JPH02222268A - Contour correction circuit - Google Patents

Abstract

PURPOSE:To attain contour correction with less foggy sense in framing of a white level of an image and its edge part by using less shoot quantity while narrow shoot width so as to apply contour correction of a video signal. CONSTITUTION:An input video signal to a differentiating circuit 3 is retarded by a delay circuit 2 so that a peak phase of a differentiating signal from the differentiating circuit 3 and the center phase of a quadratic differentiating signal from a quadratic differentiating circuit 5 are made coincident. Then the differentiating signal is rectified by a rectifier circuit 4 to obtain the differentiating waveform arranged unidirectionally and the differentiating signal and the quadratic differentiating signal are fed to a multiplier circuit 7 to obtain a contour correction signal when a narrow edge part is remarkable and added to the input video signal retarded by a delay circuit 9 so that the edge parts are made coincident thereby applying contour correction. Thus, the contour correction is attained, in which white level framing is not given to the edge of a picture and the S/N of the picture is not deteriorated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a contour correction circuit for correcting the dullness of edges of a video signal in, for example, a color television receiver.

(Prior art) Conventionally, in color television signal transmission systems, the transmission band is limited, even if the image is captured with an ideal image pickup tube, so the sharpness of the image reproduced on the receiver is limited. decreases.

For example, in the NTSC system, the band of the luminance signal is O~4.
Since the frequency is limited to 2MHz, the video signal when the image changes to black and white when transported with an ideal image pickup tube (see Figure 9 (a))
is band-limited so that the rising (or falling) of the signal is not sharper than a certain slope (see FIG. 9(b)), and the edges of the image seen on the screen appear blunt.

In order to improve the rise and fall characteristics of the edge portion of such a signal, a delay line is used to create a second-order differential signal, and contour correction is applied to the original signal (but delayed). There is.

FIG. 10 shows a block diagram of a contour correction circuit using a delay line, and FIG. 11 shows an operation waveform diagram of each part A to G of the circuit.

In FIG. 10, the input terminal 61 is connected to the video signal t (first
(See Figure 1A). When this signal passes through the delay line 62, it is delayed by 1° as shown in FIG. 11B. Similarly, at point 0, the delay line 63 is further passed through, so
There is a delay as shown in FIG. 11C. Here, it is assumed that there is no change in the gain 1 frequency characteristic due to passage of the delay line.

Next, the differential amplifier 64 is used to detect the voltage difference between points A and B, and at point D, a waveform (differential waveform) shown in Figure 11 is obtained. Similarly, the differential amplifier 65 is used to detect the voltage difference between point B and point 0, and at point E, a waveform (differential waveform) shown in FIG. 11E is obtained. When the waveforms at points D and E are combined by an adder 66, a second-order differential waveform as shown in FIG. 11F is obtained.

When the adder 69 adds the second-order differential signal passed through the amplifier 68 and the three-point signal passed through the amplifier 67, the input luminance signal is contour-corrected and the 11th
This results in a waveform with sharp edges as shown in Figure G. In addition,
In the above circuit, the gains of the amplifiers 64, 65, 67' and 68 are all set to 1.

By the way, in the conventional contour correction circuit shown in FIG.
It is possible to raise the frequency band (peaking), but there are wide shoots (preshoots P1, P3 and overshoots P2, P4) before and after the edge part.
') is added, so if the edges of the image have a white border, or if you want to make the edges steeper, you will have to increase the shot suspension (contour correction 5), which will increase the high frequency range. This increases the profit margin, and even unnecessary minute signal components such as noise components are amplified, resulting in a problem that the S/N ratio of the image deteriorates.

(Problems to be Solved by the Invention) As described above, in the conventional circuit, there are problems in that white borders are formed at the edges of the image and the S/N ratio of the image is deteriorated.

Therefore, the present invention aims to solve the above problems.
Contour correction that allows the edge to be made steeper even if the chute width is narrow and the sheet mark (contour correction amount) is small, and that no correction is applied to unnecessary minute signals such as noise. Its purpose is to provide circuits.

[Structure of the Invention] (Means for Solving and Overcoming the Problems) A first invention related to this contour correction circuit includes: a first delay circuit that delays a video signal supplied as an input; and a first delay circuit that delays a video signal supplied as an input; a second delay circuit that delays the input video signal; a differentiation circuit that differentiates the video signal from the eleven delay circuits; a rectification circuit that rectifies the differential signal from the differentiation circuit; a second-order differentiation circuit for differentiating; a multiplication circuit for multiplying the signal from the rectifier circuit by the second-order differentiation signal from the second-order differentiation circuit and outputting a contour correction signal; and a signal from the multiplication circuit. and an adder circuit that adds the video signal from the second delay circuit and outputs a video signal whose contours have been corrected.

Further, the second invention includes: a first delay circuit that delays a video signal supplied as an input; a second delay circuit that delays the video signal from the first delay circuit; a third delay circuit that delays the video signal from the third delay circuit; a fourth delay circuit that delays the video signal from the third delay circuit; and a third delay circuit that delays the video signal from the first delay circuit and the third delay circuit. a differentiating circuit that obtains the difference between the video signals from the delay circuit and generates a differential signal; a rectifier circuit that rectifies the differential signal from the differentiating circuit; while obtaining the difference between the video signals from the second delay circuit and the video signal from the fourth delay circuit, and adding these two difference outputs to generate a second-order differential signal. a second-order differential circuit that multiplies the signal from the rectifier circuit and the second-order differential signal from the second-order differential circuit, and outputs a contour correction signal; a signal from the multiplier circuit and the second and a filtering circuit that filters the video signal from the delay circuit and outputs a contour-corrected video signal.

(Function) In the present invention, basically, one signal is delayed so that the peak value phase of the differential signal from the differentiating circuit and the center phase of the second-order differential signal from the second-order differentiating circuit are made to coincide. (delays the input video signal of the differentiator circuit). and,
By rectifying the differential signal in a rectifier circuit and supplying the differential waveform aligned in one direction, the differential compensation signal and the second-order differential signal f) to a multiplication circuit, a contour with narrow edges can be obtained. Obtain the correction signal. Since the multiplication circuit performs a switching operation, the contour correction signal that is its output changes sharply. Contour correction is performed by adding this contour correction signal to the input video signal delayed so that the edge portions match.

(Example) The present invention will be explained below based on the example shown in the drawings.

FIG. 1 is a block diagram showing a contour correction circuit according to an embodiment of the present invention.

In this figure, numeral 1 is an input terminal for a video signal,
The input video signal is sent to delay circuit 2. Second order differential circuit 5. !
! It is supplied to the extension circuit 9. The delayed signal from the delay circuit 2 is differentiated by a differentiating circuit 3, rectified by a rectifier circuit 4, and supplied to a multiplier circuit 7. Further, the second-order differential signal from the second-order differential circuit 5 is amplified by an amplifier circuit 6 and supplied to the second-order circuit 7. The multiplier circuit 7 multiplies the signal from the rectifier circuit 4 and the signal from the amplification circuit 6, and supplies the signal to the adder circuit 10 via the amplification circuit 8. The adder circuit 10 adds the signal from the amplifier circuit 8 and the delayed signal from the delay circuit 9.

Output to output terminal 11. Note that the differentiating circuit 3 may be constructed of a filter circuit having band-pass characteristics, and the second-order differentiating circuit 5 is shown in FIG. 10)! It can be configured with solid circuits (circuits shown by numerals 61 to 66). Further, the rectifier circuit 4 can be configured with a circuit as shown in FIG.
It can be constructed with a double-balanced circuit as shown in Figure 5.

The operation of the above circuit will be explained with reference to FIG. FIG. 2 shows waveforms of each part of the circuit shown in FIG. 1.

First, assume that a video signal as shown in FIG. 2 is input to the input terminal 1. This signal becomes a delayed signal in the delay circuit 2 as shown in FIG. 2B.

Next, the differential circuit 3 performs differentiation, resulting in a differentiated waveform as shown in FIG. 2C. As shown in the figure, the voltage of this differential signal changes in both positive and negative directions with respect to the bias voltage. This differential waveform is rectified by the rectifier circuit 4 so that the voltage changes in one direction (here, 1. positive direction) to obtain the waveform shown in the second diagram.

On the other hand, the video signal input to the input terminal 1 is second-order differentiated by the second-order differentiation circuit 5, resulting in a waveform as shown in FIG. 2E. This second-order differential signal is amplified by the amplifier circuit 6 and multiplied by the signal shown at D by n? I. The output of the multiplication circuit 7 has a waveform as shown in FIG. 2F, and this signal is used as a contour correction signal.

Furthermore, the video signal input to the input terminal 1 is transmitted to a delay circuit 9
, resulting in a signal as shown in FIG. 2G. The delay amount of this signal is set to be the R extension necessary to match the phase with the contour correction signal obtained by the multiplication circuit 7. In the adder circuit 10, this delayed video signal and the multiplier circuit 7
The amplified contour-corrected signal from 1 is output as a contour-corrected video signal as shown in FIG. 2H. This video signal output has a waveform in which the edge portion has steep rises and falls, has a narrow shot width, and has few shots. Compared to the conventional waveform after contour correction shown in Fig. 11G, this is 1/2 at the shoot maximum, 2/3 at the shoot width, and several times shorter at the edge portion. There is.

FIG. 3 is a circuit diagram showing an example of the rectifier circuit 4, and FIG. 4 is a waveform diagram of signals at various parts of the circuit. In Figure 3, ? ! 1M21.22 is an input terminal into which the differential signal Vin from the differential circuit 3 is input. 23 is a power supply terminal that supplies DC voltage Vcc. 24 is an output terminal from which a rectified signal is taken out. This rectifier circuit includes transistors Q61.
Q62. Resistance R61, R62゜r<63. Constant current source I6
1. A differential amplifier circuit consisting of IG2 and a transistor Q6
an emitter follower circuit consisting of a transistor Q64 and a constant current source 163, an emitter follower circuit consisting of a transistor Q64 and a constant current source 164, a capacitive coupling circuit of a capacitor C61, a capacitive coupling circuit of a capacitor C62, and a transistor Q65. It consists of a maximum value detection circuit consisting of a Q66° constant current 8165. Note that the transistor Q65,
For each base of 06G, a resistor R is connected from the DC power supply 26.
A DC voltage Vx is supplied via R64 and R65. Further, the DC power supply 26 is connected to the base of a constant voltage circuit consisting of a transistor Q67 and a constant current source 166 via a resistor R66, and the 2+4 quasi-voltage Vref is taken out from the terminal 25 connected to the emitter of Q67, and the Supplied to circuits, etc.

In the above configuration, the differential signal Vin as shown in FIG. 4(a) is applied to the transistor Q61. Q62. Resistance R6
1, R62, R63, and the base terminal of a differential amplifier circuit consisting of constant current sources 161 and 162. ]・Langister Q
The collector of transistor Q61 outputs an inverted amplified signal, and the collector of transistor Q62 outputs an in-phase amplified signal. Note that the resistance values of R62 and R63 are the same. These inverted amplified and in-phase amplified signals are transmitted to transistors Q63. Q64 and constant current source i63
, 164 and a capacitive coupling circuit of capacitors C61 and C62, the transistors Q65. It is input to each base of the maximum value detection circuit consisting of Q66 and constant current source 165. 1 Helangista Q65.
The base waveform of Q66 is as shown in FIG. 4(b). The base signal of the 1-herald transistor Q65 is the differential signal V
The base signal of the transistor 066 is in phase with the signal Vin. A voltage waveform with a higher base potential is output from the common emitter of transistors Q65 and Q66. As a result, as shown in FIG. 4(C), the output terminal J 24 has a
) is obtained by rectifying the voltage waveform vOut. This output signal (200) is supplied to the multiplication circuit 7.

FIG. 5 is a circuit diagram showing an example of the multiplication circuit 7, and FIG. 6 is a waveform diagram of each part of the circuit. In Figure 5,
Reference numerals 31 and 32 denote input terminals to which a second-order differential signal @ (see FIG. 2E) is applied from the second-order differential circuit 5 as an input VA. Further, the output signal Vout shown in FIG. 3 is applied to the input terminal 33 as the input VB, and the reference voltage Vref shown in FIG. 3 is applied to the input terminal 34 as the input VC. 35 is DC voltage V
It is a power supply terminal of CC, and 36 is an output terminal from which the world output VD is taken out. This multiplication circuit consists of transistor Q81
．． Q82. A differential amplifier circuit consisting of a resistor R81, constant current sources 181 and 182, and a transistor Q81. ]・Lansistor Q83. Q84.
Q85, Q86. It consists of a double balanced differential amplifier circuit consisting of resistors R82 and R83.

In the above configuration, a rectified signal J as shown in FIG. 6(a) is input to the base of the transistor Q81. Transistor Q81. The collector current waveform of Q82 is shown in Figure 6 (
b) Furthermore, since a second-order differential signal as shown in FIG. 6(C) is applied to the input VA in FIG. 5, when the waveform of VA is on the positive (+) side, the transistor Q83.086 becomes conductive. , in the case of the negative (-) side, the transistor Q84°085 is conductive, so that a signal waveform as shown in FIG. 6(d) is output as the output signal VD. This multiplication saw passes through an amplifier circuit 8 and an adder circuit 10.
is supplied to Note that the transistor Q81. Due to the variation is in the collector current of Q82, the variation in the voltage output to the terminal 36 is 1sxR83.

As described above, the video signal outputted from the adder circuit 10 is a signal with sharp rises (or falls) at the edge portions, a narrow shoot width, and a small amount of "shu" and "ke". In addition, in the small signal region, the amplitude of the second-order differential signal obtained from the second-order differentiator circuit 5 becomes small, so the double-balanced tl)t'x circuit 7 shown in FIG. 5 performs a linear operation. . For small signals, an output corresponding to the magnitude of the input V^ is obtained, and the amplitude of the contour correction signal output vO is further attenuated, so unnecessary signal components such as noise are not emphasized (contour correction). . Therefore, if the gain of the amplifier circuit 6 is selected to an appropriate value, it is possible to perform sharp contour correction without deterioration of the S/N ratio.

FIG. 7 is a block diagram showing another embodiment of the present invention,
FIG. 8 is a signal waveform diagram of each part A-1 of the circuit. 7th
The embodiment shown in the figure shows a circuit that can operate effectively even with video signals subject to various band restrictions.
The circuit is basically the same as that shown in FIG. 1, except that a plurality of delay circuits are used before the differentiating circuit and the second-order differentiating circuit.

That is, the video signal supplied to the input terminal 41 (see FIG. 8A) is sequentially delayed by the delay circuits 42, 43, 44, 45 (see FIGS. 8B-E), and the output of the delay circuit 42 and the delay circuit 4 are sequentially delayed.
4 outputs are input to a difference detection circuit 46, and a differential signal is generated by detecting the difference between both outputs. This differential signal is then transmitted to the amplifier circuit 47. The signal is inputted to a multiplication circuit 49 through a rectifier circuit 48 (see FIG. 8G). In addition, the input video signal and the output of the delay circuit 43 are input to the difference detection circuit 50.
On the other hand, the output of the delay circuit 43 and the output of the delay circuit 45 are input to the difference detection circuit 51, and the difference outputs from both circuits 50 and 51 are added and equalized by the addition circuit 52, thereby generating a second-order differential signal. (See Figure 8F). This second-order differential signal passes through the amplifier circuit 53 and is input to the multiplication circuit 49. Multiplication circuit 4
9, the outputs of the two circuits 48 and 53 are multiplied, and the multiplication output (see FIG. 8H) and the output of the delay circuit 43 are added in an adder circuit 54 to obtain a contour-corrected video signal at the output terminal 55. (See Figure 8 ■). Note that the difference detection circuit 46
．． 50.51 can be configured with a differential amplifier.

As shown in FIG. 8, the waveforms of each part of the circuit end up being similar to the waveforms of the circuit of FIG. 1.

In the circuit configuration shown in FIG. 7, since the phase of the peak value of the differential signal obtained by the difference detection circuit 46 always matches the center phase of the second-order differential signal obtained by the addition circuit 52, the color television receiver The human-powered video signal source can be used to convert the signal source of television radio waves to
Even if the signal source is changed to a signal source with a wide bright spot band, such as an L-IS type VTR, it is possible to always obtain a sufficient effect.

[Effects of the Invention] As described above, according to the present invention, the contour correction of the video signal is performed with a narrower chute width and a smaller chute k (correction amount), thereby making the rise and fall of the edge portion steeper. This makes it possible to frame the white parts of the image and perform contour correction with less blurring at the edges, which has been a problem in the past.

Also, the noise.

In such small signal areas, no contour correction signal is output, so the S/N ratio of the image does not deteriorate.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing a contour correction circuit according to an embodiment of the present invention, Fig. 2 is a signal waveform diagram of each part of the circuit shown in Fig. 1, and Fig. 3 is a circuit diagram showing an example of the rectifier circuit shown in Fig. 1. , Figure 4 is the third
5 is a circuit diagram showing an example of the circuit shown in FIG. 1, FIG. 6 is a signal waveform diagram of each part of the circuit shown in FIG. 5, and FIG. FIG. 8 is a signal waveform diagram of each part of the circuit in FIG. 7, FIG. 9 is a waveform diagram of a video signal subjected to band limitation, and FIG. 10 is a conventional contour correction circuit. The block diagram, FIG. 11, is a signal waveform diagram of each part of the circuit shown in FIG. 1.41...Input terminal, 2.9.42.43.44.45...Delay circuit, 3.
...Differentiating circuit, 4,48... Rectifying circuit, 5... Second order differentiating circuit, 6.8.47.53... Amplifying circuit, 7.49... Multiplier circuit, 10.54...・Additional circuit,
11.55...Output terminal. Fig. 2 Fig. 1 Fig. 5 Fig. 6 Obi 1 handwriting jwL Fig. 9 Fig. 10 (b) Fig. 11

Claims (2)

[Claims] (1) A first delay circuit that delays a video signal supplied as an input; a second delay circuit that delays a video signal supplied as an input; and a video signal from the first delay circuit. a differentiating circuit for differentiating, a rectifying circuit for rectifying the differential signal from the differentiating circuit, a second-order differentiating circuit for second-order differentiating the video signal supplied as the input, and a second-order differentiating circuit for differentiating the signal from the rectifying circuit and the second-order signal. a multiplication circuit that multiplies the second-order differential signal from the differentiation circuit and outputs a contour correction signal; and a video signal that adds the signal from the multiplication circuit and the video signal from the second delay circuit to perform contour correction. A contour correction circuit comprising: an addition circuit that outputs; and a contour correction circuit. (2) A first delay circuit that delays a video signal supplied as an input; a second delay circuit that delays a video signal from this first delay circuit; and a video signal from this second delay circuit. a third delay circuit that delays the video signal from the third delay circuit; a fourth delay circuit that delays the video signal from the third delay circuit; and the video signal from the first delay circuit and the video signal from the third delay circuit. A differentiator circuit that obtains a difference between signals and generates a differential signal; A rectifier circuit that rectifies the differential signal from the differentiator circuit; and A rectifier circuit that rectifies the differential signal from the differential circuit; a second-order differential circuit that obtains the difference between the video signal from the second delay circuit and the video signal from the fourth delay circuit, adds these two differential outputs, and generates a second-order differential signal; a multiplication circuit that multiplies the signal from the rectifier circuit by the second-order differential signal from the second-order differential circuit and outputs a contour correction signal; A contour correction circuit comprising: an addition circuit that adds video signals and outputs a contour-corrected video signal;