JPH01305670A - Flicker removing device - Google Patents

Abstract

PURPOSE:To execute the removal of flicker with the sampling signal of a low frequency in a short period by executing sampling the natural number-fold period of the flashing period of a light source with a sampling frequency, which is a frequency excepting for the natural number-fold frequency of a flashing frequency being the 1/natural number of the sampling period. CONSTITUTION:A block 36 is operated as a color temperature information forming means to decide the color temperature of the light source and to generate a control signal, which controls the amplification factor of an R signal and a B signal outputted from an image pick-up terminal 10. The sampling timing of an A/D converter 24 is program-set by a microcomputer 26. Then, concerning the 2 natural number fold sampling period of the flashing period of the flashing light source, the sampling is executed by the sampling frequency, which is a frequency excepting for the natural number fold flashing frequency and being the 1/natural frequency of the sampling period. Thus, more effective sampling point can be obtained in shorter period, the low color temperature information, for which the flicker is removed, can be obtained with the low sampling frequency in the short period.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a flicker removal device.

[Conventional technology]

When photographing with an imaging device such as an electronic camera, a white subject may be photographed as colored depending on the wavelength spectrum of the illumination light source and/or the spectral sensitivity of the image sensor. Conventionally, in order to prevent this phenomenon, an automatic tracking white balance adjustment device is known that measures the color temperature of a light source and automatically adjusts the white balance of an imaging device according to the information.

Incidentally, under a flashing light source such as a fluorescent lamp, light flickers occur. This flicker has a frequency twice that of the commercial power supply frequency, and each color component has a different intensity. In human vision, this flicker
Although it is not often noticed, color sensors accurately detect periodic changes in the subject light caused by flickering of the light source, so its output also changes in magnitude at twice the frequency of the commercial power supply. .

As a countermeasure against flicker, video cameras have conventionally tried to eliminate the adverse effects of flicker using an analog low pass filter.

However, since the frequency of the signal component that must be removed is as low as 10011z, analog
A low bass filter must be provided, e.g.
There was a problem in that sufficient white balance adjustment could not be achieved within a short time after the power was turned on. This is useful for electronic still cameras, which are often photographed immediately after turning on the power.
This becomes a more prominent problem with cameras and the like.

For this purpose, a method for realizing white balance adjustment in a short time is disclosed in Japanese Patent Application Laid-Open No. 61-224796 and 61
-224797. The flicker component of a flickering light source such as a fluorescent lamp has a frequency 2f, which is twice the power supply frequency f, but in order to sample the component with a frequency of 2f, a sampling frequency of 4fs or more is required according to Nyquist's sampling theorem. It becomes necessary. Actually, flicker
contains quite a lot of harmonic components, so to remove flicker sufficiently, the sampling frequency must be 16.
It is desirable that it is f3 or more.

Conversely, since the flicker component consists only of 2f3 and its harmonics, the flicker component can be removed by taking the average value over a period that is a natural number multiple of 1/(2f,) (seconds).

Conventionally, using these principles, sampling is performed at a sampling frequency of 16fS or higher for a period of time that is a natural number multiple of 1/(2f,) [seconds], the sampling values are averaged, and the average value is based on the sampling frequency. The white balance was adjusted.

[Problem to be solved by the invention]

However, even if the above conditions are met, as shown in Figure 4, when the sampling frequency becomes a natural number multiple (n times) of 2fs, each mountain-shaped sampling point of the waveform will be in the same phase, and the sampling period will be No matter how long is, the number of effective sampling points remains n. Therefore, in order to eliminate even the harmonics of flicker, a considerably high sampling frequency was required.

As a result, when using control and calculation by a microcomputer, for example, the following problems arise. That is,
When the sampling frequency is set by a program, the operating speed becomes a burden on the program, and it is necessary to use a microcomputer with a fast operating speed. In addition, in the case of a configuration in which a large number of sampling values are collected using high-frequency sampling pulses and calculations are performed on a microcomputer after collection, memory to temporarily store the sampling values and time for calculations are required. This is unfavorable in terms of both cost and time.

Therefore, an object of the present invention is to provide a flicker removal device that eliminates such problems.

[Means to solve the problem]

The flicker removal device according to the present invention includes an optical sensor that converts light source light into an electrical signal, a sampling device that samples an electrical signal related to the color temperature of the light source light for a predetermined period, and an average of the sampling signals obtained by the sampling device. A flicker removal device comprising: averaging means, wherein the sampling means averages a frequency other than a natural number multiple of the blinking frequency for at least a sampling period that is a natural number multiple of 2 or more of the blinking cycle of a predetermined blinking light source. =4−, and is characterized in that sampling is performed at a cycle that is a natural number fraction of the sampling period.

[Effect]

By setting the sampling frequency and sampling period as described above, more effective sampling points can be obtained in a shorter period of time, and color temperature information from which flicker has been removed can be obtained with a lower sampling frequency and a shorter period of time. can.

Therefore, there is no need to use a microcomputer with high operating speed for flicker removal, and there is no need to prepare a memory for temporarily storing a large number of sampling points.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a configuration block diagram of an embodiment of the present invention,
FIG. 2 shows the sampling timing. In FIG. 1, 10 is an image sensor, 12 is an R (red) sensor with the same red spectral sensitivity as the image sensor 10, and 14 is a =〇-B (blue) sensor with the same blue spectral sensitivity as the image sensor 10. . Since the output signals 'R+'B of each sensor 12 and 14 have a very wide variation range, they are logarithmically compressed by logarithmic compression circuits 16 and 18.

The differential amplifier 20 outputs the output j! of the logarithmic compression circuit 16.18.
Signal 7 indicating the difference between og i ) 1 and it og i H! Output og(i*/1g). This results in
The ratio of the R component and the B component in the subject light is obtained.

The output of the differential amplifier 20 is applied to a D/A converter 24 via a low pass filter 22. D/A converter 24
converts the analog signal into a digital signal and supplies it to the microcomputer 26.

Note that the D/A conversion timing of the D/A converter 24, that is, the sampling timing is determined by the microcomputer 2.
The program is set by 6.

As is well known, the microcomputer 26 includes a CPU, R
It is equipped with an OM and a RAM, and the ROM stores a program for the procedure shown in FIG. The microcomputer 26 performs necessary calculations according to the procedure shown in FIG. 3, and outputs digital control signals CRn and CHD. D/A converter 2
8.30 converts the digital control signal CRD+ cnn into the analog control signal c, 1. Convert to CB.

32 is a variable gain amplifier for the R signal output from the image sensor 10, and 34 is a variable gain amplifier for the B signal output from the image sensor 10, the gains of which are controlled by control signals CR and CB, respectively. That is, the block 36 indicated by the broken line in FIG. 1 functions as a color temperature information forming means that determines the color temperature of the light source and generates a control signal for controlling the amplification factors of the R signal and B signal output from the image sensor 10. do. amplifier 32.3
White balance adjustment is performed by gain control of 4. G output of the image sensor 10 and amplifiers 32 and 34
The R signal and B signal output from the signal processing circuit 38
, where it is modulated and multiplexed to e.g.
It is converted to an SC standard television signal.

The sampling method in this embodiment will be explained with reference to FIG. 2. First, the sampling period is set to be a natural number times two or more of the blinking period of the blinking light source. Here, fluorescent lights are used as the flashing light source, and the flashing cycle is 10 (ms) in eastern Japan and 1000/120 = 50 in western Japan.
/6 Cm5). Therefore, in this embodiment, the sampling period is set to 50 (ms). In order to increase the number of effective sampling points, the sampling frequency is set to a frequency other than a natural number multiple of the blinking frequency, and the sampling period is set to a natural number fraction of the sampling period.

Specifically, we targeted fluorescent lights in eastern and western Japan.
Sampling period (50/17) as shown in Figure 2
(ms'), that is, the sampling frequency is 340 H
Perform sampling at z. In this case, the number of effective sampling points is 17.

Under the above setting conditions, the sampling frequency of 340 Hz appears to be high, but in eastern Japan it is 1000/ (10/1
7), that is, 1700Hz, and in western Japan it is 1000/ (
(50/6) /17), that is, 2040Hz.

FIG. 3 shows a flowchart of the operating program of the microcomputer 26. First, microcomputer 2
The variable n for the number of additions is set to 1, and the variable S for addition is set to O as initial values in a predetermined area of the RAM in 6 (Sl). The output of the differential amplifier 20 (i.e., the output of the LPF 22) is sampled and digitized by the A/D converter 24, and taken into the RAM area A of the microcomputer 26 (S2
). Next, let S be the sum of S and A, S3), n
It is checked whether or not is 17 (S4). If n is not 17,
Increment n (S5), adjust the time, and return to S2 (S6).

The time adjustment in S6 is such that the execution time in the loop of S2-S4-S6-S2 is set to the above-mentioned predetermined sampling period 50.
/17 (ms).

If S is equal to 17 in S4, divide S by 17 to calculate the average value AAV.
A digital control signal CRn +C6D is obtained from -AAV%CIID=c+d-AAv (S8).

Next, this control signal CHD+Cl1l is output to the D/A converter 28.30 (S9). Thereafter, in order to prepare for the next calculation, n-0+S=O is set (5IO), time is adjusted, and the process returns to step 32 (Sll).

In the above embodiment, two color sensors, R and B, were used, but instead, three color sensors, R, G, and B, are used to generate a signal eog (iu /lc) and B,
l! The same effect can be obtained by sampling the signal log(io/ic) indicating the ratio of :G to obtain the control signals CR and CB.

In addition, we have explained using an example of a light source that blinks at twice the frequency of the commercial power supply frequency, such as a fluorescent lamp, but the commercial type 1rtrW'J
The same applies to light sources that flicker at frequencies other than twice the wave number. That is, the sampling period is a period that is a natural number multiple of 2 or more of the blinking frequency of the light source, and sampling is performed at a sampling frequency that is a frequency other than a natural number multiple of the blinking frequency and has a period that is a natural number fraction of the sampling period. , flicker can be removed by averaging the sampled values.

〔Effect of the invention〕

As can be easily understood from the following explanation, according to the present invention, flicker contained in the light source light can be removed using a low frequency sampling signal and a short sampling period.

Therefore, even when setting the sampling period using a microcomputer, there are restrictions on the program,
There is no need to make the microcomputer operate particularly fast.

Furthermore, a high frequency sampling pulse generator is not required, and a memory area to store all the sampled values is also not required.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of the configuration of an embodiment of the present invention, Fig. 2 is an explanatory diagram of the sampling timing f in Fig. 1, Fig. 3 is an operation flowchart of Fig. 1, and Fig. 4 is a sampling in the conventional example. - It is an explanatory diagram of timing. 12----R (red) sensor 14-B (blue) sensor 16
．． 18 - Logarithmic compression circuit 20 - Differential amplifier 22 - Low bus filter 26 - Microcomputer 32
, 34-variable gain amplifier 36-color temperature information forming means

Claims (1)

[Claims] A flicker removal device comprising an optical sensor that converts light source light into an electrical signal, a sampling device that samples an electrical signal related to the color temperature of the light source light for a predetermined period, and an averaging device that averages the sampling signals obtained by the sampling device. The apparatus, wherein the sampling means, for a sampling period that is at least a natural number multiple of 2 or more of the blinking cycle of a predetermined blinking light source, uses a frequency other than a natural number multiple of the blinking frequency that is a natural number fraction of the sampling period. A flicker removal device characterized by sampling at a period of .