JPH07274195A - Color adaptive gain control circuit - Google Patents

Abstract

PURPOSE:To obtain a video signal processing circuit which does not exert adverse influence on a video even when a color saturation ratio is low and a hue is not specified in the circuit controlling the gain of the video signal corresponding to the hue. CONSTITUTION:Corresponding to the two value of the hue detected by a hue deducing circuit 2 and the color saturation ratio calculated by a color saturation calculation circuit 8, a color vector adapting type gain characteristic generation circuit 10 controlls the gain of the video signal. Then, when the color saturation ratio is low, the gain is fixed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a circuit for controlling the gain of a video signal level by color in the image processing field.

[0002]

2. Description of the Related Art Recently, in the field of image processing, there is a tendency to perform various kinds of image processing by controlling a gain of a video signal level according to color. For example, in the case of enhancing the image quality by enhancing the contour, it is more natural and clearer for the skin tone portion of a person not to enhance the contour. Therefore, a color adaptive gain control circuit for reducing the gain of the contour enhancement signal in the skin tone signal portion. Is being developed. As an example of this color adaptive gain control circuit,
Taking the hue adaptive contour enhancement circuit described in the specification of Japanese Patent Application No. 2-318040, its configuration is shown in FIG.
The operation will be briefly described.

Reference numeral 1 is a contour emphasis signal generation circuit, and the output of this circuit is added to video signals R, G, B by using adders 5, 6, 7.
The contour enhancement of the image can be performed by adding to each. Reference numeral 2 is a hue indexing circuit, and 3 is a gain characteristic generating circuit, which generates a desired gain characteristic corresponding to the hue from the specific hue obtained by the hue indexing circuit 2. For example, this gain characteristic is as shown in FIG. 3, and in this case, the gain near blue is lowered. The output of the gain characteristic generating circuit 3 is multiplied by the contour emphasizing signal of the output of the contour emphasizing signal generating circuit 1 using the multiplying circuit 4, and this is added to the R signal, the G signal, and the B signal. Gain control of the emphasized signal can be performed. With the gain characteristics shown in FIG. 3, the degree of edge enhancement is low when the video signal input is near blue.

Here, when the edge enhancement is performed in the configuration shown in FIG. 4, when the color saturation of the video signal is low, that is, when the color is close to white, the hue detection circuit 2 detects the hue.
Due to a slight noise, the hue to be detected is not randomly determined, and the gain characteristic shown in FIG. 3 is switched to a large degree at random in various hues. Therefore, the edge enhancement is also randomly performed in various hues and time. Done. For example, in the case of a monochrome video signal portion, since the hue originally does not exist, the output of the gain characteristic generation circuit 3 is constant, but as described above, the detected hue changes due to the influence of noise, and the gain corresponding to this hue is changed. As a result, the characteristics are switched sharply, and in the outline part of the image, parts that are not emphasized and parts that are not emphasized occur randomly, and the outline emphasis correction that should originally make the image clear further deteriorates the image of the outline part. Becomes

[0005]

In the conventional hue adaptive gain characteristic generating circuit, when the color saturation of the image signal is low and the color is close to white, the hue detection is likely to be indefinite, and the gain characteristic according to the hue is as follows. Random things occur, which adversely affects the image processed by this circuit. The present invention aims to eliminate these drawbacks and to suppress this adverse effect when the color saturation is low.

[0006]

In order to achieve the above object, the present invention adds means for changing the gain characteristic of a video signal level according to two values of hue and color saturation, thereby The gain characteristic can be made constant when the color saturation is low.

[0007]

As a result, the gain characteristic of the video signal is constant regardless of the hue when the color saturation is low,
Even when the video signal is white and the color saturation is low and the hue is not fixed, the gain characteristic is constant, and a color adaptive gain control circuit that does not cause signal deterioration can be configured.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of the present invention, which is applied to a contour emphasizing circuit, and will be described below with reference to FIG. Reference numeral 1 is a contour emphasis signal generating circuit, 2 is a hue determining circuit, 3 is a gain characteristic generating circuit according to hue, 4 is a multiplying circuit, 5, 6, and 7 are adding circuits, and the hue adaptive contour shown in FIG. It is the same as the emphasis circuit. In the present invention, the color saturation calculation circuit 8, the level adaptation circuit 9, and the color vector adaptation type gain characteristic generation circuit 10 are added thereto.
The gain characteristic of the gain characteristic generating circuit 3 is shown in FIG. 3, and is represented by G ₁ (θ) as a function. However, θ is a hue. The color saturation calculation circuit 8 calculates the value of the color saturation and sets it as L.

Here, the color saturation value is, as shown in FIG. 5, the color signal of the second level from the color signal level value of the maximum level among the three components of the video signals R, G, B. When the level value is subtracted, the subtraction value is used as the primary color component, the color signal level value of the minimum level is subtracted from the color signal level value of the second level, and the subtraction value is used as the complementary color component. The value is calculated as the value of the composite component of the value and the value of the complementary color component. The characteristic of the level adaptation circuit 9 is shown in FIG. 2 and is represented by G ₂ (L) as a function. However, L is the color saturation. The color vector adaptive gain characteristic generation circuit 10 is designed to fix the output gain characteristic to 1 when the value of the color saturation is small. The gain characteristic function G ₁ (θ) depending on the hue and the color saturation are used. It is expressed by the composition with the gain characteristic function G ₂ (L) depending on the degree, and the total gain characteristic G (θ, L) is G (θ, L) = (G
The _{1 (θ) -1) × G} 2 (L) +1.

With such gain characteristics, when the color saturation of the image input is low and close to white, the color saturation L becomes L <L ₀ as shown in FIG. 2, and G ₂ (L) → 0. And G
(θ, L) = 1. When the color saturation is high to some extent and a color component exists, L> L ₀ and G ₂ (L) = 1, so G (θ, L) = G ₁ (θ) −1 + 1 = G ₁ (θ).
Therefore, even if the color saturation is low and the hue cannot be determined, the output gain of the color vector adaptive gain characteristic generation circuit 10 is fixed to 1, and there is a problem in the case where the contour emphasis correction is performed only with the conventional hue. It can be resolved.

[0011]

According to the present invention, since the gain characteristic according to the degree of color saturation is added, the gain characteristic can be improved even if the degree of color saturation is low and the hue is not fixed in the circuit having the gain characteristic according to the hue. It is possible to fix it, and it is possible to avoid adversely affecting the image. In addition, since the color is expressed two-dimensionally by the hue and the color saturation, the circuit which performs signal processing according to the color is greatly developed.

[Brief description of drawings]

FIG. 1 is a schematic block diagram of an embodiment of the present invention.

FIG. 2 is a color saturation-gain characteristic diagram.

FIG. 3 is a hue-gain characteristic diagram.

FIG. 4 is a schematic block diagram showing a conventional technique.

FIG. 5 is a diagram for explaining the operation of the present invention.

[Explanation of symbols]

 2 Hue indexing circuit 3 Gain characteristic generation circuit 8 Color saturation calculation circuit 9 Level adaptation circuit 10 Color vector adaptive gain characteristic generation circuit

Claims (2)

[Claims] 1. A color adaptive gain control circuit, wherein gain control is performed on a video signal level of a predetermined hue according to two components of a predetermined hue and its saturation. 2. The color adaptive type according to claim 1, wherein when the color saturation of the video signal of the predetermined hue is less than or equal to a predetermined value, the gain control of the video signal level of the predetermined hue is fixed to the predetermined value. Gain control circuit.