adds the result multiplied by the multiplication device and the result corrected by the above-mentioned range correction device; and adds to the addition device An image processing device that performs image processing such as enlargement or reduction, gamma correction, and error variance. 8. An image processing method characterized by the steps of: performing low-pass filter processing and high-pass filter processing in parallel on image information within a predetermined range including a pixel of interest among read image information.

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