Motion signal detecting circuit

Abstract: A motion signal detecting circuit is adapted to an image reproducing system having a frequency unfolding circuit for generating an unfolded luminance signal by unfolding a high frequency component folded previously into low-frequency components back into the original frequency band in order to reproduce a full bandwidth image signal recorded on a recording medium having a limited bandwidth. The detecting circuit comprises a prefilter (100) for eliminating the folding carrier contained in the unfolded luminance signal and sidebands thereof and a comb filter (110) for detecting a motion signal which is the difference component between frames in the unfolded luminance signal by filtering the output of the prefilter (100).

Description: The present invention relates to motion signal detecting circuits. It is known for a standard television system, such as an NTSC or a PAL system, which represents images, to process a television signal adaptively in accordance with the degree of motion of the signal. This adaptive processing of the signal may result in quasi-motion picture regions between image regions being processed in a still picture signal processing method, and other image regions being processed in a motion picture signal processing method. If differences in the processing methods are perceived, and the different regions and the transition between them are discerned by a viewer, image quality is degraded. For example, for the purpose of separating chrominance and luminance components from a composite video signal, a frame comb filter or a line comb filter may be used. As long as there is no change in the image signal at frame time intervals, when separating chrominance and luminance components from the composite video signal using the frame comb filter, the luminance and chrominance components can be completely separated. If the scene changes, however, over the frame time intervals, then some colour information will be present in the separated luminance component and some brightness information will be present in the chrominance component. A line comb filter also used to separate the luminance and chrominance components from the composite video signal does not produce significantly degraded component signals in the presence of image motion. However, the line comb filter reduces the vertical resolution of the reproduced image in comparison with the frame comb filter. In addition, in locations where a vertical transition occurs, an image processed by the line comb filter may be degraded due to both colour information introduced into the luminance component, producing an image artifact known as hanging dots, and brightness information introduced into the chrominance, producing incorrect colours in the neighbourhood of the transition. Therefore the television signal is adaptively processed by detecting the presence or absence of image motion. In the regions in which the image is stationary, the frame comb filter is used, and in the regions in which the image is moving, the line comb filter is used. Another example of such adaptive processing is an adaptive double-scanned, non-interlaced scan converter. In such a converter, interstitial lines are displayed between lines of the current field. However, the interstitial lines may be those transferred from the preceding field, in the presence of image changes producing visible artifacts such as serrated contours. The interstitial lines may also be interpolated from lines within the current field, but the vertical resolution is reduced and line flicker may occur. In regions in which image changes are detected, intrafield interpolated interstitial lines are displayed and field-delayed interstitial lines are displayed in other ways. Yet another example is an adaptive peaking circuitry in which regions having relatively high noise are processed with a relatively low peaking factor and regions having relatively low noise are processed with a relatively high peaking factor. In all of the above examples, the television signals are processed adaptively in response to the values of estimated parameters of the image. The parameters are motion in the case of luminance/chrominance separation and double scanning non-interlace conversion, and a relative level of noise in the case of peaking. Differently processed regions, and noticeable boundaries between regions where the parameter is present and those where it is absent are undesirable artifacts introduced by the above types of adaptive processing types. U. S. Patent US-A-5113262 on the invention entitled "An improved video signal recording system" filed on August 17, 1990 by Samsung Electronics Co. Limited, describes a recording system for recording and reproducing a full bandwidth video signal on and from a recording medium having a limited bandwidth by folding the high frequency component of a luminance signal into the low frequency component of the luminance signal. In the U.S. Patent US-A-5113262, a motion signal which represents a moving image is recorded together with the folded luminance signal and the chrominance signal on the recording medium. The motion signal is used to control the transition between regions of the full bandwidth luminance signal which is unfolded into the original frequency bands when reproducing. That is, in the above invention, the high frequency component of the luminance signal is folded into the low frequency component of the luminance signal in recording. At this time, the high frequency component of the luminance signal is modulated by a folding carrier, so that the folded luminance signal has a phase difference of 180 degrees between frames, between scanning lines, and between pixels. Accordingly, in reproducing, the high frequency component folded into the low frequency component of the folded luminance signal is demodulated by the unfolding carrier having the same phase and frequency as those of the folding carrier, so that the high frequency component of the luminance signal is unfolded to the original frequency band. However, the folding carrier and the sideband thereof will be present in the unfolded luminance signal. The resultant luminance signal unfolded by the folding carrier and the sidebands thereof has a phase difference of 180 degrees between frames. As a result, the conventional motion signal detecting circuit for detecting the level difference of pixels between frames as the motion signal, has difficulty in detecting accurately the motion signal from the unfolded luminance signal due to the phase off-set between frames. U.S. Patent US-A-4,953,032 discloses in its reference to JP-A-62-111586 a motion adaptive signal generating circuit comprising a first field memory connected to an input terminal, a second field memory connected to the first field memory, and a subtraction circuit connected to the second field memory and to the input terminal. In operation, an input signal supplied to the input terminal appears one frame later at the output of the second field memory. The thus delayed signal and a subsequent input signal are supplied to the substraction circuit to generate an interframe difference signal. U.S. Patent US-A-4,831,463 discloses a folding and an unfolding circuit. Preferred embodiments of the present invention aim to provide systems for smoothing or spreading transitions between image regions included in television signals to be transmitted which are processed in a still picture signal processing method and a motion picture signal processing method, and particularly to provide a circuit for accurately detecting a motion signal which represents a moving image, from an unfolded luminance signal, so as to control the transitions between image regions of a frequency-unfolded image signal. According to a first aspect of the present invention, there is provided a motion signal detecting circuit adapted to a video signal reproducing system having a frequency-unfolding circuit for generating an unfolded luminance signal by unfolding a high frequency component folded into a low frequency component into an original frequency band, in order to reproduce an image signal having a full bandwidth from a recorded image signal in which the high frequency component is folded into the low frequency component and recorded on a recording medium having a limited bandwidth, said circuit comprising: an input line for inputting said unfolded luminance signal from signal unfolding means; prefilter means for eliminating a folding carrier contained in said unfolded luminance signal and sidebands thereof, said prefilter means comprising a horizontal comb filter, a vertical comb filter and means for varying the output from said horizontal comb filter and said vertical comb filter according to the detection or horizontal and vertical edges in the unfolded luminance signal thereby to cancel horizontal and vertical carriers; comb filter means for detecting a motion signal which is the difference component between frames of the unfolded luminance signal produced by subtracting a frame delayed signal from an undelayed signal by filtering the output of said prefilter means; and a control signal spreader connected to said comb filter means for temporally, vertically and horizontally spreading the detected motion signal, thereby removing undesirable artifacts generated due to the distinct boundaries between image regions. The invention extends to a video signal recording and/or reproducing system provided with such a motion signal detecting circuit. 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: Figure 1 is a block diagram of one example of a circuit to control transitions between image regions included in an unfolded luminance signal to be transmitted in a video reproducing apparatus to which embodiments of the present invention may be adapted; Figure 2 is a block diagram of a preferred embodiment of a motion signal detecting circuit according to the present invention; Figure 3 is a detailed circuit diagram of one example of a prefilter of the motion signal detecting circuit of Figure 2; and Figure 4 is a detailed circuit diagram of one example of a signal spreader of the motion signal detecting circuit of Figure 2. In Figure 1, an input line 5 is connected to a frequency unfolding circuit (not shown) for receiving an unfolded luminance signal. The input line 5 is connected to respective input terminals of a temporal low pass filter 10, an adaptive spatial low pass filter 20 and a motion signal detecting circuit 40. An output terminal of the temporal low pass filter 10 is connected to a first input terminal of a soft switch 30. An output terminal of the adaptive spatial low pass filter 20 is connected to a second input terminal of the soft switch 30. An output terminal of the motion signal detecting circuit 40 is connected to a control terminal of the soft switch 30. An output terminal of the soft switch 30 is coupled with an adaptive peaking circuit (not shown) through an output line 15. In operation of the circuit as shown in Figure 1, when the level of motion is low, the unfolded luminance signal Luf input through the input line 5 lies at temporal low frequencies (close to temporal direct current component). On the contrary, if the level of motion is high, the unfolded luminance signal Luf input through the input line 5 lies at spatial low frequencies. Accordingly, in the presence of a high level of motion, the image may overlap temporally with the unfolded luminance signal. In the presence of a low level of motion, the image may overlap spatially with the unfolded luminance signal Luf. The temporal low pass filter 10 separates a temporally derived luminance signal Lt from the unfolded luminance signal Luf by temporally filtering the unfolded luminance signal Luf. The adaptive spatial low pass filter 20 separates a spatially derived luminance signal Ls from the unfolded luminance signal Luf by adaptively and spatially filtering the unfolded luminance signal Luf. The motion signal detecting circuit 40 generates a motion control signal M* by detecting the motion level of the image from the unfolded luminance signal Luf. The soft switch 30 controls the proportions of the unfolded luminance signals Lt and Ls which are respectively separated temporally and spatially from the unfolded luminance signal Luf, in accordance with the motion control signal M* fed from the motion signal detecting circuit 40. When a level of the motion control signal M* is zero or nearly zero, the output of the soft switch 30 is the same as that of the temporal low pass filter 10. As the level of the motion control signal M* gradually increases, the proportion of the input from the temporal low pass filter 10 decreases and the proportion of the input from the adaptive spatial low pass filter 20 increases. When the level of the motion control signal M* is relatively high, the output of the soft switch 30 is the same as that of the adaptive spatial low pass filter 20. The motion signal detecting circuit shown in block diagram form in Figure 2 comprises an input line 105 connected to the input line 5 shown in Figure 1 and an input terminal of a prefilter 100, respectively. An output terminal of the prefilter 100 is connected to an input terminal of a frame delay device 111 and a second input terminal of a subtracter 112. An output terminal of the frame delay device 111 is coupled with a first input terminal of the subtracter 112. An output terminal of the subtracter 112 is connected to an input terminal of a control signal spreader 120. An output terminal of the control signal spreader 120 is connected to the control terminal of the soft switch 30 shown in Figure 1 through an output line 115. In operation of the circuit as shown in Figure 2, the prefilter 100 eliminates the folding carrier and sidebands contained in the unfolded luminance signal Luf by filtering the unfolded luminance signal Luf received through input line 105. An example of a circuit diagram of the prefilter 100 is described in U.S. Patent Application No. 07/562,907 on the invention entitled "An improved apparatus for eliminating the folding carrier and sidebands from the unfolded video signal" filed on August 6, 1990 by Ko et al. This patent application corresponds to Patent Application GB 91 09732.9 (Publication No. GB 2 246 926 A) filed 7 May 1991, a copy of the specification of which is filed with the present European Patent Application. An example of such a circuit is shown in Figure 3. Referring to Figure 3, equal amplitudes of the unfolded luminance signal on input line 310 are passed through a horizontal comb filter 311 and a vertical comb filter 312, and, unless affected by multipliers 314 and 319, equal amplitudes of the two signals are combined in adder 316 and the sum is available at an output 317. The horizontal comb filter 311 is designed to cancel the sidebands of the folding carrier at or about 2.5 MHz, and the vertical comb filter 312 is designed to remove the line frequency of 15,734 Hz. However, the cancellations of the carrier and sidebands may be incomplete, since they are affected by the brightness variations in the picture being scanned. Cancellation of the horizontal and vertical carriers on the output line 317 is achieved by the operation of a vertical scan edge detector 321 and a horizontal scan edge detector 322. When a "vertical" edge or discontinuity is detected during a vertical scan, a signal over line 323 and through subtracter 324 to a look-up table 327 causes a signal having a value of K over line 328 from look-up table 327 to increase the proportion of the output at 317 from the horizontal comb filter 311, whose output is not affected by the vertical edge, and decrease the proportion from the vertical comb filter 312. Likewise, when a "horizontal" edge is detected during a horizontal scan, a signal over line 325 and through subtracter 324 causes a signal having a value of K over line 328 both to increase the proportion of the output at 317 from the vertical comb filter 312, whose output is not affected by the horizontal edge, and decrease the proportion from the horizontal comb filter 311. In each case, the cancellation of carrier components is improved by increasing the output proportion from the comb filter whose output is not affected by the brightness edge encountered. Referring again to Figure 2, the frame delay device 111 delays by a time corresponding to one frame the unfolded luminance signal from which the folding carrier and sidebands are eliminated, and supplies it to the first input terminal of the subtracter 112. The subtracter 112 subtracts the output of the frame delay device 111 from the output of the prefilter 100, generates the difference signal between frames of the unfolded luminance signal, and supplies it to the control signal spreader 120 as the motion signal. The frame delay device 111 and the subtracter 112 constitute a combfilter. The control signal spreader 120 spreads the motion signal temporally, vertically, and horizontally, and supplies the spread signal to the control terminal of the soft switch 30 shown in Figure 1 as the motion control signal. The control signal spreader 120 may be constructed in the same manner as "The control signal spreader" described in U.S. Patent Application serial No. 07/531,057 on the invention entitled "A control signal spreader", filed on May 31 1990, by Ko et al. This patent application corresponds to Patent Application GB 91 08683.5 (Publication No. GB 2 245 448 A) filed 23 April 1991, a copy of the specification of which is filed with the present European Patent Application. An example of such a circuit is shown in Figure 4. In Figure 4, a horizontal widener 402 has an input terminal 414 connected to a series of six clock delays 416 through 426. The output of an OR gate 428 is connected to an output terminal 430, and seven inputs of the OR gate 428 are respectively connected to the input terminal 414 and the ends of the clock delays 416-426 that are remote from the input terminal 414. Any motion signal having an amplitude of 1 indicating the presence of a phenomenon such as motion will be repeated six times at the output terminal 430. The vertical widener 404 comprises four 1-H delays 432, 434, 436 and 438 connected in series to an input terminal 431, and an OR gate 440 of which the output is connected to an output terminal 442 and five inputs are respectively connected to the input terminal 431 and the ends of the 1-H delays 432-438 that are remote from the input terminal 431. Any line of motion signals applied to the input terminal 431 will be repeated four times at the output terminal 442. Motion signals having the logic value of 0 will pass through the horizontal widener circuit 402 and vertical widener circuit 404 without any delay and the logic value of 1, indicating the presence of a phenomenon such as motion, is repeated so as to form a rectangle of logic 1's that is 7 clock cycles wide and 5 lines high. The line signal spreader 406 is coupled to the output terminal 442 of the vertical widener 404 and functions to produce a ramp of increasing signal values along a line that increases from the value of 0 to a maximum value, such as 7, during the first 6 motion signal periods referred to. It then holds the maximum value as long as 1's appear at the terminal 444, and when they cease, it produces a ramp of decreasing signal values along the lines over a period of 6 clock cycles. This is done in the same way along the line whenever the motion signal assumes the logic value of 1, and along the 4 succeeding lines so that there are 5 identical lines. For performing the line signal spreading function just described, a multiplexer (MUX) 446 has an output 448, an input labelled 0, an input labelled 1 and a switching control input 450 to which logical values of 0 and 1 may be applied. When a logic 0 is applied to the control input 450, the output 448 is connected to the input labelled 0, and when a logic 1 is applied to the input 450, the output 448 is connected to the input labelled 1. A one clock delay element 452 and a generator 454 that performs the function f(x) = x-1 are connected in series between the output 448 and the input labelled 0. The generator 454 cannot go below a value of 0. Thus, when no motion is detected and a logic 0 is at input terminal 400, logic 0's are passed through the widener circuits 402 and 404 to terminal 444, and the output 448 of the MUX 446 will be 0. If by some chance the signal at the output 448 of the MUX 446 should be other than 0, it will be reduced to 0 in at most 4 clock cycles by the operation of the generator 454. As will be seen, the MUX 446 will produce the ramp of decreasing values previously referred to. The ramp of increasing value, previously referred to, is formed by a MUX 456. It has an output 458 that is connected to the input of MUX 446 that is labelled 1, an input labelled 0, an input labelled 1 and a switching control input 460 to which logic values of 0 or 1 may be applied. As in the MUX 446, a logic 1 at the control input 460 connects the output 458 to the input labelled 1, and a logic 0 at the control 460 connects the output 458 to the input labelled 0. A one clock delay 462 and a generator 464 that performs the function f(x) = x + 1 are connected in series between the output 458 and the input labelled 1. The generator 464 cannot produce a signal value above some selected maximum, such as 7. The input of the MUX 456 that is labelled 0 is coupled to the output 448 of the MUX 446. For making the signal values for corresponding pixels along the scan lines available, the vertical signal spreader 408 comprises four 1-H delays 466, 468, 470 and 472 and an adder 474 for adding the output 448 and the outputs of the four 1-H delays 466 through 472. Here, the motion signal values at the output 448 and at the ends of the four 1-H delays 466 through 472 that are remote from the output 448 could be respectively weighted before they are combined in the means for combining them, that is, an adder 474. Also, a temporal spreader 410 is suitably composed of a low-pass filter. It provides gradual transitions between still and motion portions of a scene in the temporal domain. The output of the temporal spreader 410 is supplied to the control switch 30 of Figure 1 through an output line 412. Here, the output line 412 is identical with the output line 115 of Figure 2. In the above described embodiment of the present invention, it is possible to detect the motion signal from the unfolded luminance signal by utilizing a comb filter after removing the folding carrier and the sidebands thereof contained in the unfolded luminance signal by the prefilter. In addition, by spreading the detected motion signal temporally, vertically and horizontally by the control signal spreader and supplying the spread motion signal as the motion control signal, undesirable artifacts due to the distinct boundaries between image regions can be removed.

Claims: A motion signal detecting circuit adapted to a video signal reproducing system having a frequency-unfolding circuit for generating an unfolded luminance signal by unfolding a high frequency component folded into a low frequency component into an original frequency band, in order to reproduce an image signal having a full bandwidth from a recorded image signal in which the high frequency component is folded into the low frequency component and recorded on a recording medium having a limited bandwidth, said circuit comprising: an input line (105) for inputting said unfolded luminance signal from signal unfolding means; prefilter means (100) for eliminating a folding carrier contained in said unfolded luminance signal and sidebands thereof said prefilter means (100) comprising a horizontal comb filter (311), a vertical comb filter (312) and means (314, 316, 319, 329) for varying the output from said horizontal comb filter (311) and said vertical comb filter (312) according to the detection of horizontal and vertical edges in the unfolded luminance signal thereby to cancel horizontal and vertical carriers; comb filter means (110) for detecting a motion signal which is the difference component between frames of the unfolded luminance signal produced by subtracting a frame delayed signal from an undelayed signal by filtering the output of said prefilter means (100); and a control signal spreader (120) connected to said comb filter means (110) for temporally, vertically and horizontally spreading the detected motion signal, thereby removing undesirable artifacts generated due to the distinct boundaries between image regions. A video signal recording and/or reproducing system provided with a motion signal detecting circuit according to claim 1.

Inventors: KO JEONG-WAN, KO, JEONG-WAN
Applicants: SAMSUNG ELECTRONICS CO LTD, SAMSUNG ELECTRONICS CO., LTD.
Application year: 1991
Main classification: H04N9
IPC codes: H04N7, H04N9, H04N5