JPH05130453A - Luminance signal clarifying circuit - Google Patents

Abstract

PURPOSE:To prevent the occurrence of ringing, picture blurring and deterioration in details or the like on a television screen by improving a waveform of a luminance signal. CONSTITUTION:This circuit is provided with separation means 2, 3, 8 separating a composite video signal (a) comprising a blanking period signal being a signal for horizontal and vertical blanking periods and a luminance signal being a signal for a video period other than the horizontal and vertical blanking periods into the blanking period signal and the luminance signal, amplitude limit means 4-7 eliminating a DC component of the separated luminance signal Y and limiting its amplitude, a bias means 9 giving a prescribed DC bias to the separated blanking period signal and coupling means 3, 8 coupling the luminance signal Y2 subject to amplitude limit and the blanking period signal receiving a prescribed DC bias.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a luminance signal clarifying circuit for improving the waveform of a luminance signal forming a composite video signal to clarify the image.

[0002]

2. Description of the Related Art In a device using a composite video signal such as a VTR, a video camera and a video disc player,
Due to the non-linearity of the signal processing system of each device, the luminance signal that constitutes the composite video signal is distorted, and various phenomena such as ringing, blurring of the image, and deterioration of details appear on the television screen.

Ringing is an oscillating transient phenomenon caused by sudden level fluctuations such as rising and falling of a pulse signal, and image blurring is caused by a response delay to the sudden level fluctuations, distortion of the fluctuation part, and the like. The rising and falling portions are blunted and the boundary portion is blurred on the TV screen, and the deterioration of the details means a phenomenon that the details are unclear on the TV screen due to the extreme attenuation of the high frequency signal.

[0004]

In the past, effective measures against the above-mentioned deterioration of image quality have not been taken, and it has been desired to realize a processing circuit for preventing such deterioration.

The present invention has been made in consideration of the above circumstances, and an object thereof is to improve the waveform of a luminance signal so as to prevent ringing, blurring of images, deterioration of details on a television screen. Another object of the present invention is to provide a luminance signal clarification circuit that clarifies an image on a television screen.

[0006]

In order to solve the above-mentioned problems, according to the present invention, a blanking period signal which is a signal of horizontal and vertical blanking periods and a period other than the horizontal and vertical blanking periods are used. Separation means for separating a composite video signal composed of a luminance signal which is a signal of a certain video period into the blanking period signal and the luminance signal, and limiting the amplitude thereof after removing the DC component of the separated luminance signal. Amplitude limiting means, bias means for applying a predetermined DC bias to the separated blanking period signal, and coupling means for coupling the amplitude-limited luminance signal and the blanking period signal given the predetermined DC bias. Luminance signal clarification circuit characterized by including.

[0007]

In the luminance signal clarifying circuit according to the present invention, as shown in FIG. 1, the composite video signal a consisting of the blanking period signal and the luminance signal is separated by the separating means 2, 3 and 8 into the blanking period signal. Separated into a luminance signal.

The separated luminance signal Y becomes a luminance signal Y1 from which a direct current component is removed, and then is amplified and amplitude-limited,
The blanking period signal of the composite video signal a is biased by the bias means 9 to a predetermined potential according to the level of the composite video signal a. The blanking period signal biased to the predetermined potential is separated from the composite video signal a'by the means 3 and 8 which are the combining means and the separating means, and are combined with the luminance signal Y2 whose amplitude is limited to obtain a new signal. It becomes the composite video signal b.

Due to the amplitude limitation, ringing and blurring generated in the luminance signal are removed, and by removing the direct current component of the luminance signal, the high luminance signal becomes a signal of a lower luminance level and the low luminance signal becomes a signal of a higher luminance level. Therefore, the luminance level of the medium luminance signal is maintained. Further, the high frequency signal is amplified to a predetermined level to clarify unclear details.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of a luminance signal clarifying circuit according to the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention. In the figure, a composite video signal a consisting of a blanking period signal which is a signal of horizontal and vertical blanking periods and a luminance signal which is a signal of a video period which is a period other than the horizontal and vertical blanking periods is a terminal. The composite synchronizing signal SYN which is input to T1 and which is also a component of the composite video signal a is input to the terminal T2.

The composite video signal a input to the terminal T1 is
The blanking period signal is separated into the luminance signal Y by the switch 2 and the switch switching circuit 3 which form the separating means. The luminance signal Y becomes a luminance signal Y1 from which the direct current component is removed by the capacitor 4.

The composite synchronizing signal SYN input to the terminal T2
Thus, the switch switching circuit 3 turns off the switch 2 during the horizontal and vertical blanking periods, and the switch 8 connects the common terminal 8c and the contact 8b. On the contrary, in the video period other than the horizontal and vertical blanking periods, the switch 2 is turned on, and the switch 8 connects the common terminal 8c and the contact 8a.

The luminance signal Y1 from which the direct current component has been removed is amplified by the amplifier circuit 5, and then the amplitude is limited by the limiter 6. The luminance signal whose amplitude is limited by the limiter 6 is attenuated by the attenuation circuit 7.
Is attenuated to become a luminance signal Y2. This luminance signal Y2
Is coupled with a blanking period signal, which will be described later, at the common terminal 8c side of the switch 8 that constitutes the separating means and the coupling means. The attenuation circuit 7 is a circuit for determining the limit level.

The reference level (zero level) of the composite video signal a input to the terminal T1 is fixed to a predetermined level according to the average level thereof by the bias circuit 9.

The composite video signal a'output from the bias circuit 9 has its luminance signal separated by the switch 8 and the switch changeover circuit 3 which are both separating means and combining means, and becomes only a blanking signal. The line signal is the luminance signal Y2 from the attenuation circuit 7 and the common terminal 8c of the switch 8.
They are combined on the side to form a composite video signal b.

That is, during the video period, the switch 8
Is connected to the common terminal 8c and the contact 8a, and the luminance signal Y2
Only the blanking period signal is input to the mixing circuit 10, the common terminal 8c and the contact 8b are connected in the blanking period, and only the blanking period signal including the horizontal and vertical synchronization signals is input to the mixing circuit 10.

In the mixing circuit 10, the average level of the input luminance signal Y2 and the reference level of the input blanking period signal have a certain level relationship according to the luminance signal level of the composite video signal a. However, this level relationship will be described later.

The new composite video signal b generated by combining the luminance signal Y2 and the blanking period signal with the switch 8 is input to the mixing circuit 10 and mixed with the color signal CHRO to form a composite color television signal c. Is output.

The composite color television signal c is power-amplified by the drive circuit 11, and the capacitor 12 and the resistor 13 are provided.
It is input to the video monitor 14 via the, and the quality of the image is monitored.

Next, the operation of the circuit of FIG. 1 will be described based on specific signals.

FIGS. 2A to 2E are waveform diagrams showing examples of the composite video signal a input to the terminal T1. 2A shows a composite video signal in which ringing occurs in a pulse signal with a duty ratio of 50%, and FIG. 2B shows a composite video signal in which blurring occurs in a pulse signal with a duty ratio of 50%. 2 (c) is a composite video signal of a medium luminance level (50% of the white peak level) on which a high frequency signal is superimposed, and FIG. 2 (d) is a low luminance level (white) on which a high frequency signal is superimposed. FIG. 2E shows a composite video signal having a high luminance level (100% level of the white peak level) on which a high frequency signal is superimposed, and FIG.

Regarding the waveform improvement of the composite video signal of FIG.
FIG. 3 showing the luminance signal Y1, amplitude limited luminance signal Y2
4 and FIG. 5 showing the decoded video signal b.

First, the waveform improvement of the composite video signal of FIG. 2A will be described. The composite video signal a in FIG. 2A is composed of a blanking period signal including the horizontal synchronizing signal HS in the blanking period t1 and a luminance signal in the video period t2, and is passed through the switch 2 and the capacitor 4 which constitute the separating means. It is input to the amplifier circuit 5. Since the switch 2 is turned on only during the video period, the blanking period signal is not transmitted, and the luminance signal Y separated and transmitted is removed by the capacitor 4 from the direct current component.
Therefore, the level of the blanking period is the average level of the luminance signal (short-shaped signal in the figure) Y, and after passing through the switch 2 and the capacitor 4, the luminance signal Y becomes the luminance signal Y1 of FIG.

The luminance signal Y1 shown in FIG. 3A is amplified by the amplifier circuit 5, and the amplitude is limited by the limiter 6. As shown in FIG. 3A, the amplitude limitation is performed with a level width of 2L centered on the average level shown by the alternate long and short dash line, that is, the bias level L0, and the signal portion exceeding the level width 2L is removed. As a result, as shown in FIG. 4A, a luminance signal Y2 from which ringing has been removed is obtained.

On the other hand, in the bias circuit 9, the composite video signal a'containing the blanking period signal whose reference level is biased as described above is generated. The bias of the reference level is, for example, in the case of the composite video signal a of FIG. 2A, since the average level L2 shown by the one-dot chain line becomes the bias level of the bias circuit 9, the bias of the level A in the negative direction from the level L2 is Become.

The luminance signal Y2 shown in FIG. 4A is supplied to the mixing circuit 10 via the contact 8a of the switch 8 which is connected only during the video period.
Entered in. Further, the composite video signal a ′ output from the bias circuit 9 with the reference level set to a predetermined level.
Is input to the mixing circuit 10 via the contact 8b of the switch 8 which is connected only during the blanking period.

In FIG. 2A, since the average level of the luminance signal Y2 is L1 and the average level of the composite video signal a'is L2, the average level L1 of the luminance signal Y2 and the reference level of the blanking period signal. And the difference is (A + L1-L2) = A
It becomes + ΔS.

Therefore, in the composite video signal b of FIG. 5 (a), the level difference between the average level L1 of the luminance signal and the reference level (zero level) is A + ΔS, and the attenuation circuit 7 is adjusted by adjusting ΔS. Bias level L
By adjusting 1 or the bias level L2 of the bias circuit 9, the brightness of the composite video signal b can be adjusted.

In this way, the luminance signal Y2 and the luminance signal Y
By combining with a blanking period signal having a reference level that is A + ΔS lower than the average level L1 of 2, a composite video signal b having an average luminance of A + ΔS is generated at the input side of the mixing circuit 10.

The composite video signal shown in FIG. 2B is the terminal T1.
2A is similar to the case of FIG. 2A, and as shown in FIG. 3B and FIG. 4B, rounding of the rising and falling portions of the pulse signal is removed. Then, the composite video signal b shown in FIG. 5B has the same waveform as that in FIG.

Next, as shown in FIG. 2 (c), the high frequency signal has a constant level (in the case of FIG. 2 (c), the white peak level is 5).
The operation when superposed on a DC signal of 0% level) will be described. In this case, the luminance signal Y1 becomes as shown in FIG.

In the case of the high frequency signal superposed on the constant DC level, the luminance signal Y1 is a signal as shown in FIG. 3 (c). Therefore, in the composite video signals shown in FIGS. 2D and 2E, the luminance signal Y1 becomes a signal as shown in FIG. 3C.

Although the amplitude shown in FIG. 3 (c) is limited by the level width 2L centering on the average level of the high frequency signal, the amplitude of the high frequency signal is small, so that the amplitude is not limited and the amplifier circuit. It is only amplified by 5. Therefore,
In the luminance signal Y2, the high frequency signal has its amplitude increased as shown in FIG. 4 (c).

On the other hand, the blanking interval signal output from the bias circuit 9 has a reference level whose average level is the average level of the composite video signal a shown by the alternate long and short dash line, that is, the bias of the bias circuit 9, as shown in FIG. The level is lower than the level L2 by the level B. Therefore, the reference level of the composite video signal b obtained by combining the luminance signal Y2 and the blanking period signal is shown in FIG.
As shown in (c), the level shifts from the average level of the luminance signal Y2 in the negative potential direction (B + ΔS).

Similarly, in the case of the black level luminance signal shown in FIG. 2D, the reference level of the composite video signal b is shown in FIG. 5D.
2B, the average level of the luminance signal Y2 is shifted in the negative potential direction (ΔS−C), and in the case of the luminance signal of the white peak level shown in FIG. 2E, the composite video signal b
The reference level of is a level shifted (D + ΔS) from the average level of the luminance signal Y2 in the negative potential direction as shown in FIG. 5 (e).

The reference level of the composite video signal a shown in FIGS. 2 (c), 2 (d) and 2 (e) will now be described. The amplitude of the horizontal synchronizing signal of the composite video signal a input to the luminance signal clarifying circuit 1 is 30, and the amplitude of the white peak luminance signal thereof is 7
0 (hence the total amplitude of the signal a is 100), 62
For a standard television signal of 5 lines and 50 fields, A = B≈
26.2, C = 2.2, and D≈54.7, so ΔS
When the value of is 8.8, A + ΔS = B + ΔS = 35.0 ... (1) ΔS−C = 6.6 ... (2) D + ΔS = 63.5 ... (3)

Therefore, as shown in FIGS. 2 (a), 2 (b) and 2 (c), when the average luminance signal level of the composite video signal a is 50% of the white peak level = 35, the equation (1) is obtained. Therefore, the average luminance signal level of the composite video signal b is 35, and in the present circuit 1, the luminance signal level does not change when the composite video signal a whose luminance signal level is 50% of the white peak level = 35 is input. Absent.

As shown in FIG. 2D, the composite video signal a
If the average luminance signal level of 0 is 0% of the white peak level = 0, from equation (2), the average luminance signal level of the composite video signal b is 6.6 = 9.3%, and the average luminance signal level is In the case of the black level, the luminance signal average level is increased by the processing in this circuit 1.

As shown in FIG. 2E, the composite video signal a
Average luminance signal level of white peak level 100% = 70
In the case of, the luminance signal average level of the composite video signal b is 63.5 = 90% from the equation (3), and when the luminance signal average level is the white peak level, the luminance signal average level is To descend.

As a result, the peak portion of the high frequency signal is not lost even if the high frequency signal is amplified, and the level of the high frequency signal is low in the composite video signal a input to the luminance signal clarifying circuit of FIG. Even if the details are unclear, the details can be made clear in the composite video signal b.

It should be noted that, when comparing FIG. 2 and FIG. 5, it is described that the brightness is increased even when the white peak level of the brightness signal average level is 50% or more (for example, FIG. 2).
The signal of 50% of the average level of the luminance signal in (c) is shown in FIG.
The composite video signal of (c) is obtained, but the signal of FIG. 5 (c) has an average luminance signal level of 50% or more), which is ΔS.
This is because, as described above, if ΔS = 8.8 (the value of ΔS is smaller than the value shown in FIG. 2), the average luminance signal level is When it is 50% or more, the brightness decreases, and when it is 50% or less, the brightness increases.

Further, in FIGS. 5A and 5B, Δ
S'level is occurring. ΔS ′ can be adjusted by the bias of the attenuator circuit 7 or the output signal amplitude of the attenuator circuit 7, and can be set to zero.

[0044]

As described above, the luminance signal clarifying circuit according to the present invention can remove the ringing and the blurring of the image by the amplitude limitation, and can amplify the minute high frequency signal without the amplitude limitation by adjusting the luminance. Therefore, it is possible to prevent ringing and blurring of the image from appearing on the TV screen, and to clarify unclear details.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a luminance signal clarifying circuit according to the present invention.

FIG. 2 is a waveform chart showing an example of a composite video signal input to the circuit of FIG.

FIG. 3 is a waveform diagram showing a luminance signal before amplitude limitation.

FIG. 4 is a waveform diagram showing a luminance signal after amplitude limitation.

FIG. 5 is a waveform diagram showing a composite video signal in which a luminance signal and a blanking period signal are combined.

[Explanation of symbols]

 1 Luminance signal clarifying circuit 2, 8 switch 3 Switch switching circuit 4 Capacitor 5 Amplifying circuit 6 Limiter 7 Attenuating circuit

Claims (1)

[Claims] 1. A composite video signal comprising a blanking period signal which is a signal of horizontal and vertical blanking periods and a luminance signal which is a signal of a video period which is a period other than the horizontal and vertical blanking periods. Separation means for separating the blanking period signal and the luminance signal, amplitude limiting means for limiting the amplitude of the separated luminance signal after removing the direct current component, and a predetermined DC bias for the separated blanking period signal. A luminance signal clarifying circuit, comprising: biasing means for providing the amplitude limited luminance signal; and coupling means for coupling the amplitude limited luminance signal and the blanking period signal given the predetermined DC bias.