JPH09224163A - Image reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correct the variance of the reading position of data on each color R, G and B caused by the fluctuation of a velocity without simply eliminating the fluctuation of the velocity of a first carriage. SOLUTION: A positional error measuring part 8 measures a positional error and output the measuring result to a positional error correcting part 9 as a differential signal. The positional error correcting part 9 generates image data obtained by correcting the positional error from read image data and the difference signal being positional error data to send to an image processing part 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading device, and more particularly to a technique for measuring a position error of a pixel of read bitmap image data and correcting the position error of a pixel of the image data.

[0002]

2. Description of the Related Art As shown in FIG. 8, a conventional image reading apparatus reads a document and outputs read data as R, G, and
B Image reading unit 1 for outputting as image data of each color
And an image processing unit 2 for performing correction of image data, document recognition, etc.
In the case of a digital copying machine, the image recording unit 3 outputs the image data output from the image processing unit 2 onto a sheet.

First, the concept of the image reading means will be described. The image reading sensor, as shown in FIG.
The R, G, and B line sensors are arranged at regular intervals. Here, when reading in the direction of arrow A,
The reading position is shifted by N lines between the R, G, and B intervals. This is corrected by line correction.

A schematic diagram of line correction is shown in FIG. With reference to B, which is the last in time, R may be delayed by the 2N line delay unit 4, and G may be delayed by the N line delay unit 5. However, since the line delay can only be an integral multiple, the line correction is performed by the line correction units 7a and 7b with reference to the peripheral lines for the decimal part.
The correction method may be a cubic convolution method or smoothing. As a result, the R, G, and B reading positions are combined and output.

Next, the image processing section 2 will be described with reference to FIG. The image processing unit 2 includes an RGBγ correction unit 11 that corrects gray balance of RGB data and converts it into density data.
A delay unit 13 that delays the RGB data in order to synchronize with the output result of the document recognition unit 12, and a character region or a pattern region is determined according to the RGB image data, and the document region is further a chromatic region or an achromatic region. A document recognition unit 12 that determines whether the area is an area;
An RGB filter section 14 for MTF correcting the GB data,
RGB data can be converted into CMY by the first-order Masinghi equation.
In order to improve the color reproduction of the image correction data and the color correction unit 15 for converting the data of the above, the UCR (under color removal) is performed on the common portion of CMY to generate the Bk data, and Y, M, C and B are generated.
UCR section 16 expressed in k4 colors and enlargement in the main scanning direction
Depending on the main scanning scaling unit 17 that performs reduction or equal-magnification processing, the frequency characteristics of the image recording unit, and the determination result of the document recognition unit,
A CMYBk filter 18 that performs smoothing processing and sharpening processing using an M × M spatial filter, and a CMYBk γ correction unit 19 that changes the γ curve and performs processing based on the frequency characteristics of the image recording unit and the determination result of the document recognition unit. And a gradation processing unit 20 that performs quantization such as dither processing according to the gradation characteristics of the image recording unit and the determination result of the document recognition unit.

Further, as a concrete conventional technique, for example, there is a technique described in Japanese Patent Laid-Open No. 6-22159. This conventional example relates to a device for reading an image using a plurality of image sensors arranged in the sub-scanning direction and parallel to each other.

Color shift occurs unless the time shift of the image data caused by arranging the sensors at intervals is completely corrected. The necessary correction amount is related to the scanning speed of reading, and if the scanning speed is uneven, it causes color misregistration.

In this technique, in order to avoid this inconvenience, the internal clock is counted by the microprocessor for the interval of pulses generated by the rotation of the F / G mounted on the motor for driving the reading carriage. The driving speed of is calculated and used as the scanning speed for reading. Then, this scanning speed is used to correct the positional deviation between the plurality of sensors.

The contents of the correction are for the purpose of correcting the positional deviation between a plurality of sensors, and the delay amount of the data of the upstream sensor and 1
For delays less than the line, the weighted average of the data before and after that is taken. The correction performed here is a correction in which the data of the upstream sensor is matched with the data of the most downstream sensor to prevent color misregistration due to misalignment between the sensors.

[0010]

In the above-mentioned prior art, since the correction is made for the deviation between a plurality of line sensors, it is not necessary to correct the data obtained from the most downstream sensor, and accordingly, there is no need for correction. It clearly states that no correction is made. Focus on the data obtained by the most downstream sensor that has not been corrected. When the scanning speed of reading fluctuates, the position being read on the original shifts compared with the case of scanning and reading at a constant speed, and as a result, the image expands and contracts due to the speed fluctuation.

In the prior art, since the upstream data is corrected and matched with the data that causes the expansion and contraction, color misregistration can be prevented as a result, but the color image as a whole is accompanied by fluctuations in the scanning speed. The deviation from the original pixel position, which appears as expansion and contraction of the image, remains.

In this conventional correction method, the correction reference is made on the assumption that the intervals between the plurality of line sensors are not changed. Since the standard is the distance between lines, the application target is limited to those having a plurality of sensors.

Further, the scanning speed is detected from the rotation of the drive motor, but a reading device of the type in which an original placed on a plane is scanned and read requires a mechanism for converting rotational movement into linear movement. It is known that it is difficult to completely eliminate the occurrence of speed unevenness due to the conversion mechanism, and it is known that the rotation unevenness of the motor does not always match the unevenness of the moving speed of the carriage. Therefore, the speed data of this prior art may not be suitable as data for correcting the positional deviation between lines.

The present invention provides an image reading apparatus capable of correcting variations in the reading position of data of R, G, and B colors due to velocity fluctuations, rather than simply eliminating velocity fluctuations of the first carriage. The purpose is to provide.

[0015]

According to a first aspect of the present invention, there is provided an R, G, B color image reading apparatus of a type in which an image is line-sequentially scanned and read at regular time intervals.
For each of the image data, while reading a pattern of a constant width with a constant inclination in the scanning direction, a region setting means for setting a continuous region corresponding to the pattern and the surrounding background portion, and the region pixel Area resetting means for resetting by sequentially moving by an integer number of units, first calculating means for calculating the position of the pattern in the area each time the area is set, and position data of the pattern before and after the movement of the area. Of the position data, and second output means for outputting a calculation result of the change of the position data.

According to a second aspect of the present invention, in the first aspect, the control means calculates an interpolation coefficient from a weighting function based on the position error data of each color of R, G, B obtained by the measurement, The image forming apparatus further comprises an interpolating unit that interpolates image data that should be obtained when there is no positional error in the sub-scanning direction of the first carriage from the interpolation coefficient and the read image data of each color.

According to a third aspect of the present invention, in the second aspect, when the image data signal read first in terms of time is R, the other G, It is characterized by comprising a correction means for correcting the reference position of B to correct the position error.

According to a fourth aspect of the present invention, in the third aspect, the difference between the position at least when there is no position error in the sub-scanning direction of the first carriage and the position when there is a position error is a line. It is characterized in that a common line memory is used for the measuring means having a memory for measuring the position error and the correcting means for correcting the position error.

According to a fifth aspect of the present invention, in the fourth aspect, the line memory used for interpolation, position error detection means for obtaining the position error, control means for calculating an interpolation coefficient from a weighting function, and R, G,
B is provided with input means for switching and inputting image data of each color.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION As shown in FIG. 1, an image reading apparatus according to the present invention measures a position error between a conventional image reading unit 1 and an image processing unit 2 and uses the measurement result as an error signal for position detection. A position error measuring unit 8 for outputting to the error correcting unit 9,
A position error correction unit 9 is provided which generates image data in which the position error is corrected from the read image data and the error signal which is the position error data.

Next, the image reading unit 1, the position error measuring unit 8 and the position error correcting unit 9 will be described with reference to FIG.
This is performed based on (b) and (c). The read data of R is a signal delayed by the 2N line delay unit 4 based on B which is the last in time, and the line delay unit 21
The read data of G is input to a and the signal delayed by the N line delay unit 5 is input to the line delay unit 21b. The read data of B is directly input to the line delay unit 21c.

In the position error measuring units 22a, 22b, 22c, line delay units 21a, 21b,
Each read data is input from 21c. The position error measuring units 22a, 22b, 22c measure the position error by a method described later, and output the measured data as an error signal to the correction coefficient computing units 23a, 23b, 23c.

In the correction coefficient calculation units 23a, 23b and 23c, the number of lines required for correction is the line delay unit 21a,
Input from 21b and 21c. The number of lines depends on the size of the position error.

The number of lines required for correction increases as the scanning speed of the first cage changes slower than the reference speed. It is sufficient to measure the variation range of the position error in advance and secure the number of lines that can be corrected in the line delay units 21a, 21b, and 21c even when the position error is the largest.

Line delay units 21a, 21b, 21c
Image data input from the position error measuring unit 22a,
The correction coefficient for each image data is calculated from the error data from 22b and 22c. This correction coefficient calculation need only be performed once per line.

The line correction units 24a, 24b and 24c perform position error correction based on the error data and the correction coefficient. Details of the correction method will be described later.

By such control, the position error can be measured and the control for correcting the position error can be performed in real time. Here, the position error can be measured by importing the error data before correction into the PC (personal computer),
It can be used to measure the performance of readers.

In the case of a color image reading apparatus having R, G, B three-line sensors, if the memory is large, the image data of R, G, B colors can be read and processed by one scan. However, because the cost of memory is high,
Usually, a method is used in which an original is scanned for each color of R, G, and B to read image data.

Therefore, it is not necessary to have the position error measuring unit 8 and the position error correcting unit 9 for each color, and as shown in FIG.
By switching the image data of each color of R, G, and B for each scan by the RGB switching unit 25, the line delay unit 21d, the position error measuring unit 22d, the correction coefficient computing unit 23.
d, the line correction unit 24d only needs to be provided in one set.

Next, the position error correction processing will be described. FIG. 4 shows a model diagram of correction using cubic convolution, and FIG. 5 shows a flow chart of correction.

Pixel positions in the sub-scanning direction when there is no speed unevenness are at equal intervals as indicated by the pixel row P. However, when there is unevenness in speed, as shown by the pixel row Q, the interval varies, and the position deviates from the correct position. FIG. 4 shows that the pixel that should originally be at the position Pn is actually at the position of the pixel Qn.

Here, the image data (density data) of the data Pn in the main scanning direction having the n-th line is calculated from the image data of the pixel row Q and the position data of the pixel row Q by a cubic function function which is a weighting function. An example of creating using a volume will be described.

2 from the position of the ideal n-th line (Pn)
Data within a pixel (r0) is detected from the position error data. In this case, Qn, Qn + 1, Qn + 2, Qn
The data of +3 and Qn + 4 is targeted (for 2 pixels: r0
The above data is not necessary because the correction coefficient is treated as 0).

The interpolation function h (r) in each data Q is obtained from the distance r from each data to Pn. This is the correction coefficient. Here, h (r) is a piecewise cubic polynomial approximation of sinx / x, and is represented by the equations (1), (2), and (3) in FIG. 4 according to the distance r from the middle.

Multiply the corresponding Q data by the correction coefficient to obtain P
Find n. Further, in order to correct the density unevenness, the total of the correction coefficients is set to 1, and the total of the correction coefficients is taken as the denominator. _{That, Pn = {Q n · h} (r1) + Q n + 1 · h (r2) + Q n + 2 · h (r3) + Q n + 3 · h (r4) + Q n + 4 · h (r5)} / {H (r1) + h (r2) + h (r3) + h (r4) + h (r5)} (4)

When this control is completed for the data of the nth line in each main scanning direction, the lines are shifted to the (n + 1) th line and repeated until the final line. At this time, in the formula (4), the sum of the interpolation coefficient h (r) and the interpolation coefficient of the denominator may be calculated once before the correction of the corresponding image data in the main scanning direction.

In this method, since the position from the start of scanning can be measured, the 2N line delay unit 4 and N
As shown in FIG. 6, the line delay unit 5 may not be specially provided. This is because the positional relationship among R, G, and B is as shown in FIG.
When there is a positional relationship such as
Positional error correction of other G and B read data is performed.

That is, focusing on the signal of B, the arrow D
The carriage is scanned in the direction shown in FIG.
The position reading measuring unit 8 detects the reading position of B close to the position of. The correction is performed in consideration of the position error d with respect to R at this time.

As shown in FIG. 4, when the position of the first data P0 at the ideal position and the position of the first data Q0 at the actual position are R in FIG. 7A, On the other hand, in the case of the signal B, the first data P0 at the ideal position is different from the first data Q0 at the actual position.
The position of is shifted in the scanning direction by d to perform the correction. Along with this, the entire Pn at the ideal position is shifted by d [(b) in the figure]. The position error of the G signal is corrected by similar control.

By such control, it is possible to create color image data when the image is read at the correct position from the read image data based on the position error data measured by this method. That is, the position error can be corrected.

[0041]

According to the first aspect of the present invention, the position error for each color of R, G, B can be measured with a resolution higher than the size of the pixel of the device without using a fine pattern.

According to the second aspect of the present invention, since the image reading and the position measurement of the first carriage, which is the main cause of the pixel position error, are performed simultaneously to correct the pixel position error, the position distortion of the pixel is corrected. Fewer color images are obtained.

According to the invention of claim 3, R, G, B
Since the data of each color corrects the image data in which the reading position varies due to the speed fluctuation, it is possible to reduce problems such as coloring around black characters, black characters becoming thin, and errors in image area separation. .

According to the fourth aspect of the present invention, when the position error is corrected, the minimum necessary data is provided, so that the accuracy of the correction is improved and a wasteful line memory is not required. Can be reduced and cost can be reduced.

According to the fifth aspect of the present invention, the line memory used for interpolation, the means for obtaining the position error, the control means for calculating the interpolation coefficient from the weighting function, and the interpolation coefficient and the read image data of each color Since it is not necessary to have a means for interpolating image data that should be obtained when there is no positional error in the sub-scanning direction of one carriage for each color of R, G, B, the circuit scale is small and the cost is reduced.

[Brief description of drawings]

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

FIG. 2 is a block diagram of a first example of a position error measuring unit and a position error correcting unit.

FIG. 3 is a block diagram of a second example of a position error measuring unit and a position error correcting unit.

FIG. 4 is an explanatory diagram showing a correction model using cubic convolution.

FIG. 5 is a flowchart of a position error correction process.

FIG. 6 is a block diagram of a third example of a position error measuring unit and a position error correcting unit.

FIG. 7 is an explanatory diagram showing a positional relationship between diagonal patterns and R, G, and B.

FIG. 8 is a block diagram of a conventional image reading device.

FIG. 9 is a layout diagram of an image reading sensor.

FIG. 10 is a block diagram of a conventional line correction unit.

FIG. 11 is a block diagram of a conventional image processing unit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 image reading section 2 image processing section 3 image recording section 4 2 N line delay section 5 N line delay section 6 1 line memory section 7a, 7b line correction section 8 position error correction section 9 position error correction section 10 image recording section 21a, 21b , 21c Line delay section 22a, 22b, 22c Position error measurement section 23a, 23b, 23c Correction coefficient calculation section 24a, 24b, 24c Line correction section 25 RGB switching section 26 Diagonal line pattern

Claims (5)

[Claims] 1. A color image reading apparatus of a type in which an image is scanned by reading it line-sequentially at regular time intervals,
Area setting means for reading a pattern having a constant width in the scanning direction with a constant inclination for each of the R, G, and B image data, and setting a continuous area corresponding to the pattern and the surrounding background area. , Area resetting means for sequentially resetting the area by moving it by an integer number of pixels, first calculating means for calculating the position of the pattern in the area each time the area is set, and before and after moving the area 2. An image reading apparatus comprising: a second calculation means for calculating a change in the position data of the pattern in 1) and an output means for outputting a calculation result of the change in the position data. 2. The control means according to claim 1, which calculates an interpolation coefficient from a weighting function based on the position error data of each color of R, G, B obtained by the measurement.
An image reading apparatus comprising: an interpolation unit that interpolates image data that should be obtained when there is no positional error in the sub-scanning direction of the first carriage from the interpolation coefficient and the read image data of each color. . 3. The method according to claim 2, wherein when the image data signal read first in terms of time is R, the other reference positions of G and B are corrected with reference to the position of R at the start of scanning. An image reading apparatus comprising a correction unit that corrects a position error. 4. The method according to claim 3, wherein at least the first
The line memory has a difference between the position when there is no position error in the sub-scanning direction of the carriage and the position when there is a position error, and a measuring means for measuring the position error and the correction for correcting the position error. An image reading apparatus characterized in that a common line memory is used for the means. 5. The line memory used for interpolation according to claim 4, position error detection means for obtaining the position error, control means for calculating an interpolation coefficient from a weighting function, and R, G for the interpolation means. , B, and an input means for switching and inputting image data of each color.