JP3461042B2 - Document 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 a document reading device mounted on a facsimile machine or the like for reading an image of a document.

[0002]

2. Description of the Related Art For example, an error diffusion process is used as one of pseudo intermediate processes when binarizing an image having a gradient in density such as a photographic image. In this error diffusion processing, the error in the surrounding pixels is accumulated in the relatively flat portion where the change in the density level in the input image is scarce, and the error is periodically eliminated. Therefore, there is a problem that a striped pattern appears periodically on the output image. This striped pattern is not noticeable when an image with a high gradation number is subjected to error diffusion processing, but when an image with a low gradation is processed,
It appears remarkably as shown in FIG. 12, which is a major cause of the deterioration of image quality.

In order to solve the above-mentioned problem, Japanese Patent Laid-Open No. 63-3509 discloses a method in which a random number is used as a threshold level for binarization when performing error diffusion processing, and a stripe peculiar to the error diffusion processing is used. A pseudo intermediate image processing device is shown which prevents the appearance of interference such as patterns.

[0004]

SUMMARY OF THE INVENTION
The pseudo-intermediate image processing device of Japanese Patent No. 63-3509 requires a random number generation circuit for generating random numbers as a threshold level. Therefore, there is a problem that the configuration of the circuit that processes the image signal becomes complicated and the cost of the device increases.

It is an object of the present invention to provide an original reading apparatus provided with a means capable of preventing the occurrence of interference such as a striped pattern peculiar to the error diffusion processing without significantly increasing the apparatus cost. .

[0006]

In order to solve the above problems, a first means of the present invention is a light source for irradiating an original with reading light and a photoelectric conversion for converting reflected light from the original into an analog image signal. An element, an analog signal amplification section for amplifying the analog image signal, a mode setting section for setting an error diffusion processing mode or a normal mode, and an amplification by the analog signal amplification section when the error diffusion processing mode is set. In an original reading apparatus including an image processing unit that performs an error diffusion process when a converted analog image signal is converted into a binary image signal, a light amount adjusting unit that adjusts the light amount of the reading light and the error diffusion processing mode setting. At this time, the light quantity adjusting unit reduces the light quantity of the reading light more than when the normal mode is set, and the analog signal amplification is performed in response to the light quantity decrease. Characterized in that a said control unit to increase the amplification factor of the analog image signal in.

The second means is a light source for irradiating the original with reading light, a photoelectric conversion element for converting the reflected light from the original into an analog image signal, and a mode setting for setting an error diffusion processing mode or a normal mode. Section, an analog / digital conversion section for converting the analog image signal into a digital image signal, and error diffusion processing when converting the digital image signal into a binary image signal when the error diffusion processing mode is set. In a document reading apparatus including an image processing unit, a light amount adjusting unit for adjusting the light amount of the reading light and the digital image signal is multiplied by an amplification coefficient when the error diffusion processing mode is set, and the digital image signal is processed by the image processing. And the light amount of the read light when the error diffusion processing mode is set and the light amount adjusting unit is more than when the normal mode is set. And a control unit to lower, the amplification factor, so as to correspond to the reduction in light quantity of said reading light during error diffusion processing mode setting, characterized in that the preset.

The third means is a light source for irradiating the original with the reading light, an image forming lens for forming an image of the reflected light from the original, and an electric image signal for the reflected light formed by the image forming lens. To a photoelectric conversion element, an electric signal amplifying unit that amplifies the electric image signal, a mode setting unit that sets an error diffusion processing mode or a normal mode, and the electric diffusion unit when the error diffusion processing mode is set. In a document reading apparatus including an image processing unit that performs error diffusion processing when converting an image signal into a binary image signal, a light amount adjusting mechanism that moves a shielding plate facing the light source, and when the error diffusion processing mode is set. The electric signal amplification unit is configured to move the shield plate to a light shielding position where the irradiation light amount of the reading light on the document is reduced by the light amount adjustment mechanism and to cope with the decrease of the irradiation light amount. Characterized by comprising a control unit for increasing the amplification factor of definitive said electrical image signal.

The fourth means is a light source for irradiating the original with reading light, an image forming lens for forming an image of the reflected light from the original, and an electric image signal for the reflected light formed by the image forming lens. A photoelectric conversion element for converting into an electric signal, an electric signal amplification section for amplifying the electric image signal, and a main scanning direction of reflected light emitted from the image forming lens, which is arranged between the image forming lens and a reading position of a document. A shading plate having slits for making the light quantity distribution uniform, a mode setting unit for setting an error diffusion processing mode or a normal mode, and a 2 from the electric image signal when the error diffusion processing mode is set. In a document reading apparatus including an image processing unit that performs error diffusion processing when converting to a value image signal, a light amount adjusting mechanism that changes an opening width of the slit is provided on the shading plate, When the error diffusion processing mode is set, the opening width of the slit is made narrower by the light amount adjusting mechanism than in the normal mode setting, and the electric amount in the electric signal amplifying section is reduced in response to a decrease in the amount of incident light to the photoelectric conversion element. And a control unit for increasing the amplification factor of the image signal.

The fifth means is a photoelectric conversion element for converting the reflected light from the document into an electric image signal, a drive section for applying a drive voltage to the photoelectric conversion element, and a normal mode or an error diffusion processing mode. A document reading apparatus including a reading mode setting unit for setting and an image processing unit for performing error diffusion processing when converting the electric image signal into a binary image signal when the error diffusion processing mode is set,
And a control unit configured to reduce the drive voltage by the drive unit when the error diffusion processing mode is set, as compared with when the normal mode is set, and to reduce an S / N ratio of an electric image signal output from the photoelectric conversion element. It is characterized by that.

[0011]

According to the above-mentioned first means, when the error diffusion processing mode is set, the control section reduces the reading light quantity by the light quantity adjusting section as compared with the normal mode setting, and the analog quantity is adjusted in response to the decrease in the light quantity. By increasing the amplification factor of the analog image signal in the signal amplification unit, the ratio of random noise superimposed on the original image signal in the analog image signal can be increased when the error diffusion processing mode is set, compared to when the normal mode is set. .

According to the second means, when the error diffusion processing mode is set, the multiplication section multiplies the digital image signal by the amplification coefficient set corresponding to the decrease in the light quantity of the reading light, and the control section By reducing the light quantity of the reading light by the light quantity adjustment unit compared to when the normal mode is set, the ratio of random noise superimposed on the original image signal in the digital image signal when the error diffusion processing mode is set is increased compared to when the normal mode is set. Can be made.

According to the third means, when the error diffusion processing mode is set, the control section causes the light amount adjusting mechanism to move the shield plate to a light shielding position where the light amount of the reading light to the original is reduced and the light is emitted. By increasing the amplification factor of the electric image signal in the electric signal amplifier in response to the decrease in the light amount, the amount of light emitted to the original in the main scanning direction is reduced more uniformly when the error diffusion processing mode is set than when the normal mode is set. In addition, the ratio of random noise superimposed on the original image signal in the electric image signal can be increased.

According to the fourth means, when the error diffusion processing mode is set, the control section causes the light amount adjusting mechanism to make the opening width of the slit in the shading plate narrower than that in the normal mode setting, and to the photoelectric conversion element. By increasing the amplification factor of the electric image signal in the electric signal amplifying section in response to the decrease in the incident light amount of It is possible to uniformly reduce the amount of incident light and increase the ratio of random noise superimposed on the original image signal in the electric image signal.

According to the fifth means, the control unit lowers the drive voltage when the error diffusion processing mode is set by the drive unit more than when the normal mode is set, and the S of the electric image signal output from the photoelectric conversion element is reduced. By reducing the / N ratio, it is possible to increase the ratio of random noise superimposed on the original image signal in the electric image signal when the error diffusion processing mode is set, compared to when the normal mode is set.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. 1 is a block diagram showing a first embodiment of a document reading apparatus of the present invention, FIG. 2 is a circuit diagram of a light amount adjusting section in the first embodiment, and FIG. 3 is a circuit diagram of an analog amplifying section in the first embodiment. FIG. 4 is a perspective view showing a document reading portion in the first embodiment. Reference numeral 1 is a light source constituted by a fluorescent lamp or the like, 2 is a light source lighting device for turning on / off a drive voltage applied to the light source 1, and 3 is a light amount adjusting section for setting a drive voltage to the light source 1. 4 is a photoelectric conversion element CCD (charge coupled device), 5
Is a CDD drive unit for applying a drive voltage to the CCD 4, and 6 is a CD
An analog amplifier for amplifying the analog image signal output from the CD 4, and an A / D 7 for converting the analog image signal amplified by the analog amplifier 6 into a digital image signal.
(Analog / digital) converter.

Reference numeral 8 is a CPU (central processing unit) for controlling the entire apparatus via a data bus 9, and 10 is a memory section for storing control programs for the CPU 8. 11 is an A / D converter 7
The image processing unit to which the digital image signal from the
It is AM (random access memory).

Reference numeral 13 denotes an operation section for inputting various operation signals, and the operation section 13 includes a mode setting section (not shown). The user selects the normal mode or the error diffusion processing mode according to the image quality of the original, and the C
Either one of the modes can be set for the PU 8.

As shown in FIG. 2, the light quantity adjusting section 3 has a resistance R
1 to R2, an open collector transistor 14 and a driver 15, and the analog amplification section 6 is composed of resistors R3 to R5, transistors 16 and 18, and a driver 17, as shown in FIG.

Further, in FIG. 4, 20 is a contact glass arranged above the light source 1, 21 is a mirror for reflecting the reflected light from the document D, 22 is a shading plate on which the reflected light from the mirror 21 is incident, 23 Is an image forming lens for forming an image of the reflected light emitted from the shading plate 22 on the CCD 4.
The shading plate 22 is provided with a slit 22a whose opening width is gradually narrowed from the end to the center in consideration of the COS4 law of the imaging lens 23. By this,
The light amount distribution of the reflected light imaged on the CCD 4 in the main scanning direction (direction of arrow B) is made uniform.

Next, the document D in the document reading device described above.
The reading operation for will be described. The document D set in the apparatus is conveyed on the contact glass 20 by a conveyance roller (not shown) in the direction of arrow A, and the reading light is emitted from the light source 1. The reflected light from the document D enters the imaging lens 23 via the contact glass 20, the mirror 21, and the shading plate 22, and the imaging lens 23 causes the CCD 4 to move.
Image on top. The CCD 4 reads the reflected light at regular intervals and converts it into an analog image signal. This analog image signal, after being amplified by the analog amplifier 6,
It is input to the A / D converter 7 and converted into a digital image signal. The A / D converter 7 outputs the digital image signal to the image processor 11 via the data bus 9. The image processing unit 11
The digital image signal is converted into a binary image signal by known image processing, and this binary image signal is output to an external image forming apparatus (not shown) connected via the RAM 12 or the data bus 9.

As described above, the document reading apparatus of this embodiment is configured so that the normal mode or the error diffusion processing mode can be set to the CPU 8 by the user's judgment. That is, the user matches the image quality of the image recorded on the document D before starting the reading of the document D described above,
Either one of the error diffusion processing mode and the normal mode is set to the CPU 8 by the operation unit 13. Generally, the error diffusion processing mode is set when reading an image having a gradient in density such as a photographic image, and the normal mode is set when reading a binary image in which characters or symbols are mainly recorded. .

FIG. 5 is a timing chart of control when reading is performed in the error diffusion processing mode. CPU8
When the error diffusion processing mode is set, outputs the error diffusion processing setting signal to the image processing unit 11, and simultaneously turns off the light amount adjustment signal and the gain adjustment signal. After the time T ₁ from this timing, the light source lighting signal is turned on to turn on the light source 1, and after the time T ₂ from turning on the light source 1, the reading of the document D is started, and the image processing unit 11 starts the image processing. At this time, the image processing unit 11 converts the digital image signal into a binary image signal due to the input of the error diffusion processing setting signal, and also performs the error diffusion processing to generate pseudo gradation in the binary image signal. Express.

The light amount adjusting section 3 causes the driver 15 to change the output of the base current from on to off when the light amount adjusting signal changes from on to off. As a result, the transistor 14 changes from on to off, and the drive voltage applied to the light source 1 when the error diffusion processing mode is set is lower than when the normal mode is set. That is, the light source lighting device 2
Is V, the drive voltage V ₁ applied to the light source 1 is V ₁ = V when the transistor 14 is on, but when the transistor 14 is off, the drive voltage V ₁ = V 1.
The drive voltage V ₂ applied to is expressed by (Equation 1).

[0025]

[Equation 1]

When the error diffusion processing mode is set, the drive voltage is set to V
By reducing the value to ₂ , the light amount of the reading light with which the document D is irradiated is lower than that in the normal mode setting. As a result, when the error diffusion processing mode is set, the ratio of random noise superimposed on the original image signal in the analog image signal that the CCD 4 reads and outputs reflected light from the document D can be increased more than when the normal mode is set. .

In the analog amplification section 6, the driver 17 changes the output of the base current from on to off when the gain adjustment signal changes from on to off. This causes transistor 16 to change from on to off,
When the error diffusion processing mode is set, the amplification factor of the analog image signal is increased more than when the normal mode is set. That is, when the transistor 16 is on, the analog amplifier 6
The amplification factor G ₁ of the analog image signal in is expressed by (Equation 2), and when the transistor 16 is off, the amplification factor G ₂ of the analog image signal is expressed by (Equation 3).

[0028]

[Equation 2]

[0029]

[Equation 3]

The amount of increase in the amplification factor G ₂ with respect to the amplification factor G ₁ is
It is set so as to compensate for the decrease in the analog image signal output from the CCD 4 due to the decrease in the amount of the reading light with which the document D is irradiated. By increasing the amplification factor to G ₂ when the error diffusion processing mode is set, the analog image signal input to the A / D conversion unit 7 can be omitted regardless of whether the normal mode or the error diffusion processing mode is set. The signal level can be kept constant, and the A / D converter 7 can process the analog image signal without being affected by the setting mode.

According to the document reading apparatus of the first embodiment described above, when the error diffusion processing mode is set, the light quantity of the reading light from the light source 1 is made lower than in the normal mode setting, and this light quantity reduction is dealt with. By increasing the amplification factor of the analog image signal with the error diffusion processing mode, the ratio of random noise superimposed on the original image signal in the analog image signal can be increased when the error diffusion processing mode is set, compared to when the normal mode is set. As a result, it is possible to prevent interference such as a striped pattern peculiar to error diffusion processing from appearing even if a random number generation circuit is not arranged in the circuit that processes the image signal. Even in such a case, it is possible to prevent a striped pattern from appearing in the reproduced image, and it is possible to obtain a document reading apparatus that can obtain a natural reproduced image at a low price.

FIG. 6 is a block diagram showing a second embodiment of the document reading apparatus of the present invention, and FIG. 7 is a circuit diagram of a multiplication unit in the second embodiment, in which the members described with reference to FIGS. Corresponding members are designated by the same reference numerals and description thereof is omitted. Reference numeral 30 denotes an A / D (analog / digital) converter that converts an analog image signal output from the CCD 4 into a digital image signal, and 31 amplifies the digital image signal input from the A / D converter 30 when the error diffusion processing mode is set. A multiplication unit that multiplies the coefficient α.

The multiplication unit 31 is composed of a multiplication circuit 32 in which a constant amplification coefficient α is set, and a changeover switch 33. The changeover switch 33 receives the changeover signal from the CPU 8 and the A / D conversion unit 30. Is connected to the contact 33a, and when the switching signal is not input, the output terminal of the A / D converter 30 is connected to the contact 33b.

As in the first embodiment, the document reading apparatus of the present embodiment is constructed so that the CPU 8 can be set to the normal mode or the error diffusion processing mode depending on the judgment of the user.

By setting the error diffusion processing mode, the light amount adjusting unit 3 reduces the light amount of the reading light with which the document D is irradiated as compared with the normal mode setting. As a result, when the error diffusion processing mode is set, the ratio of random noise superimposed on the original image signal in the analog image signal that the CCD 4 reads and outputs reflected light from the document D can be increased more than when the normal mode is set. .

Further, the CPU 8 outputs a switching signal to the multiplication circuit 32 via the data bus 9 when the error diffusion processing mode is set. By inputting the changeover signal, the changeover switch
The numeral 33 connects the output terminal of the A / D converter 30 to the contact 33a, so that the digital image signal from the A / D converter 30 is multiplied by the amplification coefficient α by the multiplication circuit 32.

The amplification coefficient α is output from the CCD 4 and decreases in the digital image signal converted by the A / D conversion unit 30 due to a decrease in the amount of reading light applied to the document D when the error diffusion processing mode is set. Is set to compensate. By multiplying the digital image signal by the amplification coefficient α when the error diffusion processing mode is set, the digital image signal input to the image processing unit 11 can be substantially omitted regardless of whether the normal mode or the error diffusion processing mode is set. The signal level can be kept constant, and the image processing unit 11 can process the digital image signal without being affected by the setting mode. Further, by compensating for the decrease in the light amount of the reading light by digital processing when the error diffusion processing mode is set, the processing of the image signal and the circuit configuration are simplified as compared with the case where analog processing is performed as in the first embodiment. You can

According to the document reading apparatus of the second embodiment, when the error diffusion processing mode is set, the light amount of the reading light from the light source 1 is made lower than in the normal mode setting, and the digital image is dealt with in response to this light amount reduction. By multiplying the signal by the amplification coefficient α, the ratio of random noise superimposed on the original image signal in the digital image signal can be increased when the error diffusion processing mode is set, compared to when the normal mode is set. As a result, it is possible to prevent interference such as a striped pattern peculiar to error diffusion processing from appearing even if a random number generation circuit is not arranged in the circuit that processes the image signal. Even if it is, it is possible to prevent a striped pattern from appearing in the reproduced image,
It is possible to obtain an original reading device that can obtain a natural reproduced image at a low price.

In the document reading apparatus of the first and second embodiments described above, when the error diffusion processing mode is set, the drive voltage applied to the light source 1 is made lower than that in the normal mode setting, so that the light enters the CCD 4. The light amount of the reflected light is reduced. However, depending on the characteristics of the light source 1,
When the drive voltage is lowered, the light amount distribution may become non-uniform in the main scanning direction. In order to uniformly reduce the light amount in the main scanning direction, the light emission intensity of the light source 1 may be kept constant and a light amount adjusting mechanism for blocking a part of the reflected light from the document D may be provided. Next, a document reading apparatus of the present invention equipped with such a light amount adjusting mechanism will be described.

FIG. 8 is a block diagram showing a third embodiment of the document reading apparatus of the present invention, and FIG. 9 is a perspective view showing an example of a light quantity adjusting mechanism in the third embodiment, based on FIGS. 1 to 4. The members corresponding to the members described are given the same reference numerals and the description thereof will be omitted. In the document reading device of the third embodiment, the light source lighting device 2 applies a constant drive voltage to the light source 1 when reading the document D, and causes the light source 1 to emit light with a constant light emission intensity. The light amount adjusting mechanism 40 is composed of a shield plate 41 and a drive unit that moves the shield plate 41, and the drive unit is connected to the drive roller 42 in pressure contact with the shield plate 41 and the rotation shaft of the drive roller 42. The drive motor 43 and the like are provided.

The CPU 8 outputs a light amount reduction signal to the light amount adjusting mechanism 40 when the error diffusion processing mode is set. By inputting the light intensity reduction signal to the light intensity adjustment mechanism 40, the drive motor
Reference numeral 43 moves the shielding plate 41 to a light shielding position that shields a part of the reading light emitted from the light source 1 to the document D. As a result, the amount of light emitted from the light source 1 to the document D can be reduced substantially uniformly in the main scanning direction, and it is possible to prevent the occurrence of uneven light intensity in the reflected light imaged on the CCD 4. At this time, the CPU 8 increases the amplification factor of the analog image signal in the analog amplifier 6 in order to compensate for the decrease in the irradiation light amount as in the case of the first embodiment. Also, CPU
Reference numeral 8 turns off the light amount reduction signal when the normal mode is set, and the drive motor 43 does not block the reading light emitted from the light source 1 to the document D by the shielding plate 41 when the light amount reduction signal is turned off. Move it to the standby position and hold it.

According to the document reading apparatus of the third embodiment, the CP
When the error diffusion processing mode is set, U8 moves the shield plate 41 to a light-shielding position that reduces the irradiation light amount of the reading light to the document D, and responds to the decrease of the irradiation light amount by the analog amplification unit 6
When the error diffusion processing mode is set, the amount of irradiation light on the original in the main scanning direction is reduced more uniformly by increasing the amplification factor of the analog image signal in Since the ratio of superimposed random noise can be increased, it is possible to prevent deterioration of image quality due to uneven light intensity in the main scanning direction. As a result, it is possible to prevent interference such as a striped pattern peculiar to error diffusion processing from appearing even if a random number generation circuit is not arranged in the circuit that processes the image signal. Even if it is, it is possible to prevent a striped pattern from appearing in the reproduced image,
It is possible to obtain an original reading device that can obtain a high quality and natural reproduced image at a low price.

FIG. 10 is a perspective view showing another example of the light quantity adjusting mechanism in the third embodiment. The light amount adjustment mechanism 50 arranged on the shading plate 22 includes an opening adjustment plate 51 and an opening adjustment plate 51.
Is moved upward or downward to change the opening width of the slit 22a.

The CPU 8 outputs a light amount reduction signal to the light amount adjusting mechanism 50 when the error diffusion processing mode is set. By inputting the light amount reduction signal to the light amount adjustment mechanism 50, the drive motor
The pin 52 rotates the pinion gear 52a meshed with the rack gear 51a of the opening adjustment plate 51 in the forward direction to move the opening adjustment plate 51 downward, thereby narrowing the opening width of the slit 22a. Also, the CPU 8
Turns off the light amount reduction signal when the normal mode is set. When the light amount reduction signal is turned off, the drive motor 52 rotates the pinion gear 52a in the reverse direction to move the opening adjustment plate 51 upward, thereby widening the opening width of the slit 22a. In the light amount adjusting mechanism 50, the opening adjusting plate 51 maintains the shape in which the opening width gradually narrows from the end of the slit 22a toward the center and narrows only the opening width.
The luminous intensity distribution of the reflected light imaged on the top can be reduced substantially uniformly in the main scanning direction.

In the document reading apparatus of the third embodiment described above, the light quantity reduction of the reading light is compensated by analog processing when the error diffusion processing mode is set, but this light quantity reduction is of course compensated for in the second embodiment. As in the case, it is possible to compensate by digital processing.

FIG. 11 is a block diagram showing the essential parts of a document reading apparatus according to the fourth embodiment of the present invention. Members corresponding to the members described with reference to FIG. 1 are designated by the same reference numerals. Omit it. FIG. 12 is a characteristic diagram showing the relationship between the CCD drive voltage and the S / N ratio. 60 is CCD4
It applies a driving voltage V _OD to a CCD driver for outputting a drive pulse P _CCD every predetermined time CCD 4.

The CPU 8 outputs a voltage drop signal to the CCD drive section 60 when the error diffusion processing mode is set. The CCD driving unit 60 receives the voltage drop signal, and the CCD 4
The drive voltage V _OD applied to V _OD1 is reduced from V _OD1 to V _OD2 .

The CCD 4 generally changes the S / N ratio of the image signal output according to the voltage value of the drive voltage V _OD . C
By driving the CD4 with the drive voltage V _OD in the recommended area shown in FIG. 12, it becomes possible to keep the S / N ratio stable and high, and as the drive voltage V _OD falls from the recommended area, the _S4 rapidly increases. The / N ratio decreases, and the drive voltage V _OD exceeds the recommended range, so that the possibility of damage increases.

Here, the drive voltage V _OD2 is set to be slightly lower than the lower limit value of the recommended area.
As a result, when the error diffusion processing mode is set, the CCD
It is possible to slightly reduce the S / N ratio of the analog image signal output from No. 4 to increase the ratio of random noise superimposed on the original image signal in the analog image signal as compared with the normal mode setting.

According to the document reading apparatus of the fifth embodiment, the random number generating circuit is not arranged in the circuit for processing the image signal.
Since it is possible to prevent the interference such as a striped pattern peculiar to the error diffusion process from appearing by simply performing the simple control of lowering the driving voltage V _OD applied to the CCD 4, it is possible to use the original image in a photograph having a density gradient. Even if there is, it is possible to prevent a striped pattern from appearing in the reproduced image, and it is possible to obtain a document reading device that can obtain a natural reproduced image at a low price.

[0051]

As described above, according to the first means of the present invention, when the error diffusion processing mode is set, the ratio of random noise superimposed on the original image signal in the analog image signal is higher than that in the normal mode setting. Since it is possible to prevent the occurrence of interference such as a striped pattern peculiar to the error diffusion processing, even if the random number generation circuit is not arranged in the circuit for processing the image signal, the density gradient of the original image can be increased. It is possible to prevent a striped pattern from appearing in a reproduced image even for a certain photograph or the like, and it is possible to obtain a document reading device that can obtain a natural reproduced image at a low price.

According to the second means, when the error diffusion processing mode is set, the ratio of random noise superimposed on the original image signal in the digital image signal can be increased more than in the normal mode setting. Even if the random number generation circuit is not arranged in the circuit that processes the signal, it is possible to prevent the occurrence of interference such as a striped pattern peculiar to the error diffusion processing, so even if the original image is a photograph with a density gradient, etc. It is possible to prevent a striped pattern from appearing in a reproduced image, and it is possible to obtain a document reading device that can obtain a natural reproduced image at a low price.

According to the third means, when the error diffusion processing mode is set, the irradiation light amount to the original in the main scanning direction is reduced more uniformly than in the normal mode setting, and the original image signal is converted into the original image signal in the electric image signal. By being able to increase the ratio of the random noise to be superimposed, even if the random number generation circuit is not arranged in the circuit that processes the image signal,
Since it is possible to prevent the occurrence of interference such as a striped pattern peculiar to the error diffusion processing, and since the uneven light intensity does not occur in the photoelectric conversion element, even if the original image is a photograph with a density gradient, etc. A pattern can be prevented from appearing, and a document reading device that can obtain a high quality and natural reproduced image can be obtained at a low price.

Further, according to the fourth means, when the error diffusion processing mode is set, the incident light amount of the reflected light of the document on the photoelectric conversion element in the main scanning direction is uniformly reduced as compared with the normal mode setting, and the electric image is obtained. Since the ratio of random noise superimposed on the original image signal in the signal can be increased, interference such as a striped pattern peculiar to the error diffusion process can be achieved without disposing a random number generation circuit in the circuit that processes the image signal. Since it is possible to prevent the occurrence of a stripe pattern in the reproduced image even when the original image is a photograph having a density gradient, it is possible to prevent a stripe pattern from appearing in the reproduced image. It is possible to obtain a document reading device that can obtain a reproduced image with high quality and at low cost.

Further, according to the fifth means, when the error diffusion processing mode is set, a simple control of lowering the drive voltage applied to the photoelectric conversion element is performed, and the electric image signal is generated more than when the normal mode is set. Since it is possible to increase the ratio of random noise superimposed on the original image signal, even if a random number generation circuit is not arranged in the circuit for processing the image signal, interference such as a striped pattern peculiar to the error diffusion process appears. Therefore, even if the original image is a photograph or the like having a density gradient, it is possible to prevent a striped pattern from appearing in the reproduced image, and obtain a document reading device that can obtain a natural reproduced image at a low price. be able to.

[Brief description of drawings]

FIG. 1 is a block diagram showing a first embodiment of a document reading apparatus of the present invention.

FIG. 2 is a circuit diagram of a light amount adjusting unit in the first embodiment.

FIG. 3 is a circuit diagram of an analog amplification unit in the first embodiment.

FIG. 4 is a perspective view showing a document reading unit in the first embodiment.

FIG. 5 is a timing chart of control when reading in the error diffusion processing mode in the document reading apparatus of the first embodiment.

FIG. 6 is a block diagram showing a second embodiment of the document reading apparatus of the present invention.

FIG. 7 is a circuit diagram of a multiplication unit in the second embodiment.

FIG. 8 is a block diagram showing a third embodiment of the document reading apparatus of the present invention.

FIG. 9 is a perspective view showing an example of a light amount adjustment mechanism in a third embodiment.

FIG. 10 is a perspective view showing another example of the light amount adjustment mechanism in the third embodiment.

FIG. 11 is a block diagram showing an essential part of a document reading apparatus according to a fourth embodiment of the present invention.

FIG. 12 is a characteristic diagram showing the relationship between the driving voltage of the CCD and the S / N ratio.

FIG. 13 is an explanatory diagram of a striped pattern generated in a reproduced image subjected to error diffusion processing.

[Explanation of symbols]

1 ... Light source, 2 ... Light source lighting device, 3 ... Light quantity adjusting unit,
4 ... CCD, 5,60 ... CCD drive section, 6 ... Analog amplification section, 7,30 ... A / D conversion section, 8 ... CPU, 11
... Image processing unit, 22 ... Shading plate, 22a ... Slit, 23 ... Imaging lens, 31 ... Multiplying unit, 40, 50 ... Light amount adjusting mechanism, 41 ... Shading plate, 51 ... Opening adjusting plate, D ...
Manuscript.

Claims (5)

(57) [Claims] 1. A light source for irradiating an original with reading light, a photoelectric conversion element for converting light reflected from the original into an analog image signal, an analog signal amplifier for amplifying the analog image signal, an error diffusion processing mode, or A mode setting unit for setting a normal mode and image processing for performing error diffusion processing when converting the analog image signal amplified by the analog signal amplification unit into a binary image signal when the error diffusion processing mode is set. And a light amount adjusting unit for adjusting the light amount of the reading light, and when setting the error diffusion processing mode, the light amount adjusting unit lowers the light amount of the reading light more than when the normal mode is set. And a control unit for increasing the amplification factor of the analog image signal in the analog signal amplification unit in response to the decrease in the light amount. An original reading device characterized by the above. 2. A light source for irradiating a document with reading light, a photoelectric conversion element for converting light reflected from the document into an analog image signal, a mode setting section for setting an error diffusion processing mode or a normal mode, and the analog image. An analog / digital conversion unit for converting a signal into a digital image signal, and an image processing unit for performing error diffusion processing when converting the digital image signal into a binary image signal when the error diffusion processing mode is set. In the original reading apparatus, a light amount adjusting unit for adjusting the light amount of the reading light, and a multiplying unit for multiplying the digital image signal by an amplification coefficient when the error diffusion processing mode is set and outputting the digital image signal to the image processing unit. And a control unit that reduces the light amount of the reading light by the light amount adjustment unit when the error diffusion processing mode is set, compared to when the normal mode is set. An original reading device, comprising: the amplification coefficient, wherein the amplification coefficient is set in advance so as to correspond to a decrease in the light amount of the reading light when the error diffusion processing mode is set. 3. A light source for irradiating a document with reading light, an image forming lens for forming an image of reflected light from the document, and a photoelectric conversion element for converting the reflected light formed by the image forming lens into an electric image signal. An electric signal amplifier for amplifying the electric image signal; a mode setting unit for setting an error diffusion processing mode or a normal mode; and a binary image from the electric image signal when the error diffusion processing mode is set. In a document reading apparatus including an image processing unit that performs error diffusion processing when converting to a signal, a light amount adjustment mechanism that moves a shielding plate facing the light source, and when the error diffusion processing mode is set,
The light amount adjusting mechanism moves the shield plate to a light-shielding position that reduces the irradiation light amount of the reading light to the original, and in response to the decrease of the irradiation light amount, the amplification factor of the electric image signal in the electric signal amplification unit. And a control unit for increasing the number of documents. 4. A light source for irradiating a document with reading light, an imaging lens for imaging reflected light from the document, and a photoelectric conversion element for converting the reflected light imaged by the imaging lens into an electric image signal. And an electric signal amplifying section for amplifying the electric image signal, and a light quantity distribution in the main scanning direction of the reflected light emitted from the imaging lens, which is arranged between the imaging lens and the reading position of the original. A shading plate having a slit formed therein, a mode setting unit for setting an error diffusion processing mode or a normal mode, and conversion of the electric image signal to a binary image signal when the error diffusion processing mode is set. In a document reading apparatus including an image processing unit that sometimes performs error diffusion processing, a light amount adjustment mechanism that changes the opening width of the slit is provided on the shading plate,
When the error diffusion processing mode is set, the opening width of the slit is narrowed by the light amount adjusting mechanism as compared to when the normal mode is set, and the amount of incident light to the photoelectric conversion element is reduced to correspond to the electric signal amplification section. An original reading apparatus comprising: a control unit that increases an amplification factor of an electric image signal. 5. A photoelectric conversion element for converting light reflected from an original into an electric image signal, a drive section for applying a drive voltage to the photoelectric conversion element, and a mode setting section for setting a normal mode or an error diffusion processing mode. In an original reading apparatus including an image processing unit that performs error diffusion processing when converting the electric image signal into a binary image signal when the error diffusion processing mode is set, when the error diffusion processing mode is set, And a control unit that lowers the drive voltage by the drive unit more than when the normal mode is set, and reduces the S / N ratio of the electric image signal output from the photoelectric conversion element. Document reader.