JPS63117589A - Video signal processing circuit - Google Patents

Abstract

PURPOSE:To reduce fogging at a high chromaticity picture by detecting the density of a color from a color difference signal so as to control the amplification factor of a luminance signal high frequency component. CONSTITUTION:A matrix circuit 13 outputs red/blue color difference signals R-Y, B-Y from a video signal from a TV camera and clamp circuits 21, 22 detect the densities of red and blue colors respectively. Then the detected density is mixed in a non-additive mixing circuit 23 to control the gain of the amplifier of a countour correction circuit 24 and the more darker the color becomes, the larger the amplification factor of the high frequency component of the luminance signal becomes. In applying proper correction to the high frequency component of the luminance signal, the fogging of countour of the high chromaticity picture is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a video signal processing circuit intended to improve image quality in a color video camera.

[Conventional technology]

FIG. 6 is a block diagram showing an example of the configuration of a signal processing circuit of a conventional color video camera. In this Figure 6, ■
is an input terminal, 2.3 is a low-pass filter, and 4 is a color signal separation circuit.

An electric signal photoelectrically converted from an image sensor is input to the input terminal 1, and this electric signal is sent to an adder circuit 17 via a low-pass filter 2, a gamma correction circuit 9, and a contour correction circuit 15. In addition, the signal is manually inputted to the matrix circuit 13 via the low-pass filter 3 and the gamma correction circuit IO.

Furthermore, the electrical signal at the input terminal 1 is filtered through a low-pass filter 5.
6, gain adjustment circuits 7 and 8, and gamma correction circuits 11 and 12, respectively, and are manually inputted to the matrix circuit 13.

The output of the matrix circuit 13 is manually inputted to the modulation circuit 14, and the modulation circuit 14 and the addition circuit 1
The output of the synchronizing signal generating circuit 16 is input to the input terminal 7. The output of the adder circuit 17 is led out to an output terminal 18.

Next, the operation will be explained. An electrical signal photoelectrically converted from the image element is applied to the input terminal l.

Due to cost constraints, home color video cameras are usually configured with one imaging element, and input terminal 1 receives a high frequency signal modulated by baseband components and color signals (or color difference signals). Ingredients are input in mixed form.

The low-pass filter 2 is a low-pass filter that cuts the modulated component and higher frequency components, and separates the luminance signal component Yw.

Further, the low-pass filter 3 is a narrow-band low-pass filter, and separates the luminance signal YL for forming the color difference signals RY and BY. Generally, in the case of a home video camera, the frequency is set to about 500K) Iz to I MHz.

The color signal separation circuit 4 is a circuit that separates color signals, and separates the modulated components into a red (R) signal and a blue (B) signal. The red and blue signals separated by the color signal separation circuit 4 are input to the gain adjustment circuit 7.8 through low-pass filters 5.6 (both having the same frequency characteristics as the low-pass filter 3).

In the case of achromatic color, the gain adjustment circuits 7 and 8 are used for the color difference signal R-
White balance adjustment is performed so that Y and B-Y become zero.

Further, the low-pass filters 2.3 are respectively sent to gamma correction circuits 9.10, and the outputs of the gain adjustment circuits 7.8 are also sent to gamma correction circuits 11 and 12, respectively.

These gamma correction circuits 9 to 12 are circuits for correcting the gamma characteristics of the cathode ray tube.

A luminance signal Y separated by a low-pass filter 2 and passed through a gamma correction circuit 9. The image quality is corrected by the contour correction circuit.

Further, the color signal is subjected to gamma characteristic correction in gamma correction circuits 10 to 12, and then passed through a matrix circuit 13 to receive a color difference signal R-
It becomes Y and B-Y.

The color difference signals R-Y and B-Y are sent to the modulation circuit 14. A subcarrier color burst signal for modulation from a synchronization signal generation circuit 16 is input to this modulation circuit 14, and this subcarrier color burst signal causes the modulation circuit 14 to
modulates the color difference signals R-Y and B-Y and outputs them to the adder circuit 17.

The synchronization signal generation circuit 16 generates horizontal and vertical synchronization signals and the above-mentioned subcarrier color burst signals, and these horizontal and vertical synchronization signals and color burst signals are sent to the adder circuit 17.
sent to.

As a result, the adder circuit 17 receives these horizontal and vertical synchronizing signals.
The color burst signal, the luminance signal output from the contour correction circuit 15, and the output of the modulation circuit 14 are mixed and sent to the output terminal 18.
Output to.

The above is an example of a commonly used color video camera. Another disadvantage of the television system is that the gamma characteristics of the cathode ray tube are non-linear, and the color signal is narrow band, so the light output of the cathode ray tube has fewer high-frequency components when the color is dark, causing it to become blurry. It has the disadvantage of being visible.

Regarding this, see NHK Giken Monthly Report 55.11 "Reducing blur in color illumination images - Proposal for improving the resolution of high-chroma images"
'' (pages 447 to 482).As an improvement method, it has also been proposed to add a high frequency component of the color difference signal to the luminance signal.

This proposal was made in three tubes for broadcasting, and the red (R)
, blue (B), and green (G) signals are all broadband, so good correction can be made.

However, in the case of a home video camera, the color signal has a narrow band as described above, and there is no high frequency component, so this method cannot be applied.

[Problem that the invention seeks to solve]

As is clear from the above, conventional video cameras have the drawback that images appear blurred when the saturation is high.

The present invention was made to solve such problems, and an object of the present invention is to obtain a video signal processing circuit that can reduce blur in high chroma images.

[Means for solving problems]

The video signal processing circuit according to the present invention has a color difference signal R-Y.
, B-Y or G-Y, and a means for varying the amplification degree of the high frequency component of the luminance signal based on the output of the color density detection means. It is something.

[For production]

In this invention, the image quality is corrected by detecting the color density from the color difference signal R-Y, B-Y, or G-Y and controlling the magnitude of the high frequency component of the luminance signal.

〔Example〕

Embodiments of the video signal processing circuit of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of one embodiment. In FIG. 1, the same parts as in FIG. 6 will be described with the same reference numerals.

FIG. 1 shows the functions of the matrix circuit 13 and subsequent parts of FIG. 6. The input sides of the matrix circuit 13 and the contour correction circuit 24 are similar to those shown in FIG.

Color difference signals R-Y and B output from the matrix circuit 13
-Y is input to the modulation circuit 14 and clamp circuits 21 and 22, and the outputs of the clamp circuits 21 and 22 are input to the non-addition mixing circuit 23.

The output of the non-additive mixing circuit 23 is output to the contour correction circuit 24, and the brightness signal component Yw is input to the contour correction circuit 24.

Further, the output of the synchronizing signal generation circuit 16 is added to the modulation circuit 14 and the addition circuit 17, and the output of the modulation circuit 14 and the output of the contour correction circuit 24 are also added to the addition circuit 17. These parts are similar to those shown in FIG.

Next, the operation of this invention will be explained. The matrix circuit 13 receives narrowband R, B, and YL multiplied signals, and outputs color difference signals R-Y and B-Y.

Up to this point, the operation is the same as in the conventional example. An example of the waveform is shown in FIG. Figure 2 (al is the waveform of the luminance signal Y. It is a signal in the order of W (white), Ye (yellow), and B (blue), and the Ye and B parts contain high frequency components. Suppose that

This luminance signal ¥8 is input to the contour correction circuit 24. The output waveform of the matrix circuit 13 is shown in the second output) and in Figure 2 (C
Shown in 1. FIG. 2 (bl is the color difference signal RY, the second
Figure (C1 shows the signal of the color difference signal B-Y. These color difference signals RY and B-Y have narrow bands, so there is no high frequency component. This color difference signal RY.

B-Y is modulated by a modulation circuit 14 and becomes a carrier color signal.

In addition, the color difference signals R-Y and B-Y are input to clamp circuits 21 and 22, respectively, and the negative sides of the color difference signals R-Y and B-Y are clipped by the clamp circuits 21 and 22, respectively, and the non-addition mixing circuit 23, this non-adding mixing circuit 23
At the output end of , as shown in Figure 2 (dl),
, FIG. 2 (the waveforms are obtained by clipping and adding the negative sides of the color difference signals R-Y and B-Y shown by c+).

This waveform is applied to the contour correction circuit 24. The contour correction circuit 24 receives a brightness signal Y. is input, and this luminance signal Y1. l is controlled by the output of the non-addition mixing circuit 23.

As a result, a waveform as shown in FIG. 2 (el) is output from the contour correction circuit 24 and added to the adder circuit 17. As can be seen by comparing the waveforms in FIG. It can be seen that the high frequency component of the B section in the luminance signals Yl, I is increased.

In this way, when the color signal component is large, the high frequency component is increased to improve image blur.

This part will be explained in more detail. FIG. 3 is a block diagram showing the internal configuration of the contour correction circuit 24. In FIG. 3, 31 and 32 are a bypass filter and a low-pass filter, respectively, to which the luminance signal 1/W is input.

By passing the bypass filter 31, the luminance signal 1
The low frequency component of /W is separated, and the high frequency component is removed from the core circuit 33.
In addition, the luminance signal 1 is also filtered by the low-pass filter 32.
The high frequency component of /W is separated and the low frequency component is added to the adder circuit 35.

The above-mentioned coring circuit 33 cuts noise in the large area portion of the output of the bypass filter 31 to improve the S/N ratio, and outputs the result to the variable gain amplifier circuit 34. This variable gain amplifier circuit 3
4 receives the output of the non-addition mixing circuit 23 of FIG. 1, and the amplification degree is high when the color is dark, and the amplification degree is low when the color is light. FIG. 4 shows the characteristics of the relationship between the control voltage and gain of this variable gain amplifier circuit 34.

The output of this variable gain control circuit 34 and the low pass filter 3
The outputs of 2 are added by an adder circuit 35 and output to the adder circuit 17 in FIG.

Figure 5 shows clamp circuits 21 and 22 and non-addition mixing circuit 23.
FIG. In this Figure 5,
The waveform of the color difference signal RY (FIG. 3(b)) is input to the input terminal 41 manually.

Further, the waveform of the color difference signal B-Y is input to the input terminal 42. Furthermore, a clamp pulse is input to the input terminal 43. Capacitor 44.45 and transistor 46.47
, resistors R1 and R2 constitute a clamp circuit 21.22.

That is, the color difference signal R-Y is applied to the collector of transistor 46 through capacitor 44, and is applied to the collector of transistor 46 through capacitor 44.
A clamp pulse is input to the base of transistor 46 through resistor R1, and the emitter of transistor 46 is connected to resistors 48 and 49.
The clamp circuit 2 is connected to the connection point P1 with the clamp circuit 2.
1.

Similarly, the color difference signal B-Y is applied to the collector of transistor 47, and the resistor R2 is applied to the base of transistor 47.
A clamp pulse is applied through, the emitter of which is connected to connection point P1 and grounded via a capacitor 50, thus forming a clamp circuit 22.

Resistors 48 and 49 are connected in series between power supply terminal 55 and ground, and the clamp potential is determined by resistors 48 and 49 and capacitor 50.

On the other hand, the transistors 51 to 53 are the main components of the non-addition mixing circuit 23, and the bases of the transistors 51 and 52 have color difference signals R-Y and B-'?, respectively. is added,
A clamp reference potential is applied to the base of the transistor 53 from the connection point Pl, and the emitters of the transistors 51 to 53 are commonly connected to the base of the transistor 54.
The highest potential portion of the three color difference signals RY, B-7, and clamp reference potential is output to the base of the transistor 54. These waveforms are shown in Figure 2tb+
~ As shown in Figure 2 fdl.

The emitters of transistors 51-53 are grounded via resistor R3. Collectors of the transistors 51 to 53 are connected to a power supply terminal 55.

The transistor 54 is an emitter follower, and also serves as temperature compensation for the base-emitter potentials (1) of the transistors 51-53. The collector of this transistor 54 is grounded, and the emitter is connected to a power supply terminal 55 and an output terminal 56 via a resistor R4.

The signal output from this output terminal 56 serves as a control signal for the variable gain amplifier circuit 34 shown in FIG.

By pumping the negative side in this way, the control voltage increases in the case of low luminance and high chroma, and blurring of the image can be reduced.

Above, we have explained an example in which the negative sides of the color difference signals R-Y and B-Y are clipped and used as control signals, but the color difference signals G-Y may also be used, and the gain can also be set appropriately for the negative sides. You can.

〔Effect of the invention〕

As explained above, this invention has color difference signals R-Y, B-
Since the magnitude of the high frequency component of the luminance signal is controlled by detecting the roughness of the approximate color from Y or G-Y, a simple circuit reduces image blurring at high saturation, which is a drawback of the television system. image quality can be improved.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an embodiment of the video signal processing circuit of the present invention, Fig. 2 is a signal waveform diagram of each part for explaining the operation of the video signal processing circuit as above, and Fig. 3 is the video signal processing circuit as above. 4 is a characteristic diagram showing the relationship between the control voltage and the gain of the variable gain amplifier circuit in the contour correction circuit, and FIG. 5 is a block diagram showing the internal configuration of the contour correction circuit in the above contour correction circuit. A circuit diagram showing the specific circuit configuration of the non-additive mixing circuit part,
FIG. 6 is a block diagram of a conventional video signal processing circuit. 13... Matrix circuit, 14... Modulation circuit, 16
... Synchronization signal generation circuit, 17... Addition circuit, 21.
22... Clamp circuit, 23... Non-addition mixing circuit,
24... Contour correction circuit. Note that the same reference numerals in the figures indicate the same or corresponding parts. Agent Masu Oiwa 1 No. 2 Figure WYe B No. 3 Kakuzu 4 35: Addition i to Figure 4 Can Lira sr2 ≧ Yu 1koku E- Procedural amendment (spontaneous) 1. Indication of case Patent application 1986 -263164 No. 2,
Name of the invention: Video signal processing circuit 3, person responsible for correction Representative Moriya Shiki\ko] 1. ...' 5, Detailed explanation of the invention in the specification subject to amendment 6, Contents of amendment (1) r /WJ'trYwJ on page 11, line 3 of the specification
I am corrected. (2) “Low frequency component of 1/w J i r
``YW high frequency component'' is corrected. (3) rY the “high frequency component of seat 1” on page 11, line 7. ``The low frequency component of'' is corrected.

Claims (4)

[Claims] (1) Narrowband color difference signal R-Y, B-Y or G-Y
and a variable gain amplifier that changes the amplification degree of the high-frequency component of the luminance signal. and contour correction means that controls the gain of the variable gain amplifier to be large and operates so that the gain of the variable gain amplifier becomes small when the color is light. . (2) Color density detection means outputs color difference signals R-Y, B-Y,
2. The video signal processing circuit according to claim 1, comprising a clipping circuit that clips the positive or negative side using one or more of G-Y. (3) Color density detection means uses color difference signals R-Y, B-Y, G
2. The video signal processing circuit according to claim 1, wherein the video signal processing circuit is constructed by performing full-wave rectification of at least one of Y. (4) The video signal processing circuit according to claim 1, wherein the color density detection means clips the plurality of color difference signals using a non-additive mixing circuit.