JP3045394B2 - Video camera - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a video camera.

[Summary of the Invention]

According to the present invention, in a video camera, a video signal in a field memory is fed back to a current video signal, and the amount of the feedback is controlled in accordance with the illuminance of a subject to obtain a video signal having excellent characteristics. It was made.

[Conventional technology]

In a video camera, when the illuminance is low, the level of the video signal is reduced, so that the S / N of the video signal is reduced and noise becomes noticeable on the screen.

Therefore, as a method of improving the S / N of the video signal, the S / N is improved by integrating random noise components by accumulating electric charges over several field periods on an imaging CCD.

The noise component is canceled using the horizontal correlation and the vertical correlation to improve S / N.

And so on.

[Problems to be solved by the invention]

However, according to the method, since electric charges are accumulated on the CCD over, for example, a four-field period, when a moving object is imaged, the moving object is swelled. This motion blur
When the subject is in low illuminance, it is unavoidable to improve the S / N, but when the subject is in high illuminance, the image quality is merely reduced.

Further, when switching between the imaging mode and the normal imaging mode is performed, the amount of integration per screen rapidly changes at the switching point, which causes unnaturalness.

Furthermore, since a video signal of the same image is extracted over, for example, four field periods, a frame is dropped.

Also, the method does not cause such a problem,
S / N improvement is not enough.

The present invention is intended to solve the above problems.

[Means for solving the problem]

According to the video camera of the present invention, an AGC circuit for performing AGC on a luminance signal obtained from an image sensor and a luminance signal output from the AGC circuit are supplied, and the level continuously changes in inverse proportion to the level of this signal. An AGC voltage forming circuit for forming an AGC voltage to be supplied to the AGC circuit and supplying the AGC voltage to the plurality of non-linear circuits and an aperture correction circuit for performing an aperture correction on a luminance signal output from the AGC circuit And a noise reduction circuit that selectively removes a field noise component using a field correlation from the luminance signal output from the aperture correction circuit,
A horizontal noise canceller circuit for removing a horizontal noise component having no horizontal correlation of the luminance signal output from the noise reduction circuit, and a vertical noise canceller circuit for removing a vertical noise component having no vertical correlation of the luminance signal output from the horizontal noise canceller circuit The aperture correction circuit includes an aperture correction level control attenuator circuit, and the attenuator circuit is supplied with an output of the AGC voltage forming circuit, and increases in a non-linear manner as the output increases. Is connected to a first non-linear circuit that outputs a control signal, and the amount of attenuation is controlled by the first control signal. The noise reduction circuit includes a noise reduction level control attenuator circuit, and the attenuator circuit includes: The output of the AGC voltage forming circuit is supplied and Connected to a second non-linear circuit that outputs a second control signal that increases in a non-linear manner in response to the addition of the second control signal, the amount of attenuation is controlled by the second control signal, and the horizontal noise canceller circuit controls the level of horizontal noise cancellation. Attenuator circuit, the output of the AGC voltage forming circuit being supplied, and the attenuator circuit increasing in a non-linear manner as the output increases.
Is connected to a third non-linear circuit that outputs a control signal, and the amount of attenuation is controlled by the third control signal. The vertical noise canceller circuit includes a vertical noise canceling level control attenuator circuit, and the attenuator circuit is Is connected to a fourth non-linear circuit that is supplied with an output of the AGC voltage forming circuit and outputs a fourth control signal that increases in a non-linear manner according to the increase in the output, and the amount of attenuation is controlled by the fourth control signal. Is controlled.

[Action]

The feedback amount is controlled according to the illuminance of the subject, and appropriate noise removal is performed.

〔Example〕

In FIG. 1, (1) shows a CCD for imaging, and this C
Although not shown, a color separation filter is provided on the light receiving surface of the CD (1), and a video signal Sv having dot-sequential color signal components corresponding to the color separation filter is extracted from the CCD (1).

The signal Sv is supplied to the variable gain amplifier (4) for AGC through the preamplifier (2) and the CDS circuit (3), and the signal Sv is extracted from the amplifier (4). An AGC voltage Va whose level continuously changes in inverse proportion to the illuminance of the object is taken out as shown in FIG. 2 and supplied to a voltage forming circuit (41), and this voltage Va is supplied to an amplifier (4) for control. Supplied as a signal,
As shown in the figure, the gain of the amplifier (3) decreases as the illuminance of the subject increases.

Therefore, the video signal Sv subjected to AGC is taken out from the amplifier (3).

Then, this signal Sv is supplied to a Y / C separation circuit (5) and separated into a luminance signal Sy and a chrominance signal Sc.
Is supplied to the noise reduction circuit (70) through the gamma correction circuit (6).

This noise reduction circuit (70) is configured as a feedback type having a field memory, and improves the S / N of the luminance signal Sy at low illuminance. That is, the signal Sy from the correction circuit (6) is supplied to the subtracting circuit (71), it is the subtraction output S _1, the field memory circuit (7
Is supplied to the 2) is one field period delayed signal S _2. Therefore, a memory circuit (72), although not shown, the A / D converter to a digital signal of the signals S _1, a field memory for delaying the digital signals S ₁ one field period, the delay from the field memory and a D / a converter for converting a signal into a signal S ₂ analog.

Then, together with the signal S ₂ is supplied to the subtracting circuit (73), the signal Sy is supplied to the difference signal _{S 3 S 3 = Sy-S} 2 ...... in the subtraction circuit (73) (i) is extracted, This signal S ₃ is output from the variable attenuator circuit (7
It is supplied to the subtraction circuit (71) through 4). in this case,
Assuming that the signal transmittance of the attenuator circuit (74) is a value k,
A 0 ≦ k <1, when k = 0, the signal S ₃ is not supplied to the subtracting circuit (71). In the subtraction circuit (71), the subtraction of S ₁ = Sy−k · S ₃ (2) is performed.

Further, AGC voltage Va is a voltage V ₅ is supplied to the non-linear circuit (75), the voltage V ₅ is supplied as a control signal to the variable attenuator (74), for example, as shown in FIG. 3, the subject When the illuminance is low, k ≒ 1 and when it is high, k = 0.
The value k is made to change non-linearly and continuously and monotonously.

The output signals S ₁ of the subtracting circuit (71) is taken out to the terminal (8) as reduced luminance signal noise components at the time of low illuminance.

Further, the signal Sc from the separation circuit (5) is output to the color processing circuit (1
1). When the video camera is a single camera, the carrier color signal Sc in the NTSC system is taken out to a terminal (12). When the video camera is an integral type with a VTR, the carrier color signal Sc subjected to low-frequency conversion is supplied to a terminal (12). It is taken out to 12).

According to such a configuration, S ₁
≒ S ₂ So reducing circuit (73) and (i) signal in equation
S ₃ is mainly a noise component having no field correlation.

When the illuminance of the subject is low, large AGC voltage Va, because the k ≒ 1, the subtracting circuit (71) (ii) that the noise component S ₃ from the luminance signal Sy is subtracted based on the formula becomes, signals S ₁ which is the operation output is a reduced luminance signal of the noise component S _3.

That is, assuming that the level of the noise component in the luminance signal Sy is “1”, the ratio L of the level of the noise component in the luminance signal S ₁ is And the noise component can be sufficiently reduced.

On the other hand, when the illuminance of the subject is high, the AGC voltage is small and k = 0, so that in the subtraction circuit (71) and the equation (ii), S ₁ = Sy regardless of the signal S ₃ . Thus, the luminance signal Sy is directly taken out as signals S ₁ to the terminal (8).

At this time, since the illuminance of the subject is high, the S / N of the luminance signal S ₁ (= Sy) is high, and even if the subtraction of the noise component S ₃ is not performed in the subtraction circuit (71), the noise component becomes a problem. No. The signal Sy is because it is output as the signal S _1, never cause motion blur on the screen.

Thus, according to the present invention, it is possible to obtain a luminance signal S _1, with this case, particularly according to the present invention, taking out noise components S ₃ by utilizing the field correlation,
When the illuminance of the subject is low, k ≒ 1 and the luminance signal Sy
Since removal of the noise component S ₃ from even the subject low-light, is never noticeable noise on the screen.

Further, when the illuminance of the subject is high, since not to feed back the noise component S ₃ as k ≒ 0, even if the noise component S ₃ contains non-field correlation component, can cause motion blur on the screen Absent.

Further, since the value k is changed using the AGC voltage Va, the feedback amount kS ₃ of the noise component S ₃ becomes a value that continuously changes in accordance with the illuminance of the subject, and unnaturalness appears on the screen. Will not occur.

In the example shown in FIG. 4, a case where the noise component S ₃ from the subtractor circuit (73) is supplied after being amplitude limited to the attenuator (74) by the limiter (76).

Therefore, according to this example, even if the subject moves when the illuminance is low, the motion blur is suppressed.

In the example shown in FIG. 5, the luminance signal Sy is further improved in characteristics.

That is, (10) indicates an aperture correction circuit, and the luminance signal Sy from the correction circuit (6) is supplied to the addition circuit (11), and the signal Sy is supplied to the band-pass filter (12) and the variable slice circuit (13). Are sequentially supplied to form an edge signal, and this edge signal is supplied to the variable attenuator circuit (1
It is supplied to the addition circuit (11) through 4).

At this time, the AGC voltage Va is applied to the non-linear circuit (1
Control voltage is formed by the control of 5). These control voltages are supplied to the circuits (13) and (14), and the luminance signal subjected to the aperture correction corresponding to the illuminance of the subject is output from the adder circuit (11). Sy is taken out.

Then, the signal Sy is supplied to the horizontal noise canceller circuit (20) through the above-described noise reduction circuit (70).

That is, the signal Sy is supplied to the subtraction circuit (21) and supplied to the high-pass filter (22) and the limiter (23) in order to extract a noise component. The noise component is passed through the variable attenuator circuit (24). It is supplied to a subtraction circuit (21). The AGC voltage Va is supplied to the non-linear circuit (25) to form a control voltage. The control voltage is supplied to the attenuator circuit (24), and the subtraction circuit (21) outputs noise corresponding to the illuminance of the subject. The canceled luminance signal Sy is extracted.

Then, this signal Sy is supplied to the vertical noise canceling circuit (2
0).

That is, the signal Sy is supplied to the subtraction circuits (31) and (32), and is also supplied to the delay circuit (33) to be delayed by one horizontal period, and this delayed output is supplied to the subtraction circuit (32) and From (32), noise components without vertical correlation are mainly extracted. Then, the noise component is supplied to the subtraction circuit (31) through the limiter (34) and the variable attenuator circuit (35).

Further, the AGC voltage Va is supplied to the non-linear circuit (36) to form a control voltage. This control voltage is supplied to the attenuator circuit (35), and the subtraction circuit (31) outputs noise corresponding to the illuminance of the subject. Canceled luminance signal Sy
Is taken out.

In the above description, it is possible to digitize the data after the separation circuit (5). In this case, the A / D converter and the D / A converter of the field memory circuit (72) become unnecessary. Also, the signal Sv or Sy is supplied to the AGC voltage forming circuit (4
A control voltage indicating the illuminance of the subject may be obtained by supplying the same to the same detection circuit as in 1).

〔The invention's effect〕

According to this invention, the taking out noise components S ₃ by utilizing the field correlation, when the illuminance of the subject is low, since the removal of the noise component S ₃ from the luminance signal Sy as k ≒ 1, the low illuminance subject However, noise is not noticeable on the screen.

Further, when the illuminance of the subject is high, since not to feed back the noise component S ₃ as k ≒ 0, even if the noise component S ₃ contains non-field correlation component, can cause motion blur on the screen Absent.

Further, since the value k is changed using the AGC voltage Va, the feedback amount kS ₃ of the noise component S ₃ becomes a value that continuously changes in accordance with the illuminance of the subject, and unnaturalness appears on the screen. Will not occur.

[Brief description of the drawings]

FIGS. 1, 4, and 5 are system diagrams of an example of the present invention, and FIGS. 2, 3 are diagrams for explanation thereof. (1) CCD for imaging, (41) AGC voltage forming circuit, (70)
Denotes a noise reduction circuit, and (72) denotes a field memory circuit.

Claims (1)

(57) [Claims] 1. An AGC circuit for performing AGC on a luminance signal obtained from an image pickup device, and an AG in which a luminance signal output from the AGC circuit is supplied and whose level continuously changes in inverse proportion to the level of this signal.
An AGC voltage forming circuit that forms a C voltage, supplies the AGC voltage to the AGC circuit, and supplies the AGC voltage to a plurality of non-linear circuits; and an aperture correction circuit that performs aperture correction on a luminance signal output from the AGC circuit. A noise reduction circuit that selectively removes a field noise component from a luminance signal output from the aperture correction circuit using a field correlation; and a horizontal noise component having no horizontal correlation of the luminance signal output from the noise reduction circuit. And a vertical noise canceller circuit for removing a vertical noise component having no vertical correlation of the luminance signal output from the horizontal noise canceller circuit. The aperture correction circuit comprises an aperture correction level control attenuator circuit. And the attenuator circuit comprises:
The output of the AGC voltage forming circuit is connected to a first non-linear circuit that outputs a first control signal that increases in a non-linear manner as the output increases, and the amount of attenuation is controlled by the first control signal. The noise reduction circuit includes an attenuator circuit for controlling the level of noise reduction, and the attenuator circuit is supplied with an output of the AGC voltage forming circuit, and increases in a non-linear manner in accordance with an increase in the output. The horizontal noise canceller circuit is connected to a second non-linear circuit that outputs a signal, and the amount of attenuation is controlled by the second control signal. The horizontal noise canceller circuit includes a horizontal noise canceling level control attenuator circuit. An output of the AGC voltage forming circuit is supplied, and a third control signal that increases in a non-linear manner as the output increases is output. The vertical noise canceller circuit includes an attenuator circuit for controlling a level of vertical noise cancellation, and the attenuator circuit is configured to control the AGC voltage generation. A fourth non-linear circuit that is supplied with an output of the circuit and outputs a fourth control signal that increases in a non-linear manner in accordance with the increase in the output; and that the attenuation is controlled by the fourth control signal. Video camera featured.