JPH09186878A - Method and device for image formation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image wherein only an image reproduced with specific density is sharp and of high quality by comparing a pixel of interest with nearby pixels, deciding that a high-density side is an image and a low-density side is a ground when the difference in density is larger than a specific value, and controlling the decided ground to specific density. SOLUTION: On the basis of an image and a ground detected by an image and ground detecting circuit A as a 1st stage, an image and ground detecting circuit B decides the image and ground as a 2nd stage. Namely, it is decided that the detected image and the part surrounded with the image are all an image and the remainder is suitably an image or ground. Then a control part 108 performs density control over the image and ground on the basis of the decision result and the density signal of a document image. Namely, the part decided to be the ground on the basis of the position signal of the image and ground is regarded as a white ground and as to the part decided to be the image, the density signal of the document image is outputted as it is. Consequently, a copy image is obtained by extracting the image and ground sharply and reproducing only the image sharply without reproducing the ground.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming method and an image forming apparatus for forming an image on an image carrier by an electrophotographic recording method or the like.

[0002]

2. Description of the Related Art Conventionally, in an electrophotographic copying apparatus, since an original image is faithfully reproduced as it is, when an original having a plurality of densities such as a map is used as an original, the background portion is It was copied to multiple densities as it was. Alternatively, when an original is a printed matter that has become old or has been once copied and has uneven density in the background of the image, the uneven density in the background is copied as it is.

Further, it is also practiced to erase a base portion which does not need to be copied at a certain threshold value. This will be described by taking a typical example of the conventional image processing method shown in FIG. 12 as an example.

FIG. 12A shows the state of an original image on one scanning line, where the horizontal axis represents the position and the vertical axis represents the density. I1 to I6 indicate images, and G1 to G7 indicate backgrounds. In this case, the background G5 has a higher density than the image I1. 12B, 12C, and 12D show the state of the image after the image processing with the threshold values X, Y, and Z, respectively.

As shown in FIG. 12B, when processing is performed with a threshold value X for erasing G5, which has the highest density in the background, only images I3, I4 and I5 are obtained, and image I
Images I, I2, and I6 were defects that were not reproduced. As shown in FIG. 12C, when I1 having the lowest density in the image is processed by the threshold value Y that somehow reproduces, the density of the image I1 is considerably low, and the backgrounds G4 and G5 are clearly reproduced. The image was difficult to see. As shown in FIG. 12D, the threshold value Z that reproduces the entire image only by erasing G1 having the lowest density in the background.
In the case of the process (1), the bases G2 to G5 were clearly reproduced as they were, and the image was difficult to see.

[0006]

As described above, in the past, when copying an original having an uneven density on the background of the image with a copying apparatus, the user often does not need to copy the background. However, there is a problem that the background is copied as it is, and the quality of the copied image is impaired.

Further, when processing is performed with a threshold value for removing the high density portion of the background in order to erase the background in the copied image, the density of light characters, fine characters, etc. in the low density portion of the background decreases and It becomes impossible to clearly reproduce characters, fine characters, etc.,
There is a problem that the quality of the copied image is impaired.

It should be noted that a multi-valued image with uneven illumination (thus resulting in uneven background density) is stored by storing the image information of the shape.
A method for performing the value conversion process is described in JP-A-4-1866 and 4-7.
4283, 5-252597, 5-28435.
No. 7 and No. 5-290152. However, when the final image is a binary image in this way, when trying to obtain a grayscale image, there is a problem that the image quality is considerably inferior, such as poor resolution and difficulty in reproducing light characters.

An object of the present invention is to provide an image forming method capable of clearly reproducing only an image without reproducing the background or with a predetermined density even for an original image having a plurality of background densities. , And an image forming apparatus.

[0010]

The above object can be achieved by an image forming method and an image forming apparatus according to the present invention.
In summary, the first invention according to the present application compares the target pixel and the neighboring pixels based on the density information of the original image, and when the density difference is equal to or more than a predetermined value, the high density side is the image and the low density side is the low density side. The image forming method is characterized in that the side is determined to be the background, and the image is formed by controlling so that the background is not reproduced.

According to a second aspect of the present invention, a pixel of interest and a neighboring pixel are compared based on density information of an original image, and when the density difference is a predetermined value or more, the high density side is an image and the low density side is an image. The image forming apparatus includes: a background detecting unit that detects a background by determining that the background is a background; and a unit that changes the detected background to a predetermined density.

A third invention according to the present application divides the image information of the original image into specific areas and detects the background density in the original image based on the density distribution of each divided area. An image forming apparatus comprising: a unit and a unit that determines a portion brighter than the background density as a background based on the detected background density and changes the determined background to a predetermined density.

According to a fourth invention of the present application, the densities of adjacent pixels of the image information of the original image are compared for each scanning line, and when the density difference between the adjacent pixels is equal to or more than a predetermined value, this is set to high and low locations. As a determination reference point, a first-stage image / background determination unit that determines a high-density side as an image and a low-density side as a background,
A means for obtaining the position and density of the judged image / background, and if the adjacent judgment reference points are images / images, all the areas between them are judged to be images, and if the adjacent judgment reference points are the background / background, the interval Is determined to be the background, and when the adjacent determination reference points are the image / background or the background / image, the determination is made so that the image and the background are divided at a predetermined position between consecutive images / background groups. An image forming apparatus comprising: a step image / background determination means; and means for changing the determined background to a predetermined density.

[0014]

Embodiments of the present invention will be described below in detail with reference to the drawings.

Embodiment 1 FIG. 1 is a block diagram showing the arrangement of a processing system used for carrying out image processing in a copying machine according to an embodiment of the present invention.

In this embodiment, the image processing system is
As shown in FIG. 1, a CCD for reading an original image
100, an A / D converter 101 for converting an analog image signal of image information from a CCD into a digital image signal, and a conversion table 102 for converting and outputting the digital image signal in consideration of reproduction characteristics of the copying apparatus. A density conversion circuit 103 for converting a light amount signal of a digital image signal into a density signal, and an image memory circuit 104 for storing the density signal converted by the density conversion circuit.
And an image / background detection circuit 105 (which is particularly referred to as an image / background detection circuit A) for performing the first-stage image / background detection based on the density-related signal, and an image / background detection circuit A.
The image / background detection circuit 106 (image / background detection circuit B) that determines the image / background in the second step based on the result of the determination process of 1. and the image / background determined by the image / background detection circuits A and B. Image / background position storage circuit 107 for storing the position of the image, and a control unit 108 for controlling the density of the image / background based on the density signal of the original image and the position signal of the image / background
And an output unit 109.

FIG. 2 is an explanatory diagram showing an image processing method for detecting an image / background in the present embodiment. Of these, FIG. 2A shows the state of the original image in one scanning line, where the horizontal axis shows the position and the vertical axis shows the density. I1 to I6 indicate images, and G1 to G7 indicate backgrounds. In this case, the background G5 has a higher density than the image I1.

FIG. 3 is an explanatory diagram of a target pixel for detecting an image / background and its neighboring pixels. FIG. 3A is an example in which the neighboring pixels to be compared are one line, and a12 is the target pixel,
a11 is a neighboring pixel. 3B and 3C are examples in which the neighboring pixels to be compared have 3 lines and 5 lines, respectively. FIG.
(D) to (f) show the positions of the pixel of interest and the weighting of neighboring pixels with respect to FIGS. 3 (a) to (c), respectively.
The * mark indicates the pixel of interest, and the number indicates the weighting of neighboring pixels.

Here, the density of the pixels a11, a12 ...
11, D12 ..., The density of the target pixel is DS, the density of the weighted neighboring pixel is DR, and the density difference between the target pixel and the neighboring pixel is ΔD. Therefore, the density difference ΔD = DS-DR between the pixel of interest and the neighboring pixel.

In the case of FIG. 3A, the neighboring pixel is an adjacent pixel, the density of the target pixel a12 is D12, the density of the neighboring pixel a11 is D11, and the weighting is 1. Therefore, the density DR of the weighted neighboring pixel is DR = D11 × 1 = D11, and the density difference ΔD between the pixel of interest and the neighboring pixel is ΔD = DS−DR = D12−D
It is 11.

If the absolute value of the density difference ΔD is compared with a predetermined value THL, and if it is larger, the image / background detection circuit A makes a first-step image / background determination, and the image / background position storage circuit 107 stores it. Store the image / background position.

That is, | ΔD | = | DS-DR | = |
In the case of D11-D12 |> THL, D12-D11> THL: the target pixel a12 is an image, and the neighboring pixel a11
Is determined to be the base D12-D11 <THL: the target pixel a12 is the base, and the neighboring pixel a11
Is judged as an image.

The image / base position storage circuit 107 initially stores the number 0 at the address corresponding to each pixel, and when it is determined to be the base, 1 is assigned to the corresponding address.
Is stored, and when it is determined to be an image, 2 is stored at the corresponding address. Therefore, the determined position of the image / background is stored.

FIG. 2B shows the result of detecting the first-stage image and the background in the original image shown in FIG. 2A in this manner. Is shown.

Next, based on the image and the background detected by the image / background detection circuit A in the first step, the image / background detection circuit B determines the image / background in the second step. That is, the detected image and the portion surrounded by the image are all determined to be the image, and the other portions are appropriately determined to be the image or the background. The result is shown in FIG.
Indicates an image, and x indicates a background.

Next, the control unit 108 controls the density of the image and the background based on the determination result shown in FIG. 2C and the density signal of the original image. That is, FIG. 2D shows a portion where the background is determined based on the image / background position signal as a white background, and a portion where the image is determined is an original image density signal as it is.

As described above, even when the density of the specific portion of the background of the original image is higher than the density of the specific portion of the image, the image and the background are sharply extracted, and only the image is clear without reproducing the background. It is possible to obtain a reproduced image reproduced in the above.

In the above, the background portion is a white background. However, the control unit 108 may perform density control by changing the density of the portion determined to be the background, and reproduce with a low density. Particularly when a multicolor image is formed, reproducing the base portion with a light color makes it possible to obtain a copy image that is easy to see.

Next, the case where the target pixel and the neighboring pixels shown in FIGS. 3B and 3C are used will be described. For example, in the example of FIG. 3B, the density DS of the target pixel a22 is D22, and the densities of the neighboring pixels a11, a12, a31, a32 are D11, D12, D.
21 and D32, the weighting is a11, a31 is 1/8, a
Since 12, a21, and a32 are 2/8, the density DR of the neighboring pixels after weighting is as follows.

Density DR of neighboring pixels DR = D11 × 1/8 + D12
X2 / 8 + D21 x 2/8 + D31 x 1/8 + D32 x 2/8

In the example of FIG. 3C, the pixel of interest is a
33, neighboring pixels are a11, a12, a13, a21, a22, a23,
a31, a32, a41, a42, a43, a51, a52, a53, and the density DS of the pixel of interest and the density DR of the weighted neighboring pixels are as follows.

Density of neighboring pixels DR = D11 × 1/45 + D
12 x 2/45 + D13 x 3/45 + D21 x 2/45 + D22
X 4/45 + D23 x 6/45 + D31 x 3/45 + D32 x
6/45 + D41 x 2/45 + D42 x 4/45 + D43 x 6
/ 45 + D51 x 1/45 + D52 x 2/45 + D53 x 3 /
45

Further, the density difference ΔD between the target pixel and the neighboring pixels is DS-DR, and similarly to the above, if the absolute value of the density difference ΔD is compared with the predetermined value THL and a series of image processing is performed. Similarly, even when the density of a specific portion of the background of the original image is higher than the density of a specific portion of the image, the image and the background are sharply extracted, and only the image is clearly reproduced without reproducing the background. An image can be formed.

In the above, by increasing the number of neighboring images to be compared, the structure becomes complicated, but there is an effect that the image and the background can be more clearly extracted from the original image having a gentle density gradient.

Example 2 In this example, the same conditions as in Example 1 were used except that the density control method in the control unit 108 was changed. That is, in this embodiment, after performing the processing of FIGS.
By the processing in the control unit 108, an output image as shown in FIG. 2 (e) is obtained.

The average value of the densities of the bases G1 and G7 at both ends adjacent to the image block in which the images I1 to I6 are continuous is DR.
A, when the density of the corresponding image block is DS,
The image density DS 'after the processing of the image portion is represented by the following formula DS' = DS-K * DRA. However, K is a constant with a value of 0 to 1.

In FIG. 2E, an output image of K = 1 is represented by a thin line S1, an output image of K = 0 is represented by a thick line S2, and K = 0.
The output image of No. 5 is shown by the dotted line S3. The output image S2 when K = 0 is the same as the output image in FIG.

When K = 1 as indicated by the thin line S1, the density difference between the pixels I1 on G1 and G2 having a low background density and the pixels I4 on G4 and G5 having a high background density becomes substantially equal. If the developing conditions are appropriate, even the image I1 on G1 and G2 having a low background density can be clearly reproduced.

As described above, according to this embodiment, even when the density of the specific portion of the background of the original image is higher than the density of the specific portion of the image, the image and the background are sharply extracted to reproduce the background. It is possible to clearly reproduce only the image without doing so, and it is also possible to clearly reproduce the image portion having a relatively low density.

In the same manner as described above, the background portion can be reproduced with a light density, and particularly when forming a multicolor image, if the background portion is reproduced with a light color, a legible copy image can be obtained.

Third Embodiment FIG. 4 is a block diagram showing the arrangement of an image processing system according to another embodiment of the present invention.

In the image processing system of this embodiment, as in the case of the first embodiment shown in FIG. 1, the CCD 100 for reading the original image and the analog image signal of the image information from the CCD are converted into digital image signals. A / D converter 10
1, a conversion table 102 for converting and outputting a digital image signal in consideration of reproduction characteristics of a copying apparatus, a density conversion circuit 103 for converting a signal relating to the light amount of the digital image signal into a signal relating to density, An image memory circuit 104 that stores a signal relating to the density converted by the density conversion circuit and an output unit 109 are provided.

Further, the image / background detection circuit 11 for performing the first-stage image / background determination based on the density-related signal.
0 (this is particularly referred to as image / background detection circuit A1), and an image / background detection circuit 111 for performing the second-stage image / background determination based on the determination processing result of the image / background detection circuit A1.
(Image / background detection circuit B1) and image / background detection circuit B
Based on the determination processing result of the image / background detection circuit 112 (image / background detection circuit C1) and the image / background detection circuit C1 which performs the image / background detection in the third step based on the determination processing result of 1. The image / background detection circuit 113 (image / background detection circuit D1) for performing the image / background detection in the fourth stage,
An image / background position storage circuit 114 that stores the position of the image / background determined by the background detection circuits A1, B1, C1 and D1, and the image / background position signal based on the density signal of the original image and the image / background position signal. Control unit 115 for controlling the density
Is provided.

In the present embodiment, the image / background detection circuits B1 and D1, the image / background position storage circuit 114, and the control section 115 are respectively the image / background detection circuits A and B and the image / background position of the first embodiment. Corresponding to the storage circuit 107 and the control unit 109, the other elements of the processing system are the same as those in the first embodiment except that the number of image / background detection circuits A1 and C1 is increased. The operation will be described in detail. .

First, the image / background detection circuit A1 compares the density of each pixel with predetermined values THL1 and THL2, and compares them with a predetermined value THL.
If it is smaller than 1, it is determined to be the background, and if it is larger than the predetermined value THL2, it is determined to be an image. The image / background position determined in the first stage is stored in the image / background position storage circuit 114. To be done. This is because the image
This is because the background detection circuit B1 can more accurately determine the second stage image / background.

Next, the image / background detection circuit C1 makes a third-stage image / background determination based on the image and background detected by the above-described pixel under detection circuits A1 and B1. Each determined image and background are used as a pixel of interest and compared with an adjacent pixel.

In FIG. 5, a22 indicated by a thick frame is a pixel of interest, and a12, a21, a23, and a32 indicated by diagonal lines are adjacent pixels. When the target pixel a22 is an image and the density of the adjacent pixel is equal to or higher than the density of the target pixel, the corresponding adjacent pixel is determined to be an image. Further, based on the newly determined image, the image is determined by comparing with the adjacent pixels, and this is repeated.

When the target pixel a22 is the background, when the density of the adjacent pixel is less than or equal to the density of the target pixel, the corresponding adjacent pixel is determined to be the background. Further, based on the newly determined background, the background is determined by comparing with the adjacent pixels, and this is repeated.

The image / background position determined as described above is stored in the image / background position storage circuit 114.

Next, the image / background detection circuits A1, B1, C
Based on the image and the background detected by 1, the image / background detection circuit D1 determines the fourth step of the image / background. That is, the determined image and the portion surrounded by the image are all determined to be the image, and the other portions are appropriately determined to be the image or the background. The determined image / background position is stored in the image / background position storage circuit 114.

Next, if the portion determined as the background by the control unit 115 is a white background and the portion determined as the image is output as it is, the copy image of FIG. 2 (d) can be obtained from the original image of FIG. 2 (a). .

According to the present embodiment, as described above, even when the density of the specific portion of the background of the original image is higher than the density of the specific portion of the image, the image and the background are more clearly extracted,
Only the image can be clearly copied without reproducing the background.

As in the past, it is possible to reproduce the background portion with a light density, and particularly when forming a multicolor image, by reproducing the background portion with a light color, a copy image that is easy to see can be obtained.

Embodiment 4 FIG. 6 is a block diagram showing the arrangement of an image processing system according to another embodiment of the present invention.

The image processing system of the present embodiment, as in the past, includes the CCD 100 for reading the original image,
An A / D converter 101 for converting an analog image signal of image information from the CCD into a digital image signal, a conversion table 102 for converting and outputting the digital image signal in consideration of reproduction characteristics of a copying apparatus, a digital image A density conversion circuit 103 that converts a signal related to the light amount of a signal into a density related signal, an image memory circuit 104 that stores the density related signal converted by the density conversion circuit, and an output unit 10.
9 is provided.

Further, the image / background detection circuit 11 for performing the first-stage image / background determination based on the density-related signal.
6 (this is particularly referred to as image / background detection circuit A2), and an image / background detection circuit 117 for performing the second stage image / background determination based on the determination processing result of the image / background detection circuit A2.
(Image / background detection circuit B2) and image / background detection circuit B
Based on the image / background detection circuit 118 (image / background detection circuit C2) that determines the image / background in the third step based on the result of the determination processing of 2 and the determination processing result of the image / background detection circuit C2. An image / background detection circuit 119 (image / background detection circuit D2) for performing image / background determination in the fourth stage
An image / background position storage circuit 119 that stores the position of the image / background determined by the background detection circuits A2, B2, C2, and D2, and an image / background image based on the density signal of the original image and the image / background position signal. Control unit 120 for controlling the concentration
And

In this embodiment, the image / background is detected by comparing the density differences of the adjacent pixels of the original image for each scanning line.

FIG. 7 is an explanatory diagram showing an image processing method for detecting an image / background in the present embodiment. FIG. 7 (a)
Shows the state of the original image on one scanning line, where the horizontal axis shows the position and the vertical axis shows the density. I1 ~
I5 is an image and G1 to G6 are bases. In this case, the base G4 has a higher density than the image I1.

First, the image / background detection circuit A2 compares the absolute value of the density difference ΔD of the adjacent pixels with a predetermined value THL, and if the absolute value of the density difference ΔD is larger, the two adjacent pixels are compared. While each of the two is used as the determination reference point, the one having a smaller pixel density of the adjacent pixels is determined as the base, and the one having the larger pixel density is determined as the image.

The image / base position storage circuit 119 initially stores the number 0 at the address corresponding to each pixel. If the base is determined in the above-described first step, the corresponding address is stored. If 1 is stored and it is determined to be an image, 2 is stored at the corresponding address. Therefore,
The image / background position of the first stage determination is stored.

FIG. 7B shows the result of detecting the image of the first stage determination and the background in the original image of FIG. 7A in this manner, and the solid circles indicate the first stage determination. , And ▲ indicates the background of the first stage judgment.

Next, the first by the image / background detection circuit A2
Based on the image and background detected by the stage judgment,
The background detection circuit B2 determines the second stage image / background. That is, when the adjacent determination reference points are images / images, all the portions between them are determined as images, and when the adjacent determination reference points are background / background, all the portions between them are determined as background. The types and positions of the determined image and background are stored in the image / background detection circuit 119. That is, when it is determined to be the background in the second stage determination, the number 3 is stored in the corresponding address, and when it is determined to be the image, 4 is stored in the corresponding address.

The result is shown in FIG. 7 (c), in which ◯ indicates the image of the second stage judgment and Δ indicates the background of the second stage judgment. ● indicates the image of the first stage judgment, and ▲ indicates the background of the first stage judgment.

Next, based on the image and background of the second stage judgment detected by the image / background detection circuit B2,
The background detection circuit C2 determines the third stage image / background. The determination reference points for which the image / background is not determined in the second stage, that is, the adjacent determination reference points are the image / background or the background / pixel,
It is determined that the image and the background are divided at a predetermined position between the background groups.

Various methods can be considered for this determination as described below. In this example, the method (3) was used.

(1) It is determined that the maximum density side is the image and the minimum density side is the background with the median of the densities of the continuous images / background groups as the boundary; (2) The center position of the continuous images / background group is At the boundary, the maximum density side is determined as an image, and the minimum density side as a background. (3) All undetermined determination reference points are determined as images.

The type and position of the determined image and background are stored in the image / background position storage circuit 119. That is, 0 is stored in the corresponding address when it is determined to be the base in the determination of the third step, and 1 is stored in the corresponding address when it is determined to be an image in the determination of the third step, and If the image is judged to be the base in the judgment of 0, 0 is stored in the corresponding address instead of 3, and if it is judged to be the image in the second judgment, 1 is stored in the corresponding address instead of 4. It Figure 7 shows the result.
(D), ◯ indicates an image, and Δ indicates a background.

Next, if the portion determined as the background by the control unit 120 is a white background and the portion determined as the image is output as it is, the copy image of FIG. 7 (d) can be obtained from the original image of FIG. 7 (a). .

As described above, according to this embodiment, even when the density of the specific portion of the background of the original image is higher than the density of the specific portion of the image, the image and the background are sharply extracted by a relatively simple method. Thus, it is possible to obtain a copied image in which only the image is clearly reproduced without reproducing the background.

As in the past, it is possible to reproduce the background portion with a low density, and especially when forming a multicolor image,
By reproducing the base portion in a light color, a copy image that is easy to see can be obtained.

Embodiment 5 FIG. 8 is a block diagram showing the arrangement of an image processing system according to still another embodiment of the present invention.

Similarly, the image processing system of the present embodiment
A CCD 100 that reads an original image, an A / D converter 101 that converts an analog image signal of image information from the CCD into a digital image signal, and a digital image signal that is converted in consideration of reproduction characteristics of a copying machine and output. And a density conversion circuit 103 for converting the light amount signal of the digital image signal into a density signal.
And an image memory circuit 104 for storing a signal relating to the density converted by the density conversion circuit, and an output unit 109.

Further, the image / background detection circuit 12 for judging the image / background in the first stage based on the density-related signal.
1 (this is particularly referred to as image / background detection circuit A3), and an image / background position storage circuit 124 that stores the type and position of the image / background determined by the image / background detection circuit A3.
An image / background detection circuit 12 for performing the second-stage image / background determination based on the determination processing result of the image / background detection circuit A3.
2 (image / background detection circuit B3), an image / background position storage circuit 125 that stores the type and position of the image / background determined by the image / background detection circuit B3, and a determination processing result of the image / background detection circuit B3. An image / background detection circuit 123 (image / background detection circuit C3) that determines the image / background in the third step based on the above, and the type and position of the image / background determined by the image / background detection circuit C3 are stored. The image / background position storage circuit 126 and the control unit 127 for controlling the density of the image / background based on the density signal of the original image and the position signal of the image / background.

In this embodiment, the document image information is divided into specific areas, and based on the density distribution of each divided area,
The background is being detected.

The applicant of the present invention has previously filed Japanese Patent Application Laid-Open No. 1-21307.
No. 3 proposed a method of detecting the background by taking a histogram of the brightness information of the original image and using the brightness in a predetermined range from a high frequency peak close to white as a threshold value.

In this embodiment, the density information is used instead of the brightness information, but either of these may be used. What is important is that the histogram is not divided over the entire area of the original, but is divided into specific areas to obtain the histogram, so that even if there is uneven density (difference in density) in the background of the original image, Can be clearly extracted. Hereinafter, this embodiment will be described in detail.

FIG. 9 is an explanatory diagram showing an example of a method of dividing the document image information into specific areas. FIG. 9A shows the first division, in which the original image is divided into T1 and T2.
, U1, U2, V1, V2. This is called a first divided area. Next, as shown in FIG. 9 (b), the original image is shifted from the above-mentioned area by T1 'and T2.
', T3', U1 ', U2', U3 ', V1', V2
, V3 ', W1', W2 ', W3'. This is called the second division.

FIG. 9C is a combination of the divided areas of FIGS. 9A and 9B, where the solid line indicates the first divided area.
The broken line indicates the second divided area. Therefore, the combination of the first divided area and the second divided area is A1-A1 ', A1
-A2 ', A2-A2', A2-A3 ', A1-B1
', A1-B2', A2-B2 ', A2-B3', B1
-B1 ', B1-B2', B2-B2 ', B2-B3'
... This is referred to as an overlapping divided area in which the first divided area and the second divided area overlap.

There are various methods for dividing into these specific areas. If the number of divisions is large, the configuration becomes complicated, and if the number of divisions is small, the configuration becomes simple. In some cases, the accuracy of the determination may deteriorate.

First, the image / background detection circuit A3 takes a histogram of the density of each pixel for the first divided area.
One example is shown in FIG. The density of the background of the original whose density is close to white shows a high frequency (H1 in the figure), and the density within a predetermined range from the peak H2 is set as the threshold value H3. A light density below the threshold value H3 is determined as a background.

The image / base position storage circuit 124 stores the type and position of the pixel determined to be the threshold value H3. That is, 0 is stored in the corresponding address when it is determined to be the background, and 1 is stored in the corresponding address when it is determined to be the image. Further, the threshold value H3 is stored.

Next, the image / background detection circuit B3 obtains a histogram of the density of each pixel for the second divided area in the same manner as described above, detects the background, and determines the threshold value H3. The types and positions of the different pixels are similarly stored in the image / base position storage circuit 125.

Next, the image / background detection circuit C3 compares the types of the images / backgrounds of the image / background position storage circuit 124 and the image / background position storage circuit 125 for each pixel, and when the two match. Is determined as it is because the previous determination is correct. If they do not match, the image / background of the undetermined pixel is determined by a predetermined method.

There are various methods for determining the image / background of the undetermined pixel, one example of which will be described below. When the threshold value in the first divided area is SH1 and the threshold value in the second divided area is SH2, there is no new information in the overlapping divided area where the first divided area and the second divided area overlap. Threshold value SH3
When the following expression SH1> SH2: SH3 = K (SH1−SH2)
+ SH2 When SH1 <SH2: SH3 = K (SH2-SH1)
Set to + SH1. However, K is a constant with a value of 0 to 1.

When K = 1, all undetermined pixels are determined to be the background, and when K = 0, all undetermined pixels are determined to be the image. When K = 0.5, it means that the average value of SH1 and SH2 is used as the threshold value.

In this embodiment, since the background determination is performed by overlapping the divided areas as described above, there is an effect of improving the determination accuracy. The types and positions of the determined image and background are stored in the image / background position storage circuit 126.

Next, a high-quality copied image can be obtained by outputting the portion determined as the background by the control unit 127 as a white background and the portion determined as the image as it is.

According to the present embodiment, as described above, the image and the background are sharpened by the relatively simple method even when the density of the specific portion of the background of the original image is higher than the density of the specific portion of the image. It is possible to form a copied image by extracting and clearly reproducing only the image without reproducing the background.

Next, FIG. 11 shows a modification of the dividing method of the second divided area shown in FIG. 9, in which the solid line shows the first divided area and the broken line shows the second divided area. Since the edge of the document is often the background, a certain degree of accuracy can be obtained even by performing the background determination once. Since the image and the background are often mixed in the central part of the document, the background determination is performed by overlapping the divided areas in order to improve the determination accuracy. If you do this,
The image and the background can be detected by a simpler method.

Next, the types of images and backgrounds in the image / background position storage circuit 124 and the image / background position storage circuit 125 are compared, and if the two do not match, another determination of the image / background detection circuit C3 is made. Some examples of the method will be described.

(1) First, an example of a method for making a judgment by comparing successive undetermined pixel blocks with adjacent pixels will be described.

Pixels at the ends of consecutive undetermined pixel blocks are set as the target pixel, and the absolute value of the density difference ΔD between all the target pixels and the demarcated pixels adjacent to the target pixel is compared with a predetermined value THL3.
When the absolute value of the density difference ΔD is larger, 1 is added when the adjacent pixel has a higher density, and −1 is added when the adjacent pixel has a lower density, and the total value is the predetermined value K1. The above case is determined to be the background, and the case of less than the predetermined value K1 is determined to be the image.

That is, when relatively adjacent pixels are recognized as an image, the undetermined pixel block is determined to be the background, and when adjacent pixels are recognized as the background, the undetermined pixel block is determined to be the image. If the predetermined value K1 = 0, the number of images of the recognized adjacent pixels is compared with the number of backgrounds.

(2) Next, an example of a method of comparing and determining specific neighboring pixels of consecutive undetermined pixel blocks will be described.

The average value DRA of the densities of consecutive undetermined pixel blocks is obtained, and the density difference ΔD between the density DS of the pixel of interest and the above-mentioned average value DRA is compared with a predetermined value THL4 with the demarcating pixel adjacent to this block as the pixel of interest. Then, when the following expression ΔD = DS-DRA> THL4 is satisfied, this target pixel is set as a new specific pixel.

This is repeated until no new specific pixel is generated. Then, when the total number of the specific pixels is equal to or more than the predetermined value K2, it is determined to be the background, and when it is less than the predetermined value K2, it is determined to be the image.

Alternatively, (3) a pixel at the end of a continuous undetermined pixel block is used as a comparison pixel, and a demarcating pixel adjacent to this pixel is used as a target pixel, and the density difference ΔD between the density DS of the target pixel and the density DR of the comparison pixel is calculated. When the following expression ΔD = DS-DRA> THL4 is satisfied as compared with the predetermined value THL4, this target pixel is set as a new specific pixel.

This process is repeated until no new pixel is generated. When the total number of the specific pixels is equal to or more than the predetermined value K2, it is determined as the background, and when it is less than the predetermined value K2, it is determined as the image.

In this way, although the structure is complicated, the image and the background can be detected with high accuracy.

[0100]

As described above, according to the first invention of the present application, the target pixel and the neighboring pixel are compared based on the density information of the original image, and when the density difference is equal to or more than a predetermined value. Since the high density side is determined to be the image and the low density side is determined to be the background and the determined background is controlled to be changed to a predetermined density, even for an original image having a plurality of background densities,
There is provided an image forming method capable of obtaining a high-quality image in which only the image is clear and which does not reproduce the background or is reproduced at a predetermined density.

According to the second invention of the present application, the target pixel and the neighboring pixels are compared on the basis of the density information of the original image, and when the difference in density is more than a predetermined value, the high density side image is
Since the background determination means for determining the low-density side as the background and the means for changing the determined background to a predetermined density are provided, the background is detected even for an original image having a plurality of background densities, There is provided an image forming apparatus capable of obtaining a high-quality image in which only the image is clear and which does not reproduce the background or is reproduced at a predetermined density.

According to the third invention of the present application, the background information for dividing the image information of the original image into specific areas and detecting the background density in the original image based on the density distribution of each divided area. Based on the density detecting means and the detected background density, a portion brighter than the density is determined to be the background,
Since a means for changing the determined background to a predetermined density is provided, even with respect to an original image having a plurality of background densities, the background can be detected relatively easily and the background is not reproduced or the predetermined density is obtained. There is provided an image forming apparatus capable of obtaining a reproduced high-quality image in which only the image is clear.

According to the fourth invention of the present application, the densities of the adjacent pixels of the image information of the original image are compared for each scanning line, and when the density difference between the adjacent pixels is equal to or more than a predetermined value, the high and low values are set. As a density reference point at a location, a means for obtaining the position and density of the density reference point, a means for obtaining a density difference between adjacent density reference points, and a density difference between adjacent density reference points are equal to or more than a predetermined value. Using this density reference point as a determination reference point, a means for determining the high density side as an image and a means for determining the low density side as a background, and if the adjacent determination reference points are images / images, all areas between them are determined as images and If the judgment reference points are the background / background, all the areas between them are judged to be the background, and if the adjacent judgment reference points are image / background or background / image, they are set at a predetermined position between consecutive images / background groups. Means to determine to divide into image and background , Since and means for changing the determined base to a predetermined concentration, even for a document image having a plurality of background density, by detecting a relatively easily ground,
There is provided an image forming apparatus capable of obtaining a high-quality image in which only the image is clear and which does not reproduce the background or is reproduced at a predetermined density.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an image processing system used for performing image processing in an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing an image processing method for detecting an image / background in the processing system of FIG.

FIG. 3 is an explanatory diagram of a target pixel and neighboring pixels for detecting an image / background.

FIG. 4 is a block diagram showing a configuration of an image processing system according to another embodiment of the present invention.

FIG. 5 is an explanatory diagram of a target pixel and adjacent pixels.

FIG. 6 is a block diagram showing a configuration of an image processing system according to still another embodiment of the present invention.

7 is an explanatory diagram showing an image processing method for detecting an image / background in the processing system of FIG.

FIG. 8 is a block diagram showing a configuration of an image processing system in still another embodiment of the present invention.

FIG. 9 is a first method of dividing document image information into specific areas.
It is explanatory drawing which shows an example.

FIG. 10 is a histogram for one divided area according to an embodiment of the present invention.

FIG. 11 is an explanatory diagram showing an example of another method of dividing document image information into specific areas.

FIG. 12 is an explanatory diagram showing a typical example of a conventional image processing method.

[Explanation of symbols]

100 CCD 101 A / D conversion unit 102 Conversion table 103 Density conversion circuit 104 Density memory circuit 105, 106, 110 to 113, 116 to 118, 1
21-123 image / background detection circuit 107, 114, 119, 124, 125, 126 image / background position storage circuit 108, 115, 120, 127 control unit 109 output unit

Claims (4)

[Claims] 1. A target pixel and a neighboring pixel are compared based on density information of an original image, and when the density difference is equal to or more than a predetermined value, the high density side is determined to be an image and the low density side is determined to be a background. Control not to reproduce or to reproduce to a predetermined concentration,
An image forming method comprising forming an image. 2. A pixel of interest and a neighboring pixel are compared on the basis of density information of an original image, and when the density difference is equal to or more than a predetermined value, it is determined that the high density side is an image and the low density side is a background. An image forming apparatus comprising: a background detecting unit that detects a background and a unit that changes the detected background to a predetermined density. 3. A background density detecting unit that divides image information of a document image into specific areas, and detects a background density in the document image based on the density distribution of each divided area.
An image forming apparatus comprising: a unit that determines a portion brighter than the background density as a background based on the detected background density and changes the determined background to a predetermined density. 4. The densities of adjacent pixels of the image information of the original image are compared for each scanning line, and when the density difference between the adjacent pixels is equal to or more than a predetermined value, this is used as a determination reference point at two high and low locations.
First-stage image / background determination means for determining the high-density side as the image and low-density side as the background, means for determining the position and density of the determined image / background, and the adjacent determination reference points for the image / image In the case of, it is determined that all of the space between them is an image, and when the adjacent determination reference points are the background / background, it is determined that all the areas between them are the background, and when the adjacent determination reference points are the image / background or the background / image, Continuous images-Second-stage image that is determined to be divided into an image and a background at a predetermined position between the background groups-
An image forming apparatus comprising: a background determination unit and a unit for changing the determined background to a predetermined density.