JP2003333336A - Image processing apparatus, image processing method, and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image processing apparatus with a simple configuration for performing thinning processing with high accuracy and outputting an image with high image quality. <P>SOLUTION: A rectangular block forming section 41 forms an optional rectangular block 53 including a target pixel 52 of received image data. A thinning discrimination processing section 42 compares the density of the target pixel 52 with a predetermined threshold value TH, calculates a density average of each column of the rectangular block 53 when the density of the target pixel 52 is greater than the threshold value TH, compares the density average with that of an adjacent column, and discriminates the target pixel 52 as an object of the thinning processing when the density average of each column is sequentially decreasing or increasing. A thinning processing section 4 applies thinning processing to the target pixel 52 being a discriminated thinning processing object so as to prevent the image quality from being deteriorated due to excessive correction. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus, an image processing method, and an image forming apparatus for extracting vertical thick lines in a digital image.

[0002]

[Prior art]

2. Description of the Related Art Generally, in a digital copying machine, a facsimile, a scanner or the like, an image of a read document has a character portion line which is thicker than that of the original document. As shown in FIG. 5, the input and black-and-white binarized input image is subjected to thinning processing by repeating matching with a matrix-shaped mask pattern prepared in advance to obtain a neat image close to the original document. I am trying. Also, OC
The thinning process is effective as a pre-process for increasing the recognition rate in R (Optical Character Reader).

[0003]

However, when the read image is subjected to thinning processing by pattern matching, it is necessary to prepare more patterns as the size of the matrix becomes larger, and the processing speed also decreases. Therefore, there is a disadvantage that hardware that enables high-speed processing is required.

Further, as shown in FIG. 7, when an original image 62 obtained by reading an original 61 having a vertical line image 60 is subjected to density correction and thinning processing is performed to obtain a thinned image 63,
In the figure, row [3] is the part that requires thinning processing.
To row [6] range and row [10] to row [13] range. If the correction process is performed for the range from row [7] to row [9], the correction becomes excessive and the image quality deteriorates. Will end up. Therefore, it is desired that the regions that require the thinning process be located at both ends of the vertical line image.

The present invention provides an image processing apparatus, an image processing method, and an image forming apparatus which are capable of outputting such a high-quality image by improving the above drawbacks and performing a highly accurate thinning process with a simple circuit structure. The purpose is to do.

[0006]

An image processing apparatus according to the present invention has rectangular block forming means, thinning determination processing means and thinning processing means, and the rectangular block forming means is
An arbitrary rectangular block including the target pixel for the input image data is formed, the thinning determination processing means compares the densities of the target pixels with a predetermined threshold value, and when the density of the target pixel is larger than the threshold value, The density average value of each column of the rectangular block formed by the rectangular block forming means is calculated and compared with the density average value of the adjacent column for each calculated column, and the density average value of each column is gradually decreased or increased. When the target pixel is determined to be a candidate for thinning processing, the thinning processing means performs thinning processing on the target pixel of the thinning processing candidate determined by the thinning determination processing means, and To prevent the image quality from deteriorating.

Further, the threshold value to be compared with the density of the pixel of interest is arbitrarily changed according to the type of the document to prevent erroneous determination.

In the image processing method according to the present invention, an arbitrary rectangular block including a target pixel for the input image data is formed, the densities of the target pixels are compared with a predetermined threshold value, and the density of the target pixel is the threshold value. When greater than
The density average value of each column of the rectangular block is calculated and compared with the density average value of the adjacent column for each calculated column, and when the density average value of each column is gradually decreasing or increasing, the pixel of interest Is determined as a candidate for thinning processing, and the thinning processing is performed on the pixel of interest of the determined candidate for thinning processing.

An image forming apparatus of the present invention is characterized by including the image processing apparatus and stably outputting a high quality image.

[0010]

1 is a block diagram of a digital copying machine according to the present invention. As shown in the figure, the digital copying machine 1 has a copying machine main body 2, an automatic document feeder (hereinafter referred to as ADF) 3, and an automatic sorting device 4. The copying machine main body 2 has a document reading unit 5, a writing unit 6, an engine unit 7, and a paper feeding unit 8. The document reading unit 5 includes a carriage 9 having a light source and a plurality of mirrors, a lens 10 and a CC.
It has a D11 and a buffer 12, and scans and reads the document sent by the ADF3. The writing unit 6 has a laser light source, a polygon mirror, etc., and emits a laser beam 13 containing image information to the engine unit 7. The engine unit 7 includes an image forming unit 14, a primary transfer unit 15, a secondary transfer unit 16 and a fixing unit 17. The image forming unit 14 includes an electrification charger 19 arranged around the photoconductor 18 and an irradiation portion of the laser beam 13 from the writing unit 5, and cyan (C), magenta (M), yellow (Y), black (K). ), A rotary type color developing unit 20 and a drum cleaning unit 21. The electrostatic latent image is formed by the laser beam 13 on the photoconductor 18 charged by the charging charger 19 and the formed electrostatic latent image is colored. Development unit 2
Visualize at 0 to form a toner image. The primary transfer unit 15 includes an intermediate transfer belt 22, a primary transfer section 23, a tension roller 24, a secondary transfer roller 25, and a cleaning section 2.
6 and a reference position sensor 27, the toner image formed on the photoconductor 18 is primarily transferred to the intermediate transfer belt 22. The intermediate transfer belt 22 is formed to be larger than A3 which is the maximum transfer paper size in the digital copying machine 1. When the transfer paper to be used is A4 size or smaller, it must hold toner images for two surfaces. You can The intermediate transfer belt 22 is separated from the surface of the photosensitive member 18 by a contacting / separating mechanism (not shown) except when the toner image on the photosensitive member 18 is primarily transferred, and the photosensitive member 18 is only transferred when the image is primarily transferred to the intermediate transfer belt 22. Pressed against the surface. Secondary transfer unit 16
Secondarily transfers the toner image transferred onto the intermediate transfer belt 22 onto the recording paper. The fixing unit 17 fixes the toner image transferred onto the recording paper with heat and pressure. The paper feeding unit 8 has a plurality of paper feeding cassettes 28 a to 28 c and a manual tray 29, and sends the recording paper to the secondary transfer unit 16.

The ADF 3 sends the document to be read to the document reading unit 5 and collects the document read by the document reading unit 5. The automatic sorting device 4 has a plurality of sorting bins 30a.
The recording paper on which an image is formed is sorted and discharged.

When the image forming cycle of the original read by the original reading unit 5 in the digital copying machine 1 starts, if the image to be formed is one color, a toner image is formed on the photoconductor 18 by the image data of the read original. Then, the formed toner image is primarily transferred to the intermediate transfer belt 22. The secondary transfer unit 16 secondarily transfers the toner image onto the recording paper fed in conformity with the tip of the toner image transferred onto the intermediate transfer belt 22. The recording paper on which the toner image is transferred is the fixing unit 1
It is sent to No. 7 and heated and pressurized to be fixed. The recording paper on which the toner image is fixed is discharged to the automatic sorting device 4. Also,
The toner remaining on the intermediate transfer belt 22 is collected by the cleaning unit 26.

When the image to be formed has two or more colors, the reference mark provided on the intermediate transfer belt 22 is used as the reference position sensor 27.
The document is read by the document reading unit 5 on the basis of the detection by the above, the read image data is stored in the image memory, and the toner image of the first color is formed on the photoconductor 18 by the image data, and the photoconductor 18 is formed. The formed toner image is primarily transferred onto the intermediate transfer belt 22. Subsequently, a second-color toner image is formed on the photoconductor 18 by the image data stored in the image memory, and the toner image formed on the photoconductor 18 is primarily transferred to the intermediate transfer belt 22. Image formation on the photoconductor 18 and primary transfer on the intermediate transfer belt 22 are repeated for each color. That is, the intermediate transfer belt 22 is rotated twice when forming a two-color image, and the intermediate transfer belt 22 is rotated four times when forming a full-color image.
The toner image formed on the photoconductor 18 is primary-transferred to the intermediate transfer belt 22 for each rotation, and the images of the respective colors are superposed without displacement. The toner image of a predetermined color is transferred onto the intermediate transfer belt 2
2 is transferred onto the intermediate transfer belt 22, the toner image is transferred onto the recording paper fed in line with the front end of the toner image transferred onto the intermediate transfer belt 22.
Next transfer is performed, and the fixing unit 17 heats and pressurizes to fix.

Further, in the two-sided chamfering mode in which the toner images of the vertically oriented original image of the standard size, eg, A4 size, are simultaneously transferred onto the intermediate transfer belt 22, the toner image on the first surface is transferred onto the intermediate transfer belt 22. After the transfer, the toner image on the second surface is transferred to the intermediate transfer belt 22 at a predetermined timing determined by the circumference of the intermediate transfer belt 22 and the document size. When forming a full-color image, the intermediate transfer belt 22 is rotated four times, and the toner image formed on the photoconductor 18 is primarily transferred to the intermediate transfer belt 22 for each rotation, and the image of each color is not displaced. Overlaid on. After the toner image of a predetermined color is transferred to the intermediate transfer belt 22, the toner image is secondarily transferred to the recording paper fed in accordance with the leading end of each toner image transferred to the intermediate transfer belt 22, and the fixing unit 17
Then, the two recording papers on which the image is formed are continuously discharged by heating, pressurizing and fixing. In this way, the image forming efficiency can be improved.

The preprocessing section 40 for processing the image read by the document reading unit 5 of the digital copying machine 1 has a configuration shown in FIG.
As shown in the block diagram of FIG. 4, the rectangular block forming unit 41, the thinning determination unit 42, the thinning processing unit 43, and the image output unit 4
Have 4. As shown in FIG. 3, the rectangular block forming unit 41 extracts the image data 51 of, for example, 5 lines from the read image 50, and selects the pixel 52 of interest which is about to be determined whether thinning is necessary. A 5 × 5 rectangular block (window) 53 including, for example, is created. The rectangular block 53 created here is not limited to the 5 × 5 block, and the size and shape may be other than that. The thinning determination processing unit 42 determines whether or not thinning is required by the rectangular block 43 created by the rectangular block forming unit 41. The thinning processing unit 43 performs thinning processing according to the determination result of the thinning determination processing unit 42. The image output unit 44 outputs the image data subjected to the thinning processing.

The operation when the image read by the document reading unit 5 is processed by the preprocessing section 40 will be described with reference to the flowchart of FIG.

When the image of the original is input to the reading preprocessing section 40 by the original reading unit 5 (step S1), the rectangular block forming section 41, as shown in FIG. The image data 51 is extracted to create a 5 × 5 rectangular block 53 including the target pixel 52 (step S2). The thinning determination processing unit 42 compares the pixel value of the target pixel 52 of the rectangular block 43 created by the rectangular block formation unit 41 with a preset threshold TH, and when the pixel value of the target pixel 52 is larger than the threshold TH,
The determination flag is set to “YES” as a thinning process candidate, and the determination flags are set to “NO” in other cases. The threshold TH used for this determination can be arbitrarily changed according to the type of the original to be read such as a dark original or a light original, and the user can directly change the threshold TH to prevent erroneous determination and obtain a desired image. To do so. Then, the determination flag is "Y
In the case of “ES”, the density average value ave [n] of pixel values of the first column to the fifth column of the 5 × 5 rectangular block 53, (n =
1 to 5) are calculated (step S4), and the calculated average density values ave [n] of the respective columns are compared. When the following conditions are satisfied as a result of this comparison, the target pixel 52 sets the determination flag to “YES” as a candidate for the thinning process, and otherwise sets the determination flag to “NO” (steps S5 and S6). Judgment condition 1; ave [1]> ave [2]> ave [3]> ave [4]> ave [5] Judgment condition 2; ave [1] <ave [2] <ave [3] <ave [4 ] <Ave [5]

FIG. 5A shows an example corresponding to the judgment condition 1. The density average value of each column decreases to the lower right, and the right end of the vertical line image is detected, and FIG. 5B shows An example corresponding to the determination condition 2 is shown, in which the density average value of each column decreases to the lower left, and the left end of the vertical line image is detected. Further, FIG. 6 shows an example in which the judgment conditions 1 and 2 are not satisfied, and the density average value of each column changes into a mountain shape, and shows the central portion of the vertical line image. By thus determining the candidates for the thinning process, the central portion of the vertical line image shown in FIG. 6 can be excluded from the thinning process, and it is possible to prevent deterioration of the image quality due to excessive correction. .

The thinning processing unit 43 is a thinning determination processing unit 42.
The thinning processing is performed by subtracting a constant value from the pixel value of the target pixel 52 of the thinning processing candidate determined in step S3, or by multiplying the pixel value of the target pixel 52 by a constant value such as pixel value × 0.75. (Step S7). This processing is performed for all the read images (steps S8, S2 to S7), and the thinning processing candidate outputs the thinning processing image data from the image output unit 44 and corresponds to the thinning processing candidate. The input pixel data is output as it is to the portion that does not.

[0020]

As described above, the present invention forms an arbitrary rectangular block including a target pixel for input image data, compares the densities of the target pixels with a predetermined threshold value, and determines the density of the target pixel. Is larger than a threshold value, the density average value of each column of the rectangular block is calculated, and each calculated column is compared with the density average value of the adjacent column, and the density average value of each column is gradually decreased or increased. When the target pixel is determined to be a candidate for thinning processing and the target pixel of the determined candidate for thinning processing is subjected to the thinning processing, the thinning processing with high accuracy is performed with a simple configuration. It is possible to prevent the deterioration of the image quality due to excessive correction and to output a higher quality image.

Further, by comparing the density average value of adjacent columns of each rectangular block to determine a candidate for thinning processing, processing utilizing the correlation between adjacent image data can be performed. , It is possible to stably determine candidates for thinning processing.

Further, the threshold value to be compared with the density of the pixel of interest is arbitrarily changed according to the type of the original document to prevent misjudgment, perform thinning processing according to the characteristics of the original image, and output a high quality image. be able to.

Further, by using this image processing apparatus, a high quality image can be stably output from the image forming apparatus.

[Brief description of drawings]

FIG. 1 is a block diagram of a digital copying machine of the present invention.

FIG. 2 is a block diagram showing a configuration of a pre-processing unit that processes a read image.

FIG. 3 is a schematic diagram showing a rectangular block.

FIG. 4 is a flowchart showing a determination process of a thinning process candidate.

FIG. 5 is a schematic diagram showing a change in density average value of each row of candidates for thinning processing.

FIG. 6 is a schematic diagram showing changes in the density average value of each column that does not correspond to a candidate for thinning processing.

FIG. 7 is a schematic diagram showing an original image, a thinning-processed image, and a density change in each column.

[Explanation of symbols]

1; digital copier, 2; copier body, 3; ADF,
4; automatic sorting device, 5; original reading unit, 6; writing unit, 7; engine section, 8; paper feeding unit, 40;
Pre-processing unit, 41; rectangular block forming unit, 42; thinning determination processing unit, 43; thinning processing unit, 44; image output unit. Four
Have 4.

Claims (4)

[Claims] 1. A rectangular block forming means, a thinning determination processing means, and a thinning processing means, wherein the rectangular block forming means forms an arbitrary rectangular block including a target pixel for input image data, The conversion determination processing means compares the densities of the target pixel with a predetermined threshold value, and when the density of the target pixel is higher than the threshold value, calculates the average density value of each column of the rectangular block formed by the rectangular block forming means. Then, each calculated column is compared with the density average value of the adjacent column, and when the density average value of each column is gradually decreasing or increasing, the pixel of interest is determined as a candidate for thinning processing, and thinning is performed. An image processing apparatus, wherein the processing means performs the thinning processing on the target pixel of the thinning processing candidate determined by the thinning determination processing means. 2. The image processing apparatus according to claim 1, wherein the threshold value to be compared with the density of the pixel of interest can be arbitrarily changed according to the type of document. 3. An arbitrary rectangular block including a pixel of interest for the input image data is formed, the density of the pixel of interest is compared with a predetermined threshold, and when the density of the pixel of interest is larger than the threshold, the rectangle The density average value of each column of the block is calculated and compared with the density average value of the adjacent column for each calculated column, and when the density average value of each column is gradually decreasing or increasing, the pixel of interest is indicated by a thin line. Determined as a candidate for
An image processing method, wherein thinning processing is performed on a target pixel of interest that has been determined as a thinning processing candidate. 4. An image forming apparatus comprising the image processing apparatus according to claim 1.