JPH04332290A - Chrome sub-nyquist sampling method - Google Patents

Abstract

PURPOSE:To provide a chroma sub-Nyquist sampling method of a reproduction system without any pseudo outline-shaped disturbance, as for the sub-Nyquist sampling of a VTR chrome signal. CONSTITUTION:The output of a sub-Nyquist sampling part 4 is transmitted through line memories 5 and 6 in order to prepare a 1H delay signal and a 2H delay signal. This device is equipped with a correlation detecting part 7 which searches the absolute value of a difference between a non-delay signal and the 1H delay signal, and the absolute value of the difference between the 1H delay signal and the 2H delay signal. Then, when the former is smaller than the latter, the non-delay signal and the 1H delay signal are used as reproduction signals, and when the former is larger than the latter, the 1H delay signal and the 2H delay signal are used as the reproduction signals. And also, this device is equipped with switches 8 and 9.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chroma sub-Nyquist sampling method for expanding the band of a chroma signal in a video tape recorder.

0002

2. Description of the Related Art In recent years, televisions have become larger and wider, and video tape recorders (hereinafter referred to as VTRs) are required to have high image quality to meet these demands.

Conventionally, the band of chroma signals in VTRs has been approximately 350 kHz, which is extremely insufficient for larger and wider screens.

[0004] The chroma sub-Nyquist sampling method aims to expand the band of the chroma signal in the above-mentioned VTR and obtain sufficient chroma image quality for larger and wider screens, and is currently not in practical use. It is progressing.

The conventional chroma sub-Nyquist sampling method will be explained below. 3 and 4 are block diagrams showing the configuration of a conventional chroma sub-Nyquist sampling circuit, with FIG. 3 showing a recording system and FIG. 4 showing a reproduction system. In addition, FIG. 5(a) shows the sub-Nyquist sampling of the recording system.
FIGS. 5(b) and 5(c) show sub-Nyquist sampling in the reproduction system.

First, the recording system circuit shown in FIG. 3 will be explained. The chroma signal Cin from the outside is demodulated by the decoder 13 and becomes a color difference signal. This color difference signal is filtered into a band of 700 by a low pass filter (hereinafter referred to as LPF) 14.
After being limited to about kHz, it is converted into a digital signal by an AD converter (hereinafter referred to as ADC) 15, and is input to a delay 16, a sub-Nyquist sampling section 17, a line memory 18, and a correlation detection section 19.

The sub-Nyquist sampling section 17 samples the input digital signal line by line in a checkered pattern at a sampling frequency lower than that of the ADC 15, as shown in FIG. 5(a). At the same time, one of the remaining three output signals is delayed by one horizontal scanning period (hereinafter referred to as 1H) by the line memory 18, and the other is input to the correlation detection section 19 as is. Furthermore, the other signal is delayed by the delay 16 by the same time as the signal delay time in the sub-Nyquist sampling section 17 . Then, the correlation detection section 19 checks the correlation between the above-mentioned two input signals, and if there is a correlation, the switch 2
0 is connected to the b terminal connected to the sub-Nyquist sampling unit 17, and if not connected to the a terminal connected to the delay 16. The output signal of switch 20 is D
After being converted into an analog signal by an A converter (hereinafter referred to as DAC) 21, the band is limited to about 700 kHz by an LPF 22, and a 3.58 MHz chroma signal C'in is converted to a chroma signal C'in by an encoder 23 and recorded on a tape.

Next, the reproduction system circuit shown in FIG. 4 will be explained. The chroma signal C'in reproduced from the tape is demodulated by the decoder 24 and becomes a color difference signal. This color difference signal is LPF25
After limiting the band to about 700kHz, ADC26
It is converted into a digital signal by the delay 27, sub-Nyquist sampling section 29, line memory 31,
The signal is input to the correlation detection section 33.

The sub-Nyquist sampling unit 29 samples the input digital signal line by line in a checkerboard pattern as shown in FIG. 5(a) at a sampling frequency lower than that of the ADC 26, as in the case of recording. Furthermore, this sampling signal is divided into two, one being a signal delayed by 1H by the line memory 30, and the other being input to the switch 34 as is. At the switch 34,
A clock signal Sc having a frequency twice the sampling frequency in the sub-Nyquist sampling section 29 switches and outputs the above two input signals. As a result, the output signal from the switch 34, as shown in FIG. 5(b), has a form in which data 1H before is inserted between the data of that line in each line. This signal is then input to switch 35. At the same time, among the output signals from the remaining three ADCs 26, one is delayed by 2H by the line memories 31 and 32, and the other is input to the correlation detection section 33 as is. Furthermore, the second one is the sub-Nyquist sampling section 29 by the delay 27.
After being delayed for a time equal to the delay time of the signal in , the signal is inputted to the switch 35 through the comb filter 28 . Then, the correlation detecting section 33 checks the correlation between the two inputted signals, and if there is a correlation, the switch 35 is connected to the switch 34, and if not, the switch 35 is connected to the comb filter 28. The output signal of the switch 35 is converted into an analog signal by the DAC 36, and then the band is reduced to 700kHz by the LPF 37.
The encoder 38 converts the signal into a 3.58 MHz chroma signal Cout and outputs it to a television or the like.

0010

[Problem to be solved by the invention] In the above-mentioned conventional configuration,
There are no problems with the recording circuit. However, in the reproduction circuit, a reproduction signal is obtained by inserting data 1H before each line of data between each line of data. Therefore, when reproducing a wavy edge portion as shown in FIG. 5(c),
If the image where one sampling data is located is different from the image where it will be inserted 1H later (the area circled in Figure 5(c)), a problem will occur; If the left-hand side of the image is represented by a solid line and the right-hand side of the area is represented by a broken line, there is a problem in that the left-hand and right-hand images appear alternately on each line at the edge.

The present invention solves the above-mentioned conventional problems, and aims to provide a chroma sub-Nyquist sampling method that does not cause any adverse effects even in the above-mentioned cases.

0012

[Means for Solving the Problems] In order to achieve the above object, the present invention provides, during reproduction, the absolute value of the difference between the current sub-Nyquist sampling signal and a signal obtained by delaying this signal by 1H, and this 1H delayed signal. Find the absolute value of the difference between the current signal and the 2H delayed signal, and if the absolute value of the former is smaller than the latter, obtain the reproduced signal from the current sub-Nyquist sampling signal and the 1H delayed signal of this signal,
In other cases, the reproduced signal is obtained from the 1H delayed signal and the 2H delayed signal of the current sub-Nyquist sampling signal.

[0013]

According to the present invention, when data is inserted between data on each line, the data that is closest in terms of waveform is inserted using the method described above. Therefore, even in the image shown in FIG. 5(c), it is possible to prevent the problem from occurring.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of a circuit according to the chroma sub-Nyquist sampling method of the present invention, and FIG.
) to (d) show the sub-Nyquist sampling. Note that the recording sub-Nyquist sampling circuit remains the same as before.

In FIG. 1, a sub-Nyquist recorded chroma signal C'in reproduced from a tape is demodulated by a decoder 1 to become a color difference signal. The band of this color difference signal is limited to about 700 kHz by the LPF 2, and then converted into a digital signal by the ADC 3 and input to the sub-Nyquist sampling section 4. Sub-Nyquist sampling section 4
In this case, the input digital signal is converted to the conventional technique shown in FIG.
As in (a), sampling is performed in a checkered pattern for each line. Output signal C0 from sub-Nyquist sampling section 4
is a 1H delayed signal C by line memories 5 and 6.
A 1, 2H delayed signal C2 is obtained, and C0, C1, and C2 are input to the correlation detection section 7 and the switch 8, respectively. The switch 8 receives a clock signal Sc having a frequency twice the sampling frequency in the sub-Nyquist sampling section 4.
, the above three input signals are switched, and the two signals C
10, outputs C12. Here, as shown in FIG. 2(a), C12 is the data 1H earlier inserted between the data of each line, and C10 is the data of each line, as shown in FIG. 2(b). The data 1H later is inserted between the data. At the same time, the correlation detection unit 7 calculates the absolute value of the difference between C1 and C0 and the absolute value of the difference between C1 and C2 from the three signals C0, C1, and C2, and the absolute value of the former is larger than the absolute value of the latter. If it is small, switch 9 is connected to C10, otherwise it is connected to C12. FIG. 2(c) shows the above-mentioned sampling in a part of the wavy edge, and the three data C'0, C'0,
In C'1 and C'2, the absolute value of the difference between C'1 and C'0 is smaller than the absolute value of the difference between C'1 and C'2. Therefore, switch 9 is connected to C10, and data C'0 1H after C'1 is inserted into C'1. Further, FIG. 2(d) shows the above-mentioned sub-Nyquist sampling on the entire wavy edge, and the sampling shown in FIG. 2(c) is performed at the portions circled in the figure. Next, the output signal of the switch 9 is converted into an analog signal by the DAC 10, and then the band is changed to 70 by the LPF 11.
Limited to around 0kHz, 3.58M with encoder 12
The signal becomes a Hz chroma signal Cout and is output to a television or the like.

As described above, in the chroma sub-Nyquist sampling method according to the embodiment of the present invention, when data is inserted between the data of each line during playback, the absolute value of the difference between the data of the previous and subsequent lines is determined and the absolute value is calculated. The data with the smaller value, that is, the data that is closest in terms of waveform, will be inserted. Therefore, as shown in FIG. 2(d), the disadvantages seen in the conventional method at the edge portions no longer occur.

[0018]

[Effects of the Invention] As is clear from the above embodiments, according to the present invention, when data is inserted between data on each line during playback, the absolute value of the difference between the data on the previous and subsequent lines is calculated. The data with the smaller absolute value, that is, the data that is closest in terms of waveform, will be inserted. Therefore, it is possible to provide a chroma sub-Nyquist sampling method that does not have the disadvantages of conventional methods.

[Brief explanation of drawings]

FIG. 1: Reproduction system circuit using a chroma sub-Nyquist sampling method according to an embodiment of the present invention.

2] (a) is a schematic diagram showing sampling in the output signal C12 of switch 8 in FIG. 1; (b) is a schematic diagram showing sampling in output signal C10 of switch 8 in FIG. 1; (c) is a schematic diagram showing sampling in the output signal C10 of switch 8 in FIG. A schematic diagram (d) showing sampling at switch 8 is a schematic diagram showing sampling at switch 8 in FIG.

[Figure 3] Block diagram of a conventional recording system chroma sub-Nyquist sampling circuit

[Figure 4] Block diagram of a conventional reproduction system chroma sub-Nyquist sampling circuit

FIG. 5 (a) is a schematic diagram showing sampling in a conventional recording system chroma sub-Nyquist sampling circuit (b
) is a schematic diagram showing sampling in a conventional reproduction system chroma sub-Nyquist sampling circuit. (c) is a schematic diagram showing the adverse effects caused by sampling in a conventional reproduction system chroma sub-Nyquist sampling circuit.

[Explanation of symbols]

4. Sub-Nyquist sampling section 5 Line memory 6 Line memory 7 Correlation detection section 8 Switch 9 Switch

Claims (1)

[Claims] Claim 1: In a video tape recorder, during playback,
The absolute value of the difference between the current sub-Nyquist sampling signal and a signal obtained by delaying the signal by one horizontal scanning period, the signal delayed by the one horizontal scanning period, and the signal obtained by delaying the sub-Nyquist sampling signal by two horizontal scanning periods. If the absolute value of the former is smaller than the absolute value of the latter, obtain a reproduced signal from the current sub-Nyquist sampling signal and a signal delayed by one horizontal scanning period of the signal;
In other cases, the chroma sub-Nyquist sampling method obtains a reproduced signal from a one-horizontal scanning period delayed signal and a two-horizontal scanning period delayed signal of the current sub-Nyquist sampling signal.