JPH03166891A - Digital clipper circuit - Google Patents

Abstract

PURPOSE:To attain clipping independently of the phase by clipping a color signal component of an input signal based on outputs of a color signal, clip coefficient and luminance signal clip circuits. CONSTITUTION:A chroma amplitude information signal which is a signal proportional to a chroma level and independent of the hue is inputted to a chroma clip control circuit 7. The circuit 7 receives a luminance signal Y from a luminance signal clip circuit 6 and an adder 14 generates a signal adding the chroma amplitude information signal to the luminance signal Y. Then a coefficient arithmetic circuit 15 detects a quantity of the signal in excess of the clip level Cp and calculates the clip coefficient to control a multiplier 16 of a chroma clip circuit 8. The result of calculation is given to the circuit 8, a multiplier 16 of which multiplies the chroma signal C inputted from the Y/C separator circuit 4 with a clip coefficient calculated by the control circuit 7 and an adder of which 17 adds the inverted result to an output of the circuit 6. Thus, the added signal is outputted to an output terminal 3 as an output video signal.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a digital clipper circuit used in an output shaping section of equipment for synthesizing video images.

[Prior Art] Conventionally, a digital white level clipper circuit is a circuit that outputs a signal at a level of a predetermined set value when an input video signal has a level higher than a predetermined set value, Used in devices that synthesize video signals.

This digital clipper circuit samples a video signal using a sampling pulse, and clips the video signal when the data obtained thereby exceeds a predetermined clipping level.

[Problem to be Solved by the Invention] However, since the conventional digital clipper circuit operates differently from the analog clipper circuit, it has the disadvantage that the color signal of the composite video signal is not clipped at a constant clip level. be.

FIG. 5(a) is a waveform diagram showing the input signal of the digital clipper circuit, and FIG. 5(b) is an analog wave and its sampling pulse, which is an enlarged time axis of the color signal shown as C1 in FIG. 5(a). The waveform diagram shown in Fig. 5(c) is the waveform diagram shown in Fig. 5(c).
FIG. 7A is a waveform diagram showing an analog wave with an enlarged time axis of the color signal indicated by C2 and its sampling pulse;

As shown in FIG. 5(a), the composite video signal is a signal in which a burst color signal component representing color is superimposed on a luminance signal component representing brightness. In this FIG. 5(a),
Since the color signal C1 and the color signal C2 have different hues, even if the degree of saturation with respect to the clip level Cp is the same, their phases are different, and the digital data sampled by the sampling pulse has different values. . In other words, as shown in FIG. 5(b), when the top of the color signal coincides with the sampling pulse,
Even in the conventional digital clipper circuit, proper clipping is performed in which the top of the signal matches the predetermined clipping level Cp, as shown by the broken line in the figure. However, Fig. 5 (
As shown in C), when the top of the color signal and the sampling pulse do not match, in the conventional digital clipper circuit, the top of the signal becomes larger than the predetermined clip level Cp, as shown by the broken line in the figure. Clipping is not performed at an appropriate clip level Cp.

That is, in the conventional digital clipper circuit, the clip level varies depending on the phase difference between the color signal and the sampling pulse. Further, if the sampling pulse is not synchronized with the color burst, there is a problem in that the color fluctuates.

It is also possible to separate the input composite video signal into R, G, and B signals, clip each signal, and then convert it to a composite video signal, but in this case, the scale of the hardware A new problem arises in that the size increases.

The present invention has been made in view of such problems, and includes:
It is an object of the present invention to provide a digital clipper circuit that is realized with small-scale hardware and whose clip level does not vary depending on hue.

[Means for Solving the Problems] A digital clipper circuit according to the present invention includes a Y/C separation circuit that separates an input signal into a luminance signal and a color signal, and a Y/C separation circuit that separates an input signal into a luminance signal and a color signal.
a luminance signal clipping circuit that clips the luminance signal component of the input signal based on the luminance signal separated by the /C separation circuit and a clip level setting input; a chroma level detection circuit that detects the amplitude of the color signal; a clipping control circuit that calculates a clipping coefficient based on the luminance signal, the clipping level setting input, and the output signal of the chroma level detection circuit; The present invention is characterized in that it includes a chroma clip circuit that clips color signal components.

[Operations] In the present invention, the luminance signal clipping circuit performs clipping on the luminance signal component of the input signal. Further, a Y/C separation circuit separates the input signal into a color signal and a luminance signal. And, with the clip control circuit,
The amount by which the color signal exceeds the clip level is calculated from the amplitude of the color signal, the clip setting input, and the luminance signal, and a clip coefficient is sent to the chroma clip circuit.

The chroma clipping circuit clips the color signal by multiplying the color signal by this clipping coefficient.

Clipping of the color signal can be performed, for example, by multiplying the color signal by a clipping coefficient, inverting the phase of the signal, and adding the result to the output of the luminance signal clipping circuit. This makes it possible to obtain signals in which the luminance signal and the chrominance signal are each clipped. In this case, the luminance signal and clip setting input are hue-independent signals. Therefore, by inputting the amplitude of the color signal to the chroma clipping circuit as a signal that is proportional to the chroma level and does not depend on the phase, it is possible to avoid variations in the clip level depending on the phase. In order to obtain such a signal, for example, the color signal may be separated into an I signal and a Q signal, and the degree of saturation of the color signal may be calculated using the processed signal and the Q signal.

Further, in the present invention, the color signals are R, G. Since the color signal is clipped without separating it into B signals, it can be realized with small-scale hardware.

[Embodiments] Next, embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a block diagram showing a digital clipper circuit according to an embodiment of the present invention, and FIG. 2 is a block diagram showing the digital clipper circuit in more detail.

The video signal supplied to the input terminal 1 is input to the Y/C separation circuit 4 and the luminance signal clipping circuit 8.

The Y/C separation circuit 4 separates this video signal into a luminance signal Y and a chroma signal C. This luminance signal Y is input to a luminance signal clipping circuit 6. The brightness signal clip circuit 6 has a comparator 9, which compares the clip level Cp input from the clip level setting terminal 2 with the brightness signal Y. Then, when the luminance signal Y is smaller than the clip level Cp, the video signal is output to the chroma clip circuit 8. Furthermore, when the brightness signal Y is larger than the clip level Cp, the clip level Cp is output instead of the video signal. The luminance signal clipping circuit 6 thus clips the luminance signal component of the video signal. Note that the delay circuit 11 delays the video signal by a time corresponding to the signal delay time by the Y/C separation circuit 4 and the comparator 9.

On the other hand, the chroma signal C separated by the Y/C separation circuit 4 is
The signal is input to a chroma level detection circuit 5 and a chroma clip circuit 8. The chroma level detection circuit 5 converts this chroma signal C into a chroma amplitude information signal. This chroma amplitude information signal is the result of, for example, separating the chroma signal C into a ■ signal and a Q signal, and calculating the square root of the I signal component and the Q signal component. The chroma amplitude information signal thus obtained is a signal that is proportional to the chroma level and independent of hue.

The chroma amplitude information signal is input to the chroma clip control circuit 7. The chroma clipping control circuit 7 inputs the luminance signal Y from the luminance signal clipping circuit 6, and generates a signal by adding the chroma amplitude information signal to the luminance signal Y at the adder 14. Then, the coefficient calculation circuit 15 detects the amount by which this signal exceeds the clip level Cp, and calculates a clip coefficient for controlling the multiplier 16 of the chroma clip circuit 8.

This calculation result is given to the chroma clip circuit 8. The chroma clip circuit 8 multiplies the chroma signal C input from the Y/C separation circuit 4 by the clip coefficient calculated by the chroma clip control circuit 7 in a multiplier 16, inverts the phase, and clips the luminance signal by an adder 17. Add to the output of circuit 6. Then, this added signal is outputted to the output terminal 3 as an output video signal. Note that the delay circuit 13
is provided to match the delay time between the clip coefficient sent from the chroma clip control signal 7 and the chroma signal C sent from the Y/C separation circuit 4. Similarly, the delay circuit 12 is a circuit provided to match the delay time between the output of the luminance signal clipping circuit 6 and the clipped chroma signal.

In the digital clipper circuit of this embodiment configured as described above, the video signal input to the video signal input terminal 1 is converted into a clip input to the clip level setting input terminal 2, as shown in the middle part of FIG. If it is larger than the level Cp, the luminance signal clipping circuit 6 outputs the clipping level Cp to the chroma clipping circuit 8. As a result, I
The video signal of the portion is clipped at the clip level Cp.

In addition, the chroma clip control circuit 7 adds the luminance signal Y output from the luminance signal clip circuit 6 and the chroma level output from the chroma level detection circuit 5, and when the added signal exceeds the clip level Cp. Detect amount.

FIG. 4 is a waveform diagram showing a signal obtained by adding the luminance signal Y and the chroma amplitude information signal by the chroma clip control circuit 7 with respect to the video signal of the portion H in FIG. In addition,
The broken line indicates the clip level Cp.

The chroma amplitude information signal is a signal with an amplitude A, and the signal obtained by adding this chroma amplitude information signal and the luminance signal Y exceeds the clip level Cp by an amplitude B. In this case,
By setting the amplitude of the chroma signal C to A-B, the chroma signal C can be set to the clip level Cp. In other words, as shown in equation (1) below, the chroma clip circuit 8
What is necessary is to determine the amplification factor G of .

G= (A-B)/A= 1-(B/A)...(1)
Therefore, the coefficient calculation circuit 16 of the chroma clipping control circuit 7 sets the clipping coefficient 01 to B/A and sends this clipping coefficient G1 to the multiplier l6 of the chroma clipping circuit 8. The chroma clipping circuit 8 multiplies the chroma signal C by this coefficient 01, inverts the phase, and adds the luminance signal to the clipped video signal.

As a result, the digital clipper circuit of this embodiment can output a composite video signal clipped at a predetermined level, regardless of hue (phase).

On the other hand, if the video signal input to the video signal input terminal 1 is smaller than the clip level Cp input to the clip level setting input terminal 2, the luminance signal clip circuit 6 to the chroma clip circuit 8 is connected to the video signal input terminal 1. The video signal input to is output as is. Further, the clipping coefficient output from the chroma clipping control circuit 7 to the chroma clipping circuit 8 is O, and the amplification factor G of the chroma clipping circuit 8 is equal to 1. Therefore, the video signal input to the video signal input terminal 1 is sent to the video signal output terminal 3 without deterioration.

Note that although this embodiment has been described in the case of white clipping, phase-independent clipping can be performed similarly in the case of black clipping.

[Effects of the Invention] As explained above, according to the present invention, an input signal is separated into a color signal and a luminance signal, a clipping coefficient is calculated from the amplitude of the luminance signal, a clip level signal, and a color signal, and the clipping coefficient is Since the color signal is clipped based on the color signal, it is possible to clip the input signal appropriately without depending on the hue using a small-scale circuit.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a digital clipper circuit according to an embodiment of the present invention, FIG. 2 is a block diagram showing the digital clipper circuit in more detail, and FIG. 3 is a waveform showing an example of an input composite video signal. 4 is a waveform diagram showing a signal obtained by adding the luminance signal Y of the chroma clipping control signal circuit and the chroma amplitude information signal. FIG. 5(a) is a waveform diagram showing the input signal to the digital clipper circuit. Figure 5 (b
) is a waveform diagram showing the analog wave and its sampling pulse, which is an enlarged version of the color signal indicated by 01 in Fig. 5(a);
FIG. 5(c) is a waveform diagram showing an enlarged analog wave of the color signal shown at 02 in FIG. 5(a) and its sampling pulse. 1: Video signal input terminal, 2; Clip level setting input terminal, 3; Video signal output terminal, 4; Y/C separation circuit, 5;
Chroma level detection circuit, 6; luminance signal clipping circuit, 7
; chroma clip control circuit, 8; chroma clip circuit,
9; Comparator, 11.12, 13; Delay circuit, 14.17
; Adder, 15; Coefficient calculation circuit, 16; Multiplier

Claims (2)

[Claims] (1) Y/C that separates the input signal into luminance signal and color signal
a separation circuit; a brightness signal clipping circuit that clips the brightness signal component of the input signal based on the brightness signal separated by the Y/C separation circuit and a clip level setting input;
a chroma level detection circuit that detects the amplitude of the color signal;
a clipping control circuit that calculates a clipping coefficient based on the luminance signal, the clipping level setting input, and the output signal of the chroma level detection circuit; and a clipping control circuit that calculates a clipping coefficient based on the chrominance signal, the clipping coefficient, and the output of the luminance signal clipping circuit; 1. A digital clipper circuit comprising: a chroma clip circuit that clips a color signal component of the digital clipper circuit. (2) The chroma level detection circuit separates the color signal into an I signal and a Q signal, and calculates the degree of saturation of the color signal using the I signal and Q signal. 2. The digital clipper circuit according to claim 1, wherein the signal is multiplied by the clipping coefficient, its phase is inverted, and the signal is added to the output of the luminance signal clipping circuit for output.