JPS5871770A - Compensating system of video signal - Google Patents

Abstract

PURPOSE:To increase the degree of modulation of video signals without deteriorating the contour part, by shaping the center part of the waveform corresponding to the information to a rectangular shape and adding this rectangular waveform to the original video signal or delay signal. CONSTITUTION:The chrominance and luminance signals C and Y which are separated from each other through a luminance-chrominance signal separating circuit 15 are fed to signal lines 17 and 16 respectively. The signal Y is fed to an input terminal 1 and then converted into a contour compensating signal E to be delivered from an adder circuit 7. For the output E, the center projected part and the projected part of the contour part are shaped to rectangular waveforms by comparators 18 and 19 to be used for compensation of video signals. AND gates 20 and 21 eliminate horizontal and vertical synchronizing signals and are controlled by the output of a synchronizing signal separating circuit 22 to transmit an output selectively. An adder circuit 25 adds the outputs F and G of level controllers 23 and 24 to the output B of a delaying circuit 2 to produce a compensating video signal H. The signal H is added with the signal C through an adder circuit 27 after passing through an LPF 26.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for correcting a video signal so that characters, etc. can be clearly displayed in a video disc method or the like.

When transmitting or recording text information in a limited frequency band, as the amount of text information increases, the degree of modulation becomes smaller, making it difficult to see the text on the playback screen.

In order to solve this kind of problem, many contour correction methods have already been proposed. FIG. 1 shows a typical conventional contour correction method with a relatively simple configuration, in which a video signal, such as a luminance signal in NTSC, supplied from an input terminal Ill is kept constant. Time (20naec)
A first delay circuit (2) for delaying the output of the first delay circuit (2), a first inverting circuit (3) consisting of an inverting amplifier for inverting the phase of the output of the first delay circuit (2), and a first delay circuit (3) for inverting the phase of the output of the first delay circuit (2). a first addition circuit (4) that adds the output of the video signal and the output of the first inversion circuit 13), and an addition circuit (4) of at.
) and a second delay circuit (5) that delays the output of
a second inverting circuit (6) consisting of an inverting amplifier that inverts the phase of the output of #g1; and a second inverting circuit (6) that adds the output of the adder circuit (4) of #g1 and the output of the second inverting circuit (6). a third inverting circuit (8) consisting of an inverting amplifier that inverts the phase of the output of the second adder circuit (7); The adder circuit (9) of w and 3 adds the outputs of the inverting circuit (8) and sends it to the output terminal αa.
).

If an NTSC black and white composite video signal, that is, a 4 degree signal, is input to the input terminal 11+ in Figure 811, and the waveform corresponding to the line indicating the black character is the AM modulated wave shown in Figure 2). , this is delayed by about 20n in the first delay circuit (2) to obtain the delayed output shown in FIG. 2(b). and,
The waveform shown in FIG. 2 (10I) is obtained by inverting the delayed output shown in FIG. 2 (b) using the inverting circuit (3) and adding it to the waveform shown in FIG. 2 (11) in the adding circuit (4).

In other words, a waveform equivalent to first-order differentiation of the waveform shown in FIG. 2+a) is obtained. Next, the output of the first adder circuit (4) (Fig. 2C) is delayed by a constant delay time (for example, 20 naec) that is the same as or close to the delay time of the first delay circuit (2). When delayed in circuit (5), the waveform becomes 1dl in Fig. 2, which is inverted in 6) to the inverting circuit, and then sent to the second adder circuit (7) to perform the first addition shown in Fig. 2 (C) K. Circuit (4)
When added to the output of , the waveform shown in FIG. 2 (61) is obtained.

That is, a waveform corresponding to the second-order differential waveform of the waveform shown in FIG. 2 1al is obtained at the output stage of the adder circuit (7). This second figure (
As is clear from the comparison with the waveform of 1g2 Fig. 1a) or (b), the waveform of 6) has a leading edge (falling part) and a trailing edge (
This is a contour correction signal in which the level of the rising portion (rising portion) is limited and the central portion (peak portion) is emphasized. This figure 2 10I
When the phase of the contour correction signal shown in (8) is inverted in the inverting circuit (8) and added to the delayed video signal in FIG. A waveform is obtained in which the contours are strengthened and the contours are weakened. That is, a video signal whose modulation degree is increased and whose contour is corrected is obtained.

By the way, when transmitting or recording a large amount of character information, the degree of modulation becomes small, so it is required to significantly increase the degree of modulation in a correction circuit to improve contrast.

In Fig. 2 if), if you increase the peak of the negative voice's protruding part Pm, the degree of change will increase and the level difference between black and white will also increase, but if you increase the amplification degree, as shown in Fig. 2 ( When the central protrusion Pa of the waveform of el is increased, the level of the protrusion Pb in the opposite direction corresponding to the contour also changes, as shown in FIG.
The protruding parts Pm and Ph of the corrected video signal indicated by fl also change in the same way. Therefore, on the reproduced screen, the black line corresponding to the black level protruding portion Pm is surrounded by the bright line corresponding to the negative phase protruding portion Pa, giving a glare and making it difficult to see the characters. For this reason, conventionally the amount of correction had to be kept relatively low. Although the correction of the black text information signal has been described above, the same problem exists when correcting the white text information signal.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a video signal correction method that can increase the degree of modulation without deteriorating the contour portion.

To achieve the above object, the present invention provides a video signal in which the front rut and the trailing edge do not change sharply but gradually change, or a contour correction signal thereof, in which the center part movement/square wave excluding the contour part is waveformed. comprising a waveform shaping circuit for shaping, and an addition circuit for adding the rectangular wave obtained from the waveform shaping circuit to the video signal or its delayed signal to output a corrected video signal with an increased modulation degree. The present invention relates to a video signal correction method characterized by the following.

According to the QIHC described above, the central part of the waveform corresponding to information is shaped into a rectangular wave, and this is added to the original video signal or its delayed signal, so the modulation level of the video signal is reduced without deteriorating the contour part. It is possible to increase your busyness.

Embodiments of the present invention will be described below with reference to FIGS. 43 and 4. However, since the parts indicated by reference numerals (11 to (7)) in FIG. The waveform in figure ~(g) is ts2 figure tal~+
Since the waveform is substantially the same as that of No. 61, the explanation thereof will be omitted.

FIG. 3 shows a video signal processing system in a video disc player, in which an optical playback head is placed opposite a video disc on which character information is recorded by an array of optical bits. playback head fla&
Since c is connected to the reproducing circuit Q3, that is, the demodulating circuit,
Line (141/C) can obtain a composite video signal of the NTSC system, but in this system, it is not output as is, but after one contour correction and modulation enhancement. A luminance signal-chrominance signal separation circuit set 9 is connected to separate the luminance signal and color signal C, and one line (
A luminance signal, that is, a black and white video signal, is sent to line ll19, and a color signal is sent to the other line αη. After the black and white video signal is input to the input terminal +IIK, it is converted into the contour correction signal shown in FIG. 4 by the same circuits as shown in FIG. 1, from the delay circuit (2) to the adder circuit (7).

The contour correction signal obtained from the adder circuit (7) of g2 is in an overcompensated state in order to significantly improve the deformation of 11 degrees, and therefore the center positive protrusion s corresponding to the black character information is
The levels of both Pa and the reverse protrusion Pb corresponding to the contour portion are high. Accordingly, if the conventional method shown in FIG. 1 is used to add the waveform shown in FIG. 4 (■) to the waveform shown in FIG.
A problem arises. In order to solve this problem, in this embodiment, the second adder circuit (the first and second comparator circuit α9 is connected to the force output line), and the center protrusion Pa and the contour in FIG. The waveform of the protruding portion Pb of the portion is shaped into a rectangular wave, and this is used for correcting the video signal.

The first comparator (1 & is the unmodulated level (signal reference level) shown as Lm in Figure 4 (g)) VC contains a reference source that provides a nearly identical reference voltage L1, and is added to this reference voltage L1. The output voltage of the adder circuit (7) is compared with the output voltage of the adder circuit (7), and a negative rectangular wave PK shown in FIG. This is to shape the positive protruding portion Pa into the negative rectangular pHC waveform shown in Figure t44 [F]. - The comparator 2, a, is a reference voltage that almost matches the non-modulation level Lm, This reference voltage R is compared with the output voltage of the adder circuit (7), and a fourth voltage is set corresponding to the period in which the output voltage of the adder circuit (7) is lower than the reference voltage L1. This generates the positive rectangular wave P1 shown in FIG. 0. That is, it shapes the waveform of the opposite phase protrusion Pb into the positive rectangular wave shown in FIG. 4Q.

The first and second comparators (first and second AND gates provided at the output stage of the 1Qμ field) 12Q (21) are gates for removing horizontal and vertical synchronization signals, and the synchronization signal separation circuit @ The output of the comparator A9 is selectively transmitted under the control of the output of the A9. In other words, the synchronization signal is processed in the same way as the video signal and output from the comparator (18) (11), so if it is output as is, the synchronization pulse of the video signal that is finally output will be disturbed.Therefore, the synchronization signal Separation circuits are provided, and the gate gate υ is controlled by the synchronous signal No. 48 detection output, and the synchronous signal period is controlled by a comparator (
The transmission of the 181us output is cut off.

First and second level l1IIIl rectifiers (to) consisting of qK low resistance provided in the output stage of gate (to) 3υ
The level of the rectangular waves P1 and P shown in FIG.

The third adder circuit (c) adds the output of the level adjuster (c) (2) and the output of the first delay circuit (2), and
It forms a signal. That is, the delayed video signal of FIG. 4 (8), the level adjustment output of the rectangular wave shown in FIG. 4 [F]K which is in phase with this, and the rectangular wave P shown in FIG.
A waveform is obtained by synthesizing the level adjustment output of .

When forming the corrected video signal shown in FIG.
A rectangular wave P with an opposite phase corresponding to the contour shown in .

The level is set so that it does not exceed the unmodulated level.

If the contour correction section P1 protrudes above the non-modulation level (reference level), a state as shown in the conventional tIN2 diagram (f) will occur, and the characters will become glare and difficult to see on the reproduced screen. In this embodiment, since the level of the rectangular wave P shown in FIG. 40 can be adjusted independently, such a problem can be easily solved. By adding the rectangular wave P shown in FIG. 4 (G) to the delayed video signal shown in FIG. As a result, it becomes possible to increase the degree of modulation without deteriorating the contour portion, and the level difference between black and white increases.

Since the output of the first delay circuit (2) includes the synchronization signal, the third addition circuit (c) outputs a corrected video signal containing the JQ signal. 41g3 addition circuit (2)
The output of passes through a low-pass filter (to) as shown in Figure 4 (I).
It has a waveform shown in , and is added to the color signal in the fourth adding circuit. That is, the third line of 20 naec is provided with a line anVc for transmitting the color signal sent out from the separation circuit u5.
The delayed color signal obtained from the delay circuit (2) in Fig. 4 (I
) is added. Then, the NT8C color video signal obtained from the adder circuit is sent to the output terminal (3) through the amplifier (C).

In FIG. 4, a video signal with black characters has been described, but a similar correction can be made in the case of a video signal with white characters.

As is clear from the above, according to this embodiment, it is possible to increase the degree of modulation while preventing an adverse effect on the contour portion.

Further, by adjusting the rectangular wave P in FIG. 4Q to an appropriate level and adding it, it becomes possible to perform contour correction in an appropriate amount. Therefore, an image signal capable of clearly reproducing characters can be easily obtained using a relatively simple circuit.

Although the embodiments of the present invention have been described above, the present invention is not limited thereto and can be further modified. For example, a phase equalizer may be provided before the first delay circuit (2). In addition, the first delay circuit (from 21 to 1@3
A line emptying ramp circuit leading to the adder circuit (c) may be provided. Further, a white clip circuit and a black clip circuit may be arranged at the output stage of the third adder circuit (c). Alternatively, the synchronization signal may be removed in advance on the input side, and only the Eirin signal may be waveform-shaped. Also, Figure 4 (
Since the waveform in (g) is substantially the same as the waveform obtained by dividing the waveform in Fig. 4 (8) into two-order circuit, The waveform shown in FIG. 4(g) may be obtained by sequentially passing the signal through an image separation circuit. Also, the fourth
If the contour correction using the rectangular wave shown in FIG. 0 is not necessary, a configuration may be adopted in which comparator 4 is omitted. In this case, the 41st signal or (5) may be input to a comparator and compared with the reference level to generate the 4th square wave.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a conventional contour correction method, FIG. 2 is a waveform diagram showing the states of each part in FIG. 1, and FIG. 3 is a block diagram showing a video signal processing method according to an embodiment of the present invention. FIG. 4 is a waveform diagram showing the state of each part in FIG. 3. Top view [fiK In the symbols used, (2) is the first delay circuit, (3) is the first inverting circuit, and (4) is the first
710 nose circuit, (5) is the second delay circuit, (6) is the second inverting circuit, (7) is the second addition circuit, Saba is the first convergence/, (11 is the second comparator) , (c) is the second level adjuster, circle is the second level adjuster, (c) is s3
This is an adder circuit. Agent Noriji Takano

Claims (2)

[Claims] (1) A waveform shaping circuit that shapes into a rectangular wave the central part of a video signal whose leading edge and trailing edge do not change sharply but gradually change, or the contour correction signal thereof, excluding the contour part, and C video 16. an addition circuit that adds the rectangular wave obtained from the waveform shaping circuit to the signal or its delayed signal and outputs a corrected video signal with increased modulation degree. Correction method. (2) The waveform forming circuit includes: a first delay circuit that delays the video signal for a certain period of time; a first inversion circuit that inverts the phase of the output of the first delay circuit; and the video signal. a first addition circuit that adds the output of the first inversion circuit; and a second addition circuit that delays the output of the first addition circuit for a certain period of time.
a second inversion circuit that inverts the phase of the output of the second delay circuit; and a second addition that adds the output of the first addition circuit and the output of the second inversion circuit. The circuit compares the output voltage of the second adder circuit with a level substantially equal to the unmodulated level of the output obtained from the second adder circuit, and determines whether the output voltage of the 1s2 adder circuit exceeds the unmodulated level. A voltage comparator that obtains a rectangular wave having a pulse width corresponding to a traversing period; and a circuit comprising the following: