JPS6240888A - Field-frame converting system - Google Patents

Abstract

PURPOSE:To prevent the occurrence of a flicker caused by the characteristic of a delay line, by performing the delay of the 1/2 horizontal scanning period of a field signal under a FM-modulated condition. CONSTITUTION:An FM luminance signal YFM has the frequency band of approximate 3-10MHz and is converted into another frequency band of 0-7MHz by means of frequency converting circuit 30 so as to make the frequency band conform the succeedding frequency band of a 0.5-H delay line 16. The frequency- converted field signal 50 is inputted to an analog switch 18 directly or through the delay line 16 after passing through a filter 33. At the switch 18 the directly inputted FM field signal and another FM field signal which is delayed by 1/2 horizontal scanning period are switched to each other at every one vertical scanning period by means of a control signal 20 and the signal 50 is converted to a frame signal 52 under an FM-modulated condition.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a field/frame conversion method used in magnetic recording, and in particular to S
The present invention relates to an improvement in a field/frame conversion method that prevents a decrease in /H and the occurrence of flicker.

[Background of the invention]

In television scanning, so-called interlaced scanning is performed in which horizontal scanning lines are skipped every few lines in order to reduce flickering to the eyes. In general, ・1
(2:1.) In the interlaced scanning method, two coarse screens (fields) created by one vertical scan are overlapped to form a single screen. (frame) is created.The number of field repetitions is, for example, 60 times per second in the NTSC system, the number of frame repetitions is 30 times per second, and one frame is generally represented by 525 horizontal scanning lines. and even field, the starting point of horizontal scanning is within the horizontal scanning period (
H) by 2, that is, 0.5H.

By the way, when recording a video signal on a magnetic tape, magnetic disk, or other various recording media, one field of signal is assigned to one track, or one field of signal is assigned to one track.
It is common to allocate frame signals. Also, in 1 field/1 track recording, an odd field and an even field are recorded one after another, so-called 1 frame/track recording.
There are two-track recording and field recording in which only one field, even or odd, is recorded. When recording,
Among the video signals, at least the luminance signal Y is generally subjected to pre-emphasis processing and then subjected to FM modulation.

FIG. 3 shows a schematic circuit configuration of a recording system in an electronic still camera using a magnetic disk. In FIG. 3, a baseband luminance signal Y passes through a pre-emphasis circuit 1 and is subjected to FM modulation on the high frequency side by an FM modulator 2. On the other hand, the two baseband color difference signals R-y and B-Y are alternately selected every horizontal scanning period (LH) by a switch 4, are line-sequentialized, and are passed through a pre-emphasis circuit 6 to an FM modulator 7. FM modulation is performed in the low band. The FM luminance signal YFM and the FM line sequential color difference signal CFi are mixed through an amplifier 3.8 and supplied to the magnetic head 9. Note that 5 is a control signal for the switch 4. Also, R-
The Y and B-Y color difference signals are FM modulated at different center frequencies to distinguish them from each other.

In the reproduction of field recording, a so-called field/frame conversion method is often used in which a frame signal is created from one type of field signal by scanning the same track twice, making use of the strong vertical correlation of video signals. This is mainly aimed at improving the recording density, allowing long-time recording for movies, and is used in still image mode, and allows for an increase in the number of frames for stills. However, when converting a field signal into a frame signal, interlaced scanning cannot be achieved by simply repeating and reproducing the same field signal twice. The reason for this is that for interlaced scanning, the time relationship between the vertical synchronization signal, the horizontal synchronization signal of each line, and the video signal needs to be shifted by 0.5I between odd and even fields; Simply repeating the signal will result in 0.
This is because a time lag of 5 H does not occur.

Therefore, the same field signal 10 after demodulation and de-emphasis that is repeatedly reproduced is as shown in FIG.
By passing the signal through a 0.5H delay line 16 and alternately selecting the through field signal 10 and the field signal 17 delayed by 0.5H using the analog switch 18 every vertical scanning period (1■). , the field signal 10 is converted into a frame signal 19. In addition, as it is, the interval between vertical synchronization signals is 1
Since there is a deviation of 0.5H from (2), it has been considered that, for example, the contacts a and b of the analog switch 18 are selected as shown in FIG. That is, of the period in which the through field signal 10 is selected, only the portion 21 from the front equalization pulse section to the back equalization pulse section is 0.
5H delay field signal 17 is selected. In any case, to convert a field signal into a frame signal, a circuit is used that selects between a through signal and a 0.5 H delay signal, as shown in FIG.

In FIG. 4, 11 is a magnetic node, 12 is a reproducing amplifier, 13 is a limiter, 14 is an FM demodulator, 15 is a de-emphasis circuit, and 20 is a control signal for the switch 18.

If the field signal in the baseband region is delayed in this way, the field signal passing through the delay circuit will always receive noise from the delay circuit, and the S/
There is a problem that the de-emphasis circuit 1 decreases by N months to 2 dB and is attenuated by the delay circuit.
Fields taken directly from 5 (word and 0.5
A difference occurs in level with the field signal delayed via the H delay line 16, causing flicker on the display screen. Even if an amplifier is installed after or before the delay line 16 to adjust the level in order to prevent the occurrence of frizz, the temperature characteristics of the amplifier and delay line
As level adjustment deteriorates over time, flickering is unavoidable.

Therefore, in order to prevent flicker caused by field/frame conversion of the field signal, an AGC circuit capable of highly accurate gain control is required to adjust the level of the field signal that has passed through the delay circuit. There is a problem that the circuit configuration becomes complicated. Furthermore, flicker due to nonlinearity of the delay line cannot be eliminated by the AGC circuit.

[Purpose of the invention]

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a field/frame conversion method that can prevent the occurrence of flicker caused by the characteristics of the delay line with a simple circuit configuration. .

[Summary of the invention]

In order to achieve the above object, the present invention combines a field signal delayed for 1/2 horizontal scanning period and a field signal not delayed for one vertical scanning period among pre-emphasized and FM modulated field signals that are repeatedly input. In a field/frame conversion method in which a field signal is converted into a frame signal by alternate selection every scanning period, the frequency of the reproduced field signal in the FM modulation state is converted to match the frequency band of the subsequent delay element. Then, the field signal is delayed by 1/2 horizontal scanning period in an FM modulation state.

〔Example〕

Hereinafter, preferred embodiments of the field/frame conversion method according to the present invention will be described with reference to the accompanying drawings. 1st
The figure shows a schematic configuration of a reproduction system to which the present invention is applied. In the same figure, a field signal repeatedly reproduced from a magnetic recording medium (not shown) by a magnetic head 11 is amplified by an amplifier 12, and then converted into an FM signal by a filter 22.
The signal is separated into a luminance signal YFM and an FM color signal CFM. Here, the description of the color signal reproduction system will be omitted since it is not directly related to the gist of the present invention. The FM luminance signal YF14 is
The frequency conversion circuit 30 converts the frequency from the high frequency side to the low frequency side. That is, the FM luminance signal YI is as shown in FIG.
), it has a frequency band of approximately 3 to 10 MH2O, and is adjusted by the frequency conversion circuit 30 to match the frequency band of the subsequent 0, 5H delay line 16 as shown in FIG.
As shown in B), it is converted into a frequency band of 0 to 7 MH2. After the frequency-converted FM luminance signal YFM, that is, the field signal 50 passes through the filter 33, it is inputted to the analog switch 18 either directly or via the 0.5H delay line 16, respectively. In the analog switch 18, the control signal 20 switches between the through FM field signal and the delayed FM field signal for 1/2 horizontal scanning period every vertical scanning period at the timing shown in FIG. 50 is converted into a frame signal 52 in an FM modulated state. Note that the filter 34 is a bandpass filter for removing noise. After noise components are removed from this frame signal 52 by the limiter 24, it is demodulated by the FM demodulator 14.

Here, the 0.5H delay line 16 uses a CCD delay element. This CCD delay element is 0~6MH2
Although this signal band is narrower than the frequency band (0 to 7 MH2) of the field signal, it does not actually matter much.

Now, the FM demodulated signal from the FM demodulator 14 is damped by the de-emphasis circuit 32 to become a baseband luminance signal Y. The limiter 24, the FM demodulator 14, and the de-emphasis circuit 32 prevent the S/N reduction caused by the field signal 50 passing through the 0.5 delay line 16 and the occurrence of flicker caused by field/frame conversion. be done.

In this way, in this embodiment, the field/frame conversion is performed while the field signal is FM modulated, so that the noise received from the delay circuit is reduced by the FM demodulation due to the field signal delay operation in the field/frame conversion. , removed by de-emphasis, and in the baseband, the S/N of the delayed field signal becomes the same as the S/N of the through field signal.

In addition, when demodulating the FM signal, a limiter is provided at the front stage, so signal attenuation due to the delay circuit, non-linear distortion, temperature characteristics of the delay circuit, and effects of aging are removed by the limiter, and free distortion is eliminated. occurrence is prevented.

Therefore, there is no need for an AGC circuit or the like for compensating for delay line characteristics or signal attenuation caused by field signal delay, as in conventional luminance signal reproducing systems.

〔Effect of the invention〕

As explained above, the present invention is configured to delay the field signal by 1/2 horizontal scanning period in the FM modulation state to perform field/frame conversion of the reproduced FM modulation state. According to the above, it is possible to prevent a decrease in S/N with a simple circuit configuration, and therefore it is possible to prevent the occurrence of flicker due to the characteristics of the delay line without providing an AGC circuit or the like.

[Brief explanation of drawings]

Figure 1 is a block diagram showing the schematic configuration of a reproduction system to which the present invention is applied, Figure 2 is a characteristic diagram showing the frequency characteristics of a field signal in an FM modulation state before and after frequency conversion, and Figure 3 is a diagram of the recording system. FIG. 4 is a block diagram showing the general structure of a conventional reproduction system, and FIG. 5 is a timing chart showing an example of the operation of the field/frame conversion switch. 11...Magnetic head, 12...Reproduction amplifier,
24...Limiter, 14...FM demodulator,
16...0°5H delay line, 18...analog switch, 30...frequency conversion circuit, 32
... De-emphasis circuit, 33.34... Filter.

Claims (2)

[Claims] (1) Pre-emphasized and F
A field signal is converted into a frame signal by alternately selecting a field signal delayed by 1/2 horizontal scanning period and a field signal not delayed among the M-modulated field signals every vertical scanning period.
In the frame conversion method, after converting the frequency of the reproduced field signal in the FM modulation state to match the frequency band of the subsequent delay element, one of the field signals is
A field/frame conversion method characterized in that a delay of /2 horizontal scanning period is performed in an FM modulation state. (2) The field system according to claim 1, wherein the delay element is a CCD delay line.
Frame conversion method.