JPH1075331A - Image reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the image reader with an automatic draft feeder by which a position error is detected with high precision. SOLUTION: In the image reader with an ADF, a pattern of slant lines LN is provided to a surface of a carrier roller 4a to feed an original with a carrier drum in the ADF to measure a position error, and the position error is corrected by reading the slant line pattern moved at a speed equal to that of the original. In this case, an operation section is used to enter optionally a thickness of the original so that the surface speed of the carrier roller 4a is equal to the carrying speed of the face of the original.

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 scale mentioned in the example is a glass scale composed of a pair of main scales and index scales having a grid of light and dark with exactly the same pitch, a light source composed of LEDs for illuminating the scale, and a light transmitted through the scale. It consists of a photodiode that detects the emitted light. Normally, 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.

The present invention has been made in view of such a background, and a first object of the present invention is to provide an image reading apparatus having high position error detection accuracy when reading an automatically fed document. is there.

It is a second object of the present invention to provide an image reading apparatus having a high position error detection accuracy by performing correction for a sheet thickness when reading an original which is automatically fed.

[0018]

In order to achieve the above object, a first means is to automatically feed an original onto a contact glass and scan the original in a line-sequential manner at a predetermined time interval. In an image reading apparatus for reading an original image, a conveying roller for conveying an original, a conveying roller on which a diagonal pattern formed by previously arranging lines having a constant inclination with respect to a scanning direction at an equal pitch, and the diagonal pattern Means for optically reading and converting into an electric signal, and setting a window in the image data of the diagonal pattern converted into an electric signal by the converting means,
Means for calculating the center of gravity of the image data in the window, means for moving the window according to the value of the center of gravity calculated by the means for calculating the center of gravity, and from the value of the center of gravity calculated by the means for calculating the center of gravity It is characterized by comprising a means for measuring a pixel position error, a transport drum and a transport roller for transporting a document. In this case, it is preferable that the transport drum is disposed on the back side of the document and the transport roller is disposed on the front side of the document.

The second means is an image reading apparatus which automatically feeds a document onto a contact glass, scans the document image line-sequentially at predetermined time intervals, and reads a document image. An oblique line pattern formed by arranging lines having a constant inclination at equal pitches, a unit for optically reading the oblique line pattern and converting the line into an electric signal, and the oblique line pattern converted into an electric signal by the converting unit. Means for setting a window in the image data of, calculating the center of gravity of the image data in the window, means for moving the window according to the value of the center of gravity calculated by the means for calculating the center of gravity, and calculating the center of gravity Means for measuring the position error of the pixel from the value of the center of gravity calculated by the means for calculating the position error and optionally a certain amount of the moving speed of the carriage It is characterized by comprising an operation panel which correction can be performed.

[0020]

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

1. Schematic Configuration of Image Reading Apparatus FIG. 1 schematically shows an image reading apparatus having an ADF according to an embodiment of the present invention. In the figure, contact glass 1
Is supported by the housing 2, and when reading a document such as a book document in a fixed manner, the document is placed on the contact glass 1 with the reading surface facing down. The original on the contact glass 1 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 mirror 20 and the third mirror 21 integrally formed, Next, photoelectric conversion elements (CCD) arranged in a line on the photoelectric conversion device by the lens 22
The image formed on the light receiving surface of the optical disc 23 and optically read is converted into an electric signal. The first mirror 3, the illumination lamp 18, the second mirror 20, and the third mirror 21 are configured to move in the illustrated A direction using a traveling body drive motor (not shown) as a drive source.

When reading an automatically fed document,
The document P placed on the document tray 12 is discharged from the discharge guide 24 through the reading position B by the pickup roller 13, the pair of registration rollers 31, 32, the transport drum 15 and the transport roller 4 in a normal reading operation. The sheet is sent to the roller pair 25 and is discharged onto the sheet discharge tray 26. When the original passes through the reading position B, the illumination lamp 18 and the reflector 19 which are moved near the reading position
The first mirror 3, the second mirror 20, and the third mirror 20 are reflected by the first mirror 3, the second mirror 20, and the third mirror.
Scanning is performed by the mirror 21. After that, the reflected light is
The light is condensed and irradiated to a photoelectric conversion element (CCD) 23, and is photoelectrically converted by the photoelectric conversion element 23.

In FIG. 1, a contact glass 1, a housing 2, an illumination lamp 18, a reflector 19, a first mirror 3, a second mirror 20, a third mirror 21, a photoelectric conversion element (CCD) 23, and a traveling body A scanner (image reading apparatus main body) 100 is configured by a drive motor, and includes a document tray 12, a pickup roller 13, and a registration roller pair 3.
An automatic document feeder (ADF) 200 includes the transport drums 1 and 32, the transport drum 15, the discharge guide 24, the discharge roller pair 25, and the discharge tray 26.

The transport drum 15 feeds the document P as shown in FIGS. 2 and 3, and the transport rollers 4 and 4a rotate together with the document P. Therefore, these transport rollers 4, 4
The peripheral speed a is the same as the transport speed of the document P. As shown in FIG. 4, a plurality of parallel oblique lines LN that are deflected by a predetermined angle from the transport direction are provided on the transport roller 4a located on the downstream side in the transport direction, as shown in FIG. In this embodiment, the angle of the oblique line LN is set to 45 °. These oblique lines LN are composed of a large number of black oblique lines with a constant width on a white background, and a pattern 10a is formed by a set of these oblique lines LN. FIG. 5 is a developed view showing the pattern 10a in a plan view by developing the transport roller 4a of FIG. The oblique line pattern 10a is read by the photoelectric conversion element (CCD) 23 during document conveyance, and image data is interpolated based on the read document.

2. System Configuration FIG. 6 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 an operation unit (speed correction unit) 108. 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 indicates the unevenness of illumination, the decrease in the amount of light around the lens, the photoelectric conversion unit 10
The shading correction unit 1 determines the difference in sensitivity between pixels 1
03, and the corrected data is input to the oblique line discriminating unit 104.
Is input to The oblique line discriminating unit 104 discriminates the oblique line pattern portion of the image data, and outputs the discrimination result to the control unit 107.
Output to The image data is stored in the position error measurement unit 105.
And outputs the error signal of the measurement result to the position error correction unit 10.
6 is output. 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 user can arbitrarily input a correction value for the paper thickness from the operation unit (speed correction unit) 108. Switching is performed, and this switching information is added to a series of position error data so that the magnification in the feed direction of the image data becomes more exactly the same as that of the document. Each part (101 to 106, 1
In step 08), the control unit 107 controls the timing, sets operation conditions, and the like, and operates 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.
It shows the arrangement of pixels of one line that the CD 23 reads simultaneously in line-sequential manner and the order on the time axis when this 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.

In FIG. 7, 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 image of a document 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. 7 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 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, the sub-scanning principle is based on the principle that the inclination of the image changes when the scanning speed varies, in other words, based on the principle that the amount of movement of the oblique line in the main scanning direction corresponds to the moving speed in the sub-scanning direction. It is possible to measure the position error of the pixel of the bitmap image due to the uneven scanning speed in the direction and the vibration of the mirror, lens, photoelectric conversion unit (CCD), and the like.

Although FIG. 7 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. 8 shows a case where the bit map has diagonal lines as in FIG. 7, 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. 10 shows a diagonal line pattern detection window of 3 pixels in the main scanning direction × 3 pixels in the sub-scanning direction, and FIGS.
The window shifted by pixel is shown.

Here, the sum Pa of the three pixel values in the diagonal direction sandwiching the center pixel in the window (X2 to X4, Y1 to 3) shown in FIG. When the sum Qa of the three pixel values in the lower right diagonal direction is 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. 10B to 10E, 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 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, if it is determined that the diagonal line pattern exists when the value of R is 500 or more, for example, it can be determined that the diagonal line pattern exists in the windows shown in FIGS. 10C and 10D.

Next, another oblique line pattern discriminating process will be described with reference to FIG. FIGS. 10 (a) to 10 (e) respectively show threshold values of the respective values in the windows shown in FIGS. 9 (a) to 9 (e).
128 shows the case of binarization, and similarly, the sum Pa of three pixel values in the upper left diagonal direction including the central pixel in each window
Calculating the sum Qa-Qe of 画素 Pe 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, Y ) = 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, it indicates that there is a diagonal pattern in the window of 3 × 3 pixels. For example, if 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. 12A to 12D 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. 10, and the binarized data is compared with the matching patterns shown in FIGS. 12 (a) to 12 (d). In this example, FIGS. 11 (c) and 12 (b) and FIG.
FIG. 12A matches FIG. 12D, and it is determined that there is a hatched pattern in this window.

In the above embodiment, the size of the window is set to 3 × 3. However, even when the window size is different, the diagonal pattern can be detected by the same 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. 13 shows a plurality of oblique lines (three oblique lines K1 to K3 in the figure) in the bit map shown in FIG. 7, 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.

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 specific 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 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, it is determined by the position error measuring section 105 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. 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. 15 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 expressed in 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. As shown in FIG. 13, when calculating the barycenter of a plurality of diagonal lines, there is no problem with lines on the same line, but when the window is moved 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 Rn of the center of gravity of the window Wn of the diagonal line K2 shown in FIG. 13 is 4.65, and the value Rn + of the center of gravity of the window Wn + 1 when moving to the next diagonal 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 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 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. 16 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. 17 is a model diagram of the correction using the cubic function convolution, and FIG. 18 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, 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 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 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, 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.
9 An ordinary reading apparatus starts reading an image after a certain speed has been reached after the carriage has started scanning. However, in FIG. 19A, 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.

[0066]

As described above, according to the first and second aspects of the present invention, a diagonal pattern for detecting a position error is provided on a transport roller for automatically transporting a document, and at the same speed as the document surface. Since the moving diagonal pattern is read,
The position error of the document surface can be detected with higher accuracy, and thereby the position error of the image can be accurately corrected.

According to the third aspect of the present invention, since the thickness of the original can be corrected from the operation unit, it is possible to correct the speed difference due to the thickness of the original between the surface of the transport roller and the original. Thus, it is possible to accurately detect and correct an image position error regardless of the thickness of the document.

[Brief description of the drawings]

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

FIG. 2 is a diagram illustrating a relationship between a transport drum and a transport roller in FIG. 1;

FIG. 3 is a diagram illustrating a relationship among a transport drum, a transport roller, and a document in FIG. 1;

FIG. 4 is a perspective view of a transport roller having a diagonal pattern provided on a surface thereof.

FIG. 5 is a developed view of the surface of the conveying roller, showing the hatched pattern of FIG. 4 in detail.

FIG. 6 is a block diagram showing a system configuration of a position error measuring device attached to the image reading device according to the embodiment of the present invention.

FIG. 7 is an explanatory diagram showing read data of an oblique line pattern according to a change in scanning speed.

FIG. 8 is an explanatory diagram showing an oblique line pattern in an enlarged manner.

FIG. 9 is an explanatory diagram showing read values of a hatched pattern in FIG. 8;

FIG. 10 is an explanatory diagram illustrating a diagonal line determination window.

FIG. 11 is an explanatory diagram showing another oblique line determination window.

FIG. 12 is an explanatory diagram illustrating a matching pattern for oblique line determination.

FIG. 13 is an explanatory diagram showing a window for measuring the center of gravity.

FIG. 14 is a flowchart illustrating a process of measuring the center of gravity in the image reading apparatus.

FIG. 15 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. 16 is an explanatory diagram showing the length and angle of a pattern.

FIG. 17 is a diagram for describing correction processing by cubic function convolution.

FIG. 18 is a flowchart illustrating a processing procedure of a correction process based on a cubic function convolution.

FIG. 19 is a diagram illustrating a state of an image before and after correction in a correction process using a cubic function convolution.

[Explanation of symbols]

 Reference Signs List 1 contact glass 2 housing 3, 20, 21 mirror 10 oblique line pattern 10a oblique line 18 light source 22 lens 23 photoelectric conversion element (line CCD) 100 ADF (automatic document feeder) 101 photoelectric conversion section 102 A / D conversion section 103 shading Correction unit 104 Oblique line determination unit 105 Position error measurement unit 106 Position error correction unit 107 Control unit 108 Operation unit (speed correction unit) 200 Scanner P Document

Claims (3)

[Claims] An image reading apparatus for automatically feeding a document onto a contact glass and scanning a document image by scanning line-sequentially at predetermined time intervals, comprising: a transport drum for transporting the document; A conveying roller on which a diagonal pattern formed by previously arranging lines having a constant inclination with respect to the scanning direction at equal pitches; a means for optically reading the diagonal pattern and converting it into an electric signal; Means for setting a window in the image data of the diagonal pattern converted into an electric signal by the above, and calculating a center of gravity of the image data in the window; and a window corresponding to the value of the center of gravity calculated by the means for calculating the center of gravity. And means for measuring the position error of the pixel from the value of the center of gravity calculated by the means for calculating the center of gravity. An image reading apparatus comprising: 2. The image reading apparatus according to claim 1, wherein the transport drum is disposed on the back side of the document, and the transport roller is disposed on the front side of the document. 3. An image reading apparatus which automatically feeds a document onto a contact glass and scans a document image by line-sequentially scanning at a predetermined time interval, wherein the image reading device has a predetermined scanning direction. A diagonal pattern formed by arranging lines having inclinations at equal pitches; a unit for optically reading the diagonal pattern and converting the diagonal pattern into an electric signal; and an image data of the diagonal pattern converted into an electric signal by the converting unit. Means for setting a window and calculating the center of gravity of the image data in the window; means for moving the window according to the value of the center of gravity calculated by the means for calculating the center of gravity; and means for calculating the center of gravity Means for measuring the position error of the pixel from the value of the center of gravity obtained, and arbitrarily correcting a certain amount of the position error or the moving speed of the carriage. And an operation panel capable of reading the image.