JPH0813100B2 - camera - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a camera that detects light from the outside and performs some control based on the detection result.

Conventional technology and its problems In cameras with automatic exposure control, the amount of incident light (subject brightness) is measured by a photometric element, and the amount of exposure is determined based on this measured amount of light.

On the other hand, since video cameras (including movie video cameras and still video cameras) handle color video signals, it is necessary to adjust the white balance of the color signals. A color temperature sensor detects the color temperature of the subject for white balance adjustment.

In a camera system in which the detection signals of such a photometric element or color temperature sensor are sampled multiple times at a predetermined cycle and taken into a control device (especially a CPU such as a microprocessor), in relation to artificial illumination light, There is a problem. That is, since the light of a natural electric light or a fluorescent light contains a ripple component having a frequency that is twice or four times the commercial frequency, only the bright part or the dark part of the ripple is sampled depending on the sampling period and sampling time. The problem is that the average incident light amount cannot be obtained.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a camera capable of measuring an average incident light amount even when photographing under an artificial illumination lamp having a ripple.

A camera according to the present invention inputs a detection signal of a ripple period measuring means for measuring a ripple period of artificial illumination light and a photodetector and samples the input detection signal at a period determined based on a given sampling control signal. Sampling circuit based on the ripple cycle measured by the ripple cycle measuring means, so that sampling is performed a plurality of times within a time corresponding to one cycle of the ripple cycle measured by the ripple cycle measuring means. The present invention is characterized by comprising sampling circuit control means for determining a sampling period of the circuit and for providing the sampling circuit with a sampling control signal representing the determined sampling period.

Here, the photodetector includes a photometric element for automatic exposure control, a color temperature sensor for white balance adjustment, and the like.

According to the present invention, the ripple cycle of the artificial illumination light is measured, and the sampling cycle of the photodetector is determined so that sampling is performed a plurality of times within the time of one cycle of the measured ripple cycle. The detection signal of the photodetector is sampled and captured a plurality of times at the determined sampling period. Therefore, it is possible to perform sampling without being biased only at a bright time point or a dark time point of the artificial illumination light having a ripple. Therefore, by calculating the average value of the sampled data, the average amount of light can be detected, and appropriate exposure control and white balance adjustment can be performed. Especially, it is possible to measure the ripple cycle of only a specific ripple component and sample at a sampling cycle determined by the measured ripple cycle. Can be detected.

Hereinafter, an embodiment in which the present invention is applied to a still video camera equipped with both a photometric element and a color temperature sensor will be described in detail. However, the present invention can be applied to a movie video camera as well. It is also applicable to a camera using a normal silver salt film, which has a color temperature sensor but does not have a color temperature sensor. Furthermore, in the following embodiments, the light of the incandescent light bulb is blocked by the bandpass filter to detect the ripple frequency of the fluorescent light, but the present invention detects the ripple frequency of the light from the incandescent light bulb and based on this. It is also possible to control the sampling period.

Description of Embodiments FIG. 1 is a block diagram showing a part of an electrical configuration of a still video camera (electronic still camera). 2 and 3 show the signal waveforms of each part of the circuit shown in FIG. 1. FIG. 2 shows those under fluorescent light, and FIG. 3 shows those under illumination by an incandescent lamp. ing.

At least the photographing process of the still video camera is controlled by the control device 10. This controller 10 is a CPU
(For example, a microprocessor), a memory (RAM, ROM, etc.) that stores the program and necessary data, and a necessary interface circuit.
As will be described later, a counter is provided for measuring the ripple frequency (cycle) of the fluorescent lamp.

The image pickup optical system includes a zoom lens system 11, an image pickup lens system 12 for forming a subject image, a diaphragm 13, a beam splitter 14 for deflecting a part of incident light to enter the photometric element 31, an infrared ray shield. It is composed of a filter 15 and a shutter 16.

The subject brightness detection signal of the photometric element 31 is input to the amplifier 33 via the logarithmic amplifier 32. Further, this luminance detection signal is smoothed by the smoothing circuit 37 on the one hand, and then the sampling circuit
Given to 38. The sampling circuit 38 samples the input signal according to the sample timing signal provided from the control device 10, as will be described later in detail.

The sampling data of the brightness detection signal is given to the control device 10, and the control device 10 calculates the average value of the input sampling data of a predetermined number of times, and based on the average value of the subject brightness, the exposure amount E _V , For example, it is determined using a graph or table stored in the memory as shown in FIG. The control device 10 further calculates the aperture value and the shutter speed using the program diagram based on the exposure amount E _V , controls the aperture 13 based on the determined aperture value, and shutters based on the determined shutter speed. Open / close control of 16.

On the other hand, the luminance detection signal of the photometric element 31 is given to the bandpass filter 34 for detecting the ripple of the fluorescent lamp, which will be described later in detail.

The color detection signal of the color sensor 41 is subjected to predetermined processing in the white balance processing circuit 42 and then given to the sampling circuit 43. The sampling circuit 43 also
Similar to sampling circuit 38, processing circuit 42 is responsive to sampling pulses provided by controller 10.
The color temperature signal output from is sampled. The average value is calculated in the control device 10 from the sampling data of the color temperature signal for a plurality of predetermined times. The average value of the color temperature is used for the amplification gain control (white balance control) of the R, G, B signals in the variable gain amplification circuit included in the signal processing circuit 21.

On the focal plane of the image pickup optical system, a solid-state electronic image pickup device 17 for three primary colors including a two-dimensional image pickup cell array such as CCD is arranged. The image data accumulated in the image pickup device 17 when the shutter 16 is opened is read out as a serial still video signal (R, G, B) in synchronization with the vertical and horizontal synchronizing signals given from the signal processing circuit 21. And is input to the signal processing circuit 21.

The signal processing circuit 21 inputs a still video signal (R,
G, B) preamplifier circuit, the variable gain amplifier circuit (white balance adjustment circuit) and the process matrix circuit. R (red) of each still video signal (R, G, B) input by the variable gain amplifier circuit,
The blending ratio of the (G (green)) and B (blue) components is adjusted under the control of the control circuit 10 based on the average value of the color signals described above. A luminance signal Y and two color difference signals RY and BY are created in the process matrix circuit. These color difference signals R-Y and B-Y are line-sequentialized, then FM-modulated together with the luminance signal and mixed, and magnetically recorded on a video floppy (not shown) by a magnetic head.

The ripple detection of fluorescent light is performed by a band pass filter (BP
F) 34 and the level discrimination circuit 35. Ripples exist not only in fluorescent light but also in light from incandescent light bulbs. A bandpass filter 34 is provided to remove the ripple component in the light emission of the incandescent lamp and detect only the ripple component of the fluorescent lamp. In Fig. 5, the spectrum of light and dark frequency (ripple frequency) of fluorescent light is shown by the solid line FL.
Then, the ripple frequency spectrum of the light from the incandescent light bulb is shown by the broken line IN. This spectrum is commercial frequency 50Hz
It is when driven by. Light from an incandescent light bulb is 100H
While it contains only the ripple component centered on the frequency of z, the fluorescent light contains the ripple component of the frequency of 200Hz which is the second harmonic in addition to 100Hz. Fluorescent light can be distinguished from incandescent light by the second harmonic component of 200Hz, which is unique to light. 60 fluorescent lights
When driven at a frequency of Hz, a frequency spectrum with peaks at 120 Hz and 240 Hz is obtained, and 120 Hz for natural bulb light.
A frequency spectrum having a peak only at is obtained.

The bandpass filter 34 is 220H which is the center of 200Hz and 240Hz.
It has a passband with a center frequency of z. An example of the output signal waveform of the filter 34 is shown in FIGS.
It is shown in FIG. FIG. 2 (A) is for fluorescent light, and FIG. 3 (A) is for incandescent light. The bandpass filter 34 is unique to the ripple component of fluorescent light.
Since it is set to pass only the signal (second harmonic) near 0 Hz, the ripple component of the natural light bulb is blocked by the filter 34, and the output signal A having the ripple is generated only in the case of the fluorescent light. can get.

The output signal A of the bandpass filter 34 is the level discrimination circuit 35.
And to the reference voltage generation circuit 36. The circuit 36 includes a capacitor for smoothing the signal A and a resistor circuit for dividing the signal A, and as shown in FIG. 2 (A), generates a reference voltage V _E having a level near the center of the ripple component,
It is given to the level discrimination circuit 35. The level discriminating circuit 35 discriminates the input signal A by this reference voltage V _E and outputs a square wave or pulse signal B as shown in FIG. 2 (B). As for the natural light bulb, as shown in FIG. 3 (B), the output signal B of the level discrimination circuit 35 does not include a square wave component.

The output signal B of the level discrimination circuit 35 is input to the control device 10. The controller 10 counts the rising (or falling) of the input signal B with a counter, measures the frequency of the signal B, that is, the ripple frequency (second harmonic) of the incident light, and calculates the ripple cycle from this.

The ripple frequency or ripple period measurement result is 2
It has one meaning and is used for two purposes.

One of them is to determine whether or not photographing is being performed under fluorescent light. The measured ripple frequency is 20
When the frequency is 0 Hz or 240 Hz or in the vicinity thereof, the control device 10 determines that the image capturing is performed under the fluorescent light. As described above, the color temperature of the subject obtained from the white balance processing circuit 42 is under the sunlight (outdoors on a sunny day).
The values are almost the same under daylight white fluorescent light, and it is difficult to distinguish them. Nevertheless, good color reproducibility cannot be expected unless white balance adjustment is performed separately for sunlight and fluorescent light. So the control device
When the measured color temperature indicates sunlight or daylight white fluorescent light, reference numeral 10 determines under which light the photographing is performed based on the measurement result of the frequency of the signal B. In the case of sunlight, the signal B shows a constant level and does not include a square wave component. Then, according to the determination result, the control device gives a gain corresponding to sunlight or daylight white fluorescent light to the above-described variable gain amplification circuit to perform white balance adjustment. This enables proper white balance adjustment even under fluorescent lighting.

It should be noted that it is possible to distinguish between the types of fluorescent lights, such as daylight white fluorescent light, daylight fluorescent light, and white fluorescent light, based on color temperature, and to adjust the white balance according to the type of fluorescent light. Is performed.

The other is to control the sampling circuits 38 and 43 based on the measured ripple period. Measured signal B
If the frequency is 200Hz, the fluorescent lamp is driven by a commercial power source of 50Hz. The main ripple frequency (first harmonic) of this fluorescent lamp is 100 Hz, so its period is 10 ms.

Therefore, in this embodiment, eight sampling pulses are output during 10 ms (one cycle), and the subject brightness and color temperature are sampled at a sampling interval of 10/8 ms.
If the measured frequency is 240Hz, the fluorescent lamp is driven by a commercial power source of 60Hz, so 1000 / 120ms
Eight sampling pulses are output from the control device 10 during (about 8 ms), and the sampling circuits 38 and 43 are activated by these sampling pulses.

In this way, since the sampling is performed eight times within one cycle of the main ripple period of the fluorescent light, the data read by the sampling is biased toward the bright or dark ripple even when photographing under the fluorescent light. Without
Averaged data can be obtained. This enables accurate white balance adjustment and exposure control. When the image is not taken under fluorescent light, sampling is performed at an appropriate fixed sampling period.

[Brief description of drawings]

FIG. 1 is a block diagram showing a part of the electrical structure of a still video camera, and FIGS. 2 (A) and (B) and FIGS. 3 (A) and 3 (B) are circuits of the circuit shown in FIG. It is a signal waveform diagram of each part, FIG. 2 (A), (B) shows the thing under fluorescent light, and FIG. 3 (A), (B) shows the thing under incandescent lamp light, respectively. FIG. 4 is a graph showing ripple frequency spectra of fluorescent light and incandescent light,
Figure is a graph showing the relationship between the signal and E _V value from the photometric device. 10 …… Control device, 31 …… Photometric element, 34 …… Band pass filter, 35 …… Level discrimination circuit, 38,43 …… Sampling circuit,
41 …… Color sensor, 42 …… White balance processing circuit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuji Ogata 1-324 Uetakecho, Omiya City, Saitama Prefecture Fuji Photo Koki Co., Ltd. (72) Inventor Kazutoshi Seki 1-324 Uetakecho, Omiya City, Saitama Prefecture Fuji Photo Optical Co., Ltd. (72) Inventor Koji Kaneko 1-324, Uetakecho, Omiya City, Saitama Prefecture Fuji Photo Optical Co., Ltd. (72) Inventor, Satoshi Mikkaji 1324, Uetakecho, Omiya City, Saitama Prefecture Address in Fuji Photo Optical Co., Ltd. (56) References JP-A-62-75323 (JP, A)

Claims (1)

[Claims] 1. A ripple cycle measuring means for measuring the ripple cycle of artificial illumination light, a detection signal of a photodetector, and a detection signal to be input,
A sampling circuit that performs sampling at a cycle determined based on a given sampling control signal, and the ripple so that sampling is performed a plurality of times within a time corresponding to one cycle of the ripple cycle measured by the ripple cycle measuring means. A camera provided with a sampling circuit control means for determining a sampling cycle of the sampling circuit based on the ripple cycle measured by the cycle measuring means and supplying a sampling control signal representing the determined sampling cycle to the sampling circuit.