JPH0220969A - Luminance signal processing circuit - Google Patents

Abstract

PURPOSE:To accurately restore an edge part and to prevent waveform rounding by detecting the parts where a white-level and a block-level edge part exceed a white clip level and a dark clip level and outputting a regenerated luminance signal and a delay signal so that their edge absent parts compensate each other. CONSTITUTION:The 1st and 2nd Schmitt trigger circuits 6 and 7 detect the parts which exceed the white clip level and dark clip level of the regenerated luminance signal. A 3rd Schmitt trigger circuit detects the edge parts of the reproduced luminance signal by using the output of a subtracter 9 as a 1st input, and the reference level to detect the edge part as a 2nd input. The regenerated luminance signal and its delay signal are switched by a switch 18 and outputted according to the output of the 1st and 2nd Schmitt trigger circuits 6 and 7, and a 3rd Schmitt trigger circuit 10. Consequently, the absence of the edge part due to white clipping and dark clipping can be corrected.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a luminance signal processing circuit useful in magnetic recording and reproducing devices such as video tape recorders.

2. Description of the Related Art In conventional video tape recorders, since demodulation noise increases as the FM modulation frequency increases, a pre-emphasis circuit is used to cope with this problem. However, when a pre-emphasis circuit is used, sharp overshoots and undershoots occur at the rise of the luminance signal to the white level and the fall to the black level, and if recorded and played back in this state, an overmodulation state will occur. This causes an inversion phenomenon.

Therefore, conventionally, overshoots and undershoots exceeding a certain level have been clipped using a clipping circuit (not shown).

Problems to be Solved by the Invention However, when recording and reproducing are performed through such a conventional clip circuit, there is a problem in that edge information is lost at the rising edge to the white level and the falling edge to the black level. had.

The present invention overcomes the above problems and provides a luminance signal processing circuit that corrects the loss of edge information due to white clips and dark clips.

Means for Solving the Problems In order to solve the above-mentioned problems, the brightness signal processing circuit of the present invention provides a brightness signal near the white clip level of a demodulated brightness signal obtained by demodulating a brightness signal that has been subjected to pre-emphasis processing and frequency modulation. a first Schmitt trigger circuit that detects a portion of the demodulated luminance signal that is above a predetermined reference level; a second Schmitt trigger circuit that detects a portion of the demodulated luminance signal that is below a predetermined reference level near the dark clip level; A first delay device that delays, a subtracter that takes the difference between the input and output of the first delay device, and a first delay device that compares the output of the subtracter with a reference level for detecting an edge portion of the demodulated luminance signal. No. 3 Schmitt trigger circuit, the output of the third Schmitt trigger circuit, and the output of the first Schmitt trigger circuit. The first one which is ANDed with the output of the second Schmitt trigger circuit. a second AND circuit; Second
An OR circuit that calculates the logical sum of the outputs of the AND circuit, a delay timing circuit that delays the output of the OR circuit and creates a control signal with a pulse of a predetermined width, and de-emphasis processing, etc., is performed on the demodulated luminance signal. The structure includes a second delay circuit that delays the obtained reproduced luminance signal, and a switch means that switches and outputs the reproduced luminance signal and the delayed reproduced luminance signal based on a control signal.

Effect of the present invention With the above-described configuration, the portion exceeding the white clip level and the dark clip level at the edge portion from the black level to the white level and from the white level to the black background of the demodulated luminance signal is set to the first and second points. A Schmitt trigger circuit detects the signal, and logical processing of an AND circuit and an OR circuit is used to create a control signal for a switch that selects and outputs the reproduced luminance signal and its delayed signal. Since the reproduced luminance signal and its delayed signal are output so as to compensate for the edge missing portions, it is possible to accurately restore the edge portions and perform processing that does not cause waveform rounding.

EXAMPLE An example of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of a luminance signal processing circuit according to an embodiment of the present invention, and FIG. 2 is a signal waveform diagram showing the operation of each part of the same.

In the figure, 1 is a demodulator that demodulates a pre-emphasized and FM-modulated luminance signal, 2 is a de-emphasis circuit that de-emphasizes the demodulated luminance signal, and 3
4 is a noise canceller, 5 is a low-pass filter (LPF), and 6 is a demodulator 1.
The demodulated luminance signal demodulated by
(RKFl) as the second signal input, 7 also uses the demodulated luminance signal as the first signal input, and uses the reference level Iv (RICy2) at a constant level near the dark clip level as the second signal input. A second Schmitt trigger circuit receives a signal as an input; 8 is a first delay device that delays the demodulated luminance signal; 9 is a subtractor that takes the difference between the output of the delay device 8 and the input; 1o is a subtractor 9; A third Schmitt trigger circuit which takes the output as a first input and a reference level for detecting the edge part as a second input, 11 inputs an edge detection pulse which is the output of the third Schmitt trigger circuit 1o. This chattering prevention circuit is used to remove noise that cannot be removed by the third Schmitt trigger circuit 1o, and does not need to be used in particular. 12 is a first AND circuit that calculates the logical product of the output of the chattering prevention circuit 11 and the output of the first Schmitt trigger circuit e; 13;
14 is a second AND circuit that takes the logical product of the output of the chattering prevention circuit 11 and the output of the second Schmitt trigger circuit 7; The OR circuit 15 and 16 takes the logical sum of the outputs of the second AND circuit, and the first OR circuit 15 and 16 delay the output of the OR circuit 14 to produce an output pulse of arbitrary width. The first delay timing circuit serves as the second delay timing circuit. This is the second monomulti circuit.

1A is a de-emphasis circuit 2. Nonlinear de-emphasis circuit 3. Noise canceller 4. A delay circuit delays the reproduced luminance signal obtained through the LPF 5 until the transient state of the edge portion ends and stabilizes; 18 is a switch for outputting the reproduced luminance signal and the signal delayed by the delay circuit 17 to the output of the monomulti circuit 16; A switch 19, which is switched based on a control signal, is a MIX circuit for mixing a color signal with the reproduced luminance signal switched on the first day of the switch or its delayed reproduced luminance signal.

The operation of the luminance signal processing circuit of this embodiment configured as described above will be described below.

First, the demodulated luminance signal demodulated by the demodulator 1 is
As shown in the figure, the signal has a signal waveform that has been white-clipped and dark-clipped (hereinafter referred to as signal a, a signal or pulse of the following function will also be expressed in the same way). This faith? j a High' emphasis circuit 2. De-emphasis processing and non-linear de-emphasis processing are performed via the non-linear de-emphasis circuit 3,
Noise canceller 4. Predetermined luminance signal processing is performed via the LPF 5, and a reproduced luminance signal g is obtained. delay device 1
7 is delayed for a period tg until the transient state of the edge portion of the reproduced brightness signal g ends and becomes stable, and a delayed signal is obtained, which is outputted to the X terminal and the X terminal of the switch 1, respectively, together with the reproduced brightness signal g.

Further, the demodulated luminance signal is a signal before being processed by the de-emphasis circuit 2, and is different from the signal a having a signal waveform that has been white-clipped and dark-clipped, and this signal a is the first signal a. input to the second Schmitt circuit 6.7,
They are compared with REF1 and REF2 to obtain signals S and C as comparison outputs, respectively, which serve as one input signal of AND circuits 12 and 13, respectively.

On the other hand, the demodulated luminance signal a, which is the output of the demodulator 1, is delayed by one to several pixels in a delay device 8, and a difference signal from the undelayed signal a is obtained in a subtracter 9.

This difference signal is input to the third Schmitt circuit 1o which has the edge-detectable repe y as a reference input, and the edge detection pulse is input to the chattering prevention circuit 11. The signal d is a signal obtained through the chattering prevention circuit 11. AND circuits 12 and 13 perform the logical product of this signal d, signal S, and signal C, and output the ANDed signals to the OR circuit 14, respectively. Signal e indicates the output of OR circuit 14. This signal e is input to the first mono multi circuit 15, delayed by a time te, and then sent to the second mono multi circuit 16.
The pulse @W is determined and becomes the switch control signal f for controlling the switch 23.

Normally, the switch 23 selects the
It is output to 9. Further, the switch 23 selects the X terminal when the switch control signal f is at a high level, and reproduces the reproduced luminance signal g with stable timing of the edge after de-emphasis
As shown in FIG. 2, the reproduced luminance signal g and the delayed signal are respectively switched and outputted to the MIX circuit 19 by the selection operation of the switch control signal f, and the edge portion is output to the MIX circuit 19. The restored signal i will be output to the MIX circuit 19.

As described above, according to this embodiment, the first . Based on the output of the second Schmitt trigger circuit 6.7 and the output of the third Schmitt trigger circuit 1° that detects the edge portion of the reproduced brightness signal, the reproduced luminance signal and its delayed signal are switched and outputted by the switch 18. It is possible to correct the loss of edges that are lost in white clips and dark clips.

Effects of the Invention As described above, according to the present invention, the black level to the white level,
At the edge of the white level to the black level, the part that exceeds the white clip level and the dark clip level is the first. Detected by the second Schmitt trigger circuit, a control signal for a switch that selects and outputs the reproduced luminance signal and its delayed signal is created by logical processing of an AND circuit and an OR circuit, and this control signal Since the reproduced luminance signal and its delayed signal are output so as to compensate for each other's missing edge portions, it is possible to accurately restore the edge portions and perform processing that does not cause waveform distortion.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a luminance signal processing circuit according to an embodiment of the present invention, and FIG. 2 is a signal waveform diagram showing the operation of each part of the same. DESCRIPTION OF SYMBOLS 1... Demodulator, 2... De-emphasis circuit, 6... First Schmitt trigger circuit, 7
...Second Schmitt trigger circuit, 8...
...First delay device, 9...Subtractor, 1o...
...Third Schmitt trigger circuit, 11...
Chattering prevention circuit, 12.13...AND circuit, 14...OR circuit, 16.16...
・Mono multi-circuit, ・・・・・・switch.

Claims (1)

[Claims] A first Schmitt trigger circuit detects a portion of a demodulated luminance signal obtained by demodulating a pre-emphasized and frequency-modulated luminance signal near a white clip level that is equal to or higher than a predetermined reference level; a second Schmitt trigger circuit that detects a portion below a predetermined reference level near the clip level; a first delay device that delays the demodulated luminance signal; and a difference between the input and output of the first delay device. a third Schmitt trigger circuit that compares the output of the subtracter with a reference level for detecting an edge portion of the demodulated luminance signal; an output of the third Schmitt trigger circuit; first and second AND circuits that take a logical product with the outputs of the first and second Schmitt trigger circuits, an OR circuit that takes a logical sum of the outputs of the first and second AND circuits, and the OR circuit a delay timing circuit that delays the output of the demodulated luminance signal to create a control signal having a pulse of a predetermined width, and a second delay circuit that delays the reproduced luminance signal obtained by performing de-emphasis processing or the like on the demodulated luminance signal; A brightness signal processing circuit comprising a switch means for switching and outputting the reproduced brightness signal and the delayed reproduced brightness signal based on the control signal.