JPS5920315B2 - display circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a display circuit that eliminates blooming that tends to occur when displaying text information superimposed on video.

For example, the display mode of teletext called Teletext, which was developed in the UK, has a specific color (including blanking state).
There are two ways to display characters, one in which characters are displayed as a background, and the other to display characters superimposed on the broadcast screen. In the latter case, as shown in Figure 1, a (negative) character signal ( Due to the addition of b) (see c), a video signal exceeding the normal video signal level (d) is applied to the cathode ray tube,
In areas with a bright background on the cathode ray tube surface, a focus blur called blooming occurred, making it difficult to read the text.

Therefore, the present invention provides a display configured so that when adding a character signal to a video signal to display characters on a screen, the level of the character signal is reduced compared to when characters are displayed against a background of a specific color. The purpose is to propose a circuit.

The present invention will be described below with reference to illustrative embodiments.

The figure shows the main circuit of this embodiment, and the figure number DM3DY is shown in the figure.
3D-R2D-G2D-B are all terminals that receive the output derived from the teletext decoder in synchronization with the video signal, and DM is a display that becomes high level in the mode where characters are displayed independently. The mode designation terminal to which the mode designation output is input, DY is the character signal input terminal to which the character signal is input, D-R, D-G2D-B are R of the character signal respectively.
Component, G component, and B component are input as negative signals. VV-Y is a video signal input terminal to which a negative video signal is input, and VR-Y is a terminal to which a negative video signal is input.
, VG-Y, and VB-Y are input terminals for the first, second, and third color difference signals obtained by subtracting the video signal from the R component, G component, and B component of the video signal, respectively. B indicates an R component output terminal, a G component output terminal, and a B component output terminal from which the R component, G component, and B component of negative display output are derived, respectively. Therefore, first, when the display format is set to the character single display mode, the output of the NOR circuit NR is always at a low level, and the first, second, and third
The diodes (D1), (D2), and (D3) are in a blocking state, and each color component of the character signal derived through the first, second, and third buffer amplifiers AR, AG, and AB is in the first, second, and third buffer amplifiers, respectively.
The emitters of the second and third transistors Trl, Tr2, and Tr3 are input as they are without being attenuated, and are led out from the collectors to the respective output terminals KB, , K-0, and K-3, and applied to the cathode terminal of the cathode ray tube. Ru.

Further, when the display format is set to superimposed display mode, the output of the NOR circuit NR becomes high level with the generation of a character signal, and the output of each of the diodes (D1) (D2) (D3)
By making conductive, the inverted output of the input character signal causes each buffer amplifier AR. ,AO,AB
The level of the color component of each character signal derived from this is inputted to the emitters of the transistors T, l, Tr2, T, and 3 together with the negative video signal, and the level of the color component of each character signal derived from
It is added to the color difference signal of the video signal input to the bases of r2 and Tr3, and each color component of the display signal is derived from the collector as a negative signal and input to each cathode terminal of the cathode ray tube.
As described above, according to the display circuit of the present invention, in a character signal display device having a single character signal display mode and a superimposed display mode, in the case of the superimposed display mode, each primary color component constituting the character signal is Since the attenuated signal is added to the color video signal and the amount of attenuation of each primary color component can be changed according to the size (luminance) of the character signal, it is supplied to a display device such as a cathode ray tube. Each color component of a character signal in the superimposed display mode can be adjusted to its optimum size, and therefore, out-of-focus due to blooming can be reliably and easily prevented.

Furthermore, in the case of the single display mode, since each color component of the character signal is added to the color video signal without attenuation, a character signal of sufficient size can be supplied to the color display means for display.

[Brief explanation of the drawing]

FIG. 1 shows signal waveforms of a conventional teletext circuit, and FIG. 2 shows an example of a circuit implementing the present invention.

Claims (1)

[Claims] 1. In a character signal display device that has a single display mode in which characters are displayed on a specific background color and a superimposed display mode in which characters are displayed on a color image, superimposition is performed in response to each designated signal of both modes. a first circuit that adds and derives an inverted output of the character signal at a predetermined ratio to each of the three primary color components of the character signal in the display mode, and directly derives each of the three primary color components in the case of the individual display mode; and a second circuit that adds each primary color component output from the first circuit to each primary color component output of the color video signal to derive the output, and supplies the three primary color component outputs from the second circuit to the color display means. A display circuit designed to