Abstract:
The technique for separating luminance(Y)/color(C) signals in NTSC-type television TV receivers is disclosed. To decrease deterioration in picture quality due to inaccuracy of Y/C signal separation in color television receivers, comb filters have been used and a three-dimensional signal processing technique using a frame memory has recently been disclosed. To avoid a complicated constitution of circuit which consists in the necessity of large scale memory, this invention provides a Y/C signal separating circuit suitable for digitalization without increasing the complication of circuit by using a line memory. Also, horizontal and vertical peaking filters utilizing horizontal and vertical correlation of video signals in said separating process are provided to change the bandwidth of the filter according to signals, thereby improving in resolution and S/N ratio.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a circuit for separating luminance signals/color signals (hereinafter referred to as &#34;the Y/C separating circuit&#34;) in a television receiver of a NTSC system, and more particularly to the Y/C separating circuit which is simplified in constitution by using only a line memory and is suitable for the digitization of video signals, and which changes the bandwidth of the filter in accordance with the signals by use of the filter utilizing the horizontal and vertical correlation of video signals, thereby to improve resolution and the signal-to-noise ratio. 
     Recently, since the integration degree of an integrated circuit(IC) has improved, the digital signal processing can be performed economically. Accordingly, a digital type television(hereinafter referred to as &#34;TV&#34;) can get to compete with an analog type TV in both price and function because reason the digital type TV makes it possible to perform the various signal processing methods which are impossible to perform in the analog type TV. 
     In a conventional color TV with an analog or digital signal processing system, the 1H type comb filter shown in FIG. 1 or the 2H type comb filter shown in FIG. 2 is used to separate the luminance/color signal from the composite video signal, thereby providing much improvement of picture quality over prior color TV. However, there still remains a problem of the deterioration in picture quality due to inaccuracy of the Y/C signal separation. Heretofore, there have been disclosed three-dimensional digital signal processing techniques in which the frame memory is used. However, these techniques have problems in which the constitution of the circuit becomes very complicated requires large scale memory and the price of the product become high. 
     SUMMARY OF THE INVENTION 
     It is, therefore, a primary object of the present invention to provide an improved luminance/color signal separating circuit. It is another object to provide a luminance/color signal separating circuit which is simplified in constitution by using only a line memory and is suitable for the digitization of video signals. 
     Another object of the invention is to provide a circuit which changes the bandwidth of the filter in accordance with the signals by use of the horizontal and vertical peaking filters utilizing the horizontal and vertical correlation of video signals, thereby improving resolution and the signal-to-noise ratio. 
     According to the present invention, there is provided, for performing said objects, a luminance/color signal separating circuit of the analog or digital signal processing system, comprising: a composite video signal delay means consisting of the delay elements made by line memories for performing the predetermined delay of the inputted composite video signal by said delay element to output the other various signals; a two-dimensional space filter means for filtering the produced signal from said composite video-signal delay means; a selecting means for selecting said spatial filter and peaking filter after operatingly comparing according to said output signals from said composite video signal delay means and detecting the vertical and horizontal correlation by said operatedly compared outputs; a low-pass filter means for peaking in the vertical direction when the horizontal correlation is higher than the vertical one; a band-pass filter means for peaking in the horizontal direction when the vertical correlation is higher than the horizontal one; a data selecting means for selecting the filter to output only the color signal from the video signal input by the outputs of said selecting means, said low-pass filter and said band-pass filter; and a luminance signal outputting means for compensating for the delay in said data selecting means, preventing the noise and the excessive peaking to compensate for the contour of the picture, and controlling the gains of the vertical and horizontal peaking signal. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     This invention will be more fully understood from the following detailed description of a preferred embodiment thereof, taken in connection with the accompanying drawings, in which: 
     FIG. 1 is a schematically illustrated block diagram showing a conventional 1H type comb filter; 
     FIG. 2 is a schematically illustrated block diagram showing a conventional 2H type comb filter; 
     FIG. 3 is a block diagram of a Y/C signal separating circuit according to an embodiment of the present invention; 
     FIG. 4 is a detailed circuit diagram of Y/C signal separating circuit shown in FIG. 3 according to the present invention; 
     FIGS. 5A and 5B are graphs which illustrate respectively the spatial spectrum and the frequency selection characteristics according to the present invention; 
     FIGS. 6A and 6B are graphs which illustrate respectively the two-dimensional spatial spectrum and the frequency selection characteristics according to the present invention; and 
     FIGS. 7A and 7B are graphs which illustrate the frequency characteristics of a low-pass filter means and a band-pass filter means, respectively, in FIG. 3 according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In FIG. 3 shown in block diagram an embodiment according to the present invention, there is shown a Y/C signal separating circuit in a TV receiver comprising a composite video signal delay means(10) consisting of the delay elements for performing the predetermined delay of the inputted composite video signal by said delay element to output the other various signals, a two-dimensional space filter means(20) for operating and filtering the produced signal from said composite video signal delay means(10), a selecting means(30) for selecting the proper spatial filter and the peaking filter by detecting the vertical and horizontal correlation according to the output from said composite video signal delay means(10), a low-pass filter means(40) for removing the chroma component from the received color signal of said two-dimensional space filter means(20) and separately outputting only the vertical peaking signal when the horizontal correlation is higher than the vertical one, a band-pass filter means(50) for separating and outputting only the horizontal peaking signal when the vertical correlation is higher than the horizontal one after receiving the luminance signal from said two-dimensional space filter means(20), a data selecting means(60) for selecting the filter to separately output only the color signal on the basis of the output signals of said selecting means(30), said low-pass filter means(40) and said band-pass filter means(50) from the video signal input, and a luminance signal outputting means(70) for compensating for the delay in said data selecting means(60) and preventing the noise and the excessive peaking to compensate for the contour of the picture, and controlling the gains of the vertical and the horizontal peaking signal which are output signals of said low-pass filter means(40) and said band-pass filter means(50) respectively. 
     Now, an embodiment of the present invention constituted as above-mentioned will be described. 
     The composite video signal delay means(10) receives at the input terminal the composite video signal to delay said signal by the delay elements thereof. The various delayed signals output from the output terminals of said delay elements are filtered by the two-dimensional space filter means(20) and are transmitted to the selecting means(30). And then, the operation of said delayed signals is executed, the numerical values of said operation results are compared with each other, and the correlation of the vertical-direction and the horizontal-direction is detected on the basis of said compared value. The proper space filter of said two-dimensional space filter means(20) and the peaking filters of the low-pass filter means(40) and the band-pass filter means(50) are selected on the basis of the detected correlation between the vertical peaking signal and the horizontal peaking signal. Namely, if the horizontal correlation is higher, the peaking in the vertical direction is performed in said low-pass filter means(40), and if the vertical correlation is higher, the peaking in the horizontal direction is performed in said band-pass filter means(50). Accordingly, in the data selecting means(60) the color signal is separated from the video signal by a compared output of said selecting means(30) and the outputs from said low-pass filter means(40) and said band-pass filter means(50). Also, by the luminance signal outputting means(70) is outputted the picture in which delay in said data selecting means (60) and the picture contour are compensated, noise is removed and the excessive peaking is prevented. 
     Referring to FIG. 4, there is shown in detail the Y/C signal separating circuit of FIG. 3 according to the present invention. In FIG. 4, TH1-TH2 and 1/2TS1-1/2TS11 are constituted by line memory, the delay element, TH, of them has a value 1/fH and TS has a value 1/fsc (where fH represents horizontal scanning frequency and fsc represents color subcarrier frequency). Assuming that on input of composite video signal is represented by V1, an output of said delay element 1/2TS1 is represented by V2, a output of the delay element 1/2TS4 is represented by V3, an output of the delay element TH1 is represented by V4, an output of the delay element 1/2TS2 is represented by V5, an output of the delay element 1/2TS5 is represented by V6, an output of the delay element TH2 is represented by V7, an output of the delay element 1/2TS3 is represented by V8, and an output of the delay element 1/2TS6 is represented by V9. Accordingly, means which is constituted to obtain each of said outputs V1-V9 corresponds to a composite video signal delay means(10). 
     Also, means which receive V2, V5 and V8 of outputs V1-V9 from said composite video signal delay means(10) to perform the logic operation by ##EQU1## is the first filter (25), means which receive V4, V5 and V6 to perform the logic operation by ##EQU2## is the 2nd filter(26), means which receive outputs V2, V5 and V8 to perform the logic operation by ##EQU3## is the 3rd filter(27), and means which receive outputs V4, V5 and V6 to perform the logic operation by ##EQU4## is the 4th filter(28). The means constituted by said the 1st-4th filters(25-28) correspond to the means(20). 
     Means which receives V2 and V8 of outputs V1-V9 from said composite video signal delay means(10) to perform the operation by |V2-V8| is the first absolute value operation means(34), means which performs the operation by |V4-V6| is the second absolute value operation means(35), and said comparator means(30) is consisted of said 1st and 2nd absolute value operation means(34 and 35), and a numerical value comparator(36) which compares outputs from said 1st and 2nd absolute value operation means(34 and 35) with each other. 
     The low-pass filter means(40) is constituted by such a manner that the color signal output 21 form the first filter(25) of said means(20) is supplied through the delay element 1/2TS7 to the delay element 1/2TS8 and to the first scale filter(42) as signal(1), the output signal(2) from said delay element 1/2TS8 is supplied the 2nd scale filter(43), and the output signal(21) from the first filter(25) is supplied to the 3rd scale filter(44), thereby to add in the first adder(45) outputs from the first to third scale filters(42-44) to provide signal(45). 
     The band-pass filter means(50) is constituted by such a manner that the luminance signal(23) output from the third filter(27) of said two-dimensional space filter means(20) is supplied to the delay element 1/2TS9 and to the 6th scale filter(54), the output signal(4) from the said delay element 1/2TS9 is supplied to the 4th scale filter(52) and to the delay element 1/2TS10, and the output signal(5) from said delay element 1/2TS10 is supplied to the 5th scale filter(53), thereby to add each of outputs from the 4th to 6th scale filters(52-54) in the second adder(55) to provide signal 51. 
     The data selecting means(60) is constituted in such a manner that outputs from the first and second filters(25 and 26) of said means(20) applied to multiplexer(MUX1), outputs from the third and fourth filters(27 and 28) are supplied to the multiplexer(MUX2), and each of outputs from said low-pass filter means(40) and said band-pass filter means(50) are applied to the multiplexer(MUX3), so that said multiplexer (MUX1-MUX3) select the data on the basis of output from said comparator means(30). 
     The luminance signal outputting means(70) includes a delay element 1/2TS11(90), a non-linear circuit(75), a gain control means(80), and a third adder(100). While multiplexer(MUX1) of said data selecting means(60) outputs the color signal C, in said luminance signal outputting means(70) the output from the multiplexer(MUX2) is supplied to said delay element 1/2TS11(90), the output from said multiplexer(MUX3) is supplied to said non-linear circuit(75), the output from the said non-linear circuit(75) is supplied to said gain control means(80) to be added to a sharpness gain signal, and the added output is supplied to the third adder(100). 
     FIGS. 5A and 5B represent the spatial spectrum selection characteristic of and frequency selection characteristic filters 25, 27, respectively, according to the present invention. 
     FIGS. 6A and 6B represent the two-dimensional spatial spectrum selection characteristic of and frequency selection characteristic filters 26, 28, respectively, according to the present invention. 
     FIG. 7 shows waveforms for the frequency characteristics of the low-pass filter means(40) and the band-pass filter mean(50), in which FIG. 7A represents the output characteristic of the low-pass filter (40) and FIG. 7B represents the output characteristic of the band-pass filter(50). 
     Now, an embodiment of the present invention will be described in detail with reference to the aforementioned drawings. 
     When the composite video signal inputted at the input terminal(11) is supplied to delay elements(TH1, TH2, 1/2TS1-1/2TS6) made by line memories of the composite video signal delay means(10) in FIG. 3 and the predetermined values(V1-V9) are obtained, if the correlation in the vertical direction is higher, the operated output value |V2-V8| from the first absolute value operation means(34) of the comparator means(30) is smaller than the operated output value |V4-V6| from the second absolute value operation means(35). In this case, the luminance signal(Y) is filtered by the third filter(27) which performs operation of ##EQU5## in the two-dimensional space filter means(20). The reason why filtering is performed by said third filter(27) is that the output from the numerical value comparator(30) of the selecting means(30) selects the terminal(1) of the multiplexers(MUX1, MUX2) in the data selecting means(60). Namely, because the correlation in the vertical direction is higher, the polarities of V5 and V2, V5 and V8 for the chroma signal component are inverted to output only the luminance(Y) signal after filtering. If, for the same reason, the color(C) signal is filtered by the first filter(25) which performs operation of ##EQU6## in the filter means(20), the luminance(Y) signal which is high in the correlation between lines is offset relative to the other to obtain only the color(C) signal. In this case, the frequency selection characteristic of the luminance(Y) signal filter becomes ##EQU7## and the frequency selection characteristic of the color(C) signal filter becomes ##EQU8## (where fv presents the vertical spatial frequency). This can be represented by two-dimensional spatial spectrum and frequency selection characteristic curves as waveforms shown in FIGS. 5A and 5B. 
     Assuming that the correlation in the horizontal direction is higher in the composite video signal, in the comparator means(30) the numerical value comparator(36) compares the output of the first absolute value operation means(34) with the output of the second absolute value operation means(35), if the output value of the first absolute value operation means (34) is larger than the output value of the 2nd absolute value operation means(35) (|V2-V8|&gt;|V4-V6|), the luminance(Y) signal is filtered by the 4th filter(28) which performs operation of ##EQU9## in the two-dimensional spatial filter means(20). Namely, because the correlation in the horizontal direction is higher, the polarities of V5 and V4, V5 and V6 for the chroma signal component are inverted to output only the luminance(Y) signal after filtering. If, for the same reason, the color(C) signal is filtered by the 2nd filter(26) which performs operation of ##EQU10## the luminance(Y) signal which is high in the horizontal correlation is offset relative to the other and removed to obtain only the color(C) signal. In this case, the frequency selection characteristic of the luminance(Y) signal filter becomes ##EQU11## and the frequency selection characteristic of the color(C) signal filter becomes ##EQU12## (where fsc represents the color subcarrier frequency). This can be represented by two-dimensional spatial spectrum and frequency selection characteristic curves as waveforms shown in FIGS. 6A and 6B. 
     The present invention selects the proper filter according to the horizontal or vertical correlation of the composite video signal inputted as the above-mentioned to perform the Y/C signal separation. Accordingly, the present invention, as compared with the conventional 1H or 2H type comb filter, can increase the accuracy of Y/C signal separation and can reduce the interference of crosstalk between Y and C signals. 
     Also, in order to increase the resolution, if the correlation in the horizontal direction is higher, then the vertical peaking signal is selected to add to the luminance(Y) signal, and if the correlation in the vertical direction is higher, then the horizontal peaking signal is selected to add to the luminance(Y) signal. Therefore, the picture contour is compensated to increase the resolution in outer appearance. 
     In FIG. 4 the principle of compensation for the contour will be explained in detail. If the correlation in the horizontal direction is higher, the color(C1) signal output from the two-dimensional space filter means(20) is passed through the low-pass filter means(40) so that the chroma component may be removed and only the vertical peaking signal is separated, thereby being added to the luminance(Y) signal in the third adder(100) through the multiplexer(MUX3), the non-linear circuit(75) and the sharpness gain means(80). 
     If the correlation in the vertical direction is higher, the luminance(Y) signal output from the two-dimensional space filter means(20) is passed through the band-pass filter means(50) so that only the horizontal peaking signal is obtained, thereby being added to the luminance(Y) signal in the third adder(100) through the multiplexer(MUX3), the non-linear circuit(75) and the sharpness gain means(80). 
     The frequency selection characteristic of the above-mentioned embodiment is as the characteristic waveforms shown in FIGS. 7A and 7B. 
     As the above-described, according to the present invention, there is provided a Y/C signal separating circuit in which the constitution of circuit is simplified by using only the line memory and which is suitable for digitization. Also this invention has advantages which can improve resolution and signal-to-noise ratio by changing the bandwidth of the filter in accordance with the signals with the use of horizontal and vertical peaking filters utilizing the horizontal and vertical correlation of video signals.