JPS62165767A - Luminance signal processing circuit - Google Patents

Abstract

PURPOSE:To automatically apply picture quality adjustment where a picture with deficient S/N is changed into an easy-to-see picture by detecting the amplitude level of a reproduced FM signal and changing the high frequency band characteristic of a reproduced luminance signal corresponding to the amplitude level. CONSTITUTION:A reproduced luminance FM signal 100 reproduced from a tape and whose frequency characteristic is corrected is given to an amplitude detection circuit 5, where the amplitude level is detected and it is inputted to an FM demodulation circuit 2 via an AGC circuit 1. The demodulated reproduced luminance signal is inputted to a de-emphasis circuit 4 via an LPF 3, and outputted to a frequency characteristic variable circuit 7 as an original luminance signal 200 the same as that at recording. On the other hand, the amplitude level of the signal 100 detected by the circuit 5 is inputted to a control signal generating circuit 6. The circuit 6 produces a control signal 50, outputs it to the circuit 7, which changes the degree of decrease in the high frequency characteristic of the signal 200 by the command of the signal 50. Thus, a reproducing luminance signal 300 is outputted and the picture quality adjustment where the picture with deteriorated S/N is changed into an easy-to-see picture is automatically attained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a luminance signal processing circuit suitable for use in video tape recorders and the like.

[Technical Blueprint of the Invention] A luminance signal processing circuit used in a home video tape recorder (VTR) or the like generally has a configuration as shown in FIG. That is, the listening luminance FM signal 100 whose frequency characteristics have been corrected after being reproduced from the tape is input to the AGC circuit 1, where the amplitude modulation component contained in the reproduced luminance FM signal is removed. The reproduced luminance FM signal from which the amplitude modulation component has been removed is demodulated by the FM demodulation circuit 2 to become a reproduced luminance signal. However, in this reproduced luminance signal, the reproduced luminance F
Since leakage of the M signal and other noises are mixed in, the signal is input to the de-emphasis circuit 4 after removing these unnecessary components by the low-pass filter 3. Here, in order to reduce the triangular noise peculiar to FM modulation during recording, the recording luminance signal is high-frequency emphasized by a high-frequency emphasis circuit. Therefore, the high-frequency component of the reproduced luminance signal is suppressed by the de-emphasis circuit 4, and the S/N ratio is improved by this amount, and the reproduced luminance signal 200 is output with the same characteristics as when recording. Note that in an actual VTR, circuits such as a noise canceller and an image quality controller 1 are added after the de-emphasis circuit 4, but these are omitted as they are not relevant to the present invention.

[Problems with the previous day's technology] By the way, the playback brightness F when played from a tape on a VTR
The signal-to-noise ratio (S/N) of the reproduced luminance signal is determined in proportion to the output level of the M signal.For this reason, when recording and playing back using a long-duration tape, When recording and reproducing in time mode, the output level of the reproduced luminance FM signal becomes small, resulting in a poor S/N ratio of the reproduced luminance signal, resulting in a screen that is difficult to view.Conventionally, the image quality adjustment volume was used. The above disadvantages have been avoided by manually lowering the level of the high-frequency components of the reproduced luminance signal to improve the apparent S/N ratio, but without manually adjusting the image quality each time. The drawback is that it takes a lot of time and effort.

[Object of the Invention] In view of the above-mentioned drawbacks, the object of the present invention is to reduce the apparent S/N.
To provide a luminance signal processing circuit that can automatically perform image quality adjustment to improve the S/N ratio and make an image with a poor S/N easy to view.

[Summary of the Invention 1] The present invention detects the amplitude level of the reproduced luminance FM signal when demodulating the reproduced luminance FM signal to obtain the reproduced luminance signal, and adjusts the high frequency of the reproduced luminance signal in accordance with this amplitude level. By changing the band characteristics, the purpose of automatically adjusting the image quality to improve the apparent S/N and make the S/N anal image easier to see is achieved.

[Embodiment of the Invention] Hereinafter, an embodiment of the present invention will be described with reference to the drawings, in which the same parts as those of the conventional example are denoted by the same reference numerals. Figure 1 shows wJ of the present invention.
1 is a block diagram showing one embodiment of a signal processing circuit; FIG.

1, the amplitude level of the input luminance FM signal is kept constant and the input level width variation=) component is removed <AGC circuit,
2 is an FM demodulation circuit that demodulates the input reproduced luminance FM signal to produce a reproduced luminance signal, and 3 is a low-pass filter that removes the luminance FM signal and other noises contained in the input reproduced luminance signal and extracts only the luminance signal component. , 4 is a de-emphasis circuit that suppresses the high frequency component of the input reproduced brightness FM signal to produce a brightness signal with the same edge as that at the time of recording, and 5 is a de-emphasis circuit that detects the amplitude level of the input reproduced brightness FM signal (edge width detection circuit). ,6
7 is a control signal generation circuit that generates a control signal for changing the frequency characteristics of the variable frequency characteristic circuit 7 based on the detection signal inputted from the amplitude detection circuit 5; 7 is a reproduced luminance signal 200 inputted from the de-emphasis circuit 4; The high frequency characteristics of the control signal 5 given from the control signal generation circuit 6
This is a variable frequency characteristic circuit that changes the frequency characteristics based on 0, and outputs the final reproduced brightness signal 300.

Next, the operation of this embodiment will be explained. Reproduction brightness tx FM corrected for multi-frequency characteristics reproduced from tape
After the amplitude level of the signal 100 is detected by the amplitude detection circuit 5, the signal 100 is directly inputted to the AGC circuit 1, where the amplitude modulation component is removed, and further inputted to the FM demodulation circuit 2. The reproduced luminance FM signal is demodulated by an FM demodulation circuit 2 to become a reproduced luminance signal, and unnecessary parts are removed by a low-pass filter 3 and input to a de-emphasis circuit 4. The de-emphasis circuit 4 suppresses the high frequency components of the input luminance signal and returns the same original luminance signal 20 as at the time of recording.
0 and outputs this to the frequency characteristic variable circuit 7. On the other hand, the reproduced 1 degree FM signal 1 detected by the amplitude detection circuit 5
The amplitude level of 00 is input to the control signal generation circuit 6.

The control signal generation circuit 6 generates a control signal @50 from the input detection signal and outputs it to the frequency characteristic variable circuit 7. The frequency characteristic variable circuit 7 controls the degree of fall of the high frequency characteristic of the input reproduced luminance signal 200 No. 11 50
After changing the brightness according to the instructions, the reproduced brightness signal 30
Output as 0.

Here, to explain the operation of the frequency characteristic variable circuit 7 in more detail, for example, when the amplitude detection circuit 5 detects that the amplitude level of the reproduced luminance FM signal is small, the control signal generation circuit 6 operates based on this. high control signal 50
is output to the variable frequency characteristic circuit 7, and the variable frequency characteristic circuit 7 is controlled so as to have the characteristic shown in FIG. 2, for example, A. Therefore, when the frequency characteristic variable circuit 7 lowers the high frequency component of the reproduced luminance signal 300 as shown in the characteristic A shown in FIG. It appears as if the target S/N ratio has been improved, resulting in an easy-to-read screen. Also,
The amplitude level of the reproduced luminance FM signal 100 is determined by the amplitude detection circuit 5.
If it is detected that the frequency is higher, the control signal generation circuit 6 outputs a control signal 50 based on this to the frequency characteristic variable circuit 7, and the frequency characteristic of this frequency characteristic variable circuit 7 is shown at the beginning of FIG. In this way, a normal reproduced luminance signal 300 is output. Further, when the amplitude level of the reproduced luminance FM signal is detected to be higher by the amplitude detection circuit 5, the control signal generation circuit 6 outputs the control signal 50 to the frequency characteristic variable circuit 7 based on this. Frequency characteristic variable circuit 7
It is also possible to make the frequency characteristic of the frequency characteristic as shown by C in FIG. In this case, since the high frequency component of the reproduced luminance signal is emphasized, the resolution of the reproduced image can be increased.

According to this embodiment, by adding the amplitude detection circuit 5, the control signal generation circuit 6, and the frequency characteristic variable circuit 7 to the luminance signal processing circuit, the reproduction luminance signal 300 is adjusted according to the amplitude level of the reproduction luminance FM signal 100. By changing the high frequency characteristics, the apparent S/N can be improved and images with poor S/N can be automatically made into easy-to-see images, which previously required manual adjustment of image quality. The operation can be omitted.

FIG. 4 is a block diagram showing another embodiment of the present invention. In this example, the amplitude detection circuit 5 is omitted, and the AGC
Input AGC detection voltage of circuit 1 Reproduction brightness FM signal 100
A detection signal 60 indicating the amplitude level of is inputted to the control signal generation circuit 6. The control signal generation circuit 6 generates a control signal 50 based on this detection signal 60, outputs it to the frequency characteristic variable circuit 7, and outputs the control signal 50 to the high frequency range of the reproduced luminance FM signal 200 input from the de-emphasis circuit 4. By changing the frequency characteristics, a final reproduction brightness signal @300 is obtained. This example also has the same effect as the previous example, but
Since the circuit configuration is simplified, it is possible to easily improve the luminance signal processing circuit used in current VTRs.

[Effects of the Invention] As described above, according to the luminance signal processing circuit of the present invention,
When demodulating the reproduced luminance FM signal to obtain the reproduced luminance signal,
By detecting the amplitude level of the reproduced brightness FM signal and changing the high frequency characteristics of the reproduced brightness signal in accordance with this amplitude level, the apparent S/N is improved and images with poor S/N are easier to see. Automatically adjusts the image quality of the image to 1q
It has the effect of

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the luminance signal processing circuit of the present invention, FIG. 2 is a diagram showing an example of frequency characteristic change of the frequency characteristic variable circuit shown in FIG. 1, and FIG. FIG. 4 is a block diagram showing another embodiment of the present invention, and FIG. 5 is a diagram showing the degree of apparent improvement in S and /N in the circuit shown in FIG. FIG. 2 is a block diagram showing an example. 1...AGC circuit 2...FM demodulation circuit 3.
...Low pass filter 4...De-emphasis circuit 5...1 Line width detection circuit 6...Control signal generation circuit 7...Variable frequency characteristic circuit Representative Patent attorney Nori Chika Hiroshi Uji

Claims (1)

[Claims] A luminance signal processing circuit that demodulates a reproduced luminance FM signal to produce a reproduced luminance signal, an amplitude detection circuit that detects the amplitude level of the reproduced luminance FM signal, and a frequency characteristic of the reproduced luminance signal that is specified by a separately given control signal. and a control signal generation circuit that generates the control signal that changes the frequency characteristics of the frequency characteristic variable circuit according to the amplitude level from the amplitude detection circuit. processing circuit.