JP2500881B2 - Clip circuit for color difference signal - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color difference signal clipping circuit.

[0002]

2. Description of the Related Art FIG. 2 shows a block diagram of an example of a conventional clipping circuit for a color difference signal of a video camera. In FIG. 2, 1 is a flip-flop that latches a color difference signal at a clock frequency, 2 is a flip-flop that latches a lower limit signal set by a microcomputer at a clock frequency, and 3 is an upper limit signal set by a microcomputer at a clock frequency Flip-flop 4 for latching, 4 is a first comparator for comparing the color difference signal and the signal level of the lower limit value, 5 is a second comparator for comparing the color difference signal and the signal level of the upper limit value,
A selector 6 outputs one from the color difference signal, the upper limit value set by the microcomputer, and the lower limit value set by the microcomputer according to the output signals of the first comparator 4 and the second comparator 5,
Reference numeral 7 is a flip-flop that latches the output signal of the selector 6 at the clock frequency.

In the conventional color-difference signal clipping circuit of a video camera constructed as described above, time series R-
The Y and BY signals are input to the flip-flop 1, the lower limit signal set by the microcomputer is input to the flip-flop 2, and the upper limit signal set by the microcomputer is input to the flip-flop 3. All of these three signals are 8-bit coded data, and the RY signal levels are now +100 and B-.
The signal level of Y is fixed at -150, the signal level of the lower limit value is set to -128, and the signal level of the upper limit value is set to +128. The first comparator 4 compares the color difference signal with the lower limit signal level set by the microcomputer, and outputs 0 when the color difference signal level is higher than the lower limit signal level, and outputs 1 when it is lower. Since the RY signal level +100 is higher than the lower limit signal level -128, the first comparator 4 outputs 0, and the BY signal level -150 is lower than the lower limit signal level -128. Therefore, the first comparator 4 is 1
Is output. Similarly, the second comparator 5 compares the color difference signal with the signal level of the upper limit value set by the microcomputer, and outputs 1 when the color difference signal level is higher than the signal level of the upper limit value, and outputs 0 when it is lower. To do. RY signal level +
Since 100 is smaller than the upper limit signal level +128, the second comparator 5 outputs 0, and the BY signal level -1.
Since 50 is smaller than the upper limit signal level +128, the second comparator 5 outputs 0. In the selector 6, the color difference signal and the three signals of the upper limit value and the lower limit value set by the microcomputer are used to output 1 from the output signals of the first comparator 4 and the second comparator 5.
Outputs two signals. That is, when both the outputs of the first comparator 4 and the second comparator 5 are 0, a color difference signal is output, and when the output of the second comparator 5 is 1 and the output of the first comparator 4 is 0 Is the upper limit value, the output of the second comparator 5 is 0, and the first comparator 4
When the output of is 1, the lower limit value is output. Therefore, the output of the selector 6 becomes RY signal level +100 for the RY signal and becomes -128 by being clipped to the lower limit signal level for the BY signal. The output of the selector 6 is input to the flip-flop 7 and output to the processing circuit in the subsequent stage.

[0004]

However, in the above-described conventional configuration, the number of gates is relatively large when the circuit is made into an LSI because the comparator includes two comparators and one selector having three inputs and one output. It has a problem that it becomes a clipping circuit for a large color difference signal.

The present invention solves the above-mentioned conventional problems, and an object thereof is to realize and provide a clip circuit for a color difference signal with a relatively small number of gates.

[0006]

To achieve this object, a color difference signal clipping circuit of the present invention comprises a first selector for outputting one of an upper limit value and a lower limit value signal according to a sign bit of the color difference signal, A comparator that compares the magnitude of the color difference signal with the output signal of the first selector; an exclusive OR circuit that takes the exclusive OR of the output signal of the comparator and the sign bit of the color difference signal; The color difference signal and the second selector that outputs one signal from the output signal of the first selector according to the output signal of the logical OR circuit.

[0007]

The present invention has two 2-inputs 1 by the above-mentioned configuration.
It can be realized by an output selector, one comparator, and one exclusive OR circuit, and the number of gates can be reduced as compared with the conventional circuit including one 3-input, 1-output selector and two comparators. .

[0008]

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of a color difference signal clipping circuit of a video camera according to an embodiment of the present invention. In FIG. 1, reference numeral 1 is a flip-flop that latches a color difference signal at a clock frequency, 2 is a flip-flop that latches a lower limit signal set by a microcomputer at a clock frequency, and 3 is a clock of an upper limit signal set by a microcomputer A flip-flop that latches at a frequency, 8 is a first selector that outputs one of the upper limit and lower limit signals set by the microcomputer according to the sign of the color difference signal, and 9 is the output signal of the first selector 8 and the color difference signal. A comparator 10 for comparing the absolute value and an exclusive OR circuit for taking N exclusive OR of the output signal of the comparator 9 and the sign bit of the color difference signal, 1
Reference numeral 1 is a second selector that outputs one of the color difference signal and the output signal of the first selector 8 according to the output signal of the exclusive OR circuit, and 7 is a flip-flop that latches the output signal of the second selector 11 at the clock frequency. It is

The operation of the color difference signal clipping circuit of the video camera of the present embodiment having the above-described configuration will be described below. The time-series RY and BY signals are input to the flip-flop 1, the lower limit signal set by the microcomputer is input to the flip-flop 2, and the upper limit signal set by the microcomputer is input to the flip-flop 3. All of these three signals are 8-bit coded data, and the RY signal level is +100 and the BY signal level is -150.
The signal level of the lower limit value is set to -128, and the signal level of the upper limit value is set to +128. The first selector 8 outputs the signal of the upper limit value set by the microcomputer when the sign bit of the color difference signal is 0, and outputs the signal of the lower limit value set by the microcomputer when the sign bit of the color difference signal is 1. To do.
Therefore, when the flip-flop 1 outputs the RY signal, the sign bit of the color difference signal is 0, so the first selector 8 outputs the upper limit signal +128, and when the flip-flop 1 outputs the BY signal. , The sign bit of the color difference signal is 1, so the first selector 8 outputs the lower limit signal −128.
Is output. In the comparator 9, the color difference signal and the first selector 8
Of the output signals of the color difference signals are compared and the level of the color difference signal is first
1 is output when the level of the output signal of the selector 8 is higher, and 0 is output when the level is lower. That is, the comparator 9 is R
-Y signal level +100 and upper limit signal level +12
8 is output and 0 is output, and the BY signal level -15
0 is output by comparing 0 with the lower limit signal level −128. The exclusive OR circuit 10 takes the exclusive OR of the output signal of the comparator 9 and the sign bit of the color difference signal. That is,
The exclusive OR circuit 10 compares the RY signal with the comparator 9
Input the output signal 0 of 0 and the sign bit 0 of the RY signal,
Of the output signal of the comparator 9 for the BY signal.
And the sign bit 1 of the BY signal is input and 1 is output.
The second selector 11 outputs 1 from the color difference signal and the output signal of the first selector 8 according to the output signal of the exclusive OR circuit 10.
Output one. That is, the second selector 11 outputs the RY signal +100 because the output signal of the exclusive OR circuit 10 is 0 in the phase of the RY signal, and outputs the RY signal +100 in the phase of the BY signal. Since the output signal is 1, the output signal of the first selector 8, that is, the signal of the lower limit value is output, and B
The -Y signal is clipped to -128. The output of the second selector 11 is input to the flip-flop 7 and output to the processing circuit at the subsequent stage.

As described above, according to this embodiment, two two
The color difference signal can be clipped by the circuit configuration of the selector having one input and one output, one comparator, and one exclusive OR circuit, and the color difference signal can be clipped with a smaller number of gates than the conventional circuit.

[0012]

As described above, the present invention has two 2-inputs 1
Since the clipping circuit can be configured by the output selector, one comparator, and one exclusive OR circuit, the color difference signal can be clipped with a smaller number of gates than the conventional circuit, and its practical effect is large.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a color difference signal clipping circuit according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a conventional color difference signal clipping circuit.

[Explanation of symbols]

 1, 2, 3, 7 Flip-flop 8 First selector 9 Comparator 10 Exclusive OR circuit 11 Second selector

Claims (1)

(57) [Claims] 1. A first selector that outputs one of two signals according to the sign bit of the color difference signal, a comparator that compares the output signal of the first selector with the magnitude of the color difference signal, and the comparison. OR circuit for exclusive ORing the output signal of the color difference signal and the sign bit of the color difference signal, and 1 from the output signal of the color difference signal and the first selector by the output signal of the exclusive OR circuit. A color difference signal clipping circuit including a second selector that outputs two signals.