JPH02305071A - Image pickup device - Google Patents

Abstract

PURPOSE:To obtain excellent picture quality for a subject which is projected with excessive follow light by a spot light, etc., by controlling the maximum value of the gain of a gain control means according to the outputs of a peak level detecting means and a dark level detecting means. CONSTITUTION:A table shows the relation among the subject to be photographed, the output (PEAK) of the peak level detecting circuit 10, the output (DARK) of the dark level detecting circuit 11 and the gain control of a gain circuit 6, and the PEAK and DARK are compared with specific level (L for PEAK and M for DARK). Here, the specific value L and specific value M are set properly to decrease the PEAK and increase the DARK for the subject projected with follow light, and the PEAK and DARK become small for the subject projected with excessive follow light by a spot light, etc. A control circuit 12 performs control for limiting the maximum gain of the gain circuit 6 by a limiting circuit 13 for a subject which is small in both PEAK and DARK. Consequently, the image pickup device which performs proper gain control with the subject projected with the excessive follow light.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an imaging device that performs optimal gain control depending on screen conditions.

2. Description of the Related Art Conventional imaging devices are disclosed, for example, in Japanese Patent Application Laid-Open No. 57-4 [11
No. 1i7.

FIG. 10 shows a block diagram of this conventional imaging device, where 1 is an aperture, 2 is a lens, and 3 is a CCD 14 for amplifying the signal from the image sensor 3 to obtain a video signal of a predetermined level. circuit, 5 is ALCl 6 which controls aperture 1
1 is a gain circuit that adjusts the gain of the video signal; 7 is a terminal connected to a signal processing unit that performs gamma processing; 100 is a peak level detection circuit that detects the peak level of the video signal;
1 is a peak level detection circuit similar to the peak level detection circuit 100, 102 is an average level detection circuit that detects the average level of a video signal, and 103 is a peak level detection circuit 10.
This is a mixing circuit that mixes the output signals of the peak level detection circuit 101 and the average level detection circuit 102 according to the output signal of 0.

The operation of the conventional imaging device configured as described above will be described.

Generally, there are two types of gain control methods: a method that controls the gain using the peak level of the photographed screen, and a method that controls the gain using the average level of the photographic screen. The peak level control method is desirable because the bright areas of the screen do not fluctuate due to the effects of dark areas of the subject, etc. However, if a part of the screen is illuminated by a light source such as a fluorescent lamp, the effects may be affected. There is a problem where the subject you want to photograph becomes black and blurred. On the other hand, in the method of controlling based on the average level, there is less blackout caused by the influence of the light source, etc., but there is a problem that the level of bright parts of the screen fluctuates due to the influence of dark parts of the subject. As described above, the two methods have advantages and disadvantages, and it is desirable to use one method depending on the situation of the subject.

Conventional imaging devices utilize the fact that the output of the peak level detection circuit 100 increases when an object including a light source is photographed, and the output of the peak level detection circuit 100 decreases when a uniform object is photographed. Then, when the output of the peak level detection circuit 100 is large, the mixing circuit 103 weights and outputs the output signal of the peak level detection circuit 101, and when the output of the peak level detection circuit 100 is small, the mixing circuit 103 weights and outputs the output signal of the peak level detection circuit 100. By weighting the output and outputting it, gain control is performed according to the situation of the subject.

Problems to be Solved by the Invention However, with the above configuration, when photographing a subject that is out of focus, such as a person in a spotlight, if the ALC controls the aperture to properly expose the person,
The m power of the peak level detection circuit 100 becomes small, and therefore the gain is controlled by the signal of the average level detection circuit 102.

At this time, since the background of the person is dark, the average level detection circuit 1
Since the output level of 02 becomes small, the gain of the gain circuit 6 becomes large, resulting in a problem that the subject to be photographed becomes washed out.

In view of the above, an object of the present invention is to provide an imaging device that performs appropriate gain control for a subject that is out of order, such as a person exposed to a spotlight.

Means for Solving the Problems The present invention provides a gain control means for adjusting the level of a video signal, a peak level detection means for detecting the peak level of the video signal, and a signal level excluding at least a bright portion of the video signal. The imaging apparatus includes dark level detection means for detecting a dark level, and control means for controlling a maximum value of the gain of the gain control means according to output signals of the peak level detection means and the dark average level detection means.

According to the above-described configuration, the control means controls the gain of the gain control means when a subject whose peak level and dark level on the screen are small is being photographed based on the output signals from the peak level detection means and the dark level detection means. Perform control to suppress the maximum value.

Embodiment FIG. 1 shows a block diagram of an imaging apparatus in a first embodiment of the present invention. In FIG. 1, the same components as those in the conventional example shown in FIG. 10 are given the same reference numerals, and their explanations will be omitted. In the figure, 10 is a peak level detection circuit that detects the peak level of a video signal, 11 is a dark level detection circuit that detects the average level of a signal obtained by clipping a video signal that exceeds a predetermined level, and 12 is a peak level detection circuit 10. A control circuit 13 outputs a signal according to the output of the dark level detection circuit 11, and a control circuit 13 controls the gain circuit 6 by limiting the gain control signal obtained from the output signal of the average level detection circuit 14 that detects the average level of the video signal. This is a limiting circuit that controls the maximum value of the gain.

Regarding the imaging device of this embodiment configured as described above,
The operation will be explained below.

Table 1 shows the subject to be photographed, the output of the peak level detection circuit 10 (hereinafter referred to as PEAK), the output of the dark level detection circuit 11 (hereinafter referred to as DARK), and the gain circuit 6.
This figure shows the relationship between gain control.

In Table 1, the magnitude of PEAK and δDARK is determined by comparing it with a predetermined level (the predetermined value of PEAK is
Let M be the predetermined value of K). Therefore, by appropriately setting the predetermined value M and the predetermined value M, PEAK becomes large and DARK becomes small for a backlit subject including a light source. Similarly, for frontlit subjects, PEAK is small and DA
RK becomes large, and when photographing a subject with excessive direct light, such as photographing a person in a spotlight, PEAK becomes small and D
ARK becomes larger. Here, in order to solve the conventional problem that the gain of the gain circuit 6 becomes too large for a subject that is too far ahead, the control circuit 12 uses a limiting circuit 13 to increase the gain for a subject that has a small PEAK and a small DARK. Control is performed to limit the maximum gain of the circuit 6.

The operation of the control circuit 12 will be explained below.

The control circuit 12 uses a limiting circuit 13 to control the maximum gain of the gain circuit 6 by using a function G (PEA
Find a function D (DARK) corresponding to K) and DARK. FIG. 2 is a diagram showing the relationship between PEAK and G (PEAK). In the same figure, the function G (PEAK) is Pl
<PEAK takes the value 2.0%; PEAK<PI takes the value 1.0. Pl and Pl are set to values around the predetermined level L of PEAK described above. Figure 3 shows DARK and D(
FIG. In the figure, the function [ ) (DARK) takes the value 2.0 when D2<DARK, and takes the value 1.0 when DARK<DI. Dl and D2 are set to values around the predetermined level M of DARK mentioned above. G (PEAK) and D (DAR) have the above characteristics.
K), the control circuit 12 determines the maximum gain (hereinafter referred to as MAXGAIN) of the gain circuit 6 using the following equation.

AXGAIN= MAX (G (PEAK), D (
DARK)) ... (1) Note that the function MA
X() outputs the maximum value.

According to the above formula, MAXGAIN becomes 1.0 when PEAK is smaller than the predetermined level L and DARK is smaller than the predetermined level M (at this time, the maximum gain of the gain circuit 6 is 1.0 times), and PEAK Or when either DARK is greater than the predetermined levels L and M, 2
．． 0 (at this time, the maximum gain of the gain circuit 6 is 2.0 times). The limiting circuit 13 sets the maximum gain of the gain circuit 6 to MA.
Control to below XGAIN.

As described above, according to this embodiment, the peak level detection circuit 10 and the dark level detection circuit 11 are provided, and the maximum gain of the gain circuit 6 is controlled according to the outputs of the peak level detection circuit 10 and the dark level detection circuit 11, thereby photographing a person in the spotlight. For objects that are too close to each other, it is possible to control the signal without saturation without increasing the gain of the circuit.

Note that this embodiment can also be configured as shown in FIG. 4. In FIG. 4, a limiting circuit 20 controls the maximum gain of the gain circuit 6 similarly to the limiting circuit 13 in FIG. 21
is a division circuit that calculates the ratio between the output of the average level detection circuit 14 and the gain control target value R1.

The control circuit 12 has a function G (
The limiting circuit 13 and the limiting circuit 20 were controlled according to the characteristics of the function D (DARK) and the function D (DARK).
The characteristics shown in FIGS. 3 and 3 are merely examples, and the characteristics are not limited thereto.

Similarly, the maximum gain of the gain circuit 6 does not need to be limited to 2.0 times.

FIG. 5 is a block diagram of an imaging device according to a second embodiment of the present invention. In this figure, the same components as in FIGS. 1 and 10 are given the same reference numerals, and detailed explanation thereof will be omitted.

In the figure, 61 is a control circuit that outputs a signal according to the outputs of the peak level detection circuit 10 and the dark level detection circuit 11.

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

The control circuit 61 of this embodiment controls the maximum gain of the gain circuit 6 by controlling the limiting circuit 13 according to the outputs of the peak level detection circuit 10 and the dark level detection circuit 11, as in the first embodiment. Furthermore, the mixing circuit 103 is controlled according to the output of the peak level detection circuit 10. -For example,
The case where the mixing circuit 103 is controlled with the characteristics shown in FIG. 2 will be explained.

If the output of the peak level detection circuit 101 is Pl and the output of the average level detection circuit 102 is A, then the mixing circuit 103
The output (hereinafter referred to as MIX) is MIX= (G(PE
AK)-11・A+(2-G(PEAK))-P
・It can be obtained using (2).

According to the above formula, for objects with a large PEAK, the gain is controlled by the output of the average level detection circuit 102 to prevent blackout caused by the influence of the light source, and for objects with a small PEAK, the gain is controlled by the output of the peak level detection circuit 101. By doing this, it is possible to suppress fluctuations in the level of bright areas of the screen due to the influence of dark areas of the subject.

As described above, according to this embodiment, the peak level detection circuit 101, the average level detection circuit 102, and the mixing circuit 10
3, in addition to the effects shown in the first embodiment, it becomes possible to perform optimal gain control according to the situation of the subject, as in the conventional example.

Note that this embodiment can also be configured as shown in FIG. In this figure, the same components as in FIGS. 4 and 5 are given the same reference numerals, and detailed explanation thereof will be omitted. Further, when the configuration shown in FIG. 6 is adopted, it is possible to share the peak level detection circuit 10 and the peak level detection circuit 101, thereby reducing the circuit scale.

FIG. 7 is a block diagram of an imaging device according to a third embodiment of the present invention. This embodiment implements the second embodiment using a microcomputer.

In FIG. 7, the same components as those in FIG. 1 are given the same reference numerals, and detailed explanation thereof will be omitted.

In the figure, 80 is an analog-to-digital conversion circuit (A
D conversion circuit) 81 is a multiplication circuit, 82 is a terminal connected to a signal processing unit that performs gamma processing, etc., 83 is a peak level detection circuit that detects the peak level of a video signal, and 84 is 25 blocks, taking a shooting screen as an example. A block averaging circuit 85 is a microcomputer that divides the signal into blocks and outputs the average level of each block.

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

FIG. 9 is a flowchart showing the processing of the microcomputer 85. In the same figure, the microcomputer 85 first receives the output of the peak level detection circuit 88 (hereinafter referred to as PEAK) and the average data Di, D2°D3. ..., reads D25 (a in the same figure). Next, the average data of the block divisions are rearranged in order of size, and the data is 81.82. S3...
-, 825 (SL>82>83>...>825) (b of the same figure).

Next, the average level (hereinafter referred to as A), the dark level (hereinafter referred to as DARK), and the peak level (hereinafter referred to as P) of the video signal are determined using the following formulas (C in the figure).

B Next, the signal level MIX for gain control and MAXGAIN that defines the maximum value of gain are determined using equations (1) and (2) as in the first and second embodiments (d in the figure).

The microcomputer 85 calculates the multiplication value (hereinafter referred to as "the multiplication value") of the multiplication circuit 81.

GAIN) is calculated as e) in the same figure, and GAIN is MA.
If it is less than XGAIN, multiply the GAIN as is by the circuit 81
If GAIN exceeds MAXGAIN, G
MAXGAIN is assigned to A4N and output to the multiplication circuit 81 (f, g, h in the same figure).

As described above, according to this embodiment, by using the microcomputer 85, the same effects as in the second embodiment can be achieved with a simple configuration. Note that the above average level (P), dark level (DARK), and peak level (P) are examples, and are not limited thereto. Furthermore, the characteristics of each block can be changed simply by changing the number of pieces of average data of the block divisions to be added. For example, the average level (A) can be calculated using the following formula, excluding bright areas of the screen, and gain control can be performed without being affected by the light source, etc.

Furthermore, except for the peak level detection circuit 83, the block averaging circuit 84 detects PE in the same way as the peak level (P) described above.
You may also ask for AK.

DETAILED DESCRIPTION OF THE INVENTION According to the present invention, the maximum value of the gain of the gain control means is controlled according to the outputs of the peak level detection means and the dark level detection means, thereby detecting a person in the spotlight. Good image quality can be obtained without any problems caused by increasing the gain when photographing a subject that is poorly illuminated, and the effect is significant.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an imaging device according to a first embodiment of the present invention;
2 and 3 are characteristic diagrams of the control circuit 12 of the same embodiment, FIG. 4 is another configuration diagram of the same embodiment, and FIG. 5 is a block diagram of the imaging device of the second embodiment of the present invention. FIG. 6 is another configuration diagram of the same embodiment, FIG. 7 is a block diagram of the third embodiment of the present invention, FIG. 8 is a block diagram of the block averaging circuit 84 of the same embodiment, and FIG. 9 is the same block diagram. A flowchart of the processing of the microcomputer 85 in the embodiment, and FIG. 10 is a block diagram of a conventional imaging device. 6... Gain circuit, 10... Peak level detection circuit, 11... Dark level detection circuit, 12.
...Control circuit, 13...Limiting circuit, 14...
・Average level detection circuit. Figure 2 Figure 3 vt D2 DARK

Claims (1)

[Scope of Claims] Gain control means for adjusting the level of a video signal, peak level detection means for detecting a peak level of the video signal, and dark control means for detecting the level of a signal excluding at least a bright part of the video signal. An imaging apparatus comprising: a level detection means; and a control means for controlling a maximum value of the gain of the gain control means according to output signals of the peak level detection means and the dark level detection means.