JPH05161000A - Original reader - Google Patents

Abstract

PURPOSE:To reproduce an accurate image by correcting a picked-up image which is distorted owing to the curve of an original by detecting how much the original is curved. CONSTITUTION:The document is photographed and read from above and a distance measuring circuit 22 measures height at plural points on the original. The distance measurement results are interpolated by a spline interpolating circuit 24 to detect the shape of the original and an image expansion rate calculating circuit 25 calculates the displacement of the photographed image as compared with a flat original. An image expanding circuit 34 corrects the read data according to the calculation result to reproduce the beautiful easy-to-see image as well as the flat document even if the original is curved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a document reading device for photographing a document from above and for detecting and correcting the degree of bending of a document that is spatially curved.

[0002]

2. Description of the Related Art When a document is photographed from above, a flat document can be photographed beautifully. However, when photographed from above, a bound document is photographed because the document is bent near the seam. The image is compressed near the seam and the image is distorted. Therefore, conventionally, in a document reading apparatus that photographs a document using a line sensor or the like, the distance between the line sensor and the document surface is measured by using a distance sensor that measures the distance between the document and the line sensor according to the measured value. By changing the reading pitch in the sub-scanning direction,
It is known that image data is corrected (see, for example, Japanese Patent Application Laid-Open No. 62-143557). Also, there is a method in which a document surface is irradiated with a line beam, the shape of the document is measured by an image of reflected light, and image data is corrected based on the measured shape (see, for example, Japanese Patent Laid-Open No. 3-117965).

[0003]

However, in the former device described above, the mechanical load at the time of scanning, which is to change the reading pitch in the sub-scanning direction, is large.
The structure is complicated, and the cost is high because the distance sensor is used. Further, in the latter device, since image data is not interpolated based on the result of shape measurement of the document, accurate shape measurement may not be possible. The present invention solves the above problem, and when a document is photographed from above, by detecting the degree of bending of the document that is spatially curved, and correcting the data during reproduction,
It is an object of the present invention to provide a document reading apparatus that can reproduce an image exactly as if it was photographed on a flat surface without applying a mechanical load during scanning as in the related art.

[0004]

In order to achieve the above object, the present invention provides a document reading unit for reading a document, a measuring unit for measuring a distance between a plurality of points on the document, and a plurality of units obtained from the measuring unit. The document reading apparatus includes an interpolating unit that interpolates document reading data based on measured values, and a correcting unit that corrects the output of the document reading unit according to the output of the interpolating unit.

[0005]

According to the above structure, the document is read by the document reading unit, and the distance between a plurality of points of the document is measured by the measuring unit. This distance measurement makes it possible to detect the degree of bending of the document. The original reading data is interpolated by the interpolating means based on the plurality of measurement values obtained from the measuring means, and the original reading output is corrected by the correcting means according to the output of the interpolating means. As a result, it is possible to decompress the image compressed by the bending of the document.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the external structure of a document reading apparatus according to an embodiment of the present invention. A document 1 is placed facing upward on a document table of a desk-shaped apparatus body, and a reading unit 2 is provided at a position where the document 1 can be read from above. The reading unit 2 is supported by the supporting member 3, and a predetermined space is provided between the document 1 and the reading unit 2. This distance is such that at least the readable area on the surface of the original 1 is always visible, and this space forms a working space between the surface of the original 1 and the reading unit 2. Further, the device is provided with operation switches 4 and a bend correction circuit unit 5.

2 and 3 show the configurations of the document table 10 on which the document 1 is placed and the reading unit 2. The image information of the document 1 is transferred to the image sensor 6 through the imaging lens 7 of the reading unit 2.
Read in. The image sensor 6 is a semiconductor photoelectric conversion element such as a CCD and may be an area sensor or a line sensor. 2 shows an area sensor, and FIG. 3 shows a line sensor. The bend detection board 9 is provided with an infrared light emitting element 8a and a light receiving element 8b. The board 9 is scanned to
Measure the change in the height of the document surface. That is, the light emitting element 8
The infrared light emitted from a is reflected by the document surface by the light receiving element 8b to measure the height of the document surface by the triangulation method. The distance measuring method is not limited to the triangular distance measuring method, and a phase difference distance measuring method may be used.

FIG. 4 is a block diagram of signal processing of this apparatus, and FIG. 5 is a flow chart showing processing of copy operation by this apparatus. Hereinafter, the process of correcting the bending of the imaged data according to FIGS. 4 and 5 will be described. In FIG. 4, C
The PU 21 controls the distance measuring circuit 22 and the CCD driving circuit 29. The output of the distance measuring circuit 22 is input to the spline interpolation circuit 24 via the A / D converter 23, and is further input to the image expansion rate calculation circuit 25. This output is stored in the memory 28. On the other hand, C driven by the CCD drive circuit 29
The image pickup signal of the CD 30 (the above-mentioned image pickup sensor 6) is A / D.
It is input to the image restoration circuit 33 through the converter 31, and the output is output together with the data in the memory 28 to the image expansion circuit 34.
The image data decompressed and expanded is sent to the output unit 35.

The processing of the copy operation by this apparatus will be described with reference to FIG. First, the original is set (# 1). When the copy button is turned on after the document is set (#
2) The distance measuring circuit 22 is driven by an instruction from the CPU 21. Then, the bending detection board 9 of FIGS. 2 and 3 scans and measures the heights of 10 points on one page and 20 points on the entire surface of the document (# 3). Hereinafter, one page will be described. The height is measured by triangulation. The above measurement data is spline-interpolated by the cubic spline interpolation circuit 24 (#
4) Further, the image expansion rate calculation circuit 25 calculates the image expansion rate (# 5). Next, the CCD 30 captures an image (# 6), the image restoration circuit 33 restores the image (# 7), the image extension circuit 34 extends the image (# 8), and then the printout is performed (#). 9).

Each of the above processes will be described below. FIG. 6 is a diagram for explaining the processes of # 3 and # 4. Figure 6
(A) shows the height measurement data and the position, and the envelope shows the bending of the document. The broken line arrow in FIG. 6B is data obtained by cubic spline interpolation. By this interpolation, measurement data having a height of 450 points is obtained in accordance with the number of dots of the reproduction printer.

The reason why the interpolated measurement data is necessary will be described below. FIG. 7 shows the relationship between the length of the compressed image due to the bending of the original and the original image. X1- in FIG. 6 (a)
Regarding x2, at points A, B, and C shown in FIG.
The length of the line segment actually photographed is AC, as shown in FIG.
When the curve AB corresponding to the length of the document can be approximated to a straight line (when the points AB are close), the length of the document can be approximated to the straight line AB. When the image is actually expanded, it is shown in FIG.
Thus, the length between AB can be obtained from the length between AC with AB = AC · (1 / cos θ).

However, in reality, as shown in FIG. 7B, since the bending of the document is a curve, it cannot be approximated by a straight line. On the other hand, if a large amount of height measurement data is taken and the measurement points are closely spaced, a straight line approximation as shown in FIG. 7A becomes possible. Therefore, when the number of measurements is small and the curve of the original cannot be approximated by a straight line, interpolation is performed with a cubic spline function to obtain a curve that approximates the curve of the original, and the characters and pictures of the original are uniformly extended. it can.
When cubic spline interpolation is performed by scanning the detection board 9, 10 points are measured in this embodiment.
The most accurate linear approximation can be realized by obtaining the same number of measurement data as the number of images of one line imaged from the CCD.
For the above reasons, for example, when there are 10 measurement points, interpolated measurement data is necessary.

In the cubic spline interpolation, x1 in FIG.
In order to obtain the cubic spline interpolation function of ~ x10, the data of unknown x0 and x11 shown in FIG. 8 is required. As shown in FIG. 8, x0 is the fold portion of the book,
The height h ₀ = 0 may be set. Further, in order to obtain the interpolation data in the section [x0, x1] near the fold of the document, the distance measurement data of x _{- 1} shown in FIG. 8 is required. x _{- 1} in the height h _- By approximating a _{1 = -h 1, [x0,} x
It is possible to obtain the interpolation data in the section [1]. Also, x
Since 11 is the end portion of the document, the document and the document table may be substantially horizontal, so the height of x11 h _{1 1} = h ₁
You can set it to ₀ . As described above, the cubic spline function can be obtained in the entire range of the document surface. Alternatively, it is possible to interpolate with a quadratic spline function, which further simplifies the process.

Next, the height data interpolated by the spline interpolation circuit 24 of FIG. 4 is sent to the image expansion rate calculation circuit 25 for processing. The details of this processing will be described below. X1 determined by spline interpolation circuit 24, ..., height data h ₁ of x450 point, ..., to calculate the image elongation than the data of h _{4 5 0.} The image expansion rate is the value of AB / AC in FIG. The image expansion rate α is calculated from FIG.

[Equation 1]

[0015] By sequentially calculating this from k = 1, α (1), ..., α (449) can be obtained. Image expansion rate α (k) (k = 1, ..., 44
The image expansion rate calculation circuit 25 performs the process of obtaining 9). Next, when the above processing is completed, the CCD driving circuit 29 is driven by the command of the CPU 21 of FIG. 4, and the original image is picked up by the CCD 30. Next, the imaged data is taken from the A / D of FIG.
The converter 23 performs A / D conversion, sends the image data to the image restoration circuit, and restores the image. The details of this processing will be described below.

Image restoration consists of blur restoration and luminance unevenness correction.
Do about the points. First, blur restoration will be described. Since the document is largely inclined near the fold line of the document and the difference in height between the documents is large, the blur of the focus becomes large. A Laplacian process is a method for repairing this blur. By performing the Laplacian processing on the image data, the edges in the gradation of the bright and dark parts of the image are emphasized, and the blur of the image pickup is improved. Further, when the A / D conversion process or the D / A conversion process is performed on the path through which the electric signal flows as in the present embodiment, noise of the electric signal is likely to occur, and therefore noise is generated by the gamma (γ) conversion process. By removing it, sharpening of the image can be further realized.

Next, the brightness unevenness correction processing will be described. For example, in the read image data, the image data in the i-th row and the j-th column before the luminance unevenness correction processing is set to a (i, j),
The image data after the brightness unevenness correction processing is set to b (i, j). In the brightness unevenness correction processing, first, a (k, j) is detected as one line of data in a white background portion without letters or pictures at the upper end portion or the lower end portion of the document. This a
The density distribution at (k, j) is as shown in FIG. The density distribution of FIG. 12 corresponds to the x-axis direction of FIG. In FIG. 12, the point A where the density has decreased corresponds to the seam portion of the document placed upward, and in order to correct the image data of this portion, the value of max / a (k, j) is calculated, By multiplying this value by the data of each pixel on the k-th row, the uneven brightness is eliminated. This is shown in FIG. The above ma
When the value of x / a (k, j) is multiplied by the data of all the pixels in the same corresponding column, the uneven brightness is corrected for the data of all the pixels.

The above is expressed by the following equation. Image data a in the i-th row and the j-th column before the brightness unevenness correction
(I, j) and similarly, if the image data in the k-th row before the brightness unevenness correction processing is a white background, the image data b (i, j) after the brightness unevenness correction processing is

[Equation 2] Calculated as Image restoration can be realized by the above-described blur correction processing and luminance unevenness correction processing.

Next, the processing by the image expansion circuit 34 will be described. The image data restored by the image restoration circuit 33 as described above is sent to the image expansion circuit 34. The image expansion circuit 34 includes an image expansion rate calculation circuit 2
The value of the image expansion rate calculated in 5 and stored in the memory 28 is read. The image expansion circuit 34 performs image expansion processing based on this image data and the image expansion rate data. The method of decompressing image data will be described below. _{9, [x k, x k +} 1] as an example ten image data in the interval, indicating the case of decompression processing by the image expansion rate 1.4. In this _{example, [x k, x k +} 1] of the section 10 the number of pixels in the, from x1 sequentially 1,2,
…, 10 Here, the i-th pixel is the image expansion rate α
If the number of expanded pixels of the i-th pixel is j and the cumulative number of expanded pixels is n, the relational expression j = α · i−i−n holds.

In the above relational expression, when i = 1, j = 1.4 × 1-1-0 = 0.4. However, since j is not an integer as it is, it is not possible to determine whether the number of pixels after decompression is 0 or 1, so the value of j is rounded to an integer. From the above, the relational expression of the expansion process is as follows: j = f (α · i−i−n) f (x) = y + 1 (x−y ≧ 0.5) f (x) = y (x−y < 0.5) x: value of (α · i−n) y: value of integer part of (α · i−n) can be expressed. Therefore, when i = 1, j = f (0.4) = 0. Therefore, the image data of i = 1 has k = f in FIG.
The image data is 1. In this case, the cumulative number of pixels after decompression is 0, so that n = 0.

Similarly, when i = 2, j = f (1.8) = 2. Therefore, the data of the pixel of i = 2 is k in FIG.
= 2 and k = 3. In this case, the cumulative number of pixels after expansion is 1, so that n = 1. Hereinafter, similar calculations are performed for i = 3, 4, ... In FIG. 10, for the pixels of k = 1, 2, ..., 14 in FIG. 9, the data of the pixel number of the pixels of i = 1, 2, ..., 10 before the decompression process is applied after the decompression process. This is what is shown. These processes [x1, x450]
The image can be expanded by applying it to the pixels in all the sections.

Furthermore, as a better method, when the data of the i-th pixel is expanded to m, the data of the i-th pixel is not actually put into the m pixels after the expansion processing, but Processing as shown in FIG. 11 is performed based on the data of the i-th and i + 1-th pixels. That is, the data of the pixel to be expanded is subjected to density interpolation while adding an average density gradation to expand the image. (J + 1) in FIG.
The (l = 0,1, ..., m-1) th image data a (j +
l) can be calculated by the following formula.

[Equation 3] When m = 0 a (j + 1) = a (j)

Next, the reason why the image restoration is performed before the image expansion is explained. Since the density interpolation is performed when the image is expanded, the gradation of the image data after the expansion processing becomes small and the edge becomes gentle. Therefore,
Even if the above-described Laplacian process in image restoration is performed after the image expansion, the edge is less likely to be emphasized, and the image restoration effect is small. On the other hand, when the image is expanded after the Laplacian processing, the edges are emphasized and become thicker, which is extremely effective for restoring thin characters or small characters.

The image sensor, which is a means for reading a document, may be a line sensor or an area sensor, and its application range is wide. In addition, when measuring the distance,
As shown in FIG. 4, it is possible to increase the distance measurement data in the vicinity of the fold of the document and decrease the distance measurement data as the distance from the fold is increased.
Highly accurate spline interpolation is possible. Further, the spline interpolation can be performed with any number of distance measurement data. With this, it is possible to perform an appropriate interpolation process according to the specifications of the device (hardware).

A distance measuring means according to another embodiment different from the distance measuring means described above is shown in FIGS. In this example, the document table 1
0 and the photosensor 91 perpendicular to the platen 10.
The board 90 is placed, the original 1 is brought into close contact with the board 90, and the original 1 is arranged so that the photosensor 91 is shielded from light at the portion where the original 1 is present. With this configuration, the height of the surface of the document 1 can be measured in accordance with the output of the photo sensor 91.

[0026]

As described above, according to the present invention, by measuring distances at a plurality of points of an original when reading the original, the degree of bending of the spatially bent original is detected, and the original is read according to the degree of bending. Since the data is interpolated and the compressed image is expanded, the same output as when the original is flat can be realized, and a beautiful and easily viewable image can be reproduced. In particular, even if the number of distance measurement data is small, the shape of the document can be accurately measured by performing the interpolation process using, for example, a cubic spline function, and the distortion due to the bending of the document can be corrected beautifully. it can.
Furthermore, if the number of distance measurement points is reduced, the required memory is reduced, and the circuit configuration for distance measurement can be simplified and the cost can be reduced.

[Brief description of drawings]

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

FIG. 2 is a perspective view showing a configuration of a reading unit.

FIG. 3 is a perspective view showing a configuration of a reading unit.

FIG. 4 is a block diagram showing a flow of an electric signal.

FIG. 5 is a flowchart of an image copy operation.

FIG. 6 is an explanatory diagram of spline interpolation.

FIG. 7 is an explanatory diagram of linear approximation.

FIG. 8 is an explanatory diagram of approximate data in spline interpolation.

FIG. 9 is an explanatory diagram of image expansion processing.

FIG. 10 is an explanatory diagram of image expansion processing.

FIG. 11 is an explanatory diagram of density reproduction interpolation.

FIG. 12 is a diagram showing a density distribution before correction of luminance unevenness.

FIG. 13 is a diagram showing a density distribution after luminance unevenness correction.

FIG. 14 is an explanatory diagram of spline interpolation when the number of measurement points is changed depending on the location.

FIG. 15 is an external configuration diagram of a document reading apparatus according to an embodiment using a photo sensor as a distance measuring unit.

FIG. 16 is a side view of distance measuring means using a photo sensor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Original 2 Reading section 5 Bending correction circuit section 6 Image sensor 8a Infrared light emitting element 8b Light receiving element 10 Original table 21 CPU 22 Distance measuring circuit 24 Spline interpolation circuit 25 Image expansion rate calculation circuit 28 Memory 30 CCD 34 Image expansion circuit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Nobuyuki Okis, 2-13-3 Azuchi-cho, Chuo-ku, Osaka, Osaka International Building Minolta Camera Co., Ltd. (72) Satoshi Nakamura, Azuchi-cho, Chuo-ku, Osaka 3-13-3 Osaka International Building Minolta Camera Co., Ltd. (72) Inventor Toshihiko Karazaki 2-33-1 Azuchi-cho, Chuo-ku, Osaka City Osaka International Building Minolta Camera Co., Ltd.

Claims (1)

[Claims] 1. An original reading means for reading an original, a measuring means for measuring a distance between a plurality of points of the original, and an interpolating means for interpolating the original read data based on a plurality of measurement values obtained from the measuring means. A document reading apparatus comprising: a correction unit that corrects the output of the document reading unit according to the output of the interpolation unit.