JPH01151894A - Video camera - Google Patents

Abstract

PURPOSE:To attain low power consumption by providing a feedback loop decreasing the gain of an AGC circuit when a level of a luminance signal is a prescribed value or over accordingly. CONSTITUTION:The constitution is adopted such that feedback is applied to an AGC circuit 18 only when a luminance signal level represented by an output signal of an LPF(low pass filter) is larger than a level of a reference signal in case of the feedback of the output signal of the LPF 22 to the AGC circuit 18 via a level detection circuit with a small time constant. The gain of the AGC circuit 18 is decreased only in this case. Since the level of a signal multiplexed with a color difference signal is changed, both the luminance signal component and the color difference signal component are changed in the same ratio and the ratio of the levels between both the signal components is always constant. The ratio of the level between both the signal components is always constant. Then the color signal is unchanged and correct color reproduction is attained to attain low power consumption.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a video camera, and more particularly to control of signal level in a video camera using a complementary color filter.

[Prior Art] In conventional video cameras, the aperture is adjusted according to the amount of incident light, and when the aperture is fully open and the amount of incident light is small, the gain of the AGC circuit is increased to raise the output above a predetermined level. I'm trying to get a signal. That is, as shown in FIG. 5, the aperture degree of the aperture 16 in the optical lens system 14 is controlled by an ALC (automatic level adjustment) circuit 1'2 that responds to an output signal from the image sensor 10. The AGC (automatic gain control) circuit 18 that responds to the output signal from the image sensor 10 is an ALC circuit 121
Therefore, even if the aperture 16 is fully opened, when the amount of incident light is small, the gain is increased to maintain the output level above a predetermined value. That is, the aperture opening detection circuit 17 detects the aperture 16.
When it is detected that the switch 19 is fully open, the contact point of the switch 19 is switched to b, and a signal from the AGC detection circuit 28 is sent to the AGC circuit 18 as a control signal. On the other hand, when the aperture 16 is not fully open, the switch 19
selects contact a, and a constant voltage V 1 is applied to the AGC circuit 18.

When the amount of incident light is large, that is, when a signal with high brightness is incident, the ALC circuit 12 narrows down the aperture 16 to reduce the amount of light incident on the image sensor 10, and the output signal level of the image sensor 10 is lowered to a predetermined value or less. The structure is designed to suppress the

However, if the area of the high brightness portion is small or if the brightness suddenly increases, the aperture 1B cannot be stopped immediately due to the time constant of the ALC circuit 12. Therefore, in such a case, a signal with a relatively high level is output from the image sensor 10.

In this way, the ALC circuit 12 alone may provide a signal of a predetermined level or higher to the circuit downstream of the image sensor 10. Therefore, in the conventional video camera shown in FIG. is provided to limit the signal level to a predetermined value or less so as not to adversely affect subsequent stages. The output signal of the white clipping circuit 20 is given to an LPF (low pass filter) 22 for removing the color difference signal superimposed on the high frequency band of the luminance signal, and a color separation circuit 24, and both of these output signals are sent to the process circuit. 2
At step 6, the signal is subjected to processing such as gamma correction, and then supplied to an encoder 30 to be converted into a video signal. The luminance signal among the output signals of the process circuit 2B is given to the AGC detection circuit 28 and the AGC
A control signal is generated to control circuit 18.

FIG. 2 is a diagram showing a part of a complementary color filter used with the image sensor IO of the conventional video camera shown in FIG. 5 and the image sensor of the video camera according to the present invention. When an image is captured using such a complementary color filter, an output signal in which a color difference signal is superimposed on a high frequency region of a luminance signal is obtained. That is, if the signals of the n-th line and the n+1-th line in the scanning line are Sn and Snya1, respectively, then S −Y +Csin ωt . . .
・・11) n n n 5nil −Ynil +Cn+l ”1nωt ・・
...It can be expressed as (2). However, ω represents the carrier wave angular frequency of the color difference signal, "n"'n+1 represents the luminance signal component,
C0°Cn+1 represents a color difference signal component, and is expressed by the following equation.

Yo-Yo+, -2R+3G+2B ・------(
3) C-2R-G ・・・・・・・・・(4)
C-2B-G ・・・・・・・・・(5)n+
1 In the above equations (3) and (4), G included in Cn and Cn+1 is almost equal to the luminance signal component, so in order to obtain a color signal, Yn is added to Cn''n+1, respectively.

``N+1 may be added at a predetermined ratio.

[Problems to be Solved by the Invention] FIG. 6 is a signal waveform diagram showing how the signal from the AGC circuit 18 in the circuit of FIG. 5 is clipped by the white clip circuit 20, and FIG. It is a waveform diagram which expanded the time axis of the waveform diagram of a figure. As shown in Figure 6, when the upper limit of the signal amplitude is limited by the white clip level shown by the dashed line, the color difference signal component is significantly cut off at the peak of the waveform, and the luminance signal component is also reduced as shown by the dotted line. do. Looking at this in detail in FIG. 7, it can be seen that although both the color difference signal component and the luminance signal component are reduced by the white clip, the manner in which the former is reduced is considerably greater than the latter. In other words, when limiting by white clipping, the color difference signal component and the luminance signal component do not decrease at the same rate;
It can be seen that the former is significantly reduced.

Since the ratio of the luminance signal and the color difference signal component changes before and after white clipping in this way, a color signal indicating the accurate color of the subject cannot be obtained. Therefore, the color in the reproduced image changes in the clipped portion. In particular, when a light source such as a light is photographed, a colored and very unnatural reproduced image appears on the monitor screen, even though it is originally white. As a countermeasure to this problem, it is theoretically possible to increase the dynamic range of the entire signal processing circuit of the video camera by increasing the power supply voltage.

However, this results in an increase in power consumption and is difficult to implement, especially in a vertices type video camera.

[Means for Solving the Problems] In order to solve the above problems of the conventional video camera, the present invention provides the AGC circuit output directly to the LPF and color separation circuit without using the conventional white clip circuit, and also provides the following steps: LP
The configuration is such that when the output signal of F is greater than a predetermined value, it is fed back to the AGC circuit via a level detection circuit with a small time constant.

That is, according to the present invention, in a video camera having an image sensor using a complementary color filter, when the aperture that adjusts the amount of light incident on the image sensor is fully open, the signal is separated from the output signal of the image sensor. In the video camera, the video camera includes an AGC circuit that increases the level of the output signal according to the brightness signal, and a feedback loop that decreases the gain of the AGC circuit when the level of the brightness signal is equal to or higher than a predetermined value. A video camera is provided.

[Function] As mentioned above, when the output signal of the LPF is fed back to the AGC circuit via the level detection circuit with a small time constant, only when the luminance signal level represented by the output signal of the LPF is higher than the level of the reference signal. Since the configuration is such that feedback is applied to the AGC circuit, the gain of the AGC circuit can be reduced only in such cases.

Therefore, since the level of the multiplexed color difference signal changes, both the luminance signal component and the color difference signal component can be changed at the same ratio, and the level ratio between both signal components is always constant. . Therefore, the color signal does not change and it is possible to perform correct color reproduction.

[Implementation example] Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of a preferred embodiment of the video camera of the present invention. The optical lens system 14 is provided with an aperture 16, and incident light is applied to the image sensor 10 via the aperture 16. The image sensor IO has a complementary color filter shown in FIG. 2, and its output signal is given to the ALC circuit 12 and the AGC circuit 18.

The ALC circuit 12 adjusts the aperture degree of the diaphragm 16 according to the output signal level from the image sensor 10. AGC circuit 18
The fifth method is to increase the gain and obtain an output signal above a predetermined level when the amount of incident light is small even when the aperture 16 is fully open.
In addition to the effect similar to that of the conventional example shown in the figure, the present invention also performs an effect unique to the present invention of lowering the gain and limiting the amplitude of the output signal when the amount of incident light exceeds a predetermined value, as will be described later. The most open state of the diaphragm 16 is detected by the diaphragm open detection circuit 17, and when the diaphragm 16 is fully open, the switch 19 is switched from contact a to contact b to output the output of the first AGC detection detection path 28 instead of the constant voltage V. The configuration is such that the signal is sent to the AGC circuit 18 via the adder 36 as a control signal. In this embodiment, the aperture open detection circuit 17 is configured to detect the output signal of the ALC circuit 12 using a comparator or the like, but is not limited to this, and may have a configuration that can detect the fully open state of the aperture 16. That's fine. Further, the first AGC detection circuit 28 has a configuration that combines an integrator and a peak detector, for example, and is configured to output a signal according to the luminance signal level.

The output signal of the AGC circuit 18 is directly given to a color separation circuit 24 and an LPF 22 for removing the color difference signal superimposed on the high frequency range of the luminance signal, and a luminance signal and a color signal are obtained, and both are given to the process circuit 26. After performing processing such as gamma correction and blanking correction, the signal is sent to the encoder 30 to form a composite video signal. Further, the luminance signal from the LPF 22 is given to a second AGC detection circuit 34 and a comparator 32. This second AGC detection circuit 34 is connected to the LPF 22
This circuit detects the peak of the luminance signal from the sensor, and it is desirable that the time constant be small in order to reduce the time delay in detection. When the frequency band of the luminance signal is 0 to f y llz, the time constant is preferably 1/1OfYsec or less. The output signal of the second AGC detection circuit 34 is applied to the other input of the adder 3B via a switch 38. 0N10FF of this switch 38 is controlled by the output signal of the comparator 32. That is, the comparator 32 compares the luminance signal level from the LPF 22 with a predetermined reference voltage V, and sets the output signal to H when the luminance signal level is equal to or higher than the predetermined value, thereby closing the switch 38 and performing the second AGC detection. The output signal of the circuit 34 is given to the adder 3B.

In the video camera shown in FIG. 1, when the aperture 1B is fully open, the output signal of the first AGC detection circuit 28 is selected by the switch 19, while when it is not fully open, the DC constant voltage V
is selected and applied to adder 3B. Therefore, the second
The output signal of the AGC detection circuit 34 is added to either the output signal of the first AGC detection circuit 28 or the constant voltage V 1 to be used as a control signal for the AGC circuit 18 . Furthermore, when only the above-mentioned constant voltage V is input to the AGC circuit 18, the AG
The gain of the C circuit 18 is kept constant, and when only the output signal of the first AGC detection circuit 28 is input, the gain of the AGC circuit 1
The gain of the AGC circuit 18 is increased, and when only the output signal of the second AGC detection circuit 34 is input, the gain of the AGC circuit 18 is decreased. Also, if a high brightness signal is suddenly input when the aperture 16 is fully open, the first AGC detection circuit 28 and the second AG
The output signals of the C detection circuit 34 are both applied to the adder 36, but in this case, since the response of the AGC detection circuit 34 in box 2 is faster than that of the first AGC detection circuit 28, the output signals of the AGC detection circuit 34 in box 2 are actually applied to the second AGC detection circuit 28. AGC only by the output signal of
Circuit 18 is controlled.

FIG. 3 is a signal waveform diagram showing the operation of the embodiment shown in FIG. 1, and shows the output signal waveform of the AGC circuit 18. FIG. 4 is a waveform diagram in which the time axis of FIG. 3 is expanded. As can be seen from FIGS. 3 and 4, in areas with high brightness, the AGC circuit 18 is controlled by a feedback loop via the second AGC detection circuit 34 in FIG.
In FIGS. 3 and 4, the input signal indicated by the solid line becomes the output signal at the level indicated by the dotted line. Therefore, the amplitude is controlled while the ratio of the color difference signal component and the luminance signal component is always kept constant.

In addition, the AGC circuit 18 L P F 22 and the second AG
AG so that the output signal level of the feedback loop including the c detection circuit 34, that is, the output signal level of the LPF 22, is equal to or higher than the white saturation level in the process circuit 26.
By setting the gain of the C circuit 18, the brightness is not adversely affected by the provision of this feedback loop.

[Effects of the Invention] As is clear from the above detailed explanation, in the video camera of the present invention, the luminance signal component is extracted and used in the AGC circuit without using the white clip circuit that was conventionally used at the subsequent stage of the AGC circuit. In particular, since the gain is reduced only when the level of the luminance signal component is above a predetermined level, the amplitudes of both the luminance signal component and the color difference signal component are always controlled at a constant ratio.

Therefore, it is possible to create a video signal that can prevent signals with excessive levels and provide images with correct color reproduction. In particular, portable video cameras are required to have low power consumption, and video signals having correct color difference signal components can be created without increasing the power supply voltage to widen the dynamic range. Also, the conventional A
The configuration is simply adding a comparator, an AGC detector, and an adder to the GC circuit, and it is easy to integrate into an IC, so there is no cost increase.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the video camera of the present invention, FIG. 2 is a diagram showing part of a complementary color filter used in the imaging probe used in the conventional video camera and the video camera of the present invention, and FIG. 4 is an output signal waveform diagram of the AGC circuit in FIG. 1, FIG. 5 is a block diagram of a conventional video camera, and FIG.
7 and 7 are output signal waveform diagrams of the AGC circuit of FIG. 5. 10...Image sensor 12...ALC circuit 14...Optical lens system 16...Aperture 17
...Aperture open detection circuit 18...AGC circuit 19
, 38...Switch 22...LPF24・
...Color separation circuit 26...Process circuit 28
...First AGC@output circuit 30...Encoder 32...Comparator 34
...Second AGC detection circuit 3B... Adder O5 Fig. 2 Fig. 3 Fig. 4 <:>\:

Claims (3)

[Claims] (1) In a video camera having an image sensor using a complementary color filter, when the aperture that adjusts the amount of light incident on the image sensor is fully open, the video camera responds to the luminance signal separated from the output signal of the image sensor. In a video camera having an AGC circuit that increases the level of the output signal,
A video camera characterized in that a feedback loop is provided that reduces the gain of the AGC circuit when the level of the luminance signal is equal to or higher than a predetermined value. (2) The video camera according to claim 1, wherein the feedback loop includes a peak value detection circuit. (3) A comparator detects whether the level of the luminance signal is equal to or higher than the predetermined value, and the output signal of the comparator controls a switch provided in the feedback loop. A video camera according to item 1 of the scope of the invention.