JPS59182690A - Sampling system of composite color television signal - Google Patents

Abstract

PURPOSE:To attain the sampling of a composite color TV signal and to improve the system performance attended with digitization by sampling the composite color TV signal so that the phase of a subcarrier is made alternate with that of a preceding scanning line at each prescribed time and also at each scanning line. CONSTITUTION:After R, G, B inputs from an image pickup camera are converted into a luminance signal Y, color difference signals I, Q by a matrix converting circuit 3 of a color encoder 1, a chrominance subcarrier fSC is vertical- modulated by a modulation circuit 6 via LPFs 4, 5 as to the color difference signals I, Q and outputted as an NTSC signal. On the other hand, a frequency signal near (2n+1)th fH is generated by a VCO7, a signal having a frequency fH being 1/(2n+1) is obtained by a frequency divider 8, the signal is compared 9 with the phase of the horizontal synchronism signal of the NTSC signal so as to attain phase locking. This is formed into (n+1/2)th fH by a frequency divider 10 so as to drive an A/D converter 11. Then, the luminance signal Y being a band overlapped with the reflected component is eliminated by a fC of the LPF2.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a sampling method for composite color television signals, and more specifically, to a sampling system for composite color television signals, and more specifically, a method for sampling subcarriers using two color signals such as a color television signal such as the NTSC system. The present invention relates to a method for sampling a composite color television signal that is modulated and frequency-multiplexed with a brightness signal at a sampling frequency that is lower than the Nyquist rate.

[Background of the invention]

As is generally well known, in order to sample and transmit a signal with the highest frequency fy, it must be sampled at a frequency fs of 21M or more, according to Nyquist's theorem. For example, the highest frequency of an NTSC color television signal is 4.2'MHz, so fs = 8.4MHz.
It is necessary to make more than one sample.

However, a method is known that makes good use of the properties of the signal or the properties of vision and performs sampling with a round mantissa that is less than the Nyquist rate. For example, the color subcarrier frequency fsc (3; 579 MHZ) of an NTSC composite color television signal
) (f s , = 7.17'8MH2) has been proposed. This takes advantage of the property that in color television signals, sample values at 90' phase shifts in color subcarriers can be interpolated.

However, in order to match the transmission speed of the transmission line, there are cases where it is desired to select a sampling frequency without being limited to the above-mentioned specific frequency.

However, with the conventionally known sampling frequency of fs=2fsc, it may not be possible to match the speed of the transmission path.

[Purpose of the invention]

It is an object of the present invention to realize a sampling method for a composite color television signal that is less than the Nyquist rate, is not limited to twice the color subcarrier frequency, and can be curved by interpolation without deteriorating image quality. It is.

[Summary of the Invention] In order to achieve the above object, the present invention samples a composite color television signal such that the subcarrier phase is shorter than 180 degrees and alternates with the previous scan line every -scan line. It is characterized by being made to be

Preferably, about 21 to 26 color subcarrier frequencies are sampled.

Hereinafter, the present invention will be explained in detail using the drawings.

Figure 1 shows the well-known composite color television (TV)
FIG. 3 is a diagram showing a frequency spectrum of a signal.

A strong component of the luminance signal exists at an integer multiple of the horizontal set frequency fn, and the intermediate frequency, that is, the frequency (n+2)
A color signal component exists at fH (n is an integer).

Its center is the color subcarrier frequency fsc55 , −×fH=(227+-!-)2 at fH exists in

Sate, now, 'a book conversion cycle ti number fs = (m+L)
When sampling with fn (m is an integer), the frequency spectrum at that time becomes as shown in FIG. In FIG. 2, the high frequency components of the luminance signal are omitted because they are at a much lower level than the color signal components.

If sampling is performed at such a sampling frequency, the luminance signal component will be located at 1 (m+-1)fFl among the frequency spectrum components (white area in the figure) of the signal generated by sampling. Also, the color signal component is located at m//fH. Note that m' and m'' are integers that are true to m.

As can be seen from Figure 2, from a microscopic perspective, strong signal components do not overlap in frequency. However, from a macro perspective, as shown in FIG. 3, the signals overlap in a frequency region higher than the frequency fc (minimum frequency when sampled).

As a result, from a microscopic perspective, if the signals are separated using a comb filter, only the original signal components can be extracted. What is important here is that the sample color frequency f8 is not particularly required to be around twice the color signal frequency aflc. That is, as shown in the figure, frequency 2
fsc may be higher or lower.

Note that the high frequency component of the luminance signal does not necessarily need to be removed as long as the component is small, but in terms of image quality, it is desirable to remove it in advance.

[Embodiments of the invention]

Hereinafter, the present invention will be explained by examples.

FIG. 4 is a block diagram showing the configuration of a color television signal transmitter that implements the sampling method according to the present invention.

In FIG. 4, reference numeral 1 is a so-called color encoder which is completely normal except for the continuous frequency of the low-pass p-wave generator 2. That is, after converting the R, o, and B inputs from the imaging camera into luminance signals Y1 and color difference signals I and Q signals in the matrix conversion circuit 3,
The color difference signals I and Q pass through low-band P wave generators 4 and 5, and are quadrature-modulated on a subcarrier 78fgc by a modulation circuit 6, and are output as NTSC signals.

On the other hand, the voltage controlled oscillator 7 generates a frequency signal around (2n+iJf□), and the frequency divider 8 generates a frequency signal of 1/(2n+1).
A signal having a frequency fH is obtained, and this signal is compared with the phase of the horizontal synchronizing signal of the NTSC signal by a phase comparator 9 to extract the phase. This is divided into 1/2 frequency by frequency divider 1o, that is,
(n+l/2) fn k is obtained and the A/D conversion 11 is driven.

Now, what particularly requires explanation here is the low-frequency p-wave device 2. Normally, the am1 frequency of this F-wave device is 4.2 MH
Set to Z. However, as explained in Figures @2 and 3, it is desirable to remove 10 or more Y components of the luminance signal.

Therefore, the cutoff frequency of the low-pass P wave generator 2 is set to 4.2 M
If you use fc instead of HZ, the above conditions will be satisfied,
It is possible to remove the luminance signal Y in the band that overlaps with the folded component. In this way, the sampling frequency fs = (n
+, You can sample it using Ifsc. According to the general method described later, it is necessary to perform 2fs sampling and A/D conversion, but in this embodiment, f is sufficient, which is preferable in terms of circuit configuration.

Incidentally, the same thing can be done with the output of a camera having an inferior image power, M of the I'i picture tube.

FIG. 5 shows the configuration of another embodiment of a transmitter implementing the sampling method according to the present invention. In the drawing, the configurations of the color encoder and the control circuit of the voltage controlled oscillator 7 are the same as in FIG. 1, and are therefore omitted.

In this embodiment, the color television signal which is the output of the color encoder 1 is converted to a frequency 2fs which is twice the sampling frequency fs by the analog-to-digital converter 11 = (2n+1)
fu, convert it into a digital signal, and pass it through a @-type filter consisting of a one-line delay element 12, 13, an adder 14, and a high-pass filter 15 as shown in the figure. The sample value coefficient signal of the sampling frequency f is obtained by resampling at the sampling frequency f.

Regarding the configuration and operation of the @ type filter in this example, the frequency relationship is different, but the configuration is exactly the same.
It is known as a type filter (for example, Reference 1 (Takahiko Fukinuki, Digital Signal Processing for Artists, 1970, Nikkan Kogyo Shimbun), Reference 2 (Tatsuo Ishiguro et al., 32 Mb/S page tangential coding (H 〇-DPCM) color television transmission system, Institute of Electronics and Communication Engineers technical report C375-69, July 1984), etc.), so detailed explanation will be omitted.

Note that it is well known that this method can also be performed in an analog manner.

Note that it is necessary to reproduce the original signal again on the demodulation side. That is, it is necessary to remove components caused by sampling. As is clear from FIG. 2, this can be achieved by using the comb filter shown in FIG. Note that the specific method for this is detailed in the above-mentioned literature.

The present invention is not limited to the above embodiments, and for example, the following modifications are included within the scope of the present invention.

(D) In the case of a conventional sampling frequency close to 2fsc, the method shown in the first embodiment of the present invention, that is, the method of band-limiting the luminance signal Y in advance in an analog manner, is fully applied.

(if) The method described in (1) above, in which each of the R, G, and H components is band-limited by tightening.

01D In a digital color encoder, perform WJ operations such as (i) and (ii> above) using digital calculations.

〔Effect of the invention〕

According to the present invention, the following becomes possible, and composite color T
This greatly contributes to improving the performance and functionality of systems that involve sampling and digitizing V signals.

(1) Sub-Nyquist sampling is possible not only with the sampling frequency that is approximately twice the color subcarrier frequency fsc, but also with a sampling frequency that is greater than twice the color subcarrier frequency fsc, for example, 2.4 times. becomes. Therefore, the degree of freedom in system configuration increases.

(11) In particular, according to the method of "limiting the band of the luminance signal component using a so-called color encoder" described in the embodiment, a comb filter is not required, and the operation of the A/'D converter remains at the sampling frequency. The circuit configuration can be simplified.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the frequency spectrum of an NTSC composite color TV signal, Fig. 2 is a spectral diagram for explaining the present invention showing the micro-relationships when sub-Nyquist sampling is applied to it, and Fig. 3 is a diagram showing the frequency spectrum of an NTSC composite color TV signal. The figure also shows a spectrum diagram for macroscopic explanation, FIG. 4 shows block components in the first embodiment of the invention, and FIG. 5 shows a block diagram in the second embodiment of the invention. 1...So-called color encoder, 2...Low frequency door wave device, 1 piece of flute 3 Figure 4 Figure 5 Figure

Claims (1)

[Claims] 1. A composite color television signal whose subcarrier phase is 1.
1. A method for sampling a composite color television signal, characterized in that sampling is performed at intervals as short as 80° and alternately with previous scanning lines for each scanning line. 2. A sampling method for a composite color television signal according to item 1, wherein the sampling frequency is set in a range of 2.1 to 2.6 times the subcarrier frequency. 3. After controlling the frequency component of the luminance signal component, the frequency-multiplexed composite color television signal is sampled in such a way that sampling pixels alternate on the previous and current scanning lines for each scanning line. A sampling method for composite color television signals.