Luminance signal noise suppressor

Abstract: A luminance signal noise suppressor for suppressing noise of a video luminance signal ( a ) automatically in a television receiver or the like in response to possible large noise which is detected as a high voltage by detecting high frequency components of an input video luminance signal band ( a ), and a noise suppression circuit (5) is enabled or the correction quantity of a contour correction circuit (10) is decreased.

Description: BACKGROUND OF THE INVENTION The present invention relates to luminance signal noise suppressor for a television receiver, a video tape recorder, a television tuner and the like, and relates to those able to automatically suppress noise in video signals inputted with much noise in weak electric field receiving regions or zones. In recent years, as color television receivers become large in size, encountered is a problem of noise included in a video signal such that the noise is also more conspicuously viewable on their displays. Thus a luminance signal noise suppressor which suppresses noise in a video luminance signal for the purpose of displaying a picture image more clearly has been regarded as important particularly in a weak electric field zone. On the other hand, there are many strong electric field zones depending on broadcasting channel, and it is required for conventional receivers to put ON/OFF such a noise suppressor every time the receiving channel is selected, which gives rise to a problem of complexity in operation. An example of such conventional luminance signal noise suppressors will be described hereafter with reference to the drawings. Fig. 4 shows a block diagram of a conventional luminance signal noise suppressor. In Fig. 4, a noise suppression circuit 21 reduces noise in an input luminance signal a and outputs an output luminance signal f . A switch 22 is operated to enable or to disable the noise suppression circuit 21. The operation of a luminance signal noise suppressor, constructed as described above, will now be described. The input luminance signal a is input to the noise suppression circuit 21, which suppresses or eliminates noise in accordance with a state of the switch 22, or the input signal is otherwise output as the output luminance signal f . In above-described construction, however, switch 22 must be ON for a signal including much noise in the case of a weak electric field signal, and OFF each time for a signal including comparatively less noise in the case of a strong electric field signal, because detail information of a video signal is generally missing in the state where the noise suppression circuit 21 is ON. These operations are complicated and thus disadvantageous. EP-A-0 212 674 discloses a noise suppression circuit with gain control wherein, to suppress noise included in a video signal, the noise level is detected, by a noise level detecting circuit, which operates only within a blanking period. The noise level is suppressed by a gain control circuit in accordance with an output signal from the noise level detecting circuit. The gain control circuit is a voltage controlled variable gain amplifier, which is interposed between a limiter and a subtractor of an in-line noise suppressing circuit. A vertical correlation noise canceller is used in combination so that a gain control circuit, interposed between a limiter and a subtractor, is also controlled. The features of the invention are defined by Claim 1. It is an object of the invention to reduce correction quantity of the contour correction circuit, or to reduce the correction quantity zero automatically in the case of much noise, in a weak electric field, thereby suppressing noise emphasis, and to improve sharpness by increasing the correction quantity of the contour correction circuit in the case of sufficient high frequency components of an input video signal in the case of a strong electric field. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a block diagram showing a luminance signal noise suppressor; Fig. 2 is a block diagram showing an embodiment of a luminance signal noise suppressor according to the invention; Fig. 3 is a block diagram showing another embodiment of a luminance signal noise suppressor according to the invention; and Fig. 4 is a block diagram of a conventional luminance signal noise suppressor. DESCRIPTION OF THE PREFERRED EMBODIMENTS Fig. 1 is a block diagram showing a luminance signal noise suppressor. In Fig. 1, a high-pass filter circuit 1 extracts high frequency components including noise and detail information signals of an input luminance signal a , and outputs them as a high frequency luminance signal b . A full-wave rectification circuit 2 applies full-wave rectification to the high frequency luminance signal b and outputs a rectified high frequency luminance signal c . A sample-hole circuit 3 receives an input of noise detection pulse e , smoothes a rectified high frequency luminance signal c holds the smoothed voltage until receiving the input of a next noise detection pulse e and outputs it as a noise detection voltage d . A noise detection pulse generating circuit 4 shapes a waveform of a vertical synchronizing signal m so as to exclude or eliminate portions of video signal, character multiplexed signal and the like from the signal m, and outputs it as the detection pulse e . A numeral 5 denotes a noise suppression circuit. The operation of a luminance signal noise suppressor constructed as described above will be described hereafter with reference to Fig. 1. First, the input luminance signal a is inputted to the high-pass filter circuit 1 and outputted as a high frequency luminance signal b with the high frequency components separated, which is inputted to the full-wave rectification circuit 2. The high frequency luminance signal b is applied with full-wave rectification by means of the full-wave rectification circuit 2, thus obtaining the rectified output signal c . Then, the rectified signal c is inputted to the sample-hold circuit 3, the rectified signal c is smoothed in the period of the noise detection pulse e which is inputted from the noise detection pulse generating circuit 4, and the smoothed voltage is held at the same time as the pulse disappears, which is outputted as a noise detection voltage d . The noise detection voltage d is inputted to a noise suppression circuit 5 which is similar to that in the conventional example, and controls the noise suppression quantity for the input luminance signal a which is inputted to the noise suppression circuit 5. In other words, an automatic control can be made so that the noise suppression quantity is increased when the noise detection voltage d is high (much noise, and the suppression quantity is reduced or made to zero automatically in a case contrary to the above. As a result, a noise suppressed output luminance signal f is obtained. In the above, the noise detection pulse is produced during a vertical synchronizing period free from influences of an effective video signal, thereby enabling an accurate noise quantity detection. As described above, according to the present embodiment, it is possible to put a noise suppression circuit ON automatically in case a video signal including much noise is inputted in a weak electric field and the like so as to control the suppression quantity automatically by detecting high frequency components of a video signal with a high-pass filter circuit and rectifying these high frequency components in a full-wave rectification circuit, then sample-holding in a sample-hold circuit by a noise detection pulse, and controlling suppression quantity of a noise suppression circuit with a noise detection voltage obtained as the result of the foregoing. In the next place, a second embodiment of the present invention will be described with reference to the drawing. Fig. 2 is a block diagram of a luminance signal noise suppressor showing a second embodiment of the present invention. In Fig. 2, a numeral 1 denotes a high-pass filter circuit, 2 denotes a full-wave rectification circuit, 3 denotes a sample-hold circuit, and 4 denotes a noise detection pulse generating circuit, and these units are the same as those in the first embodiment. A contour correction circuit 6 functions to correct the contour of an input luminance signal a so as to increase the sharpness. In such correction in general, such processing that secondary differential components of an input luminance signal are obtained by using a filter or a delay line and added to an original signal with gain control is employed. Thus, there is such a drawback that the deeper the correction is applied the more the noise is emphasized. A high frequency component quantity detection circuit 7 is composed of a smoothing circuit and a switch circuit, and averages voltages of a rectified high frequency luminance signal c during the period when the noise detection pulse is not being inputted and outputs the result as a video high frequency component detection voltage ℓ. The operation of the luminance signal noise suppressor constructed as described above will be described hereafter with reference to Fig. 2. First, the process until the noise detection voltage d is obtained is similar to that of the first embodiment. In the present embodiment, the noise is prevented from being emphasized by inputting the noise detection voltage d to the contour correction circuit 6, and suppressing the correction quantity of the contour correction circuit automatically in the same manner as the first embodiment in case of much noise. Further, in the present embodiment, a high frequency component quantity detection circuit 7 is provided, and the rectified high frequency luminance signal c is smoothed during a period when the noise detection pulse e is not being inputted, in a word, a period of an effective video signal, thereby to detect the quantity of high frequency components included in the video luminance signal, and, in case the quantity of high frequency components during the effective video signal period is large and the noise detection voltage d is low (noises are less), the correction quantity of the contour correction circuit is increased on the contrary and contours of detail portions and contour portions of the video signal are emphasized without increasing the noise so much, thus making it possible to increase the sharpness. As described above, it is possible to suppress the correction quantity of the contour correction circuit and suppress the noise automatically when the noise is much, and the correction quantity is increased automatically when there is no noise and high frequency components of the video signal are much, thereby making it possible to improve the sharpness by applying the noise detection voltage to the contour correction circuit, providing a high frequency component quantity detection circuit, detecting the quantity of the high frequency video signal component during the effective video signal period, and controlling the correction quantity of the contour correction circuit in accordance with the detection result. Fig. 3 is a block diagram of a luminance signal noise suppressor showing another embodiment of the invention. In Fig. 3, a numeral 1 denotes a high-pass filter circuit, 2 denotes a full-wave rectification circuit,3 denotes a sample-hold circuit, and 4 denotes a noise detection pulse generating circuit, and these units are similar to those in the first embodiment. A high frequency component quantity detection circuit 7 is similar to that in the second embodiment. The difference from the construction of the second embodiment exists in that circuits for correcting a contour portion (edge having a comparatively large amplitude of a video signal) and a detail portion (comparatively detail amplitude component of a video signal) are provided separately in place of the contour correction circuit 6. A contour portion - detail portion separating circuit 8 applies primary differentiation to a video luminance signal a , divides the variation portion of the video luminance signal a into a detail portion and a contour portion in accordance with the amplitude thereof, and outputs a detail portion signal g and a contour portion signal g based on the result. A detail portion correction circuit 9 applies primary differentiation to the detail portion signal g , and outputs a detail portion correction signal i after applying gain control to the amplitude thereof by a noise detection voltage d and a video high frequency component detection voltage ℓ. A contour portion correction circuit 10 applies primary differentiation to a contour portion signal h , and outputs the result as a contour portion correction signal j . A delay circuit 11 delays the input luminance signal a by the time delay portion due to correction of the contour portion and the detail portion, and outputs a delayed luminance signal n . A first adding circuit 12 adds the detail portion correction signal i to the contour portion correction signal j , and outputs a correction signal k . A second adding circuit 13 adds the correction signal k to the delayed luminance signal n , and outputs an output luminance signal f . The operation of the luminance signal noise suppressor constructed as described above will be described hereafter. First, the noise detection voltage d is produced in a same manner as the first embodiment. Further, a video high frequency component detection voltage ℓ is produced in a same manner as the second embodiment. The present embodiment is characterized in that the detail portion containing a noise and the like and the contour portion containing none of them are corrected by means of separate correction circuits, respectively, in accordance with the amplitudes of variation portions of the video signal in place of the contour correction circuit 6. Among them, by controlling the detail portion correction circuit 9 which corrects the detail portion containing a noise and the like with those detected voltages similarly to the second embodiment, the correction quantity of the detail portion correction circuit 9 is reduced automatically in case much noise is contained, and the correction quantity is increased in case no noise and much high frequency components of the video signal are contained, thus making it possible to increase the sharpness. Besides, the circuit 2 indicates a full-wave rectification circuit in above-described embodiments, but similar operation may be performed with a half-wave rectification circuits. According to the preferred embodiment of the invention, there are provided a high-pass filter circuit, a full-wave rectification circuit, a sample-hold circuit, a noise detection pulse generating circuit, a high frequency component quantity detection circuit, a noise suppression circuit, a contour correction circuit, a detail portion correction circuit, a contour portion correction circuit, a contour portion - detail portion separating circuit, a delay circuit, a first adding circuit and a second adding circuit, thus making it possible to automatically suppress the noise when a weak electric field signal is input and also to increase the sharpness of a video luminance signal automatically in a signal containing less noise and much high frequency components which is very effective in practical applications.

Claims: A luminance signal noise suppressor, comprising: a high-pass filter circuit (1) for extracting from an input video signal high frequency components in a video luminance signal band (a); a full-wave rectification circuit (2) for full-wave rectifying the extracted high frequency components; a sample-hold circuit (3) for sampling to produce a mean voltage of the full-wave rectified components during a period of a vertical synchronizing signal of the input video signal and holding the sampled mean voltage during a period until a next vertical synchronizing signal; a noise detection pulse generating circuit (4) for driving said sample-hold circuit (3); and a noise suppression circuit (5) for suppressing noise of the luminance signal (a); characterized in that: said noise suppression circuit (5), includes a contour correction circuit (6) for correcting a contour of the input video luminance signal, so that when the input luminance signal contains noise in a weak electric field and the output voltage of said sample-hold circuit (3) is large, the amount of noise suppression by said noise suppression circuit (5) is increased to automatically reduce the noise, and at the same time, the amount of contour correction by said contour correction circuit (6) is decreased to automatically suppress the amount of contour correction to prevent the noise from being emphasized, thereby to obtain a clear picture with less noise. A luminance signal noise suppressor according to claim 1 characterized in that said noise suppressing circuit (5) is solely constituted by the contour correction circuit (6) for reducing the amount of correction of contour of the luminance signal in accordance with an increase in the output voltage of said sample-hold circuit (3), so that when the input luminance signal contains noise in a weak electric field and the output voltage of said sample-hold circuit is increased, the amount of contour correction is decreased to automatically suppress the amount of contour correction by said contour correction circuit to prevent the noise from being emphasized, thereby to obtain a clear picture with less noise. A luminance signal noise suppressor according to claim 2 characterized in that a video high frequency component quantity detection circuit (7) is further provided, which detects a mean value of full-wave rectified signal other than said vertical synchronizing signal period and delivers a detection voltage to said contour correction circuit (6), and said contour correction circuit (6) is controlled by the output voltage of said sample-hold circuit (3) and the detection voltage of said video high frequency component quantity detection circuit (7), so that when the input luminance signal contains noise in a weak electric field and the output voltage of said sample-hold circuit (3) is increased, the amount of contour correction by said contour correction circuit (6) is decreased to automatically suppress the amount of contour correction to prevent the noise from being emphasized, and when the output voltage of said sample-hold circuit (3) is small and the detection voltage of said video high frequency component quantity detection circuit (7) is large, the amount of contour correction by said contour correction circuit is automatically increased, thereby to emphasize the contour of a detail portion and a contour portion of the luminance signal without intensifying the noise, to increase sharpness. A luminance signal noise suppressor according to claim 1 characterized in that a contour portion-detail portion separating circuit (8) is further provided, which separates the input video luminance signal into a detail portion which contains noise and a contour portion which does not contain the noise, said noise suppressing circuit (5) is constituted by a detail portion correction circuit (9) for selectively contour-correcting a detail amplitude component of the video luminance signal which contains the noises, and a contour portion correction circuit (10) for selectively contour-correcting a large amplitude component which does not contain the noise, and an adder means (12) is further provided, which addes a detail portion correction signal from said detail portion correction circuit to a contour portion correction signal from said contour portion correction circuit, and outputs a correction signal to correct the video luminance signal, wherein the amount of contour correction by said detail portion correction circuit (9) is controlled in accordance with the output voltage of said sample-hold circuit (3), so that when the input luminance signal contains the noise in a weak electric field and the output voltage of said sample-hold circuit is increased, the amount of contour correction by said detail portion correction circuit (9) is decreased to automatically reduce the amount of correction of said correction signal (k) thereby to prevent the noise from being emphasized. A luminance signal noise suppressor according to claim 4 characterized in that a video high frequency component quantity detection circuit (7) is further provided, which detects a mean value of full-wave rectified signal other than said vertical synchronizing signal period and delivers a detection voltage to said detail portion correction circuit (9), wherein the amount of contour correction by said detailed portion correction circuit (9) is controlled in accordance with the output voltage of said sample-hold circuit (3) and the detection voltage of said video high frequency component quantity detection circuit (7), so that when the input luminance signal contains the noise in a weak electric field and the output voltage of said sample-hold circuit is increased, the amount of contour correction by said detail portion correction circuit (9) is decreased to automatically reduce the amount of correction of said correction signal (k) thereby to prevent the noise from being emphasized, and when the input luminance signal contains much high frequency components in a strong electric field and the detection voltage of said video high frequency component quantity detection circuit (7) is large, the amount of correction of said detail portion correction circuit (9) is automatically increased, thereby to emphasize a detail portion of the video luminance signal without intensifying the noise, to increase sharpness.

Inventors: KAGEYAMA ATSUHISA, KAGEYAMA, ATSUHISA
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1991
Main classification: H04N5
IPC codes: H04N5, H04B1