JPH0457562A - Picture reader - Google Patents

Abstract

PURPOSE:To eliminate a difference from an output due to radiating light quantity by sampling and holding a signal outputted synchronously with idle transmission of a dummy signal among picture element signals outputted from a CCD and using the sampled and held value as a correction value so as to apply dark current correction processing. CONSTITUTION:The reader is provided with a storage time control circuit 202 controlling a charge storage time of a charge coupled device(CCD) 201 and a light quantity control circuit 203 controlling light quantity of a light source 204 lighting the CCD 201. Then an output at a dark state generated from a light receiving face of the CCD 201 is corrected by using a correction value obtained by controlling the light quantity inputted to the light receiving face for the storage time of the CCD 201. Moreover, the output at dark state generated from a storage electrode and the CCD register is corrected by using the correction value obtained through sample and hold of the signal outputted synchronously with idle transmission of a dummy signal among picture element signals outputted from the CCD 201. Thus, a difference from an output value due to radiating light quantity is eliminated.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to an image reading device used in an electrophotographic device, a facsimile, a video camera, etc., and particularly relates to dark current correction of an image reading device using a CCD image sensor. It is something.

[Conventional technology]

Image sensors such as CCDs (charge-coupled devices) used as photoelectric conversion elements in document reading devices such as scanners, video cameras, etc. output a voltage even when no light is incident on them. It has an output called dark output.

This tends to increase as the operating speed of the image sensor decreases, in other words, as the charge accumulation time increases, and as the temperature increases.

FIG. 5 shows a dark output voltage-temperature characteristic diagram of a general CCD (TCDl 16DC).

As is clear from this figure, the dark output voltage/saturated output voltage changes significantly even if the storage time or temperature changes slightly. Here, the saturated output voltage refers to a voltage value beyond which the output voltage does not increase even if the amount of light is increased.

Furthermore, although the storage time can be made constant by an electrical timing signal, the temperature can vary by several tens of degrees depending on the conditions of use. Therefore, the dark output at low temperatures and the dark output at high temperatures are significantly different.

For example, within the range of normal use, the dark output doubles for every 8°C rise.

In addition, since the dark output is mixed into each pixel signal output from the CCD, in order to obtain the true image signal, the CCD
It is necessary to perform a so-called dark current correction process in which the dark output value is subtracted from the CD output.

This dark current correction process is performed while referring to FIGS. 6 to 8.
This will be explained in more detail.

FIG. 6 is a chip circuit diagram showing an example of a typical CCD (TCDI 16DC). The CCD shown in the figure is a 146-inch sensor with five high-sensitivity CCD sensor chips arranged in a staggered pattern.
It is a 40-pixel contact type color CCD linear image sensor.

The CCD 600 shown in this figure includes a photodiode array 602 having a plurality of photodiode cells 601,
A barrier electrode 603 arranged on the side of the photodiode array 602, a storage electrode 604, and the barrier electrode 60
3 and the storage electrode 604, respectively.
5, and line shift gates (1 to 7) 606 and shift gates 607 arranged on the sides of the storage electrode 604.
and a horizontal CCD register 608 arranged outside the shift gate 607.

It also includes reset gates 609a and 609b respectively arranged on the other end side of the horizontal CCD register 608, and an output section 610 that takes in the pixel signal output from the horizontal CCD register 608 and outputs it from the output terminal O8. There is.

The bin names in the figure are as follows.

φIA-Clock (1st phase) φ2A-Clock (2nd phase) φ2B-Final stage clock (2nd phase) φ■, ~φV7...-Line shift gate SH-Shift gate R3-Reset gate OD---Power supply O3-Signal output SS--Ground In the above configuration, the operation will be explained based on the timing chart shown in FIG.

The shift gate 607 is supplied with a shift signal SH (FIG. 7(a)
)), each pixel signal obtained by the up-and-down operation of the CCD 600 is sent to the shift gate 607.
It is transferred to the horizontal CCD register 608 side via.

Thereafter, the clock signals φIA, φ2A, φ28 (FIGS. 7(b) and (C)),
Every time the reset signal R3 (Fig. 7(d)) is supplied,
Each pixel signal stored in the horizontal CCD register 608 is output pixel by pixel, and this is output to the output section 610.
As shown in FIG. 7(e), the output terminal O5
is output from.

Furthermore, in this case, the pixel signal (FIG. 7(e)) output from the CCD 600 is divided into a dummy signal (for 72 pixels) and an effective pixel signal (for 292B pixels).

Here, the effective pixel signal indicates the read image,
An image can be reproduced by reproducing this signal. In addition, the above dummy signal includes an empty signal for empty feeding (
24 pixels) and a light-shielded pixel signal (48 pixels) output from the light-shielded cells of the photodiode cells 601.

In the dark current correction process, the light shield pixel signal is sampled and held based on the signal DS (Figure 7) output in synchronization with the light shield pixel signal, and then the value of each effective pixel signal is The true signal voltage is obtained by subtracting the value of the light shield pixel signal from

FIG. 8 shows a circuit that executes dark current correction processing such as the sample hold processing and subtraction processing described above.

This dark current correction circuit includes an operational amplifier 805, an analog switch 806, a capacitor 801, and three resistors 8
02 to 804, and DS signal (Figure 7))
is supplied, the analog signal is closed, and the voltage value of the light shield pixel signal supplied at this time is transferred to the capacitor 80.
Keep it at 1.

Further, while each effective pixel signal is being supplied, an operational amplifier 805 subtracts the voltage value held in the capacitor 801 from the value of each effective pixel signal to extract a difference, and this difference is used for dark current correction. The pixel signal is supplied to a subsequent circuit (not shown) as a completed pixel signal (true pixel signal).

Note that the voltage value held in the capacitor 801 is held until the next DS signal is input.

[Problem to be solved by the invention]

The dark current correction process in the above conventional example is a signal DS (see Fig. 7) which is output in synchronization with this light shield pixel signal.
Based on this, the light shield pixel signal is sampled and held, and then the value of the light shield pixel signal is subtracted from the value of each effective pixel signal to obtain the true signal voltage.

In this way, the circuit configuration samples and holds the output value of the light-shielded pixel of the CCD and subtracts it from the image signal, but even though it is a light-shielded pixel, it may be There is a problem that there is a difference in output values.

In particular, in the case of an image sensor composed of a plurality of CCD chips, this causes a difference in output values, which becomes a difference between the chips and adversely affects the output image.

Furthermore, the above-mentioned dark output appears as the sum of what is generated on the light-receiving surface of the CCD and what is generated in the storage electrode and CCD register. Therefore, unless both dark outputs are effectively corrected, reliable dark current correction processing cannot be achieved.

The present invention has been made in view of the above, and eliminates the difference in output values caused by the amount of irradiated light, eliminates the negative effect on the output image, and eliminates the dark output that occurs in the storage electrode and CCD register. Instead, it is an object of the present invention to effectively correct the dark output generated on the light-receiving surface of a CCD, and always perform reliable dark current correction processing.

[Means to solve the problem]

In order to achieve the above object, the present invention provides an image reading device that performs image capturing processing using a CCD. The present invention provides an image reading device including a control means for sample-holding the sample-and-holding value and executing dark current correction processing using the sample-and-held value as a correction value.

Further, in an image reading device that performs imaging processing using a CCD, at least one of an accumulation time of the CCD and an amount of light input to a light receiving surface is controlled, and the CCD
Among the pixel signals output from the dummy signal, the image is equipped with a control means for sample-holding a signal output in synchronization with the blank feed portion of the dummy signal, and executing dark current correction processing using the sample-held value as a correction value. A reading device is provided.

[For production]

The image reading device according to the present invention corrects the dark output generated on the light-receiving surface of the CCD using a correction value obtained by controlling at least one of the storage time of the CCD and the amount of light input to the light-receiving surface. Of the pixel signals output from the CCD, the dark output generated by the register is sampled and held, and the signal output in synchronization with the blank feed portion of the dummy signal is corrected using the correction value obtained by this sample and hold.

〔Example〕

Hereinafter, one embodiment of the present invention will be described with reference to the drawings.
A detailed explanation will be given in the order of correction for the dark output generated on the light receiving surface of the CCD.

(2) Correction of dark output generated in storage electrodes and CCD registers FIG. 1 is a timing diagram corresponding to FIG. 7 described above.

The other configurations (FIG. 6) are the same as those described above, so the same numbers will be cited and explained.

A shift signal SH is applied to the shift gate 607 (FIG. 1(a)).
is supplied, each pixel signal obtained by the imaging operation of the CCD 600 up to that point is transferred to the horizontal CCD register 608 via the shift gate 607.

Thereafter, the clock signals φIA, φ2A, φ28 (FIG. 1(b), (C)),
Every time the reset signal R3 (Fig. 1(d)) is supplied,
Each pixel signal stored in the horizontal CCD register 608 is output pixel by pixel, and this is output to the output section 610.
As shown in Figure 1(e), output terminal O
Output from 8.

Further, in this case, the pixel signal (FIG. 1(e)) output from the CCD 600 is divided into a dummy signal (for 72 pixels) and an effective pixel signal (for 2928 pixels).

Here, the effective pixel signal indicates the read image,
An image can be reproduced by reproducing this signal. In addition, the above dummy signal includes an empty signal for empty feeding (
24 pixels) and a light-shielded pixel signal (488 pixels) output from the light-shielded cells of the photodiode cell 601.

The dark current correction process in this embodiment samples and holds the above-mentioned idle-feeding portion based on the signal DS (see Fig. 7) outputted in synchronization with the above-mentioned idle-feeding portion, and uses it as a correction value to The true signal voltage is obtained by subtracting the correction value from the value of each effective pixel signal.

As a result, the problem of difference in output value depending on the amount of irradiated light, which occurs when the light shield pixel signal is sampled and held, is solved.

■ Correction of the dark output generated on the light receiving surface of the CCD Fig. 2 is a block diagram showing an embodiment of the image reading device of the present invention. an accumulation time control circuit 202 that controls charge accumulation time of the CCD 201;
The white reference output output from C01 is taken in and the C0D
A light amount control circuit 203 that controls the amount of light from a light source 204 that illuminates the light source 201 is provided.

The operation of the above configuration will be explained with reference to FIG.

First, the dark output value and the reference image output value (white reference output) are detected at room temperature and with a fixed accumulation time and light intensity (FIG. 3(a)). Here, the reference image is
For example, the white reference plate 2 placed at the end of the CCD 201
This is an image of 05. However, it is assumed that each pixel signal obtained by imaging this white reference plate 205 is not saturated.

Next, when the temperature rises and the dark output value increases as shown in FIG. 3(b), the accumulation time control circuit 202 detects this and shortens the accumulation time of the CCD 201, as shown in FIG. (C
), the dark output value is set to be the same as that at room temperature. At this time, the white reference output value also decreases, so the light amount control circuit 203 controls the light source 204 to reduce the amount of light emitted from the light source 204. Increase the light amount and increase the white reference output value.

In this case, even if the amount of light emitted from the light source 204 is increased, the dark output value hardly changes, so as shown in FIG. 3(d), the dark output and white reference output are the same as at room temperature. can be obtained.

As mentioned above, the fact that the white reference output value does not change means that
Since the result is the same as if the normal image output value did not change, it is the same as compensating for the effect of temperature rise.

Further, the above embodiment will be specifically explained with reference to FIGS. 4A and 4B.

FIG. 4A is a block diagram showing a specific example of the accumulation time control circuit 202 shown in FIG.
02 is a comparator 401 that compares the dark output output from the CCD 20 and the dark output at a specific temperature of room temperature, an MPU 402 that calculates an accumulation time control signal based on the output of the comparator 401, and the MPU 40
A shift signal SH is generated at a repeating period based on an accumulation time control signal outputted from 2, and the shift signal S
Shift signal generation circuit 4 that supplies H to the CCD 201
03.

In the above configuration, the dark output sequentially output from the CCD 201 becomes larger (or smaller) than the dark output at a certain room temperature, and the output value of the comparator 401 becomes °゛L'' (or °``H''). ), MP
The U402 detects this and shortens (or lengthens) the repetition period of the shift signal SH output from the shift signal generation circuit 403 to stabilize the dark output value output from the CCD 201.

In addition, FIG. 4B shows the light amount control circuit 8203 shown in FIG.
is a block diagram showing a specific example of the light amount control circuit 203.
A comparator 404 that compares the white reference output output from the CCD 201 and a white reference output at a certain normal temperature, an MPU 405 that calculates a light amount control signal based on the output of the comparator 404, and a light amount output from the MPU 405. and a light amount control signal generation circuit 406 that generates a light amount control signal based on the control signal and supplies it to the light source 204.

In the above configuration, the white reference output sequentially output from the CCD 201 becomes thicker ((or smaller) than the white reference output at a certain room temperature, and the comparator 4
If the output value of 04 becomes "L" (or "'H"),
The MPU 405 detects this and controls the brightness of the illumination light emitted from the light source 204 by reducing (or increasing) the light amount control signal value output from the light amount control signal generation circuit 406, and controls the brightness of the illumination light emitted from the light source 204. The value of the white reference output output from is made constant.

In the above embodiment, the storage time of the CCD 201 and the brightness of the light source 204 are controlled so that the dark output and the white reference output are always kept constant even if the temperature changes. This prevents the dynamic range and S/N ratio from changing, or the effective pixel signal value from exceeding the correction range, even if the dark output changes significantly due to temperature changes. can do.

In addition, in the above embodiment, the accumulation time of the CCD and the brightness of the light source are controlled based on the dark output output from the CCD and the white reference output, but a temperature sensor is installed near the CCD. and MP based on the output information of the temperature sensor.
The storage time control signal and the light amount control signal may be output from U or the ROM.

Furthermore, in the above embodiment, the brightness of the light source is directly controlled, but a liquid crystal filter or the like is provided between the light source and the light receiving surface of the CCD, and the amount of light transmitted through the liquid crystal filter is controlled. A configuration may also be used in which the amount of light received by the CCD is controlled.

〔Effect of the invention〕

As explained above, according to the image reading device of the present invention, C
The dark output generated on the light-receiving surface of the CD is the accumulation time of the CCD,
The dark output generated in the storage electrode and CCD register is corrected by the correction value obtained by controlling at least one of the amounts of light input to the light-receiving surface. The signal that is output in synchronization with is sampled and held, and the correction value obtained by this sample and hold is used to correct the difference in output value caused by the amount of irradiated light, eliminating any negative effects on the output image. In addition, it effectively corrects not only the dark output generated by the storage electrode and CCD register, but also the dark output generated by the light receiving surface of the CCD, and always performs reliable dark current correction processing. can do.

[Brief explanation of drawings]

FIG. 1 is a timing chart showing the operation of a CCD in an image reading device according to the present invention, FIG. 2 is a block diagram showing an embodiment of the image reading device according to the present invention, and FIGS.
d) is a schematic diagram explaining the operation of the embodiment shown in FIG. 2;
Figure 4A is a block diagram showing the configuration of the accumulation time control circuit shown in Figure 2, Figure 4B is a block diagram showing the configuration of the light amount control circuit shown in Figure 2, and Figure 5 is a general CCD (
TCD116DC) dark output voltage-temperature characteristic diagram, Part 6
The figure shows a chip circuit diagram showing the configuration of a general CCD (TCD 116DC), and Figure 7 shows a conventional CCD (TCD 116DC).
16DC), and FIG. 8 is a circuit diagram showing a general dark current correction circuit. Explanation of symbols 201--CCD 202-accumulation time control circuit 20
3.-Light amount control circuit 204-Light source 205--White reference plate 600-CCD 602--Photodiode array 603--Barrier electrode 604-Storage electrode 605--Voltage dividing circuit 606-Lingid gate 60''1- --Shift gate 608-Horizontal CCD register

Claims (2)

[Claims] (1) In an image reading device that performs imaging processing using a CCD, among the pixel signals output from the CCD, a signal output in synchronization with the idle feed portion of the dummy signal is sampled and held; An image reading device comprising: a control means for executing dark current correction processing using the calculated value as a correction value. (2) In an image reading device that performs imaging processing using a CCD, at least one of the accumulation time of the CCD and the amount of light input to the light receiving surface is controlled, and among the pixel signals output from the CCD, An image reading device comprising: a control means for sample-holding a signal output in synchronization with the idle feed portion of a dummy signal, and executing dark current correction processing using the sample-and-hold value as a correction value.