JPH0575798A - Digital scanner - Google Patents

Abstract

PURPOSE:To make the service life of a light source long by controlling a light storage time of a photoelectric conversion element in response to an output signal of the photoelectric conversion element. CONSTITUTION:When a scanning section (not shown) reaches a position at which a reference white board at an end of an original platen (not shown) reads, the mode enters the shading correction data mode. At first, a gate 16 is opened by a signal Gate 1 and a picture signal at the outside of an original read region enters an arithmetic operation section 23 as digital data via a CCD 20, an amplifier 21 and an A/D converter 22 by plural lines. An output of the arithmetic operation 23 enters a comparator 30 synchronously with a line synchronizing signal PHISG via ROMs 24,25 and a latch 27. The comparator 30 compares the output of the arithmetic operation section 23 with a count of a counter 29 representing a main scanning time and outputs the result to a CCD 20 as a control signal TC. The storage time of the CCD 20 is controlled with the control signal TC in proportion to an output signal voltage of the CCD 20, resulting that the MTF in the subscanning direction is corrected and the resolution of the picture is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital scanner for reading a document.

[0002]

2. Description of the Related Art Conventionally, in a digital scanner, while a document is sub-scanned at a constant speed by the movement of a traveling body, the document is illuminated by a light source composed of a fluorescent lamp and its reflected light image is reflected by a CCD (charge coupled device) or the like. There is a type of converting into an image signal by the photoelectric conversion element of. Here, the fluorescent lamp is driven via an inverter circuit (fluorescent lamp ballast) and blinks. C
A photoelectric conversion element such as a CD is used which converts a reflected light image from a document into electric charges, accumulates the electric charges for a predetermined time, converts the electric charge amount into an image signal, and outputs it. Also, in general,
An image signal from the photoelectric conversion element is A / D converted by an A / D converter after being controlled to have a constant voltage by an automatic gain control (AGC) amplifier.

In this digital scanner, since the traveling body moves within the light accumulation time of the photoelectric conversion element, the image signal from the photoelectric conversion element is blurred, that is, the image from the photoelectric conversion element is compared with the original image. It is known that the resolution of an image represented by a signal decreases (the MTF deteriorates).

Therefore, in the above digital scanner, the MTF is improved by shortening the lighting time of the fluorescent lamp to be shorter than the light accumulation time of the photoelectric conversion element to reduce the influence of the movement of the traveling body.

FIG. 2 shows the relationship between the ratio of the effective light accumulation time to the one-line sub-scan time of the photoelectric conversion element and the MTF. As can be seen from FIG. 2, the MTF decreases as the ratio of the effective light accumulation time to the one-line sub-scan time of the photoelectric conversion element increases.

Further, in a copying machine using a digital scanner, the background density of the original is detected to prevent the influence of the background density on the copy so as to prevent the influence of the background density on the copy. It is known to vary the reference voltage of.

Further, Japanese Unexamined Patent Publication No. 60-10590 describes a device for controlling the light amount of a light source for the purpose of dimming, and Japanese Unexamined Patent Publication No. 62-111561 discloses one for controlling the light amount by dimming. Have been described.

[0008]

In the above digital scanner, since the fluorescent lamp is made to blink, the output signal of the inverter circuit does not turn off immediately when the fluorescent lamp is turned off and there is afterglow, and a pulse signal with a low duty ratio. Therefore, when the fluorescent lamp is driven through the inverter circuit and blinked, the pulse signal does not match the light amount of the fluorescent lamp. Further, when a fluorescent tube having a thin tube such as φ8 is used, the life of the fluorescent lamp is shortened because the end portion of the fluorescent lamp is severely deteriorated especially by blinking the fluorescent lamp. In addition, since the amount of light of a fluorescent lamp changes depending on the tube temperature, an image signal is generally transmitted by an AGC.
A / D by controlling to a constant voltage with an amplifier
Since the A / D conversion is performed by the converter, the AGC amplifier is expensive and it is very difficult to widen the variable range of the gain of the AGC amplifier.

Similarly, in the copying machine using the digital scanner, the background voltage of the original is detected and the reference voltage of the A / D converter is varied, so that the image is displayed when the reference voltage of the A / D converter is low. There was a problem that the S / N of the signal deteriorates.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a digital scanner capable of improving the above-mentioned drawbacks and having a high accuracy and a low cost and a long life of a light source.

[0011]

In order to achieve the above-mentioned object, the invention of claim 1 is a photoelectric conversion element capable of controlling the light accumulation time independently of the scanning time of one line,
In a digital scanner having a light source for illuminating an original, and a sub-scanning unit for sub-scanning the original and causing an optical image from the original to enter the photoelectric conversion element and convert into an image signal,
The invention further comprises a light accumulation time control means for controlling a light accumulation time of the photoelectric conversion element according to an output signal of the photoelectric conversion element. A photoelectric conversion element capable of controlling the storage time, a light source for illuminating an original, and a sub-scanning unit for sub-scanning the original and causing an optical image from the original to enter the photoelectric conversion element to be converted into an image signal. The digital scanner having the optical scanner further comprises a light accumulation time control means for controlling a light accumulation time of the photoelectric conversion element according to an output signal of the photoelectric conversion element to correct a light quantity variation of the light source. According to the invention, the photoelectric conversion element capable of controlling the light accumulation time independently of the scanning time of one line, the light source for illuminating the original, the optical image from the original while the sub-scanning is performed on the original. To In a digital scanner having a sub-scanning means for projecting and converting into an image signal, a control signal for controlling the light accumulation time of the photoelectric conversion element is obtained from the output signal of the photoelectric conversion element, and an effective image of the scanning means is obtained. The digital scanner according to claim 4 is provided with a light storage time control means for changing the light storage time outside the scanning region, and in the digital scanner according to claim 1, a pixel address for controlling the light storage time of the photoelectric conversion element is provided. A counter that outputs a proportional output signal, and a comparator that compares the output signal of this counter with a value for determining the light accumulation time of the photoelectric conversion element and controls the light accumulation time of the photoelectric conversion element according to the comparison result. In the digital scanner according to claim 4, the light accumulation time control means has the light accumulation time control means. There is for controlling the light accumulating time of the photoelectric conversion element by varying the value.

[0012]

According to the first aspect of the invention, the original is illuminated by the light source, and the sub-scanning unit makes the optical image from the original incident on the photoelectric conversion element while sub-scanning the original to convert it into an image signal. Then, the light accumulation time control means controls the light accumulation time of the photoelectric conversion element according to the output signal of the photoelectric conversion element.

According to the second aspect of the present invention, the original is illuminated by the light source, and the sub-scanning unit makes the optical image from the original incident on the photoelectric conversion element while sub-scanning the original to convert it into an image signal. Then, the light accumulation time control means controls the light accumulation time of the photoelectric conversion element according to the output signal of the photoelectric conversion element to correct the light amount fluctuation of the light source.

According to the third aspect of the present invention, the original is illuminated by the light source, and the sub-scanning unit makes the optical image from the original incident on the photoelectric conversion element while sub-scanning the original to convert it into an image signal. The light accumulation time control means obtains a control signal for controlling the light accumulation time of the photoelectric conversion element from the output signal of the photoelectric conversion element and changes it outside the effective image scanning area of the scanning means.

According to a fourth aspect of the invention, in the digital scanner according to the first aspect, the light accumulation time control means outputs an output signal proportional to the pixel address for controlling the light accumulation time of the photoelectric conversion element by the counter. The output signal of the counter and a value for determining the light accumulation time of the photoelectric conversion element are compared by the comparator, and the light accumulation time of the photoelectric conversion element is controlled by the comparison result.

According to a fifth aspect of the present invention, in the digital scanner according to the fourth aspect, the light accumulation time control means controls the light accumulation time of the photoelectric conversion element by varying the value.

[0017]

First, an outline of an embodiment of the present invention will be described. This embodiment is an example in which a CCD whose light storage time (charge storage time) can be changed by a control signal TC is used as a photoelectric conversion element capable of controlling the light storage time independently of the scanning time of one line. The output signal voltage of the CCD can be controlled by controlling the width of the control signal TC. FIG. 4 shows the relationship between the control signal TC and the line synchronization signal ψSG. In FIG. 4, t ₀ is the main scanning time (the cycle of the line synchronization signal ψSG), t ₁ is the light accumulation time of the control signal TC, and t ₂ is the delay time of the control signal TC.

In this embodiment, the control signal TC is used to improve the MTF in the sub-scanning direction to realize the light amount correction of the light source made of a fluorescent lamp and the AE mechanism (background removal mechanism). An output signal proportional to the amount of received light (lx · sex) is output. Therefore, a change in the light amount of the light source or a change in the reflected light amount due to the background density of the document is corrected by changing the light accumulation time of the CCD in inverse proportion to the change amount of the light amount.

Now, an A obtained by A / D converting the output signal of the CCD
If the D / D conversion data is D ₀ and the target value to be controlled is Da, Then, the MTF in the sub-scanning direction can be improved if t ₁ 'is set to a new light accumulation time of the CCD. However, the control signal TC
When the line synchronization signal ψSG has the timing as shown in FIG. 4, it is better to manage the delay time t ₂ more than the line synchronization signal ψSG by directly managing the light accumulation time t ₁ of the control signal TC.

Then, substituting t ₁ = t ₀ -t ₂ into the above equation (1), It is understood that t ₂ may be varied by performing the calculation. In this way, in this embodiment, the control value can be determined by calculation, so that open loop control is possible.

Next, this embodiment will be described in detail. FIG. 1 shows a circuit configuration of this embodiment, and FIG. 3 shows a mechanical portion of this embodiment.

When the print switch is turned on, the light source 11 composed of a fluorescent lamp is turned on and the fluorescent lamp 11 and the mirror 12 are turned on.
The scanning unit consisting of 14 starts moving from the home position (HP) in the sub-scanning direction at a constant speed. A scale 16 is arranged adjacent to the end of the document table 15.
A reference white plate 17 having a reference white density is arranged on the lower side of 6. Then, the fluorescent lamp 11 irradiates the reference white plate 17, the document on the document table 15 and the like with light while moving, and the reflected light is imaged on the CCD 20 via the mirrors 12 to 14, the shading correction plate 18 and the lens 19. Photoelectrically converted into an image signal. The CCD 20 is driven by the line synchronization signal ψSG via the inverter 33.

When the scanning units 12 to 14 reach the position where the reference white plate 15 is read, the shading correction data fetching operation is started. At this time, first, as shown in FIG. 5, the gate 16 is opened by the gate signal Gate1 from the control unit (not shown), and the image signal of the effective main scanning area (outside the original reading area) is transmitted from the CCD 20 via the amplifier 21 for a plurality of lines. Digital data D after being A / D converted by the A / D converter 22
_It becomes ₀ , and this digital data D ₀ is input to the arithmetic unit 23 through the gate 16. The calculation unit 23 performs calculations such as detecting peak values of the input image signals for a plurality of lines and calculating an average value thereof, and the calculation result D ₁
Is output to the ROM 24. The ROM 24 performs a calculation of D ₂ = Da / D ₁ (3) from the data D ₁ from the calculation unit 23 and the target value Da, and outputs the result D ₂ to the ROM 25.

At this time, the selector 26 selects the initial value Db by the selection signal Sel from the control unit (not shown) and outputs it as the data D ₄ to the ROM 25, and the ROM 25 D ₃ = (1−D ₂ ) Dmax + D ₂ D ₄ (4) is calculated and output to the latch circuit 27. here,
Dmax is a value obtained by changing the main scanning time t ₀ to the count value of the counter 29, and the data D ₄ is the line synchronization signal ψS.
The value corresponds to the delay time t _{2 of} G. Counter 2
9 is cleared by the line synchronization signal ψSG, counts the pixel clock synchronized with the pixel signal in the image signal, and outputs a count value proportional to the pixel address.
The latch circuit 27 latches the output data D _{3 of the} ROM 25 in synchronization with the line synchronization signal ψSG by the gate signal Gate2 input from the control unit (not shown) via the OR circuit 28, and the selector 26 receives the selection signal Sel by the latch circuit 2.
Output data from 7 is selected. The comparator 30 outputs the output data of the selector 26 to the count value D of the counter 29.
It is compared with c and the result of this comparison is output to the CCD 20 as the control signal TC whose high level time changes. CCD
The light accumulation time t _{1 of} 20 is controlled by the control signal TC from the comparator 30 so as to be proportional to the output signal voltage of the CCD 20, the MTF in the sub-scanning direction is corrected, and the image resolution is improved. The image signal from the CCD 20 is an amplifier 2
1, shading circuit 31 via A / D converter 22
Is sent to the shading correction circuit 31, and the shading correction circuit 31 creates shading correction data from the image signal from the A / D converter 22 and stores the shading correction data in the memory.

After this correction is completed, the AE (background removal mechanism) mode is not selected and the AE mode signal AE
When MODE has not risen, the gate 16 is closed by the gate signal Gate1 and the image signal from the CCD 20 is sent to the shading circuit 31 via the amplifier 21 and the A / D converter 22. The shading correction circuit 31 performs shading correction on the image signal D ₀ from the A / D converter 22 using the shading correction data,
The image is output to the image processing device 32, subjected to predetermined processing, and then output to a printer for recording.

When the AE mode is selected,
When the AE mode signal AEMODE and the gate signals Gate1 and Gate2 from the control unit rise at the timings shown in FIG. 7, the gate 16 causes the gate signal Gate1 to detect the background portion of the original in the image signal within a plurality of lines. It is turned on so as to detect each part, and each part in a plurality of lines is passed through, and the arithmetic unit 23 selects the peak value of each line from the image signal from the gate 16 and outputs it as data D ₁ . This data D ₁ is calculated by the ROMs 24 and 25 as D ₃ = (1−D ₂ ) Dmax + D ₂ D _{4 in the same} manner as in the above-mentioned formula (4) and output to the latch circuit 27.

The gate signal Gate2 is always active high during the document reading period in the AE mode, and the line synchronizing signal ψSG is input to the latch circuit 27 via the OR circuit 28 so that the output signal D _{3 of the} ROM 25 for each line. It is updated by being latched before. Accordingly, the amount of light received by the CCD 20 due to the influence of the background density of the document is corrected in real time.

The output signal of the latch circuit 27 is selected by the selector 26 by the selection signal Sel, and the comparator 30
The control signal TC is generated by comparison with the count value Dc of the counter 29, the CCD 20 controls the light accumulation time by the control signal TC from the comparator 30, and the MTF in the sub-scanning direction is corrected, thereby improving the image resolution. To do.

When the light storage time t ₁ of the CCD 20 is changed by the control signal TC, as shown in FIG.
There is the resolution of the change to the image changes, changes in MTF by the light accumulating time t _1/1 line scanning time of CCD20 the latch timing of the latch circuit 27 is controlled to be 30% or less by the control unit The effect of is ignored. However, this MTF in the sub-scanning direction is subject to the performance of a lens for forming an original image on the CCD 20, and if the resolution of the printer is poor, there is no point in improving the resolution of the scanning unit, which is systematic. since also vary by thinking, the fact that either below percentage light accumulating time t _1/1 line scanning time of the CCD20 is to be determined in consideration of these things.

According to this embodiment, since the light accumulation time of the CCD 20 is controlled according to the output signal of the CCD 20, it is not necessary to blink the fluorescent lamp 11, the life of the fluorescent lamp 11 can be extended, and the AGC amplifier can be used. Since it is not necessary to use it, the cost is low, and the S / N ratio of the image signal is improved, so that the accuracy can be improved. In addition, the CCD 20 is independent of the one line cycle.
Since the light accumulation time t _{1 of} is controlled by the control signal TC,
Since the output signal of the CCD 20 can be controlled by one signal line, the structure can be simplified, and the signal TC for controlling the light accumulation time t ₁ is changed outside the effective image area (outside the original image reading area). be able to. Moreover, the control signal T
Since the pulse width of C and the output signal of the CCD 20 are proportional to each other, open loop control of the light accumulation time t ₁ of the CCD 20 is possible and the speed of the control system may be slow, and the input signal voltage of the analog processing circuit may be reduced. Can be made constant and S / N can be increased. Since the variable range of the output signal voltage of the CCD 20 is wide, it is possible to adjust the light amount of the fluorescent lamp 11 and the sensitivity difference of the CCD 20 without adjustment. In addition, the control signal TC
Is a pulse signal, the control step can be easily made fine. Furthermore, since the cycle of one line is constant, it can be controlled by an external synchronization signal.

FIG. 6 shows the configuration of the arithmetic unit 23. The arithmetic unit 23 is composed of a peak hold circuit 34, an average value circuit 35, and a selector 36. The peak hold circuit 34 is cleared by the line synchronization signal ψSG, and peak-holds the data D ₀ from the gate 16. The output signal of the peak hold circuit 34 is averaged by the average value circuit 35, and the selector 36 outputs the output signal of the peak hold circuit 34 and the average value circuit 3 by the AE mode signal AEMODE.
One of the 5 output signals is selected and output as data D ₁ .

[0032]

As described above, according to the present invention, since the light accumulation time of the photoelectric conversion element is controlled according to the output signal of the photoelectric conversion element, the light source can be highly accurate and inexpensive and can have a long service life.

[Brief description of drawings]

FIG. 1 is a block diagram showing a circuit configuration of an embodiment of the present invention.

FIG. 2 is a characteristic curve diagram showing a relationship between a ratio of effective light accumulation time to one line sub-scanning time of a photoelectric conversion element and MTF.

FIG. 3 is a cross-sectional view showing a mechanism portion of the above embodiment.

FIG. 4 is a timing chart showing the relationship between the control signal and the line synchronization signal in the above embodiment.

FIG. 5 is a timing chart of the above embodiment.

FIG. 6 is a block diagram showing a calculation unit of the above embodiment.

FIG. 7 is a timing chart of the above embodiment.

[Explanation of symbols]

 16 gate 20 CCD 22 A / D converter 23 arithmetic unit 24, 25 ROM 26 selector 27 latch circuit 28 OR circuit 29 counter 30 comparator

Claims (5)

[Claims] 1. A photoelectric conversion element capable of controlling a light accumulation time independently of a scanning time of one line, a light source for illuminating a document, and a light image from the document while the document is sub-scanned. In a digital scanner having a sub-scanning unit that is incident on an element and converted into an image signal, a light accumulation time control unit that controls a light accumulation time of the photoelectric conversion element according to an output signal of the photoelectric conversion element is provided. A digital scanner characterized by. 2. A photoelectric conversion element capable of controlling the light accumulation time independently of the scanning time of one line, a light source for illuminating an original, and a light image from the original while photoelectrically converting the original while photoelectrically converting the original. In a digital scanner having a sub-scanning unit which is incident on an element and converted into an image signal, a light accumulation time of the photoelectric conversion element is controlled according to an output signal of the photoelectric conversion element to correct a light amount variation of the light source. A digital scanner comprising a light storage time control means. 3. A photoelectric conversion element capable of controlling the light accumulation time independently of the scanning time of one line, a light source for illuminating a document, and a light image from the document while the sub-scanning is performed on the document. In a digital scanner having a sub-scanning unit which is incident on an element and is converted into an image signal, a control signal for controlling a light accumulation time of the photoelectric conversion element is obtained from an output signal of the photoelectric conversion element, and a control signal of the scanning unit is obtained. A digital scanner comprising a light accumulation time control means for changing outside the effective image scanning area. 4. A digital scanner according to claim 1, wherein the counter outputs an output signal proportional to a pixel address for controlling the light accumulation time of the photoelectric conversion element, the output signal of the counter and the photoelectric conversion element. A digital scanner characterized in that the light accumulation time control means has a comparator for comparing with a value for determining the light accumulation time and controlling the light accumulation time of the photoelectric conversion element according to the comparison result. 5. The digital scanner according to claim 4, wherein the light storage time control means controls the light storage time of the photoelectric conversion element by varying the value.