JPH1188676A - Image-reading method and system thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image-reading method and system where a background of a pasted original or the like is eliminated, without increasing a processing time by preliminary scanning and mount of a page memory. SOLUTION: A 1st background detection section 18 detects a 1st background that is a base for a read original, a 2nd background detection section 20 detects a pixel with a density different from that of the 1st background, a frequency discrimination section 22 counts number of pixels and when the number is consecutive for a prescribed number or over, the area is discriminated to be the 2nd background and a threshold level decision circuit section 25 decides a threshold level for each background and a binarizing section 26 binarizes read image data.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading method and apparatus, and more particularly, to an image reading method and apparatus capable of reading an image by removing backgrounds having different densities.

[0002]

2. Description of the Related Art An image reading apparatus that optically scans a document image and outputs an electric signal converted by a photoelectric conversion element as image data is used in a copying apparatus, a facsimile apparatus, an image scanner, and the like.

[0003] Image reading devices include a device that moves a scanning device with respect to a document fixed at a predetermined position to acquire image data, and a device that moves a document with respect to a fixed scanning device to acquire image data. There is something to do.

Here, as an example of the image reading device,
The configuration of an image reading apparatus that scans a document fixed at a predetermined position will be described.

FIG. 8 is a diagram showing the configuration of an image reading apparatus. FIG. 8A is a perspective view of the entire image reading apparatus, and FIG. 8B is a diagram showing an optical configuration.

Referring to FIG. 8, an image reading device 501 is provided.
Are the platen cover 502 and the platen cushion 50
3, tip register guide plate 504, platen glass 505,
The scanning device 506 includes a scanning device 506, a lens 507, and a CCD image sensor 508.
61, a reflector 562, a first mirror 563, a second mirror 564, and a third mirror 563.

[0007] The image reading device 501 includes a document 59
0 is placed on the platen glass 505 and is fixed by being sandwiched between the platen cushion 503. The original 590 is irradiated with the light 595-1 emitted from the lamp 561 and the reflected light 595-2 of the light 595-1 by the reflector 562, and the light 595-2 reflected by the original is reflected by the first mirror. 563, second mirror 564, third mirror 565
595-3, 595-4, 595-
5, 595-6 imaged by lens 507 and CCD
The light enters the image sensor 508 and is converted into an electric signal. The scanning device 506 scans the original 590 by moving in the reading direction (sub-scanning direction) shown in the drawing.

The image converted into an electric signal by the CCD image sensor 508 is binarized based on a predetermined threshold. However, the density of the background of the document and the density of the image are different for each document. Therefore, if the threshold value is fixed at a fixed value, an image may not be accurately read.

FIGS. 9A and 9B show the relationship between the original and the image data. FIG. 9A shows the original, FIG. 9B shows the read image data of the original, and FIG. 9 (d) shows image data binarized by the threshold value different from that shown in FIG. 9 (c).

A document 601 shown in FIG. 9A is formed by cutting and pasting a document 602 having different background densities. The density of the characters 603 and the background of the document 602 are equal, and the characters 604, 605, and 606 have the same density. The concentrations are assumed to be the same. Therefore, the scanning line 6 of the original 601
The read image data at 10 is as shown in FIG. 9B, and the output data A obtained by binarizing the read image data with a threshold A is as shown in FIG. The converted output data B is as shown in FIG.

As can be seen from FIGS. 9 (c) and 9 (d), when binarization is performed with a relatively large threshold value A, the original 60
Although the background of No. 2 can be removed, the character 603 is also removed, and if binarization is performed with a relatively small threshold B, the background of the document 602 cannot be removed.

In the case where the background of the cut and pasted original 602 and the density of the character 603 are the same as the original 601, the background cannot be removed even if any threshold is used for binarization. .

Furthermore, even if it is assumed that the density of the character (image) and the background are not the same, it is difficult to determine the threshold value in advance because the density of the image and the background differs depending on the document to be read. is there.

Japanese Patent Laid-Open No. Hei 4-37258 has proposed a technique for addressing such a problem. JP-A-4-3
No. 7258, a document is scanned once as a pre-scan, an optimum threshold value for background removal is determined for each region on the document from the image information, and the document is scanned again as a main scan and the threshold value for each region is used. Obtained digitized image data.

[0015]

As described above, in the conventional image reading apparatus, when reading a document having a background having different densities by cutting and pasting, the background cannot be removed, or not only the background but also the image cannot be removed. There is a problem that incomplete image data is obtained with a part removed.

Further, when the technique proposed in Japanese Patent Application Laid-Open No. Hei 4-37258 is used, it is necessary to perform two scans, one pre-scan and one main scan, on one document, so that the processing time is long. And it is necessary to provide a page memory for storing image data obtained by the prescan.

Therefore, the present invention provides a method that does not increase the processing time due to the pre-scan and does not incorporate a page memory.
It is an object of the present invention to provide an image reading method and apparatus capable of removing the background of a cut and pasted document or the like.

[0018]

In order to achieve the above object, according to the present invention, an original image is divided into a plurality of scanning lines, and each scanning line is optically scanned. In the image reading method for converting the obtained pixel information into image data of a binary digital signal, a density level of the pixel information is detected and a predetermined density level is determined as a first background density, which is different from the first background density. When the pixel information of the density level is continuously obtained for a predetermined number or more, the area where the pixel information is obtained is detected as a background area, and in the background area, the pixel information of the first background density is obtained. The pixel information is binarized using a threshold value different from that of one background area.

Here, the background area is a second area in which pixel information having the highest density level is continuously obtained for a predetermined number or more.
It is a background area, and the threshold value can be configured to have two values corresponding to the first background area and the second background area.

The background area is a second background area in which pixel information of a density level detected most frequently in the scan line is continuously obtained for a predetermined number or more, and the threshold value is the first background area. It can be configured to have two values corresponding to the area and the second background area.

Here, the background area may be configured such that pixel information lower than a predetermined density level is continuously obtained for a predetermined number or more.

Further, the background area may be a plurality of areas corresponding to the pixel information, and the threshold value may be different by the number of the background areas.

Further, the background area may be configured to include an area in which pixel information of a density level different from the first background density is obtained at a predetermined ratio or more.

Further, according to the present invention, an original image is divided into a plurality of scanning lines, optical scanning is performed for each scanning line, and pixel information obtained and sampled by the scanning is converted into image data of a binary digital signal. A density detecting means for detecting a density level of the pixel information; a first background density determining means for determining a predetermined density level as a first background density; and a density different from the first background density. Frequency determining means for determining that the pixel information of the level has been continuously obtained for a predetermined number or more; and a region where the pixel information determined to be continuous for the predetermined number or more by the frequency determining means is obtained. Background area detection means for detecting as an area, and different thresholds for the first background area from which the pixel information of the first background density is obtained and the background area detected by the background area detection means Characterized by comprising a threshold value determining means for determining.

Here, the background area detecting means is a second background area detecting means for detecting a second background area in which pixel information having the highest density level is continuously obtained for a predetermined number or more, and the threshold value determination is performed. The means may be configured to determine two thresholds corresponding to the first background area and the second background area.

The background area detection means detects a second background area in which pixel information of a density level detected most frequently from the scan lines is continuously obtained for a predetermined number or more. Means, wherein the threshold value determining means can be configured to determine two threshold values corresponding to the first background area and the second background area.

Here, the background area detecting means may be configured to detect an area in which pixel information lower than a predetermined density level is continuously obtained for a predetermined number or more.

Further, the background area detection means includes area storage means for storing a plurality of areas corresponding to the pixel information, and the threshold value determination means includes a plurality of areas corresponding to the number of background areas stored in the area storage means. It can be configured to determine different values.

Further, the frequency determination means may be configured to include a ratio calculation unit that determines that pixel information having a density level different from the first background density is obtained at a predetermined ratio or more.

[0030]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an image reading method and apparatus according to the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram showing the configuration of the image reading apparatus.

In FIG. 1, an image reading device 1 includes a photoelectric conversion unit (CC) for converting reflected light on a document into an electric signal.
D) 11, an analog signal processing unit 12 for amplifying an electrical signal converted by the photoelectric conversion unit 11 and removing noise, an A / D conversion unit 13 for converting an analog signal into a digital signal, the photoelectric conversion unit 11 and an analog signal processing unit 12 and A / D converter 1
Signal control unit 14 for controlling the A / D conversion unit 1
A shading correction unit 1 for correcting the influence of unevenness such as illuminance of a light source (not shown) in the digital signal output by
5, a correction memory 16 for storing information required by the shading correction unit 15, and a buffer memory 1 for temporarily storing image data output by the shading correction unit 15.
7. A first background detection unit 18 for detecting a first background (largest area) serving as a base of a document from the image data output by the shading correction unit 15, and a first background based on the output of the first background detection unit 18. The first background determining unit 19 that determines the density of the image and the second background that has a higher density than the first background are detected from the image data output by the shading correction unit 15.
The second background determination unit 21 that determines the density of the second background based on the outputs of the background detection unit 20 and the second background detection unit 20, whether the pixels having the density detected by the second background detection unit 20 are continuous for a predetermined number or more. Is detected by the second background detection unit 20,
A frequency determination unit 22 that determines whether the image is an image or a ground;
A region detection unit 23 for detecting a region of the second background, a binarization processing unit 24 for binarizing the image data,
The binarization processing unit 24 includes a threshold value determination circuit unit 25 that determines a threshold value based on each output of the first background determination unit 19, the second background determination unit 21, and the region detection unit 23, and a threshold value determined by the threshold value determination circuit unit 25. And a binarizing unit 26 for binarizing the image data temporarily stored in the buffer memory 17 based on.

The solid arrows in FIG. 1 indicate the flow of image data, and the broken arrows indicate control signals.

Here, the operation of the image reading apparatus 1 will be described with reference to FIGS.

FIG. 2 is a diagram showing a relationship between a document and output data, and FIG. 3 is a diagram showing a document image before reading and a document image after reading.

Now, the original 30 shown in FIG.
An area 31 having the same density as the original 30 shown in FIG. When the original 30 is scanned on the scanning line 35, the image data converted into an electric signal by the photoelectric conversion unit 11 is converted into an analog signal by the analog signal processing unit 12.
The A / D converter 13 converts the digital signal into a digital signal expressed in density by three bits (D0 to D7). As shown in the read image data of FIG. The density of the background is D1, the density of the background in the area 31 is D5, and the density of the characters on the original 30 and the area 31 is D7.
It is represented by Here, for the sake of simplicity, the digital signal to be converted by the A / D converter 13 is 3 bits. However, in practice, it is often converted to a 6-bit or 8-bit digital signal. No restrictions.

From the read image data, the first background detection unit 18 and the second background detection unit 20 detect the background density as shown in FIG. 2C, and based on the background density, the threshold value determination circuit 25 A threshold value corresponding to each skin density and region as shown in FIG. 2 (d) is determined.

Next, when the binarizing section 26 binarizes the read image data based on the threshold value determined by the threshold value determining circuit section 25, the image data becomes as shown in FIG. Is an image from which the background has been removed as in an image 40 shown in FIG.

The operation of the image reading apparatus 1 for reading an image and removing background will now be described with reference to FIG.

FIG. 4 is a flowchart showing the flow of the operation of the image reading apparatus 1.

When the image reading apparatus 1 starts operating (step 101) and starts scanning an original image (step 102), the original image is converted into a photoelectric conversion unit 11, an analog signal processing unit 12, an A / D conversion unit. The read image data is converted into read image data of a digital signal via the digital signal 13, and the digital signal is subjected to shading correction by the shading correction unit 15, and is temporarily stored in the buffer memory 17.

At this time, the first background detection unit 18 detects the density Dx of the first background which is the base of the read document (step 103), and the first background determination unit 19 determines the first background density as the threshold value determination circuit unit 25. And the second background detection unit 20 outputs the first background density Dx as a provisional value of the second background density Dy.
Is held (step 104).

When the scanning is continued and the second background detection unit 20 detects a pixel having a density Dy0 higher than the value Dy held as the second background density (YES in step 105), the area detection unit 20 23 stores the detected position of the pixel with the density Dy0 as the start area of the second background (step 106), the frequency determination unit 22 counts the number of pixels where the pixels with the density Dy0 are continuous (step 107), and If a predetermined number of pixels continue (YES in step 107), the area detection unit 23 determines that this area is the background of the density Dy0 and stores the position where the pixel of the density Dy0 ends as the end area of the second background. (Step 10
8) The second background detection unit 20 holds Dy0 as a provisional value of the second background density Dy (step 109).

On the other hand, if the pixels having the density Dy0 do not continue for a predetermined number or more in step 107 (step 107).
NO), the process returns to step 105 assuming that the pixel having the density Dy0 is image information.

These processes are repeated while scanning is performed until the end of the document (line end of the scanning line) (NO in step 110). When scanning is performed up to the line end (YES in step 110), finally, The second background determining unit 21 determines the background having the highest density as the second background, and the threshold determination circuit 25 determines the thresholds of the first background and the second background in one line, and based on the threshold, The binarizing unit 26 binarizes the read image data for one line stored in the buffer memory 17 and terminates the scanning of one line (step 111).

The image reading apparatus 1 scans all lines in the same manner to remove the background of the entire original image.

In this embodiment, the detected density Dy
Although 0 is set to be larger than Dy, an upper limit value and a lower limit value are further provided for the density of Dy0, and a pixel having a density higher than a predetermined density can be used as image information without performing the counting in step 107. Thus, it is possible to correspond to the second background having a lower density than the first background, including the detected density Dy0 lower than Dy.

Next, a description will be given of a second embodiment of the image reading method and apparatus according to the present invention. In the second embodiment, a case where two or more types of backgrounds having different densities are removed will be described.

FIG. 5 is a block diagram showing the configuration of an image reading apparatus capable of removing two or more types of backgrounds having different densities.

Referring to FIG. 5, an image reading device 50 includes a photoelectric conversion unit (CC) for converting reflected light on a document into an electric signal.
D) 51, an analog signal processing unit 52 that amplifies an electric signal converted by the photoelectric conversion unit 51 and removes noise, an A / D conversion unit 53 that converts an analog signal into a digital signal, a photoelectric conversion unit 51, and an analog signal processing unit 52 and A / D converter 5
Signal control unit 54 for controlling A / D conversion unit 5
A shading correction unit 5 for correcting the influence of unevenness such as the illuminance of a light source (not shown) in the digital signal output by 3;
5, a correction memory 56 for storing information required by the shading correction unit 55, and a buffer memory 5 for temporarily storing image data output by the shading correction unit 55
7. A first background detection unit 58 that detects a first (largest area) background as a base of the document from the image data output by the shading correction unit 55, and a first background based on the output of the first background detection unit 58 The first background determination unit 59 that determines the density of the image and the nth background that detects the nth background having a different density from the first background from the image data output by the shading correction unit 55
The background detection unit 60, the n-th background determination unit 61 that determines the density of the n-th background based on the output of the n-th background detection unit 60, whether a predetermined number of pixels of the density detected by the n-th background detection unit 60 are continuous or not. Is detected by the n-th background detection unit 60,
A frequency determination unit 62 for determining whether the image is an image or a background;
The image processing apparatus includes an area detection unit 63 that detects an n-th background area, an n-th background storage unit 64 that stores an n-th background area, and a binarization processing unit 65 that binarizes image data. The value processing section 65 includes a first background determination section 59 and an n-th background determination section 6
1. A threshold value determining circuit unit 66 that determines a threshold value based on each output of the n-th background storage unit 64. The image data temporarily stored in the buffer memory 57 is determined based on the threshold value determined by the threshold value determining circuit unit 66. It is configured to include a binarizing section 67 for binarizing.

The solid arrows in FIG. 5 indicate the flow of image data, and the broken arrows indicate control signals.

Here, the operation of the image reading device 50 for image reading and background removal will be described with reference to FIG.

FIG. 6 is a flowchart showing the flow of the operation of the image reading apparatus 50.

When the image reading device 50 starts operating (step 201) and starts scanning a document image (step 202), the document image is converted into a photoelectric conversion unit 51, an analog signal processing unit 52, an A / D conversion unit. The image data is converted into read image data of a digital signal via 53, is subjected to shading correction by a shading correction unit 55, and is temporarily stored in a buffer memory 57.

At this time, the first background detecting section 58 detects the density D1 of the first background, which is the base of the read document, and stores the start area X1 (START) of the first background (step 203). The determination unit 59 outputs the first background density to the threshold value determination circuit unit 66.

When the scanning is continued and the n-th background detecting section 60 detects a pixel having a density D1 different from the first background density D1 (YES in step 204), the area detecting section 63 detects a pixel having the density D1. The determined position is stored as the second background area X2 (START) (step 20).
5) The frequency determination unit 62 counts the number of pixels in which the pixels of density D1 are continuous (step 206), and when the number of pixels of density D1 is greater than or equal to a predetermined number (YES in step 206),
It is assumed that this area is the background of the density D1 and the area detection unit 63
Is stored as the end area X2 (END) of the second background (step 207).
The start area X2 (START) and the end area X2 (E
ND) is stored in the n-th background storage unit 64 as a second background region.

On the other hand, if the density D1 pixels do not continue for a predetermined number or more in step 206 (NO in step 206), the process returns to step 204 assuming that the density D1 pixels are image information.

These processes are repeated while scanning is performed until the end of the document (the line end of the scanning line) (NO in step 208), and the value of n is sequentially increased as in the third background and the fourth background. To detect all background.

When scanning is performed up to the line end (YES in step 208), the threshold value determination circuit unit 66 determines the threshold value of each skin in one line, and based on the threshold value, the binarization unit 67 uses the buffer memory. The read image data for one line stored in 57 is binarized, and the scan for one line is completed (step 209).

The image reading apparatus 1 scans all lines in the same manner to remove the background of the entire original image.

FIG. 7 shows an example of a read original and image data.

FIG. 7A shows an example of an original to be read. In the original 90, areas 91 and 92 having different background densities are shown.
93 are present.

When the image reading device 51 scans the scanning line 95 of the original 90, the area detecting section 63 detects (steps 205 and 207 in FIG. 6) the starting area Xn.
(START) and the end area Xn (END) are shown in FIG.
The read image data of one line temporarily stored in the buffer memory 57 is as shown in FIG.

The first background detecting section 58 and the n-th background detecting section 60 are obtained from the read image data shown in FIG.
FIG. 7D shows the background density of the document 91 detected by the.

Here, the image reading device 50 is provided with a ratio calculating unit (not shown) for transmitting and receiving signals to and from the frequency judging unit 62, and this ratio calculating unit calculates the ratio of the number of pixels counted by the frequency judging unit 62. By ignoring pixels less than a predetermined ratio in the n-th background area, it is possible to prevent erroneous determination even when the background density of the read document lacks continuity due to missing density or the like. .

[0066]

As described above, according to the present invention, the first background as the base of the read original is detected, and when a predetermined number or more of pixels having a density different from that of the first background continue, the corresponding background is detected. Since the region is determined to be a background having a different density from the first background, a threshold value is determined for each of the backgrounds having different densities, and the read image data is binarized. It is possible to remove the background of images having backgrounds with different densities, such as cut and pasted originals, without mounting a page memory.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of an image reading apparatus.

FIG. 2 is a diagram illustrating a relationship between a document and output data.

FIG. 3 is a diagram showing a document image before reading and a document image after reading.

FIG. 4 is a flowchart showing a flow of the operation of the image reading apparatus 1;

FIG. 5 is a block diagram illustrating a configuration of an image reading device according to a second embodiment.

FIG. 6 is a flowchart showing a flow of the operation of the image reading apparatus 50.

FIG. 7 is a diagram illustrating an example of a read original and image data.

FIG. 8 is a diagram illustrating a configuration of an image reading device.

FIG. 9 is a diagram showing a relationship between a document and image data.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 image reading device 11 photoelectric conversion unit (CCD) 12 analog signal processing unit 13 A / D conversion unit 14 analog signal control unit 15 shading correction unit 16 correction memory 17 buffer memory 18 first background detection unit 19 first background determination unit Reference Signs List 20 second background detection section 21 second background determination section 22 frequency determination section 23 area detection section 24 binarization processing section 25 threshold value determination circuit section 26 binarization section 30 document 31 area 35 scanning line 40 image 50 image reading apparatus 51 Photoelectric conversion section (CCD) 52 analog signal processing section 53 A / D conversion section 54 analog signal control section 55 shading correction section 56 correction memory 57 buffer memory 58 first background detection section 59 first background determination section 60 n-th background detection Unit 61 nth background determination unit 62 frequency determination unit 63 region detection unit 64 nth background憶部 65 binarization processing unit 66 threshold value determination circuit 67 binarizing section 90 document 91, 92, 93 region 95 scan lines

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Kenichi Kobori, Inventor 3-7-1, Fuwauchi, Iwatsuki-shi, Saitama Prefecture Fuji Xerox Co., Ltd. Iwatsuki Office (72) Inventor Tomoyuki Yamada 3-7-1, Funai, Iwatsuki-shi, Saitama Prefecture No. Fuji Xerox Co., Ltd. Iwatsuki Office

Claims (12)

[Claims] An image in which a document image is divided into a plurality of scanning lines, optical scanning is performed for each scanning line, and pixel information obtained and sampled by the scanning is converted into image data of a binary digital signal. In the reading method, a density level of the pixel information is detected, a predetermined density level is determined as a first background density, and pixel information having a density level different from the first background density is continuously obtained for a predetermined number or more. In this case, the area where the pixel information is obtained is detected as a background area. In the background area, the pixel information is binarized using a threshold different from that of the first background area where the pixel information of the first background density is obtained. An image reading method, comprising: 2. The background area is a second background area in which pixel information having the highest density level is continuously acquired for a predetermined number or more, and the threshold value is set to a value between the first background area and the second background area. 2. The image reading method according to claim 1, wherein there are two kinds of values corresponding to. 3. The background area is a second background area in which pixel information of a density level detected most frequently from the scan lines is continuously obtained for a predetermined number or more, and the threshold is the first background area. 2. The image reading method according to claim 1, wherein there are two kinds of values corresponding to an area and the second background area. 4. The apparatus according to claim 1, wherein the background area is an area in which pixel information lower than a predetermined density level is continuously obtained for a predetermined number or more.
4. The image reading method according to any one of claims 1 to 3. 5. The image reading method according to claim 1, wherein the background area is a plurality of areas according to the pixel information, and the threshold value is different from the background area by the number of the background areas. 6. The image reading method according to claim 1, wherein the background area includes an area in which pixel information of a density level different from the first background density is obtained at a predetermined ratio or more. 7. An image obtained by dividing a document image into a plurality of scanning lines, optically scanning each scanning line, and converting pixel information obtained and sampled by the scanning into image data of a binary digital signal. In the reading device, a density detecting unit that detects a density level of the pixel information; a first background density determining unit that determines a predetermined density level as a first background density; and pixel information having a density level different from the first background density. Frequency determining means for determining that a predetermined number or more of pixels are continuously obtained, and detecting the area where the pixel information determined to be continuous for a predetermined number or more by the frequency determining means is a background area. A background area detecting unit, and a threshold value for determining a different threshold value between the first background area from which the pixel information of the first background density is obtained and the background area detected by the background area detecting unit. Image reading apparatus characterized by comprising a constant section. 8. The background area detection means for detecting a second background area in which pixel information having the highest density level is continuously acquired for a predetermined number or more, wherein the threshold value determination means. 8. The image reading apparatus according to claim 7, wherein two threshold values corresponding to the first background area and the second background area are determined. 9. The second background area detection means for detecting a second background area in which pixel information of a density level detected most frequently in the scan line is continuously obtained for a predetermined number or more. The image reading apparatus according to claim 7, wherein the threshold value determining means determines two threshold values corresponding to the first background area and the second background area. 10. The apparatus according to claim 7, wherein said background area detecting means detects an area in which pixel information lower than a predetermined density level is continuously obtained for a predetermined number or more. An image reading device according to claim 1. 11. The background area detection means includes area storage means for storing a plurality of areas according to the pixel information, and the threshold value determination means includes a plurality of areas corresponding to the number of background areas stored in the area storage means. The image reading device according to claim 7, wherein different values are determined. 12. The apparatus according to claim 7, wherein the frequency determination unit includes a ratio calculation unit that determines that pixel information having a density level different from the first background density is obtained at a predetermined ratio or more. Image reading device.