JPH09247381A - Image reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reproduce an image of high quality by the image reader which has a document mounted faceup and photographs it by minimizing reference light which is scattered on the document surface and suppressing the adverse influence of an image not for height detection of the document surface on reading operation. SOLUTION: Only at the time of read which is made at specific intervals, a light projection part is made to emit light and the document surface is irradiated with linear reference light parallel to a vertical scanning direction. The document height is calculated from the position in the horizontal scanning direction where the reference light is read by an image pickup sensor, and distortion of an image caused by unevenness of the height of the image read by the image pickup sensor is corrected according to the calculated document height.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for measuring the height of a document surface and performing focus adjustment and image distortion correction in an image reading apparatus in which a thick document such as a book is placed face up to perform photographing. Is.

[0002]

2. Description of the Related Art Conventionally, in an image reading apparatus for picking up images of a thick original such as a book, the shape of the original is measured by projecting a line-shaped reference light on the surface of the original and detecting the reflected light. There is known a device that does.

[0003]

However, in the conventional image reading apparatus for projecting and reading the reference light as described above, when an illuminating device such as an incandescent lamp is used as the reference light, the original surface on the original is read. There was a problem that the operator felt a glare due to a bright band of light. Further, when an illuminating device such as a laser beam is used as the reference beam, there is a problem in that the laser beam is scattered on the surface of the document and is not preferable to the operator. Further, even when any of the illumination devices is used, the reference light may change the brightness of the document surface, which may adversely affect the detection results such as the document size, the background density, and the finger position performed during the preliminary scanning. as a result,
The reproduced image might be of low quality. The present invention has been made to solve the above-mentioned problems, and
The purpose of is to suppress the reference light scattered on the document surface to a minimum, to prevent the laser light and the like from falling on the operator, and to improve the safety. The second purpose is It is to suppress adverse effects on the image reading operation other than the detection of the height of the document surface to be performed and to enable high-quality image reproduction.

[0004]

In order to achieve the above object, the invention of claim 1 is an image reading apparatus for picking up an image of an original such as a book, and moving the line sensor in the sub-scanning direction. A reading means for reading a document at predetermined intervals, a light beam irradiating means for irradiating the surface of the document with a line-shaped reference light parallel to the sub-scanning direction, and a reading means for reading at a predetermined interval only. A light emission control means for controlling the light emitting means to emit light; a height calculation means for calculating the height of the document from the position in the main scanning direction where the reference light is read by the reading means; The image processing unit corrects the distortion of the image caused by the correction according to the height of the original document calculated by the height calculation unit. In the above structure, the reading means moves the line sensor in the sub-scanning direction to read the document at predetermined intervals,
The light beam irradiating means irradiates the surface of the document with a line-shaped reference light parallel to the sub-scanning direction, and the light emission control means controls the light beam irradiating means to emit light only at the time of reading executed at predetermined intervals. The height calculation unit calculates the height of the document from the position in the main scanning direction where the reference light is read by the reading unit, and the image processing unit corrects the image distortion caused by the unevenness of the document height.
Correction processing is performed according to the calculated document height. In this way, the reference light is turned on only when the document height is detected at predetermined intervals, so that the reference light is not adversely affected.

According to a second aspect of the present invention, in the structure according to the first aspect, the height calculation means does not emit the image data read when the reference light is emitted and the reference light is not emitted. Compared with the image data read in,
The position of the reference light is recognized. In this configuration, since the position of the reference light is recognized by using the difference between the images when the reference light is turned on and when the reference light is turned off, it is possible to eliminate the adverse influence on the detection by the ambient light.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is an overall configuration diagram of the image reading apparatus. The apparatus 1 includes a document table 3 on which a thick document 2 such as a book or a file is placed in an upward facing spread state. Above the document table 3, a CCD line sensor or the like for reading an image of the document 2 is provided. A camera head unit 5 having an image sensor 4 is installed. An illumination unit 6 for irradiating the document 2 is arranged above the document table 3 and an operation unit 7 for setting image reading conditions and the like is arranged below the document unit 3, and the document table 3 is made to start reading. A start key 8 and a stopper 9 for positioning the document 2 placed on the document table 3 are provided. The image of the original document 2 irradiated with the light from the illumination unit 6 is imaged on the image sensor 4 by the projection lens 12 after changing the optical path by the reflection mirror 11 in the camera head unit 5, where it is converted into an electrical signal. To be converted. By scanning the image sensor 4 left and right, a two-dimensional image of the document can be obtained. The camera head unit 5 is provided with a light projecting unit 13 (light beam irradiating unit) that projects a line-shaped reference light onto the surface of the original 2.

FIG. 2 is a block diagram of a circuit of a photographing function in the main scan of the image reading apparatus 1. The device 1 includes a CPU 21 for controlling the entire device and a sensor movement control means 23.
a, lens movement control means 23b, image processing control circuit 25
Etc. are provided. The CPU 21 controls the sensor movement control means 23a to read the original by optical scanning, and performs a preliminary scan operation and a main scan operation. The image signal read by the image sensor 4 during the preliminary scan is A /
After being A / D converted by the D converter 27, it is temporarily stored in an arithmetic memory (not shown). The CPU 21 creates a brightness histogram from the read image signal, calculates the background brightness and the character part brightness threshold value from this, and further obtains the character part frequency and the like (see FIG. 10). The CPU 21 controls the image processing control circuit 25 based on these pieces of information to perform various kinds of image processing.

The image processing control circuit 25 includes an illuminance correction unit 3
1, MTF correction unit 32, scaling unit 33, density correction unit 3
4. Control the masking unit 35. The image data subjected to these various processes is output to the printer 40, which is an output device. The printer 40 prints an image on a sheet based on the image data and outputs a hard copy.

FIG. 3 is a flowchart showing the outline of the operation of the image reading apparatus 1. The operation of reading the document by the apparatus 1 will be described below with reference to FIG. When the start of the photographing operation is instructed, the CPU 21 causes the image sensor 4 to perform a preliminary scanning operation which is a document state detecting operation (#
2). Based on the imaged data obtained by the preliminary scan, processing such as distance measurement of the document surface, detection of background density, detection of document size, and recognition for erasing a finger image holding the document are performed. Further, the control parameters required for image correction and processing are calculated (# 3). Finally, the original is read in the main scan operation (# 4). In the main scan, image data is obtained in parallel with the sensor movement control for the image reading operation, and images such as illuminance correction, AF (autofocus), distortion correction, AE (automatic density control), and unnecessary finger images are obtained. Perform masking processing to erase.

FIG. 4 shows the mechanism of the sensor movement control means 23a for scanning the image sensor 4. A one-dimensional CCD sensor is used as the image sensor 4, and the pixel direction is arranged in the vertical direction of the document, and is linearly moved in a direction perpendicular to this. The scanner 41 to which the image sensor 4 is attached is
The movement direction is restricted to the left and right by the two guide shafts 42. One of the guide shafts 42 is a slide shaft, and the other is a shaft that restricts rotation. A feed screw 43 is used as a feed mechanism of the scanner 41, and a scanner motor 45 coupled via a belt 44 rotates the feed screw 43 to move the scanner 41 having a fixed nut to the left and right. The CPU 21 sends a signal for driving the scanner motor 45, and controls the rotation direction and the number of rotations thereof.

Photoelectric sensors 46 and 48 are used to control the position of the scanner 41. These photoelectric sensors 46 and 48 are
The light-emitting / light-receiving portions are placed at a certain distance, and the light-shielding plate 49 fixed to the scanner 41 moves in and out between them to detect the position. The photoelectric sensors 46 and 48 are a first standby position sensor that also serves as a home sensor that detects an initial position when the power is turned on, and a limit sensor that prevents the scanner 41 from running out of control.

FIG. 5 is a perspective view of the projector 1 as viewed from the side.
3 shows a light projection optical path by the light beam irradiation means. Projector 13
The reference light 13r emitted from the laser light vertically enters the back side of the document surface, and the shape of the light beam changes depending on the height of the document. FIG.
Shows the configuration of the light projecting unit 13. The light projecting unit 13 is composed of a semiconductor laser 13a which is a light emitting element, and a cylindrical lens 13b which is a light condensing device that collects the light in a line. With these configurations, it is possible to obtain the sharp reference light 13r with a small change in the line width. The light projecting unit 13 is controlled to be intermittently lit by the CPU 21 via a drive circuit (not shown) when the height of the document is detected.

FIG. 7 shows a state of an image obtained by reading the document surface on which the reference light is projected by the image sensor 4. The reference light 13r projected on the document surface is linear when viewed from directly above,
Since the image sensor 4 reads the projected reference light 13r from an oblique direction, the reference light 13r is read by curving up and down according to the height of the document. The portion of the document surface on which the reference light 13r is projected is photographed brighter than the other document surfaces. Further, the document table 3 is imaged on the outer periphery (hatched portion) of the document image.

FIG. 8 shows an output example of one line in the main scanning direction read by the image sensor 4 (line sensor). The number of pixels of the line sensor on the horizontal axis (right: the back side of the document,
Left: near side), the vertical axis shows the sensor output. L1 is an illuminance threshold for detecting the document surface, L2
Is an illuminance threshold value for detecting the reference light 13r.
n1 is the minimum value (upper original edge) of pixels whose sensor output exceeds the threshold value L1, and n4 is the same (lower original edge). Pixel numbers n1 to n4 correspond to the document surface, and the outside thereof corresponds to the document table portion. n3 is a pixel (fixed value) corresponding to a document height of 0 mm. This is shown in Figure 7.
The reference light 13r of is corresponding to the position in the main scanning direction projected on the document table (hatched portion). n2 is a position where the tip R is generated in the sensor output by the reference light 13r, and n1
From n to n3, the sensor output is the minimum value of the pixels exceeding the threshold value L2. Where (n3-n2) is
The number of pixels corresponds to the displacement amount of the reference light, and corresponds to the document height. By moving the line sensor to the left or right (in the sub-scanning force direction), the value of n2 changes, and a value corresponding to the displacement amount distribution of the reference light 13r, that is, the document height distribution can be obtained.

Further, in FIG. 8, (n4-n1) is the number of pixels corresponding to the original size in the vertical direction, the line sensor is moved left and right (sub scanning direction), and the original size in the vertical direction is "0". It is possible to obtain the document size in the left-right direction (corresponding number of pixels) by detecting the position where When detecting the document size,
The reference light 13r is turned off.

FIG. 9 is an optical path diagram of the reading system viewed from the side. When the angle between the reference light 13r and the photographing light on the original table 3 is θ, when the original surface having the height H is read,
The displacement ΔY of the reference beam 13r on the document surface is expressed by the following equation. The distribution of displacement amount (pixel unit) calculated above is converted into the distribution of displacement amount (length) on the document surface using the shooting magnification and reading resolution, and is substituted into this formula to obtain the height data of the document. Can be obtained.

## EQU1 ## ΔY = H × tan θ

FIG. 10 shows an example of a luminance histogram for one line of the image sensor. From this, the background luminance LB, the character luminance LC, and the character portion frequency (hatched portion) of the document are detected. The frequency of the luminance peak of the histogram is obtained, and the lower side luminance value having a value of half the frequency is used as the background luminance L of the line.
Let's call it B. A value obtained by subtracting a constant value a (a fixed value obtained by an experiment) from the background luminance LB is set as a threshold value of the character luminance LC. As in the case of detecting the document size described above, in order to accurately detect the background luminance LB of the document, the reference light 13r is turned off when the background luminance LB is detected.

11A and 11B show the distribution of the document height and the distribution of the background luminance in the left-right direction (scan direction) of the document. By controlling the density conversion curve during the main scan according to this distribution, it is possible to obtain an image of uniform density.

FIG. 12 shows a state in which a document is pressed with fingers. The margins on the left and right of the document are detected, the effective area of the image is determined, and the image of the finger pressing the document located outside this area is erased from the image. FIG. 13 shows the distribution of the character frequency obtained in FIG. 10 in the left-right direction of the document (scanning direction). By detecting the position where the character frequency becomes “0” on the left and right of the document, this is recognized as the position where the finger is placed.

FIG. 14 is a flowchart of the preliminary scan operation. The CPU 21 repeats the above detection operation at regular line intervals during the preliminary scan. To explain this process, the lamp of the illumination unit 6 is turned on (# 11), the preliminary scan is started (# 12), the reference light from the light projecting unit 13 is turned on (# 13), and the height of the document is detected. That is, FIG.
Obtain the distribution of the height data of the original described in (# 14),
Turn off the reference light (# 15) and detect the document size (# 1
6), background luminance detection (# 17), character frequency detection (# 1
8) is performed until the preliminary scan is completed (# 13 to #).
19). When the preliminary scan is completed, various parameter calculations required for image processing are performed (# 20). in this way,
Since the reference light is turned on only when the height of the original is detected and is turned off at other times, it does not affect the detection of the background luminance and the original size. Further, the background luminance and the detection of the finger can be detected by using the data on the same line.

In this embodiment, the photographing resolution is 400 dpi.
This detection cycle is repeated every 64 lines. Since each detection operation uses image data for one line, the lighting time of the reference light may be at least one line in one detection cycle. The irradiation amount can be reduced to 1/64 as compared with the case where the reference light is kept on during the preliminary scan.

FIG. 15 is a block diagram of a circuit used for the distance measurement detection (height detection) function performed in the preliminary scan operation, which corresponds to the area surrounded by the one-dot chain line in FIG. The output of the line sensor 4 is digitally converted by the A / D converter 27 and then input to the comparator 28. The threshold value of the illuminance is set in the comparator 28 by the CPU 21. The counter 29 counts the pixel number of the sensor 4 and the comparator 2
When data exceeding the threshold value is input to 8, CPU2
1 stores this count value in the memory 30. This count value is the number of pixels corresponding to the size and height of the document in FIG. The digitally converted image data is branched into a plurality of circuit buses and is switched according to the function.

FIG. 16 shows the structure of a lens moving unit for focusing. Focusing is performed by moving the projection lens 12 during the main scan according to the detected change in the height of the document. Like the scanner unit, the projection lens 12 is regulated to move in the optical axis direction by two guide shafts. The movement of the projection lens 12 uses the cam 19 and the follower 20 to rotate the lens motor 18. Then, the projection lens 12 is converted into a rectilinear motion.

FIG. 17 is a conceptual diagram for correcting image distortion. When a three-dimensional document is photographed from above, image distortion occurs vertically and horizontally. This is because the object is photographed large when the document approaches the image sensor 4 (when the document is high), and small when the document approaches the image sensor 4 (when the document is low), similar to human perception. is there. Further, where the pages are inclined such as the binding portion of the document, the image of the document is contracted in the left-right direction due to the inclination, and the image is taken. Therefore, in the present embodiment, the image processing control circuit 25 (FIG. 2) capable of arbitrarily changing the imaging magnification in the two directions of the main scanning and the sub-scanning is used, and imaging is performed according to the height of the document obtained as described above. The image distortion is corrected by determining the magnification and continuously performing image processing with the photographing magnification.

FIG. 18 shows the concept of main scanning correction, and FIG. 19 shows the concept of sub scanning correction. Regarding the curving correction in the main scanning direction, control is performed such that the pixel size of the read line is enlarged as much as the magnification. When the size of the pixel (for example, P1) is enlarged, a residue is generated in the corresponding corrected pixel (Q1) (0.3 minutes). This surplus and pixel (P
The pixel (Q2) after correction is created by combining 1) with the adjacent pixel (P2). For the density of the newly created pixel (Q2), the density value of each pixel (P1, P2) is distributed and added according to the size ratio (Q2 = P1).
× 0.3 + P2 × O. 7) Obtain by doing.

Regarding the shrinkage correction in the sub-scanning direction, enlargement control is performed by repeating the line of the read image by the photographing magnification. In FIG. 19, assuming that the partial inclination angle of the document surface is 60 degrees, the enlargement factor is "2" which is the reciprocal of the cosine. Therefore, the read image data is stored in the temporary memory line by line, and the read image data is repeatedly read twice to obtain an enlarged corrected image.

FIG. 20 is a diagram for explaining the operation of the embodiment in which the reference light is intermittently turned on and the document height is measured using the difference between the images when the reference light is turned on and when the light is turned off. FIG. 7A shows the state of sensor output when disturbance noise light is incident on the upper part of the document with the reference light turned on. In such a case, the luminance of the document surface increases due to the disturbance noise light, and if the sensor output exceeds the threshold value L2 even at a position other than the irradiation position of the reference light, the height of the document cannot be correctly measured. . Therefore, the output during the document size detection operation when the reference light shown in FIG. 7B is turned off is obtained, and further, as shown in FIG. 7C, the output of FIG. The difference output is compared with the threshold value L3 set separately. This makes it possible to remove the influence of ambient light and detect the position of the reference light, that is, the pixel number (n2). That is, the height of the document can be accurately detected even when the ambient light falls on it.

FIG. 21 is a circuit block diagram for implementing the embodiment shown in FIG. In this example, a subtractor 36 to which the signal digitally converted by the A / D converter 27 is input is added to the distance measuring block similar to that shown in FIG.
And a line memory 37. The image data obtained at the height detection function when the reference light is lit is A / D
After being digitally converted by the converter 27, the line memory 37
Sent to and stored. The subtractor 36 takes the difference between this image data and the image data obtained during the original size detection function in which the reference light is off. The difference data is sent to the comparator 28 constituting the distance measuring block, and the number of pixels exceeding the threshold value is counted by the counter 29, whereby the height of the document can be obtained.

According to the embodiment of the present invention, the reference light is turned on only when the height of the original is detected, the locus of the light beam is detected to measure the height of the original, and the light is turned off at other times. Therefore, there is no influence on the detection of the background brightness and the document size. Further, the height of the original can be accurately detected even on a thin page such as a back cover of a book original, and the reference light scattered on the original surface can be minimized. There is no problem even when the above is used, it is possible to suppress adverse effects on the image reading operation other than the detection of the height of the document surface, and it is possible to reproduce a high-quality image. The present invention is not limited to the configuration of the above embodiment, and various modifications can be made without departing from the spirit of the invention.

[0030]

As described above, according to the image reading apparatus of the present invention, the line-shaped reference light is projected on the surface of the original by intermittent lighting, and the trajectory of this light beam is detected to determine the height of the original. Since the measurement is performed, the height of the document can be accurately detected, and the amount of light scattered on the document surface can be minimized, and even when using laser light, etc. It is possible to improve the safety, suppress the influence of ambient light from the outside on the document or the device on the measurement, and detect the document height accurately, and the image distortion depending on the document height. Since the correction is performed, it is possible to reproduce a high-quality image.

[Brief description of drawings]

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

FIG. 2 is a block diagram of a circuit of a photographing function in a main scan of the image reading apparatus.

FIG. 3 is a flowchart showing an outline of the operation of the image reading apparatus.

FIG. 4 is a diagram showing a mechanism of a sensor movement control unit for scanning an image sensor.

FIG. 5 is a diagram showing a light projecting light path by a light projecting unit when the present apparatus is viewed from the side.

FIG. 6 is a diagram showing a configuration of a light projecting unit.

FIG. 7 is a diagram showing a state of an image obtained by reading an original surface onto which reference light is projected by an image sensor.

FIG. 8 is a diagram showing an output example of one line in the main scanning direction read by an image sensor.

FIG. 9 is an optical path diagram of the reading system as viewed from the side.

FIG. 10 is a diagram showing an example of a luminance histogram for one line of the image sensor.

11A and 11B are diagrams showing the distribution of the document height and the distribution of the background luminance in the left-right direction of the document.

FIG. 12 is a diagram showing a state where a document is pressed with fingers.

FIG. 13 is a diagram showing a distribution of character frequencies in the left-right direction of a document.

FIG. 14 is a flowchart of a preliminary scan operation.

FIG. 15 is a block diagram of a circuit used for a distance measurement detection function performed in a preliminary scan operation.

FIG. 16 is a diagram showing a configuration of a lens moving unit that performs focusing.

FIG. 17 is a conceptual diagram for correcting image distortion.

FIG. 18 is a conceptual diagram of main scanning correction.

FIG. 19 is a conceptual diagram of sub-scanning correction.

FIG. 20 is a diagram for explaining the operation of the embodiment in which the reference light is intermittently turned on and the document height is measured using the difference between the images when the reference light is turned on and when the light is turned off.

FIG. 21 is a circuit block diagram for implementing the embodiment shown in FIG. 20.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image reading device 2 Original document 4 Imaging sensor (reading means) 13 Light projecting section (light emitting means) 21 CPU (height calculation means) 28 Comparator 25 Image processing control circuit (image processing means)

Claims (2)

[Claims] 1. An image reading apparatus for picking up an image of a document such as a book facing upward, and moving the line sensor in the sub-scanning direction to read the document at predetermined intervals; and a reading unit on the surface of the document. A light beam irradiating means for irradiating a reference light in a line shape parallel to the sub-scanning direction, and only at the time of reading at a predetermined interval in the reading means,
The light emission control means for controlling the light emitting means to emit light, the height calculation means for calculating the height of the document from the position in the main scanning direction where the reference light is read by the reading means, and the unevenness of the document height An image reading apparatus comprising: an image processing unit that corrects the generated image distortion according to the height of the document calculated by the height calculation unit. 2. The height calculation means compares the image data read when the reference light is irradiated with the image data read when the reference light is not irradiated to compare the position of the reference light. The image reading apparatus according to claim 1, wherein the image reading apparatus recognizes