JPH10285351A - Image reading device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain correct position error data by separating and correcting a position shift of an oblique line pattern and a shift from an average scanning speed of a scanner. SOLUTION: A position shift amount of a measurement pattern 10 is detected based on a difference between position error data obtained from two oblique line patterns 10a and 10b different from each other in a scanning direction.
Since the amount of displacement does not normally change, the amount of displacement of the oblique line patterns 10a and 10b is stored in the storage unit 108, and at the time of normal reading, one of the right and left oblique line patterns 10a and 10b is used. The position error of the oblique line pattern is detected by measuring the position error, reading the position error amount of one of the oblique line patterns 10a and 10b from the storage unit 108 as needed, and correcting the measured position error data. In this case, the one pattern and the other pattern each have a certain inclination in the opposite direction, and the one pattern 1 is overlapped in the sub-scanning direction.
The other pattern 10b was arranged close to 0a.

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 Unexamined Patent Application Publication No. 2000-252, “scanning line pitch measurement method” (conventional example 2) is also known. 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]

In the first prior art, data obtained by reading patterns of the same shape is different due to the difference in the positional relationship between the edge of the pattern of the equal pitch line and the sampling timing of the reading. There is a phenomenon called moiré. 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 influence of moiré is neglected, 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.

[0006] Further, in pattern refinement, the frequency band of the measurement is widened in a higher direction, and the accuracy cannot be increased. Therefore, a process of interpolating the 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.

Further, since a specific light receiving element in the photoelectric conversion device uses image data obtained by scanning in the sub-scanning direction, the noise of the light receiving element itself affects the accuracy of the measurement itself. To degrade the 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.

To solve these problems, the present applicant has already filed Japanese Patent Application No. Hei 7-260438. Among them, some positional deviations occurring when a pattern formed from a plurality of lines having a constant inclination with respect to the scanning direction for measuring the positional error is installed in the image reading apparatus are detected, and the positional error is detected. Proposed technologies that can be sought.

In this technique, in order to correct a positional shift when a diagonal pattern is set, the inclination of the diagonal pattern is determined by linear approximation from measured position error data to correct the positional deviation.

However, even when the average scanning speed of the scanner is not a predetermined value, the position error data has a slope. Therefore, it is possible to separate the inclination due to the positional shift of the oblique line pattern or the slope due to the deviation of the average scanning speed of the scanner. Was not taken into account. Although it is obvious that the cost increases as the number of readings increases with respect to the cost of the apparatus, no consideration has been given to lowering the cost in consideration of the number of CCDs.

SUMMARY OF THE INVENTION The present invention has been made in view of such a background, and a first object of the present invention is to correct an error by separating and correcting a position shift of an oblique line pattern and a shift of a scanning speed of a scanner from an average speed. An object of the present invention is to provide an image reading apparatus that can obtain position error data, corrects an error in the position of a pixel based on the position error data, and has no position shift.

A second object of the present invention is to provide an image reading apparatus capable of reducing the number of pixels of a CCD and reducing costs.

A third object of the present invention is to provide an image forming apparatus in which even if dirt or other patterns are present in the background portion of a diagonal pattern, correct measurement cannot be performed due to these dirt or patterns. Is to provide.

[0015]

In order to achieve the above object, a first means is provided in an image reading apparatus for scanning an image line-sequentially at regular time intervals and reading the image outside a scanning area of a document. A first pattern composed of a plurality of lines having a constant inclination with respect to the scanning direction, and a first pattern having a constant inclination in a direction opposite to the first pattern and overlapping in the sub-scanning direction. The second pattern consisting of a plurality of lines arranged in close proximity to the first pattern and the first and second patterns are read to measure the position error of the pixel corresponding to each of the patterns having different inclinations. Means for correcting the position error of the pixel based on the value measured by the measuring means, and means for correcting the corrected position error of the pixel. To have.

The second means further includes means for obtaining a position error from the first pattern, the first means, and the second means.
Means for obtaining a position error from the pattern, means for obtaining the difference between the position errors of the two patterns obtained by the two means, and means for storing the difference between the obtained position errors,
At the time of normal reading, the position error is measured by using one of the first and second patterns, and the position error of the pixel is corrected based on the value of the difference between the position errors stored in the storage unit. Means is provided.

The third means is characterized in that the storing means in the second means is nonvolatile.

The fourth means includes a means for obtaining a position error from the first pattern, the first means, and the second means.
Means for calculating a position error from the first pattern, image data obtained by reading the first and second patterns when the measurement of the position error starts from the first pattern,
Means for setting a window including the pattern part of the above, means for sequentially moving and resetting the window by an integer number of pixels, and moving the window in the main scanning direction when the window is moved to a certain position. Means for setting the window including the second window portion, means for calculating the position of the pattern in the set area every time the window is set, and means for calculating the change in the position data of the pattern before and after the movement of the window. Means for calculating a position error by calculating;
Means for correcting the position error data from the position error obtained from the pattern.

[0019]

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

1. First, an outline of a reading apparatus according to the present embodiment will be described with reference to FIG. The contact glass 1 is supported by the housing 8, and the original is placed on the contact glass 1 with the reading surface facing down. The original on the contact glass 1 is illuminated by the light source 2, and the reflected light on the reading surface is sequentially reflected by the first mirror 3, the second mirror 4, and the third mirror 5, and then the lens 6 forms a line on the photoelectric conversion device 7. The image is formed on the light receiving surface of the photoelectric conversion element and converted into an electric signal.

The light source 2 and the first mirror 3 are mounted on a first carriage (not shown). The first carriage is driven by a driving device (not shown) while keeping the distance from the original surface constant so as to read the original line-sequentially. It moves in the sub-scanning direction (left-right direction in the figure). The second mirror 4 and the third mirror 5 are attached to a second carriage (not shown), and the second carriage moves in the sub-scanning direction at half the speed of the first carriage. By such a method, a predetermined range on the contact glass 1 can be read line-sequentially.

As shown in FIG. 2, a reference density plate 9 for causing a photoelectric conversion element to read a reference density for shading correction is provided on a housing 8 around the contact glass 1 so as to extend in the main scanning direction. Attached to
In order to detect the scanning position or scanning speed of the first carriage in the sub-scanning direction, as shown in FIG.
The measurement pattern 10 on which two types of oblique line patterns 10a and 10b of a large number of black oblique lines L having angles of 5 ° and 135 ° are formed at equal pitches in two stages in the sub-scanning direction. The reference density plate 9 is read by the photoelectric conversion device 7 and is used for correcting variations in sensitivity among the linear photoelectric conversion elements, uneven illumination, a decrease in the amount of light around the lens 6, and the like. The first and second oblique line patterns 10a and 10b are similarly read by the photoelectric conversion device 7. Since the oblique line patterns 10a and 10b are read by the photoelectric conversion device 7 together with the image data, it is necessary to form an image on the light receiving surface of the photoelectric conversion element similarly to the original, and is provided on the surface of the contact glass 1 on which the original is placed. But,
When an image is taken into a computer or the like and the position error is measured, the oblique line patterns 10a and 10a
b may be installed.

FIG. 3 is an enlarged view of the first and second diagonal patterns 10a and 10b and the main part of the contact glass 1 in FIG. The oblique line patterns 10a and 10b are composed of a plurality of straight lines having a certain relative inclination in the scanning direction. Originally, it is desirable that the measurement pattern 10 be parallel to the scanning direction. However, the position may be shifted due to the material of the measurement pattern 10 or variation in assembling, and FIG. The state at the time of shifting has been shown. According to the present invention, a position error is obtained in consideration of the position deviation and the deviation from the average scanning speed of the image reading apparatus.

In the diagonal pattern 10, the first diagonal pattern 10a and the second diagonal pattern 10b intersect in the sub-scanning direction, and the leading end of each pattern reaches a position close to the side surface of the other pattern. I have.

2. System Configuration FIG. 4 shows a system configuration of a position error measuring device incorporated in the image reading device according to the 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 correction unit 106, a control unit 107, and a storage unit 108. The photoelectric conversion unit 101 includes:
In this embodiment, a line CCD is used, and a read image is converted 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 like.
The corrected data is input to the oblique line determination unit 104. In the oblique line determination unit 104, the measurement pattern 10
The part is determined, and the result of the determination is output to the control unit 107. Further, the image data is input to the position error measurement unit 105, which measures the position error between lines for each read line in the sub-scanning direction, and outputs an error signal of the measurement result. The position error measuring unit 105 measures the position error with respect to the oblique line patterns 10a and 10b composed of a plurality of oblique lines having a constant inclination with respect to the scanning direction, and corrects the two measured position error data into correct position error data. The measured position error data is output as an error signal. The position error correction unit 106 generates image data in which a position error has been corrected from the image data and the error signal that is the position error data, and outputs the image data 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. In addition, the storage unit 108 stores a positional shift amount of the oblique line patterns 10a and 10b described later.

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. 5 is a row of pixels of one line that the line CCD 7 simultaneously reads line-sequentially as a photoelectric conversion device (corresponding to the photoelectric conversion unit 101 in FIG. 4), and converts the parallel data into serial data. It shows the order on the time axis when it is done. 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 unit, there is a type in which the scanning optical system is moved while the original is fixed as shown in FIG. 2, and a type in which the original is moved while the scanning optical system is fixed, as shown in FIG.

In FIG. 5, when 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 shows read data a of 45 ° oblique lines when the scanning speed in the sub-scanning direction does not fluctuate when the pixel sizes in the main scanning direction and the sub-scanning direction are equal.
And the read data b when the scanning speed fluctuates are 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 read data b has a different inclination according to the change in 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 twice the predetermined speed, and the angle is about 63.4 °.

Therefore, as a measurement principle, the inclination of the image changes when the scanning speed fluctuates. In other words, based on the measurement principle, the amount of movement of the oblique line in the main scanning direction corresponds to the moving speed in the sub-scanning direction. In the case of reading by the method, unevenness in the scanning speed of the carriage in the sub-scanning direction and
In the case of reading by the automatic document feed system, the unevenness of the feed speed of the document, the mirrors 3 to 5, the lens 6, the photoelectric conversion unit (C
The position error of the pixel of the bitmap image caused by the vibration of the CD 7 can be measured.

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. 7 shows 8 bits (0 to 25) in that case.
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) each show a window shifted by one pixel 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, as for 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 three pixels (including the center pixel) in the lower right diagonal direction is obtained, 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. FIGS. 9A to 9E respectively show FIGS.
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 central pixel and the three pixels in the lower right diagonal direction (including the central 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, it indicates that the oblique line patterns 10a and 10b are present in the 3 × 3 pixel window.
When the value of Re is 2 or more, the oblique line patterns 10a and 10b
Is determined, it can be determined that the oblique line patterns 10a and 10b are present in the windows shown in FIGS. 9 (c) and 9 (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). to decide. In this example, FIGS. 9 (c) and 10 (b)
9 (d) and FIG. 10 (a) match, and it is determined that there are oblique line patterns 10a and 10b in this window.

In the above embodiment, the size of the window is set to 3 × 3. Of course, even when the window size is different, the oblique line pattern 10
a and 10b can be detected. In general, however, the larger the window size, the higher the accuracy of the determination, but the longer the processing time and the larger the circuit size.

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 (five oblique lines Ka1 to Ka3 and Kb1 to Kb2 in the figure) of the oblique line patterns 10a and 10b in FIG. 3 in the bit map shown in FIG.
A window W of 10 × 3 size for measuring a position error using the plurality of oblique lines is shown.

First, the oblique line K of the oblique line pattern 10a on the left side
The case where the position error is obtained from a1 will be described. First, the center of gravity in the main scanning direction is calculated to obtain the data position in the window W. The window W is sequentially shifted obliquely to the lower left by 45 ° in the order of Wa1, Wa2, and Wa3. At this time, control is performed such that the hatched line Ka2 always falls within the window. Then, when the window reaches a predetermined address in the main scanning direction, in this case, when the window reaches the window Wan, the window W is moved only in the main scanning direction and moved to the next window Wan + 1 indicated by the oblique line Ka3. . The window moves in the same manner as Wan + 1 → Wan + 2 → Wan + 3.

Similarly, for the diagonal line pattern Kb1 on the right side, the window W is sequentially shifted obliquely downward and to the right by 45 °, such as Wb1.fwdarw.Wb2.fwdarw.Wb3. And
When the window reaches the address in the predetermined main scanning direction, in this case, when the window reaches the window Wbn, the window W is moved only in the main scanning direction and is moved to the next window Wbn + 1 indicated by the oblique line Kb2. The window moves in the same manner as Wbn + 1 → Wbn + 2 → Wbn + 3.

Here, when the value of the center of gravity changes, it means that the position of the pixel has moved for some reason, and thus 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.

Although various noises including noise unique to the CCD are included in the image data, since the data of a large number of pixels including the data of peripheral pixels is used to obtain the center of gravity, the center of gravity is determined. The influence of noise is reduced in the process of obtaining, and measurement with a high S / N ratio becomes possible. in this case,
Normally, as the number of pixels in the window increases, the S / N ratio 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 process starts at the same time as the start of scanning of the document. First, the coordinate values X and Y in the main scanning direction and the sub-scanning direction are initialized (X = 0, Y = 0) (step S1). The coordinate values X and Y are coordinates of a certain pixel position, for example, a center pixel in a 3 × 3 window for oblique line determination. Next, a variable i indicating the number of measurements for one oblique line is initialized (i = 0) (step S2).

Next, the position error measuring unit 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 deviation 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 at a time. 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 in this manner, 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 in the oblique line pattern. The read value is 8 bits and is represented by decimal (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.
0, X1 to X9 as 18, 50, 202, respectively
427, 590, 562, 345, 150, 37, 14
Ask for. 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 obtaining the center of gravity is that the calculation can be simplified and speeded up without the need for pre-processing 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 Ran of the center of gravity of the window Wan of the diagonal line Ka2 shown in FIG. 11 is 4.65, and the value Ran of the center of gravity of the window Wan + 1 when moving to the next diagonal line Ka3
+1 is 4.38, the value of the center of gravity Ran + 2 of the window Wan + 2 is 4.40, and the value of the center of gravity Ran + 3 of the window Wan + 3 is 4.4.
When it becomes 1, the difference ΔRa of the center of gravity in the line where the window has moved is calculated as follows: ΔRa = Ran−Ran + 1 = 4.65−4.38 = 0.27

This value ΔRa is added to the value of the center of gravity of the oblique line Ka3, and a position error is obtained using the result of addition as the value of the center of gravity.
In this case, the value of the center of gravity Ran + 2 of the window Wan + 2 and the value of the center of gravity Ran + 3 of the window Wan + 3 are Ran + 2 = Ran + 2 + ΔRa = 4.40 + 0.27 = 4.6.
7 Ran + 3 = Ran + 3 + ΔRa = 4.41 + 0.27 = 4.6
8 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 Ka2
When moving from an to the window Wan + 1 of the oblique line Ka3, the oblique lines Ka2 and Ka3 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. 9.1 First Method FIGS. 15, 16 and 17 are partially enlarged oblique line patterns 10a and 10b each composed of a plurality of 45 ° oblique lines facing the contact glass 1 with respect to the scanning direction. FIG.

FIG. 15 shows a case in which the measurement pattern 10 is set in parallel with the contact glass 1 without any displacement and the average speed is also predetermined. In this case, a 45 ° oblique line pattern is also formed in the above-described bitmap pattern.
The measurement result of the position error in this case is as shown in FIG.
In this figure, the distance in the sub-scanning direction from the original position to the actual scanning position with respect to the position in the sub-scanning direction is shown as a position error. The unit is a dot. When the average speed is a predetermined value at the time of equal magnification, a position error is measured around "0" as shown in FIG. At this time,
No difference is observed between the left and right oblique line patterns 10a and 10b.

FIG. 16 shows a case where the measurement pattern 10 is set in parallel with the contact glass 1 without any displacement and the average speed is slightly higher than a predetermined value. In this case, the bitmap pattern is formed at an angle slightly larger than 45 °, that is, in the direction in which the left and right oblique line patterns 10a and 10b open. FIG. 19 shows the measurement result of the position error at this time. As can be seen from this figure, when the average speed is different from the predetermined value, a tilt occurs in the measurement result of the position error. If it is faster than the predetermined value, the slope increases. At this time, there is no difference between the left and right oblique line patterns 10a and 10b.

FIG. 17 shows a case in which the measuring pattern 10 is set slightly inclined with respect to the contact glass 1 and the average speed is higher than a predetermined value. In this case, when the oblique line patterns 10a and 10b are inclined as shown in FIG. 17, the left oblique line pattern 10b is inclined in a direction in which the angle becomes smaller with respect to the scanning direction, and the right oblique line pattern 10a is inclined with respect to the scanning direction. Tilt in the direction to increase the angle. FIG. 20 shows a measurement result of the position error in this case. In FIG. 20, the oblique line pattern 10b on the left side is detected in a direction in which the speed is faster than the actual average speed by an amount corresponding to the inclination of the oblique line, and is measured in a direction in which the inclination increases. Conversely, the oblique line pattern 10a on the right side is detected in a direction in which the speed is slower by the slanted line than the average speed, and is measured in a direction in which the inclination decreases. Since the position error measurement data obtained from the left oblique line pattern 10b and the position error measurement data obtained from the right oblique line pattern 10a are averaged, the inclination of both oblique line patterns 10a and 10b is obtained. And true position error data can be obtained regardless of the inclination of the measurement pattern 10.

As described above, the position error of the measurement pattern 10 and the deviation of the average speed from a predetermined value are separated by measuring the respective position errors by using the oblique line patterns 10a and 10b having different angles with respect to the scanning direction. And right and left oblique line patterns 10a and 10a.
By averaging the position error data b, even if the measurement pattern 10 has a position shift, the position error can be accurately measured.

FIG. 21 is a result obtained by plotting the difference between the position error data measured using the right oblique line pattern 10a and the position error data measured using the left oblique line pattern 10b in the measurement result of FIG. This line indicates the inclination of the measurement pattern 10. As described above, the amount of displacement of the measurement pattern 10 can be detected from the difference between the data of the position errors obtained from the two different oblique line patterns 10a and 10b in the scanning direction.

9.2 Second Method The position shift of the oblique line pattern can be detected by the control as in the first method described above, but the amount of this position shift does not usually change. Therefore, the amount of misalignment of the oblique line patterns 10a and 10b shown in FIG.
08, and at the time of normal reading, the position error is measured using one of the left and right oblique line patterns 10a and 10b, and the positional deviation amount of any of the oblique line patterns 10a and 10b is stored from the storage unit 108 as needed. By correcting the read and measured position error data, the amount of position shift of the oblique line pattern can be detected. Since the positional shift of the oblique line pattern does not usually change, it may be performed at power-on or at the time of adjustment by a service person. In this case, if a non-volatile storage unit, for example, a non-volatile RAM is used as the storage unit 108, the amount of displacement can be stored even when the power is turned off. There is no need to calculate.

10. Noise Removal Method If there is dust or scratches on the contact glass 1 or the measurement pattern 10, any attempt to measure a position error will appear as noise. When the window wa is at the position as shown in FIG. 22, the user wants to obtain the center of gravity of the portion A of the left oblique line pattern 10a.
Since 0b is also within the window Wa, it is necessary to set the image data of the B portion of the oblique line pattern 10b to 0.

As shown in FIG. 23, the data of the main scanning line of the image data obtained by reading the oblique line pattern 10 monotonously increases in an area corresponding to one edge of the oblique line, and increases in an area corresponding to the opposite edge. Monotonically decreases. Using this characteristic, a position corresponding to the center position of the oblique line is obtained, and the data of the pixel at a position separated from the position by a predetermined distance or more is set to 0.

As another method, there is a method of removing an isolated point. In this method, since the width of the diagonal line is fixed, if the distance from the monotonically increasing position to the monotonically decreasing position is equal to or less than the diagonal line width as described above, it is determined to be an isolated point and removed. If there is the same diagonal line width, the right diagonal pattern 10b is set to 0 when calculating the position error of the left diagonal pattern 10a. By performing such processing, noise can be reduced, and measurement accuracy can be improved.

11. 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, the correction is performed using the cubic function convolution. FIG. 24 is a model diagram of the correction using the cubic function convolution, and FIG. 25 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 at the position of pixel Qn.

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

When using the cubic function convolution, data within two pixels (r0) from the ideal position of the nth 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 formula is used according to 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, in equation (5), the interpolation coefficient h
The calculation of the sum of (r) and the interpolation coefficient of the denominator and the calculation of the reciprocal thereof may be performed once before the correction of the corresponding image data in the 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.
6 is shown. A normal reading apparatus starts reading an image after a certain speed has been reached after the carriage has started scanning. However, in FIG. 26A, 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 this 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.

12. Number of pixels of CCD FIG. 27 shows a pattern of the present embodiment in which diagonal patterns overlap in the sub-scanning direction, and FIG. 28 shows a conventional pattern in which diagonal patterns do not overlap in the sub-scanning direction.
As can be seen from a comparison between the two, a CCD row for reading a diagonal pattern is conventionally required for the width D2, whereas FIG.
In the present embodiment, the width D1 is sufficient. Therefore, even if the number of pixels of the CCD corresponding to D2-D1 is reduced, the oblique line pattern can be sufficiently read, whereby the cost can be reduced by the reduced number of pixels.

[0076]

As described above, according to the first aspect of the present invention, the position error of the pixel in the sub-scanning direction can be measured with high accuracy without requiring a precise pattern positioning mechanism or a precise pattern. And also corrects the position error of the image based on the measured position error data,
Image data without positional displacement can be obtained. Further, since the width of the pattern portion in the main scanning direction is reduced, the number of CCD pixels required for reading the pattern portion can be reduced, thereby reducing the cost.

According to the second aspect of the invention, in addition to the effect of the first aspect, at the time of normal reading, only one position error is measured, and the value of the difference between the position errors determined in advance is used. Thus, the position error data is corrected, so that the calculation time can be shortened.

According to the third aspect of the present invention, in addition to the effect of the second aspect of the present invention, even if the power is turned off, the amount of displacement can be stored. There is no need to calculate the amount, and processing can be performed quickly.

According to the fourth aspect of the present invention, in the calculation of the center of gravity, the noise at a position farther from the center of gravity has a greater effect. However, since the center of gravity is calculated after reducing the noise of the image data, the measurement is performed. Accuracy can be improved.

[Brief description of the drawings]

FIG. 1 is a sectional view of an image reading apparatus according to an embodiment of the present invention.

FIG. 2 is a plan view of the image reading apparatus of FIG. 1;

FIG. 3 is an enlarged view of a main part of a measurement pattern and a contact glass attached to the image reading apparatus.

FIG. 4 is a block diagram showing a system configuration of a position error measuring device attached to the image reading device of FIG. 1;

FIG. 5 is an explanatory diagram of read data of an oblique line pattern according to a change in 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 partially enlarged view showing an example of a pattern composed of a plurality of 45 ° oblique lines facing the contact glass 1 with respect to the scanning direction.

FIG. 16 is a partially enlarged view showing another example of a pattern composed of a plurality of oblique lines at 45 ° facing the contact glass 1 with respect to the scanning direction.

FIG. 17 is a partially enlarged view showing still another example of a pattern composed of a plurality of oblique lines at 45 ° facing the contact glass 1 with respect to the scanning direction.

FIG. 18 is a diagram showing a position error measurement result of the pattern of FIG.

FIG. 19 is a diagram showing a position error measurement result of the pattern of FIG. 16;

20 is a diagram showing a position error measurement result of the pattern of FIG. 17;

21 is a diagram in which the difference between the position error data measured using the left oblique line pattern and the position error data measured using the right oblique line pattern in the measurement result of FIG. 20 is plotted.

FIG. 22 is an explanatory diagram showing a state in which windows are applied to both adjacent oblique line patterns inclined in different directions.

FIG. 23 is a diagram showing image data obtained by reading oblique lines along a main scanning line.

FIG. 24 is a model diagram of correction using cubic function convolution.

FIG. 25 is a flowchart illustrating a correction processing procedure.

FIG. 26 is a diagram showing a state before and after correction.

FIG. 27 is an enlarged view of a diagonal line pattern according to the embodiment.

FIG. 28 is an enlarged view of a hatched pattern according to the conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Contact glass 2 Light source 3, 4, 5 Mirror 6 Lens 7 Photoelectric conversion element (line CCD) 8 Case 10 Measurement pattern 10a, 10b Oblique line pattern 101 Photoelectric conversion unit 102 A / D conversion unit 103 Shading correction unit 104 Oblique line discrimination Unit 105 Position error measurement unit 106 Position error correction unit 107 Control unit 108 Storage unit

Claims (4)

[Claims] 1. An image reading apparatus which scans an image line-sequentially at a fixed time interval and reads the image, wherein the image reading device comprises a plurality of lines provided outside a scanning area of a document and having a certain inclination with respect to a scanning direction. A first pattern and a plurality of lines having a constant inclination in a direction opposite to the first pattern and being arranged close to the first pattern so as to overlap in the sub-scanning direction. A means for measuring a position error of a pixel corresponding to each of the patterns having different inclinations by reading the first and second patterns; and a pixel based on a value measured by the measuring means. An image reading apparatus comprising: means for correcting a position error; and means for correcting the corrected position error of a pixel. A means for obtaining a position error from the first pattern; a means for obtaining a position error from the second pattern; a means for obtaining a difference between the position errors of the two patterns obtained by the two means; Means for storing the difference between the obtained position errors, and measuring the position error using one of the first and second patterns during normal reading, and storing the position error stored in the storage means. 2. The image reading apparatus according to claim 1, further comprising: means for correcting a position error of a pixel based on a value of the difference. 3. The image forming apparatus according to claim 2, wherein said storing unit is non-volatile. 4. A means for sequentially setting a window for the read diagonal pattern image data and calculating a center of gravity of the image data in the window, and measuring a position error of a pixel of the reading device to obtain a noise of the image data of the window. 2. The image according to claim 1, further comprising: means for reducing noise of the image data by means for reducing noise, and thereafter calculating the center of gravity of the window by means for calculating the center of gravity. Forming equipment.