JP2650162B2 - Video signal processing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video signal processor for digitally processing a television color signal.

[0002]

2. Description of the Related Art FIG. 6 is a block circuit diagram of a conventional video signal processing apparatus. A sampling circuit 1 samples a chroma input signal at a sampling frequency obtained by multiplying a color subcarrier frequency Fsc by four. 2 is a digital color signal processing circuit, 3 is a D / A converter, and 4 is an analog low-pass filter (hereinafter, referred to as "LPF").

[0003] Figures 7 and 8 are diagrams for explaining how signals in the digital color signal processing circuit 2 and the D / A converter 3. In the figure, reference numeral 7 denotes a chroma input signal, which is a carrier chrominance signal obtained by quadrature balanced modulation of a 3.579545 MHz carrier signal in the NTSC system by two color difference signals (RY, BY). Reference numeral 8 denotes a sampling point for sampling the chroma signal 7, and 9 denotes a chroma signal obtained as a result of the D / A conversion.

Next, the operation will be described. The chroma signal 7 is sampled by the sampling circuit 1 at a frequency obtained by multiplying the color subcarrier frequency Fsc by four, and sampling data A to D at each sampling point 8 are obtained. When the digital data A to D obtained as described above are directly subjected to D / A conversion, a chroma signal 9 as shown in FIG. 7 is obtained. Also, the phase difference between the sampling point 8 and the chroma input signal 7 is
In the case of FIG. 8, the chroma signal 9 is as shown in FIG. Next, the chroma signal 9 passes through the LPF 4 and the chroma output signal.
11 is restored.

[0005]

The conventional video signal processing apparatus has to design a fairly complicated filter in order to restore the output chroma signal to a sine wave.
There were problems such as hue shift and color density unevenness. There is also a means to increase the sample frequency itself, but since the signal processing speed itself increases,
It was difficult to realize.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and it is possible to make a chroma output signal close to a chroma input signal without increasing a sample frequency, and to achieve hue shift and color density unevenness. It is an object of the present invention to obtain a video signal processing device capable of suppressing the image quality.

[0007]

In the video signal processing apparatus according to the present invention, since the chroma signal is a sine wave, the digital signal is interpolated using a trigonometric function, and the original digital data is interpolated. The output chroma signal is restored from the obtained data.

[0008]

In the digital data interpolation of the present invention, the chroma signal sampled by 4 Fsc in digital processing is interpolated by 8 Fs
The sampling data of c is used, and this data is restored to a chroma signal. For this reason, more accurate restoration can be performed.

[0009]

FIG. 1 is a block circuit diagram of one embodiment of the present invention. In the figure, reference numeral 5 denotes an operation circuit for performing a trigonometric function operation, and reference numeral 6 denotes an interpolation circuit for interpolating data calculated by the operation between the original data.

FIGS. 2, 3, 4 and 5 are diagrams for explaining the state of the chroma input signal 7 and the chroma signal 9 in the present embodiment. A case will be described in which sampling is performed at four times and the data thus obtained is restored at a frequency eight times as high as fsc. In the figure, 10
Is an interpolation point for performing data interpolation.

Next, the operation will be described. By sampling the chroma input signal 7 at a frequency obtained by multiplying the chrominance subcarrier frequency Fsc by 4, sampling data A to D at each sampling point 8 can be obtained. The arithmetic circuit 5 calculates interpolation data a to d between the obtained digital data A to D, and the interpolation circuit 6 calculates the interpolation data calculated at each interpolation point 10. After interpolating a to d to make the data amount twice as large as the conventional one, it is converted into an analog chroma signal 9 by the D / A converter 3 and carrier recovery is performed by the LPF 4 so that the chroma output signal 11 is obtained. can get.

Here, a method of interpolating digital data A to D will be described. Since the waveform of the chroma signal is always represented by a sine wave, the point to be interpolated can be obtained by a trigonometric function. That is, if a certain phase of the sampled data A is 0 ° , the phase of the sampled data B is 90 ° and the phase of the interpolation data a is 45 °. = Α sin θ, the data B and a are: B = α sin (θ + 90 °) = α cos θ a = α sin (θ + 45 °) = (1 / √2) (α sin θ + α cos θ) = (1 / √ 2) (A + B ).

Similarly, data of b, c and d can be obtained. Specifically, since 1 / {2 = 0.707106... = 0.5 + 0.125 + 0.0625 +...}, Approximation up to the first term of the equation is performed as the arithmetic circuit 5 which can be easily implemented. In order to determine, FIG. 2 or FIG.
When the number of terms is increased, that is, when the coefficient is 1
In the case of / √2 is as shown in FIG. 4 or 5.

In the above embodiment, 8Fsc is used as the carrier restoration frequency. However, the restoration accuracy can be further improved by using a higher frequency and increasing the interpolation data. Further, the relationship of the trigonometric function, the interpolation data of point 10 of the interpolation - although the coefficients of the equation for data a~d was 1 / √2, exhibits a sufficient effect if approximate values.

[0015]

As described above, according to the present invention, the interpolation data is obtained by using the trigonometric function based on the phase relationship between the sampling point 8 and the interpolation point 10.
The chroma output signal is output as a sinusoidal waveform without being deformed by the phase difference between the chroma input signal to be sampled and the sampling clock, so that there is an effect that the change in hue and saturation can be suppressed.

[Brief description of the drawings]

FIG. 1 is a block diagram of the present invention.

[Figure 2] and the waveform of the chroma input signal 7 of the present embodiment, the sump
Ring point 8, chroma output signal 9 and interpolation point
FIG. 10 shows the chroma input signals 0, π / 2, π,
The case where sampling is performed at a phase of 3π / 2 is shown .

[3] and the waveform of the chroma input signal 7 of the present embodiment, the sampling point 8, a diagram showing a chroma output signal 9 and the interpolation point 10, the chroma input signal [pi / 3.pi./4 /
When sampling at 4,5π / 4,7π / 4 phase
Is shown .

FIG. 4 is a diagram showing a waveform of a chroma input signal 7, a sampling point 8, a chroma output signal 9, and an interpolation point 10 according to the present embodiment, wherein 0, π / 2, π,
The case where sampling is performed at a phase of 3π / 2 is shown .

[5] and click Roma input signal 7 waveform of this embodiment, the sump
Ring point 8, chroma output signal 9 and interpolation point
FIG. 10 is a diagram showing π / 4, 3π /
When sampling at 4,5π / 4,7π / 4 phase
Is shown .

FIG. 6 is a block diagram of a conventional video signal processing circuit.

[7] conventional example waveform of the chroma input signal 7 of a diagram showing a sampling point 8 and the chroma output signal 9, click
In the 0, π / 2, π, 3π / 2 phase of the Roma input signal,
This shows a case where the pulling is performed .

[8] and the waveform of the conventional example of click Loma signal 7, the sampling
FIG. 8 shows a point 8 and a chroma output signal 9 ;
Π / 4, 3π / 4, 5π / 4, 7π / 4 places of input signal
This shows a case where sampling is performed in phases .

[Explanation of symbols]

 Reference Signs List 1 sampling circuit 2 digital color signal processing circuit 3 D / A converter 4 low-pass filter 5 arithmetic circuit 6 interpolation circuit

 ────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-62-174874 (JP, A) JP-A-1-234903 (JP, A)

Claims (1)

(57) [Claims] 1. A means for sampling a television color signal at four times the carrier frequency, and C = (1 / √) for two temporally continuous values A and B obtained by the sampling means.
2) means for calculating (A + B) or its approximate value;
Means for interpolating the calculated value C between the sample values A and B and outputting them in the order of A, C and B in time.