JPS61236271A - Light quantity adjusting device for image reader - Google Patents

Abstract

PURPOSE:To obtain stable images even when an exposure lamp is used at the commer cial frequency and to obtain constant-level image signals for originals having the same density by providing a delay circuit, a D/A converter, an adder, etc. CONSTITUTION:When an original is read, a standard pattern 30 having constant density is lighted as an original 6 by an exposure lamp 2 and then an analog signal correspond ing to the reflection density is outputted from an image pickup element 20 and written in a RAM 50 through an A/D converter 44, etc. The AC component of the output of a light quantity sensor 32 which detects the quantity of light of the exposure source is synchronized with the reference voltage of a converter 44 through a delay circuit 34 and added at a specific ratio by an adding circuit 36, so that the sum is used as the reference voltage of the converter 44. Then, this reference voltage is used to con vert the output voltage during next output operation from analog to digital and the quantity of light is adjusted until contents written in the RAM 50 attains to a specific value. Thus, the output of the image pickup element 20 which uses the exposure lamp 2 turned on at the commercial frequency is corrected with the signal obtained by delaying the output of the light quantity sensor 32 to stabilize an image signal.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an image reader that uses an image sensor to read the density of a document irradiated by an exposure source.

(Prior art) In an image reader, a document placed on a document glass table is irradiated with an exposure source, and the density of the document is measured by an image sensor (C
OD).

(Problems to be Solved by the Invention) When an AC-lit exposure lamp is used as the exposure source of an image reader, ripples corresponding to the commercial frequency of the AC power source appear in the image signal. In particular, when converting an analog signal into a multi-value digital signal, the influence of this ripple is large. Furthermore, even for originals with the same density, constant image signals cannot be obtained due to changes in the exposure lamp over time.

On the other hand, problems when using an expensive halogen lamp as an exposure lamp include that changing the lighting voltage shortens the life of the lamp, that the color temperature of the emitted light changes, and that the cost increases.

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

(Means for Solving the Invention) A light amount adjustment 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 irradiates the standard pattern and original, a light sensor that detects the amount of light from the exposure source, an image sensor that detects the amount of reflected light from the standard pattern and the original, and a light sensor that adjusts the output of the light sensor to accommodate delays in the output of the image sensor. a delay circuit that delays the image sensor, and an A/D that converts the analog output of the image sensor into a digital value.
a conversion means, a storage means for storing an output value of the A/D conversion means, and a level 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; A level setting means for outputting a voltage in synchronization with the output of the image sensor, and adding the output of the delay circuit and the output of the level setting means at a predetermined ratio,
the addition means outputs to the reference voltage input terminal of the /D conversion, and when the standard pattern is irradiated by the exposure source, the output value of the A/D conversion means stored in the storage means becomes a predetermined level. and determining means for changing the output of the level setting means until reaching a predetermined level and maintaining the output after reaching a predetermined level.

(Function) When a standard pattern of a certain density (for example, white) is irradiated with an exposure lamp lit by alternating current, the reflected light is detected by an image sensor and output as an analog signal, but as shown in Figure 2. In addition, both the output A of the image sensor and the output B of the light amount sensor that directly receives the light from the exposure lamp include ripples corresponding to the frequency of the alternating current. Note that the phase of the output A of the image sensor lags behind the phase of the output B of the light amount sensor by t, which is the reading time of the ■ 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 alternating current portion of the output of the light amount sensor of the exposure lamp by a predetermined time t3 are added, and the voltage of the A/D converter is Let the reference voltage be ref.

(Example) Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

FIG. 3 is a sectional view of the structure of the image reader according to the present invention. A halogen lamp 2 serving as an exposure source irradiates an original 6 placed on an original glass 4 . halogen lamp 2
Reflections! t8 and an infrared cut filter 10.

The reflected light from the original 6 is transmitted to the first mirror 12 and the second mirror 1.
4 and the third mirror 16, and passes through the lens 18 to the image sensor 2 consisting of a one-dimensional array of CCDs.
0.

The image sensor 20 is held by an image sensor holding section 22,
Additionally, the position and angle are adjusted. Further, the image sensor holding section 22 and the lens 18 are attached to a movable table 24.

The magnification is adjusted by moving the moving table 24 in the optical axis direction using a moving mechanism (not shown).

Focus adjustment is performed by moving the image sensor 20 in the optical axis direction using a motor (not shown) attached to the moving table 24.

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

Furthermore, a standard pattern 30 of a constant density (white) is placed outside the original 6 at the edge of the original glass 4.

Further, a light amount sensor 32 that detects the amount of light from the exposure source 2 is provided.

FIG. 1 is a block diagram of a circuit for detecting concentration.

Clock generation circuit 40 is connected to CPU 42 and used as a clock. Further, a necessary SH (Sample Hold) signal is also provided to the image sensor 20. The image sensor 20 converts an optical signal into an electrical signal. A/
The 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 sensor, and is given its timing by the CPU 42. The output of the shading circuit 46 is input to a comparison circuit 48 and a line RAM 50. Comparison circuit 4
8 compares the signal selected by the shading circuit 46 and the selector 52, and outputs the result in one bit. The output circuit 54 outputs a 1-bit image signal and a valid image signal (synchronization signal) to the outside. line RAM
50 stores the shading-corrected signal for one scan in a memory.

This write signal is output from the CPU 42 and
2 refers to this line RAM 50, -
Obtain image information for a line. The attribute information stored in the RAM 56 has a binary or dither attribute determined by the CPU 42 based on the information written in the line RAM 50, and this attribute is not used during data transfer (scanning). The selector 52 is replaced with the comparison circuit 48.
Output to.

The pattern generation circuit 58 generates a threshold value during dithering, and the threshold value is generated by a matrix of IIXn. The selector 52 has a pattern generation circuit 58 and a RAM 5.
Threshold data to be sent to the comparison circuit 48 is selected from the threshold information and attribute information from 6.

If the attribute is dither, data from the pattern generation circuit 58 is sent to the comparison circuit 48, and if the attribute is binary, threshold information from the RAM 56 is sent to the comparison circuit 48. The CPU 42 controls the entire system from the above signals, motor signals, lamp signals, fixed position signals, etc.

The delay circuit 34 delays the alternating current component of the output of the light amount sensor 32 by a predetermined time (reading time 1 for one line).

When adjusting the light amount, the image sensor 2 is stored in the line RAM 50.
The density of the standard pattern 30 detected by 0 is written. The CPU 42 converts the light amount level signal corresponding to the density of the standard pattern 30 stored in the line RAM 5Q into a D/D/
Output to A 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 and outputs the result to the reference voltage input terminal V rer of the A/D converter 44 .

FIG. 4 shows the delay circuit 34 and the adder circuit 36.

The photodiode which is the light amount sensor 32 has a voltage of 100V,
A voltage corresponding to the amount of light received from the halogen lamp 2 driven at 60 Hz is generated. This voltage is OP amplifier A
It is input between the 10th input terminal and the 1st terminal of I. The tenth input terminal of the OP amplifier A1 is grounded via a resistor R5.

One input terminal and output terminal of OP amplifier A1 are resistor R1
Connected by The output terminal of the OP amplifier A1 is further connected to capacitors CI and C2 via a resistor R2. Capacitor CI is grounded. Capacitor C2
is grounded via variable resistor R3.

In this circuit, the OP amplifier AI is connected to the light amount sensor 32.
Outputs the voltage as is. Capacitor CI is used to delay the output of OP amplifier AI. Various other delay elements may also be used.

Capacitor C2 is used to transmit only the alternating current portion of the output voltage to the next circuit.

On the other hand, the output of the D/A converter 35 is transmitted via the resistor R4.
On the one hand, the variable terminal of variable resistor R3, on the other hand, OP
Connected to the 10 input terminal of amplifier A2. OP amplifier A2
One input terminal of is connected to an output terminal. OP amplifier A
2 is the reference voltage vref of the A/D converter 44.
becomes.

In this circuit, the AC component of the output voltage of the light 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, flows through the resistor R4 and a part of the resistor R3. flows. 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 intensity adjustment is performed as described below for each original reading operation, and as a result, even if the exposure source is driven by an AC power source, an image signal with a stable density can be obtained every time.

When reading a document, first, a certain density (for example, white) is read.
When a standard pattern is used as a document and illuminated with a lamp, an analog signal corresponding to the reflection density is output from the image sensor 20. The analog signal is converted into a multi-bit digital signal by the A/D converter 44 based on the Vrer signal described above, subjected to shading correction, and then written to the line RAM 50. The CPU 42 is connected to the line RA
The initial value of the light level signal proportional to the contents of M50 is set to D/
This value is output to the A converter 35, and the D/A converter 35 converts this value into an analog voltage. On the other hand, the alternating current portion 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. D/A converter 3
4 and the output voltage of the delay circuit are added at a predetermined ratio in an adder circuit, and the reference voltage V r of the A/D converter 44 is
Used as ef.

This V. f is used to perform A/D conversion of the output voltage of the image sensor 20 again at the next output, and similarly, the line RAM
Write to 50.

The CPU 42 determines whether the detected value stored in the line RAM 50 is at a predetermined level.

If so, the light amount adjustment is completed and normal document reading is started.

If the detected value is not at a predetermined level, the CPU 42 changes the light amount level signal by a predetermined value.

Thereby, the reference voltage vref of the A/D converter 44 is changed.

Next, the output of the image sensor 20 is again converted into a digital value and written into the line RAM 50. The CPU 42 again determines whether the value stored in the line RAM 50 is at a predetermined level. If so, finish adjusting the light intensity,
If not, change the light level signal again. Let r change.

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

If you scan the original after completing the light intensity adjustment, the image sensor output using an exposure lamp lit at a commercial frequency can be corrected with a signal that is a delayed output from the light intensity sensor, making it possible to stabilize the image signal. (Effects of the invention) Stable images can be obtained even when using an exposure lamp as an exposure source of an image reader at a commercial frequency and a constant voltage, and image signals of a certain level can be obtained for originals of the same density. This prevents effects such as changes in color temperature. Moreover, the cost of the exposure source can be reduced as a whole.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an image reader. Figure 2 shows the output of the image sensor, the output of the light amount sensor, and the V
It is a graph showing 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. 1. 2...Exposure lamp, 6...Original, 18...
- Lens, 20... CCD1 30... Standard pattern, 32... Light amount sensor.

Claims (1)

[Claims] (1) A standard pattern with a constant density, an exposure source that is driven by an AC power source and irradiates the standard pattern and the document, a light sensor that detects the amount of light from the exposure source, and a light amount sensor that detects the amount of reflected light from the standard pattern and the document. An image sensor, a delay circuit that delays the output of the light amount sensor in accordance with the delay in the output of the image sensor, and an A/D converter that converts the analog output of the image sensor into a digital value.
A D conversion means, a storage means for storing the output value of the A/D conversion means, and a level 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. A level setting means for outputting a voltage in synchronization with the output of the image sensor; and a standard for A/D conversion of the A/D conversion means by adding the output of the delay circuit and the output of the level setting means at a predetermined ratio. Addition means outputs to the voltage input terminal and when the standard pattern is irradiated by the exposure source, the output value of the A/D conversion means stored in the storage means reaches a predetermined level. A light quantity adjustment device for an image reader, comprising a determining means for changing the output of the setting means and maintaining the output after reaching a predetermined level.