JPH065857B2 - Light amount adjustment device for image reader - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an image reader for reading the density of a document illuminated by an exposure source with an image sensor.

(Prior Art) In an image reader, a document placed on a document glass table is illuminated by an exposure source to determine the density of the document by an image sensor (C
CD).

(Problems to be Solved by the Invention) When an exposure lamp of AC lighting is used as an exposure source of an image reader, a ripple corresponding to a commercial frequency of an AC power source appears in an image signal. In particular, when the analog signal is converted into a multi-valued digital signal, this ripple has a great influence. Further, even for originals having the same density, a constant image signal cannot be obtained due to changes with time of the exposure lamp.

On the other hand, the problem with using an expensive halogen lamp as the exposure lamp is that the life is shortened by changing the lighting voltage, the emission color temperature is changed, and the cost is increased.

An object of the present invention is to provide an image reader that uses an exposure source lit at a commercial frequency and has a stable image signal.

(Means for Solving the Invention) A light amount adjusting device for an image reader according to the present invention is driven by a standard pattern having a constant density and an AC power source,
An exposure source that illuminates the standard pattern and the original document, a light amount sensor that detects the light amount of the exposure source, an image sensor that detects the reflected light amount of the standard pattern and the original document, and an output of the light amount sensor that corresponds to the delay of the output of the image sensor. Delay circuit for delaying the output and A / D for converting the analog output of the image sensor to a digital value
A conversion unit, a storage unit for storing the output value of the A / D conversion unit, and a level corresponding to the output value of the A / D conversion unit stored in the storage unit when the standard pattern is irradiated by the exposure source. The level setting means for outputting the voltage in synchronism with the output of the image pickup device, the output of the delay circuit and the output of the level setting means are added at a predetermined ratio, and A of the A / D converting means is added.
The output value of the A / D conversion means stored in the storage means becomes a predetermined level when the standard pattern is irradiated by the addition means for outputting to the reference voltage input terminal of the / D conversion. Up to the above, there is provided discriminating means for changing the output of the level setting means and for maintaining the output after reaching a predetermined level.

(Function) When a standard pattern having a constant density (for example, white) is irradiated by an exposure lamp lit by alternating current, the reflected light is detected by the image sensor and output as an analog signal. As shown in FIG. The output A of the image pickup device and the output B of the light amount sensor for directly receiving the light of the exposure lamp also include ripples corresponding to the AC frequency. The phase of the output A of the image sensor is delayed from the phase of the output B of the light amount sensor by the reading time t _{s of} one line.

In the present invention, a voltage proportional to the output of the image sensor for the standard pattern and a voltage obtained by delaying the output of the light amount sensor of the exposure lamp by the predetermined time t _s for the AC component are added, and the A / D converter is added. The standard voltage of V _ref .

(Examples) Examples of the present invention will be described below with reference to the accompanying drawings.

FIG. 3 is a sectional view of the mechanism of the image reader according to the present invention. A halogen lamp 2 as an exposure source illuminates a document 6 placed on a document glass 4. Halogen lamp 2
Is equipped with a reflecting mirror 8 and an infrared cut filter 10.

The reflected light from the original 6 is reflected by the first mirror 12 and the second mirror 1.
4 and the third mirror 16 and then passes through the lens 18 to pass through the lens 18 and the image pickup device 2 formed of a one-dimensional CCD
It is incident on 0.

The image sensor 20 is held by the image sensor holding section 22,
Moreover, the position and the angle are adjusted. Further, the image pickup device holding portion 22 and the lens 18 are attached to the moving table 24.

The adjustment of the magnification is performed by moving the moving table 24 in the optical axis direction by a moving mechanism (not shown).

The focus is adjusted by moving the image pickup device 20 in the optical axis direction by a motor (not shown) attached to the moving table 24.

When scanning the document 6, as is well known, the light source 2 and the mirrors 12 to 16 are moved in the scanning direction.

Further, a standard pattern 30 having a constant density (white) is set outside the document 6 at the end of the document glass 4. A light amount sensor 32 that detects the light amount of the exposure source 2 is also provided.

FIG. 1 is a block diagram of a circuit for detecting the density.

The clock generation circuit 40 is connected to the CPU 42 and used as a clock. Also, a necessary SH (Sample Hold) signal is given to the image pickup device 20. Image sensor 2
0 converts an optical signal into an electrical signal. A / D converter 44
Converts the analog output of the image sensor 20 into a digital signal. The shading circuit 46 is for correcting unevenness in the amount of light in the main scanning direction and variation between bits of the image pickup element, and its timing is given from the CPU 42.
The output of the shading circuit 46 is input to the comparison circuit 48 and the line RAM 50. The comparison circuit 48 compares the shading circuit 46 with the signal selected by the selector 52, and outputs the result in 1 bit. The output circuit 54 outputs a 1-bit image signal and an effective image signal (synchronization signal) to the outside. The line RAM 50 stores the shading-corrected signal in the memory for one scan. This write signal is output from the CPU 42, and CP
The U42 obtains image information for one line by referring to the line RAM 50. The attribute information stored in the RAM 56 is a binary or dither attribute determined by the CPU 42 on the basis of the information written in the line RAM 50, and during data transfer (during scanning).
The selector 52 is switched based on this attribute and is output to the comparison circuit 48.

The pattern generation circuit 58 generates a threshold value at the time of dither, and the threshold value is generated in an m × n matrix. The selector 52 sends the threshold data from the pattern generation circuit 58 and the RAM 56 to the comparison circuit 48 based on the threshold information and the attribute information to select threshold data. If the attribute is dither, the data from the pattern generation circuit 58 is used. If the attribute is binary, the data is RAM.
The threshold information from 56 is sent to the comparison circuit 48. CPU 42
Controls the whole from the above signals, the motor signal, the ramp signal, the fixed position signal, and the like.

The delay circuit 34 delays the AC component of the output of the light amount sensor 32 by a predetermined time (reading time t _{s for} one line). When adjusting the light quantity, the line RAM 50 stores the image sensor 20.
The density of the standard pattern 30 detected by is written. The CPU 42 outputs the light amount level signal corresponding to the density of the standard pattern 30 stored in the line RAM 50 to the D / A.
Output to the converter 35. The adder circuit 36 adds the output signal of the D / A converter 35 and the output signal of the delay circuit 34,
It outputs to 44 reference voltage input terminals V _ref of the A / D converter.

FIG. 4 shows the delay circuit 34 and the adder circuit 36. The photodiode, which is the light amount sensor 32, generates a voltage corresponding to the amount of light received from the halogen lamp 2 driven at 100 V and 60 Hz. This voltage is input between the + input terminal and the-terminal of the OP amplifier A1. + Of OP amplifier A1
The input terminal is grounded via the resistor R5. The-input terminal and the output terminal of the OP amplifier A1 are connected by the resistor R1. The output terminal of the OP amplifier A1 is further connected to the resistor R
2 is connected to capacitors C1 and C2. The capacitor C1 is grounded. The capacitor C2 is grounded via the variable resistor R3.

In this circuit, the OP amplifier A1 includes a light amount sensor 32.
The voltage of is output as it is. The capacitor C1 is used to delay the output of the OP amplifier A1. Various other delay elements may be used. The capacitor C2 is used to transfer only the AC component of the output voltage to the next circuit.

On the other hand, the output of the D / A converter 35 is output via the resistor R4.
On the one hand, to the variable terminal of the variable resistor R3, on the other hand, OP
It is connected to the + input terminal of the amplifier A2. OP amplifier A2
The-input terminal of is connected to the output terminal. OP amplifier A
2 is the reference voltage V _{ref of the} A / D converter 44.
Becomes

In this circuit, the AC component of the output voltage of the light amount sensor 32 flows through the resistor R3, while the output voltage of the D / A converter 35, which is proportional to the output of the image sensor 20, is the same as that of the resistors R4 and R3. Flowing through. Therefore, both output voltages are added to the + input terminal of the OP amplifier A2 at a predetermined ratio.
This ratio may be determined in advance by adjusting the variable terminal of the variable resistor R3.

The light amount adjustment is performed as described below for each original reading operation on the first floor, whereby a stable image signal of density can be obtained every time even when the exposure source is driven by an AC power source.

When reading a document, first set a certain density (for example, white)
When the standard pattern (1) is used as a document and illuminated by a lamp, an analog signal corresponding to the reflection density is output from the image sensor 20. The analog signal is converted into a digital signal of a plurality of bits by the A / D converter 44 on the basis of the _Vref signal described above, is subjected to shading correction, and then written in the line RAM 50. CPU 42 is line R
The initial value of the light amount level signal proportional to the content of AM50 is D
It outputs to the / A converter 35, and the D / A converter 35 converts this value into an analog voltage. On the other hand, the AC component of the output of the light amount sensor 30 that detects the light amount of the exposure source is synchronized with the output of the image sensor 20 via the delay circuit 34. The output voltage of the D / A converter 34 and the output voltage of the delay circuit are added at a predetermined ratio by an adder circuit, and the reference voltage V of the A / D converter 44 is added.
Used as _ref .

Using this V _ref , the output voltage of the image sensor 20 at the time of the next output is again A / D converted, and similarly, the line RAM
Write 50.

The CPU 42 determines whether or not the detection value stored in the line RAM 50 is at a predetermined level. in that case,
The adjustment of the light amount is completed, and the normal document reading is started.

If the detected value is not the predetermined level, the CPU 42 changes the light amount level signal by the predetermined value. This gives A
The reference voltage V _ref of the / D converter 44 is changed.

Next, the output of the image pickup device 20 is converted into a digital value again and written in the line RAM 50. The CPU 42 determines again whether or not the value stored in the line RAM 50 is at a predetermined level. If so, the adjustment of the light amount is ended, and if not, the light amount level signal is changed again, and V
Change _ref .

In this way, the light amount is adjusted until the content written in the line RAM 50 reaches a predetermined value.

When the document is read after the light amount adjustment is completed, the image sensor output using the exposure lamp lit at the commercial frequency can be corrected by the signal obtained by delaying the output from the light amount sensor, so that the image signal can be stabilized. .

(Effects of the Invention) A stable image can be obtained even when an exposure lamp as an exposure source of an image reader is used at a constant frequency and a commercial frequency, and an image signal of a constant level can be obtained for an original having the same density. It is possible to prevent the influence of changes in color temperature. Also, the cost of the exposure source can be reduced as a whole.

[Brief description of drawings]

FIG. 1 is a block diagram of an image reader. FIG. 2 shows the output of the image sensor, the output of the light amount sensor, and V.
It is a graph which shows the time dependence of _ref . FIG. 3 is a sectional view of the image reader. FIG. 4 is a circuit diagram of a part of the block diagram of FIG. 2 ... Exposure lamp, 6 ... Original, 18 ... Lens, 20 ... CCD, 30 ... Standard pattern, 32 ... Light amount sensor.

Claims (1)

[Claims] 1. A standard pattern having a constant density, an exposure source driven by an AC power source to illuminate the standard pattern and an original, a light amount sensor for detecting the light amount of the exposure source, and a reflected light amount of the standard pattern and the original. An image sensor for detection, a delay circuit for delaying the output of the light amount sensor in correspondence with the delay of the output of the image sensor, and an A / A for converting the analog output of the image sensor into a digital value.
D conversion means, storage means for storing the output value of the A / D conversion means, and corresponding to the output value of the A / D conversion means stored in the storage means when the standard pattern is irradiated by the exposure source. The level setting means for outputting the level voltage in synchronization with the output of the image pickup device and the output of the delay circuit and the output of the level setting means are added at a predetermined ratio, and the A / D conversion of the A / D conversion means is performed. When the standard pattern is illuminated by the adding means for outputting to the reference voltage input terminal and the output value of the A / D converting means stored in the storage means reaches the predetermined level, A light quantity adjusting device for an image reader, comprising: a discriminating means for changing the output of the level setting means and maintaining the output after reaching a predetermined level.