JP2000032298A - Contour correction circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a contour correction circuit capable of preventing the degradation of the S/N of video signals and preventing the generation of overshoots and preshoots in the contour part of the video signals. SOLUTION: The video signals S1 are over-sampled in an ADC 102 and then, time-sequentially stored in delay circuits 103-107. In the meantime, the video signals S1 are differentiated in a differentiation circuit 109 and the rising and falling levels are ranked in a comparator 111. A data selector 108 takes out and outputs video signal data from one of the delay circuits 103-107 corresponding to ranking signals from the comparator 111.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a contour correction circuit, for example, to a contour correction circuit in a television receiver.

[0002]

2. Description of the Related Art For example, in a television receiver, as a method for improving the sharpness of an image, a contour correction circuit using a secondary differential signal has been conventionally known.

FIG. 4 shows a configuration diagram of an example of a conventional contour correction circuit. Referring to FIG. 1, the conventional contour correction circuit includes a secondary differentiation circuit 501, a coring circuit 502, a signal inversion circuit 503, and an addition circuit 504.

Next, the operation of this circuit will be described.
FIG. 5 is a timing chart showing an operation of an example of a conventional contour correction circuit.

Referring to FIG. 5, FIG. 5A shows an input video signal of a black and white pattern as an example.

First, this input video signal is supplied to a secondary differentiating circuit 5.
01, a video signal edge component is extracted (FIG. 9B).
reference).

Next, a noise component is removed from the video signal edge component by a coring circuit 502 (see FIG. 1C).

The video signal edge component from which the noise component has been removed is inverted by the signal inversion circuit 503 (see FIG. 1D).

The inverted video signal edge component is added to the input video signal by the adding circuit 504 and output (see FIG. 3E).

That is, overshoot 5 in the input video signal
11 and the preshoot 512 are added to emphasize the outline of the video signal.

[0011]

However, since the second differential signal is added to the input video signal, the S / N of the video signal is deteriorated, and the overshoot 511 and the pre-shoot 511 are generated at the outline. There is a disadvantage that an image becomes unnatural due to the occurrence of the shoot 512.

On the other hand, a contour correction circuit for preventing occurrence of overshoot and preshoot in a contour portion is disclosed in Japanese Patent Application Laid-Open No. Sho 61-33078.

This circuit performs second differentiation of the input video signal,
The clock signal is frequency-modulated by the secondary differential signal, and the input video signal is sampled by the frequency-modulated signal.

This sampling is alternately performed at a constant period by two sampling circuits. On the other hand, during sampling, the other reads out sampled data at a clock signal rate.

In this manner, data sampled alternately from the two sampling circuits is read.

Therefore, an object of the present invention is to prevent the deterioration of the S / N of a video signal and to generate an overshoot and a preshoot at a contour portion of the video signal by a configuration completely different from the circuit disclosed in this publication. An object of the present invention is to provide a contour correction circuit capable of preventing the above.

[0017]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides sampling means for sampling an input video signal at a constant rate, and wherein the video signals sampled by the sampling means are stored in time series. A plurality of storage means, differentiating means for differentiating the video signal,
Selecting means for selecting a sampled video signal from one of the plurality of storage means in accordance with the rising and falling levels of the video signal differentiated by the differentiating means.

According to the present invention, the input video signal is sampled at a constant rate, and the sampled data is stored in a plurality of storage means in a time series. Then, one of the data stored in the storage means is selected according to the level of the signal obtained by differentiating the video signal.

As described above, since the contour correction circuit is constructed without using a means for adding the signal obtained by differentiating the video signal and the video signal, deterioration of the S / N of the video signal is prevented, and the contour of the video signal is prevented. It is possible to prevent overshoot and preshoot from occurring in the section.

[0020]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a configuration diagram of a contour correction circuit according to a preferred embodiment of the present invention.

The contour correction circuit includes a low-pass filter (hereinafter, referred to as LPF) 101, an oversampling circuit (hereinafter, referred to as ADC) 102, a first delay circuit (hereinafter, referred to as DELAY) 103, and a plurality of series-connected circuits. Second delay circuit (hereinafter referred to as DFF) 104 to 107
, A data selector 108, a differentiating circuit 109, a coring 110 for removing a small amplitude of a signal, and a comparator 111.

When the basic sampling frequency is f, the ADC 102 oversamples at the frequency (N + 1) · f (where N is a positive even number). or,
The number of DFFs is N. In the present embodiment, a case where N = 4 is shown as an example.

Next, the operation will be described. The input video signal S <b> 1 is oversampled by the ADC 102 after the low-frequency portion is extracted by the LPF 101.

The oversampled video signal S2 is stored in a plurality of DFFs 104 to 107 in a time series after being given a fixed delay in the DELAY 103.

Then, DELAY 103 and DFF 10
The outputs of each of 4 to 107 are input to data selector 108.

On the other hand, the video signal S2 oversampled by the ADC 102 is also input to the differentiating circuit 109 at the same time, where it is differentiated.

The differentiated video signal S3 is further shaped by a coring 110, and then subjected to a comparator 111.
Is input to

The comparator 111 performs a process of ranking the level of the waveform-shaped video signal S4 into a plurality of levels.

Then, the DELAY 103 and the plurality of DFFs 10 are selected by the data selector 108 in accordance with the rank.
4 to 107 are selected, and the selected D
The data S5 stored in the ELAY 103 or the DFFs 104 to 107 is output from the comparator 111.

The timings of storing data in the DFFs 104 to 107, ranking by the comparator 111 and selecting by the data selector 108 are AD.
This is performed in synchronization with the sampling in C102.

As described above, the contour of the edge portion of the video signal S1 can be corrected by correcting the contour of the edge portion of the video signal S1. Further, since the configuration is not adopted in which the two differential signals are added to the input video signal S1, it is possible to prevent the deterioration of the S / N of the video signal S1 and the occurrence of overshoot and preshoot in the contour portion. it can.

Next, this embodiment will be described in further detail with reference to this embodiment.

[0033]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, a first embodiment will be described. FIG. 1 is also referred to for the first embodiment.

The input video signal S1 is first supplied to the LPF 10
At 1 the band is limited to 1 / 2f.

Then, the band-limited video signal S6 is A
It is quantized by the DC 102.

Further, the quantized video signal S2 passes through a DELAY 103 which delays data in synchronization with oversampling in order to match a phase with a selector control signal S7 from a comparator 111, an input 1 (121) of a DFF 104 and a data selector 108. Is input to The output data from the DELAY 103 is displayed as S5-1.

DFF1 connected in series of four
The video signals S5-2 to S5-5 delayed by one clock by 04 to 107 are input to the inputs 2 to 5 (122 to 125) of the data selector 108.

The DFFs 104 to 107 delay the signal in synchronization with the oversampling clock of the ADC 102.

At the same time, the video signal S2 oversampled by the ADC 102 is input to the coring circuit 110 after the edge component of the video signal is extracted by the differentiating circuit 109.

The coring circuit 110 removes noise components and small signal edge signals from the differentiated video signal S3.

The signal S4 output from the coring circuit 110 is input to the comparator circuit 111.

In the comparator 111, four types of slice levels are set, and the data selector 108 selects one of the inputs 1 to 5 (121 to 125) according to the slice level. A signal in which the contour of the video signal edge has been corrected is obtained.

Next, the operation of the first embodiment will be described in more detail. FIG. 2 is a timing chart showing the operation of the first embodiment. In the first embodiment, a monochrome white pattern is used as a video signal.

FIG. 2A shows an output video waveform S5-3 of the DFF 105. Note that, in the figure, a mark “○” is a basic sampling point, and a mark “x” is an oversampling point.

FIG. 2B shows a waveform S 3 obtained by differentiating the data oversampled by the ADC 102 by the differentiating circuit 109.

FIG. 2C shows an output waveform S 4 of the coring 110.

FIG. 2D shows an output waveform S8 of the data selector 108.

The comparator 111 has four slice levels 1 to 4. The slice level 1 is a level at which the level of the output waveform S4 of the coring 110 is higher than the zero level by a certain level.

The slice level 2 is a level higher than the slice level 1 by a certain level.

The slice level 3 is a level at which the level of the output waveform S4 of the coring 110 is lower than the zero level by a certain level.

The slice level 4 is a level lower than the slice level 3 by a certain level.

If the coring output value S4 is smaller than the slice level 1 and equal to or larger than the slice level 3, the comparator 111 inputs the input 3 (123) to the data selector 108.
Is output.

The coring output value S4 is the slice level 3
If less than and slice level 4 or higher, comparator 1
11 outputs a control signal S7 that causes the data selector 108 to select the input 2 (122).

Similarly, when the coring output value S4 is lower than the slice level 4, the comparator 111 controls the data selector 108 to select the input 1 (121).
Is output.

The coring output value S4 is the slice level 1
If the value is equal to or more than the slice level 2, the comparator 1
Reference numeral 11 outputs a control signal S7 for causing the data selector 108 to select the input 4 (124).

When the coring output value S4 is equal to or higher than the slice level 2, the comparator 111 outputs a control signal S7 for causing the data selector 108 to select the input 5 (125).

By controlling the data selector 108 in accordance with the level of the coring output value S4 in this manner, the output of the data selector 108 is shown in FIG. 2A as indicated by "●" in FIG. 2D. A waveform having a sharper falling and rising edge than the waveform is obtained. Further, neither overshoot nor preshoot occurs in the outline of the video signal.

Next, a second embodiment will be described. Second
The configuration of the embodiment is the same as that of the first embodiment. The second embodiment uses a black and white pattern as a video signal. FIG. 3 is a timing chart showing the operation of the second embodiment.

FIG. 3A shows an output video waveform S5-3 of the DFF 105. Note that, in the figure, a mark “○” is a basic sampling point, and a mark “x” is an oversampling point.

FIG. 3B shows a waveform S 3 obtained by differentiating the data oversampled by the ADC 102 by the differentiating circuit 109.

FIG. 3C shows an output waveform S 4 of the coring 110.

FIG. 3D shows an output waveform S8 of the data selector 108.

The comparator 111 has the same four slice levels 1 to 4 as described above.

The operations of the comparator 111 and the data selector 108 are the same as described above.

As a result, a waveform having a steeper rise and fall than the waveform shown in FIG. 3A is obtained at the output of the data selector 108, as indicated by "●" in FIG. 3D. Further, neither overshoot nor preshoot occurs in the outline of the video signal.

Next, a third embodiment will be described. First
In the second embodiment, the video signal S8 is output from the data selector 108 at the oversampled data rate, but in the third embodiment, the data selector 108 thins out the video signal S8 to output it.

That is, in FIG. 2D and FIG. 3D, only the basic sampling point “○” (however, in the portion that temporally overlaps with the “●” point, The same effect as in the first and second embodiments can be obtained by extracting the intermediate sampling point).

[0068]

According to the present invention, sampling means for sampling an input video signal at a constant rate, a plurality of storage means for storing the video signals sampled by the sampling means in time series, Differentiating means for differentiating a signal, and selecting means for selecting a sampled video signal from one of the plurality of storage means according to the rising and falling levels of the video signal differentiated by the differentiating means. , The S / N of the video signal is prevented from deteriorating, and an overshoot and an overshoot are generated in the outline of the video signal by a completely different configuration from the circuit disclosed in Japanese Patent Application Laid-Open No. 61-33078. A contour correction circuit capable of preventing the occurrence of preshoot is obtained.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a contour correction circuit according to a preferred embodiment of the present invention.

FIG. 2 is a timing chart showing the operation of the first embodiment.

FIG. 3 is a timing chart showing the operation of the second embodiment.

FIG. 4 is a configuration diagram of an example of a conventional contour correction circuit.

FIG. 5 is a timing chart showing an operation of an example of a conventional contour correction circuit.

[Explanation of symbols]

 Reference Signs List 102 oversampling circuit 103 first delay circuit 104 to 107 second delay circuit 108 data selector 109 differentiating circuit 111 comparator

Claims (7)

[Claims] 1. Sampling means for sampling an input video signal at a constant rate, a plurality of storage means for storing the video signals sampled by the sampling means in time series, and differentiating means for differentiating the video signal And selecting means for selecting a sampled video signal from one of the plurality of storage means according to the rising and falling levels of the video signal differentiated by the differentiating means. Contour correction circuit. 2. The contour correction circuit according to claim 1, wherein said video signal is stored in said plurality of storage means in a time series in synchronization with sampling by said sampling means. 3. The contour correction circuit according to claim 1, wherein the selection unit selects the video signal after the sampling in synchronization with sampling by the sampling unit. 4. When the level of the video signal differentiated by the differentiating means is in a constant positive / negative range centered on a zero level, the selecting means stores the video signal in a time series intermediate storing means among the plurality of storing means. 4. The contour correction circuit according to claim 1, wherein the stored video signal is selected. 5. The storage means, wherein when the level of the video signal differentiated by the differentiation means is lower than the fixed positive / negative range, the storage means is a time series of the plurality of storage means and which is newer than the middle. 4. The contour correction circuit according to claim 1, wherein the video signal stored in the memory is selected. 6. The storage means, when the level of the video signal differentiated by the differentiation means is higher than the fixed positive / negative constant range, the storage means being older in time series than the middle of the plurality of storage means. 4. The contour correction circuit according to claim 1, wherein the video signal stored in the memory is selected. 7. The contour correction circuit according to claim 1, wherein said sampling means is an oversampling circuit obtained by multiplying a basic sampling frequency by a positive number.