JP2000156782A - Image processing method and device thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve legibility by eliminating a background pattern from an original with the background pattern added thereto, so as to clearly reproduce only the required information and to enhance a compression rate of an image. SOLUTION: An output signal of an image sensor 76 is subjected to A/D conversion 102, the converted signal is subjected to a shading correction 104, a background density of an original is detected, a limiting value for eliminating a background is set, the limiting value is used to separate a background density of an original from an image signal subject to shading correction, the result is smoothed, sharpening processing is applied to the smoothed signal, and binary processing is applied to the result by using a prescribed threshold. When the original is read through a slit exposure system, the background density is detected at the upper stream side from the image read position of the original and the result is used to set the limit value for eliminating the background.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image processing method and apparatus for reading an image of a document with a background pattern such as a bill or a check by an image sensor.

[0002]

2. Description of the Related Art In a bill or a check, a fine pattern (also referred to as a ground pattern or a ground pattern) is attached to the background,
There is a case where information is written in the character of a check writer with little ink. When a document such as a bill or a check is used as a document, it is important to remove the ground pattern and clearly reproduce only necessary information such as characters with thin ink of a check writer.

To meet such demands, image sharpening processing has been widely used. This process emphasizes a change in image density (that is, an outline). This processing is very effective for enhancing the legibility of the characters, and particularly for reproducing the characters of a check writer with light ink.

[0004]

However, in this sharpening process, the change in the density (contour) is emphasized. Therefore, when the present invention is applied to the reading of the above-mentioned bills and checks, the background pattern is also emphasized. Unnecessary information is also reproduced and read. For this reason, the readability of the read image is reduced. In addition, if the background pattern is included, the amount of information is significantly increased, which causes a problem that the compression ratio of the image is reduced.

The present invention has been made in view of the above circumstances, and removes the background pattern from a document having the background pattern to clearly reproduce only necessary information to improve readability. It is a first object of the present invention to provide an image processing method capable of increasing the compression ratio of an image. It is another object of the present invention to provide an image processing apparatus directly used for implementing the method.

[0006]

According to the present invention, a first object of the present invention is to provide an image processing method for reading an image of a document with a background pattern by an image sensor. A) A / D converting an output signal of the image sensor; B) performing shading correction, c) detecting the background density of the document and setting a limit value for background removal,
d) separating and smoothing the background density of the original from the shading-corrected image signal using the limit value, e) performing a sharpening process, and f) performing a binarization process using a predetermined threshold value. An image processing method,
Is achieved by

Here, when the original is read by the slit exposure method, the background density is detected upstream of the image reading position of the original, and the limit value for removing the background is set using the result. Good. The background density detection sensor is formed by a photo sensor that detects the density of the document through the light receiving window, and is determined using at least one of a mode value, a median value, and an average value in the image data of the document read by the image sensor. The size of the light receiving window can be set so that a density value close to the value can be received. In this case, the output of the photosensor can be used as it is or as a limit value by making a slight correction, and the configuration can be simplified.

Instead of using such a light receiving window,
The limiter value may be calculated. For example, it may be determined by calculation using at least one of a mode, a median, and an average of image data obtained by reading a document with an image sensor.
In this case, the arithmetic expression is set as a result of an experiment.

A second object of the present invention is to provide an image processing apparatus for reading an image of a document on which a background pattern is attached by an image sensor, an A / D converter for A / D converting an output image signal of the image sensor, and an A / D converter. A shading correction unit for performing shading correction on the A / D-converted image signal, a background density detection unit for detecting the background density of the original, and a limit value for background removal based on the detected background density. A limit value setting unit to be obtained, a background removal processing unit that separates and smoothes the background density using the limit value from the image signal subjected to shading correction, and sharpens the image signal from which the background has been removed. Sharpening processing unit for processing, and binarization for binarizing the sharpened image signal The image processing apparatus characterized by comprising a processing section, is achieved by.

When reading an original by the slit exposure method, the image sensor can be formed by a line sensor, for example, a CCD line sensor. In this case, the background density detection sensor can be formed by a photosensor that detects the density of the document at a position upstream of the image reading position of the document on the conveyance path. This background density detection position is preferably illuminated by an illumination light source lamp at the image reading position of the document. In this case, it is preferable that the incident angles of the illuminating light are aligned so as to be substantially the same at both positions. This is because the document density can be detected under conditions close to the image reading illumination conditions.

[0011]

FIG. 1 is an external view of one embodiment of the present invention, FIG. 2 is a left side view of the same, FIG. 3 is a plan view showing the arrangement of a mirror group, and FIG. 4 is a front view showing the mirror group and an optical system. ,
5 is a diagram showing an outline of the arrangement of each unit, FIG. 6 is a perspective view showing an optical system, and FIG. 7 is a left side view in which the vicinity of an image reading unit is enlarged. An image reading apparatus to which the image processing method of the present invention is applied will be described with reference to these drawings.

In FIG. 1, reference numeral 10 denotes an image reading device, which is mounted on a base box 14 for accommodating a printer 12.
The image reading apparatus 10 is provided with a document feeder 16 at the front thereof and a document discharger 18 near the center of the upper surface. The upper surface is formed in a mountain shape in a side view, and a liquid crystal display panel 20 is mounted on a slope on the front side thereof. The image reading apparatus 10 is housed in a substantially box-shaped main body case 22, and an upper portion of the main body case 22 is a mountain-shaped lid 26 which can be opened and closed upward around a fulcrum 24 (FIG. 2). The display panel 20 can be opened and closed upward about a fulcrum 28 (FIG. 2). Therefore, the internal inspection and maintenance can be performed by opening the display panel 20 or the lid 26 upward.

The original 30 is fed from the original feeder 16,
The sheet is divided for each sheet by the double feed prevention unit 32 and enters the conveyance unit 40. The double feed prevention unit 32 includes a feed roller 36 driven by a belt by a paper feed motor 34 and a reverse roller 38 driven to rotate in a reverse direction. The document 30 enters between the feed roller 36 and the reverse roller 38, and the double feed is prevented, so that only one document 30 is separated.

Reference numeral 40 denotes a transport unit. The transport unit 40 is driven by a reduction shaft 44 driven by a belt by a transport motor 42, a group of drive rollers 51 driven by a belt 46 wound around the reduction shaft 44, and an intermediate shaft 48 driven by the belt 46. Belt 50 and belt 46
A plurality of driven roller groups 52 sequentially arranged in the vertical direction in opposition to the above, and a detachable pressing roller support 54 that holds the driven roller groups placed on the conveyor belt 50 from above and arranged in an approximately L-shape And

The transport belt 50 and the pressing roller support 54 transport the original 30 sent from the double feed prevention unit 32 substantially horizontally while sandwiching the original 30 from above and below, and further drive the drive roller group 51 and the driven roller group 51 upward. The group 52 is entered. The document 30 is sandwiched between the driving roller group 51 and the driven roller group 52, is sent almost vertically upward, and is discharged to the document discharge unit 18. The holding roller support 54 is provided with the original feeding unit 31.
By opening (FIGS. 1 and 2) forward (front side) about the fulcrum 35, the hand can be put in and out from the front, and the original 30 jammed in the transport path 40 can be removed.

In the middle of the vertical transport path of the drive roller group 51, a pair of photographing glass
(56a, 56b) are provided. Glass for photography 5
6, a horizontal and long light source lamp 58 (58a, 58a) is provided.
b) is provided (see FIGS. 2 and 7). Here, each of the lamps 58a and 58b has a different height. That is, the lamp 58a that illuminates the front side of the document 30 is lower than the lamp 58b that illuminates the back side, and therefore, the front image reading position 60a is lower than the back image reading position 60b (FIG. 7).

A black light-shielding film 62 (62a, 62b) is formed on each of the glasses 56a, 56b in order to prevent the transmitted light of the opposite lamps 58b, 58a from being incident. Each of the lamps 58a and 58b is provided with a light shielding plate 64 (64
a, 64b) and a light shielding plate 66 to block unnecessary light. Reference numeral 68 denotes a reflector, which is a lamp 5 for illuminating the front side.
A part of the light 8a is reflected and guided to the surface of the document 30 before entering the space between the glasses 56.

The illuminance on the surface of the document 30 illuminated by the light reflected by the reflector 68 is a light receiving window 69 having a predetermined size (FIG. 7).
Through a photosensor (phototransistor) 70, and the output of the photosensor 70 causes a lamp 58
Is automatically controlled. That is, automatic exposure control is performed. Here, the angle of incidence θ ₂ of the reflected light of the reflecting plate 68 with respect to the document 30 is made equal to the angle of incidence θ ₁ of the lamp 58a with respect to the image reading position 60a.
Illumination conditions for 0a and the illuminance detection position are aligned.

Here, the photo sensor 70 functions as a background density detection sensor for the original 30. In other words, since the density detection position is illuminated by aligning the illumination conditions with the image reading position 60a on the front surface of the original 30, the light source lamp 58a
The exposure condition is correctly changed with respect to the fluctuation of the luminance of the image. The light receiving window 69 conditions, such as the distance between the diameter and the document 30 so as to be optimal for setting the limit value L _m to be described later is the amount of light received by the photo-sensor 70 is determined.

The images on the front and back sides of the original 30 are
When passing between a and b, the image is read by the slit exposure method at the respective image reading positions 60a and 60b. That is, the images on the front and back sides are the slits 7 shown in FIG.
2 (72a, 72b) and further through a mirror group shown in FIG. 6 to one imaging lens 74, where they are imaged on one CCD line sensor 76. Here, the mirror group includes a pair of first mirrors 78 (78a, 78b).
, A second mirror 80 (80a, 80b), and a third mirror 82 (82a, 82b).

The first mirror 78 has a distance of about 4
The wiring is horizontally arranged so as to form an angle of 5 °, and the images on the front and back surfaces of the document 30 are guided horizontally to the left side surface of the main body case 22 through the glass 56. Second mirror 80 (80a, 80b)
Is arranged along the upper left corner of the main body case 22,
The reflection image of the first mirror 78 is guided downward. Third mirror 8
2 is arranged along the lower left corner of the main body case 22,
The light reflected by the second mirror 80 is received and guided to the imaging lens 78.

Here, the first mirror 78a and the second mirror 80a with respect to the front surface are set at the same height as the image reading position 60a, and the first mirror 78b and the second mirror 80b with respect to the back surface are similarly positioned with the image reading position 60b. They are set at the same height. That is, the difference A between the heights of the image reading positions 60a and 60b is, as shown in FIG.
Equal to the height difference of 80b. The distances B ₁ and C ₁ between the original 30 and the first mirrors 78a and 78b (for example, the distance between the center of the image of the original 30) are lower than the distance B ₁ between the lower first mirror 78a and the higher first mirror 78a. It is larger than the interval C1 between the _first and second electrodes 78b.

The image reading position 6 of the imaging lens 74
The intervals B ₁ and C ₁ are set so that the conjugate lengths for 0a and 60b are the same. Here, the conjugate length is equivalent to the optical path length here, and the first mirror 78 and the second mirror 8
A + (C ₁ + C ₂ ) = B ₁ where B ₂ and C ₂ are distances from zero.
It is set to + B _2. Here, the third mirror 82a,
82b is formed by one common mirror. In the drawing, reference numeral 84 denotes a magneto-optical disk drive device, which is opened to the right as viewed from the front of the main body case 22. The image data read by the CCD line sensor 76 is processed by an image processing device (not shown),
4 is recorded on a magneto-optical disk (MO).

In FIG. 5, reference numeral 86 denotes a trailing edge sensor for detecting the trailing edge of the original 30 being conveyed, 88 a skew sensor for detecting the inclination of the original 30, 90 a start detection sensor for finding a reference position for starting image reading, and 92. Is a paper ejection sensor.

In the embodiment described above, the number of components is further reduced because the number of CCD line sensors 76 is one, but separate line sensors may be arranged on a straight line to read front and back images separately. A mirror group may be formed so that the front and rear images are formed into two upper and lower images by the imaging lens 74. In this case, two line sensors may be arranged in parallel. A two-dimensional area sensor may be used instead of the two line sensors.

Next, the image processing apparatus will be described with reference to FIGS. 8 is a block diagram illustrating the configuration, FIG. 9 is a diagram illustrating a process of processing an image signal, FIG. 10 is a diagram illustrating shading correction, and FIG. 11 is a diagram illustrating a function of a background removal processing unit. In FIG. 8, reference numeral 100 denotes an image processing unit, which is formed by a microcomputer (CPU) and an image processing circuit. The image processing unit 100 uses the operation software and various data stored in the memory as shown in FIG.
Has various functions shown in FIG.

The output image signal of the line sensor 76 is
The signal is converted into a digital signal by the A / D converter 102 and input to a shading correction unit 104 which is one function of the image processing unit 100. Shading correction unit 104
Is the illuminance unevenness of the illumination lamp 58 and the COS of the imaging lens 74.
The density variation caused by the 4θ rule or the like is corrected.

That is, the illuminance distribution of the image is higher (brighter) at the center of the pixel row and gradually lowers (darker) toward both edges as shown in FIG. 10 (A). The image data is corrected so as to have a constant image illuminance distribution.

Here, the correction data 106 shown in FIG. 8 obtained by measuring the illuminance distribution on the original reading surface in advance is stored in advance, and the image data is corrected using the correction data 106. Instead of or in combination with such software, an optical correction plate may be provided in the optical path between the imaging lens 74 and the document 30.

After the shading correction unit 104 corrects the density of the image data, the background removal processing unit 108
, The background, that is, the image data of the background pattern is removed. In this process, the limit value _Lm is determined based on the output of the photo sensor 70 for measuring the density of the background portion of the bill or the check as the document 30. In FIG. 8, the output of the photo sensor 70 is A / D
In converter 110 is converted into a digital signal, the limit value L _m is determined by the limit value setting section 112.

The limit value setting unit 112 calculates the limit value L by a calculation using the mode of the density (the density gradation having the highest appearance frequency), the median value, or the average value in the image data of the line sensor 76. _m can be determined. Here, the arithmetic expression is determined by performing experiments. Further, in order to simplify or eliminate this calculation, it is possible to determine the size of the light receiving window 69 so that the amount of light received by the photo sensor 70 becomes appropriate.

For example, it is preferable that the output of the photo sensor 70 be detected by a peak hold circuit to detect the density of the brightest part, and that the light receiving window 69 be circular with a diameter of 10 mm for bills and checks. Further, as described above, since the density detection position of the photo sensor 70 is illuminated by the illumination lamp 58a of the document, even if the luminance of the lamp 58a changes and the amount of light received by the line sensor 76 changes, this change is detected by the photo sensor 70. Can be detected simultaneously. Here, since the irradiation angle of the illumination light is also aligned with the image reading position, it is possible to cope with a change in the reflectance of the document surface. The photosensor 70 used here is preferably as close as possible to the characteristics of the line sensor 76 in terms of color sensitivity and linearity.

FIG. 9A shows image data subjected to shading correction, and includes a background portion and an embossed character portion printed by a check writer. Limit value L _m which is determined as above is set to be slightly darker density than the image data of the background portion. The background removal processing unit is formed by a limiter circuit having the characteristics of FIG.
The image data of the background pattern is converted to the limit value _Lm.
Is changed to a constant concentration. That is, the background density is separated and smoothed. As a result, the image data is as shown in FIG.

The image data shown in FIG. 9B is input to the sharpening processing unit 114 next. In this case, UM coefficients are stored using USM coefficients (Unsharp Mask coefficients) 116 stored in advance.
SM filter processing is performed. That is, for example, a USM filter composed of a 3 × 3 matrix is applied to a 3 × 3 pixel area to emphasize a change in density. FIG. 9 (C)
Indicates image data after the sharpening process. This figure 9
Comparing (C) with (A), it can be seen that the density difference, ie, the margin, between the necessary data and the unnecessary background data is increased.

After the sharpening process, the binarizing unit 118 performs the binarizing process. Threshold T used here
_h is set to a density close to the density of the background portion within the margin width shown in FIG. 9C. In Figure 8 120 is a setting unit of the threshold _{T h.} The binarized image data is shown in FIG.
As shown in (D), the background portion and the embossed character portion are clearly separated, and only necessary data can be clearly reproduced.

The image data after the binarization is data-compressed and recorded in an image memory or transmitted to another image processing device. Also, output to an appropriate image display screen,
Printed out by printer.

In this embodiment, the slit exposure system is used, but the present invention can be applied to other photographing systems. As the image sensor, a two-dimensional image sensor (area sensor) can be used in place of the line sensor according to the imaging method. In the above-described embodiment, the predetermined process is performed by detecting only the background density on the front surface of the document 30, but the same process may be performed on the back surface. In this case, a sensor for detecting the background density
It may be separately provided image processing unit 100 shown in may be used in addition as it is or modify to the limit value L _m obtained with respect to the surface.

[0038]

According to the first aspect of the present invention, as described above, the background removal processing is performed before the sharpening processing, so that the background pattern is not emphasized during the sharpening processing, and necessary information is obtained. Can be clearly reproduced and legibility can be improved. Further, since information such as unnecessary background patterns has disappeared, it is possible to increase the image compression ratio.

The original can be read by a slit exposure method. In this case, a one-dimensional line sensor, for example, a CCD line sensor can be used as the image sensor. In this case, the background removal limit value can be set based on the output of a background density detection sensor provided upstream of the image reading position of the document. If the limit value is obtained from the output of this sensor by a hardware circuit, the limit value can be determined at a high speed, and the document carrying speed can be increased to increase the processing capacity.

For example, this sensor is formed by a photo sensor, and is configured to receive light through a light receiving window facing the document surface. By appropriately setting the dimensions and the position of the light receiving window, the output of the sensor is directly used. Alternatively, it can be used as a limit value by adding a slight correction (claim 4). For example, the light receiving window may be formed such that the density value is close to a limit value determined using at least one of a mode value, a median value, and an average value in image data read by the image sensor.

According to the fifth aspect of the present invention, there is provided an image processing apparatus directly used for implementing the method of the first aspect. In this case, a line sensor is used as the slit exposure method (claim 6), and a photosensor for detecting the background density is provided upstream of the image reading position of the document (claim 7). In this case, the light from the illumination lamp at the image reading position is guided to the background density detection position, and the angle of incidence of the illumination light at both positions is made substantially the same, so that the luminance change of the illumination lamp and the reflection of the document surface are reduced. An accurate background concentration can be detected in response to a change in the rate. Therefore, the setting of the limit value becomes accurate, and the image reproducibility and legibility are further improved (claim 8).

[Brief description of the drawings]

FIG. 1 is an external view of an embodiment of the present invention.

FIG. 2 is a left side view of the same.

FIG. 3 is a plan view showing the arrangement of mirror groups.

FIG. 4 is a front view showing a mirror group and an optical system.

FIG. 5 is a diagram showing an outline of an arrangement of each unit.

FIG. 6 is a perspective view showing an optical system.

FIG. 7 is a left side view in which the vicinity of an image reading unit is enlarged.

FIG. 8 is a block diagram of an image processing apparatus.

FIG. 9 is a diagram showing the processing steps.

FIG. 10 is an explanatory diagram of shading correction.

FIG. 11 is a diagram illustrating functions of a background processing unit.

[Explanation of symbols]

REFERENCE SIGNS LIST 10 image reading device 16 document feeding section 18 document discharging section 22 body case 30 document 40 transport section 58a, 58b light source lamp 60a, 60b image reading position 69 light receiving window 70 photosensor (phototransistor) as background density detecting section 74 imaging lens 76 line sensor 100 image processing unit 102 A / D conversion unit 104 shading correction unit 108 background removal processing unit 112 limit value setting unit 114 sharpening processing unit 118 binarization processing unit

[Procedure amendment]

[Submission date] January 28, 1999 (1999.1.2
8)

[Procedure amendment 1]

[Document name to be amended] Drawing

[Correction target item name] All figures

[Correction method] Change

[Correction contents]

FIG.

FIG. 2

FIG. 7

FIG. 10

FIG. 3

FIG. 4

FIG. 6

FIG. 11

FIG. 5

FIG. 8

FIG. 9

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) RR02 RR14 RR21

Claims (8)

[Claims] 1. An image processing method for reading an image of a document with a background pattern by an image sensor, comprising: a) A / D converting an output signal of the image sensor; b) performing shading correction; Detecting the background density of the document and setting a limit value for removing the background; d) using the limit value to separate and smooth the background density of the document from the shading-corrected image signal; e) sharpening F) performing binarization processing using a predetermined threshold value. 2. The image processing method according to claim 1, wherein the original is sent at a constant speed along a conveying path, and the image sensor reads an image by a slit exposure method. 3. The limit value for background removal is:
3. The image processing method according to claim 2, wherein the setting is performed based on an output of a background density detection sensor disposed upstream of the image reading position on the document conveyance path. 4. The background density detection sensor is formed by a photo sensor that receives light through a light receiving window facing a document surface, and at least one of a mode value, a median value, and an average value in document image data read by the image sensor. 4. The image processing method according to claim 1, wherein the size of the light receiving window is set so that a density value close to a value determined by using the light receiving window can be received. 5. An image processing apparatus for reading an image of a document on which a background pattern is attached by an image sensor, wherein the A / D conversion of an output image signal of the image sensor is performed.
/ D conversion unit, a shading correction unit for performing shading correction on the A / D-converted image signal, a background density detection unit for detecting the background density of the document, and a background density detection unit based on the detected background density. A limit value setting unit for obtaining a limit value for ground removal, a background removal processing unit for separating and smoothing background density from the shading-corrected image signal using the limit value, and a process for removing the background. An image processing apparatus, comprising: a sharpening processing unit that performs a sharpening process on a sharpened image signal; and a binarization processing unit that binarizes the sharpened image signal. 6. The image processing apparatus according to claim 5, wherein the original is fed at a constant speed by a transport unit, and the image sensor is formed by a line sensor that reads an image by a slit exposure method. 7. The image processing apparatus according to claim 6, wherein the background density detection section is formed by a photosensor that detects the density of the document at a position upstream of the image reading position of the document. 8. The image processing apparatus according to claim 6, wherein the light source lamp for illuminating the document illuminates the image reading position and the background density detection position at substantially the same angle.