JPH0678207A - Fluorescent lamp flicker detector - Google Patents

Abstract

PURPOSE:To provide a fluorescent lamp flicker detector capable of detecting fluorescent lamp flicker from the high frequency component of an inputted video signal. CONSTITUTION:This detector is the fluorescent lamp flicker detector provided with a peak hold circuit 6 which holds the peak value of a video signal obtained from an image pickup device 3, plural sample-and-hold circuits 7, 8, 9, and 10 which sample and hold a peak-held input signal, and a means 11 which compares the output of a first sample-and-hold circuit and that of a last sample- and-hold circuit, thereby, an automatic focusing device from which the change of an optical path modulation signal due to the fluorescent lamp flicker can be eleiminated and with high precision can be provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fluorescent lamp flicker detection device suitable for application to an autofocus device for a color camera.

[0002]

2. Description of the Related Art Conventionally, in an autofocus device for a color camera, a method has been adopted in which a high frequency component of a video signal is detected, a signal level difference due to blur of a subject is detected, and a focus adjustment is performed based on the result. Was there.

[0003]

However, in such a conventional autofocus device for a color camera, a signal level difference occurs even with a change in the light amount of the light source. Therefore, light source flicker occurs in photographing under a fluorescent lamp. There was a problem that malfunction occurred.

The present invention solves the above problems, and an object of the present invention is to provide a fluorescent light flicker detection device capable of canceling fluorescent light flicker from high frequency components of a video signal to improve the accuracy of an automatic focusing device. And

[0005]

In order to achieve the above object, the present invention provides a peak hold circuit for holding a peak value of a video signal obtained from an image pickup device, and a peak hold input signal. A fluorescent lamp flicker detection device is provided which comprises a plurality of sample and hold circuits for sample and hold, and means for comparing a difference between an output of the first sample and hold circuit and an output of the last sample and hold circuit. .

[0006]

With the above configuration, the peak hold circuit peaks high frequency components of the video signal obtained from the image pickup device.
The peak-held signal is held and sample-held by a plurality of stages of sample-hold circuits, and the video signal is compared with the sample-hold signal after a certain vertical scanning period delay. Detect changes in signal level

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows the configuration of an automatic focusing device to which an embodiment of the present invention is applied. In FIG. 1, 1 is a focus lens, 2 is an optical path modulator, 3 is an imaging device,
4 is a bandpass filter, 5 is a detection circuit, 6 is a peak
Hold circuits, 7, 8, 9, and 10 are sample and hold circuits, and 11 is a differential amplifier. Reference numeral 12 is a drive circuit for driving the optical path modulator 2, and 13 is a drive circuit 12 for the optical path modulator 2.
The signal output of the differential amplifier 11 is synchronously detected in the driving cycle of
Rotation direction / speed detection circuit that detects the rotation direction of the focus lens 1 and its speed, 14 is the focus
A driving device for the lens 1 and a sync signal generating circuit 15 are provided.
16 is an output terminal of 4 times the vertical scanning period (15 Hz), 1
7 is a reset pulse output terminal, 18, 19, 20, 21
Is a sample and hold pulse output terminal, and 22 is fluorescent lamp flicker information.

In the above configuration, the fluorescent lamp flicker detection apparatus includes a peak hold circuit 6 for peak holding the peak value of the high frequency component of the video signal obtained from the image pickup device 3 for each vertical scanning period, and a peak hold circuit. 6
Four sample-and-hold circuits 7, 8, 9, and 10 arranged in series for sequentially sampling and holding the output of the above-mentioned sample at a double vertical scanning period, and the first sample-and-hold circuit 7.
2 and the output of the last sample and hold circuit 10. The fluorescent light flicker information 22 is information indicating whether to shoot under fluorescent light or not.

The operation of the fluorescent lamp flicker detection device according to the above embodiment will be described below. FIG. 2 shows a signal waveform in the automatic focusing device, and a is a pulse of a vertical scanning period (hereinafter abbreviated as Vp). Reference numeral b is a modulated wave of the optical path modulator 2, and the optical path-modulated light is converted into a video signal by the image pickup device 3 and a high frequency component is detected by the bandpass filter 4. Next, the detection circuit 5 detects the video signal, and the peak hold circuit 6 obtains a signal d synchronized with the modulated wave b. c is a reset pulse. The signal d is sampled and held at the timing e in the sample and hold circuit 7 of the first stage, and the output signal g is sampled and held at the timing f by the sample and hold circuit 8 of the second stage to output the output signal h. To get

If there is no fluorescent light flicker information 22, that is, if the image is not taken under a fluorescent light, the sample and hold circuits 9 and 10 in the third and fourth stages remain in the sample and hold state, and the first stage. The output signal g of the sample-and-hold circuit 7 and the output signal h of the second-stage sample-and-hold circuit 8 are input to the differential amplifier 11. The differentially amplified signal is the focus direction of the focus lens 1.
It is input to the speed detection circuit 13.

FIG. 3 shows a method for detecting the rotation direction and speed. Optical path modulation means Foc
Since this corresponds to shifting the us position, the output signal increases when vibrating as Near-Far at the position of a, which is before the focus. Also, at a position B farther than the focus, Ne
The vibration of ar-Far reduces the signal level. When vibrating near the in-focus point, the change in signal level becomes small. From the above operation, if the vibration of the optical path modulator 2 and the changing direction of the output signal of the differential amplifier 11 are compared,
The rotation direction of the lens 1 is determined, and the focusing speed is determined by the signal level. Therefore, according to the information of the rotation direction / speed detection circuit 13, the driving device 14 focuses on
The lens 1 is driven to perform focusing.

However, when there is a fluorescent lamp flicker, the signal d in FIG. 2 is not only modulated in the optical path, but also the fluorescent lamp flicker is simultaneously superimposed. Therefore, it is necessary to remove this fluorescent light flicker. The method will be described below.

Fluorescent lamp blinking cycle i and vertical scanning cycle j shown in FIG.
Comparing with, it can be seen that the luminance level is the same at a rate of once per 6 times the vertical scanning period, that is, Vp1 and Vp7. Therefore, if there is fluorescent light flicker information 22,
The signal h sampled and held by the sample-and-hold circuit 7 in the first stage is further processed by the sample-and-hold circuits 8, 9 and 10 in the second and subsequent stages, respectively.
The sample signal is sequentially sampled and held by k and l, and the output signal n is obtained by delaying the signal h by 6 times the vertical scanning period.
The fluorescent lamp flicker can be detected by comparing and with the differential amplifier 11.

[0014]

The present invention can detect a fluorescent lamp flicker with the above-described structure, and by applying this to an automatic focusing device, the accuracy of removing the change in the optical path modulation signal due to the fluorescent lamp flicker can be eliminated. It is possible to realize a high-performance autofocus device.

[Brief description of drawings]

FIG. 1 is a block diagram of an autofocus device to which a fluorescent lamp flicker detection device according to an embodiment of the present invention is applied.

FIG. 2 is a waveform diagram showing signal waveforms of various parts in the automatic focusing device shown in FIG.

FIG. 3 is a principle diagram showing a rotation direction / speed detection method of a focus lens in the automatic focusing device shown in FIG.

[Explanation of symbols]

 1 Focus Lens 2 Optical Path Modulator 3 Imaging Device 4 Band Pass Filter 5 Detection Circuit 6 Peak Hold Circuit 7, 8, 9, 10 Sample and Hold Circuit 11 Differential Amplifier 12 Drive Circuit 13 Rotation Direction / Speed Detection Circuit 14 Drive Device 15 Synchronous signal generation circuit 16 Vertical scanning cycle output terminal 17 Reset pulse output terminal 18, 19, 20, 21 Sample and hold output terminal 22 Fluorescent light flicker information

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tadayuki Morishita 4-17-15 Tarumachi, Kohoku Ward, Yokohama City, Kanagawa Central Engineering Co., Ltd.

Claims (1)

[Claims] 1. A peak hold circuit for peak-holding a peak value of a high frequency component of a video signal obtained from an image pickup device for each vertical scanning cycle, and a vertical scanning cycle for doubling the peak-held input signal. Compare the difference between the output of the first sample-and-hold circuit and the output of the last sample-and-hold circuit of the four sample-and-hold circuits connected in series Flicker detection device comprising: