JPH057297A - Image reader - Google Patents

Abstract

PURPOSE:To prevent the blackening of an output image by preventing the reference voltage of an analog/digital conversion (ADC) circuit 14 performing A/D conversion of an original reading image signal from being affected by incoming noise light, etc. CONSTITUTION:This system is provided with the ADC circuit 14 performing the A/D conversion of an original reading image signal SIG, amplifiers 5 and 6 converting the background concentration picture element reading signal of the original into DC signal and then into the reference voltage of the ADC circuit 14, an amplifier circuit 12, etc., and a clamping circuit selecting any one of plural clamping voltage corresponding to the reference voltage and clamping the signal SIG.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading device.

[0002]

2. Description of the Related Art Conventionally, an image reading apparatus has an ABC (Auto).
The image signal obtained by reading a certain section of the document image is converted into a DC signal through a peak / Halt circuit or the like, and this DC signal is converted into an ADC signal.
(A / D conversion) Used as the reference voltage of the circuit. At this time, if an external noise light is picked up, such as when the original has a hole, the integration time constant in the peak and halt circuit is relatively small, so these effects have peaks.
It has a configuration that greatly affects the halt circuit.

[0003]

However, in the above-mentioned conventional example, the peak / Halt output when the external noise light is picked up, that is, the fluctuation of the reference voltage of the ADC circuit is
There is a drawback that the quality of the output image is greatly affected. In particular, there is a defect that the density of the output image is darker than it should be or that the output image is an all black image.

Therefore, an object of the present invention is to provide an image reading apparatus which solves the above problems.

[0005]

In order to achieve the above object, the present invention provides an analog / digital conversion means for converting a document read image signal into a digital signal, and a background density pixel read signal of a document to a direct current signal for converting the signal. Reference voltage forming means as a reference voltage of the analog / digital converting means, a plurality of clamping means for clamping the original reading image signal at different levels, and a DC voltage from the reference voltage forming means of the plurality of clamping means. Means for selecting a clamping means suitable for the signal level.

[0006]

According to the present invention, the clamp circuit according to the level of the reference voltage is selected, and the abnormal level image signal due to the influence of the external noise light in the case where the original is perforated by the selected clamp circuit. Is clamped. A DC signal as a reference voltage is created from the clamped image signal, and the fluctuation of the reference voltage due to the abnormal level image signal is suppressed.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a drawing that best represents the features of the present invention, and this drawing shows the ABC circuit in FIG. First, the image reading device shown in FIG. 2 will be described. In the figure, 21 is a document, 22 is a glass plate, 23 is an LED as a light source, 24 is a SELFOC lens for collecting reflected light, and 25 is photoelectric conversion for the collected image light. Image sensor, 26 is image sensor 2
Amplifier circuit that amplifies 5 outputs, 27 is A that creates a reference voltage for A / D conversion from the sensor output
BC circuit, 14 is an A / D converter (ADC circuit), 2
Reference numeral 9 denotes a shading distortion correction circuit for correcting shading distortion of the image signal digitized by the ADC circuit 14. The operation of the image reading apparatus having such a configuration will be described below.

First, prior to the start of document reading, the light source L
It is assumed that the ED 23 is lit. Next, when reading the original image, the light emitted from the light source LED 23 illuminates the original surface through the glass plate 22, and the reflected light is condensed by the SELFOC lens 24. When collected, an image is formed on the image sensor 25. The image sensor 25 photoelectrically converts this image-forming light and outputs it as a read image. This output is amplified by the amplifier circuit 26 from a weak signal to an appropriate level, and the ABC circuit 2
7 is sent.

By repeating the above reading operation,
The background density image of the document is read and converted into a DC signal by the ABC circuit 27. This DC signal is used as the reference voltage of the ADC circuit 14. In the ABC circuit 27, the read image signal is bypassed to the ADC circuit 14 side, in addition to creating the DC signal. ADC circuit 14
On the basis of the reference voltage from the ABC circuit 27, A / D-converts the read image signal and sends the output to the shading distortion correction circuit 29. In the shading distortion correction circuit 29, shading distortion correction such as variation in the light amount of the light source is performed on this digital signal,
Output.

The above is the overall operation at the time of reading the image. Next, FIG. 1 which best illustrates the features of the present invention will be described.

In the figure, 1 is an amplifier, 2 and 3 are resistors (R ₁ and R ₂ ), 4 is a clamp circuit of the present invention, and 5 is
6 is an amplifier, 7 is a capacitor element, 8 is a resistor (R
₃ ), 9 is an analog switch, 10 is a diode element,
Reference numeral 11 is a limiter circuit having a constant reference voltage, 12 is an amplifier circuit for adjusting a DC signal to the peak value of a read image signal, 13 is a diode element, and 14 is an A / D converter shown in FIG. The operation will be described below.

First, the image signal (SIG) obtained by reading the background density using the leading edge margin of the original is amplified to an appropriate level by an amplifier circuit composed of an amplifier 1 and resistors R ₁ and R _2. To be done. The amplified image signal is sent to the ADC circuit 14 and, on the other hand, is sent to the clamp circuit 4 and the + side of the amplifier 5. A series of circuits composed of the amplifiers 5 and 6 is a peak and halt circuit for detecting the peak value of the read image signal and converting it to a DC signal. Therefore, the image signal input to the amplifier 5 is compared with the-side of the amplifier 5, and when it is larger than this-side, the amplifier 5 outputs the differential voltage. This output signal is the diode element 13
The capacitor element 7 is charged via. The resistor 8 is a resistor for discharging, has a sufficiently large value, and has no effect on this charging. The circuit composed of the limiter circuit 11 and the diode element 10 is
This is a limiter circuit for keeping the + side of the amplifier 6 from falling below a certain voltage.

When the capacitor element 7 is charged, its voltage is transmitted to the + side of the amplifier 6. Since the amplifier 6 operates as a voltage follower circuit with a gain of 1, the + side voltage is directly transmitted to the output. This output signal is sent to the amplifier circuit 12. In the amplifier circuit 12, the gain is preset so that the DC signal in the saturated state among the image signals of one line output from the amplifier 1 becomes the level of the peak pixel. Therefore, the DC signal sent to the amplifier circuit 12 is amplified by this gain, and the output is the clamp circuit 4 and the ADC circuit 1.
4 is sent to the reference terminal.

By repeating the operations described above, the capacitor element 7 is charged as a DC signal from the background density image signal of the read document. By reading several lines of the document as the ground density pixels, the charging voltage in the capacitor element 7 is saturated.

Next, even when the image signal of the original is read, the operation described above is repeated. In this case, AD
Based on the DC signal transmitted to the reference terminal of the C circuit 14, the read image signal from the amplifier 1 is sequentially A / D converted in the ADC circuit 14.

Now, in the present invention, the amplifier circuit 12
Therefore, in the clamp circuit 4 receiving the DC signal at the same level as the reference terminal of the ADC circuit 14, this DC signal level is judged, and the abnormal signal in the read image signal from the amplifier 1 should be clamped properly. Clamp circuit is selected and the clamp operation is executed. By doing so, the level of the signal converted from the background density image signal of the original document into the capacitor element 7 as a DC signal does not greatly change even if an abnormal read signal is input.

Next, FIG. 3 is a diagram showing the operation of the clamp circuit 4 in detail. In FIG. 3, 30 to 34 are comparator elements, 35 to 39 and 55 to 58 are AND elements, and 40 to 40. 44 is a flip-flop (F
F) 45 to 49 are analog switches, 50 is a Zener diode with a Zener voltage of 4.0 V, 51 is a Zener diode with a Zener voltage of 3.5 V, 52 is a Zener diode with a Zener voltage of 3.0 V, and 53 is a Zener voltage of 2. 5V Zener diode, 54 is a Zener diode with a Zener voltage of 2.0V, and 59 to 68 are resistors. The operation of the figure will be described below.

First, as shown in FIG. 1, the ADC circuit 14
The reference voltage V _Ref signal of is input and sent to the-side terminals of the comparator elements 30 to 34, respectively. On the other hand, the + side of the comparator elements 30 to 34 has + 3.5V, + 3.0V, and + 2.5V as reference voltages due to resistance voltage division.
V, +2.0 V, and +1.5 V (V _R5 , V _R4 , V _R3 ,
Resistors 59 to 63 (R4 to R4) so that V _R2 and V _R1 )
8) is set.

As described with reference to FIG. 1, when the reading operation of the original is started, as shown in the timing chart of FIG. 4, as the reference voltage increases, the reference voltage V _R1 is exceeded. First, the output V _cp1 of the comparator element 34 is turned on. This V _cp1 output is sent to one input terminal of the AND element 39. Further, when the synchronizing pulse SI of the read line is sent to the other input terminal of the AND element 39, the AND element 39 takes the product of two inputs,
It is sent to the D input terminal of the flip-flop 44. The flip-flop 44 turns on the output Q of the input signal based on the synchronous clock signal CLK of the read image signal.

This ON signal is sent to the AND element 58. Here, the upper flip-flops 40 to 43
Is reset as an initial state. Therefore, the inverted output Q of the flip-flop 43 is a "1" signal, and the AND element 58 takes the product of these two input signals and sends it to the gate terminal of the analog switch 49. The analog switch 49 is turned on by this gate signal V _G1 . Then, as the output of the amplifier 1 shown in FIG. 1, the signal V _in2 input to the clamp circuit 4 flows into the resistor 68. Furthermore, the Zener diode 54 in parallel with the resistor 68 clamps the signal V _in2 at the Zener voltage V _Z1 .

[0021] FIG. 4 shows a timing chart of the operation of the in each portion in FIG. 3, the operation described above, the output V _cp2 reference voltage from the comparator device 33 to the comparator device 30, V _cp3, V _{Even when the cp4} and V _cp5 are raised until they are set to "1", respectively, FIG.
The same operation is repeated as shown in FIG.

FIG. 5 shows the relationship between the image signal and the reference voltage when an abnormal level occurs in the read image signal SIG. The description of FIG.
Since an abnormal level has occurred in the image signal on the line,
The image signal is clamped by the clamp voltage V _Z3 , and the reference voltage V _R1 up to that point fluctuates to V _Z3 . As a result, the clamp circuit is switched, and the clamp voltage is V on the (n + 2) th line. Indicates that it has become _Z4 .

[0023]

As described above, according to the present invention, an appropriate image can be read without using a complicated hardware structure, and for example, the black color of an output image generated by picking up external noise light leaking from a document hole or the like. There is an effect that can be prevented.

[Brief description of drawings]

FIG. 1 is an ABC of an image reading apparatus according to an embodiment of the present invention.
It is a circuit diagram of a circuit.

FIG. 2 is a block diagram of the image reading apparatus.

FIG. 3 is a circuit diagram of a clamp circuit in the image reading apparatus.

FIG. 4 is a diagram showing an operation timing chart in the clamp circuit.

FIG. 5 is a diagram showing a relationship between an image signal and a reference voltage when an abnormal level is input with respect to a read image signal SIG in the image reading apparatus.

[Explanation of symbols]

 1 amplifier 2 resistor 3 resistor 4 clamp circuit 5 amplifier 6 amplifier 7 capacitor element 8 resistor 9 analog switch 10 diode element 11 limiter circuit 12 amplifier circuit 13 diode element 14 A / D converter 21 manuscript 22 glass plate 23 light source LED 24 Selfoc lens 25 Image sensor 26 Amplifier circuit 27 ABC circuit 29 Shading distortion correction circuit 30-34 Comparator element 35-39 and 55-58 AND element 40-44 Flip-flop element 45-49 Analog switch 50-54 Zener Diode 59-68 resistor

Claims (1)

Claim: What is claimed is: 1. An analog / digital conversion means for converting a document reading image signal into a digital signal, and a reference of the analog / digital converting means for converting a background density pixel reading signal of a document into a DC signal. Voltage reference voltage forming means, a plurality of clamp means for clamping the original read image signal at different levels, and a clamp means adapted to the DC signal level from the reference voltage forming means among the plurality of clamp means. And an image reading device including means for selecting.