JPH0338972A - Video signal contour corrector - Google Patents

Abstract

PURPOSE:To acquire a satisfactory picture, for which noise is reduced and sharpness is high, by preparing a contour correcting signal by two delay circuits, adder circuit and two subtracting circuits, removing the noise component of a contour correcting period by a gate pulse and a trap, slicing a tip part and afterwords, adding the contour correcting signal to an original input video signal. CONSTITUTION:First and second delay circuit parts 16 and 17 are provided to delay the input video signal for prescribed time. A signal, for which the output signals of those delay circuits are added with the input video signal, and a signal subtracting them are calculated and a contour gate pulse 22 is prepared by the subtracted signal. By using this pulse, a noise removing trap 23 is inserted to the contour part of the added signal. On the other hand, a signal slicing 25 the second subtracting signal, for which the output signal of the first delay circuit 16 and the added signal are subtracted, at a prescribed level is added to an output signal passing through the noise removing trap 23. Afterwards, the noise component in the transient part of the video signal is removed and processing is executed to a signal adding a peak signal. Thus, a contour is emphasized and the sharpness of a picture is improved without generating saturation in the waveform of the original signal.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is applied to video playback devices such as television receivers, video tape recorders (hereinafter referred to as VTRs), and disk players. The present invention relates to a video signal contour correction device configured to correct the contour of the video signal in order to improve the sharpness of the video signal.

[Prior Art] Image quality in video playback devices such as television receivers, VTRs, and disc players is determined by the balance of three factors: S/N, resolution, and sharpness of the video signal.

FIG. 3 is a block diagram showing the configuration of a video signal contour correction device for a conventional VTR, which aims to improve image quality determining factors. In the figure, (1) is a demodulation circuit, and this demodulation circuit (1) demodulates a 3.4 MHz to 4.4 MHz FM modulated video signal picked up by a playback head (not shown) into a baseband video signal. do.

(2) is a de-emphasis circuit, which suppresses the high-frequency components of the recorded video signal by emphasizing the high-frequency components using a pre-emphasis circuit (not shown) during recording. It reduces high-frequency noise components generated in the recording/reproducing system, and has characteristics opposite to those of the pre-emphasis circuit described above.

(3) is a low-pass filter (hereinafter referred to as LPF),
Linearizes the high frequency band of the video signal.

(4) is a second-order division circuit that differentiates the transient part and noise component of the video signal. (5) is an attenuator that sets the differentiated signal level to a predetermined level.

(6) is an adder circuit, which includes an LPF (3) of 0 or more that adds the output signal of the LPF (3) and the output signal of the attenuator (5), a quadratic division circuit (4), and an attenuator (5).
), the addition circuit (8) creates a quadratic image quality processing circuit (
23).

Next, the operation of the above configuration will be explained.

The video signal is FM modulated to 3.4 MHz to 4.4 MHz, high frequency components are emphasized through a pre-emphasis circuit, and recorded on a recording medium, and the video signal is picked up by a playback head and input to the demodulation circuit (1). According to
This FM modulated video signal is demodulated into a baseband video signal.

Next, this demodulated video signal is input to a de-emphasis circuit (2) having a characteristic opposite to that of the pre-emphasis circuit, thereby suppressing high-frequency components and reducing high-frequency noise components.

In the case of only emphasis processing as described above, many noise components (n) remain as shown in FIG. 4(a). In particular, if the quality of the VTR's magnetic tape is poor,
A considerable noise component (n) remains.

Next, a video signal as shown in FIG. 4(a) containing many noise components (n) is processed by a two-dimensional image quality processing circuit (2
3), first, the video signal becomes L P F
(3), the high frequency components and noise components are removed as shown in FIG. 4(b).

On the other hand, the transient part (1) in which the level of the video signal that has passed through the quadratic division circuit (4) suddenly changes is divided twice and the noise component is also differentiated, and this differentiated signal passes through the attenuator (5). As a result, the level is set to an appropriate level, resulting in a waveform signal as shown in FIG. 4(C).

Continuing, the fourth output from L P F (3) above is
The signal shown in FIG. 4(b) and the signal shown in FIG. 4(c) outputted from the attenuator (5) are added in an adder circuit (6) to produce a signal as shown in FIG. 4(d). becomes. Although the signal shown in FIG. 4(d) includes a noise component (n), the rising transient portion of the original video signal shown in FIG. 4(a) that suddenly changes from the white level to the black level, and Moderate peaks (pl), (p
2) is added, resulting in a video signal with increased image quality and sharpness.

The conventional video signal contour correction device described above is a means for emphasizing the contour portion of a video signal, and will be explained in more detail as follows.

Figure 5 shows the Journal of the Institute of Electronics and Communication Engineers (July 1983 issue Vol.
J66-B No. 7) (7) It is a diagram showing how a step waveform rises due to conventional edge enhancement shown in the paper "A method for calculating sharpness in television images."

As is clear from the figure.

A conventional correction means for emphasizing the contour portion is configured to obtain a second-order signal of the J+X signal waveform, multiply this signal by a certain coefficient, and then add the original signal waveform.

To explain based on Fig. 5, the step waveform ■2 (=Q(x)) is the original signal that has been band-limited on the transmission path.
Find the second-order waveform Ql (maximum) of , and calculate the coefficient -a
A contour correction signal waveform I2+Id is obtained by adding the multiplied waveform Id to the original signal waveform I2.

When the amount of improvement in rise time by such a contour correction means is expressed in terms of time to amplitude change (response), the original signal waveform I2 is Vl/XI, whereas the signal waveform I20rd with one contour correction is V2 / becomes X2 and stands.”
It can be seen that the heating time is significantly improved.

In this way, the sharpness of the image is improved by improving the rise of the signal that corresponds to the contour portion of the video signal, that is, by emphasizing the contour portion.

[Problems to be Solved by the Invention] The conventional video signal contour correction device configured as described above obtains the second derivative of the original signal waveform, multiplies this signal waveform by a certain coefficient, and then calculates the second derivative of the original signal waveform. Therefore, if the level of the original signal waveform is exceeded, as shown in the shaded area in Figure 5, and the original signal waveform has the maximum amplitude of the dynamic range of the transmission system, the saturation of the waveform will be reduced. There was a problem with causing it.

Also, if you try to increase the amplitude of the peak value of the second derivative when the level of the original signal waveform is small.

The peak time may become longer, or after the peak the peak time may become longer (Figure 4).
There were problems such as ringing (crossing) occurring as shown in c) and (d). Therefore, in the end, not only is it not possible to improve the S/N much, but there are also problems such as strong overshoot and preshoot resulting in a harsh and unclear image quality, and ringing phenomenon resulting in an unsightly image. was there.

This invention was made to solve the above-mentioned problems, and it emphasizes the contour without causing saturation of the original signal waveform. It is an object of the present invention to provide a video signal contour correction device that can improve the sharpness of a J image, eliminate noise in the contour portion, and obtain an image quality with high sharpness without ringing phenomenon. do.

[Means for Solving the Problems] A video signal contour correction device according to the present invention includes: a first delay circuit that delays an input video signal for a predetermined time;
a second delay circuit that delays the output signal by a predetermined time longer than the delay circuit, and obtains a signal obtained by adding and subtracting the output signal of the second delay circuit and the input video signal, and also obtains a signal obtained by adding and subtracting the output signal of the second delay circuit and the input video signal, Create a contour gate pulse,
A noise removal trap is inserted into the contour of the signal added by this gate pulse, while a second subtraction signal obtained by subtracting the output signal of the first delay circuit and the addition signal is sliced at a predetermined level, and further, The present invention is characterized in that the sliced signal is added to the output signal that has passed through the noise removal trap, noise components in the transient portion of the video signal are removed, and the signal is further processed by adding a peak signal.

[Operation] According to this IJI, the noise components of the falling retransient part and the falling retransient part of the input video signal are removed by two delay circuits, an adder circuit, and two subtracter circuits, and then the contour is A contour correction signal is created by adding a thin and deep peak to emphasize the . This results in
It is possible to obtain image quality with high sharpness and no edge noise.

[Embodiment of the Invention] Hereinafter, an embodiment of the present invention will be described based on the drawings.

FIG. 1 is a block diagram showing the configuration of a video signal contour correction device according to an embodiment of the present invention.
1) and (2) are a demodulation circuit and a de-emphasis circuit similar to the conventional case shown in FIG.

(+8), (17) are the first and second connected in series.
, the delay circuit (18) is an adder circuit, and this adder circuit (!
8) adds the input video signal (a) and the output signal (C) that has passed through the first and second delay circuits (1B) and (+7).

(13) is a 1/2 attenuator, (20) is a subtraction circuit, and this subtraction circuit (20) is the 1/2 attenuator (
The output signal (d) of 19) is passed through the first and second delay circuits (1B) and (1?) to the first delay circuit (1?) on the input side.
16) from the output signal (b).

(21) is a subtraction circuit, which outputs the output signal (C) from the input video signal (a) through the above two delay circuits (te) and (17).
) is subtracted. (22) is a gate pulse circuit which generates a positive noise gate pulse signal (h) having the same pulse width from the output signal (g) of the subtraction circuit (21).

(23) is a noise removal trap for removing high frequency noise components, which is operated only on the contour portion of the output signal (d) of the 1/2 attenuator (19) to remove high frequency noise components.

(24) is an adder circuit, and the above noise removal trap (23)
) is added to the output signal (k) of the level adjuster (26).

(25) is a slicer circuit; this slicer circuit (25)
slices the output signal (e) of the subtraction circuit (20) at predetermined slice levels (s1) and (s2). (
26) is a level adjuster, and this level adjuster (26) controls the level of the sliced signal (f) to an appropriate level.

The above first and second delay circuits (18), (17
) adder circuit (18), (24), 1/2 attenuator (19).

Subtraction circuit (20), (21), slicer circuit (25)
), the signal processing circuit (
27).

Next, the operation of the above configuration will be explained.

An input video signal as shown in FIG. 2(a) containing a noise component (Ha) is input to the first and second delay circuits (1B), (
+7), resulting in a signal delayed by τsec and 2τ3eC, as shown in FIGS. 2(b) and 2(c).

By adding the signal (C) delayed by 2τsec and the input video signal (a) in the adder circuit (18), the rising part and the falling part are stacked as shown in FIG. 2(d). A certain signal is obtained.

Here, since the polarity and phase of the noise component (Ha) are not constant and are random, addition and subtraction are not easy, and both can be expressed as the square root of the square of each noise 7jl (Ha).

What should be noted here is that the original signal part is doubled,
By passing such a signal through the 1/2 attenuator (19), the original signal part becomes 1
In addition, the amount of noise becomes 7 times t 7 p = o, the noise component becomes smaller, and the S/N ratio improves.

Next, by subtracting the signal shown in FIG. 2(d) from the signal shown in FIG. 2(b) outputted from the first delay circuit (18) in the subtraction circuit (20), the signal shown in FIG.
The signal shown in figure (e) is obtained. This signal (e) is the result of generation of fine transient pulses at the rise and fall of the video signal, and this signal (e) is used as a contour correction signal.

On the other hand, in the subtraction circuit (21), the first and second i
l! l! By subtracting the signal (C) delayed by 2τsec through the delay circuits (1B) and (17) from the input video signal (a), a positive and negative pulse signal is obtained as shown in the fJsZ diagram (g).

Using this positive and negative pulse signal (g) as a reference, a gate pulse signal (h) for a transient portion as shown in FIG. 2(h) is created in a gate pulse circuit (22). This gate pulse signal (h) is then input to the noise removal trap (23) to operate this trap (23).

That is, by operating the noise removal trap (23) at the timing of the stage of the signal (d) which has stages at the rising and falling parts after passing through the l/2 attenuator (19), high frequency noise is removed and the second A signal as shown in (J) is obtained.

Next, the signal shown in FIG. 2(e) is applied to the slicer circuit (25
) and enter the predetermined slice level (St).

By slicing in step (S2), noise at the tip of the transient pulse portion is removed as shown in FIG. 2(f).

Next, this sliced signal (f) is passed through a level adjuster (
2B) and adjust it to a predetermined level, and add this adjusted signal (k) to the signal (j) that has passed through the noise removal trap (23) in the adding circuit (20). A video signal with a waveform as shown in Figure 2(i) is obtained.This video signal (i) has fine transient pulses added at the rise and fall of the video signal, and there is no noise at all in the transient pulses. There will be no.

In other words, a high-quality video signal is obtained in which a thin contour correction signal is added and no random noise is superimposed on the thin transient portion.

Here, in the subtraction circuit (20) and addition circuit (24), the noise component is the square root of the square, as in the addition circuit (18), so by providing an appropriate attenuator, f
XX By changing the ratio of acid component and noise component, the resulting S/N
The ratio can be improved.

Examining the frequency characteristics and distortion occurrence of the video signal created as described above, the following can be said.

If the video signal (a) output from the de-emphasis circuit (2) is Va −sinωt, then the adder circuit (18
) output chi 3 (dO) is Vdo −Va + Va(L−1r)−sin ω
t + sinω (t-2r)-2sinω (t-
r) −cos ωt.

Therefore, the output signal of the 1/2 attenuator (19) (
d), the output signal (e) of the subtraction circuit (20), and the output signal (i) of the addition circuit (24) are Vd-t721 Vdo-sin (1) (t-
r) ・cos ωtVe-Vb-Vd -sinω (with -) -sinω (t-τ)cos
ω Cape sin ω (-τ) (1-cos ωt) Vi ”
Vb + Vek = sin (&l (t-τ
)+k(1-cos ωt) sinω(t-r)=
(1+ k −k cosωt)・sinω (t−τ
). Here, k is a level adjustment value.

That is, the output video signal (i) is the input video signal (a)
is output with a delay of τ sec, and both signals (i)
, (a) phase difference (θ) is θ=ω(at t-)-
ω becomes -ω, and it becomes a linear straight line with respect to the phase ω, that is, with respect to the frequency.

Also, the first and second delay circuits (16).

The group delay characteristic of (17) can be obtained by differentiating the phase with respect to ω, that is, dθ/dω (−ω1)−,
It is a function of only the delay time τ and does not change with frequency.In other words, signal processing with flat group delay characteristics is possible regardless of the frequency band, and there is no distortion in the video signal, making it ideal. It is possible to process video signals in various states.

Although delay line elements of 50 n5ec and N100 n5ec are generally used as the delay circuits (+6) and (17), the delay line elements are not limited thereto, and may be constructed of, for example, an active filter. In particular, if it is configured with an active filter, it is AA in terms of IC implementation.

Furthermore, in the above embodiment, the delay circuits (16) and (17
) are connected in series to form the first delay circuit and the second delay circuit, however, two delay circuits having different delay times may be provided separately.

Further, in the above embodiment, the present invention is applied to a reproduced video signal contour correction device for a VTR, but the same effect can be obtained even if the present invention is applied to video signal processing for a disc player or a television receiver.

[Effects of the Invention] As described above, according to the present invention, a contour correction signal is created by two delay circuits, an addition circuit, and two subtraction circuits, and the noise component in the contour correction period is eliminated by a gate pulse and a trap. By slicing the first part containing the noise component of the contour correction pulse signal that should be completely removed and added, and then adding it to the original input video signal, the noise component is not included in the contour part, and the transient It is possible to create a contour correction signal that has thin and deep peaks in certain parts. As a result, it is possible to improve the S/N ratio and obtain a clear image with high sharpness. In addition, saturation of the original signal waveform is not caused, overshoot, preshoot, and ringing phenomena are not caused, and a good image with very little noise and high sharpness can be obtained as a whole.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a video signal contour correction device according to an embodiment of the present invention, FIG. 2 is an operating signal waveform diagram thereof, and FIG. 3 is a block diagram showing the configuration of a conventional video signal contour correction device. , FIG. 4 is a diagram of the operating signal waveform of FIG. 3, and FIG. 5 is a detailed diagram of the differential waveform produced by the conventional contour correction means of the quadratic division method. (16), (171...first and second delay circuits, (18), (24)...addition circuit, (19)
...Attenuator, (20), (21)...Subtraction circuit, (22)...Gate pulse circuit, (23)
... Noise removal trap, (25) ... Slicer circuit. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Claims] (1) a first delay circuit that delays the input video signal for a predetermined time; a second delay circuit that delays the input video signal for a predetermined time longer than the delay time of the first delay circuit; an addition circuit that adds the output signal of the delay circuit and the input video signal; a subtraction circuit that subtracts the input video signal from the output signal of the second delay circuit; A subtraction circuit that subtracts the output signal of the addition circuit, a slicer circuit that slices the output signal of the subtraction circuit at a predetermined level, and a gate pulse circuit that gates the transient part of the input video signal from the output signal of the subtraction circuit. , comprising a noise removal trap that removes noise components in the transient portion of the output signal of the adder circuit, and an adder circuit that adds the output signal of the slicer circuit and the output signal of the noise removal trap. Video signal contour correction device.