JPS6255760B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for suppressing chroma signals that are undesirable from the viewpoint of visual S/N in a color video camera or the like without giving an unnatural feeling. Concerning a suppression device.

There are two undesired areas in the above-mentioned color video camera and the like: near the black level and near the white peak of the luminance signal. Generally, when a color video camera captures a scene that is relatively dark and has few colors, the image reproduced by the television receiver has almost no color-related signals, and only the noise in the image increases. There is a phenomenon.
This phenomenon is caused by a change in the signal-to-noise ratio (S/N) of the composite color video signal. Furthermore, if a color signal exceeds 100% of the white level of the luminance signal, the white balance will be disrupted due to the unevenness of the saturation values of the R, G, and B electron beams in the image pickup tube, resulting in false color signals and significant image quality. It damages the As mentioned above, the S/N ratio for the chroma signal near the black level and the white peak of the luminance signal is poor, and visually better results can be obtained by suppressing the chroma signal.

Conventionally, the above-described suppression near the black level and near the white peak was performed linearly, so it was possible to avoid visual unnaturalness with respect to the chroma signal at the time of suppressing the near black level and the white peak. I couldn't do it.

The present invention has been made in view of the above-mentioned circumstances, and the present invention has been made in view of the above-mentioned circumstances. The visual unnaturalness of the chroma signal is reduced by simultaneously suppressing both chroma signals below and above the above-mentioned level in the direction, and gradually suppressing both of the above-mentioned cases. In addition, it is an object of the present invention to provide a chroma signal suppressing device that has a simple circuit configuration consisting of a level detection means and a multiplication means, thereby reducing the size and stabilization of the circuit.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings, and the explanation will be given on the case where the above-described suppression in the black direction and the white direction is performed simultaneously.

FIG. 1 is a block diagram showing the circuit configuration of an embodiment according to the present invention, and FIG. 2 is a waveform diagram for explaining its operation. Note that waveforms 1 to 5 shown in FIG. 2 are the same as waveforms 1 to 5 shown in the block diagram of FIG.
The waveform corresponding to the point is shown.

In FIG. 1, T ₁ is an input terminal to which a luminance signal E _Y whose DC component has been reproduced is supplied, and T ₂ is an output terminal to which a chroma signal with undesired regions suppressed is output. 1 is a first level detector for detecting a luminance signal below a predetermined level in the black direction, and 2 is a second level detector for detecting a luminance signal above a predetermined level in the white direction. and 3 is a multiplier which receives the output signals from the first and second level detectors 1 and 2 and is composed of, for example, a double balanced gain control amplifier. Note that e _C is a chroma signal supplied to the other input of the multiplier 3.

Thus, the luminance signal E _Y shown in _FIG . . As shown in FIG. 2, the output of the first level detector 1 has an output voltage of E _p1 (“0” signal output) for a luminance signal lower than the suppression level E _i1 in the black direction. And the level E _i1 mentioned above
For the above luminance signal, the output voltage of E _p2 (“1”
signal output) is obtained. Furthermore, as shown in FIG. 2 and 3, the output of the second level detector 2 has an output voltage of E p1 for a luminance signal lower than the suppression level E _i2 in the white direction, and an output voltage of E _p1 which is equal to or higher than the level E _i2 described above. An output voltage of E _p2 is obtained for a luminance signal of . Note that the first and second level detectors 1 and 2 described above are
As will be described later, the output changes from "0" to "1" or from "1" to "0" using a resistor interposed between the emitters of the differential amplification transistor, which is composed of a differential amplifier consisting of emitter coupling. It is constructed to have transient characteristics.

The output from the first level detector 1 (see FIG. 2 2) and the output from the second level detector 2 (see FIG. 2 3) described above are each supplied to one input terminal of the multiplier 3. be done. The other input terminal of the multiplier 3 is supplied with a chroma signal e _C as shown in FIG. 2 . Note that the waveform of the chroma signal e _C shown in FIG. 2 above is shown by way of example in the case where only one color of R (red) is imaged. As mentioned above, when the multiplier 3 is supplied with the chroma signal e _C (see FIG. 2, 4) together with the signals from the first and second level detectors 1 and 2 (see FIG. 2, 2 and 3), the From the output terminal _T2, the chroma signals below the predetermined suppression level in the black direction and above the predetermined suppression level in the white direction, as shown in FIG. 2, are gradually suppressed from the point of suppression. An output signal is obtained. That is, in FIG. 2 5, T ₁
(in the black direction) and T ₂ (in the white direction) are suppressed periods in the undesired region of the chroma signal, and at this time, the suppression is not carried out linearly at the point of suppression, but gradually and gradually. It can be done.
This includes the first and second level detectors 1,
This is because 2 has transient characteristics upon suppression. Fig. 2 5' shows the output waveform of the multiplier 3 when the above suppression is performed linearly, and in this case, visual unnaturalness with respect to the chroma signal at the time of suppression is unavoidable. It is something.

In the above embodiment, the case where the suppression of the vicinity of the black level and the vicinity of the white peak is performed simultaneously is explained, but it goes without saying that this can also be carried out by performing the suppression of the vicinity of the black level and the suppression of the vicinity of the white peak separately. When performing the above suppression separately, the level detecting means detects a luminance signal below a certain level near the black level or a luminance signal above a certain level near the white peak, and the detection period is "0". It can be implemented as a configuration in which a "1" signal is output and a "1" signal is output during other periods.

FIG. 3 is an example of an actual circuit according to an embodiment of the present invention. Although FIG. 3 only shows a circuit that detects the white peak side of the luminance signal and gradually suppresses the chroma signal near the white peak, a similar circuit configuration detects the black level side and suppresses the chroma signal near the white peak. It is possible to gradually suppress the chroma signal near the level, or alternatively, by providing another similar circuit to simultaneously detect the black level side and the white peak side, the chroma signal near the black level and the white peak side in the undesired area can be suppressed. It is also possible to gradually suppress the signal at the same time.

The level detector is composed of a differential amplifier in which transistors Q1 and Q2 are emitter-coupled, and each of the emitters of the transistors Q1 and Q2 has a resistor R1 and a resistor R1 for providing transient characteristics during suppression.
R2 is interposed. It goes without saying that the suppression transient characteristic adjustment resistors R1 and R2 described above can also be implemented as variable resistors. The base of one transistor Q1 constituting the above differential amplifier is supplied with a luminance signal E _Y whose DC component has been regenerated from an input terminal T ₁ . Also, the other transistor Q
A voltage that sets the suppression level on the white peak side from the connection point between the resistors R4 and R5 is supplied to the base of the resistors R4 and R5. 3 is a multiplier composed of well-known, for example, double balanced gain control amplifiers, and ~
The terminal has a chroma signal e as shown in Fig. 2.
_C is supplied. In addition, the terminal of the multiplier 3 is
Transistor Q2 constituting the above level detector
and the connection point between resistors R6 and R7, and the terminal is connected to the connection point between resistors R8 and R9. An output terminal _T2 is connected to the terminal, from which an output as shown in FIG. 2 is taken out, in which the chroma signal in the undesired region near the white peak is gradually suppressed. Multiplier 3 above
When the potential difference between the ~ terminals is zero, its output is also zero, and an output corresponding to the gain of the amplifier appears only when a potential difference occurs between the ~ terminals.

Therefore, when the transistor Q2 is in the off state (at this time, the transistor Q1 is in the on state), the level of the luminance signal _E resistors R6, R7, R8, and R so that the voltage at the terminal of the multiplier 3 becomes equal to the voltage at the terminal when
By setting the resistance value of each of the multipliers 9, the output of the multiplier 3 can be set to zero, and chroma signals having a predetermined level or higher in the vicinity of the white peak can be gradually suppressed. Note that during the period in which the level of the luminance signal _E A potential difference occurs between the voltage at the connection point of the resistors R8 and R9, that is, the potential difference occurs between the terminals of the multiplier 3.
An output is obtained from output terminal T _{2 of} . As described above, the chroma signal is not suppressed during the period in which the level of the luminance signal E _Y does not reach the predetermined suppression level in the white direction, and the level of the luminance signal E _Y The chroma signal can be gradually suppressed when it exceeds the suppression level.

Although only the suppression on the white peak side has been described above, suppression on the black level side can also be performed using a circuit configuration completely similar to that shown in FIG. In this case, by setting the resistance values of each of the resistors R6, R7, R8, and R9 so that the voltage at the terminal of the multiplier 3 is equal to the voltage at the terminal when the transistor Q2 is in the on state, The black level side can be suppressed in the same manner as described above. In order to suppress this black level side, a positive horizontal blanking signal is supplied to the connection point between the emitter of the transistor Q1 and the resistor R1 through a series circuit of a resistor and a diode, and the trailing edge of the horizontal synchronizing signal is To prevent an inserted color burst signal from being suppressed.

As described above, according to the present invention, the chroma signal in the undesired region is gradually suppressed, so that the image at the time of suppressing the chroma signal is better than that in which the suppression is performed linearly. It is possible to provide a chroma signal suppression device that can appear natural.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the device according to the present invention, FIG. 2 is a waveform diagram for explaining one embodiment of the present invention, and FIG. 3 is an example of an actual circuit of one embodiment of the present invention. be. 1, 2... Level detector, 3... Multiplier, Q1, Q
2...Transistor for differential amplification, R1, R2...Resistance for adjusting transient characteristics.

Claims (1)

[Claims] 1 Detects a luminance signal above a certain level near the white peak or a luminance signal below a certain level near the black level, and outputs a “0” signal during the detection period and a “1” signal during other periods. and a multiplication means for multiplying the output from the level detecting means by the chroma signal, and suppressing the chroma signal in an undesired region, wherein the level detecting means is configured to suppress the chroma signal in an undesired region. The transient when the output changes from "0" to "1" or from "1" to "0" is controlled by a resistor interposed between the emitters of the transistors constituting the differential amplifier. A chroma signal suppression device characterized by controlling characteristics.