JPH0526868Y2 - - Google Patents

Description

[Detailed Description of the Invention] (a) Industrial Application Field The present invention relates to a luminance signal processing circuit for the purpose of improving image quality in a video tape recorder (VTR).

(b) Conventional technology In a VTR, the luminance signal recorded by FM modulation is
For the purpose of improving the N ratio, the recording/reproducing circuit is provided with a pre-emphasis circuit and a de-emphasis circuit. Furthermore, recently, in order to increase the S/N improvement effect, non-linear emphasis has been adopted in which the amount of emphasis is automatically changed according to the level of the input luminance signal.

In this non-linear emphasis method, the amount of emphasis and de-emphasis changes depending on the level of the input signal, but the amount of emphasis and de-emphasis changes depending on the level of the input signal.
Due to waveform distortion and noise in the reproduction process, this changing operation may malfunction, resulting in increased waveform distortion.

Furthermore, in Japanese Patent Application Laid-Open No. 58-31668 (H04N5/14), a contour correction circuit for video signals is equipped with two types of peaking circuits with different characteristics, and the optimum peaking circuit is selected according to the level of the input signal. A configuration for selecting is shown.

However, the above-mentioned known example has nothing to do with recording and reproducing in a VTR, and does not disclose any configuration similar to de-emphasis.

(c) Problems that the invention aims to solve As mentioned above, in the conventional nonlinear emphasis circuit, the pre-emphasis and de-emphasis operations malfunction during recording/reproducing operations, resulting in large waveform distortion of the reproduced signal. I was afraid.

(d) Means for solving the problem The present invention includes a plurality of pre-emphasis circuits having different characteristics, a means for detecting the level of a luminance signal to be recorded, and a means for selecting the plurality of pre-emphasis circuits based on the detection result. a means for recording a signal by adding information indicating a selected pre-emphasis circuit; a de-emphasis circuit corresponding to the plurality of pre-emphasis circuits; and a de-emphasis circuit for detecting the information included in the playback output during playback. This is a luminance signal processing circuit comprising means for selecting.

(e) Effect In other words, since information indicating the pre-emphasis circuit selected at the time of recording is recorded, this information can be discriminated and the corresponding de-emphasis circuit can be selected at the time of reproduction. Therefore, there is no possibility of malfunction occurring as in the non-linear emphasis method.

(f) Examples Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of the recording side.
The figure is a block diagram showing the configuration of the reproducing side.

In FIG. 1, 50 is an input terminal for the color television signal to be recorded, 1 is a luminance (Y) signal and chrominance (C) signal separation circuit, 2 is a chrominance signal processing circuit,
3 is a clamp circuit for the Y signal, 4 is a sync separation circuit that separates luminance information (hereinafter referred to as Y' signal) and a sync signal from the Y signal, 7 is a 1H delay circuit that receives the Y' signal as input, 8 and 9 are These are first and second pre-emphasis circuits which have different characteristics and are supplied with the output of the 1H delay circuit 7. The first and second pre-emphasis circuits 8 and 9 basically have different emphasis amounts, with the second pre-emphasis circuit 9 having a larger emphasis amount.

5 is a weighting circuit that receives the Y' signal as input;
Functionally, it has the characteristic of emphasizing high frequencies. 6 is a detection circuit that level-detects the output of the weighting circuit 5;
A synchronizing signal is applied to make the determination every horizontal period.

12 is a first circuit controlled by the output of the detection circuit 6.
a changeover switch; 10 is a first amplifier that makes the synchronization signal have a first amplitude; 11 is a second amplifier that makes the synchronization signal a second amplitude; 13 is a second changeover switch; The first and second amplifier outputs are selected according to the circuit 6 output. 20 is a third pre-emphasis circuit for synchronizing signals, and 14 is a mixing circuit of the output of the first changeover switch 12 and the output of the third pre-emphasis circuit 20.

15 is white/dark clip circuit, 16 is
17 is a mixing circuit of the FM modulation circuit 16 output and the color processing circuit 2 output, 18 is a recording amplifier, and 19 is a video head.

Next, the configuration on the playback side will be explained. 22 is a preamplifier which receives the playback output of the video head 19;
3 is a low pass filter (LPF) that separates the C signal (low frequency converted) from the output of the preamplifier 22, 24 is a reproduction color processing circuit, and 25 is a high pass filter (LPF) that separates the signal related to FM modulated luminance. HPF), 26 is a limiter/FM demodulation circuit that inputs the HPF25 output, 27 is a limiter/FM
Pre-emphasized from demodulation circuit 26 output
This is a sync separation circuit that separates the Y' signal and sync signal. This synchronization separation circuit 27 is supplied with the output of a VCO 28 which is forcibly locked in a vertical blanking section where there is no video signal using a head switching pulse signal from a terminal 51 and generates a horizontal synchronization mask pulse.

29 is the first pre-emphasis circuit 8 of the recording system.
30 is a second de-emphasis circuit corresponding to the second pre-emphasis circuit 9; 32 is a third de-emphasis circuit corresponding to the third pre-emphasis circuit 20.

The output of the third de-emphasis circuit 32 is supplied to a level detection circuit 33 and a waveform shaping circuit 34 that keeps the amplitude constant. The outputs of the first and second de-emphasis circuits 29 and 30 are supplied to a third changeover switch 31, and one of them is selected according to the output of the level detection circuit 33. 35 is a mixing circuit of the output of the third changeover switch 31 and the output of the waveform shaping circuit 34, 36 is a noise canceler, 37 is a mixing circuit of the C signal and the Y signal from the noise canceler, 38 is an output amplifier,
52 is a video output terminal.

Next, the operation will be explained. The level of the Y' signal is determined by the detection circuit 6. When the level is high, the first pre-emphasis circuit 8 with a small amount of emphasis is selected, and when the level is a small signal, the second pre-emphasis circuit 9 with a large amount of emphasis is selected. be done. At the same time, in order to instruct the selected pre-emphasis circuit, in the case of the first pre-emphasis circuit 8, the amplitude of the synchronization signal is set to the first amplitude (smaller), and in the case of the second pre-emphasis circuit 9, the amplitude of the synchronization signal is set to the first amplitude (smaller). 2 amplitude (large).

The detection circuit 6 has an appropriately determined number of time points, and since the horizontal synchronization signal is used to create the change timing of the discrimination output,
Depending on the level of the Y' signal, a determination output for the next IH period is output. Therefore, first,
Supplied to the second pre-emphasis circuits 8 and 9
The Y' signal is delayed by 1H period through the 1H delay circuit 7. Incidentally, in addition to providing this 1H delay circuit 7, the color signal may be delayed by 1H.

Furthermore, the high frequency range of the input signal to the detection circuit 6 is emphasized by the weighting circuit 5. Therefore, there is a sudden change in the Y' signal (high frequency component)
Sometimes the amount of emphasis will be reduced.

During playback, it is determined whether the amplitude of the synchronization signal is at the first level or the second level,
Since the de-emphasis circuit is selected, de-emphasis is executed in correspondence with pre-emphasis during recording.

In the embodiment, the pre-emphasis characteristics are identified based on the amplitude of the synchronizing signal, but in cases other than self-recording/playback, there is a possibility that the identification may be mistaken. To prevent this, the form of the added information signal may be changed. For example, a method may be considered in which a digital signal indicating the pre-emphasis characteristic is inserted into the horizontal blanking period.

Furthermore, the number of types of emphasis may be three or more.

(g) Effects of the invention As described above, according to the invention, information regarding the emphasis characteristics during recording is simultaneously recorded, so the de-emphasis characteristics during playback can be selected based on this information, which makes it possible to select the de-emphasis characteristics during playback. This method is practical because it does not cause such inconveniences.

[Brief explanation of the drawing]

The drawings relate to an embodiment of the present invention; FIG. 1 is a block diagram showing the configuration on the recording side, and FIG. 2 is a block diagram showing the configuration on the reproducing side. 6...Detection circuit, 8, 9...First and second pre-emphasis circuits, 12...First changeover switch, 1
3...Third changeover switch, 14...Mixing circuit, 2
9, 30...first and second de-emphasis circuits,
31...Third changeover switch, 33...Level detection circuit.

Claims (1)

[Scope of utility model registration request] Multiple pre-emphasis circuits with different characteristics,
means for detecting the level of the luminance signal to be recorded; means for selecting the plurality of pre-emphasis circuits based on the detection result; means for recording the signal by adding information indicating the selected pre-emphasis circuit; A luminance signal processing circuit comprising: a de-emphasis circuit corresponding to the pre-emphasis circuit; and means for detecting the information included in the reproduced output during reproduction and selecting the de-emphasis circuit.