JPS63254871A - Image pick-up device - Google Patents

Abstract

PURPOSE:To execute the correction when a subject sinks darkly by increasing the weight of the output of respective large area and small area level detecting circuits and controlling a diaphragm in accordance with the size of the contrast of the subject. CONSTITUTION:An image pick-up signal obtained through a diaphragm 1, a lens 2, an amplifying circuit and an A/D converter 5 is inputted to small area and large area level detecting circuits 11 and 12. The circuit 11 obtains the maximum value of the average value of the small area image pick-up level and outputs it to a contrast discriminating circuit 13 and a weight circuit 14. The circuit 12 obtains the average value of the image pick-up signal level of the whole of the image pick-up surface and outputs it to circuits 13 and 14. The circuit 13 obtains a ratio K of the output level of circuits 11 and 12 and outputs it to the circuit 14. The circuit 14 decides whether or not the difference in brightness is larger with the size of the K, and in case of K<4, namely, when the contrast is smaller, a weighting coefficient is 0, the diaphragm control is executed by the output of the circuit 11, and in case of K>6, namely, when the contrast is larger, the coefficient is m=1, and the diaphragm control is executed by the output of the circuit 12.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an imaging apparatus having an automatic aperture circuit that performs effective aperture correction when capturing images in backlit situations where there is a large difference in brightness and darkness.

2. Description of the Related Art Aperture control in conventional imaging apparatuses has been performed using a method that combines a peak value method and an average value method. FIG. 8 is a block diagram showing the configuration of this conventional imaging device, in which 1 is an aperture, 2
3 is a lens, 3 is an image pickup device such as a CCD, 4 is an amplifier circuit that amplifies the output signal of the image pickup device 3 to obtain an image pickup signal of a predetermined level, 6 is an analog/digital conversion circuit, and 6 is an analog/digital conversion circuit.
A peak value detection circuit detects the peak value of the image signal output from the digital conversion circuit 5, an average value detection circuit 7 detects the entire average value of the image signal output from the analog-to-digital conversion circuit 6, and 8 an aperture. Aperture drive circuit to drive, 9
10 is a signal processing circuit that performs gamma processing, etc., and 10 is a digital signal processing circuit.
This is an analog conversion circuit.

In the conventional imaging device configured as described above, the aperture 1 drive circuit 8 controls the aperture 1 so that a signal obtained by mixing the output signal of the peak value detection circuit 6 and the output signal of the average value detection circuit 7 becomes equal to the reference. to drive.

Problems to be Solved by the Invention However, in the conventional configuration described above, when backlit imaging or when imaging an object with a large difference in brightness and darkness, including a light source, the aperture is closed by the output signal of the peak value detection circuit 6, and the image cannot be captured. This has the problem that the subject you want to photograph becomes dark and dark.

In view of this problem, the present invention provides an imaging device having a correction function that corrects for the subject to be photographed to appear dark by determining conditions such as backlight where there is a large difference in brightness and controlling the aperture opening. This is the purpose.

Means for Solving the Problems In order to achieve the above object, the imaging apparatus of the present invention includes a small area level detection circuit that detects the average value of the imaging signal level of a part of the small area of the imaging screen, and a large area level detection circuit that detects the average value of the imaging signal level in an area larger than the area detected by the level detection circuit; a contrast discrimination circuit that determines the contrast of the subject; and an output of the small area level detection circuit and the A weighting circuit that takes two outputs of the area level detection circuit as input, increases the weight of the output of the small area level detection circuit when the contrast of the object is small, and increases the weight of the output of the large area level detection circuit when the contrast of the object is large. and an aperture control circuit that controls the aperture according to the output of the weighting circuit.

According to the present invention, with the above-described configuration, a contrast discrimination circuit discriminates the brightness and darkness of the subject, and upon receiving the output of the contrast discrimination circuit, a weight is applied when imaging a subject with a small difference in brightness and darkness, that is, a subject with low contrast. By increasing the weight of the output of the small area level detection circuit, the circuit performs aperture control that eliminates signal saturation, and when imaging a subject with a large difference in brightness and darkness, that is, a subject with high contrast, the weight circuit increases the weight of the output of the small area level detection circuit. By increasing the weight of the output of the level detection circuit, control is performed so that the aperture is not closed due to the influence of bright areas and the subject to be photographed does not appear dark.

Embodiment Hereinafter, an imaging apparatus according to an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of an imaging device according to a first embodiment of the present invention. Note that configurations similar to those of the prior art are designated by the same reference numerals and detailed explanation thereof will be omitted.

In FIG. 1, 1 is an aperture, 2 is a lens, 3 is an image sensor such as COD, 4 is an amplifier circuit, 6 is an analog-to-digital conversion circuit, 8 is an aperture drive circuit, and 9 is a signal processing circuit that performs gamma processing, etc. , 10 are digital-to-analog conversion circuits, which have the same configuration as shown in FIG. 8.

Reference numeral 11 denotes a small area level detection circuit that calculates the average value of the image signal level in a part of the image capture screen in a small area and detects the maximum value of these average values. Reference numeral 12 indicates the signal level of the image capture signal in the entire image capture screen. A large area level detection circuit detects the average value; 13 is a contrast discrimination circuit that discriminates the contrast of the subject; 14 receives the outputs of the small area level detection circuit 11 and the large area level detection circuit 12; and the output of the contrast discrimination circuit 13; Based on the signal, a small area level detection circuit 11. This is a weighting circuit that weights the output signal of the large area level detection circuit 12.

Regarding the imaging device of this embodiment configured as described above,
The operation will be explained below. FIG. 2 is a front view of the screen showing the principle of small area level detection.

One small area is, for example, 8 pixels horizontally and 4 lines vertically. This corresponds to approximately 3% of the effective area of a screen with 420 pixels horizontally and 500 pixels vertically. In the figure, when 8 consecutive pixels of each line are considered as 1 data, 8
One piece of data obtained by averaging the image signal levels of the pixels is compared with other data of that line, and the maximum value of the signal level of the image signal for each line (Dl, D2.Ds, . . .
....

DI, ..., D250) is calculated. Next, add four pieces of this data in the vertical direction, and add the data (xl.

X2. X3. ...-,XN,-...,,! 25
0) By determining the O maximum value, the maximum of the average value of the imaging signal level of the small area is isometrically determined. The large area level detection circuit 12 detects the average value of the imaging signal level of the entire imaging screen.

Next, the operations of the contrast discrimination circuit 13 and the weighting circuit 14 will be explained.

The contrast discrimination circuit 13 is a small area level detection circuit 1
1 and the output level of the large area level detection circuit 12 (this value is designated as K) is calculated and output.

Letting the output level of the small area level detection circuit 11 be Peak and the output level of the large area level detection circuit 12 be e, then K=Peak/muva (1). Generally, when capturing an image of a subject with a large difference in brightness and darkness, including a light source, etc., the level (Peak) corresponding to the bright part is set.
As the value of K increases, the value of K increases. Therefore, depending on the magnitude of K, it can be determined whether the subject has a large difference in brightness and darkness, including the light source, etc.

The weighting circuit 14 outputs a value Ci ratio determined by the following formula % formula % ((1).The weighting coefficient m of the above formula
is determined according to the output of the contrast discrimination circuit 13. The operation of the weighting circuit 14 is shown in solid lines in FIG. In the figure, the weighting circuit 14 performs aperture control on the reference using the output of the small area level detection circuit 11 to eliminate signal saturation by setting m=o under the condition of K<4, that is, when the contrast is small. Then, by setting m=1 under the condition of K) e, that is, when the contrast is large, the output of the large area level detection circuit 12 is selected to reduce the influence of bright parts such as light sources, in other words, it has characteristics close to those of the peak value detection circuit. The aperture control is performed by reducing the influence of the output signal of the small area level detection circuit 11 having the aperture. In the figure, since the weighting coefficient m changes smoothly around K=5, the operation of the diaphragm does not change abruptly and moves smoothly.

Another example of the operation of the weighting circuit 14 is shown by the broken line in FIG. In the same figure, the aperture is controlled at a level that is a mixture of the output of the small area level detection circuit 11 and the output of the large area level detection circuit 12 at K (4).At this time, by changing the weighting coefficient m, the characteristics of the aperture can be arbitrarily controlled. For example, K
If the weighting coefficient m is increased with <4, the diaphragm control becomes close to the average value, and the change in the diaphragm characteristics around K=5 becomes small. Note that the operation of the weighting circuit 14 is not limited to this.

As described above, according to this embodiment, the contrast discrimination circuit 13 discriminates the brightness and darkness of the subject, and when the subject with a small difference in brightness and darkness is imaged, the small area level detection circuit 11
The output of the large area level detection circuit 12 is weighted with respect to the output of the large area level detection circuit 12 to eliminate saturation of the signal. A good image can be obtained by performing aperture control that weights the output of the small area level detection circuit so that the subject to be photographed does not appear dark.

Note that the small area level detection circuit 11 is configured to calculate the average value of the signal level of the imaging signal in a small area of the imaging screen and output the maximum value of these average values, but the larger value of the average values of the small area It is also possible to have a configuration in which the average of a plurality of values is output.

Also, the position where the reference and signal levels are compared is the 4th position.
As shown in the figure, the small area level detection circuit 11 and the large area level detection circuit 1 are connected to the input side, not the output side, of the weighting circuit 14.
It is also possible to perform the configuration for each of 2.

Next, an imaging device according to a second embodiment of the present invention will be described. The second embodiment has the same configuration as the first embodiment, except that the functional configuration of the large area level detection circuit 12' is different.

The large area level detection circuit 12 divides the imaging screen into 25 blocks as shown in FIG. 6, and calculates the average value (825 from B1) of the signal level of the imaging signal in each block. Next, the average value of each block is taken into an arithmetic circuit composed of a microcomputer, etc. of the large area level detection circuit 12, and the following processing is performed.

First, the average values of each block (B1 to B25) are sorted in descending order of value. At this time, the 25 pieces of data arranged in descending order are newly added to Sl, 32. B3゜・・・・・・、
S26.

Next, the rearranged data (Sl, B2.B3゜...
..., 525), data of very bright parts corresponding to light sources, etc., and data of very dark parts corresponding to shadows, etc. are excluded, added and averaged, and output.

The Hth to Lth data of the data sorted in ascending order is added and averaged, and the added average output is Aw.
If it is e, then it becomes. - For example, if H=L=4, 16 bright areas and 16 dark areas of the screen can be removed. By increasing the value of H, it is possible to remove the influence of bright areas such as large-area light sources.

As described above, according to this embodiment, the extremely bright portion corresponding to the light source etc. can be removed, so it is less affected by the bright portion such as the light source than the large area level detection circuit 12 of the first embodiment. You can control the aperture with . Therefore, a good image can be obtained by properly exposing the main subject.

Next, the third embodiment has the same configuration as the second embodiment, but the function of the arithmetic circuit such as a microcomputer in the large area level detection circuit 12 is changed.

The large area level detection circuit 12 divides the captured screen into 26 blocks as in the second embodiment, and calculates the average value (B1 to B25) within each block. Next, the average value of each block is taken into an arithmetic circuit such as a microcomputer.

The arithmetic circuit calculates the average values of each block (B1 to 825) shown in FIG. 6, B7. B 8. B9゜B1
2. B131 B14. B17. B18
．． B19°B2.2. B23. The data of B24 is averaged and output. If the additive average is Mmae, then Mve
x(BT+B8+B9+B12+B13+B14+B1
7+B18+B19+B22+B23+B24)/12. In the non-standard method, data at the center of the screen is used in the large area level detection circuit 12. Therefore, when photographing an object that includes a bright part such as a light source in the center of the screen, the output Ava of the large area level detection circuit 12 obtained using this method is smaller than the output of the large area level detection circuit 12 of the first embodiment. The level becomes higher, and as a result, the output X of the contrast discrimination circuit 13 determined by equation (1) takes a smaller value. Therefore, depending on the size of the bright area at the center of the screen, the aperture control will change to a characteristic that eliminates signal saturation. On the other hand, when a bright part such as a light source enters the periphery of the screen, the output Ave of the large area level detection circuit 12 becomes lower in level than in the first embodiment, so the output of the contrast discrimination circuit 13 takes a large value. , the aperture control changes to a characteristic that ignores bright areas such as light sources.

As described above, according to this embodiment, it is possible to realize aperture control that focuses on the center of the screen, and to obtain a good image without causing the aperture to close due to the influence of a bright part such as a light source entering the periphery of the screen.

In addition, the second. Although the imaging screen is divided into 26 blocks in the third embodiment, the number of block divisions is not limited to this. Also,
The form of block division in the third embodiment is not limited to this.

Next, a fourth embodiment of the present invention will be described with reference to FIG. The difference in the configuration of FIG. 7 from that shown in FIG. 1 is that the second small area level detection circuit 2° calculates an average value in an area smaller than that of the small area level detection circuit 11 and outputs the maximum value. Contrast discrimination circuit 1
3 is a structure in which the contrast is determined by comparing the output of the large area level detection circuit 12 and the output of the second small area level detection circuit 20. With the above configuration, the second small area level detection circuit 20 detects the maximum value in a smaller area, so even if an object including a small light source is imaged, it can be determined that the object has a large difference in brightness, so it is possible to It is possible to control the aperture so that the subject does not appear dark.

Effects of the Invention According to the present invention, there is provided a small area level detection circuit that detects the entire average value of the imaging signal level in a part of the imaging screen, and a small area level detection circuit that detects an area larger than the area detected by the small area level detection circuit. A large area level detection circuit that detects the average value of the signal level, a contrast discrimination circuit that discriminates the contrast of the object, and two inputs: the output of the small area level detection circuit and the output of the large area level detection circuit, When the contrast of the subject is small, the weight of the output of the small area level detection circuit is increased based on the output of the contrast discrimination circuit, and when the contrast of the subject is large, the weight of the output of the large area level detection circuit is increased based on the output of the contrast discrimination circuit. Because the configuration includes a weighting circuit that increases the weight and an aperture control circuit that controls the aperture according to the output of the weighting circuit, when backlit imaging or imaging an object with a large difference in brightness including a light source, etc. Since the weight of the output of the area level detection circuit is increased, the influence on control by the output of the small area level detection circuit, which performs level detection similar to that of a conventional peak value detection circuit, is small, and as a result, the aperture is closed. This will prevent the subject from being photographed in a dark, submerged image. Further, when an object with a small difference in brightness and darkness is imaged, the weight of the output of the small area level detection circuit is increased, so that the contrast of the image is improved. As a result, it is possible to obtain a good image with proper exposure depending on the subject.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an imaging device according to an embodiment of the present invention, FIG. 2 is a configuration diagram of a small area level detection circuit of the imaging device, and FIG. 3 is a characteristic diagram of a weighting circuit of the imaging device. , FIG. 4 is a block diagram showing a configuration in which the arrangement position of the reference of an imaging device according to an embodiment of the present invention has been changed, and FIG. 6 is a large area level detection circuit of an imaging device according to a second embodiment of the invention. 6 is a front view of the imaging screen illustrating the operation of the large-area level detection circuit of the imaging apparatus according to the third embodiment of the present invention, and FIG. Fourth
FIG. 8 is a block diagram showing the configuration of the conventional imaging device. 1...Aperture, 3...Image sensor, 8...
...Aperture drive circuit, 11...Small area level detection circuit, 12...Large area level detection circuit, 1
3... Contrast discrimination circuit, 14...
・Weight circuit. Name of agent: Patent attorney Toshio Nakao and 1 other person2'
＼ Figure 2

Claims (5)

[Claims] (1) A small area level detection circuit that detects the average value of the imaging signal level in a part of the imaging screen; and a small area level detection circuit that detects the average value of the imaging signal level in an area larger than the area detected by the small area level detection circuit. A large area level detection circuit to detect, a contrast discrimination circuit to judge the contrast of the object, and two inputs: the output of the small area level detection circuit and the output of the large area level detection circuit, and when the contrast of the object is small, a weight that increases the weight of the output of the small area level detection circuit based on the output of the contrast discrimination circuit, and increases the weight of the output of the large area level detection circuit based on the output of the contrast discrimination circuit when the contrast of the subject is large; and an aperture control circuit that controls an aperture according to the output of the weighting circuit. (2) A patent characterized in that the small area level detection circuit detects the average value of each small area obtained by dividing the imaging screen into a plurality of small areas, and adds and averages an arbitrary number of large values among these average values. An imaging device according to claim 1. (3) The imaging device according to claim 1 or 2, wherein the large area level detection circuit calculates the average value by weighting the center of the imaging screen. (4) The imaging device according to claim 1, 2, or 3, wherein the large area level detection circuit calculates the average value excluding areas where the amplitude of the imaging signal is large. (5) The contrast determination circuit determines the contrast based on a value obtained by comparing the output of the small area level detection circuit and the output of the large area level detection circuit. The imaging device according to item 3 or 4.