JP3927709B2 - Image processing method and apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
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 check by an image sensor.
[0002]
[Prior art]
Some bills and checks have a fine pattern (also referred to as a background pattern or ground pattern) on the background, while information is written in check writer characters with little ink. When such a bill or check is used as a manuscript, it is important to remove the ground pattern and clearly reproduce only necessary information such as characters with light ink of the check writer.
[0003]
Conventionally, image sharpening processing has been widely used for such demands. This process emphasizes a change in image density (ie, contour). Applying this processing is very effective for enhancing the legibility of characters, and particularly for reproducing characters of a check writer with light ink.
[0004]
[Problems to be solved by the invention]
However, this sharpening process emphasizes density changes (outlines), so when applied to the above-mentioned reading of bills and checks, the background pattern is also emphasized, and unnecessary information is reproduced and read. It will be. For this reason, the readability of the read image is reduced. In addition, if the background pattern is included, the amount of information is remarkably increased, which causes a problem that the compression rate of the image is lowered.
[0005]
The present invention has been made in view of such circumstances, and by removing this background pattern from a document with a background pattern, only necessary information is clearly reproduced to improve legibility, and image quality is improved. A first object is to provide an image processing method capable of increasing the compression rate. It is another object of the present invention to provide an image processing apparatus that is directly used for carrying out this method.
[0006]
[Structure of the invention]
The first object according to the invention, the document background pattern is attached is sent to the transport path at a constant speed, in the image processing method of reading by the image sensor an image of the original is slit exposure type, a) Image A document is received by a photosensor that receives light through a light receiving window whose size is set so that a density value close to a value determined by using at least one of a mode value, a median value, and an average value in document image data read by the sensor can be received. The background density is detected and a limit value for background removal is set, b) A / D conversion is performed on the output signal of the image sensor that reads the image of the original after passing through the photosensor , and c) shading correction is performed. On the other hand, d) separating vital background density of the original from the image signals obtained by the shading correction using the limit value And smoothing, e) sharpening processing, binarization processing using the f) predetermined threshold, it is achieved by an image processing method, characterized in that.
[0007]
The background density detection sensor is formed by a photo sensor that detects the density of an original through a light receiving window, and is determined using at least one of a mode value, a median value, and an average value in image data of the original read by the image sensor. Since the size of the light receiving window is set so that a density value close to the value can be received , the output of the photosensor can be used as a limit value as it is or with slight modification, and the configuration can be simplified. .
[0009]
A second object is to provide an image processing apparatus in which a document with a background pattern is fed at a constant speed along a conveyance path, and an image of the document is read by an image sensor using a slit exposure method .
A density value close to a value determined by using at least one of a mode value, a median value, and an average value in document image data arranged upstream of the image reading position of the document and read by the image sensor can be received. A background density detector comprising a photosensor for detecting the background density of the document through a light receiving window whose size is set to a limit value, and a limit value setting unit for obtaining a background removal limit value based on the detected background density; An A / D converter that performs A / D conversion on the output image signal of the image sensor read by the image sensor on the downstream side of the background density detector, and shading correction for the A / D converted image signal a shading correction unit that performs, back from the shading corrected image signal using the limit value A background removal processing unit that separates and smooths the land density, a sharpening processing unit that sharpens the image signal from which the background has been removed, and binarizes the sharpened image signal. This is achieved by an image processing device comprising a value processing unit.
[0010]
The background density detection position is preferably illuminated by an illumination light source lamp at the image reading position of the document, and in this case, the incident angle of the illumination light should be 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 illumination conditions for image reading.
[0011]
Embodiment
1 is an external view of an embodiment of the present invention, FIG. 2 is a left side view, FIG. 3 is a plan view showing the arrangement of mirror groups, FIG. 4 is a front view showing the mirror groups and the optical system, and FIG. FIG. 6 is a perspective view showing the optical system, and FIG. 7 is an enlarged left side view of the vicinity of the image reading unit. An image reading apparatus to which the image processing method of the present invention is applied will be described with reference to these drawings.
[0012]
In FIG. 1, reference numeral 10 denotes an image reading device, which is placed on a table box 14 that houses a printer 12. The image reading apparatus 10 is provided with a document feeding unit 16 on the front surface, and a document discharge unit 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 attached to the slope on the front side. The image reading apparatus 10 is accommodated 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 that can be opened and closed upward around a fulcrum 24 (FIG. 2). The display board 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 plate 20 or the lid 26 upward.
[0013]
Documents 30 are input from the document feeder 16 and are separated one by one by the double feed prevention unit 32 and enter 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 the reverse direction. The document 30 enters between the feed roller 36 and the reverse roller 38 to prevent double feeding, and only one document 30 is separated.
[0014]
Reference numeral 40 denotes a transport unit. The transport unit 40 is driven by a speed reducing shaft 44 driven by a transport motor 42, a drive roller group 51 driven by a belt 46 wound around the speed reducing shaft 44, and an intermediate shaft 48 driven by the belt 46. Belt 50, a number of driven roller groups 52 arranged in sequence in the vertical direction facing the belt 46, and a detachable holding group of driven rollers placed on the conveyor belt 50 from above and arranged in a substantially L shape. Possible presser roller support 54.
[0015]
The conveyance belt 50 and the presser roller support 54 convey the document 30 sent from the double feed prevention unit 32 substantially horizontally with the upper and lower sides sandwiched from above and below, and further upwardly drive roller group 51 and driven roller group 52. Let go between. The document 30 is sandwiched between the driving roller group 51 and the driven roller group 52, is sent substantially vertically upward, and is discharged to the document discharge unit 18. The presser roller support 54 can be put in and taken out from the front by opening the document feeding unit 31 (FIGS. 1 and 2) forward (front side) with the fulcrum 35 as the center, and can enter and leave the conveyance path 40. The jammed document 30 can be removed.
[0016]
In the middle of the vertical conveyance path of the drive roller group 51, a pair of photographing glasses 56 (56a, 56b) that sandwich the document 30 from both sides are disposed. A long horizontal light source lamp 58 (58a, 58b) is disposed outside the photographing glass 56 (see FIGS. 2 and 7). Here, the lamps 58a and 58b have different heights. That is, the lamp 58a that illuminates the front surface of the document 30 is lower than the lamp 58b that illuminates the back surface, and therefore the image reading position 60a on the front surface is lower than the image reading position 60b on the back surface (FIG. 7).
[0017]
Further, a black light shielding film 62 (62a, 62b) is formed on each glass 56a, 56b in order to prevent the transmitted light from the opposite lamps 58b, 58a from entering. The lamps 58a and 58b are surrounded by a light shielding plate 64 (64a and 64b) and a light shielding plate 66, and shield unnecessary light. Reference numeral 68 denotes a reflecting plate that reflects part of the light from the lamp 58 a that illuminates the front side and guides it to the surface of the document 30 before entering between the glasses 56.
[0018]
The illuminance on the surface of the original 30 illuminated with the light reflected by the reflecting plate 68 is detected by a photosensor (phototransistor) 70 through a light receiving window 69 (FIG. 7) having a predetermined size. Illuminance is controlled automatically. That is, automatic exposure control is performed. Here, the incident angle θ ₂ of the reflected light of the reflecting plate 68 with respect to the original 30 is made equal to the incident angle θ ₁ with respect to the image reading position 60 a of the lamp 58 a, thereby aligning the illumination conditions of the image reading position 60 a and the illuminance detection position. ing.
[0019]
Here, the photo sensor 70 functions as a background density detection sensor of the document 30. That is, since the density detection position is illuminated by aligning the illumination condition with the image reading position 60a on the surface of the document 30, the exposure condition is correctly changed with respect to the luminance variation of the light source lamp 58a. 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.
[0020]
The images on the front and back surfaces of the document 30 are read by the slit exposure method at the respective image reading positions 60a and 60b when passing between the glasses 56a and 56b. That is, the images on the front and back surfaces pass through the slits 72 (72a, 72b) shown in FIG. 7 and are further guided to one imaging lens 74 via the mirror group shown in FIG. Imaged. 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).
[0021]
The first mirror 78 is horizontally wired so as to form about 45 ° with the document 30 in between, and guides the images of the front and back surfaces of the document 30 to the left side surface of the main body case 22 through the glass 56. The second mirror 80 (80a, 80b) is disposed along the upper left corner of the main body case 22, and guides the reflected image of the first mirror 78 downward. The third mirror 82 is disposed along the lower left corner of the main body case 22, receives the reflected light from the second mirror 80, and guides it to the imaging lens 78.
[0022]
Here, the first mirror 78a and the second mirror 80a with respect to the front surface are set to the same height as the image reading position 60a. Similarly, the first mirror 78b and the second mirror 80b with respect to the rear surface are the same height as the image reading position 60b. Is set to That is, the height difference A between the image reading positions 60a and 60b is equal to the height difference between the second mirrors 80a and 80b, as shown in FIG. The distances B ₁ and C ₁ between the document 30 and the first mirrors 78a and 78b (for example, the distance between the centers of the images of the document 30) are the first mirrors at which the distance B ₁ between the lower position and the first mirror 78a is higher. It is larger than the interval C ₁ with 78b.
[0023]
The distances B ₁ and C ₁ are set so that the conjugate lengths of the imaging lens 74 with respect to the image reading positions 60a and 60b are the same. Here, the conjugate length has the same meaning as the optical path length, and the distance between the first mirror 78 and the second mirror 80 is B ₂ and C ₂ , and is set to A + (C ₁ + C ₂ ) = B ₁ + B _2. The Here, the third mirrors 82a and 82b are formed by one common mirror. In the drawing, 84 is a magneto-optical disk drive device, which opens to the right side when viewed from the front of the main body case 22. Image data read by the CCD line sensor 76 is processed by an image processing device (not shown) and recorded on a magneto-optical disk (MO) loaded in the disk drive device 84.
[0024]
In FIG. 5, 86 is a trailing edge sensor that detects the trailing edge of the document 30 being conveyed, 88 is a skew sensor that detects the inclination of the document 30, 90 is a start detection sensor that determines a reference position for starting image reading, and 92 is paper discharge. It is a sensor.
[0025]
In the embodiment described above, the number of parts is further reduced because the number of CCD line sensors 76 is one, but separate line sensors may be arranged on a straight line so that the front and back images are read separately. In addition, the mirror group may be configured so that the front and back 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 in place of the two line sensors.
[0026]
Next, the image processing apparatus will be described with reference to FIGS. FIG. 8 is a block diagram showing the configuration, FIG. 9 is a diagram showing the processing process of the image signal, FIG. 10 is an explanatory diagram of shading correction, and FIG. 11 is a diagram showing the function of the 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 has various functions shown in FIG. 8 according to operation software and various data stored in the memory.
[0027]
The output image signal of the line sensor 76 is converted into a digital signal by the A / D converter 102 and input to the shading correction unit 104 which is one function of the image processing unit 100. The shading correction unit 104 corrects unevenness in density caused by illuminance unevenness of the illumination lamp 58, COS4θ rule of the imaging lens 74, and the like.
[0028]
That is, the illuminance distribution of the image is high (brighter) at the center of the pixel row as shown in FIG. 10A and gradually lower (darker) toward both edges, so that this is a constant image as shown in FIG. 10B. The image data is corrected so as to obtain an illuminance distribution.
[0029]
Here, 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 using such software or in combination with this, an optical correction plate may be provided in the optical path between the imaging lens 74 and the document 30.
[0030]
After the shading correction unit 104 corrects the density of the image data, the background removal processing unit 108 removes the background, that is, removes the background pattern image data. In this process, the limit value _Lm is determined based on the output of the photo sensor 70 that measures the density of the background portion of the handprint / check as the document 30. In Figure 8, the output of the photosensor 70 is converted into a digital signal by the A / D converter 110, the limit value L _m is determined by the limit value setting section 112.
[0031]
The limit value setting unit 112 determines the limit value L _m by calculation using the mode of density (density gradation with the highest appearance frequency), median value, and average value in the image data of the line sensor 76. be able to. Here, the calculation formula is determined through experiments. But also in the present invention in order to eliminate or simplify this operation, Ru dimensioned for receiving window 69, as the amount of light received by the photo sensor 70 becomes properly.
[0032]
For example, it is preferable that the output of the photosensor 70 detects the density of the brightest part by a peak hold circuit, and the light receiving window 69 is circular with a diameter of 10 mm for a bill / check. As described above, since the density detection position of the photosensor 70 is illuminated by the illumination lamp 58a of the original, 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 photosensor 70. Can be detected simultaneously. Here, since the illumination 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.
[0033]
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. Background removal processing unit is formed by a limiter circuit having a characteristic of FIG. 11 is to vary the image data of the background pattern on the constant concentration of the limit value L _m. That is, the background density is separated and smoothed. As a result, the image data is as shown in FIG.
[0034]
Next, the image data shown in FIG. 9B is input to the sharpening processing unit 114. Here, USM filter processing is performed using previously stored USM coefficients (Unsharp Mask coefficients) 116. That is, for example, by applying a USM filter made of a 3 × 3 matrix to a 3 × 3 pixel region, the density change is emphasized. FIG. 9C shows the image data after the sharpening process. When FIG. 9C is compared with FIG. 9A, it can be seen that the density difference, that is, the margin between the necessary data and unnecessary background data is increased.
[0035]
After the sharpening process as described above, the binarization processing unit 118 performs the binarization process. Threshold T _h used here is set to a concentration close to the concentration of background portions in the margin width shown in (C) of FIG. In Figure 8 120 is a setting unit of the threshold _{T h.} In the binarized image data, as shown in FIG. 9D, the background portion and the embossed character portion are clearly separated, and only necessary data can be reproduced clearly.
[0036]
The binarized image data is compressed and recorded in an image memory or transmitted to another image processing apparatus. Further, it is output to an appropriate image display screen or printed out by a printer.
[0037]
Ime Jisensa can be used an image sensor (area sensor) two dimensions instead of the line sensor in accordance with the photographing mode. In the above embodiment, only the background density on the front surface of the document 30 is detected and the predetermined processing is performed, but the same processing may be performed on the back surface. In this case, a sensor for detecting the background density on the back surface and the image processing unit 100 shown in FIG. 8 may be separately provided. However, the limit value L _m obtained for the front surface may be used as it is or after being modified. Also good.
[0038]
【The invention's effect】
As described above, since the background removal process is performed before the sharpening process, the background pattern is not emphasized during the sharpening process, and only necessary information is clearly reproduced. The legibility can be improved. In addition, since information such as unnecessary background patterns disappears, the image compression rate can be increased.
[0039]
The Ime Jisensa Ru can be used one-dimensional line sensor, for example, a CCD line sensor.
[0040]
Photo sensors for the background density detection is configured to receive through the receiving window facing the document surface, by setting the dimensions of the light receiving window appropriately, added as such or slightly corrects the output of the sensor As a limit value . That is, the light receiving window may be formed so that the density value is close to the limit value determined using at least one of the mode value, the median value, and the average value in the image data read by the image sensor.
[0041]
According to the second aspect of the present invention, an image processing apparatus used directly for carrying out the method of the first aspect is obtained . In this case, the light from the illumination lamp at the image reading position is guided to the background density detection position, and the incident angles of the illumination light at both positions are substantially matched, thereby changing the brightness of the illumination lamp and reflecting the original surface. An accurate background concentration can be detected in response to a change in rate. Accordingly, the setting of the limit value becomes accurate, and the image reproducibility and the legibility are further improved (claim 3 ).
[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. FIG. 3 is a plan view showing the arrangement of mirror groups. FIG. 4 is a front view showing mirror groups and an optical system. FIG. 6 is a perspective view showing an optical system. FIG. 7 is an enlarged left side view of the vicinity of the image reading unit. FIG. 8 is a block diagram of the image processing apparatus. FIG. 10 is a diagram illustrating shading correction. FIG. 11 is a diagram illustrating the function of the background processing unit.
DESCRIPTION OF SYMBOLS 10 Image reading device 16 Original paper feeding part 18 Original paper discharge part 22 Main body case 30 Original 40 Carrying part 58a, 58b Light source lamp 60a, 60b Image reading position 69 Light-receiving window 70 Photosensor (phototransistor) as a background density detection part
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

Claims (3)

In an image processing method in which a document with a background pattern is sent through a conveyance path at a constant speed, and an image of the document is read by an image sensor using a slit exposure method .
a) Photo received through a light receiving window whose size is set so that a density value close to a value determined by using at least one of a mode value, a median value, and an average value in document image data read by an image sensor can be received. The sensor detects the background density of the document and sets the limit value for background removal.
b) A / D-converting the output signal of the image sensor that reads the image of the document after passing through the photosensor ;
c) While performing shading correction,
d) to separate the background density of the original from the image signals obtained by the shading correction and blunted with the limit value,
e) sharpening treatment,
f) Perform binarization using a predetermined threshold value.
An image processing method. In an image processing apparatus in which a document with a background pattern is fed at a constant speed along a conveyance path, and an image of the document is read by an image sensor using a slit exposure method .
A density value close to a value determined by using at least one of a mode value, a median value, and an average value in document image data arranged upstream of the image reading position of the document and read by the image sensor can be received. A background density detector comprising a photosensor for detecting the background density of the document through a light receiving window whose size is set to a limit value, and a limit value setting unit for obtaining a background removal limit value based on the detected background density; An A / D converter that performs A / D conversion on the output image signal of the image sensor read by the image sensor on the downstream side of the background density detector, and shading correction for the A / D converted image signal a shading correction unit that performs, back from the shading corrected image signal using the limit value A background removal processing unit that separates and smooths the land density, a sharpening processing unit that sharpens the image signal from which the background has been removed, and binarizes the sharpened image signal. An image processing apparatus comprising: a value processing unit. 3. An image processing apparatus according to claim 2 , wherein the light source lamp for illuminating the original illuminates the image reading position and the background density detection position at substantially the same angle.

Images