JP2002374420A - Image processor and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the reliability on isolated-point detection and to output an image of high picture quality. SOLUTION: This image processor applies aliasing to image data, regards a pixel of interest as an isolated point when antialiased data of all the pixels in a 9×3 pixel matrix including the pixel of interest in its center are all <=1 as a threshold, and converts image data in a 3×3 pixel matrix area to an isolated-point erasure level. The image processor is equipped with a 1st decision means (36 to 42 in Fig. 16) which generates primary characteristic data Cd1 showing that the pixel of interest is a primary isolated-point candidate '1' or primary unisolated-point candidate '0', a 2nd decision means (43 to 48 in Fig. 17) which generates secondary characteristic data Cd2 as extended data of the isolated-point candidate, a 3rd decision means (49 to 54 in Fig. 17) which generates tertiary characteristic data Cd3 as extended data of an unisolated- point, and a data converting means (58 in Fig. 17) which converts image data on a pixel decided finally as the isolated point to the isolated point erasure level.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an image processing apparatus for removing unnecessary points from a digital image and an image forming apparatus using the same. This type of processing includes what is referred to as isolated point removal.

[0002]

2. Description of the Related Art Generally, in a copying machine, facsimile, printer, or the like, an image from a reading device or the like has an unnecessary point (hereinafter referred to as an isolated point), and the image quality deteriorates when image processing is performed by a digital filter or the like. It is a cause to cause.
Japanese Patent Application Laid-Open No. 6-30265 discloses a method of performing binarization processing on image data that has been subjected to a filter such that a gradual density change becomes a steep density change, and detecting an isolated point. I have.

[0003]

However, in the above-mentioned prior art, the contrast between black and white is emphasized for a halftone image composed of a collection of small points. There is a possibility of erroneous detection.

Accordingly, a first object of the present invention is to increase the reliability of isolated point detection, and a second object is to enable high-quality image output.

[0005]

Means for Solving the Problems (1) Based on image data of a plurality of A (A = 25-1) peripheral pixels distributed two-dimensionally around a pixel of interest and its surroundings, each pixel of the pixel group is Smoothing means (7, 22 in FIGS. 5 and 6) for generating smoothed data representing the sum of a part of the density to the pixel of interest and executing this as each pixel of interest in the two-dimensional distribution; If the density represented by the smoothed data of a plurality of B (B = 27-1) peripheral pixels distributed two-dimensionally around the pixel is less than the threshold, the image data addressed to the pixel of interest is isolated point erasing level (background density)
An image processing apparatus (20) including data conversion means (8 to 25 in FIGS. 5 and 6) for sequentially changing the pixel of interest and executing the same.

[0006] In order to facilitate understanding, corresponding items of the embodiment described later, or corresponding elements or symbols of the corresponding items are added in parentheses for reference. The same applies to the following.

According to this, when the target pixel is an isolated point, since the density value of the image data of the peripheral pixel is low at the background level, the smoothed data of the target pixel has a low density representing a part of the density of the target pixel. Value. That is, the density is lower than the density value represented by the original image data. On the other hand, when the pixel of interest is, for example, a halftone dot, the density value of the peripheral pixel is high, so that the density represented by the smoothed data of the pixel of interest does not decrease particularly. Therefore, when the pixel of interest is an isolated point, the smoothed data is less than the threshold value, and when the pixel of interest is a halftone dot, the smoothed data is greater than the threshold value.

If the spread of a pixel group (9 × 3) consisting of a plurality of B peripheral pixels distributed two-dimensionally around the target pixel and its surroundings is, for example, about the halftone pitch, if there is a halftone dot in the effective image, In this case, one of the pixels in the pixel group is equal to or larger than the threshold value. In this case, the pixel of interest is likely to be a part of the effective image, and the image data is not changed. If the smoothed data of the pixel group (9 × 3) is less than the threshold value, the pixel of interest is likely to be a background or an isolated point. In this case, the image data of the pixel of interest has a level of no image or background. The level is changed to the isolated point elimination level value. That is, isolated points are removed.

The image data at the isolated point is converted into a low density value (smoothed data thereof) by smoothing the image data to emphasize the density difference from halftone dots and other effective images, and a pixel group having a predetermined spread is used. It is confirmed that there is no high density equal to or higher than the threshold value (corresponding to the background area), and the image data of the pixel of interest at the center is changed to image data representing the isolated point erasing level value (background density). The point removal processing is realized, and higher-quality image output can be performed. The possibility that an effective image is erroneously detected and removed as an isolated point is reduced.

(2) A first pixel matrix area including a plurality of (5 × 5) pixels in the main and sub-scanning directions, including a pixel of interest and surrounding pixels, on an image represented by input image data.
As a window (Mat1), the image data level of the edge pixel is compared with a threshold value (Th2), and a primary isolated point candidate (“1”) or a primary non-isolated point (“1”) in which the target pixel is surrounded by low-density pixels. 0 "), and generates the primary characteristic data (Cd1), and executes this as each pixel of a two-dimensional distribution as a target pixel (36 to 42 in FIG. 16); the target pixel and its surroundings A pixel matrix area including a plurality of pixels (5 × 3) in both the main and sub-scanning directions including pixels is defined as a second window (Mat2) and primary characteristic data (Cd1) therein.
Is generated by extending the primary isolated point candidate ("1") to the pixel of interest in the second window, and executing this as the pixel of interest using each pixel of the two-dimensional distribution. 2 determination means (43 to 48 in FIG. 17): A pixel matrix area including a target pixel and its surrounding pixels and including a plurality of pixels (5 × 3) in both the main and sub-scanning directions is defined as a third window (Mat3). Secondary characteristic data (Cd2)
Tertiary characteristic data (Cd3) in which the secondary non-isolated point ("0") is also extended to the pixel of interest in the third window,
Third determination means (49 to 54 in FIG. 17) for executing each of the pixels of the two-dimensional distribution as a pixel of interest; Data conversion means (5 in FIG. 17)
8).

The isolated point is surrounded by background level pixels. According to the present embodiment, the first determination means extracts a pixel meeting this condition as a primary isolated point candidate. The second determination means generates a secondary isolated point candidate obtained by enlarging the primary isolated point candidate pixel within a second window (Mat2) centered on the primary isolated point candidate pixel. As a result, the primary isolated point candidates dispersed at extremely short distances form a group area, and isolated points leaked in the primary isolated point candidate determination are also absorbed by the group area, and the reliability of isolated point detection is increased. .

[0012] The third determining means determines a second non-isolated point pixel not determined as a secondary isolated point candidate as a third pixel centered on the second non-isolated point pixel.
A tertiary non-isolated point candidate expanded to all pixels of the window (Mat3) is generated. As a result, 2 spread to non-isolated points
The edge of the next isolated point candidate area is narrowed, the possibility that a significant image or the background is processed as an isolated point is low, and the reliability of isolated point detection is further increased.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (1a) The data conversion means of the above (1) comprises a plurality of B pixels distributed two-dimensionally around a pixel of interest and its periphery.
If the density represented by the smoothed data of the peripheral pixels of (B = 27-1) is less than the threshold, a plurality of Cs (C = 9-1) and C ≦ B distributed two-dimensionally around the target pixel and its surroundings It is assumed that the image data addressed to the peripheral pixels represents an isolated point erasing level (background density).

According to this, all the image data of the pixel group (3 × 3) including the target pixel determined to be an isolated point is converted into data representing the isolated point erasing level (background density). DPI
In the case of a small pixel having a large (DotPer Inch), noise dots (isolated points) are generally a set of several pixels. According to the present embodiment, in the case of such a large DPI, the isolated point removal processing can be quickly completed without significantly impairing the isolated point removal accuracy.

(1b) Image data addressed to each pixel of the pixel matrix 1 including the pixel of interest and its surrounding pixels and having an extension (5 × 5) of a plurality of pixels in each of the main scanning direction x and the sub-scanning direction y is selected. Means (MEa, 7 in FIGS. 5 and 6)
22), an operation means (7, 22 in FIGS. 5 and 6) for performing a filtering process on the image data of the target pixel using the image data in the pixel matrix 1, and a main scanning direction x and a sub-scanning direction y, respectively. Means (MEb, 15 in FIGS. 5 and 6) for selecting the image data after the filter processing, destined for each pixel of the pixel matrix 2 having a spread of a plurality of pixels (9 × 3);
A means (8, 23 in FIGS. 5 and 6) for comparing the selected image data after the filter processing with a predetermined threshold value 1 and, based on the comparison result, lowering the image data of some pixels in the pixel matrix 2 Means for determining whether or not to use a density value (1 in FIG. 6)
5) and an image processing apparatus (33/33).
p).

According to this, with a simple circuit configuration,
By performing the isolated point removal processing with high accuracy, it is possible to output a higher quality image.

(1c) The filtering process for the pixels in the pixel matrix 1 is a smoothing filtering process (FIGS. 5 and 6).
7, 22), wherein the image processing apparatus according to (1b) above.

According to this, by using the smoothing filter, it is possible to obtain image data having a high correlation between the target pixel and its surrounding pixels, to reduce false detection of valid image data, and to achieve higher image quality. Image output becomes possible.

(1d) When the comparison result of the comparing means (15 in FIG. 6) indicates that the filtered image data of all the pixels in the pixel matrix 2 is equal to or less than a predetermined threshold 1, The image processing apparatus according to the above (1b) or (1c), wherein the image data of the pixels of the section is set to a low density value.

According to this, compared to a plurality of pixels including the pixel of interest, a higher quality image can be output by performing processing on a wide area.

(3) With each pixel of the two-dimensional distribution as a target pixel, the target pixel is a tertiary isolated point candidate (“1”) represented by the tertiary characteristic data (Cd3) and another tertiary isolated point candidate (“1”). C
d3 = “1”), the fourth judging means for judging the pixel of interest as an isolated point (56, 57 in FIG. 17);
And the data conversion means (58 in FIG. 17)
The image processing device according to (2) above, wherein the image data of the pixel determined as the isolated point by the fourth determining means is rewritten to the background erasing level.

When a plurality of pixels of the tertiary isolated point candidate are continuous, it is highly probable that those pixels are significant pixels higher than the background level. In the present embodiment, only the pixels of the tertiary isolated point candidate where such a condition is not satisfied are removed as regarded as isolated points, so the possibility of erroneous erasure of significant image pixels is reduced, and the reliability of isolated point removal is reduced. Higher and higher quality image output is possible.

(4) First judging means (36 to 4 in FIG. 16)
2) When the target pixel of the first window (Mat1) is equal to or more than the predetermined value (Th1), the first window (Ma1)
The image data level of the edge pixel at t1) is set to a threshold value (Th2).
And generating primary characteristic data (Cd1) indicating whether the target pixel is a primary isolated point candidate (“1”) or a primary non-isolated point (“0”) surrounded by low-density pixels. One window (Ma
When the pixel of interest at t1) is less than the predetermined value (Th1), the primary non-isolated point (“0”) is obtained without performing the above comparison.
Generating the primary characteristic data (Cd1) representing the following: (2) or (3).

For pixels at the background level where there is no possibility of an isolated point pixel, the first window (Mat1) is formed, and the determination processing for comparing the density of the pixels inside the window with the threshold value (Th2) is omitted. 1 representing the primary non-isolated point ("0")
Since the next characteristic data (Cd1) is generated, the first determination processing is simplified, and the processing speed is improved.

(5) First judgment means (36 to 4 in FIG. 16)
2) is the primary characteristic data (Cd1) representing the primary isolated point candidate addressed to the target pixel when all the pixels at the edge of the first window (Mat1) are low-density pixels less than the threshold (Th2).
= “1”), and any pixel at the edge is threshold (T
h2) or more, the primary non-isolated point (Cd1 =
Primary characteristic data (Cd1 = “0”) representing “0”) is generated; the image processing device of (2) or (3) above. According to this, the reliability of extracting only isolated point pixels as isolated points is high.

(5a) Second determination means (43-4 in FIG. 16)
8) is that if at least one pixel of the second window (Mat2) is a primary isolated point candidate (Cd1 = "1"),
The secondary characteristic data (Cd2) of the pixel of interest is defined as a secondary isolated point candidate ("1"); the image processing device of (2), (3) or (4) above.

Since a primary isolated point candidate is generated by expanding the primary isolated point candidate pixel to all pixels in the second window (Mat2) centered on the primary isolated point candidate pixel, the primary isolated point candidate dispersed at a very short distance is generated. Becomes a group area, and isolated points leaked in the primary isolated point candidate determination are also absorbed by the group area, and the reliability of isolated point detection is increased.

(5b) Fourth judgment means (56, 5 in FIG. 17)
7) indicates that the target pixel is a tertiary isolated point candidate (Cd3 = “1”)
And all the pixels adjacent thereto are tertiary non-isolated points (Cd3
= "0"), the image data of the target pixel is rewritten to the background erasing level; any one of the above-mentioned image processing apparatuses (2) to (5a).

Even if a pixel is a tertiary isolated point candidate, only if all of its adjacent pixels are tertiary non-isolated points,
Since the pixels of the tertiary isolated point candidate are regarded as isolated points and removed, the possibility of erroneous erasure of significant image pixels is reduced, the reliability of isolated point removal is high, and higher quality image output is possible.

(5c) All pixels adjacent to the pixel of interest are edges of a fourth window (Mat4) of a pixel matrix area including a plurality of pixels (3 × 3) in the main and sub-scanning directions centering on the pixel of interest. (5b)
Image processing device.

Whether an isolated point is finely detected on a pixel-by-pixel basis, the possibility of erroneous erasure is reduced, the reliability of removal of the isolated point is high, and a higher quality image can be output.

(5d) The isolated point erasing level of (1) or (2) is a low density having a fixed density value. That is,
If the image data represents, for example, a density value, all the bits are set to “0”, that is, the density is 0, or the background density of the image, or a value between the density 0 and the background density. In any case, if the target pixel is an isolated point, that is, a noise dot, it disappears.

(5e) The isolated point elimination level of (1) or (2) is the background density of the image represented by the image data group addressed to the two-dimensionally distributed pixel group.

According to this, if the target pixel is an isolated point, that is, a noise dot, it is buried in the background. That is, it disappears. When the background image density is removed in the subsequent image processing, image characteristics such as character image or photographic image are detected before and after that, and image correction processing corresponding to the image characteristics is applied, white points occur after removing isolated points Therefore, the detection of the image characteristics and the image correction processing are not disturbed.

(5f) The original is illuminated, the reflected light of the original is projected on the image sensor, an image signal is generated by the image sensor, and the A / D
Document scanner that converts digital data into image data by conversion means
And (200 + 20 /) an image processing device (20 / IPU) according to (1) or (2), wherein the isolated point is removed using the image data of the document scanner as input image data. 200 + IPU).

According to this, image data representing a clear image without noise dots of a document read by the document scanner (200) can be obtained.

(6) The image processing apparatus (20 / IPU) according to the above (1) or (2); means for converting the image data processed by the image processing apparatus into image data for forming a visible image by a printer ( 22-28 / 114-124); and forming an electrostatic latent image on the photoreceptor in accordance with the image data for forming the visible image, developing the electrostatic latent image into a visible image with a developing device, and directly or intermediately. An image forming apparatus comprising: a printer (400/100) for transferring to a transfer sheet via a transfer medium.

According to this, given image data is
Even when an image including noise dots is represented, a beautiful image from which noise dots have disappeared is printed out.

(7) A document scanner (2) that illuminates a document, projects reflected light of the document onto an image pickup device, generates an image signal with the image pickup device, and digitally converts the image signal into image data by A / D conversion means.
00); the image processing apparatus (20 / IPU) according to (1) or (2), wherein the isolated points are removed using the image data of the original scanner as input image data; Means (22-28 / 114-124) for converting into image data for forming a visible image by means of: and forming an electrostatic latent image on the photoconductor in accordance with the image data for forming the visible image,
An image forming apparatus comprising: a printer (400/100) for converting an electrostatic latent image into a visible image with a developing device and transferring the latent image directly or via an intermediate transfer medium to transfer paper.

According to this, even when there are noise dots in the given original document and when there are dirt dots on the contact glass of the scanner, a beautiful original image from which the noise dots have disappeared is printed out.

Other objects and features of the present invention will become apparent from the following description of embodiments with reference to the drawings.

[0042]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment FIG. 1 shows an outline of a mechanism of an image forming apparatus equipped with an image processing apparatus according to an embodiment of the present invention. This embodiment is a digital full-color copying machine. A color image reading device (hereinafter referred to as a document scanner) 200 converts an image of a document 180 on a contact glass 202 into an illumination lamp 20.
5, forming an image on the color sensor 207 via the mirror group 204A, 204B, 204C, etc., and the lens 206, and converting the color image information of the original into, for example, blue (hereinafter, referred to as blue).
B), green (hereinafter, referred to as G) and red (hereinafter, referred to as R) are read for each color separation light and converted into an electric image signal. In this example, the color sensor 207 is constituted by a three-line CCD sensor, and B, G,
The R image is read for each color. B obtained by the scanner 200,
Based on the color separation image signal intensity levels of G and R, color conversion processing is performed by an image processing unit (20: FIGS. 2 and 3) not shown, and black (hereinafter referred to as Bk) and cyan (hereinafter referred to as Bk). , C), magenta (hereinafter, referred to as M), and yellow (hereinafter, referred to as Y) are obtained.

Using the color image data, a color image recording apparatus (hereinafter referred to as a color printer) 4 described below
00, the images of Bk, C, M, and Y are overlaid on the intermediate transfer belt and transferred to a transfer sheet. The document scanner 200 receives a scanner start signal synchronized with the operation of the color printer 400, and scans a document in the direction of the left arrow by an illumination / mirror optical system including an illumination lamp 205 and mirror groups 204A, 204B, and 204C. One color image data is obtained for each scan. Each time, while sequentially visualizing the color printer 400,
These are superposed on the intermediate transfer belt to form four full-color images.

The writing optical unit 401 as an exposure unit of the color printer 400 is
Is converted into an optical signal, optical writing corresponding to the original image is performed, and an electrostatic latent image is formed on the photosensitive drum 414. The optical writing optical unit 401
It comprises a laser light emitter 441, a light emission drive controller (not shown) for driving the light emission, a polygon mirror 443, a rotation motor 444 for rotating the polygon mirror 443, an fθ lens 442, a reflection mirror 446, and the like. Photoconductor drum 41
4 rotates counterclockwise as shown by the arrow,
Around the photosensitive member cleaning unit 421, a neutralizing lamp 414M, a charger 419, a potential sensor 414D for detecting a latent image potential on the photosensitive drum, a selected developing device of the revolver developing device 420, and a developing density pattern detector 414P, an intermediate transfer belt 415, and the like are arranged.

The revolver developing device 420 includes a BK developing device 420K, a C developing device 420C, an M developing device 420M, and a Y developing device 420Y. (Not shown). In order to visualize the electrostatic latent image, each of these developing devices rotates developing sleeves 420 KS and 420 which rotate by contacting the ears of the developer with the surface of the photosensitive drum 414.
CS, 420MS, 420YS, and a developing paddle that rotates to assemble and stir the developer. In the standby state, the revolver developing device 420 is set at a position where development is performed by the BK developing device 420, and when a copy operation is started, reading of BK image data starts at a predetermined timing by the original scanner 200,
Based on the image data, optical writing by a laser beam, that is, latent image formation starts. Hereinafter, the electrostatic latent image based on the Bk image data is referred to as a Bk latent image. The same applies to each of the C, M, and Y image data. In order to enable development from the front end of the Bk latent image, before the front end of the latent image reaches the development position of the Bk developing device 420K, the rotation of the developing sleeve 420KS is started to develop the Bk latent image with Bk toner. . And after that,
The developing operation of the Bk latent image area is continued, but the rear end of the latent image is
Immediately after passing the latent image position, the Bk developing device 42
The revolver developing device 420 is driven to rotate from the development position at 0K to the development position at the next color developing unit. This rotation operation is completed at least before the leading end of the latent image based on the next image data arrives.

When the image forming cycle is started, the photosensitive drum 414 rotates counterclockwise as indicated by an arrow, and the intermediate transfer belt 415 is rotated clockwise by a drive motor (not shown). Move. Intermediate transfer belt 41
5, the BK toner image formation, the C toner image formation, the M toner image formation, and the Y toner image formation are sequentially performed, and finally, on the intermediate transfer belt 415 in the order of BK, C, M, and Y. , A toner image is formed. The formation of the BK image is performed as follows.

That is, the charger 419 uniformly charges the photosensitive drum 414 with a negative charge to about -700 V by corona discharge. Then, the laser diode 441
Performs raster exposure based on the Bk signal. When the raster image is exposed in this manner, in the initially exposed portion of the photosensitive drum 414 that is uniformly charged, the charge proportional to the amount of exposure light disappears, and an electrostatic latent image is formed. The toner in the revolver developing device 420 is negatively charged by stirring with the ferrite carrier, and the BK developing sleeve 420KS of the developing device is
A power supply circuit (not shown) biases the 14 metal base layers to a potential at which a negative DC potential and an AC are superimposed. As a result, the toner does not adhere to the portion of the photosensitive drum 414 where the charge remains, and the Bk toner is adsorbed to the portion having no charge, that is, the exposed portion, and the Bk visible light similar to the latent image is obtained. An image is formed. The intermediate transfer belt 415 includes a driving roller 415D, a transfer opposing roller 4
15T, the cleaning opposing roller 415C, and a group of driven rollers, which are driven to rotate by a drive motor (not shown).

The B formed on the photosensitive drum 414
The k toner image is transferred by a belt transfer corona discharger (hereinafter, referred to as a belt transfer unit) 416 to the surface of the intermediate transfer belt 415 that is driven at a constant speed in contact with the photoconductor. Hereinafter, the photosensitive drum 414 to the intermediate transfer belt 4
Transfer of the toner image onto the transfer belt 15 is referred to as belt transfer. Some untransferred residual toner on the photoconductor drum 414 is cleaned by the photoconductor cleaning unit 421 in preparation for reuse of the photoconductor drum 414. The toner collected here is
The toner is stored in a waste toner tank (not shown) via a collection pipe.

On the intermediate transfer belt 415, Bk, C, M, and Y toner images sequentially formed on the photosensitive drum 414 are sequentially aligned on the same surface, and a four-color superimposed belt transfer image is formed. After that, batch transfer is performed on transfer paper by a corona discharge transfer device. By the way, the photosensitive drum 41
On the fourth side, the process proceeds to the C image forming process after the BK image forming process.
The reading of the C image data by 00 starts, and the formation of the C latent image is performed by writing the laser light with the image data. The C developing device 420C rotates the revolver developing device with respect to the developing position after the trailing edge of the previous Bk latent image has passed and before the leading end of the C latent image has arrived.
The latent image is developed with C toner. Thereafter, the development of the C latent image area is continued, but when the rear end of the latent image has passed, the revolver developing device 420 is driven as in the case of the Bk developing device, and the C developing device 420C is sent out. M developing unit 42
0M is located at the development position. This operation is also performed before the leading end of the next M latent image reaches the developing unit. Note that M
In the process of forming each image of Y and Y, the operations of reading image data, forming a latent image, and developing are performed in the above-described B mode.
The description is omitted because it is in accordance with the steps of the k image and the C image.

The belt cleaning device 415U includes an inlet seal, a rubber blade, a discharge coil, and a mechanism for contacting and separating the inlet seal and the rubber blade. 1
While the second, third, and fourth color images are being transferred to the belt after the Bk image of the color is transferred to the belt, the entrance seal, the rubber blade, and the like are separated from the intermediate transfer belt surface by the blade contact / separation mechanism. .

A paper transfer corona discharger (hereinafter, referred to as a paper transfer device) 417 uses an AC corona discharge method to transfer the superposed toner image on the intermediate transfer belt 415 to transfer paper.
+ DC or a DC component is applied to the transfer paper and the intermediate transfer belt.

Transfer paper is stored in the transfer paper cassette 482, and is fed and conveyed by the paper feed roller 483 in the direction of the registration roller pair 418 R. Note that reference numeral 412B
Reference numeral 2 denotes a paper feed tray for manually feeding OHP paper or thick paper. At the time when the image formation is started, the transfer paper is fed from the paper feed tray and the registration roller pair 418R is used.
Waiting at the nip. Then, the paper transfer device 417
When the leading edge of the toner image on the intermediate transfer belt 415 is approaching, the registration roller pair 418R is driven so that the leading edge of the transfer paper coincides with the leading edge of the image, and the paper and the image are aligned. In this way, the transfer paper is superimposed on the color superimposed image on the intermediate transfer belt and passes over the paper transfer unit 417 connected to the positive potential. At this time, the transfer paper is charged with a positive charge by the corona discharge current, and most of the toner image is transferred onto the transfer paper. Subsequently, when the transfer paper passes through a separation static eliminator by a static elimination brush (not shown) disposed on the left side of the paper transfer device 417, the transfer paper is discharged, separated from the intermediate transfer belt 415, and moved to the paper transport belt 422. The transfer paper on which the four-color superimposed toner image is collectively transferred from the intermediate transfer belt surface is transported to the fixing device 423 by the paper transport belt 422, and the fixing roller 423A is controlled to a predetermined temperature.
The toner image is fused and fixed at the nip portion of the pressure roller 423B, sent out of the main body by the discharge roll pair 424, and stacked face up on a copy tray (not shown).

The photosensitive drum 414 after belt transfer
Is cleaned by a photoreceptor cleaning unit 421 including a brush roller, a rubber blade, and the like.
Further, the charge is uniformly removed by the charge removing lamp 414M. Further, the intermediate transfer belt 415 after transferring the toner image to the transfer paper
Again, the blade is pressed by the blade contact / separation mechanism of the cleaning unit 415U to clean the surface.
In the case of the repeat copy, the operation of the scanner and the image formation on the photoconductor are continued from the first-color image process on the first sheet, and then proceed to the first-color image process on the second sheet at a predetermined timing. In the case of the intermediate transfer belt 415, the second Bk toner image is belt-transferred to an area whose surface has been cleaned by a belt cleaning device, following a batch transfer process of the first four-color superimposed image onto transfer paper. So that Thereafter, the operation is the same as that of the first sheet.

The color copying machine shown in FIG. 1 is provided from a host such as a personal computer via a LAN or a parallel I / F.
When the print data is given through the MFP, the color data can be printed out (image output) by the color printer 400, and the image data read by the original scanner 200 can be transmitted to a remote facsimile, and the received image data can be printed out. Is a color copier. This copier is connected to a public telephone network via a private branch exchange PBX, and can communicate with a facsimile communication and a management server of a service center via the public telephone network.

FIG. 2 shows an electric system of the copying machine shown in FIG. Document scanner 200 for optically reading a document
In the reading unit 4, the reflected light of the lamp irradiation on the document is condensed on the light receiving element 207 by a mirror and a lens in the reading unit 4. The light receiving element (CCD in this embodiment) is provided in a sensor board unit SBU (hereinafter simply referred to as SBU), and an image signal converted into an electric signal in the CCD is a digital signal on the SBU, ie, a read image. After being converted into data, it is output from the SBU to the image processor 20.

The system controller 6 and the process controller 1 communicate with each other via the parallel bus Pb and the serial bus Sb. The image processing 20 performs a data format conversion for a data interface between the parallel bus Pb and the serial bus Sb therein.

The read image data from the SBU is transferred to the image processor 20, where the image processing is performed to degrade the signal due to the quantization into the optical system and the digital signal (the signal deterioration of the scanner system: the read image data due to the scanner characteristics). ), The image data is transferred to the copy function controller MFC, and written into the memory MEM. Alternatively, a process for printer output is performed and the result is given to the printer 400.

That is, the image processing 20 includes a job for storing read image data in the memory MEM and reusing the job.
Video data control VDC without storing in memory MEM
(Hereinafter simply referred to as VDC), and there is a job in which the laser printer 400 forms and outputs an image. As an example of storing the data in the memory MEM, when copying a plurality of originals, the reading unit 4 is operated only once, the read image data is stored in the memory MEM, and the stored data is read a plurality of times. is there. As an example where the memory MEM is not used, when only one document is copied, it is only necessary to process the read image data as it is for the printer output, and there is no need to write the data to the memory MEM.

First, when the memory MEM is not used, the image processing 20 performs image reading correction on read image data, and then performs image quality processing for conversion to area gradation. The image data after the image quality processing is transferred to the VDC. The post-processing relating to the dot arrangement and the pulse control for reproducing the dots are performed by the VDC on the signal changed to the area gradation, and the reproduced image is formed on the transfer paper in the image forming unit 5 of the laser printer 400. I do.

When additional processing, for example, rotation in the image direction, synthesis of images, and the like are performed when the data is stored in the memory MEM and read out from the memory MEM, the image data subjected to the image reading correction is transmitted via the parallel bus Pb. It is sent to the image memory access control IMAC (hereinafter simply referred to as IMAC). Here, the image data and the memory module MEM (hereinafter, simply referred to as MEM) are controlled based on the control of the system controller 6.
Access control, expansion of print data (character code / character bit conversion) of an external personal computer PC (hereinafter simply referred to as PC), and compression / expansion of image data for effective use of memory. The data sent to the IMAC is stored in the MEM after data compression, and the stored data is read as needed. The read data is decompressed and returned to the original image data from the IMAC via the parallel bus Pb for image processing 2.
Returned to 0.

Upon returning to the image processing 20, image quality processing and pulse control at VDC are performed, and a visual image (toner image) is formed on the transfer paper in the image forming unit 5.

FAX transmission function, which is one of the composite functions,
Image processing is performed on the image data read by the original scanner 200.
The image reading correction is performed by the FAX control unit FCU (hereinafter simply referred to as FCU) via the parallel bus Pb.
Transfer to The FCU performs data conversion to a public line communication network PN (hereinafter simply referred to as PN) and transmits the data to the PN as FAX data. For FAX reception, the line data from the PN is converted to image data by the FCU, and the parallel bus Pb
And transferred to the IPP via the CDIC. In this case, no special image quality processing is performed, dot rearrangement and pulse control are performed in the VDC, and a visible image is formed on the transfer paper in the image forming unit 5.

In a situation where a plurality of jobs, for example, a copy function, a facsimile transmission / reception function, and a printer output function, operate in parallel, the allocation of the reading unit 4, the imaging unit 5, and the right to use the parallel bus Pb to the job is performed by the system. It is controlled by the controller 6 and the process controller 1.

The process controller 1 controls the flow of image data, and the system controller 6 controls the entire system and manages the activation of each resource. The function selection of this digital multifunction copying machine is made by selecting and inputting through the operation board OPB, and setting the processing contents such as the copy function and the FAX function.

FIG. 3 shows an outline of the image processing function of the image processing 20. R, G,
The B-color image signals are A / D converted and output as 8-bit color image data. This image information is subjected to various kinds of processing in the image processing 20, and then,
Output to 0.

The image processing 20 includes the scanner gamma correction 2
1, isolated point removal 33, RGB smoothing / edge enhancement filter 22, background removal 23, color correction / under color removal (UCR) / U
The circuit includes a CA 24, a selector 25, a main scanning variable magnification 26, a printer gamma correction 27, a gradation process 28, and an image area separation 29, an ACS 30, and a background detection 31 in parallel with the scanner gamma correction 21. Scanner gamma correction 2
In step 1, R, G, and B image data of linear reflectance read by the document scanner 200 are converted into R, G, and B image data of linear density.

In the isolated point removal 33, a noise dot, that is, an isolated point is detected, and the image data of the area corresponding to the isolated point is
Replace with a value representing the background density detected by the background detection unit 31.

The RGB smoothing filter 22 performs a smoothing process for suppressing moiré caused by a halftone dot document and emphasizes edge information of a character portion or a picture portion. Background removal 2
No. 3 performs a process of skipping a highlight portion of the background of the document (replacement with white).

In the color correction / UCR / UCA circuit 24,
The image information of each color of R, G, B, that is, the image data of each color read, is converted into the image information of each color of Y, M, C, that is, the complementary color thereof, that is, the image data of each color record. The color correction / UCR / UCA circuit 24 further extracts a black component included in the color of the image signal obtained by synthesizing all the image information of the Y, M, and C colors, outputs it as a black BK signal, and outputs the remaining black component. The black component is removed from the color image signal, and the YMC component is added.

The selector 25 selects any one of the Y, M, C and BK color signals and outputs it to the next block. When providing read image data to a personal computer or FCU, the selector 25
The image data is output to (the parallel bus Pb). Conversely, when printing out the image information from the personal computer or FCU, the image information from the personal computer or FCU is transmitted via the controller MFC (parallel bus Pb).
The data is received by the selector 25 and transmitted to the main scanning variable magnification 26 or less.

In the printer gamma correction 27, a curve corresponding to the printer characteristics is set, and the density is linearized in anticipation of the processing content (gradation processing mode) in the gradation processing 28 in the subsequent stage. The gradation processing 28 is a circuit for binarizing the inputted 8-bit density information (recorded image data) or multi-valued. In the character area, binarization or multi-level multi-level processing is performed, and in the photograph area, dither processing is performed. The processed data is output to the laser printer 400.

The output of the scanner gamma correction 21 is sent to the image area separation 29, the ACS 30, and the background detection 31. The image area separation 29 has a circuit for determining whether an input image is a character part or a photograph (including a picture) part, and an image area separation signal (mode signal) representing the determination result.
Is sent to the processing block below the filter 22 in units of one pixel. In each processing block, the processing is switched according to the determination result (character / photograph) of the image area separation 29.

The ACS 30 determines whether the original set on the scanner 200 is a black-and-white original or a color original, and sends the result to the system controller 6 at the end of scanning the Bk plate. If the original is a color original, the remaining three scans are performed, and if the original is a black and white original, the operation is terminated by Bk scan.

The background detection 31 is a circuit for detecting the background density of the original set on the scanner 200. In the case of full color copy, the background density is detected at the time of scanning the Bk plate.
The result is returned to the system controller 6. The system controller 6 calculates the amount of background removal based on the result, and sets the calculated value in the background removal 23 at the time of CMY plate scanning, thereby performing background removal. In the case of black-and-white copying, since the Bk plane scan is performed only once, the detected background density value is directly returned to the background removal 23, and the background removal is performed.

At the time of image formation in the copy mode, a scanner start signal which is timed with the operation of the color printer 400 is given to the document scanner 200 from the system controller 6 in the multifunction controller MFC. The original scanner 200 performs image processing on control signals such as a frame valid period signal, a line synchronous signal (sub-scan synchronous signal), an image data valid period signal on a line, a pixel synchronous signal (main scanning synchronous signal), and read image data. Give to 20,
The image processing control 32 gives a control signal in the image processing 20 synchronized with these control signals to each of the processing functions 21 to 28. The R, G, B image data (each 8 bits) generated by the original scanner 200 is given to the scanner γ correction 21 at the head of the image processing.

From the original scanner 200 to the scanner γ correction 2
The R, G, and B image data lines between 1 are each shown in the drawing, but since each color image data is 8 bits, one signal line is actually 8 bits. These are the signal lines.

FIG. 4 shows a schematic processing flow of the isolated point removal 33. The outline will be described here. In the present embodiment, the isolated point removal processing is performed for each of the three scans of the remaining color meters when the Bk plate scan is performed and the ACS 30 determines that the document is a color original. In the following, only the case of reading a monochrome 256-gradation image during Bk scanning will be described. In this Bk scan image reading, black and white logic is defined as white: 0, black: 255
And That is, the image data has an 8-bit configuration representing a black density value.

First, from the image data of 5 lines read and input by the scanner, 5 image data centered on the pixel of interest are obtained.
× 5 pixel matrix rectangular block (pixel matrix M
xa) is specified (p1, p2 in FIG. 4). This process is shown in FIG. Here, a rectangular block of a 5 × 5 pixel matrix Mxa having 5 pixels in both the main scanning direction x and the sub-scanning direction y is used.
The shape may be other than that.

Next, filter processing is performed on the rectangular block (p3). As the filter coefficient used here, a 5 × 5 threshold matrix TMxa as shown in FIG. 8B is used. The threshold value matrix TMxa is obtained by associating a coefficient value for multiplying the image data of each pixel of the pixel matrix Mxa with those pixels. In this example, the highest value is assigned to the central target pixel. , The smoothing filter coefficient that becomes lower as the distance from it increases. For the calculated smoothed data, 1/48 of the coefficient value in the threshold value matrix TMxa is reflected.

That is, the 5 × 5 threshold value matrix TMxa
D (m, n); m: x position 1,2,3, ... 5 on Mxa; n: y position 1,2,3, ... on Mxa .5; T (m, n); m: x position 1, 2, 3,... 5 on TMxa; n: y position 1, on TMxa 2, 3,... 5, the smoothed data PMxa of the target pixel (m = 3, n = 3), which is the central pixel of the pixel matrix Mxa, is expressed as PMxa = ｛ΣT (m, n) · D ( (m, n)｝ / ΣT (m, n) (1) In the numerical example shown in FIG. 8B, it is calculated that ΣT (m, n) = 48.

By using a smoothing filter, for effective image data such as characters, image data having a high correlation between the target pixel and the peripheral pixels can be obtained. Therefore, the correlation between peripheral pixels such as isolated points is low. It is possible to reduce erroneous detection with data. For example, if the image data of each pixel of the pixel matrix OMxa1 having a line image as shown in FIG. 8C is subjected to a smoothing process, after the smoothing, as shown in the matrix PMxa1, one pixel is located near the line image. Although the partial density is diffused, since the matrix OMxa1 has many high-density pixels (line image components), the high density remains in the smoothed matrix PMxa1, and the background portion near the line image component also has high density smoothing. Data. On the other hand, when the pixel matrix OMxa2 includes only noise dots or only the background, the pixel of interest is noise dots
In Mxa2, the density is diffused to the surroundings by the smoothing filter processing, and the smoothed data PMxa2 of the target pixel becomes extremely lower than the density of the original image data. When the pixel matrix OMxa2 is only the background, the smoothed data remains as low as the density of the original image data. Note that the filter coefficient shown in FIG. 8B is an example, and other filter coefficients may be used.

Next, a rectangular block (pixel matrix Mxb) of a 9 × 3 pixel matrix centering on the target pixel is specified from the three lines of smoothed data (p4 in FIG. 4). This process is shown in FIG. Here, a rectangular block of a 9 × 3 pixel matrix Mxb of 9 pixels in the main scanning direction x and 3 pixels in the sub-scanning direction y is used, but the size / shape may be other. In particular, by making the size of the pixel matrix Mxb larger than the halftone dot pitch, erroneous detection of a halftone image or the like can be reduced.

The pixels in the 9 × 3 pixel matrix Mxb are compared with a predetermined threshold value 1. When at least one of the pixels in the matrix Mxb is larger than the threshold value 1, the isolated point determination flag is set to NO. Otherwise, the isolated point determination flag is set to YES (p5 in FIG. 4; (b) in FIG. 9).

When the isolated point determination flag is YES,
The 3 × 3 pixel matrix Mxc centered on the pixel of interest, which is the central pixel in the 3 × 3 pixel matrix Mxb, is determined to be an isolated point area, and all the input image data of the pixels in the 3 × 3 pixel matrix Mxc are set to “0”. (P6 in FIG. 4; (c) in FIG. 9). When the isolated point determination flag is NO, it is determined that the 3 × 3 pixel matrix Mxc is not an isolated point area, and the input image data is output as it is.
Here, the isolated point area is a rectangular block of the 3 × 3 pixel matrix Mxc, but the size / shape may be any other size as long as it is within the 9 × 3 pixel matrix Mxb.

In this case, the 3 ×
Although the input image data in the three-pixel matrix Mxc is all replaced with “0”, the input image data may be a predetermined value that becomes the background level of the original image or a detected background level.

Next, isolated point removal 3 of the embodiment shown in FIG.
The process 3 will be described in detail. The isolated point removal 33 is an ASIC (Application Specific IC) incorporating an input / output buffer memory and an image data processing MPU. The input / output buffer memory has a first 5 × 5 pixel matrix Mxa
, A 5-line input image memory MEa for specifying image data
The smoothed data is "1" at threshold 1 (above threshold = image part) /
"0" (less than threshold value = non-image part: noise dot or background)
A three-line binary memory MEb for storing binarized binary smoothed data, and a five-line output image memory MEc for storing processed image data from which isolated points have been removed.
Is assigned.

FIG. 7A schematically shows the distribution of image data write cells in the 5-line input image memory MEa.
In this method, one area for writing input image data (8 bits) addressed to one pixel is defined as one small cell, and their distribution is defined as a two-dimensional image corresponding to the pixel distribution in the main scanning direction x and the sub-scanning direction y of the original image. This is schematically shown in an array.

When calculating the smoothed data of the image data of each pixel on one line, the image data processing MPU of the isolated point removal 33 firstly executes the third line (y =
3) The first pixel (x = 1) is set as a target pixel, and the smoothed data is stored in a memory M of x = −1 to 3 and y = 1 to 5.
The image data is calculated as in the above equation (1) using the image data addressed to each pixel of the 5 × 5 pixel matrix of Ea and the filter coefficient shown in FIG. The calculated smoothed data is
The same x of the third line of the memory MEb is binarized by the threshold value 1
Write at position (x = 1).

Then, the target pixel is set to 1 in the main scanning direction x.
The pixel shift is changed to x = 2, that is, the second pixel (x = 2) of the third line (y = 3) of the memory MEa is set as the target pixel, and the smoothed data is set to x = 0. ~
4, image data of a 5 × 5 pixel matrix of the memory MEa of 1 to 5 and the filter coefficient shown in FIG. The calculated smoothed data is binarized by the threshold value 1 and written at the same x position (x = 2) on the third line of the memory MEb.

Then, the target pixel is set to 1 in the main scanning direction x.
The pixel shift is changed to x = 3, that is, the third pixel (x = 3) of the third line (y = 3) of the memory MEa is set as a target pixel, and the smoothed data is set to x = 1. ~
5, using the image data of the 5 × 5 pixel matrix of the memory MEa of y = 1 to 5 and the filter coefficient shown in FIG. The calculated smoothed data is binarized by the threshold value 1 and written at the same x position (x = 3) on the third line of the memory MEb. Similarly, the pixel of interest is sequentially shifted in the x direction, its smoothed data is calculated, binarized, and written into the third line of the memory MEb.

FIG. 7B shows a three-line binary memory ME.
4 schematically shows the distribution of binary smoothed data write cells b. In this method, one area in which binary smoothed data (1 bit) addressed to one pixel is written is defined as one small cell, and their distribution is defined as the pixel distribution corresponding to the pixel distribution in the main scanning direction x and the sub-scanning direction y of the original image. This is a two-dimensional array schematically shown.

When determining whether each pixel on one line is an image area (effective image component) (noise dot area or background area), the image data processing MPU of the isolated point removal 33 first executes the second line of the memory MEb. The first (x = 1) pixel (x = 1, y = 2) of (y = 2) is the pixel of interest, and x = −3 to 5, and y = 1 to 3 memories MEb centered on the pixel of interest. It is checked whether all of the binary smoothed data (1 bit per pixel, 27 bits in total) of the second 9 × 3 pixel matrix are “0” (no image = noise dot or background).

When the binary smoothed data of the second 9 × 3 pixel matrix is all “0”, the image data processing MPU of the isolated point removing unit 33 executes the processing for the pixel (x =
X = 0 to 2, y = 1 to 3 centered on (1, y = 2)
All of the image data (8-bit configuration) of the third 3 × 3 pixel matrix is rewritten to data representing the background density detected by the background detection unit 31 (FIG. 3). When all the binary smoothed data of the second 9 × 3 pixel matrix is not “0”, that is, when there is an effective image component in the 9 × 3 pixel matrix, the data is not rewritten to the memory MEc.

Then, the target pixel is set to 1 in the main scanning direction x.
The pixel is shifted to x = 2, that is, the second pixel (x = 2) of the second line (y = 2) of the memory MEb is set as the target pixel, and x = −2 around the target pixel. ~ 6
It is checked whether all of the binary smoothed data of the second 9 × 3 pixel matrix of the memory MEb of y = 1 to 3 are “0”. If they are all “0”,
The image data processing MPU of x = 1 to 3 and the isolated point removal 33 centering on the pixel (x = 2, y = 2) has y = 1 to 3.
All of the image data of the third 3 × 3 pixel matrix is rewritten into data representing the background density detected by the background detection unit 31. 2 of the second 9 × 3 pixel matrix
When all the value smoothed data are not “0”, that is, when there is an effective image component in the 9 × 3 pixel matrix, the data is not rewritten to the memory MEc.

Then, the target pixel is set to 1 in the main scanning direction x.
The pixel is shifted to x = 3, that is, the third pixel (x = 3) of the second line (y = 2) of the memory MEb is set as the target pixel, and x = −1 centered on the target pixel. ~ 7,
It is checked whether all of the binary smoothed data of the second 9 × 3 pixel matrix of the memory MEb of y = 1 to 3 are “0”. If all of them are “0”, the image data processing MPU of the isolated point removal 33 outputs the pixel (x =
3, y = 2), x = 2-4, y = 1-3
All of the image data of the third 3 × 3 pixel matrix is rewritten into data representing the background density detected by the background detection unit 31. 2 of the second 9 × 3 pixel matrix
When all the value smoothed data are not “0”, that is, when there is an effective image component in the 9 × 3 pixel matrix, the data is not rewritten to the memory MEc. Similarly, the pixel of interest is sequentially shifted in the x direction,
It detects whether it is an effective image component and, if not, rewrites the data on the memory MEc. The above is the content of the isolated point determination & data correction.

FIG. 7C schematically shows the distribution of input image data write cells in the 5-line output image memory MEc. In this method, one area for writing image data (8 bits) addressed to one pixel is defined as one small cell, and their distribution is represented by a two-dimensional array corresponding to the pixel distribution in the main scanning direction x and the sub-scanning direction y of the original image. This is schematically shown.

As described above, the calculation of the smoothed data of all the image data of the third line on the memory MEa and the calculation of 2
After the binarization and the writing of the binary data to the third line of the memory MEb are completed, it is determined whether or not all pixels on the second line on the memory MEb are valid image components (noise dots or background). When the rewriting of the input image data in the memory MEc at the time of the above is completed, that is, when the isolated point removal processing of one line is completed, the image data processing MPU of the isolated point removal 33 is the first of the five-line output image memory MEc. The image data of the line is output to the next stage of the RGB smoothing / edge enhancement filter 22 (FIG. 3), and the memory MEa,
Data shift of one line in the −y direction of MEb and MEc is performed. That is, the memories MEa, MEb and M
In each Ec, the data of the second (y = 2) line is written to the first line, and the data of the third line is written to the second line. Further, in the memories MEa and MEc, the fourth
The data of the line is written to the third line, and the data of the fifth line is written to the fourth line. Then, isolated point removal 33
The image data processing MPU writes the next one line of image data, that is, input image data, from the scanner 200 after the scanner gamma correction 21 (FIG. 3) in the fifth line of each of the memories MEa and MEc. Then, the above-described smoothing processing of the image data of the third line on the memory MEa, binarization of the obtained smoothed data, writing of the binary smoothed data on the third line of the memory MEb, and The determination as to whether or not each pixel on the second line on the memory MEb is an effective image component (noise dot or background) and the rewriting of the input image data on the memory MEc when the determination is negative are performed. The above processing is performed by the scanner 20
Repeat until 0 reaches the data end (end of reading).

FIGS. 5 and 6 show the flow of the above-described isolated point removal processing of the image data processing MPU of the isolated point removal 33. First, refer to FIG. The MPU (hereinafter, simply referred to as MPU) receives a processing start instruction from the image processing control 32 immediately before the document image data is supplied from the scanner 200, and in response to this, the MPU receives the input / output memory ( MEa, b, c) are cleared (initialized), and the line number of the image data is cleared. The data of the register j storing j is initialized to 0 (step 1). In the following, the word “step” is omitted in parentheses, and step N
o. Write only numbers.

When the image data of the first line is given from the scanner 200, the MPU writes it in the fifth line of the memories MEa and MEc (2). And line N
o. j is incremented by one (3), MEa and ME
c, the image data of the second line is the first line, the image data of the third line is the second line, the image data of the fourth line is the third line, the image data of the fifth line is the fourth line, Writing is performed sequentially in this order (5). Hereinafter, such movement of image data is referred to as “1 in the −y direction of image data”.
It is expressed as "shift of line."

When image data for the next one line is received from the scanner 200, it is written to the fifth line of the memories MEa and MEc (2). Then, the image data of the third line (j = 3) on the original is stored in the fifth memory of the memories MEa and MEc.
When writing to the line, the MPU reads y =
The above-described smoothing processing, binarization, and writing of the binary smoothed data to the y = 3 line of the memory MEb of the image data of the third line are performed (6 to 9).

Next, the MPU operates the memories MEa, MEb, M
The Ec data is shifted by one line in the -y direction (12), and waits for the scanner 200 to send one line of image data.
Write to the fifth line of a, MEc (13). Then, the input image data line No. j is incremented by one (1
4) Perform the above-described smoothing processing, binarization, and writing of the binary smoothed data to the y = 3 line of the memory MEb (6 to 10). As described above, the image data of the first to fourth lines of the original exists at y = 2 to 5 in the memories MEa and MEc.
At y = 2 and y = 3 of the memory MEb, there are binary smoothed data of the first line and the second line of the document, respectively.

Next, reference is made to FIG. Here, since j = 4, the MPU proceeds to step 15 in FIG. 6, and each pixel of one line of y = 2 on the memory MEb is sequentially set as a target pixel, and each is an effective image component area. Is determined (noise dot or background), and if not, the input image data of each pixel of the 3 × 3 pixel matrix centered on the target pixel on the memory MEc is rewritten to the background density data. Processing, that is, isolated point determination & data correction is performed.

Next, the MPU outputs one line of data of y = 1 in the memory MEc to the RGB smoothing / edge emphasis filter 22 (FIG. 3) of the next stage (16). When j = 4, the output data is not the first line of the input image data obtained by reading the original image, but is one line of dummy data preceding the original image data for the filter 22.

Next, the MPU operates the memories MEa, MEb, M
The Ec data is shifted by one line in the −y direction (17), and waits for the scanner 200 to send one line of image data.
Write to the fifth line of a, MEc (19). Then, the input image data line No. j is incremented by one (2
0), the above-described smoothing processing, binarization, and writing of the binary smoothed data to the y = 3 line of the memory MEb are performed (21 to 25). As described above, the image data of the first to fifth lines of the original are stored in the memories MEa and MEc at y = 1 to 5, and are stored in the memories MEb at y = 1 to 3 respectively.
There is binary smoothed data for the line, the second line, and the third line.

Next, the MPU proceeds to step 15 and performs the above-described isolated point determination and data correction. Next, the MPU converts the y = 1 data of the memory MEc for one line into the next stage RG.
The signal is output to the B smoothing / edge enhancement filter 22 (FIG. 3) (16). This output data when j = 5 is for the first line of the input image data obtained by reading the document image. Hereinafter, the MPU reads the RGB smoothing / edge enhancement filter by reading the data of the last line from which the isolated point has been removed from y = 1 in the memory MEc by the scanner 200 ending the feeding of the image data of the entire surface of one original. Until the transmission to 22 is completed, the processing of the above-described steps 16 to 25 and 16 is repeatedly executed.

Second Embodiment FIG. 10 shows the appearance of a multifunction full-color digital copying machine according to a second embodiment of the present invention. This full-color copying machine generally includes an automatic document feeder ADF and an operation board OPB.
, Color scanner 200, color printer 100
A finisher 34 having a stapler and a tray capable of stacking formed sheets, and a double-sided drive unit 33.
And a paper feed bank 35 and a large capacity paper feed tray 36. A LAN (Local Area Network) to which a personal computer PC is connected is connected to a system controller 306 (FIG. 12) on a motherboard 90 in the machine, and a telephone line PN (facsimile communication line) is connected to a facsimile control unit FCU. Exchange PBX is connected. Color printer 10
The printed sheet of “0” is discharged onto the discharge tray 108 or the finisher 34.

FIG. 11 shows the mechanism of the color printer 100. The color printer 100 of this embodiment is a laser printer. In the laser printer 100, four sets of toner image forming units for forming images of each color of magenta (M), cyan (C), yellow (Y), and black (black: K) are arranged in a moving direction of the transfer paper. (From the lower right to the upper left in the figure), they are arranged in this order. That is, 4
This is a continuous drum type full-color image forming apparatus.

The magenta (M), cyan (C), yellow (Y), and black (K) toner image forming units are provided with photosensitive drums 111M, 111C, and 11D, respectively.
Photoconductor unit 110M having 1Y and 111K,
110C, 110Y and 110K and developing unit 1
20M, 120C, 120Y and 120K. The arrangement of the toner image forming units is such that the rotation axes of the photoconductor drums 111M, 111C, 111Y and 111K in each photoconductor unit are parallel to the horizontal x-axis.
In addition, the transfer paper movement direction (4
5-the left-upper line) and a predetermined pitch. As the photoconductor drum of each photoconductor unit, a photoconductor drum having an organic photoconductor (OPC) layer on the surface and having a diameter of 30 mm was used.

In addition to the toner image forming unit, the laser printer 100 carries an optical writing unit 102 by laser scanning, paper feed cassettes 103 and 104, a pair of registration rollers 105, and a transfer paper. Transfer conveyor belt 160 that conveys the paper so as to pass through the transfer position of the forming unit
, A belt fixing type fixing unit 107, a paper discharge tray 108, a double-sided drive (surface reversal) unit 33, and the like. The laser printer 100 also includes a manual tray, a toner supply container, a waste toner bottle, and the like (not shown).

The optical writing unit 102 includes a light source, a polygon mirror, an f-loud tower Y, a reflection mirror, and the like, and based on image data, the respective photosensitive drums 111M, 111C, 11C.
The surface of 1Y and 111K is irradiated with laser light while swinging and scanning in the x direction. A dashed line on FIG. 11 indicates a transfer path of the transfer paper. Paper cassette 103, 1
The transfer paper fed from 04 is conveyed by conveyance rollers while being guided by a conveyance guide (not shown), and sent to the registration roller pair 105. The transfer paper sent to the transfer conveyance belt 160 at a predetermined timing by the registration roller pair 105 is carried by the transfer conveyance belt 160 and
The sheet is conveyed so as to pass through the transfer position of the image forming unit.

The photosensitive drum 111 of each toner image forming unit
The toner images formed on M, 111C, 111Y and 111K are transferred to transfer paper carried and conveyed by the transfer / conveyance belt 60, and the transfer paper on which the toner images of the respective colors are superimposed, ie, the color image is formed, is fixed to a fixing unit. It is sent to 107. That is, the transfer is a direct transfer method in which a toner image is directly transferred onto a transfer sheet. When passing through the fixing unit 107, the toner image is fixed on the transfer paper. The transfer paper on which the toner image has been fixed is discharged or fed to the discharge tray 108, the finisher 36, or the double-sided drive unit 33.

The outline of the yellow Y toner image forming unit will be described below. Other toner image forming units have the same configuration as that of yellow Y. The yellow Y toner image forming unit is the photoconductor unit 110Y as described above.
And a developing unit 120Y. The photoconductor unit 110Y includes, in addition to the photoconductor drum 111Y, a brush roller that applies a lubricant to the surface of the photoconductor drum, a swingable blade that cleans the surface of the photoconductor drum, and a static elimination lamp that irradiates light to the surface of the photoconductor drum. And a non-contact type charging roller for uniformly charging the surface of the photosensitive drum.

In the photoconductor unit 110Y, the surface of the photoconductor drum 111Y uniformly charged by the charging roller to which the AC voltage is applied is modulated by the optical writing unit 102 based on print data and deflected by the polygon mirror. When the laser beam L is irradiated while being scanned, an electrostatic latent image is formed on the surface of the photosensitive drum 111Y. The electrostatic latent image on the photosensitive drum 11IY is
To form a yellow Y toner image. At the transfer position where the transfer paper on the transfer conveyance belt 160 passes, the toner image on the photosensitive drum 11IY is transferred to the transfer paper. After the toner image has been transferred, the surface of the photosensitive drum 111Y is coated with a predetermined amount of lubricant by a brush roller, cleaned by a blade, and neutralized by light emitted from a static elimination lamp. It is prepared for forming an electrostatic latent image.

The developing unit 120Y contains a two-component developer containing a magnetic carrier and a negatively charged toner. A developing roller disposed so as to be partially exposed from an opening of the developing case 120Y on the photosensitive drum side;
Transfer screw, doctor blade, toner concentration sensor,
A powder pump and the like are provided. The developer contained in the developing case is frictionally charged by being agitated and transported by the transport screw. Then, a part of the developer is carried on the surface of the developing roller. The doctor blade uniformly regulates the layer thickness of the developer on the surface of the developing roller, and the toner in the developer on the surface of the developing roller is transferred to the photosensitive drum, thereby forming a toner image corresponding to the electrostatic latent image on the photosensitive drum. Appears on drum 111Y. The toner density of the developer in the developing case is detected by a toner density sensor. When the density is insufficient, the powder pump is driven to supply toner.

The transfer conveyor belt 160 of the transfer belt unit 106 has a photosensitive drum 111 of each toner image forming section.
It is wrapped around four grounded stretching rollers so as to pass through each transfer position in contact with and facing M, 111C, 111Y and 111K. Of these stretch rollers,
An electrostatic attraction roller to which a predetermined voltage has been applied from a power supply is arranged so as to face the entrance roller on the upstream side in the transfer paper moving direction indicated by the two-dot chain line arrow. The transfer paper that has passed between these two rollers is electrostatically attracted onto the transfer / conveying belt 160. The exit roller on the downstream side in the transfer paper moving direction is a drive roller that frictionally drives the transfer conveyance belt, and is connected to a drive source (not shown). Further, a bias roller to which a predetermined cleaning voltage is applied from a power supply is arranged to be in contact with the outer peripheral surface of the transfer conveyance belt 160. The bias roller removes foreign matter such as toner adhered to the transfer / conveying belt 160.

The photosensitive drums 111M, 111C,
A transfer bias applying member is provided so as to be in contact with the rear surface of the transfer conveyance belt 160 which forms a contact facing portion that faces and contacts 111Y and 111K. These transfer bias applying members are fixed brushes made of Mylar, and a transfer bias is applied from each transfer bias power supply. By the transfer bias applied by the transfer bias applying member, transfer charges are applied to the transfer / conveyance belt 160, and a transfer electric field having a predetermined intensity is formed between the transfer / conveyance belt 160 and the surface of the photosensitive drum at each transfer position. .

FIG. 12 shows a main part of the electric system of the copying machine shown in FIG. In the color document scanner 200 that optically reads a document, a reading unit condenses reflected light of lamp irradiation on the document on a light receiving element by a mirror and a lens. The light receiving element (CCD in this embodiment)
The RGB image signal, which is provided in the sensor board unit of the reading unit and converted into an electric signal in the CCD, is converted into a digital signal at an image reading data input I / F (interface) 304, that is, an 8-bit multi-valued R signal read. , G, B image data, and after calibration of the image data array such as CCD line-to-line correction and main scan registration adjustment, is transmitted to an image data processing unit IPU (hereinafter sometimes simply referred to as IPU). Given.

FIG. 13 shows an outline of the data processing function of the IPU. The IPU applies reading correction (shading correction 112, isolated point removal 118, scanner combination 11) to each of the input RGB image data (R, G, B image data).
4 and filter processing 115), and then color correction 1
At step 16, the RGB image data is converted into recording color CMYK image data (each 8 bits), and the image represented by the RGB image data is one in which the shading of characters, lines, and the like is binary (hereinafter simply referred to as characters). Or a halftone image such as a photograph (hereinafter simply referred to as a photograph), separation generation 113, that is, image area separation is performed, and 1-bit image area data representing a determination result (character / photograph), that is, a separation signal is generated. I do. Then, the CMYK image data and the separation signal are transmitted to a data controller CDIC (hereinafter, sometimes simply referred to as CDIC). The processing of the isolated point removal 118 will be described later with reference to FIG.

The CDIC shown in FIG.
After scaling the MYK image data and masking the data in the unnecessary area, the CMYK image data is compressed by irreversible fixed-length primary compression, and the compressed data is separated and generated.
Is transmitted to the parallel bus Pb as transfer data. The transfer data is converted by the CDIC into parallel data and sent to the parallel bus Pb. The transfer data transmitted to the parallel bus Pb is subjected to reversible secondary compression by a memory controller IMAC (hereinafter sometimes simply referred to as IMAC), and then stored in the MEM.

The IMAC manages input / output of image data to / from the parallel bus Pb, and stores / reads image data to / from the MEM and expands code data mainly input from an external personal computer PC into image data. Control. P
The code data input from C is stored in a line buffer in the IMAC, that is, data is stored in a local area.
Expand to image data. The expanded image data or the image data input from the parallel bus Pb is stored in the MEM. In this case, reversible secondary compression of data is performed in order to increase the memory use efficiency, and the secondary compressed data is stored in the MEM while managing the address of the MEM.

When reading the compressed data stored in the MEM, the compressed data is expanded (expansion of secondary compression). The decompressed data is compressed by a parallel bus Pb for transfer.
The next compressed data and the separation signal are transferred to the CDIC via the parallel bus Pb.

The CDIC decompresses primary compressed data into recording color data. The separation signal is accumulated for the entire line length, and when the recording color data is accumulated for the entire line length,
The recording color data and the corresponding separation signal are transferred to the IPU.

Referring to FIG. 13, the IPU performs output correction on the recording color data based on the separation signal to improve the image quality. In this output correction, a printer combination 122 is added, and further converted into binary data CpMpYpKp for print output by gradation processing 123. The gradation processing 123 includes density gradation processing, dither processing, error diffusion processing, and the like, and the main processing is area approximation of gradation information. One of them is performed according to the image processing mode designation or the separation signal. Binary data CpM for print output
pYpKp is a writing I / F 305 shown in FIG. 12, and is written in a buffer memory separately for four systems Cp, Mp, Yp, and Kp in accordance with the four-drum tandem system in accordance with the four-drum tandem system. Are read out separately with a timing shift corresponding to the above, and are given to the laser modulators corresponding to each color of the optical writing unit 2 of the printer 100. That is, in the printer 100, C, M, Y and K image data Cp, M binarized by gradation processing
p, Yp and Kp are the Y,
The binary electrostatic latent images for forming the respective color images are supplied to the laser modulators of the M, C and K image forming units,
1C, 11M, 11Y and 11K.

A facsimile control unit FCU (hereinafter sometimes simply referred to as “FCU”) for performing facsimile transmission and reception shown in FIG. 12 converts image data into a communication format and transmits it to an external line PN. The data is returned to image data, and the external I / F unit and the parallel bus P
The data is output by the printer 100 via the terminal b. FC
U comprises a facsimile image processor, an image memory, a memory controller, a facsimile controller, an image compressor / decompressor, a modem and a network controller. A part of the image data output buffer function is completed by IMAC and MEM.

In the FCU, when starting transmission of image information, the facsimile control unit in the FCU instructs the memory control unit to sequentially read out the stored image information from the image memory in the FCU. The read image information is
The original signal is restored by FAX image processing in the FCU, density conversion processing and scaling processing are performed, and the result is added to the facsimile control unit. The image signal applied to the facsimile control unit is code-compressed by the image compression / decompression unit, modulated by the modem, and transmitted to the destination via the network control device. Then, the image information whose transmission has been completed is deleted from the image memory. At the time of reception, the received image is temporarily stored in the image memory in the FCU, and if the received image can be recorded and output at that time, the received image is recorded and output when the reception of one image is completed.

Referring again to CDIC, CDIC is:
It has a function of converting between parallel data transferred on the parallel bus Pb and serial data transferred on the serial bus Sb. The system controller 306 controls the parallel bus Pb
, And the process controller 301 transfers the data to the serial bus Sb. The CDIC performs parallel / serial data conversion for communication between the two controllers 306 and 301. The CDIC performs serial data transfer with the IPU.

CDIC represents RGB image data and YM
Regarding the CK image data and the separation signal accompanying them,
A system controller 306 for controlling data transfer between the PU and the parallel bus Pb, and overall control of the digital copying machine shown in FIG.
0, and communication related to image data transfer and other control between the process controller 301 which controls the image forming process of the color printer 100.

The system controller 306 and the process controller 301 communicate with each other via the parallel bus Pb, the CDIC, and the serial bus Sb. CDIC
Performs a data format conversion for a data interface between the parallel bus Pb and the serial bus Sb inside.

As described above, the color original scanner 200
Of the read RGB image data is subjected to image area determination by the IPU, and is converted into CMYK image data of recording color.
The image data is primarily compressed, and the compressed data and the separation signal indicating the determination result are sent to the parallel bus Pb via the CDIC. The data transmitted to the parallel bus Pb is secondarily compressed by the IMAC and written to the MEM. The data read out from the MEM, expanded in the secondary compression and read out to the parallel bus Pb is output to the IPU or to the FCU in the case of facsimile transmission.

The CDIC includes a job for storing the CMYK image data and the separation signal in the MEM and reusing the job.
The CMYK image data is output corrected based on the separation signal by the IPU without being stored in the color component output data CpMp.
There is a job for converting to YpKp and printing out. As an example of storing the data in the MEM, when copying a plurality of originals, the scanner 200 is operated only once, the multiplexed data is stored in the MEM, and the stored data is read a plurality of times. As an example without using the MEM, when copying only one document, it is only necessary to convert the CMYK image data as it is into the color component output data CpMpYpKp by the IPU, so that writing to the MEM is not necessary.

In the above data flow, the IMAC
The read / write control of the image data with respect to the MEM and the parallel bus Pb and the bus control between the IPU and the parallel bus Pb of the CDIC realize the composite function of the digital copying machine. The facsimile transmission function, which is one of the copy functions, uses the RGB
The image data is read and corrected by the IPU, converted to YMCK image data by the IPU if necessary, and transferred to the FCU via the CDIC and the parallel bus Pb. FCU
Performs data conversion to a public line communication network PN (hereinafter simply referred to as PN), and transmits the data to the PN as FAX data.
In the FAX reception, the line data from the PN is converted into image data by the FCU and transferred to the IPU via the parallel bus Pb and the CDIC. If the received data is RGB image data, it is converted to YMCK image data by the IPU. If the received data is YMCK image data, no special intermediate processing is performed and the image is sent to the printer 100 to form an image.

In a situation where a plurality of jobs, for example, a copy function, a facsimile transmission / reception function and a printer output function, operate in parallel, the right to use the color original scanner 200, the color printer 100, the parallel bus Pb and the IPU is allocated to the job. Is controlled by the system controller 306 and the process controller 301.

A process controller 301 controls the flow of image data, and a system controller 306 controls the entire system and manages the activation of each resource. The function selection of this digital multi-function color copier is
Select and input on the PB to set processing contents such as copy function and FAX function. The processing content of the printer output function responding to the print command of the personal computer PC is set by the print command of the personal computer PC.

Next, the image data processing in the isolated point removal 118 of the IPU shown in FIG. 13 will be described. In FIG.
4 shows a schematic flow of an isolated point removal process performed by the IPU. In this embodiment, R, R, and R are generated by the color original scanner 200 and input to the IPU via the input I / F 304.
Eliminating the isolated points of the image represented by the G image data from the RGB image data of each 8-bit configuration in which the respective G and B component densities are represented by gradations of 0 (base density) to 255 (highest density) (basal density Then, the R image data and the B image data at the position corresponding to the isolated point are also converted to the isolated point erasing level (basal density value in this embodiment). That is, an isolated point is detected based on the G image data, and the RGB image data at the position of the isolated point is converted into an isolated point erasing level. When the background density is automatically detected or when the background density is given, the isolated point elimination level may be set to the background density.

Referring to FIG. First, the scanner 200
The input RGB image data is read (pl0), each of the read G image data is sequentially identified as the image data of the pixel of interest, and compared with the threshold value Th1 of the background level (p11). When the image data is equal to or larger than the threshold Th1, the isolated point removal processing is executed. Here, it is possible to avoid erroneous detection of isolated points by setting the threshold value Th1 to a value or the like corresponding to the density of the background of the document.

In the isolated point removal processing, first, G for five lines
A window Mat1, which is a 5 × 5 rectangular block of a 5 × 5 pixel matrix area centered on the target pixel, is set for the image data (p12; FIG. 19A). Although the window Mat1 is a 5 × 5 rectangular block here, the size / shape may be other than that. It is assumed that pixels in the window Mat1 are denoted by reference numerals as shown in FIG.

Next, the edge pixel (FIG. 19 (c)) of the window Mat1 is compared with a predetermined threshold value Th2 (FIG. 19 (d)). All edge pixels P11 to P5
1, P15 to P55, P12 to P14 and P52 to P
If 54 is less than the threshold Th2, 1
The next feature data Cd1 is "1" which means a primary isolated point candidate
And Otherwise, the primary feature data Cd1 is set to 1
It is set to “0” meaning the next non-isolated point (p13; (d) of FIG. 19).

In the example of FIG. 19D, the threshold value Th2 = 3
When it is 0, all the pixels to be compared (edge pixels of the window Mat1) are smaller than the threshold Th2, so the primary feature data Cd1 of the target pixel is “1”. If the threshold value Th2 = 24, there is a pixel having a value larger than the threshold value Th2 among the edge pixels to be compared, so the primary feature data Cd1 of the target pixel is “0”.
Becomes Here, by changing or adjusting the threshold Th2, processing according to the image quality mode such as character priority / photo priority can be performed. In addition, by allowing the user to change the value to an arbitrary value, it is possible to obtain the image quality desired by the user.

With respect to the primary feature data Cd1, a second window Mat2 of a 5 × 3 rectangular block which is a 5 × 3 pixel matrix area centered on the primary feature data Cd1 of the target pixel is set (p14; FIG. 20). (A)). Here, the second window Mat2 is a 5 × 3 rectangular block, but the size / shape may be other. In particular, by increasing the size of the window, it is possible to reduce erroneous detection of a halftone image or the like.

When there is at least one primary isolated point candidate “1” in the primary feature data Cd1 in the second window Mat2, the secondary feature data Cd2 for the pixel of interest
Is set to "1" meaning a secondary isolated point candidate, and otherwise, the secondary feature data Cd2 is set to "0" meaning a secondary non-isolated point (p15; (c) and (d) of FIG. 20). ). Thereby, the primary isolated point candidate “1” for one pixel
Expands to the secondary isolated point candidate “1” of all the pixels in the second window Mat2 centered on it.

Next, for the secondary feature data Cd2, a third window Mat3, which is a 5 × 3 rectangular block of a 5 × 3 pixel matrix area centered on the secondary feature data Cd2 of the target pixel, is set (p16; FIG. 21 (a)).
Here, the third window Mat3 is a 5 × 3 rectangular block, but the size / shape may be other. In particular, by reducing the size of the window, erroneous detection can be reduced for a halftone image or the like.

When at least one or more secondary non-isolated points “0” exist in the secondary feature data Cd2 in the third window Mat3, the tertiary feature data Cd3 for the target pixel is referred to as “tertiary non-isolated point”. 0 ”and the window Mat
If all of the secondary feature data Cd2 in 3 is “1” meaning secondary isolated point candidate, the tertiary feature data Cd3 is set to “1” meaning tertiary isolated point candidate (p17; FIG. 21) (C) and (d)). As a result, the secondary non-isolated point “0” of one pixel is shifted to the third window Mat3 centered on it.
Are enlarged to the tertiary non-isolated point “0” of all the pixels within.

Next, regarding the tertiary feature data Cd3, 3 ×
The fourth, which is a 3 × 3 rectangular block of a three-pixel matrix area,
The window Mat4 is set (p18; FIG. 22A). Here, the rectangular block is 3 × 3, but the size / shape may be other than that.
In particular, the fourth window Mat4 is taken into consideration in consideration of the characteristics of the original.
By setting the size, it is possible to further improve the accuracy of detecting an isolated point.

Edge pixel P11 of fourth window Mat4
To P31, P13 to P33, P11 and P32 (FIG.
(B) and (c) of FIG. 2 are all tertiary non-isolated points “0” and the pixel of interest is 3
If the next isolated point candidate is “1”, it is assumed that the target pixel is a fourth-order isolated point candidate. When the tertiary feature data Cd3 of at least one edge pixel is “1” indicating a tertiary isolated point candidate, the pixel of interest is a quaternary non-isolated point (p19; FIG. 2).
2 (d) and (e)). This fourth-order isolated point candidate / fourth non-isolated point is determined as the final determination.

Next, the above-described detection of the isolated point and the process of removing the isolated point, which is shown in FIG. 13 as the isolated point removal 118 and whose outline is shown in FIG. 14, will be described in detail. The IPU executing the isolated point removal 118 includes a buffer memory and an image data processing MP.
An ASIC (Application Specific IC) incorporating U.

FIG. 15 shows several examples of buffer memories ME1 to ME1.
The outline of ME5 is shown. The input buffer memory ME1 has 5
5 × 5 rectangular block Mat which is a 5 × 5 pixel matrix area
This is a 5-line input image memory for specifying one G image data. ME2 to ME4 store binary primary to tertiary feature data (intermediate processing data) Cd1 to Cd3 for isolated point determination, respectively, and a 5 × 3 rectangular block which is a 5 × 3 pixel matrix area Mat2 primary feature data C
Secondary characteristic data Cd2 for specifying d1 and also for 5 × 3 rectangular block Mat3 which is also a 5 × 3 pixel matrix area, and tertiary characteristic data Cd3 for specifying 3 × 3 and rectangular block Mat4 which is also a 3 × 3 pixel matrix area It is for identification.
The output buffer memory ME5 is a 6-line output image memory (one set for each of R, G, and B, a total of three sets) for storing processed image data from which isolated points have been removed.

FIG. 15 shows buffer memories ME1 to ME.
5 schematically shows the distribution of image data write cells 5; This means that the input / output memories ME1 and ME5 have one area for writing input / output image data (8 bits) addressed to one pixel.
These distributions are schematically shown in a two-dimensional array corresponding to the pixel distribution of the original image in the main scanning direction x and the sub-scanning direction y. An arrangement of pixels in the x direction is a row (line), and an arrangement of pixels in the y direction is a column. The intermediate memories ME2 to ME4 define one area in which feature data (one bit) for one pixel is written as one small cell, and their distribution corresponds to the pixel distribution of the original image in the main scanning direction x and the sub-scanning direction y. Are schematically shown. x
The arrangement of pixels in the direction is a row (line), and the arrangement of pixels in the y direction is a column.

FIGS. 16, 17 and 18 show the flow of the above-described isolated point removal processing. First, reference is made to FIG.
Immediately before the document image data is given from the scanner 200, the IPU receives a processing start instruction from the process controller 301, and in response to this, the IPU clears (initializes) the input / output memories (ME1 to ME5), Line No. of the image data The data of the register j storing j is initialized to 0 (31).

When the first line of RGB image data is given from the scanner 200, the IPU sends the G image data to the fifth line of the memory ME1 and the RGB image data to ME5.
(For R, G, and B, one set for each, a total of three sets) is written on each sixth line (32). And line No. j is incremented by 1 (33), the image data of the second line of ME1 and ME5 is set to the first line, the image data of the third line is set to the second line, the image data of the fourth line is set to the third line,
The image data of the fifth line is stored in the fourth line,
The image data of the line is sequentially written on the fifth line in this order (35). Hereinafter, such movement of the image data is referred to as “shift of the image data by one line in the −y direction”.

Then, similarly to receiving the next one line of RGB image data from the scanner 200, the G image data is stored in the fifth line of the memory ME1 and the RGB image data is stored in the fifth line of the memory ME1.
5 (one set for each of R, G, and B, a total of three sets) is written to each sixth line (32). Hereinafter, the manner of writing the RGB image data is the same. Then, the third line (j =
The G image data of 3) is stored in the fifth line of the memory ME1 by R
When the GB image data is written to the sixth line of the memory ME5, the IPU performs an isolated point removing process by sequentially setting each pixel of one line of y = 3 on the memory ME1 as a target pixel.

That is, the target pixel is specified on the y = 3 line in the memory ME1 (36), and it is checked whether the specified target pixel is equal to or larger than the first threshold Th1 (37).
If it is less than Th1 (corresponding to the background), y =
The primary feature data Cd1 = "0", which means a primary non-isolated point, is written to the x address addressed to the target pixel of three lines (40).

When the target pixel is equal to or larger than the first threshold value Th1,
Since it may be an isolated point, the edge pixels (P11 to P51, P15 to P15 in FIG. 19B) of the first window Mat1 centered on the target pixel (i, y = 3) of ME1.
P55, P12 to P14, and P52 to P54) are read from the ME1, and all of them are read as the second threshold value T.
It is checked whether it is less than h2 (38). If all the edge pixels are less than the threshold Th2, the primary feature data Cd1 = “1” meaning a primary isolated point candidate, otherwise the primary feature data Cd1 = “0” meaning a primary non-isolated point "
The data is written to the x address of the target pixel on the y = 3 line in the memory ME2 (39, 40; FIG. 19D).

The IPU performs the above processing by sequentially designating each image data addressed to each pixel of one line of y = 3 of ME1 as a target pixel (37 to 42). When one line is completed, the primary feature data Cd1 addressed to each pixel of one line of ME1 at y = 3 has been written to y = 3 of the memory ME2.

Here, referring to FIG. 17, the IPU specifies the target pixel on the y = 2 line in the memory ME2 (43, 44), and sets the 5 × 3 pixel centered on the specified target pixel.
A rectangular block is defined as a second window Mat2 ((b) in FIG. 20), and one of all pixels in the second window Mat2 is
It is checked whether all the next feature data Cd1 are primary non-isolated points “0” (44). If so, the secondary feature data Cd2 = “0” indicating the secondary non-isolated point is converted to y = 3 of ME3. Is written to the x address addressed to the pixel of interest (46; (d) in FIG. 20). However, if at least one pixel in the second window Mat2 is also a primary isolated point candidate “1”, the secondary feature data Cd2 = “1” indicating the secondary isolated point candidate is assigned to the x-address addressed to the target pixel of y = 3 of ME3. (45; FIG. 20 (c)).

The IPU performs the above process by sequentially designating each image data addressed to each pixel of one line of y = 2 of ME2 as a pixel of interest (43 to 48). When the processing is completed for one line, the secondary feature data Cd2 addressed to each pixel of one line of y = 3 of ME1 has been written to y = 3 of the memory ME3.

Here, the IPU is set to y = 2 on the memory ME3.
A target pixel is specified on the line (49, 50), and a 5 × 3 rectangular block centered on the specified target pixel is set as a third window Mat3 ((b) in FIG. 21), and all pixels in the third window Mat3 are set. Are all 1
It is checked whether it is the next isolated point candidate "1" (50), and if so, the tertiary feature data Cd3 indicating the tertiary isolated point candidate
= “1” is written to the x address addressed to the target pixel of y = 3 of ME 4 (52; (d) of FIG. 21). However, if even one pixel in the third window Mat3 is the primary non-isolated point “0”, the tertiary feature data Cd3 = “0” indicating the tertiary non-isolated point.
Is written to the x address addressed to the target pixel of y = 3 of ME4 (53; (c) of FIG. 21).

The IPU performs the above processing by sequentially designating the image data addressed to each pixel of one line of y = 2 of the ME 3 as the pixel of interest (49 to 54). When the processing is completed for one line, the tertiary feature data Cd3 addressed to each pixel of one line of y = 3 of ME1 has been written to y = 3 of the memory ME4.

Here, the IPU corresponds to y = 2 on the memory ME4.
A target pixel is designated on the line (55, 56), and it is checked whether the tertiary feature data Cd3 of the target pixel is a tertiary isolated point candidate "1" (56). A 3 × 3 rectangular block centered on the fourth window Mat
4 (FIG. 22B), if all of the tertiary feature data Cd3 of the edge pixel (FIG. 22C) is a tertiary non-isolated point "0", the target pixel is set to an isolated point ( Fourth-order isolated point candidate:
It is determined that Cd4 = “1” (FIG. 22 (d)), and y = of the memory ME5 (each of three sets for R, G, and B).
The image data of all the pixels of the 5 × 5 pixel matrix centering on the target pixel on the three lines is rewritten to the background level data (57, 58). Tertiary feature data Cd3 of the pixel of interest
Is a tertiary non-isolated point "0", and when at least one of the edge pixels of the fourth window Mat4 is a tertiary isolated point candidate (Cd3 = "1") ((e) in FIG. 22). Does not rewrite the image data of ME5.

The IPU performs the above processing by sequentially designating each of the tertiary feature data Cd3 to each pixel of one line of y = 2 of ME4 as a pixel of interest (55-60). When the processing is completed for one line, the image data of the isolated point among the image data of y = 1 to y = 5 of ME5 has been rewritten to the isolated point erasing level. In the present embodiment, when the target pixel is determined to be an isolated point, 5 × 5
Since the image data of all the pixels in the pixel matrix is rewritten to the isolated point erasing level, the image data of the lines from y = 2 to y = 5 on the ME 5 can be converted by the isolated point removal processing that updates the subsequent lines. There is. Therefore, as described below, the image data of the line of y = 1 of the ME 5 is output to the scanner γ-conversion 114 and the separation generation 113 as the data obtained by removing the isolated points.

In another embodiment in which when the pixel of interest is determined to be an isolated point, the image data of all pixels in the 3 × 3 pixel matrix centered on the pixel is rewritten to the isolated point erasing level, the ME 5 is a 5-line memory. And the target pixel is y =
When the removal of the isolated point of one line is completed, the image data of the y = 1 line is output to the scanner γ conversion 114 and the separation generation 113. In another embodiment in which only the image data of the pixel of interest is rewritten to the isolated point erasing level when the pixel of interest is determined to be an isolated point, the ME 5 is a 4-line memory, and the pixel of interest is set to y = 1, and When the removal of the isolated points of one line is completed, the image data of the y = 1 line is output to the scanner γ conversion 114 and the separation generation 113.

Referring to FIG. In this embodiment, the IP
If j ≧ 5, it is possible to output valid image data for one line from which y = 1 of the output memory ME5 with isolated points removed, so that the memory ME5 (for R, G and B)
R, G, B image data of y = 1 (for a total of three sets) are output to the scanner γ conversion 114 and the separation / generation unit 113 (6).
1, 62).

Next, the IPU shifts the data in the memories ME1 to ME5 by one line in the -y direction (63).
Waits for the scanner 200 to send one line of image data, and then sends the G image data to the fifth line of the memory ME1 and the RGB image data to the sixth line of the ME5.
Write to the line (65). Then, the input image data line No. j is incremented by one (66), and the above-described isolated point removal processing is performed in the same manner. When the scanner 200 finishes sending the image data of the entire surface of one document, the IPU stores the data of the last line, from which the isolated points have been removed, in the memory ME5.
= 1, and until it is sent to the scanner γ conversion 114 and the separation generation 113, the above-described steps 62 and 63 are performed.
Is repeatedly executed.

[0163]

(1) The image data of an isolated point is converted into a low density value (smoothed data) by smoothing the image data to emphasize the density difference from halftone dots and other effective images, and Since it is confirmed that there is no high density equal to or larger than the threshold value in the spread pixel group (corresponding to the background area), the image data of the target pixel at the center is changed to image data representing the isolated point elimination level value.
A highly accurate isolated point removal process is realized, and higher-quality image output can be performed. The possibility that an effective image is erroneously detected and removed as an isolated point is reduced.

(2) The second determining means generates a secondary isolated point candidate in which the primary isolated point candidate pixel is enlarged within the range of the second window (Mat2) centered on the primary isolated point candidate pixel. The primary isolated point candidates dispersed by distance become a group area, and isolated points leaked in the primary isolated point candidate determination are also absorbed by the group area, so that the reliability of isolated point detection increases. The third determining means generates a tertiary non-isolated point candidate in which a secondary non-isolated point pixel not determined as a secondary isolated point candidate is enlarged to all pixels of a third window (Mat3) centered on the secondary non-isolated point pixel. Therefore, the edge of the area of the secondary isolated point candidate spread to the non-isolated point is narrowed, and the possibility that the significant image or the background is processed as the isolated point is low, and the reliability of the isolated point detection is further improved.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing an outline of a mechanism of a digital multifunction color copier incorporating an image processing apparatus according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing an outline of an electric system of the copying machine shown in FIG.

FIG. 3 is a block diagram illustrating a functional configuration of an image processing unit 20 illustrated in FIG. 2;

FIG. 4 is a flowchart showing an outline of a processing flow of an isolated point removal 33 shown in FIG. 3;

FIG. 5 is a flowchart showing a part of a specific example of a processing flow of an isolated point removal 33 shown in FIG. 3;

6 is a flowchart showing the remaining part of a specific example of the processing flow of the isolated point removal 33 shown in FIG.

7 (a), (b) and (c) respectively show a five-line input image memory MEa and three lines 2 assigned to the input / output buffer memory of the isolated point removal 33 shown in FIG.
Value memory MEb and 5-line output image memory ME
3C is a plan view schematically illustrating a two-dimensional distribution of cells (small cells) storing image data addressed to one pixel.

FIG. 8A is a plan view showing a process of specifying image data addressed to each pixel of a 5 × 5 pixel matrix from original image data using a 5-line input image memory MEa;
(B) is a plan view showing the distribution of filter coefficients used for calculating the smoothed data to a 5 × 5 pixel matrix, and (c) is an image on a document and 5 cut out therefrom.
FIG. 4 is a plan view showing images OMxa1 and 2 of a 5 × 5 pixel matrix and smoothed images PMxa1 and 2 of these 5 × 5 pixel matrices.

FIG. 9A shows whether a target pixel indicated by an asterisk (*) is a pixel representing an effective image component from a smoothed image (binary smoothed data) using a three-line binary memory MEb (noise). FIG. 4B is a plan view showing a process of specifying a 9 × 3 pixel matrix area for determining whether the pixel is a dot or a background. FIG. Judgment result of distribution and effective image component (NO)
FIG. 3C is a plan view showing the smoothed data distribution, in which the input image data is represented by white or the background level when the pixel of interest marked * is determined to be an isolated point or background (YES). FIG. 3 is a plan view showing a 3 × 3 pixel area to be rewritten.

FIG. 10 is a front view showing an overview of a multifunction full-color copying machine according to a second embodiment of the present invention.

11 is an enlarged vertical sectional view schematically showing an image forming mechanism of the printer 100 shown in FIG.

12 is a block diagram showing a system configuration of image data processing of the copying machine shown in FIG.

13 is a block diagram illustrating an outline of a functional configuration of the image data processing device IPU illustrated in FIG. 12;

14 is an image data processing device IPU shown in FIG.
5 is a flowchart showing an outline of image data processing in isolated point removal 118 of FIG.

15A is a plan view schematically showing image data storage sections corresponding to pixels in the input image memory ME1 used for setting the window Mat1 for the input image data in the isolated point removal 118 by small cells, and FIG. ), (C) and (d) respectively show pixel-wise feature data storage sections of the intermediate buffer memory for storing binary feature data Cd1, Cd2 and Cd3 generated for isolated point determination with small squares. (E) Isolated point removal 1
FIG. 19 is a plan view schematically showing image data storage sections corresponding to pixels in an output image memory ME5 for temporarily storing image data from which isolated points have been removed at 18 by small cells.

16 is an image data processing device IPU shown in FIG.
5 is a flowchart showing in detail a part of the content of the image data processing in the isolated point removal 118 of FIG.

17 is an image data processing device IPU shown in FIG.
7 is a flowchart showing in detail another part of the content of the image data processing in the isolated point removal 118.

FIG. 18 is an image data processing device IPU shown in FIG.
7 is a flowchart showing in detail the remaining part of the content of the image data processing in the isolated point removal 118.

FIG. 19A is a diagram illustrating an example of a 5-by-5 rectangular block of a 5-by-5 pixel matrix area, which is obtained by the image data processing apparatus IPU shown in FIG. FIG. 2B is a plan view showing a process of specifying image data addressed to each pixel; FIG. 2B is a plan view showing an identification code addressed to each pixel of a 5 × 5 rectangular block;
FIG. 4 is a plan view showing edge pixels of a 5-by-5 rectangular block centered on a target pixel by dot-filling; (D) is a plan view showing the density value of each pixel of the 5-by-5 rectangular block.

20A shows primary characteristic data Cd1, which is generated by the image data processing apparatus IPU shown in FIG. 13 and is written as a primary isolated point candidate in the intermediate buffer memory ME2.
A plan view showing a process of specifying characteristic data Cd1 addressed to each pixel of a 5 × 3 rectangular block in a 5 × 3 pixel matrix area;
(B) is a plan view showing an identification code addressed to each pixel of the 5 × 3 rectangular block, and (c) is a primary isolated point candidate in any of the primary characteristic data Cd1 of the 5 × 3 rectangular block. FIG. 5D is a plan view of a 5 × 3 rectangular block showing a process of giving “1” to the target pixel at the center of the block when “1” means that the block is a secondary isolated point candidate. ) Is 5
If all the primary characteristic data Cd1 of the three rectangular blocks are “0”, which means that they are primary non-isolated points, a process of giving “0” that means that the pixel of interest is a secondary non-isolated point FIG.

FIG. 21 (a) is a diagram showing a case where the image data processing device IPU shown in FIG. 13 generates secondary isolated point candidates written in the intermediate buffer memory ME3 and indicates whether or not the secondary characteristic data Cd2 is a secondary isolated point candidate.
FIG. 4B is a plan view showing a process of specifying the secondary characteristic data Cd2 addressed to each pixel of the 5 × 3 rectangular block in the 5 × 3 pixel matrix area, and FIG. 12B shows an identification code addressed to each pixel of the 5 × 3 rectangular block; FIG. 3C is a plan view of FIG.
If any of the next characteristic data Cd2 has “0” indicating that it is a secondary non-isolated point, “0” indicating that it is a tertiary non-isolated point is given to the target pixel at the center of the block. A plan view of a 5 × 3 rectangular block showing the process, and FIG. 9 (d) is noted as “1” meaning that all of the secondary characteristic data Cd2 of the 5 × 3 rectangular block are secondary isolated point candidates. FIG. 13 is a plan view showing a process of giving “1” to a pixel, which is a tertiary isolated point candidate.

FIG. 22 (a) is a diagram illustrating a case where the image data processing device IPU shown in FIG. 13 generates the tertiary isolated point candidate C3 written in the intermediate buffer memory ME4 and indicating whether or not it is a tertiary isolated point candidate.
FIG. 4B is a plan view showing a process of specifying the tertiary characteristic data Cd3 addressed to each pixel of the 3 × 3 rectangular block in the 3 × 3 pixel matrix area, and FIG. 12B shows an identification code addressed to each pixel of the 3 × 3 rectangular block; FIG. 4C is a plan view showing the edge pixels of the 3 × 3 rectangular block centered on the target pixel by dot-filling. (D) is a plan view showing the distribution of the tertiary characteristic data Cd3 of the edge pixel in which the target pixel is finally determined as a (fourth) non-isolated point. (E), the tertiary characteristic data Cd3 of any edge pixel is “1” representing a tertiary isolated point candidate, and the pixel of interest is finally determined to be a (fourth) isolated point (candidate). It is a top view showing distribution of tertiary characteristic data Cd3 of a pixel.

[Explanation of symbols]

200: Document scanner 400: Printer VDC: Video data control IMAC: Image memory access control FCU: FAX transmission / reception unit SBU: Sensor board unit PN: Public line 205: Exposure lamp ADF: Automatic document feeder 90: Motherboard PC: Personal computer PBX: Exchanger 102: Optical writing unit 103, 104: Paper cassette 105: Registration roller pair 106: Transfer belt unit 107: Fixing unit 108: Discharge tray 110M, 110C, 110Y, 110K: Photoconductor unit 111M, 111C , 111Y, 111K: photosensitive drums 120M, 120C, 120Y, 120K: developing unit 160: transfer and conveyance belt

Claims (6)

[Claims] 1. Smoothed data representing the sum of a part of the density of each pixel of a pixel group based on image data of a plurality of A peripheral pixels distributed two-dimensionally around the pixel of interest and the periphery thereof is addressed to the pixel of interest. And smoothing means for executing each of the pixels of the two-dimensional distribution as a pixel of interest; and a density represented by the smoothed data of the pixel of interest and a plurality of B peripheral pixels distributed two-dimensionally around the pixel of interest. An image processing apparatus comprising: a data conversion unit that sets the image data addressed to the target pixel to an isolated point erasure level when the value is less than the target pixel, and sequentially changes the target pixel. 2. An image data of an edge pixel of an image represented by input image data, wherein a pixel matrix area including a pixel of interest and its surrounding pixels and including a plurality of pixels in both main and sub scanning directions is used as a first window. The level is compared with a threshold to generate primary characteristic data indicating whether the target pixel is a primary isolated point candidate or a primary non-isolated point surrounded by low-density pixels. A first determination means, which is executed as a first window; a pixel matrix area including a target pixel and its surrounding pixels and including a plurality of pixels in both the main and sub-scanning directions is defined as a second window, and a primary isolated point candidate of primary characteristic data therein is set as a second window. , Second
Second determining means for generating secondary characteristic data extended also to a pixel of interest in the window and executing this as each pixel of a two-dimensional distribution as a pixel of interest; main and sub scanning directions including the pixel of interest and its surrounding pixels A pixel matrix area composed of a plurality of pixels is used as a third window, and tertiary characteristic data in which the secondary non-isolated point of the secondary characteristic data is extended to the pixel of interest in the third window is generated. Third determining means for executing each pixel of the two-dimensional distribution as a target pixel; and
An image processing device comprising: data conversion means for converting image data of a pixel which has become an isolated point candidate after the next characteristic data to an isolated point erasing level. 3. If each pixel of the two-dimensional distribution is a pixel of interest and the pixel of interest is a tertiary isolated point candidate represented by tertiary characteristic data and is separated from other tertiary isolated point candidate pixels, the pixel of interest is 4. a fourth determining unit that determines that the pixel is an isolated point, wherein the data conversion unit rewrites image data of a pixel determined as an isolated point by the fourth determining unit to a background erasure level;
An image processing apparatus according to claim 1. 4. The method according to claim 1, wherein when the pixel of interest in the first window is equal to or greater than a predetermined value, the image data level of an edge pixel of the first window is compared with a threshold value to determine whether the pixel of interest is a low density pixel. Primary characteristic data indicating whether the enclosed primary isolated point candidate or primary non-isolated point is generated, and when the pixel of interest in the first window is less than a predetermined value, the primary non-isolated without performing the above comparison. The image processing apparatus according to claim 2, wherein primary characteristic data representing points is generated. 5. A method according to claim 1, wherein said first determining means generates primary characteristic data representing a primary isolated point candidate addressed to a pixel of interest when all pixels at an edge of said first window are low-density pixels less than a threshold value.
4. A primary characteristic data representing a primary non-isolated point is generated when any pixel at the edge is equal to or larger than a threshold value.
Or the image processing device according to 4. 6. An image processing apparatus according to claim 1; means for converting image data processed by said image processing apparatus into image data for forming a visible image by a printer; A printer that forms an electrostatic latent image according to image data for image formation, develops the electrostatic latent image with a developing device, and transfers the latent image to transfer paper directly or via an intermediate transfer medium;
An image forming apparatus comprising: