JPH08122890A - Ac light source detecting device and camera using it - Google Patents

Abstract

PURPOSE: To magnetically record light source information on a film to allow a proper color correction at printing in a processing station. CONSTITUTION: The output of a D/A converter 3 is set to a prescribed voltage value by the digital output signal of a CPU 6, and a comparator 4 compares the output of a light receiving circuit 2 with the output of the D/A converter 3 and outputs the result. When a light receiving element 1 receives a subject light including flicker, the comparator 3 outputs a rectangular wave with the output voltage of the D/A converter 3 as threshold. Further, the CPU 5 discriminates the frequency of the rectangular wave output, whereby it is judged whether the light source of a subject field to be photographed is an AC light source or a natural light. When the light source is the AC light source, particularly, the kind of the light source is also judged.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AC light source detection device for determining the presence or type of an AC light source that illuminates a shooting field or an AC light source in the shooting field when shooting with a camera or the like. Regarding the camera to use.

[0002]

2. Description of the Related Art Conventionally, when a photograph is taken by an image pickup device such as a camera, the influence of a photographing environment, particularly an AC light source that illuminates a subject appears in a print. Therefore, a technique for reducing the influence is desired. ing.

For example, in Japanese Unexamined Patent Publication No. 51-89420, it is felt when looking at a specific spectral intensity and flicker noise obtained from at least two or more light receiving means, that is, a projection image whose brightness changes periodically. The light source that illuminates the subject depending on whether there is a change in brightness or darkness is natural light (daylight),
A technique for determining whether the light is fluorescent light or tungsten light is disclosed. Further, there is also known a technique of detecting flicker noise by sampling a photometric output voltage at a constant cycle in a photometric circuit of a camera.

[0004]

However, the technique disclosed in Japanese Patent Laid-Open No. 51-89420 does not disclose any specific method for detecting flicker noise. Further, the method of sampling the photometric output voltage at a constant cycle requires an analog / digital converter that operates at a high speed, which causes a problem of increasing the cost of the camera.

The present invention has been made in view of the above problems. An object of the present invention is to detect a flicker noise of an illumination light source in a field by using a simple light receiving circuit so that the illumination light source is the sun. Whether it is light or an AC light source is discriminated, and the light source information is magnetically recorded on a film to enable appropriate color correction at the time of printing at a developing place, and release depending on the time required for detecting the illumination light source. -To prevent an increase in time lag.

[0006]

In order to achieve the above object, an AC light source detection device according to a first aspect of the present invention includes a light receiving element that receives at least light from an AC light source, and an output from the light receiving element. The voltage changing means for changing the current into the voltage, the reference voltage outputting means for outputting a predetermined voltage corresponding to the output range of the light receiving element, the output of the voltage changing means and the output of the reference voltage outputting means are compared. Comparison means,
It is determined whether the output of the comparison means is a rectangular wave, and if it is not a rectangular wave, the reference voltage output by the reference voltage output means is changed based on the output of the comparison means. And a discrimination control means for discriminating the frequency.

In the AC light source detection device according to the second aspect, the output of the reference voltage output means is an average voltage value when the output of the light receiving element is sampled a plurality of times.

Further, the camera according to the third aspect is a camera capable of magnetic recording using a film with a magnetic recording portion, and a light receiving element capable of receiving the brightness of an object and light from an AC light source, and the light receiving element. A voltage changing means for changing the output current to a voltage, a reference voltage outputting means for outputting a predetermined voltage corresponding to the output range of the light receiving element, an output of the voltage changing means and an output of the reference voltage outputting means. Comparing means for comparing and judging whether or not the output of the comparing means is a rectangular wave, and if it is not a rectangular wave, change the reference voltage output by the reference voltage output means based on the output of the comparing means, In the case of a rectangular wave, a discriminating control means for discriminating the type of the AC light source from the frequency and a magnetic recording means for recording the discriminating content of the discriminating control means in the magnetic recording portion of the film are provided. The features.

[0009]

That is, in the AC light source detecting device according to the first aspect of the present invention, at least the light from the AC light source is received by the light receiving element, and the output current from the light receiving element is changed to the voltage by the voltage changing means. The voltage output means outputs a predetermined voltage corresponding to the output range of the light receiving element,
The comparison means compares the output of the voltage changing means with the output of the reference voltage output means, and the discrimination control means
It is determined whether or not the output of the comparison means is a rectangular wave, and if it is not a rectangular wave, the reference voltage output by the reference voltage output means is changed based on the output of the comparison means. The frequencies are discriminated.

In the AC light source detection device according to the second aspect, the output of the reference voltage output means is an average voltage value when the output of the light receiving element is sampled a plurality of times. Furthermore, the camera according to the third aspect is a camera capable of magnetic recording using a film with a magnetic recording section, wherein the light receiving element receives the brightness of the subject and the light from the AC light source, and the voltage changing means causes the light receiving element to operate. Output current from is changed to voltage, by the reference voltage output means,
A predetermined voltage corresponding to the output range of the light receiving element is output, the comparison means compares the output of the voltage changing means with the output of the reference voltage output means, and the discrimination control means outputs the output of the comparison means. Whether it is a rectangular wave or not is determined. If it is not a rectangular wave, the reference voltage output by the reference voltage output means is changed based on the output of the comparison means. Is determined,
The magnetic recording means records the discrimination content of the discrimination control means in the magnetic recording portion of the film.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. First, FIG. 1 shows a conceptual diagram of an AC light source detection device of the present invention, which will be described. As shown in the figure, in the AC light source detection device of the present invention, the light receiving element 1 that receives the subject light is connected to the light receiving circuit 2 that receives the current output of the light receiving element 1 and outputs the voltage corresponding to the current. The output of the light receiving circuit 2 is connected to the inverting input of the comparator 4. The output of the comparator 4 is connected to the input of the CPU 5, and the output of the CPU 5 is connected to the input of the D / A converter 3. The output of the D / A converter 3 is connected to the non-inverting input of the comparator 4.

In such a configuration, the output of the D / A converter 3 is set to a predetermined voltage value by the digital output signal of the CPU 5, and the predetermined voltage value is output. Then, the comparator 4 outputs the output of the light receiving circuit 2 and A /
The output of the D converter 3 is compared and output. When the light receiving element 1 receives the subject light including flicker, the comparator 4 outputs a rectangular wave with the output voltage of the D / A converter 3 as a threshold.

Further, the CPU 5 discriminates whether the light source of the field to be photographed is an AC light source or natural light by discriminating the frequency of the rectangular wave output. In particular, when the light source is an AC light source, the type of the light source can also be determined.

Next, FIG. 2 shows the structure of a camera to which the AC light source detection device of the present invention is applied and described. In the figure,
A silicon photodiode (SPD) 14 is a light receiving element that receives subject light, and generates a predetermined photocurrent according to the amount of incident light.

This photocurrent is input to the photometric circuit 12,
The logarithmically compressed voltage value is output from the photometric circuit 12 and input to the inverting input terminal of the comparator 11. D / A converter 1
3 generates a predetermined constant voltage according to the 8-bit serial data transferred from the CPU 10, and is input to the non-inverting input terminal of the comparator 11.

The comparator 11 outputs the output voltage V of the photometric circuit 12.
comparing out1 and the output voltage Vout2 of the D / A converter 13,
Binary data of high level "H" or low level "L" is output to the CPU 10 from the output terminal CPO.

In this way, when it is detected that the subject light of the frame photographed in the circuit contains AC light, the magnetic recording unit 15 and the magnetic head 16 photograph the film 17 capable of magnetic recording under an AC light source. A predetermined code indicating that is magnetically recorded.

As described above, the recorded light source information is read at the time of printing, and predetermined color correction and the like are performed.
The recording on the film 17 is not limited to magnetic recording, and it goes without saying that optical recording such as a bar code may be used.

Next, FIG. 3 shows in detail how the photometric circuit 12 is constructed in a monolithic manner. As shown in FIG. 3, the reference current source 20 is connected to the anode of the diode 21, and the cathode of the diode 21 is G
It is connected to ND. The connection point between the current source 20 and the anode of the diode 21 is connected to the non-inverting input terminal of the buffer amplifier 22, and the output of the buffer amplifier 22 is connected to the non-inverting input of the head amplifier 24. The SPD 23 corresponds to the SPD 14 described above. The anode of the compression diode 25 is the head amplifier 2
4 is connected to the inverting input terminal of the compression diode 2
The cathode of 5 is the output of the head amplifier 24 and the operational amplifier 2
6 non-inverting input terminals.

The open-up amplifier 26 and the resistors 27 and 28 form a non-inverting amplifier. The photocurrent generated in the SPD 23 is logarithmically compressed by the compression diode 25 and then amplified by the non-inverting amplifier at a predetermined amplification factor to generate CP.
It is output to the A / D input port of U10. The reference current source 20, the diode 21, and the buffer amplifier 22 constitute a known IS (reverse saturation current) compensating circuit.

In such a structure, first, assuming that the current source of the reference current source 20 is Iref, the potential V1 of the anode of the diode 21 becomes V1 = VTln (Iref / IS). Here, VT = kT / q. Where k is Boltzmann's constant, T is absolute temperature,
q: unit charge amount, IS: reverse saturation current of transistor (diode).

Next, if the output voltage of the buffer amplifier 22 is V2, then V2 = V1.

Since the photocurrent IP output from the SPD 23 flows through the compression diode 25, the voltage generated across the compression diode 25 is VT.multidot.ln {IP / IS}.

Therefore, the output voltage V3 of the head amplifier 24
Is V3 = V2-VT * ln {IP / IS} = VT * ln.
It becomes {Iref / IP}.

Further, the output voltage Vou of the non-inverting amplifier 26
t is Vout1 = n.VT.ln {Iref / IP} = n.VT.
ln2 · log2 {Iref / IP}. Here, n is the amplification factor of the non-inverting amplifier 26 and is determined by the resistance values of the resistors 27 and 28. That is, when the photocurrent IP has the same brightness as Iref, the output voltage Vout1 becomes 0 V. As the photocurrent IP becomes darker by 1 EV, that is, as the photocurrent IP becomes half, the output voltage Vout1 becomes n ・ VT × ln2
Only increase. That is, the output voltage Vout1 becomes a logarithmically compressed output.

Next, the configuration of the A / D converter 13 will be described in detail with reference to FIG. In the figure, serial data output from the CPU 10 is input from an input 30, converted into parallel output by a serial-parallel conversion circuit 31, and a predetermined switch of a switch group 32 is turned on. When the predetermined switch is turned on, the sum of the currents weighted with the predetermined current I as shown in FIG. 4 flows as the collector current I1 of the transistor 34. The transistor 34 and the transistor 35 form a current mirror circuit, and a voltage (Vref-R · I1) is output to the output Vout2 by causing a current substantially equal to I1 to flow in the resistor 36.

Next, FIG. 5 shows the relationship between the output Vout1 of the photometric circuit, the output Vout2 of the D / A converter, and the output CPO of the comparator 11 when shooting is performed in daylight (under sunlight). It is an example. As is clear from the figure, since daylight does not include an AC component, Vout1 and Vout2 do not cross.
Therefore, in such a case, the output CPO of the comparator 11 remains at the low level "L".

On the other hand, FIG. 6 is an example showing the relationship between Vout1, Vout2 and CPO when photographing is performed under an AC light source such as a fluorescent lamp. In this case, because of the AC light source, Vout1
Vibrates at a specified frequency (depending on the type of light source), and Vout2
Therefore, the CPO outputs a rectangular wave having a predetermined frequency. When the CPU 10 determines that the rectangular wave is output, the CPU 10 recognizes that the shooting is performed under the AC light source.

Further, the type of the light source can be specified by discriminating the frequency of the rectangular wave. For example,
When the frequency is about 100 Hz, it is recognized that the light source is a glow start fluorescent lamp, and when it is about 100 KHz, it is an inverter fluorescent lamp.

Hereinafter, referring to the flow chart of FIG.
A method of setting the output voltage Vout2 of the D / A converter 13 will be described. Basically, the voltage output of the photometric circuit 12 is A / D converted at a predetermined frequency multiple times and the output voltage is averaged.

That is, first, #a is set to the variable N as the number of times the A / D conversion is performed (step S1), and the time interval (corresponding to the predetermined frequency) at which the A / D conversion is to be performed is set (step S1). S2), the voltage output Vout1 is A / D converted (step S3). Next, the A / D conversion result is converted to R
Store in AM (step S4), and above steps S2 to S
After repeating #a times up to 6 (steps S5 and S6), the average value of the plurality of A / D conversion results is calculated and stored in the RAM (step S7), and the process returns. In the present invention, the CPU 10 controls the D / A converter 13,
Known successive approximation A / D conversion can be performed.

Next, the light source detection method will be described with reference to the flowchart of FIG. First, the voltage output Vout1 is A / D converted, and the A / D conversion results are averaged (step S1).
0), the average value is transferred from the CPU 10 to the D / A converter 13 (step S11). Here, under an AC light source, a rectangular wave having a frequency according to the type of light source is output from the CPO. Thus, the alternating-current light source is specified by discriminating the frequency of the rectangular wave (step S12).

Here, when the relationship of Vout1 <Vout2 is as shown in FIG. 9, the duty of the rectangular wave output of the CPO becomes very narrow, and it becomes difficult for the CPU 10 to discriminate the frequency. Therefore, in such a case, as shown in the flowchart of FIG. 10, Vout2 is shifted by a predetermined voltage to enable frequency discrimination.

That is, Vout1 is A / D converted and the A / D conversion results are averaged (step S20).
0 to the D / A converter 13 (step S2)
1). Here, under an AC light source, a rectangular wave having a frequency according to the type of light source is output from the CPO. Thus
An AC light source is specified by frequency-discriminating the rectangular wave (step S22). Next, the average value of the A / D result is saved in the RAM (step S23), and the average value is #.
The value shifted in the positive direction by b is transferred to the D / A converter 13 (steps S24, 25), and the CPO output is frequency discriminated (step S26). Similarly, the average value
The value shifted in the negative direction by b is transferred to the D / A converter 13 (steps S27, 28) and frequency discrimination is performed (step S29).

In the present invention, two types of shifts are performed, but it goes without saying that the shift width and the number of shifts can be changed as necessary. By the way, if the AC light source detection of the present invention is operated during photometry performed prior to the exposure, the release time lag is increased. In view of this point, in the present invention, the AC light source detection is performed from the end of exposure to the start of magnetic recording.

Hereinafter, such characteristics will be described with reference to the flowchart of FIG. That is, when a first release switch (not shown) is pressed, the CPU 5 performs photometry on the object field (step S40), distance measurement (step S41), distance measurement calculation (step S42), and exposure calculation (step S42). Step S43). Next, when a second release switch (not shown) is pressed (step S44), the CPU 5 performs focus adjustment (step S45) and performs exposure (step S44).
46), the light source is detected (step S47), and the light source detection result is magnetically recorded while winding the film (step S48).

As described above in detail, the light source detection device of the present invention detects the flicker of the subject light, so that the illumination light source can appropriately discriminate between sunlight and AC light, and yet at high speed. Since an A / D conversion circuit that operates at high speed for detecting such flicker is not required, an inexpensive camera can be provided. Further, it is possible to prevent the release time lag from increasing due to the flicker detection.

According to the above embodiment of the present invention, the following constitution can be obtained. (1) In a camera capable of magnetic recording using a film with a magnetic recording unit, a light receiving element capable of receiving the brightness of an object and light from an AC light source, and a voltage change for changing an output current from the light receiving element into a voltage Means, reference voltage output means for outputting a predetermined voltage corresponding to the output range of the light receiving element, comparison means for comparing the output of the voltage changing means and the output of the reference voltage output means, and the comparison means. It is determined whether the output is a rectangular wave, and if it is not a rectangular wave, the reference voltage output by the reference voltage output means is changed based on the output of the comparing means. It comprises a discrimination control means for discriminating the type of the light source, and a magnetic recording means for recording the discrimination contents of the discrimination control means in the magnetic recording portion of the film. Camera, characterized in that the operation during the magnetic recording to Lum.

[0039]

According to the present invention, the flicker noise of the illumination light source in the field is detected by using a simple light receiving circuit,
The time required for detecting the illumination light source by determining whether the illumination light source is sunlight or an alternating current light source, magnetically recording the light source information on the film, and enabling appropriate color correction at the time of printing at the developing place. It is possible to provide an alternating-current light source detection device and a camera using the same, which can prevent an increase in release time lag due to the above.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an AC light source detection device according to an embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of a camera according to an embodiment of the present invention.

FIG. 3 is a diagram showing a detailed configuration of a photometric circuit 12 in FIG.

4 is a diagram showing a detailed configuration of a D / A converter 13 in FIG.

FIG. 5: Inputs Vout1 and Vout2 of the comparator under daylight
It is a figure which shows the state of the output CPO.

FIG. 6 Inputs Vout1 and Vou of the comparator under an AC light source
It is a figure which shows the state of t2 and output CPO.

FIG. 7 is a flowchart showing a method for setting an output voltage Vout2 of the D / A converter 13.

FIG. 8 is a flowchart showing a method of light source detection.

FIG. 9 is a diagram showing an example of a state in which the duty of the rectangular wave output of the CPO is extremely narrowed and the frequency discrimination in the CPU 10 becomes difficult.

FIG. 10 is a flowchart showing a method of frequency discrimination in the case of FIG.

FIG. 11 is a flowchart showing a shooting sequence of the camera of the embodiment.

[Explanation of symbols]

 1 ... Light receiving element 2 ... Light receiving circuit 3 ... Digital / analog converter 4 ... Comparator 5 ... CPU

Claims (3)

[Claims] 1. A light receiving element for receiving at least light from an AC light source, voltage changing means for changing an output current from the light receiving element into a voltage, and a predetermined voltage corresponding to an output range of the light receiving element. Reference voltage output means, comparing means for comparing the output of the voltage changing means with the output of the reference voltage output means, and determining whether or not the output of the comparing means is a rectangular wave. An AC light source detection device comprising: a discrimination control unit that changes the reference voltage output by the reference voltage output unit based on the output of the comparison unit and discriminates the frequency in the case of a rectangular wave. . 2. The AC light source detection device according to claim 1, wherein the output of the reference voltage output means is an average voltage value when the output of the light receiving element is sampled a plurality of times. 3. A camera capable of magnetic recording using a film with a magnetic recording unit, wherein a light receiving element capable of receiving the brightness of an object and light from an AC light source, and an output current from the light receiving element are converted into voltage. Voltage changing means, reference voltage output means for outputting a predetermined voltage corresponding to the output range of the light receiving element, comparing means for comparing the output of the voltage changing means with the output of the reference voltage output means, and the comparison It is determined whether the output of the means is a rectangular wave, and if it is not a rectangular wave, the reference voltage output by the reference voltage output means is changed based on the output of the comparing means. And a magnetic recording means for recording the discrimination content of the discrimination control means in the magnetic recording portion of the film.