JPH0353769A - Video signal contour correction circuit - Google Patents

Abstract

PURPOSE:To obtain a picture with high sharpness whose contour is emphasized by using two delay circuits whose delay time is revised, two adder circuits and a subtraction circuit to generate a contour correction signal with a thin and high notch to a transient part of an input video signal and devising the circuit so that the time axis width of the peak is revised optionally. CONSTITUTION:A video signal l is inputted to the 1st and 2nd delay circuits 16, 17. Then a signal (o) outputted from an adder circuit 18 is fed to a 1/2 attenuator 19 to obtains signal (p) which is attenuated to have a half amplitude. Then the signal (p) outputted from the 1/2 attenuator 19 is subtracted by a subtraction circuit 20 to obtain a signal (q). The signal (q) is equivalent to a transient pulse whose width is thin at the leading and trailing of the video signal and the signal (q) is used as a contour correction signal.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention relates to a video signal contour correction circuit for improving the sharpness and definition of video signals in color television receivers, video table recorders, etc. be.

[Prior art] Figure 5 shows the Journal of the Institute of Electronics and Communication Engineers (July 1983 issue Vol.
'J66-B No. 7) (7) M text r A diagram showing how the rising edge of a step waveform is improved by the conventional edge emphasis shown in a method J for calculating sharpness in a television image C.

It is well known that enhancing the contours of a television image improves its sharpness, and is often applied to luminance signals that determine the shape of objects.

The conventional correction means for emphasizing the contour part is configured to obtain a second-order differential signal of the original signal waveform, multiply this signal by a certain coefficient, and then add it to the original signal waveform, as shown in Figure 5. be.

To explain with Fig. 5, the second differential waveform Ql(X) of the step waveform I2 (=Q(x)), which is the original signal that has been band-limited in the transmission path, is obtained and multiplied by a certain factor -a. Adding waveform 1d to original signal waveform I2 to obtain contour correction signal waveform 12
+Id is obtained. When the amount of improvement in the rise time by this contour correction means is expressed in terms of time relative to amplitude change, it is Vl /Xi for the original signal waveform I2, while for the contour correction signal waveform 12
+Id becomes V2/X2, indicating that the rise time is considerably improved. The sharpness of the image is improved by improving the rise of the signal corresponding to the outline of the television image, that is, by emphasizing the outline. [Problems to be Solved by the Invention] The conventional video signal contour correction circuit obtains a second-order differential signal of the original signal waveform, multiplies this signal by a certain coefficient, and then adds it to the original signal waveform. As shown in the shaded area in Fig. 5, since the level exceeds the level of the original signal waveform, there is a problem in that when the original signal waveform has the maximum amplitude of the dynamic range of the transmission system, it causes waveform saturation.

Another problem is that when the frequency of the original signal is low, the peak portion is large and ringing phenomenon easily occurs, and when the frequency of the original signal is high, the peak portion is small and it is almost impossible to perform contour correction as specified. was there. This invention was made to solve the above problems, and improves the sharpness of images by emphasizing and correcting the contours of video signals without causing saturation and ringing phenomena in the original signal waveform. The purpose is to provide a video signal contour correction circuit that can perform the following functions. [A Thousand Steps to Solve the Problem] A video signal contour correction circuit 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 input video signal for a longer time than the delay circuit; The subtracted signal is added to the output signal of the first delay circuit to form a peak signal of the transient portion of the video signal, and the time axis width of this peak signal is determined by adding the subtracted signal to the output signal of the first delay circuit. The present invention is characterized in that the peak portion of the contour portion of the video signal is controlled by varying the delay time of the delay circuit.

[Operation] According to the present invention, two delay circuits with different delay times, two adder circuits, and one subtracter circuit are used to adjust the contours of the rising retransient portion and the falling transient portion of the input video signal. An image with high sharpness can be obtained by adding a contour correction signal with a fine and deep peak to emphasize the area, and by arbitrarily changing the width of the peak part by varying the delay time of two delay circuits. It will be done. [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 circuit according to an embodiment of the present invention.
e), (17) are the first and second connected in series.
The specific configuration of these delay circuits will be described later. ([1) is a first adder circuit, and input video signal (l).
and the above two delay circuits (16). (17) and the output signal (n) are added. (19) is a 1/2 attenuator, (20) is a subtraction circuit, and the output signal (p) of the above 1/2 attenuator (19) is sent to the first delay circuit (16).
Subtract from the output signal (a). (27) is a slicer circuit, and this slicer circuit (27) is the subtraction circuit (20).
) output signal (q) at a predetermined slice level (51)
, (S2). (28) is a level adjuster, and this level adjuster (28) controls the level of the sliced k signal to an appropriate level. (22) is a second addition circuit;
2) is the output signal of the level adjuster (28) and the first
and the output signal (ffi) of the delay circuit (16). (29) is a delay time control voltage generator, which is connected to the first and second delay circuits (16). (17) A control voltage for changing the delay time is generated.

The above first and second delay circuits (16), (1
7), first and second addition circuits (18), (2
2), 1/2 attenuator (19), subtraction circuit (20)
, a slicer circuit (27), a level adjuster (28), and a delay time control voltage generator (29) constitute a signal processing circuit (26). Next, the operation of the above configuration will be explained with reference to the signal waveform diagram in Figure 2.
Delay circuit (16). (17), as shown in Fig. 2(m). As shown by (+1), the signal is delayed by τsec. In this way, the signal delayed by 2τsec (
By adding the input video signal (1) and the input video signal (1) in the adder circuit (18), a signal with stages in the rising and falling parts is obtained, as shown in FIG. 2 (0). Then, FIG. 2 (0) output from the adder circuit (18)
By applying this signal to the 1/2 attenuator (19), a signal as shown in Fig. 2(p) whose amplitude is attenuated by half is obtained. Next, the signal shown in FIG. 2 (p) output from the 1/2 attenuator (l9) is subtracted from the signal shown in FIG. 2 (ffl) output from the first delay circuit (l6). By subtracting in 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 (q), edge noise will be superimposed on the contour portion, significantly impairing the image quality. The signals shown in are inputted to the slicer circuit (27), and the signals shown in . By slicing in (S2), 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 in the adder circuit (22>).
By adding it to the signal (fil) output from (16), a video signal having a waveform as shown in FIG. 2 (S) is obtained.

Here, the first and second delay circuits (16). (
The delay time τ of l7) is set by the delay time control voltage generator (29).
By changing the width of the peak part of the video signal as shown in FIG. 2(S), the width of the peak part of the video signal changes as shown in FIG. Examining the frequency characteristics and distortion occurrence of the video signal created as described above, the following can be said.

Input video signal (phase of jN (vj2) Vl=s
If inωt, the output signal (0) of the adder circuit (18)
The phase (Vo) of is Vo − Vjl + VJ! (t-2τ) sin
ωt + sin ω(t-2r)2sinω(t
-r )COS (L)t. Therefore, the output signal of the 1/2 attenuator (19) (
p) phase (Vp) The phase (Vq) of the output signal (q) of the subtraction circuit (20) and the phase (Vs) of the output signal (S) of the addition circuit (22) are respectively Vp = 1722 VolIsin 6J (t
−T) cosωtVq−Vm−Vp−slnω(t−τ)−sinω(t−r)
cos act- sinω(t-τ) (1-c
osωt)Vs − Vm * Vq K − sin
ω(t - τ) + K(1-cosωt) sina+
(t − r) (1.+κ−K cosωr) si
It becomes na+(t-τ). Here, K is the level adjustment value. That is, the phase of the output video signal (S) (Vs
) is output with a delay of τsec with respect to the phase (vft) of the input video signal (F), and both signals (S). (n)
The phase difference (θ) is θ=ω(t−τ)−ωt−ωt, which is a linear straight line with respect to the phase ω, that is, with respect to the frequency. Further, the first and second delay circuits (16), (1
The group delay characteristic of 7) can be obtained by differentiating the phase with respect to ω,
In other words, dθ/dω (1 ωt) 1, which is a function of only the delay time τ, and does not change with frequency.In other words, signal processing with a flat group delay characteristic is possible regardless of the frequency band. No distortion occurs in the signal. FIG. 3(a) shows the first and second delay circuits (1B). A circuit diagram showing a specific configuration example in which the delay time of (17) is made variable, FIG. 3(b) is an equivalent circuit diagram thereof. Akiba Publishing Supervised translation by Ken Yanagisawa 588
This is a variation of the Delyiannis circuit of the second-order all-pass circuit shown in page 18.

In the figure, (CI), (C2) are variable capacitance diodes, (Rl) . (R2). (R3).
(R4) is a voltage dividing resistor, (OP) is an operational amplifier, and by changing the voltage generated by the delay time control voltage generator (29), the delay time (delay amount) D (0) is changed.

That is, the delay time D(0) in Fig. 3(b) is D (o) 2 Q where q is the sharpness and is 1/2 · 571 degrees. To actually obtain a high-quality contour correction signal, it takes 120 nsec~
It is desirable to vary within a range of 150 nsec. Two delay circuits (16) as shown in FIG. 3 above.
(17) are connected in series, and these delay circuits (18)
, (17) from the control voltage generator (29), when the delay time (τ) is small, a contour positive signal as shown in FIG. 4 (Sl) is generated, and the delay time ( When τ) is large, a contour correction signal as shown in FIG. 4 (S2) can be created. Note that in the above embodiment, the first and second delay circuits (
As a specific example of 1B) and (17), a modification of the secondary all-bus circuit (Delyiannis circuit) was shown.
It is also possible to use a delay circuit using a CCD or the like. In this case, the amount of delay can be easily changed by changing the frequency of the clock signal. Further, in FIG. 1, the slice level of the slicer circuit (27) can be configured to be variable, so that the amplitude of the peak portion can be controlled.

Further, in the above embodiment, the circuit is applied to a contour correction circuit for a reproduced video signal of a VTR, but it can also be applied to a video signal processing circuit for a disc player, a color television receiver, etc. Deepen the effect.

[Effects of the Invention] As described above, according to the present invention, by using two delay circuits, two adder circuits, and one subtractor circuit that can change the delay time, a narrow and deep peak can be generated in the transient portion of an input video signal. By creating a contour correction signal with a contour correction signal and making it possible to change the time axis width of its peak portion arbitrarily, it is possible to create an image with high sharpness with emphasized contours, regardless of the frequency of the original signal. Obtainable. In addition, it is possible to obtain an overall good high-quality image without causing saturation, overshoot, bristling, or linking.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the structure of a video signal contour correction circuit according to an embodiment of the present invention, FIG. 2 is a waveform diagram of its operating signal, and FIG. 3(a) is a delay circuit that can change the amount of delay. The specific circuit diagram of , Figure 3(b) is its equivalent circuit diagram, and Figure 4
The figure is a waveform diagram of the contour correction signal of the video signal, and FIG. 5 is a detailed diagram of the differential waveform produced by the conventional quadratic differential type contour correction means. (1B), (17)...delay circuit, (ta)
, (22)...addition circuit, (19)...1/2 attenuator, (20)...subtraction circuit, (27)...
- Slicer circuit, (29)...Delay time control voltage generation circuit. Note that the same reference numerals in the figures indicate the same or corresponding parts. Figure 2 Figure 3 (Q) (b) Figure 4 Figure 5

Claims (1)

[Claims] (1) A first delay circuit that can delay an input video signal by a predetermined time and change the delay time; and a first delay circuit that can delay the input video signal by a longer time than the delay time of the first delay circuit and change the delay time. a possible second delay circuit;
a first addition circuit that adds the output signal of the delay circuit and the input video signal; a subtraction circuit that subtracts the output signal of the first addition circuit from the output signal of the first delay circuit; and this subtraction circuit. and a second addition circuit that adds the output signal of the first delay circuit and the output signal of the first delay circuit, and corrects the contour portion of the video signal by varying the delay time of the first and second delay circuits. A video signal contour correction circuit characterized in that it is configured to perform the following.