JPH0666960B2 - Chroma signal recording / playback method - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to a chroma signal recording / reproducing method in a magnetic time recording / reproducing apparatus.

[Prior art and its problems] Conventionally, there is V-2000 method of Philips Corporation for improving the tracking performance as a technology of 8 mm VTR. As a sound quality improving technology, frequency modulation of an audio signal is performed and frequency multiplexing recording is performed on a video track. It has been known for a long time to do.

However, in the above method, the pilot signal and FM
There is a problem that the audio signal interferes with the chroma signal and deteriorates the chroma image quality. As a means for solving such a problem, it is considered that the chroma signal is pre-emphasized and recorded, and at the time of reproduction, de-emphasis is performed contrary to the time of recording. However, even in this case, the center frequencies of the pre-emphasis and de-emphasis of the chroma signal may change due to changes in the environment such as temperature and humidity and changes over time in the element.In such cases, pre-emphasis and de-emphasis Cannot be performed reliably, and the chroma image quality may deteriorate.

[Object of the Invention] The present invention has been made in view of the above points, and can stably perform chroma pre-emphasis and chroma de-emphasis, and even when the environment such as temperature and humidity is changed, the chroma image quality is improved. It is an object of the present invention to provide a chroma signal recording / reproducing method capable of surely preventing deterioration of the signal.

[Points of the Invention] In the present invention, in a chroma signal recording system, pilot signals “f ₀ + Δf” and “f ₀ −Δf” are added in advance to the vertical blanking period or horizontal blanking period of the chroma signal. Pre-emphasis processing is performed, and the pilot signal (f ₀ + Δf), “f ₀
The deviation of the center frequency f ₀ of the pre-emphasis circuit is detected from the level of −Δf ”and the deviation of the frequency is corrected, and in the reproduction system of the chroma signal, after the reproduced chroma signal is de-emphasized, the pilot Signal “f ₀ × △
The deviation of the center frequency f ₀ of the de-emphasis process is detected by the level of “f” “f ₀ −Δf”, and the deviation of the frequency is corrected.

[Examples of the Invention] Examples in which the present invention is applied to an 8 mm VTR will be described below. First, the configuration of the chroma signal recording system will be described with reference to FIG. In FIG. 1, reference numeral 10 denotes an input terminal to which a recorded video signal is input. The video signal input to the input terminal 10 passes through an AGO circuit 11 to a luminance signal / chroma signal separation circuit (hereinafter referred to as Y / C separation circuit 1). (Abbreviated) 12 is input.
The Y / C separation circuit 12 separates the luminance signal Y and the chroma signal C, and the luminance signal Y is a luminance signal processing circuit (not shown).
And outputs the chroma signal C to the ACC circuit 14 via the bandpass filter 13. The ACC circuit 14 keeps the output signal constant and outputs it to the pilot signal addition circuit 15 even if the chroma input signal fluctuates. Further, in FIG. 1, reference numeral 16 is a Δf oscillator for creating two pilot signal carriers which are Δf apart from the subcarrier frequency f ₀ , and the transmission frequency Δf is usually “Δf <500 KHz”. Is set.
The oscillation output Δf of the Δf oscillator 16 is sent to the frequency conversion circuit 17 together with the subcarrier signal f ₀ . This frequency conversion circuit 17 uses the subcarrier signal f ₀ and the Δf oscillator 16
A pilot signal of "f ₀ + Δf" and "f ₀ -Δf" is created from the signal Δf from the signal and output to the gate circuit 18. The gate circuit 18 outputs a pilot signal “f ₀ ± Δf” at a predetermined timing in the vertical period, and the output signal is a high pass filter 19 and a low pass filter 20.
Sent to. The high pass filter 19 includes a gate circuit 18
Only the signal of "f ₀ + Δf" out of the signals output from is output to the selection circuit 21, and the low-pass filter 20 outputs "f _0-
Only the signal of “Δf” is extracted and output to the selection circuit 21. Further, the head switching signal HSW is input to the selection circuit 21. The selection circuit 21 uses the head switching signal HSW to output the signal "f ₀ + from the high pass filter 19 for each field.
“Δf” and the signal f ₀ −Δf ”from the low pass filter 20 are alternately selected and output to the pilot signal adding circuit 15.
This pilot signal adding circuit 15 is for the chroma signal,
A pilot signal sent from the selection circuit 21 is added during the vertical blanking period and output to the pre-emphasis circuit 22. This pre-emphasis circuit 22 is
Pre-emphasis processing with f ₀ as the center frequency is performed and output to the low frequency conversion circuit 23 and the pilot signal gate circuit 24. The pilot signal gate circuit 24 selects a pilot signal “f ₀ ± ₀ ” from the output signals of the pre-emphasis circuit 22.
Only "f" is taken out and output to the selection circuit 25. The selection circuit 25 outputs the signals "f ₀ + Δf" and "f ₀ -Δf" output from the pilot signal gate circuit 24 to the head switching signal HSW.
And outputs to the detection circuit 26a or the detection circuit 26b. The detection circuits 26a and 26b are for detecting the peak value of the pilot signal, and the detection outputs thereof are input to the "+" terminal and the "-" terminal of the comparator 27, respectively. Also, hold capacitors 28a and 28b for holding the peak level are connected to the input terminals of the comparator 27, respectively. Then, the output signal of the comparator 27 is input to the pre-emphasis circuit 22 via the low-pass filter 29. This pre-emphasis circuit 22
The center frequency f ₀ of pre-emphasis is corrected by the signal from the low pass filter 29. Then, the chroma signal pre-emphasized by the pre-emphasis circuit 22 is sent to the low frequency conversion circuit 23 as described above. The low frequency conversion circuit 23 converts the chroma signal into a low frequency signal and inputs it to the recording amplifier 31 via the low pass filter 30. The recording amplifier 31 amplifies the signal from the low-pass filter 30 and outputs it to the video head 32 to record the chroma signal on the video tape.

Next, the circuit configuration of the reproduction system of the chroma signal will be described with reference to FIG. The chroma signal reproduced by the video head 32 is amplified by the reproduction amplifier 41 and then sent to the high frequency conversion circuit 44 via the low-pass filter 42 and the ACC circuit 43. The high frequency conversion circuit 44 inversely converts the reproduced chroma signal, which has been low frequency converted, into the original chroma signal, and outputs the original chroma signal to the de-emphasis circuit 46 via the band pass filter 45. The signal de-emphasized by the de-emphasis circuit 46 is sent to the pilot signal gate circuit 47. The pilot signal gate circuit 47 selects the pilot signal “f ₀ ± Δ from the output signals of the de-emphasis circuit 46.
Only "f" is taken out and output to the selection circuit 48. The selection circuit 48 selects the signals "f ₀ + Δf" and "f ₀ -Δf" output from the pilot signal gate circuit 47 according to the head switching signal HSW, and sends them to the detection circuit 49a or the detection circuit 49b. Output. The detection circuits 49a and 49b are for detecting the peak value of the pilot signal, and the detection outputs thereof are input to the "+" terminal and the "-" terminal of the comparator 50, respectively.
Moreover, hold capacitors 51a and 51b for holding the peak level are connected to the input terminals of the comparator 50, respectively. The output signal of the comparator 50 is passed through the low-pass filter 52 and the de-emphasis circuit.
Entered in 46. The de-emphasis circuit 46 corrects the center frequency of de-emphasis by the signal from the low pass filter 52. And this de-emphasis circuit
The chroma signal de-emphasized by 46 is sent to the Y / C mixing circuit 54 after the pilot signal is erased by the pilot signal erasing circuit 53. A reproduction luminance signal is applied to the Y / C mixing circuit 54 from a luminance signal reproducing circuit (not shown). The Y / C mixing circuit 54 includes a luminance signal Y and a chroma signal C from the pilot signal erasing circuit 53.
Are mixed, a synchronizing signal is added by the buffer circuit 55, and output as a reproduced video signal.

Next, the operation of the above embodiment will be described. When recording a video signal, the recording video signal is input to the input terminal 10 in FIG. This recording video signal is sent to the Y / C separation circuit 12 with the input signal level kept constant by the AGC circuit 11. The video signal output from the AGC circuit 11 is the third
As shown in FIG. 3A, the Y / C separation circuit is used for the composite video signal.
At 12, the luminance signal Y and the chroma signal C are separated.
Then, the chroma signal C is sent to the ACC circuit 14 via the band pass filter 13, and is held at a constant signal level by the ACC circuit 14 as shown in FIG. Sent to. On the other hand, the Δf oscillator 16, the frequency conversion circuit 17, and the gate circuit 18 generate a pilot signal of “f ₀ ± Δf” at a predetermined timing of the vertical blanking period, for example, the back porch portion of the vertical synchronizing signal. and then, "f ₀ by the high-pass filter 19
The signal “f ₀ −Δf” is extracted by + Δf ”and the low-pass filter 20 and sent to the selection circuit 21. This selection circuit 21
Are pilot signals “f ₀ + Δf”, “f ₀ −Δ”
"f" is alternately selected for each field by the head switching signal HSW and output to the pilot signal coding circuit 15. As shown in FIG. 3C, the pilot signal adding circuit 15 responds to the chroma signal C from the ACC circuit 14 by "f ₀ +" in an odd field in the back porch portion of the vertical blanking period.
The pilot signal of “Δf” is added, and in the even field, the pilot signal of “f ₀ −Δf” is added and sent to the pre-emphasis circuit 22. This pre-emphasis circuit 22
Is the subcarrier frequency f as shown in FIG.
Pre-emphasis is performed symmetrically around ₀ (3.58 MHz) and output to the low frequency conversion circuit 23 and the pilot signal gate circuit 24. This pilot signal gate circuit 24 is
The pilot signals “f ₀ + Δf” and “f ₀ −Δf” are extracted from the output signals of the pre-emphasis circuit 22 and selected by the selection circuit 25.
Output to. The selection circuit 25 uses the pilot signal “f ₀ + Δf” output from the pilot signal gate circuit 24.
“F ₀ −Δf” is distributed according to the head switching signal HSW, the pilot signal “f ₀ + Δf” is output to the detection circuit 26a in the odd field, and “f ₀ −Δf” is detected in the even field. Output to circuit 26b. The detection circuits 26a and 26b detect the pilot signals and output them to the comparator 27. In this case, the peak values of the detection outputs of the detection circuits 26a and 26b are held by the hold capacitors 28a and 28, respectively, and the peak values are compared by the comparator 27. FIG. 4 (a) in the pre-emphasis circuit 22.
If pre-emphasis is correctly performed around the subcarrier frequency f ₀ , as shown in, “f ₀ + Δf”
The pilot signals of “f ₀ −Δf” have the same level of a, the output of the comparator 27 is held at a constant value, and the signal sent to the pre-emphasis circuit 22 via the low pass filter 29 does not change. Therefore, the pre-emphasis circuit
22 holds the center frequency f ₀ at that time as it is and performs pre-emphasis processing.

However, as shown in FIG. 4 (b), the center frequency f ₀ of the pre-emphasis in the pre-emphasis circuit 22 shifts to a higher one and becomes f ₀ ′ due to some cause, for example, environmental changes such as temperature and humidity. Then, the level of the pilot signal of "f ₀ + Δf" is b, and the level of the pilot signal of "f ₀ -Δf" is c. That is, the pre-emphasis circuit
The signal pre-emphasized by 22 is shown in Fig. 3 (d).
As shown in, the pilot signal of “f ₀ + Δf” is small,
The pilot signal of “f ₀ −Δf” becomes large. Above "f ₀
The pilot signals of + Δf ”and“ f ₀ −Δf ”are selected by the selection circuit 25 and input to the detection circuits 26a and 26b, as shown in FIGS. 3 (e) and 3 (f). Therefore, the detection output of the detection circuit 26a is small, the detection output of the detection circuit 26b is large, the comparator 27 and the low-pass filter 29.
The output signal level of is increased. When the output signal level of the low pass filter 29 becomes low, the pre-emphasis circuit 22 lowers the center frequency f ₀ ′ at that time to bring it closer to the reference frequency f ₀ . Then, when the center frequency f ₀ ′ matches f ₀ , the pre-emphasis processing is continued while holding the frequency f ₀ at that time until the output of the low pass filter 29 returns to the reference level. Further, when the center frequency f ₀ is shifted to the lower side, “f ₀ + Δf” becomes larger than the pilot signal “f ₀ −Δf”, and as a result, the output signal of the comparator 27 is different from the above case. Changes in the opposite direction to correct the center frequency. The chroma signal subjected to the pre-emphasis process as described above is sent to the low-frequency conversion circuit 23, converted into the low-frequency band, and sent to the recording amplifier 31 via the low-pass filter 30. Then, the video head 32 is driven by the output signal of the recording amplifier 31, and the signal is recorded on the video tape.

On the other hand, in the chroma signal reproduction system shown in FIG. 2, the chroma signal reproduced by the video head 32 is reproduced by the reproduction amplifier.
After being amplified by 41, it is sent to the high frequency conversion circuit 44 via the low pass filter 42 and the ACC circuit 43. The high-frequency conversion circuit 44 reverse-converts the reproduced chroma signal, which has been low-frequency converted, into the original chroma signal, and outputs the original chroma signal to the a-emphasis circuit 46 via the bandpass filter 45. Then, the de-emphasis circuit 46 and the pilot signal gate circuit 47,
Selection circuit 48, the detection circuit 49a, 49, the comparator 50, the closed loop of the low-pass filter 52, de-emphasis processed as pre-emphasis process in the chroma signal recording system shown in Figure 1 is performed, the center frequency f ₀
If the frequency shifts, the frequency shift is corrected.

Although the pilot signal is inserted in the vertical blanking period in the above embodiment, it may be inserted in the horizontal blanking period. Further, in the above-mentioned embodiment, the case where it is applied to the 8 mm VTR has been described, but in addition, the VTR using the chroma emphasis is used.
Can be applied to.

[Effects of the Invention] As described in detail above, according to the present invention, in the recording system of the chroma signal, the pilot signals “f ₀ + Δf” and “f ₀ −Δ” are obtained.
f ”is added to the chroma signal and pre-emphasis processing is performed at the center frequency f ₀ , and the pilot signals“ f ₀ + Δf ”and“ f ₀ ”are added.
The deviation of the center frequency f ₀ of the pre-emphasis circuit is detected from the level of −Δf ”and the deviation of the frequency is corrected, and in the reproduction system of the chroma signal, after the reproduced chroma signal is de-emphasized, the pilot Signal "f ₀ + △
Since the deviation of the center frequency f ₀ of the de-emphasis process is detected by the levels of “f” and “f ₀ −Δf” and the deviation of the frequency is corrected, even if the environment such as temperature or humidity changes. The pre-emphasis and the de-emphasis can be surely performed, the chroma signal can be surely reproduced, and the chroma image quality can be kept excellent.

[Brief description of drawings]

The drawings show an embodiment of the present invention. FIG. 1 is a block diagram showing a circuit configuration of a chroma signal recording system, FIG. 2 is a block diagram showing a circuit configuration of a chroma signal reproducing system, and FIG. 3 is an operation. 4A is a timing chart for explaining FIG.
Shows a normal pre-emphasis characteristic, FIG. 4 (b)
FIG. 6 is a diagram showing a pre-emphasis characteristic when the center frequency is shifted to the higher side. 11 …… AGC circuit, 12 …… Y / C separation circuit, 13,45 …… Band pass filter, 14,43 …… ACC circuit, 15 …… Pilot signal addition circuit, 16 …… △ f oscillator, 17 …… Frequency conversion circuit, 18 ... Gate circuit, 19 ... High-pass filter,
20 …… Low-pass filter, 21, 25, 48 …… Selection circuit, 22
...... Pre-emphasis circuit, 23 …… Low frequency conversion circuit, 24,
47 …… Pilot signal gate circuit, 26a, 26b, 49a, 49b
...... Detection circuit, 27, 50 …… Comparator, 28a, 28b, 49
a, 49b …… Hold condenser, 31 …… Recording amplifier, 32
...... Video head, 41 ...... Reproduction amplifier, 44 …… High frequency conversion circuit, 46 …… De-emphasis circuit, 53 …… Pilot signal erasing circuit, 54 …… Y / C mixing circuit, 55 …… Buffer.

Claims (2)

[Claims] 1. A chroma signal recording / reproducing method in which a chroma signal is pre-emphasized at a center frequency f ₀ and recorded on a recording medium, and a chroma signal read from the recording medium is de-emphasized at a center frequency f _0. predetermined frequency higher around the center frequency f ₀ before "f ₀ + △ f" signal with a predetermined frequency lower "f ₀ -
The “Δf” signal is superimposed in the vertical or horizontal retrace period of the chroma signal, pre-emphasized, and then a predetermined frequency higher than the center frequency f ₀ superimposed from the chroma signal by “f ₀ + Δ”.
The “f” signal and the “f ₀ −Δf” signal lower by a predetermined frequency are extracted,
A predetermined frequency higher than the extracted center frequency f ₀ , “f ₀
The center frequency f ₀ of the pre-emphasis is controlled based on the level difference between the level of the + Δf ”signal and the level of the“ f ₀ −Δf ”signal lower by a predetermined frequency, and the pre-emphasis read from the recording medium is performed. after chroma signal and the de-emphasis, the center frequency f ₀ given higher frequencies around the "f ₀ + △ f" signal with a predetermined frequency lower superimposed on the chroma signal - extracting "f ₀ △ f" signal Then, a predetermined frequency higher than the extracted center frequency f ₀ is given by “f ₀ + Δ
A chroma signal recording / reproducing method characterized in that the center frequency f _{0 of the} de-emphasis is controlled based on the level difference between the level of the "f" signal and the level of the "f ₀ -Δf" signal lower by a predetermined frequency. 2. A high frequency "f ₀ + Δ" centered on the center frequency f ₀ from the chroma signal after the de-emphasis.
2. The chroma signal recording / reproducing method according to claim 1, wherein the "f" signal and the "f ₀ -Δf" signal whose frequency is lower than the predetermined frequency are erased.