JPH10304148A - Image reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain reading with high quality by estimating a height of a part of an original hidden by an obstacle and controlling reading depending on estimate height data denoting an estimated height distribution and valid height data so as to set correct operation depending on the height distribution of the original. SOLUTION: A height of an original face S1 within a sampling range where height data are not effective is estimated based on discriminated valid height data. That is, a change characteristic of the valid height data DH is approximated linearly to interpolate missing height data. For example, when the change in the valid height data DH is constant, it is regarded that the height of missing parts is changed linearly, and invalid height data dH are replaced with estimated height data Dh that change similarly to the valid height data DH. When the valid height data DH changes arithmetically, it is regarded the height of missing parts is changed along with a curve, invalid height data dH are replaced with estimated height data Dh that change similarly to the valid height data DH.

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 suitable for reading bound originals such as books and magazines.

[0002]

2. Description of the Related Art An image reading apparatus called a book scanner has been commercialized. In this apparatus, a photographing system is arranged above a platen, and an open space having a height of several tens cm exists between the platen and the photographing system. When reading a book-shaped original such as a book or magazine (this is referred to as a “book original”), the user sets the book original upward on a platen with the book original opened. In response to turning on of the start key, scanning of a facing surface (document surface) which is a reading target surface (original surface) is started, and the read images are sequentially output to an external device. If the external device is a printer, a copied image is formed in real time. When a book scanner is used, pages can be turned on a document table, so that the efficiency of reading many pages can be improved.

[0003] Unlike a sheet document, the document surface of a book document is curved. That is, the height varies depending on the position in the facing direction (left-right direction). For this reason, what is called out-of-focus or distortion occurs in the read image. The book scanner measures the height distribution of the document surface and performs focus adjustment and distortion correction according to the measurement result. As a method of measuring the height distribution of the document surface, there is a method of photographing the document end surface in a direction perpendicular to the spread direction (hereinafter, referred to as a vertical direction) and judging the shape (Japanese Patent Laid-Open No. Hei 5-161002). By arranging the mirror obliquely upward on the platen, the end surface can be photographed using a photographing system for reading. As other measurement methods, there are a method using a distance measuring sensor and a slit light projection method, and a method of calculating the height from the degree of curvature of a vertical edge on a document surface.

[0004]

In reading a book document, there are cases where the user must hold both ends of the spread surface in order to maintain the spread state. In this case, there is a problem that the height of a portion of the document surface hidden by the user's finger or arm cannot be measured, and focusing and distortion correction cannot be performed correctly. According to the method of examining the degree of curvature of the vertical edge, since the user holds down the edge in the facing direction, the height can often be measured over the entire length in the facing direction. However, the degree of curvature may not be detected correctly due to the book binding of the book document becoming out of shape, or being incorrectly distinguished from the edge of the cover.

SUMMARY OF THE INVENTION It is an object of the present invention to realize a high-quality reading by setting a correct operation according to a height distribution of a document even when the user holds the document by hand.

[0006]

Focusing on the fact that the height change of the document surface of the spread document is gradual, it is determined whether or not the height data at each sampling position is appropriate, and the height of the non-conforming position is determined as the conformity data. Is determined by an operation based on The hand of the user holding the document is three-dimensional, and the apparent height changes abruptly at the boundary between the portion of the document surface hidden by the hand and another portion. Height data at locations outside this boundary is irrelevant.

According to a first aspect of the present invention, there is provided an apparatus having a document table for supporting a document, and a photographing system for photographing the document, wherein the photographing system is disposed above the document table and has an upward setting type image. A reading device for measuring a height distribution of a subject surface photographed by the photographing system; Means for extracting effective height data corresponding to the document surface from the height data of the document, and a portion of the document surface hidden by the object with respect to the photographing system based on the extracted effective height data. It has means for estimating the height distribution, and means for controlling the reading operation in accordance with the estimated height data indicating the estimated height distribution and the effective height data.

[0008]

FIG. 1 is a perspective view showing the appearance of a book scanner 1, and FIG. FIG. 3 is a diagram illustrating a state in which a document is pressed.

The book scanner 1 is an image reading apparatus suitable for reading a book original (spread original) BD.
It has a main body housing 10 for accommodating a power supply circuit and the like, a dark document table 20 for supporting a document, an imaging unit 30 for converting a document image into an electric signal, and a lamp unit 40 for illuminating the document. The platen 20 is the main body housing 1
0 is located on the front side. The imaging unit 30 is arranged above the document table 20 and is supported in a cantilever manner by a support column 12 extending upward from the upper surface of the main body housing 10. The lamp unit 40 is attached to the rear end of the lower surface of the imaging unit 30 and illuminates the document table 20 from obliquely above. A space 80 between the document table 20 and the imaging unit 30 is open to a free space outside the apparatus, and has a sufficient size for setting a book document BD. The distance between the document table 20 and the lower surface of the imaging unit 30 is 30 cm or more.

An operation panel OP is provided on the upper end of the front surface of the main body housing 10, and a projection plate 18 for detecting the height of the document surface is fixed to the lower end. On the operation panel OP, together with the liquid crystal display, buttons for specifying a reading mode and reading conditions (reading size, magnification, number of output sheets, density, etc.) are arranged. The front surface of the projection plate 18 is a glossy surface and is a 45 ° inclined surface with respect to the upper surface of the document table 20. An image of the vertical end face S3 of the book document BD is projected on the projection plate 18, and the projection plate 18 in that state is photographed together with the document image. The upper end surface of the projection plate 18 is used as a white plate for shading correction.

Operation panel O in main body housing 10
A main switch 51 is provided on a side surface on the right side toward P. A start key 5 for the user to instruct the start of reading is provided on both sides of the platen 20 in the left-right direction.
2 and 53 are provided one by one, and an armrest 25 is provided on the front side.

The image pickup unit 30 includes a line sensor 31 composed of a CCD array, an imaging lens 32, and a mirror 33.
have. The original image is projected on the light receiving surface of the line sensor 31 by the optical system OS including the mirror 33 and the imaging lens 32. The imaging lens 32 is provided so as to be movable in the front-rear direction, and has an AF mechanism (lens driving unit) 13.
2 position. The line sensor 31 is attached to a movable body of a sub-scanning mechanism (not shown),
The parallel movement is performed along the left-right direction (sub-scanning direction) M2 while keeping the arrangement direction of the elements in the up-down direction. By this parallel movement, a two-dimensional document image is captured. The main scanning direction of the document image is a front-back direction on the document table 20 and a vertical direction on the imaging surface. In the present embodiment, the image pickup unit 30 and the above-described projection plate 18 constitute a photographing unit for the end face S3. In the preliminary scanning, the image pickup unit 30 takes pictures of the document surface S1 and the end face S3 simultaneously. Note that an area sensor can be used instead of the line sensor 31. By combining the book scanner 1 having the above configuration with a digital copying machine, a comprehensive copying system suitable for various types of documents can be constructed.

When using the book scanner 1, the user places the book document BD upward on the document table 20 such that the facing direction of the book document BD is the left-right direction of the document table 20. At this time, the boundary (spread center) between the left page and the right page on the spread surface S1, which is the document surface, is aligned with the mark indicating the center of the document table 20 in the left-right direction, and
The book document BD is pressed against the lower edge of the document to position in the front-back direction. The boundary between the projection plate 18 and the document table 20 is a reference line for setting the document. The center of the reference line is the reference position Ps (see FIG. 2). Further, the user holds the left and right ends (or one end) of the book document BD as needed, as shown in FIG. 3, and maintains the spread state. Start key 52, 53 while holding book original BD
Can be operated. The document table 20 is supported by a spring mechanism so that it can move up and down independently of the left and right in accordance with the weight of the document. Thus, regardless of the thickness of the book document BD, the height of the left and right pages becomes substantially the same regardless of which page is opened, and the shooting distance is a value within a certain range.

The book scanner 1 performs preliminary scanning and main scanning on one document. The preliminary scanning is performed in order to obtain document information (height distribution of the document surface S1, document size, background luminance, and the like) necessary for setting the operation of the main scanning. That is, the book scanner 1 responds to the information obtained by the preliminary scanning,
The main scanning operation conditions such as a focus adjustment amount (lens movement amount), a magnification for distortion correction, and a masking range are set. The image output to the external device is performed during the main scanning. The reading mode of the book scanner 1 includes a mode for reading both left and right pages at once (sheet document mode) and a mode for reading left and right pages separately (book division mode). In either mode, preliminary scanning and main scanning are performed on each page.

FIG. 4 is a diagram for explaining an outline of a method of measuring the height distribution of the document surface. The broken line in the figure indicates the position of the line of interest. Here, it is assumed that the photographing was performed without the user pressing the document.

The read image G0 is a photographed image (upper surface image) G1 of the upper surface of the book document BD, a photographed image G20 of the document table 20,
And a photographed image G18 of the projection plate 18. The image G181 of the photographed image G18 indicates the shape of the end surface S3 of the set book document BD. Images 180 other than the image (end face image) G181 of the captured image G18
Is a background image reflected on the projection plate 18. Since a subject near the imaging surface is photographed larger than a distant subject, both edges in the main scanning direction (vertical direction) of the top surface image G1 are curved.

Since the platen 20 is dark, the photographed image G2
0 is a darker image than other images. Further, since the end surface S3 is also illuminated together with the document surface S1, the end surface image G181 is brighter than the background image G180. Therefore, it is possible to extract the top surface image G1 and the end surface image G181 by judging the magnitude of the luminance, and measure the document size and the height distribution of the document surface S1. Specifically, for each sampling position (line) at a predetermined interval, the luminance (pixel value) is sequentially determined from the top pixel in the main scanning direction.
Is checked, and the pixel position (pixel number) n1 on the head side of the range where the luminance exceeds the first threshold th1 and the luminance is set to the second threshold th2
Pixel positions n3 and n4 on the leading and trailing ends of the range exceeding (th2> th1) are detected. The number of pixels between the pixel position n1 and the known pixel position n2 corresponding to the front edge of the projection plate 18 corresponds to the height of the document surface S1 in the line,
The number of pixels between pixel position n3 and pixel position n4 corresponds to the document size in the main scanning direction. The actual size is obtained by the calculation of dividing the number of pixels by the imaging resolution. The curved state of the document surface S1, that is, the height distribution is specified by a set of data indicating the height of the document surface S1 in each of all the sampled lines. Further, the respective positions of the first line and the last line where the pixel positions n3 and n4 are detected correspond to both end positions of the document in the sub-scanning direction.

Next, estimation of height data specific to the present invention will be described. FIG. 5 shows a read image G0 corresponding to FIG.
b, FIG. 6 is a diagram showing the measurement results of the height distribution, FIG.
FIG. 4 is a diagram showing an example of a sudden change in height distribution. In FIG. 5, components corresponding to those in FIG. 4 are denoted by the same reference numerals regardless of the difference in shape.

The read image G0b is composed of an upper surface image G1, a photographed image GH of the user's hand, a photographed image G20 of the document table 20, and a photographed image G18 of the projection plate 18. The photographed image G18 includes an end face image G181 and a hand image Gh. That is, in shooting in this case, the user's hand is the subject together with the book document BD.

When the height distribution is measured by determining the brightness of the photographed image G18, the height of the upper surface of the user's hand is measured at the end in the sub-scanning direction as shown in FIG. That is, part of the height data of the document surface S1 is lost. The book scanner 1 calculates the height of the end of the document surface S1 in the following manner.

With respect to the height of the book document BD, the following conditions can be given. The height does not change abruptly in the vicinity of the spread center Pc and other than at the end (hem). In most documents, the height decreases toward the left and right edges. Even when the end side is high due to “warpage” or “undulation”, the height change is gradual and the change amount in the minute section is small.

Therefore, the difference value between the height data of adjacent sampling positions (lines) is determined in order from the center of the page to the end, so that the measured height data is converted to the effective height corresponding to the document surface S1. Data and invalid data corresponding to the user's hand can be determined.
The position where the sign of the difference is reversed and the difference value exceeds a certain value is the boundary between the document area and the user's hand area in the height distribution.

FIG. 7A shows a case where only a portion ahead of the user's wrist is projected on the projection plate 18 with a predetermined brightness. The height of the n-th sampling position and (n-1)
The difference Δh (n) from the height of the second sampling position is a relatively small negative value. On the other hand, the difference Δh (n + 1) between the height of the (n + 1) th sampling position and the height of the (n) th sampling position is a positive value exceeding a predetermined threshold. That is, the (n + 1) th sampling position is the boundary between the document area and the area of the user's hand, and the height data at the (n + 1) th sampling position and a position outside the (n + 1) th sampling position are invalid data. FIG. 7 (B)
This shows a case where a portion of the user's wrist and the arm are projected on the projection plate 18 with a predetermined brightness. Also in this example, the difference Δh (n
+1)) is extremely large, and the height data at the (n + 1) th sampling position and the position outside the (n + 1) th sampling position are invalid data.

As a reference value (threshold value) for discriminating the magnitude of the difference, for example, when sampling the height at a pitch of 1 mm, about 2 mm is appropriate. This is because even if the end portion is high due to “warpage” or the like, it is almost impossible to increase at a rate of 2 mm or more per 1 mm.

FIG. 8 is a schematic diagram of correction of height data.
Based on the effective height data determined in the above manner, the document surface S in the sampling range where the height data is invalid
Estimate the height of 1. That is, the change characteristics of the effective height data DH are linearly approximated, and the missing height data is interpolated. For example, if the change amount of the effective height data DH is constant as shown in FIG. 8A, it is considered that the height of the missing portion also changes linearly, and the invalid height data dH is used as the effective height data. It is replaced with estimated height data Dh that changes in the same manner as DH. If the effective height data DH changes by an equal difference as shown in FIG. 8B, it is considered that the height of the missing part also changes in a curved line, and the invalid height data dH is converted to the effective height. The estimated height data Dh is changed in the same manner as the data DH. In such a height estimation, the value of the height data outside the document edge is forcibly set to 0 by referring to the document size in the sub-scanning direction measured in advance. Interpolation calculation value is 0
The value is forcibly set to 0 even when the value becomes below. This allows
The height distribution is corrected as indicated by a mark in FIG. 8C. The correction is not limited to the linear approximation, but may be performed by calculating the curvature of the change characteristic curve or obtaining a function that fits the curve.

FIG. 9 is a functional block diagram of the main part of the book scanner 1. As shown in FIG. The book scanner 1 is controlled by a CPU 101 having a microcomputer. CPU
101 is a CC that supplies a clock to the line sensor 31.
D drive circuit 130, sub-scanning mechanism 131, AF mechanism 13
2. An operation instruction is given to each control target of the lamp control circuit 140 for controlling the lighting of the lamp unit 40 and the image processing circuit 103. The operation panel OP, the switch group 50, and various sensors are connected to the CPU 101.

The photoelectric conversion signal output from the line sensor 31 of the imaging unit 30 is converted by the AD converter 102 into, for example, 8-bit image data D1. In the preliminary scanning, the image data D1 is input to the height measuring unit 104 in the order of pixel arrangement. The height measuring unit 104
It consists of a comparator and a counter, and counts the number of pixels exceeding the threshold th1. That is, the height of the document surface S1 is measured. The count value from the height measuring unit 104 is sent to the CPU 101 as height data D104. CPU 101
Includes three functional elements: a height determination unit 111, a height estimation unit 112, and an operation setting unit 113. Height discriminator 11
1 extracts effective height data DH from the height data D104. The height estimation unit 112 calculates the estimated height data Dh by an interpolation operation based on the effective height data DH.
The operation setting unit 113 prepares focusing and distortion correction control data in accordance with the height distribution of the document surface specified by the effective height data DH and the estimated height data Dh.

In the main scanning, focusing is performed in accordance with the progress in the sub-scanning direction, and image data D 1 taken in a focused state is input to the image processing circuit 103. The image processing circuit 206 performs MTF correction, density correction, and distortion correction. The distortion correction is a magnification change processing 61 for the curvature of the document surface. For example, in the main scanning direction, a plane at a constant height above the document table 20 is used as a reference plane, and the read image is scaled in accordance with the height difference between the reference plane and the document surface at each line position. In the sub-scanning direction, the magnification is changed according to the ratio of the creeping distance of the document surface and the projection distance to the document table 20 for each minute section. Image data that has undergone image processing is output to an external device in real time. External devices include printers and digital copiers.
There are a display, an image memory device, and an image editing device (computer system).

FIG. 10 is a flowchart showing the outline of the reading operation of the book scanner 1. Start key 52
Preliminary scanning is executed in response to turning on (or 53) (# 1, # 2). In the preliminary scanning, height measurement is performed by determining the shape of the end face S3. After the completion of the preliminary scanning, the height data D104 is determined (# 3),
If there is invalid height data corresponding to the user's finger or arm, the height is estimated (# 5). Then, the main scanning is performed by setting necessary operations (# 6, # 7).

FIG. 11 is a flowchart of a height data determination subroutine. First, based on the height data D104 near the reference position Ps, the position of the spread center Pc where the inclination of the document surface S1 is reversed is calculated (# 30). For each of the left and right sides of the spread center Pc, a difference in height between adjacent sampling positions in order from the spread center Pc toward the edge is determined (# 31). If the edge side is low, the counter for detecting the height change corresponding to the finger or the arm is cleared, and the operation of advancing the target sampling position by one is repeated until it reaches the outside of the document range (# 33, # 33)
34, # 35). If the edge is higher than the center, it is checked whether the height change is abrupt (# 36). If it is abrupt, the counter for detecting the height change corresponding to the arm is incremented, and when the count value exceeds the threshold value TH1, a flag indicating that is set (# 37, # 37).
38, # 39). If the height change is not rapid, the counter for detecting the height change corresponding to the finger is incremented, and when the count value exceeds the threshold TH2, a flag indicating that is set (# 40, # 41, # 4
2).

FIG. 12 is a flowchart of a height estimation subroutine. A plurality of effective height data DH is extracted and their difference is calculated (# 50, # 51). The estimated height data Dh is calculated by analyzing the change characteristics of the difference, and the estimated height data Dh is sequentially replaced with the estimated height data Dh from the center invalid data (# 52, # 53). When the estimated value of the height is negative, the height is forcibly set to 0 (# 54, 55). The correction of the height data D104 is advanced toward the edge, and when the height data D104 is reached, the process returns (# 56, 57).

According to the above embodiment, the imaging unit 3
Since 0 is also used for photographing the document surface S1 and the end surface S3, the configuration can be simplified and the height measurement can be performed with high accuracy. However, the present invention is not limited to such a configuration. In addition to the imaging unit 30, an optical system and an imaging device for imaging the end face S3 may be incorporated.
The present invention can be applied to the case where the height of the document surface S1 is directly measured by the distance measuring sensor.

[0033]

According to the first aspect of the present invention, even when the user holds down the original by pressing it with his / her hand, correct operation setting is performed in accordance with the height distribution of the original to realize high-quality reading. Can be.

[Brief description of the drawings]

FIG. 1 is a perspective view illustrating an appearance of a book scanner.

FIG. 2 is a schematic diagram of reading by a book scanner.

FIG. 3 is a diagram illustrating a state where a document is pressed.

FIG. 4 is a diagram for explaining an outline of a method of measuring a height distribution of a document surface.

FIG. 5 is a diagram showing a read image corresponding to FIG. 3;

FIG. 6 is a diagram showing a measurement result of a height distribution.

FIG. 7 is a diagram showing an example of a sudden change in height distribution.

FIG. 8 is a schematic diagram of correction of height data.

FIG. 9 is a functional block diagram of a main part of the book scanner.

FIG. 10 is a flowchart schematically showing a reading operation of the book scanner.

FIG. 11 is a flowchart of a height data determination subroutine.

FIG. 12 is a flowchart of a height estimation subroutine.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Book scanner (image reading apparatus) 20 Platen 30 Imaging unit (photographing system) 101 CPU 104 Height measuring unit 111 Height discriminating unit 112 Height estimating unit 113 Operation setting unit BD Book original (document) D104 Height data DH Effective height data S1 Original surface (subject surface) Δh Difference (degree of height change)

Claims (1)

[Claims] 1. An upward-setting type image reading apparatus, comprising: a document table supporting a document; and a photographing system for photographing the document, wherein the image pickup system is disposed above the document table. Means for measuring the height distribution of the object surface photographed by the photographing system; and, based on the degree of height change in the measured height distribution, the height of each position obtained by subdividing the object surface from the original surface. Means for extracting effective height data corresponding to the following: means for estimating a height distribution of a portion of the document surface hidden by the object with respect to the photographing system based on the extracted effective height data An image reading apparatus, comprising: reading means for controlling a reading operation in accordance with estimated height data indicating an estimated height distribution and the effective height data.