JPH04114562A - Picture reader - Google Patents

Abstract

PURPOSE:To facilitate manufacture by connecting in series an amplifier circuit which can set plural different amplification factors with an A/D conversion circuit provided with a means which finely changes a reference voltage (+REF). CONSTITUTION:CPU 24 selects the appropriate amplification factor from a detected amplitude level (maximum value) and the amplification factor is newly reset. A white reference board 5 is read again in such a state and the maximum value of a picture signal is detected in CPU 24. For making the detected maximum value of the picture signal coincide with the potential (+REF) of +REF, CPU 24 calculates the discharge time of a capacitor 17. The relation of the discharge time (t) and the +REF voltage depends on (+REF)=3exp(-t/T). However, T is time constant expressed by the product of the resistance value of a resistor 19 connected between an analog switch 21 and ground and the electrostatic capacitance of the capacitor 17. A control signal is set to SW=1 and SW2=ON for calculated discharge time (t) and an original picture is read and scanned while the potential of the capacitor 17 is held in the state of SW 1=OFF and SW2=OFF. Thus, manufacture becomes facile and a reader can be supplied at a low cast.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention is directed to converting analog image signals into analog-digital (A
/D) The present invention relates to an image reading device having a processing function of converting into a digital signal by conversion.

[Prior Art] Conventionally, a CCD (charge coupled device) line sensor or the like has been used as an image sensor. For example, the amplitude of an image signal output from a CCD line sensor depends on the amount of light from an illumination lamp illuminating the document and the CCD sensor. is proportional to the product of the sensitivities of However, there are individual differences in the brightness of the illumination lamp and the sensitivity of the CCD sensor. For example, CCD
The sensitivity variation of the sensor is about ±30%, and the brightness of the lighting lamp is +/- if you take into account deterioration over time.
It may range from 20% to -40%. What is the amplitude of the image signal at this time? The variation between them is about +56% to -58%.

In response to these circumstances, the amplitude of the input signal of an A/D conversion IC (integrated circuit) is limited to a narrower range. For example, a certain 5V [volt] single power supply flash type A/
In the case of a D conversion IC, the reference voltage of the input signal is 2V (M
INl ~3V (MAXI "In". Therefore, a circuit is required to appropriately amplify and adjust the gain to allow A/D conversion for the image input signal that has variations in amplitude as described above. This circuit is generally called a gain control circuit.

There are three methods for controlling the gain of conventional image reading devices. That is, they are a volume adjustment method, a D/A (digital-to-analog) conversion IC method, and an analog division IC method.

The volume adjustment method is a method of adjusting the volume of the amplitude gain while observing the image signal at the time of device shipment. The circuit configuration is, for example, shown in FIG. 5(a), in which a volume (variable resistor) 101 is connected to the negative feedback of an inverting amplifier circuit consisting of an operational amplifier 100 to enable adjustment of the amplification factor. There is. In addition, 103 is an A/D conversion IC
It is.

The D/A conversion IC method means that if an 8-bit D/A conversion IC considers the high level of the analog reference voltage as input X and the digital input value as input Y, the output analog signal will be x(Y/25
This takes advantage of the fact that the number is 61. For example, if the circuit is configured as shown in FIG. 5(b), the CPU (not shown) (
Gain control can be performed by setting an appropriate value Y as the gain setting value in the central processing unit (central processing unit). In addition, 104 is a D/A conversion IC 1105 is an A/D
It is a conversion IC.

Next, a method using an analog division IC shown in FIG. 5(c) will be explained. This method divides the analog image signal by the amplitude value of the analog image signal itself. As a result, the amplitude of the analog image signal is always adjusted to a constant value. In addition, 106 is an analog division IC, 107
1 is an amplitude detection circuit, and 108 is an A/D conversion IC.

[Problems to be Solved by the Invention] However, the conventional gain control method as described above has the following problems to be solved.

First, although the first volume adjustment method has a simple circuit configuration, it cannot be said to be advantageous in terms of manufacturing cost since it requires an additional step of volume adjustment during assembly. In addition, there remain problems such as the inability to cope with a decrease in light intensity due to aging of the illumination lamp.

Regarding the second D/A conversion IC method and the third analog division IC method, although it is possible to solve the problems in the polyneme adjustment method,
Since an A conversion IC or an analog division IC is newly required, there is a problem to be solved in that the manufacturing cost increases.

In view of the above-mentioned points, an object of the present invention is to provide an image reading device that is easy to manufacture and can be supplied at low cost.

In an image reading device, an analog image signal output from a sensor is amplified by an amplifier circuit, and the amplified analog image signal is converted into a digital signal by an A/D conversion circuit. means for changing the amplification factor to a plurality of different amplification factors according to the width;
The present invention is also characterized by comprising means for continuously changing the difference between the high-level reference voltage value and the low-level reference voltage value of the A/D conversion circuit.

[Function] In the present invention, an amplifier circuit capable of setting a plurality of different amplification factors and an A/D conversion circuit equipped with means for slightly changing the reference voltage (+REF) are connected in series. An image reading device that is easy to manufacture and can be supplied at low cost can be obtained.

[Means to solve the problem]
[Embodiments] In order to achieve the above objects, the present invention will be described below with reference to the drawings. Examples in detail,
2 sensors to read the image, and the image 7
explain.

FIG. 1 shows the main circuit configuration of an image reading apparatus according to a first embodiment of the present invention, and FIG. 2 shows an example of the internal structure of the apparatus.

First, the internal structure of the apparatus of this embodiment will be explained with reference to FIG.

A document to be read (not shown) is placed on document table glass 1 with its reading surface facing downward, and is illuminated by illumination lamp 2 . The reflected light from the original is passed through an optical system consisting of a mirror and a lens 4 to a CCD linear sensor 6, which is an image sensor.
image is formed on the light-receiving surface of. The CCD linear sensor 6 is a semiconductor device in which a plurality of photoelectric conversion elements are arranged in a straight line, and has a structure in which an analog signal proportional to the amount of light received by each photoelectric conversion element is sequentially output.

In this way, the CCD linear sensor 6 scans in one direction of the reading area. This scanning is called main scanning. Also,
Scanning in a direction perpendicular to main scanning is called sub-scanning. The sub-scanning is performed by transporting the first traveling body 3 carrying the lamp 2 and the second traveling body 7 consisting of two mirrors using a stepping motor (not shown).

The present invention relates to means for amplifying the amplitude of an image read signal obtained by the above-described scanning method to an appropriate value. 1st
The figure shows the circuit configuration of an electric circuit according to an embodiment of the present invention, which is a specific example of the means.

In FIG. 1, the input analog image signal is at ground level when the amount of received light is O, and the signal increases in the positive direction in proportion to the amount of received light. Ideal white background (100% reflectance)
) The standard voltage value of the analog image signal corresponding to
mv (millivolt), but due to the variation in the light intensity of the lamp 2 and the sensitivity variation of the CCD sensor 6, which were mentioned earlier in the conventional technology section, the range is from a minimum of 630mV to a maximum of 2340mV.
It can take values up to .

This analog image signal is input to a preamplifier (hereinafter referred to as an operational amplifier) 11.
The operation of a circuit consisting of eight resistors from resistor RO to resistor R7 connected in series to the output terminal of operational amplifier 11 and eight-channel analog switch 12 will be explained. This 8-channel analog switch 12 is a relatively inexpensive general-purpose IC (integrated circuit) 74H (:4051), and operates according to three-man digital control signals (A, B, C) set by the output board of the CPU 24. , the terminal connected to the terminal COM is determined.The terminal COM of the 8-channel analog switch 12 is connected to the operational amplifier 11.
The amplification factor of the operational amplifier 11 is determined by the connection state of the switch 12 because the terminals O to 7, which are connected to the inverting input terminal of the switch 1 and the terminal CON, are connected to the respective contacts of the resistors RO to R7.

FIG. 3 shows the relationship between the constant values of the resistors RO to R7, the levels of the digital control signals A, B, and C, and the amplification factor of the operational amplifier 11. Here, L indicates a low level, H indicates a high level, and O to 7 in the rCOMJ column indicate the connection terminal ends.

15 is an A/D conversion IC whose input terminal is connected to the output terminal of the operational amplifier 11. This A/D converter ICl3 makes the potentials from -REF to +REF correspond to 0 to 255, converts the input signal into an 8-bit digital value, and outputs it. In this embodiment, -REF is set to the ground level. The voltage charged on the capacitor 17 is input to the REF terminal. Here, the A/D conversion IC 15 (
7) The reference voltage of the input signal is 2V (MIN) to 3V (M
AX).

The operational amplifier 16 connected to the +REF terminal of the A/D conversion ICI 5 is a voltage follower and functions to transmit the input voltage to the output as it is. The electric charge accumulated in the capacitor 17 connected to the positive input terminal of the operational amplifier 16 is determined by the digital signal SWI set by the CPU 24.
Controlled by SW2. Digital signal SW
I, SW2 are control signals that control on/off of the analog switch 20 and the analog switch 21, respectively, and these control signals S stomach 1. When the S stomach 2 is at a high level, the analog switches 20 and 21 are in a conductive state, and when it is at a low level, the analog switches 20.2
1 is in the off state. As will be explained later, the potential of +REF is the A/D when the CCD linear sensor 6 reads the white background.
It is controlled to be equal to the maximum value of the input signal.

The image signal converted into a digital signal by the A/D conversion ICl3 is subjected to necessary image processing such as shading correction processing, γ conversion, and binarization in the signal processing circuit 22, and then
It is sent to an external device via the interface circuit 23.

Further, the signal processing circuit 22 includes a circuit that holds the maximum value of the data of the l line and allows the CPU 24 to detect the maximum value. Note that 13 and 14 are diodes for overvoltage protection.

Next, the reading sequence of the embodiment of the present invention will be explained with reference to FIG. 4(a) and FIG. 2.

(Step 5-1) When there is a reading command, first, a stepping motor (not shown) is driven to change the reading position of the first traveling body 3 to the main scanning white reference plate reading position 5 (provided outside the image reading area). Figures 2 and 4
(See figure (a)).

(Step 5-2) Control signals SWI and SW output from the CPU 24 in FIG.
2 is set to 5W1=on and SW2: OFF, thereby setting the potential of the +REF terminal of the A/D conversion IC 15 (7) to (+REF)=3V. Further, control signals A, B, and C of the CPU 24 are all set to L (low level), and the amplification factor of the operational amplifier 11 is set to 1. In this state, the white reference plate 5 is read, and the maximum value in one line of the image signal is detected by the CPU 24 via the signal processing circuit 22.

(Step 5-3) Amplitude level (maximum value) detected in step S-2 above
The CPU 24 selects an appropriate amplification factor from , and sets the amplification factor anew. Here, an appropriate amplification factor means that the maximum value of the image signal does not exceed 3V.

In this state, the white reference plate 5 is read again, and the CPU 24 detects the maximum value of the image signal.

(Step 5-4) The maximum value of the image signal detected in step S-3 above and +
In order to match the potential of REF (+REF), the CPU
24 calculates the discharge time of the capacitor 17. The relationship between the discharge time t and the +REF voltage is expressed by the following equation.

(+REF) = 3exp (-t/T) where T is a time constant expressed by the product of the resistance value of the resistor 19 connected between the analog switch 21 and the ground and the capacitance of the capacitor 17.

(Step 5-5) Control signals SWI and SW2 are set to S for the calculated discharge time t.
Set stomach 1 = OFF, S stomach 2 = ON, then 5W
1=OFF.

Reading and scanning of the original image is performed while holding the potential of the capacitor 17 in the state of 5W2=OFF.

A second embodiment of the present invention is adapted to cope with changes in the amount of light from the illumination lamp 2 during reading of one page.

What is newly required for this purpose is a white reference plate 41 in the sub-scanning direction shown in FIG. Therefore, a circuit for detecting the level of the input image signal is also required.

The reading sequence of this embodiment will be explained below.

(Step 5-11 First, determine the amplification factor of the operational amplifier 1.1 and the potential of +REF in the same manner as in the first embodiment of the present invention described above.

(Step 5-2) The CPU 24 stores the signal level of the sub-scanning white reference position obtained from the signal processing circuit 22 in its internal memory, and sets it as VO.

(Step S-3) Sub-scan one line. This scanning involves moving the first traveling body 3 and the second traveling body 7 by a predetermined distance and reading the image data of 1 line.

(Step S-4) Compare the signal level VW of the sub-scanning white reference position of the last read line with the signal level vO stored in the internal memory, and if VW>VO+dV, Between the predetermined reference period dT and the control signal SW
I, SW2 are set to 5Wl=ON and 5W2=OFF to charge the capacitor 17. On the other hand, when vo-dv≦vw≦VO+dV, set 5Wl=OFF and 5W2=OFF to charge the capacitor 17. When vw<VO+dV, 5W1=OF during a predetermined reference period dT.
F.

Set SW2 to ON to discharge the charge in the capacitor 17. Here, dV is a preset constant.

(Step 5-5) Unless the read image signal is the last line, the process returns to step S-3. When it is the last line, the reading process ends.

By reading the original image according to the above reading sequence, +REF of the A/D conversion ICl3 can be controlled in accordance with the change in the light amount of the illumination lamp 2.

[Effects of the Invention] As explained above, according to the present invention, an amplifier circuit capable of setting a plurality of different amplification factors and a reference voltage (+
Since the A/D conversion circuits each having a means for slightly changing REF) are connected in series, an image reading device that is easy to manufacture and can be supplied at a low cost can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the circuit configuration of the first embodiment of the present invention, FIG. 2 is a schematic sectional view showing the internal configuration of the first embodiment of the present invention, and FIG. 3 is a resistor An explanatory diagram showing the relationship between the constant values from RO to 87, the digital control signals A, B, C, and the amplification factor of the operational amplifier 11, FIGS. 4(a) and 4(b) are the first embodiment of the present invention. 5(a), (b), and (C) are block diagrams showing the circuit configurations of the conventional gain controller and troll circuit. It is. 1... Original table glass, 5... Main scanning white reference plate, 6... CCD linear sensor (image sensor), 8...
... Electric circuit board, 9 ... Cover 11 ... Operational amplifier (preamplifier), 12 ... 8 channel analog switch, 13, 14 ... Diode for overvoltage protection, 15 ... A/ D conversion IC. 16... Operational amplifier, 17... Capacitor, 20, 21... Analog switch, 22... Signal processing circuit, 23... Interface circuit, 24... CPU. Fig. 3 (b) Fig. 5 E9σ times Nfl's calamity securitization Φf power half-7 side (G) Fig.

Claims (1)

[Claims] 1) An image is read using an image sensor, an analog image signal output from the image sensor is amplified by an amplifier circuit, and the amplified analog image signal is converted into an A/
In an image reading device that converts into a digital signal by a D conversion circuit, the amplifier circuit is capable of changing a plurality of different amplification factors according to the width of the amplitude of the analog image signal, and the A/D conversion circuit includes: An image reading device comprising means for continuously changing the difference between a high-level reference voltage value and a low-level reference voltage value.