JPH04172080A - Image pickup device - Google Patents

Abstract

PURPOSE:To enable an appropriate photometry even in a backlignt photographing or a photographing generating a discolor by discriminating a brightness distribution state in a screen, and executing a photometry according to the discriminated result. CONSTITUTION:A brightness distribution state discriminating circuit 15 detecting the brightness level of an optional area in the screen and discriminating the brightness distribution state in the screen, a gate pulse generating circuit 13 outputting a gate pulse for setting a prescribed area, and a changeover circuit 16 selecting the gate pulse then outputting are provided. That is, by the brightness distribution state discriminating circuit 15, the brightness distribution state is discriminated, and the gate pulse is selected according to the discriminated result. And the photometry of the prescribed area in the screen set by the selected gate pulse is executed, and based on the photometry result, an optimum exposure control is performed. Thus, a natural and bright video can be obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to imaging devices such as video cameras and still cameras;
In particular, the present invention relates to an imaging device capable of automatic exposure control.

[Conventional technology]

2. Description of the Related Art Imaging devices such as video cameras and still cameras are conventionally known to be equipped with an automatic exposure control device that automatically sets exposure to an optimal value.

FIG. 5 is a block diagram showing the circuit configuration of an imaging device such as a consumer video camera equipped with this type of automatic exposure control device. In the figure, 1 is a photographing lens, 2 is an aperture that limits the amount of incident light, 3 is an image sensor such as a CCD that performs photoelectric conversion of imaging light, and 4 is a sample hold circuit that samples and holds the signal output from the image sensor 3. , 5 is a gate circuit for photometry of a predetermined 1ffLt set within the screen, to which the output signal of the sample and hold circuit 4 is input, and is controlled by a gate pulse. 6 is an integration circuit that integrates the output of the gate circuit 5; 7 is an aperture drive circuit that drives the diaphragm 2 according to the output of the integration circuit 6; and 8 is a circuit that converts the analog imaging signal output from the sample hold circuit 4 into a digital signal. The A/D converter, 9 is a signal processing circuit that processes the digitized imaging signal and separates the luminance signal and color signal, and 9.10 performs AGC (auto gain control) and γ (gamma) processing, etc. An encoder circuit to which the luminance signal from the signal processing circuit 9 is input; 11 is a color signal processing circuit that processes the color signal from the signal processing circuit 9 and outputs it to the encoder circuit 10; 12 is a color signal processing circuit for outputting the luminance signal from the encoder circuit 10. A D/A converter converts a digital video signal into an analog signal, and outputs a composite video signal. Reference numeral 13 denotes a gate pulse generation circuit that outputs a gate pulse to the gate circuit 5.

In the above configuration, the imaging light from the object that enters the image sensor 3 through the lens 1 and the aperture 2 is photoelectrically converted into an electrical signal by the image sensor 3, and then passes through the sample and hold circuit 4 to the A/D converter 8. The signal is input to the signal processing circuit 9, where it is converted into a digital signal and output to the signal processing circuit 9. In the signal processing circuit 9, after predetermined signal processing such as gain control and gamma processing is performed, the signal is separated into a luminance signal and a color signal (specifically, two color difference signals) as described above, and the luminance signal is directly The signal is input to the encoder circuit 10. Further, the color signal is inputted to the encoder circuit 10 after being subjected to predetermined signal processing in a 10-signal processing circuit 11 . Then, in this encoder circuit 10, the luminance signal and the color signal are synthesized,
After being further converted into an analog signal by the D/A converter 12,
It is output as a composite video signal from the output terminal.

The imaging signal output from the sample hold circuit 4 is also input to the gate circuit 5, where the subject in a predetermined area within the screen gated by the gate pulse from the gate pulse generation circuit 13 is always given the optimal signal. The control signal that becomes the level is passed through the integrating circuit 6 to the aperture drive circuit 7.
is output to. The aperture drive circuit 7 drives the aperture 2, thereby performing the automatic exposure control described above.

(Problem to be Solved by the Invention) However, in an imaging device equipped with the automatic exposure control function as described above, when photographing a cantle service at a wedding, etc., for example, it is difficult to Because there is a large difference in brightness between the subject and the background, there are problems such as the person in the center being overshadowed and the subject not being able to be clearly photographed, or conversely, colors being blown out, resulting in an unnatural image. be.

The present invention was made in view of these problems, and
To provide a photographing device capable of performing proper light metering and controlling exposure in an accurate manner even in backlight photography or photography in which color skipping occurs, and providing natural and clear images.

[Means for Solving the Problems] The imaging device of the present invention is an imaging device that performs exposure control by photometering a predetermined area set within the screen, and which controls the brightness level of the entire screen and any area within the screen. a brightness distribution state determination circuit that detects and determines the brightness distribution state within the screen, a gate pulse generation circuit that outputs a plurality of gate pulses for setting the predetermined area, and a switch that selects and outputs those gate pulses. and a circuit configured to control the switching circuit in accordance with the determination result of the brightness distribution state determination circuit.

[Effect]

In the imaging device of the present invention, the brightness distribution state determining circuit determines the brightness distribution state within the screen, and the gate pulse is selected according to the result of the determination. Then, photometry of a predetermined area within the screen is performed using the selected gate pulse, and optimal exposure control is performed based on the photometry result.

〔Example〕

FIG. 1 is a block diagram showing a circuit bridge construction of an imaging device according to an embodiment of the present invention. In the figure, 1 to 13 are the same components as in FIG. 5, but a gate pulse generation circuit 13 outputs a plurality of gate pulses aNc for setting a predetermined @ area within the screen. 14 is a gate circuit that gates the image signal digitized by the A/D converter 8 using the gate pulse C from the gate pulse generation circuit 13 and outputs the gate signal; 15 is an A/D
A brightness distribution state determination circuit that detects the brightness level of the entire screen and any area within the screen based on the signal manually inputted from the converter 8 and the signal manually inputted from the gate circuit 14, and determines the brightness distribution state within the screen. Here, backlighting or overexposure is determined from the brightness distribution pattern obtained by converting the input signals from the A/D converter 8 and the gate circuit 14 into a pistogram.

16 is a gate pulse a from the gate pulse generation circuit 13
, b and outputs it to the gate circuit 5, which is controlled by the determination result of the brightness distribution state determination circuit 15.

In the imaging device configured as described above.

Similar to the device shown in FIG. 5, automatic exposure control is performed by weighted photometry of a predetermined area set within the screen. First of all,
Imaging light from a subject that is incident on the image sensor 3 through the photographic lens 1 and the aperture 2 is photoelectrically converted into an electrical signal, which is input to the A/D converter 8 via the sample and hold circuit 4. Ru. The input image signal is converted into a digital signal at high speed by the A/D converter 8 and output to the signal processing circuit 9. This signal processing circuit performs gain control, gamma processing, etc., and divides the signal into a luminance signal and a color signal. Among them, the separated luminance signal is directly input to the encoder circuit 10.

The color signal is input to the free encoder circuit 10, which undergoes predetermined signal processing in the color signal processing circuit 11. The video signal synthesized by the encoder circuit 10 is then sent to the D/A converter 1.
2, the signal is returned to an analog signal and then output as a composite video signal.

Further, among the image signals sampled and held by the sample and hold circuit 4 and digitized by the A/D converter 8, the luminance signal is also input to the gate circuit 14. This gate circuit 14 is gated with a gate pulse C corresponding to a central area C within the entire screen area X shown in FIG. Also,
The luminance signal digitized by the A/D converter 8 is also directly input to the luminance distribution state determination circuit 15 . The brightness distribution state determining circuit 15 converts the two input signals into histograms, and determines whether the signal is backlit or overexposed based on the brightness distribution pattern.

FIG. 3 shows an example of a pistogram of the brightness level of the entire screen X based on the signal directly input from the A/D converter 8. As shown in the figure, when shooting against the light or when shooting with overexposure, the brightness is often distributed only at an extremely high level and an extremely low level compared to when shooting in general. Therefore, when the histogram is as shown in FIG. 3, it is determined that the shooting is backlit or overexposed.

FIG. 4 shows a histogram of the brightness level of the central area C within the screen based on a signal input manually through the gate circuit 14. What is shown in FIG. 4(a) is the area C.
Most of the time is when the brightness is extremely low, and in this case it is determined that the photograph is against the light. Furthermore, what is shown in FIG. 4(b) is a case where most of the area C has extremely high brightness, and in this case, it is determined that this is an overexposed photograph such as that during a candle service.

As described above, when it is determined from the histograms of FIGS. 3 and 4 (a) and (b) that the shooting is backlit or overexposure, the brightness distribution state determination circuit 15 sends the switching circuit 16 to make a determination according to the determination result. A signal is output. At this time, switching circuit 1
6 is a normally wide gate pulse a (area A shown in FIG.
However, when the above-mentioned backlight/overexposure discrimination (, E is manually performed, the gate pulse b corresponding to area B (A>B>C) is selected, which is smaller than the tilted castle A (A>B>C). is selected and output to the gate circuit 5.Then, the output signal of the sample hold circuit 4 gated by the gate pulse C is integrated by the integration circuit 6 and supplied to the aperture drive circuit 7. A drive signal corresponding to the integral value is output, and this drive signal drives the diaphragm 2.In other words, when shooting backlight or overexposure, light metering is performed with more emphasis on the center than in normal light metering. Optimal exposure control is performed so that the subject in the center can be photographed clearly.

In this way, the brightness level of the entire screen and any area within the screen is converted into a histogram, and based on the pattern, it is determined whether the image is backlit photography or overexposure photography. and,
By switching to more center-weighted metering when taking these types of shots, you can automatically perform optimal metering for subjects such as people looking through a window or people in a cantle service, and you can achieve natural, natural-looking shots. Clear images can be obtained.

〔Effect of the invention〕

As described above, according to the present invention, the brightness distribution state within the screen is determined and light metering is performed according to the determination result, so even when shooting against the light or when shooting with color skipping, it is possible to accurately measure the brightness. The effect is that you can control the optimal exposure by metering the light, and get natural and clear images.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the circuit configuration of an imaging device according to an embodiment of the present invention, FIG. 2 is an explanatory diagram showing each gate area within the screen, and FIG. 3 is an example of a histogram of the brightness level over the entire screen. FIG. 4 is an explanatory diagram showing an example of a histogram of the brightness level in the central area of the screen, and FIG. 5 is a block diagram showing the circuit configuration of a conventional example. 1...Photographing lens 2...Aperture 3...Image sensor 4...Sample hold circuit 5...Cate circuit 7... ... Aperture drive circuit 8 ... A/D converter 9 ... Signal processing circuit lO ... Encoder circuit 13 ... Gate pulse generation circuit 14 ... ...
・Gate circuit 15... Brightness distribution state determination circuit 16...
・Switching circuit

Claims (1)

[Claims] An imaging device that performs exposure control by metering a predetermined area set within the screen, and detects the brightness level of the entire screen and any area within the screen to determine the brightness distribution state within the screen. It is equipped with a discrimination circuit, a gate pulse generation circuit that outputs a plurality of gate pulses for setting the predetermined area, and a switching circuit that selects and outputs the gate pulses, and according to the discrimination result of the luminance distribution state discrimination circuit. An imaging device characterized by controlling a switching circuit.