JPH01227582A - Exposure control device - Google Patents

Abstract

PURPOSE:To eliminate an exposure shortage and a flicker phenomenon by deciding the period of a luminance ripple when an illuminating light source has the luminance ripple, and executing an exposure in an exposure time to be integer-fold that of the period and, simultaneously, to be shorter than 1 period of a field frequency. CONSTITUTION:A photoelectric output from a WB sensor 42 is fluctuated corresponding to the ripple of a fluorescent lamp, a period T is detected by a ripple period detecting circuit 44, and it is inputted to a CPU 26. The CPU 26 executes the exposure in the exposure time to be integer-fold that of the period and to be shorter than 1 period of the field frequency. Thus, even under the light source to have the luminance ripple such as the fluorescent lamp, a sharp video without the flicker phenomenon can be image-picked up with the correct exposure.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an exposure control device for use in a video camera.

[Conventional technology]

Fluorescent lamps, which have a long life and consume less power, have become popular as a means of indoor lighting, replacing traditional incandescent light bulbs.
Most of the indoor photography is done under fluorescent lighting. By the way, fluorescent lamps have ripples that depend on the commercial frequency of the power supply (
brightness ripple, color ripple), so if you shoot a video movie under fluorescent lighting with a shutter speed faster than the ripple cycle, the brightness ripple may cause insufficient exposure or flicker. Sometimes it comes out. Further, a similar problem occurs in a device in which exposure control is performed based on the storage time of the image sensor, that is, the time during which the image sensor photoelectrically converts light from a subject and stores it.

Therefore, an exposure control device has been proposed that determines the frequency of ripples of an illumination light source and provides an exposure time of one cycle or more of this frequency.

An example of exposure using this exposure control device will be explained with reference to FIG. 3(A). For example, in an area where the commercial frequency of radio waves is 507, the brightness of fluorescent lamps changes at a ripple frequency of 100 cells, and the period is 10 m5.

Therefore, if the exposure time is 10m5 or more, 10m
Compared to the case where the value is less than 5, the rate of change in the amount of illumination light relative to the total amount of exposure is reduced, so underexposure and flicker phenomena are reduced. For example, code a indicating exposure timing
Expose from 1 to 1 until the mark indicating the end of exposure is reached, and the exposure time is 1.
It should be 5m5.

The exposure amount at this time is the area of the area A indicated by diagonal lines.

[Problem to be solved by the invention]

However, when exposing from code C to code d as shown in FIG.
Although the exposure time is 15 m5, which is the same as above, the amount of exposure indicated by the area of region B is clearly increased compared to the amount of exposure indicated by the area of region A. Therefore, although it is possible to reduce underexposure and flicker phenomena to some extent by making the exposure time longer than one cycle with conventional exposure control devices, it is not possible to completely eliminate them, and under illumination light with ripples, The amount of exposure when photographing is not accurately controlled.

[Object of the Invention] The present invention has been made to solve the above-mentioned problems, and the present invention has been made to improve the timing of exposure to a solid-state image sensor with respect to the phase of the repetition frequency of the light source ripple when photographing under illumination light having ripples. An object of the present invention is to provide an exposure control device that can always perform accurate exposure control even when the values are different, and can eliminate insufficient exposure and flicker phenomena.

[Means to solve the problem]

In order to achieve the above object, the exposure control device of the present invention includes:
determining whether the illumination light source has luminance ripple;
If there is a brightness ripple, the period of the brightness ripple is determined, and exposure is performed with an exposure time that is an integral multiple of the period and shorter than one period of the field frequency.

[Effect]

According to the above configuration, first, it is determined whether or not there is a luminance ripple in the illumination light source. If there is brightness ripple,
The period is determined, and the exposure time is controlled to be an integral multiple of the period.

Embodiments of the present invention will be described in detail below with reference to the drawings.

〔Example〕

In FIG. 1 showing a block diagram of an exposure control device of the present invention and an optical system of a video camera l incorporating this exposure control device, the optical system of the video camera 1 includes two groups (lens loa
, 10b), an aperture 11 disposed between the lens 10a and the lens tab. Beam splitter 12. Half mirror 13-, focusing screen 14. Condenser lens 15. pentaprism 16
．． It consists of an eyepiece lens 17, and a 5PD 19, which is a light receiving element for photometry, is arranged below the beam splitter 12 via an imaging lens 18. Also, half mirror 13
A CCD 21, which is a solid-state imaging device for field images, is arranged behind the camera.

The AE-CPU 20 is connected to the 5PD 19, and the AE-CPU 20 has a CPU that operates according to the sequence program written in the program ROM 24.
PU26 is connected.

The AE-CPU 20 calculates the exposure amount P based on the brightness signal from the 5PD 19, controls the diaphragm 11 according to a command from the CPU 26, and provides an appropriate amount of light to the CCD 21. Further, 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 the light source illuminating the subject.
is used. This WB sensor 42 includes, for example, a blue light receiving section and a red light receiving section. And condensing lens 4
0. A signal calculation circuit 43 outputs the photoelectric output obtained by adjusting the amount of blue light and red light included in the external light received through the diffuser plate 41.
′. The signal calculation circuit 43 calculates the color temperature based on the ratio of the photoelectric output from the WB sensor 42, and outputs this to the CPU 26 as a digital signal.

Further, one of the photoelectric outputs from the WB sensor 42 is also supplied to a ripple period detection circuit 44 . This ripple period detection circuit 44 performs processing such as sample hold and digitization on the photoelectric output from the WB sensor 42 according to the period of the sampling pulse supplied from the CPU 26, and detects the frequency of the ripples of the illumination light. Detect and CPU2
Output to 6.

A signal processing circuit 3o is connected to the C0D 21, and this signal processing circuit 30 records data to a VTR connected to a video output terminal 32 via an encoder circuit 31. Further, a CCD drive circuit 29 for driving the CCD 21 is connected to the CCD 21, and a CCD drive circuit 29 for instructing the time and start timing for photoelectrically converting and storing light from the subject. A CPU 26 is connected. A synchronization signal generation circuit 28 is connected to the second CPU 26 and the CCD drive circuit 29, which synchronizes various pulses necessary to drive the C0D 21 with each other, and also generates a master clock pulse for controlling the sequence of the CPU 26. is occurring.

Next, the operation of the exposure control apparatus of the present invention configured as described above will be explained. First, when power is turned on to the video camera 1, the synchronization signal generation circuit 28 outputs a signal from the CPU 26. CCD
A master clock pulse is sent to the drive circuit 29, and each drive is started.

When the photographic lens 10 is directed toward a subject, the optical image of the subject captured by the photographic lens 10 is transmitted through a beam splitter 12, reflected by a half mirror 13, and formed on a focusing screen 14.

This formed object image is condensed by a condenser lens 15, and a pentaprism 16. It is observed by the photographer through 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
At the same time as it is imaged on the PD 19, it passes through the half mirror 13 and is imaged on the CCD 21. The optical image formed on the 5PD19 is converted into a luminance signal by the 5PD19, and the AE-
The CPU 20 performs amplification and digitization processing to calculate an appropriate exposure amount P, which is input to the CPU 26 .

When the light source illuminating the subject is sunlight or tungsten light, the photoelectric output from the WB sensor 42 hardly changes over time, so the period T is not detected by the ripple period detection circuit 44. In this case, the CPU 26 identifies that the light source illuminating the subject is not a fluorescent lamp, and performs automatic exposure control in the normal mode, as shown in the flowchart of FIG. That is, based on the exposure amount P, the CPU 26 determines the accumulation time of the CCD 21 and the aperture diameter of the diaphragm 11.
A correction signal is output from the signal processing circuit 30 to the signal processing circuit 30. Thereby, the signal processing circuit 30 amplifies the blue signal and the red signal among the primary color signals outputted from the CCD 21 with an amplification factor corresponding to the correction signal, thereby adjusting the white balance.

If the light source illuminating the subject is a fluorescent lamp, W
The photoelectric output from the B sensor 42 is the ripple of the fluorescent lamp (the third
(see figure). Therefore, the period T is detected by the ripple period detection circuit 44 and the CPU 26
is input. CP[26 follows the sequence shown in Figure 2. First, the period T is 10 m5 (the frequency of the power supply is 5 m5).
07 district)). Cycle 10m5
If it matches, the CPU 26 sends a command to the CCD drive circuit 29 to set the storage time of the CCD 21 to be an integral multiple of 1011Is and within the field period, and
The aperture diameter of the diaphragm 11 is set based on the accumulation time of the CCD 21 and the exposure amount P.

If the period T does not match the period 10m5, the period is 8゜3m.
s. Period T is period 8゜311I
If it matches s, the accumulation time of C0D21 is 8, 3
It is set to be an integral multiple of tts and within the field period, and the aperture diameter of the diaphragm 11 is set based on the accumulation time of the CCD 21 and the exposure amount P.

Furthermore, if the cycle T does not match the cycle 8.3 ms, the illumination light source is identified as having ripples but is not a normal fluorescent lamp, and automatic exposure control is performed in the normal mode.

Note that the accumulation time of the CCD 21 is selected to be as short as possible in order to prevent manual play, and the aperture value corresponding to the accumulation time is set in the aperture 11; If the speed is exceeded, the storage time of the CCD 21 is sequentially shifted to the lower speed side (for example, 2°l1lS).

In this state, press the release button halfway to release the AP (
(not shown), decide on the composition while observing the finder image, and press the release button (not shown).

As a result, the release switch 35 is turned on, and at the same time, an optical image controlled to an appropriate amount of light is displayed on the CCD 2.
1, the signal is converted into a video signal, subjected to various well-known processes and white balance adjustment in a signal processing circuit 30, and outputted from a video output terminal 32 via an encoder circuit 31. This is the VTR connected to the video output terminal.
(not shown).

In addition, in FIG. 3 showing an exposure example of a conventional exposure control device, although the exposure time is the same (both 15 m5) in FIG. 3 (A) and FIG. This indicates that the area is different (area of area A times area of area B). On the other hand, in the exposure control device of the present invention,
As described above, by performing exposure at an exposure time that is an integral multiple of the period of the luminance ripple and within the field period, an accurate amount of exposure can always be given to the image sensor.

In addition, in this embodiment, a well-known method was used for white balance adjustment, but once it is identified that the illumination light source is a fluorescent lamp, the color temperature calculated from the light received during the ripple cycle is adjusted. If the white balance is adjusted based on this, an image with better color reproduction can be obtained.

As explained above, in this embodiment, the exposure time is controlled by controlling the accumulation time of CC021, but the shutter of the liquid crystal etc.
Of course, the exposure time may be controlled by installing the shutter just before the shutter 21 and controlling the opening/closing time of this shutter.

〔Effect of the invention〕

As explained above, according to the exposure-gutter device of the present invention, it is possible to detect whether or not the light source illuminating the subject has luminance ripples, and if it has luminance ripples, The period is determined, and exposure is performed with an exposure time that is an integral multiple of the period and shorter than one period of the field frequency.

Therefore, it is possible to provide an exposure control device for a video camera that can capture clear images without flickering with accurate exposure even under a light source with brightness ripples such as a fluorescent lamp.

[Brief explanation of the drawing]

FIG. 1 is a block diagram schematically showing the structure of an embodiment of the present invention. FIG. 2 is a flowchart showing the main part of the sequence program according to the embodiment of the present invention. FIGS. 3A and 3B are schematic diagrams showing an example of exposure in a conventional exposure control device. 1... Video camera - 11... Aperture 19... 5PD 20... AE-CPU 21... CCD 26... CPU 44... Ripple period detection circuit.

Claims (1)

[Claims] (1) a luminance ripple detection means for detecting whether the light source has a luminance ripple; and a period determination means for determining the period of the luminance ripple when the luminance ripple is detected by the luminance ripple detection means; An exposure control device for a video camera, comprising an exposure time determining means that determines an exposure time that is an integral multiple of the period of the luminance ripple and shorter than one period of the field frequency.