JPH04154391A - Backlight correction circuit - Google Patents

Abstract

PURPOSE:To prevent color oozing from occurring in forward light and to improve the S/N of a chrominance signal when counter light is corrected by varying the feedback coefficient K of a comb liner filter circuit corresponding to the size of the amplification gain of the chrominance signal. CONSTITUTION:The chrominance signal C from a Y/C separation circuit 13 goes to a signal with level in accordance with the size of the level of the output DC signal of an integration circuit(CR) 12 at a gain control(GC) circuit 14, and is outputted to the comb line filter circuit(CF) 15. A feedback coefficient control circuit 20 performs control so that the feedback coefficient K in the CF 15 can be varied in proportion to the size of the output level of the CR 12. The degree of improvement of the S/N of the CF 15 can be increased by increasing the feedback coefficient K, therefore, the output level of the CR 12 can be increased in the counter light, and when the level of a dark part is increased by increasing the gain of the GC 14, the feedback coefficient K of the CF 15 is also increased, and the improving effect of the S/N can be increased, thereby, the correction of the counter light for the chrominance signal can be performed with satisfactory S/N.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to a backlight correction circuit in a video camera.
More specifically, the present invention relates to a backlight correction circuit that improves the S/N ratio of color signals during backlight correction.

[Conventional technology]

FIG. 4 is a block circuit showing a backlight correction circuit of a conventional video camera. In the figure, (1) is a lens, (2) is an aperture mechanism, (3) is an image sensor, (4) is an amplifier circuit, and (5) is an aperture mechanism.
) is an integral circuit, and (6) is an aperture control circuit.

(7) is an automatic gain control circuit (rAGC).
18] is an integration circuit, (9) is an AGC control circuit, (10) is a gate circuit, (11) is a voltage comparator, (12) is an integration circuit, and (13) is a color separation circuit (hereinafter referred to as "circuit").
(rY/C separation circuit), (+4) is a gain control circuit for backlight correction, (+51C<L-type filter circuit, (16) is a color signal output terminal, and (!7) is a gain for backlight correction. A control circuit, (18) a luminance signal processing circuit, and (19) a luminance signal output terminal.

Next, the operation will be explained. The amount of light passing through the lens (1) is limited by an aperture mechanism (2), converted into an electrical signal by an image sensor (3), and then input to an amplifier circuit (4). The output of the amplifier circuit (4) is integrated by the integrating circuit (5),
A DC signal corresponding to the level of the input signal is input to the aperture control circuit (6).

The aperture control circuit (6) compares the level of the human-powered DC signal with a reference voltage, and outputs a control signal to operate the aperture mechanism (2) so that the output signal level of the amplifier circuit (4) remains constant. .

On the other hand, the output of the amplifier circuit (4) input to the AGC circuit (7) becomes a constant level signal and is input to the integrating circuit (8), the gate circuit (] I0, and the Y/C separation circuit (13). The integrating circuit (8) integrates the human input signal and outputs a DC signal corresponding to the output level of the AGC circuit (7) to the AGC control circuit (9), and the AGC control circuit (9) converts this DC signal into a reference voltage. The AGC control signal corresponding to the difference is fed back to the AGC circuit (7).
control so that the output signal level is constant.

On the other hand, the gate circuit (10) to which the output signal of the AGC circuit (7) is input extracts the video signal at the center of the screen and inputs it to the voltage comparator (11). The voltage comparator (I +1 outputs an H level signal when the input signal is below the reference level, and an L level signal when it is above the reference level. Therefore,
When the output of this voltage comparator (11) is integrated by the integrating circuit (12), the output of the AGC circuit (7) is lower than the reference level of the video signal at the center of the screen extracted by the gate circuit (10). A DC signal with a level corresponding to the area of the part is obtained.

On the other hand, the output of the AGC circuit (7) input to the Y/C separation circuit (13) is separated into a luminance signal Y and a color signal C.
The luminance signal Y is transmitted through a gain control circuit for backlight correction (
17), and the gain is controlled by the output signal of the integrating circuit (12). For this reason, when there are many dark areas in the center of the screen, such as when there is backlight, the gain increases according to the area of the dark area, and the signal level of the dark areas increases to perform backlight compensation. Later, the luminance signal processing circuit (1
8), various signal processing is performed on the signal and the signal is output from the output terminal (19).

Further, the color signal C input to the gain control circuit (14) is subjected to the same gain control as the luminance signal by the output signal of the integrating circuit (12), and the chrominance signal C input to the gain control circuit (14) is subjected to the same gain control as the luminance signal.
5). The comb filter circuit (15) scans the color signal C for one horizontal scanning time (hereinafter referred to as r I HJ).
If the amount of feedback is increased by increasing the amount of feedback, the delayed color signal is fed back to improve the S/N ratio of the color signal.
It is configured so that the degree of improvement in the S/N ratio increases, and the S
The color signal C with improved /N ratio is output from the output terminal (I6).

[Problems to be Solved by the Invention] Conventional backlight correction circuits perform backlight correction by increasing the gain of the color signal gain control circuit (I4), and the S/N ratio deteriorates due to this by using a comb filter. circuit(
This is prevented by increasing the feedback coefficient K in 15).

However, if the feedback coefficient K is increased, there is a problem in that color fringing occurs in the vertical direction in front light.

This invention was made to solve the above-mentioned problems, and it is an object of the present invention to obtain a backlight correction circuit that does not cause color blurring in front light and has a good S/N ratio of color signals during backlight correction. With the goal.

[Means to solve the problem]

The backlight correction circuit according to the present invention is characterized in that it includes a feedback coefficient control circuit that changes the feedback coefficient of the comb filter circuit in accordance with the level of gain of the gain control circuit for backlight correction of color signals. .

[Effect]

The feedback coefficient control circuit according to the present invention changes the feedback coefficient of the comb filter circuit in accordance with the gain level of the color signal gain control circuit. Therefore, since the feedback coefficient becomes small in front light, vertical color blur does not occur, and a reproduced image with a good color signal S/N ratio can be obtained in back light.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. 1st
In the figure, (20) is a feedback coefficient control circuit, which controls the feedback coefficient K in the comb filter circuit (15) to be large or small depending on the level of the output signal of the integrating circuit (12).

Next, the operation of this embodiment, which differs from the conventional example shown in FIG. 4, will be explained.

The color signal C output from the Y/C separation circuit (13) is converted into a signal of a level corresponding to the level of the output DC signal of the integration circuit (12) by the gain control circuit (14) and then passed through the comb filter. It is output to the circuit (15). As shown in FIG. 2, the feedback coefficient control circuit (20) includes an integrating circuit (
The feedback coefficient K in the comb filter circuit (15) is controlled to be large or small in proportion to the output level of the filter (12). As shown in Fig. 3, the comb-shaped filter circuit (15) improves the S/N ratio more as the feedback coefficient K increases, so the output level of the integrating circuit (12) increases when backlighting occurs. As the gain of the gain control circuit (I4) increases and the level of the dark part increases, the feedback coefficient of the comb filter circuit (15) also increases, causing S
Since the effect of improving the S/N ratio is also large, backlight correction with good S/N of color signals is performed.

Also, when the gain of the gain control circuit (14) is low in front light, there is less noise, and the comb filter circuit (15) has less noise.
) is also small, the effect of improving the S/N ratio is small, and no vertical color blurring occurs.

[Effects of the Invention] As described above, according to the present invention, the feedback coefficient K of the comb filter circuit is configured to be changed depending on the level of the amplification gain of the color signal. When the gain is large and the noise is large, the degree of improvement in the S/N ratio in the comb filter circuit becomes large and backlight correction with a good S/N can be performed, and when the amplification gain during forward light is small and there is little noise. Since the degree of improvement in the S/N ratio is made smaller, color blurring in the vertical direction is reduced in front light, and it is possible to perform backlight correction that always provides a well-balanced color signal.

[Brief explanation of drawings]

Fig. 1 is a block circuit diagram of an embodiment of the present invention, Fig. 2 is a characteristic diagram of a feedback coefficient control circuit, and Fig. 3 is a characteristic diagram showing the relationship between the feedback coefficient of a comb filter circuit and the degree of S/N improvement. ,
FIG. 4 is a block circuit diagram of a backlight correction circuit for a conventional video camera. (10)...Gate circuit, fi+)...Comparator,
112)...integrator circuit, (141, (+71...
Gain control circuit, (15)...comb filter circuit, (I8)...luminance signal processing circuit, (20)...
...Feedback coefficient control circuit. In each figure, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] (1) Backlight compensation is performed by controlling the gains of the luminance signal and chrominance signal that form the video signal so that the brightness in the center of the screen is at a predetermined level, and this chrominance signal is passed through a comb filter circuit for one horizontal In a backlight correction circuit configured to improve the signal-to-noise ratio by feeding back a color signal delayed in scanning time, the feedback coefficient in the comb filter circuit changes in size depending on the level of amplification gain of the color signal. 1. A backlight correction circuit characterized by comprising feedback gain control means for controlling the gain so that