JPH04329080A - Solid-state image pick-up device - Google Patents

Abstract

PURPOSE:To prevent the deterioration of S/N at the time of low illuminance by performing the automatic gain control having a target value different from the target value of the output of a diaphragm control when the object with low illuminance is image-picked up. CONSTITUTION:The two-dimensional image information obtained by a CCD image pick-up element 3, after each processing is performed by a compound double sampling(CDS) circuit 4, a gain control part 5 and a gamma control part 6, is detected by a detector 7. The detecting output becomes a feedback signal, is sent to a diaphragm control part 2 and a gain control part 5 and becomes each control signal. Thus, the output signal converged to a certain set target value is sent through a Y/C separating part 8 to an encoder 9 and the target value of each different diaphragm control and the target value of the gain control are set.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state imaging device having automatic aperture control and automatic gain control for a video camera.

0002

[Background Art] In recent years, the performance of video cameras and their peripheral equipment has been improved, and in particular, in order to meet the needs of users of the highest quality models, various methods have been used to improve the performance of video cameras and their peripheral equipment. ing. Among these, image quality at low illuminance is the biggest obstacle in achieving higher image quality. Therefore, improving the SN ratio at low illuminance is an essential element in improving the image quality of video cameras. Furthermore, in order to improve image quality under low illumination, it is essential to consider the characteristics of automatic aperture control and automatic gain control.

FIG. 3 shows the signal flow of a conventional video camera using automatic aperture control and automatic gain control, and the flow of each control signal.

In the figure, 1 is an aperture, 2 is an aperture control section, and 3 is an aperture control section.
is a CCD image sensor, 4 is a composite double sampling circuit (
(hereinafter referred to as a CDS circuit), 5 is a gain control section, 6 is a gamma control section, 7 is a detector, 8 is a Y/C separation section, and 9 is an encoder.

The secondary image signal obtained by the CCD image sensor 3 is subjected to various processing in a CDS circuit 4, a gain control section 5, a gamma control section 6, etc., and then detected by a detector 7. This detection output becomes a feedback signal and is sent to the aperture control section 2 and gain control section 5, respectively, and a control signal for aperture control,
and becomes a control signal for gain control. As a result, the output signal that has converged to a certain set target value is separated into Y/C and sent to the encoder 9. At this time, the target value for diaphragm control and the target value for gain control are set to the same value.

[0006] By doing this, even when objects with different amounts of light are imaged, the aperture and gain change depending on the brightness, and an image with appropriate brightness can be reproduced.

[0007]

[Problem to be Solved by the Invention] However, with the above configuration, when capturing an image of a subject with low illumination, the aperture is opened and the gain is set to its maximum value in order to obtain an image with the same brightness as a bright subject. The value is close to . In this way, if you forcibly increase the originally small signal by gain control, the noise component will be amplified more than the signal component, resulting in a significant S/N ratio.
The problem was that the ratio deteriorated.

In view of the above problems, the present invention provides a device that prevents S/N deterioration at low illuminance by performing automatic gain control with a target value different from the target value of the output of the aperture control. It is something.

[0009]

[Means for Solving the Problems] In order to solve the above problems, the solid-state imaging device of the present invention includes an automatic aperture control section that opens and closes the aperture depending on the amount of incident light, and an automatic aperture control section that controls the amount of incident light. An automatic gain control section inputs video signal information converted into an electric signal by a CCD image sensor and controls the output signal by changing the gain depending on the magnitude of the input signal, and detects the output signal of the automatic gain control section and outputs the detected signal. A control signal is sent to the automatic aperture control unit so that the first target value is set, and if the output is not sufficient even when the aperture is opened, a control signal is sent to the automatic aperture control unit so that the first target value is set. It has a detector that sends a control signal to the automatic gain control section so that the target value of 2 is reached, and the output signal converges to an appropriate target value depending on the magnitude of the incident light.

0010

According to the present invention, with the above-described configuration, even in low illumination, the automatic gain control has an appropriate target value, so that noise is not greatly amplified and an image with an excellent S/N ratio can be reproduced.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a block diagram of a system in one embodiment of the present invention.

In FIG. 1, 1 is an aperture, 2 is an aperture control section,
3 is a CCD image sensor, 4 is a composite double sampling circuit (hereinafter referred to as CDS circuit), 5 is a gain control section, 6 is a gamma control section, 7 is a detector, 8 is a Y/C separation section, and 9 is an encoder. be.

The flow of signals will be explained below using FIG. The two-dimensional image information obtained from the CCD image sensor 3 is C
After each process is performed by the DS circuit 4, gain control section 5, gamma control section 6, etc., the signal is detected by the detector 7. This detection output becomes a feedback signal and is sent to the aperture control section 2 and the gain control section 5, and becomes a control signal for aperture control and a control signal for gain control, respectively. As a result, the output signal that has converged to a certain set target value is sent to the encoder 9 through Y/C separation. At this time, the target value for the aperture control and the target value for the gain control are set to different values.

FIG. 2 shows the relationship between the target value for aperture control, the target value for gain control, and the amount of incident light. In the figure, the horizontal axis represents the amount of incident light, and the vertical axis represents the detected output after convergence. At this time, automatic aperture control and automatic gain control prevent output oscillation, so when the amount of incident light is sufficiently large, only automatic aperture control operates, and the amount of incident light decreases and the aperture is completely opened. Automatic gain control is assumed to operate after this, and two controls are prevented from operating at the same time. Target value setting sets the target value of the gain control operating during low illuminance to a value smaller than the target value for aperture control.

As described above, according to this embodiment, even in low illuminance, the automatic gain control has an appropriate target value, so noise is not greatly amplified and images with excellent S/N ratio can be reproduced. Can be done.

[0016]

As described above, the solid-state imaging device of the present invention has an automatic diaphragm control section that opens and closes the diaphragm depending on the amount of incident light and controls the amount of incident light.
An automatic gain control section inputs a video information signal converted into an electric signal by an image sensor, changes the gain depending on the magnitude of the input signal, and controls the output signal, and detects the output signal of the automatic gain control section and outputs the detected signal. A control signal is sent to the aperture control section so that the first target value is set, and if the output is not sufficient even when the aperture is opened, a second target value having a value different from the first target value is sent. It has a detector that sends a control signal to the gain control section so that the target value is reached, and the output signal converges to the appropriate target value depending on the magnitude of the incident light. It becomes possible to reproduce images with a high S/N ratio, and this has great practical effects.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the flow of image information signals in an embodiment of the present invention.

[Figure 2] Characteristic diagram showing the relationship between the amount of incident light and the output signal level in the same example

[Figure 3] Block diagram showing the flow of image information signals in the conventional method

[Figure 4] Characteristic diagram showing the relationship between the amount of incident light and the output signal level in the same method

[Explanation of symbols]

1 Aperture 2 Aperture control section 3 CCD image sensor 4 Composite double sampling circuit 5 Gain control section 6 Gamma control section 7 Detector 8 Y/C separation section 9 Encoder

Claims (1)

[Claims] 1. An automatic aperture control section that opens and closes an aperture depending on the amount of incident light to control the amount of incident light; and an input of a video information signal that passes through the aperture and becomes an electric signal by a CCD image sensor. an automatic gain control section that controls the output signal by changing the gain depending on the magnitude of the signal; and an automatic aperture control section that detects the output signal of the automatic gain control section and controls the detected output to a set first target value. sends a control signal, and also sends a control signal to the gain control unit so that when the output is not sufficient even when the aperture is opened, a second target value that is different from the first target value is set; What is claimed is: 1. A solid-state imaging device, comprising a detector, and performing an operation in which output signals converge to appropriate target values depending on the magnitude of incident light.