JP2001325598A - Image processor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image processor which can suppress the increase in the processing time of image data even if the number of patterns on a recording form is large when the center position of the patterns on the recording paper is found. SOLUTION: Each of pixels (i) is thinned out and selected for every 256 horizontal scanning line and the density of the horizontal scanning lines of the selected horizontal scanning lines is found to generate a histogram showing the density distribution of all the horizontal scanning lines, and each of pixels is thinned out and selected for every 256 vertical scanning line (j) and the density of the vertical scanning lines of the selected pixels is found to generate a histogram showing the density distribution of all the vertical scanning lines. The two histograms which are thus generated are used to find the center position of the patterns.

Description

DETAILED DESCRIPTION OF THE INVENTION

[Detailed Description of the Invention]

[0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus for determining a center position of a pattern included in an image.

[0003]

2. Description of the Related Art As is well known, in a color image forming apparatus, respective toner images of yellow, magenta, cyan, black, etc. are formed on respective photosensitive drums, and these toner images are transferred onto a recording paper and superposed. By fixing together,
A color image is formed on recording paper. Therefore, if the toner images of the respective colors are not superimposed satisfactorily, color misregistration occurs in the color image and a desired color cannot be reproduced, resulting in a very unsightly color image.

Therefore, a color misregistration amount determination pattern for measuring the color misregistration amount is formed on a recording sheet or a carrier of the recording sheet, and an image of the formed color misregistration amount determination pattern is inspected. Is measured. In this inspection, the oldest was to visually inspect an image recorded on a recording sheet using a high-magnification loupe with a scale or the like. Alternatively, the amount of color misregistration has been mechanically measured using a special measuring device. However, there is a problem that the cost for adjusting the color misregistration is increased because equipment dedicated for inspection is required and measurement requires a long time.

[0005] In some cases, an image forming apparatus is provided with a color shift inspection means. However, in this case, an image reading means for reading the color shift amount determination pattern on the recording paper is required. If the image reading device is specially provided only for this inspection, the cost of the image forming apparatus itself increases, so it is assumed that the image forming device is originally provided with the image reading device for reading the original. Become. The color misregistration amount determination pattern is read using this image reading means, the color misregistration amount is measured, and the registration of the image of each color is adjusted according to the color misregistration amount.

For example, in Japanese Patent Application Laid-Open No. Hei 3-139996, a test chart is formed on recording paper by a plurality of image forming heads, the test chart is read by image reading means, and the test chart is read based on the read test chart. The amount of color misregistration is measured, and the recording timing of each image forming head is corrected in accordance with the amount of color misregistration, thereby eliminating the inaccuracy of the visual inspection and the complexity of the operation.

[0007]

However, when the test chart formed on the recording paper is read by the image reading means as in the above-mentioned prior art, the rotation of the photosensitive drum and the linearity of the LSU are affected. Then, the color shift amount cannot be measured accurately. For this reason, a test chart containing a larger number of patterns is applied, and the amount of color misregistration is measured and averaged for each of these patterns, thereby suppressing measurement errors. However, in this case, there is a problem that the processing amount of the image data increases, and even if the size of the image read by the image reading unit is limited, the access time to the memory and the calculation time associated with the processing of the image data are greatly reduced. Unavoidable increase cannot be avoided. Specifically, in measuring the amount of color misregistration, a histogram indicating the density distribution is created for each pattern, and the peak position of the density is determined as the center position of the pattern for each histogram of each pattern (see, for example, Japanese Patent Application Laid-open No. -95474), and it took a long time to create histograms of these patterns.

In the method of detecting the center position of a pattern on the basis of a histogram indicating the density distribution of the pattern, if the recording paper itself has a slight color or the print quality of the pattern is poor, the density distribution may be reduced. Because of the influence, the detection accuracy of the center position of the pattern is deteriorated.

In view of the above, the present invention has been made in view of the above-described conventional problem. In determining the center position of a pattern on a recording sheet, the present invention is applied to a case where the number of patterns on the recording sheet is large.
An object of the present invention is to provide an image processing apparatus capable of suppressing an increase in processing time of image data.

Further, according to the present invention, when the center position of a pattern is obtained based on a histogram indicating the density distribution of the pattern, even if the recording paper itself has a slight color or the print quality of the pattern is poor, the pattern It is an object of the present invention to provide an image processing apparatus capable of detecting the center position of the image with high accuracy.

[0011]

In order to solve the above-mentioned problems, the present invention processes an image composed of a plurality of pixels arranged in a main scanning direction and a sub-scanning direction, and processes a center of a pattern included in the image. In the image processing device for determining the position, for each of a plurality of main scanning lines along the main scanning direction of the image, each pixel on the main scanning line is thinned out and selected, and then the density of the main scanning line is determined. A histogram indicating the density distribution of the image is created, and for each of a plurality of sub-scanning lines along the sub-scanning direction of the image, the density of the sub-scanning line is determined after thinning and selecting each pixel on the sub-scanning line, Histogram creation means for creating a histogram indicating the density distribution of each sub-scanning line, histogram indicating the density distribution of each main scanning line, and histogram indicating the density distribution of each sub-scanning line Based on and a center position calculation means for calculating the center position of the pattern.

According to the present invention having such a configuration, the density of each main scanning line is determined after thinning out and selecting each pixel on the main scanning line for each main scanning line, and the density of each main scanning line is determined. A histogram showing the distribution is created, and the density of the sub-scanning line is obtained after thinning out and selecting each pixel on the sub-scanning line for each sub-scanning line, and a histogram showing the density distribution of each sub-scanning line is obtained. Creating. Therefore, it is possible to reduce the amount of calculation and the time required to create a histogram by the amount of each thinned pixel. The two histograms thus created are used to determine the center position of the pattern.

According to another aspect of the present invention, there is provided an image processing apparatus for processing an image composed of a plurality of pixels arranged in a main scanning direction and a sub-scanning direction and obtaining a center position of a pattern included in the image. Histogram creating means for creating a histogram indicating the density distribution of a plurality of main scanning lines along the direction, and creating a histogram indicating the density distribution of the plurality of sub-scanning lines along the sub-scanning direction of the image; The maximum value and the average value are obtained from the histogram showing the density distribution of the density distribution, and two positions where the density is substantially equal to the threshold value between the maximum value and the average value are obtained on the histogram, and the main position passing through the center of these positions is obtained. The center line along the scanning direction is obtained, and the maximum value and the average value of the histogram showing the density distribution of each sub-scanning line are obtained. The maximum value and the average value are obtained on this histogram. The two positions at which the density is substantially equal to the threshold between the average values are obtained, the center line along the sub-scanning direction passing through the center of these positions is obtained, and the intersection position along each center line in the main scanning direction and the sub-scanning direction is obtained. As a center position of the pattern.

According to the present invention having such a configuration, the maximum value and the average value are obtained from the histogram indicating the density distribution of each scanning line for each of the main scanning direction and the sub-scanning direction, and the maximum value and the average value are obtained on the histogram. Two positions having a density substantially equal to the threshold value between the average values are obtained, and a center line passing through the center of these positions is obtained. Here, the threshold between the maximum value and the average value of the histogram can be appropriately set even if the recording paper itself is colored or the print quality of the pattern is poor. For this reason, a center line passing through the centers of the two positions having the density substantially equal to the threshold value can be accurately obtained.
If the two center lines are accurately obtained in the main scanning direction and the sub-scanning direction in this manner, the center position of the pattern, which is the intersection of the two center lines, can be obtained accurately.

[0015]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram showing an embodiment of the image processing apparatus of the present invention. FIG. 2 is a side view showing a schematic mechanism of a color image forming apparatus to which the image processing apparatus of the present embodiment is applied, and FIG. 3 is a block diagram showing a schematic configuration of an operation control unit in the color image forming apparatus. .

First, an outline of the color image forming apparatus will be described with reference to FIGS. 1, 2 and 3.

This color image forming apparatus performs so-called copying in which an image on a document is read and the same image is recorded on a recording sheet. As shown in FIG. 2, in this color image forming apparatus, a platen 1
11 are provided. An operation panel, which will be described later, is provided near the document table 111. An image reading unit 110 and an image forming unit 210 are provided inside the apparatus main body 1. On the platen 111, a double-sided automatic document feeder (RADF; Recirculating A
utomatic Document Feeder) 112 is provided.

The two-sided automatic document feeder 112 includes
11 and conveys the original to a predetermined position,
After the image reading unit 110 finishes reading an image on one side of the document, the document is turned upside down, and then the document is transported to a predetermined position on the document table 111 again. 110 allows the image on the other side of the original to be read. And a two-sided automatic document feeder 1
When the image reading on both sides of the original is completed, the original 12 is discharged, and the next original is transported and inverted.
The operation of transporting and reversing such a document is controlled in relation to the operation of the entire color image forming apparatus. Of course, it is also possible to discharge the document only by reading the image on one side of the document without reading the other side.

An image reading section 110 reads an image of a document conveyed onto a document table 111 by a double-sided automatic document feeder 112. The image reading unit 110 includes the platen 11
The scanner includes first and second original scanning bodies 113 and 114 that reciprocate in parallel along the lower surface of the optical disc 1, an optical lens 115, and a CCD line sensor 116 that is a photoelectric conversion element.

The first original scanning body 113 reciprocates in parallel at a predetermined scanning speed while maintaining a constant distance with respect to the lower surface of the original platen 111. Has a first mirror for deflecting the reflected light in a predetermined direction. Also, the second original scanning body 11
Numeral 4 reciprocates in parallel while maintaining a constant speed relationship with the first original scanning body 113, receives reflected light from the original via the first mirror of the first original scanning body 113, and receives the reflected light. Are further provided with second and third mirrors for deflecting in a predetermined direction.

The optical lens 115 is connected to the second original scanning body 11.
The reflected light of the document deflected by the second and third mirrors is condensed, and the reflected light is condensed to project an optical image on the CCD line sensor.

The CCD line sensor 116 sequentially photoelectrically converts the light image, reads a black and white image or a color image, and outputs an image signal indicating the image. This CCD
The line sensors 116 are R (red), G (green), B (blue)
Is a three-line color CCD that outputs line data color-separated into each color component as an image signal.

Here, the first and second original scanning bodies 113,
114 is a sub-scan, and the CCD line sensor 1
Assuming that the scan by 16 is the main scan, the main scan is repeated a plurality of times during one sub-scan, thereby reading the image on the document. During this reading, line data corresponding to each pixel on the main scanning line is repeatedly output from the CCD line sensor 116, and these line data (image signals) are continuously obtained. This image signal is
The image data is transferred to an image processing unit described later and processed.

On the other hand, below the image forming unit 210, the recording paper (recording medium) P is separated one by one and the image forming unit 21 is separated.
A paper feed mechanism 211 for supplying the image data to the printer 0 is provided. The recording paper P is cut sheet-shaped paper, stacked and accommodated in a paper tray, separated by a paper feed mechanism 211 one by one, and supplied to the image forming unit 210. The recording paper P is guided to a pair of registration rollers 212 disposed in front of the image forming unit 210, and when the leading end of the recording paper P is detected by a sensor (not shown), recording is performed in response to a detection signal of the sensor. The paper P is temporarily stopped by the registration rollers 212, and thereafter, the recording paper P is transported to the image forming unit 210 while the transport timing is controlled by the registration rollers 212. The image forming unit 210 records an image on one surface of the recording paper P. After this, the recording paper P
Is turned over and then guided again to each registration roller 212, an image is recorded on the other surface of the recording paper P by the image forming unit 210, and then the recording paper P is discharged. Of course, it is also possible to discharge the recording sheet P without recording the image on the other side only by recording the image on one side of the recording sheet P.

Below the image forming section 210, a transfer and transport belt mechanism 213 is disposed. The transfer conveyance belt mechanism 213 includes a driving roller 214, a driven roller 215,
And a transfer / transport belt 216 stretched between the rollers 214 and 215, and transports the recording paper P in the direction of arrow Z while electrostatically attracting the recording paper P onto the transfer / transport belt 216. During the transfer by the transfer and transfer belt mechanism 213, a toner image is transferred and formed on the recording paper P as described later.

The paper suction (brush) charger 228 is disposed immediately after each of the registration rollers 212 and charges the transfer / transport belt 216 so that the recording sheet P is securely attracted onto the transfer / transport belt 216. The sheet is conveyed in the image forming unit 210.

A static eliminator 229 is provided between the image forming section 210 and the fixing device 217. This static eliminator 229
, An alternating current is applied to peel off the recording paper P electrostatically attracted to the transfer conveyance belt 216 from the transfer conveyance belt 216.

On the downstream side of the transfer / conveyance belt mechanism 213,
A fixing device 217 is provided. This fixing device 217
Has a pair of fixing rollers, receives the recording paper P from the transfer and transport belt mechanism 213, and fixes the toner image transferred and formed on the recording paper P to the recording paper P.
Thereafter, the recording paper P is discharged through a conveyance switching gate 218 by a discharge roller 219 to a discharge tray 220 attached to an outer wall of the apparatus main body 1.

The switching gate 218 selectively switches between a path for discharging the recording sheet P after fixing to the discharge tray 220 and a path for supplying the recording sheet P after fixing to the image forming section 210 again. . When the recording sheet P is again supplied to the image forming unit 210 by the switching gate 218, the recording sheet P is turned upside down via the switchback conveyance path 221 and is guided to the image forming apparatus 210.

The first image forming station Pa, the second image forming station Pb, the third image station Pc, and the fourth image forming station 210 are located above the transfer conveying belt 216 in the image forming section 210 and from the upstream side of the conveying path of the recording paper P. The image stations Pd are provided side by side. As described above, the recording sheet P on the transfer conveyance belt 216 is conveyed in the direction of arrow Z. Thereby, the recording paper P passes through the first, second, third, and fourth image forming stations Pa, Pb, Pc, and Pd in the same order. The first to fourth image forming stations Pa to Pd have substantially the same configuration, and each of the photoconductive drums 222 is driven to rotate in the direction of arrow F.
a, 222b, 222c, 222d.

In the vicinity of each of the photosensitive drums 222a to 222d, each of the chargers 223a, 223b, 223c, 223 for uniformly charging each of the photosensitive drums 222a to 222d.
d, laser beam scanner units 227a, 227b, 227c, 227d for forming respective electrostatic latent images on the respective photosensitive drums 222a to 222d, and developing the respective electrostatic latent images on the respective photosensitive drums 222a to 222d. Developing devices 224a, 224b, 22 for forming respective toner images
4c, 224d, and each transfer discharger 2 for transferring each toner image on each of the photosensitive drums 222a to 222d to the recording paper P.
25a, 225b, 225c, 225d, and cleaning devices 226a, 226b, 226 for removing the toner remaining on the photosensitive drums 222a to 222d.
c, 226d are arranged.

Each laser beam scanner unit 227
a to 227d denote a semiconductor laser device (not shown) for emitting a laser beam modulated in accordance with an image signal, a polygon mirror (deflecting device) 240 for deflecting the laser beam from the semiconductor laser device in the main scanning direction, An fθ lens 241 for condensing the laser beam deflected by the polygon mirror 240 on each of the photosensitive drums 222a to 222d to form an image, and mirrors 242 and 243 are provided.

The laser beam scanner 227a inputs an image signal corresponding to a black component image of a color image, modulates a laser beam according to the image signal, and supplies a laser beam corresponding to the black component image to the photosensitive drum 222a. Irradiate. The laser beam scanner 227b inputs an image signal corresponding to a cyan component image of a color image, modulates a laser beam according to the image signal, and irradiates the photosensitive drum 222b with a laser beam corresponding to the cyan component image. I do. The laser beam scanner 227c receives an image signal corresponding to the magenta color component image of the color image, modulates the laser beam according to the image signal, and outputs the laser beam corresponding to the magenta color component image to the photosensitive drum 222.
Irradiate c. The laser beam scanner 227d inputs an image signal corresponding to a yellow component image of a color image, modulates a laser beam according to the image signal, and irradiates a laser beam corresponding to the yellow component image to the photosensitive drum 222d. I do. By exposing the photosensitive drum with the laser beam, the electrostatic latent image of the black component image, the electrostatic latent image of the cyan component image, and the electrostatic latent image of the magenta component image are formed on the photosensitive drums 222a to 222d. A latent image and an electrostatic latent image of a yellow component image are formed.

The developing device 227a contains black toner, and the black toner is supplied to the photosensitive drum 222a.
The toner adheres to the electrostatic latent image of the upper black component image, whereby the black toner image is developed. The developing device 227b contains cyan toner, and the cyan toner adheres to the electrostatic latent image of the cyan component image on the photosensitive drum 222b, whereby the cyan toner image is developed. You. The developing device 227c contains magenta toner, and the magenta toner adheres to the electrostatic latent image of the magenta component image, whereby the magenta toner image is developed. The developing device 227d contains yellow toner, and the yellow toner adheres to the electrostatic latent image of the yellow component image, whereby the yellow toner image is developed.

With the rotation of the photosensitive drums 222a to 222d, the photosensitive drums 222a to 222d are sequentially pressed against the recording paper P on the transfer / conveying belt 216, and the toner images on the photosensitive drums 222a to 222d are removed. The images are sequentially superimposed and transferred on the recording paper P. Thereafter, the recording paper P is transported to the discharging discharger 229, where the static electricity is discharged by the discharging discharger 229, and the transfer conveyance belt 21 is discharged.
After being peeled from the fixing member 6, the sheet is guided to the fixing device 217.
The fixing device 217 includes a pair of fixing rollers, receives the recording sheet P from the transfer / conveyance belt mechanism 213, and
The recording paper P is passed through the nip portion between these fixing rollers, whereby the toner image transferred and formed on the recording paper P is fixed on the recording paper P. The recording paper P is discharged to the discharge tray 220 by the discharge roller 219 through the conveyance switching gate 218 or the switching gate 21.
8 is turned upside down via the switchback conveyance path 221 and then guided again to the image forming apparatus 210.

Although the image is written on each of the photosensitive drums 222a to 222d by the laser beam scanner units 227a to 227d, the laser beam scanner units 227a to 227d are used.
Instead of 7d, a writing optical system (LED head) including a light emitting diode array and an imaging lens array may be used. This LED head is smaller in size than a laser beam scanner unit, and has no moving parts and no operating noise. For this reason, an LED head is suitable for an image forming apparatus such as a tandem type digital color copying machine that requires a plurality of writing units.

Next, the configuration and functions of the image processing apparatus according to the present embodiment applied to the color image forming apparatus will be described with reference to FIG. In FIG. 1, the same reference numerals are given to the portions that perform the same operations as those in FIG.

The image processing apparatus of this embodiment includes an image data input unit 40, an arithmetic processing unit 41, an image memory 43 composed of a hard disk device or a RAM (random access memory), an image data output unit 42, and a CPU (central processing unit). (Processing device) 44, an image editing unit 45, and external interface units 46 and 47.

The image data input unit 40 reads a black-and-white image or a color image on a document, and outputs line data separated into R, G, and B (red, green, and blue components) as image signals. CCD 116 and C
A shading correction circuit 40b for correcting the level of the image signal output from the CD 116, a three-line CCD 11
6, a line matching unit 40 composed of a line buffer or the like for correcting the deviation of the line data of each color read by
c, a sensor color correction unit 40d that performs color correction on line data of each color, an MTF correction unit 40e that corrects line data of each color so that a change in each pixel is sharp, and corrects image brightness. It comprises a gamma correction unit 40f that performs visibility correction.

The arithmetic processing unit 41 includes an image data input unit 40
Line data of each color from (R, G, B image signals)
The image signals of the R, G, and B data are generated by the monochrome data generator 41a, which generates an image signal indicating a more monochrome image (black and white image), and the second, third, and fourth image forming stations Pb, Pc, and Pd of the image forming unit 210. An input processing unit 41 that converts the image signals into C, M, and Y (cyan, magenta, and yellow) image signals and performs clock conversion.
b, an area separating unit 41c that separates the image indicated by the image signal into a character area, a halftone photographic area, and a photographic paper photographic area, and an undercolor based on the C, M, and Y image signals from the input processing unit 41a. A black generation unit 41d that performs a removal process to generate a K (black component) image signal; a color correction circuit 41e that corrects each color indicated by the C, M, and Y image signals based on each color conversion table; Each zoom processing circuit 41f that processes an image signal so that the image is enlarged or reduced according to the magnification, each spatial filter 41g, each print data input unit 41i, and expresses gradation such as multi-level error diffusion and multi-level dither. And a tracking pattern output unit 41j.

The C, M, Y, K image signals processed by each halftone processing unit 41h of the arithmetic processing unit 41 are temporarily stored in the image memory 43. Each of the C, M, Y, and K image signals is serially output for each pixel in 8 bits (C, M, Y).
M, Y, and K, each having 32 bits), and such image signals of C, M, Y, and K are stored in the hard disks 43a, 43b, 43c, and 43d as image data of each color. .

Since the first, second, third, and fourth image forming stations Pa, Pb, Pc, and Pd of the image forming section 210 are spaced apart from each other, each image formed by these image forming stations is Are different in formation timing. For this reason, each of the hard disks 43a, 43b, 43
The image data of each color in c and 43d is temporarily stored in each delay buffer memory 43e, and after being given each delay time, is sent out to each image forming station as an image signal of each color. Thereby, the images are superimposed on the same recording paper P without being shifted in each image forming station.

The image data output section 42 includes laser beam scanner units 227a to 227d and a laser control unit 42a for pulse width modulating a drive signal of each laser beam scanner unit in accordance with an image signal of each color from the image memory 43. Have. Each of the laser beam scanner units 227a to 227d inputs the respective drive signals subjected to pulse width modulation, and controls the output level of the laser beam according to these drive signals.

The CPU 44 controls the entire image processing unit, and includes an image data input unit 40, an arithmetic processing unit 41, an image memory 43, an image data output unit 42, an image editing unit 45, and external devices. Interface 46, 47
Are controlled based on a predetermined sequence.

The image editing unit 45 performs a predetermined image editing process on the image data in the image memory 43, and performs the editing process in the image memory 43. The image data in the image memory 43 is stored in the image data input unit 4.
0 or an external interface 46 (or 4
7) and processed by the arithmetic processing unit 41.

The external interface 46 is a communication interface for receiving image data from an external terminal (communication portable terminal, digital camera, digital video camera, etc.). The external interface 46
Is also converted into data that can be handled by the image forming apparatus 210 by being once input to the image processing unit 41 and subjected to color space correction and the like.
It is stored in the image memory 43.

The external interface 47 stores image data created by a personal computer or F
This is for inputting image data by AX reception, and it is possible to input either black and white or color image data. The image data input through the interface 47 is already an image signal of C, M, Y, and K, and is stored and managed in the image memory 43 after being processed by the halftone processing unit 41h.

Next, the configuration and functions of the operation control section in the color image forming apparatus will be described with reference to FIG. Note that, in FIG. 3, the same reference numerals are given to portions that perform the same operations as those in FIGS. 1 and 2.

This operation control section includes not only the image data input section 40, the arithmetic processing section 41, the image memory 43, the image data output section 42 and the CPU 44 shown in FIG.
An operation board unit 50, an ADF drive unit 51, a disk drive unit 52, an FCU drive unit 53, a scanner drive unit 54, and a printer drive unit 55 are provided.

The CPU 44 sends a control signal to each of the driving units 51 to 55, and manages these driving units 51 to 55 by performing sequence control.

The CPU 44 controls the operation board unit 5
0 is communicably connected. When the operation unit of the operation board unit 50 is operated by the operator, the operation board unit 50 forms a control signal indicating a copy mode in accordance with the operation, and transmits the control signal to the CPU 4.
4 In response to this control signal, the CPU 44
The image processing unit shown in FIG. 1 and the operation control unit shown in FIG. 3 are collectively controlled to perform copying in the copy mode.

Further, the CPU 44 transmits to the operation board unit 50 a control signal indicating the current operation state of the color image forming apparatus. In response to this, the operation board unit 50 displays the current operation state on the display of the operation board unit 50 to notify the operator.

In the color image forming apparatus having such a configuration, the first, second, third, and fourth image forming stations Pa, Pb, Pc, and Pd are formed on the recording sheet P by the fixing device 217. K, C, M, Y to be fixed
If each image of the (black component, cyan component, magenta component, and yellow component) is shifted on the recording paper P, the color image becomes unclear and its quality is deteriorated.

Therefore, in this color image forming apparatus, a set pattern image Qo as shown in FIG. 4A is formed on the recording paper P, and the image of each color is formed based on the set pattern image on the recording paper P. The shift amounts are measured, and these shift amounts are adjusted and canceled.

The set pattern image Qo includes two black main patterns K1 and K1 'and these main patterns K1 and K1'.
It includes a magenta sub-pattern M1, a cyan sub-pattern C1, and a yellow sub-pattern Y1 arranged between 1 '. The feature of this set pattern image Qo is that, assuming a reference straight line H connecting the centers of the main patterns K1 and K1 ', each of the sub-patterns C1, M1, Y on this reference straight line H
The center of 1 is in line.

The set pattern image Qo corresponds to the recording paper P
There is no problem if the image is recorded exactly on top, and it is not necessary to adjust the deviation of the image of each color. However, actually, due to uneven operation of the image forming station,
The set pattern image Qo shown in FIG. 4A is not accurately recorded on the recording paper P, and becomes a set pattern image Q1 as shown in FIG. 4B, for example. This set pattern image Q1
In, the centers of the sub-patterns C1, M1, Y1 deviate from the reference straight line H connecting the centers of the main patterns K1, K1 'in the sub-scanning direction.

In this case, the recording sheet P is placed on the document table 111, the set pattern image Q1 on the recording sheet P is read by the image reading section 110, and the sub-patterns C1, M1, Y1 from the reference straight line H are read. Shift amounts ΔC1, ΔM1,
ΔY1 is measured, and each of the deviation amounts ΔC1, ΔM1, and ΔY1
Adjust the misalignment of each color image so that

Here, in the calculation process for obtaining the reference straight line H connecting the centers of the main patterns K1 and K1 'and the deviation amounts .DELTA.C1, .DELTA.M1 and .DELTA.Y1 of the sub-patterns C1, M1 and Y1, the first step is as follows. At the stage, each main pattern K1, K
The center position of 1 'and the center positions of the sub-patterns C1, M1, Y1 are determined. The outline is that, in the entire image (including the set pattern image Q1 in FIG. 4B) read by the image reading unit 110, each image in a pre-positioned image area is cut out, and each image in these image areas is cut out. The center position of each of the main patterns K1, K1 'is determined based on the image, and the center position of each of the sub-patterns C1, M1, Y1 is determined.

For example, if the pre-positioned image area is 2
56 pixels × 256 pixels (the number of pixels arranged in the main scanning direction ×
(The number of pixels arranged in the sub-scanning direction)
The number of main scanning lines in which 256 pixels are arranged in the main scanning direction is 2
There are 56 lines, and similarly, there are 256 sub-scan lines in which 256 pixels are arranged in the sub-scan direction. The density Ts (j) of the main scanning line can be obtained for each of the 256 main scanning lines j (j = 1 to 256) based on the following equation (1), and the densities of all the main scanning lines j are graphed. When plotted above, a histogram showing the density distribution of all the main scanning lines j can be obtained. Similarly, for each of the 256 sub-scan lines i (i = 1 to 256), the density Tm (i) of the sub-scan lines can be obtained based on the following equation (2). When the density is plotted on the graph, a histogram showing the density distribution of all the sub-scanning lines i can be obtained.

[0061]

(Equation 1)

[0062]

(Equation 2)

Where data is the density level of one pixel.

However, when the calculations shown in the above equations (1) and (2) are performed for each pattern, if the number of each pattern increases, the amount of calculation (the amount of processing of image data) becomes enormous, and the processing time becomes longer. It will be long.

Therefore, in this embodiment, for each of the 256 main scanning lines j, each pixel on the main scanning line is thinned and selected, and the density of the main scanning line composed of the selected pixels is obtained. , A histogram indicating the density of all the main scanning lines is created, and each pixel on the sub-scanning line is thinned out and selected for each of the 256 sub-scanning lines i. The density of the line is obtained, and a histogram showing the density distribution of all the sub-scanning lines is created. Here, assuming that the thinning interval of each pixel on the main scanning line is n, the main scanning line j (j = 1 to 2)
56), the density Ts' (j) of the main scanning line can be obtained based on the following equation (3). When the densities of all the main scanning lines j are plotted on a graph, the results are as shown in FIG. A histogram 5J indicating the density distribution of all the main scanning lines j can be obtained. Similarly, assuming that the thinning interval of each pixel on the sub-scanning line is n, the sub-scanning line i (i
= 1 to 256), the density Tm '(i) of the sub-scanning line
Is calculated based on the following equation (4). When the densities of all the sub-scanning lines i are plotted on a graph, a histogram 5I indicating the density distribution of all the sub-scanning lines i as shown in FIG. 5 is obtained. be able to. In FIG. 5, S is an image area of 256 pixels × 256 pixels.

[0066]

(Equation 3)

[0067]

(Equation 4)

As described above, in the present embodiment, the density of each scanning line is obtained after thinning out each pixel on the scanning line for each scanning line. Therefore, the accuracy of each of the histograms 5J and 5I is substantially degraded. In addition, the amount of calculation can be reduced and the processing time can be reduced. Further, when the pattern is a cross shape as shown in FIG. 4, even if each pixel on the scanning line is appropriately thinned out for each scanning line, the accuracy of the histograms 5J and 5I does not deteriorate. Alternatively, regardless of the shape of the pattern, if the method of thinning out each pixel on the scanning line is determined according to the shape, the accuracy of each of the histograms 5J and 5I does not deteriorate.

After obtaining the histograms 5J and 5I in this way, the center position of the pattern is obtained based on the histograms 5J and 5I. In the present embodiment, the center lines J and I along the main scanning direction and the sub-scanning direction are obtained based on the histograms 5J and 5I, and the intersection of these center lines is obtained as the center position of the pattern. .

Now, assuming that the histogram is as shown in FIG. 6, first, the maximum density Pmax and the average density Pave are obtained. Then, an average value ((Pmax + Pave) / 2) of the maximum density Pmax and the average density Pave is obtained, and this average value is used as a threshold value. Further, the density P is equal to a threshold value ((Pmax + Pave) /
Two positions ia and ib reaching 2) are obtained, and a center line passing through the center position ((ia + ib) / 2) of these positions ia and ib is obtained.

Such an operation is performed for each of the histograms 5J and 5I.
Separately, the center line J along the main scanning direction as shown in FIG.
(Indicating the center position of the pattern in the sub-scanning direction) and a center line I (indicating the center position of the pattern in the main scanning direction) along the sub-scanning direction, and determining the intersection position q of these center lines J and I. Determined as the center position of the pattern.

The operation of obtaining the center position of the pattern based on the histogram so far is performed for each main pattern K1.
, K1 'and each of the sub-patterns C1, M1, Y1 so that the center position of each pattern can be determined in each image area. Thereafter, the center position of each pattern in each image area is shifted to the set pattern image Q1, and in this set pattern image Q1, the center position of each main pattern K1, K1 'and each sub pattern C1, M1 are set.
, Y1 are determined.

As described above, in this embodiment, the average value of the maximum density Pmax and the average density Pave is used as a threshold value for each of the histograms 5J and 5I, and two positions ia and i reaching the threshold value are used.
b, the center position of these positions ia and ib ((i
The center line passing through a + ib) / 2) is obtained, and thereafter, the intersection of the center line J along the main scanning direction and the center line I along the sub-scanning direction is obtained as the center position q of the pattern. When the average value of the maximum density Pmax and the average density Pave is used as the threshold value, the average density Pave becomes high due to the color of the recording paper P itself, or there is an error in the maximum density Pmax due to the poor print quality of the pattern. However, this threshold is set appropriately. For this reason, the center line J along the main scanning direction and the center line I along the sub-scanning direction can be accurately obtained, and the center position of the pattern, which is the intersection position q of each of the center lines J and I, can be accurately obtained. it can.

Here, the average value of the maximum density Pmax and the average density Pave is used as the threshold value, but any value between the maximum density Pmax and the average density Pave can be used as the threshold value. For example, after appropriately weighting at least one of the maximum density Pmax and the average density Pave, an average value of both densities may be obtained, and this average value may be used as a threshold value.

Next, the procedure for measuring and adjusting the amount of deviation of the image of each color in the color image forming apparatus will be specifically described.

First, in order to record the set pattern image Q0 shown in FIG. 4A, the operation board unit 50 is operated and the test mode is instructed to the CPU 44. In response to this, the CPU 44 controls the paper feed mechanism 211, the transfer / transport belt mechanism 213, the transport switching gate 218, and the like to supply, transport, and discharge the recording paper P. At the same time, the CPU 44 reads the set pattern image Q0 stored in the image memory 43 in advance, and supplies an image signal indicating the set pattern image Q0 to the image data output unit 42. The image data output unit 42 drives and controls each of the laser beam scanner units 227a to 227d of the first to fourth image forming stations Pa to Pd according to the image signal. Accordingly, in the first to fourth image forming stations Pa to Pd, each of the photosensitive drums 2 by each of the laser beam scanner units 227a to 227d.
Writing of the respective electrostatic latent images to the developing devices 224a and 22d is performed.
4b, 224c, and 224d, the developed toner images on the photosensitive drums 222a to 222d are sequentially transferred onto the recording paper P being conveyed and recorded.

When the set pattern image Q1 shown in FIG. 4B is recorded on the recording paper P, the recording paper P is placed on the document table 111. Thereafter, the operation board unit 50 is operated to instruct the CPU 44 to read the set pattern image Q1 on the recording paper P. In response to this the CPU
44 controls the image reading unit 110 and the image data input unit 40 to read an image. Image data input unit 40
, Each color (R,
G, B) is output, and color correction, MTF correction, light / dark correction, γ correction, and the like are performed on the line data of each color. Thereafter, in the arithmetic processing unit 41, C, M, Y, and K image signals are formed from the line data of each color, and various processes are performed on these image signals. Then, these image signals are temporarily stored in the image memory 43.

The CPU 44 stores C,
The M, Y, and K image signals are read out, and the above-described image processing is performed. That is, the entire image read by the image reading unit 110 (the set pattern image Q in FIG.
1), each image in each image region positioned in advance is cut out. Then, based on each image in each image area, the center position of each main pattern K1, K1 'and the center position of each sub-pattern C1, M1, Y1 are determined. Thereafter, in the set pattern image Q1, each main pattern K
1, K1 'and the sub-pattern C1
, M1, Y1 are determined. Finally, each sub-pattern C from the reference straight line H connecting the main patterns K1 and K1 '
The shift amounts ΔC1, ΔM1, and ΔY1 of 1, M1, and Y1 are measured, and these shift amounts are stored.

Thus, the deviation amounts ΔC 1, ΔM 1, ΔY 1
After the measurement is completed, when an arbitrary color image is recorded on the recording paper P, the CPU 44 determines that each of the deviation amounts ΔC1
, .DELTA.M1, and .DELTA.Y1 become 0, the writing timing in the sub-scanning direction of the second to fourth image forming stations Pb to Pd is adjusted. For example, when reading out the C, M, and Y image signals indicating an arbitrary color image once stored in the image memory 43, each of the C, M, and Y image signals is read in accordance with each of the deviation amounts ΔC1, ΔM1, and ΔY1. Are shifted, thereby correcting the deviation of the image of each color. As a result, the quality of the color image recorded on the recording paper P is improved.

At this time, the deviation amounts ΔC 1, ΔM 1, ΔY are determined with reference to a reference straight line H connecting the main patterns K 1, K 1 ′.
1 is obtained, the sub-scanning direction of the other second to fourth image forming stations Pb to Pd is determined with reference to the writing timing in the sub-scanning direction of the first image forming station Pa for recording the black main patterns K1 and K1 '. Adjust the write timing in the scanning direction.

In this embodiment, each main pattern K1
, K1 ', the respective deviation amounts .DELTA.C1 with respect to the reference straight line H connecting the centers thereof.
, .DELTA.M1, and .DELTA.Y1 are the sum of all deviation amounts in the process from when the set pattern image Qo shown in FIG. 4A is recorded on the recording paper P and read. Therefore, the respective deviations caused by the respective photosensitive drums 222a to 222d, the CCD sensor 116 and the like are eliminated at once.

Further, the deviation amounts ΔC 1, ΔM 1, ΔY 1
Is the amount of deviation from the reference straight line H connecting the centers of the main patterns K1 and K1 '. For this reason, when reading the set pattern image Q1 on the recording paper P, even if the recording paper P is arranged inclined on the document table 111 as shown in FIG. 4C, for example, each of the deviation amounts ΔC1, ΔM1, and ΔY1 Can be determined accurately. In other words, even if the recording paper P is placed on the document table 111 at an angle or deviated from a predetermined position, each deviation from the reference straight line H connecting the centers of the main patterns K1 and K1 'on the recording paper P. The quantities ΔC1, ΔM1, Δ
Y1 does not change. Therefore, in the present embodiment, the measured shift amount does not depend on the inappropriate arrangement position of the recording paper.

More specifically, as shown in FIG. 7, the center positions of the main patterns K1, K1 'are set to (Xk1, Yk1), (Xk2, Yk).
2), and the center position of the cyan sub-pattern C1 is (Xc
1, Yc1), the inclination θ of the reference straight line H connecting the center positions (Xk1, Yk1) and (Xk2, Yk2) of the main patterns K1 and K1 ′ can be obtained based on the following equation (5). The shift amount ΔC1 of the cyan sub-pattern C1 can be obtained based on the following equation (6).

Θ = arctan ((Yk2−Yk1) / (Xk2−Xk1)) (5) ΔC1 = (Xc1−Xk1) sin (−θ) + (Yc1−Yk1) cos (−θ) (6) Similarly, the yellow and magenta sub-patterns Y1,
The deviation amounts ΔY1 and ΔM1 of M1 can be obtained.

By the way, if the photosensitive drum is eccentric or the like, the result of measurement of the deviation amount of the sub-pattern varies depending on where the sub-pattern is recorded around the photosensitive drum. In this case, even if the shift amount of only one sub-pattern is obtained, the shift amount in the sub-scanning direction cannot be obtained accurately.

Therefore, a plurality of set pattern images Q0 as shown in FIG. 8A are arranged in the sub-scanning direction, and these are recorded on the recording paper P. As a result, if each set pattern image Q1 as shown in FIG. 8B is obtained on the recording paper P, for each set pattern image Q1, a reference straight line H connecting the main patterns K1 and K1 ', A reference straight line H connecting the main patterns K2 and K2 ', a reference straight line H connecting the main patterns K3 and K3', and each main pattern K
4 and a reference straight line H connecting K4 'is obtained. And
The deviation amounts ΔY1, ΔY2, ΔY of the yellow sub-patterns Y1, Y2, Y3, Y4 with respect to the respective reference straight lines H
Y3 and .DELTA.Y4 are obtained, and the average value of these deviation amounts is obtained. Similarly, for cyan and magenta, the shift amount of each sub-pattern with respect to each straight line is obtained, and the average value of these shift amounts is obtained.

After the average value of the shift amounts of the respective colors is obtained in this manner, when an arbitrary color image is recorded on the recording paper P, the second to fourth colors are set so that the average value of the shift amounts of the respective colors becomes zero.
The writing timing of the image forming stations Pb to Pd in the sub-scanning direction is adjusted, and the deviation of each color image in the sub-scanning direction is adjusted.

In short, the average value of the deviation amounts of the sub-patterns of the same color arranged in the sub-scanning direction is obtained, and the deviation of the color image in the sub-scanning direction is adjusted according to the average value.
This minimizes the influence of the deviation in the amount of deviation due to the eccentricity of the photosensitive drum, and satisfactorily suppresses the color deviation at any position in the sub-scanning direction.

In the above description, the displacement of each color image in the sub-scanning direction has been measured. However, the displacement can be measured in the main scanning direction in the same procedure as in the sub-scanning direction. That is, a set pattern image is recorded and formed on a recording sheet along the sub-scanning direction, a reference straight line connecting each main pattern is obtained, and a deviation amount of the sub-pattern in the main scanning direction with respect to the reference straight line is determined for each color. Ask. Further, the adjustment of the deviation of the image of each color in the main scanning direction is different from the adjustment of the deviation of the image of each color in the sub-scanning direction. Second to fourth image forming stations Pb to Pb
This is performed by shifting the head write timings of cyan, magenta, and yellow by d.

Although the displacement in the main scanning direction is caused by the movement of the recording paper P and the photosensitive drum, the deviation amount also varies depending on the position in the main scanning direction. In order to reduce the influence of the deviation in the amount of deviation, a plurality of set pattern images Q0 arranged in the main scanning direction are prepared as shown in FIG. May be used as a measurement target.

However, for example, even if each set pattern image Q1 as shown in FIG. 9B is obtained on the recording paper P, the deviation amount of the head sub-pattern of one color in the main scanning direction is the same thereafter. Since it affects the shift amount of each color sub-pattern, similar to the above-described average of the shift amount in the sub-scanning direction,
There is no point in simply averaging the deviation amounts of the sub-patterns of the same color along the main scanning direction.

Here, in FIG. 9B, for example, the deviation amounts ΔC01, ΔC01 of the cyan sub-patterns C01, C11, C21, respectively.
Focusing on C11 and ΔC21, these deviation amounts ΔC0
1, ΔC11 and ΔC21 are proportional to the positions of the sub-patterns C01, C11 and C21 in the main scanning direction as shown in FIG. The position of the sub-pattern is YC, and the deviation amount of the sub-pattern is XC
Then, the position YC is represented by the following equation (7).

YC = aXC + b (7) In the equation (7), the coefficient b is a timing at which the first image forming station Pa writes a cyan head by the second image forming station Pb with respect to a reference black head writing timing. Shows the amount of deviation. Also,
The coefficient a indicates the correction amount of the frequency of the write clock signal of the second image forming station Pb. Accordingly, each of the deviation amounts ΔC01, ΔC11, ΔC21 and each of the sub patterns C01, C11,
If the coefficients a and b of the above equation (7) are derived based on the position of C21, and the head write timing of cyan and the frequency of the write clock signal are adjusted based on these coefficients a and b, then in the main scanning direction, Of the cyan image can be adjusted.

Similarly, with respect to the other magenta and yellow colors, based on the above equation (7), the amount of deviation (= b) between each of the magenta and yellow head write timings with respect to the reference black head write timing. ) And the correction amount (= a) of the frequency of the write clock signal of the third and fourth image forming stations Pc and Pd.

When a plurality of cyan sub-patterns are arranged in one set pattern image as shown in FIGS. 9 (a) and 9 (b), the cyan The average value of the deviation amounts of the respective sub-patterns is obtained, and these average values can be made to correspond to the variable XC of the above equation (7). Similarly, for the other magenta and yellow colors, the average value of the shift amounts of the sub-patterns of the same color is obtained for each set pattern image, and these average values correspond to the variable XC of the above equation (7). Can be done. If the average value of the shift amounts is obtained and used in this way, it is possible to suppress variations in the shift amounts in the sub-scanning direction.

Further, a set pattern image is recorded along the main scanning direction, and the amount of deviation in the sub-scanning direction is measured and adjusted. Rather than measuring and adjusting the shift amount completely independently, the set pattern image along the main scanning direction and the set pattern image along the sub-scanning direction are simultaneously recorded, and the shifts in the sub-scanning direction and the main scanning direction are recorded. May be sequentially adjusted. For example, as shown in FIG. 11, a plurality of set pattern images Q01 are arranged in the sub-scanning direction, and a plurality of set pattern images Q02 are arranged in the main scanning direction.
The average value of the deviation amount in the main scanning direction is measured based on each set pattern image Q01, and the average value of the deviation amount in the main scanning direction is measured based on each set pattern image Q02. The deviation in the sub-scanning direction and the main scanning direction are sequentially adjusted based on the average value of the deviation amount in the direction and the average value of the deviation amount in the main scanning direction.

In FIG. 8, FIG. 9 and FIG. 11, the number of set pattern images is increased, and the average value of the amount of deviation of each pattern is obtained, so that the eccentricity of the photosensitive drum, the recording paper P and the photosensitive drum Although the effects of blur and the like are avoided, as the number of set pattern images increases, the number of patterns also increases, and the amount of calculation for finding the center position of these patterns increases. However, in this embodiment,
As described above, since each pixel on the scanning line is thinned out when creating the histogram, the amount of calculation for finding the center position of each pattern is extremely small compared to the amount of calculation in which such thinning is not performed. Can be suppressed.

The present invention is not limited to the above embodiment, but can be variously modified. For example,
The shape of the main pattern and the sub-pattern may be changed, and the shape of the image area may be changed. Further, the size and shape of the image area may not be fixed but may be changed according to the type of pattern. Further, in order to adjust the deviation amount of each color in the sub-scanning direction and the main scanning direction, not only the timing of reading each image signal from the image memory is changed, but also
The rotational speed of the polygon mirror may be changed, or the amount of deviation of each color may be adjusted by combining these methods.

Further, in preparing the above-mentioned histogram, each pixel on the scanning line is thinned out, and a center line along the scanning direction is obtained on the histogram based on a threshold between the maximum density and the average density, and the main scanning direction is determined. And finding the intersection position q of each center line J, I along the sub-scanning direction as the center position of the pattern can be separately adopted. For example, a histogram is created by thinning out each pixel on the scanning line in the main scanning direction and the sub-scanning direction, and then, according to another known method different from the present invention, the center position of the pattern is obtained using this histogram. However, the amount of calculation can be reduced. Conversely, a histogram is created based on another known method different from the present invention, and a center line along the scanning direction is obtained on the histogram based on a threshold between the maximum density and the average density, and the main scanning direction and the sub-scanning direction are determined. Even if the intersection position q of each of the center lines J and I along the scanning direction is determined as the center position of the pattern, the center position of the pattern can be determined without being affected by the color of the recording paper P itself or the poor print quality of the pattern. Can be determined accurately.

[0100]

As described above, according to the present invention, each pixel on the main scanning line is thinned out and selected for each main scanning line, and then the density of the main scanning line is obtained. While creating a histogram showing the density distribution of, and for each sub-scanning line, after thinning out and selecting each pixel on the sub-scanning line, determine the density of the sub-scanning line,
A histogram indicating the density distribution of each sub-scanning line is created. Therefore, it is possible to reduce the amount of calculation and the time required to create a histogram by the amount of each thinned pixel.

Further, according to the present invention, the maximum value and the average value are obtained from the histogram indicating the density distribution of each scanning line in the main scanning direction and the sub-scanning direction, and the maximum value and the average value are calculated on the histogram. Are obtained, and a center line passing through the center of these positions is obtained. Therefore, even if the recording paper itself is colored or the print quality of the pattern is poor, the center position of the pattern, which is the intersection of the two center lines in the main scanning direction and the sub-scanning direction, can be accurately obtained. .

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an embodiment of an image processing apparatus according to the present invention.

FIG. 2 is a side view illustrating a schematic mechanism of a color image forming apparatus to which the image processing apparatus according to the embodiment is applied.

FIG. 3 is a block diagram illustrating a schematic configuration of an operation control unit in the color image forming apparatus.

FIG. 4A is a diagram illustrating a prototype of a set pattern image according to the present embodiment, and FIG. 4B is a diagram illustrating a state in which the set pattern image is recorded on recording paper;
FIG. 3C is a diagram showing a state in which the recording paper on which the set pattern image is recorded is arranged at an angle.

FIG. 5 is a diagram showing an image area, a histogram of density distribution of each main scanning line, and a histogram of density distribution of each sub-scanning line.

FIG. 6 is a diagram illustrating a histogram of a density distribution of each scanning line.

FIG. 7 is a diagram used to explain a calculation procedure for obtaining a shift amount of a sub pattern with respect to a reference straight line connecting each main pattern.

8A is a diagram illustrating a plurality of set pattern images arranged in the sub-scanning direction, and FIG. 8B is a diagram illustrating a state in which each set pattern image of FIG. .

9A is a diagram illustrating a plurality of set pattern images arranged in the main scanning direction, and FIG. 9B is a diagram illustrating a state in which each set pattern image of FIG. .

FIG. 10 is a graph showing a change in a shift amount with respect to a position of a sub pattern in a main scanning direction.

FIG. 11 is a diagram showing a plurality of set pattern images arranged in the main scanning direction and the sub-scanning direction.

[Explanation of symbols]

 Reference Signs List 1 apparatus main body 40 image data input unit 41 arithmetic processing unit 42 image data output unit 43 image memory 44 central processing unit 45 image editing unit 46, 47 external interface unit 50 operation board unit 51 ADF drive unit 52 disk drive unit 53 FCU drive unit 54 scanner drive unit 55 printer drive unit 110 image reading unit 112 double-sided automatic document feeder 116 CCD line sensor 210 image forming unit 211 paper feed mechanism 220 discharge trays 222a to 222d photosensitive drum H reference straight line P recording paper Pa first image formation Station Pb Second image forming station Pc Third image forming station Pd Fourth image forming station Qo Set pattern image K1, K1 'Main pattern C1, M1, Y1 Sub-pattern

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Shoichi Fukudome 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (72) Inventor Kazunobu Takahashi 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka (72) Inventor Yoshitaka Okahashi 22-22, Nagaikecho, Abeno-ku, Osaka-shi, Osaka Japan Sharp Corporation (72) Inventor Takao Horiuchi 22-22, Nagaike-cho, Abeno-ku, Osaka-shi, Osaka F term (reference) 2C061 AQ06 AR01 KK04 KK18 KK25 KK26 KK28 KK32 5C076 AA22 BA06 BA08 BB06 5L096 AA02 AA06 BA07 EA03 FA37 GA07 HA13 JA11

Claims (2)

[Claims] An image processing apparatus for processing an image composed of a plurality of pixels arranged in a main scanning direction and a sub-scanning direction and obtaining a center position of a pattern included in the image. After each pixel on the main scanning line is thinned out and selected for each main scanning line, the density of the main scanning line is obtained, a histogram showing the density distribution of each main scanning line is created, and the sub-scanning of the image is performed. Histogram creating means for obtaining the density of each sub-scanning line after thinning and selecting each pixel on the sub-scanning line for each of a plurality of sub-scanning lines along the direction, and creating a histogram indicating the density distribution of each sub-scanning line And a center position calculating means for obtaining a center position of the pattern based on a histogram indicating the density distribution of each main scanning line and a histogram indicating the density distribution of each sub-scanning line. The image processing apparatus characterized in that it comprises and. 2. An image processing apparatus for processing an image composed of a plurality of pixels arranged in a main scanning direction and a sub-scanning direction and obtaining a center position of a pattern included in the image. Histogram creation means for creating a histogram indicating the density distribution of the main scanning line of the main scanning line, and creating a histogram indicating the density distribution of a plurality of sub-scanning lines along the sub-scanning direction of the image; The maximum value and the average value are obtained from the histogram shown, two positions having a density substantially equal to the threshold value between the maximum value and the average value are obtained on the histogram, and the two positions along the main scanning direction passing through the center of these positions are obtained. A center line is obtained, and a maximum value and an average value of a histogram showing the density distribution of each sub-scanning line are obtained. On this histogram, a threshold value between the maximum value and the average value is obtained. 2 is substantially equal to concentration
A center position calculating means for obtaining two positions, obtaining a center line along the sub-scanning direction passing through the center of these positions, and obtaining an intersection position of each center line along the main scanning direction and the sub-scanning direction as a center position of the pattern; An image processing apparatus comprising: