JPH0287780A - Intermediate tone correction circuit for video signal - Google Patents

Abstract

PURPOSE:To prevent an intermediate part from being invisible even if most part of a picture is at a white level by increasing a level of the intermediate part when the increase in the share occupied by a high level component is discriminated in a picture by one pattern. CONSTITUTION:A video signal 100 is inputted to gradation converters 21-2n and to a high level discriminator 1. The converters 21-2n have a gradation characteristic of an output video signal so that the intermediate tone approaches a white level as the number (n) is increased. On the other hand, the discriminator 1 discriminates the rate of the high level component of the input video signal 100 shared in one pattern of a monitor TV 4 and outputs a signal 60 corresponding to the discrimination to a switch circuit 3 and the switch circuit 3 is switched to select an output signal of the converters 21-2n. That is, the high level signal is more, the output of the converter with larger number (n) is selected and the result is inputted to the monitor TV 4.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) The present invention is directed to correcting the halftones of a video signal and outputting it to a monitor television (hereinafter referred to as monitor TV). This invention relates to a correction circuit.

(Prior Art) Conventionally, when a video tape recorder (VTR) or a video signal such as a television broadcast is played back on a monitor TV, the method shown in FIG.
If you input a video signal like the one shown in > to your TV monitor,
The image on this monitor TV is as shown in Figure 4 (B).
The gradation from black to white of the video signal shown in Figure (A) is reproduced by changing from a black area to a white area and from this white area to a black area in the horizontal direction of the screen. Next, if a video signal in which the gradation from black to white changes linearly at a constant v1 as shown in Fig. 5(A) is input to the monitor TV, the If the reproduction characteristics were linear, the reproduced image would have a brightness that changes linearly from black to white in the horizontal direction, as shown in FIG. 5(B).

Therefore, in a video signal as shown in FIG. 6(A), if the signal in section A is a person, the image on the monitor TV into which this video signal is input will be as shown in FIG. 6(B). That is, the screens at both ends in the horizontal direction are black, the center screen is white, and a person is displayed in the center. This image is incident on the viewer's pupil, and at this time, external light is also incident on the pupil. On the other hand, with a video signal as shown in FIG. 7(A),
If the signal in section A is a person, the image on the monitor TV into which this video signal is input will be as shown in FIG. 7(B). When struck, the entire image becomes white with a person in the center and black vertical stripes on either side of the person. This image is incident on the viewer's pupil, and at this time, external light is also incident on the pupil. In the case shown in Figure 7, if only a small amount of external light other than the light emitted from the monitor TV screen enters the pupil orifice, the aperture of the pupil orifice as shown in Figure 6 is affected by the high level of white in the image. Compared to the example shown in Figure 6, the disadvantage is that the person displayed on the monitor TV in Figure 7 (B) is darker and harder to see than the person displayed on the monitor TV in Figure 6 (B) because of the narrowing down. was there.

(Problem to be Solved by the Invention) As mentioned above, only a small amount of external light other than the light from the image displayed by inputting the video signal from the VTR or TV broadcast directly to the monitor TV enters the observer's body. In this case, if the image on the monitor TV is mostly made up of high-level white parts, there is a drawback that the mid-tone parts of the image become difficult to see due to the influence of the high-level white parts. Ta.

SUMMARY OF THE INVENTION Therefore, the present invention aims to eliminate the above-mentioned drawbacks when only a small amount of external light other than the light from the image on the monitor television is incident on the observer's eyes, and when the majority of the image is a high level white color. It is an object of the present invention to provide a halftone correction circuit for a video signal that can prevent the halftone portion of the same image from becoming unclear even when

[Structure of the Invention] (Means for Solving the Problems) A halftone correction circuit for a video signal of the present invention is capable of correcting high-level components (in the white direction) in one screen of an input video signal. a determining means for determining the ratio; and when the determining means determines that the ratio of high-level (white direction) components in the C-screen image has increased, the intermediate of the video signal is determined. The present invention has a configuration including a gradation conversion means for increasing the level of the tone portion toward white.

(effect) In the video signal halftone correction circuit of the present invention.

The determining means determines the proportion of high-level (in the white direction) components in one screen of the input video signal, and informs the gradation converting means of the determination result.

When the determining means determines that the proportion of high-level components (in the white direction) in one screen of images has increased, the gradation conversion means changes the level of the halftone portion of the video signal in the white direction. Raise it to

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a video signal halftone correction circuit according to the present invention. 1 is the input video signal 10
A high level discriminator that discriminates the high level (white direction) portion of 0, 21 to 2o are tone converters that convert the tone characteristics of the input video signal, and 3 is the output of the tone converters 21 to 2o. a switch circuit that selects one of the signals; 4 a monitor TV that displays an image corresponding to the input video signal; 5;
is the eye of the observer viewing the image on this monitor TV. Further, 10 indicates light from the screen of the monitor TV 4, and 11 indicates external light.

Next, the operation of this embodiment will be explained. The input video signal 100 is input to the gradation converters 21 to 2o, and is also input to the high level discriminator 1.

Here, the characteristics of the tone converters 21 to 2o are as shown in FIG. 2, and the characteristics of each tone converter are slightly different. That is, the characteristics of the gradation converter 21 are such that when the gradation of the input video signal changes from black to white, the gradation of the output video signal also changes linearly.

This characteristic forms a curve in which as the classification number n of the tone converter increases, the intermediate tone approaches the white level.

On the other hand, the high level discriminator 1 discriminates the proportion of the high level (white direction) component of the input video signal 100 in one screen of the monitor TV 4, and outputs a switching signal 50 corresponding to this discrimination to the switch circuit 3. do. That is, as shown by the horizontal axis in FIG. 3, the high level discriminator 1 determines the image occupancy rate of the high level signal, and then selects the gradation converter 21 in order from the lowest occupancy rate. ,22...2. a control signal 50 for switching the switch circuit 3 to select the output signal of
Output. Therefore, the input video signal 1 is input to the monitor TV4.
00, the video signal 100 is inputted via the gradation converter 21, but as the input video signal 100 increases in high level components, the video signal 100 becomes Gradation converters 22, 23...
- Input to monitor TV4 via 2o. Therefore, the gray level of the screen of the monitor TV4 is adjusted to be closer to the white level as the white level occupies a larger proportion of the entire screen.

Therefore, according to this embodiment, the light 101 from the image on the monitor TV 4; Even when the image is dark, the halftone portion of the image does not appear dark, and it is possible to prevent the image from becoming difficult to see.

Note that the circuit shown in FIG. 1 takes into account only the brightness (luminance information), and information such as color chart and hue does not change by this circuit. The color information may be separated from the luminance signal before the circuit shown in FIG. 1, and may be directly input to the monitor TV 4, bypassing this circuit.

[Effects of the Invention] As described above, according to the video signal halftone correction circuit of the present invention, when only a small amount of extraneous light from the monitor television image enters the observer's pupil, and when the above-mentioned Even when the majority of the image is a high level of white, this has the effect of preventing the halftone portions of the image from becoming difficult to see.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the video signal halftone correction circuit of the present invention, FIG. 2 is a diagram showing an example of the characteristics of the tone converter shown in FIG. 1, and FIG. Figure 1 shows the relationship between the discrimination level of the high level classifier and the selected gradation converter, and Figures 4 and 5 show the relationship between the video signal waveform input to the TV monitor and the image. 6 and 7 are diagrams showing the relationship between a video signal waveform including a halftone level input to a monitor TV and an image. 1...High level discriminator 21-2o...Gradation converter...Switch circuit 4...Monitor television agent Patent attorney Rule Near point Yudo Hiroshi UjiFigure 2Figure 3 Figure stand (△ ) Figure 6 Figure 7 Figure 5

Claims (1)

[Claims] A high level (
a determining means for determining the proportion occupied by high-level components (in the white direction); and when the determining means determines that the proportion occupied by high-level components (in the white direction) in one screen of images has increased, the said image 1. A halftone correction circuit for a video signal, comprising: tone conversion means for increasing the level of a halftone portion of the signal toward white.