JPH03151790A - Contour correction circuit for color signal - Google Patents

Abstract

PURPOSE:To realize contour correction while a chroma contour signal component is reduced by adding to an original signal the edge addition information whose amplitude level is obtained through the signal processing so as to make a negative signal component zero with respect to a high frequency signal component extracted from a color signal. CONSTITUTION:A high frequency component extraction circuit 1 extracts high frequency signal components IH, QH, from color difference signals I, Q. A nonlinear processing circuit 2 applies nonlinear signal processing to make the negative level component of the signal components IH, QH, zero to generate edge addition information signals IE, QE used for the contour correction. These signals are added to a primary color difference signal subjected to delay adjustment by a delay circuit 3 at an adder circuit 4 to form correction signals IC, QC. Thus, a contour correction circuit with stable operation for a color signal is realized with simple circuit configuration.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) (Field of Industrial Application) The present invention relates to a color signal contour correction circuit for improving the sharpness of an image represented by a color image signal.

[Conventional technology]

Methods for improving the sharpness of an image represented by an image signal include spatial frequency response correction of the image signal, which includes conventionally used aperture correction, contour compensation, and the like.

Regarding spatial frequency response correction for color signals constituting a color image, Japanese Patent Publication No. 51-45423
As described in the above publication, contour correction is performed to reduce the chroma contour signal component added as a complementary color to the outside of each colored portion.

[Problem to be solved by the invention]

The above-mentioned conventional technology has problems in operational stability and the like because the control for reducing or removing the chroma outer signal component is complicated.

An object of the present invention is to solve the above-mentioned problems and provide an axis (2) contour correction circuit that realizes spatial frequency response correction of a color signal that aims to reduce chroma contour signal components with a simple WJ circuit configuration. It is in.

Another object of the present invention is to provide a contour correction circuit that realizes spatial frequency response correction that is compatible with visual characteristics and does not give an unnatural feeling, for narrowband color signals such as those used in current color television systems. It is in.

[Means to solve the problem]

In order to achieve the above objective, edge additional information obtained by performing signal processing on high frequency signal components extracted from color signals such that signal components with negative amplitude levels become zero is added to the original signal. As a result, contour correction is realized in which the chroma outer edge signal component is reduced.

Furthermore, in the contour area of the image, by changing the amount of edge additional information added to the original signal according to the distance from the contour boundary, we have added a spatial frequency that does not look unnatural even for narrow-band color signals. This realizes response correction.

[Effect]

FIG. 1 shows a signal waveform diagram showing the process of forming a correction signal waveform in spatial frequency response correction (3) positive according to the present invention.

A high-frequency signal component B is extracted from the original signal A by performing operations such as second-order differentiation. For this signal component B, signal processing is performed to reduce the amplitude value to zero in a region where the amplitude polarity is a negative level, and an edge additional information signal C is generated. This signal C is then added to the original signal A to form a correction signal. Note that when the high frequency signal component B is added as is to the original signal, a correction signal having the characteristics shown by the dotted line in the figure is formed, and a chroma outer part signal is generated. however,
By adding the signal C as in the present invention, a correction signal from which this type of chroma outer part signal is removed can be formed.

On the other hand, the chrominance signal often has a narrower signal bandwidth than the luminance signal, and its signal waveform often has a characteristic in which the waveform changes gradually, as shown in FIG. For this type of signal, the high-frequency signal component F is extracted and the signal component with a negative polarity level is set to zero.The edge-added information signal G obtained by signal processing is added to the original signal (4) No. E. The corrected signal engineer has the characteristics shown in the dotted line. Visually, the image is perceived as a bordered pattern, creating an unnatural feeling.

For this reason, in one contour area, by changing the edge addition coefficient ke as shown in H in the figure and controlling the amount of edge addition information signal added to the original signal, a correction signal with the characteristic shown by the solid line in the figure can be obtained. By forming , it is possible to reduce the fringing pattern that occurs at the border and realize contour correction without an unnatural feeling.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. This embodiment shows an example in which color difference signals I and Q are used as color signals.

The high frequency component extraction circuit 1 extracts the high frequency signal component IotQo from the color difference signals I and Q. Nonlinear processing circuit 2
Then, non-linear signal processing is performed on the HIQH signal to zero the negative polarity level component to generate an edge additional information signal IEI QE used for contour correction. These signals are added to the primary color difference signal whose delay has been adjusted by the delay circuit 3 in the adder circuit 4 (5), and
Correction signals Ic and Qc are formed.

A configuration example and characteristic example of the high frequency component extraction circuit 1 are shown in the third section.
As shown in FIGS.

In FIG. 3, signals delayed by a time τ in a τ delay circuit 5 are sent to a coefficient weighting circuit 6 by a time of 1/4.
1/2. By applying coefficient weighting of -1/4 and adding these in the adder circuit 7, high frequency components are extracted with the characteristics shown in FIG.

Further, FIG. 5 shows an example of a configuration in which high frequency components are extracted using horizontal and vertical two-dimensional frequency characteristics, and is configured by continuously connecting a vertical HPF circuit 8 and a horizontal HPF circuit 9. Of these, the vertical HPF circuit 8 applies coefficients -1/4, 1/2, etc. to the signals delayed by one scanning line in the one-line delay circuit 10, as shown in FIG. 6, for example. This can be realized by a configuration in which -1/4 is weighted and added. In addition, the horizontal HPF circuit 9
This can be realized, for example, by the configuration shown in FIG. 3 above.

On the other hand, the nonlinear processing circuit 2 has an input/output characteristic such that an output signal is proportional to the input signal when the input signal is at a bell level, and an output signal is zero when the input signal is at a negative level. If the signal processing is digital, as shown in Figure 8, the ROM
The table lookup method by the function ROMII
This characteristic can be easily realized by

As described above, according to this embodiment, a color signal contour correction circuit with a simple circuit configuration and good operational stability can be realized.

Next, another embodiment of the present invention is shown in FIG.

This embodiment is a configuration example in which the edge addition coefficient ke is changed in the contour region to change the amount of the edge addition information signal to be added to the original signal. The difference from the embodiment shown in FIG. 2 above is that a function for setting the edge addition coefficient ke is added.

In this embodiment, the high frequency component signal IHIQH of the color difference signal is
Accordingly, the edge addition coefficient ke determining circuit 12 detects the contour area and sets the edge addition coefficient ke. Then, the edge additional information signal IEIQH is multiplied by ke (7) in the coefficient multiplication circuit 13, and the obtained keIE and keQE are added to the original signal to form correction signals Ic and Qc.

FIG. 10 shows an example of the configuration of the edge addition coefficient ke determining circuit 12. The quantization circuit 14 has input/output characteristics as shown in FIG. 11, and the input circuit 15 performs spatial smoothing processing to generate an output signal S AV[E.

An example of the structure of this smoothing circuit is shown in FIG.

This is a type of LPF circuit, in which a signal sequence delayed by one pixel in a pixel delay circuit 17 is weighted by coefficients a-Z+a-t, ao, al, a2 in a coefficient weighting circuit 18, and then in an adder circuit 19. These are added to generate the smoothed output signal SAVE. In this smoothing process, the coefficient a
By setting +, arbitrary characteristics can be realized, and a typical example thereof is shown in FIG.

Note that in this configuration example, smoothing processing is performed only in the horizontal direction, but by also using pixels from adjacent upper and lower scanning lines, smoothing processing can also be performed in the horizontal and vertical two-dimensional frequency (8) frequency domain. It is possible.

The ke setting circuit 16 sets an edge addition coefficient ke from 0 to α, for example, as shown in FIG. 14, depending on the level of the smoothing signal 5AVE. This characteristic is shown by the solid line,
Alternatively, it can be realized by various things as shown by the dotted line.

As described above, according to this embodiment, by changing the edge addition coefficient ke in the contour region of the image, it is possible to easily realize spatial frequency response correction that is more consistent with visual characteristics.

Next, FIG. 15 to FIG. 18 show another embodiment of the present invention. FIG. 15 shows a configuration example in which the edge addition coefficient ke is set from a signal having a wider band than a color difference signal, such as a luminance signal. That is, the high frequency component Y of the luminance signal Y
H is extracted by the contour information detection circuit 20. And this Y
Based on the H-fold signal, the edge addition coefficient ke determination circuit 12
Set ke.

Further, the embodiments shown in FIGS. 16 and 17 are similar to the embodiment shown in FIG.
In the embodiments shown in FIG. 1 and FIG. 15, the non-(9) linear processing circuit 2 is omitted to simplify the circuit.

Furthermore, the embodiment shown in FIG. 18 is an example of a configuration in which the contour area of the image is extracted from the color difference signals I and Q.

〔Effect of the invention〕

According to the present invention, it has a simple configuration and matches visual characteristics.
Since it is possible to create a contour correction circuit that realizes spatial frequency response correction of color signals without any unnatural appearance, it has a great effect on improving the quality of images.

In this embodiment, the color signal is a color difference signal I.
, Q has been described, but the present invention is not limited thereto, and it is obvious that the present invention can also be applied to other color difference signal combinations such as RY, BY, and the like.

It is also clear that the form of signal processing can be analog, digital, or a mixture of both.

[Brief explanation of the drawing]

FIG. 1 is a signal waveform diagram showing the process of forming the correction signal (10) waveform in the contour correction circuit of the present invention; FIGS. 2 and 9;
Figures 15 to 18 are overall block configuration diagrams of an embodiment of the present invention, and Figures 3 to 6 are examples of the configuration and characteristics of a high-frequency component extraction circuit, which is one of the components. FIGS. 7 and 8 are diagrams showing an example of the characteristics and configuration of a nonlinear processing circuit, and FIGS. 10 to 14 are diagrams showing an example of the configuration and characteristics of the edge addition coefficient ke determining circuit. It is a diagram. 1... High frequency component extraction circuit, 2... Nonlinear processing circuit,
3... Delay circuit, 4... Adding circuit, 5... τ delay circuit, 6... Coefficient weighting circuit, 7... Adding circuit, 8...
・Vertical HPF circuit, 9 ・Horizontal HPF circuit, 10・
・・1 line delay circuit, 11・・Function ROM, 12・
... edge addition coefficient ke determination circuit, 13 ... coefficient multiplication circuit, 14 ... quantization circuit, 15 ... smoothing circuit,
16...ke setting circuit, 17...pixel delay circuit, 1
8... Coefficient addition circuit, 19... Addition circuit, 20...
・Contour information detection circuit.

Claims (1)

[Claims] 1. In a contour correction circuit that extracts high-frequency components of an original signal and adds them to the original signal as an edge-added information signal to correct the response characteristics of the original signal to suit visual perception, the color difference that makes up the color image is corrected. A contour correction circuit for a color signal, characterized in that a signal is the original signal, and a signal with a negative polarity portion of the high frequency component set to zero level is used as an edge additional information signal. 2. having means for controlling the level of the edge addition information signal in accordance with the edge addition coefficient ke;
2. The color signal contour correction circuit according to claim 1, wherein characteristics of the contour correction applied to the color difference signal can be arbitrarily modified by changing the edge addition coefficient ke in the contour region of the color image. .