JPH10322573A - Contour corrector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a contour corrector composed of a digital circuit which can correct a contour without adding any shoot component. SOLUTION: A maximum value detection circuit 6 acquires a signal B3 by detecting a maximum value out of five pixels with a signal B1 as a center. A minimum value detection circuit 7 acquires a signal B4 by detecting a minimum value out of five pixels with the signal B1 as a center. An HPF 8 generates a high frequency signal component corresponding to the signal B1, and this component is made double into signal B2 by a multiplier 9. An adder 10 adds the signals B1 and B2 into signal B5. A maximum value detection circuit 11 selects any larger one of signals B4 and B5 into signal B6 and a minimum value detection circuit 12 selects any smaller one of signals B3 and B6 into signal B7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a contour correcting device for sharpening a contour of a video signal displayed on an image display device such as a television receiver or a display device.

[0002]

2. Description of the Related Art There have been proposed various contour correcting devices for sharpening the contour of a video signal displayed on an image display device such as a television receiver or a display device. In general, the contour correction device corrects the contour by adding an overshoot and a preshoot (or undershoot) to the contour of the video signal. On the other hand, there is also a contour correction device configured to remove a shoot component after adding an overshoot and a preshoot. An example of this type of conventional contour correction device is disclosed in Japanese Patent Application Laid-Open No. 5-292522.

[0003] The contour correction device described in the above-mentioned prior application is constituted by an analog circuit, and performs an outline correction operation on an analog signal as described in the specification of the above-mentioned prior application.
However, even if the delay circuit in the contour correction device described in the above-mentioned prior application is simply replaced with a one-clock delay element to constitute a digital circuit, the contour correction operation is not performed. This will be described with reference to FIGS. FIG. 14 is a block diagram in which the delay circuit in the contour correction device described in the above-mentioned prior application is replaced with a one-clock delay element to constitute a digital circuit, and FIG. 15 is a waveform diagram for explaining the operation of FIG.

In FIG. 14, a digital signal input from an input terminal 201 is sequentially input to D flip-flops 202 and 203, which are one-clock delay elements, and is delayed by one clock. The digital signal input from the input terminal 201 is also input to a maximum value detection circuit 204, a minimum value detection circuit 205, and a high-pass filter (HPF) 206.

The outputs of the D flip-flops 202 and 203 are output from a maximum value detection circuit 204 and a minimum value detection circuit 2 respectively.
05, input to the HPF 206. A signal B <b> 1 delayed by one clock from the input signal output from the D flip-flop 202 is the signal shown in FIG. 15A, and the signal B <b> 1 is input to the adder 208. This signal B1 is set as a target pixel.

The maximum value detection circuit 204 detects a pixel of the maximum level from the three input pixels centering on the signal B1, which is the target pixel, and outputs a signal B3 shown in FIG. This signal B3 is input to the minimum value detection circuit 210. The minimum value detection circuit 205 detects a pixel of the minimum level from the three input pixels centering on the signal B1, and detects the pixel of FIG.
The signal B4 shown in (D) is output. This signal B4 is input to the maximum value detection circuit 209.

The HPF 206 is, for example, a three-tap filter having a tap gain of (-1/2, 1, -1/2). The HPF 206 generates a high frequency signal component at an edge portion of the signal B1 from three input pixels centered on the signal B1. The output of the HPF 206 is
Assuming that the gain coefficient is 2, for example, the signal is input to the multiplier 207 and is doubled to obtain a signal B2 shown in FIG.
This signal B2 is input to the adder 208.

[0008] The adder 208 adds the input signal B1 and the signal B2, and outputs a signal B5 shown in FIG. This signal B5 is a signal obtained by adding a high frequency signal component to the signal B1. The signal B5 is input to the maximum value detection circuit 209.

The maximum value detection circuit 209 selects the larger one of the signals B4 and B5 and outputs a signal B6 shown in FIG. The undershoot portion of the signal B5 is removed by the maximum value detection circuit 209. The signal B6 is input to the minimum value detection circuit 210. The minimum value detection circuit 210 selects the smaller one of the signals B3 and B6, and outputs a signal B7 shown in FIG. This minimum value detection circuit 210 removes an overshoot portion in signal B6. Signal B7
Is output from the output terminal 211.

The signal B1 shown in FIG.
As can be seen by comparing the signal B7 shown in FIG. 14G, the signal B1 and the signal B7 have exactly the same signal waveform, and FIG.
In the configuration shown in (1), no contour correction operation is performed.

[0011]

By the way, in the conventional contour correction device which corrects the contour by adding a shoot component to the contour of the video signal, if the correction amount of the contour correction is increased, the shoot component is inevitable. And the image quality deteriorates. In addition, considering that the contour correction device is used not only for a television receiver but also for various devices such as a computer device and a printer device, it is preferable that the device be configured with a digital circuit instead of an analog circuit.

Therefore, there is a demand for a contour correction device using a digital circuit, which can satisfactorily correct a contour without adding a shoot component that degrades image quality.
Moreover, in this case, it is more preferable to have excellent noise resistance.

However, as mentioned above,
Even if a contour correction device using an analog circuit configured to remove a shoot component as described in JP-A-292522 is simply configured by a digital circuit, the contour correction operation is not performed, and the above-mentioned demand cannot be satisfied. .

Further, depending on the type of the image to be contour-corrected or the type of equipment using the contour correcting device, it is desirable to add no shoot component at all, and to add a certain amount of shoot component. It is sometimes desirable. Therefore, a contour correction device capable of arbitrarily adding a shoot component as needed is also desired.

SUMMARY OF THE INVENTION The present invention has been made in view of such problems, and an object of the present invention is to provide a contour correction device using a digital circuit capable of favorably correcting a contour without adding a shoot component. That is. It is another object of the present invention to provide a contour correction device using a digital circuit to which a shoot component can be arbitrarily added as needed. Still another object of the present invention is to provide a contour correction device using a digital circuit having excellent noise resistance.

[0016]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems of the prior art, the present invention relates to a contour correcting apparatus for correcting the contour of an input digital video signal. An upper limit detecting means for detecting, as an upper limit, a pixel having a level higher than the central level from an area of at least 5 pixels around the pixel; Lower limit detection means for detecting a pixel as a lower limit value, high frequency signal component generation means for generating a high frequency signal component for the pixel of interest, and addition means for adding the high frequency signal component to the pixel of interest, The signal level of the output of the adding means,
An object of the present invention is to provide an outline correction device characterized by comprising an amplitude limiting means for limiting the amplitude between the upper limit value and the lower limit value.

[0017]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view showing a contour correcting apparatus according to the present invention. FIG. 1 is a block diagram showing a first embodiment of the contour correcting device of the present invention, FIGS. 2 and 3 are waveform diagrams for explaining the operation of the first embodiment of the contour correcting device of the present invention, and FIG. FIG. 5 is a block diagram showing a second embodiment of the contour correcting device of the present invention. FIGS. 5 and 6 are waveform diagrams for explaining the operation of the second embodiment of the contour correcting device of the present invention. FIGS. 12 and 13 are block diagrams showing third to seventh embodiments of the contour correction device of the present invention.
FIG. 10 is a waveform chart for explaining the operation of the contour correcting device of the present invention shown in FIG. 9 in the fourth and fifth embodiments.

In general, a baseband video signal is composed of three primary color signals of red (R), green (G), and blue (B), or a signal of three channels of a luminance signal and two color difference signals. In the following description, only one channel is shown for simplification. That is, the input digital signal is R,
One of the three primary color signals of G and B, or a luminance signal and a color difference signal.

<First Embodiment> In FIG.
The input digital signal is sequentially input to D flip-flops 2 to 5 which are one-clock delay elements, and is delayed by one clock. The digital signal input from the input terminal 1 is also input to a maximum value detection circuit 6, a minimum value detection circuit 7, and a high-pass filter (HPF) 8.

The outputs of the D flip-flops 2 to 5 are input to a maximum value detection circuit 6, a minimum value detection circuit 7, and an HPF 8, respectively. The signal B1 delayed by two clocks with respect to the input signal output from the D flip-flop 3 is shown in FIG.
The signal B1 is input to the adder 10. This signal B1 is set as a target pixel.

The maximum value detection circuit 6 detects the pixel of the maximum level from the five input pixels centering on the signal B1 as the target pixel, and outputs a signal B3 shown in FIG. That is, the maximum value detection circuit 6 is an upper limit detection unit that detects a maximum value as an upper limit value from the input five pixels. This signal B3 is input to the minimum value detection circuit 12. The minimum value detection circuit 7 detects a pixel of the minimum level from the five input pixels centering on the signal B1, and outputs a signal B4 shown in FIG. That is, the minimum value detection circuit 7 is a lower limit detection unit that detects the minimum value as the lower limit value from the input five pixels. This signal B4 is input to the maximum value detection circuit 11.

The HPF 8 has a tap gain of (−1/4, −1, 5/2, −1, − ／) as an example.
It is a tap filter. The HPF 8 generates a high frequency signal component at an edge portion of the signal B1 from the input five pixels centered on the signal B1. Note that the high frequency signal component is a signal having no AC component but only an AC component.
The tap gain of the HPF 8 is not limited to this, and may be set appropriately.

The output of the HPF 8 is input to the multiplier 9 and multiplied by 2 assuming that the gain coefficient is 2, for example, to obtain a signal B2 shown in FIG. 2B. This signal B2 is input to the adder 10. The adder 10 receives the input signal B
1 and the signal B2 are added, and a signal B5 shown in FIG. This signal B5 is a signal obtained by adding a high frequency signal component to the signal B1. The signal B5 is input to the maximum value detection circuit 11.

The maximum value detection circuit 11 outputs the signal B4 and the signal B
5 and the larger one is selected, and the signal B shown in FIG.
6 is output. The undershoot portion of the signal B5 is removed by the maximum value detection circuit 11. The signal B6 is input to the minimum value detection circuit 12. The minimum value detection circuit 12 selects the smaller one of the signals B3 and B6 and outputs the signal B7 shown in FIG. With this minimum value detection circuit 12, an overshoot portion in the signal B6 is removed.

The maximum value detection circuit 11 and the minimum value detection circuit 12 output the signal B5 between the maximum value (upper limit value) of the maximum value detection circuit 6 and the minimum value (lower limit value) of the minimum value detection circuit 7. It can be seen that the device operates as amplitude limiting means for limiting the amplitude.

By the above operation, the signal B7 becomes the signal B1
The inclination near the center of the inclination is doubled as compared with, and the edge becomes steep, so that the contour is corrected without adding a shoot component. The signal B7 is output from the output terminal 13. Note that the slope of the signal B7 near the center of the slope can be freely set by the value of the gain coefficient of the multiplier 29.

As described above, in the present invention, the maximum level pixel and the minimum level pixel are detected from the area of 5 pixels centering on the target pixel in the video signal, and as shown in FIG. Perform the contour correction operation. In the present embodiment, the area is composed of 5 pixels. Of course, the maximum level pixel and the minimum level pixel may be detected from the area of 6 pixels or more, and it is sufficient if at least 5 pixels or more.

Here, consider a case where a signal containing noise is input to the contour correction device of the first embodiment shown in FIG. FIG. 3 shows an example of an operation signal waveform of each unit when a signal mixed with noise is input. In FIG.
(A) to (G) show the waveforms of the signals B1 to B7, respectively. In the signal B1 shown in FIG.
N2 is noise. When such a single noise is added, in the output signal B7, the noise is expanded over the area of three clocks as shown in FIG. 3 (G). That is, in the contour correction device of the first embodiment shown in FIG. 1, the noise resistance is not good.

<Second Embodiment> The second embodiment shown in FIG. 4 has improved noise resistance. In FIG. 4, digital signals input from an input terminal 21 are sequentially input to D flip-flops 22 to 25, which are one-clock delay elements, and are delayed by one clock. Input terminal 2
The digital signal input from 1 is transmitted to the upper limit detection circuit 26,
It is also input to a lower limit detection circuit 27 and a high pass filter (HPF).

The outputs of the D flip-flops 22 to 25 are an upper limit detection circuit 26, a lower limit detection circuit 27, and an HPF, respectively.
28. The signal B1 delayed by two clocks with respect to the input signal output from the D flip-flop 23 is
The signal B1 is a signal shown in FIG.
Input to 0. This signal B1 is set as a target pixel.

The upper limit detection circuit 26 detects not the pixel of the maximum level but the pixel of the second largest level from the five input pixels centering on the signal B1 as the target pixel,
The signal B3 shown in FIG. 5C is output. Note that the upper limit detection circuit 26 detects a pixel having a level higher than the central level, excluding the pixel at the maximum level, among the input pixels, and the configuration of FIG. Therefore, the pixel is necessarily the second largest pixel. This signal B3 is input to the minimum value detection circuit 32.

The lower limit detection circuit 27 is not a pixel having the minimum level than the input five pixels centered on the signal B1, and is
The pixel having the second lowest level is detected, and a signal B4 shown in FIG. 5D is output. This signal B4 is the maximum value detection circuit 3
1 is input. Note that the lower limit detection circuit 27 detects pixels having a level lower than the center level, excluding the minimum level pixel, from among the input pixels, and in the configuration of FIG. Therefore, the pixel is inevitably the second smallest pixel.

As an example, the HPF 28 sets the tap gain to (−1/4, −1, 5/2, −1, − 例).
It is a tap filter. The HPF 28 generates a high frequency signal component at the edge portion of the signal B1 from the input five pixels centered on the signal B1.

The output of the HPF 28 is input to the multiplier 29 and multiplied by two, assuming that the gain coefficient is 2, for example, and becomes a signal B2 shown in FIG. 5B. This signal B2
Is input to the adder 30. The adder 30 adds the input signal B1 and the input signal B2, and outputs a signal B5 shown in FIG. This signal B5 is a signal obtained by adding a high frequency signal component to the signal B1. The signal B5 is input to the maximum value detection circuit 31.

The maximum value detection circuit 31 outputs the signal B4 and the signal B
5 and the larger one is selected, and the signal B shown in FIG.
6 is output. The undershoot portion in the signal B5 is removed by the maximum value detection circuit 31. The signal B6 is input to the minimum value detection circuit 32. The minimum value detection circuit 32 selects the smaller one of the signals B3 and B6 and outputs a signal B7 shown in FIG. The minimum value detection circuit 32 removes an overshoot portion in the signal B6.

The maximum value detection circuit 31 and the minimum value detection circuit 32 operate as amplitude limiting means for limiting the amplitude of the signal B5 between the upper limit value by the upper limit detection circuit 26 and the lower limit value by the lower limit detection circuit 27. You can see that it is.

By the above operation, the signal B7 becomes the signal B1
The inclination near the center of the inclination is doubled as compared with, and the edge becomes steep, so that the contour is corrected without adding a shoot component. The signal B7 is output from the output terminal 33. Note that the slope of the signal B7 near the center of the slope can be freely set by the value of the gain coefficient of the multiplier 29. The signal B7 shown in FIG.
As can be seen by comparing the signal B7 shown in FIG. 4G with the signal B7 in the configuration of FIG.
7 has the same signal waveform.

Here, a case where the same noise as that described with reference to FIG. 3 is mixed in the contour correcting apparatus of the second embodiment shown in FIG. 4 will be described with reference to FIG. In FIG. 6, (A)
(G) show the waveforms of the signals B1 to B7, respectively. In the signal B1 shown in FIG. 6A, N1 and N2 are noise.

As described above, in the configuration of the second embodiment, the upper limit detection circuit 26 detects pixels having a level higher than the center level (here, the second level) except for the maximum level pixel among the input pixels. Large level pixels)
The lower limit detection circuit 27 detects a pixel having a level lower than the central level (here, a pixel having the second lowest level) among the input pixels except for the pixel at the minimum level. Therefore, in the output signal B7, as shown in FIG. 6G, noise is completely removed, and the signal waveform becomes the same as that of FIG. 5G. Therefore, according to the second embodiment, it is possible to provide a contour correction device having excellent noise resistance.

As described above, in the configuration in which the upper limit value and the lower limit value are detected from the five input pixels centering on the signal B1 as the target pixel, if noise occurs one shot at a distance of 5 pixels or more, Even if the upper limit value is the maximum value or the second largest level, and the lower limit value is the minimum value or the second smallest level, the obtained waveform is the same. When noise continues for two or more pixels, FIGS.
In the above configuration, the obtained waveform will be different. It can be said that the configuration of FIG. 1 is desirable when the contour correction is regarded as important, and the configuration of FIG. 4 is desirable when the noise resistance is regarded as important.

<Third Embodiment> A third embodiment shown in FIG.
This is a two-dimensional extension of the contour correction device of the second embodiment. In FIG. 7, the digital signal input from the input terminal 50 is sequentially input to the delay elements 51 to 54 for one horizontal period, and is delayed by one horizontal period. The digital signal input from the input terminal 50 is sequentially input to D flip-flops 55 to 58, which are one-clock delay elements, and
Delayed by clock. The digital signals output from the delay elements 51 to 54 are respectively D flip-flops 59 to 62 and 63 to 6 which are also one clock delay elements.
6, 67-70, 71-74, and are delayed by one clock.

The digital signal input from the input terminal 50 is also input to an upper limit detection circuit 75, a lower limit detection circuit 76, and a two-dimensional high-pass filter (two-dimensional HPF) 77. D
Outputs of the flip-flops 55 to 74 are input to an upper limit detection circuit 75, a lower limit detection circuit 76, and a two-dimensional HPF 77, respectively. As described above, the upper limit detection circuit 75, the lower limit detection circuit 76, and the two-dimensional HPF 77 have the D flip-flop 6
A signal of 25 pixels in total, consisting of 5 pixels in the horizontal direction and 5 pixels in the vertical direction, with the signal B1 output from 4 as the center, is input. The signal B1 is input to the adder 79.

The upper limit detection circuit 75 ranks the input 25 pixels centered on the signal B1 as the target pixel from 1 to 25 in ascending (or descending) order of the level. For example, a pixel at the fourth largest level from the maximum level is detected instead of the pixel at the level, and the signal B3 is output. This signal B3 is output from the minimum value detection circuit 32.
Is input to

The upper limit detection circuit 75 detects a pixel having a level higher than the central level among the input pixels except for the pixel at the maximum level. More preferably, the upper limit detection circuit 75 divides the input pixel from the minimum level to the maximum level into three parts, a small level part, an intermediate level part, and a large level part. Pixels at levels excluding are detected. Therefore, in the configuration of FIG.
The pixel at the fifth highest level or the pixel at the fifth highest level may be used. What level of the pixel is detected by the upper limit detection circuit 75 may be selected in accordance with the relationship between the noise removal effect and the contour correction effect.

The lower limit detection circuit 76 ranks the input 25 pixels centered on the signal B1 from 1 to 25 in ascending (or descending) order of the level. Instead, a pixel at the fourth lowest level from the minimum level is detected and a signal B4 is output.
This signal B4 is input to the maximum value detection circuit 80.

Note that the lower limit detection circuit 76 detects a pixel having a level lower than the central level among the input pixels except for the pixel at the minimum level. More preferably, the lower limit detection circuit 76 divides the input pixel from the minimum level to the maximum level into three parts, a small level part, an intermediate level part, and a large level part. Pixels at levels excluding are detected. Therefore, in the configuration of FIG.
It may be the pixel of the fifth lowest level or the pixel of the fifth lowest level. What level of pixels is detected by the lower limit detection circuit 76 may be selected in accordance with the relationship between the noise removal effect and the contour correction effect.

The two-dimensional HPF 77 sets the tap gain as follows, for example. -1/256 -4/256 -6/256 -4/256 -1/256 -4/256 -16/256 -24/256 -16/256 -4/256 -6/256 -24/256 220 / 256 -24/256 -6/256 -4/256 -16/256 -24/256 -16/256 -4/256 -1/256 -4/25 6 -6/256 -4/256 -1/256 Here, the filter is a 25-tap filter, and the tap gain is symmetric with respect to the center.

The two-dimensional HPF 77 generates a high frequency signal component at the edge of the signal B1 from the input 25 pixels centered on the signal B1. And two-dimensional HPF7
Assuming that the gain coefficient is 2, for example, the output of the multiplier 7 is
8 and doubled to obtain a signal B2. This signal B2 is input to the adder 79.

The adder 79 adds the input signals B1 and B2 and outputs a signal B5. This signal B5
Is a signal obtained by adding a high frequency signal component to the signal B1. The signal B5 is input to the maximum value detection circuit 80.

The maximum value detection circuit 80 outputs the signal B4 and the signal B
5, the larger one is selected, and a signal B6 is output. The undershoot portion in the signal B5 is removed by the maximum value detection circuit 80. The signal B6 is input to the minimum value detection circuit 81. The minimum value detection circuit 81 outputs the signal B
3 and the signal B6, the smaller one is selected, and the signal B7 is output. The minimum value detection circuit 81 removes an overshoot portion in the signal B6. Note that the maximum value detection circuit 80 and the minimum value detection circuit 81 output the signal B5
Is determined by an upper limit value detection circuit 75 and a lower limit detection circuit 76.
It can be seen that the apparatus operates as amplitude limiting means for limiting the amplitude between the lower limit value and the lower limit value.

By the above operation, the signal B7 becomes the signal B1
The inclination near the center of the inclination becomes steeper than that of the above, and the contour is corrected without adding a shoot component. The signal B7 is output from the output terminal 82. The slope near the center of the slope of the signal B7 can be freely set by the value of the gain coefficient of the multiplier 78.

Also in the third embodiment shown in FIG. 7, the upper limit detection circuit 75 detects a pixel having a level higher than the central level among the input pixels except for the pixel at the maximum level. Among the input pixels, pixels having a level lower than the center level are detected except for the pixels at the minimum level, so that even if noise is mixed in the input signal, the noise is completely removed. Therefore, according to the third embodiment, it is possible to provide a contour correction device having excellent noise resistance.

In the third embodiment described above, the area of the two-dimensional HPF 77 for generating the high frequency signal is 25 taps in the horizontal direction 5 and the vertical direction 5, and the area by the upper limit detection circuit 75 and the lower limit detection circuit 76 is also Although the two regions are set to be the same as 25 pixels in the horizontal direction 5 and the vertical direction 5, it is not always necessary to make them the same. For example, two-dimensional H
Good contour correction can be achieved even if the PF 77 has 25 taps in the horizontal direction 5 and the vertical direction 5 and the upper limit detection circuit 75 and the lower limit detection circuit 76 have 15 pixels in the horizontal direction 5 and the vertical direction 3.

The third embodiment shown in FIG. 7 is a two-dimensional extension of the configuration of the second embodiment shown in FIG. 4 in consideration of noise resistance. However, the input digital signal contains noise. In such a case, the configuration of the first embodiment shown in FIG. 1 may be extended two-dimensionally. In this case, a maximum value detection circuit may be used instead of the upper limit detection circuit 75 and a minimum value detection circuit may be used instead of the lower limit detection circuit 76 in FIG.

The contour correcting devices according to the first to third embodiments described above can correct a contour without adding a shoot component. By the way, when a display device of a video signal enlarges an image by an optical system and projects the image on a screen like a projection television, a high-frequency signal component of the displayed image is reduced.

As described above, in the case of a display device in which the spatial high-frequency characteristic is reduced, a blurred image will be displayed even if the contour of the video signal is corrected. Therefore, this problem can be solved by newly generating a high frequency signal component and adding it to the contour-corrected signal in order to correct the spatial frequency characteristics of the display device.

In view of the above, the fourth to seventh embodiments shown in FIGS. 8 to 11 are designed to intentionally add a shoot component to correct the spatial frequency characteristics. Of course, in this case, since the shoot component acts to correct the spatial frequency characteristics, the visual quality is improved without deteriorating the image quality. 8 to 11, the same parts as those in FIG. 7 are denoted by the same reference numerals, and the description of the same parts will be appropriately omitted.

<Fourth Embodiment> In FIG. 8, outputs of D flip-flops 55 to 74 are input to a two-dimensional high-pass filter (two-dimensional HPF) 101. 2D HPF
Reference numeral 101, like the two-dimensional HPF 77, generates a high-frequency signal component at the edge of the signal B1 from the input 25 pixels centered on the signal B1. In addition, two-dimensional HPF1
The tap gain of 01 may be the same as the tap gain of the two-dimensional HPF 77, but it is desirable that the two are different from each other in order to make the tap gain of the two-dimensional HPF 101 optimal according to the spatial high frequency characteristics of the display device. .

The output of the two-dimensional HPF 101 is
Is input to The multiplier 102 is provided with a gain coefficient, and the high-frequency signal component output from the two-dimensional HPF 101 is gain-adjusted. The output of the multiplier 102 is the adder 1
03 and added to the contour-corrected signal B7 output from the minimum value detection circuit 81. And the adder 10
3 is output from the output terminal 104. In this manner, in the fourth embodiment shown in FIG. 8, by adding the high frequency signal component, it is possible to intentionally perform the contour correction in which the shoot component is additionally generated.

<Fifth Embodiment> A fifth embodiment shown in FIG.
It is simplified by sharing the two-dimensional HPF 77 and the two-dimensional HPF 101 in FIG. That is, two-dimensional HP
The output of F77 is input to both the multiplier 78 and the multiplier 102.

The operation of the fourth and fifth embodiments shown in FIGS. 8 and 9 will be described with reference to the waveform chart shown in FIG. FIG.
2 shows a one-dimensional signal waveform for simplification. FIG. 12A shows a signal B7 output from the minimum value detection circuit 81 in which the contour has been corrected without adding a shoot component. FIG. 12B shows a high frequency signal component output from the multiplier 102. FIG. 12 (C)
Is a signal B7 shown in FIG.
And a high-frequency signal component shown in FIG. 12B. The signal shown in FIG. 12C is a signal B7
Has a waveform close to a signal obtained by adding a shot component slightly to the signal.

As can be seen from the above description, FIGS.
, The multiplier 102 and the adder 103 are provided with a maximum value detection circuit 80 and a minimum value detection circuit 8 constituting the amplitude limiting means.
A high frequency signal component is added to the signal whose amplitude is limited by 1 to operate as a shoot component generating means for additionally generating a shoot component.

<Sixth Embodiment> A sixth embodiment shown in FIG. 10 is configured to add a shoot component by another configuration. 10, the signal B3 output from the upper limit detection circuit 75 and the signal B4 output from the lower limit detection circuit 76 are input to a subtractor 110. Subtractor 110
Subtracts signal B4 from signal B3, and outputs signal B3 and signal B
The difference value with the value of 4 is input to the multiplier 111. Multiplier 111
Is given a constant gain coefficient, and the output of the subtracter 110 is multiplied by the gain coefficient. If the gain coefficient is, for example, 0.1, the output of the multiplier 111 is
0.1 × (upper limit value−lower limit value).

The output of the multiplier 111 is input to the adder 112 and the subtractor 113. The subtractor 113 subtracts the output of the multiplier 111 from the signal B4, which is the lower limit, to reduce the undershoot clip level to a level lower than the lower limit, and inputs the same to the maximum value detection circuit 80. The adder 112 adds the signal B3, which is the upper limit, to the output of the multiplier 111 to set the clip level of overshoot to a level higher than the upper limit, and inputs the clip level to the minimum value detection circuit 81.

As a result, finally, the minimum value detection circuit 8
An overshoot and an undershoot are added to the signal B7 output from 1. The amount of the shoot component is determined by the gain coefficient multiplied by the multiplier 111. Therefore, a shoot component can be arbitrarily added as needed. Also in this case, the signal B7 is
The signal is as shown in FIG.

<Seventh Embodiment> A seventh embodiment shown in FIG. 11 is a slightly modified configuration of FIG. That is, in FIG. 10, the difference value between the signal B3 and the signal B4 output from the subtractor 110 is input to the multiplier 111, and the output of the multiplier 111 is input to the adder 112 and the subtractor 113. 11, the difference value between the signal B3 and the signal B4, which is the output of the subtractor 110, is input to the multipliers 111 and 114, and the output of the multiplier 111 is output to the subtractor 113.
, And the output of the multiplier 114 is input to the adder 112.

The multipliers 111 and 114 are given a constant gain coefficient, and multiply the output of the subtracter 110 by the gain coefficient and output the result. If the gain coefficient is, for example, 0.1, the outputs of the multipliers 111 and 114 have a value of 0.1 × (upper limit value−lower limit value).

The subtracter 113 subtracts the output of the multiplier 111 from the signal B4, which is the lower limit, to set the undershoot clip level to a level lower than the lower limit, and inputs the same to the maximum value detection circuit 80. The adder 112
By adding the signal B3, which is the upper limit, to the output of the multiplier 114, the overshoot clip level is set to a level higher than the upper limit, and is input to the minimum value detection circuit 81.

As a result, finally, the minimum value detection circuit 8
An overshoot and an undershoot are added to the signal B7 output from 1. The amount of the shoot component is determined by the gain coefficient multiplied by the multipliers 111 and 114. Therefore, a shoot component can be arbitrarily added as needed. Also in this case, the signal B7 is
The signal is as shown in FIG.

As can be understood from the above description, the multiplier 111, the adder 112, and the subtractor 113 in FIG. 10 and the multipliers 111 and 114, the adder 112,
The subtractor 113 increases the upper limit value by the upper limit detection circuit 75 and decreases the lower limit value by the lower limit detection circuit 76, thereby limiting the amplitude by the maximum value detection circuit 80 and the minimum value detection circuit 81 constituting the amplitude limiting means. The signal operates as a shoot component generating means for additionally generating a shoot component as a result.

In general, a video signal display device has a so-called gamma characteristic in which the relationship between an input signal and an output signal is non-linear. For example, a cathode ray tube (CR
In the case of T), when the signal level is normalized from 0 to 1, it is said that the signal level has characteristics close to the 2.2th power of the signal level. For this reason, comparing the case where the high-frequency small-amplitude signal is superimposed on a dark video signal and the case where it is superimposed on a bright video signal, the latter has a larger amplitude.

Therefore, when a shoot component is added to correct the spatial frequency characteristic, it is desirable to use a shoot component corresponding to the gamma characteristic. For example, in order to cope with the gamma characteristic of the CRT, the amplitude of the negative polarity portion of the high frequency signal component (shoot component) may be made larger than the amplitude of the positive polarity portion. Which of the positive portion and the negative portion of the shoot component is increased depends on the nonlinear characteristics of the display device. If there is a display device having characteristics opposite to the gamma characteristic of the CRT, the amplitude of the positive polarity portion may be made larger than the amplitude of the negative polarity portion.

Of the fourth to seventh embodiments shown in FIGS. 8 to 11, the fourth, fifth and seventh embodiments can make the positive and negative portions of the shoot component asymmetric. It is.
It is a more preferable embodiment to make the size of the positive portion and the negative portion of the chute component different from each other in accordance with the non-linear characteristics of the display device so as to be asymmetric.

First, in FIG. 8 and FIG.
The size of the positive-polarity part and the negative-polarity part of the high frequency signal component input to 03 is made different. That is, the multiplier 102
When multiplying the high frequency signal component output from the two-dimensional HPF 101 by the gain coefficient, the coefficient in the positive polarity part and the coefficient in the negative polarity part may be different. As an example of the specific configuration, the two-dimensional HPF 10
A discriminator for discriminating the polarity of the output of No. 1 is provided, and a gain coefficient in a positive polarity portion and a gain coefficient in a negative polarity portion are switched by a switch according to the output of the discriminator.

As another configuration example, a non-linear processing circuit is provided between the multiplier 102 and the adder 103 to make the magnitudes of the positive and negative parts of the high frequency signal component asymmetric. As described above, various configurations are conceivable in which the positive portion and the negative portion of the high frequency signal component are asymmetric, and as a result, the positive portion and the negative portion of the shoot component are asymmetric.

On the other hand, in FIG.
By making the gain coefficient given to 114 different, the positive and negative portions of the shoot component can be made asymmetric. The multiplier 111 determines the level at which the undershoot clip level decreases from the lower limit, and the multiplier 114 determines the level at which the overshoot clip level increases from the upper limit. Therefore, when the gain coefficient of the multiplier 111 is set to be larger than the gain coefficient of the multiplier 114, the amplitude of the negative portion of the shoot component may be made larger than that of the positive portion so as to correspond to the gamma characteristic of the CRT. it can.

FIG. 13 shows waveforms when the positive and negative portions of the shoot component in FIGS. 8 and 9 are asymmetric. FIG. 13 also shows a one-dimensional signal waveform for simplification. FIG.
(A) is a signal B7 output from the minimum value detection circuit 81 that has been contour-corrected without adding a shoot component.
FIG. 13B illustrates a high-frequency signal component output from the multiplier 102 in which the positive and negative portions are asymmetric. FIG. 13C shows the result of FIG.
This is a signal obtained by adding the signal B7 shown in (A) and the high frequency signal component shown in FIG. 13 (B).

In FIG. 11, the signal B7 output from the minimum value detection circuit 81 has the same waveform as that shown in FIG.

8 to 11, when the noise resistance is not regarded as important, a maximum value detection circuit may be used instead of the upper limit detection circuit 75, and a minimum value detection circuit may be used instead of the lower limit detection circuit 76.

In the first and second embodiments described above, the upper and lower limits are detected from five pixels in the horizontal direction. In the third to seventh embodiments, the upper and lower limits are detected from 25 pixels in the horizontal and vertical directions. And the lower limit are detected. It is also possible to configure to detect the upper limit value and the lower limit value from five pixels in the vertical direction.
In this case, an effect is exerted on noise in the vertical direction. The upper limit value and the lower limit value may be detected from an area of at least 5 pixels in the horizontal or vertical direction with the target pixel as the center.

[0081]

As described above in detail, the contour correction apparatus of the present invention can be used to detect an area of at least 5 pixels or more around the pixel of interest in an input digital video signal.
An upper limit detecting means for detecting a pixel at a level higher than the central level as an upper limit value, a lower limit detecting means for detecting a pixel at a level lower than the central level as a lower limit value in an area of at least five pixels or more around the pixel of interest, A high-frequency signal component generating means for generating a high-frequency signal component for the pixel, an adding means for adding the high-frequency signal component to the pixel of interest, and a signal level of the output of the adding means, the upper limit value and the lower limit value. Since the apparatus is provided with the amplitude limiting means for limiting the amplitude between them, it is possible to satisfactorily correct the contour without adding a shoot component.

Further, by setting the upper limit value to pixels excluding the pixels at the maximum level and setting the lower limit value to pixels excluding the pixels at the minimum level, noise can be removed even if the input video signal contains noise. As a result, a contour correction device having excellent noise resistance can be obtained. Therefore, this case is extremely effective when displaying an image on a large screen display.

Further, if a shoot component generating means for additionally generating a shoot component is provided, the shoot component can be arbitrarily added as required.
The spatial frequency characteristics of the display device can be corrected, and the contour can be corrected more favorably. At this time, if means for making the amplitude of the positive and negative portions of the chute component asymmetric is included, the contour can be corrected even better in response to the non-linear characteristics (gamma characteristics) of the display device. It becomes possible.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment of the present invention.

FIG. 2 is a waveform chart for explaining the operation of the first embodiment of the present invention.

FIG. 3 is a waveform chart for explaining the operation of the first embodiment of the present invention.

FIG. 4 is a block diagram showing a second embodiment of the present invention.

FIG. 5 is a waveform chart for explaining the operation of the second embodiment of the present invention.

FIG. 6 is a waveform chart for explaining the operation of the second embodiment of the present invention.

FIG. 7 is a block diagram showing a third embodiment of the present invention.

FIG. 8 is a block diagram showing a fourth embodiment of the present invention.

FIG. 9 is a block diagram showing a fifth embodiment of the present invention.

FIG. 10 is a block diagram showing a sixth embodiment of the present invention.

FIG. 11 is a block diagram showing a seventh embodiment of the present invention.

FIG. 12 is a waveform chart for explaining operations in the fourth and fifth embodiments of the present invention.

FIG. 13 is a waveform chart for explaining operations in the fourth and fifth embodiments of the present invention.

FIG. 14 is a block diagram showing a conventional example.

FIG. 15 is a waveform chart for explaining the operation of the conventional example.

[Explanation of symbols]

2-5, 22-25, 55-74 D flip-flop 6 Maximum value detection circuit (upper limit detection means) 7 Minimum value detection circuit (lower limit detection means) 8, 28 High pass filter (high frequency signal component generation means) 9, 29, 78, 102, 111, 114 Multiplier 10, 30, 79 Adder (addition means) 11, 31, 80 Maximum value detection circuit (amplitude restriction means) 12, 32, 81 Minimum value detection circuit (amplitude restriction means) 26, 75 Upper limit detection circuit (upper limit detection means) 27, 76 Lower limit detection circuit (lower limit detection means) 77, 101 Two-dimensional high-pass filter (high frequency signal component generation means) 103, 112 Adders 110, 113 Subtractors

Claims (6)

[Claims] 1. An outline correction apparatus for correcting an outline of an input digital video signal, wherein a pixel having a level higher than a central level in an area of at least 5 pixels or more around a pixel of interest in the input digital video signal. Upper limit detecting means for detecting as an upper limit value; lower limit detecting means for detecting, as a lower limit, a pixel having a level smaller than a central level from an area of at least five pixels or more around the target pixel; a high frequency signal for the target pixel A high frequency signal component generating means for generating a component; an adding means for adding the high frequency signal component to the pixel of interest; and a signal level of an output of the adding means between the upper limit value and the lower limit value. And an amplitude limiting means for limiting the amplitude of the contour. 2. The contour correction device according to claim 1, wherein the upper limit value is a pixel of a maximum level, and the lower limit value is a pixel of a minimum level. 3. The contour correction device according to claim 1, wherein the upper limit value is a pixel excluding a pixel at a maximum level, and the lower limit value is a pixel excluding a pixel at a minimum level. 4. The contour correcting apparatus according to claim 1, wherein a high frequency signal component is added to the signal whose amplitude is limited by said amplitude limiting means, so that a shoot component is additionally generated. An outline correction device comprising a shoot component generation means. 5. The contour correcting device according to claim 1, wherein the upper limit value is increased and the lower limit value is decreased, so that a shot component is added to an output of the amplitude limiting means. A contour correction device comprising a chute component generating means for generating. 6. The contour correcting device according to claim 4, wherein said shoot component generating means includes means for making the amplitudes of a positive part and a negative part of the shoot component asymmetric. A contour correction device that is a feature.