JPS6229295A - Image pickup device - Google Patents

Abstract

PURPOSE:To exactly perform a color preventing process even when a luminance level is changed extremely by performing the color preventing process detecting a high luminance portion at the output side of an AGC circuit. CONSTITUTION:A color preventing signal generating circuit 31 detects the high luminance portion according to the output of an AGC circuit 15 and according to the detecting output, a color preventing signal is obtained. By constituting a circuitry in such way, so that even when the electrical signal level of Y at the input point of the AGC circuit 15 is under a reference level of L2, it is exceeded over L2 at its output point if the output of the AGC circuit 15 is saturated, the color preventing signal generating circuit 31 can be generate the color preventing signal. Therefore, even when a small light source of 100% level is image-picked up at quite a dark place or when an image pickup position is switched from a dark place to a bright one, it is prevented that an object image is reproduced in a different color from an actual one.

Description

[Detailed description of the invention] [Technical field of invention] The present invention relates to an imaging device.

[Technical background of the invention]

In a camera using a single-tube or single-plate video camera, the balance of color levels output from the image sensor in high-brightness areas may vary, causing the subject image to be colored differently from the actual color. A phenomenon occurs in which

For example, in a frequency multiplexing imaging device that frequency-multiplexes a color signal into a luminance signal, R(
The photoelectric conversion characteristics of red) and B (blue) saturate faster than the photoelectric conversion characteristics of Y (luminance), and in high-brightness areas (areas where the incident light amount level of the image sensor is 51 or higher), the subject image changes to the actual color. It is colored a different green.

In order to solve such problems, in imaging devices, processing to prevent coloring in high-brightness portions is no longer performed than in the past. This process will be explained using FIG. 3. FIG. 3 shows a schematic configuration of the imaging device. In FIG. 3, first, subject light taken in by the lens section 111C is converted into an electrical signal by the image sensor 12. This electric signal is transmitted through an amplifier circuit 13, a clamp circuit 14, an automatic gain control circuit (hereinafter referred to as
The signal is applied to a low-pass filter 16 and a color separation circuit 17 via an AGC circuit (referred to as an AGC circuit) 15, and is separated into Y, R, and B electrical signals. These three types of signals are applied to the modulation circuit 18 and converted into a carrier color signal. From this carrier color signal and the output of the AGC circuit I5, a process filter I9 is used.
The electric signal Y extracted in step 1 and the synchronization signal S are added in an adder circuit 22 and output as a video signal through an amplifier circuit 23.

In this configuration, the coloring prevention process is performed by providing a gain control circuit 20 at the output stage of the modulation circuit 18, and
This is done by reducing the gain of 0 in high brightness areas. This gain control is performed by a coloring prevention signal generation circuit 21 which detects a high brightness portion from the output of the clamp circuit 14 and generates a coloring prevention signal in accordance with this detection output.

According to such a configuration, the gain of the gain control circuit 20 is lowered in the high-brightness portion, and the subject image is reproduced in pale green or colorless. This solves the visual problem caused by the subject image being colored in a color different from the actual color.

[Problems with background technology]

However, conventional imaging devices have a problem in that coloration prevention processing is not performed when there is an extreme change in brightness level. This will be explained below.

In recent years, as the performance of the image sensor 12 has improved, attempts have been made to increase the gain of the AGC circuit 15 in order to improve sensitivity. For example, what used to be 6 dB has been reduced to 12 dB in recent years.
It is increased by dB. On the other hand, it is necessary to lower the power supply voltage in order to reduce power consumption, and it is not possible to ensure sufficient power supply voltage.

Under the above-mentioned situation, the following phenomenon occurs. Now, let us consider a case where there is a miniature light bulb with a brightness of 100 chilepels in terms of the electrical signal level at the output point of the image sensor 12 in a pitch-dark background. The aperture of the lens is wide open, and A
Let us consider the case where GC is applied. In this case, the electrical signal output from the image sensor 12 includes a white component of 10096 as shown in FIG. Therefore, AGC
works, and if the gain of the AGC circuit 15 is 12 dB, then A
The output white level of the GC circuit 15 is 400%. In this case, if the dynamic range of one circuit is 400% or less, the signal will be saturated at that point. For this reason, the balance of color levels shifts t5°.In other words, in a system where the color signal is multiplexed with the luminance signal, such as a frequency separation system, when the circuit approaches saturation, the differential gain DC1 and the differential phase DP change. Bad υ.Of course, at the output point of the AGC circuit, R
, B saturates earlier than the electric signal level of Y.

On the other hand, in this case, at the output point of the clamp circuit 14, the electrical signal level of Y is often below the standard level L shown in FIG. Therefore, the coloring prevention signal generation circuit 21
No anti-coloring signal can be obtained from this method. Therefore, an unreasonable situation arises in which no anti-coloration signal is obtained even though the color level is out of balance, and the subject image is different from the actual color, as is the case when no anti-coloration processing is performed in high-brightness areas. A phenomenon occurs in which objects are colored in different colors.

The above-mentioned phenomenon also occurs when the imaging position is instantly changed from a pitch-dark place to a bright place. Due to this change, the imaging device switches from a state in which AGC is applied to a state in which it is not applied, but this state change does not occur immediately with the change in the imaging position, but occurs after a slight delay.

During this delay period, the output of the AGC circuit 15 becomes saturated, resulting in erroneous coloring.

From the above, conventionally, due to improved performance of the image sensor 12, the AG
Although it has become possible to increase the gain of the C circuit 15, it has not been possible to significantly increase the gain due to constraints on the dynamic range of one circuit.

[Purpose of the invention]

The present invention has been made to address the above-mentioned circumstances, and an object of the present invention is to provide an imaging device that can reliably perform coloring prevention processing even when there is an extreme change in brightness level. purpose.

[Summary of the invention]

The present invention achieves the above object by detecting a high brightness portion on the output side of an AGC circuit and performing coloring prevention processing.

[Embodiments of the invention]

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a diagram showing the configuration of an embodiment of the present invention. In FIG. 1, the same parts as in FIG. 3 are given the same reference numerals, and detailed explanations will be omitted.

The difference between FIG. 1 and FIG. 3 is that a coloring prevention signal generating circuit 31 detects a high brightness portion according to the output of the AGC circuit 15 and obtains a coloring prevention signal according to this detection output.

According to such a configuration, even if the electric signal level of Y at the main power point of the AGC circuit 150 is below the standard level L, if the output of the AGC circuit 15 is saturated, the electric signal of Y at the output point will be reduced. Since the signal level is above L3, the coloring prevention signal generation circuit 31 can generate the coloring prevention signal. Therefore, according to this example:
Even when imaging a small light source at 100% level in a pitch-dark location, or when switching the imaging position from a pitch-dark location to a bright location, the subject image may be reproduced in a color different from the actual color. This can be prevented.

Further, since this embodiment has the above-mentioned effects, the gain of the AGC circuit 15 can be set without being restricted by the circuit's dynamometer cleanliness, and the sensitivity can be improved. can.

〔Effect of the invention〕

As detailed above, in this invention, the high brightness portion is detected at the output point of the AGC circuit, so even if there is an extreme brightness change, coloring prevention processing can be reliably executed. be able to.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing the configuration of an embodiment of the present invention, and FIG.
The figure is a characteristic diagram showing an example of the photoelectric conversion characteristics of an image sensor.
The figure is a circuit diagram showing the configuration of a conventional imaging device, and FIG. 4 is a diagram for explaining the problems of the conventional image pickup apparatus. 12... Image sensor, 15... AGC circuit, 16...
・Row) 4 filter, 17...color separation circuit, I8・
. . . Modulation circuit, 20 . . . Gain control circuit, 31 . . . Coloring prevention signal generation circuit. Applicant's representative Patent attorney Takehiko Suzue Figure 2 H1 This Yomikura period-1 Figure 4

Claims (1)

[Scope of Claims] Photoelectric conversion means for converting incident light from a subject into an electrical signal; automatic gain control means for automatically controlling the gain of the electrical signal output from the photoelectric conversion means; and this automatic gain control. a carrier color signal generation means for generating a carrier color signal from an output signal of the means; a gain control means capable of controlling the gain of the carrier color signal output from the carrier color signal generation means; and an output signal of the automatic gain control means. and a high-brightness portion detection means for detecting a high-brightness portion based on the brightness portion, and lowering the gain of the gain control means at this high-brightness portion.