JPH06325194A - Image pickup device - Google Patents

Abstract

PURPOSE:To prevent the flicker of a picked-up image due to the pulsation of illumination light without detecting the pulsation period of the illumination light. CONSTITUTION:A CCD image sensor 10 consists of a photodetection part 20, a shift register 22, a transfer gate 24, and a sweeping-out transfer gate 26 and operates with output pulses from a CCD driving circuit 30. Namely, the sweeping-out transfer gate 26 lets the photodetection part 20 be in operation at every timing point obtained by dividing the pulsation period of the illumination light by fives and the transfer gate 24 transfers electric charges obtained by the operation to the shift register 22 in order. Then the shift register 22 accumulates electric charges of exposure for 5 times transferred from the transfer gate 24 and outputs the accumulated electric charges as an image signal. Consequently, the image signal is hardly affected by the pulsation of the illumination light and the generation of its flicker can be suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image pickup apparatus for picking up an object illuminated by illumination light including a pulsating component, such as illumination light from a fluorescent lamp turned on by a commercial power source, and more particularly, imaging by pulsating illumination light. The present invention relates to an imaging device that suppresses flicker that occurs in a captured subject image.

[0002]

2. Description of the Related Art Conventionally, an image of a subject is picked up by using an image pickup device such as a CCD image sensor, and the picked-up subject image is processed to obtain a barcode or an O mark attached to the subject.
An optical information reading device for reading optical information such as CR characters is known.

Further, in this type of apparatus, when the image pickup apparatus picks up an image of a subject with illumination light from a fluorescent lamp that is turned on by a commercial power supply, the illumination light generated according to the power supply frequency of the commercial power supply is used. Since the captured image may fluctuate due to pulsation, in order to prevent this, for example, as shown in FIG. 6A, the exposure cycle of the image sensor constituting the imaging device is synchronized with the pulsation cycle of the illumination light. . In addition,
FIG. 6A shows the amount of illumination light when the imaging device is operated at an exposure period of 2 msec. In an exposure period that is synchronized with the pulsation period 1/120 sec. Of the illumination light that occurs when the power supply frequency is 60 Hz. And the exposure timing of the imaging device.

However, when such a device is used in an area where the power supply frequency is different, the pulsation cycle of the illumination light changes, so that flicker occurs in the picked-up image and it becomes impossible to read the optical information accurately. That is, for example, as shown in FIG. 6A, the pulsation cycle 1 of the illumination light generated when the exposure cycle of the image sensor is the power frequency 60 Hz.
The imaging device set to synchronize with / 120 sec.
As shown in FIG. 6B, when used in an area where the power supply frequency is 50 Hz, the pulsation cycle of the illumination light becomes 1/100 sec., And the exposure cycle of the image sensor does not synchronize with the pulsation cycle of the illumination light. The amount of light incident on each image sensor during exposure is
It changes at each exposure timing. For example, when a signal from the image pickup device is binarized to read a barcode,
Due to such a change in the amount of incident light, the binarized data changes, making it impossible to read the barcode accurately.

Therefore, conventionally, in an image pickup apparatus for picking up an image of a subject illuminated by illumination light from a fluorescent lamp containing a pulsating component corresponding to a power supply frequency, the subject is stabilized even if the pulsation cycle of the illumination light changes. The pulsation cycle of the illumination light itself or the power supply frequency of the commercial power supply that turns on the fluorescent lamp is detected in order to enable the image pickup to be performed, and the exposure cycle of the image pickup element that constitutes the image pickup apparatus is detected according to the detection result. Is considered to be controlled (JP-A-4-130866,
JP-A-1-303878).

[0006]

However, since such an image pickup device detects the pulsation period of illumination light, the frequency of a commercial power source, etc., and sets the exposure period of the image pickup element, it is not a general image pickup device. The detection circuit for detecting the pulsation cycle of the illumination light or the frequency of the commercial power supply, and the control circuit for setting the exposure cycle of the image sensor according to the detection result must be provided, which complicates the apparatus configuration. There was such a problem.

The present invention has been made in view of the above problems, and does not detect the pulsation cycle of illumination light, the frequency of a commercial power source, or the like, and does not change the exposure cycle of an image pickup device constituting an image pickup apparatus. The purpose is to prevent flicker of a captured image caused by a change in the pulsation cycle of illumination light.

[0008]

SUMMARY OF THE INVENTION The present invention, which has been made to achieve the above object, receives reflected light from an object illuminated by illumination light containing a pulsating component and accumulates electric charges according to the amount of received light. A light-receiving unit composed of a large number of one-dimensionally or two-dimensionally arranged image pickup devices and a predetermined exposure period preset corresponding to the pulsating period of the illumination light are used to expose the light-receiving unit for a predetermined exposure time. Exposure control means for accumulating electric charges in the respective image pickup devices, and taking in the electric charges accumulated in the respective image pickup devices by the operation of the exposure control means, converting the electric charges into an image signal representing the subject image, and outputting the image signal. In the image pickup device having the output means, the exposure time is divided into a plurality of times, and the exposure control means is configured to expose the light receiving section a plurality of times within the exposure cycle,
Each time the exposure control means exposes the light receiving portion within the exposure cycle, the charge accumulated in each of the image pickup devices is taken in,
A storage unit for accumulating is provided, and further, the output unit is configured to convert the charge accumulated in the storage unit within the exposure cycle into an image signal representing the subject image and output the image signal. There is.

[0009]

In the image pickup apparatus of the present invention configured as described above, the exposure control means first exposes the light receiving section a plurality of times within the exposure cycle set corresponding to the pulsation cycle of the illumination light.
Therefore, in each of the image pickup devices in the light receiving section, an electric charge corresponding to the amount of reflected light from the subject is accumulated each time the exposure is performed. Also,
Since the electric charge accumulated in the light receiving unit by the exposure is sequentially taken in by the electric storage unit, the electric storage unit stores the total amount of the electric charges accumulated in the image pickup device by the plurality of exposures in the exposure cycle. Then, the output unit converts the electric charges accumulated in the power storage unit within the exposure cycle into an image signal representing a subject image and outputs the image signal.

That is, in the image pickup apparatus of the present invention,
Rather than exposing the light receiving section only once within the exposure cycle set corresponding to the pulsating cycle of the illumination light as in the conventional apparatus, the exposure time for accumulating charges in each image sensor during the exposure cycle is set. By dividing the image sensor into a plurality of parts, the exposure of each image sensor is performed multiple times within the exposure cycle without changing the exposure time within the exposure cycle of each image sensor, and the charge obtained by this exposure is temporarily stored in the power storage unit. After being accumulated and the exposure within the exposure cycle is completed, the electric charges are converted into an image signal representing a subject image and output.

Therefore, even if the reflected light from the subject pulsates due to the pulsation of the illumination light, the amount of charge accumulated in the power storage unit substantially corresponds to the average value of the reflected light from the subject, and the Even if the pulsation cycle of the illumination light changes from the design value due to the change, the amount of charge accumulated in the power storage unit does not change significantly due to the pulsation of the illumination light, and the image signal changes significantly at each exposure cycle. You will be able to suppress.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. First, FIG. 2 is a configuration diagram showing a schematic configuration of a bar code reader of an embodiment to which the present invention is applied.

As shown in FIG. 2, the bar code reader 2 of this embodiment uses a fluorescent lamp 4 for illumination, which is installed indoors and is turned on by a commercial power source, and emits illumination light from the fluorescent lamp 4. The barcode label 6 is imaged by the reflected light reflected from the barcode label 6, and the barcode printed on the barcode label 6 is read from the captured image. The barcode label 6 is imaged. This one-dimensional CCD image sensor 10 and the reflected light from the barcode label 6
A mirror 12 for guiding the light to the side, a lens 14 for collecting reflected light from the barcode label 6 and forming an image of the barcode label on the light receiving surface of the CCD image sensor 10,
The control circuit 16 drives the CCD image sensor 10 to capture an image of the barcode label 6 and processes the captured image to read the barcode.

As shown in FIG. 1, the CCD image sensor 10 has a large number of image pickup elements arranged in a line for converting the reflected light from the bar code label 6 incident through the mirror 12 and the lens 14 into electric charges. The light receiving section (so-called photodiode array) and the electric charges transferred from the image pickup elements of the light receiving section 20 are respectively accumulated, and the accumulated charges are sequentially output by drive pulses φ1 and φ2 input from the outside. A shift register 22, a transfer gate 24 that receives a transfer pulse φTG input from the outside and transfers the charge accumulated in each image sensor of the light receiving unit 20 to the shift register 22, and a sweep input from the outside Pulse φ
Upon receiving the TGE, the sweep transfer gate 26 that sweeps out the charge accumulated in each image sensor of the light receiving unit 20, and the output signal from the shift register 22, that is, the image signal that is the image pickup result of the barcode label 6 is amplified. The control circuit 1 is a well-known device including an amplifier 28 for outputting to a signal processing circuit for reading a bar code provided in the control circuit 16.
6 receives various control pulses .phi.1, .phi.2, .phi.TG, .phi.TGE output from the CCD drive circuit 30 provided in the circuit 6.

Further, these various control pulses φ1, φ2,
As shown in FIG. 3, the CCD drive circuit 30 that outputs φTG and φTGE operates by receiving an internal clock output from an oscillator (not shown) provided in the control circuit 16.
It is mainly composed of four pulse generation circuits 31, 32, 33, 34 and three AND circuits 36, 37, 38.

Each of the pulse generating circuits 31 to 34 has a built-in timer which counts an internal clock and counts the time. The pulse signals P1, P2, P3 and P4 are different from each other in accordance with the timing result of the timer. To occur. That is, as shown in FIG.
A pulse signal P1 having a duty ratio of about 6% (pulse width of about 10 μsec.) With 0 sec. As one cycle, and a pulse ratio of about 24% (pulse width of 1/600 sec. Is about 0.4 msec.) Pulse signal P2
The pulse generation circuit 33 outputs a pulse signal P3 having a duty ratio of 50% with one cycle of 1 μsec., And the pulse generation circuit 34 has a duty ratio of 50 with a cycle of 1/60 sec.
% Pulse signals P4 are generated respectively.

A synchronizing signal is input from the pulse generating circuit 31 to the pulse generating circuit 32 which outputs the pulse signal P2 so that the falling edge of the pulse signal P2 coincides with the falling edge of the pulse signal P1. Next, the AND circuit 36 outputs the pulse signal P1 and the pulse signal P4 to the AN
In the D circuit 37, the pulse signal P2 and the pulse signal P4 are
The inverted signal of the pulse signal P4 inverted by the NOT circuit NOT1 and the pulse signal P3 are input to the AND circuit 38, respectively. And these AND circuits 36 to 38
Is Hi only when each input pulse is high level.
gh level, and either one of the input pulses becomes Lo
If it is at w level, it outputs a signal at Low level.

Therefore, from the AND circuit 36, the pulse signal P is output every one cycle (1/60 sec.) Of the pulse signal P4.
4 is at a high level for 1/120 sec., A pulse signal corresponding to the pulse signal P1 is output, and this pulse signal is transferred to the transfer gate 24 in the CCD image sensor 10 as a transfer pulse φTG shown in FIG. It is output as is.

Further, the pulse signal P4 is output from the AND circuit 37 every one cycle (1/60 sec.) Of the pulse signal P4.
During 1/120 sec. When it becomes High level, pulse signal P2
A pulse signal corresponding to is output. Then, this pulse signal is inverted by the NOT circuit NOT2 to become the sweep pulse φTGE shown in FIG. 4, and is output to the sweep transfer gate 26 in the CCD image sensor 10.

Furthermore, from the AND circuit 38, the pulse signal P4 is output every one cycle (1/60 sec.) Of the pulse signal P4.
4 is at a low level for 1/120 sec., A pulse signal corresponding to the pulse signal P3 is output, and this pulse signal is directly output to the shift register 22 in the CCD image sensor 10 as the driving pulse φ1 shown in FIG. To be done.

The pulse signal from the AND circuit 38 is not only output to the shift register 22 as the drive pulse φ1 but also to the NOT circuit NOT3 provided in the CCD drive circuit 30, and this NOT circuit NOT3. Will be reversed at. Then, the inverted signal of the drive pulse φ1 is used as the drive pulse φ2, and the CCD image sensor 10
It is output to the internal shift register 22.

The CCD drive circuit 30 thus constructed
In the CCD image sensor 10 that operates by receiving the output pulses φ1, φ2, φTG, and φTGE from, the sweep transfer gate 26 first removes the charges in the light receiving unit 20 while the sweep pulse φTGE is at the high level. Since the light is discharged, the charges corresponding to the image of the barcode label 6 are not accumulated in the light receiving unit 20, and the light receiving unit 20 corresponds to the image of the barcode label 6 after the sweep pulse φTGE becomes the low level. The accumulated charge is accumulated. That is, the sweep transfer gate 26 functions as an electronic shutter in the CCD image sensor 10, and implements the exposure control means of the present invention together with the CCD drive circuit 30 that generates the sweep pulse φTGE.

Next, before the rising of the sweep pulse φTGE, the transfer pulse φTG is at the High level.
When the electric charge corresponding to the image of the barcode label 6 is accumulated in the light receiving unit 20, the transfer gate 24 operates and the light receiving unit 20
The electric charges accumulated in the shift register 22 are transferred to the shift register 22.

The drive pulses φ1 and φ2 for driving the shift register 22 do not change during 1/120 sec. When the pulse signal P4 is at the high level, and 1 μsec. Is one cycle during the next 1/120 sec. And repeatedly invert. Therefore, in the shift register 22, 0.4 msec. Is applied to the light receiving unit 20 by the sweep pulse φTGE in 1/120 sec.
The electric charge accumulated during the exposure time of is transferred five times through the transfer gate 24.

On the other hand, the shift register 22 of this embodiment is
So-called 2 which operates by two drive pulses φ1 and φ2
Since it is a phase clock CCD, drive pulses φ1, φ2
Is stable, the inputted charges are sequentially accumulated. Therefore, the shift register 22 sequentially accumulates the charges transferred from the transfer gate 24 five times in 1/120 sec., And in the subsequent 1/120 sec., The accumulated exposure time 2 msec. (= 0.4 msec. ..Times.5) charges are sequentially output as image signals by the drive pulses .phi.1 and .phi.2. That is, the shift register 22 operates as a power storage unit and an output unit in the present invention.

As described above in detail, in the bar code reader 2 of the present embodiment, when the bar code label 6 is imaged, the charge storage time (that is, exposure time) per one time of the light receiving section 20 is 0.4 msec. . As the light receiving unit 2
0 is operated 5 times during 1/120 sec., The charges accumulated in the light receiving section 20 by the 5 operations are sequentially accumulated in the shift register 22, and during the next 1/120 sec.
The electric charge for 2 msec. Of exposure time accumulated in the shift register 22 is output as an image signal.

Therefore, the bar code reader 2 of this embodiment is used.
Is used in an area where the power supply frequency is 60 Hz, and the pulsation cycle of the illumination light from the fluorescent lamp 4 is 1/120 sec.
As shown in FIG. 5A, since the electric charge corresponding to the image of the barcode label 6 is accumulated in the light receiving unit 20 at a specific timing obtained by dividing the pulsation cycle into five parts, the dotted line is shown in FIG. As described above, the amount of electric charge output as an image signal from the CCD image sensor 10 does not change due to the pulsation of the illumination light.

Further, when the bar code reader 2 of the present embodiment adapted to the region of the power source frequency of 60 Hz is used in the region of the power source frequency of 50 Hz, FIG.
Since the pulsating cycle of the illumination light is 1/100 sec., The charge accumulation timing (that is, the exposure timing) of the light receiving section 20 is not constant within the pulsating cycle of the illumination light, but the CCD image sensor 10 The charge output as an image signal is the total amount of charge obtained by five exposures, and therefore its value does not change significantly due to the pulsation of illumination light, as shown by the dotted line in FIG. Without
It is possible to prevent the image signal output from the CCD image sensor 10 from changing due to the pulsation of the illumination light.

In this embodiment, the electric charge accumulated in the light receiving portion 20 by exposure is sequentially accumulated in the shift register 22. However, for example, a capacitor or the like may be provided between the transfer gate 24 and the shift register 22. You may make it provide the electric storage part for charge accumulation which consists of.

Further, in the present embodiment, the description has been made on the assumption that the electric charge which is the photoelectric conversion result is stored in the light receiving portion 20 which performs photoelectric conversion, but in order to increase the sensitivity of the light receiving portion 20,
The light receiving unit 20 may be composed of a photoelectric conversion unit and a charge storage unit. Further, in the present embodiment, the bar code reader using the one-dimensional sensor as the CCD image sensor has been described, but the present invention can be applied not only to the two-dimensional image sensor, but also to a television camera or the like. Any device can be applied as long as it is a device that captures a subject image by reflected light from the subject.

[0031]

As described above in detail, in the image pickup apparatus of the present invention, the light receiving portion is exposed a plurality of times within the exposure cycle set corresponding to the pulsation cycle of the illumination light, and the exposure is obtained by this exposure. The electric charge is once stored in the power storage unit, and after the exposure within the exposure cycle is completed, the electric charge is converted into an image signal representing a subject image and output. Therefore, according to the present invention, the pulsation cycle of the illumination light is changed without detecting the pulsation cycle of the illumination light, the frequency of the commercial power source, or the like, and without changing the exposure cycle of the image pickup device constituting the image pickup apparatus. It is possible to suppress the flicker of the captured image caused by.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a CCD image sensor of an embodiment.

FIG. 2 is a configuration diagram illustrating a schematic configuration of a barcode reader according to an embodiment.

FIG. 3 is a circuit diagram showing a configuration of a CCD drive circuit according to an embodiment.

FIG. 4 is a time chart showing the operation of the CCD drive circuit of the embodiment.

FIG. 5 shows an image pickup operation of the CCD image sensor of the embodiment,
It is explanatory drawing represented for every area where a power supply frequency differs.

FIG. 6 is an explanatory diagram showing an image pickup operation of a conventional image pickup apparatus for each region having a different power supply frequency.

[Explanation of symbols]

2 ... Bar code reader 4 ... Fluorescent lamp 6 ... Bar code label 10 ... CCD image sensor 16 ... Control circuit 2
0 ... Light receiving part 22 ... Shift register 24 ... Transfer gate 26 ...
Sweeping transfer gate 30 ... CCD drive circuit 31, 32, 33, 34 ... Pulse generation circuit 36, 37, 38 ... AND circuit

Claims (1)

[Claims] 1. A light receiving section comprising a large number of one-dimensionally or two-dimensionally arranged image pickup elements for receiving reflected light from a subject illuminated by illumination light containing a pulsating component and accumulating charges according to the amount of received light. An exposure control unit that exposes the light receiving unit for a predetermined exposure time at a predetermined exposure cycle that is preset corresponding to the pulsating cycle of the illumination light, and accumulates electric charges in each of the image pickup devices; An image pickup apparatus comprising: an output unit that takes in the electric charge accumulated in each of the image pickup devices by the operation of the exposure control unit, converts the electric charge into an image signal representing the subject image, and outputs the image signal. And the exposure control means is configured to expose the light receiving section a plurality of times within the exposure cycle, and each time the exposure control means exposes the light receiving section within the exposure cycle. Image sensor It captures the accumulated charge,
An electric storage unit for accumulating is provided, and the output unit is configured to convert the electric charge accumulated in the electric storage unit within the exposure cycle into an image signal representing the subject image and output the image signal. Image pickup device.