JPH1188609A - Image input method, its system and record medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To properly eliminate moire stripes, while suppressing deterioration in an original component by obtaining a proper focal position prior to reception of full image information. SOLUTION: This system is provided with an optical read section 10 that receives a specific position of an original as image information at each focal position, a 1st frequency characteristic distribution extract section 31 that extracts the image as a 1st frequency characteristic distribution, including an original component and a dot component, a 2nd frequency characteristic distribution extract section 33 that extracts a 2nd frequency characteristic distribution where a dot component is reduced, a presence degree calculation section 34 that calculates a degree of presence of the dot component with respect to the original component for each focal position and a focal position setting section 16 that sets the focal position corresponding to the minimum presence degree as a reception focal position, and receives full image information of an original in a state set to the reception focal position.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image input method and apparatus for capturing a reflection original or a transparent original in an out-of-focus state and a recording medium, and more particularly to a technique for removing an adverse effect caused by a halftone component of the original. About.

[0002]

2. Description of the Related Art Conventional image input devices of this type include:
For example, as shown in FIG. 12, a focus position setting unit 110 that adjusts the focus position of the optical reading unit 100 based on an operator's instruction or the like, and an image storage unit that stores image information output from the optical reading unit 100 120. Further, such an image input device is often connected to an image processing unit 130 capable of performing various processes on the image information stored in the image storage unit 120. Image processing is performed.

In the apparatus having such a configuration, when reading is performed with the optical reading unit 100 focused on the original, the periodic structure of the halftone dot component contained in the original and the optical reading unit Interference fringes (Moiré fringes) are generated due to the pitch of elements such as CCDs built in 100.
Therefore, in order to reduce the moire fringes, the original is blurred with the optical reading unit 100 out of focus, and the original is taken in this state.

[0004] The extent to which the optical reading unit 100 is shifted from the in-focus position and the degree of blurring of the document is usually determined based on an instruction from the operator to the focus position setting unit 110. . That is, 100 lines / mm, 133 lines / mm, 1
An appropriate focus position at which an out-of-focus state is set is set according to the number of printed lines indicating the cycle of a halftone dot component such as 50 lines / mm, 175 lines / mm, and 200 lines / mm.

[0005]

However, the prior art having such a structure has the following problems. That is, when it is difficult to know the number of printed lines of the document, the operator cannot specify the number of printed lines as described above, so that moire fringes can be reduced regardless of the number of printed lines of the document. In many cases, an out-of-focus focal position (a large blur state) is set so that a halftone component in a wide frequency range can be removed. For example, if the focal position is set so that the halftone dot component can be removed when the number of printing lines is 150 lines / mm to 200 lines / mm, 200 lines / mm
In the case of a fine document of mm, a part of the document component (low frequency) having a larger cycle than the halftone dot component is removed, and the image is unnecessarily blurred. On the other hand, 1
In the case of an original having a coarse size of 00 lines / mm, halftone components cannot be removed, and problems such as moire fringes occur. In other words, not only the halftone dot component to be blurred, but also the original document component that needs to be kept as sharp as possible is blurred, and even if the original document component can be kept sharp, the halftone dot component can hardly be reduced. There is.

[0006] Even if the number of lines printed on an original is correctly instructed by an operator, it is often impossible to remove only halftone components with high accuracy due to various fluctuation factors. In other words, when the original is floated, the variation is caused by the assembling accuracy of the optical reading unit 100, the variation of the optical coefficient having the temperature dependency caused by the variation of the ambient temperature, or the light amount of the light source of the optical reading unit 100 is automatically changed. This is because the focal position of the optical reading unit 100 varies with time or day, or varies from one device to another, due to a change in the depth of focus caused by the aperture that is dynamically adjusted.

The present invention has been made in view of such circumstances, and by determining an appropriate focus position prior to capturing all image information, it is possible to appropriately suppress moiré fringes while suppressing deterioration of original components. It is an object of the present invention to provide an image input method, an apparatus thereof, and a recording medium capable of removing the image.

[0008]

The present invention has the following configuration in order to achieve the above object. That is, in the image input method according to claim 1, in the image input method for inputting a document in an out-of-focus state, a specific position of the document is captured while changing a focal position of an optical reading unit, and an image for each focal position is acquired. Acquiring information, obtaining a frequency characteristic distribution for each focal position based on the image information, and extracting as a first frequency characteristic distribution including a document component and a halftone dot component; A process of filtering to reduce a halftone component and extracting a second frequency characteristic distribution for each focal position; and for each of the focal positions, based on the first frequency characteristic distribution and the second frequency characteristic distribution. Calculating the existence degree of the halftone dot component with respect to the document component; and taking the focus position corresponding to the smallest one of the existence degrees as the capture focal position, It is characterized in that the process of setting the readout means, and to capture the entire image information of the document after performing.

[0009] The image input method according to the second aspect is characterized in that:
2. The image input method according to claim 1, wherein, before obtaining a frequency characteristic distribution from the image information, the image information is converted into a gray component, and a frequency characteristic distribution for each focal position is obtained based on the gray component. It is characterized in that it is extracted as a first frequency characteristic distribution.

[0010] The image input method according to the third aspect is characterized in that:
3. The image input method according to claim 1, wherein a process for reducing a low frequency component included in the image information or the first frequency characteristic distribution is performed. It is.

[0011] The image input method according to claim 4 is characterized in that:
The image input method according to any one of claims 1 to 3, wherein the filter processing is performed by a smoothing filter.

[0012] The image input method according to a fifth aspect is characterized in that:
The image input method according to any one of claims 1 to 3, wherein the filter processing is performed by a median filter.

[0013] The image input device according to the sixth aspect is characterized in that:
In an image input apparatus for inputting a document in an out-of-focus state, an optical reading unit that captures a specific position of the document while changing the focal position and captures the image as image information for each focal position, and for each focal position based on the image information, Is obtained as a first frequency characteristic distribution including a document component and a halftone component, and the first frequency characteristic distribution is filtered to reduce the halftone component. Frequency characteristic distribution extracting means for extracting as a frequency characteristic distribution, and presence degree calculation for calculating the degree of existence of a halftone dot component with respect to the document component for each of the focal positions based on the first frequency characteristic distribution and the second frequency characteristic distribution. Means and a focal position corresponding to the smallest one of the degrees of presence as a capture focal position, and the optical reading means is set at the capture focal position. And a focus position setting means for,
The image capturing apparatus is characterized in that all image information of the document is taken in a state where it is set at the taking focus position.

Further, the image input device according to the present invention is characterized in that:
7. The image input device according to claim 6, further comprising a gray component conversion unit that converts the image information captured by the optical reading unit into a gray component, and outputs the gray information as image information to the frequency characteristic distribution extraction unit. It is characterized by the following.

Further, the image input device according to the present invention is characterized in that:
8. The image input device according to claim 6, further comprising a low frequency component reducing unit configured to reduce a low frequency component included in the image information or the first frequency characteristic distribution. It is assumed that.

Further, the image input device according to the ninth aspect provides
The image input apparatus according to any one of claims 6 to 8, wherein the frequency characteristic distribution extracting means performs the filtering by a smoothing filter.

According to a tenth aspect of the present invention, in the image input device according to any one of the sixth to eighth aspects, the frequency characteristic distribution extracting means performs the filtering by a median filter. It is characterized by doing so.

The recording medium according to the present invention is a recording medium storing a program for inputting an original in an out-of-focus state, wherein the identification of the original is performed while changing a focal position of an optical reading unit. A process of capturing a position and capturing image information for each focal position; a process of obtaining a frequency characteristic distribution for each focal position based on the image information and extracting the frequency characteristic distribution as a first frequency characteristic distribution; Extracting the second frequency characteristic distribution for each focal position by filtering the halftone dot component with respect to the document component for each focal position based on the first frequency characteristic distribution and the second frequency characteristic distribution. Processing for calculating the presence degree;
A process of setting the optical reading means at the capture focal position with a capture position corresponding to the smallest one of the degrees of presence as the capture focal position, so that all image information of the document is captured after the process is performed. It stores a program for controlling a computer.

[0019]

The operation of the method according to the first aspect is as follows. First, an image at a specific position of a document is captured while changing the focal position of the optical reading unit, image information for each focal position is stored, and the frequency characteristic distribution of the image information is extracted as a first frequency characteristic distribution. Although the extracted first frequency characteristic distribution for each focal position has a different profile, the intensity is strongly mountain-shaped in the low frequency region due to the characteristics of the document component, and the intensity gradually increases toward the high frequency region. It is getting smaller. In the high frequency region, a peak appears at a position corresponding to the cycle due to the characteristics of the halftone dot component. Next, the first frequency characteristic distribution is filtered to extract a second frequency characteristic distribution for each focal position in which the intensity of the halftone dot component is attenuated. Then, based on the first frequency characteristic distribution including the document component and the halftone dot component and the second frequency characteristic distribution in which the halftone dot component is attenuated and processed to substantially only the document component, the focus component for each focus position is determined. The degree of existence of the halftone dot component is calculated, and the focal position where the degree of existence is minimum is taken in as the focal point position. When the entire document is read and all image information is captured, the capture focal position obtained as described above is set to the focal position of the optical reading unit.

According to the second aspect of the present invention, when the original is color, it is necessary to perform processing for each color after capturing image information at a specific position.
By converting to a gray component, the object to be processed later can be only one gray component.

According to the third aspect of the present invention, the low-frequency component included in the image information or the first frequency characteristic distribution is reduced by, for example, a high-pass filter or a band-pass filter, whereby Document components in the first frequency characteristic distribution and the second frequency characteristic distribution are reduced. Therefore, since the ratio of the halftone dot component to the original document component increases, the existence degree of the halftone dot component can be obtained with high sensitivity.

According to the fourth aspect of the present invention, when the first frequency characteristic distribution is processed by the smoothing filter, the peak of the halftone dot component occurring in the high frequency region can be smoothly attenuated. Therefore, the second frequency characteristic distribution can be substantially made only of the document component, and the existence degree of the halftone dot component with respect to the document component can be obtained.

According to the fifth aspect of the present invention, when the first frequency characteristic distribution is processed by a median filter (also referred to as a median filter), a steep change in the original component of the first frequency characteristic distribution occurs. Even if it exists, it is possible to accurately attenuate only the halftone dot component without causing an adverse effect on the portion (deterioration of a sharply changed portion due to smoothing). Therefore, the second frequency characteristic distribution can be substantially made only of the document component, and the existence degree of the halftone dot component with respect to the document component can be obtained with high accuracy.

The operation of the device invention according to claim 6 is as follows. First, an image at a specific position of a document is captured while changing the focal position of the optical reading unit, and image information for each focal position is stored. Next, the frequency characteristic distribution of the image information is extracted as a first frequency characteristic distribution by a frequency characteristic distribution extracting unit, and is filtered to be extracted as a second frequency characteristic distribution. And
Based on the first frequency characteristic distribution including both the document component and the halftone component, and the second frequency characteristic distribution in which the halftone component is attenuated and processed into almost only the document component, the focus component is calculated for each focus position. The existence degree of the halftone dot component is calculated by the existence degree calculation means. The focal position corresponding to the minimum one of the degrees of existence of the halftone components calculated in this way is taken as the focal position, and this is set in the optical reading means by the focal position setting means.

According to the apparatus described in claim 7, when the original is color, it is necessary to perform processing for each color after fetching image information at a specific position.
By converting to a gray component by the gray component conversion means, the subsequent processing target can be only one gray component.

Further, according to the invention, the low frequency component contained in the image information or the first frequency characteristic distribution is reduced by a low frequency component reducing means such as a high pass filter. Accordingly, the document components in the first frequency characteristic distribution and the second frequency characteristic distribution are reduced. Therefore, since the ratio of the halftone dot component to the original document component increases, the existence degree of the halftone dot component can be obtained with high sensitivity.

According to the ninth aspect of the present invention, when the frequency characteristic distribution extracting means processes the first frequency characteristic distribution by the smoothing filter, the peak of the halftone dot component occurring in the high frequency region is smoothly attenuated. Can be done. Therefore, the second frequency characteristic distribution can be substantially made only of the document component, and the existence degree of the halftone dot component with respect to the document component can be obtained.

According to the tenth aspect of the present invention, when the frequency characteristic distribution extracting means processes the first frequency characteristic distribution by a median filter (also called a median filter), the original component of the first frequency characteristic distribution Even when there is a steep change in the inside, it is possible to accurately attenuate only the halftone dot component without causing any adverse effect on that portion. Therefore, the second frequency characteristic distribution can be substantially made only of the document component, and the existence degree of the halftone dot component with respect to the document component can be obtained with high accuracy.

Further, by causing a computer to execute the program stored in the recording medium according to the eleventh aspect, a focal position at which an out-of-focus state is set is set as follows. First, an image at a specific position of a document is captured while changing the focal position of the optical reading unit, and image information for each focal position is stored, and the frequency characteristic distribution of the image information is extracted as a first frequency characteristic distribution. Then
The first frequency characteristic distribution is filtered to attenuate the intensity of the halftone dot component to extract a second frequency characteristic distribution for each focal position. Then, based on the first frequency characteristic distribution including the document component and the halftone component, and based on the second frequency characteristic distribution in which the halftone component is attenuated and substantially processed only for the document component,
The degree of existence of the halftone dot component with respect to the document component is calculated for each focal position, and the focal position at which the degree of existence is minimized is determined as the captured focal position. When the entire document is read and all image information is captured, the capturing focal position obtained as described above is set to the focal position of the optical reading unit.

[0030]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a schematic configuration of an image input device according to the present invention. The optical reading unit 10 (optical reading unit) optically reads a document containing a document component and a halftone dot component printed with a certain number of printing lines under the control of the control unit 12. At this time, the read image information including the RGB color information is stored in the image memory 14 by the control unit 12. For reading a document, the focal position (L) of the optical reading unit 10 is passed through a focal position setting unit 16 corresponding to a focal position setting unit of the present invention.
While changing the position of the original, only the specific position of the original is taken in, the image information for each focal position is stored in the image memory 14, and based on the image information, an appropriate take-in focal position is obtained for the original. There are two types of “main scan” in which a document is read at the capture focal position obtained by scanning and all image information is collected. Note that all image information stored in the image memory 14 is subjected to appropriate processing by the image processing unit 20 connected to the image input device.

The control unit 12 includes a gray component conversion unit 30, a first frequency characteristic distribution extraction unit 31, a filter processing unit 32, a second frequency characteristic distribution extraction unit 33, and a presence degree calculation unit 34. Is connected.

The gray component conversion unit 30 corresponding to the gray component conversion means in the present invention converts the color information for the image information for each focal position (L) stored in the image memory 14, and Only what you want. As described above, in the present apparatus, each color information of RGB is first converted into a gray component, so that the subsequent processing may be performed only on the gray component and the processing efficiency can be improved. Note that the following processing may be individually performed on each of the RGB colors without conversion to the gray component.

The first frequency characteristic distribution extracting section 31 extracts a frequency characteristic distribution including a document component and a halftone dot component from the image information for each focal position converted into only a gray component, and extracts the first frequency characteristic for each focal position. Obtained as a frequency characteristic distribution. In order to extract the frequency characteristic distribution from the image information, for example, a one-dimensional Fourier transform may be performed as described later. The first frequency characteristic distribution extracted in this way is further subjected to filter processing for reducing low frequency components by the filter processing unit 32 (low frequency component reduction means). For this filter processing, for example, a high-pass filter or a band-pass filter may be used. Although details will be described later,
This low frequency component reduction processing can improve the accuracy of detecting the degree of existence of the halftone dot component. However, this processing may be omitted as long as the detection accuracy of the presence degree does not extremely decrease.

The first frequency characteristic distribution from which the low-frequency component has been reduced is further filtered by the second frequency characteristic distribution extraction unit 33, and the second frequency characteristic distribution is extracted for each focal position. This filtering process is a process for reducing the halftone component of the original component and the halftone component included in the first frequency characteristic distribution. For example, a median filter (well-known in the field of image processing) (Also called a median filter). By this filtering, the second frequency characteristic distribution can be extracted by substantially reducing only the halftone component of the first frequency characteristic distribution.

The first frequency characteristic distribution extracting section 31 and the second frequency characteristic distribution extracting section 33 correspond to frequency characteristic distribution extracting means in the present invention.

The presence degree calculating section 34 corresponding to the presence degree calculating means includes a first frequency characteristic distribution including both the original component and the halftone component, and a second frequency characteristic in which the halftone component is reduced to almost the original component. Based on the characteristic distribution, the existence degree of the halftone dot component with respect to the document component is calculated for each focal position (L). If the degree of existence of the halftone dot component with respect to the original document component is the minimum, it indicates that the focus position can minimize the halftone dot component that causes moire fringes by minimizing the deterioration of the original document component. The focal position calculated by the "pre-scan" is taken as the focal position, which is set in the optical reading unit 10 and the "main scan" is performed, and then all image information of the document is acquired.

Next, the "pre-scan" which is a main part of the method of the present invention will be described in detail with reference to the flowchart of FIG. Note that the processing shown in this flowchart corresponds to a program of the image input method according to the present invention, and is stored in a recording medium (not shown). Therefore, even if the apparatus does not have the configuration as shown in the block diagram of FIG. 1, by reading and executing the recording medium storing the program,
The same operation and effect as those of the device having the above configuration can be obtained.

Step S1 (Collect Image Information for Each Focus Position) The control unit 12 takes in only a specific position of the document via the optical reading unit 10 and reads the image information. To change the focal position L and read image information for each focal position L. Image information for each focal position L is stored in the image memory 14. Note that the variable range of each focal position L may be set according to the number of printing lines of the document.

Step S2 (Gray Component Conversion) The image information for each focal position L stored in the image memory 14 includes the respective color information of RGB, but in order to speed up the subsequent processing, the gray component conversion unit 30 Convert to gray component only. Let the gray component be d (x, y),
The read value of n colors is s (x, y, n), each pixel position of the image information is x, y, the read color is n (N = 2 for RGB), and the gray component coefficient of each color (sum 1 ) Is k _n , the conversion to the gray component d (x, y) can be obtained by performing weighted addition of each color by the following equation.

[0040]

(Equation 1)

Step S3 (extract first frequency characteristic distribution) The first frequency characteristic distribution extracting section 31 extracts a frequency characteristic distribution from the gray component d (x, y) for each focal position L, The characteristic distribution is defined as Ps0 (L). To extract the frequency characteristic distribution, first, for example, 1
The following equation is executed by using the FFT method for performing a high-speed calculation of the dimensional Fourier transform.

[0042]

(Equation 2)

Note that w in the above equation is the frequency (w =
1 / cycle), x is a pixel position, and S (w, L)
Represents the component of the frequency w at the focal position L by a complex vector.

From the frequency component S (w, L) for each focal position L calculated as described above, a power spectrum Ps (w, L) is calculated by the following equation.

[0045]

(Equation 3)

Here, this power spectrum Ps
Let (w, L) be the first frequency characteristic distribution Ps0 (w, L). Each focus position L (= 1 to 1) thus extracted
FIGS. 5A to 5D schematically show the first frequency characteristic distribution Ps (w, L) for each 4). Note that the focal position L = 1 in FIG. 5A is close to the in-focus state, and is in an out-of-focus state in which the focus position L = 4 in FIG. As is clear from these, as the focal position L increases and the blur increases, the intensity (power spectrum) of the document component in the high frequency region decreases, and the intensity of the halftone dot component also decreases. .

As described above, the image information is converted to a gray component, but the original is usually printed in four CMYK plates. Therefore, when the image information read by the optical reading unit 10 is converted into a gray component, the components of each plate are mixed, and the first frequency characteristic distribution Ps0 (w, L) obtained therefrom also shows the frequency of each plate. The components will be mixed. The frequency of the halftone dot component that can be extracted by one-dimensional reading by the optical reading unit 10 can be accurately extracted when the halftone dot angle is 0 degree as shown in FIG. At the halftone dot angle, the frequency is extracted lower than the frequency of the actual halftone dot component. Specifically, since the maximum value of the halftone dot angle is 45 °, it is extracted as low as cos45 ° = 0.7071 times.
In general, the halftone dot angle of each CMYK plate in a document is different for each CMYK plate as shown in FIG. Therefore, the extracted first frequency characteristic distribution Ps0
Although (w, L) includes the above-mentioned problem of mixing and lowering, the method of the present invention states that “the original component has a gradual distribution characteristic in which the intensity gradually decreases toward the high frequency region. "And halftone dot components have a steep peak characteristic in a higher frequency range than the original document component.

Step S4 (reducing low frequency components) The first frequency characteristic distribution Ps0 is
The low frequency component of (w, L) is reduced. As the method, for example, reduction of a low frequency component using a high-pass filter or a band-pass filter can be mentioned. As a result, FIG.
As shown in FIGS. 6A to 6D, it is possible to obtain a first frequency characteristic distribution Ps0 (w, L) in which only the intensity of the document component is reduced in the low frequency region while the intensity of the halftone dot component is kept as it is. it can. By reducing the low-frequency components of the document components in this manner, the ratio of the halftone components in the document components in the subsequent processing can be increased, and the degree of existence of the halftone components finally desired can be increased with high sensitivity. You can ask. Note that this filter processing may be omitted if the detection accuracy of the presence degree does not extremely decrease as described above.

Step S5 (extract the second frequency characteristic distribution) Next, the first frequency characteristic distribution Ps0 in which the low frequency components have been reduced
(W, L) is filtered by the second frequency characteristic distribution extraction unit 33 to reduce only halftone components among the original components and halftone components. In the filtering process, a known median filter is used so that only halftone dot components can be reduced so as not to affect the document components as much as possible. This filtering process is performed by using each focus position L shown in FIGS. 6A to 6D.
7A to 7D, for example. By performing processing using a median filter, even if a step-like profile exists in the document component, almost halftone dot components can be faithfully attenuated with little effect on that portion. In addition,
Hereinafter, this second frequency characteristic distribution is referred to as Ps1 (w, L).

Step S6 (Extracting Existence of Halftone Component) First, a first frequency characteristic distribution Ps0 (w, L) including a document component and a halftone component, in which low frequency components are reduced, and a second frequency characteristic distribution The difference from Ps1 (w, L) is calculated for each focal position L, and only the halftone dot component for each focal position L is obtained. That is, FIGS. 7A to 7D are subtracted from the above-described FIGS. 6A to 6D, and for example, FIGS.
As shown in FIG. 8D, only the halftone dot component at each focal position L can be extracted. 8 (a) to 8 (d), the halftone dot component of FIG. 8 (d) at the focal position L = 4 is minimized.

Next, the focal position L obtained as described above
The ratio of the halftone dot component to the original document component is calculated. That is, the difference is divided by the second frequency characteristic distribution Ps1 (w, L), which is substantially only the document component. The degree of existence C (L) of the halftone dot component calculated in this manner is expressed by the following equation.

[0052]

(Equation 4)

Thus, the degree of existence C of the halftone dot component
A description will be given assuming, for example, that the result of calculating (L) is as follows. Focus position L = 1 C (1) = 32 Focus position L = 2 C (2) = 16 Focus position L = 3 C (3) = 8 Focus position L = 4 C (4) = 10

Here, looking only at the intensity of the halftone dot components shown in FIGS. 8A to 8D, the focal position L = 4 is the smallest, but FIG. 7A. Since the integral value of the document component of the second frequency characteristic distribution Ps (w, L) in FIG. 7D is extremely small, the denominator of the above equation becomes small, and as a result, the presence degree C (4) is minimized. That is, the existence degree C (3) of the focal position L = 3 is minimized.

In the above description, the existence degree C of the halftone dot component
The equation for calculating (L) is represented by Equation 4, but may be represented by Equation 5 below instead.

[0056]

(Equation 5)

In Equation 5, the coefficient A is a fixed value (normalization coefficient) for normalizing the integral value of the document component, and has a value close to the integral value of the document component. The index B
Is a constant that determines the sensitivity to the amount of change in the document component. For example, when the index B is large (1.0 or more),
It acts to make the amount of change of the integral value of the document component more prominent, and the sensitivity to the amount of change is increased. In addition, it is possible to easily obtain an appropriate value for each of the coefficient A and the index B through an experiment.

Step S7 (set as capture focal position) Existence degree C (L) of the halftone dot component obtained as described above
Means that the document component is large and
Indicates that the halftone dot component is small. Therefore, it is possible to set the focus of the optical reading unit 10 at the focal position L and set the focus to the out-of-focus state, and reduce the moire fringes due to the halftone dot component while suppressing the deterioration of the original by taking in the original. . Therefore, the control unit 12 sets the focal position L = 3 corresponding to the minimum existence degree to the focal position setting unit 16.
Set via.

Step S8 (Importing All Image Information) The above steps S1 to S7 are "prescan" for obtaining an appropriate focal position, and then "book" for collecting all information of the original. Scan ”. That is, the entire surface of the document is scanned via the optical reading unit 10 set in the out-of-focus state as described above.
Then, all image information is collected and stored in the image memory 14.

As described above, a part of the original is collected as image information while changing the focal position, and the ratio of the halftone component to the original component is obtained as the degree of existence of the halftone component.
An out-of-focus focal position that can appropriately reduce moiré fringes while suppressing deterioration of document components can be determined. Therefore, it is possible to set an optimal focus position where only the halftone dot component can be reduced without the operator instructing the number of lines of the document as in the conventional example. In addition, since the optimal capture focal position is determined before reading the entire document, it is possible to absorb fluctuation factors such as variations between devices and daily fluctuations, and to reliably remove moiré fringes and obtain all image information of the document. Can be collected.

In the above description, in the filter processing for extracting the second frequency characteristic distribution Ps1 in which the halftone dot component is reduced from the first frequency characteristic distribution Ps0,
Although the median filter is used, a smoothing filter may be used instead.

For example, the first frequency characteristic distribution Ps0 is shown in FIG.
In the case where the signal has the distribution shown in FIG. 10, the portion where the signal strength changes sharply is smoothed by filtering with a smoothing filter to obtain the second frequency characteristic distribution Ps1 shown in FIG. FIG. 11 shows the difference between the first frequency characteristic distribution Ps0 and the second frequency characteristic distribution Ps1. In this difference, before and after the frequency of the halftone dot component is negative, the existence degree C of the halftone dot component is as described above.
In the equation (L), since the integration is performed after taking the absolute value, it is possible to obtain substantially the same result as the above-described processing by the median filter.

When a smoothing filter is used in the case where a step-like profile appears in the first frequency characteristic distribution Ps0 as shown by a dotted line in FIG. 9, a step-like shape is obtained as shown by a dotted line in FIG. Is smoothed and the profile collapses. In such a case, the area (dotted line in FIG. 11) which becomes negative when the difference is obtained is increased, and apparently the degree of existence C (L) of the halftone dot component is calculated to be small. . Therefore, in such a case, it may not be possible to obtain an appropriate focus position, and thus it is preferable to use a median filter rather than a smoothing filter.

In the above-described embodiment, the document components existing in the low frequency region of the first frequency characteristic distribution are reduced in order to enhance the detection sensitivity of the degree of presence, but the first frequency characteristic distribution is extracted. Beforehand, a filter process for reducing a low-frequency region may be performed on the image information of the captured document.

In the above description, the halftone dot component has one peak, but a plurality of peaks generally occur in a narrow frequency range. Since these plural peaks generally have a prominent intensity in a frequency region higher than that of the original document component, the same processing can be performed by performing the above-described processing, and the same effect is obtained. be able to.

[0066]

As is apparent from the above description, according to the method of the first aspect, prior to reading the entire original and taking in all the image information, the existence degree of the halftone dot component with respect to the original component is determined. The minimum focal position is obtained and set as the capture focal position of the optical reading means. Therefore, it is possible to set an optimal focal position where only the halftone dot component can be reduced without indicating the number of lines of the original, and it is possible to appropriately remove the moire fringes while suppressing the deterioration of the original component.

Furthermore, since the optimum capturing focal position is obtained before reading the entire document, it is possible to absorb fluctuation factors such as variations between apparatuses and daily fluctuations, and to reliably remove moire fringes. .

According to the second aspect of the present invention, by converting to a gray component, only the gray component can be processed later, and the capturing focal position can be set at high speed. it can.

According to the third aspect of the present invention, by reducing the low frequency component, the ratio of the halftone dot component in the first frequency characteristic distribution increases, and the degree of existence of the halftone dot component can be increased with high sensitivity. You can ask. Therefore, the capturing focal position can be obtained with high accuracy.

According to the fourth aspect of the present invention, by processing with a smoothing filter, the peak of the halftone dot component occurring in the high frequency region is smoothly attenuated, and the existence degree of the halftone dot component is obtained. be able to.

According to the fifth aspect of the present invention, when processing is performed by the median filter, even if a steep change exists in the original component of the first frequency characteristic distribution, it is possible to reduce the The halftone dot component can be attenuated without adversely affecting the portion. Therefore, the second frequency characteristic distribution can be substantially made only of the document component, and the accuracy can be improved as compared with the case where the processing is performed by the smoothing filter.

Further, according to the device inventions of claims 6 to 10, the method inventions of claims 1 to 5 can be suitably implemented.

According to the recording medium of the eleventh aspect, the method of the first aspect can be executed by causing a computer to execute a program stored in the recording medium.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a schematic configuration of an image input device according to an embodiment.

FIG. 2 is a flowchart illustrating an image input process.

FIG. 3 is a schematic diagram illustrating a relationship between a halftone dot angle and a frequency component.

FIG. 4 is a diagram for explaining the relationship between halftone dot angles of CMYK plates.

FIG. 5 is a graph schematically showing a first frequency characteristic distribution.

FIG. 6 shows a first example in which low-frequency components are reduced by filtering.
4 is a graph schematically showing a frequency characteristic distribution.

FIG. 7 is a graph schematically showing a second frequency characteristic distribution.

FIG. 8 is a graph schematically showing a difference between a first frequency characteristic distribution in which a low frequency component is reduced and a second frequency characteristic distribution.

FIG. 9 is a graph illustrating an example of processing by a smoothing filter.

FIG. 10 is a graph illustrating an example of processing by a smoothing filter.

FIG. 11 is a graph illustrating an example of processing by a smoothing filter.

FIG. 12 is a block diagram showing an image input device according to a conventional example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... Optical reading part (optical reading means) 12 ... Control part 14 ... Image memory 16 ... Focus position setting part (focal position setting means) 20 ... Image processing part 30 ... Gray component conversion part (gray component conversion means) 31 ... first frequency characteristic distribution extraction unit (frequency characteristic distribution extraction means) 32 ... filter processing unit (low frequency component reduction means) 33 ... second frequency characteristic distribution extraction unit (frequency characteristic distribution extraction means) 34 ... presence degree calculation unit ( Existence degree calculating means) L: Focus position Ps0: First frequency characteristic distribution Ps1: Second frequency characteristic distribution

Claims (11)

[Claims] 1. An image input method for inputting a document in an out-of-focus state, wherein a step of capturing a specific position of the document while changing a focal position of an optical reading unit and capturing image information for each focal position; Obtaining a frequency characteristic distribution for each focal position based on the information and extracting it as a first frequency characteristic distribution including a document component and a halftone component; and filtering the first frequency characteristic distribution to obtain a halftone component. Reducing and extracting a second frequency characteristic distribution for each focal position; and existence of a halftone dot component with respect to the document component for each focal position based on the first frequency characteristic distribution and the second frequency characteristic distribution. Calculating a degree, and setting a focal position corresponding to the smallest one of the degrees of presence as a capture focal position, and setting the optical reading means to the capture focal position. Image input method characterized by the extent, after performing was to capture the entire image information of the document. 2. The image input method according to claim 1, wherein the image information is converted into a gray component before obtaining a frequency characteristic distribution from the image information, and a frequency characteristic for each focal position is determined based on the gray component. An image input method, wherein a distribution is obtained and extracted as a first frequency characteristic distribution. 3. The image input method according to claim 1, wherein a process for reducing a low frequency component included in the image information or the first frequency characteristic distribution is performed. An image input method characterized by the following. 4. The image input method according to claim 1, wherein said filter processing is performed by a smoothing filter. 5. The image input method according to claim 1, wherein said filter processing is performed by a median filter. 6. An image input device for inputting a document in an out-of-focus state, wherein: an optical reading unit which captures a specific position of the document while changing a focal position and captures the image as image information for each focal position; A frequency characteristic distribution for each focal position is obtained based on the calculated frequency characteristic, and extracted as a first frequency characteristic distribution including a document component and a halftone dot component. The first frequency characteristic distribution is filtered to reduce the halftone component. Frequency characteristic distribution extracting means for extracting as a second frequency characteristic distribution for each position; based on the first frequency characteristic distribution and the second frequency characteristic distribution, determining a degree of existence of a halftone dot component with respect to the document component for each of the focal positions. Means for calculating the presence degree to be calculated; and a focus position corresponding to the smallest one of the presence degrees as a capture focus position; And a focus position setting means for setting only takes means, image input device being characterized in that so as to capture the entire image information of the document in a state set in the capture focal position. 7. An image input device according to claim 6, wherein the image information taken in by said optical reading means is converted into a gray component, and this is output as image information to said frequency characteristic distribution extracting means. An image input device comprising: means. 8. The image input device according to claim 6, further comprising a low frequency component reducing unit configured to reduce a low frequency component included in the image information or the first frequency characteristic distribution. An image input device characterized in that: 9. An image input device according to claim 6, wherein said frequency characteristic distribution extracting means performs said filter processing by a smoothing filter. . 10. The image input apparatus according to claim 6, wherein said frequency characteristic distribution extracting means performs said filter processing by a median filter. . 11. A recording medium storing a program for inputting an original in an out-of-focus state, wherein a specific position of the original is taken in while changing a focal position of an optical reading means, and image information for each focal position is obtained. A process of obtaining a frequency characteristic distribution for each focal position based on the image information, and extracting it as a first frequency characteristic distribution; and a process of filtering each of the first frequency characteristic distributions for each focal position. A process of extracting a second frequency characteristic distribution; a process of calculating a degree of existence of a halftone dot component with respect to the document component for each of the focal positions based on the first frequency characteristic distribution and the second frequency characteristic distribution; Setting the focal position corresponding to the smallest one of the degrees as the capturing focal position, and setting the optical reading means to the capturing focal position. A recording medium storing a program for controlling a computer so that all the image information of the original is fetched.