JPH1051628A - Image reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the generation of abnormal image at a low cost by precisely measuring the positional error of the pixel of an image reader reading an original by a bit map form to be simple arithmetic processing to correct based on the measuring result. SOLUTION: The image reader provided with an automatic document feeder(ADF) and a scanner and line sequentially reading the original fed by ADF at fixed time intervals set in advance prints a hatched line pattern constituted by previously arranging lines with a fixed inclination with respect to a scanning direction at equal pitches on the original to read. At this time, this hatched line pattern is optically read by the photoelectric conversion part 101 of the scanner to convert to an electric signal, a hatched line pattern discriminating part 104 sets a window to image data of the hatched line pattern converted into the electric signal to calculate the centroid of image data within the window and a positional error measuring part 105 moves the window according to the value of the calculated centroid to measure the positional error of the pixel.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image reading apparatus for measuring a position error of read bitmap image data and correcting a position error of a pixel of the image data.

[0002]

2. Description of the Related Art As an image reading apparatus of this kind, for example, "Development of a high-definition image input apparatus" (conventional example 1) announced at the 71st Ordinary General Meeting of the Japan Society of Mechanical Engineers (IV)
It has been known. Here, an interpolation operation is performed on an image obtained by reading a test chart of equi-pitch lines arranged in the sub-scanning direction, that is, image data discretized at line intervals in the sub-scanning direction. By obtaining the center position of the black line and the white line of the equal pitch line, and reading the difference from the reference pitch of the test chart, the reading position error of the image data due to the vibration of the apparatus or the like is detected.

Another conventional example is disclosed in Japanese Patent Laid-Open No. 6-297758.
Japanese Patent Application Laid-Open Publication No. 2000-214, “Scanning Line Pitch Measurement Method” (Conventional Example 2).
In this known example, a hard copy pattern in which data of an equal pitch pattern is written is read, and pitch unevenness of a writing scan line of a hard copy device is measured.

[0004] As an optical linear scale, for example, "Basic and Application of Servo Sensors" published by Ohmsha (Kojiro Oshima and Yuji Akiyama) [published February 20, 1988] (conventional example 3) is also known. ing. In this conventional example, a position scale is taken as an example of a linear scale. The linear scales mentioned in the examples are a glass scale composed of a pair of main scales and index scales each having a light and dark grid of exactly the same pitch,
It is composed of a light source composed of an LED that illuminates the scale and a photodiode that detects light transmitted through the scale. Usually, the index scale is fixed and the main scale moves, but the output of the photodiode changes with the movement. The output is maximum when the transmission portions of the two glasses coincide, and when the transmission portion and the opaque portion on which chrome is deposited overlap, the output is 0 in an ideal state. Therefore, the output waveform is ideally a triangular wave. However, since the light and dark grating pitch is actually as small as 8 μm, there is an effect of light diffraction and an effect of reflection on the chromium deposition surface. Output in form. Since the interval between the peaks of this output waveform corresponds to the pitch of the scale, the amount of movement can be known by counting the number of peaks.

[0005]

By the way, in the above-mentioned conventional example 1, data obtained by reading a pattern having the same shape due to the difference in the positional relationship between the edge of the pattern of the equal pitch line and the timing of sampling for reading is obtained. There is a phenomenon called moiré that is different. The read data does not necessarily correspond to the position of the edge of the pattern due to the moiré, so that the measurement accuracy of the position error is deteriorated. The effect of moiré becomes very noticeable when the pitch of the equi-pitch line pattern is refined and approaches the resolution of the reader, and it becomes impossible to measure the position error depending on the conditions. Therefore, in this method, a position error close to or lower than the resolution of the reading device cannot be measured with high accuracy.

Further, since a pattern of equal pitch lines is used, even if the effect of moiré is ignored, if the pitch of the pattern is refined in order to measure the position error of a high frequency component, the MTF (Modulation) of the imaging optical system will be reduced. Tr
The difference in the density signal of the obtained image is reduced due to the limit of the transfer ratio, and the measurement accuracy must be degraded.

[0007] Further, in pattern refinement, the frequency band of measurement is widened in a higher direction, and the accuracy cannot be increased. Therefore, a process of interpolating sampled data is performed. In order to perform better interpolation, more peripheral data is used or complicated arithmetic processing is required, and the processing time becomes longer. Further, the interpolation is an interpolation to the last, and it is inevitable that a deviation from true data occurs, which is a factor of deteriorating the measurement accuracy. In addition, since one specific light receiving element in the photoelectric conversion device uses image data obtained by scanning in the sub-scanning direction, noise of the light receiving element itself affects the accuracy of the measurement itself. ,
Degrades accuracy.

In the conventional example 2, since data obtained by reading a pattern by the photoelectric conversion device is used at the time of measurement, reading is performed under the condition that there is no scanning unevenness at the time of reading a hard copy, and pitch unevenness of the hard copy is measured. I have. Although not particularly described, there is a problem of moire similar to that of the above-described conventional example 1.

In the conventional example 3, in the above-described linear scale, the light emitted from the light source (LED) is converted into parallel rays by a collimating lens, and the light passing through the overlap of the main scale and the index scale is detected by the light receiving element. Therefore, a fine and accurate main scale, index scale, and precise collimation are required. As a result, the cost naturally increases.

On the other hand, in a line scanning image reading apparatus in which a plurality of R, G, and B image sensors are spaced apart in the sub-scanning direction and arranged in parallel, generally, the same position of a document read by each sensor is detected. There is a time lag in the image data, so if you do not make corrections so that the image data at the same position on the document can be obtained from each sensor, a color shift will occur when reading a color image, and it will be necessary to read the color correctly. Can not. This shift is determined according to the interval between the sensors and the scanning speed, and if the scanning speed is uneven, it causes color shift.

In order to avoid the above problem, for example, Japanese Patent Laid-Open Publication No. Hei 6-22159 discloses that a microprocessor counts an internal clock during a period of a pulse generated with rotation of a motor for driving a reading carriage. Find the driving speed of the motor and use it as the actual scanning speed,
There has been proposed a method for correcting a displacement between a plurality of sensors based on the scanning speed. In this method, data of the upstream sensor is matched with that of the downstream sensor in the sub-scanning direction, and the displacement between the sensors is corrected.

The purpose of the correction is to correct the positional deviation between the plurality of sensors, and the amount of delay of the data of the upstream sensor is calculated.
For a delay less than one line, a weighted average of the data before and after the delay is taken. The correction performed here is a correction of matching data of the upstream sensor with the sensor of the most downstream, so as to prevent a color shift due to a shift between the sensors.

In this prior art, the detection of the scanning speed in the sub-scanning direction is detected from the rotation of the drive motor.
A scanning device that scans and reads a document placed on a flat surface requires a mechanism that converts the rotational motion of the motor into a linear motion, and thus completely eliminates the occurrence of uneven speed caused by the mechanism. I can't. Further, since the unevenness of the rotation of the motor and the unevenness of the moving speed of the carriage do not always coincide with each other, the scanning speed cannot be accurately detected. As a result, the speed data in the prior art corrects the positional deviation between the lines. In some cases, the data may not always be appropriate.

Further, in the above-mentioned conventional reading apparatus, data of an upstream sensor is matched with that of a downstream sensor.
Of course, there is no need to correct the data obtained from the most downstream sensor. Here, paying attention to the data obtained from the most downstream sensor that does not perform correction, the reading position on the document is shifted when the reading scanning speed fluctuates as compared with the case of scanning and reading at a constant speed, As a result, there is a problem that the image expands and contracts due to the speed fluctuation.

That is, in the above-described conventional reading apparatus, since the data of the upstream sensor is corrected with respect to the data in which the expansion and contraction occurs, the color shift can be prevented as a result. However, it is impossible to prevent the expansion and contraction of the image due to the fluctuation of the scanning speed, and the positional deviation from the original pixel remains. Further, in this conventional reading device, since the interval between a plurality of line sensors does not change and is used as a correction reference, it cannot be applied to a reading device having only one sensor.

On the other hand, as image quality has advanced as recently, a reading device having a high density of about 600 DPI has become common. With such high image quality, image abnormalities such as jitter and pixel shift immediately become a problem.
The reading device mechanism is required to be more and more precise, and the reading device itself is also expensive.

The present invention has been made in view of such a situation of the prior art, and a first object of the present invention is to provide a simple arithmetic processing method which can reduce positional errors of pixels of an image reading apparatus which reads an original in a bitmap format. It is an object of the present invention to provide an image reading apparatus capable of preventing occurrence of an abnormal image at low cost by measuring with high accuracy and correcting based on the measurement result.

A second object of the present invention is to provide a low-cost image reading apparatus which does not need to prepare an oblique line pattern on the apparatus side.

It is a third object of the present invention to provide an image reading apparatus which can easily correct image processing.

[0020]

In order to achieve the above object, a first means comprises a document feeding means for automatically feeding a document onto a contact glass, and a means for setting a fed document in advance. And a reading means for reading a document image by scanning line-sequentially at a constant time interval, wherein a line having a certain inclination with respect to the scanning direction is arranged in advance on the read document at an equal pitch. Means for printing a diagonal pattern in advance, and means for reading the diagonal pattern printed on the original fed by the original feeding means and converting the optical pattern into an electric signal; A window is set in the image data of the diagonal pattern converted into an electric signal by the above, and a means for calculating the center of gravity of the image data in the window and a means for calculating the center of gravity are calculated. Depending on the value of the center of gravity is a means for moving the window, characterized in that a means for measuring a position error of the pixel from the calculated center of gravity values by means for calculating the center of gravity.

The second means is characterized in that the uniform pitch oblique line pattern printed on the read original in the first means is set at a pitch based on inches.

According to a third means, in the first and second means, the diagonal line pattern is printed within a range of one inch from the outer edge of the sheet.

[0023]

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

1. Schematic Configuration of Image Reading Apparatus FIG. 2 shows a schematic configuration of an image reading apparatus including an ADF according to an embodiment of the present invention. In FIG. 1, a contact glass 1 is supported by a housing 2, and when an original such as a book original is fixedly read, the original is placed on the contact glass with the reading surface down. The original on the contact glass is illuminated by the reflected light of the illumination lamp 18 and the reflector 19, and the reflected light of the reading surface is sequentially reflected by the first mirror 3, the second and third mirrors 20 and 21 integrally formed, and then. An image is formed on a light receiving surface of a photoelectric conversion element (CCD) 23 arranged in a line on the photoelectric conversion device by a lens 22, and the optically read image is converted into an electric signal. First mirror 3, illumination lamp 18, second mirror 20
The third mirror 21 is configured to move in the illustrated A direction using a traveling body drive motor (not illustrated) as a drive source.

When reading an automatically fed document,
In a normal reading operation, the document P placed on the document tray 12 passes through a reading position B by a pickup roller 13, a pair of registration rollers 31, 32, a transport drum 15, and a transport roller 4, and then to a discharge roller pair 25. The paper is sent and discharged onto the paper discharge tray 26. When the document passes the reading position B, the document is illuminated by the reflected light of the illumination lamp 18 and the reflector 19 which are moving near the reading position B, and the reflected light of the illumination light applied to the document is reflected by the first mirror 3, Scanning is performed by the second mirror 20 and the third mirror 21. After that, the reflected light is condensed by the lens 22 and irradiated to the photoelectric conversion element (CCD) 23, where the reflected light is photoelectrically converted.

In FIG. 2, the contact glass 1, the housing 2, the illumination lamp 18, the reflector 19, the first mirror 3, the second mirror 20, the third mirror 21, and the lens 2 are shown.
2. A scanner (image reading apparatus main body) 100 is configured by a photoelectric conversion element (CCD) 23 and a traveling body drive motor, and includes a document tray 12, a pickup roller 13, pairs of registration rollers 31, 32, a transport drum 15, and a pair of discharge rollers. An automatic document feeder (ADF) 200 is constituted by the paper feed tray 25 and the paper discharge tray 26.

FIG. 3 shows the automatic document feeder (AD
F) shows the format of the document 300 fed by the scanner 200 and read by the scanner 100. As can be seen from this format, the outer edge 301 of the original 300
For example, a 45 ° oblique line pattern 10 as shown in the enlarged view of FIG. Each oblique line 10a represents a pitch L based on inches.
It is formed with. If the oblique line pattern 10 is printed on the entire outer periphery of the document 300, the reading direction may be vertical or horizontal with respect to the paper feeding direction.

When the oblique line pattern 10 has a pitch of 0.5 inch, when reading 300 DPI, the DPI between the oblique lines
Means reading 150 dots. 300 for 1 inch
It becomes a dot, and serves as a standard for correcting expansion and contraction of an image. The read dot number can be set for other DPIs in the same way.

In FIG. 2, the oblique line pattern 10 is formed in parallel to a predetermined direction. However, if the oblique line pattern 10 is formed so as to intersect as shown in FIG. 3, the user feels more uncomfortable than when only the oblique line 10a is used. Is reduced. In addition, various patterns can be used as the oblique line pattern 10, and any pattern can be used as long as a readable oblique line pattern is provided for measuring the position error.
The image area 302 as the original 300 is an area inside the area where the oblique line pattern 10 is formed, in other words, an area that is one inch or more inside the original from the outer edge 301 of the original 300.

2. 1. System Configuration FIG. 1 shows a system configuration of a position error measuring device incorporated in an image reading device according to an embodiment of the present invention. The position error measuring device is incorporated as an additional function to the image reading device, and measures a position error of a pixel in real time.

That is, the position pixel measuring device includes a photoelectric conversion unit 101, an A / D conversion unit 102, a shading correction unit 103, a diagonal line discrimination unit 104, and a position error measurement unit 1.
05, a position error measuring unit 106, and a control unit 107. In this embodiment, the photoelectric conversion unit 101 includes a line CCD, and converts a read image into an electric signal. The image converted into the electric signal is converted by the A / D converter 102 into digital multi-valued image data. The converted data is corrected by the shading correction unit 103 for unevenness of illumination, a decrease in the amount of light around the lens, a difference in sensitivity between pixels of the photoelectric conversion unit 101, and the corrected data is input to the oblique line determination unit 104. Is done. Oblique line determination unit 104
Then, the oblique line pattern portion of the image data is determined, and the determination result is output to the control unit 107. Further, the image data is input to the position error measurement unit 105, and an error signal of the measurement result is output to the position error correction unit 106. Position error correction unit 1
In step 06, image data in which a position error has been corrected is generated from the image data and an error signal which is position error data, and is output as a video signal. The respective units (101 to 106) are controlled by the control unit 107 to control timing, set operating conditions, and the like, and operate in association with each other.

3. Measurement Principle Next, the measurement principle of the reading error in the position error measurement unit will be described.

First, the processing for measuring the position error is as follows. The main scanning direction indicated by the arrow in FIG.
D7 indicates an arrangement of pixels of one line to be read simultaneously in a line-sequential manner, and an order on the time axis when the parallel data is converted to serial data. The sub-scanning direction indicated by an arrow indicates a reading direction while sequentially moving the reading range of one line in the main scanning direction. As a moving means, as shown in FIG. 2, in addition to a method in which the original sent by the ADF 100 is fixed at a predetermined position on the contact glass 1 and the scanning optical system is moved, the original is moved while the scanning optical system is fixed. There is a format to make it.

In FIG. 5, if a rectangular area surrounded by parallel lines in the main scanning direction and the sub-scanning direction is defined as a pixel, a plane formed by the pixel is used when an original image is converted into an electric signal. It can be understood that the mappings of the original images are arranged as they are. This may be called a bitmap. When this data is output from the line CCD 7 in real time, the main scanning direction and the sub-scanning direction have a chronological order, but each pixel can be arbitrarily accessed in the state of being stored in the memory. , Sub-scanning direction, and time.

FIG. 5 also shows that, when the pixel size in the main scanning direction and the sub-scanning direction is the same, the read data a of the 45 ° oblique line LN when the scanning speed in the sub-scanning direction does not change, and the scanning speed changes. The read data b at the time is shown in correspondence with the bit map. That is, the read data a indicates a time when scanning is performed at a predetermined constant speed corresponding to a clock for controlling the read timing in the sub-scanning direction, and is a 45 ° oblique line image as a bit map.

On the other hand, the inclination of the read data b varies depending on the fluctuation of the scanning speed. Section AB in the sub-scanning direction
Indicates that the scanning speed is "0". In this case, since the reading position does not change even if the address of the bitmap advances by the clock for controlling the reading timing in the sub-scanning direction, the line becomes a line parallel to the sub-scanning direction. . Section B
-C indicates the case where the scanning speed is 1/2 of the predetermined speed. In this case, even if the address of the bit map advances, an image at a position where only half of the address advances is read, so that the angle of the read image is about 26.57 °. (Tan θ = 0.5). Section CD shows when scanning at a predetermined speed, and is 45 °.
Is obtained. The section after D shows the case where the scanning speed is 1.5 times the predetermined speed, and the angle is about 56.31 °.

Therefore, the sub-scanning principle is based on the principle that the inclination of the image changes when the scanning speed fluctuates. Scanning speed unevenness, mirrors 3 to 5, lens 6, photoelectric conversion unit (CCD) 7
It is possible to measure the position error of the pixel of the bitmap image caused by the vibration of the image.

Although FIG. 5 shows a square pixel,
The pixels are not square, for example, the resolution in the main scanning direction is 4
The present invention can be applied to a pixel having a resolution of 00 dpi and a resolution of 600 dpi in the sub-scanning direction. Similarly, even if a diagonal line other than 45 ° is used, the relationship that the amount of movement of the diagonal line image in the main scanning direction depends on the reading speed in the sub-scanning direction is established. it can.

4. Oblique Line Pattern Determination Process Next, the oblique line pattern determination process in the oblique line determination unit will be described. FIG. 6 shows a case where the bit map has diagonal lines as in FIG. 5, and FIG.
5) shows the read value. Note that 0 = white, 255
= Black, coordinates in the main scanning direction are Xn, and coordinates in the sub-scanning direction are Ym. FIG. 8 shows three pixels in the main scanning direction.
8 (a) to 8 (e) show windows shifted one pixel at a time in the main scanning direction.

Here, the window (X) shown in FIG.
2 to X4, Y1 to 3), the sum Pa of the three pixel values in the diagonal direction sandwiching the center pixel in the diagonal direction, that is, the upper left diagonal direction including the center pixel, and the sum Qa of the three pixel values in the lower right diagonal direction are calculated. Pa = (X2, Y1) + (X3, Y1) + (X2, Y2) = 3 + 1 + 1 = 5 Qa = (X4, Y2) + (X3, Y3) + (X4, Y3) = 3 + 4 + 8 = 15

Similarly, with respect to FIGS. 8B to 8E, Pb = (X3, Y1) + (X4, Y1) + (X3, Y2) = 1 + 4 + 2 = 7 Qb = (X5, Y2) + (X4, Y3) + (X5, Y3) = 13 + 8 + 201 = 222 Pc = (X4, Y1) + (X5, Y1) + (X4, Y2) = 4 + 2 + 3 = 9 Qc = (X6, Y2) + (X5, Y3) ) + (X6, Y3) = 216 + 201 + 250 = 667 Pd = (X5, Y1) + (X6, Y1) + (X5, Y2) = 2 + 18 + 13 = 33 Qd = (X7, Y2) + (X6, Y3) + (X7) , Y3) = 248 + 250 + 252 = 750 Pe = (X6, Y1) + (X7, Y1) + (X6, Y2) = 18 + 220 + 216 = 454 Qe = (X8, Y2) + (X7, Y3) + (X8, Y3) = 250+ 252 + 249 = 751.

Next, when the difference R between the center pixel and the three pixels (including the center pixel) in the lower right diagonal direction is calculated, Ra = 15-5 = 10 Rb = 222-7 = 215 Rc = 667-9 = 658 Rd = 750-33 = 717 Re = 751-454 = 297

When the value of the difference R is large, it indicates that there is an oblique line pattern in the window of 3 × 3 pixels. Therefore, for example, when it is determined that the oblique line pattern exists when the value of R is 500 or more, it can be determined that the oblique line pattern exists in the windows shown in FIGS. 8C and 8D.

Next, another oblique line pattern discriminating process will be described with reference to FIG. 9 (a) to 9 (e) respectively show FIG.
Each value in the windows shown in FIGS.
8 shows a case where binarization is performed, and similarly, sums Pa to P of three pixel values in the upper left diagonal direction including the center pixel in each window.
Calculating the sum Qa to Qe of e and three pixel values in the lower right diagonal direction, Pa = (X2, Y1) + (X3, Y1) + (X2, Y2) = 0 + 0 + 0 = 0 Qa = (X4, Y2) + (X3, Y3) + (X4, Y3) = 0 + 0 + 0 = 0 Pb = (X3, Y1) + (X4, Y1) + (X3, Y2) = 0 + 0 + 0 = 0 Qb = (X5, Y2) + (X4 Y3) + (X5, Y3) = 0 + 0 + 1 = 1 Pc = (X4, Y1) + (X5, Y1) + (X4, Y2) = 0 + 0 + 0 = 0 Qc = (X6, Y2) + (X5, Y3) + ( X6, Y3) = 1 + 1 + 1 = 3 Pd = (X5, Y1) + (X6, Y1) + (X5, Y2) = 0 + 0 + 0 = 0 Qd = (X7, Y2) + (X6, Y3) + (X7, Y3) = 1 + 1 + 1 = 3 Pe = (X6, Y1) + (X7, Y1) + (X6, Y2) 0 + 1 + 1 = 2 Qe = (X8, Y2) + (X7, Y3) + (X8, Y3) = 1 + 1 + 1 = 3.

Next, the differences Ra to Re between the center pixel and the three pixels in the lower right diagonal direction (including the center pixel) are obtained. Ra = 0-0 = 0 Rb = 1-0 = 1 Rc = 3-0 = 3 Rd = 3-0 = 3 Re = 3-2 = 1

Therefore, also in this case, the difference R
Is large in the window of 3 × 3 pixels. For example, when it is determined that the value of Ra to Re is 2 or more, it is determined that there is a diagonal pattern.
It can be determined that there is an oblique line pattern in the windows shown in (c) and (d). Further, by binarizing the pixel value in this way, the addition operation can be simplified.

FIGS. 10A to 10D show matching patterns for oblique line pattern detection, in which white areas represent "0" and black areas represent "1". First, the image data is binarized as shown in FIG. 9, and the binarized data is compared with the matching patterns shown in FIGS. 10 (a) to 10 (d). In this example, FIG. 9 (c), FIG. 10 (b), and FIG. 9 (d)
And FIG. 10A, and it is determined that there is an oblique line pattern in this window.

In the above embodiment, the size of the window is set to 3 × 3. Obviously, even when the window size is different, a diagonal pattern can be detected by a similar determination method. In general, the larger the window size, the higher the discrimination system, but the longer the processing time and the larger the circuit scale.

5. Position Error Measurement Processing Next, position error measurement processing in the position error measurement unit will be described. FIG. 11 shows a plurality of oblique lines (three oblique lines K1 to K3 in the figure) in the bit map shown in FIG. 5, and a size of 10.times.3 for measuring a position error using the plurality of oblique lines. Is shown in FIG. First, the center of gravity in the main scanning direction is calculated to obtain the data position in the window W.
Window W 45 ° diagonally lower left like 1 → W2 → W3
Is shifted one pixel at a time. When the last window Wn of the oblique line K2 is reached, the window W is moved only in the main scanning direction, and the window Wn + of the next oblique line K3 is moved.
Move to 1.

Here, the position of the center of gravity in the main scanning direction is 45
In the case of the oblique line of °, if the position of the pixel does not move due to some error factor, if the window W is shifted as shown in the figure, it should move one pixel at a time in the main scanning direction. If the movement amount of the pixel is not one pixel, the position of the pixel fluctuates for some reason, and therefore, a position error can be obtained. If it is known that the main factor of the position error is caused by the unevenness of the scanning speed in the sub-scanning direction, it is easy to convert the data of the position error to the uneven speed.

Here, various noises including noise unique to the CCD are included in the image data. However, since the data of a large number of pixels including the data of the peripheral pixels is used to obtain the center of gravity, the center of gravity is used. In the process of obtaining the value of, the effect of noise is reduced, and measurement with a high S / N ratio becomes possible. In this case, the S / N ratio generally increases as the number of pixels in the window increases. The shape of the window is desirably large in the main scanning direction because the center of gravity in the main scanning direction is obtained, and the size in the sub-scanning direction can be measured even for one line.

6. Center-of-gravity measurement process Next, the center-of-gravity measurement process is performed according to the procedure shown in the flowchart of FIG.

This processing is started at the same time as the start of the scanning of the original. First, each coordinate value X, X in the main scanning direction and the sub scanning direction is set.
Y is initialized (X = 0, Y = 0) (step S1). These coordinate values X and Y are, for example, 3 ×
The coordinates of a certain pixel position, for example, the center pixel in the window No. 3. Next, a variable i indicating the number of measurements for one oblique line is initialized (i = 0) (step S).
2).

Next, the position error measuring section 105 determines whether or not a diagonal line pattern exists in the 3 × 3 window for diagonal line determination (step S3).
The x3 window is shifted by one pixel in the main scanning direction (X =
X + 1) (step S4). Note that this shift amount is determined according to the size of the window and the thickness of the oblique line, and
Pixels or more may be used. If there is a diagonal pattern in step S3, a window W1 of, for example, 10.times.3 for measuring the center of gravity is set, and the center of gravity in the window W1 is obtained (step S5). At this time, in accordance with the size of the window W1 and the thickness of the diagonal line, the position of the pixel determined to be diagonal is shifted by an integer number of pixels in the main scanning direction so that the diagonal line is near the center of the window W1. Window W1 may be set.

When the measurement of the center of gravity is completed, the displacement of the center of gravity is calculated (step S6), and then the window W2 shifted by -1 pixel in the main scanning direction and +1 pixel in the sub scanning direction.
Is set, and the count value i for the number of measurements is incremented by one (step S7). In this embodiment, the window W is moved one pixel at a time. However, if the frequency band such as vibration that causes a position error of the pixel is low, the window W may be moved two or more pixels. The time required for the measurement can be reduced by the method.

Next, if i = n does not hold for the preset number of measurements n of the same line, step S8
Then, the process returns to step S5, and when i = n, that is, when the window Wn is reached, the window is moved to the next hatched window Wn + 1 (step S8 → S9). As the method, the window coordinate is shifted in the main scanning direction by an integer pixel m from the pixel corresponding to the interval of the diagonal lines in the main scanning direction, the measurement count value i is cleared (step S2), and the diagonal line discrimination processing ( It returns to step S3). Similarly, the window Wn + 1, Wn + 2 for one oblique line
, Wn + 3 to measure the position error.

By measuring the position error using a plurality of oblique lines as described above, the position error can be measured over the entire sub-scanning area even if the reading range of the reading device is vertically long. Further, since the measurement is performed only in the narrow width in the main scanning direction, the measurement can be performed separately at the center, the front side, and the back side in the main scanning direction. Also, when measuring the position error with a high resolution, it is not necessary to make the hatched pattern thin, and a wide pattern can be used without being restricted by the MTF of the system.

Further, when a pattern having a wide width is used, the window becomes larger in accordance with the width, so that the measurement accuracy can be improved as a result. Therefore, the width of the diagonal line may be set in consideration of the balance between the processing speed, the size of the buffer when performing real-time processing, the economics of the circuit scale, and the like. Further, a position error can be measured by detecting an edge on one side using a wide pattern. Furthermore, for example, moiré is a problem when a black and white pattern is arranged in the sub-scanning direction regardless of the reading timing in the sub-scanning direction. The occurrence of moire is not a problem, and as a result, the position error can be measured with high accuracy.

7. Calculation of Window Data and Centroid Next, calculation of window data and centroid will be described in detail.

FIG. 13 shows the relationship between the window data and the read value of each pixel of the oblique line pattern. The read value is 8 bits and is represented by a decimal number (0 to 255). In order to obtain the center of gravity in the main scanning direction, the sum of each column (for three lines) in the sub-scanning direction is obtained, and as shown in FIG.
18, 50, 202, 42 as 0 to X9, respectively
7, 590, 562, 345, 150, 37, and 14 are obtained. If the center coordinates of each pixel in the main scanning direction are 0 to 9 in order from the left, and the center of gravity in the main scanning direction is Rm, the moment around the center of gravity Rm is 0, so X0 (Rm-0) + X1 (Rm-1) ... + X9 (R
m-9) = 0, and Rm = 4.36 is obtained by substituting numerical values.
2 is obtained.

The reason for finding the center of gravity is that the calculation can be simplified and the speed can be increased without the need for preprocessing such as interpolation. Further, when obtaining the image position, a method of obtaining a data string of a predetermined resolution by interpolation from the arrangement of the sum of the data of each column and obtaining the position where the peak value exists from the data can be used.

8. Calculation of Center of Gravity of Chart Next, a case of calculating the center of gravity of a chart composed of a plurality of oblique lines will be described. When calculating the barycenter of a plurality of diagonal lines as shown in FIG. 11, there is no problem with lines on the same line, but when the window moves to a different line, the distance between the diagonal lines in the main scanning direction before and after the movement is different. Since the value of the center of gravity is different unless the number of pixels is exactly an integer, it must be corrected. As an example, the value of the center of gravity Rn of the window Wn of the hatched line K2 shown in FIG. 11 is 4.65, and the value of the center of gravity Rn + of the window Wn + 1 when the window is moved to the next hatched line K3.
1 is 4.38, the value of the center of gravity Rn + 2 of the window Wn + 2 is 4.40, and the value of the center of gravity Rn + 3 of the window Wn + 3 is 4.4.
When it becomes 1, the difference ΔR of the center of gravity in the line where the window has moved is calculated as follows: ΔR = Rn−Rn + 1 = 4.65−4.38 = 0.27

This value ΔR is added to the value of the center of gravity of the oblique line K3, and the result of this addition is used as the value of the center of gravity to obtain a position error.
In this case, the value of the center of gravity Rn + 2 of the window Wn + 2 and the value of the center of gravity Rn + 3 of the window Wn + 3 are as follows: Rn + 2 = Rn + 2 + ΔR = 4.40 + 0.27 = 4.67 Rn + 3 = Rn + 3 + ΔR = 4.41 + 0.27 = 4.68 Therefore, even if a chart composed of a plurality of oblique lines is used, the position error can be continuously measured with high accuracy. However, the window W of the oblique line K2
When moving from n to the window Wn + 1 of the oblique line K3, the oblique lines K2 and K3 must exist simultaneously in the main scanning direction.

FIG. 14 shows an arrangement relationship of oblique lines, and the length L1
Are arranged at an angle θ with respect to the main scanning direction,
If the start point and the end point of the oblique line in the main scanning direction are the same, assuming that the oblique line interval in the main scanning direction is L2, the oblique lines can be arranged such that the following relationship holds: L2 <L1 × cos θ (1) Since the diagonal lines overlap in the main scanning direction, the window can be moved in the main scanning direction to continuously measure the center of gravity of the next diagonal line.
Here, as the length L1 of the oblique line and the positions of the start point and the end point of the oblique line in the main scanning direction become smaller, the greater the magnitude relation of the equation (1), the less precision is required.

9. Position Error Correction Processing The correction of the read data in the position error correction unit is performed as follows.

That is, in this embodiment, correction is performed using cubic function convolution. FIG. 15 is a model diagram of the correction using the cubic function convolution, and FIG. 16 is a flowchart showing the processing procedure of the correction. As can be seen from the figure, the pixel positions in the sub-scanning direction when there is no speed unevenness are equally spaced as shown by the pixel row P. However, when there is unevenness in the speed, as shown by the pixel column Q, the interval varies and deviates from a correct position. The figure shows that the pixel that should originally be at the position of Pn is actually the pixel Q
Indicates that it is at position n.

Here, the image data (density data) of the data Pn in the certain scanning direction on the nth line is created from the image data of the pixel array Q and the position data by using a cubic function convolution which is a weighting function. An example will be described.

When the cubic function convolution is used, data within two pixels (r0) from the ideal n-th line (Pn) is detected from the position error data (steps 171 and 172). In this case, Qn, Qn + 1,
The data of Qn + 2, Qn + 3, and Qn + 4 are targeted. Here, the reason why the number of pixels is within two pixels is that data of r0 or more is treated as having a correction coefficient of 0, so that no more data is necessary. Then, the distance r of each data from Pn
To find the interpolation function h (r) for each data Q. This becomes the correction coefficient (step 173). Here, the interpolation function h (r) is a piecewise cubic polynomial approximation of sinx / x, and the following equation is given by the distance r from the center: h (r) = 1-2 | r | 2+ | r | 3 (2) where 0 ≦ | r | <1 h (r) = 4−8 | r | +5 | r | 2− | r | 3 (3) where 1 ≦ | r | < 2 h (r) = 0 (4) where 2 ≦ r | Then, under the interpolation function h (r), the correction coefficient is multiplied by the corresponding Q data to obtain Pn. Further, in order to correct the density unevenness, the sum of the correction coefficients is set to the denominator so that the sum of the correction coefficients becomes 1. That is, Pn = {Qn.h (r1) + Qn + 1.h (r2) + Qn + 2.h (r3) + Qn + 3.h (r4) + Qn + 4.h (r5)} / {h (r1) + H (r2) + h (r3) + h (r4) + h (r5)｝ (5) (step 174).

When this control is completed for the data in the main scanning direction of the n-th line, the line to the (n + 1) -th line is shifted and repeated until the last line (step 175). At this time, the interpolation coefficient h (r
) And the sum of the denominator interpolation coefficients and their reciprocal are
It may be executed once before the correction of the image data in the corresponding main scanning direction. By performing such control, it is possible to create image data when the image is read at the correct position from the read image data based on the position error data measured as described above, thereby correcting the position error. Becomes possible.

The state before and after the correction as described above is shown in FIG.
FIG. An ordinary reading device starts reading an image after a certain speed has been reached after the carriage has started scanning. However, in FIG. 17A, the image reading is started immediately after the carriage starts scanning in order to show a large positional error. The figure which started reading has been illustrated. At this time, a 45-degree oblique line is also read at the same time, a position error is obtained from the image of the oblique line pattern portion by the above-described method, and an image obtained by correcting the position error from the position error data and the read image data is shown in FIG. This is shown in b). It can be seen that by performing the correction in this manner, an image faithful to the original can be reproduced even if the position error is read very large.

[0071]

As described above, according to the first aspect of the present invention, without adding an extra hardware-
By software, in other words, it is possible to measure the positional error of the pixel of the device that reads the original in a bitmap format by a simple arithmetic processing programmed, thereby eliminating the occurrence of an abnormal image and the displacement of the image. .

According to the first aspect of the present invention, by using an original on which a diagonal pattern is printed in advance, it is possible to read a high-precision image without providing a diagonal pattern in the main body of the reading apparatus.

Further, according to the second and third aspects of the present invention, since the oblique line pattern is formed on the basis of inches, the image density used in this type of image reading apparatus, so-called dot / inch (DPI). , And the expansion and contraction of the image can be detected on the basis of inches during the calculation, and the calculation for correction becomes easier.

[Brief description of the drawings]

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

FIG. 2 is a cross-sectional view illustrating an image reading apparatus including an ADF according to an embodiment of the present invention.

FIG. 3 is a plan view showing the overall configuration of a document on which a diagonal pattern is printed.

FIG. 4 is an enlarged plan view showing a main part of a document on which another oblique line pattern is printed.

FIG. 5 is an explanatory diagram showing read data of a hatched pattern according to a change in a scanning speed.

FIG. 6 is an explanatory diagram showing an oblique line pattern in an enlarged manner.

FIG. 7 is an explanatory diagram showing read values of a hatched pattern in FIG. 6;

FIG. 8 is an explanatory diagram showing a diagonal line determination window.

FIG. 9 is an explanatory diagram showing another oblique line determination window.

FIG. 10 is an explanatory diagram illustrating a matching pattern for oblique line determination.

FIG. 11 is an explanatory diagram showing a window for measuring the center of gravity.

FIG. 12 is a flowchart illustrating a process of measuring the center of gravity in the image reading apparatus.

FIG. 13 is an explanatory diagram showing a read value and a method of measuring the center of gravity in the window for measuring the center of gravity.

FIG. 14 is an explanatory diagram showing the length and angle of a pattern.

FIG. 15 is a diagram for describing correction processing by cubic function convolution.

FIG. 16 is a flowchart illustrating a processing procedure of a correction process based on a cubic function convolution.

FIG. 17 is a diagram illustrating states of an image before and after correction in a correction process using cubic function convolution.

[Description of Signs] 1 contact glass 2 housing 18 light source 3, 20, 21 mirror 10 oblique line pattern 10a oblique line 22 lens 23 photoelectric conversion element (line CCD) 100 ADF 101 photoelectric conversion unit 102 A / D conversion unit 103 shading correction unit 104 Oblique line determination unit 105 Position error measurement unit 106 Position error correction unit 107 Control unit 200 Scanner 300 Document 301 Outer edge of document

Claims (3)

[Claims] 1. A document feeding means for automatically feeding a document onto a contact glass, and a reading means for scanning a fed document line-sequentially at predetermined time intervals to read a document image. An oblique line pattern formed by arranging lines having a constant inclination with respect to the scanning direction at equal pitches is printed on a read original in advance. Means for optically reading the diagonal pattern printed on the original fed by the means and converting the pattern into an electric signal; and setting a window in the image data of the diagonal pattern converted to the electric signal by the converting means. Means for calculating the center of gravity of the image data in the window, and means for moving the window according to the value of the center of gravity calculated by the means for calculating the center of gravity. Image reading apparatus is characterized by providing a means for measuring a position error of the pixel from the calculated center of gravity values by means for calculating the center of gravity. 2. The image reading apparatus according to claim 1, wherein the uniform pitch oblique line pattern printed on the read document is set at a pitch based on an inch unit. 3. The image reading apparatus according to claim 1, wherein the oblique line pattern is printed within a range of one inch from an outer edge of the sheet.