JPH10327321A - Picture reader and its method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To read a picture free from blur without adjusting a distance between the surfaces of a contact sensor and an original platen by each solid body by deciding edge emphasizing gain and a filtering coefficient based on a modulation transfer function(MTF) obtained by calculating the maximum and minimum values of picture data read from a stripe belt. SOLUTION: Before reading an original, a shading correction circuit 14 generates a shading correcting value, a line imaging sensor 10 reads a stripe belt and an MTF value arithmetic circuit 16 generates an MTF value from maximum and minimum values in one line of picture data to store in a register 18. At the time of reading the original, an edge emphasizing & filtering circuit 17 sets high edge emphasizing gain and a low filtering coefficient in the case of a low MTF value and sets low edge emphasizing gain and a high filtering coefficient in the case of a low MTF value. Thereby, the blur and roughness of the picture is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading apparatus and an image reading method, and more particularly to an image reading apparatus and an image reading method suitable for reading an original in a facsimile apparatus or a copying apparatus.

[0002]

2. Description of the Related Art Conventionally, an image reading apparatus for reading a document is mounted on a facsimile apparatus or a copying apparatus having a book document reading mode for scanning and reading a book or the like placed on a document table. In an image reading apparatus of this type, mechanical components constituting the apparatus have a short focal depth, particularly in an image reading apparatus using a contact sensor as one-dimensional photoelectric conversion means for photoelectrically converting reflected light from a document and outputting a video signal. Therefore, it is necessary to adjust the distance from the surface of the contact sensor to the surface of the original, that is, the distance from the surface of the original table glass to each individual. For this reason, the number of manufacturing steps is increased, leading to an increase in cost.

[0003]

However, in the above-described conventional image reading apparatus, it is necessary to adjust the distance from the surface of the contact sensor to the surface of the original, that is, the distance from the surface of the original table glass to each individual. For,
The manufacturing process increased and the cost increased, but if the above distances were not accurately adjusted, the MTF (Modulat
ion transfer function (a change in contrast of a sine wave pattern image as a function of spatial frequency) is deteriorated and the image is blurred. Also,
If the precision of the mechanical parts is increased so that the distance to the surface of the platen glass does not have to be adjusted for each individual, there is a problem that the parts themselves increase in cost.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described circumstances, and does not increase the precision of mechanical parts and does not adjust the distance from the surface of the contact sensor to the surface of the document table glass for each individual. Even if the distance slightly varies, the MTF
It is an object of the present invention to provide an image reading apparatus and an image reading method capable of reading an image in which the image is not too low and the image is not blurred.

[0005]

According to an aspect of the present invention, there is provided an image reading apparatus for shading correction of a video signal obtained by photoelectrically converting reflected light of a document based on shading correction data. After generating the shading correction data and before reading the original,
Calculation means for calculating the MTF based on the maximum and minimum values of image data read from a stripe for MTF (Modulation Transfer Function) measurement, and determination means for determining an edge emphasis gain and a smoothing coefficient based on the calculation result And characterized in that:

In order to achieve the above object, according to a second aspect of the present invention, when the MTF is low, the determining means increases the edge emphasis gain and lowers the smoothing coefficient,
Is high, the software control is performed so that the edge enhancement gain is low and the smoothing coefficient is high.

In order to achieve the above object, the invention according to claim 3 is characterized in that, when the MTF is low, the determining means increases the edge emphasis gain and lowers the smoothing coefficient.
Is high, the edge enhancement gain is low and the smoothing coefficient is high.

According to a fourth aspect of the present invention, there is provided an image reading method for shading correction of a video signal obtained by photoelectrically converting reflected light of a document based on shading correction data. Later, before scanning the original, the MTF (Modulatio
n Transfer Function: a calculation step of calculating the MTF based on the maximum value and the minimum value of the image data read from the stripe band for measurement, and a determination step of determining an edge enhancement gain and a smoothing coefficient based on the calculation result. It is characterized by having.

In order to achieve the above object, the invention of claim 5 is characterized in that in the determining step, the edge enhancement gain is increased and the smoothing coefficient is decreased when the MTF is low, and the edge enhancement gain is decreased when the MTF is high. It is characterized in that control is performed to increase the smoothing coefficient.

[0010]

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

FIG. 2 is an external perspective view showing an external configuration of the image reading apparatus according to the present embodiment. The image reading device includes a platen glass 2 on which a document to be read is placed.
1, a white reference plate and a stripe band 2 used for generating a shading correction value by a shading correction circuit described later and measuring and calculating an MTF value by an MTF calculation circuit
2 is provided in the apparatus main body 20. still,
The other configuration of the image reading apparatus is not related to the essence of the present invention, and the description is omitted.

FIG. 1 is a block diagram showing the internal configuration of the image reading apparatus according to the present embodiment. The image reading device includes a line image sensor 10, a sample hold / offset correction circuit 11, an A / D conversion circuit 12,
An auto gain control (AGC) circuit 13, a shading correction circuit 14, a line memory 15,
F value calculation circuit 16 and edge emphasis & smoothing circuit 1
7, a register 18, and a binarization circuit 19.

The function of each part of the image reading apparatus will be described in detail. The line image sensor 10 is a one-dimensional photoelectric conversion element (CCD or contact sensor), and photoelectrically converts reflected light from a document and outputs a video (VDO) signal. I do.
The sample hold / offset correction circuit 11 samples and holds the video signal output from the line image sensor 10 and performs offset correction. A / D
The conversion circuit 12 converts an analog signal output from the sample hold / offset correction circuit 11 into a digital signal.

Auto gain control (AGC: Aut)
o Gain control circuit 13 adjusts the range of the signal output from the A / D conversion circuit 12. The shading correction circuit 14 performs shading correction (correction of color unevenness of the input image generated by the line image sensor 10) on the signal output from the auto gain control circuit 13 based on the shading correction data stored in the line memory 15. Do. The line memory 15 stores shading correction data.

The MTF value calculation circuit 16 calculates the MTF (Modulation T) from the maximum value and the minimum value in one line of image data.
ransfer Function: a value representing the change in contrast of the sine wave pattern image as a function of the spatial frequency. The edge emphasis & smoothing circuit 17 selects an edge emphasis gain and a smoothing coefficient (smoothing: a process of performing smoothing so that jagged lines do not occur as much as possible). The MTF value calculated by the MTF value calculation circuit 16 is stored in the register 18. The binarization circuit 19
The image data is binarized by gamma conversion or error diffusion processing.

FIG. 3 is an explanatory diagram showing the stripe band 22 described above. The stripe band 22 is a line alternating between black and white as shown in the figure, and its line density is such that the resolution of the line image sensor (contact sensor) 10 is 400 d, for example.
For pi (dot per inch), the stripe is, for example, 3
With 96 dpi, moiré occurs once in 100 pixels. FIG. 4 is an explanatory diagram showing a video image output from the line image sensor (contact sensor) 10 when the stripe band 22 is read. That is, the video image output of the line image sensor (contact sensor) 10 has undulation as shown in FIG.

Next, the operation of the image reading apparatus according to the present embodiment having the above configuration will be described.
Before reading the original, first, the shading correction circuit 14
Then, the MTF value is calculated and generated by the MTF value calculation circuit 16 by reading the stripe band 22 by the line image sensor (contact sensor) 10. The generation of the shading correction value is omitted here. In order to generate the MTF value, a line image sensor (contact sensor) 10 is moved by a driving unit (not shown) to the stripe band 2.
Move to position 2. Here, the reading operation is performed as follows.

That is, the video image output from the line image sensor (contact sensor) 10 is subjected to sample hold and offset correction by a sample hold / offset correction circuit 11, and A / D conversion is performed by an A / D conversion circuit 12. Will be Further, the range is adjusted by an auto gain control (AGC) circuit 13, and shading correction is performed by a shading correction circuit 14 based on shading correction data stored in a line memory 15. Further, the MTF value calculation circuit 16
, The MTF value is calculated from the maximum value and the minimum value in the image data of one line, and the MTF value is stored in the register 18.

The MTF value is MTF = (max-mi
n) / (max + min) (max: maximum value, min: minimum value). Aperture (a) of line image sensor (contact sensor) 10
When the area (area where light easily passes, aperture) is large, the MTF value is small and the image is blurred. When the aperture of the line image sensor (contact sensor) 10 is small, the MTF value is large and the image is sharp. . Also, line image sensors (contact sensors)
If the distance from the surface of the platen 10 to the surface of the platen glass 21 deviates from the design value, the MTF value decreases and the image becomes blurred.

Next, when a document is read by the image reading device, the image reading device operates as follows.
That is, the drive means (not shown) moves the line image sensor (contact sensor) 10 to a document reading reference position beside the white reference plate 22. While reading the document from the start position, the drive means (not shown) moves the line image sensor (contact sensor) 10 along the document table glass 21 in the right front direction in FIG.

The video image output from the line image sensor (contact sensor) 10 is a sample-and-hold
The sample / hold and offset correction are performed by the offset correction circuit 11, and the A / D conversion circuit 12 performs A / D conversion.
D conversion is performed. Further, the range is adjusted by an auto gain control (AGC) circuit 13, and shading correction is performed by a shading correction circuit 14 based on shading correction data stored in a line memory 15. Further, according to the MTF value stored in the register 18, the edge emphasis & smoothing circuit 17 selects an edge emphasis gain and a smoothing coefficient when performing the processing.

Here, for example, when the MTF value is low, the blur of the image is corrected by setting the gain of the edge enhancement high. When the MTF value is high, by setting the gain of edge enhancement low, it is possible to prevent the image from being roughened due to excessive edge enhancement. When the MTF value is low, the blurring of the image is prevented by setting a low smoothing coefficient, and when the MTF value is high, the smoothing coefficient is set high to prevent the moire and prevent the line image sensor. (Contact sensor) Prevents an image from being rough due to a sensitivity variation of the sensor 10.

After the edge emphasis gain and smoothing coefficient are selected by the edge emphasis & smoothing circuit 17 as described above, the binarization circuit 19 performs γ conversion (γ: ratio of change in image brightness to input / output voltage). ) And error diffusion processing, the image data is binarized.

As described above, according to the present embodiment,
A line image sensor that photoelectrically converts reflected light from a document and outputs a video signal;
A shading correction circuit 14 for performing shading correction on the basis of the shading correction data, a white reference plate for generating shading correction data and a stripe band 22 for MTF measurement, and a stripe band after generating the shading correction data and before reading the original. 22, an MTF value calculation circuit 16 for calculating the MTF based on the maximum value and the minimum value of the image data read from the image data 22;
When F is high, there is an edge emphasis & smoothing circuit 17 for setting the edge emphasis gain to be low and the smoothing coefficient to be high. Even if the distance slightly varies without adjusting the distance to the surface 21 for each individual, it is possible to perform image reading in which the MTF does not become too low and the image is not blurred.

The present invention may be applied to a system constituted by a plurality of devices or to an apparatus constituted by a single device. A storage medium storing software program codes for realizing the functions of the above-described embodiments is supplied to a system or an apparatus, and a computer (or CPU or MPU) of the system or the apparatus executes the program code stored in the storage medium. Needless to say, this can also be achieved by executing the reading.

In this case, the program code itself read from the storage medium implements the functions of the above-described embodiment, and the storage medium storing the program code constitutes the present invention.

As a storage medium for supplying the program code, for example, a floppy disk, hard disk, optical disk, magneto-optical disk, CD-ROM, CD
-R, a magnetic tape, a nonvolatile memory card, a ROM, or the like can be used.

When the computer executes the readout program code, not only the functions of the above-described embodiment are realized, but also the OS and the like running on the computer are actually executed based on the instructions of the program code. It goes without saying that a part or all of the above-described processing is performed, and the functions of the above-described embodiments are realized by the processing.

Further, after the program code read from the storage medium is written into a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer, based on the instruction of the program code, It goes without saying that the CPU included in the function expansion board or the function expansion unit performs part or all of the actual processing, and the processing realizes the functions of the above-described embodiments.

[0030]

As described above, according to the first aspect of the present invention, there is provided an image reading apparatus for shading-correcting a video signal obtained by photoelectrically converting reflected light of a document based on shading correction data. After the data is generated and before the original is read, the MTF (Modul
Calculation means for calculating the MTF based on the maximum and minimum values of the image data read from the stripe band for measurement (Transfer Function), and determination means for determining the edge enhancement gain and the smoothing coefficient based on the calculation result. Therefore, without increasing the precision of the mechanical parts, and without adjusting the distance from the surface of the photoelectric conversion unit that photoelectrically converts the reflected light of the original and outputting a video signal to the surface of the original placing glass for each individual. , Even if the distance varies slightly,
It is possible to perform image reading in which the MTF is not too low and the image is not blurred.

According to the second aspect of the present invention, the determining means increases the edge enhancement gain and lowers the smoothing coefficient when the MTF is low, and lowers the edge enhancement gain and increases the smoothing coefficient when the MTF is high. Since the software control is performed in this manner, it is possible to perform image reading without blurring the image, similarly to the first aspect of the present invention.

According to the third aspect of the present invention, the determining means increases the edge enhancement gain and lowers the smoothing coefficient when the MTF is low, and decreases the edge enhancement gain and increases the smoothing coefficient when the MTF is high. Is configured as a hardware circuit that controls
As in the first aspect of the present invention, it is possible to perform image reading without blurring the image.

According to a fourth aspect of the present invention, there is provided an image reading method for shading correction of a video signal obtained by photoelectrically converting reflected light of a document based on shading correction data, wherein the shading correction data is generated before the document is read. In addition, MTF (Modulation Transfer Funct
ion) has a calculation step of calculating the MTF based on the maximum value and the minimum value of the image data read from the measurement stripe band, and a determination step of determining an edge emphasis gain and a smoothing coefficient based on the calculation result. Without increasing the precision of the mechanical parts, and without adjusting the distance from the surface of the photoelectric conversion means that photoelectrically converts the reflected light of the original and outputting a video signal to the surface of the original placing glass for each individual, Even if the distance slightly varies, it is possible to perform image reading in which the MTF does not become too low and the image is not blurred.

According to the fifth aspect of the present invention, in the determining step, when the MTF is low, the edge enhancement gain is increased and the smoothing coefficient is decreased, and when the MTF is high, the edge enhancement gain is decreased and the smoothing coefficient is increased. With such control, it is possible to perform image reading without blurring the image, similarly to the invention of the fourth aspect.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an internal configuration of an image reading device according to an embodiment of the present invention.

FIG. 2 is an external perspective view showing an external configuration of the image reading apparatus according to the embodiment of the present invention.

FIG. 3 is an explanatory diagram showing a stripe band of the image reading device according to the embodiment of the present invention.

FIG. 4 is an explanatory diagram showing a waveform of a video image output signal when the image reading device according to the embodiment of the present invention reads a stripe band.

[Explanation of symbols]

 Reference Signs List 10 line image sensor 11 sample hold offset correction circuit 12 A / D conversion circuit 13 AGC circuit 14 shading correction circuit 15 line memory 16 MTF value calculation circuit 17 edge emphasis & smoothing circuit 18 register 19 binarization circuit

Claims (5)

[Claims] An image reading apparatus that performs shading correction on a video signal obtained by photoelectrically converting reflected light of a document based on shading correction data, the MTF (Modulation Transfer Function) after generating the shading correction data and before reading the document. A) calculating means for calculating the MTF based on the maximum value and the minimum value of the image data read from the measuring stripe band; and determining means for determining an edge emphasis gain and a smoothing coefficient based on the calculation result. Characteristic image reading device. 2. The method according to claim 1, wherein when the MTF is low, the edge enhancement gain is increased and the smoothing coefficient is decreased.
2. The image reading apparatus according to claim 1, wherein when the MTF is high, software control is performed so that the edge enhancement gain is low and the smoothing coefficient is high. 3. The determining means increases an edge emphasis gain and lowers a smoothing coefficient when the MTF is low,
2. The image reading device according to claim 1, wherein the image reading device is configured as a hardware circuit that controls the edge enhancement gain to be low and the smoothing coefficient to be high when the MTF is high. 4. An image reading method for performing shading correction on a video signal obtained by photoelectrically converting reflected light of a document based on shading correction data, wherein the MTF (Modulation Transfer Function) is generated after the shading correction data is generated and before the document is read. A) calculating the MTF based on the maximum value and the minimum value of the image data read from the measurement stripe band; and determining the edge enhancement gain and the smoothing coefficient based on the calculation result. Characteristic image reading method. 5. In the determining step, when the MTF is low, the edge enhancement gain is increased and the smoothing coefficient is decreased. When the MTF is high, the edge enhancement gain is decreased and the smoothing coefficient is increased. Image reading method.