JPH03274871A - Video camera - Google Patents

Abstract

PURPOSE:To prevent the generation of a white jump by controlling the gain of a gain controller based on an output signal of a low peak detecting circuit. CONSTITUTION:An image pickup signal outputted from a gain controller 21 is supplied to a low level gain controller 23 and supplied to a low peak detector 24, and a peak of a black side of the image pickup signal. An output signal of the low peak detector 24 is supplied to a level detector 25 and averaged, and thereafter, supplied as a control signal to a gain controller 23 through a DC amplifier 26. In the gain controller 23, control is executed so that the smaller a level of the control signal is, the larger the gain becomes. A level of a high level part of the image pickup signal does not become high, therefore, for instance, in the case of night image pickup, a lamp part of a neon sign and an illumination signboard, etc., is not saturated, what is called a white jump is not generated, and a normal colored screen can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to video cameras, and more particularly to gain adjustment techniques for image pickup signals.

[Prior Art] FIG. 5 shows an example of the circuit configuration of a video camera. In the figure, image light from a subject (not shown) is transmitted through an imaging lens l and an iris 2 to an imaging element 3, such as a CCDCD.
A solid-state image element is provided.

The output signal of this image sensor 3 is processed by a sample hold circuit (S
/H circuit) 4, and this S/H circuit 4 outputs an imaging signal.

The imaging signal output from the S/H circuit 4 is supplied to a level detector 5 that constitutes an auto iris controller.
The detection signal is supplied to the iris driver 6. The driver 6 supplies the iris 2 with an iris drive voltage according to the detection signal, and the opening of the iris 2 is controlled.

FIG. 6 is a diagram showing the relationship between iris drive voltage and illuminance. When the illuminance becomes higher than a predetermined illuminance (for example, 1000 lux), the iris drive voltage changes according to the illuminance, the opening of the iris 2 is controlled, and the amount of incident light is limited. When the illuminance is below a predetermined level, the iris drive voltage is maximized and the iris 2 is controlled to be open. Act &Ia in FIG. 7 shows the relationship between the level (average level) of the Il image signal output from the S/H circuit 4 and the illuminance.

Further, the imaging signal output from the S/H circuit 4 is supplied to the AGC amplifier 7. The output signal of this AGC amplifier 7 is supplied to a level detector 8 constituting the AGC circuit, and the detection signal is supplied as an AGC control voltage to the AGC amplifier 7 via an amplifier 9, so that the gain of the AGC amplifier 7 is controlled. .

FIG. 8 is a diagram showing the relationship between AGC control voltage and illuminance. If the iris 2 is opened at a predetermined illuminance or lower, the AG will change depending on the illuminance up to a certain illuminance (for example, several tens of lux).
The AGC control voltage changes and the gain of the AGC amplifier 7 is controlled so that the level of the output signal is constant.
An action is taken. Figure 9 fruit &! a shows the relationship between the level (average level) of the imaging signal output from the AGC amplifier 7 and the illuminance.

Further, the imaging signal output from the AGC amplifier 7 is supplied to the process circuit 10, and the process circuit 10 outputs a luminance signal Y and color difference signals (red difference signal RY, !color difference signal B-Y).

The luminance signal Y output from the process circuit 10 is sent to the encoder 13 via the comma correction circuit 111 and the amplifier 12.
is supplied to Further, the color difference signals R-Y and B-Y output from the process circuit IO are supplied to the encoder 13.

In the encoder 13, a synchronization signal is added to the luminance signal Y, a burst signal is added to the color difference signal, color modulation, etc. are performed, and a carrier color signal C is formed.
Further, the luminance signal Y and the carrier color signal C are added to form a color video signal SV.

The color video signal SV thus formed by the encoder 13 is output to the output terminal 14.

[Problem H to be solved by the invention] Here, consider a case where a part of the subject includes a light emitting source (hereinafter referred to as a "lamp part") such as a neon sign or an illuminated signboard.

The level of the imaging signal from the S/H circuit 4 corresponding to the lamp section is as shown by the solid line in FIG.

That is, when the iris operation is performed when the illuminance is higher than a predetermined illuminance, the iris 2 is narrowed down as the illuminance increases, so the amount of light from the lamp section is also limited, and as the illuminance increases, the level of the imaging signal corresponding to the lamp section decreases. is decreasing.

On the other hand, when the illuminance is below the predetermined level and the iris 2 is opened, the amount of light from the lamp section is not limited, so even if the illuminance changes, the level of the imaging signal corresponding to the lamp section remains constant.

Next, the level of the imaging signal from the AGC amplifier 7 corresponding to the lamp section is as shown by the solid line in FIG.

That is, when the illuminance is higher than a predetermined value and the iris operation is performed, the AGC operation is not performed, so as the illuminance increases, the level of the imaging signal corresponding to the lamp section decreases.

On the other hand, when the illuminance is below a predetermined level and the iris 2 is opened, the AGC operation is performed, so as the illuminance decreases, the gain of the AGC amplifier 7 increases, and the level of the imaging signal corresponding to the lamp section increases. go.

Therefore, when the light intensity of the lamp section is large from the beginning,
The level of the imaging signal corresponding to the lamp section reaches the saturation level as shown by the solid line in FIG.

Therefore, in the example shown in FIG. 5, for example, when capturing images of night scenes, the imaging signals corresponding to neon signs, illuminated billboards, etc. often become saturated, resulting in so-called overexposure.

Therefore, the present invention provides a video camera in which the above-described overexposure does not occur.

[! ! Means for Solving the Problem] The present invention provides a gain controller that controls the level of a low-level portion of an image signal from an image sensor, and a low peak detection circuit that detects the peak of abuse in the image signal output from the gain controller. and controls the gain of the gain controller based on the output signal of the low peak detection circuit.

C Effect] In the above configuration, for example, when the iris 2 is opened, the low peak detection circuit 2
The black peak of the imaging signal S detected at 4 is lowered. Therefore, as the illuminance decreases, the gain control -
The gain of the laser 23 is increased and controlled so that the low level portion of the imaging signal becomes higher by 1 noher.

In other words, with gain controller 23! , ni Since the level of the high-level portion of the imaging signal is not raised, there is no possibility of overexposure occurring. Furthermore, since the gain controller 23 increases the level of the low-level portion of the imaging signal, a predetermined minimum object illuminance can be ensured. Furthermore, since the gain of the gain controller 23 is controlled according to the black peak of the imaging signal, the increase in radiation volume at low illuminance is small, and the S/N can be increased compared to conventional methods. In addition, during nighttime imaging, images are taken darkly and faithfully IIi 5i; +1
Reproduced.

L Embodiment] Hereinafter, an embodiment of the present invention will be described with reference to FIG. 1. In FIG. 1, parts corresponding to those in FIG. 5 are designated by the same reference numerals, and detailed explanation thereof will be omitted.

In the figure, an image signal output from the S/H circuit 4 is supplied to a gain controller 21.

Adjust the gain controller 21's gain with volume 2.
2, the level of the imaging signal during iris operation is adjusted to a predetermined level.

Further, the imaging signal output from the gain controller 21 is supplied to the low level gain controller 23.

This gain controller 23 controls the intensity of the low level portion of the imaging signal.

At this time, the gain is controlled to be larger in the lower level portion.

The imaging signal output from the gain controller 523 is supplied to the low peak detector 24, and the black peak of the imaging signal is detected. For example, as shown in FIG. 2, the low peak detection 624 includes a diode F'
- It is composed of C.

Here, the discharge time constant in the low peak detector 24 is set to be relatively long, for example, approximately 1/4 vertical scan bright interval. When the input signal to the low peak detector 240 is as shown in FIG. 3A, the output signal is as shown in the solid line in FIG. 3B.

The output signal of the low peak detection W24 is supplied to the level detector 25, averaged by C, and then supplied to the gain controller 23 as a control signal via the DC amplifier 26. The gain controller 23 is controlled so that the smaller the level of the control signal, the larger the gain.

The imaging signal output from the gain controller FrJ-ra 23 is supplied to the pro-7 bus circuit 1o.

In the above configuration, when the iris operation is performed at higher than a predetermined amplitude (for example, 1000 lux), the level of the imaging signal output from the gain controller 21 <
As shown by the solid line a in FIG. 4, the average level remains constant even if the illuminance changes.

Therefore, the output level of the level detector 25 (hereinafter referred to as "
) is the fruit of the same figure &! c, and the gain in the gain controller 23 remains constant for the high level portion and the low level portion of the imaging signal.

Therefore, the level (average level) of the m-image signal output from the gain controller 23 remains constant even if the illuminance changes, as shown by the solid line a in the figure, and is output from the gain controller 23. The level of the imaging signal corresponding to the lamp section decreases as the illuminance increases, as shown in mb in the figure.

Furthermore, when the iris 2 is opened to a lower illuminance than a predetermined illuminance, the level of the imaging signal output from the gain controller 21 (the average level decreases as the illuminance decreases, as shown in Figure a'). .

Therefore, the dark level is as shown by the solid line C in the same figure.
As the illuminance decreases, it decreases, and the dark area level is controlled to be a constant level shown by the broken line C' in the figure. In other words, the gain in the gain controller 23 is
The low-level portion of the imaging signal is controlled to increase as the illuminance decreases. The gain of the gain controller 23 is, for example, set to be the maximum gain at the lowest object illuminance, for example, 2 lux.

Therefore, the level of the imaging signal output from the gain controller 23 increases as shown by the solid line a in the figure.
As the illuminance decreases, the rate of increase is increased to correct dark areas.

Here, the gain controller 23 is controlled so that the gain for the low-level portion of the imaging signal becomes large, so the gain for the imaging signal corresponding to the ramp portion remains constant, and the gain for the imaging signal corresponding to the ramp portion remains constant. As shown by the solid line in the figure, the level does not increase even when the illuminance decreases and remains at a constant level.

In this way, according to this example, the gain controller 23 does not raise the level of the high-level portion of the imaging signal, so that the lamp portion of a neon sign, illuminated signboard, etc. does not become saturated during nighttime imaging, and so-called overexposure is prevented. This does not occur and a normally colored screen can be obtained.

Further, in the gain controller 23, the gain for the low level portion of the imaging signal is increased to perform dark area correction, so that the same minimum object illuminance as in the prior art can be ensured.

Furthermore, in this example, when the iris 2 is opened, gain control is performed according to the peak level of the layer side of the imaging signal, and unlike the conventional AGC operation, the gain control is performed as shown in FIG. Compared to the example, it is several tens ~i ooo
The amplification factor of the imaging signal up to the lux becomes small (see N in FIGS. 4 and 9), and the S/N ratio at low illuminance can be increased.

Also, for example, when the illuminance is several tens of lux, conventionally
The level is the same as that at 00 lux, and images are captured at night with the same brightness as during the day, but in this example, the level is lower than at 1000 lux. Therefore, the image is captured darkly as a nighttime screen, and the screen can be faithfully reproduced.

In the above embodiment, the iris 2 is opened when the lux is 1000 lux or less, and the gain of the gain controller 23 is set to be the maximum gain at 2 lux, but the present invention is not limited to this. isn't it.

Further, the gain controller 23 in the above embodiment is
Although the gain of the high-level portion of the imaging signal is assumed to be constant, if the gain increase of the high-level portion is smaller than the gain increase of the low-level portion, the same effect can be obtained. I can do it.

[Effects of the Invention] As explained above, according to the present invention, the gain controller does not increase the level of the high-level portion of the imaging signal, so that, for example, parts such as neon signs and illuminated billboards do not become saturated during nighttime imaging. Therefore, it is possible to obtain a normally colored screen without causing so-called overexposure. Further, since the gain controller increases the level of the low-level portion of the imaging signal and performs dark area correction, a predetermined minimum object illuminance can be ensured.

Furthermore, since the gain of the gain controller is controlled according to the peak level of the image pickup signal, the amplification factor is small in low illuminance, making it possible to increase the S/N compared to conventional methods, and making it possible to improve night imaging. It is possible to reproduce a faithful screen by capturing a dark image.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention, FIGS. 2 to 4 are diagrams for explaining the same, and FIG. 5 is a configuration diagram of a conventional example.
FIGS. 6 to 9 are diagrams for explaining the same. 5, 25 0 3 - Iris, image sensor, level detector, iris driver, process circuit, encoder 2 Gain controller 23 - Low level gain controller 24 - Low peak detector 6- - DC amplifier

Claims (1)

[Claims] (1) The low peak detection circuit includes a gain controller that controls the level of the low level portion of the image signal from the image sensor, and a low peak detection circuit that detects the black peak of the image signal output from the gain controller. A video camera characterized in that the gain of the gain controller is controlled based on the output signal of the video camera.