JPH04321384A - Image pickup device - Google Patents

Abstract

PURPOSE:To improve a problem of a conventional image pickup device in which a rate of back light/excess forward light is decided based on a ratio of an exposure evaluation value (luminance integration value) of an area of an object to an exposure evaluation value of other area, a reference voltage given to an aperture control circuit is obtained from resulting ratio so that the ratio is changed largely when the object is moved a little and the back light/excess forward light may not accurately be corrected. CONSTITUTION:The correlation between a luminance frequency distribution of an area in the middle of a pattern and a luminance frequency distribution of other area is obtained and a weight alpha being a ratio of a major object component of each area and weight beta being a ratio of non-major object components are obtained based on the correlation and the ratio of back light/excess forward light is decided based on the ratio of (exposure evaluation value of non-major component)/(exposure evaluation value of major component) by taking the wieghts alpha, beta into account.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an imaging device such as a video camera having a lens aperture mechanism.

0002

2. Description of the Related Art FIG. 1 is a block circuit diagram of an imaging apparatus having an automatic gain control mechanism when the screen is divided as shown in FIG. In the figure, 1 is a lens, 2 is an aperture, 3 is an image sensor, 4 is a preamplifier that amplifies the output of the image sensor 3 to an appropriate size, 5 is a process section consisting of a γ correction circuit, a WB circuit, etc., and 6 is a process section. An encoder section 7 converts the output of the processing section 5 into a specific signal system, and 7 is a photometric circuit that extracts a signal corresponding to the photometric region shown in FIG. 5 from the video signal output from the preamplifier 4.

[0003] 8 is a detection circuit, 9 is an A/D converter, 10 -
18 is an electronic switch; 19 to 27 are integration circuits (exposure evaluation value detection means) that calculate exposure evaluation values corresponding to each area of the screen divided as shown in FIG. Means for calculating the frequency distribution, 37 an interface circuit, 38 a microcomputer, 39 a vertical and horizontal synchronizing pulse, etc., are connected to the electronic switches 10 to 10.
a pulse generation circuit that generates a pulse signal to control 18;
40 is a D/A converter that converts the digital signal input from the microcomputer 38 into an analog signal;
1 is an aperture control circuit.

Next, the operation will be explained. The light that has passed through the lens 1 forms an image on the image sensor 3. This formed optical image is converted into a video signal, which is an electrical signal, by the image sensor 3, amplified by the preamplifier 4 to a size that can be easily processed in the subsequent stage, and then converted to a digital signal by the A/D converter 9. , electronic switches 10 to 18 controlled by the output signal of the pulse generation circuit 39 distribute the signals to integration circuits 19 to 27 and frequency distribution calculation means 28 to 36 corresponding to each divided screen area.

The digital signals distributed to the integrating circuits 19 to 27 are integrated to detect an exposure evaluation value. On the other hand, the digital signals distributed to the frequency distribution calculating means 28 to 36 are counted according to their size, and a frequency distribution as shown in FIG. 3 is detected for each region. These detection signals are held in the interface circuit 37, then selected by a control signal sent from the microcomputer 38, and input to the microcomputer 38.

The microcomputer 38 has the following 1
- Perform the processing in section 4. 1. Calculation of correlation value Since the main subject is often located in the center of the screen, it is assumed that the main subject is always included in the central area (area 5 in the case of screen splitting as shown in Figure 2). Then, the correlation between this central area and other areas is determined from the brightness frequency distribution. This correlation value is calculated using the arithmetic expression shown in Equation 1, for example. In this calculation formula, if the correlation is strong, the correlation value will be small, and if the correlation is weak, the correlation value will be large.

[0007]

[Math 1]

2. The main subject area is determined using a correlation value obtained using an arithmetic expression with a discrimination number of 1 between the main subject area and the minor non-main area. If the correlation is stronger than a predetermined threshold value (the correlation value according to Equation 1 described above becomes smaller), it is determined as a main subject region, and if not, it is determined as a non-main subject region.

3. Calculating the ratio of exposure evaluation values The ratio of the exposure evaluation values of the main subject area and the non-main subject area (exposure evaluation value of the non-main subject area/exposure evaluation value of the main subject area) is calculated. When the calculated ratio is greater than 1, it indicates the degree of backlighting, and when it is smaller than 1, it indicates the degree of over-frontlighting.

4. Control of reference voltage For example, from the characteristic diagram shown in Figure 4, compare the reference voltage determined by the ratio found in section 3 with the current reference voltage, and if the current reference voltage is larger, the reference voltage The voltage is output after being decreased by a predetermined value, and if the current reference voltage is smaller, the reference voltage is increased by a predetermined value and output. The above operations are then repeated until the difference between the two becomes within a predetermined value.

The reference voltage output from the microcomputer 38 is converted into an analog signal by a D/A converter 40, and is input to an aperture control circuit 41 as a reference voltage. From the video signal amplified by the preamplifier 4, only the signal in the detection region shown in FIG. 5, for example, is input to the detection circuit 8 and integrated by the photometry circuit 7. This integrated video signal becomes a detection signal with a level corresponding to the average brightness of the photometric area (see FIG. 5), and is sent to the aperture control circuit 41.
is input. The aperture control circuit 41 performs feedback control on the aperture 2 so that this value matches the reference voltage.

0012

[Problems to be Solved by the Invention] As described above, in conventional imaging devices, the main subject area is determined based on whether the correlation value is larger or smaller than a certain threshold value. , the detection results for the degree of backlighting and excessive forwardlighting sometimes changed significantly. Therefore, there is a problem in that the amount of correction changes greatly, making it impossible to accurately correct backlight and forward light by adjusting the aperture. The present invention has been made to solve the above-mentioned problems, and the detection result of the degree of backlighting/excessive lighting does not change significantly when the position of the subject shifts slightly, and it is possible to adjust the aperture by adjusting the aperture. An object of the present invention is to obtain an imaging device that can accurately correct backlighting and excessive forwardlighting.

[0013]

[Means for Solving the Problems] The imaging device according to the present invention obtains an exposure evaluation value from the integrated value of the luminance components of the video signal of each region of a screen divided into a plurality of regions, and also calculates a plurality of luminance components of each region. Dividing the screen into stages and counting the number of appearances at each stage to obtain a luminance frequency distribution, from these luminance frequency distributions, calculate the correlation between the area in the center of the screen and other areas, and from this correlation value Calculate the weight α of the main subject component and the weight β of the non-main subject component, calculate the exposure evaluation value of the main subject component and the exposure evaluation value of the non-main subject component from the weights α, β of each area and the exposure evaluation value, The degree of backlighting/excessive lighting is detected from the ratio of the exposure evaluation value of the main subject area and the exposure evaluation value of the non-main subject area, and based on this detected value, the brightness of the video signal obtained from the imaging means is set to a certain level. The aperture is adjusted so that

According to the present invention, the exposure evaluation value of the main subject component and the exposure evaluation value of the non-main subject component in each area are determined, and the degree of backlighting/excessive lighting is detected from the comparison value between the two. Therefore, even if the subject moves a little, the detection results for backlighting and forward lighting will not change significantly.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. The hardware of this embodiment is the same as that of the conventional example shown in FIG. Figure 6 is a characteristic diagram showing the relationship between the weight and correlation value of each area for determining the exposure evaluation value of the main subject component, and Figure 7 is a characteristic diagram of each area for determining the exposure evaluation value of the non-main subject component. FIG. 3 is a characteristic diagram showing the relationship between weights and correlation values.

Next, the operation will be explained. The steps up to the point where the correlation value is determined by the microcomputer 38 are the same as in the conventional example, and will therefore be omitted. Next, the microcomputer 38 determines the components of the main subject included in each area,
Components of non-main subjects are found from the correlation values of each area. FIG. 6 is a diagram showing the relationship between the correlation value and the weight α of the main subject component, and the weight changes from small to large as the correlation becomes stronger in the middle part of the correlation value. FIG. 7 is a diagram showing the relationship between the correlation value and the weight β of the non-main subject component, and the weight changes from small to large as the correlation becomes weaker in the middle part of the correlation value.

Next, the microcomputer 38 calculates the exposure evaluation value of the main subject component and the exposure evaluation value of the non-main subject component using the following equation shown in Equation 2.

[0018]

[Math 2]

Next, the microcomputer 38 calculates the ratio of the exposure evaluation value of the main subject component to the exposure evaluation value of the non-main subject component (exposure evaluation value of the non-main subject component/exposure evaluation value of the main subject component). . Next, from the characteristic diagram shown in FIG. 8, the reference voltage determined by the ratio of the exposure evaluation values of the main subject component and the non-main subject component is compared with the current reference voltage, and if the current reference voltage is larger, then The reference voltage is decreased by a predetermined value and output to the aperture control circuit 41. Furthermore, if the current reference voltage is small, the reference voltage is increased by a predetermined value and output to the aperture control circuit 41. The above operations are then repeated until the difference between the two becomes within a predetermined value. The operation from here on is similar to the conventional example.

When such control is performed, when the correlation value in a certain area is medium, for example, point V in FIG.
At point W in Figure 7, the main object component is α in this area.
This means that the non-main subject components are included at a rate of v, and the non-main subject components are included at a rate of βw. Here, Figure 6 is changed to Figure 9.
If the weighting characteristics shown in FIG. 7 are changed to those shown in FIG. 10, the same operation as the conventional example will be obtained. In this way, any given area will contain only the main subject component or only the non-main subject component. In other words, it does not contain both components.

Next, the operation when controlled as in this embodiment will be explained. When the main subject shifts from the central area, the correlation will gradually change from weak to strong in a certain area, so a slight shift in the main subject will cause the exposure evaluation values of the non-main subject components and the main subject description to change. does not change significantly, and as a result, the ratio of (exposure evaluation value of main subject component / exposure evaluation value of non-main subject component) does not change significantly, so the detection result of the degree of backlighting/excessive lighting will not change significantly.

[0022] In the above embodiment, the weights α,
Although the relationship between β and the correlation value is shown as changing in a straight line as shown in FIGS. 6 and 7, it does not necessarily have to be a straight line; The relationship may be a combination of the following.

[0023]

As described above, according to the present invention, the main subject component and non-main subject component included in each area are weighted based on the correlation value, and the main subject component is The exposure evaluation value of the subject and the exposure evaluation value of the non-main subject components are calculated, and the degree of backlighting/over-frontlighting is detected from the ratio of the two and the aperture is adjusted, so even if the position of the subject is slightly shifted, the backlighting will be avoided.・The detection result of the degree of excessive light does not change significantly. As a result, it is possible to obtain an imaging device that can accurately correct backlighting and excessive forwardlighting.

[Brief explanation of the drawing]

FIG. 1 is a block circuit diagram showing the hardware configuration of an imaging device according to an embodiment of the present invention and a conventional example.

FIG. 2 is a diagram showing an example of screen division.

FIG. 3 is a frequency distribution diagram of brightness in each region.

FIG. 4 is a characteristic diagram showing the relationship between the reference voltage and the ratio between the exposure evaluation value of the main subject component and the exposure evaluation value of the non-main subject component.

5 is a diagram showing a detection area on the screen by the detection circuit 8. FIG.

FIG. 6 is a characteristic diagram showing the relationship between the correlation value of each region and the weight α of the main subject component.

FIG. 7 is a characteristic diagram showing the relationship between the correlation value of each region and the weight β of the non-main subject component.

FIG. 8 is a characteristic diagram showing the relationship between the reference voltage and the ratio between the exposure evaluation value of the main subject and the exposure evaluation value of the non-main subject component in this embodiment.

FIG. 9 is a characteristic diagram showing the relationship between the correlation value of each region and the weight α of the main subject component, corresponding to a conventional example.

FIG. 10 is a characteristic diagram showing the relationship between the correlation value of each region and the weight β of a non-main subject component, corresponding to a conventional example.

[Explanation of symbols]

2 Aperture 7 Photometric circuit 8 Detection circuit 9 A/D converters 10 to 18 Electronic switches 19 to 27 Integration circuit (evaluation value detection means) 28 to 36
Frequency distribution calculation means 38 Microcomputer 39 Pulse generation circuit 40 D/A converter 41 Aperture control circuit

Claims (1)

[Claims] Claims: 1. Imaging means for outputting a video signal; automatic gain control means for amplifying the video signal; an evaluation value detection means for detecting an evaluation value; a luminance frequency distribution calculation means for dividing the input luminance component into a plurality of stages for each of the plurality of regions and counting the number of times the luminance appears in each stage; Correlation calculation means for calculating a correlation value of each area with respect to the area at the center of the screen from the luminance frequency distribution of each area, and a weighting α of the main subject component of each area and a weighting β of the non-main subject components of each area to the correlation value. means for calculating the exposure evaluation value of the main subject component and the exposure evaluation value of the non-main subject component from the weights α and β of each area and the exposure evaluation value, and the exposure evaluation value of the main subject component. means for detecting the degree of backlighting or overlighting from the ratio of the evaluation value and the exposure evaluation value of the non-main subject component; and the automatic gain control means for controlling the average brightness of the video signal to be constant based on the detection result. An imaging device comprising means for controlling.