JP3464736B2 - Pixel position error measuring device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a position error measuring device for measuring a position error in a sub-scanning direction of a read pixel caused by a fluctuation or vibration of a scanning position or a scanning speed in a sub-scanning direction by a document reading device.

[0002]

2. Description of the Related Art Conventional methods of this type include, for example, (1) "Development of high-definition image input device", [No. 940-10].
Proceedings of the 71st Ordinary General Meeting of the Japan Society of Mechanical Engineers (IV)
The technology proposed in [1994-3.29-31, Tokyo] is known. In this method, an image obtained by reading a test chart of equal pitch lines arranged side by side in the sub-scanning direction,
In other words, interpolation calculation is performed on image data that has been discretized at line intervals in the sub-scanning direction, the center positions of the black and white lines of the equal pitch line are calculated from this interpolation calculation result, and the difference from the reference pitch of the test chart is calculated. By reading, the position error of the pixel in the sub-scanning direction due to the vibration of the device is calculated.

As another conventional example, for example, (2)
Japanese Unexamined Patent Publication No. 6-297758 proposes a method of measuring a pattern unevenness of a writing scanning line of a hard copy device by reading a pattern of a hard copy in which data of an equal pitch line is written.

[0004]

However, the conventional method of the above (1) has the following problems.

1. Even if the pattern of the same shape is read, the obtained data is different due to the moire phenomenon due to the difference in the positional relationship between the edge of the pattern of the equal pitch line and the sampling timing at the time of reading. Due to this moire, the read data does not necessarily correspond to the position of the edge of the pattern, which deteriorates the measurement accuracy of the position error. In particular, when the pattern of equal pitch lines is made finer and closer to the resolution of the reading device, the influence of moire becomes remarkable and the position error cannot be measured at all under some conditions.
Therefore, this method has a problem that it is not possible to measure a position error close to or less than the resolution of the reading device with high accuracy.

2. Since the pattern of equal pitch lines is used, even if the influence of moire is ignored, if the pitch of the pattern is made fine in order to measure the position error of the high frequency component, the MTF (Modulation Transfer Ra
Due to the limit of tio), the difference between the grayscale signals of the obtained image becomes small, and therefore the problem that the measurement accuracy deteriorates is inevitable.

3. As described above, in the above method, it is impossible to widen the measurement frequency band to the higher side to improve the accuracy in the refinement of the pattern. Therefore, the process of interpolating the sampled data is performed. As a result, in order to perform higher interpolation, it is necessary to use more peripheral data and perform complicated arithmetic processing. Furthermore, the interpolation is merely an interpolation, and it is unavoidable that there is a deviation from the true data, which causes deterioration of measurement accuracy.

4. Since the image data obtained by scanning the specific light receiving element of the photoelectric conversion device in the sub-scanning direction is used, the noise of the light receiving element itself affects the accuracy of the measurement itself, and the accuracy deteriorates.

Further, in the above method (2), since the data obtained by reading the pattern by the photoelectric conversion device is used at the time of measurement, the point that the pitch unevenness is measured from the read data is similar to the above method (1). The hard copy is read on the assumption that there is no scanning unevenness in reading during measurement.

In view of the above-mentioned conventional problems, the present invention is capable of highly accurately measuring the position error of the read pixel in the sub-scanning direction due to the fluctuation of the scanning position or scanning speed in the sub-scanning direction by the document reading device. It is an object of the present invention to provide a position error measuring device that can be used.

[0011]

[Means for Solving the Problems] of a pixel according to the first aspect
In order to achieve the above object, the position error measuring device includes a scanning unit that scans and reads a document line-sequentially in the main scanning direction and the sub-scanning direction at a constant time interval, and a scanning unit that has a constant width in the main and sub-scanning directions. A window for setting a window for image data when the scanning means reads a pattern of a plurality of diagonal lines which are oblique and are arranged at equal pitches in the sub-scanning direction.
Dow setting means and at least the center pixel in the window
The first pixel on the diagonal line of the center and this first pixel
On the other hand, a second pixel located symmetrically with respect to the central pixel
Threshold value and the difference between the first pixel and the second pixel
By comparing with the value, the diagonal pattern in the window
Oblique pattern recognition means for recognizing whether or not it exists
And the diagonal pattern recognition means detects the diagonal pattern.
If it is recognized that the window exists
The position of the diagonal line in each window
Position error in the sub-scanning direction of read pixels based on displacement
And a position error measuring means for measuring .

The second means is the same as the first means .
The diagonal direction of the diagonal and the diagonal direction of the diagonal pattern are the same.
And characterized in that.

A third means is the first means, the
The diagonal pattern recognition means is on a diagonal line with the first pixel.
The first sum of density values of a region not including
And the second sum of density values of the area not including up to the diagonal
Therefore, the difference between the first density value sum and the second density value sum is compared with the threshold value.
By comparing, there is a diagonal pattern in the window.
It is characterized by determining whether or not it exists .

[0014] The fourth means is the third means to the first free, the length of the oblique line L _1, the distance in the main scanning direction of the oblique line L _2, the angle with respect to the main scanning direction of the diagonal line as θ , L ₂ <L ₁ × cos θ.

[0015]

[0016]

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. 1 is a block diagram showing an embodiment of the image reading device according to the present invention, FIG. 2 is a sectional view showing the image reading device of FIG. 1, FIG. 3 is a plan view showing the image reading device of FIG. 2, and FIG. 3 is an enlarged plan view showing a corner portion of the contact glass in FIG. 3, FIG. 5 is an explanatory view showing a diagonal pattern, FIG. 6 is an explanatory view showing read data of the diagonal pattern according to variations in scanning speed, and FIG. 7 is a diagonal line. FIG. 8 is an explanatory view showing an enlarged pattern, FIG. 8 is an explanatory view showing a reading value of the diagonal line pattern of FIG. 7, FIG. 9 is an explanatory view showing a diagonal line judgment window, and FIG. 10 is an explanatory diagram showing another diagonal line judgment window. ,
FIG. 11 is an explanatory diagram showing a matching pattern for oblique line determination,
12 is an explanatory view showing a center of gravity measurement window, FIG. 13 is a flowchart for explaining processing of the image reading apparatus of FIG. 1, and FIG. 14 is an explanatory view showing a reading value and a center of gravity measurement method in the center of gravity measurement window. 15 is an explanatory view showing the length and angle of the diagonal lines.

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 driving device (not shown) with 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.

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
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 diagonal 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 sensitivity variations among the linear photoelectric conversion elements, uneven illumination, a decrease in the amount of light around the lens 6, and the like. Is also read by the photoelectric conversion device 7.

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 scanning speed of the first carriage in the sub-scanning direction is the original reading range. The slanted line pattern 10 extends to a standby state before the leading end of the reading range of the document by the first carriage so as to be accommodated at the leading end.

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 line CCD, and converts an original image formed on the light receiving portion of the CCD into an electric signal. This electric signal is sent to the A / D converter 21.
Is converted into digital multi-valued data, and then the shading correction unit 22 performs shading correction based on the reference density of the reference density plate 9. Then, the slanting line discriminating unit 23 discriminates the slanting line pattern 10 based on this data, and then the position error measuring unit 24 measures the positional error of the pixel in the sub-scanning direction based on the discrimination result.

The control unit 20 includes a photoelectric conversion device 7, an A / D converter 21, a shading correction unit 22, and an oblique line discrimination unit 23.
Also, timing control of the position error measuring unit 24, operation condition setting, and the like are performed, and a video control signal is output. The position error measuring unit 24 outputs a video signal and a position error (error signal) in synchronization with the video control signal.

Next, the process of measuring the position error will be described. The main scanning direction indicated by the arrow in FIG. 6 is a line CCD.
7 is a line-sequential arrangement of pixels read simultaneously in line-sequential,
The sequence on the time axis when this parallel data is converted to serial data is shown. The sub-scanning direction indicated by the arrow is
The reading direction is shown while sequentially moving the reading range of one line in the main scanning direction. As the moving means, as shown in FIG. 2, in addition to the form in which the original is fixed and the scanning optical system is moved, there is a form in which the scanning optical system is fixed and the original is moved.

In FIG. 6, assuming that a rectangular area surrounded by parallel lines in the main scanning direction and the sub-scanning direction is a pixel, the plane formed by the pixel is the original when the image of the original is converted into an electric signal. It can be seen as the image maps are lined up as they are. Note that this is sometimes 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 temporal order, but in the state of being stored in the memory, each pixel can be accessed arbitrarily, so the main scanning direction is It can be handled regardless of the order of sub-scanning direction and time.

In FIG. 6, when the pixel sizes in the main scanning direction and the sub-scanning direction are the same, the read data a of the oblique line 10 of 45 ° and the scanning speed change when the scanning speed in the sub-scanning direction does not change. The read data b at this time is shown in correspondence with the bitmap. That is, the read data a indicates a time when scanning is performed at a predetermined constant speed corresponding to the clock that controls the read timing in the sub-scanning direction, and is a 45 ° diagonal image even as a bitmap.

On the other hand, the inclination of the read data b differs depending on the variation of the scanning speed. Section A-B in the sub-scanning direction
Indicates that the scanning speed is "0". In this case, the reading position does not change even if the address of the bitmap advances by the clock that controls the reading timing in the sub-scanning direction, so the line is parallel to the sub-scanning direction. . Also, 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 bitmap advances, the image at the position where it advances by only half is read, so the angle of the read image is about 26.57 °. (Tan θ = 0.5). Section C-D shows a case where scanning is performed at a predetermined speed, and 45 °
The angle of 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, as the measurement principle, the inclination of the image changes when the scanning speed changes, in other words, the movement amount of the slanted line in the main scanning direction corresponds to the movement speed in the sub scanning direction. It is possible to measure the positional error of the pixel of the bitmap image due to the unevenness of the scanning speed in the direction, the vibration of the mirrors 3 to 5, the lens 6, the photoelectric conversion device 7, and the like.

Although square pixels are shown in FIG. 6,
The pixel is not square, and the resolution in the main scanning direction is 4
It can also be applied to pixels having a resolution of 00 dpi and a resolution in the sub-scanning direction of 600 dpi. 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, and thus the pixel position error can be measured. it can.

Next, the diagonal line pattern discrimination processing will be described. FIG. 7 shows a case where the bitmap has diagonal lines as in FIG. 6, and FIG. 8 shows the read value of 8 bits (0 to 255) in that case. Note that 0 = white, 255 = black, the coordinates in the main scanning direction are Xn, and the coordinates in the sub-scanning direction are Y.
m. Further, FIG. 9 shows a diagonal 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
2 to X4, Y1 to 3) in a diagonal direction sandwiching the central pixel, that is, a sum Pa of three pixel values in the diagonally upper left direction including the central pixel and a sum Qa of three pixel values in the lower right diagonal direction are calculated. , Pa = (X2, Y1) + (X3, Y1) + (X2, Y2) = 3 + 1 + 1 = 5 Qa = (X4, Y2) + (X3, Y3) + (X4, Y3) = 3 + 4 + 8 = 15.

Similarly, with respect to FIGS. 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+ It becomes 252 + 249 = 751.

Next, when the difference R between the center pixel and the 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 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. 9C and 9D.

Next, another oblique line pattern discrimination processing will be described with reference to FIG. FIGS. 10A to 10E show threshold values of the values in the windows shown in FIGS. 9A to 9E, respectively.
In the case of binarization with 128, similarly, the sum Pa to P of three pixel values in the upper left diagonal direction of the center pixel in each window is shown.
When the sum Qa to Qe of e and three pixel values in the lower right diagonal direction is calculated, 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 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
10 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.

11 (a) to 11 (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. 10, the binarized data is compared with the matching patterns shown in FIGS. 11A to 11D, and when they match, it is determined that there is a diagonal line pattern. In this example, and FIG. 10 (c)及 Beauty Figure 10 (d) and FIG. 11
Since ( b ) matches, 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 becomes, but the processing time becomes longer and the circuit scale becomes larger accordingly.

Next, the position error measuring process will be described. FIG. 12 shows a plurality of slanted lines (three slanted lines K _{1 to} K _{3 in} the figure) in the bitmap shown in FIG. 11, and 10 × for measuring a position error using the plurality of slanted lines. Three
Shows a window W of size First, in order to obtain the data position in the window W, the center of gravity in the main scanning direction is calculated, and thereafter, the window W is set diagonally to the lower left 45 ° as shown by W ₁ → W ₂ → W ₃ with respect to the diagonal line K _2. Shift pixel by pixel. Then, the last window W _n of the diagonal line K2
When it reaches, the window W is moved only in the main scanning direction to the window W _{n + 1} of the next diagonal line K3.

Here, the position of the center of gravity in the main scanning direction is 45.
In the case of the oblique line of °, unless the pixel position moves 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 amount of movement of the pixel is not one pixel, it means that the position of the pixel has changed for some reason, and therefore the position error can be obtained. If it is known that the main cause of the position error is uneven scanning speed in the sub-scanning direction, it is easy to convert data of position error data into uneven speed.

Here, various noises including noise peculiar to the CCD are included in the image data, but since the data of many pixels including the data of the peripheral pixels are used to obtain the center of gravity, the center of gravity is used. In the process of obtaining, it is possible to reduce the influence of noise and perform measurement with a high S / N ratio. In this case, usually, the larger the number of pixels in the window, the higher the S / N ratio. 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 with one line.

Next, the processing of measuring the center of gravity will be described. FIG.
The process shown in (1) 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 the coordinates of a certain pixel position, for example, the 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 oblique line discriminating unit 23 performs 3 for oblique line discrimination.
It is determined whether or not a diagonal pattern exists in the × 3 window (step S3). If not, the 3 × 3 window 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 a diagonal line pattern is present in step S3, a 10 × 3 window W ₁ for measuring the center of gravity is set, and the center of gravity in the window W ₁ is obtained (step S5). At this time, depending on the size of the window W ₁ and the thickness of the slanted line, the position of the pixel determined as the slanted line is shifted by an integer number of pixels in the main scanning direction, and the slanted line portion is near the center of the window W _1. Like window W
_May be set to ₁ .

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 W _{2 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 if 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 a preset number of times n of measurement of the same line, step S8
The process returns from step S5 to step S5. On the other hand, when i = n, that is, when the window W _n is reached, the window W _{n + 1} is moved to the next diagonal line (step S8 → S9). As a method thereof, 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, for one diagonal line, the window W _{n + 1} ,
W _{n + 2} , W _{n + 3 The} position error is measured by moving as shown.

By measuring the position error using a plurality of diagonal lines in this way, 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 a high resolution, it is not necessary to make the diagonal 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. Further, the position error can be measured by detecting the edge on one side of the pattern having a wide width. Further, if 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 becomes a problem, 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.

Next, the calculation of the window data and the 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 hatched pattern. The read value is 8 bits and is shown in decimal (0 to 255). In order 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, and as shown in the figure, Z0 and Z1 to Z9 are set to 18 and 5, respectively.
0, 202, 427, 590, 562, 345, 15
0, 37, 14 are calculated. 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 Z0 (Rm-0) + Z1 (Rm-1) ... Z9 (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 pre-processing such as interpolation is not required and the operation 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 weight of the chart consisting of a plurality of diagonal lines
The case of calculating the mind will be described. As shown in Figure 12
When calculating the center of gravity of a diagonal line consisting of multiple
It does not matter with the line, but the window moves to a different line
When moving, before and after moving between the diagonal main scanning direction
The value of the center of gravity is different unless the distance is exactly an integer number of pixels.
So we have to correct it. An example is shown in FIG.
Window W with diagonal line K2 _nCenter of gravity value R_nIs 4.65
And the window W when moving to the next diagonal line K3_{n + 1}
Center of gravity value R_{n + 1}Is 4.38, window W_{n + 2}Center of gravity of
Value of R_{n + 2}Is 4.40, window W_{n + 3}Center of gravity value R
_{n + 3}Is 4.41, the window has moved
The difference ΔR of the center of gravity at the in is calculated. That is, ΔR = R_n-R_{n + 1}= 4.65-4.38 = 0.27 Becomes

This value ΔR is added to the value of the center of gravity of the diagonal line K3, and the position error is obtained by using the addition result as the value of the center of gravity.
In this case, the value R _{n + 2} of the center of gravity of the window W _{n + 2} and the value R _{n + 3} of the center of gravity of the window W _{n + 3} are: R _{n + 2} = R _{n + 2} + ΔR = 4.40 + 0.27 = 4 .67 R _{n + 3} = R _{n + 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 W _{n of the} diagonal line K2
When moving from the window W _{n + 1} of the diagonal line K3 to the diagonal line K3, the diagonal lines K2 and K3 must simultaneously exist in the main scanning direction.

FIG. 15 shows the positional relationship of the diagonal lines, and the length L ₁
Are arranged at an angle θ with respect to the main scanning direction,
When the start point and the end point of the slant line in the main scanning direction are the same, and the slant line interval in the main scanning direction is L ₂ , the slant line is formed so that the relationship of L ₂ <L ₁ × cos θ (1) holds. by arranging, hatched since heavy becomes the main scanning direction, it is possible to move the window in the main scanning direction continuously measuring the center of gravity of the next hatching. Here, the greater the magnitude relationship of Expression (1), the less the precision is required for the length L ₁ of the diagonal line and the positions of the starting point and the ending point of the diagonal line in the main scanning direction.

Next, the relationship between the amount of movement of the diagonally shaded image in the main scanning direction and the pixel position error in the sub scanning direction 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 line is read is observed. When the pixel is a square and is measured using diagonal lines of 45 °, as described above, the deviation between the windows of the movement amount in the main scanning direction becomes the position error in the sub scanning direction as it is. 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.

FIG. 16 shows the second embodiment, and the oblique line discriminating section 23 and the position error measuring section 24 in the first embodiment are omitted. With such a configuration, the image data corrected by the shading correction unit 23 can be output to an external memory, and the position error of the data can be measured by a computer. In this method, image data can be temporarily written in a magneto-optical disk or the like and stored, and read when necessary to measure a position error, which is convenient in some cases. When the same-size sensor is used as the photoelectric conversion device 7, there is no problem that the amount of peripheral light decreases due to the characteristics of the lens, and thus the shading correction unit 23 in the first and second embodiments is omitted. There is also.

[0056]

According to the present invention as described above, according to the present invention, c
The first image on the diagonal line centered on the central pixel in the window
With the pixel centered on the center pixel with respect to the first pixel
The second pixel at a symmetrical position and the first pixel
By comparing the difference with the second pixel with a threshold value, the win
Recognize whether there is a diagonal pattern in the dough,
Move window forward if pattern is recognized to exist
Sequentially shift in the direction of the diagonal lines and move within each window.
Sub-scanning method of read pixel based on change in position of diagonal line
The horizontal position error is measured, so the diagonal line pattern can be reliably determined.
It can be different .

[0057]

[0058]

[0059]

[0060]

[0061]

[0062]

[0063]

[Brief description of drawings]

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

FIG. 2 is a cross-sectional view showing the image reading apparatus of FIG.

3 is a plan view showing the image reading device 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 an explanatory diagram showing a diagonal pattern.

FIG. 6 is an explanatory diagram showing read data of a diagonal pattern according to variations in scanning speed.

FIG. 7 is an explanatory view showing an enlarged hatched pattern.

FIG. 8 is an explanatory diagram showing read values of the hatched pattern in FIG.

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 diagram 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 process of the image reading apparatus in FIG.

FIG. 14 is an explanatory diagram showing a reading value and a centroid measuring method in the centroid measuring window.

FIG. 15 is an explanatory diagram showing lengths and angles of diagonal lines.

FIG. 16 is a block diagram showing an image reading device according to a second embodiment.

[Explanation of symbols]

7 Photoelectric conversion device 10 diagonal pattern 23 Diagonal line discriminator 24 Position error measuring unit L diagonal

Continuation of front page (56) Reference JP-A-60-256267 (JP, A) JP-A-5-298448 (JP, A) JP-A-8-51527 (JP, A) JP-A-5-300341 (JP , A) JP-A-7-105487 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H04N 1/04

Claims (4)

(57) [Claims] 1. A scanning unit which scans an original by scanning it line-sequentially in a main scanning direction and a sub-scanning direction at regular time intervals, and a scanning unit which has a constant width and is oblique to the main and sub-scanning directions and in the sub-scanning direction. Window setting means for setting a window for image data when the scanning means reads a pattern of a plurality of diagonal lines arranged at equal pitch; and a diagonal line centered at least on a central pixel in the window.
The first pixel above and the central image for the first pixel.
A second pixel at a symmetrical position with respect to a pixel;
Comparing the difference between one pixel and the second pixel with a threshold
Check if there is a diagonal pattern in the window.
An oblique line pattern recognizing means for recognizing and judging, and an oblique line pattern exists by the oblique line pattern recognizing means.
If it is recognized that the window is the angle direction of the diagonal line
To the position change of the diagonal line in each window.
Position error of the read pixel in the sub-scanning direction based on
Position error measuring apparatus of pixels comprising: the position error measuring means for constant, the. 2. The diagonal direction of the diagonal and the diagonal pattern
2. The pixel position error measuring device according to claim 1 , wherein the tilt directions of the pixels are the same . 3. The diagonal pattern recognition means is the first
First sum of density values of the area not including the pixels of
And the first pixel of the area not including the second pixel and the diagonal line.
The density value sum of 2 is calculated, and the first density value sum and the second density value sum
Within the window by comparing the difference between
Characterized by determining whether or not a diagonal pattern exists
The pixel position error measuring device according to claim 1 . 4. The length of the diagonal line is L ₁ , the interval of the diagonal line in the main scanning direction is L ₂ , and the angle of the diagonal line with respect to the main scanning direction.
As the degree theta, any one of claims 1 to 3, characterized in that it is _L 2 _{<L 1} × _{cosθ 1}
Item 7. A pixel position error measuring device according to item .