Abstract:
An encoding apparatus for encoding color television signals which improves the quality of a display image by selecting a most effective passband of a motion and pattern adaptive 3-D filter filters according to a shape of a pattern or the still and motion image signals an further prevents a mixing of a luminance signal and a chrominance signal at an encoding site to obtain the highest resolution for the display image.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a circuit of encoding a composite image signal by synthesizing the composite image signal especially for use in a television, and more particularly to a circuit and method for encoding a color television signal, which improves a resolution of the display image and removes interferences between a chrominance signal and a luminance signal by pre-filtering, in use of a pattern and motion adaptive variable bandwidth filter. 
     Recently, a digital signal processing technique is employed more frequently as a method to improve the quality of an image signal. Especially, in an IDTV (Improved Definition TV) and EDTV (Enhanced Definition TV), a motion adaptive signal processing technique is used for a digital filter that separates a chrominance signal and a luminance signal; and a scanning line conversion circuit that converts an interlaced scanning image signal with 525 scanning lines into a non-interlaced scanning image signal. By using the method stated above for a television receiver, it is possible to improve the resolution of the display image by efficiently removing cross luminance, components which occur a chrominance signal is mixed to a luminance signal, and cross color components which occur when a luminance signal is mixed to a chrominance signal. 
     A prior art for achieving the improvements as stated above is shown in FIG. 1 wherein a luminance signal Y and the color difference signals R-Y (I) and B-Y (Q) are separated respectively from the red (R), green (G), and blue (B) color signals which are applied to a gamma correction matrix 4. The color difference signals I, Q are filtered by the corresponding low pass filters 10, 11 and modulated by a quadrature phase modulator 5 according to a chrominance sub-carrier signal 1 and a burst flag signal 2. 
     The signal output from the quadrature phase modulator 5 and the luminance signal Y from the gamma correction matrix 4 are combined at a mixer 6 according to an input signal 3 which is a synchronous and blocking pedestal signals. To obtain a resulting encoded video signal CV, the combined signal output from the mixer 6 is low-pass-filtered by the low pass filter 8. 
     Since the stated prior art is not a fundamental processing method which removes the cross luminance components from the luminance signal and the chrominance signal, low quality in a resolution of the display image and interference of the image by the chrominance signal and the luminance signal often follow. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a circuit and method of improving the quality of a display image at a receiving site by selecting a most effective bandwidth of the filters according to a shape of a pattern or the still and motion image signals, while elevating the resolution of the display image by using a motion and pattern adaptive three dimensional filter, which prevents a mixing of a luminance signal and a chrominance signal at an encoding site and sustains the best resolution. 
     To achieve the above and other objects of the present invention, the frequency zones of a vertical, horizontal, and temporal axes in a three dimensional filter are adjusted according to a motion signal detected on the basis of an intrafield image signal pattern and a frame difference signal so as to reduce an interference of a luminance signal and chrominance signal and to use an image frequency zone effectively during an encoding of red (R), green (G), and blue (B) color signals which may be provided from, for example, a camera into a composite image signal. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying diagrammatic drawings, in which: 
     FIG. 1 shows an encoding circuit of the prior art; 
     FIG. 2 shows one embodiment of a circuit of encoding color television signal according to the present invention; 
     FIG. 3 shows another embodiment of a circuit of encoding color television signal according to the present invention; 
     FIG. 4 shows a detailed circuit diagram of the first, second and third filters 12-14 of FIG. 2 and the first filter 12 a FIG. 3 according to the present invention; 
     FIGS. 5A through 5C are spatial frequency zone selecting characteristics of vertical, horizontal, and horizontal-vertical filters 49-51 of FIG. 4 according to the present invention, respectively; 
     FIG. 6 shows a detailed circuit diagram of the fourth filter 16 of FIG. 3 according to the present invention: 
     FIGS. 7A through 7C are views of spatial frequency zone selecting characteristics of a horizontal, vertical and horizontal-vertical filters 69-71 in FIG. 6 according to the present invention: 
     FIG. 8 shows a detailed circuit diagram of the pattern detecting circuit 7a of FIGS. 2, 3, 4, and 6 according to the present invention; and 
     FIG. 9 shows a detailed circuit diagram of the motion detecting circuit 7b of FIGS. 2, 3, 4, and 6 according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 2, the like reference numerals and symbols will represent the like construction and function of the same in FIG. 1. That is, low pass filters 10, 11 are connected to a gamma correction matrix 4, and a signal output from a quadrature phase modulator 5 is combined with a luminance signal Y at a mixer 6. Then, the combined signal is low-pass-filtered at a low pass filter 8. 
     In detail, the luminance signal Y separated from the red (R), green (G), and blue (B) color signals by the gamma correction matrix 4 is connected to an input terminal of a first filter 12. The color difference signals R-Y (I) and B-Y (Q) separated by the gamma correction matrix 4 are connected to input terminals of low pass filters 10 and 11; and the outputs from the low pass filters 10 and 11 are connected to input terminals of a second filter 13 and a third filter 14 respectively. The luminance signal Y is also connected to a pattern and motion detecting circuit 7 to detect a pattern and motion of the luminance signal Y. The signal output from the pattern and motion detecting circuit 7 is applied to first, second and third filters 12-14, the output from the first filter 12 is connected to a mixer 6, and the outputs from the second filter 13 and the third filter 14 are applied to a quadrature phase modulator 5. 
     FIG. 3 is another embodiment of the circuit of encoding color television signal according to the present invention in which similar symbols are used to refer to the gamma correction matrix 4, the low pass filters 10 and 11, the mixer 6, the low pass filter 8, and the quadrature phase modulator 5. In FIG. 3, the luminance signal Y of the gamma correction matrix 4 is input into a first filter 12, and a pattern and motion detecting circuit 7. The color difference signals R-Y (I) and B-Y (Q) are input into the quadrature phase modulator 5 through the first and second low pass filters 10 and 11; and the output from the quadrature phase modulator 5 is input into an input terminal of a fourth filter 16. The output of the pattern and motion detecting circuit 7 is input into the first and the fourth filters 12, 16, and the outputs of the first filter 12 and the fourth filter 16 are input into the mixer 6. 
     FIG. 4 is a detailed circuit diagram of the first, second and third filters 12-14 in FIG. 2 and a fourth filter 16 in FIG. 3. In the drawing, first and second clock delay circuits 41, 42 coupled in series are connected to a luminance input terminal Yi. A first horizontal delay circuit 47 is also connected to the luminance input terminal Yi. The output of the first horizontal delay circuit 47 is coupled to a third clock delay circuit 43 and a fourth clock delay circuit 44 in series. A second horizontal delay circuit 48 is connected to the output of the first horizontal delay circuit 47; and the output of the second horizontal delay circuit 48 is successively coupled to a fifth clock delay circuit 45 and a sixth clock delay circuit 46. 
     A horizontal filter 49 is connected to an output S4 from the first horizontal delay circuit 47 and outputs S5 and S6 from the third and fourth clock delay circuits 43, 44. A vertical filter 50 is connected to outputs S2, S5, and S8 from the first, third, and fifth clock delay circuits 41, 43, and 45, respectively. A horizontal-vertical filter 51 is connected to outputs S4 and S7 from the first and the second horizontal delay circuits 47 and 48 and to outputs S2, S3, S5, S6, S8, and S9 from the first through sixth clock delay circuits 41-46. A multiplexer 53 selects an output from one of the vertical, horizontal, and horizontal-vertical filters 49-51 according to an output from the pattern detector 7a. A gain controller 55 takes an output from a frame delay circuit 52 as an input to delay the input signal S5 from the output of the third clock delay circuit 43 by a frame unit; and a mixer 56 outputs a mixed gain-controlled signal that is gain-controlled by the gain controllers 54 and 55 according to an output from the motion detector 7b. 
     FIGS. 5A through 5C show spatial frequency zone selecting characteristics of the horizontal filter 49, the vertical filter 50, and the horizontal-vertical filter 51 in FIG. 4 according to the present invention. FIG. 5a shows frequency selecting characteristics of the horizontal filter 49; FIG. 5b shows frequency selecting characteristics of the vertical filter 50; and 5c is frequency selecting characteristics of the horizontal-vertical filter. 
     FIG. 6 is a specific circuit diagram of the fourth filter 16 in FIG. 3 according to the invention, wherein the reference numerals 67 and 68 represent horizontal delay circuits; numerals 61 through 66 represent clock delay circuits; numerals 69 represents a horizontal filter; numerals 70 represents a vertical filter; numerals 71 represents a horizontal-vertical filter; numerals 72 represents a multiplexer; and numerals 74 and 75 represent gain controllers, having the same connection as shows in FIG. 4. 
     FIGS. 7A through 7C are spatial frequency zone selecting characteristics of the vertical, horizontal, and horizontal-vertical filters 69-71 in FIG. 6 according to the present invention, respectively. 
     FIG. 8 is a detailed diagram of the pattern detector 7a as shown in FIGS. 4 and 6 according to present invention. In FIG. 8, comparators 81-84 compare the outputs from the first and second horizontal delay circuits 47, 48 and the first through sixth clock delay circuits 41-46 with a plurality of threshold voltages. Inverters 85-88 invert the output from the comparators 81-84; and the selection signals to be provided to the selection terminals A and B of the multiplexer 53 are generated by AND gates 89-92 and OR gates 93-99, which perform a specific logic combination for the signals output from the comparators 81-84 and the inverters 85-88. The multiplexer 53 selects one of the output signals Y h , Y v  and Y hv  from the horizontal filter 49, the vertical filter 50, and the horizontal-vertical filter 51 in accordance with the selection signals at the selection terminals A and B to provide a pattern value signal. 
     FIG. 9 is a detailed circuit diagram of the motion detector 7b as shown in FIG. 4 and 6, in which a frame memory 101 delays the luminance signal input Yi by one frame, and a subtractor 102 subtracts the output from the frame memory 101 from the luminance signal input Yi. Then, an absolute value circuit 103 converts the output from the subtractor 102 to its absolute value. A motion signal processing circuit 104 then processes the output from the absolute value circuit 103 to provide a motion signal. 
     Referring back to FIGS. 2-9, the operations of each embodiments of the present invention will be discussed. First of all, with reference to an operating effect of the first filter 12, in the event that there is no edge in a horizontal direction (the horizontal correlation is high), that is |S4-S6|≦Kh and |Yh2-Yh8|≧Kyv for the luminance signal Y. In addition, the multiplexer 53 in FIG. 4 selects the output from the horizontal filter ,i.e., Yh=0.25.S4+0.5.S5+0.25.S6, if there is an edge in a vertical direction is detected. In this case, the selecting characteristics in the spatial frequency zone is the same as shown in FIG. 5A. Here, the fact that there is no edge in the horizontal direction means a signal spectrum is distributed to a lower zone of a horizontal frequency direction. On other hand, there is an edge in the vertical direction, higher frequency components in the signal spectrum are contained in a vertical direction. Therefore, a filter which has the characteristics as shown in FIG. 5A is adequate. 
     In case where |S2-S8|≦Kv and |Yv4-Yv6|≧Kyh; there is no edge in the vertical direction (the vertical correlation is high), but there is edge in a horizontal direction, the multiplexer 53 in FIG. 4 selects an output from the vertical filter 50. Thus, Yv=0.25.S2+0.5.S5+0.25.S8. In this case, selecting characteristics in the spatial frequency zone is the same as FIG. 5B. Here, the fact that there is no edge in the vertical direction means a signal spectrum is distributed to a lower zone of a vertical frequency direction. On the other hand, when there is an edge in the horizontal direction, higher frequency components in the signal spectrum are contained in a horizontal direction. Therefore, a filter which has the characteristics as shown in FIG. 5B is adequate. 
     In case where |S2-S8|≦Kv and |Yv4-Yv6|≧Kyh, and |S4-S6|≦Kh and |Yhz-Yh8|≧Kyv, the multiplexer 53 in FIG. 4 selects an output from the horizontal-vertical filter 51. Thus, Yhv 3/4.S5+1/8.(S2+S8+S4+S6)-1/16.(S1+S3+S7+S9). In this case, selection characteristics in the spatial frequency zone is the same as FIG. 5C. Here, it means either there is no edge in both of the vertical and horizontal directions or there is edge in both of the vertical and horizontal directions. 
     If there are edges in both directions, the signal spectrum is distributed widely in both vertical and horizontal directions, thus it is necessary to remove the signal spectrum occupied by a modulated chrominance signal as FIG. 5C to prevent the modulated chrominance signal from an interference. Also, if there is an edge in neither direction, the signal spectrum is distributed lower parts of the vertical and horizontal frequency directions, thus selecting characteristics in the spatial frequency zone as in FIG. 5C is adequate. 
     In addition, the color difference signals I and Q are filtered by the second and third filters which have similar effects to the first filter 12 and then modulated by the quadrature phase modulator 5. The output from the quadrature phase modulator 5 is combined with the output from the first filter 12. At this time, a spatial frequency of a chrominance sub-carrier for the quadrature phase modulator 5 is fh=fsc and fv=525/4 to separate the luminance signal and the modulated chrominance signal. 
     Referring to the operation of FIG. 3, for the luminance signal Y, it is the same as in FIG. 2, but for the color difference signal I and Q, a quadrature phase modulation is performed by a well-known method, and the modulated output is filtered by the fourth filter 16 which uses a similar principle as the first filter 12. The output from the fourth filter 16 and the luminance signal Y filtered by the first filter 12 are combined to form a composite image signal. 
     In case where |S4-S6|≦Kh and |Yh2-Yh8|≧Kyv, the multiplexer 72 in FIG. 6 selects the horizontal filter 69; Ch=-1/4·N4+1/2·N5-1/4·N6. In other words, for the luminance signal Y, there is no edge in a horizontal direction, but there is an edge in a vertical direction. The selecting characteristics of a spatial frequency zone for the horizontal filter 69 is as shown in FIG. 7A. 
     In case where |S2-S8|≦Kv and |Yv4-Yv6|≧Kyv, the multiplexer 72 in FIG. 6 selects the vertical filter 70; Cv=-1/4·N2+1/2·N5-1/4·N8. In other words, for the luminance signal Y, there is no edge in a vertical direction, but there is an edge in a horizontal direction. The selecting characteristics of a spatial frequency zone for the horizontal filter 70 is as shown in FIG. 7B. 
     In case where |Yh2-Yh8|≧Kyv and |Yv4-Yv6|≧Kyh, and |S4-S6|≦Kh and |S2-S8|≦Kv, the multiplexer 72 in FIG. 6 selects a horizontal-vertical filter 71; Chv=1/4·N5-[-1/8·(N2+N8+N4+N6)]+1/16·(N1+N3+N7+N9). The selecting characteristics of a spatial frequency zone for the horizontal filter 71 is as shown in FIG. 7C. 
     The detailed diagram of the pattern detecting circuit 7a is shown in FIG. 8. The pattern detecting circuit 7a includes comparators 81-84, inverters 85-88, AND gates 89-92, and OR gates 93, 94. In case where there is no edge in horizontal direction, that is |S4-S6|≦Kh, the output of the comparator 81 becomes logic high. When there is an edge in the vertical direction, that is |Yh2-Yh8|≧Kyv, an output from the comparator 82 becomes logic high. Here, Yh2=1/4·(S1+2S2+S3), and Yh8=1/4·(S7+2S8+S9). When there is no edge in a vertical direction, that is |S2-S8|≦Kv, the output of the comparator 83 becomes logic high. When there is edge in a horizontal direction, that is |Yv4-Yv6|≧Kyh, the output of the comparator 84 becomes logic high. Here, Yv4=1/4·(S1+2S4+S7), and Yv6=1/4·(S3+2S6+S9). The combination signals output from the comparators 81-84, the inverters 85-88, the AND gates 89-92, and the OR gates 93, 94 are used to select one of the horizontal, vertical, horizontal-vertical filters 69-73 and 49-51. It is clear that anyone who has general knowledge in this field can easily understand the operating principle of FIG. 8. 
     A detailed diagram of the motion detecting circuit 7b is shown in FIG. 9. The current luminance signal Y and the output of the frame memory 101 are used to obtain the frame difference signal between the current frame and a preceding frame, and an absolute value of the frame difference signal is calculated by the absolute value circuit 103. The output of the absolute value circuit 103 is applied to the motion signal processing circuit 104 to obtain a quantity of motion to control a gain (where, 0≦k≦1) of the gain controllers 54, 55. If the quantity of the motion becomes larger, then the k value becomes larger. Especially, when the k value is identical to 1, the outputs of the filters 49-51 and 69-71 in FIGS. 4 and 6 are equal to the output from the multiplexers 53, 73 and when the k value is zero, outputs of the filters 49-51 and 69-71 are one-frame-delayed signals. When the k value is a value between zero and one, the outputs of the filters 49-51 and 69-71 in FIGS. 4 and 6 become Yo=k· Sv+(1-k)·St and Co=k·Nv+(1-k)·Nt, respectively. 
     While the invention has been particularly shown and described with reference to a preferred embodiment , it will be understood by those skilled in the art that the horizontal-vertical filter 51 alone can be used without using the horizontal and vertical filters 49, 50 and the pattern detection circuit 7a of FIG. 4 and that the horizontal-vertical filter 71 alone can be used without using the horizontal and vertical filters 69, 70 and the pattern detection circuit 7a of FIG. 6 without departing from the spirit and scope of the invention. 
     If the encoding method invented is used at a transmitting site, it is still possible to sustain a compatibility with an existing TV system. Furthermore, by applying three dimensional decoding at a receiving site, a quality of an image can be improved dramatically. 
     As stated above, in a composite image signal encoding circuitry such as TV camera and VTR, the present invention has an advantage in that a best picture quality is sustained at a receiving site by decreasing interference between luminance signal and color signal, shifting the bandwidth of the filters according to still and motion image, and selecting a most effective bandwidth of a filter according to a shape of a pattern.