Video signal processing circuits

0001This invention relates to video signal processing circuits and to circuits for separating luminance and chrominance signals from video signals.

0002It has previously been proposed, in video signal separating systems, to use horizontal correlation, vertical correlation and time (frame) correlation of both a luminance signal Y and a carrier chrominance signal (chroma signal) C to separate the signals. In the foregoing respects, correlation means how the signals change along a line, from line to line, or from frame to frame, respectively. Previously proposed Y/C separating circuits utilising the above respective correlation techniques will be described with reference to Figures 8A to 10B of the accompanying drawings.

0003It has also been proposed in EP-A-169052 to provide a noise reduction circuit in which an input video signal is fed through series connected horizontal, vertical and frame correlation based noise reduction circuits.

0004Figure 8A illustrates a horizontal correlation Y/C separating circuit. A video signal applied to an input terminal 1 is supplied in common to a low pass filter 2Y and a bandpass filter 2C. A luminance signal Y_H is supplied to an output terminal 3Y from an output of the low pass filter 2Y, and a chroma signal C_H is supplied to an output terminal 3C from an output of the bandpass filter 2C.

0005Figure 8B illustrates a vertical correlation Y/C separating circuit. A video signal applied to an input terminal 1 is supplied in common to a 1H delay line 4 (1H = one line period), an adder 5Y and a subtracter 5C. An output from the 1H delay line 4 is supplied in common to the adder 5Y and the subtracter 5C. As a result, a luminance signal Y_V from the adder 5Y is supplied to an output terminal 6Y and a chroma signal C_V from the subtracter 5C is supplied to an output terminal 6C.

0006Figure 8C illustrates a frame correlation Y/C separating circuit. A video signal applied to an input terminal 1 is supplied in common to an adder 8Y, a subtracter 8C and a frame memory 7 which constitutes a one frame delay line. An output of the frame memory 7 is supplied to the adder 8Y and the subtracter 8C. As a result, a luminance signal Y_F from the adder 8Y is supplied to an output terminal 9Y and a chroma signal C_F from the subtracter 8C is supplied to an output terminal 9C.

0007While the frame memory 7 is inherently designed to process a digitised signal, it is shown to process an analog signal for the sake of simplicity. Therefore, an A/D (analog-to-digital) converter at the input side thereof and a D/A (digital-to-analog) converter at the output side thereof are not shown but are understood to be included.

0008Figures 9A to 9C illustrate frequency vs. amplitude characteristics of the Y/C separating circuits shown in Figures 8A to 8C, respectively.

0009In Figure 9A, a bold solid curve represents the pass band characteristic of the low pass filter 2Y and a dashed curve represents the pass band characteristic of the bandpass filter 2C. In Figure 8A, the low pass filter 2Y can be replaced by a subcarrier trap. In this case, the pass band characteristic is indicated as both bold and fine solid curves in Figure 9A.

0010The vertical correlation Y/C separating circuit of Figure 8B comprises a known comb filter. The pass band characteristic of this comb filter relative to the luminance signal Y_V is made, as shown by a solid curve in Figure 9B, to have a maximum degree of attenuation at a subcarrier frequency fsc and at respective points spaced apart therefrom by distances which are integral multiples of the horizontal frequency f_H, and a minimum degree of attenuation at each of intermediate points between these points, that is at each of the points spaced apart from the subcarrier frequency fsc by a distance equal to an odd number times 1/2 of the horizontal frequency f_H, that is (2n + 1) f_H/2. On the other hand, the pass band characteristic thereof relative to the chroma signal C_V is made, as shown by a dashed curve in Figure 9B, to have a minimum degree of attenuation at the subcarrier frequency fsc and respective points spaced apart therefrom by distances which are integral multiples of the horizontal frequency f_H, and a maximum degree of attenuation at each of the points spaced apart from the subcarrier frequency fsc by a distance equal to an odd number times 1/2 of the horizontal frequency f_H, that is (2n + 1) f_H/2.

0011The reason for this is that, by virtue of the known technique of frequency interleaving, as shown by dashed lines in Figure 10A, the spectral components of the chroma signal C are located between the spectral components of the luminance signal Y as shown by solid lines in the same figure.

0012The frame correlation Y/C separating circuit of Figure 8C comprises, as mentioned above, a known comb filter. The pass band characteristic of this comb filter relative to the luminance signal Y_F is made, as shown by a solid curve in Figure 9C, to have a maximum degree of attenuation at the subcarrier frequency fsc and respective points spaced apart therefrom by distances which are integral multiples of the frame frequency f_F (= f_V/2), and a minimum degree of attenuation at each of the intermediate points between these points. that is at points spaced apart from the subcarrier frequency fsc by distances equal to an odd number times 1/2 of the frame frequency f_F, that is (2n + 1) f_F/2. On the other hand, the pass band characteristic thereof relative to the chroma signal C_F is made, as shown by a dashed line in Figure 9C, to have a minimum degree of attenuation at the subcarrier frequency fsc and respective points spaced apart therefrom by distances which are integral multiples of the frame frequency f_F, and a maximum degree of attenuation at respective points spaced apart from the subcarrier frequency fsc by distances equal to an odd number times 1/2 of the frame frequency f_F, that is (2n + 1) f_F/2.

0013The reason for this will be understood from the following. As shown in Figure 10B, which is a partially enlarged view of Figure 10B, by virtue of the know technique of frequency interleaving, a side band wave (shown by an open circle) of the vertical frequency f_V accompanied by an odd higher harmonic wave of the horizontal frequency f_H and a side band wave (shown by a solid circle) of the vertical frequency f_V accompanied by an even higher harmonic wave are spaced apart from each other by a distance equal to the frame frequency f_F = f_V/2. Then, the subcarrier frequency fsc and the side band wave of the vertical frequency f_V accompanied thereby are located between the frequency intervals of the frame frequency f_F.

0014The above described previously proposed Y/C separating apparatuses, individually utilising various correlations, cause the quality of the reproduced picture to deteriorate at places where no correlation exists.

0015When horizontal correlation is utilised, the deterioration of picture quality, such as the deterioration of a frequency characteristic and the occurrence of crosstalk, occurs on the picture at right hand and left hand side edges of longitudinal stripes as shown in Figure 11A of the accompanying drawings when the levels of the luminance signal Y and the chroma signal C change abruptly in the horizontal direction.

0016When vertical correlation is utilised, the deterioration of picture quality, such as the occurrence of crosstalk and the appearance of dots of the subcarrier, occurs on the picture at the top and bottom edges of horizontal stripes as shown in Figure 11B of the accompanying drawings when the levels of the luminance signal Y and the chroma signal C change abruptly in the vertical direction.

0017When frame correlation is utilised, as shown in Figure 11C1 to 11C3 of the accompanying drawings, crosstalk occurs in part or wholly in peripheral edges of the picture related to the direction in which a figure in the picture is moved in the directions shown by arrows. Also, the quality of the picture is considerably deteriorated, such as by way of multiple-line interference or the like, when the peripheral edge of the figure is doubled or tripled.

0018In order to solve such problems, consideration might be given to switching the separated outputs in response to the amount of movement of the picture element at a proper timing. In this case, the signal processing circuit or apparatus would need a moving picture element detecting section which would cause the apparatus to be large in size and complicated.

0019According to one aspect of the present invention there is provided a video signal processing circuit for separating luminance and chrominance component signals from a video signal, said video signal processing circuit comprising:    a first component signal separating means for separating the luminance and chrominance component signals from the video signal using horizontal correlation of the video signal;    a second component signal separating means for separating the luminance and chrominance component signals from the video signal using vertical correlation of the video signal;    a third component signal separating means for separating the luminance and chrominance component signals from the video signal using frame correlation of the video signal; characterised by    intermediate value selecting means for selecting for output the luminance component signal having an intermediate value from among the three luminance component signals each separated using either horizontal, vertical or frame correlation of the video signal, and for selecting for output the chrominance component signal having an intermediate value from among the three chrominance component signals each separated using either horizontal, vertical or frame correlation of the video signal.

0020In this way, a changing video signal can be processed by correlation in a proper direction without detecting a moving image of the displayed picture, so that the quality of the reproduced picture can be improved.

0021Other aspects of the present invention are defined in claims 9 and 12.

0022Preferred embodiments of this invention described in detail hereinbelow provide a video signal luminance and chrominance signal separating apparatus which can improve the quality of a reproduced picture without requiring a moving picture element detecting section.

0023The invention will now be further described, by way of illustrative and non-limiting example, with reference to the accompanying drawings, in which: <ul id="ul0001" list-style="none"><li>Figure 1 is a block diagram of a video signal processing apparatus or circuit embodying the invention which is applied to Y/C separation;</li><li>Figures 2 and 3 are block diagrams shown alternative implementations of intermediate value selecting circuits of the embodiment shown in Figure 1;</li><li>Figure 4 is a block diagram of another embodiment of the present invention which is applied to Y/C separation;</li><li>Figure 5 is a block diagram of intermediate value selecting circuits of the embodiment shown in Figure 4;</li><li>Figure 6 and Figures 7A and 7B are block diagrams of respective further embodiments in which the present invention is applied to noise elimination;</li><li>Figures 8A to 8C are block diagrams of respective previously proposed Y/C separating circuits;</li><li>Figures 9A to 9C are graphs showing frequency vs. amplitude characteristics of the Y/C separating circuits shown in Figures 8A to 8C, respectively;</li><li>Figures 10A and 10B are spectral diagrams of a video signal; and</li><li>Figures 11A to 11C3 are respective conceptual diagrams showing pictures reproduced in the case of the previously proposed Y/C separating circuits.</li></ul>

0024A signal processing apparatus embodying the present invention will now be described with reference to Figures 1 and 2, in which this embodiment is applied to the process of Y/C separation.

0025Figure 1 illustrates the circuit arrangement of this embodiment. In Figure 1, parts corresponding to like parts of Figure 8A to 8C are designated by the same references and are not further described.

0026The apparatus shown in Figure 1 comprises a horizontal correlation Y/C separating circuit H Corr, a vertical correlation Y/C separating circuit V Corr, and a frame correlation Y/C separating circuit F Corr, which are constructed as shown in Figures 8A, 8B and 8C, respectively. A video signal applied to an input terminal 11 is supplied in common to the Y/C separating circuits H Corr, V Corr and F Corr. Further, the apparatus shown in Figure 1 comprises intermediate value selecting circuits 12Y and 12C.

0027The intermediate value selecting circuit 12Y is supplied with output signals Y_H, Y_V and Y_F of the low pass filter 2Y, the adder 5Y and the adder 8Y, respectively. The intermediate value selecting circuit 12C is supplied with output signals C_H, C_V and C_F of the low pass filter 2C, the subtracter 5C and the subtracter 8C, respectively.

0028Figure 2 illustrates an example of a circuit arrangement that can be employed for each of the intermediate value selecting circuits 12Y and 12C. The appropriate output signals of the Y/C separating circuits H Corr, V Corr and F Corr of Figure 1 are received at input terminals 21H, 21V, and 21F, respectively. First, second and third maximum value selecting circuits 22, 23 and 24, respectively, are connected such that an input signal from the input terminal 21H is supplied to the third and first maximum value selecting circuits 24 and 22, an input signal from the input terminal 21V is supplied to the first and second maximum value selecting circuits 22 and 23, and an input signal from the input terminal 21F is supplied to the second and third maximum value selecting circuits 23 and 24. Outputs A, B, C of the first to third maximum value selecting circuits 22 to 24, respectively, are all supplied to a minimum value selecting circuit 25 and an output from the minimum value selecting circuit 25 is delivered to a terminal 13.

0029The operation of the intermediate value selecting circuit of Figure 2 will be now described for the case in which the circuit is the intermediate value selecting circuit 12Y.

0030Assume that the amplitudes or levels of the luminance signals Y_H, Y_V and Y_F supplied from the Y/C separating circuits H Corr, V Corr and F Corr of Figure 1 to the respective input terminals 21H, 21V and 21F of the intermediate value selecting circuit of Figure 2 satisfy the condition (amplitude or level relationship) that, for example, Y_H > Y_V > Y_F.

0031The luminance signals Y_H and Y_V are supplied to the first maximum value selecting circuit 22. Since the luminance signal Y_H has an amplitude larger than that of the luminance signal Y_V, the luminance signal Y_H appears at the output A of the circuit 22. The second maximum value selecting circuit 23 is supplied with the luminance signals Y_V and Y_F. Since the luminance signal Y_V has an amplitude larger than that of the luminance signal Y_F, the luminance signal Y_V appears at the output B of the circuit 23. Further, the third maximum value selecting circuit 24 is supplied with the luminance signals Y_F and Y_H. Since the luminance signal Y_H has an amplitude larger than that of the luminance signal Y_F, the luminance signal Y_H appears at the output C of the circuit 24.

0032The minimum value selecting circuit 25 is supplied with the outputs A, B and C, that is the luminance signals Y_H, Y_V and Y_H from the maximum value selecting circuits 22 to 24, and generates the luminance signal Y_V which has the smallest amplitude. Since the condition that Y_H > Y_V > Y_F is satisfied, the intermediate value Y_V is thus selected by the circuit arrangement of Figure 2.

0033Table 1 below shows the outputs produced by the intermediate value selecting circuit of Figure 2 in the case in which the condition (amplitude or level relationship) relating the three luminance signals Y_H, Y_V and Y_F is as set forth above and in other cases in which the condition is different from that set forth above. For all conditions, the intermediate value of the three luminance signals Y_H, Y_V and Y_F is selected by the intermediate value selecting circuit. <tables id="tabl0001" num="0001"><img file="EP0246878B1_D0001.tif" /></tables>

0034If the amplitudes or levels of two input signals applied to the maximum value selecting circuits 22 to 24 are equal to each other, either one of them may be selected. In this case, the intermediate value selecting circuit of Figure 2 never selects a third input signal and the relationships indicated in Table 1 are established.

0035The intermediate value selecting circuit 12C, which is also illustrated in Figure 2, is operated relative to the chroma signals C_H, C_V and C_F in the same way as described above for the circuit 12Y.

0036The operation of the embodiment shown in Figure 1 will now be described. The picture shown in Figure 11A has correlation in the vertical direction, that is the displayed image is relatively constant in the vertical direction. Conversely, the picture shown in Figure 11B has correlation in the horizontal direction. Further, correlations in the frame (time) directions appear in the still pictures shown in Figures 11C1 to 11C3, that is some part of the picture remains relatively constant from frame to frame.

0037When the picture has a correlation in any of the horizontal, vertical and time directions, there is a large probability that, of the outputs from the Y/C separating circuits H Corr, V Corr and F Corr of Figure 1, the output corresponding to the direction having correlation will become an intermediate value while the output corresponding to the direction having no correlation becomes either larger or smaller than the output corresponding to the correlation. For this reason, according to the embodiment of Figure 1, the intermediate value selecting circuit 12Y selects the luminance signal Y corresponding to the direction in which the picture has correlation. At the same time, the other intermediate value selecting circuit 12C selects the chroma signal C corresponding to the direction in which the picture has correlation. Thus, optimum Y/C separation for various pictures which are changing at any time is carried out, so that the quality of the reproduced picture is improved.

0038The intermediate value selecting circuits 12Y or 12C can alternatively be constructed, as shown in Figure 3, by replacing the maximum value selecting circuits 22, 23 and 24 of Figure 2 with minimum value selecting circuits 26, 27 and 28 and by replacing the minimum value selecting circuit 25 of Figure 2 with a maximum value selecting circuit 29. The circuits 26, 27 and 28 produce outputs D, E and F, respectively.

0039For different amplitude or level relationships of the three luminance signals Y_H, Y_V and Y_F, the intermediate value selecting circuit of Figure 3, for the case in which the circuit is the intermediate value relating circuit 12Y, operates in accordance with Table 2 below. For the case in which the intermediate value selecting circuit of Figure 3 is the intermediate value selecting circuit 12C, it is operated in the same way relative to the chroma signals C_H, C_V and C_F. <tables id="tabl0002" num="0002"><img file="EP0246878B1_D0002.tif" /></tables>

0040If the amplitudes or levels of two input signals applied to the minimum value selecting circuits 26 to 28 are equal to each other, the intermediate value selecting circuit of Figure 3 never selects a third input and the relationships indicated in Table 2 are established.

0041Another signal processing apparatus embodying the present invention will now be described with reference to Figures 4 and 5, in which this embodiment is applied to Y/C separation.

0042Figure 4 illustrates the circuit arrangement of this embodiment. In Figure 4, parts corresponding to like parts of Figure 1 are identified by the same references and are not further described.

0043The apparatus shown in Figure 4 comprises a transversal filter 31 including four unit delay lines 32₁, 32₂, 32₃ and 32₄ connected in series with one another and a weighting adding circuit 33. The input side of the first unit delay line 32₁, each of the junctions between adjacent ones of the first to fourth unit delay lines 32₁ to 32₄ and the output side of the fourth unit delay line 32₄ are connected to the weighting adding circuit 33. The transversal filter 31 is equivalent to the horizontal correlation Y/C separating circuit H Corr which is formed of the low pass filter 2Y and the bandpass filter 2C as shown in Figure 1, and is operated at a clock frequency of, for example, 4 fsc. Each of the unit delay lines 32₁ to 32₄ has a delay time D.

0044The output from the fourth unit delay line 32₄ of the transversal filter 31 is supplied to a first memory 34. An output from the first memory 34 is supplied in common to an adder 35Y and a subtracter 35C, and an output developed at the junction between the second and third unit delay lines 32₂ and 32₃ is supplied in common to the adder 35Y and the subtracter 35C. The delay time of the first memory 34 is selected to be 1H-2D. The memory 34 and the third and fourth unit delay lines 32₃ and 32₄ of the transversal filter 31 constitute a line memory whose delay time is selected to be 1H. The line memory, the adder 35Y and the subtracter 35C constitute a vertical correlation Y/C separating circuit V Corr.

0045The output from the first memory 34 is supplied to a second memory 37 and an output of the second memory 37 is supplied in common to a second adder 38Y and a second subtracter 38C. An output developed at the junction between the second and third unit delay lines 32₂ and 32₃ of the transversal filter 31 is supplied in common to the adder 38Y and the subtracter 38C. The second memory 37 has a delay time of 1F-1H, where 1F = one frame period. The second memory 37, the first memory 34 and the third and fourth unit delay lines 32₃ and 32₄ of the transversal filter 31 constitute a frame memory of which the delay time is selected to be 1F (one frame period). This frame memory, the second adder 38Y and the second subtracter 38C constitute a frame correlation Y/C separating circuit F Corr.

0046The intermediate value selecting circuit 12Y is supplied with the outputs Y_H, Y_V and Y_F of the transversal filter 31, the adder 35Y and the adder 38Y, respectively. The other intermediate value selecting circuit 12C is supplied with the outputs C_H, C_V and C_F of the transversal filter 31, the subtracter 35C and the subtracter 38C, respectively.

0047Figure 5 illustrates an example of a circuit arrangement that can be employed for each of the intermediate value selecting circuits 12Y and 12C according to this embodiment. Input signals applied to input terminals 21H, 21V and 21F are supplied in common to a maximum value selecting circuit 41, a minimum value selecting circuit 42 and an adder 43. Outputs G and H from the maximum value selecting circuit 41 and the minimum value selecting circuit 42, respectively, are supplied to a second adder 44. An output from the first adder 43 and an output J from the second adder 44 each are supplied to the subtracter 45 in which the output J is subtracted from the output of the adder 43.

0048In accordance with six amplitude or level relationships between the three luminance signals Y_H, Y_V and Y_F, for the case in which the intermediate value selecting circuit of Figure 5 is the intermediate value selecting circuit 12Y, the circuit is operated in accordance with Table 3 below. The intermediate value selecting circuit is operated in the same way relative to the chroma signals C_H, C_V and C_F for the case in which the circuit is the circuit 12C. <tables id="tabl0003" num="0003"><img file="EP0246878B1_D0003.tif" /></tables>

0049Even when two out of the three input signals are equal to each other in level, the relationships shown in Table 3 are established.

0050The intermediate value selecting circuit shown in Figure 5, together with the horizontal correlation and frame correlation Y/C separating circuits H Corr and F Corr of Figure 4, are formed of digital circuits. This is also true for the intermediate value selecting circuits which are constructed fundamentally as shown in Figures 2 and 3.

0051In this way, the embodiment of Figure 4 is operated in the same way as that of the embodiment of Figure 1, so that for a picture changing at any time, the luminance signal Y and the chroma signal C in the direction in which the picture has correlation are selected to thereby carry out optimum Y/C separation, thus improving the quality of the reproduced picture.

0052A further signal processing apparatus embodying the present invention will now be described with reference to Figure 6, in which this embodiment is applied to a noise eliminating circuit. A noise eliminating circuit 50 comprises horizontal, vertical and frame correlation detecting circuits 51, 52 and 53 and an intermediate value selecting circuit 54 which is supplied with outputs from the correlation detecting circuits 51 to 53. The correlation detecting circuits 51 to 53 correspond to the signal separating circuits described above and generate signals of the same kind as that of the aforementioned luminance signals Y_H, Y_V and Y_F. Further, the intermediate value selecting circuit 54 is constructed as shown in Figure 2, Figure 3 or Figure 5.

0053In the embodiment shown in Figure 1 or Figure 4, for one of the luminance signal Y and the chroma signal C, the other signal to be separated may be noise. Further, since the video signal has correlation and the noise has no correlation, it will easily be understood that the noise eliminating circuit of this embodiment is operated in the same way as that of the Y/C separating circuit shown in Figure 1 or Figure 4 to thereby separate the video signal and the noise. In other words, it will be easily understood that noise can be eliminated from the video signal.

0054As shown in Figure 7A, a noise eliminating apparatus of a recursive type may be made up of the noise eliminating circuit 50 of the embodiment shown in Figure 6 and a subtracter 55.

0055Further, as shown in Figure 7B, a first subtracter 56 may be connected to the input side of the noise eliminating circuit 50 and a second subtracter 57 may be connected to the output side of the circuit 50. The second subtracter 57 subtracts the output signal (which hardly contains any noise) of the noise eliminating circuit 50 from the input signal (which does contain the noise) to the noise eliminating circuit 50 to thereby separate the noise component from the video signal. Then, the separated noise component, which is obtained from the output of the subtracter 57, is subtracted by the subtracter 56 connected to the input side of the noise eliminating circuit 50 so as thereby to eliminate the noise contained in the input signal applied to the noise eliminating circuit 50. Thus, the signal-to-noise (S/N) ratio of the output signal can be improved even more.

0056The noise eliminating apparatus to which the present invention can be applied is not limited to the above-described embodiment: many modifications and variations could be effected by those skilled in the art.

0057According to the embodiments of the invention as set forth above in detail, video signal correlations in a plurality of ways, senses or directions are detected and the intermediate value of these detected correlation values is selected, so that, without the necesssity of detecting a moving picture element, the correlation of the optimum way, sense or direction can be utilised for the picture changing at any time. According, it is possible to obtain a signal separating apparatus which can improve the quality of the reproduced picture.