JPH09163081A - Image reading device - Google Patents

Abstract

(57) Abstract: To obtain image data in which there is no pixel position shift even if the scanning speed of the carriage in the sub-scanning direction changes. SOLUTION: A magnetic tape 10 on which a signal of a constant frequency is written in order to detect the position or speed of a first carriage in the sub-scanning direction is attached so as to extend in the main scanning direction, and is written on the magnetic tape 10. Signal is the first
The scanning speed of the first carriage is detected by being read by the magnetic head 12 attached to the carriage.
The position error correction unit 23 corrects the image data of each pixel of the correction target line by the interpolation method based on the image data of the lines before and after that and the speed error signal from the control unit 20, and outputs it as a video signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading apparatus that corrects an error in pixel position of image data according to scanning speed unevenness or scanning position deviation in the sub-scanning direction.

[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 separated in the sub-scanning direction and arranged in parallel, the same position of an original 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, color misregistration will occur when reading a color image, and the color will be read correctly. I can't. This deviation is determined according to the interval between the sensors and the scanning speed for reading, and if the scanning speed is uneven, it causes color misregistration.

In order to avoid the above-mentioned problems, for example, Japanese Patent Laid-Open No. 6-22159 discloses a motor in which a microprocessor counts an internal clock during an interval of pulses generated by the rotation of a motor for driving a reading carriage. A method has been proposed in which the driving speed of the sensor is calculated as the actual scanning speed, and the positional deviation between the plurality of sensors is corrected based on this 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.

[0004]

However, in the conventional reader, since the scanning speed in the sub-scanning direction is detected by the motor, the mechanism for converting the rotational motion of the motor into the linear motion causes uneven rotation of the motor and the carriage. The movement speed irregularities do not always match, the scanning speed cannot be detected accurately, and as a result, there is a problem in that the pixel position shift occurs.

Further, since the carriage, which is mounted with a light source for illuminating an original and moves in the sub-scanning direction, has a large width in the main scanning direction, the both ends are not always moving at the same speed, and therefore, both ends are moved. If the carriages are not moving at the same speed, pixel displacement occurs at both ends of the carriage.

Further, in the above-mentioned conventional reading device, since the data of the upstream sensor is matched with the data of the downstream sensor, of course, 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 device, since the data of the upstream sensor is corrected with respect to the data which causes the expansion and contraction, the color shift can be prevented as a result, but the entire color image is prevented. As a result, the expansion and contraction of the image due to the change in the scanning speed cannot be prevented, 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.

[0008] Here, as another method for obtaining image data in which the pixel position is not displaced due to speed fluctuation, Japanese Patent Laid-Open No. 1988-63-
Japanese Patent No. 287167 proposes a method in which a position sensor is arranged in the vicinity of a document and the output timing of the position sensor controls the reading timing of the image sensor. However, in this method, since the reading timing is not constant, the accumulation time of the CCD changes and the apparent sensitivity fluctuates, which requires correction of the sensitivity.

Further, when the read image data is subjected to processing such as filtering and halftone processing over a plurality of lines and the time intervals between the lines are different, the processing is performed by a clock synchronization system in a normal processing system. It will be difficult to deal with it as we proceed, and a buffer memory is required to deal with this.

In view of the above-mentioned conventional problems, it is an object of the present invention to provide an image reading apparatus capable of obtaining image data having no pixel positional deviation even if the scanning speed of the carriage in the sub-scanning direction varies. And

[0011]

In order to achieve the above object, the first means is to mount a light source for illuminating a document and move the carriage in the sub-scanning direction; and a scanning position of the carriage in the sub-scanning direction. A detecting means for detecting the scanning speed; and an interpolating means for interpolating the read data into the data when the scanning position or the scanning speed has no error based on the scanning position or the scanning speed detected by the detecting means. Is characterized by.

A second means is characterized in that the detecting means of the first means detects a scanning position or a scanning speed of the document in the sub-scanning direction at at least two points in the main scanning direction of the carriage.

A third means is characterized in that the detecting means of the first or second means detects the scanning position or the scanning speed of the carriage in the sub-scanning direction in synchronization with the line-sequential reading timing. .

A fourth means is a pattern in which the detecting means of the first or second means is arranged obliquely with respect to the main and sub-scanning directions and arranged in the reading area of the document at equal pitches in the sub-scanning direction. The scanning position or scanning speed of the carriage in the sub-scanning direction is detected by reading.

In a fifth means, the detection means of the first means outputs the scanning position or the scanning speed of the carriage in the sub-scanning direction as a continuous amount on the time axis, and the interpolation means reads line-sequentially. The feature is that interpolation is performed based on this continuous amount at the timing.

In a sixth means, the detecting means of the first means outputs the scanning position or the scanning speed of the carriage in the sub-scanning direction at a predetermined sampling interval, and the interpolating means,
It is characterized in that the interpolation is performed based on the scanning position or the scanning speed in the predetermined sampling interval.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

1. First Embodiment FIG. 1 is a block diagram showing an embodiment of an image reading device according to the present invention, FIG. 2 is a sectional view showing the image reading device of FIG. 1, and FIG. 3 is a plan view showing the image reading device of FIG. FIG. 4 is an enlarged plan view showing a corner portion of the contact glass of FIG. 3, FIG.
6 is a cross-sectional view showing a magnetic tape and a magnetic head, and FIG. 6 is an explanatory view showing a positional error of read data.

First, the outline of the reading apparatus of this embodiment will be described with reference to FIG. The contact glass 1 is supported by the housing 8, and 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 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 is linearly formed on the photoelectric conversion device 7 by the lens 6. An 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 attached to a first carriage (not shown), and this first carriage is read by a driver (not shown) while keeping a constant distance from the surface of the original in order to read the original line-sequentially. It moves in the sub-scanning direction (left and 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 a speed half that of the first carriage. By such a method, a predetermined range on the contact glass 1 can be read line-sequentially.

Further, as shown in FIG. 3, a casing 8 around the contact glass 1 has a reference density plate 9 extending in the main scanning direction for allowing the photoelectric conversion element to read the reference density for shading correction. Attached to the
A magnetic tape 10 in which a signal of a constant frequency is written to detect the scanning position or 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 sensitivity variations among the linear photoelectric conversion elements, illumination unevenness, a decrease in the amount of light around the lens 6, and the like. It is read by the magnetic head 12 (see FIG. 5) attached to one carriage.

FIG. 4 is an enlarged view of the area surrounded by the chain double-dashed line CL in FIG. 3, in which the transient phenomenon at the start of the measurement of the scanning position or the scanning speed of the first carriage in the sub-scanning direction is the original reading range. The magnetic tape 10 extends to a standby state before the leading edge of the reading range of the document by the first carriage so that the magnetic tape 10 is accommodated at the leading edge of the. The magnetic tape 10 is attached to the lower surface of the contact glass 1 as shown in FIG. 5, and the cushioning member 11 is 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 10 and the head 12 and for preventing the tape 10 from being damaged by a strong force acting between the tape 10 and the head 12. Although not shown, the head 12 is biased toward the tape 10 by a spring with respect to the first carriage, and moves while keeping contact with the tape 10 as the first carriage moves.

Next, the reader of the present embodiment will be described in detail with reference to FIG. The photoelectric conversion device 7 is, for example, line C.
It is a CD and converts the original image formed on the light receiving portion of the CCD into an electric signal. This electric signal is converted into digital multi-valued data by the A / D converter 21, then shading-corrected by the shading correction unit 22 based on the reference density of the reference density plate 9, and applied to the position error correction unit 23.

When the first carriage moves during the reading of the original, the magnetic data of the tape 10 is converted by the magnetic head 12 into an electric signal having a frequency corresponding to the moving speed (scanning speed) of the first carriage. The magnetic head 1
The frequency read by 2 is about 10 times the repetition frequency of the timing of reading the line, and is set so that almost continuous amount of speed data can be obtained.

The signal of this frequency is amplified by the head amplifier 24 and then F (frequency) / V (voltage) converter 25.
Is converted into a voltage corresponding to the frequency by S
It is sampled and held by the (sample) / H (hold) circuit 26 and applied to the control unit 20. Here, as the timing for sampling, a timing signal synchronized with the signal for reading the line is applied from the control unit 20 to the S / H circuit 26, and as a result, the control unit 20 has the scanning speed at the timing synchronized with the signal for reading the line. Obtain data (error signal).

The position error correction unit 23 has a memory for at least three lines, and the image data of each pixel of the line to be corrected from the shading correction unit 22 is interpolated to obtain the image data of the lines before and after it and the control unit 20. It is corrected based on the speed error signal of and output as a video signal. The control unit 20 also controls the timing of the photoelectric conversion device 7, the A / D converter 21, and the shading correction unit 22,
It also sets operating conditions.

Next, referring to FIG. 6, the position error correction unit 23
Will be described. In FIG. 6, the vertical axis represents the value of image data after shading correction, that is, the position error correction unit 23.
The value of the input image data of
It is a value of 0 to 255 in the base system. The horizontal axis represents the position of the line to be read line by line, and the position to which a positive integer is assigned is the position of each line corresponding to the line read timing signal generated by dividing the oscillation frequency of the crystal oscillator by the control unit 20. Indicates the position. That is, since the stability of the oscillation frequency of the crystal unit is very high, the position assigned with an integer indicates the position that the image line should originally have. This interval is also the reading resolution of the system (400 dpi).
Corresponding to the distance between the dots.

Here, in order to minimize the amount of memory, the pixel position is corrected in real time in this embodiment. In order to carry out the processing in real time, it is necessary to simplify the calculation involved in the processing. If it is simplified, the circuit scale of the processing system will be small and the cost will be low. Therefore, in this embodiment, the processing resolution is 1/16 dot. . Therefore, a scale divided into 16 is provided between the integers on the horizontal axis shown in FIG.

In FIG. 6, the control unit 2 is operated at the horizontal axis position "0".
It is shown that the position determined by 0 and the actually read image position a match. There are various causes for the pixel position error, but the biggest cause is that the speed of the carriage fluctuates. Therefore, in FIG. 6, the speed of the first carriage is 1/16 dot, that is, about 6% faster than the predetermined value. It shows a state where the state continues. In this case, the image (large ◯ mark) at the position originally corresponding to the position of the integer “1” on the horizontal axis should be read, but since the carriage is fast, the image at the position b 1/16 dot ahead (small size) is actually read. ○
Will be read.

At this time, when the position error correction unit 23 receives the error signal of 1/16 dots and the image data in order to sequentially perform the position deviation of the next line with respect to the line position of the preceding line as a reference, The calculation method of the center of gravity in position error measurement is higher than 1/16, but the result is 1/1
Round to a resolution of 6.

Further, in the example shown in FIG. 6, since the speed of the carriage continues to be high, the position error obtained by measurement in relation to the data read one line before is also 1/16. is there. However, since the line position one line before has already deviated by 1/16 from the line position of the next integer "2" that should be originally determined by the system clock, it will be further deviated by 1/16. It means that the image data at the position c deviated by 2/16 is being read. Similarly, at the next reading position of the integer "3", the image data at the position d shifted by 3/16 is read, and the positions e, f, g are sequentially shifted by 4/16, 5/16, 6/16, respectively. You are reading image data. That is, the position of the read image data is determined by accumulating the position error measured for each line, so 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 the position error as shown in the positions a to g, for example, the data at the position “2” which is corrected by the interpolation method to the data corresponding to the positions “0” to “7” that should originally be Position "2" when seeking
The two read data at the positions a and b before and the read data at the positions c and d after the position “2” are obtained by the cubic interpolation method (Cubic Convolution). Read data is used.
Note that the interpolation method and the read data to be used are not limited thereto.

2. Second Embodiment Next, a second embodiment will be described with reference to FIG. 7. In this embodiment, in order to detect the fluctuation of the scanning speed, the acceleration pickup 27 is attached to the first carriage, the acceleration of the scanning speed is detected, the acceleration is amplified by the charge amplifier 28, and then the scanning speed is changed by the integrator 29. The data is converted and sampled and held by the S / H circuit 26. 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 voltage is applied to the H circuit 26, and as a result, the control unit 20 obtains the scanning speed data (error signal) at the timing synchronized with the signal for reading the line.

3. Third Embodiment In the third embodiment, the magnetic tape 10 of the first embodiment is used.
Further, instead of the magnetic head 12, an 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 be read. Then, when the optical sensor reads the slit pattern while the carriage is traveling, the pulse generator 30 shown in FIG. 8 generates a pulse train according to the presence or absence of the slit, and the control unit 20 counts the number of pulses in a predetermined time. Detect the scanning speed.

Here, in the third embodiment, the pulse frequency is inevitably 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. Only the velocity data with low sampling data can be obtained. However, in order to correct the position error of the pixel, a signal synchronized with the reading of the line is required. Therefore, the interpolation calculation unit 31 interpolates the velocity data having low sampling data to obtain the signal synchronized with the reading of the line. obtain. It should be noted that this method can be realized at a relatively low price as compared with the first and second embodiments.

Further, 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, even the speed data obtained by the third embodiment will be sufficient. It is possible to correct the pixel position error.

4. Fourth Embodiment Next, a fourth embodiment will be described with reference to FIGS. 9 to 25.

4.1 Measuring Principle First, the measuring principle in this embodiment, which is executed by reading the diagonal lines, will be described. FIG. 9 is a diagram for explaining the measurement principle of the present embodiment assuming a typical case. In the figure, an arrow 101 written as main scanning indicates an array of pixels of an image of one line that is simultaneously read by a device that reads a line-sequential image and the order on the time axis when this parallel data is converted into linear data. . An arrow 102 written as sub-scan in the drawing indicates the direction of reading while sequentially moving the reading range of one column of main scanning. As means for moving, a mirror for projecting an image of a document onto a photoelectric conversion element, a means for mechanically moving an illumination lamp and the like, a means for moving a document, and a method for integrally moving a photoelectric conversion element and its imaging optical system There are things. Here, each square enclosed by lines parallel to the main scanning direction and the sub-scanning direction is referred to as a pixel.
The plane formed by the pixels can be regarded as a bitmap, in which data obtained by converting an image of an original into electric signals is an image in which mappings of the image of the original are arranged as they are. When output from the reading device in real time, the main scanning and sub-scanning directions indicate the time sequence, but when the output data is stored in the memory, each pixel can be accessed arbitrarily. Yes, it is possible to handle the data in any order of main scanning, sub-scanning, and time.

FIG. 9 shows the case where the pixel sizes of the main scanning and the sub scanning are equal, and when the scanning speed in the sub scanning direction fluctuates and when the oblique line of 45 ° is read at a constant speed, it is projected on the photoelectric conversion device. , An image corresponding to a bitmap without any deterioration. That is, a is when scanning is performed at a predetermined constant speed corresponding to a clock for controlling the timing of reading in the sub-scanning direction, and a 45 ° image is formed on the bit map. b is an image when the speed fluctuates, and the inclination is different according to the speed.

In other words, AB is the position where the original is read even when the scanning speed in the sub-scanning direction is 0, and the address of the sub-scanning direction bitmap is advanced by the clock for controlling the reading timing in the sub-scanning direction. Does not change, resulting in a line parallel to the sub-scanning direction.

In BC, when the scanning speed in the sub-scanning direction is 1/2 of the predetermined speed, it means that even if the address of the bitmap advances, the image is read at a position where only half of the address is read. The angle with the line in the sub-scanning direction is tan θ =
From 0.5 to about 26.57 °.

CD is when scanning at a predetermined speed, and the inclination is 45 °. Similarly, after D-, the scanning speed is 1.5 times, and the angle is about 56.31 °.
In other words, based on the measurement principle that the inclination of the image differs depending on the scanning speed, in other words, the amount of movement of the oblique line in the main scanning direction corresponds to the moving speed in the sub-scanning direction, unevenness in the moving speed in the sub-scanning direction, mirror, The position error of the pixel of the bitmap image due to the vibration of the lens and the photoelectric conversion device is measured.

In the above description, the case where the pixel has square pixels and a line of 45 ° is used, but the pixel is not a square pixel. For example, the resolution of main scanning is 400 dpi and the resolution of sub-scanning is 60.
It can also be applied to image data of a reading device such as 0 dpi, and similarly, even if oblique lines other than 45 ° are used, the amount of movement of the oblique line image in the main scanning direction depends on the speed in the reading direction in the sub-scanning direction. Since the relationship is established, the position error of the pixel can be measured.

4.2 System Configuration FIG. 10 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 the image reading device and measures the position error in real time. To do. This system has a photoelectric conversion unit 7,
The A / D conversion unit 21, the shading correction unit 22, the position error measurement unit 23, and the control unit 20 are basically configured.

The photoelectric conversion device 7 is, for example, a 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 shading-corrected image data is input to the position error measuring unit (circuit) 23, and an error signal corresponding to the measurement result is output. 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 device using an equal-magnification sensor as a photoelectric conversion device, there is no problem of a reduction in the amount of peripheral light due to the characteristics of the lens. Therefore, shading correction may be omitted. The present application can be applied.

4.3 Position Error Measurement Processing FIG. 11 is for explaining the processing for measuring the position error when the image data a with diagonal lines is included in the bit map similar to FIG. W1 is an 11 × 3 window for performing an operation for obtaining the position of the image data. In order to find the position of the data in the window, the center of gravity in the main scanning direction is calculated. In this calculation, the center of gravity is obtained while sequentially moving the position of the window to W2, W3.
In the case where the position of the center of gravity in the main scanning direction is a line of 45 °, if the position of the pixel does not move due to some error factor, if the window is moved as shown in the figure, 1 in the main scanning direction.
It should move pixel by pixel. If the movement amount of the pixel is different from that of one pixel, it means that the position of the pixel has changed for some reason, and a position error can be obtained. If it is known that the main cause of the position error is unevenness in the scanning speed in the sub-scanning direction, it is easy to convert the data into position error data or speed unevenness.

Since a large number of pixel data including the data of the peripheral pixels are used for obtaining the center of gravity, various noises including CCD-specific noise are included in the image data. The impact is reduced,
Measurement with high S / N is possible. Normally, the S / N increases as the number of pixels in the window increases.

The shape of the window is preferably large on the main scanning side because the center of gravity in the main scanning direction is obtained. The measurement can be performed even if the sub-scanning direction is 1.

FIG. 12 illustrates the movement of the window and the processing associated therewith when the positional error is measured using a plurality of diagonal lines K1, K2 and K3. Similar to the example of FIG. 11, the windows are sequentially moved, and when the preset Wn is reached, the window is moved to Wn + 1 as the next window. The distance between the diagonal patterns K1 and K2 before and after the movement is determined at the stage of creating the measurement chart, and the value of the distance is corrected when the movement of the center of gravity in the main scanning direction is calculated. Wn + 1, Wn + 2,
Wn + 3 ... Move. If the interval between patterns is set to an integral multiple of the pixel size, it is easy to correct when the window is jumped, and it is also convenient to input this correction amount to the measuring device prior to measurement.

Although the window is moved pixel by pixel in this example, the window may be moved by two pixels or more when the frequency band such as vibration that causes a pixel position error is low. By doing so, the time required for measurement can be shortened.

Further, if the position error is measured using a plurality of diagonal lines, it is possible to measure the entire position in the sub-scanning direction even if the reading range of the reading device is vertically long. Further, if the measurement is performed only in the narrow width in the main scanning direction, it is possible to measure the position error separately for the central portion, the front side, and the back side in the main scanning direction.

As is clear from these figures, in the present application, even if the position error is measured with high resolution, it is not necessary to make the slanted line pattern thin accordingly, and there is no influence of the MTF constraint of the system. The feature is that a wide pattern can be used. If a wide pattern is used, the window is correspondingly enlarged, and as a result, the accuracy of the measurement can be increased. When processing speed and real-time processing are performed, the width of the pattern may be set in balance with the size of the buffer, the economy of the circuit scale, and the like.

As another example, it is possible to measure the position error in the same way by using a pattern of a wide line and using the data of the edge on either side.

Further, since the relationship between the sub-scanning read timing and the diagonal line is always the same, the problem of moire that cannot be avoided by the black and white pattern arranged at equal intervals in the sub-scanning direction as in the above-mentioned known example. Can be avoided, and highly accurate position error measurement is possible.

4.4 Centroid Measurement Process Next, the centroid measurement process will be described. The circuit shown in FIG. 13 is an example in which the position error can be corrected by calculating the correction amount of the difference between left and right with respect to the circuit shown in FIG. First
~ Similar to the processing in the third embodiment and the circuit in FIG. 10, the original image formed on the light receiving portion of the line CCD of the photoelectric conversion device 7 is converted into an electric signal, and this electric signal is A / D converted. It is converted into digital multi-valued data by the device 21, and then shading correction is performed by the shading correction unit 22 based on the reference density of the reference density plate 9. Next, in this embodiment, the following processing is performed by the position error measuring unit 32, the left / right difference correction amount calculating unit 33, and the position error correcting unit 23a under the control of the control unit 20.

That is, in the flow chart of FIG. 14, this process is started at the same time when the scanning of the original is started, and 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 central pixel in a 3 × 3 window for diagonal line discrimination. Next, a variable i indicating the number of times of measurement for one diagonal line is initialized (i = 0) (step S2).

Next, the position error measuring unit 32 determines whether or not a diagonal line pattern exists in the 3 × 3 window for diagonal line discrimination (step S3).
3 is shifted by one pixel in the main scanning direction (X = X
+1) (step S4). The shift amount is determined according to the size of the window and the thickness of the diagonal line, and may be one pixel or more. If there is a diagonal pattern in step S3, for example, a 10 × 3 window W1 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. The 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 is 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 1 (step S7). Although the window W is moved pixel by pixel in this embodiment, it may be moved by two pixels or more when the frequency band such as vibration that causes a pixel position error is low. Depending on the method, the time required for measurement can be shortened.

Next, if i = n does not hold for the preset number of times n of measurement of the same line, step S8
Then, the process returns to step S5. On the other hand, when i = n, that is, when the window Wn is reached, the window is moved to the next hatched window Wn + 1 (steps S8 → S9). As the method, after shifting the window coordinates in the main scanning direction by an integer number of pixels m from the pixels corresponding to the intervals in the main scanning direction of the diagonal lines, the measurement count value i is cleared (step S2), and the diagonal line discrimination processing ( Return to step S3). Similarly, windows Wn + 1 and Wn + 2 are applied to one diagonal line.
, Wn + 3 to move and measure the position error.

By measuring the position error using a plurality of diagonal 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 only the narrow width in the main scanning direction is measured, it is possible to separately measure the central portion, the front side, and the back side in the main scanning direction. Further, even when the position error is measured with high resolution, it is not necessary to make the slanted line 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 according to the width, and as a result, the measurement accuracy can be improved. Therefore, the width of the diagonal line may be set in consideration of the processing speed, the size of the buffer in the case of performing real-time processing, the economy of the circuit scale, and the like. It is also possible to measure the position error by detecting the edge on one side using a pattern with a wide width. Further, for example, if a black and white pattern is arranged in the sub-scanning direction regardless of the reading timing in the sub-scanning direction, moire may occur, but in the present embodiment, the relationship between the reading timing in the sub-scanning direction and the diagonal lines is always the same. The occurrence of moire does not pose a problem, and as a result, the position error can be measured with high accuracy.

4.5 Calculation of Window Data and Center of Gravity Next, calculation of window data and center of gravity will be described in detail. FIG. 15 shows the relationship between the window data and the read value of each pixel in the hatched pattern. The read value is 8 bits and is shown in decimal (0 to 255). To obtain the center of gravity in the main scanning direction, the sum of each column (three lines) in the sub scanning direction is obtained. That is, as shown in the figure, if this is set to X0 to X9 from the left side, 18, 50, 2 respectively.
02, 427, 590, 562, 345, 150, 3
Find 7 and 14. Then, assuming that the center coordinates of each pixel in the main scanning direction are sequentially 0 to 9 from the left and the barycentric position in the main scanning direction is Rm, the moment around the barycentric position Rm becomes 0, so X0 (Rm-0) + X1 (Rm-1) ... X9 (Rm
-9) = 0 holds, and when a numerical value is substituted and calculated, Rm = 4.36
2 is obtained.

The reason for obtaining the center of gravity is that preprocessing such as interpolation is not required and the calculation can be simplified and speeded up. Further, when obtaining the image position, it is possible to use a method of obtaining a data sequence having 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.

Next, the case of calculating the center of gravity of a chart composed of a plurality of diagonal lines will be described. When calculating the center of gravity of a plurality of diagonal lines as shown in FIG. 12, it does not matter if the lines are 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 is the same before and after the movement. The value of the center of gravity is different unless the number of pixels is an integer, so 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. 12 is 4.65, and the window Wn + 1 when moving to the next diagonal line K3.
Value of center of gravity Rn + 1 of 4.38, value of center of gravity Rn + 2 of window Wn + 2 of 4.40, value R of center of gravity of window Wn + 3
When n + 3 becomes 4.41, the difference ΔR between the centers of gravity of the lines on which the window has moved is calculated to be 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 shaded line K3, and the result of this addition is used as the value of the center of gravity to determine the 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 Rn + 2 = Rn + 2 + ΔR = 4.40 + 0.27 = 4.67 Rn + 3 = Rn + 3 + ΔR = 4.41 + 0.27 = 4.68. Therefore, the position error can be continuously and accurately measured even by using the chart composed of a plurality of diagonal lines. However, the window Wn of the diagonal line K2
When moving from the window Wn + 1 to the diagonal line K3, the diagonal lines K2 and K3 must exist in the main scanning direction at the same time.

4.6 Width of diagonal line When calculating the center of gravity, the width of the diagonal line is not a problem as long as the data can be read properly, but the pixel is square,
If the angle of the oblique line is 45 ° and the scanning speed of the image is measured from the predetermined target speed with a higher degree of accuracy, the width of the oblique line in the main scanning direction is set to an integral multiple of the pixel. Even if is moved in the oblique direction, the relationship between the oblique lines and the pixels becomes the same on both sides of the oblique lines, the error factors of the image data are balanced, and the accuracy of calculating the position of the image can be improved.

4.7 Relationship between Moving Amount of Image in Diagonal Line in Main Scanning Direction and Positional Error of Pixel in Sub-scanning Direction In this method, the image in which oblique line is read in order to measure the positional error of pixel in the sub-scanning direction. The movement of the image position in the main scanning direction is observed. When the measurement is performed using a 45 ° oblique line with a square pixel, the deviation between the windows in the amount of movement in the main scanning direction directly becomes a position error in the sub-scanning direction, as is clear from the above description. If the pixel is not a square or if the angle of the oblique line is not 45 °, it is necessary to perform conversion to obtain the position error in the sub-scanning direction.

4.8 Measurement Processing Procedure FIG. 16 is a flowchart showing the measurement processing procedure. In this processing procedure, first, the W. P. (Window pointer) is set (step S1601), and then W. P. The data of the window designated by is fetched (step S160
2) The sum V of the fetched data is calculated (step S1603). Then, it is checked whether the total sum V of the data has a preset value between a and b (step S1604). A and b in this check
If it is in the range between and, the center of gravity is calculated (step S
1605), after further calculating the shift of the center of gravity (step S1606), the next W. P. Is set (step S1607). After that, the process returns to step S1602 and the processes after the data fetch are repeated.

On the other hand, in step S1604, if the total sum V of the data is not between a and b, the process exits from the loop and the process ends.

It should be noted that the process sum total is checked in step S1604 by the W. P. Is set incorrectly, so that when there is no hatched data in the window, it is possible to prevent the measurement result from being output even when the correct measurement has not been performed. Also,
If the length of the diagonal line used for measurement is shortened, it can be cut off at the position where the diagonal line is interrupted, and unnecessary measurement can be saved.

4.9 Diagonal Pattern FIG. 17 is an explanatory view showing an oblique pattern tape in the fourth embodiment, and FIG. 18 is an explanatory diagram showing the oblique pattern of FIG. 17 in detail.

In the fourth embodiment, as shown in FIG. 17, two oblique pattern tapes 10L and 10R are provided at positions where the scanning optical system can read at both ends in the main scanning direction. As shown in FIG. 18, a large number of black diagonal lines LN having a constant width and an angle of 45 ° are formed on the white background.
Patterns 10a are formed at equal pitches in the sub-scanning direction.

4.10 Discrimination of Oblique Line Pattern FIG. 19 is an explanatory diagram showing an enlarged oblique line pattern, FIG. 20 is an explanatory diagram showing read values of the oblique line pattern of FIG. 19, and FIG.
1 is an explanatory view showing a diagonal line determination window, FIG. 22 is an explanatory view showing another diagonal line determination window, and FIG. 23 is an explanatory diagram showing a diagonal line determination matching pattern.

Next, the diagonal line pattern discrimination processing will be described. FIG. 19 shows a case where the bitmap has diagonal lines as in FIG. 9, and FIG. 20 shows 8 bits (0 to 25) in that case.
5) shows the read value. Note that 0 = white, 255
= Black, coordinates in the main scanning direction are Xn, and coordinates in the sub-scanning direction are Ym. Further, FIG. 21 shows a diagonal line pattern detection window of 3 pixels in the main scanning direction × 3 pixels in the sub scanning direction, and FIGS. 21 (a) to 21 (e) respectively show 1 in the main scanning direction.
A window shifted by pixel is shown.

Here, the sum Pa of three pixel values in the diagonal direction sandwiched by the central pixels in the windows (X2 to X4, Y1 to 3) shown in FIG. When the sum Qa of 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.

21B to 21E, 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 It becomes + 252 + 249 = 751.

Next, when the difference R between the central pixel and the three pixels (including the central 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 line pattern in the window of 3 × 3 pixels. Therefore, for example, if the value of R is 500 or more and it is determined that there is a diagonal pattern, it can be determined that there is a diagonal pattern in the windows shown in FIGS.

Next, another diagonal line pattern discrimination processing will be described with reference to FIG. 22A to 22E show a case where each value in the windows shown in FIGS. 22A to 22E is binarized with a threshold value of 128, and similarly, the central pixel in each window is included. Sum P of three pixel values in the upper left diagonal direction
a to Pe and the sum of three pixel values in the lower right diagonal direction Qa to Qe
Calculate: 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 center pixel and the three pixels in the lower right diagonal direction (including the center pixel) are obtained, Ra = 0-0-0 = 0 Rb = 1-0 = 1 Rc = 3-0 = 3 Rd = 3-0 = 3 Re = 3-2 = 1.

Therefore, in this case as well, this difference R
22 indicates that there is a diagonal line pattern in the window of 3 × 3 pixels, and if the value of Ra to Re is 2 or more, it is determined that there is a diagonal line pattern, FIG.
It can be determined that there is a diagonal pattern in the windows shown in (c) and (d). Further, by binarizing the pixel value in this way, the addition operation can be simplified.

23 (a) to 23 (d) show matching patterns for detecting a diagonal pattern, in which the white area represents "0" and the black area represents "1". First, the image data is binarized as shown in FIG. 22, the binarized data is compared with the matching patterns shown in FIGS. 23A to 23D, and when they match, it is determined that there is a diagonal line pattern. In this example, FIG. 22 (c), FIG. 23 (b), and FIG.
23D matches with FIG. 23A, 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. Of course, even if the window size is different, the diagonal pattern can be detected by the same determination method. However, in general, the larger the window size, the higher the discrimination system, but the longer the processing time and the larger the circuit scale.

4.11 Arrangement of Oblique Lines FIG. 24 shows the arrangement relation of the 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 positions of the start and end points of the oblique lines in the main scanning direction. If the diagonal lines in the main scanning direction are L2, if the diagonal lines are arranged so that the relationship of L2 <L1 x cos θ (1) holds, the diagonal lines overlap in the main scanning direction. The center of gravity of the next diagonal line can be continuously measured by moving the window in the main scanning direction.
Here, the greater the magnitude relationship of Expression (1), the less the precision is required for the length L1 of the diagonal line and the positions of the starting point and the ending point of the diagonal line in the main scanning direction.

4.12 Moving amount of diagonally shaded image in main scanning direction and positional error of pixel in sub-scanning direction Next, the moving amount of diagonally shaded image in the main scanning direction and positional error of pixel in the sub-scanning direction are shown. The relationship will be described. In this embodiment, in order to measure the position error of the pixel in the sub-scanning direction, the movement of the image position in the main scanning direction of the image in which the diagonal lines are read is observed. When measuring with a 45 ° diagonal line for a square pixel,
As described above, the deviation between the windows of the movement amount in the main scanning direction directly becomes the position error in the sub scanning direction. However, if the pixel is not a square pixel and the angle of the oblique line is not 45 °, it is necessary to perform conversion to obtain the position error in the sub-scanning direction.

Next, with reference to FIG. 25, a case where the detection error of the left and right position errors is corrected will be described. The vertical axis shown in FIG. 25 represents the cumulative error of the pixel position error at a certain read clock in units of 1/16 of the pixel size, and the vertical axis numbers represent only integers when expressed as integer multiples of 1/16. Shows. The horizontal axis represents the main scanning direction. Reference characters A and D respectively indicate positions for measuring the respective position errors on the upstream side and the downstream side in the main scanning direction, and in the case of diagonal lines, they have a predetermined width but are substantially at the center thereof. B and C show respective end portions when the document is read in the main scanning direction.

In the example shown in FIG. 25, the position error at position A at a certain read clock is 34, and the position error at position D is 7. These measurement points are connected by diagonal lines, and the diagonal line is broken in the figure, but it is actually a continuous line, and this diagonal line approximates the cumulative error based on the left and right cumulative errors. .

Here, when the maximum reading size is A3 size, the distance between BC is about 300 mm, and 400 d
In case of pi, the number of CCD pixels used for reading is about 5
000. Assuming that the number of pixels between ADs is 5000, the difference between the accumulated errors on the left and right is 27 (= 34-7). Therefore, the nearest integer obtained by dividing 5000 by 27 is 185. Then, when arranging the read image data when this cumulative error is obtained, the cumulative error “34” is applied until the number of pixels in the main scanning direction starting from A is 185, and thereafter, the cumulative error “34” is applied. Reduces the cumulative error “34” by 1 for each 185 pixels. That is, as shown in FIG. 25, a stepwise cumulative error is applied for every 185 pixels.

If the value obtained by subtracting the value at position D from the cumulative error at position A is positive, the cumulative error is reduced, but if it is negative, it is increased. When the accumulated error at the position A and that at the position D are equal, the difference is "0", and since division cannot be performed with "0", "1" is used instead of "0".
Are treated in the same manner and the number of pixels “5000” is set as one unit. That is, the cumulative error is not corrected in the middle of the main scanning direction. As shown in FIG.
3 ”sends a signal for determining the position of the pixel in the main scanning direction thus obtained to the position error correction unit 23a as a correction position signal, and the position error correction unit 23a is the same as in the first to third embodiments. The position error is corrected by the interpolation method as shown in FIG.

5. Others Although the diagonal lines are used in the fourth embodiment, the magnetic tape 10, the magnetic head 12 and the second tape in the first embodiment are used.
The left and right position error may be detected by the acceleration pickup 27 of the embodiment and the slit pattern of the third embodiment, and the scanning speed is detected by providing a linear encoder on the first carriage. Good. Further, the scanning device is not limited to the fixed document / moving optical system moving type reading device, and in the case of the fixed document moving / scanning optical system side, a scanning speed can be detected by providing a rotary encoder on a roller for conveying the original document, for example. it can.

In this case, in the first embodiment in which the magnetic tape 10 and the magnetic head 12 are provided, the position error and the accumulated position error which are synchronized with the read clock are obtained from the speed data, but they are attached on both sides instead. The positions of the magnetic tape 10 and the magnetic head 12 may be replaced with the number of pixels in the main scanning direction.

Further, since the acceleration sensor does not hinder reading of the original on the original table, it can be mounted not in the both ends of the first carriage but in the reading area.
The width of the carriage does not increase and, as a result, the size can be reduced. Further, since the measurement positions A and D shown in FIG. 22 enter between the document positions BC, a straight line connecting the respective measurement points can be drawn, and as a result, the accumulation corresponding to the scanning start position of the line sensor in the main scanning direction can be drawn. The error can be calculated.

[0094]

As described above, according to the first aspect of the present invention, the scanning position or scanning speed of the carriage in the sub-scanning direction is detected, and the read data is scanned based on the scanning position or scanning scanning speed. Alternatively, since the data is interpolated in the case where there is no error in the scanning scanning speed, it is possible to obtain image data in which there is no pixel displacement even if the scanning speed of the carriage changes.

According to the second aspect of the invention, since the scanning position or the scanning speed of the carriage in the sub scanning direction at at least two points in the main scanning direction of the carriage is detected, both ends of the carriage are moving at the same speed. If there is no pixel, it is possible to obtain image data without pixel displacement.

According to the third aspect of the present invention, since the scanning position or scanning speed of the carriage in the sub-scanning direction is detected in synchronization with the line-sequential reading timing, the scanning position or scanning speed is detected in synchronization with the line-sequential reading timing. According to the invention of claim 4, which is capable of detecting the scanning speed, the carriage of the carriage is read by reading the pattern which is oblique to the scanning direction and is arranged in the reading area of the document at equal pitches in the sub-scanning direction. Since the scanning position or the scanning speed in the sub-scanning direction is detected, the scanning position or the scanning speed of the carriage can be detected by using the document reading unit, and therefore the detection can be performed with a simple configuration.

According to the fifth aspect of the invention, the scanning position or scanning speed of the carriage in the sub-scanning direction is output as a continuous amount on the time axis, and interpolation is performed based on this continuous amount at the line-sequential reading timing. By detecting the scanning position or the scanning speed of the carriage that is not synchronized with the line-sequential reading timing, it is possible to obtain image data without pixel displacement.

According to the sixth aspect of the present invention, the scanning position or scanning speed of the carriage in the sub-scanning direction is output at a predetermined sampling interval, and interpolation is performed based on the scanning position or scanning speed at this predetermined sampling interval. ,
Even if the detection signal has a large sampling interval, it is possible to obtain image data having no pixel displacement.

[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.

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

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

FIG. 5 is a cross-sectional view showing a magnetic tape and a magnetic head.

FIG. 6 is an explanatory diagram showing a positional error of read data.

FIG. 7 is a block diagram showing an image reading device according to a second embodiment.

FIG. 8 is a block diagram showing an image reading device according to a third embodiment.

FIG. 9 is an explanatory diagram showing read data of a hatched pattern according to a change in scanning speed.

FIG. 10 is a block diagram showing a basic circuit for explaining a measurement principle and the like in the fourth embodiment.

FIG. 11 is a diagram for explaining a process when measuring a position error when the bitmap has diagonal line image data.

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

FIG. 13 is a block diagram showing an image reading device according to a fourth embodiment.

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

FIG. 15 is an explanatory diagram showing a reading value and a centroid measuring method in the centroid measuring window.

FIG. 16 is a flowchart showing a processing procedure for measuring the center of gravity.

FIG. 17 is an explanatory diagram showing a diagonal pattern tape according to a fourth embodiment.

18 is an explanatory diagram showing in detail the hatched pattern of FIG.

FIG. 19 is an explanatory view showing an enlarged hatched pattern.

20 is an explanatory diagram showing read values of the hatched pattern in FIG.

FIG. 21 is an explanatory diagram showing a diagonal line determination window.

FIG. 22 is an explanatory diagram showing another oblique line determination window.

FIG. 23 is an explanatory diagram showing a matching pattern for oblique line determination.

FIG. 24 is an explanatory diagram showing lengths and angles of patterns.

FIG. 25 is an explanatory diagram showing a correction process for the deviation of the left and right accumulated errors.

[Explanation of symbols]

 1 Contact Glass 2 Light Sources 3, 4, 5 Mirror 6 Lens 7 Photoelectric Conversion Element 10 Magnetic Tape 10L, 10R Diagonal Pattern Tape 10a Diagonal Pattern 12 Magnetic Head 23, 23a Position Error Corrector 27 Accelerometer 30 Pulse Generator 32 Position Error Measurement Part 33 Left and right difference correction amount calculation part LN Diagonal line

Claims (6)

[Claims] 1. A carriage which is mounted with a light source for illuminating an original and moves in a sub-scanning direction, a detecting unit which detects a scanning position or a scanning speed of the carriage in the sub-scanning direction, and a scanning which is detected by the detecting unit. An image reading apparatus comprising: an interpolating unit that interpolates read data into data when there is no error in the scanning position or the scanning speed based on the position or the scanning speed. 2. The detecting means detects the scanning position or scanning speed of the carriage in the sub-scanning direction at least at two points in the main scanning direction of the document.
The image reading device according to claim 1. 3. The image reading apparatus according to claim 1, wherein the detection unit detects the scanning position or scanning speed of the carriage in the sub-scanning direction in synchronization with the line-sequential reading timing. 4. The scanning position in the sub-scanning direction of the carriage by reading the pattern arranged in the reading area of the document at an equal pitch in the sub-scanning direction and oblique to the main and sub-scanning directions. 3. The image reading device according to claim 1, wherein the scanning speed is detected. 5. The detecting means outputs the scanning position or scanning speed of the carriage in the sub-scanning direction as a continuous amount on the time axis, and the interpolating means interpolates based on the continuous amount at the line-sequential reading timing. The image reading apparatus according to claim 1, wherein: 6. The detecting means outputs a scanning position or a scanning speed of the carriage in the sub-scanning direction at a predetermined sampling interval, and the interpolation means interpolates based on the scanning position or the scanning speed at the predetermined sampling interval. The image reading apparatus according to claim 1, wherein: