JPH11239297A - Image input device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image input device capable of eliminating flickers generated in the case of photographing an object illuminated with a fluorescent lamp by controlling the time interval of reading the signal charges from a CCD solid-state image pickup element. SOLUTION: This device is provided with a CCD driving means 6 for controlling the storage, read and transfer of electric charges in the CCD solid-state image pickup element 1, and the CCD solid-state image pickup element 1 is controlled so as to execute storage, read and transfer of the electric charges per every two fields by the CCD driving means 6. Further, it is provided with a control means 7 for dividing the interval of reading the signal charges into first, second and third intervals and periodically controlling the interval of reading.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image input apparatus using a solid-state image pickup device, which has a function of removing a flicker of an image generated when an image is captured by illumination of a fluorescent lamp.

[0002]

2. Description of the Related Art Conventionally, as a means for communicating with a person at a remote place, there has been known a video conference system which simultaneously transmits video information in addition to audio information. With the spread of the Internet and the Internet, a video conference system that realizes image encoding / decoding by software using a CPU of a personal computer has appeared.

The above-described image encoding / decoding processing is called a codec, and is a technology corresponding to the heart of a video conference system. In this image encoding process, intra-frame encoding for compressing an image only in one frame and inter-frame encoding for compressing an image by detecting a motion vector from a difference between a plurality of frames are used together. , Realizes highly efficient encoding.

Therefore, the smaller the difference between frames, that is, the smaller the change in the image, the more the amount of compressed data can be reduced, and high-quality image transmission becomes possible. In particular, when an image is processed in real time by software using a personal computer, it is desirable that the amount of data handled is as small as possible.

[0005]

By the way, a video conference is usually held in a room illuminated by a fluorescent light or the like.

However, under fluorescent lamp illumination, flicker may occur in the image signal due to the relationship between the frequency of the power supply and the vertical scanning frequency of the video camera.

To explain the occurrence of flicker, FIG. 5 shows a case where a subject illuminated by a fluorescent lamp operating at a power supply frequency of 50 Hz is photographed by an NTSC video camera (for example, the electronic shutter speed is set to 1/250. (When the time is set to seconds).

FIG. 6 is a general block diagram for explaining the structure of an interline transfer type CCD solid-state imaging device 1 used in a video camera. The optical image of the subject is converted into an electric signal by the photoelectric conversion unit 11 in FIG.

This charge is used as a vertical synchronizing signal (FIG. 5B).
The unnecessary charges are accumulated for a necessary period immediately before being read out to the vertical transfer CCD 12 at a timing synchronized with the above, and unnecessary charges before that are discharged to another place (for example, a deep part of the substrate).
That is, like the shutter pulse shown in FIG.
In a period in which charge accumulation is unnecessary, a pulse is applied to sweep out (discard) the charge, and the pulse is stopped only for the accumulation period (1/250 second in this example) immediately before reading is performed.
Electric charges are stored in the photoelectric conversion unit 11.

The vertical transfer pulse shown in FIG. 5D is an example of a pulse for driving the vertical transfer CCD 12, and has a ternary level. The level of this vertical transfer pulse is H
By setting the signal level to the IGH level (read pulse in FIG. 5D), the signal charges stored in the photoelectric conversion unit 11 can be read out to the vertical transfer CCD 12. The charges read to the vertical transfer CCDs 12 are sequentially transferred through the vertical transfer CCDs 12 by the number of stages corresponding to one scanning line during the horizontal blanking period, and finally transferred to the horizontal transfer CCDs 13. Then, the charges for one scanning line are sequentially transferred through the horizontal transfer CCD 13 during the horizontal scanning period, and then converted and amplified into a voltage signal by the charge detection / output amplifier unit 14 and output.

When an NTSC video camera is used at a power supply frequency of 50 Hz, flicker is caused by the brightness cycle of the fluorescent lamp (FIG. 5A) and the vertical scanning cycle of the video camera (FIG. 5A).
Since this is repeated every 50 mS, which is the least common multiple of (b), the video signal output from the CCD solid-state imaging device changes every three fields as shown in FIG. 5 (e).

The flicker caused by such a fluorescent lamp increases the difference signal between frames, increases the amount of data to be processed in the codec, increases the load on the system, and also reduces the image quality itself. Measures are needed.

For this purpose, Japanese Patent Application Laid-Open No. Hei 9-270950 proposes a method of thinning out image data in accordance with a flicker occurrence period. However, this method limits the frame rate of an image that can be transmitted. There is a problem.

In a recent video conference system, a method of fixing an electronic shutter speed to 1/100 second is often used. However, the electronic shutter speed is reduced to 1/10
If it is fixed to 0 seconds, the exposure time cannot be changed, so the video signal will be saturated near the window or in a brightly lit place, causing loss of whiteness. There is a problem that the video signal cannot be obtained.

The present invention has been made in view of such a point, and in a region where a power supply frequency is 50 Hz, an electronic shutter speed of a video camera is fixed to 1/100 second under an environment illuminated by a fluorescent lamp. It is an object of the present invention to provide an image input device capable of completely removing a flicker component without performing.

[0016]

According to the present invention, there is provided an image input apparatus for transmitting an image picked up by a CCD solid-state image pickup device as a digital signal to an external device. The CCD drive means for controlling the accumulation, readout and transfer of the electric charge in the above-described C drive so that the charge, accumulation and readout and transfer of the electric charge are performed once every two fields by the CCD drive means
The CD solid-state imaging device is controlled, and furthermore, the interval for reading out signal charges is divided into first, second, and third intervals, and the interval for reading out signal charges is periodically controlled.

Further, the image input device of the present invention is characterized in that the CC
The D driving means controls the accumulation time of the signal charge in the CCD solid-state imaging device to be longer than one field period.

Further, the image input device of the present invention includes a power supply frequency detecting means, and sets an interval for reading out signal charges in the CCD solid-state imaging device by the CCD driving means in accordance with the power supply frequency detected by the detecting means. It is intended to be controlled.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an image input apparatus according to the present invention will be described below with reference to FIGS.

<First Embodiment> FIG. 1 is a block diagram showing an embodiment of an image input apparatus according to the present invention. In FIG. 1, an optical image of a subject is converted into an electric signal by a CCD solid-state imaging device 1. Then, the CDS (Cor
related Double Sampling: Correlated Double Sampling, AGC (Automatic)
Gain Control: Automatic gain adjustment), ADC
(Analog to Digital Cover
ter: A / D converter) and the like, and is converted into a digital signal. Further, this digital signal is separated into a luminance signal and a chrominance signal by the signal processing means 3, subjected to white balance processing, gamma correction and the like, and converted into an appropriate image signal format (for example, YUV422,
YUV411 etc.).

The I / F means 5 is an interface circuit for inputting and outputting data to and from a personal computer (for example, a PC
I bus, PC card, USB, IEEE 1394, etc. are used.) The image memory 4 is used when the transfer speed of the image signal output from the signal processing unit 3 and the processing speed of the I / F unit 5 do not match. , For performing a speed conversion by buffering the image signal (if the transfer speed of the I / F means 5 is higher than the speed of the image signal output from the signal processing means 3, The above image memory 4
May be omitted).

The CCD driving means 6 includes various pulses for driving the CCD solid-state imaging device 1 and the pre-processing means 2.
The pulse necessary for the CDS / ADC of the above is generated. The control means 7 manages and controls the entire image input device.

Further, the image input apparatus of the present invention has a detecting means 8 for detecting a power supply frequency. The detection means 8 automatically detects a power supply frequency from a waveform of an AC power supply, automatically determines a power supply frequency from a flicker occurrence cycle, and provides a switch or the like to provide an area used by a user. May be manually set in accordance with the power frequency of the power supply.

FIG. 2 is a timing chart when an object illuminated by a fluorescent lamp flickering at a power frequency of 50 Hz is photographed by the image input device according to the first embodiment of the present invention. a) is a flickering cycle of the fluorescent lamp, (b), (c) and (d) are pulses generated by the CCD driving means 6 and (e) is an output of the CCD solid-state imaging device 1.

The CCD solid-state imaging device 1 employs an interline transfer system generally used in general-purpose video cameras as shown in FIG.

The signal charges stored in the photoelectric conversion unit 11 of the CCD solid-state imaging device 1 are read out to the vertical transfer CCD 12 by the first read pulse shown in FIG. Thereafter, the signal charges are sequentially transferred in the vertical transfer CCD 12 by the first transfer pulse in FIG. 2D, and are output via the horizontal transfer CCD 13 and the charge detection / output amplifier unit 14 (FIG. e)).

The CCD driving means 6 sets the power frequency to f
p (Hz), the interval between the first read pulse and the second read pulse of the vertical transfer pulse (FIG. 2D) (first
Read interval) and the interval between the second read pulse and the third read pulse (second read interval) is 3 / (2f
p), and the interval between the third read pulse and the next first read pulse (third read interval) is set to 4 / (2fp).
Set to seconds (in the present embodiment, the power supply frequency is 50H
Because of z, the first read interval and the second read interval are 0.03 seconds, and the third read interval is 0.04 seconds.)

As a result, the readout interval is an integral multiple of the flickering cycle of the fluorescent lamp, so that the charge accumulation period is always at the same timing as the flickering of the fluorescent lamp, and flicker can be prevented.

In the CCD driving means 6, if the period of the vertical synchronizing signal (FIG. 2B) is 262.5H (1H is one horizontal scanning period and 1/15734 second), the first readout interval is set. And the second reading interval to 472.5H,
Further, the third reading interval may be set to be 630H.

In a general video conference system,
In order to eliminate the difference in the TV system (for example, NTSC system, PAL system, etc.) of the imaging device to be used, an image signal is converted into a common intermediate format (Common Interme).
date Format: hereinafter abbreviated as CIF, the number of pixels is 360 (horizontal) × 288 (vertical) × 30 frames / second)
Has been converted to. For this reason, when the image input device according to the present invention is used in a video conference system, a frame rate of 30 frames / second is required. However, as shown in FIG. Since the charge is read once every two times, the frame rate required by the CIF can be secured, and a smooth screen display can be realized.

Further, since the read interval is set so that the read pulse is not applied during the vertical transfer period, the charge during the vertical transfer and the signal charge read from the photoelectric conversion unit do not mix in the vertical transfer CCD. A general-purpose CCD solid-state imaging device can be used without requiring a special storage mechanism in the CCD solid-state imaging device itself.

<Second Embodiment> Next, a second embodiment of the image input apparatus of the present invention will be described.

It is desirable that the subject to be photographed by the image input device be properly illuminated, but in practice, the illumination may be inappropriate. In particular, in a place where the illumination is dark, not only the screen becomes dark, but also the gain of the video signal is increased by the AGC processing of the preprocessing means 2, so that the noise increases,
There is a problem that the S / N ratio is deteriorated.

When the vertical synchronizing frequency is 60 Hz, the signal charge of the conventional image input device is 1/60 second (= 0.60 seconds) at maximum.
0167 seconds), whereas in the image input apparatus of the present invention, when the power supply frequency is 50 Hz,
3 / (2fp), which is the minimum value of the signal charge readout interval
It is possible to increase the maximum accumulation time of the signal charge until the second (= 0.03 second) (the accumulation time can be increased to 1.8 times the conventional value).

Therefore, when the illumination is dark, the shutter pulse is set by the CCD driving means 6 so that the accumulation time of the signal charge in the CCD solid-state imaging device 1 is longer than one field period (maximum 3 / (2 fp) seconds). By controlling the sweeping period of the CCD solid-state imaging device 1,
And the S / N ratio can be improved.

FIG. 3 is a timing chart for explaining the operation of the image input apparatus according to the second embodiment of the present invention (for example, when the electronic shutter speed is set to 0.025 seconds).

When the illuminance of the object is low, the number of shutter pulses (FIG. 3 (c)) to be discharged is reduced by the CCD driving means 6, and the accumulation period is increased. As a result, the accumulation time of the signal charge in the photoelectric conversion unit 11 of the CCD solid-state imaging device 1 is prolonged, and the amount of accumulated charge is increased, so that the sensitivity can be improved.

<Third Embodiment> Next, a third embodiment of the image input apparatus of the present invention will be described.

In Japan, there are an area where the power supply frequency is 50 Hz and an area where the power frequency is 60 Hz.

Therefore, as shown in FIG. 1, the image input apparatus of the present invention includes a detecting means 8 for detecting a power supply frequency. The power frequency detected by the detection means 8 is transmitted to the CCD driving means 6 via the control means 7.
Conveyed to. Then, the CCD driving means 6 generates various pulses for driving the CCD solid-state imaging device 1 according to the power supply frequency.

When the power supply frequency is 50 Hz, the above CCD
The driving means 6 drives the CCD solid-state imaging device 1 by the method described in the first and second embodiments.

FIG. 4 is a timing chart for explaining the operation of the image input device according to the third embodiment of the present invention when the power supply frequency is 60 Hz.

The CCD driving means 6 sets the power frequency to f
Assuming that p (Hz), when the power supply frequency is 60 Hz,
The interval between the first read pulse and the second read pulse of the vertical transfer pulse (FIG. 4D) (first read interval), the second
The interval between the read pulse and the third read pulse (second read interval) and the interval between the third read pulse and the next first read pulse (third read interval) are all 4 /
(2 fp) seconds (in the present embodiment, since the power supply frequency is 60 Hz, the first read interval = second read interval = third read interval = 0.0333 seconds).

As a result, the readout interval is an integral multiple of the flickering cycle of the fluorescent lamp, so that the charge accumulation period is always at the same timing as the flickering of the fluorescent lamp, thereby preventing flicker.

The CCD driving means 6 is provided with the CC driving means.
The accumulation time of signal charges in the D solid-state imaging device 1 is set to be longer than one field period (maximum 4 / (2 fp)).
Seconds), the shutter pulse sweep period can be controlled, so that when the illumination of the subject is dark, the sensitivity of the CCD solid-state imaging device 1 can be improved, and the S / N ratio can be improved.

[0046]

According to the first aspect of the present invention, since the image input apparatus of the present invention is configured as described above, the interval at which charges are read out from the CCD solid-state imaging device is set to an integral multiple of the blinking cycle of the fluorescent lamp. Therefore, the charge accumulation period is always at the same timing with respect to the flickering of the fluorescent lamp, and the occurrence of flicker can be prevented.

Further, it is possible to secure a frame rate (30 frames / second) required by the CIF employed in a general video conference system. Further, since the read interval is set so that a read pulse is not applied during the vertical transfer period, a special storage mechanism is not required for the CCD solid-state imaging device itself, and a general-purpose CCD solid-state imaging device can be used.

According to the second aspect of the present invention, the CC
Since the accumulation time of the signal charge in the CCD solid-state imaging device can be set to be longer than one field period by the D driving means, the sensitivity of the CCD solid-state imaging device is improved even in a dark place, and the S / N ratio is improved. be able to.

Further, according to the third aspect of the present invention, there is provided a detecting means for detecting a power supply frequency, and an interval for reading out signal charges in the CCD solid-state imaging device by the CCD driving means is controlled according to the power supply frequency. Therefore, even when the power supply frequency is 60 Hz, the effects described in the first and second aspects can be realized.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of an image input device of the present invention.

FIG. 2 is a timing chart for explaining the operation of the image input device according to the first embodiment of the present invention;

FIG. 3 is a timing chart for explaining the operation of the second embodiment of the image input apparatus of the present invention.

FIG. 4 is a timing chart for explaining an operation of the third embodiment of the image input apparatus of the present invention.

FIG. 5 is a general timing chart for explaining flicker occurring when an object illuminated by a fluorescent lamp operating at a power supply frequency of 50 Hz is captured by an NTSC video camera.

FIG. 6 is a general block diagram for explaining the structure of an interline transfer type CCD solid-state imaging device used in a video camera.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 CCD solid-state image sensor 2 Preprocessing means 3 Signal processing means 4 Image memory 5 I / F means 6 CCD drive means 7 Control means 8 Detection means 11 Photoelectric conversion part 12 Vertical transfer CCD 13 Horizontal transfer CCD 14 Charge detection / output amplifier part

Claims (3)

[Claims] An image input device for transmitting an image captured by a CCD solid-state imaging device as a digital signal to an external device.
A CCD driving means for controlling reading and transfer; controlling the CCD solid-state imaging device so that the CCD driving means performs accumulation, readout and transfer of electric charge once every two fields; An image input device, wherein an interval is divided into first, second, and third intervals, and control is performed to periodically control a reading interval. 2. An image input apparatus according to claim 1, wherein said CCD driving means controls the accumulation time of signal charges in said CCD solid-state imaging device to be longer than one field period. 3. An apparatus according to claim 1, wherein an interval at which said CCD driving means reads out signal charges in said CCD solid-state imaging device is controlled in accordance with a power supply frequency detected by said power supply frequency detection means. Image input device.