JPS6170867A - Fluorescent light flicker detector - Google Patents

Abstract

PURPOSE:To detect a fluorescent light flicker component in a video signal in a video camera by providing a circuit holding a peak value of a luminance signal at each vertical period and at each N times period, comparing outputs of both the circuits to detect the flicker. CONSTITUTION:An electric signal subject to photoelectric conversion in an image pickup device 1 is converted into a luminance signal by a processing circuit 2. An H.V gate 3 extracts the luminance signal of a required pattern area, a peak hold circuit 4 detects a peak of the luminance signal at each vertical period to execute holding. A sample-and-hold circuit 5 samples and holds an output of the peak hold circuit 4 at each 6-times of vertical period (frequency of vertical period of video camera is 60Hz and power frequency of fluorescent light is 50Hz). Outputs of the circuits 4, 5 are compared at comparators 8, 9 and when the reference level is at the outside of the peak hold value, an output of an NOR circuit 10 goes to H.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a fluorescent flicker detection device in a video camera.

Conventional configuration and its problems Since the two lighting frequencies of the fluorescent lamp under the 5011z power supply voltage and the vertical period frequency (60 Hz) of the video camera cannot be synchronized, when a subject is photographed with a video camera, There was a drawback that the brightness level of the video signal changed. For example, in an autofocus method that captures a subject and changes the optical path length of the light that enters the imaging device, and detects changes in the frequency components of the video signal to determine if the focus is out of focus, the frequency components of the video signal There was a problem in that it was not possible to determine whether the change in the output signal level was due to a shift of 7 orcus or the change in the brightness level of the fluorescent lamp flicker.

OBJECTS OF THE INVENTION The present invention eliminates the drawbacks of the above-mentioned conventional example, and detects a fluorescent lamp flicker component contained in a video signal captured by a video camera under, for example, 5011z fluorescent lamp illumination. The purpose is to

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a peak hold circuit that peak-holds the peak value of a luminance signal obtained by an imaging device for each vertical period, and a peak-hold circuit that holds the peak value of a luminance signal obtained by an imaging device every vertical period. It consists of a sample hold circuit that holds a value, and a flicker detection circuit that compares the outputs of both circuits and obtains information about the light source.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings. In FIG. 1, 1 is an imaging device.

2 is a luminance signal processing circuit, 3 is a gate circuit for extracting a luminance signal corresponding to a desired screen area, and 4 is a peak hold circuit for detecting the peak of the signal output from the H-V gate circuit 3. , hold and reset once every lV. 5 is a sample hold circuit, 6 and 7 are level shift circuits that shift the voltage level, 8 and 9 are comparator circuits, 10 is an OR circuit, 12 is a synchronization signal generation circuit, and 14 is an H − generated by the synchronization signal generation circuit 12. V gate pulse output terminal, 15 is the V pulse output terminal.

16 is a seven-node pulse output terminal, 17 is 1 every 6 ■
The output terminal 18 is the output terminal for the 6V pulse to be output, and is the output terminal for the comparison pulse. 11 is a level detection circuit, and the output level obtained from the OR circuit 10 is sent to the comparison pulse output terminal 1.
8, it is determined whether or not the value is when a pulse is present, and the level is detected. 13 is an output terminal for the level detection result.

Next, the operation of the above embodiment will be explained. In FIG. 1, an imaging device 1 converts light into an electrical signal. A luminance signal is obtained by passing the electrical signal converted by the imaging device 1 through the luminance signal processing circuit 2.

This is passed through H-■ gate circuit 3 to I-1- shown in FIG.
Only the luminance signal of the necessary screen area is taken out by the V gate and pulse b and inputted to the peak hold circuit 4, where the peak of the luminance signal is detected and held for each IV. As shown in FIG. 2, the held value is reset by the input pulse C from the synchronizing signal generating circuit 12 before the next V/% pulse a arrives. Since the 50Hz fluorescent lamp lighting cycle and the vertical cycle of the video camera match only at 6 times the V cycle, the 6V pulse d holds the peak of the luminance signal from the peak hold circuit 4 once every 6V as shown in Figure 3. The sample and hold circuit 5 samples and holds the value, and a level shift circuit 6.7 sets reference levels 1'l+E2 above and below it. The comparator 8 compares the peak-held luminance signal of the 1V period with the voltage level EI + E2 in the reference range set after sample-holding.
Compare each at 9, and input to OR and circuit IO. Otherwise, when the peak hold value goes out of the reference level, 011
．． The circuit 10 outputs υH. OIt, the output of the circuit 10 is detected by the level detection circuit 11 at the timing of the comparison pulse e in FIG. The lighting frequency of a 50Hz fluorescent lamp is 10011z, and the vertical cycle of the video camera is 6
It is 011z. Therefore, 5 times the period of 100fiz and 6
The two match at three times the period of 011z and the period of 2011z. FIG. 4 shows the timing of the vertical cycle (pulse of vl''-V7) and the fluorescent lamp light intensity level at that time.

It can be seen from FIG. 4 that the brightness levels match at a cycle of 3V. However, v, , v3. v, , v, is an odd field periodic pulse, V2, ``4, ``a
U This is a periodic pulse of an even field, and depending on the position of the scanning line, the brightness levels at the timings of vl and V4 may not match depending on the subject. Therefore, sample and hold is performed once every 6V, but the timing of the comparison pulse e must be performed at a timing outside the 3V cycle. When the comparison pulse is output, the input is high.
If so, it can be determined that there is fluorescent lamp flicker.

In the above embodiment, the case where the (.V gate circuit 3) is included is described, but the present invention is not limited to the case where the gate circuit 3 is included.

Effects of the Invention The present invention has the above-described configuration, and if fluorescent lamp flicker can be detected and this is added to the video camera to correct the fluorescent lamp flicker, it can be used when performing automatic focus adjustment in the video camera. performance can be further improved.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a fluorescent lamp flicker detection device according to an embodiment of the present invention, and FIGS. 2 to 4 are timing charts illustrating the operation of FIG. 1. 1... Imaging device, 2... Luminance signal processing circuit, 3
...H・■Gate circuit, 4...Peak hold circuit, 5...Sample hold circuit, 6,7...Level shift circuit, 8,9...Comparator, 10...O
R circuit, 11...level detection circuit.

Claims (2)

[Claims] (1) A peak hold circuit that holds the peak value of the luminance signal obtained from the imaging device every vertical period, a sample hold circuit that holds the peak value every N times the vertical period, and the outputs of both of the above circuits. A fluorescent lamp flicker detection device consisting of a flicker detection circuit that compares the light source and obtains flicker information of the light source. (2) The flicker detection circuit comprises a circuit that level shifts the output of the sample hold circuit, and a circuit that compares the output of this circuit with the output of the peak hold circuit to detect fluorescent lamp flicker. Fluorescent lamp flicker detection device as described in .