JP2520930B2 - camera - Google Patents

Description

TECHNICAL FIELD The present invention relates to a camera such as an electronic still camera and a silver salt camera.

[Conventional technology]

As an indoor illumination means, a fluorescent lamp having a long life and low power consumption has been widely used in place of the conventional incandescent light bulb, and indoor photography is mostly performed under the fluorescent lamp.
By the way, since fluorescent lamps have ripples (luminance ripples and color ripples), when shooting under a fluorescent lamp at a shutter speed faster than the ripple cycle, an electronic still using an image sensor with a narrow dynamic range is used. In a camera, the amount of exposure may be insufficient due to the influence of brightness ripple. The same problem occurs even when the exposure control is performed according to the storage time of the image sensor, that is, the time during which the image sensor photoelectrically converts the light from the subject and stores it.

In addition, since the color temperature changes cyclically due to the effect of color ripples, when sampling is performed for a time shorter than the ripple cycle, which part of the color temperature changing during one cycle is sampled? Therefore, the color temperature data for adjusting the color balance is different each time. Therefore, even if the white balance is adjusted based on such color temperature data, an image with good color balance cannot be obtained.

Therefore, determine the ripple frequency of the illumination light source,
There has been proposed a camera that provides an exposure time of one cycle or more of this frequency and also performs sampling for one cycle or more when determining the color temperature. An example of exposure in this camera will be described with reference to FIG. For example, in an area where the commercial frequency of telephones is 50Hz, the brightness of fluorescent lamps changes at a ripple frequency of 100Hz,
The cycle is 10ms. Therefore, if the exposure time is set to 10 ms or more, the rate of change of the illumination light amount with respect to the entire exposure amount is reduced as compared with the case where the exposure time is set to less than 10 ms. For example, a symbol a indicating the exposure timing
To the symbol b indicating the end of exposure, and the exposure time is 15
You can use ms. The exposure amount at this time is the area A indicated by diagonal lines.
Area. Also, when determining the color temperature,
For example, the determination is made based on the color temperature data obtained from the light received by the color temperature sensor within 15 ms.

[Problems to be Solved by the Invention]

However, when exposure is performed from the code c to the code d with the conventional camera as described above, as shown in FIG.
The exposure amount shown by the area of is clearly increased as compared with the exposure amount shown by the area of the region A. Therefore, although the conventional camera can reduce the exposure shortage and the flicker phenomenon to some extent by making the exposure time longer than one cycle, this cannot be completely eliminated, and shooting is performed under the illumination light having ripples. In this case, the amount of exposure is not precisely controlled.
Similarly, when determining the color temperature, the determined color temperature becomes the average color temperature of the sampled color temperature data, and therefore the degree of color temperature variation is reduced by receiving light for longer than one cycle. However, the color temperature cannot be detected accurately, and the color balance cannot be perfectly adjusted.

[Object of the Invention]

The present invention has been made to solve the above-mentioned problems, and when shooting under illumination light having ripples, an accurate exposure level and good color reproduction are realized by eliminating the effect of the ripples of the illumination light source. The purpose is to provide a camera that can.

[Means for solving the problem]

To achieve the above object, the camera of the present invention determines whether or not the illumination light source has a brightness ripple, and if it has a brightness ripple, determines the cycle of the brightness ripple and determines the cycle. Exposure with a shutter speed priority is performed with an exposure time that is an integral multiple of, and the color temperature is detected by receiving light from the illumination light source for an integral multiple of one cycle, and the white balance is adjusted for this color temperature. I am trying to do it.

[Action]

According to the above configuration, it is first determined whether or not the illumination light source has a brightness ripple. If there is a brightness ripple, its cycle is determined, and the exposure time is controlled to be an integral multiple of that cycle. At the same time, the white balance is adjusted by the color temperature data obtained by integrating the color temperature signal in this cycle.

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

〔Example〕

In FIG. 1 showing the structure of an electronic still camera 1 which is an embodiment of the present invention, the optical system of the electronic still camera 1 is
Shooting lens 10 and lens 10a of 2 groups (lens 10a, 10b) configuration
Aperture type aperture stop located between lens and lens 10b 1
1, beam splitter 12, quick return movable mirror 13, focusing screen 14, condenser lens 1
5, a penta prism 16 and an eyepiece lens 17, and below the beam splitter 12, an SPD 19 which is a light receiving element for photometry is arranged via an imaging lens 18. Further, behind the movable mirror 13, a CCD 21 which is a solid-state image pickup device for image pickup is arranged.

An AE-CPU 20 is connected to the SPD 19 and the AE-
The CPU 26 is connected to the CPU 26 which operates according to the sequence program written in the program ROM 24.
The AE-CPU20 is instantly narrowed down to the aperture diameter set based on the calculation result calculated from the photometric data, and CC
A diaphragm 11 for adjusting the amount of exposure given to D21 is connected. A release switch 35 is connected to the CPU 26.

A white balance sensor (hereinafter referred to as WB sensor) 42 is used to detect the color temperature of a light source illuminating a subject. The WB sensor 42 includes, for example, a blue light receiving portion and a red light receiving portion. Then, a photoelectric output proportional to the amounts of blue light and red light included in the external light received through the condenser lens 40 and the diffusion plate 41 is supplied to the signal calculation circuit 43.
The signal calculation circuit 43 calculates the color temperature based on the ratio of the photoelectric output from the WB sensor 42, and outputs it to the CPU 26 as a digital signal.

Further, one of the photoelectric outputs from the WB sensor 42 is also supplied to the sample hold circuit 44. The sample hold circuit 44 samples and holds the photoelectric output from the WB sensor 42 according to the cycle of the sampling pulse supplied from the CPU 26. The signal from the sample hold circuit 44 is digitized by the A / D converter 45 and then the CPU
It is output to 26.

A signal processing circuit 30 is connected to the CCD 21, and the signal processing circuit 30 writes a video signal to a still video floppy (hereinafter, referred to as video floppy) 33 via an FM modulation circuit 31 and a head amplifier 32. Of magnetic head 34. Below the magnetic head 34,
A motor 36 for rotating the video floppy 33 at a constant speed
Is arranged, and a driver 37 for driving the motor 36 is connected to the motor 36. Further, a CPU 26 for controlling these is connected to the CCD drive circuit 29, the signal processing circuit 30, the driver 37 and the head amplifier 32.

A CCD drive circuit 29 for driving the CCD 21 is connected to the CCD 21, and a synchronization signal generation circuit 28 is connected to the CCD drive circuit 29. The synchronization signal generation circuit 28 is connected to the CPU 26, and synchronizes various pulses necessary for driving the CCD 21 with each other, and also generates a master clock pulse for controlling the sequence of the CPU 26.

Next, the operation of the electronic still camera 1 of the present invention configured as described above will be described. First, electronic still camera 1
When the video floppy 33 is loaded into the device and the power is turned on, a master clock pulse is sent from the synchronizing signal generating circuit 28 to the CPU 26 and the CCD driving circuit 29, and the respective driving is started. A signal is sent from the CPU 26 to the driver 37 and the motor 36
Is driven and the loaded video floppy 33 starts rotating, and reaches a steady rotation speed of 60 rotations per second in about 30 ms.

When the shooting lens 10 is aimed at the subject, the optical image of the subject captured by the shooting lens 10 passes through the beam splitter 12,
Focusing screen 14 reflected by movable mirror 13
Is imaged. The formed subject image is condensed by the condenser lens 15 and is observed by the photographer via the pentaprism 16 and the eyepiece lens 17. On the other hand, a part of the optical image of the subject is guided to the imaging lens 18 by the beam splitter 12 and is imaged on the SPD 19. The optical image formed on the SPD 19 is converted into a brightness signal by the SPD 19, and the AE-CPU 20 performs amplification and digitization processing to calculate an appropriate exposure amount P, which is input to the CPU 26.

On the other hand, the light passing through the condenser lens 40 and the diffusion plate 41 is applied to the WB sensor 42. As a result, the WB sensor 42 outputs a photoelectric output according to the amounts of blue light and red light. On the other hand, for example, a photoelectric output proportional to the amount of blue light is input to the sample hold circuit 44. The sample hold circuit 44 updates the photoelectric output for each sampling pulse from the CPU 26 and inputs it to the CPU 26 as a digitized ripple signal V _T.

When the light source illuminating the subject is sunlight or tungsten light, the photoelectric output from the WB sensor 42 hardly changes with time, and therefore the ripple signal V _T from the A / D converter 45 is It is a constant value. In this case, the CPU 26 discriminates that the light source illuminating the subject is not a fluorescent lamp and controls the automatic exposure in the normal mode, as shown in the flowchart of FIG. That is, based on the exposure amount P, the CPU 26 causes the accumulation time of the CCD 21 and the aperture 11
Determine the aperture diameter of. Further, white balance adjustment is also performed in the normal mode, and a correction signal is output from the CPU 26 to the signal processing circuit 30 in response to the color temperature signal output from the signal calculation circuit 43. As a result, the signal processing circuit 30 becomes
Among the primary color signals output from 1, the blue signal and the red signal are amplified with an amplification factor corresponding to the correction signal, and the white balance is adjusted.

If the light source illuminating the subject is a fluorescent light,
The photoelectric output from the WB sensor 42 varies according to the ripple of the fluorescent lamp (see FIG. 3). Therefore, the ripple signal V _T input from the A / D converter 45 to the CPU 26 has a different value for each sampling. Then, in this case, the processing of the CPU 26 is switched to the fluorescent lamp mode,
The fluctuation period _T of the ripple signal V _T is obtained.

In order to obtain the fluctuation period T of the ripple signal V _T , CP
U26 monitors the increase / decrease state of the ripple signal V _T for each sampling period. Then, first, the first peak of the ripple signal V _T is detected. To do this, for example, the ripple signal
It suffices to detect the time when V _T changes from an increasing tendency to a decreasing tendency.

When it is confirmed that the start flag S is reset to "0" at the time when the first peak is detected, the period measurement timer starts counting time, and at the same time,
The start flag is set to "1". Then, the value of the ripple signal V _T is monitored every time sampling is performed, and the time when the next peak comes is detected. And again the ripple signal
When V _T shifts from an increasing tendency to a decreasing tendency, the second peak is detected, and after confirming that the timer timing has started, the timer timing is stopped.

Through the above processing, the timer measures the time from peak to peak of the ripple signal V _T , that is, the ripple cycle T. The cycle T thus obtained is 10 ms when the fluorescent lamp is turned on by a power source with a frequency of 50 Hz.
And becomes 8.3 ms when the frequency is 60 Hz.

Automatic exposure control is performed in the fluorescent lamp mode based on the ripple period T of the illumination light source detected in this way and the exposure amount P. For example, when the ripple cycle T is 10 ms,
The CPU 26 sends a command signal to the CCD drive circuit 29 to set the accumulation time of the CCD 21 to an integral multiple of 10 ms.
Based on the accumulation time and the exposure amount P, the AE-CPU 20 is instructed to set the aperture diameter of the diaphragm 11.

White balance adjustment is also performed in the fluorescent light mode. That is, the detected period T is fed back to the signal calculation circuit 43, and the WB is detected at this period T (10 ms in this case).
The photoelectric output from the sensor 42 is sampled, and the color temperature is calculated based on the ratio of this photoelectric output. In this way, the CP corresponding to the color temperature signal output from the signal calculation circuit 43
A correction signal is output from U26 to the signal processing circuit 30. As a result, the signal processing circuit 30 amplifies the blue signal and the red signal of the primary color signals output from the CCD 21 by the amplification factor corresponding to the correction signal, and the white balance is adjusted. Even when the period T is 8.3 ms, similarly, the accumulation time of the CCD 21 is set to an integral multiple of 8.3 ms, and the aperture diameter of the diaphragm 11 is determined and the white balance is adjusted based on this accumulation time.

Note that the CCD21 storage time is selected as short as possible to prevent camera shake, and the aperture diameter of the diaphragm 11 is determined according to the CCD21 storage time. When it exceeds, the accumulation time of the CCD 21 is sequentially shifted to the low speed side (for example, 20 ms).

In this state, the AE lock mechanism (not shown) is activated by half-pressing the release button, and while observing the viewfinder image, determine the composition and push the release button (not shown). As a result, at the same time when the release switch 35 is turned on, the movable mirror 13 jumps up, and immediately thereafter, the CCD 21 and the diaphragm 11 are driven according to the accumulation time of the CCD 21 and the aperture diameter of the diaphragm 11 stored by the AE lock mechanism. At the next moment, the movable mirror 13 returns to its original position to restore the viewfinder field, and the optical image controlled to the proper light amount is converted into a video signal by the CCD 21, and the signal processing circuit 30 performs various well-known processes and white. The balance is adjusted and the head amplifier 32 is passed through the FM modulation circuit 31.
Is input to The head amplifier 32 operates the magnetic head 34 in accordance with a command from the CPU 26, and instantly records the video signal read from the CCD 21 on the video floppy 33.

In addition to the method described above, the method of measuring the cycle T may be the method shown in FIGS. As shown in FIG. 4, the voltage V _T of the luminance output resistor 47 a voltage V _- and ₍₎
It is divided into V ₍₊₎ and input to the comparator 48. The waveforms of the voltages V _(-) and V ₍₊₎ are as shown in Fig. 5 (a). Corresponding to this, the output voltage V _T from the comparator 48
OUT is as shown in (b) in the figure. Therefore, this V _T O
The period T can be obtained by measuring the time from the attenuation time a of the UT to the next attenuation time b.

In addition, in FIG. 6 showing an example of exposure of a conventional camera,
Simultaneous (a) and same figure (b) have the same exposure time (both 15
However, if the exposure timing is different, the exposure amount is different (area A area <area B area). On the other hand, in the camera of the present invention, as described above, the exposure is performed at an integral multiple of the period of the luminance ripple, so that an accurate exposure amount can be always given to the image sensor, and the white balance can be obtained. Since the adjustment is also performed based on the color temperature calculated from the light received during the period of the brightness ripple, it is possible to obtain an image with a very good exposure level and color reproduction.

〔The invention's effect〕

As described above, according to the camera of the present invention, it is detected whether or not the light source illuminating the subject has the brightness ripple, and if it has the brightness ripple, the cycle thereof is determined. To do. Shutter speed priority exposure is performed at an integral multiple of this cycle, and light from the light source is received for an integral multiple of one cycle to detect color temperature, and white balance is adjusted for this color temperature. I have to.

Therefore, even under a light source with a brightness ripple such as a fluorescent lamp, it is possible to always perform accurate exposure even when an image sensor with a narrow dynamic range such as an electronic still camera is used, and good color reproduction can be achieved. It will be possible to provide a camera that can obtain an image of.

[Brief description of drawings]

FIG. 1 is a block diagram schematically showing the structure of an embodiment of the present invention. FIG. 2 is a flow chart showing the main part of the sequence program of the embodiment of the present invention. FIG. 3 is a waveform diagram of the detected luminance ripple. FIG. 4 is a schematic circuit diagram for measuring the ripple cycle from the voltage of the luminance output in another embodiment of the present invention. FIG. 5A is a waveform diagram of a luminance signal having a luminance ripple detected in another embodiment of the present invention. FIG. 5B is a waveform diagram showing V _T OUT of the luminance signal having the luminance ripple detected in another embodiment of the present invention. FIGS. 6A and 6B are schematic views showing an example of exposure in the conventional camera. 1 …… Electronic still camera 11 …… Aperture 19 …… SPD 20 …… AE-CPU 21 …… CCD 22 …… Shutter 26 …… CPU 42 …… WB sensor 43 …… Signal calculation circuit 44 …… Sample hold circuit.

Claims (1)

(57) [Claims] 1. A ripple cycle measuring means for measuring a ripple cycle of an illumination light source of an object, and when the cycle detected by the ripple cycle measuring means depends on a commercial frequency, an exposure which is an integral multiple of this cycle. Shutter speed priority exposure control means that operates so as to give time, color temperature detection means that detects the color temperature by receiving light from the illumination light source for an integral multiple of one cycle of the ripple, and this color temperature A camera comprising: a white balance adjusting means for adjusting the color balance in accordance with the color temperature obtained by the detecting means.