JP2575060B2 - Video signal creation device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video signal generating apparatus, and more particularly to a video signal generating apparatus used for an image capturing apparatus to improve a video signal obtained under a periodic fluctuation of the amount of light incident on an image capturing element. The present invention relates to a video signal generating apparatus to be used.

2. Description of the Related Art An imaging device, such as a video camera or a camera-integrated VTR (video tape recorder), obtains two color difference signals and a luminance signal from an electric signal output from an image sensor, and combines these signals to obtain two color difference signals and a luminance signal. Create a video signal. At that time, the imaging device represents the illuminance of the subject, so that the video signal level is constant regardless of the illuminance of the subject,
The two color difference signals and the luminance signal are amplified with a gain corresponding to the level of the electric signal from the image sensor. Further, the imaging device creates a color difference signal corresponding to the illumination condition (color temperature) of the subject in order to accurately reproduce the actual color of the subject in the reproduced image.

FIG. 4 is a schematic block diagram showing an example of a configuration of a video signal creation unit of a conventional imaging device. Referring to the figure, reflected light from a subject, which is incident via an optical system (not shown), is a solid-state image sensor (here, a CCD (Charge-Coupled Device).
e)) Form an image of the subject on 1. The CCD 1 accumulates electric charges corresponding to the illuminance and the color temperature of the subject, that is, accumulates electric signals corresponding to the amount of electric charge accumulated every 1/60 sec for the next 1/60 sec. Output in between.
Next, the sample and hold circuit (abbreviated as S / H in the figure) extracts necessary signal components from the electric signal from the CCD1,
This is given to the luminance signal processing unit 100 and the color signal processing unit 200.

The luminance signal processing unit 100 includes a luminance signal automatic gain control circuit (hereinafter abbreviated as Y · AGC) 3 and a gamma (γ) circuit 5.
And a low-pass filter (hereinafter abbreviated as LPF) 6.
First, the signal component input to the luminance signal processing unit 100 is YA
It is amplified to a predetermined constant level by GC3. Y ・ AGC3
To perform such a function, its own output,
That is, the amplified signal is received via the integration circuit 20, and the circuit gain at the time of luminance signal amplification is controlled accordingly. The integration circuit 20 detects the illuminance of the subject by integrating the output signal from the YAGC 3 and detecting the average level of the electric signal from the CCD 1 (the average level of the luminance signal). Y ・ AG
The internal circuit of C3 is configured to receive the average level and increase the gain if the average level is lower than the level corresponding to the constant level, and decrease the gain if the average level is higher than the level corresponding to the constant level. You. In other words, Y
The gain of the AGC 3 changes according to the illuminance of the subject. In this way, the output of Y • AGC3 is fed back, and Y • AGC3
The level of the signal amplified by is kept constant.

Next, the gamma circuit 5 performs gamma correction on the signal amplified to a certain level by the YAGC 3 and supplies the signal to the LPF 6. LPF6
Extracts only the luminance signal component Y from the output signal of the gamma circuit 5 and supplies it to the encoder circuit 14.

On the other hand, the color signal processing unit 200 includes a color separation sample hold circuit (abbreviated as S / H in the figure) 7 and 8, a W / B (white balance) and matrix circuit 9, a color difference signal automatic gain control circuit (hereinafter, referred to as S / H). C. AGC) 11, a gamma circuit 12, and an LPF 13. First, two different types of color signals are separated from the signal components input to the color signal processing unit 200 by the color separation sample / holds 7 and 8. These color signals are converted by the W / B and matrix circuit 9 into color difference signals RY and BY corresponding to the color temperature of the subject by white balance processing, and applied to the C / AGC 11.

The W / B and matrix circuit 9 receives its output signals, that is, the color difference signals RY and BY via an auto white balance circuit (hereinafter abbreviated as AWB circuit) 21. The AWB circuit 21 is an image processing type auto white balance circuit that integrates the color difference signals RY and BY separately and detects the color temperature of the subject by detecting the average level of each signal. The W / B and matrix circuit 9 receives the output of the AWB circuit 21 (hereinafter, referred to as a white balance control signal), that is, the integrated value of each of the color difference signals RY and BY, and receives these predetermined values. The circuit gain at the time of generating the color difference signal is controlled so that the reference level becomes. As a result, the average level of the color difference signals RY and BY output from the W / B and matrix circuit 9 is kept constant, and the white balance processing that follows the change in the color temperature of the subject in the color signal is automatically performed. It is performed. Such white balance processing is called full auto white balance processing.

Next, the C / AGC circuit 11 amplifies the color difference signals RY and BY with a gain corresponding to the output of the integration circuit 20. That is, since the gain of the C / AGC circuit 11 is also controlled according to the illuminance of the object, the color difference signal R−
The levels of Y and BY are always the signal levels output from Y · AGC3, that is, the levels that match the average level of the luminance signal. As described above, the color difference signals RY and BY amplified by the C / AGC circuit 11 are subjected to gamma correction by the gamma circuit 12 and then high-frequency components are removed by the LPF 13 to be supplied to the encoder circuit 14.

The encoder circuit 14 combines the luminance signal Y from the luminance signal processing unit 100 with the color difference signals RY and BY from the chrominance signal processing unit 200, and further synthesizes a composite synchronization signal (C-SY in the figure).
Abbreviated as NC. ) Is added to create a composite video signal, and this is output as a video output.

FIG. 4 is a schematic diagram, and a line-sequential synchronization circuit and the like related to the generation of color difference signals, which are necessary in an actual circuit configuration, are omitted in FIG.

In the conventional imaging apparatus as described above, each of the integrating circuit 20 for detecting the average level of the luminance signal and the integrating circuit for detecting the average level of each of the two color difference signals in the AWB circuit 21 for white balance are: This is a continuous integration circuit that continuously averages the input signal level. FIG. 5A is a general circuit diagram of a continuous integration circuit used in the integration circuit 20 and the AWB circuit 21. Referring to the drawing, this continuous integration circuit is provided between input terminal T1 and ground GND, and is a time constant circuit formed by series connection of resistor 15 and capacitor 17, and a connection point of resistor 15 and capacitor 17 and an output terminal. Buffer circuit (BF) provided between T2 and 18
And The signal input to the input terminal T1 is smoothed according to the time constant determined by the resistance value of the resistor 15 and the capacitance of the capacitor 17, and is output to the output terminal T2 via the buffer circuit 18.
Taken out of FIG. 5 (b) is a waveform diagram showing an example of input / output signals in the continuous integration circuit as shown in FIG. 5 (a). If the input signal waveform input to the input terminal T1 of the continuous integration circuit in FIG. 5A is a rectangular wave as shown in FIG. 5B, the output signal taken out from the output terminal T2 is , as shown in FIG. 5 (c), varies by u ₀ to and below the mean level V ₀ which input signal. However, in the integration circuit for detecting the level of the input signal,
A capacitor 17 having a large capacitance value is used so that u ₀ ≒ 0, and the time constant of the time constant circuit is set sufficiently large. That is, by doing so, the level of the output signal indicates the average level of the input signal, and integrating the input signal and detecting the average level of the input signal are equivalent.

[Problems to be Solved by the Invention] As described above, in the conventional imaging apparatus, a circuit for generating a feedback signal to the automatic gain control circuit and a white balance control signal, that is, a circuit for performing white balance processing The circuit that creates the feedback signal to
In both cases, a continuous integration circuit is used. For this reason, the light quantity and color temperature of the light source illuminating the subject periodically fluctuate, and the cycle is the output cycle (sampling cycle) of the image sensor 1 / 60se
A video signal created when the value is not an integral multiple of c is discontinuous in terms of luminance level, color level, and color temperature. Since a so-called flicker occurs in a reproduced image obtained from such a video signal, the reproduced image is unsightly.

A typical example of the periodic fluctuation of the light amount and the color temperature of the light source is a flicker of a fluorescent lamp which is turned on by a 50 Hz AC power supply. Hereinafter, the reason why the above-described discontinuous video signal is created will be described by taking such flicker of a fluorescent lamp as an example. FIG. 6 is referred to for the description. FIG. 6 is a waveform diagram schematically showing a process of creating a discontinuous video signal under flicker of a fluorescent lamp.

Generally, the amount of light of a fluorescent lamp fluctuates at twice the AC frequency of a power supply for lighting the fluorescent lamp, thereby causing flicker. Along with this, the color temperature of the subject also changes in the same cycle as the light quantity change cycle. Accordingly, as shown in FIG. 6 (b), the quantity of light of the fluorescent lamp and the color temperature of the subject which are lit by the 50 Hz AC power supply (see FIG. 6 (a)) have a frequency of 100 Hz, that is, 1/100 sec. It fluctuates with the period. On the other hand, the sampling cycle of the image sensor is 1/60 sec
(1 vertical period = 1V). FIG. 6C is a waveform diagram of a vertical synchronizing signal (hereinafter, referred to as a VD pulse), and shows a sampling cycle of the image sensor. Therefore, at 1V,
The sum of the light intensity of the fluorescent lamp is the frequency of the light intensity fluctuation of the fluorescent lamp at 100 Hz.
The frequency fluctuates at a frequency of 20 Hz, which is the greatest common divisor of the sampling frequency of the image sensor and 60 Hz, that is, at a cycle of 3 V (1/20 sec). For this reason, the average accumulated charge amount for each 1 V of the image sensor also fluctuates at a cycle of 3 V as shown in FIG. 6D. As a result, the luminance signal level and the color difference signal level also fluctuate in a 3 V cycle. The feedback signal to the automatic gain control circuit and the white balance control signal are obtained by integrating the luminance signal level and the color difference signal level by a continuous integration circuit (see FIG. 5). Therefore, the feedback signal to the automatic gain control circuit and the white balance control signal obtained in this case are shown in FIG.
An input signal having a waveform as shown by the above is continuously smoothed with a large time constant by the above-described continuous integrator circuit (No. 6).
FIG. In other words, the levels of the feedback signal to the automatic gain control circuit and the level of the white balance control signal within the period corresponding to the levels of the luminance signal and the color difference signal are different for each 1V within 3V. Are all at the same level. Therefore, the luminance signal and the color difference signal that fluctuate in a 3 V cycle are all amplified with the same gain by the automatic gain control circuit that receives such a constant level feedback signal. As a result, as shown in FIG. 6 (g), the levels of the finally obtained luminance signal and color difference signal are directly affected by the fluctuation of the light quantity of the fluorescent lamp and fluctuate in a 3V cycle. Further, the white balance processing at the time of generating the color difference signal is performed according to the level of the white balance control signal. Therefore, despite the fact that the color temperature of the subject fluctuates in a 3V cycle, the color difference signal obtained by performing the white balance processing using such a constant level white balance control signal is the color temperature fluctuation of the fluorescent lamp. Does not follow the color temperature fluctuation of the subject due to

Due to the fluctuation of the luminance signal level and the color difference signal level and the non-following property of the color difference signal with respect to the color temperature of the subject, the finally obtained video signal becomes discontinuous which causes flicker in a reproduced image.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-described problems and to create a feedback signal that can create a continuous and stable video signal without causing flicker in a reproduced image even under a periodic fluctuation of the light source light amount. It is another object of the present invention to provide a video signal generating device capable of reducing costs.

[Means for Solving the Problems] According to the present invention, in order to achieve the above object,
A video signal creation device used in an imaging device includes input means for inputting an image signal, the image signal includes a luminance signal and a chrominance signal, and means for performing automatic gain control on the luminance signal; And means for supplying a time-division integrated signal to the means for performing automatic gain control for color and luminance signals. The means for supplying the time-divided integrated signal includes a resistance means connected to the input means, a plurality of capacitance means to be respectively connected to the resistance means, and a vertical synchronization signal of the imaging device. Divides the signal into a predetermined number to generate at least two timing signals having different phases. Based on at least two timing signals from the frequency dividing means, an electric connection between the resistance means and the plurality of capacitance means is generated. Means for changing the combination of logical connections.

[Operation] Since the video signal generating apparatus according to the present invention is configured as described above, the time-division integrated signals are separately supplied to the luminance signal and the chrominance signal, and the gain amplifier circuit is not required. .

[Embodiment] FIG. 1 is a schematic block diagram showing an embodiment of the present invention and showing a configuration of a video signal creating section of an imaging apparatus. Referring to the figure, this video signal creation unit is similar to a video signal creation unit of a conventional imaging device, and includes a solid-state imaging device (here, CCD) 1 and
It includes a sample and hold circuit 2, a luminance signal processing unit 100, a chrominance signal processing unit 200, and an encoder circuit 14. The internal configurations of the luminance signal processing unit 100 and the color signal processing unit 200 are the same as those of the conventional imaging device shown in FIG. The video signal creation unit further includes an integration circuit 4 for creating a feedback signal to Y • AGC3 in the luminance signal processing unit 100 and a C • AGC11 in the chrominance signal processing unit 200, as in the related art. It includes a W / B in the processing unit 200 and a feedback signal to the matrix circuit 9, that is, an AWB circuit 10 that creates a white balance control signal. The process from the generation of the electric signal output from the CCD 1 to the creation of the final video signal by the above-described series of functional units is as described in the “prior art”.

However, the integration circuit 4 and the AWB circuit 10 include a time division integration circuit for temporally dividing and smoothing the input signal instead of the conventional continuous integration circuit.

FIG. 2 is a circuit diagram of the integration circuit 4 and the time division integration circuit included in the AWB circuit 10. Referring to the figure, this time-division integrating circuit includes an input terminal T1, an output terminal T2, a resistor 15
And capacitors C1, C2 and C3, resistor 15 and capacitor
An analog switch 16 provided between C1 and C3 and a resistor
15 and a buffer circuit 18 provided between the output terminal T2,
A frequency divider 19 for dividing the VD pulse by 3 to generate two timing pulses A and B having different phases. Next, the operation of the time division integration circuit will be described. It should be noted that FIGS. 3A to 3C are referred to for the description. 3 (a) to 3 (c) are waveform diagrams for explaining the function of the frequency divider 19. FIG.

The frequency divider 19 divides the 60 Hz VD pulse (FIG. 3 (a)) by 3 and makes the timing pulse A (FIG. 3 (b)) and the timing pulse A which become "H" level by 1V in a 3V cycle by 1V. And a timing pulse B (FIG. 3 (c)) whose phase is shifted by 1V is given to the analog switch 16. The analog switch 16 responds to the timing pulses A and B. Specifically, when both of the timing pulses A and B are “L”, only the level of the timing pulse A is “H”.
The internal connection is switched so that the capacitors C1 to C3 are alternately connected to the resistor 15 in a certain order in each of the case of the level and the case where only the level of the timing pulse B is "H". Therefore, the signal input to the input terminal T1 has a 3V cycle,
15, smoothed by a time constant circuit composed of
The data is output from the output terminal T2 via the buffer circuit 18. That is, the signal supplied to the input terminal T1 is smoothed by 1V by the same time constant circuit every 3V.

The time-division integrating circuit as described above is composed of the integrating circuit 4 and the AWB.
When used in the circuit 10, when the average accumulated charge amount per 1 V of the CCD 1 fluctuates in a 3 V cycle due to fluctuations in the light source light amount, for example, a fluorescent light in which the light source illuminating the subject is lit by a 50 Hz AC power supply In this case, a video signal different from the conventional one is created as follows.

FIGS. 3 (d) to 3 (h) are waveform diagrams showing the process of creating a video signal when the light source is a fluorescent lamp which is turned on by a 50 Hz AC power supply. If the light source is a fluorescent lamp that is lit by a 50 Hz AC power supply, the light amount of the light source fluctuates at a period of 1/100 sec as described above (FIG. 6 (b)). The average amount of accumulated charges fluctuates in a 3 V cycle (FIG. 3 (d)). As a result, the level of the luminance signal component input to the integration circuit 4 and the level of the color difference signal input to the AWB circuit also fluctuate in a 3 V cycle. That is, the level of the input signal to the time-division integrator shown in FIG. 2 also fluctuates at a cycle of 3 V as shown in FIG. 3 (e).
On the other hand, in the time-division integrating circuit shown in FIG. 2, the analog switch 16 connects three capacitors to the resistor 15 alternately every 1V. Therefore, the capacitor used for smoothing the input signal is, for example, as shown in FIG.
.., C1, C2, C3, C1,... Are switched every 1 V in a fixed order. As a result, the input signal to the time-division integrator shown in FIG. 2 is smoothed by a unique time constant circuit for each of three levels (in the figure, l1, l2, and l3) within the level fluctuation period 3V. You. That is, since input signals of the same level are smoothed by the same time constant circuit, the output signal from the time-division integrator shown in FIG. 2 becomes the level of the input signal as shown in FIG. Reproduce the fluctuation. This is because the integrating circuit 4 and the AWB circuit 10 follow the fluctuation of the light source light amount and the accompanying color temperature fluctuation of the subject.
This means that a feedback signal and a white balance control signal to Y • AGC3 and C • AGC11 that fluctuate in a cycle of 3V are generated. Therefore, Y • AGC3 and C • AGC11 that receive such a feedback signal amplify the luminance signal component and the color difference signal with a gain corresponding to the average light source light amount for each 1V. As a result, the level fluctuations of the color difference signal and the luminance signal under the flicker of the fluorescent lamp are reduced, and the levels of the color difference signal and the luminance signal do not fluctuate discontinuously as in the prior art (see FIG. 6 (g)). As shown in FIG. 3 (h), it is stabilized to the extent that it can be regarded as substantially constant.

Further, the W / B and matrix circuit 9 receives a white balance control signal at a level following the variation of the average light source light amount for each 1V. White balance processing that follows the fluctuation of As a result, the color difference signal always follows the color temperature of the subject even under the flicker of the light source. Therefore, the continuity of the levels of the luminance signal and the color difference signal in the video signal created by synthesizing the luminance signal and the color difference signal, and the responsiveness to the color temperature of the subject are improved even under the flicker of the light source. For this reason, even when photographing is performed under illumination of a light source that generates flicker, such as a fluorescent light, a reproduced image with reduced flicker can be obtained.

It should be noted that the internal circuits of the Y-AGC3 and the C-AGC11 have such characteristics that the gains thereof become different values in response to the level fluctuation of each 1V due to the flicker of the light source of the feedback signal from the integration circuit 4. Must be configured. Similarly, the internal circuit of the W / B and matrix circuit 9 also responds to a feedback signal from the AWB circuit 10 due to flicker of the light source, that is, a white signal different from the color signal in response to a level change of the white balance control signal for each 1V. It is necessary to be configured to have a characteristic of performing a balance process. The characteristics of Y • AGC3 and C • AGC11 are determined by the time constant set value of the time-division integrator constituting the integrator 4,
The characteristics of the W / B and the matrix circuit 9 are affected by the set value of the time constant of the time-division integrator constituting the AWB circuit 10, respectively. Furthermore, the set value of the time constant of the time division integrator is
It also affects the stability of the output signal level within 1V. Therefore, the time constant of the time-division integrating circuit must be set to an appropriate value in consideration of these effects.

In the present embodiment, the number of time constant circuits of the time-division integrating circuit is three, but this number may be arbitrarily selected according to the flicker cycle of the light source. In this embodiment, a time-division integrating circuit is created by alternately connecting a plurality of capacitors to a single resistor using an analog switch. However, the configuration of the time-division integrating circuit is not limited to this, and may be any configuration that can realize the same function as this.

[Effects of the Invention] As described above, according to the video signal generating device of the present invention, the time-division integrated signal is supplied to the luminance signal and the chrominance signal gain control means, and the automatic gain control is performed based on the integrated signal. Therefore, no flicker occurs in the reproduced image even under the periodic fluctuation of the light source luminous intensity.
A feedback signal that can create a continuous and stable video signal can be created. Further, since only the automatic gain control is performed for the color signal, a gain amplifying circuit is not necessary. As a result, it is possible to provide a video signal creation device capable of reducing costs.

[Brief description of the drawings]

FIG. 1 is a schematic block diagram of a video signal processing unit of an image pickup apparatus showing one embodiment of the present invention, and FIG. 2 is a circuit diagram showing an example of a time-division integrating circuit included in the integrating circuit and the AWB circuit in FIG. FIG. 3 shows an imaging apparatus according to the present invention.
FIG. 4 is a waveform diagram for explaining a video signal generation process under a light source that generates flicker. FIG. 4 is a schematic block diagram showing an example of a video signal generation unit of a conventional imaging apparatus. FIG. 5 is an integration circuit shown in FIG. FIG. 6 is a circuit diagram showing an example of an integrating circuit included in the AWB circuit, and a waveform diagram for explaining a function of the continuous integrating circuit. FIG. 6 is a waveform diagram for explaining a problem of the conventional imaging apparatus. In the figure, 1 is an image sensor, 2 is a sample hold circuit, 3 is a Y.AGC, 4 and 20 are integrating circuits, 5 and 12
Is a gamma circuit, 6 and 13 are LPFs, 7 and 8 are color separation sample and hold circuits, 9 is a W / B and matrix circuit, 10 and 21 are AWB circuits, 11 is a C / AGC circuit, 14 is an encoder circuit, and 15 is an encoder circuit. A resistor, 16 is an analog switch, 17 and C1 to C3 are capacitors, 18 is a buffer circuit, 19 is a frequency divider, 100 is a luminance signal processing unit, and 200 is a color signal processing unit. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

(57) [Claims] 1. A video signal generating device for generating a video signal based on an image signal captured by an image capturing device, comprising input means for inputting the image signal, wherein the input image signal is a luminance signal. Means for performing automatic gain control on the luminance signal, means for performing automatic gain control on the color signal, and means for performing automatic gain control on the luminance signal and the color signal. Means for supplying a time-division integrated signal to the input means, wherein the means for supplying the time-division integrated signal includes a resistance means connected to the input means, and a plurality of resistance means respectively connected to the resistance means. Number of capacitor means, frequency dividing means for receiving a vertical synchronizing signal of the imaging device, dividing the vertical synchronizing signal to a predetermined number, and generating at least two timing signals having different phases, and the frequency dividing means Or At least two on the basis of the timing signal, and means for changing the combination of the electrical connection between said resistor means and said plurality of capacitor means, the video signal generating device.