JPH1023257A - Binarization circuit and image reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To automatically set an input image range of a binarization means to a proper value, in response to an actual state of an analog signal outputted from an image sensor. SOLUTION: An analog image signal ASIG, generated by applying photoelectric conversion to a reflected light from an original D by an image sensor 1, is binarized by an A/D converter 91. A low reference VREF-, being the lower limit of an input range of the A/D converter 91, is generated variably by a D/A converter 92 depending on a low reference decision means 11a, based on a black reference signal outputted from the image sensor 1, when a light source 6 is not lighted. Furthermore, a high reference VREF+, being the higher limit of an input range, is generated variably by the D/A converter 92 depending on a high reference decision means 11b, based on a white reference signal generated by the image sensor 1, by applying photoelectric conversion to the reflected light from a transmission white roller 5f.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a binarization circuit for binarizing an image signal in an analog state to generate binary image data, and using the binarization circuit, a reflected light from a document by an image sensor. The present invention relates to an image reading apparatus that binarizes an image signal generated by photoelectric conversion and generates binary image data corresponding to an image formed on the document.

[0002]

2. Description of the Related Art FIG. 4 is a diagram showing a configuration of a main part of a conventional image reading apparatus.

An analog image signal ASIG output from an image sensor 1 using a CCD (Charge Coupled Device) or the like is amplified by an amplifier 2 and then input to an A / D converter 3. The A / D converter 3 samples and holds the analog image signal ASIG, and then performs binarization to generate binary data (binary image data).

The A / D converter 3 takes in a signal in a level range represented by reference voltages VREF + and VREF-. That is, in the example of FIG. 4, the reference voltage VREF
+ Is 3 V, which is a voltage of 5 V reduced by the voltage drop of the diode in the reverse direction, and the reference voltage VREF- is 0 V when grounded.
The analog image signal ASIG is taken in the following range.

[0005]

Therefore, as shown in FIG. 5, the reference voltages VREF + and VREF- are all within the input range of the binarizing means such as the A / D converter 3, as shown in FIG. It is desirable that the maximum level of the analog image signal ASIG is set as close as possible to the reference voltage VREF +, and the minimum level of the analog image signal ASIG is set as close as possible to the reference voltage VREF-.

Conventionally, however, the reference voltage VREF
+ And VREF- are fixedly determined. For this reason, in order to maintain an appropriate relationship between the input range of the binarizing means and the level of the analog image signal ASIG, it is necessary to improve the variation accuracy of the output level of the image sensor.

Further, even if the accuracy of the variation of the output level of the image sensor is improved, the variation cannot be completely eliminated. Therefore, it is necessary to appropriately set the reference voltages VREF + and VREF- so as to cope with a certain variation. There is. For this purpose, it is necessary to perform a detailed analysis work, which requires a lot of time, and also requires advanced know-how.

The present invention has been made in view of such circumstances. The first object of the present invention is to set the input range of the binarizing means to an appropriate value corresponding to the actual state of the analog signal. To provide a binarization circuit which can be easily set.

Second, there is provided an image reading apparatus capable of automatically setting an input range of a binarizing means to an appropriate value according to an actual state of an analog signal output from an image sensor. It is in.

[0010]

In order to achieve the first object, the present invention provides a method for converting an input analog signal into, for example, an A / D signal.
Binarization means such as a converter takes in a range of a predetermined low-level reference voltage or more and a predetermined high-level reference voltage or less to binarize, and the low-level reference voltage is set to a low-level reference value specified from the outside. In response, a low-level reference voltage generating means such as a D / A converter is variably generated, and the high-level reference voltage is set to, for example, D in accordance with a high reference setting value specified from the outside.
A high-level reference voltage generating means such as a / A converter is variably generated.

According to another aspect of the present invention, an analog signal having a level corresponding to the amount of reflected light generated by photoelectrically converting reflected light from a document by an image sensor, for example, A A predetermined low-level reference voltage or more by binarizing means such as a / D converter,
The data is taken in a range equal to or less than a predetermined high-level reference voltage and binarized, and the low-level reference voltage is determined by a row reference setting unit determined by a row reference determining unit based on a predetermined black reference signal output from the image sensor. For example, a low-level reference voltage generating means such as a D / A converter is variably generated according to the value, and the high-level reference voltage is determined by a high-reference determining means based on a predetermined white reference signal output from the image sensor. High-level reference voltage generating means such as a D / A converter is variably generated according to the determined high reference setting value.

By taking these means, an arbitrary analog signal to be inputted or an analog signal generated by the image sensor is converted by the binarizing means into a predetermined low-level reference voltage or more and a predetermined high-level reference voltage or less. The low-level reference voltage and the high-level reference voltage are taken in the range and binarized, respectively, in response to an external instruction or a predetermined black reference signal and a white reference signal output by the image sensor. It is variably set according to the low reference setting value and the high reference setting value determined by the low reference determining means and the high reference determining means based on the setting. Therefore, it is possible to appropriately set the input range of the binarization unit according to the actual state of the analog signal supplied to the binarization unit.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing a main configuration of an image reading apparatus according to this embodiment. The same parts as those in FIG. 4 are denoted by the same reference numerals, and detailed description thereof will be omitted.

As shown in FIG. 1, the image reading apparatus according to the present embodiment comprises a line sensor 1, an amplifier 2, a document transport mechanism 5, a light source 6, a light source driving unit 7, a sensor driving unit 8, a binarizing circuit 9, It has a signal level detection unit 10 and a control unit 11. Among them, the light source driving unit 7, the sensor driving unit 8, the binarizing circuit 9, and the signal level detecting unit 10 are connected to the control unit 11 via the system bus 12.

The document transport mechanism 5 includes a kick roller 5a,
The self-supply rubber plate unit 5b, self-supply roller 5c, transmission drive roller 5d, pinch roller 5e, transmission white roller 5f, transmission drive roller 5g, and pinch roller 5h. The original transport mechanism 5 is configured such that the kick roller 5a, the self-supply roller 5c, the transmission driving roller 5d, and the transmission driving roller 5g receive the torque of a motor (not shown) via a transmission mechanism (not shown) and rotate. The documents D set on the document tray T are conveyed one by one from right to left in the figure.

The light source 6 irradiates the original D transported by the original transport mechanism 5 with light below the transmission white roller 5f. The light source driving unit 7 supplies power to the light source 6 and controls turning on / off.

The line sensor 1 is formed by integrating a large number of photoelectric conversion elements (not shown) in a one-dimensional array, and a direction in which the arrangement direction of the photoelectric conversion elements intersects the conveying direction of the document D (depth in the figure). Direction). The line sensor 1 generates and outputs an analog image signal ASIG for one line by sequentially outputting electric charges obtained by each photoelectric conversion element performing photoelectric conversion of light emitted from the light source 6 and reflected by the document D. . Drive control of the line sensor 1 is performed by the sensor drive unit 5, and the above-described operation is performed by the sensor drive unit 8.
Is periodically repeated at a timing synchronized with the drive signal given from the controller. Then, the analog image signal ASIG output from the line sensor 1 is given to the amplifier 2. Amplifier 2
Amplifies the analog image signal ASIG with a gain determined so that the analog image signal ASIG is at a level suitable for performing the binarization processing in the binarization circuit 9, and performs the binarization circuit 9 and signal level detection. Give to part 10.

The binarizing circuit 9 comprises an A / D converter 91 and D / A converters 92 and 93.
The analog image signal ASIG amplified by the amplifier 2 is A
/ D converter 91.

The A / D converter 91 outputs the row reference VREF- and D
Reference VR output from the A / A converter 93
The analog image signal ASIG is taken in a level range determined by EF +, binarized, and binary data is generated.

The D / A converters 92 and 93 are respectively
It is connected to the control unit 11 via the system bus 12. The D / A converter 92 outputs a low reference VREF- having a voltage level corresponding to the low reference set value set by the control unit 11, and the D / A converter 93 outputs a high reference set by the control unit 11. Outputs the high reference VREF + at the voltage level according to the set value. In this embodiment, the D / A converters 92 and 93 are each supplied with 5 V as a high level and 0 V as a low level by grounding. VREF- and high reference VREF + are
It is changed within the range of 5V.

The signal level detecting section 10 detects the level of the analog image signal ASIG amplified by the amplifier 2,
The detection result is notified to the control unit 11 via the system bus 12.

The control section 11 controls the overall operation of each section to realize the operation as an image reading apparatus.
The control unit 11 includes, for example, a microcomputer as a main control circuit, and includes a row reference determination unit 11a in addition to a well-known general control unit in an image reading apparatus.
And high reference determining means 11b. The row reference determining means 11a determines the level of the row reference VREF- based on the level of the analog image signal ASIG in a state where the light source 6 is not turned on, that is, the level of the black reference signal, and sets the corresponding row reference VREF-. The processing for setting the value in the D / A converter 92 is performed. Further, the high reference determining means 11b determines the level of the analog image signal ASIG when the line sensor 1 photoelectrically converts the reflected light from the transmission white roller 5f with the light source 6 turned on, that is, the level of the white reference signal. Thus, the level of the high reference VREF + is determined, and a process of setting the high reference set value corresponding to the level to the D / A converter 93 is performed.

Next, the operation of the image reading apparatus configured as described above will be described. First, the control unit 11 performs the following preparatory operation before starting the reading operation. That is, as shown in FIG. 2, the control unit 11 first instructs the sensor driving unit 8 to start driving the line sensor 1 (step ST1). In response to this, the sensor driver 8 starts supplying a drive signal to the line sensor 1 and
To work. As a result, the line sensor 1 performs the photoelectric conversion operation and outputs the analog image signal ASIG. However, since the light source 6 is not turned on, no light is incident on the line sensor 1 and the above-described analog image signal is output. Signal ASIG
Is the lowest level.

Then, the control unit 11 recognizes the lowest level of the analog image signal ASIG by taking in the detection result of the signal level detection unit 10 in that state (Step S).
T2). Then, the control unit 11 determines the level of the row reference VREF- based on the lowest level of the analog image signal ASIG by the row reference determining unit 11a,
The corresponding row reference set value is set in the D / A converter 92 (step ST3). Note that the level of the row reference VREF- is, for example, the analog image signal AS
Set to a value slightly smaller than the lowest level of IG.

Subsequently, the control section 11 instructs the light source drive section 7 to turn on the light source 6 (step ST4). In response to this, the light source driving unit 7 starts supplying power to the light source 6 and turns on the light source 6. Thus, light is emitted from the light source 6, and the light reflected by the transmission white roller 5f enters the line sensor 1. Here the transmission white roller 5
f has a uniform white surface. Therefore, the analog image signal ASIG in this state has the highest level.

Then, the control unit 11 recognizes the highest level of the analog image signal ASIG by taking in the detection result of the signal level detection unit 10 in that state (Step S).
T5). Then, the control unit 11 determines the level of the high reference VREF + based on the highest level of the analog image signal ASIG by the high reference determination unit 11b,
The corresponding high reference set value is set in the D / A converter 93 (step ST6). Note that the level of the high reference VREF + is, for example, an analog image signal.
Set a value slightly higher than the highest level of ASIG.

With the above preparation operation, the line sensor 1 actually outputs the input range of the A / D converter 91 indicated by the low reference VREF- and the high reference VREF + output by the D / A converters 92 and 93. Considering the signal level, the analog image signal ASIG
Is set so that all can be input. That is, FIG.
As shown in (a) and (b), if the level of the analog image signal ASIG differs, the low reference VREF- and the high reference VREF + also change.

Thereafter, the control section 11 controls the document transport mechanism section 5
Is operated to transport the document D. Thus, the line sensor 1 reads an image formed on the document D and outputs a corresponding analog image signal ASIG. After the analog image signal ASIG is amplified by the amplifier 2, all the signals are taken in by the A / D converter 91 and binarized.
Converted to value data.

As described above, according to the present embodiment, the binarizing circuit 9 can arbitrarily change the input range of the A / D converter 91 according to the set values of the D / A converters 92 and 93. , According to the characteristics of the line sensor 1,
The input range of the A / D converter 91 can be set appropriately. Therefore, even if the characteristics of the line sensor 1 vary from product to product, the input range of the A / D converter 91 can be appropriately set according to the characteristics of the line sensor 1 actually mounted. Optimal binarization processing can be performed.

According to this embodiment, the level of the black reference signal and the level of the white reference signal are detected, and the row reference VREF- is determined based on the level of the black reference signal.
High reference VR based on the level of the white reference signal
Since each EF + is automatically determined, the trouble of the user and the maintenance person does not increase, and the setting error can be prevented.

According to the present embodiment, every time a reading operation is required, the setting of the low reference VREF- and the high reference VREF +, that is, the setting of the input range of the A / D converter 91 is performed as a preparatory operation. Therefore, even when the characteristics of the line sensor 1 fluctuate due to the influence of the ambient temperature or the like, the input range of the A / D converter 91 can always be appropriately set in accordance with the current situation, and the optimum binarization processing is always performed. Can do it.

The present invention is not limited to the above embodiment. For example, in the above-described embodiment, the embodiment as an image reading apparatus is described. However, the binarization circuit 9 may be made independent and used to binarize an arbitrary analog signal.

In the above-described embodiment, the low reference and the high reference are automatically set based on the black reference signal and the white reference signal output from the image sensor 1. The manual setting may be enabled by accepting and setting the low reference and the high reference to the level specified by the reception.

In the above-described embodiment, the row reference and the high reference are automatically set each time the reading operation is started. However, the automatic setting of the row reference and the high reference is performed, for example, periodically at a constant period. Alternatively, it may be performed at an arbitrary timing, such as in response to an execution instruction from a user or a maintenance person.

In addition, various modifications can be made without departing from the gist of the present invention.

[0037]

According to the present invention, an analog signal to be input is fetched and binarized by a binarizing means such as an A / D converter in a range from a predetermined low-level reference voltage to a predetermined high-level reference voltage. And the low-level reference voltage is, for example, D / A according to a row reference set value specified externally.
A low-level reference voltage generating means such as a converter is variably generated, and the high-level reference voltage is variably generated by a high-level reference voltage generating means such as a D / A converter in accordance with a high reference set value specified from the outside. So that 2
A binarization circuit that can easily set the input range of the value conversion means to an appropriate value according to the actual state of the analog signal.

Further, according to the present invention, an analog signal having a level corresponding to the amount of the reflected light generated by photoelectrically converting the reflected light from the original by an image sensor is converted into, for example, an A / A signal.
Binarization means such as a D-converter takes in a range from a predetermined low-level reference voltage or higher to a predetermined high-level reference voltage or lower and binarizes, and the low-level reference voltage is a predetermined level output from the image sensor. A low-level reference voltage generator such as a D / A converter is variably generated according to a row reference set value determined by the row reference determiner based on the black reference signal, and the high-level reference voltage is controlled by the image sensor. The high-level reference voltage generating means such as a D / A converter is variably generated according to the high reference setting value determined by the high reference determining means based on a predetermined white reference signal output by Set the input range of the Jisensa automatically becomes possible image reading apparatus to be set to an appropriate value corresponding to the actual state of the analog signal to be output.

[Brief description of the drawings]

FIG. 1 is a diagram showing a main configuration of an image reading apparatus according to an embodiment of the present invention.

FIG. 2 is a flowchart showing a processing procedure of a control unit 11 in FIG.

FIG. 3 is a diagram showing an example of a setting state of a low reference VREF- and a high reference VREF + with respect to the state of an analog image signal.

FIG. 4 is a diagram illustrating a main configuration of a conventional image reading apparatus.

FIG. 5 is a diagram showing a relationship between an input range and an input signal of the A / D converter 3 in FIG. 4;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Line sensor 2 ... Amplifier 5 ... Document conveyance mechanism part 6 ... Light source 7 ... Light source drive part 8 ... Sensor drive part 9 ... Binarization circuit 91 ... A / D converter 92, 93 ... D / A converter 10 ... Signal level Detector 11 ... Controller 11a ... Low reference determining means 11b ... High reference determining means

Claims (3)

[Claims] 1. A binarizing means for receiving an input analog signal in a range from a predetermined low-level reference voltage to a predetermined high-level reference voltage and converting the analog signal into a binary value, Low-level reference voltage generating means for variably generating the low-level reference voltage in response to the high-level reference voltage, and high-level reference voltage generating means for variably generating the high-level reference voltage in response to a high-reference set value specified externally. A binarization circuit, comprising: 2. An image sensor for photoelectrically converting reflected light from a document to generate an analog signal having a level corresponding to the amount of the reflected light, and converting the analog signal generated by the image sensor into a predetermined low-level reference voltage. As described above, binarization means for taking in and binarizing within a range of a predetermined high-level reference voltage or less, and low-level reference voltage generation for variably generating the low-level reference voltage according to a row reference set value specified from the outside Means, high-level reference voltage generating means for variably generating the high-level reference voltage according to a high-reference set value specified from the outside, and the low-level reference voltage based on a predetermined black reference signal output from the image sensor. Determine the reference setting value, and A low reference determining means for specifying to the pressure generating means; and a high reference determining means for determining the high reference setting value based on a predetermined white reference signal output from the image sensor and specifying to the high level reference voltage generating means. And an image reading device. 3. The low reference determining means and the high reference determining means determine and designate a low reference setting value and a high reference setting value as a preparatory operation before starting document reading. The image reading device according to claim 1.