JP3230874B2 - Image reading device - Google Patents

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 which is applied to, for example, a facsimile apparatus and reads light reflected from a document by a CCD (Charge Coupled Device) line sensor and converts the light into an image signal.

[0002]

2. Description of the Related Art FIG. 8 is a schematic diagram showing a conventional image reading apparatus.

Reference numeral 1 denotes a pair of rollers for transporting the original P, 2 a transparent plate for guiding the original P and preventing foreign substances from entering the apparatus, and 3 illuminating the original P transported on the transparent plate 2. A light source, 4 is a mirror that reflects the reflected light from the document P, 5 is a white reference correction plate that corrects unevenness in the amount of light, 6 is a CCD line sensor that reads the formed reflected light and converts it into an electric signal, and 7 is This lens forms an image of the reflected light.

The above-mentioned known image reading apparatus is used, for example, in a facsimile apparatus. At this time, the resolution of the image reading apparatus is, for example, 8 pixels / mm in the main scanning direction, 3.85 pixels / mm in the sub-scanning direction. 7.7 pixels / m
m or about 15.4 pixels / mm, and has a relatively low resolution as compared with, for example, an image reading apparatus used in a copying machine. In such an image reading apparatus, it is difficult to accurately read the image of the document P, and a "line break", which is an image defect, may occur in a thin line portion in an output image.

In a conventional image reading apparatus, a white reference correction plate 5 is arranged in the optical path of reflected light in order to accurately read an original image and prevent "line breakage". The white reference correction plate 5 is formed with a slit 5a long in the main scanning direction M as shown in the explanatory view of FIG. 9, and this slit 5a is a slit having an opening width in the sub-scanning direction from the end toward the center position. The width is formed so as to be gradually narrowed, and has a minimum slit width d at the center position.

The reflected light that has passed through the lens 7 is unevenly distributed on the image plane such that the illuminance at the optical axis position has a peak corresponding to the cosine fourth law. Therefore, the image reading apparatus is configured so that the unevenness of the illuminance distribution in the main scanning direction M of the reflected light formed by the CCD line sensor 6 is corrected by cutting a part of the reflected light by the slit 5a. Have been. This allows C
Since the reading accuracy of the CD line sensor 6 is improved, occurrence of “line break” can be suppressed.

[0007]

However, since the illuminance distribution is geometrically corrected by the slit 5a,
When the slit width d is smaller than a predetermined value, there is a problem that the resolution is reduced due to the wave optics. That is, since the reflected light from the sub-scanning direction S is smaller than the main scanning direction M, the effective numerical aperture NA decreases, and the effective numerical aperture NA decreases.
The effective F-number defined by the reciprocal of

FIG. 11 shows an optical path length from the image surface of the document P to the lens 7 as L,

[0009]

[Outside 1]

[0010] Further, as shown in FIG.
Let D be the pupil diameter of the lens 7 held by. At this time, the effective numerical aperture NA _m in the main scanning direction M is NA _m = sin θ ₁ defined by the pupil diameter D as shown in the explanatory diagram of FIG.
The effective numerical aperture NA _{s in the} sub-scanning direction is defined by the slit width d as shown in the explanatory view of FIG.
A _s = sin θ ₂ . Also, the wavelength of the reflected light is λ, the effective F
Assuming that the number is F, the resolution ε (mm) in the optical system is represented by the equation (1) according to Rayleigh's law of resolution.

[0011]

Ε = 1.22 × λ × F When the slit width d is very narrow compared to the length of the slit 5a, the resolution ε _{s in the} sub-scanning direction S is larger than the resolution ε _{m in the} main scanning direction M. Therefore, in the image reading apparatus, the resolving power for the horizontal line formed in the main scanning direction M is deteriorated. For this reason, it is difficult to set the slit width d narrow so that the unevenness of the illuminance distribution of the reflected light is completely corrected.

FIGS. 14 and 15 show a line width and a CCD in an image.
FIG. 4 is a characteristic diagram illustrating a relationship with a video output output from a line sensor.

As shown in FIG. 16, the CCD line sensor 6 has a plurality of light receiving patterns 6a formed in the main scanning direction M on the reflected light image forming plane, and outputs the light exposure amount in each light receiving pattern 6a as a white output. Convert to output.

[0014] In FIG. 14, a video output which is output from the light receiving patterns 6a around the central portion in the main scanning direction M, which shows the relationship between the line width of the image at the scanning position, a line of V _m is the image shows a case where the horizontal lines formed in the main scanning direction M, V _s represents the case where the vertical line the line in the image is formed in the sub-scanning direction S.
Here, since the correction by the slit 5a of the white reference correction plate 5 is insufficient, the video output V of the horizontal line has the same line width.
_m has become a high output from the video output V _s of the vertical line. FIG. 15 shows the relationship between the video output output from the light receiving pattern 6a near the end in the main scanning direction M and the line width at the scanning position. The light receiving patterns 6a near the end, constant video output V _m corresponding to the direction, independent of the line width of the line, it is V _s is obtained. As a result, when a horizontal line scanned by the light receiving pattern 6a near the center is a fine line, "line breakage" easily occurs in the corresponding line in the output image.

An object of the present invention is to provide an image reading apparatus in which a video output output from a CCD line sensor is leveled without lowering resolution.

[0016]

In order to solve the above-mentioned problems, a first means of the present invention is that a slit for correcting the illuminance distribution of the reflected light upon incidence of reflected light from an original image surface is used for main scanning. A white reference correction plate formed in the direction, a lens for forming an image of the reflected light corrected by the white reference correction plate, and a plurality of light receiving patterns for reading the reflected light formed by the lens are arranged in the main scanning direction. An image reading device provided with a CCD (charge coupled device) line sensor, wherein the slit is formed so that a slit width is continuously narrowed from an end to a center position, and the slit at the center position is formed. The center position is set so that the resolution in the sub-scanning direction in the optical system defined by the effective numerical aperture calculated based on the width is substantially equal to the pitch between pixels read by the light receiving pattern. Characterized in that setting the slit width.

The second means includes a lens for forming an image of reflected light from a document image surface, and a CCD line on which a plurality of light receiving patterns for reading the reflected light formed by the lens are arranged in the main scanning direction. In the image reading apparatus provided with the sensor, the light receiving width in the sub-scanning direction of the light receiving pattern on the optical axis side is formed stepwise narrower than the light receiving pattern on the end side in the main scanning direction.

[0018]

The third means includes a lens for forming an image of the reflected light from the original image surface, and a plurality of means for reading the reflected light formed by the lens and outputting an electric signal having an intensity corresponding to an exposure amount. Are arranged in the main scanning direction,
A light receiving element disposed near the optical axis of the lens; and a CCD line sensor for converting the electric signal into an image signal by a shift register connected to the light receiving element. A grounded resistance element is connected in parallel with the connected shift register.

The fourth means includes a lens for forming an image of the reflected light from the original image surface, and a plurality of lenses for reading the reflected light formed by the lens and outputting an image signal having an intensity corresponding to the exposure amount. And a CCD line sensor in which the photoelectric conversion elements are arranged in the main scanning direction, wherein the photoelectric conversion elements are moved in the main scanning direction on the original image surface based on the image signal output from the photoelectric conversion elements. Judging that the formed horizontal pixels have been scanned, the lens
The photoelectric conversion element corresponding to near the optical axis and other than near the optical axis
The output levels of the image signals output from
As described above, the photoelectric device disposed near the optical axis of the lens.
The image processing apparatus further includes a correction unit that corrects the output level of the image signal output from the conversion element so as to decrease the output level.

[0021]

According to the first means, the resolution of the CCD line sensor is reduced by the white reference correction plate whose slit width is set so that the resolution in the sub-scanning direction is substantially equal to the pitch between pixels. Instead, part of the reflected light is cut so as to correct the unevenness of the illuminance distribution of the reflected light in the main scanning direction.

According to the second means, the light receiving width of the light receiving pattern arranged on the optical axis side in the sub-scanning direction becomes smaller stepwise than the light receiving pattern arranged on the end side in the main scanning direction.
The exposure area of the reflected light in the light receiving pattern is set by the D line sensor in accordance with the unevenness of the illuminance distribution of the reflected light in the main scanning direction, so that the exposure amount in the light receiving pattern is equalized.

[0023]

According to the third means, the illuminance distribution of the reflected light in the vicinity of the optical axis and in the area other than the vicinity of the optical axis is controlled by the resistance element connected between the light receiving element and the shift register near the optical axis of the lens. Even if it is non-uniform, a part of the electric signal output from the light receiving element is diverted to the resistive element corresponding to the non-uniform illuminance distribution, so that the electric signal input to the shift register is equalized.

According to the fourth means, the photoelectric conversion element
Photoelectric conversion elements document based on the image signal output from
The correction to that correction means to decrease the output level of the trigger image signals by the fact that scanning the horizontal pixels formed in the main scanning direction at the image plane, the photoelectric conversion element in the vicinity of the optical axis by scanning the horizontal line output The image signal to be output is selectively corrected.

[0026]

Embodiments of the present invention will be described below with reference to the drawings. In FIGS. 1 to 6, members corresponding to those described with reference to FIGS. 7 to 16 are denoted by the same reference numerals, and description thereof is omitted.

FIG. 1 is an explanatory view of a slit of a white reference correction plate in a first embodiment of the image reading apparatus of the present invention.

The effective numerical aperture NA _s effective numerical aperture NA _m and the sub-scanning direction S in the main scanning direction M is calculated by the formula in equation (2) as described with reference to FIGS. 12 and 13.

[0029]

(Equation 2)

[0030]

(Equation 3)

Here, the effective F number F in the main scanning direction M
effective F-number F _s of _m and the sub-scanning direction S is the effective numerical aperture NA _m respectively, are calculated based on the NA _s.

[0032]

(Equation 4)

[0033]

(Equation 5)

In the white reference correction plate 5 of the first embodiment,
The slit width d of the slit 15a is set so as not to lower the resolution of the CCD line sensor 6 and to exhibit the maximum correction capability for reflected light. To this end, if the pixel pitch in the sub-scanning direction S read by the CCD line sensor 6 is p, the resolution ε calculated by the equation (Equation 1) is not more than the pixel pitch p, and the slit width is as small as possible. It is sufficient to set d to be narrow, and this conditional expression is shown in (Equation 6).

[0035]

(Equation 6)

By transforming equation (6), equation (7) is obtained.

[0037]

(Equation 7)

By setting the slit width d to the minimum value obtained by (Equation 7), the unevenness of the illuminance distribution in the main scanning direction M of the CCD line sensor 6 can be maximized without lowering the resolution of the CCD line sensor 6. The video output can be flattened because the limit can be corrected. This improves the reading accuracy for horizontal lines, and
Can be suppressed.

[0039]

[Outside 2]

FIG. 2 shows a CCD according to a second embodiment of the present invention.
FIG. 4 is an explanatory diagram of a light receiving pattern of a line sensor.

A plurality of light receiving patterns 16a are formed in the main scanning direction M on the image plane of the CCD line sensor 6, and the light receiving patterns 16a arranged near the center are sub-scanned from the light receiving patterns 16a near the ends. The opening width in the direction S is reduced, and the opening area is reduced. Further, the light receiving pattern 16a in the vicinity of the central portion is formed such that the opening width in the sub-scanning direction S gradually decreases from the one arranged on the end side to the one arranged at the central optical axis position. Thus, the aperture area is minimized in the light receiving pattern 16a at the optical axis position.

The reflected light passing through the lens 7 is distributed such that the illuminance has a peak at the optical axis position as described above. In the CCD line sensor 6 of the second embodiment, the opening area of the light receiving pattern 16a is set so that the exposure amount in each light receiving pattern 16a is made equal in accordance with the illuminance distribution of the reflected light. As a result, the white reference correction plate 5
Therefore, even when the illuminance distribution near the center cannot be completely corrected, the exposure amount of the light receiving pattern 16a is flattened, and the reading accuracy of the CCD line sensor 6 with respect to the horizontal line can be improved without lowering the resolving power.

FIG. 3 is a configuration diagram of a CCD line sensor according to a reference example of the present invention.

The CCD line sensor 6 has a plurality of light receiving elements 6b arranged in the main scanning direction M, and each light receiving element 6b has a light receiving pattern 6a serving as an exposure area for reflected light. The light receiving elements 6b are each connected to a shift register 6d via a synchronous switch 6c. The shift register 6d is turned on when a contact signal output from the synchronous signal output circuit 21 goes high, and goes low. It turns off by becoming. When the synchronous switch 6c is turned on, the light receiving element 6b transfers the charge corresponding to the exposure amount of the light receiving pattern 6a to the shift register 6d. When the synchronous switch 6c is turned off, the shift register 6d transfers the accumulated charge. Output as video output.

The synchronizing signal output circuit 21 outputs a contact signal A which becomes H level at a constant period as shown in the timing chart of FIG. This contact signal A is directly output to the synchronous switch 6c near the end of the CCD line sensor 6, and is output via the delay circuit 22 to the synchronous switch 6c near the center. The delay circuit 22 delays the timing at which the H level for a contact signal A by the delay time t _r, and outputs a contact signal B H level is shortened with respect to the synchronous switch 6c. This allows
The charge accumulation time per pixel by the shift register 6d for the light receiving element 6b near the center is shorter than that near the end.

By shortening the accumulation time of the shift register 6d near the center by the delay circuit 22, the unevenness of the illuminance distribution of the reflected light causes the light receiving pattern 6 near the center to be reduced.
The CCD line sensor 6
Since the video output from the shift register 6d can be shared without lowering the resolution of the CCD line sensor 6, the reading accuracy of the CCD line sensor 6 with respect to the horizontal line can be improved.

Further, by variably capable of setting the delay time t _r at the delay circuit 22, by setting a longer delay time t _r of the optical axis side of the lens 7 from the end side, of the CCD line sensor 6 The reading accuracy can be further improved.

FIG. 5 shows a CCD according to a third embodiment of the present invention.
FIG. 4 is a configuration diagram of the line sensor. Members corresponding to the members described based on FIG.

A grounded resistance element 31 is connected in parallel between the synchronous switch 6c and the shift register 6d near the center. The resistance value of the resistance element 31 is set so that the resistance value on the optical axis side is lower than that on the end side.

When the synchronous switch 6c is turned on by the contact signal from the synchronous signal output circuit 21, electric charges corresponding to the exposure amount in the light receiving pattern 6a are output from the light receiving element 6b to the shift register 6d. At this time, since the resistance element 31 is connected in parallel between the synchronous switch 6c and the shift register 6d near the center, a part of the electric charge is shunted to the resistance element 31. The shunted charge is
It increases on the optical axis side from the end side.

By diverting a part of the electric charge output from the light receiving element 6b near the center to the resistance element 31, the exposure amount of the light receiving pattern 6a near the center is reduced due to the uneven illuminance distribution of the reflected light. Even if the light receiving pattern 6a is larger than the light receiving pattern 6a in the vicinity and the exposure amount in the light receiving pattern 6a near the end portion and the optical axis near the center is not uniform, the shift is performed without lowering the resolution of the CCD line sensor 6. Since the accumulated charge amount in the register 6d can be made equal, the reading accuracy of the CCD line sensor with respect to the horizontal line can be improved.

FIG. 6 is a structural view showing a main part in a fourth embodiment of the present invention. Members corresponding to those described with reference to FIG. 3 are denoted by the same reference numerals and description thereof is omitted. FIG. 7 is a flowchart showing processing for video output in the correction circuit of the fourth embodiment.

The shift register 6d near the end is connected to a data processing unit 51 such as a facsimile machine and outputs a video output to the data processing unit 51. The shift register 6d near the center is used for output correction. It is connected to a correction output terminal 41a which is one input terminal of the circuit 41, and outputs a video output to the output correction circuit 41. Correction circuit
A reference output α from a control unit (not shown) is input to a reference output terminal 41b, which is the other input terminal of 41.

The output correction circuit 41 outputs the video output V output from the shift register 6d at an arbitrary scanning timing n.
Execute the correction process for _(n) . As shown in FIG. 7, the output correction circuit 41 outputs the video output V _(n-1) output at the scanning timing n-1 one sub-scanning line before the scanning timing n.
Is larger than the reference output α (S1), and step S1 is performed.
If YES in step 1, it is determined whether the video output V _(n) is equal to or smaller than the reference output α (S2), and in step S2, YES
In this case, it is determined whether the video output V _{(n + 1)} output at the scanning timing n + 1 one sub-scanning line after the scanning timing n is larger than the reference output α (S3). In the case of YES in step S3, the light receiving element 6b moves horizontally at the scanning timing n.
It is determined that the pixel has been scanned, and the video output V _(n) is corrected by multiplying it by a correction coefficient γ (S4), and S1 to S3
If NO in any of the steps, the video output V _(n) is not corrected. Here, the correction coefficient γ is
This constant is set in each output correction circuit 41 so as to correspond to the unevenness of the reflected light in the range of 0 <γ <1. After outputting the video output V _(n) at the scan timing n to the data processing unit 51, the output correction circuit 41 calculates a value obtained by adding 1 to n in order to execute a correction process on the video output V _{(n + 1)} . n
(S5) Further, it is determined whether the reading of the image is completed at the scanning timing n (S6). If the reading is completed, the correction process is terminated. If the reading is not completed, the process returns to step S1 to return to step S1. The correction process for the output V _(n) is continued.

By the output correction circuit 41 connected to the shift register 6d near the center, the video output V _{(n-1) at} the continuous scanning timings n-1, n, n + 1 is obtained.
By comparing V _(n) and V _{(n + 1)} with the reference output α, it is determined that the light receiving element 6b has scanned the horizontal pixels at the scanning timing n, and when the horizontal line has been scanned, the video output V _{(n )}
By correcting to reduce the horizontal line, the reading of the horizontal line can be accurately determined, and the reflected light of only the video output when reading the horizontal line can be corrected according to the unevenness of the illuminance distribution, so that the video corresponding to the original image can be corrected. Output to data processing section
51 can be output.

[0056]

As described below, according to the first aspect of the present invention, the reflected light is corrected so as to correct the unevenness of the illuminance distribution in the main scanning direction without lowering the resolution of the CCD line sensor. By partially cutting, the exposure amount in the light receiving pattern becomes flat, so that the reading accuracy for the horizontal line can be improved.

Further, according to the second means, the exposure area of the reflected light in the light receiving pattern is set corresponding to the uneven illuminance distribution of the reflected light in the main scanning direction, and the exposure amount in the light receiving pattern is made equal. As a result, the reading accuracy for the horizontal line can be improved.

[0058]

According to the third means, a part of the electric signal output from the light receiving element is shunted in response to the uneven illuminance distribution of the reflected light near the optical axis and other than near the optical axis.
By flattening the electric signal input to the shift register, the reading accuracy with respect to the horizontal line can be improved.

According to the fourth means, even if the illuminance distribution of the reflected light is non-uniform near the optical axis and near the optical axis, the horizontal line is scanned and output in accordance with the non-uniform illuminance distribution. The image signal corresponding to the original image can be output to, for example, an image forming apparatus by selectively correcting the image signal to be output.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a slit of a white reference correction plate in a first embodiment of the image reading apparatus of the present invention.

FIG. 2 is an explanatory diagram of a light receiving pattern of a CCD line sensor according to a second embodiment of the present invention.

FIG. 3 is a configuration diagram of a CCD line sensor according to a reference example of the present invention.

FIG. 4 is a timing chart of a contact signal for a synchronous switch according to a reference example.

FIG. 5 is a configuration diagram of a CCD line sensor according to a third embodiment of the present invention.

FIG. 6 is a configuration diagram showing a main part in a fourth embodiment of the present invention.

FIG. 7 is a flowchart showing a process for a video output in a correction circuit according to a fourth embodiment of the present invention.

FIG. 8 is a schematic configuration diagram showing a conventional image reading apparatus.

FIG. 9 is an explanatory diagram of a slit of a white reference correction plate in a conventional image reading apparatus.

FIG. 10 is an explanatory diagram of a pupil diameter of a lens in a conventional image reading apparatus.

FIG. 11 is an explanatory diagram of an optical path length in the image reading apparatus.

FIG. 12 is an explanatory diagram of an effective numerical aperture in the main scanning direction.

FIG. 13 is an explanatory diagram of an effective numerical aperture in the sub-scanning direction.

FIG. 14 is a characteristic diagram showing a relationship between a line width in an image and a video output output from a CCD line sensor.

FIG. 15 is a characteristic diagram showing a relationship between a line width in an image and a video output output from a CCD line sensor.

FIG. 16 is an explanatory diagram of a light receiving pattern of a CCD line sensor in the image reading device.

[Explanation of symbols]

5 White reference correction plate 5a, 15a Slit 6 CC
D line sensor, 6a: light receiving pattern, 6b: light receiving element, 6c: synchronous switch, 6d: shift register,
7: Lens, 21: Synchronous signal output circuit, 22: Delay circuit, 31: Resistive element, 41: Output correction circuit.

Claims (4)

(57) [Claims] 1. A white reference correction plate having a slit formed in a main scanning direction for correcting the illuminance distribution of the reflected light upon incidence of reflected light from a document image surface, and a reflection corrected by the white reference correction plate. An image reading apparatus comprising: a lens for imaging light; and a CCD (charge coupled device) line sensor in which a plurality of light receiving patterns for reading reflected light imaged by the lens are arranged in a main scanning direction. Is formed such that the slit width is continuously reduced from the end toward the center position, and in the sub-scanning direction in the optical system defined by the effective numerical aperture calculated based on the slit width at the center position. An image reading apparatus, wherein a slit width at a center position is set such that a resolution is substantially equal to a pitch between pixels read by the light receiving pattern. 2. A CC in which a lens for forming an image of reflected light from a document image surface and a plurality of light receiving patterns for reading the reflected light formed by the lens are arranged in the main scanning direction.
In the image reading apparatus provided with a D-line sensor, the light receiving width in the sub-scanning direction in the light receiving pattern on the optical axis side is formed stepwise narrower than the light receiving pattern on the end side in the main scanning direction. Image reading device. 3. A lens for imaging reflected light from a document image surface, and a plurality of light receiving elements for reading the reflected light formed by the lens and outputting an electric signal having an intensity corresponding to an exposure amount. A CCD line sensor arranged in the scanning direction and converting the electric signal into an image signal by a shift register connected to the light receiving element, wherein the light receiving element is arranged near the optical axis of the lens. And a shift register connected to the light receiving element, wherein a grounded resistance element is connected in parallel. 4. A lens for imaging reflected light from an original image surface, and a plurality of photoelectric conversion elements for reading the reflected light formed by the lens and outputting an image signal having an intensity corresponding to an exposure amount. An image reading apparatus including a CCD line sensor disposed in the main scanning direction, wherein the photoelectric conversion element is formed on the original image plane in the main scanning direction based on an image signal output from the photoelectric conversion element. Is determined to have been scanned, and the vicinity of the optical axis of the lens and the optical axis
Image output from the photoelectric conversion 換素Ko corresponding to the non-close
In order to make the output levels of the image signals uniform with each other,
Output from the photoelectric conversion element disposed near the optical axis of the lens.
Image reading apparatus characterized by comprising a correction means for correcting to reduce the output level of the image signal.