Video signal superimposing device

Abstract: A video signal superimposing device for superimposing and clearly displaying video signals produced from at least two discrete systems comprises an input terminal for inputting a color complex video signal, a separation circuit for separating a first brightness signal and a first chroma signal from the color complex video signal, a first generator for generating a second brightness signal, a first mixer circuit for mixing the second brightness signal and the first brightness signal separated by the separation circuit, a second generator for generating a sec­ ond chroma signal, a second mixer circuit for mixing the sec­ ond chroma signal and the first chroma signal separated by the separation circuit, and a third mixer circuit for mixing the mixed brightness signal applied from the first mixer circuit and the mixed chroma signal applied to the second mixer circuit.

Description: The present invention relates to a video signal superimposing device and, more particularly, to a device for superimposing and clearly displaying video signals produced from at least two discrete systems, e.g. a device for superimposing a personal computer data on a picture of a television broadcast. Recently, personal computers have been increasingly used in homes, and it has been attempted to connect a household color television receiver with a personal computer as a CRT display unit to display the data supplied from the personal computer on the screen of the television. New devices have been developed which superimpose the personal computer picture data on the television broadcast picture. However, the devices cannot make the superimposed computer picture data clear and record the composite picture. JP-A-56-166683 describes a circuit for mixing two color television signals in which both signals are separated into brightness and chrominance components before mixing. The combined brightness and chrominance signals are then mixed to form the combined TV signal. This document does not disclose any means of synchronising the two signals before or during mixing. US 3,296,367 describes a circuit for mixing two colour complex video signals to achieve certain special effects, in particular fading of one picture into another, and insertion of a part of one picture into another. This prior art circuit likewise splits each colour complex video signal into its brightness and chrominance components, separately combines the two brightness components and the two chrominance components and then mixes the combined brightness signal with the combined chrominance signal. The two chrominance signals are each demodulated into their colour difference signal before being mutually combined, the combined colour difference signals then being remodulated onto a new colour sub-carrier. This arrangement, particularly in the NTSC system, avoids difficulties which would otherwise arise, when trying to effect a simple weighted sum of the two complex signals, in avoiding drift of the reference phases of the two sub-carriers. The article entitled "Neue Einschübe zum Prüfzeilen-Signalgenerator SPZF" in NEUES VON ROHDE & SHCHWARZ 72, January 1976, pages 14 to 18, discloses a test signal generator which can generate video signals for testing the different TV picture transmission stages from the camera to the domestic receiver. The generator can generate its test video signal with its colour sub-carrier phase locked with the colour sub-carrier of a TV picture signal with which the test signal is to be mixed. The present invention aims to provide an improved superimposing device for superimposing and clearly displaying video signals produced from at least two discrete systems on a display screen. According to one aspect of the invention there is provided a video signal superimposing device for superimposing and displaying video signals produced from at least two systems comprising: input means for inputting a colour complex video signal; separation means for separating the complex video signal into a first brightness signal and a first chroma signal; input means for inputting a second video signal; first mixer means for mixing a second brightness signal derived from said second video signal and the first brightness signal separated by the separation means; second mixer means for mixing a second chroma signal derived from said second video signal and the first chroma signal separated by the separation means; and third mixer means for mixing the mixed brightness signal applied from the first mixer means and the mixed chroma signal applied from the second mixer means, characterised by : said second video signal comprising R, G, B signals; first generation means for generating said second brightness signal based on the R, G, B signals; second generation means for generating said second chroma signal based on the R, G, B signals; means for producing a burst signal from said colour complex video signal; and colour subcarrier generation means operable to use said burst signal to produce a colour subcarrier signal in synchronisation with the colour subcarrier signal of the first chroma signal for use in generation of said second chroma signal. According to another aspect of the invention there is provided a video signal superimposing device for superimposing and displaying video signals produced from at least two systems comprising: input means for inputting a colour complex video signal; separation means for separating a first brightness signal component and a first chroma signal component from the colour complex video signal; input means for inputting a second video signal; first mixer means for mixing a second brightness signal derived from said second video signal and the first brightness signal separated by the separation means; means for producing a second chroma signal representing a combination of the colour components of the colour complex video signal and the second video signal; and third mixer means for mixing the mixed brightness signal and the second chroma signal, characterised by : said second video signal comprising R, G, B signals; first generation means for generating said second brightness signal based on the R, G, B signals; said means for producing a second chroma signal comprising: demodulation means for demodulating the first chroma signal separated by the separation means so as to form second R, G, B signals; second mixer means for mixing the inputted R, G, B signals with the second R, G, B signals produced from the demodulation means, respectively; and third generation means for generating said second chroma signal based on the mixed R, G, B signals; and in that: the video signal superimposing device further comprises: means for producing a burst signal from said colour complex video signal; and colour subcarrier generation means operable to use said burst signal to produce a colour subcarrier signal in synchronisation with the colour subcarrier of the first chroma signal for use in generation of said second chroma signal. The two discrete systems providing signals to the superimposing device may be a video imaging system such as a television, a video recorder, a video disc, or the like and a personal computer system. In order that the present invention may be better understood a detailed description will be given of an embodiment thereof, by way of example, and with reference to the accompanying drawings wherein: FIG. 1 shows a block diagram of a superimposing device according to an embodiment of the present invention; FIGS. 2(A) - 2(I) show signal waveforms for explaining the operation of the superimposing device of FIG. 1; FIG. 3 shows a block diagram of a superimposing device according to another embodiment of the present invention; and FIGS. 4(A) - 4(H) show signal waveforms for explaining the operation of the superimposing device of FIG. 3. A color complex video signal produced by a television, a video recorder, a video disc, or the like is inputted into a video signal input terminal 1. The color complex video signal is applied to a burst gate circuit 2 and a brightness signal chroma signal separation circuit 7. The burst gate circuit 2 separates a burst signal component from the inputted color complex video signal. The burst signal is applied to a color subcarrier generator 3, and the color subcarrier generator 3 generates a color sub-carrier signal of 3.58 MHz based on the burst signal separated by the burst gate circuit 2. The color subcarrier signal of 3.58 MHz is applied to a chroma signal generator 6. R.G.B. signals (Red, Green, Blue signals) such as signals for data formed by a personal computer, or the like are inputted into R.G.B. signal input terminals 4a, 4b, and 4c, respectively. The R.G.B. signals inputted into the R.G.B. signal input terminals 4a, 4b, and 4c are applied to a brightness signal generator 5 and the chroma signal generator 6. The brightness signal generator 5 outputs a brightness signal Y2 based on the R.G.B. signals, and the brightness signal Y2 is applied to brightness signal mixer circuit 8. The chroma signal generator 6 outputs a chroma signal C2 based on the R.G.B. signals inputted from the R.G.B. signal input terminals 4a, 4b, and 4c and the color sub-carrier signal generated by the color subcarrier generator 3, and the chroma signal C2 is applied to a chroma signal mixer circuit 9. The color complex video signal applied to the brightness signal-chroma signal separation circuit 7 is separated into a brightness signal Y1 and a chroma signal C1 by the brightness signal-chroma signal separation circuit 7. The brightness signal Y1 outputted by the brightness signal-chroma signal separation circuit 7 is applied to the brightness signal mixer circuit 8. The brightness signal mixer circuit 8 mixes the brightness signal Y1 separated by the brightness signal-chroma signal separation circuit 7 and the brightness signal Y2 produced by the brightness signal generator 5, and the mixed brightness signal Y is applied to a brightness signal-chroma signal mixer circuit 10. The chroma signal mixer circuit 9 mixes the chroma signal C1 separated by the brightness signal-chroma signal separation circuit 7 and the chroma signal C2 generated by the chroma signal generator 6, and the mixed chroma signal C is applied to the brightness signal-chroma signal mixer circuit 10. The brightness signal-chroma signal mixer circuit 10 mixes the brightness signal Y produced by the brightness signal mixer circuit 8 and the chroma signal C produced by the chroma signal mixer circuit 9 so as to form a color composite video signal for superimposing and clearly displaying two video signals produced from two discrete systems on a display means. The output of the brightness-chroma signal mixer circuit 10 is applied to the display means through a video signal output terminal 11, so that two video signals produced by the different systems are superimposed and clearly displayed on the display means. The operation of the video signal superimposing device comprising above circuit will be described below with reference to FIGS. 2(A) - 2(I). If the color complex video signal is applied from a color television receiver and the R.G.B. signals are applied from the other apparatus such as the personal computer, the color complex video signal as shown in FIG. 2(A) is applied to the signal input terminal 1, and the R.G.B. signals are applied to the R.G.B. signal terminals 4a, 4b, and 4c, respectively. The color complex video signal is inputted into the burst gate circuit 2 and the brightness signal-chroma signal separation circuit 7. The burst gate circuit 2 separates and outputs the burst signal component as shown in FIG. 2(B) from the color composite video signal so as to introduce it into the color subcarrier generator 3. On the other hand, the brightness signal-chroma signal separation circuit 7 separates and outputs the brightness signal Y1 as shown in FIG. 2(C) and the chroma signal C1 as shown in FIG. 2(D). The brightness signal Y1 outputted from the brightness signal-chroma signal separation circuit 7 is introduced into the brightness mixer circuit 8. The chroma signal C1 outputted from the brightness-chroma signal separation circuit 7 is introduced into the chroma signal mixer circuit 9. In this time, the color subcarrier genarator 3 generates continuously the color subcarrier signal of 3.58 MHz based on the burst signal inputted from the burst gate circuit 2. The color subcarrier signal of 3.58 MHz corresponds with a frequency and a phase of the burst signal from the burst gate circuit 2. The color subcarrier signal is applied to the chroma signal generator 6. In response to the color subcarrier signal, the chroma signal C2 as shown in FIG. 2(F) is formed by the chroma signal generator 6 based on the R.G.B. signals applied via the R.G.B. signal input terminals 4a, 4b, 4c, and is applied to the chroma signal mixer circuit 9. The brightness signal generator 5 mixes the R.G.B. signals applied via the R.G.B. signal input terminals 4a, 4b, and 4c by a ratio of Red signal:Green signal:Blue signal = 0.31 : 0.59 : 0.11 so as to form the brightness signal C2 as shown in FIG. 2(E). The brightness signalmixer circuit 8 mixes two type brightness signals Y1 and Y2 applied from the brighness signal-chroma signal separation circuit 7 and the brightness signal generator 5, so that the mixed or composite brightness signal Y as shown in FIG. 2(G) produced by the brightness signal mixer circuit 8 is outputted into the brightness signal-chroma signal mixer circuit 10. The chroma signal mixer circuit 9 mixes two type chroma signals C1 and C2 outputted from the brightness signal-chroma signal separation circuit 7 and the chroma signal genarator 6, so that the mixed or composite chroma signal C is produced as shown in FIG. 2(H) and is applied to the brightness-chroma signal mixer circuit 10, also. The composite brightness signal Y and the composite chroma signal C are mixed by the brightness signal-chroma signal mixer circuit 10, and a single color composite video signal as shown in FIG. 2(I) for superimposing and clearly displaying one video signal on the other video signal is produced by the brightness-chroma signal mixer circuit 10, and the single color composite video signal is applied to the display means via the output terminal 11. According to the embodiment of the present invention, the color complex video signal applied to the input terminal 1 is separated into the brightness signal component and the chroma signal component. The brightness signal component and the chroma signal component are mixed with the brightness signal and the chroma signal applied from the other system, respectively, and thereafter, the composite brightness signal and the composite chroma signal are further mixed so as to eventually output a single color composite video signal superimposing and clearly displaying two discrete system video signals. As described above, in the video signal superimposing device of the embodiment of the present invention, after the color complex video signal is separated into the brightness signal component and the chroma signal component, and after the brightness signals and the chroma signals produced from the two discrete systems are individually mixed, the composite brightness signal and the composite chroma signal are further mixed so as to form the single color composite video signal for superimposing and clearly displaying the two type video signals, so that the brightness signal and the chroma signal rarely interfere mutually as compared with the conventional interferance between the brightness signal and the chroma signal when two system color complex video signals are directly mixed. Accordingly, when the video signals produced from the two discrete systems are superimpopsed and displayed on the screen of the display means by using the single composite video signal outputted from the video signal superimposing device of the present invention, it does not happen that colors are crossed and mixed. FIG. 3 shows a circuit diagram of a video signal superimposing device according to another embodiment of the present invention. Like elements corresponding to the parts of FIG. 1 are denoted by like reference characters in FIG. 3. With an exception and addition to FIG. 1, in the circuit of FIG. 3, a demodulation circuit 12 is provided for demodulating the chroma signal C1 separated by the brightness signal-chroma signal separation circuit 7 based on the color subcarrier signal produced from the color subcarrier generator 3 so as to produce R.G.B. signals. A R.G.B. signal mixer circuit 13 mixes individually the R.G.B. signals produced by the demodulation circuit 12 and the R.G.B. signals introduced via the input terminals 4a, 4b, and 4c, respectively. A chroma signal generator 14 forms the chroma signal C based on the mixed R.G.B. signals produced by the R.G.B. signal mixer circuit 13 and the color subcarrier signal generating from the color subcarrier signal generator 3. According to another embodiment of the present invention, if the color complex video signal is applied to the input terminal 1 from the color television receiver and the R.G.B. signals are applied to the R.G.B. signal input terminals 4a, 4b, 4c from the other apparatus such as the personal computer, the color complex video signals as shown in FIG. 4(A) is applied to the signal input terminal 1, and the R.G.B. signals are applied to the R.G.B. signal terminals 4a, 4b, and 4c, respectively. The color complex video signal is inputted into the burst gate circuit 2 and the brightness signal-chroma separation circuit 7. The burst gate circuit 2 separates and outputs the burst signal as shown in FIG. 4(B) so as to introduce it into the color subcarrier generator 3. On the other hand, the brightness signal-chroma signal separation circuit 7 separates and outputs the brightness signal Y1 as shown in FIG. 4(C) and the chroma signal C1 as shown in FIG. 4(D). The brightness signal Y1 outputted from the brightness-chroma signal separation circuit 7 is introduced into the brightness mixer circuit 8. The chroma signal C1 outputted from the brightness-chroma signal separation circuit 7 is introduced into the demodulation circuit 12. In this time, the brightness signal generator 5 mixes the R.G.B. signals applied from the R.G.B signal input terminals 4a, 4b, and 4c based on a ratio of Red signal : Green signal : Blue signal = 0.31 : 0.59 : 0.11 so as to form the brightness signal Y2 as shown in FIG. 4(E). The brightness signal Y2 is inputted into the brightness mixer circuit 8. The brightness signal mixer circuit 8 mixes two types of brightness signals Y1 and Y2 produced from the brightness signal-chroma signal separation circuit 7 and the brightness generator 5 so as to form a composite brightness signal Y as shown in FIG. 4(F). On the other hand, the color subcarrier generator 3 generates continuously the color subcarrier signal of 3.58 MHz in response to the burst signal inputted from the burst gate circuit 2. The color subcarrier signal of 3.58 MHz corresponds with a frequency and a phase of the burst signal from the burst gate circuit 2. The color subcarrier signal is applied to the demodulation circuit 12 and the chroma signal generator 14. The demodulation circuit 12 demodulates the chroma signal separated by the brightness signal-chroma signal separation circuit 7 based on the color subcarrier signal produced from the color subcarrier generator 3 so as to produce the R.G.B, signals. The R.G.B. signals produced by the demodulation circuit 12 are applied to the R.G.B. signal mixer circuit 13. The R.G.B. signal mixer circuit 13 mixes the R.G.B. signals inputted from the demodulation circuit 12 and the R.G.B. signals inputted from the R.G.B. signal input terminals 4a, 4b, and 4c, respectively. The addition-composite R.G.B. signals outputted from the R.G.B. signal mixer circuit 13 are applied to the chroma signal genarator 14. The chroma signal generator 14 produces the chroma signal C as shown in FIG. 4(G) based on the color subcarrier signal and the addition-composite R.G.B. signals, and the chroma signal C is introduced into the brightness-chroma mixer circuit 10, and the brightness signal-chroma signal mixer circuit 10 mixes the brightness signal Y produced from the brightness signal mixer circuit 8 and the chroma signal C produced from the chroma signal generator 14, so that a single color composite video signal as shown in FIG. 3(H) for superimposing and clearly displaying one video signal on the other video signal on the screen of the display means is generated and introduced into the video output terminal 11. According to said another embodiment of the present invention, the color complex signal applied to the input terminal 1 is separated into the brightness signal component and the chroma signal component, and the chroma signal is demodulated by the demodulation circuit so as to produce the R.G.B. signals. The brightness signal component and the R.G.B. signals are mixed with the brigntness signal component and the R.G.B. signals applied from the other system, respectively, and thereafter, the addition-composite R.G.B. signals are mixed and transformed into the chroma signal, and the brightness signal and the chroma signal are further mixed so as to produce a single color composite video signal for superimposing and clearly displaying one video signal on the other video signal. The color composite video signal for superimposing two video signals is applied to the display means through the output terminal 11. As described above, in the video signal superimposing device of another embodiment of the present invention, after the color complex video signal is separated into the brightness signal component and the chroma signal component, the chroma signal component is demodulated so as to produce the R.G.B. signals. The brightness signal and the R.G.B. signals are mixed with the brightness signal and the R.G.B. signals from the other system, respectively, and the mixed R.G.B. signals are transformed into the chroma signal, and thereafter, the brightness signal and the chroma signal are further mixed, so that the single color composite video signal for superimposing and clearly displaying the video signals from the two different systems is produced. For example, the color complex video signal inputted into the terminal 1 may be produced by a television, a video recorder; a video disc, a laser disc, or the like. The R.G.B. signals inputted into the R.G.B. signal input terminals may be produced by a personal computer, or the like. The video signal superimposing device according to the present invention may be included into a personal computer, a video imaging device such as a television, a video recorder, a video disc, or the like, and the video signal superimposing device may be provided separately. According to the present invention, the number of systems producing the video signals should be limited to two as described above.

Claims: A video signal superimposing device for superimposing and displaying video signals produced from at least two systems comprising: input means (1) for inputting a colour complex video signal ((a)); separation means (7) for separating the complex video signal into a first brightness signal ((c)) and a first chroma signal ((d)); input means (4a, 4b, 4c) for inputting a second video signal; first mixer means (8) for mixing a second brightness signal ((e)) derived from said second video signal and the first brightness signal separated by the separation means; second mixer means (9) for mixing a second chroma signal ((f)) derived from said second video signal and the first chroma signal separated by the separation means; and third mixer means (10) for mixing the mixed brightness signal ((g)) applied from the first mixer means (8) and the mixed chroma signal ((h)) applied from the second mixer means (9), characterised by: said second video signal comprising R, G, B signals; first generation means (5) for generating said second brightness signal ((e)) based on the R, G, B signals; second generation means (6) for generating said second chroma signal ((f)) based on the R, G, B signals; means (2) for producing a burst signal ((b)) from said colour complex video signal; and colour subcarrier generation means (3) operable to use said burst signal to produce a colour subcarrier signal in synchronisation with the colour subcarrier signal of the first chroma signal for use in generation of said second chroma signal. A video signal superimposing device for superimposing and displaying video signals produced from at least two systems comprising: input means (1) for inputting a colour complex video signal ((a')); separation means (7) for separating a first brightness signal component ((c')) and a first chroma signal component ((d')) from the colour complex video signal; input means (4a, 4b, 4c) for inputting a second video signal; first mixer means (8) for mixing a second brightness signal ((e')) derived from said second video signal and the first brightness signal separated by the separation means; means (12, 13, 14) for producing a second chroma signal ((g')) representing a combination of the colour components of the colour complex video signal and the second video signal; and third mixer means (10) for mixing the mixed brightness signal ((f')) and the second chroma signal, characterised by: said second video signal comprising R, G, B signals; first generation means (5) for generating said second brightness signal ((e')) based on the R, G, B signals; said means for producing a second chroma signal comprising: demodulation means (12) for demodulating the first chroma signal ((d')) separated by the separation means (7) so as to form second R, G, B signals; second mixer means (13) for mixing the inputted R, G, B signals with the second R, G, B signals produced from the demodulation means, respectively; and third generation means (14) for generating said second chroma signal ((g')) based on the mixed R, G, B signals; and in that: the video signal superimposing device further comprises: means (2) for producing a burst signal ((b')) from said colour complex video signal; and colour subcarrier generation means (3) operable to use said burst signal to produce a colour subcarrier signal in synchronisation with the colour subcarrier of the first chroma signal for use in generation of said second chroma signal. A video signal superimposing device according to claim 1 wherein said second generation means (6) is operable to modulate the colour subcarrier signal produced by the colour sub-carrier generation means (3) using the R.G.B. signals to generate said second chroma signal. A video signal superimposing device according to claim 2 wherein said demodulation means (12) is operable to demodulate the first chroma signal in accordance with the colour subcarrier signal produced by the colour subcarrier generation means (3) and said third generation means (14) is operable to modulate said colour subcarrier signal using the mixed R.G.B. signals to generate said second chroma signal. A video signal superimposing device according to any preceding claim wherein the two systems are a video imaging system and a personal computer system. A video signal superimposing device according to claim 5 wherein the video imaging system is a television, a video recorder, or a video disc player. A video signal superimposing device according to any preceding claim, wherein the superimposing device is incorporated in a personal computer. A video signal superimposing device according to any of claims 1 to 6, wherein the video signal superimposing device is incorporated in a video imaging system.

Inventors: ABUMI TAKAO, UENO ATSUSHI, ABUMI, TAKAO, UENO, ATSUSHI
Applicants: SHARP KK, SHARP KABUSHIKI KAISHA
Application year: 1984
Main classification: H04N9
IPC codes: H04N9, H04N5