JPS62110369A - Image pickup device - Google Patents

Abstract

PURPOSE:To correct signal level of a main object at the center properly in backlighted shot etc. by detecting the level of an image pickup signal of the center of a picture and the signal of peripheral parts, making arithmetic processing making the two detection output signals input, and controlling amplitude of image pickup signals by the arithmetic output signal. CONSTITUTION:Output signals of an AD conversion circuit 10 are supplied to gate circuits 14, 16. Circuits 14 and 16 supply image pickup signals of the center of a picture and peripheral part to level detecting circuits 15, 17 respectively. Detecting circuits 15, 17 output average values P1 and P2 of amplitude of image pickup signals of the central part and peripheral part of the picture respectively. A mixing circuit 19 finds out an average value P0 of the whole picture making P1 and P2 input. A comparator circuit 20 compares the value P0 and a reference level VT and outputs an error signal, and a driving circuit 9 drives a diaphragm 2 by the error signal. On the other hand, values P1, P2 are supplied to an arithmetic circuit 18. The arithmetic circuit 18 has characteristic as shown in the figure, and indicates P2/P1=k. The vertical axis is output signals of the arithmetic circuit 18 and determines gain of a gain control circuit 11. Accordingly, the average level of the central part is corrected properly by giving gain of (1+k)/2 to the circuit 11.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an imaging device such as a video camera, and more particularly to an imaging device that performs appropriate gain control depending on the state of the screen.

With conventional video cameras, good images can be obtained when shooting in front light, where the main subject such as a person and the background are evenly illuminated, but when the main subject such as a person is captured against the sky, There is a drawback that when capturing a backlit image where the subject is located in the center of the screen, the subject becomes dark. This is because the conventional aperture control mechanism is controlled to keep the average level or peak level of the imaging signal constant.

Figure 2 shows the relationship between the brightness on the screen and the frequency of the small areas with that brightness by finely dividing the image into small areas from one frame of imaging signal. The scale indicates the number of image signals corresponding to the brightness of the image.

FIG. 2(a) shows the case of front-light imaging, and the distribution is centered around the average level AV of the imaging signal. At this time, the average level of the main subject located at the center of the screen is generally equal to the average level AV of the entire image pickup signal, so if the aperture p is controlled at the average level, the main subject can obtain an appropriate level.

Figure 2 fb) shows the case of backlit imaging, where a very bright area in the background forms a first peak in the area where the amplitude is large, and the main subject such as a person forms a second peak in the area where the amplitude is small. are doing. At this time, the average level P1 of the main subject at the center of the screen is different from the average level AV of the entire image signal, and if the aperture is controlled using the average level AV, the main subject will become dark.

Therefore, an aperture control device that is an improvement over the conventional method has been announced, and is disclosed in, for example, Japanese Patent Application Laid-Open No. 55-87129.

FIG. 7 shows a block configuration diagram of this conventional aperture control device, in which 1 is a lens, 2 is an aperture, 3 is an imaging device, and 4 is an imaging signal that amplifies the output signal of the imaging device 3 to a predetermined level. 5 is a signal processing circuit that performs signal waveform processing such as gamma correction, 6 is a nonlinear amplifier circuit that has a characteristic of decreasing the absolute value of the amplification degree as the imaging signal increases, and 7 is a nonlinear amplifier circuit. 8 is a comparison circuit that compares the average level with a reference level VL and outputs an aperture control signal; 9 is a drive circuit that drives the aperture. .

In the aperture control device configured as described above, the amplitude of the imaging signal corresponding to backlight is compressed by making the nonlinear amplifier circuit 6 have the characteristics shown in FIG. 3, and the output of the average level detection circuit 7 is This prevents the signal from becoming too large.

Since the main subject to be imaged is generally located in the center, the gain of the non-linear amplifier circuit 6 at the center of the screen is made larger than the gain at the periphery so that the imaging signal at the periphery does not greatly affect the aperture control signal. This prevents the diaphragm from closing and making the center of the screen too dark when backlit or when capturing images that include a light source.

Problems to be Solved by the Invention However, in the above configuration, the nonlinear amplifier circuit θ
Since correction is performed by compressing a signal of a predetermined level or higher with the characteristics of , inappropriate correction may be performed. For example, when the screen is uniform and very bright, the imaging signal is compressed by the nonlinear amplifier circuit 6, and the output signal of the average level detection circuit 7 changes in the direction of opening the aperture compared to the case without correction. This is a problem. Furthermore, even if the gain at the center of the screen of the nonlinear amplifier circuit 6 is made larger than the gain at the periphery to reduce the influence of the imaging signal at the periphery, if a strong light source is located at the periphery of the screen, the center of the screen becomes slightly darker due to this effect. On the other hand, if the gain at the periphery of the nonlinear amplifier circuit 6 is set to zero in order to eliminate the influence of the periphery of the screen, the output signal of the imaging device 3 will become saturated when a strong light source enters the periphery of the screen, causing a problem. Met.

In view of this, an object of the present invention is to provide an imaging device that appropriately corrects the signal level of the main subject in the center of the screen by gain control when backlit or when capturing an image of a subject that includes a light source in the periphery. do.

Means for Solving the Problems The present invention includes a first level detection unit that detects the level of the imaging signal in the center of the imaging screen, and a first level detection unit that detects the level of the imaging signal in the peripheral area other than the central part of the imaging screen. a second level detection section that performs arithmetic processing using the output signals of the first level detection section and the second level detection section as input, and a gain control that changes the amplitude of the imaging signal based on the output signal of the calculation section. It is an imaging device comprising a section.

Effect The present invention has the above-described configuration, so that the arithmetic unit outputs the output signal P1 of the first level detection unit and the output signal P2 of the second level detection unit.
By calculating this, it is determined whether the peripheral part of the image contains a light source, etc., and the gain of the gain control section is continuously controlled depending on the situation, so that the central part of the image is at an appropriate signal level. The correction is made so that

Embodiment FIG. 1 is a block diagram of an imaging apparatus according to a first embodiment of the present invention. In Fig. 1, 1 is a lens, 2 is an aperture, 3 is an imaging device, 4 is an amplifier circuit, and the above is the seventh
The configuration is similar to that shown in the figure. 1o is an AD conversion circuit that digitizes the imaging signal. Reference numeral 11 constitutes a gain control circuit techine control section having a function of multiplying the output signal of the AD conversion circuit 1o and the output signal of the arithmetic circuit 8. 6a is a signal processing circuit that performs signal processing such as gamma correction and outputs a video signal, and 12 is a DA conversion circuit that converts the digital video signal into analog.

The output signal of the AD conversion circuit 10 is supplied to a gate circuit 14 and a gate circuit 16.

The gate circuit 14 converts the image signal of the screen central portion S1 indicated by diagonal lines in the image pickup screen shown in FIG. 4 to the level detection circuit 15.
The gate circuit 16 supplies the image signal of the peripheral area S2 of the screen to the level detection circuit 17. 13 is a gate pulse generation circuit that generates a gate pulse to control the gate circuit.

The level detection circuit 15 adds and averages the output signals of the gate circuit 14 and outputs the average value P1 of the amplitude of the image signal at the center of the screen, and the level detection circuit 17 is a circuit similar to the level detection circuit 16 and outputs the average value P1 of the amplitude of the image signal at the periphery of the screen. The average value P2 of the amplitude of is output. The gate circuit 14 and the level detection circuit 15 constitute a second level detection section, and the gate circuit 16 and the level detection circuit 17 constitute a second level detection section.
constitutes a second level detection section.

Reference numeral 19 indicates an average value P of the entire screen by inputting the output signal P1 of the level detection circuit 16 and the output signal P2 of the level detection circuit 17. P0=+P1++P2 ・・・・・・(
2Q is a comparison circuit that compares the output signal of the mixing circuit 19 with the reference level vT and outputs an error signal; 9 is a drive circuit that drives the aperture 2 using the error signal. .

On the other hand, the output signals of the level detection circuit 15 and the level detection circuit 17 are supplied to an arithmetic circuit 18 constituting an arithmetic section. The arithmetic circuit 1 day has the characteristics shown in FIG. 6 (al). In FIG. The output signal determines the gain of the gain control circuit 11.

The operation of the imaging apparatus of this embodiment configured as described above will be described below.

In the case of imaging that includes a light source, etc. at the periphery of the screen, the average level P2 of the imaging signal at the periphery of the screen and the average level P at the center of the screen
1 becomes as shown in FIG. 2(C).

Here, since the aperture 2 is controlled using the average value P0 of Pl and P2 as shown in the above equation, the central part of the screen where the main subject is located generally appears dark. On the other hand, if the ratio of Pl and P2 is k, then by substituting this into equation (1), Po=+P1++#kP1 1-)-= (-) Pl ・・・・・・(2)1
It becomes +. Therefore, in the case of this embodiment, if a gain of □ is given to the gain control circuit 11, the average level at the center of the screen can be corrected to an appropriate level.

For example, when =3, the gain is 2. Although the maximum gain is limited to 2 in FIG. 5(a), this is determined depending on the relationship with noise and is not limited to 2. In this embodiment, since the gain is variable up to twice, when the signal at the maximum amplitude is output from the imaging device 3, the gain control circuit 11 exceeds a predetermined level. Therefore, the signal processing circuit 6a has the gamma correction characteristic shown in a of FIG. Compared to the general characteristic A, the characteristic a allows the output signal to be compressed without being clipped even if a signal with a large amplitude is input. In addition, characteristic a
is just one example, and there is no need to limit it to this.

As described above, according to this embodiment, when a light source such as a fluorescent lamp enters the periphery of the screen in an imaging device having an automatic aperture control device, the center of the screen appears dark due to the influence of the light source. The brightness can be automatically corrected to the appropriate brightness by controlling the gain of the gain control circuit. Therefore, even when shooting a backlit image of a person against the sky, or when shooting a subject that includes a light source at the periphery of the screen, the main subject in the center of the screen can always maintain a constant brightness without any special operations. .

Next, another embodiment in which the characteristics of the arithmetic circuit 18 and the mixing circuit 19 of the first embodiment are changed will be described below.

In the embodiment described above, the mixing circuit 19 simply averages the average values of the amplitudes of the peripheral part of the screen and the center part of the screen to determine the average value of the amplitude of the entire screen and controls the aperture. It is also possible to control the aperture by weighting the center of the screen so as not to greatly affect the control. The output signal of the mixing circuit 19 is 2w2m1P1+rrL2P2...(3)
When (ml>m2.m1+m2=1), it is possible to control the aperture weighted at the center of the screen. At this time, by substituting P2=kP1 into equation (3), it becomes 2w2m1P1+flight kP1=(m1+m2k)Pl--(4). Therefore, depending on the ratio k of Pl and P2, ml-1-! n
By applying a gain of 2 to the gain control 11, the amplitude level at the center of the screen reaches the appropriate level (b).

In this second embodiment, the characteristic curve of the arithmetic circuit 18 is made gentler by controlling the diaphragm weighted at the center of the screen, and the maximum source of the tine control circuit 11 is lower than that in the first embodiment. It is possible to capture images without being affected by such factors.

Note that the characteristics of the arithmetic circuit 18 in the first and second embodiments can be arbitrarily determined. The gain is increasing with the same slope as the analogy line. With this method, the area is enlarged compared to the second embodiment.

DETAILED DESCRIPTION OF THE INVENTION Accordingly, according to the present invention, when an object is captured that includes backlight or a light source at the periphery of the screen, the central part of the screen, which conventionally appears dark, can be brought to the appropriate brightness. It can be automatically corrected. Therefore, the main subject at the center of the screen can maintain a constant brightness without being affected by the light source or the sky at the periphery of the screen.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an imaging device according to an embodiment of the present invention, FIG. 2 is a diagram showing the relationship between the brightness of the imaging screen and the power,
FIG. 3 is a characteristic diagram of a non-linear amplifier circuit of a conventional imaging device, FIG. 4 is a divided diagram of an imaging screen, FIG. 5 is a characteristic diagram of an arithmetic circuit of each embodiment of the present invention, and FIG. 6 is a characteristic diagram of the present invention. FIG. 7 is a block diagram of a conventional imaging device. 2...Aperture, 6a...Signal processing circuit,
11... Kane control circuit, 13...
・・C gate pulse generation circuit, 14, 16...
Gate circuit, 16,1 completion...Level detection circuit,
18...Arithmetic circuit, 19...Mixing circuit. Name of agent: Patent attorney Toshio Nakao and 1 other person 2nd
Figure 1 JV Counterfeit Bell Pt
AV 1 line 11V Hell I't
Po F'z

Claims (2)

[Claims] (1) a first level detection unit that detects the level of the imaging signal in the center of the imaging screen; a second level detection unit that detects the level of the imaging signal in the peripheral area other than the center of the imaging screen; The present invention is characterized by comprising: a calculation unit that performs calculation processing using the output signals of the first level detection unit and the second level detection unit as input; and a gain control unit that changes the amplitude of the imaging signal based on the output signal of the calculation unit. imaging device. (2) The calculation unit calculates the ratio value P_2/of the output signal P_1 of the first level detection unit and the output signal P_2 of the second level detection unit.
The gain G of the gain control section when P_1 is larger than a predetermined value is G≧G with respect to the reference gain G_o.
_o, and outputs a signal such that the gain G of the gain control unit satisfies G≦G_o when the value of the ratio is smaller than the predetermined value. Imaging device.