JPH09284634A - Image pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain an automatic focus operation with high accuracy and high speed response by detecting a change pattern of a video signal level so as to select a shutter speed based on the result thereby excluding adverse effect of production of flicker onto an automatic focus operation. SOLUTION: An image pickup signal from an image pickup section 2 is given to a signal level detector 9, which obtains a signal level for each field and stores the level. Then a signal level for a prescribed field number is obtained and a flicker detection section 10 discriminates whether or not a fluctuation due to flicker is in existence in the signal level. When the presence of flicker is discriminated, an electronic shutter control circuit 11 is activated to set a shutter speed of 1/100sec, and a timing generator 12 drives an image pickup section 2 with a shutter speed of 1/100sec (shutter period is 1/60sec). When possibility of flicker is lost, the shutter speed is restored manually to 1/60sec and image pickup in a bright state is conducted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image pickup apparatus, and more particularly to an image pickup apparatus which eliminates adverse effects of flicker on autofocus operation.

[0002]

2. Description of the Related Art Conventionally, in image pickup apparatuses such as television cameras, various technical problems have been solved in order to improve the quality of picked-up images. Among them, technology related to autofocus that automatically focuses on the object to be photographed, technology that prevents flicker that occurs in relation to the shutter cycle of the camera, shutter speed, and the cycle of illumination light, and the effect of flicker on autofocus Elimination and the like was also an important issue.

Next, referring to FIG. 4 for the structure of a conventional autofocus device and FIG. 5 for the evaluation value calculation circuit, an autofocus device having an evaluation value calculation circuit which eliminates the influence of flicker. About Figure 6
This will be described with reference to FIG.

First, the conventional autofocus device is shown in FIG.
As shown in FIG. 1, a photographing unit 100 including a focus-adjustable lens 1, an image pickup unit 2 for converting an image formed by the lens 1 into a video signal, and a drive unit 3 for driving the focus adjustment function of the lens 1. A luminance calculation section 4 for calculating luminance from a video signal from the photographing unit 100, an evaluation value calculation circuit 7 including a high frequency detection section 5 and a peak detection section 6, and a drive section based on the results of the evaluation value calculation circuit 7. 3 and a lens control unit 8 for driving the same. Evaluation value calculation circuit 7
As will be described later in detail, the state of the in-focus point is determined from the calculation result of the brightness calculation section 4, and a signal corresponding to the deviation from the in-focus point is output.

The structure and operation of the evaluation value calculation circuit 7 will be described with reference to FIG. Luminance Y is A / D converter 20
The image is converted into digital data in synchronism with the sampling pulse 26, the high-frequency component is taken out by the high-pass filter 21 formed by digital technology, the absolute value is obtained by the absolute value processing circuit 22, and the output is the image to be auto-focused. An evaluation value for autofocus is calculated by integrating over the entire area.

That is, this integration adds all the data in the horizontal line in the range set by the horizontal frame control signal 23H (reference 24H), and then sets it by the vertical frame control signal 23V. In the range thus defined, the evaluation value is obtained by integrating in the vertical direction (reference numeral 24V) while synchronizing with the horizontal synchronizing signal 25.

Next, flicker will be described. For example, when a subject under a fluorescent lamp is photographed, the frequency of the commercial power source is 50%.
Hz illumination change and video signal field frequency 60
Due to the close proximity and different frequencies of Hz, the signal level of the video signal fluctuates and flicker occurs. This flicker will affect the calculation of the above-mentioned evaluation value as noise.

As a countermeasure against this, the frequency of the commercial power source is 50H.
In the z area, manually set the shutter speed of the imaging device to 1 /
By switching to 100 seconds, the occurrence of flicker was prevented in advance. However, in this method, in the case of a slight flicker, it may not be possible to judge it only by looking into the viewfinder, and since this switching is manual, there is a risk of erroneous operation.

Further, conventionally, a method of eliminating the influence of flicker when automatically calculating an evaluation value has been proposed.
An example thereof is shown in FIG. 6, in which a moving average circuit 27 is provided after the absolute value processing circuit 22 of the evaluation value calculation circuit 7 described with reference to FIG. In the method, the moving average of the signal level is taken in units of a plurality of fields to eliminate the influence of flicker. However, according to this method, it is impossible to detect the evaluation value for each field because the average is taken in units of a plurality of fields.

[0010]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an image pickup apparatus which eliminates the adverse effects on the autofocus operation due to the occurrence of flicker and has a high-speed responsiveness and which can perform a highly accurate autofocus operation. To do.

[0011]

The present invention has been made in view of the above problems, and at least an imaging optical system capable of focus control and an image formed by the imaging optical system are converted into video signals. Image pickup means, a luminance signal calculation means for calculating a luminance signal from the video signal, and an evaluation value calculation for extracting a high frequency component of a specific image region including a subject from the luminance signal to calculate an evaluation value for focus control Means, control value calculation means for controlling the image pickup optical system based on the calculation result of the evaluation value calculation means, and drive means for driving the image pickup optical system based on the calculation result of the control value calculation means A function, and further, at least a detection means for detecting the level of the video signal in field units,
A flicker determination unit that detects a change pattern of a video signal level based on the result of the detection unit and determines the presence or absence of flicker based on the detection result, and a shutter speed of the imaging unit based on the determination result of the flicker determination unit. The above problem is solved by configuring an image pickup apparatus having a flicker prevention function including a shutter speed switching unit for switching between.

Therefore, as described above, by automatically detecting the occurrence of flicker and switching the shutter speed to prevent the occurrence of flicker, the adverse effect of flicker on the autofocus operation is eliminated and the responsiveness is improved. Can realize fast and highly accurate autofocus operation.

[0013]

Embodiments of the present invention will be described with reference to FIGS. FIG. 1 is a diagram for explaining the occurrence of flicker and its prevention, and FIG. 2 is a diagram showing the flicker occurrence level. Further, FIG. 3 is a circuit block diagram showing a configuration of an image pickup apparatus using autofocus according to the present invention.

First, the occurrence of flicker will be described.
FIG. 1A shows the waveform of the illumination power source, which is expressed by the equation (1).

[Equation 1] Here, E ₀ is the amplitude and f _P is the frequency of the power supply, which is 50 Hz.

FIG. 1B shows the brightness when the fluorescent lamp is turned on by this power source, and is expressed by the equation (2).

[Equation 2] Therefore, the cycle becomes 100 Hz, which is twice the power supply frequency. Here, a is a constant indicating the amplitude of brightness.

FIG. 1C shows a case where the shutter cycle and shutter speed of the camera are 1/60 seconds, and it is assumed that the lighting power supply and the fluorescent lamp lighting cycle are deviated by Δt at time t = 0. In this case, t _{1 to} t ₃ , t _{3 to} t ₅ ,
charges corresponding to the quantity in the period of t ₅ ~t ₇ is accumulated in the imaging element. The phase relationship between the shutter cycle and the fluorescent lamp lighting cycle shows that the shutter cycle is 3
The fluorescent lamp lighting cycle is 5 times. That is, the shutter cycle is 1/60 seconds × 3 times = 1/20 seconds, and the fluorescent lamp lighting cycle is 1/100 seconds × 5 times = 1/20 seconds, which are the same.

In FIG. 1D, the shutter cycle of the camera is 1
/ 60 seconds and the shutter speed is 1/100 seconds. In this case, t _{1 to} t ₂ , t _{3 to} t ₄ , t _{5 to} t
_In the period of ₆ , the charge corresponding to the light amount is accumulated in the image sensor. Since this shutter speed of 1/100 second coincides with the fluorescent lamp lighting cycle, the light quantity for any one cycle of the fluorescent lamp lighting is taken in. Therefore, as will be described later using mathematical expressions, in this case, although it becomes dark, flicker does not occur.

Next, the occurrence of flicker will be explained. As described above, the flicker is caused by a slight deviation between the shutter cycle, the speed and the illumination cycle.
The light amount S (t) obtained by integrating the illumination light represented by the equation (2) in an arbitrary cycle is represented by the equation (3).

(Equation 3) Here, T is a period and Δt is a delay time.

In the equation (3), when the shutter speed is 1/60 seconds (T = 1/60), the light quantity S (t) is represented by the equation (4).

(Equation 4)

FIG. 2 shows one cycle of the equation (4). The central value is a / 60, the maximum value is a / 60 + √3 × a / 200π, and the minimum value is a / 60−√3 × a /. It becomes a sine wave with 200π. One cycle 2π is 1/100 second, and 1/60 is calculated every time the start time of integration is shifted by 1/100 second.
The fluctuation of the accumulated light amount (accumulated electric charge) for one second makes a round.

Here, when Δt = 0, 6 periods of the shutter (1/60, 2/60, 3/60, 4/60, 6
/ 60, 6/60), the light quantity is calculated as follows: First cycle (1/60) ... A / 60 + √3 × a / 4
00π second period (2/60) ... a / 60−√3 × a / 2
00π Third period (3/60) ... a / 60 + √3 × a / 4
00π 4th period (4/60) ... a / 60 + √3 × a / 4
00π Fifth period (5/60) ... a / 60−√3 × a / 2
00π 6th period (6/60) ... a / 60 + √3 × a / 4
00π, and the accumulated light amount fluctuates every three cycles, that is, every 1/20 second, and this is recognized as flicker. Further, as a more general expression, the accumulated light amount when there is a deviation time Δt takes a value at a point (marked by X) that is moved by a time Δt from each point in FIG. 2, and similarly, every three cycles, that is, 1/20. The accumulated light amount changes every second. This is consistent with what was described with reference to FIG.

On the other hand, assuming that the shutter speed is 1/100 second, and T = 1/100 second in the equation (3), S (t) = a / 100 holds and becomes constant regardless of the time t. . So this is
As described with reference to FIG. 1 above, this is consistent with the fact that when the shutter speed is 1/100 second, uneven light amount, that is, flicker does not occur.

Therefore, the object of the present invention is to automatically detect flicker caused by the difference between the frequency of the illumination light source 1/50 seconds and the shutter speed of the camera 1/60 seconds, and switch the shutter speed to 1/100 seconds. It is to prevent the occurrence of flicker.

FIG. 3 shows an image pickup apparatus according to the present invention, which is different from the conventional image pickup apparatus shown in FIG. 5 in that a signal level detector 9, a flicker detector 10, an electronic shutter control circuit 11 and a timing generator 12 are added. It is a thing. Therefore, the same parts as those of the related art are designated by the same reference numerals, and the description thereof will be omitted.

First, the image pickup signal from the image pickup section 2 is input to the signal level detector 9, and the signal level is obtained and stored for each field. Next, after obtaining the signal level of a predetermined number of fields, the flicker detection unit 10 determines whether or not the signal level has fluctuation due to flicker. When it is determined that there is flicker, the electronic shutter control circuit 11 is operated to set a shutter speed of 1/100 second, and the timing generator 12 then sets the shutter speed to 1/100 second (shutter cycle is 1/60 second). The image pickup unit 2 is driven by.

Although not shown, a means for manually returning the shutter speed from 1/100 seconds to 1/60 seconds is provided to eliminate the possibility of flickering.
By operating this, you can return it to its original state and shoot in a bright state.

Therefore, as described above, when the occurrence of the flicker is detected, the occurrence of the flicker can be prevented by automatically switching the shutter speed from 1/60 seconds to 1/100 seconds. It is needless to say that the configuration for detecting the occurrence of flicker and switching the shutter speed is not limited to the above-described one, and other configurations that realize the technical idea of the present invention may be used.

[0028]

Therefore, according to the present invention, as described above, the occurrence of flicker is detected and the shutter speed is switched,
By using a means for preventing the occurrence of flicker in the autofocus device, it is possible to eliminate the adverse effect of the flicker on the autofocus operation, and to configure an imaging device having a highly accurate autofocus function with high-speed response. it can.

[Brief description of drawings]

1A and 1B are diagrams for explaining the occurrence and prevention of flicker, in which FIG. 1A is a voltage waveform of a 50 Hz illumination power supply, and FIG. 1B is a diagram showing an illumination light amount by lighting a fluorescent lamp. Yes, (c) shows that the shutter cycle and speed of the camera are 1 /
The case of 60 seconds is shown, and (d) shows the case where the shutter cycle of the camera is 1/60 seconds and the shutter speed is 1/100 seconds.

FIG. 2 is a diagram for explaining a flicker generation level.

FIG. 3 is a circuit block diagram showing a configuration of an image pickup apparatus using autofocus according to the present invention.

FIG. 4 is a circuit block diagram showing a configuration of a conventional image pickup apparatus using autofocus.

FIG. 5 is a block diagram of an example of a circuit that calculates an evaluation value.

FIG. 6 is a circuit block diagram showing a configuration of conventional autofocus in which the influence of conventional flicker is prevented.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Lens, 2 ... Imaging part, 3 ... Driving part, 4 ... Luminance calculation part, 5 ... High frequency detection part 6 ... Peak detection part, 7 ... Evaluation value calculation circuit, 8 ... Lens control part 9 ... Signal level detection part, 10 ... Flicker detector 11 ... Electronic shutter control circuit 12, 35 ... Timing generator 20, 31 ... A / D converter, 21 ... HPF, 22 ...
Absolute value processing circuit 25 ... Horizontal sync signal, 26 ... Sampling pulse, 30
... image sensor 32 ... pre-processing circuit, 33 ... signal processing circuit, 34 ... control circuit

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location H04N 5/238 G03B 3/00 A

Claims (1)

[Claims] 1. An imaging optical system capable of at least focus control, an imaging means for converting an image formed by the imaging optical system into a video signal, and a brightness signal calculating means for calculating a brightness signal from the video signal. An evaluation value calculation unit that extracts a high frequency component of a specific image region including a subject from the brightness signal to calculate an evaluation value for focus control; and the imaging optical system based on the calculation result of the evaluation value calculation unit. An autofocus function including a control value calculating unit for controlling and a driving unit for driving the image pickup optical system based on the calculation result of the control value calculating unit, and further, at least the level of the video signal is detected in field units. Detecting means, and a flicker that detects a change pattern of a video signal level based on the result of the detecting means and determines the presence or absence of flicker based on the detection result. An image pickup apparatus having a flicker prevention function including a judgment unit and a shutter speed switching unit that switches a shutter speed of the imaging unit based on a judgment result of the flicker judgment unit.