JPH03206776A - Video signal contour correction device - Google Patents

Abstract

PURPOSE:To obtain picture quality with high sharpness at all times in response to an input video signal by inputting the video signal to two delay circuits, and an adder circuit and a subtraction circuit so as to emphasize contour so as to obtain a contour correction signal controlled in response to the frequency component of the input video signal. CONSTITUTION:Two delay circuits 16, 18 varying a delay time, two adder circuits 18, 22 and a subtraction circuit 20 are used to generate a contour correction signal, and the frequency component of an input video signal is detected to control the delay time of 1st and 2nd delay circuits 16, 18 according to the result of detection. Thus, the time axis width of a peak signal of a transient part of the video signal is increased or decreased automatically in response to the frequency component of the video signal and a minute peak correction signal is added when a minute pattern is reproduced and a correction signal with a large peak width is added when a rough and large pattern is reproduced and the peak signal in matching with the reproduced picture is added in any case. Thus, the sharpness is remarkably improved and high quality reproduced picture suitable for any reproduced pattern is obtained.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention is applied to video playback devices such as television receivers, video table recorders (hereinafter referred to as VTRs), and disk players, S/N of
The present invention relates to a video signal contour correction device that corrects the contour of this video signal so as to improve resolution, sharpness, and the like.

[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. 5 is a block diagram showing the configuration of a video signal contour correction device for a conventional VTR aimed at improving the above three picture quality determining factors. In the figure, (1) is a demodulation circuit; ) is a frequency of 3.4 MHz to 4.4 MHz that is boosted by a playback head (not shown).
demodulates the FM modulated video signal into a baseband video signal. (2) is a de-emphasis circuit. This de-emphasis circuit (2) suppresses the high-frequency components of the recorded video signal by emphasizing the high-frequency components using the de-emphasis circuit during recording, and suppresses the high-frequency components generated in the video signal recording and reproducing system. This circuit reduces high-frequency noise components, and has characteristics opposite to those of the pre-emphasis circuit described above.

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

(4) is a second-order differentiator 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 that adds the output signal of the LPF (3) and the output signal of the attenuator (5).

The above L P F (3) second-order differential circuit (4),
The attenuator (5) and the adder circuit (6) constitute a second-order differential image quality processing circuit (23).

(7) is a high-pass filter (hereinafter referred to as HPF),
Picks up noise components contained in video signals.

(8) is a noise amplifier that amplifies the noise component, (9) is a limiter that limits the amplitude of the noise component, (10) is a polarity inversion circuit, and (11) is an attenuator.
9) The amplitude of the noise component limited by step 9) is set to an optimal value. (12) is an adder circuit that adds the output signal of the second-order differential type image quality processing circuit (23) and the noise component signal whose polarity is inverted.

H P F (7) Noise amplifier (8)
A noise canceller circuit (24) is composed of a limiter (9), a polarity inversion circuit (10), an attenuator (11), and an addition circuit (12).

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

3.4 M}Iz ~ 4.4 MHz FM modulated,
The video signal recorded on the recording medium with high frequency components emphasized through the pre-emphasis circuit is picked up by the playback head and input to the demodulation circuit (1), thereby converting this FM modulated video signal into a baseband video signal. Demodulate. Next, this demodulated video signal is input to a de-emphasis circuit (2) having characteristics opposite to those of the pre-emphasis circuit, thereby suppressing high-frequency components and reducing high-frequency noise components.

However, in the case of only such emphasis processing,
As shown in FIG. 6(a), many noise components (n) remain. In particular, if the quality of the VTR magnetic tape is poor, a considerable amount of noise component (n) remains.

Next, a video signal as shown in FIG. 6(a) containing many noise components (n) is processed by a second-order differential image quality processing circuit (2
3), the video signal is L P F (3
), the Takagi component and noise component are removed as shown in FIG. 6(b).

On the other hand, the transient part (1) in which the level of the video signal that has passed through the second-order differentiator (4) changes suddenly is differentiated twice, and the noise component is also differentiated, and this differentiated signal is sent to the attenuator (5). By passing through the signal, the level is set to an appropriate level, resulting in a waveform signal as shown in FIG. 6(C).

Continuing, the sixth output from the above L P F (3)
The signal shown in Fig. 346 (b) and the signal shown in Fig. 6 (C) output from the attenuator (5) are added in the adder circuit (6), resulting in a signal as shown in Fig. 346 (d). Become.

Although the signal shown in FIG. 6(d) includes a noise component (n), the rising transient portion of the original video signal shown in FIG. 6(a) that suddenly changes from the white level to the black level, and the white level Appropriate peaks (pi) for each of the falling transient parts that suddenly change to the level. (
p2) is added, resulting in a video signal with increased image quality and sharpness.

Next, the video signal shown in FIG. 6(d) with increased sharpness is input to the noise canceller circuit (24). The video signal input to this noise canceller circuit (24) first passes through the H P F (7) noise amplifier (8), and as shown in FIG.
and high frequency components of the video signal are amplified.

Next, the amplitude of the noise component (n) is limited by the limiting levels (Ll) and (L2) set by the limiter (9), resulting in a signal as shown in FIG. 6(f). The polarity of the signal shown in FIG. 6(f) is inverted by a polarity inversion circuit (10) and attenuated to an appropriate level by an attenuator (l1), and then inputted to an adder circuit (l2). At (l2), by adding the signal shown in FIG. 6(d), a signal as shown in FIG. 6(g) is output. The signal shown in FIG. 6(g) has peaks (pi) and (p2) in the rising transient part and the falling transient part by the second-order differential method.
This is a video signal with sharpness obtained by removing noise (n) from a video signal with .

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

Figure 7 is from the Journal of the Institute of Electronics and Communication Engineers (July 1983 issue Vol.
J 6 6 - B No 7) I) This is a diagram showing how the step waveform rises due to conventional edge enhancement shown in the paper "A method for calculating sharpness in telephoto images", and it is clear from the diagram that As shown, the conventional means for emphasizing and correcting the contours of a video signal is to obtain a second-order differential signal of the original signal waveform, multiply this signal by a certain coefficient, and then add the original signal waveform. .

To explain based on Figure 7, the step waveform ■2 (=Q(x)) is the original signal that has been band-limited on the transmission path.
A second-order differential waveform Q 1 (x) is obtained, and a waveform Id obtained by multiplying this by a certain coefficient 1a is added to the original signal waveform generator 2 to obtain a contour correction signal waveform I2+Id.

When the amount of improvement in the rise time by such contour correction means is expressed in terms of time to amplitude change (response), the original signal waveform I2 is Vl/Xi, while the contour correction signal waveform I2+Id is V2/X2, It can be seen that the rise time is considerably improved.

The sharpness of the image is improved by improving the rise of the signal corresponding to the contour portion of the video signal, that is, by emphasizing the contour portion.

[The invention tries to solve ii! The conventional video signal contour correction device configured as described above calculates the second derivative of the original signal waveform, multiplies this signal waveform by a certain coefficient, and then adds it to the original signal waveform. If the level of the original signal waveform exceeds the level of the original signal waveform, as shown in the shaded area in Figure 7, and the original signal waveform has the maximum amplitude of the dynamic range of the transmission system, waveform saturation is likely to occur, and the original video A relatively desirable peak signal can be obtained when the signal has a low frequency, such as a rectangular wave, but as the frequency of the original video signal increases, the peak value becomes smaller, making it impossible to perform contour correction as specified. was there.

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 time width of the peak will become longer, or the peak value will become larger after the peak (see Figure 6(c), (
There were problems such as ringing (IL) occurring as shown in d) and (g). Therefore, depending on the frequency components of the original video signal, overshoot and bristle may be strong, resulting in harsh and unnatural image quality, or ringing may occur, resulting in an unsightly image.
Even if an image has good sharpness in one scene, such as an image with almost no peak value, images with good sharpness cannot always be obtained in various scenes.

This invention was made to solve the above-mentioned problems, and regardless of the frequency content of the original video signal, it can always emphasize the outline appropriately without causing saturation of the original signal waveform. Image sharpness can be improved, and there is no ringing phenomenon.
It is an object of the present invention to provide a video signal contour correction device that can obtain image quality with high sharpness.

[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 by a predetermined time and varies the delay time; and a second delay circuit that delays the time and varies the delay time, adds the output signal of the second delay circuit and the input video signal, and converts the added signal into the output signal of the first delay circuit. The subtracted signal is added to the output signal of the delay circuit of 'ts1 to process the signal so as to add the peak signal of the transient part of the video signal to the human video signal, while the input video signal The present invention is characterized in that a frequency detection circuit for detecting a frequency difference is provided, and the delay times of the first and second delay circuits are controlled by the output signal of the frequency detection circuit.

[Operation] According to the present invention, a video signal is transmitted through two delay circuits and one delay circuit each.
By inputting into two adder and subtracter circuits,
A thin and deep peak is added to the rising and falling transient parts of this human video signal to emphasize the outline, and the peak width of the peak signal of this transient part is adjusted according to the frequency components of the input video signal. It is possible to obtain a contour correction signal controlled by As a result, image quality with high sharpness can always be obtained depending on the input video signal.

[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.
) and (2) are a demodulation circuit and a de-emphasis circuit similar to those in the conventional example shown in FIG. 345.

In Figure 1, (11) is the LPF, and (12) is its LPF.
a subtraction circuit that subtracts the human output signal of P F (11);
(13) is the limiter, (technique 4) is its limiter (l3)
This is a subtraction circuit that subtracts the human output signal. (l5) is an addition circuit, and this addition circuit (15) is the subtraction circuit (14).
) and the output signal of L P F (11) above are added.

The above L P F (11), subtraction circuit (12).
(14) Limiter (13). The noise canceller circuit (25) is monitored by the adder circuit (15).

(16) and (17) are first and second delay circuits connected in series, and (18) is an adder circuit. This adder circuit (18) is the adder circuit (l5) in the noise canceller circuit (25) Output signal and the first and second delay circuits (16). (17) is added to the output signal.

(19) is a 1/2 attenuator, (20) is a subtraction circuit, and this subtraction circuit (20) is the 1/2 attenuator (1
9) is subtracted from the output signal of the first delay circuit (16).

(27) is a slicer circuit; this slicer circuit (27)
slices the output signal of the subtraction circuit (20) at a predetermined slice level. (28) is a level adjuster, and this level adjuster (28) controls the level of the above-mentioned sliced signal to an appropriate level. (22) is an adder circuit, and this adder circuit (22) controls the above-mentioned level. The output signal of the circuit (28) and the output signal of the first delay circuit (16) are added.

The above first and second delay circuits (16) and (17
) Adding circuit (18). (22) A signal processing circuit (26) is composed of a 1/2 attenuator (19), a subtraction circuit (20), a slicer circuit (27), and a level adjuster (28).

(30) is a frequency component detection circuit that detects the frequency component of the output video signal of the noise canceller circuit (25). As this frequency component detection circuit (30), an inexpensive one such as a band pass filter configured by RC or an expensive one consisting of multiple filters each having their own band such as an active filter can be considered. . (31) is a detection circuit, and the frequency doctrine detection circuit (3
Detect the output signal of 0) and convert it into a DC signal.

Next, the operation of the above configuration will be explained with reference to FIG. 1, FIG. 2, and FIG.'s3.

The second signal is demodulated by the demodulation circuit (1) and whose high frequency components are suppressed by the de-emphasis circuit (2).
A video signal containing a noise subtraction (n) shown in FIG. 3(a) is input to a noise canceller circuit (25). and,
First, by passing L P F (11),
For example, noise components in flat image areas that are large and visually noticeable, such as the sky or walls, are concentrated at the low level of the Takagi signal. The signal will be as shown in Figure 2 (h).

Figure 2 (h) output from this L P F (11)
By subtracting the signal shown in FIG. 2 from the original video signal (a) in the subtraction circuit (12), a difference signal component as shown in FIG. 2(i) is obtained.

Next, the difference signal component (i) is input to the Riyotsuta (13) and the limiting level (t.t) is set. (L2
), a signal component as shown in FIG. 2 U) is obtained.

Next, the signal component (l) output from the limiter (13) is subtracted from the difference signal component (i) output from the subtraction circuit (12) in the subtraction circuit (l4). ), a spike-like difference signal component containing almost no noise is obtained.This spike-like difference signal component (k) is sent to the adder circuit (15) and output from the above L P F (11). Figure 2 (h
), a video signal containing almost no noise components can be obtained, as shown in FIG. 2 (flooding).

As described above, the noise canceller circuit (25) can remove most of the noise component (n) without changing the waveform of the original video signal (a).

Next, the video signal from which most of the noise components (n) have been removed is input to a signal processing circuit (26). First, the video signal (J2) is transferred to the delay circuit (
16). (17), as shown in Fig. 2(m).
As shown by (n), the signal is delayed by τsec. As a result, by adding the signal (n) delayed by 2τsec and the video signal (It) in the adder circuit (18), as shown in FIG. A certain signal is obtained. here,
As for the noise component (n), the polarity and phase are not constant,
Since it is random, addition and subtraction are not easy, and both can be expressed as the square root of the square of each noise amount Na.

As shown in FIG. 2 (0), the original signal portion becomes twice as large, but the amount of noise becomes Na+Na, which is twice as large. By passing such a signal through the 1/2 attenuator (19), as shown in Figure 2 (p), the original signal part becomes 1 times, and the amount of noise becomes 2/2 = 0.7 times, Noise and components are reduced, and the S/N ratio is improved.

Then, the delay circuit (16) outputs the signal shown in FIG.
By subtracting the signal shown in FIG. 2 (p) above from the signal shown in m) in the subtraction circuit (20), the signal shown in FIG. 2 (q
) is obtained. This signal (q) generates fine transient pulses at the rise and fall of the video signal, and this signal (q) is used as the contour correction signal.

If random noise is superimposed on the fine transient pulse width portion of this contour correction signal, edge noise will be superimposed on the contour portion, significantly degrading the image quality. input to the slicer circuit (27) and set the predetermined slice level (51).
．． By slicing in (52), noise at the tip of the transient pulse portion is removed. Next, this sliced signal is sent to a level adjuster (28).
is adjusted to a predetermined level, and this adjusted signal is sent to the first delay circuit (22) in the adder circuit (22).
16), a video signal having a waveform as shown in FIG. 2 (S) is obtained.

Here, in the subtraction circuit (20) and the addition circuit (22), as in the addition circuit (18), the noise division is the square root of the square, so by providing an appropriate attenuator, the ratio of the signal component to the noise component As a result, the S/N ratio can be improved.

That is, the noise canceller circuit (25) removes large noise on the entire screen, and the signal processing circuit (25) removes large noise from the entire screen.
6) reduces fine noise superimposed on the signal, removes edge noise in the transient part of the signal, and adds a sharp contour correction signal to the transient part.

On the other hand, the video signal (J2) from which most of the noise components have been removed after passing through the noise canceller circuit (25) is applied to the frequency component detection circuit (30), which determines the frequency of the input video signal <X>. The detection circuit (3
In step 1), the current is changed to direct current.

To be more specific, if the input video signal (color) is a scene like a field of small flowers, for example, as shown in Figure 3A,
In the case of a configuration with many high frequency components, the frequency component detection circuit (3
0) detects that there are many high frequency components, and the detection circuit (
31) becomes high, and this DC voltage becomes the first
's1 and second delay circuits (16) and (17) in the figure
) to reduce 1 by the amount of delay. As a result, an output signal as shown by (S) in FIG. 3A is obtained.

On the other hand, if the input video signal (J2) is, for example, a scene where a single tulip flower is up in front of a wall and has a configuration with many low frequency components as shown in Figure 3B, the frequency component The detection circuit (30) detects that there is almost no high-frequency signal component, and the DC output voltage of the detection circuit (31) becomes low, and this DC voltage is transmitted to the first and second delay circuits (16), (17) is added to increase the delay amount τ2. As a result, (S
) is obtained as shown in the output signal. Note that FIG. 4A shows the first and k42 delay circuits (
Figure 4B is an equivalent circuit diagram of a concrete example of varying the delay time of lfi) and (17). P588, it is known as the Delyiannis circuit.

When calculating the amount of delay in Fig. 4B, Delay amount D (0) depth 2/ω0 ・Q Here, Q-1/2 R3/Rl ωO − 1/CI・C2・R3・Rl.

Here, when Cl and C2 shown in the $4A diagram are variable capacitance diodes and the output voltages of the frequency component detection circuit (30) and its detection circuit (31) are changed, the delay time (
delay amount) D (0) changes. When calculating the delay amount D (o) based on the specific numerical example written in parentheses in Figure i4A, it is found that approximately 1
20 nsec, but in order to actually obtain a high-quality contour correction signal, it takes 80 nsec to 150 nsec.
It is desirable to vary within the range of sec.

As described above, the contour correction signal processing circuit includes the first and second delay circuits (18) and (17) of variable delay time type, and the circuit (30) for detecting the frequency components of the reproduced video signal. By providing this, the peak width of the peak correction signal is narrowed so that details appear better when there is a detailed screen content with many high-frequency components, and the peak width of the peak correction signal is narrowed so that the details appear clearly when there is a large screen content with many low-frequency components. The peak width of the correction signal can be widened.

Note that in the above embodiment, the first and second delay circuits (1
6), Delyianni as a specific example of (17)
Although a modification of the s circuit is shown, it can also be configured with a delay circuit using a CCD or the like. In this case, the amount of delay can be easily changed by slightly changing the frequency of the clock signal. There are various other delay circuits that can vary the delay time, but regardless of the configuration, care must be taken to ensure that the waveform does not change when the signal passes through the delay circuit.

Further, the first and second delay circuits (16) and (17)
) are generally desirable to have the same circuit configuration, but for scanning a television screen, the delay amount of the delay circuit (16) of 's1 is made slightly larger than the delay amount of the second delay circuit (17), and the visual You can get a high quality screen.

Furthermore, in the above embodiments, the explanation has been given of a circuit that is applicable to a contour correction circuit for a reproduced video signal of a VTR, but the same effect can be achieved even if it is applied to video signal processing of a disc brake or a television receiver.

[Effects of the Invention] As described above, according to the present invention, a contour correction signal is created using two delay circuits that vary the delay time, two addition circuits, and two subtraction circuits, while the frequency components of an input video signal are By detecting and controlling the delay times of the first and second delay circuits according to the detection results, the time axis width of the peak signal of the transient portion of the video signal is automatically increased or decreased according to the frequency component of the video signal. When playing a detailed screen, a fine peak correction signal is added, and when a coarse, large screen is playing, a correction signal with a large peak width is added, and in either case, the reproduced image By adding a peak signal suitable for the image, the sharpness can be significantly improved, and a high-quality reproduced image suitable for any reproduction screen can be obtained.

[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 operation waveform diagram of the contour correction device, and FIGS. A signal waveform diagram showing how the signal changes, Fig. 4A shows a specific configuration of a delay circuit that varies the amount of delay, Fig. 4B is an equivalent circuit diagram of Fig. i4A,
FIG. 5 is a block diagram showing the configuration of a video signal contour correction device using a conventional quadratic differential method contour correction means, FIG. 6 is an operating waveform diagram of FIG. 5, and FIG. 7 is a conventional quadratic differential method contour correction device. FIG. 6 is a detailed diagram of a differential waveform produced by contour correction means. (16)...'s1 delay circuit, (17)...second
delay circuit, (18). (22)...addition circuit,
(20)...Subtraction circuit, (25)...Noise canceller circuit, (26)...Signal processing circuit, (30)...
...Video signal frequency component detection circuit, (3l)...
・Detection 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 by a predetermined time and varies the delay time; and a second delay circuit that delays the input video signal by a longer time than the first delay circuit and varies the delay time. a delay circuit, a first addition circuit that adds the output signal of the second delay circuit and the input video signal, and subtracts the output signal of the first addition circuit from the output signal of the first delay circuit; a second addition circuit that adds the output signal of the subtraction circuit and the output signal of the first delay circuit, and a frequency component detection circuit that detects the frequency component of the input video signal, A video signal contour correction device characterized in that the delay time of the first and second delay circuits is controlled by the output signal of the frequency component detection circuit.