JPH1042109A - Image reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image reader in which a position deviation between images in the subscanning direction read by a sensor of a plurality of lines is avoided. SOLUTION: In order to detect a reference position of picture elements in the subscanning direction and a scanning position or a scanning speed of a 1st carriage in the subscanning direction, lots of black slant patterns 10 at an angle of 45 deg. with a prescribed width on a white background are formed at an equal pitch in the subscanning direction. An origin/position error measurement section 23 obtains a position error of the picture element based on a line clock in the subscanning direction when the slant patterns 10 are read and a position error correction section 24 corrects a position error of the picture element based on data of the obtained position error.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image reading apparatus for correcting an error in a pixel position of image data in accordance with an uneven scanning speed in a sub-scanning direction or a deviation of a scanning position.

[0002]

2. Description of the Related Art Generally, in a line scanning type image reading apparatus in which a plurality of R, G, and B image sensors are spaced apart in a sub-scanning direction and arranged in parallel, the same position of a document read by each sensor is determined. 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 pulse interval generated by rotation of a motor for driving a reading carriage. A method has been proposed in which the actual driving speed is obtained by calculating the driving speed of the sensor, and the displacement between a plurality of sensors is corrected 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.

In US Pat. No. 4,882,631, a triangular mark is provided near a document reading start position, and the mark is read by a document reading element in synchronization with a line clock in the sub-scanning direction. A method of obtaining a signal of the leading edge of a document by detecting a mark from image data of the line is shown.

[0005]

However, in the conventional reading apparatus disclosed in Japanese Patent Application Laid-Open No. Hei 6-22159,
Since the scanning speed in the sub-scanning direction is detected from the motor,
Due to the mechanism that converts the rotational motion of the motor into linear motion, the unevenness of the rotation of the motor and the unevenness of the moving speed of the carriage do not always match, and the scanning speed cannot be accurately detected. There is a problem that it occurs.

[0006] Further, since a carriage mounted with a light source for illuminating a document and moving in the sub-scanning direction has a large width in the main scanning direction, both ends are not necessarily moved at the same speed. Are not moving at the same speed, pixel displacement occurs at both ends of the carriage.

Further, in the above-described conventional reading apparatus, since the data of the upstream sensor is matched with the data of the downstream sensor, it is not necessary 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-mentioned conventional reading apparatus,
Since the data of the upstream sensor is corrected for the data that causes the expansion and contraction, the color shift can be prevented as a result, but the expansion and contraction of the image due to the fluctuation of the scanning speed as a whole color image. Can not be prevented,
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.

In the conventional reading apparatus disclosed in US Pat. No. 4,882,631, marks are read by a document reading element in synchronization with a line clock in the sub-scanning direction, so that an image is discretized at line intervals. Therefore, there is a problem that the uncertainty corresponding to the line interval cannot be avoided at the detection position. In other words, the head position cannot be detected with a high accuracy that is less than the line interval.

Although there is a distance between the mark reading position and the document head position, it is assumed that the carriage scans at a constant speed at least until the carriage moves from the mark position to the document head position. If there is an error in the scanning position and the scanning speed at this distance, there is a problem that a position error of the pixel in the sub-scanning direction occurs.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and a first object of the present invention is to provide an image reading apparatus capable of eliminating positional displacement in the sub-scanning direction between images read by a plurality of lines of sensors. Is to provide.

A second object of the present invention is to provide an image reading apparatus capable of detecting a position error of a document without providing a dedicated device for measuring a speed or a position at which the document is scanned.

A third object is to provide an image reading apparatus capable of simplifying the process of measuring the position error of a pixel.

A fourth object of the present invention is to provide an image capable of eliminating a displacement in the sub-scanning direction between images read by a plurality of lines of sensors by using a conventionally used means for detecting the speed of scanning a document. A reading device is provided.

[0015]

In order to achieve the first object, the first means reads and scans a document line-sequentially by photoelectric conversion means comprising a plurality of lines of sensors having different spectral sensitivities. In the image reading device, means for obtaining a position error of a pixel based on a line clock for sub-scanning, and means for correcting a position error of the pixel based on data of the position error obtained by the means for obtaining the position error are provided. It is characterized by having.

In order to attain the second object, the second means is a means for obtaining a position error in the first means, wherein the means for obtaining a position error is provided outside the original reading area and has a line inclined with respect to the sub-scanning direction. The pattern composed of the same pitch arrangement is read together with the image of the original, and the window for calculating the center of gravity is sequentially set for each of the hatched images obtained from the plurality of read lines, thereby moving the center of gravity in the main scanning direction. , The position of the pixel in the sub-scanning direction is obtained.

In order to attain the third object, the third means includes a second means for calculating a position error of image data obtained from a line other than the plurality of lines read by the second means. Is shifted by the number of sub-scanning clocks corresponding to the line intervals of a plurality of lines of sensors to obtain data on the position error of another reading line.

In order to achieve the fourth object, the fourth means is the first means, wherein the means for obtaining the position error of the pixel detects a speed or a position at which the document is scanned, and outputs a detection output to the document. Is converted into data at a timing synchronized with the line clock of the sub-scan to obtain position error data corresponding to an image read by any one of the plurality of lines of the sensor. It is characterized in that the data is shifted by the number of sub-scanning clocks corresponding to the line interval of the sensor and used as position error data of another read line.

[0019]

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

1. 1. First Embodiment 1.1 Schematic Configuration of Apparatus First, an overview of an image reading apparatus according to the present embodiment will be described with reference to FIG. 2, the image reading apparatus basically includes a contact glass 1, a light source 2, first to third mirrors 3, 4, 5, a lens 6, a photoelectric conversion device 7, and a housing 8. I have.

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 a constant distance from the document surface in order to read the document 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. 3, 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.
A large number of black oblique line patterns 10 having an angle of 5 ° are formed at equal pitches in the sub-scanning direction. The reference density plate 9 is read by the photoelectric conversion device 7 and is used to correct 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. Are also read by the photoelectric conversion device 7.

FIG. 4 is an enlarged view of a region surrounded by a two-dot chain line circle CL in FIG. 3, and an excessive phenomenon at the time of starting the measurement of the scanning position or scanning speed of the first carriage in the sub-scanning direction is caused by the reading range of the original. The oblique line pattern 10 extends to the standby state before the leading end of the document reading range by the first carriage.

1.2 System Configuration Next, the reading apparatus of the present embodiment will be described in detail with reference to FIG. The photoelectric conversion device 7 is, for example, a three-line CCD of R, G, and B, and converts an original image formed on a light receiving unit of the CCD into R, G, and B electric signals. This R, G, B
Are converted into digital multivalued data by an A / D converter 21 and then a shading correction unit 22
Thus, shading correction is performed based on the reference density of the reference density plate 9. The oblique line pattern 10 is determined by the origin detection / position error measurement unit 23 based on the data, and the origin position and the position error are measured. Then, based on the measurement result, the position error correction unit 24 determines the pixels in the sub-scanning direction. Are corrected and output via the three-line buffer 25.

The control unit 20 controls the timing of the photoelectric conversion device 7, the A / D converter 21, the shading correction unit 22, the origin detection / position error measurement unit 23, the position error correction unit 24 and the line buffer 25, and controls the operation conditions. It makes settings and outputs a video control signal. The line buffer 25 outputs R, G, and B video signals in synchronization with the video control signal.

1.3 Principle of Position Error Measurement Next, the principle of measuring the position error will be described.

The main scanning direction indicated by the arrow in FIG.
It shows an arrangement of pixels of one line that the CD 7 reads simultaneously in a line-sequential manner and an order on the time axis when this parallel data is converted into serial data. The sub-scanning direction indicated by an arrow indicates a reading direction while sequentially moving the reading range of one line in the main scanning direction. As a moving means, there is a form in which the original is fixed and the scanning optical system is moved, as well as a form in which the scanning optical system is fixed and the original is moved, as shown in FIG.

In FIG. 6, 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 these pixels is used when an image of the original is converted into an electric signal. It can be understood that the mappings of the 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. 6 shows the read data a of 45 ° oblique lines L 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 1.5 times the predetermined speed, and the angle is about 56.31 °.

Therefore, the principle of measurement is that the inclination of the image changes when the scanning speed fluctuates. In other words, the principle of measurement is 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 caused by the unevenness of the scanning speed in the direction and the vibration of the mirrors 3 to 5, the lens 6, the photoelectric conversion device 7, and the like.

Although FIG. 6 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.

1.4 Oblique Pattern Discriminating Process Next, the oblique line pattern discriminating process will be described. 7 shows a case where the bit map has diagonal lines as in FIG. 6, and FIG. 8 shows a read value of 8 bits (0 to 255) in that case. Note that 0 = white, 255 = black, and the coordinates in the main scanning direction are Xn and the coordinates in the sub-scanning direction are Ym. Also,
FIG. 9 shows a diagonal line pattern detection window of 3 pixels in the main scanning direction × 3 pixels in the sub-scanning direction, and FIGS. 9A to 9E show windows 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

9B to 9E, 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 a diagonal pattern in the window of 3 × 3 pixels. Therefore, if it is determined that there is a diagonal pattern when the value of R is 500 or more, for example, it can be determined that there is a diagonal pattern in the windows shown in FIGS. 9C and 9D.

Next, another oblique line pattern discriminating process will be described with reference to FIG. FIGS. 10 (a) to 10 (e) show each value in the window shown in FIGS. 9 (a) to 9 (e) as a threshold =
128 shows the case of binarization, and similarly, the sum Pa to P of the three pixel values in the upper left diagonal direction of 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, when the differences Ra to Re between the central pixel and three pixels (including the central pixel) in the lower right diagonal direction are obtained, Ra = 0-0 = 0 Rb = 1-0 = 1 Rc = 3-0 = 3 Rd = 3-0 = 3 Re = 3-2 = 1

Therefore, also in this case, the difference R
Is large in the window of 3 × 3 pixels, for example, 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. 11A to 11D 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. 11 (a) to 11 (d). In this example, FIGS. 10 (c) and 11 (b) and FIG.
FIG. 11A matches FIG. 11D, and it is determined that there is a diagonal line pattern in this window.

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

1.5 Position Error Measurement Process Next, the position error measurement process will be described. FIG. 12 shows FIG.
A plurality of diagonal lines (three diagonal lines K1 to K3 in the figure) in the bit map shown in FIG. 1 are shown, and a window W of 10 × 3 size for measuring a position error using the plural diagonal lines is shown. Is shown. 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 shifted one pixel at a time to the obliquely lower left direction at 45 ° with respect to the oblique line K2 as shown by W1 → W2 → W3. Then, when reaching the last window Wn of the oblique line K2,
The window W is moved only in the main scanning direction and the next oblique line K
3 is moved to the window Wn + 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 unique to the CCD are included in the image data. However, since the data of a large number of pixels including the data of the peripheral pixels is used to obtain the center of gravity, the center of gravity is used. In the process of obtaining the value of, the effect of noise is reduced, and measurement with a high S / N ratio becomes possible. In this case, the S / N ratio generally increases as the number of pixels in the window increases. The shape of the window is preferably 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 by one line.

1.6 Center-of-gravity measurement processing Next, the center-of-gravity measurement processing will be described. The process shown in FIG. 13 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 origin detection / position error measuring section 23 determines whether or not a diagonal line pattern exists in the 3 × 3 window for diagonal line determination (step S3). The window is shifted by one pixel (X = X + 1) in the main scanning direction (step S4). The shift amount is determined according to the size of the window and the thickness of the oblique line, and may be one or more pixels. If a diagonal pattern exists in step S3, for example, 10
A × 3 window W1 is set, and the center of gravity in the window W1 is determined (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. The window W1 may be set.

When the measurement of the center of gravity is completed, the displacement of the center of gravity is calculated (step S6), and then the window W2 shifted by -1 pixel in the main scanning direction and +1 pixel in the sub scanning direction.
Is set, and the count value i for the number of measurements is incremented by one (step S7). In this embodiment, the window W is moved one pixel at a time. However, if the frequency band such as vibration that causes a position error of the pixel is low, the window W may be moved two pixels or more. 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 a method thereof, 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 line in the main scanning direction, the measurement count value i is cleared (step S2), and the diagonal line determination 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 way, even if the reading range of the reading device is vertically long, the position error can be measured over the entire sub-scanning area. 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.

1.7 Calculation of Window Data and Center of Gravity Next, calculation of window data and center of gravity will be described in detail. FIG. 14 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 a decimal number (0 to 255). In order to obtain the center of gravity in the main scanning direction, the sum of each column (for three lines) in the sub-scanning direction is obtained, and as shown in FIG.
0, X1 to X9, 18, 50, 202, respectively
427, 590, 562, 345, 150, 37, 14
Becomes Then, assuming that 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 Z0 (Rm-0) + Z1 (Rm-1) ... + Z9 (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 arithmetic operation can be simplified and speeded up without the need for preprocessing such as interpolation. Further, when obtaining the image position, a method of obtaining a data string of a predetermined resolution by interpolation from the arrangement of the sum of the data of each column and obtaining the position where the peak value exists from the data can be used.

Next, the case of calculating the center of gravity of a chart composed of a plurality of oblique lines will be described. When calculating the center of gravity of a plurality of oblique lines as shown in FIG. 12, there is no problem with lines on the same line, but when the window moves to a different line, the distance between the oblique 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 oblique line K2 shown in FIG. 12 is 4.65, and the window Wn + 1 when the window Wn is moved to the next oblique line K3.
The value of the center of gravity Rn + 1 of the window Wn + 2 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 R of the window Wn + 3 is R
When n + 3 becomes 4.41, the difference ΔR of the center of gravity of the line to which the window has moved is calculated. Then, ΔR = Rn−Rn + 1 = 4.65−4.38 = 0.27.

This value ΔR is added to the value of the center of gravity of the oblique line K3, and the result of this addition is used as the value of the center of gravity to obtain a position error.
In this case, the value Rn + 2 of the center of gravity of the window Wn + 2 and the value Rn + 3 of the center of gravity 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 such a chart including a plurality of oblique lines is used, the position error can be continuously measured with high accuracy. However, the window Wn of the oblique line K2
To move to the window Wn + 1 of the oblique line K3, the oblique lines K2 and K3 must exist simultaneously in the main scanning direction.

1.8 Relationship of Arrangement of Oblique Lines FIG. 15 shows an arrangement relationship of oblique lines. A plurality of oblique lines having a length L1 are arranged at an angle θ with respect to the main scanning direction, and the start point and the end point of the oblique lines in the main scanning direction. Is the same, if the distance between the oblique lines in the main scanning direction is L2, the oblique lines are arranged so as to satisfy the following relationship: L2 <L1 × cos θ (1) If the oblique lines overlap in the main scanning direction. Therefore, the window can be moved in the main scanning direction to continuously measure the center of gravity of the next oblique 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.

1.9 Relationship between Movement of Image in Oblique Line in Main Scanning Direction and Positional Error of Pixel in Subscanning Direction In the present embodiment, an image obtained by reading the oblique line in order to measure the positional error of pixel in the subscanning direction. Of the image position in the main scanning direction. In the case where the measurement is performed using a 45-degree oblique line with a square pixel, the deviation between the windows in the amount of movement in the main scanning direction directly becomes the position error in the sub-scanning direction as described above. However, if the pixel is not a square pixel, and if the angle of the oblique line is not 45 °, it is necessary to perform conversion to obtain a position error in the sub-scanning direction.

1.10 Detection of Origin Position in Sub-scanning Direction Next, processing for detecting the origin position in the sub-scanning direction will be described. FIG. 16A shows a diagonal line pattern and its main scanning direction and sub-scanning direction. The leftmost diagonal line is used for both measuring the position error and determining the origin position. A rectangle overlapping the oblique line indicates a window for measuring the center of gravity. FIG. 16B shows a read clock in the sub-scanning direction. This clock is a timing signal generated based on the oscillation of the crystal oscillator in the control unit 20 and does not depend on the speed fluctuation of the carriage. Note that the illustrated waveform is not a clock waveform but a rising or falling edge.

FIGS. 16 (c), (d) and (e) show the timings of the R, G and B read signals, respectively. This is because they are arranged apart from each other in the scanning direction. R,
In each of the signals G and B, the leading end position indicated by a solid line indicates the leading end position of the document on the contact glass 1, and the position indicated by the broken line at a position earlier than the leading end position is that before the carriage reaches the leading end position of the document. This is also for explaining that the measurement of the position error and the determination of the origin position are performed based on the hatched image data read by the sensors of each color.

Here, as described in US Pat. No. 4,882,631, the specific position where the reading device performs reading and the clock are not usually in a synchronous relationship.
The read position and the clock phase do not match. In the present embodiment, in order to determine a specific position to be read with an accuracy equal to or less than the clock interval, a window for measuring the center of gravity is set with respect to the oblique line pattern 10 provided upstream and near the leading edge of the original. Then, the center of gravity of the oblique line pattern 10 in the main scanning direction is obtained and set as the origin position A. The position A of the center of gravity is not set as a shape, but defines a value A obtained when the center of gravity is calculated as a center of gravity. This value is stored in a memory in the control unit 20. In FIG. 16, the position corresponding to this value is indicated by the same symbol A.

In order to measure the center of gravity, a window as shown in FIG. 16 is set, and the window is moved in the oblique line direction, and the center of gravity in the main scanning direction is calculated for each window. The calculated center of gravity of each window is compared with the center of gravity A stored in the memory in the control unit 20, and is continued until the center of gravity A is exceeded. Stored in memory.

FIG. 17 shows the calculation contents when determining the center of gravity A. The centers of gravity of the windows before and after the center of gravity A are gn-1 and gn, respectively, and the clocks at that time are n-1 and n.
Is obtained by linear approximation. In this calculation, a fraction may occur, and therefore, the rounding is performed at 1/16 of the clock interval to simplify the correction of the pixel position. Therefore,
The center of gravity A unique to this apparatus is obtained with an accuracy of 1/16 of the line clock in the sub-scanning direction. In the example shown in the figure, the center of gravity A is obtained at the position of 12/16 from clock n-1 to clock n. .

FIG. 18 shows a process for determining the position of the center of gravity A. First, it is checked whether or not the first carriage has started reading away from the home position HP (step S11). A window for measuring the center of gravity is set, and it is checked whether or not the center of gravity of the window exceeds the center of gravity A, and the check is continued until the window exceeds the center of gravity (step S12). When the center of gravity of the set window exceeds the center of gravity A, the positions of the centers of gravity at the clocks before and after the center of gravity are acquired, and the center of gravity A is updated (step S13).
The origin position thus obtained prior to the leading end position of the document is used to correct the position error of the read pixels of the document in the sub-scanning direction.

1.11 Process of Position Error Correction Unit Next, the process of the position error correction unit 24 will be described with reference to FIG. In FIG. 19, the vertical axis indicates the value of the image data after the shading correction, that is, the value of the input image data of the position error correction unit 24.
２５255. The horizontal axis indicates the position of the line to be read line by line, and the position where a positive integer = 0 to 7 is assigned corresponds to the line read timing signal generated by the control unit 20 dividing the oscillation frequency of the crystal oscillator. This indicates the position of each line. That is, since the stability of the oscillation frequency of the crystal unit is very high, the position where the integer is assigned indicates the position where the image line should be. This interval is also the reading resolution of the system (400 dpi).
Corresponding to the distance between the dots. Also, the horizontal axis (0) ~
The position indicated by (6) indicates a position shifted by 12/16 from the originally required position = 0 to 6 with respect to the origin position.

Here, in order to minimize the amount of memory, in this embodiment, the position of the pixel is corrected in real time. In order to perform the processing in real time, it is necessary to simplify the operation involved in the processing. If the processing is simplified, the circuit scale of the processing system is reduced and the cost is reduced. Therefore, in this embodiment, the processing resolution is set to 1/16 dot. . Therefore, FIG.
The scale divided into 16 is provided between the integers on the horizontal axis shown in FIG.

Although there are various causes of the pixel position error, the most significant cause is that the speed of the carriage fluctuates. FIG. This shows a state in which the state that is 6% faster continues. In this case, the image at the position corresponding to the position of integer = 1 on the horizontal axis (large 大 き な mark) should be read. However, since the carriage is fast, the image at the position b 1/16 dot ahead (small ○ mark) is actually used. Mark).

At this time, the position error correction unit 24 receives the error signal of 1/16 dot and the image data in order to sequentially shift the position of the next line for each line with reference to the line position of the previous line. The calculation accuracy of the center of gravity in the position error measurement is higher than 1/16, but the result is 1/1.
Rounding is performed so that the resolution becomes 6.

In the example shown in FIG. 19, the carriage speed continues to be high, so that the position error obtained by measuring in relation to the data read one line before is also 1/16. is there. However, the line position of the next integer = 2, which should be originally determined by the system clock, is shifted by 1/16 since the line position of the previous line has already been shifted by 1/16, and as a result, This means that the image data at the position c shifted by 2/16 is being read. Similarly, at the next reading position of integer = 3, the image data at the position d shifted by 3/16 is read, and the image data at positions e, f, and g shifted by 4/16, 5/16, and 6/16 are read in sequence. You are reading image data.
That is, the position of the read image data is determined by the accumulation of the position error measured for each line, and thus the read data is assigned to the horizontal axis having a resolution of 1/16.

The correction of the read data is performed as follows.
Based on the read data having a position error as shown in positions a to g, for example, the positions (0) to (7) are obtained by interpolation.
For example, when obtaining data at the position (1), two read data at the positions a and b before the position (1) and positions c and d after the position (1) are corrected. Is obtained by the cubic interpolation method (Cubic Convolution) using the two read data in
Two read data before and after are used. Note that the interpolation method and the read data to be used are not limited thereto.
If the origin position is corrected, the clock will have a phase difference with the read clock.However, it is simpler to output the clock with a delay and output it in phase with the read clock, rather than outputting the clock with the phase shifted. Can be
Also, the processing is simplified.

FIGS. 20 and 21 show other origin detection marks. The mark shown in FIG. 20 is an isosceles triangle having two oblique lines with equal angles, and the mark shown in FIG. 21 is a right triangle having two oblique lines and a straight line extending in the sub-scanning direction. 20 and 21, a plurality of vertical lines extending in the main scanning direction indicate clock timings in the sub-scanning direction, and the time axis is not shown, but the sub-scanning is performed from left to right in the drawing as time passes. Is done.

When this triangle is read by the line sensor, focusing on the position where the clock in the sub-scanning direction overlaps the two sides of the triangle, the length in the main scanning direction corresponding to this overlap is obtained. In the case of the triangle shown in FIGS. 20 and 21,
Since this length becomes longer as the clock in the sub-scanning direction advances, a predetermined length L is set in advance, and by using the lengths of the clocks before and after the length L, the first length using the center of gravity A is used. Similarly to the embodiment, the position of the length L can be determined based on the clocks of the two lengths with an accuracy equal to or less than the resolution of the clock.

FIG. 22 shows a case where a circular pattern is used as another origin detection mark. Here, when the first carriage moves at a predetermined scanning speed and reads this circular pattern, the read data becomes a circular pattern. On the other hand, when the scanning speed fluctuates and this circular pattern is read,
When the scanning speed is twice the predetermined scanning speed, the length in the sub-scanning direction is an ellipse of half, and when the scanning speed is half, the ellipse is twice the length in the sub-scanning direction. Therefore, since the center of gravity in the sub-scanning direction in each case changes as shown in the figure, it does not become a unique origin for the device.

In this embodiment, the reading device of the original fixed / moving optical system moving type is exemplified. However, the reading device of the original moving / scanning optical system fixed type may be used. For example, a rotary encoder may be provided on a shaft of a roller for conveying a document.

The correction method has been described for the case where correction is performed in real time using a buffer memory. However, the read data and the position error data are temporarily fetched into the page memory, corrected on the page memory, and output. You may. Further, the position error data may be output to the outside, and may be used for adjustment of the apparatus and failure diagnosis.

1.12 Conclusion When performing full-color reading as a sensor of a plurality of lines, a three-line sensor that reads an original through R, G, and B filters is usually used. At this time,
If the speed of scanning the original changes, the read image expands and contracts in the sub-scanning direction, and the positions of the RGB images are shifted. As a result, there was a problem that the edge of the solid portion of the image becomes a different color, a fine line or the like is blurred, or the color becomes another color. A means for obtaining a position error of the pixel with reference to the reference (origin detection / position error measuring unit 23) and a means for correcting the position error of the pixel based on the data of the position error obtained by the means for obtaining the position error (position error Correction unit 2
4), and such correction is made so that the position of the image is precisely adjusted, so that such a problem does not occur.

Further, in the color copying period, etc., the YMC data is read from the RGB data read when the color image is output.
In many cases, full-color prints are obtained by sequentially obtaining and superimposing K image data. That is, in the first original scanning, the three-line color sensor is used for RGB.
Is read, and for example, Y image data is created and output from the three color data. In the next scan, RGB data is read.
The image data of YMCK is sequentially output by a method of generating and outputting M image data from the data of. That is, 4
The original is scanned multiple times to obtain YMCK data to form a full-color image. In this case, since the YMCK image is superimposed to obtain a full-color image, if there is a positional shift between the YMCKs, the edge of the solid portion of the image becomes another color,
There has been a problem that a fine line or the like becomes blurred or becomes a different color. However, by configuring as in this embodiment, there is a problem of pixel position shift between RGB in one original scanning and a plurality of problems. The problem of misalignment between images during the original scanning can be solved together.

2. 2. Second Embodiment 2.1 Schematic Configuration of Apparatus FIG. 23 is a block diagram illustrating a system configuration of an image reading apparatus according to a second embodiment, and FIG. 24 is a cross-sectional view illustrating a magnetic tape and a magnetic head.

The reading apparatus according to this embodiment is different from the first embodiment shown in FIGS. 2, 3 and 4 in that the magnetic tape 10a on which a signal of a constant frequency is written in place of the diagonal pattern is moved in the main scanning direction. , Except that it is attached so as to extend to the right. That is, in this embodiment, a reference density plate 9 for causing the photoelectric conversion element to read the reference density for shading correction is provided in the housing 8 around the contact glass 1 in the main scanning direction as shown in FIG. A magnetic tape 10a on which a signal of a certain frequency is written to detect a scanning position or a scanning speed of the first carriage in the sub-scanning direction is attached so as to extend in the main scanning direction. The reference density plate 9 is used to correct 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 signal written on the magnetic tape 10a is It is read by the magnetic head 12 (see FIG. 24) attached to one carriage.

The magnetic tape 10a is moved from the leading end of the original reading range by the first carriage so that the transient phenomenon at the start of the measurement of the scanning position or scanning speed of the first carriage in the sub-scanning direction falls at the leading end of the original reading range. Extends to the previous standby state. The magnetic tape 10a is attached to the lower surface of the contact glass 1 as shown in FIG. 24, and the buffer member 11 is further attached to the lower surface of the magnetic tape 10. The cushioning member 11 is provided for the purpose of ensuring the contact between the tape 10a and the head 12, and for preventing the tape 10a from being damaged by a strong force acting between the tape 10a and the head 12. Although not shown, the head 12 is attached to the first carriage with a tape 10a by a spring.
, And moves while maintaining contact with the tape 10a with the movement of the first carriage.

2.2 System Configuration Next, the reading apparatus of this embodiment will be described in detail with reference to FIG. The photoelectric conversion device 7 is, for example, a three-line CCD, and converts a document image formed on a light receiving portion of the three-line CCD into an electric signal. This electric signal is converted into digital multi-value data by the A / D converter 21, and then subjected to shading correction by the shading correction unit 22 based on the reference density of the reference density plate 9, and is applied to the position error correction unit 24.

When the first carriage moves during reading of an original, the magnetic data of the tape 10a is converted by the magnetic head 12 into an electric signal of a frequency corresponding to the moving speed (scanning speed) of the first carriage. The frequency read by the magnetic head 12 is about 10 times the repetition frequency of the line read timing, and is set so that a substantially continuous amount of speed data can be obtained.

After the signal of this frequency is amplified by the head amplifier 31, the F (frequency) / V (voltage) converter 32
Is converted into a voltage corresponding to the frequency by S
The signal is sampled and held by a (sample) / H (hold) circuit 33 and applied to the control unit 20. Here, a timing signal synchronized with a signal for reading a line is applied from the control unit 20 to the S / H circuit 33 as timing for performing sampling, and as a result, the control unit 20 scans at a timing synchronized with the signal for reading the line. Obtain data (error signal).

The position error correction unit 24 has a memory for at least three lines. The image data of each pixel of the line to be corrected from the shading correction unit 22 is interpolated by the interpolation method into the image data of the preceding and succeeding lines and the control unit 20. Is corrected based on the speed error signal, and is output as a video signal. Note that the control unit 20 also performs timing control of the photoelectric conversion device 7, the A / D converter 21, and the shading correction unit 22, setting of operating conditions, and the like.

The other parts not particularly described are the same as those of the first embodiment.
The configuration and the operation are the same as those of the first embodiment.

3. Third Embodiment Next, a third embodiment will be described with reference to FIG. In this embodiment, in order to detect a change in the scanning speed, an acceleration pickup 34 is attached to the first carriage, the acceleration of the scanning speed is detected, the acceleration is amplified by the charge amplifier 35, and then the scanning speed is reduced by the integrator 36. It is converted and sampled and held by the S / H circuit 33. Similarly, in this embodiment,
As a timing for performing sampling, a timing signal synchronized with a signal for reading a line is sent from the control unit 20 to the S / S.
The control unit 20 obtains scanning speed data (error signal) at a timing synchronized with a signal for reading a line.

The other parts not particularly described are the same as those of the first embodiment.
The configuration and the operation are the same as those of the second embodiment.

4. Fourth Embodiment In a fourth embodiment, the magnetic tape 10 according to the second embodiment is used.
Instead of a and the magnetic head 12, the optical sensor is provided on the first carriage, and a slit pattern that is repeated at regular intervals is provided on the housing 8 at a position where the optical sensor can read. Then, the optical sensor reads the slit pattern while the carriage is running, whereby FIG.
A pulse train corresponding to the presence or absence of the slit is generated by the pulse generator 37 shown in FIG. 3, and the scanning speed is detected by counting the number of pulses in a predetermined time by the control unit 20.

In the fourth embodiment, the pulse frequency must be lower than the frequency of the signal for reading the line due to restrictions such as the resolution of the slit reading and the processing speed of the control unit 20. As a result, the sampling data is reduced. Only low speed data can be obtained. However, in order to correct the pixel position error, a signal synchronized with the reading of the line is required. obtain. This method can be realized at a relatively low price as compared with the second and third embodiments.

If the time constant of the motion determined by the loss due to the friction between the mass of the first carriage and the sliding portion is made longer than the sampling interval, the speed data obtained by the third embodiment will be sufficient. Pixel position errors can be corrected.

The other parts not particularly described are the same as those of the first embodiment.
The third embodiment is configured and operates in the same manner as the third embodiment.

[0092] 5. Fifth Embodiment FIG. 27 is a block diagram showing an example of a basic system configuration of such a position error measuring device, which is incorporated as an additional function to an image reading device and measures the position error in real time. is there. This system has a photoelectric conversion unit 7,
It is basically composed of an A / D conversion unit 21, a shading correction unit 22, a position error measurement unit 24, and a control unit 20.

The photoelectric conversion device 7 is, for example, a three-line CCD.
Thus, the image is converted into an electric signal. The image converted into the electric signal is converted into digital multi-valued image data by an A / D converter (device) 21. The converted data is subjected to shading correction by the shading correction unit 22 for unevenness in illumination, a decrease in the amount of light around the lens, a difference in sensitivity between pixels of the photoelectric conversion device, and the like. The image data that has been subjected to the shading correction is input to the position error measurement unit (circuit) 24, and outputs an error signal corresponding to the measurement result. At the same time, the reading device outputs image data as a video signal. Each of the functional blocks is controlled by the control unit 20 to control timing, set operating conditions, and the like, and operates in association with each other.

In a reading apparatus using an equal-magnification sensor as a photoelectric conversion apparatus, there is no problem of a decrease in the amount of peripheral light due to the characteristics of the lens. Therefore, the shading correction may be omitted in some cases. The present application can be applied.

The other parts not particularly described are the same as those in the first embodiment.
In addition, the configuration and the operation are the same as those of the fourth to fourth embodiments.

6. Relationship between Sub-scanning Clock of RGB Three-Color Lines and Value of Read Image FIG. 28 shows the RG when the original is read by a reading element in which the three RGB lines are arranged at 8 dots apart from each other.
FIG. 7B is a diagram showing the relationship between the position of each digitized data in the sub-scanning direction and the corresponding sub-scanning clock on the horizontal axis, and the value of the read image on the vertical axis. Each vertical axis indicates the value of the read image, but the entry of a mark or the like indicating the value is omitted. The numbers on the horizontal axis are clock numbers, and the solid line drawn corresponding to the numbers corresponds to the position on the document to be read corresponding to the clock when there is no change in the scanning speed of the document. However, in reality, it is difficult to completely eliminate unevenness in the speed at which the original is scanned, so that the position where the original is read based on the clock is shifted from the position where the original should be read, as indicated by a dashed line. . The reason why the position of RGB is shifted with respect to the number of the clock is that the document is illuminated on each line of the photoelectric conversion element composed of three color lines,
This is because the image projected by the mirror, the lens, and the like is configured to be separated into eight clocks in terms of the length on the document. This relationship is determined by the projection magnification of the optical system that forms an image on the document, and is independent of the speed at which the document is scanned. If this is expressed with reference to the clock for reading in the sub-scanning, if the clock at a certain moment is, for example, the clock 0 in FIG.
The image obtained as the G signal is an image at a position corresponding to a distance corresponding to 8 clocks on the original with respect to the position of the image obtained as the R signal, and the image obtained as the B signal is generated at 16 clocks on the original. This indicates that the image is located at a position separated by a corresponding distance. Since this relationship depends only on the imaging magnification of the optical system, the relationship always holds for clocks other than zero.

Therefore, the speed at which the original is scanned fluctuates from the predetermined speed, and at the time of the first clock, R is shifted to the position of the chain line slightly to the right of the solid line corresponding to the first clock in FIG. When there is a shift of reading the image,
G and B read the image at this position or the image shifted by 8 clocks or 16 clocks, respectively. That is, at the time of the first clock, the deviation of the image read by G and B from the position to be read, that is,
The difference between the position of the solid line and the position of the chain line is the same as R. Since this relationship holds for any clock, the position error between the lines in the sub-scanning direction of the R image, that is, the pixel position error can be expressed as the RGB line interval of the reading element by expressing the individual pixels. The position error of the G and B pixels can be obtained by shifting by the corresponding number of lines, for example, 8 clocks and 16 clocks in this embodiment. In the first to fifth embodiments, the process for obtaining the pixel position error is performed for each of RGB. In this embodiment, if the pixel position error is obtained only for one color, Since the data can be applied to data of another color, measurement of the position error can be simplified.

The correction of the position error based on the obtained position error data of the pixel is as follows.

That is, the correction of the position error of the pixel with respect to each color data has been described in detail in the first embodiment and will not be described. Correction and R
The mutual relationship between the images of the three colors GB is as follows.

For each color, the value of the image at the position of the solid line shown as the position corresponding to the clock in the figure is obtained from the values of the image data and the position data in the vicinity thereof by interpolation. RGB3
Full-color image data read in color is expressed as a set of values obtained by separating an image at the same position on a document into three colors of RGB.
In FIG. 28, since the horizontal axis indicates the position of the image,
The positions common to B are the 16th of R, the 8th of G, and the 0th of B
It is in a position that is on the vertical line as described above. Since the position of the pixel when the correction of the position error of the pixel is not performed is indicated by the dashed line, the position is shifted from the original position as shown by a and b. In a reading device that does not perform correction, the read data is used as it is as the RGB data, so that the data at the position indicated by the dashed line is treated as the data at the position indicated by the solid line with the same value.
Both color shift and image position shift have drawbacks. In the present application, the RGB values indicated by solid lines in FIG.
Since the value of the image at the position common to B is obtained, both the color shift and the position shift are corrected. However, in the conventional example, for example, the values of the G and B pixels at a certain position of the R data are obtained by interpolation, and the purpose is to prevent color misalignment. It is not targeted. Therefore, scanning multiple times
In the case where an image of K is to be obtained, the method of the conventional example is useless unless the unevenness in the speed of the original scanning a plurality of times is repeated exactly the same.

Further, in the second to fifth embodiments, the measurement of the speed unevenness and the position error of the first carriage is not performed by the image data obtained by reading the repetitive pattern of the oblique lines,
Although the data read from the magnetic tape is used, in this method, it is not possible to measure the speed unevenness or the position error corresponding to each of RGB, so that the data is converted into the data of the timing synchronized with the sub-scanning clock. Thereafter, the data is shifted to correct the pixel position error. Other parts that are not particularly described are configured in the same manner as in the first to fifth embodiments.

[0102]

As described above, according to the first aspect of the present invention, a pixel position error is obtained based on the sub-scanning line clock, and the pixel position error is obtained based on the obtained position error data. Is corrected, the positional deviation in the sub-scanning direction between images read by the plurality of line sensors can be eliminated.

According to the second aspect of the present invention, a pattern which is arranged outside the reading area of the original and is constituted by lines arranged at equal pitches of lines inclined with respect to the sub-scanning direction is read together with the image of the original. The window for calculating the center of gravity is sequentially set for each of the hatched images obtained from the plurality of lines, and the position of the pixel in the sub-scanning direction is obtained from the movement of the center of gravity in the main scanning direction. Without providing a dedicated device for measuring the position, the position error of the pixel can be detected by using the function of reading the original, thereby making it possible to suppress an increase in cost related to the measurement.

According to the third aspect of the present invention, the position error of the image data obtained from the lines other than the plurality of read lines is obtained by substituting the measured position error data into the sub-scan corresponding to the line interval of the plurality of line sensors. Is shifted by the number of clocks to obtain data on the position error of another read line, so that processing for obtaining the position error of the pixel only for data from a predetermined one of a plurality of lines may be performed. As a result, the circuit scale of the processing system involved in this processing is reduced to a fraction of the line, and the processing relating to the measurement of the pixel position error is simplified. In addition, a sufficient effect of correcting the position error of the pixel of the image data obtained from another reading line can be obtained.

According to the fourth aspect of the present invention, the speed or position at which the original is scanned is detected, and the detection output is converted into data at a timing synchronized with the line clock of the sub-scan for reading the original, and the sensor output of the plurality of lines is detected. The position error data corresponding to the image read by any one line is obtained, and the position error data is shifted by the number of sub-scanning clocks corresponding to the line interval of the plural lines of sensors, and the position of the other read line is shifted. Since the error data is used, even when the number of pixels of the sensor of a plurality of lines is insufficient and an image outside a region for reading a document cannot be read, it can be applied, and an image read by a plurality of line sensors can be used. The positional deviation in the sub-scanning direction can be eliminated.

[Brief description of the drawings]

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

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

FIG. 3 is a plan view illustrating the image reading apparatus of FIG. 2;

FIG. 4 is an enlarged plan view showing a corner portion of the contact glass of FIG. 3;

FIG. 5 is an explanatory diagram showing a diagonal pattern.

FIG. 6 is an explanatory diagram showing read data of an oblique line pattern according to a change in scanning speed.

FIG. 7 is an explanatory diagram showing an oblique line pattern in an enlarged manner.

FIG. 8 is an explanatory diagram showing read values of a hatched pattern in FIG. 7;

FIG. 9 is an explanatory diagram showing a diagonal line determination window.

FIG. 10 is an explanatory diagram showing another oblique line determination window.

FIG. 11 is an explanatory view showing a matching pattern for oblique line determination.

FIG. 12 is an explanatory diagram showing a window for measuring the center of gravity.

FIG. 13 is a flowchart illustrating a position error measurement process of the image reading apparatus of FIG. 1;

FIG. 14 is an explanatory diagram showing a read value and a method of measuring the center of gravity in a window for measuring the center of gravity.

FIG. 15 is an explanatory diagram showing the length and angle of oblique lines.

FIG. 16 is an explanatory diagram showing the timing of oblique lines and RGB read pixels.

FIG. 17 is an explanatory diagram showing an origin position detection method.

FIG. 18 is a flowchart illustrating an origin position detection process.

FIG. 19 is an explanatory diagram showing a position error correction process.

FIG. 20 is an explanatory diagram showing another origin detection mark.

FIG. 21 is an explanatory diagram showing another origin detection mark.

FIG. 22 is an explanatory diagram showing another origin detection mark.

FIG. 23 is a block diagram illustrating a system configuration of an image reading apparatus according to a second embodiment.

FIG. 24 is a sectional view showing a magnetic tape and a magnetic head.

FIG. 25 is a block diagram illustrating a system configuration of an image reading apparatus according to a third embodiment.

FIG. 26 is a block diagram illustrating a system configuration of an image reading apparatus according to a fourth embodiment.

FIG. 27 is a block diagram illustrating a system configuration of an image reading apparatus according to a fifth embodiment.

FIG. 28 is a graph in which the horizontal axis represents the relationship between the position in the sub-scanning direction of the image data of the RGB three-color lines and the corresponding clock.
FIG. 4 is an explanatory diagram showing a value of a read image on a vertical axis.

[Explanation of symbols]

 Reference Signs List 1 contact glass 2 light source 3, 4, 5 mirror 6 lens 7 photoelectric conversion device 8 housing 9 reference density plate 10 oblique line pattern 10a magnetic tape 12 magnetic head 20 control unit 21 A / D conversion unit 22 shading correction unit 23 origin detection / Position error measurement unit 24 Position error correction unit 25 Line buffer 31 Head amplifier 32 F / V conversion unit 33 S / H circuit 34 Acceleration pickup 35 Charge amplifier 36 Integrator 37 Pulse generator 38 Interpolation calculation unit L Oblique line

Claims (4)

[Claims] 1. An image reading apparatus that scans an original line-by-line by a photoelectric conversion unit constituted by a plurality of lines of sensors having different spectral sensitivities, and obtains a position error of a pixel based on a sub-scanning line clock. An image reading apparatus comprising: means for correcting a position error of a pixel based on position error data obtained by the means for obtaining the position error. 2. The apparatus according to claim 1, wherein the means for obtaining the position error is provided outside the reading area of the document, and reads a pattern formed by arranging lines at an equal pitch with respect to the sub-scanning direction together with the image of the document. A window for calculating a center of gravity is sequentially set for each of the hatched images obtained from the plurality of lines, and a position of a pixel in a sub-scanning direction is obtained from a movement of the center of gravity in a main scanning direction. The image reading device according to claim 1. 3. A position error of image data obtained from a line other than the plurality of read lines is obtained by shifting measured position error data by the number of sub-scanning clocks corresponding to a line interval of a plurality of line sensors. 3. The data of a position error of another read line.
The image reading device according to claim 1. 4. A means for obtaining a position error of a pixel detects a speed or a position at which a document is scanned, converts a detection output into data at a timing synchronized with a line clock of a sub-scan for reading the document, and outputs data of a plurality of lines. Position error data corresponding to an image read by any one line of the sensor is obtained, and the position error data is shifted by the number of sub-scanning clocks corresponding to the line interval of the plurality of sensors to obtain another read line. 2. The image reading apparatus according to claim 1, wherein the data is position error data.