JPS5923673A - Video halftone circuit - Google Patents

Abstract

PURPOSE:To facilitate discrimination of character video and figure video in the same display period and to prevent deterioration of picture quality due to defective white balance by providing a halftone setting circuit between a reference voltage source and a signal switching circuit. CONSTITUTION:The first and the second video signals S1, S2 from the first and the second input terminals 1R-1B and 2R-2B are added to signal switching circuits 3R-3B and a switching composite output S5 is outputted to an output terminal by a switching insertion signal S3 from a terminal 4. This composite output S5 is added to halftone switching circuits 6R-6B through a resistance 5. A halftone level setting circuits 7R-7B are provided between the output side of circuits 3R-3B and a bright voltage supply source 8. A halftone output is added to circuits 6R-6B from circuits 7R-7B and a halftone composite output S6 is outputted. Clamping circuits 11R-11B are provided between the output side of circuits 6R-6B and the supply source 8. Thus, discrimination of video in simultaneous display period is facilitated and deterioration of picture quality is prevented.

Description

[Detailed Description of the Invention] (Technical Field of the Invention) The present invention provides a method for displaying a plurality of independent three-primary color video signals simultaneously on a color cathode ray tube, for example, in order to emphasize one signal. , relates to a video half 1-1 circuit in which the other signal is switched to half 1-channel No. 18 for a predetermined period of time.

[Background technology of invention]

In general, a plurality of independent video signals (+ signals or VTR
A video signal such as ``H1'' can be displayed on the display screen. In this case, the simultaneous display and the display in which images PIA (moving images/still images) such as characters and figures are embossed on the IJ background image (so-called superimposed display) are covered.

These independent image signals are simultaneously displayed in the 51st case, and the first . There is a problem that the second character/figure image is difficult to see. Does this occur in two cases? Ru.

First, the background image is expressed with white as the main color; Second
This is a case where characters and graphic images are also displayed in white-based colors. The second case is when a text/graphic image is displayed in a dark color when the background is white, and the text/graphic image may be saturated and displayed as if it bleeds into the background image.

To solve this problem, processing is performed to reduce the brightness of the background image by half. This processing is performed for video half 1-
The circuit for this purpose is called a video halftone circuit. According to this process, for example, if the background pixels are white and the characters are also white, the background pixels are turned into halftone gray and the characters can be clearly depicted.

[Problems with backward technology]

In the above process, the background image is white7. If the image is displayed only in black gradation, if the background image signal is lowered in level by the signal that detects the display period of the character/graphic image, the background image signal will be lowered to a white character/graphic image. On the other hand, the background image becomes dark and a halftone signal can be easily obtained.

However, when only the background image south, or when both the text/graphic image and the background image 19 contain color information, it is difficult to obtain a uniform halftone between the three primary color signals, which are each color information, using the current color display technology 1fi. I have a lot of difficulty. That is, in order to reproduce a general color image signal, such as a color preview signal, a color signal having a predetermined band is transmitted using the frequency interpolation method. A carrier color signal is extracted from the signal, and a predetermined υ1 sum η" color difference signal is synthesized from this IIRiM color signal to produce an I signal and a Q I signal.
A signal is demodulated from the color subcarrier of 2'-) (or a color difference signal is obtained directly), and this 4g signal (or color difference 18
month) and gradation? l'lli degree signal and R (red)/G
(green) and (old) three primary color signals are reproduced. These three primary color signals reproduce predetermined colors on the color cathode ray tube surface according to scanning. On the other hand, characters/graphics 1 The three primary color signals of the signal are obtained by decoding the 21 straight 15 code which encodes the three primary color signals based on the color information for displaying characters and figures in color.This output is converted into ab'cog and color It is applied to a cathode ray tube. Therefore, when performing halftone processing, the level of the signal components of each R-G-B' three primary color signal is lowered at the same rate, and
It is necessary that the DC components of the primary color signals have no variation among the signals and do not change. That is, even if there is a slight variation, color disturbances due to poor white balance will occur in the background image in the half 1 to -1 periods.

Furthermore, as will be explained later, in order to display the images simultaneously, it is necessary to switch and synthesize each image signal during the period in which the background image is displayed and the period in which the character/graphic images are displayed. Even in this switching synthesis, it is necessary to ensure that the accuracy of both sides of the display is not affected by electrical effects by changing the switching speed of the signal set to the half-tone level.

In a video halftone circuit that satisfies these conditions, it is difficult to obtain an effective circuit because, for example, when it is integrated into an integrated circuit, the signal components and DC components of each of the three primary color signals fluctuate due to the resistance component for reducing the level. It was something.

(Object of the Invention) The present invention has been made in view of the above-mentioned points, and it is possible to obtain a stable halftone signal without variations in the signal components and DC components of each of the three primary color signals made into a halftone level, and to obtain a stable halftone signal for a simultaneous display period. An object of the present invention is to provide a video bar circuit that allows characters and graphic images to be easily identified and prevents deterioration of screen quality due to poor white balance.

[Summary of the invention]

That is, the present invention switches and inserts a first video signal that becomes a character/graphic image 1τ into a second video signal that becomes a background image for each of the three primary color signals, and then performs C synthesis to reproduce the DC level. The DC component of the synthesized video signal (full tone signal) after synthesis is set based on the reference voltage of a predetermined reference voltage source, and the half 1-tone signal whose amplitude is limited by a predetermined ratio is set to 1q, This half 1--on signal and the composite video signal are switched and outputted using a half-i--on switching signal.Half!・The halftone composite output after the -tone switching is such that the DC level of the half I/-tone signal during that halftone period is the DC level set by the clamp circuit for reproducing the -C DC level due to the M quasi-voltage. This is a video halftone circuit that can form a halftone signal with no change in DC level.

[Example of light]

Fig. 1 is a circuit diagram showing an embodiment of the present invention, and shows the case where it is used in a color television receiver II. Fig. 2 is a waveform diagram showing waveforms for explaining the operation of Fig. 1. .

First, the configuration shown in FIG. 1 will be explained. Each first input terminal I
R, IG, and 1B are terminals to which the first three primary color signals S1 reproduced from the first video signal 1p+ input via an antenna or wire are input, and the second input terminals 2R, 2c, and 2a are respectively input terminals.
is a terminal to which the second three primary color signal S2 reproduced from the second video signal coming in through the same route is input. Here,
The first video signal is a background image signal, and the second video signal is a character/graphic image signal. Each 1st. The first signal that enters the second input terminal. Second three primary color signals S+, S2°Ss
is a signal switching circuit 3R consisting of two human-operated one-output switches.
, 3c, 3e each /? to each input terminal. applied. The signal switching circuits 3R, 3G, and 3F have a control fll terminal, and a switching insertion signal 83 for switching and inserting the second video signal is applied from the terminal 4 to the control 11 terminal. The switching composite output (also referred to as a full tone signal) Ss derived from each output terminal of the signal switching circuits 3R, 3c, and 3s is connected via a resistor 5 to a half 1-output switch composed of two single-output switches.
-on switching circuits 6R, 6c, and 6s, respectively;
The signal is branched and supplied to half 1 to -n level setting circuits 7R, 7c, and 7B. These half level setting circuits (hereinafter referred to as half level setting circuits) 7R, '7G, and 7B are used to regenerate and override the DC level. Receives voltage Ve (
It sets the direct current level of the switched combined output S5 and limits the amplitude of the signal level, and is constructed of, for example, a resistor divider circuit. These half level setting circuits 7R, 7c, 7
Each halftone output of B is outputted from the half 1 to half tone switching circuit 6R.

6G and 6e, respectively, and is applied from the terminal 9 to the halftone switching circuits 6R, 6c, and 6e.
-on signal is switched and selected, output terminals 10R, 10c
, 10s, respectively.

The halftone composite output 3) 6 obtained by this switching and 31 selections is the basis of the voltage supply circuit 8 for the BL1-voltage supply circuit 8. Clamp circuit 11p, 11cm based on $ lightning voltage s.

11B reproduces the DC level and outputs the output terminal 10R.
, 10c, and 10s are supplied to the color cathode ray tube.

Figure 2 shows the above configuration;
Ss is one waveform, each horizontal axis shows one horizontal period,
The circuit operation during this one horizontal period will be explained below. still,
For the purpose of explanation, the R signal circuit will be explained as a representative.

First, at time T1, when the back porch of the horizontal synchronizing pulse ends, a video display period begins. At this time, since the switching insertion signal S3 of the terminal 4 is at the first video signal selection level L1, the signal switching circuit 3R changes the switching composite signal S5 to the first 3rd video signal selection level L1.
The primary color signal S1 is supplied to a halftone switching circuit 6p via a resistor 5. Furthermore, at this time, since the half-tone switching signal S4 at the terminal 9 is at the level L2 which selects the switching composite signal S5, the first R signal S1 is outputted to the output terminal 10R. This period continues until time T2 when the level of the half-1 Hoene switching signal S4 is switched, and at this time T2, the halftone switching circuit 6R
selects the output of the half level setting circuit 7R. As a result, the halftone output -j S,l of the OR-selected first R signal S1 is derived as the halftone synthesis output ESa.

Next, at time T3, the level of switching insertion No. 18 83 changes to 2nd picture l! 0 signal selection level L3, the switching composite signal S5 outputs the second R signal S, F as its output component. At the same time, the halftone switching signal S4 becomes level 1-4, which selects the switching composite signal S5, so that the halftone signal S+'l-1 of the front overculm is switched to the second R signal S2. Subsequently, the signal switching circuit 3R changes the level of the switching insertion signal S3 to the level L1 at time T, +) the display period of the second R signal St, and the signal itself is no longer the main signal. Select. At this time, in order to switch to the half i-tone switching signal $
4 becomes the level and the first R signal S1 is
- Select RS+', then press 1--
This signal S+' is derived through the switchover circuit 6R.

When there is no need to make it half 1--
The -1, 7J conversion signal S4 is again halved to the level L2I, and the first R signal S1 is derived.

This signal S1 continues until time T6 when one horizontal period ends.

In the above operation, the switching composite signal S5 derived from the signal switching circuit 3R) and the half 1 to -1 composite output signal S6
Since the DC level is determined by the reference voltage VsL, for example, the half level setting circuit 7R is configured with a series circuit consisting of two resistors, with both ends thereof being P+ and P2, and the middle being P3. Each of these terminals P+-P
3 potential and output terminal 10R.

The potentials of both can be the same.

A specific example is shown in FIG. In FIG. 3, elements that are the same as those in FIG. 1 are designated by the same symbols.

The input terminal 12 receives the switching composite signal S from the signal switching circuit 3R.
5 is connected via a transistor 13 to one end of the -C resistor 5, that is, one end P1 of the half level setting circuit 7R. This bar level pel setting circuit 7R has a resistor 14.
15 in series, in which the resistor P3 and the resistor 5 (l
! ! The end is 1 helangister 16.17. diode 18,
1 list)? 1+ is connected to the base of each transistor 16.17 of the amplifier section 6RA that constitutes the halftone switching circuit 6R.The emitter f of each of the transistors 16, 17 is In response to the signal output from the halftone switching circuit 6R, the halftone switching circuit 6R receives the halftone switching circuit 6R, and switches between halftones 1 and 81'.
The full tone signal S5 is outputted to the receiver as a halftone composite output S6 in response to a halftone switching signal 84 applied to the base of the transistor 23.

Next, the other end of the half level setting circuit 7R (resistance 15 side)
is connected to the emitter of transistor 24. This transistor 24 is a level diode for ¥25,
Transistor 26, transistor 27 and variable resistor 28
The bright voltage supply circuit 8 is configured such that the voltage V8 at the 1st driving terminal of the variable resistor 29 is applied to the emitter of the 1-transistor 24 as a reference voltage VB to the half level setting circuit 7R in an ffl manner. . This reference voltage is supplied to the clamp circuit 11R, and the DC level of the halftone composite output S6 of the output terminal 10R is reproduced by a well-known operation. Note that the symbol Vcc is a power supply terminal, and Ecc is also a power supply terminal.

In the above, the DC level of the output terminal 10tq is compensated by the clamp circuit 11R, so that 8. Further, one end P1 of the half level setting circuit is also a diode 18,
The voltage becomes Ve due to the conduction of the i-transistor 16 and the application of the reference voltage VB to the other end P2.

Therefore, the potential of the midtone P3 is also v8, and the halftone synthesizer S6, which is a combination of the full tone signal S+' and the full tone signal M35, is output without any factor causing a change in the DC level. .

Therefore, a halftone signal 81' in which only the signal component is amplitude-limited by the values of the resistors 14 and 15 can be obtained for the middle school P3.

In addition, for the entire three primary color signals, Child C also explained that (([The bright 1-voltage (base 11% voltage) V[] is applied to each circuit exactly, so there are variations between the signals...) It never comes to life.

〔Effect of the invention〕

As explained above, in the present invention, in order to display two independent video signals at different display periods and simultaneously on the same screen, each circuit stage changes the signal. Since a half-level setting circuit for obtaining a half-tone signal is installed between the reference voltage supply source for fixing the DC level of the video signal and the half-tone signal, a full-tone signal and a half-tone signal 1 (to, 1: Furthermore, even among the J3 primary color signals, a uniform DC current level is produced, which results in a cheap composite output, resulting in a screen with good halftone signal discrimination. It has the effect of making you look at it again.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing one embodiment of Mitsuaki Ki, 8r! Figure 2 is a waveform diagram showing the operation waveforms of the 11th crop in Figure 1, and Figure 33 is a waveform diagram showing the operation waveforms of the 11th crop in Figure 1.
A circuit diagram of a tree-based example. 3) "shi, 3 (= , 3o...1 angle of signal cut) °
8, 5...Resistance, 6r+, G, 6[]...Half!・-on switching circuit, 7R, 7c, 7n...Half i-on 1 novel setting circuit (14,"15...11
℃ resistance), 8...Bright voltage supply source, 1 in
,'l IG,'l 1B...clamp circuit, V[l
...Reference voltage. Proxy rr person dialect 1! I! :l; Kensuke Norichika (and 1 other person) Figure 1 373- Figure 2

Claims (1)

[Claims] When displaying multiple independent video signals simultaneously on the same screen, in order to emphasize one video signal, half 1 is used only during the simultaneous display period during which the other video signals are limited.
- a signal switching circuit that switches to a second video signal during a display period of the first video signal;
A half-tone level setting circuit that limits the amplitude of the full-tone signal generated by this signal switching and converts it into a halftone signal, sets the first video signal during the halftone period to a full-tone level setting circuit.
A halftone switching circuit that switches and selects the second video signal of 1 to 2 and outputs a composite output, a clamp circuit that fixes the DC level of the composite output signal, and a reference voltage that serves as a fixed reference for this clamp circuit. a reference voltage source for supplying a reference voltage, and the halftone level setting circuit has a reference voltage source Nf
f: A video halftone circuit characterized by being interposed between an FA and an output end of a signal switching circuit.