JPH10178554A - Image reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image reader that improves image quality by adjusting image emphasis processing and a threshold level depending on the presence and the magnitude of noise. SOLUTION: An image reader reads a white reference board for a prescribed number of times before reading an original and discriminates whether or not noise of a prescribed level is generated from the maximum level H and the minimum level L of an image signal of the same picture element of a digital image signal at this time. When the noise is generated, the operation of a modulation transfer function(MTF) correction part is put off of an MTF correction coefficient set to the MTF correction part is set small and usual reading of the original is started (step S1 to S6). When no noise is generated, the operation of the MTF correction part is put on and usual reading of the original is started without revising the MTF correction coefficient set to the MTF correction part (step S7).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image reading apparatus, and more particularly, to an image reading apparatus which appropriately responds to noise of an image signal obtained by reading an image of a document.

[0002]

2. Description of the Related Art In recent years, C in which light receiving elements are arranged on a straight line has been developed.
An image of a document is scanned and read by a CD (Charge Coupled Device) image sensor or the like, and an image signal corresponding to the document image output in chronological order from the image sensor is quantized by digital technology to be a quantized image signal. Digital image reading apparatuses, such as digital copiers and digital facsimile apparatuses, which visualize or transmit a visual image on recording paper in response, have been put to practical use.

In photoelectric conversion from a document image to an image signal by an image sensor or the like, the MTF (Modu
lation transfer function). This MT
The deterioration of F is caused by optical components such as a lens and a mirror, and is caused by the image sensor itself such as aperture opening degree, transfer efficiency, and afterimage of the light receiving surface of the image sensor.
When a two-dimensional image sensor or the like is used, it is caused by an integration effect and scanning unevenness due to physical scanning (sub-scanning) in a direction orthogonal to individual scanning (main scanning). The higher the area, the greater the degradation.

[0004] The deterioration of the MTF is caused by a decrease in resolution of an image,
It usually causes image blur, blurred line images, etc.
Some correction processing is performed so that a good image signal can be obtained. As a specific implementation method, a method of correcting a target pixel by obtaining a correction value using peripheral pixels and performing high-frequency emphasis is the most general method.

Further, in recent years, external radio noises such as cellular phones and radio waves have been increasing.
It is an analog small signal and is easily affected by such external radio noise. In an image reading apparatus, how to deal with noise included in such an image signal is an important problem.

Conventionally, on the premise that noise is constantly generated, the image signal is intended to suppress the generation of noise due to minute fluctuations of the image signal and to obtain a good MTF correction effect. Processing device (Japanese Patent Laid-Open No. 7-24472)
No. 5 publication) has been proposed.

In this image signal processing apparatus, for example, on the assumption that noise is constantly generated, the slice level for binarization of an MTF-corrected output image signal is high, and Is conspicuous, the M corresponding to the negative direction
By setting the TF correction coefficient small, the effect of enhancing the negative fluctuation of the image signal is reduced or not enhanced,
Further, by setting the MTF correction coefficient corresponding to the positive direction edge to a required size, it is intended to suppress noise in a solid white portion and achieve a sufficient MTF correction effect. Similarly, when the slice level is low and the white noise in the solid black portion is conspicuous, the MTF correction coefficients in the respective edge directions are set in an inverse relationship to suppress the noise in the solid black portion and achieve a sufficient MTF correction effect. Trying to give up.

[0008]

However, in such a conventional image signal processing apparatus, an object of the present invention is to remove the noise on the assumption that the noise is constantly generated. Therefore, even when no noise is generated in the image signal, the processing is performed on the assumption that there is noise, so that there is a problem that the image quality is rather deteriorated. Also, the level of the noise generated in the image signal varies, and the conventional image signal processing device
Since the magnitude of the noise is not taken into consideration, there is a problem that appropriate processing cannot be performed and the image quality is rather deteriorated.

Therefore, according to the first aspect of the present invention, the noise level is determined based on the change level of the image signal of the same pixel among the digital image signals when the reading means reads the predetermined white reference member a plurality of times. If the noise level exceeds a predetermined level, the MTF correction coefficient or the like set in the image correction means for performing a change point enhancement process such as MTF correction on the digital image signal based on the noise level is changed. If the analog image signal contains extraneous noise by reading the document by relaxing the emphasis processing of the image change point by a predetermined amount, or turning off the emphasis processing, Detecting the magnitude of the extraneous noise and adjusting the degree of correction for emphasizing a change point of the image, such as MTF correction, in accordance with the presence and the magnitude of the extraneous noise. Or turning off the emphasis processing to make appropriate the emphasis processing of the change point such as the MTF correction when the external noise is not included, and to perform the MTF correction or the like when the external noise is included. It is an object of the present invention to provide an image reading apparatus capable of performing a process of emphasizing a change point while suppressing the influence of the external noise and improving the image quality of a read image.

According to a second aspect of the present invention, when the noise level exceeds a predetermined level, the threshold value of the binary conversion means converts the image signal into a binary image signal based on the threshold level based on the noise level. By changing the level, whether or not external noise is included in the analog image signal, the level of the external noise is detected, and the threshold is determined in accordance with the presence or absence and the level of the external noise. By changing the level, the binary conversion of the image signal when the external noise is not included is made appropriate, and the conversion of the noise to the black image signal when the external noise is included is prevented. Accordingly, it is an object of the present invention to provide an image reading apparatus capable of improving the image quality of a read image.

According to a third aspect of the present invention, the noise level is:
If the level exceeds the predetermined level and is equal to or lower than the second predetermined level, M
By changing the TF correction coefficient or the like, the emphasis processing of the image change point is relaxed by a predetermined amount, or the emphasis processing is turned off, and when the noise level exceeds the second predetermined level, the threshold of the binary conversion means is changed. By changing the level,
In accordance with the noise level, the threshold value of the image change point enhancement process and the binary conversion is appropriately adjusted to more appropriately prevent the influence of noise according to the size of the noise, and the image quality of the read image is improved. It is an object of the present invention to provide an image reading device that can be further improved.

According to a fourth aspect of the present invention, when the noise level exceeds a predetermined level and the set value of the MTF correction coefficient or the like or the threshold level is changed, the white reference member is read again and the digital image signal at that time is read. Performs an image enhancement process by an image correction unit and a conversion into a binary image signal by a binary conversion unit. If the binary image signal contains a black image signal exceeding a predetermined number, an MTF correction coefficient or the like After further changing the set value of the threshold level, the same processing is performed again from reading of the white reference member, and when the number of black image signals included in the binary image signal becomes equal to or less than a predetermined number, the MTF correction coefficient and the like at that time By reading the original at the threshold level and the threshold level, the threshold level of the image change point emphasis processing and the threshold level of the binary conversion are adjusted more appropriately, and the noise level is reduced. Based sound into a binary image signal which is the final image is more appropriately prevented, and its object is to provide an image reading apparatus capable of further improving the image quality of the read image.

[0013]

According to a first aspect of the present invention, there is provided an image reading apparatus which reads an image of a document and outputs an analog image signal, and outputs the analog image signal output by the reading means. Digital conversion means for converting the digital image signal into a digital image signal;
Image correction means for performing an MTF correction or the like based on a TF correction coefficient to emphasize a change point of an image; and converting the image signal corrected by the image correction means into a binary image signal based on a predetermined threshold level. Value conversion means, and the reading means reads a predetermined white reference member a plurality of times and performs digital conversion by the digital conversion means, of the digitally converted image signals, based on the change level of the image signal of the same pixel. The noise level is detected, and if the noise level exceeds a predetermined level, the MTF correction coefficient or the like set in the image correction means is changed based on the noise level to perform the emphasis processing of the image change point by a predetermined amount. The above-mentioned object is achieved by providing a control means for reading the original by relaxing the emphasis processing or turning off the emphasis processing. To have.

According to the above construction, the noise level is detected based on the change level of the image signal of the same pixel among the digital image signals obtained when the reading means reads the predetermined white reference member a plurality of times. If the noise level exceeds a predetermined level, an MTF correction coefficient or the like set in an image correction unit that performs change point enhancement processing such as MTF correction on a digital image signal based on the noise level is changed.
Since the reading of the original is performed by relaxing the emphasizing process of the image change point by a predetermined amount or turning off the emphasizing process, if the analog image signal contains extraneous noise, Detect the magnitude of the extraneous noise and, depending on the presence and magnitude of the extraneous noise,
It is possible to adjust the degree of correction for emphasizing a change point of an image such as MTF correction, or to turn off the emphasis processing, and to appropriately perform an emphasis processing of a change point such as MTF correction when no external noise is included. In addition to this, it is possible to perform a process of enhancing a change point such as MTF correction when external noise is included while suppressing the influence of the external noise. Therefore, the image quality of the read image can be improved.

In this case, for example, when the noise level exceeds the predetermined level, the control means determines that the threshold level of the binary conversion means is based on the noise level. May be changed.

According to the above arrangement, when the noise level exceeds a predetermined level, the threshold level of the binary conversion means for converting the image signal into a binary image signal based on the threshold level based on the noise level is set. Since the external noise is included in the analog image signal, or when it is included, the magnitude of the external noise is detected, and according to the presence or absence and the magnitude of the external noise,
The threshold level can be changed, the binary conversion of the image signal when no external noise is included can be made appropriate, and when the external noise is included, the noise can be converted to a black image signal. Can be prevented. Therefore, the image quality of the read image can be improved.

Further, for example, as set forth in claim 3, the control means sets the MTF to the image correction means when the noise level is higher than a predetermined level and equal to or lower than a second predetermined level. The enhancement process of the image change point is relaxed by a predetermined amount by changing a correction coefficient or the like, or the enhancement process is turned off, and the noise level is reduced to the second level.
The threshold level of the binary conversion means may be changed when the predetermined level is exceeded.

According to the above configuration, if the noise level is higher than the predetermined level and lower than the second predetermined level, the MTF
If the noise level exceeds a second predetermined level by changing the correction coefficient or the like to reduce the emphasis processing of the image change point by a predetermined amount, or if the emphasis processing is turned off, the threshold level of the binary conversion means , The threshold value of the image change point enhancement process and the threshold level of the binary conversion can be appropriately adjusted according to the noise level, and the influence of noise can be more appropriately prevented according to the size of the noise. be able to. Therefore, the image quality of the read image can be further improved.

Further, for example, as set forth in claim 4, the control means, when the noise level exceeds the predetermined level and changes a set value of the MTF correction coefficient or the like or the threshold level, The reading means is made to read the white reference member again, and the digital image signal output from the digital conversion means when the white reference member is read is subjected to the emphasis processing by the image correction means and the binary processing by the binary conversion means. After the conversion to an image signal, if the binary image signal contains a black image signal exceeding a predetermined number, after further changing the set value of the MTF correction coefficient or the like or the threshold level, The same processing is performed again from the reading of the white reference member,
When the number of black image signals included in the binary image signal becomes equal to or less than a predetermined number, the original may be read based on the MTF correction coefficient or the like and the threshold level at that time.

According to the above arrangement, when the noise level exceeds a predetermined level and the set value of the MTF correction coefficient or the like or the threshold level is changed, the white reference member is read again and the digital image signal at that time is read. The image enhancement processing by the correction means and the conversion to a binary image signal by the binary conversion means are performed. If the binary image signal contains a predetermined number of black image signals, the MTF correction coefficient or the threshold level is determined. After further changing the set value of, the same processing is performed again from reading of the white reference member, and when the number of black image signals included in the binary image signal becomes equal to or less than a predetermined number,
Since the original is read with the MTF correction coefficient and the like at that time and the threshold level, the threshold value of the image change point enhancement process and the binary conversion can be more appropriately adjusted, and the influence of noise is the final image. Prevention can be performed more appropriately based on the binary image signal. Therefore, the image quality of the read image can be further improved.

[0021]

Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings. It should be noted that the embodiments described below are preferred embodiments of the present invention, and therefore, various technically preferable limitations are added. However, the scope of the present invention is not limited to the following description. The embodiments are not limited to these embodiments unless otherwise specified.

FIGS. 1 to 5 show an image reading apparatus to which the first embodiment of the image reading apparatus of the present invention is applied. FIG. 1 shows a first embodiment of the image reading apparatus of the present invention. FIG. 3 is a main part circuit block diagram of the image reading apparatus 1 to which the embodiment is applied.

In FIG. 1, an image reading apparatus 1 includes a scanner 2, an image processing circuit 3, and a CPU (Central Processing Unit).
nit) 4 and a memory 5 and the like.
Includes an A / D converter 6, an MTF correction circuit 7, a black-and-white binary converter 5, and other image processing units (not shown). Other image processing units include, for example, a shading correction unit and a filter processing unit.

The scanner 2 is, for example, a CCD (Charge C).
An image scanner or the like using an Oupled Device is used to scan an original, read an image of the original at a predetermined resolution, and output an analog image signal to the A / D converter 6 of the image processing circuit 3. . Although not shown, the scanner 2 is provided with a white reference plate (white reference member) having a white surface and providing a reference white level, and the white reference plate is read at the time of noise processing described later.

An A / D converter (digital converter) 6 of the image processing circuit 3 converts an analog image signal input from the scanner 2 into a digital image signal, and outputs the digital image signal to the MTF correction unit 7. When noise is detected, the digitally converted digital image signal is
Output to U4.

The MTF correction section (image correction means) 7
It operates under the control of U4, and performs a predetermined filtering process, specifically, a spatial filtering process, on the digital image signal input from the A / D converter 6 based on the correction coefficient set from the CPU 4. As a result, high-frequency emphasis processing for compensating for MTF deterioration is performed, and output to the black-and-white binary conversion unit 8.

That is, the image signal output from the scanner 2 includes optical components such as lenses and mirrors, the aperture opening of the light receiving surface of the CCD image sensor, the transfer efficiency and residual image of the CCD image sensor, and the integration effect due to physical scanning. (Modulation Transfer Fu) caused by scanning and scanning unevenness
nction), and the MTF correction unit 7
Is compensated for. Further, since the deterioration of the MTF is more remarkable in a high frequency range, the MTF correction unit 7 performs an emphasis process on the image signal in the high frequency range to repair “blur” and improve the image quality. ing. As described above, since the MTF correction improves the quality of the image, if noise is included in the image signal, black spot noise is likely to occur on the ground by capturing the edge of the noise.
Therefore, the image reading device 1 has a CPU 4 as described later.
Detects the presence or absence of noise and the noise level, and performs MTF correction according to the presence or absence of noise and the noise level based on the value of an MTF correction coefficient set based on the presence or absence of the noise and the noise level, or turning off the MTF correction. ing.

The black-and-white binary conversion unit (binary conversion means) 8
The threshold level set from the PU 4 and the image signal input from the MTF correction unit 7 are compared, and the MTF correction unit 7
The image signal inputted from is converted to black and white binary and output to the CPU 4.

The memory 5 stores programs such as a basic processing program and a noise processing program of the image reading apparatus 1 and various data and system data necessary for executing the basic processing and the noise processing. It is used to temporarily store an image signal, and is also used as a work memory of the CPU 4.

The CPU (control means) 4 executes basic processing as the image reading apparatus 1 using the memory 5 as a work memory based on a program stored in the memory 5, and performs noise processing to be described later. I do.

Next, the operation of this embodiment will be described. In the image reading apparatus 1, an original is set on a scanner 2, and FIG.
As shown in (1), when the scan start key for instructing the start of reading is turned on (step S1), the CPU 4 sets the same line of the white reference plate in the scanner 2 as n.
(Step S2). An image signal obtained when the white reference plate is read n times is sequentially output from the scanner 2 to the A / D converter 6 of the image processing circuit 3, A / D converted by the A / D converter 6, and A / D converted. It is output to the CPU 4 as a D-converted image signal. The CPU 4 determines whether or not noise has occurred based on the A / D converted image signal input from the A / D converter 6 (Steps S3 and S3).
4, S7). That is, the CPU 4 reads the A / D-converted image signals for n times read by the n-time reading operation input from the A / D conversion unit 6 in, for example, (a) to (d) of FIG.
As shown in FIG. 3, the signal level of each reading is detected for each same pixel, and the highest signal level H (in FIG. 3, the A / D read at the (n-2) th time) among the n image signals of the same pixel is detected. The level B of the converted image signal and the lowest signal level L (level D of the A / D-converted image signal read n-th in FIG. 3) are obtained, and by comparing these, specifically, the highest signal is obtained. The difference between the level H and the lowest signal level L (H−
L is larger than a predetermined value ([H−
L]> constant value, or is a value obtained by dividing the difference (HL) between the highest signal level H and the lowest signal level L by the lowest signal level L larger than a predetermined constant% ([H−
L] / L> constant%), it is determined whether or not noise has occurred in the image signal (step S3).

In step S3, when [HL]> constant value or [HL] / L> constant%, the CPU 4
Determines that noise has occurred (step S4),
The MTF operation of the MTF correction unit 7 is turned off or the correction coefficient set in the MTF correction unit 7 is changed (step S5). Specifically, when noise is occurring, the CPU 4 turns off the operation of the MTF correction unit 7 or sets a small MTF correction coefficient to be set in the MTF correction unit 7.

When completing the setting of the MTF correction unit 7, the CPU 4 causes the scanner 2 to start reading of a normal document (regular scan), and reads the document (step S6).

If [HL]> constant value or [HL] / L> constant% in step S3, the CPU 4 determines that noise has not occurred (step S7). The scanner 2 starts reading a normal document (regular scan) without turning on the MTF operation of the MTF correction unit 7 and changing the correction coefficient set in the MTF correction unit 7 to read the document ( Step S6).

As described above, according to this embodiment, before reading the original, the white reference plate is read a plurality of times, and the signal level of the A / D converted image signal output from the A / D converter 6 at that time is changed. By making a comparison, the presence or absence of noise is detected, and when noise is occurring, the MTF correction unit 7 is turned off or the correction coefficient set in the MTF correction unit 7 is changed to a small value, and noise is generated. MTF when not
Since the manuscript is read without turning on the correction unit 7 and changing the correction coefficient to be set, the MTF correction unit 7 is appropriately operated according to the presence or absence of noise to improve image quality. When noise is occurring, the MTF correction unit 7 is turned off or the correction coefficient to be set is changed to a small value to prevent black spots from occurring on the background due to noise, thereby improving image quality. Can be done. That is, when noise occurs, the MTF correction unit 7 is turned on or the MTF correction unit 7 is turned on.
Is operated with the correction coefficient when there is no noise, as shown in FIG. 4, the noise N of the image signal when the original is read is emphasized by the MTF correction unit 7 and the black and white binary conversion unit 8 performs the predetermined operation. If the MTF correction unit 7 is turned off or the correction coefficient is changed to a small value, the noise N is reduced to the MTF correction unit 7 as shown in FIG. Are not emphasized so much, and are converted into white levels by the binarization processing in the black-and-white binary conversion unit 8, and do not appear as black points. As a result, the quality of the read image can be improved.

FIGS. 6 to 12 show a second embodiment of the image reading apparatus according to the present invention. In this embodiment, the MTF correction coefficient is set finely according to the noise level. The threshold level for binarization is set finely.

This embodiment is applied to the same image reading apparatus as that of the first embodiment. In the description of this embodiment, the image reading apparatus 1 shown in FIG. The description will be made by using the used symbols as they are.

In the image reading apparatus 1 of the present embodiment, a noise level / set level conversion table 10 as shown in FIG. 6 is stored in the memory 5, and the CPU 4 executes the MTF based on the detected noise level. The correction coefficient set in the correction unit 7 and the threshold level set in the black-and-white binary conversion unit 8 are changed. That is, as shown in FIG. 6, for example, as shown in FIG.
Six noise levels are set from level A to level F, and corresponding to these noise levels A to F, setting levels 1 to 6 correspond to MTF correction coefficients of “medium” and “small”, respectively. ”,“ OFF (OF
F) and threshold levels “large”, “medium”, “small”.

As shown in FIG. 2, the image reading apparatus 1 of the present embodiment reads a white reference plate a plurality of times when a scan is started, as in the image reading apparatus 1 of the first embodiment. The presence or absence of noise is determined by comparing the noise level of the same pixel.

When the CPU 4 determines that there is noise as shown in FIG. 7 (step S11), the CPU 4 converts the noise level into the noise level stored in the memory 5 and the set level as shown in FIG. It is checked which of the noise levels A to F in the table 10 is, and the noise level is obtained (step S1).
2). In FIG. 7, the noise level B is obtained. In this case, if the CPU 4 determines that there is noise without directly detecting the noise level, the noise level B may be set first.

After the noise level is set, the CP
U4 sets the set level set in the noise level-set level conversion table 10 corresponding to the noise level in the MTF correction unit 7 and the monochrome binary conversion unit 8 (step S13). In FIG. 7, the setting level is set to 2, and the setting level 2 is set to the MT level as shown in FIG.
The F correction coefficient is set to “small”.

Next, the CPU 4 causes the scanner 2 to read the white reference plate (step S14). The A / D converter 6 converts the image signal obtained by reading the white reference plate by the scanner 2 into an A / D signal.
After the conversion, the MTF correction unit 7 sets the above-mentioned set level 2 and the MTF correction unit 7 makes the MTF correction by the correction coefficient of the set level 2. Black and white binary conversion is performed according to the level (step S15). Since the set level is now set to the set level 2, the CPU 4 sets “high” as the threshold level in the monochrome binary conversion unit 8.

The CPU 4 detects the number of black points in the binary-converted image signal and checks whether the number of black points is smaller than a preset reference number (step S).
16) If the number of detected black points is larger than the reference number, it is determined that the influence of noise is large, and the set level that has been set is incremented by “1”, and step S14 is performed.
Return to (Step S17). At this time, in FIG. 7, the CPU 4 sets the setting level 3 as the setting level.

That is, since the white reference plate is provided in white, even if the image signal obtained by reading the white reference plate is converted into binary data, all the pixels should normally be converted to white data. As shown in FIG. 8, when noise is generated in the image signal read by the scanner 2, the MTF is added to the image signal.
When the correction unit 7 performs the MTF correction and the black-and-white binary conversion unit 8 performs the black-and-white binary conversion, black pixels (black points) are included as shown in FIG. Therefore, the CPU 4 detects the number of black points and checks whether the number of detected black points is smaller than a reference number set in advance as the number of black points where the influence of noise can be ignored.

Next, the CPU 4 causes the scanner 2 to read the white reference plate again (step S14), as described above.
This scanner 2 converts the image signal obtained by reading the white reference plate into an A /
A / D conversion is performed by the D conversion unit 6, the MTF correction unit 7 sets the set level 3 incremented, and the MTF correction unit 7 performs MTF correction using the correction coefficient of the set level 3, and then converts it to a black-and-white binary conversion unit. 8, the binary conversion is performed according to the threshold level set by the CPU 4 (step S1).
5). At this time, since the MTF correction coefficient is “OFF” and the threshold level is “high” as shown in FIG.
Without performing the correction, the digitally converted image signal of the A / D converter 6 is input to the black-and-white binary converter 8, and the black-and-white binary converter 8 performs black-and-white binary conversion at a "large" threshold level.

The CPU 4 detects the number of black points of the binary-converted image signal, and checks whether the number of black points is smaller than a preset reference number (step S16). When the number of black points is larger than the reference number, the set level is incremented by “1” and the same processing is performed as described above. At this time, if the set level is sequentially increased, the MTF correction by the MTF correction unit 7 is set to “OFF” and only the threshold level of the monochrome binary conversion unit 8 is reduced. As described above, by reducing the threshold level, it is possible to prevent white pixels from being read as black pixels due to the influence of noise. That is, as shown in FIG. 11, when the MTF correction is “OFF” and the threshold level is “high” or “medium”,
When the image signal due to noise lower than the threshold level is converted to a black pixel by the value conversion unit 8, as shown in FIG. 12, when the threshold level is lowered, the image signal due to noise becomes larger than the threshold level. Therefore, it is not converted to a black pixel, but is converted as a white pixel. Therefore, the influence of noise can be eliminated by reducing the threshold level.

In step S16, if the number of black points in the binary-converted image signal is smaller than the reference number, it is determined that the influence of noise has been appropriately suppressed, and the scanner 2 reads a normal document. (Normal scan) is started, and the document is read (step S18).

As described above, according to the present embodiment, when the noise level exceeds a predetermined level, the threshold level of the black-and-white binary conversion unit 8 is changed based on the noise level. Whether or not external noise is included in the image signal of the image signal, when the external noise is included, the magnitude of the external noise is detected, and the threshold level can be changed according to the presence and the magnitude of the external noise, It is possible to appropriately perform binary conversion of an image signal when no external noise is included, and to prevent conversion of the noise into a black image signal when external noise is included. it can. Therefore, the image quality of the read image can be improved.

If the noise level exceeds the predetermined level and is equal to or lower than the second predetermined level (noise level C in FIG. 7), the MTF correction coefficient is changed to reduce the emphasis processing of the image change point by a predetermined amount. Alternatively, the emphasizing process is turned off, and if the noise level exceeds the second predetermined level, the threshold level of the black-and-white binary conversion unit 8 is changed, so that the image change point is emphasized according to the noise level. The threshold levels of the processing and the binary conversion can be appropriately adjusted, and the influence of noise can be more appropriately prevented according to the magnitude of the noise. Therefore, the image quality of the read image can be further improved.

Further, when the noise level exceeds a predetermined level and the set value of the MTF correction coefficient or the threshold level is changed, the white reference plate is read again, and the digital image signal at that time is enhanced by the MTF correction unit 7. Processing (MTF correction processing) and conversion to a black-and-white binary image signal by the black-and-white binary conversion unit 8, and if the black-and-white binary image signal contains a black image signal exceeding a predetermined number, the MTF correction coefficient Alternatively, after further changing the set value of the threshold level, the same processing is performed again from the reading of the white reference plate. Since the original is read at the coefficient and threshold level,
The threshold level of the image change point enhancement process and the threshold value of the binary conversion can be adjusted more appropriately, and the influence of noise can be more appropriately prevented based on the binary image signal that is the final image. Therefore, the image quality of the read image can be further improved.

Although the invention made by the inventor has been specifically described based on the preferred embodiments, the invention is not limited to the above-described embodiments, and various modifications may be made without departing from the gist of the invention. Needless to say, it can be changed.

In the above-described embodiment, only the MTF correction unit 7 is provided as an image correction means for performing an emphasis process on a change point of an image, but another image correction circuit may be provided.

[0053]

According to the image reading apparatus of the present invention, the change level of the image signal of the same pixel among the digital image signals when the reading means reads the predetermined white reference member a plurality of times. , And if the noise level exceeds a predetermined level, the MT set in the image correction means for performing a change point enhancement process such as MTF correction on the digital image signal based on the noise level.
By changing the F correction coefficient or the like, the emphasis processing of the image change point is relaxed by a predetermined amount, or the emphasis processing is turned off, and the original is read. Therefore, external noise is included in the analog image signal. Or if it is included,
Detecting the magnitude of the extraneous noise, adjusting the degree of correction that emphasizes a change point of an image, such as MTF correction, or turning off the emphasis processing in accordance with the presence / absence and magnitude of the extraneous noise. It is possible to appropriately perform a process of enhancing a change point such as MTF correction when external noise is not included, and to enhance a process of enhancing a change point such as MTF correction when external noise is included. Can be performed while suppressing the influence of the external noise. Therefore, the image quality of the read image can be improved.

According to the image reading apparatus of the second aspect, when the noise level exceeds a predetermined level, the image signal is converted into a binary image signal based on the threshold level based on the noise level. Since the threshold level of the binary conversion means is changed, whether or not external noise is included in the analog image signal, the level of the external noise is detected, and the presence or absence and the level of the external noise are detected. , The threshold level can be changed in accordance with, the binary conversion of the image signal when the external noise is not included can be made appropriate, and when the external noise is included, the threshold level can be changed. Can be prevented from being converted into a black image signal. Therefore, the image quality of the read image can be improved.

According to the image reading apparatus of the third aspect, when the noise level is higher than the predetermined level and equal to or lower than the second predetermined level, the MTF correction coefficient or the like is changed to enhance the image change point. If the noise level exceeds the second predetermined level, the threshold level of the binary conversion means is changed. The threshold levels of the point enhancement processing and the binary conversion can be appropriately adjusted, and the influence of noise can be more appropriately prevented according to the magnitude of the noise. Therefore, the image quality of the read image can be further improved.

According to the image reading apparatus of the fourth aspect, when the noise level exceeds a predetermined level and the set value of the MTF correction coefficient or the like or the threshold level is changed, the white reference member is read again and the white reference member is read. Image enhancement processing by the image correction means to the digital image signal at the time
The conversion into a binary image signal by the value conversion means is performed,
If the value image signal contains more than a predetermined number of black image signals, the MTF correction coefficient or the like or the threshold level is further changed, and the same process is performed again from the reading of the white reference member. When the number of black image signals included in the binary image signal becomes equal to or less than a predetermined number, the original is read at the MTF correction coefficient or the like and the threshold level at that time.
The threshold level of the image change point enhancement process and the threshold value of the binary conversion can be adjusted more appropriately, and the influence of noise can be more appropriately prevented based on the binary image signal that is the final image. Therefore, the image quality of the read image can be further improved.

[Brief description of the drawings]

FIG. 1 is a main part circuit block diagram of an image reading apparatus to which a first embodiment of the image reading apparatus of the present invention is applied.

FIG. 2 is a flowchart illustrating noise processing performed by the image reading apparatus of FIG. 1;

3 is a diagram showing an example of an image signal when a white reference plate is read a plurality of times in order to detect noise by the image reading device of FIG. 1;

FIG. 4 is a diagram illustrating an example of an image signal in a case where a noise image signal is converted as a black point while MTF correction is on.

FIG. 5 is a diagram illustrating an example of an image signal when MTF correction is turned off and a noise image signal is reduced and converted as a white point.

FIG. 6 is a diagram illustrating an example of a noise level-setting level conversion table stored in a memory of the image reading apparatus according to the second embodiment of the present invention.

FIG. 7 is a flowchart illustrating noise processing performed by the image reading apparatus according to the second embodiment of the present invention;

FIG. 8 is a diagram illustrating an example of an analog image signal in a state where noise has occurred in an analog image signal obtained by reading a white reference plate.

9 is a diagram showing an image signal obtained by performing MTF correction on the analog image signal of FIG. 8 with a large MTF correction coefficient and performing black-and-white binary conversion at a large threshold level.

FIG. 10 is a diagram illustrating an image signal obtained by performing MTF correction on the analog image signal of FIG. 8 with a small MTF correction coefficient or not performing MTF correction, and performing a black-and-white binary conversion at a small threshold level.

FIG. 11 is a diagram illustrating a state in which noise is binary-converted as a black point by a large threshold level when MTF correction is off.

FIG. 12 is a diagram showing a state in which noise is binary-converted as a white point by a small threshold level when MTF correction is off.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image reading apparatus 2 Scanner 3 Image processing circuit 4 CPU 5 Memory 6 A / D conversion part 7 MTF correction part 8 Monochrome binary conversion part 10 Noise level-setting level conversion table

Claims (4)

[Claims] A reading means for reading an image of a document and outputting an analog image signal; a digital converting means for converting the analog image signal output from the reading means into a digital image signal; and the digital converting means At least a predetermined MT
Image correction means for performing MTF correction or the like based on an F correction coefficient to emphasize a change point of an image, and converting the image signal corrected by the image correction means into a binary image signal based on a predetermined threshold level. Value conversion means, and the reading means reads a predetermined white reference member a plurality of times and performs digital conversion by the digital conversion means, of the digitally converted image signals, based on the change level of the image signal of the same pixel. The noise level is detected, and if the noise level exceeds a predetermined level, the MTF correction coefficient or the like set in the image correction means is changed based on the noise level to perform the emphasis processing of the image change point by a predetermined amount. Control means for reading the document by relaxing only or turning off the emphasis processing. 2. The apparatus according to claim 1, wherein said control means changes said threshold level of said binary conversion means based on said noise level when said noise level exceeds said predetermined level. Image reading device. 3. When the noise level is higher than a predetermined level and equal to or lower than a second predetermined level, the control means changes the MTF correction coefficient and the like set in the image correction means to change the image change point. Of the emphasis processing is reduced by a predetermined amount, or the emphasis processing is turned off, and the noise level is
2. The image reading apparatus according to claim 1, wherein the threshold level of the binary conversion means is changed when the threshold value exceeds the second predetermined level. 4. The control means causes the reading means to read the white reference member again when the noise level exceeds the predetermined level and the set value of the MTF correction coefficient or the like or the threshold level is changed. Causing the digital image signal output by the digital conversion unit when the white reference member is read to be subjected to the enhancement processing by the image correction unit and conversion to a binary image signal by the binary conversion unit. If the binary image signal contains more than a predetermined number of black image signals, the MTF correction coefficient or the like or the threshold level is further changed, and the same processing is performed again after reading the white reference member. And when the number of black image signals included in the binary image signal becomes equal to or less than a predetermined number, the MTF correction coefficient and the like and the threshold Le, the image reading apparatus according to any one of claims 1 to 3, characterized in that reading of the document.